Protein-based conjugation carriers

Abstract

The present technology relates to the field of drug delivery and provides molecules comprising or consisting of at least one protein-based carrier building block, wherein the protein-based carrier building block comprises at least one, preferably at least two, attachment point(s) or conjugation site(s). In particular, the technology provides a molecule comprising at least one protein-based building block, wherein the at least one protein-based building block: a) comprises at least one conjugation site or attachment point; b) has a molecular mass of 2.5 to 70 kDa; c) has a globular three-dimensional (3D) structure; d) has a solubility of 10 mg / mL or more, measured in an aqueous solution at room temperature; and does not specifically bind to any human protein or binds one or more human proteins with a KD value greater than 5x10-4 mol / litre.

Description

[0001] PROTEIN-BASED CONJUGATION CARRIERS FIELD OF THE TECHNOLOGY The present technology provides molecules comprising or consisting of at least one protein- based carrier building block, wherein the protein-based carrier building block comprises at least one, preferably at least two attachment point(s) or conjugation site(s). The present technology further relates to nucleic acids encoding such molecules or part of such molecules; to host cells comprising such nucleic acids and / or expressing or capable of expressing such molecules or part of such molecules; to compositions, and in particular to pharmaceutical compositions that comprise such molecules, nucleic acids and / or host cells; and to uses of such molecules, nucleic acids, host cells and / or compositions, in particular for labelling, prophylactic, therapeutic and / or diagnostic purposes. TECHNOLOGICAL BACKGROUND Protein-based therapeutics (referred to as “Biologicals”) are creating new therapeutic strategies which are hard to achieve via the classic, small molecule-based therapeutics. One fast-growing field comprises conjugation-based therapeutics such as antibody-drug conjugates (ADCs). For instance, Fatima SW. and Khare SK. (“Benefits and challenges of antibody drug conjugates as novel form of chemotherapy”, J Control Release, 2022, 341:555- 565) review recent clinical advances of each component of ADCs (antibody / linker / payload) and how the individual component influences the activity of ADCs. This is also shown, e.g., in Rader, C., “Chemically programmed antibodies”, Trends in Biotechnology, 2014, 32(4). Antibody-drug conjugates typically rely on the high specificity and affinity of the antibodies, their extended circulatory half-life as well as other effector functions (e.g., complement- dependent cytotoxicity (CDC), antibody-dependent cellular cytotoxicity (ADCC) and antibody- dependent cellular phagocytosis (ADCP). Hence, antibody-drug conjugates and related molecules, such as chemically programmed antibodies, are chosen because of at least one of these functionalities (their targeting properties, half-life extension properties and / or other effector functions, as described above). Currently, the manufacture of biologicals mainly relies on recombinant production and is hence restricted to polypeptide production which can combine naturally into one functional unit (i.e., IgGs). Typical conjugation strategies are based on site specific cysteine or stochastic lysine conjugations (see, e.g., Zhou et al., 2021, Pharmaceuticals, 14: 672; Sadiki et al., 2020, Antibody Therapeutics, 3: 271). The rise of non-canonical or novel Amino Acids (nAAs) further add options for conjugation methodology (see, e.g., Malyshev and Romesberg, 2015, Angew Chem Int Ed Engl., 54(41); Zhang et al., 2017, PNAS, 1141317). There is a need of further therapeutic strategies which allow for versatile production and cargo conjugation. SUMMARY OF THE TECHNOLOGY The current technology aims at simplifying the generation of conjugation-based therapeutics and / or to create a plug-and play strategy that can create alternative formats which allow for versatile conjugation of different cargos. Whereas classic conjugation strategies need to focus on preserving the functionality of the involved polypeptides, a described above, the present technology employs a non-targeting protein-based carrier building block which solely serves as a site-specific conjugation vehicle (protein-based carrier building block). This protein-based carrier building block can be contained within a genetic construct, thus be the product of one manufacturing campaign or, alternatively, can be produced separately (e.g., recombinantly or by alternative means such as solid-phase peptide synthesis, SPPS) and later connected to the active and / or targeting moiety (i.e., the cargo), as it will be explained in detail below. The latter strategy renders more freedom for cargo conjugation conditions onto the protein-based carrier building block. Such freedom can translate into making use of site-specific conjugation onto common amino acids which are usually used in a stochastic way (e.g., lysines) or into conjugation conditions which might impair the functionality / quality of the targeting building block(s) or into alternative production platforms (e.g., chemical synthesis). The position and number of the conjugation sites or attachment points can be engineered / tuned to the specific application. Hence, the present technology provides molecules comprising or consisting of at least one protein-based carrier building block, and to the protein-based carrier building block as such, as described below, wherein the protein-based carrier building block comprises at least one attachment point or conjugation site, preferably at least two attachment points or conjugation sites. The at least one conjugation site or attachment point is suitable for conjugation or attachment of cargos to the protein-based carrier building block. A “cargo” is any molecule which is / may be attached or conjugated to the protein-based carrier building block through the attachment point(s) or conjugation site(s) present therein. For instance, cargos which may be attached or conjugated to the protein-based carrier building block of the present technology are proteins, peptides, polyethylene glycol (PEG), small molecules, glycans, lipids, chelators, fluorophores, radio isotopes, vitamins such as folic acid or biotin, nucleic acids such as oligonucleotides or siRNA, etc. Hence, in a further embodiment, the present technology provides the protein-based carrier building block attached to at least one cargo, as described herein, i.e., the molecule of the present technology comprises (or, alternatively, consists of) at least one protein-based building block and at least one cargo attached or conjugated to it through the at least one conjugation site or attachment point. The protein-based carrier building block of the present technology comprises (and, preferably, consists of) at least part of a protein, preferably a whole protein. Hence, preferably, the protein-based carrier building block is a polypeptide. The protein-based carrier building block has a globular 3D structure and is soluble. In addition, the protein-based carrier building block comprised in the molecule of the present technology has a size (molecular mass or molecular weight, MW) of about 2.5 to about 70 kDa, preferably of about 2.5 to less than 50 kDa, more preferably of about 2.5 to about 30 kDa, even more preferably of about 2.5 to about 16 kDa, such as about 6 kDa, or about 7 kDa, or about 16 kDa. Finally, the protein-based carrier building block of the present technology does not specifically bind to any human protein, although it may show non-specific binding to one or more human proteins, as explained in detail herein. In this case, the protein-based carrier building block may bind to human proteins with low specificity and / or low selectivity, as defined herein. Preferably, the protein-based carrier building block does also not specifically bind to any non- protein (preferably human) molecule, such as DNA, RNA, lipids (e.g., such as phosphatidylserine (PS)) or glycans. The protein-based carrier building block may derive from a target-binding protein (such as an immunoglobulin single variable domain (ISVD), a DARPin, an affibody or an affitin), as described below. It may also derive from other proteins which show specific binding towards, e.g., human proteins, such as small globular human proteins. This is the so-called “protein-based carrier building block precursor”. In these cases, preferably, the protein-based building block does also not specifically bind to any molecule (including non-human proteins) to which the protein-based carrier building block precursor specifically binds (if any). For example, if the precursor of the protein-based carrier building block is an anti-RSV (respiratory syncytial virus) ISVD, the protein-based carrier building block preferably does not specifically bind RSV. Hence, preferably, the protein-based carrier building block does also not specifically bind to the precursor’s target, should the precursor have a target and should this be a non-human molecule, such as a non-human protein, or a human non-protein molecule, such as human DNA, RNA, glycans, lipids, etc. In a further preferred embodiment, the protein-based carrier building block does not specifically bind any human protein, non-human protein and / or non-protein molecule when a cargo is conjugated to the at least one, preferably at least two, attachment points or conjugation sites on the protein-based carrier building block. Hence, the at least one protein-based carrier building block of the present technology: a) Has at least one attachment point (also referred to as conjugation site in the present description), preferably at least two attachment points or conjugation sites, wherein an attachment point or conjugation site is a reactive group in the side chain of a non-natural or natural amino acid (e.g., Cys, Lys, Tyr, Orn, etc.) preferably located at a solvent-accessible position in the protein-based carrier building block, and / or the N-terminal primary amine, and / or the C-terminal carboxylic group of the protein-based carrier building block, if these are available. The at least one, preferably at least two, attachment point(s) or conjugation site(s) is(are) thus preferably located at solvent-accessible positions in the protein-based carrier building block; b) Has a size (molecular mass) of from about 2.5 to about 70 kDa, preferably from about 2.5 to about 50 kDa, such as from about 2.5 to less than 50 kDa, more preferably from about 2.5 to about 30 kDa, even more preferably from about 2.5 to about 16 kDa; c) Has a solubility of about 10 mg / mL or more, measured in an aqueous solution at room temperature (RT), preferably measured in a buffer or water at RT, more preferably measured in a buffer such as citrate buffer or phosphate-buffered saline (PBS) at pH 7.0 or 7.4, at RT, or histidine buffer at pH 6.5, at RT (comprising histidine (10 mM to 100 mM, such as 10 mM), sucrose (1% to 10%, such as 10%) and, optionally, Tween 80 (0.001% to 1%, such as 0.01%)), or phosphate buffer pH 7.0, at RT (comprising NaH2PO4 / Na2HPO4(10 and 50 mM, such as 10 mM), sodium chloride (NaCl) (100-150 mM, such as 130 mM NaCl) and, optionally, Tween 80 (0.001% to 1%, such as 0.01%)), preferably wherein the buffer is citrate buffer 5 mM or PBS, at pH 7.0 or 7.4; d) Has a globular 3D structure, as described below; e) Does not specifically bind to any human protein (or binds one or more human proteins with a KD (KD value) greater than 5x10-4mol / litre), preferably it does also not specifically bind to the precursor’s target (or binds the precursor target, which may be a non-human protein or a non-protein molecule, with a KD (KD value) greater than 5x10-4mol / litre), and preferably it also does not specifically bind to any non-protein molecule, such as nucleic acids (e.g., DNA, RNA), lipids or glycans, preferably it does not specifically bind to any human non-protein molecule (or binds any non-protein molecule with a KD (KD value) greater than 5x10-4mol / litre), preferably it also does not specifically bind to any non-protein molecule (such as nucleic acids (e.g., DNA, RNA), glycans, lipids, etc.), to which the building block precursor binds specifically, if any, for instance as determined by cell-binding assay or by surface plasmon resonance (SPR), for instance as described herein and / or in Ober et al.2001, Intern. Immunology 13: 1551-1559, or does not specifically bind to any human cell or binds one or more human cells with a KD (KD value) greater than 5x10-4mol / litre, preferably as determined by cell-binding assay or by SPR; f) optionally, does not specifically bind to any (non-human) molecule which the protein-based carrier building block precursor specifically binds to, such as protein F of RSV, or binds to any (non-human) molecule which the protein-based carrier building block precursor specifically binds to, such as protein F of RSV, with a KD (KD value) greater than 5x10-4mol / litre, preferably as determined by cell-binding assay or by SPR; g) optionally, does not specifically bind to any human cell and / or cell type, or binds to a human cell and / or cell type with a KD(KDvalue) greater than 5x10-4mol / litre, preferably as determined by cell-binding assay; h) optionally, does not specifically bind any microorganism such as bacteria, fungi, protists, yeast and / or to any virus, or binds to a microorganism such as bacteria, fungi, protists, yeast and / or to virus with a KD(KDvalue) greater than 5x10-4mol / litre, preferably as determined by cell-binding assay and / or SPR, as described herein; i) optionally, does not specifically bind to any biomolecule, including human biomolecules and non-human biomolecules, such as plant biomolecules, virus biomolecules and / or microorganism biomolecules (such as bacteria, fungi, protists and / or yeast), or binds to biomolecules, including human biomolecules and non- human biomolecules, with a KD (KD value) greater than 5x10-4mol / litre, preferably as determined by cell-binding assay and / or SPR, as described herein; j) optionally, does not specifically bind to any biomolecule, including human biomolecules and non-human biomolecules, such as plant biomolecules, virus biomolecules and / or microorganism biomolecules (such as bacteria, fungi, protists and / or yeast), or binds to biomolecules, including human biomolecules and non- human biomolecules, with a KD (KD value) greater than 5x10-4mol / litre, preferably as determined by cell-binding assay and / or SPR, as described herein, when it has at least one cargo attached to it (via the at least one conjugation sites or attachment points comprised therein); k) optionally, does not comprise or consists of an amino acid sequence selected from SEQ ID NO.: 1-34 as depicted on Tables A-1 and A-2 of WO 2016 / 055656 and / or SEQ ID NO.: 1-12 as depicted on Table A-1 of WO 2010 / 139808; and l) optionally, does not comprise or consists of the amino acid sequence as defined in SEQ ID NO.: 214. In a first aspect, the present technology relates to a molecule comprising at least one protein- based building carrier block, wherein the at least one protein-based carrier building block: a) comprises at least one conjugation site or attachment point, preferably at least two attachment points or conjugation sites; b) has a molecular mass of about 2.5 to about 70 kDa, preferably of about 2.5 to about 50 kDa, such as from about 2.5 kDa to less than 50 kDa, more preferably of about 2.5 to about 30 kDa, even more preferably of about 2.5 to about 16 kDa; c) has a globular 3D structure; d) has a solubility of 10 mg / mL or more, measured in an aqueous solution at RT, preferably measured in a buffer or water at RT, more preferably in a buffer such as citrate buffer or phosphate-buffered saline (PBS) at pH 7.0 or 7.4, at RT, or histidine buffer at pH 6.5, at RT (comprising histidine (10 mM to 100 mM, such as 10 mM), sucrose (1% to 10%, such as 10%) and, optionally, Tween 80 (0.001% to 1%, such as 0.01%)), or phosphate buffer pH 7.0, at RT (comprising NaH2PO4 / Na2HPO4 (10 and 50 mM, such as 10 mM), sodium chloride (NaCl) (100-150 mM, such as 130 mM NaCl) and, optionally, Tween 80 (0.001% to 1%, such as 0.01%)); e) does not specifically bind to any human protein or binds one or more human proteins with a KD(KDvalue) greater than 5x10-4mol / litre, preferably as determined by cell-binding assay or by surface plasmon resonance (SPR), for instance as described herein and / or in Ober et al. 2001, Intern. Immunology 13: 1551-1559, or does not specifically bind to any human cell or binds one or more human cells with a KD (KD value) greater than 5x10-4mol / litre, preferably as determined by cell-binding assay or by SPR; f) optionally, does not specifically bind to any (non-human) molecule which the protein-based carrier building block precursor specifically binds to, such as protein F of RSV, or binds to any (non-human) molecule which the protein-based carrier building block precursor specifically binds to, such as protein F of RSV, with a KD (KD value) greater than 5x10-4mol / litre, preferably as determined by cell-binding assay or by SPR; g) optionally, does not specifically bind to any human cell and / or cell type, or binds to a human cell and / or cell type with a KD (KD value) greater than 5x10-4mol / litre, preferably as determined by cell-binding assay; h) optionally, does not specifically bind any microorganism such as bacteria, fungi, protists, yeast and / or to any virus, or binds to a microorganism such as bacteria, fungi, protists, yeast and / or to virus with a KD(KDvalue) greater than 5x10-4mol / litre, preferably as determined by cell-binding assay and / or SPR, as described herein; i) optionally, does not specifically bind to any biomolecule, including human biomolecules and non-human biomolecules, such as plant biomolecules, virus biomolecules and / or microorganism biomolecules (such as bacteria, fungi, protists and / or yeast), or binds to biomolecules, including human biomolecules and non- human biomolecules, with a KD(KDvalue) greater than 5x10-4mol / litre, preferably as determined by cell-binding assay and / or SPR, as described herein; j) optionally, does not specifically bind to any biomolecule, including human biomolecules and non-human biomolecules, such as plant biomolecules, virus biomolecules and / or microorganism biomolecules (such as bacteria, fungi, protists and / or yeast), or binds to biomolecules, including human biomolecules and non- human biomolecules, with a KD(KDvalue) greater than 5x10-4mol / litre, preferably as determined by cell-binding assay and / or SPR, as described herein when it has at least one cargo attached to it (via the at least one conjugation sites or attachment points comprised therein); k) optionally, does not comprise or consists of an amino acid sequence selected from SEQ ID NO.: 1-34 as depicted on Tables A-1 and A-2 of WO 2016 / 055656 and / or SEQ ID NO.: 1-12 as depicted on Table A-1 of WO 2010 / 139808; and a) optionally, does not comprise or consists of the amino acid sequence as defined in SEQ ID NO.: 214 (EVQLQASGGGLAQPGGSLRLSVTVSGSIDVINNMAWYRQAPGNARELVATITSGFSTNYA SSVKGRFTISRDNAKKAVYLQMNSLKPEDTADYYSKVHLIRLGAARAYDYWGQGTQVTVS). Preferably, in the molecule of the present technology, the at least one protein-based carrier building block does not specifically bind to any non-protein molecule, e.g., to any human non- protein molecule, such as human DNA, human RNA, human lipids or human glycans. The molecule of the present technology may comprise more than one protein-based carrier building block, such as, e.g., two, three, four, five, six or more protein-based carrier building blocks. These protein-based carrier building blocks may be directly linked to each other, or linked to each other through a linker, as described herein. Preferably, the at least one protein-based carrier building block comprised in the molecule of the present technology comprises more than one conjugation site or attachment point, preferably at least two conjugation sites or attachment points, such as two conjugation sites or attachment points, or at least three conjugation sites or attachment points, such as three, four, five, six, seven, eight or nine conjugation sites or attachment points, which are preferably reactive groups present in the side chain of a natural or non-natural amino acids comprised in the protein-based carrier building block, or which may be (additionally or alternatively) the N- terminal primary amine and / or the C-terminal carboxylic acid group of the protein-based building block. For instance, the at least one conjugation site or attachment point comprised in the at least one protein-based carrier building block is a free or capped thiol group, a free or capped hydroxyl group and / or a free or capped primary amine. In a further embodiment, the at least one conjugation site or attachment point comprised in the at least one protein-based carrier building block is a reactive group present in the side chain of a cysteine and / or in the side chain of a tyrosine, and / or in the side chain of a lysine, and / or in the side chain of an ornithine. In another further embodiment, the at least one protein-based building block comprises a N- and / or a C-terminal Cys and / or a N- and / or a C-terminal Tyr, preceded or followed by a (GG) or (G4S1)1-3GG sequence, such as CGG-, -GGC, YGG-, -GGY, -(G4S1)1-3GGY, Y(G4S1)1-3GG-, YGG(S1G4)1-3-, or YGG(G4S1)1-3-. Preferably, the at least one protein-based carrier building block present in the molecule of the present technology is (i) a building block based on small globular non-human proteins, such as an ISVD-based building block, a DARPin-based building block, an affibody-based building block or an affitin-based building block or (ii) a building block based on small globular human proteins, such as cyclin-dependent kinase subunit 1 (CDK-1). In one embodiment, the least one protein-based building block is derived from a heavy chain ISVD, preferably from a VH, VHH, including a camelized VH or humanized VHH. In another embodiment, the at least one protein-based building block is derived from an ISVD belonging to the “VH3 class”, preferably wherein the resulting building block comprises at least one (preferably engineered) cysteine, at least one (preferably engineered) lysine, at least one non- natural amino acid and / or at least one (preferably engineered) tyrosine at one or more solvent-accessible positions of the protein-based building block. In another embodiment, the least one protein-based building block is derived from RSV001A04 , SEQ ID NO.: 179. In one embodiment, the at least one protein-based building block is an ISVD-based building block which comprises a Leu or a Gln, preferably a Leu at position 108, according to Kabat numbering, preferably wherein the ISVD-based building block comprises a Val or a Leu, preferably a Val at position 11 and / or a Val, a Thr or a Leu, preferably a Leu at position 89, according to Kabat numbering. In another embodiment, the at least one protein-based building block comprises or, alternatively, consists of SEQ ID NO.: 186: X1VX2LX3EX4X5GX6X7X8X9X10X11GX12X13X14IX15CX16AX17X18X19X20LX21X22X23VLGWFRX24AX25X26X2 7X28X29X30FVAAINX31X32X33X34X35X36X37X38PX39X40VX41X42X43FX44IX45X46X47X48X49X50X51TGX52LX5 3MX54X55LX56X57X58DX59AX60YX61CGAGX62PX63X64X65X66AYX67X68X69X70SYX71X72X73GX74X75TX76V X77VX78X79X80X81X82, wherein X1 (position 1 according to Kabat numbering) can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X2 (position 3 according to Kabat numbering) can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X3 (position 5 according to Kabat numbering) can be Val or any amino acid with a reactive group in its side chain, such as cysteine; X4 (position 7 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X5(position 8 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X6(position 10 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X7(position 11 according to Kabat numbering) can be Leu, Val Ser, Met, Trp, Phe, Thr, Gln, Glu, Ala, Arg, Gly, Lys, Tyr, Asn, Pro or Ile, preferably Leu or Val, or any other amino acid with a reactive group in its side chain, such as cysteine; X8(position 12 according to Kabat numbering) can be Val or any amino acid with a reactive group in its side chain, such as cysteine; X9(position 13 according to Kabat numbering) can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X10 (position 14 according to Kabat numbering) can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X11(position 15 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X12(position 17 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X13 (position 18 according to Kabat numbering) can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X14 (position 19 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X15: (position 21 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X16: (position 23 according to Kabat numbering) can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X17: (position 25 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X18: (position 26 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X19: (position 27 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X20: (position 28 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X21: (position 30 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X22: (position 31 according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X23: (position 32 according to Kabat numbering) can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X24: (position 39 according to Kabat numbering) can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X25: (position 41 according to Kabat numbering) can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X26: (position 42 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X27: (position 43 according to Kabat numbering) can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X28: (position 44 according to Kabat numbering) can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X29: (position 45 according to Kabat numbering) can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X30: (position 46 according to Kabat numbering) can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X31: (position 52a according to Kabat numbering) can be Trp or any amino acid with a reactive group in its side chain, such as cysteine; X32: (position 53 according to Kabat numbering) can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X33: (position 54 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X34: (position 55 according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X35: (position 56 according to Kabat numbering) can be Ile or any amino acid with a reactive group in its side chain, such as cysteine; X36: (position 57 according to Kabat numbering) can be Thr or any amino acid with a reactive group in its side chain, such as cysteine; X37: (position 58 according to Kabat numbering) can be Ile or any amino acid with a reactive group in its side chain, such as cysteine; X38: (position 59 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X39: (position 61 according to Kabat numbering) can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X40: (position 62 according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X41: (position 64 according to Kabat numbering) can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X42: (position 65 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X43: (position 66 according to Kabat numbering) can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X44: (position 68 according to Kabat numbering) can be Thr or any amino acid with a reactive group in its side chain, such as cysteine; X45: (position 70 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X46: (position 71 according to Kabat numbering) can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X47: (position 72 according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X48: (position 73 according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X49: (position 74 according to Kabat numbering) can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X50: (position 75 according to Kabat numbering) can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X51: (position 76 according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X52: (position 79 according to Kabat numbering) can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X53: (position 81 according to Kabat numbering) can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X54: (position 82a according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X55: (position 82b according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X56: (position 83 according to Kabat numbering) can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X57: (position 84 according to Kabat numbering) can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X58: (position 85 according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X59: (position 87 according to Kabat numbering) can be Thr or any amino acid with a reactive group in its side chain, such as cysteine; X60: (position 89 according to Kabat numbering) can be Leu, Val Ser, Met, Trp, Phe, Thr, Gln, Glu, Ala, Arg, Gly, Lys, Tyr, Asn, Pro or Ile, preferably Leu or Val, or any other amino acid with a reactive group in its side chain, such as cysteine; X61: (position 91 according to Kabat numbering) can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X62: (position 96 according to Kabat numbering) can be Thr or any amino acid with a reactive group in its side chain, such as cysteine; X63: (position 98 according to Kabat numbering) can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X64: (position 99 according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X65: (position 100 according to Kabat numbering) can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X66: (position100a according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X67: (position100d according to Kabat numbering) can be Ile or any amino acid with a reactive group in its side chain, such as cysteine; X68: (position100e according to Kabat numbering) can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X69: (position 100f according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X70: (position 100g according to Kabat numbering) can be Trp or any amino acid with a reactive group in its side chain, such as cysteine; X71: (position 101 according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X72: (position 102 according to Kabat numbering) can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X73: (position 103 according to Kabat numbering) can be Trp or any amino acid with a reactive group in its side chain, such as cysteine; X74: (position 105 according to Kabat numbering) can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X75: (position 106 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X76: (position 108 according to Kabat numbering) can be Gln, Leu, Arg, Pro, Glu, Lys, Ser, Thr, Met, Ala or His; preferably Gln or Leu or any other amino acid with a reactive group in its side chain, such as cysteine; X77: (position 110 according to Kabat numbering) can be Thr or any amino acid with a reactive group in its side chain, such as cysteine; X78: (position 112 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine. X79: (position 113 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X80: is absent or Gly; X81: is absent or Gly; X82: is absent or Cys, or a sequence which has 80% or more identity with SEQ ID NO.: 186, preferably a sequence which has 85% or more, 90% or more, 95% or more, 97% or more or 99% or more sequence identity with SEQ ID NO.: 186, provided that the building block has a globular 3D structure, is soluble, has a size (molecular mass) of about 2.5 to about 70 kDa, such as about 2.5 to about 50 kDa, such as about2.5 to less than 50 kDa, more preferably of about 2.5 to about 30 kDa, such as about 2.5 to about 16 kDa, such as about 5 to about 16 kDa, or about 7 to about 16 kDa, or about 10 to about 16 kDa, and does not specifically bind to any human protein, as described herein. In another embodiment, the at least one protein-based building block is a DARPin-based building block, preferably derived from the DARPin K27 as defined in SEQ ID NO.: 187. SEQ ID NO.: 187: DLGKKLLEAARAGQDDEVRILMANGADVNAHDTFGFTPLHLAALYGHLEIVEVLLKNGADVNADDSYGR TPLHLAAMRGHLEIVEVLLKYGADVNAADEEGRTPLHLAAKRGHLEIVEVLLKNGADVNAQDKFGKTAFD ISIDNGNEDLAEILQKL In one embodiment, the protein-based building block is a DARPin-based building block which comprises, or alternatively, consists of, SEQ ID NO.: 188: X1X2GX3X4LLX5AAX6X7X8X9X10X11X12VX13X14LMX15X16X17AX18VX19AX20X21X22X23GX24TPLHLAAX25 X26X27X28X29X30IVX31VLLX32X33X34AX35VX36AX37DX38X39GATPLHLAAX40X41X42X43X44X45IVX46VLLX4 7X48X49AX50VX51AX52DX53X54GATPLHX55AAX56X57X58X59X60X61IVX62X63LX64X65X66X67AX68X69X70AX 71DX72X73X74X75TAX76X77ISX78X79X80X81X82X83X84LAX85X86LX87X88X89X90, wherein: X1 can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X2 can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X3 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X4 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X5 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X6can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X7can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X8can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X9can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X10can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X11can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X12can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X13can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X14can be Ile or any amino acid with a reactive group in its side chain, such as cysteine; X15can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X16can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X17 can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X18can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X19can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X20 can be His or any amino acid with a reactive group in its side chain, such as cysteine; X21can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X22 can be Thr or any amino acid with a reactive group in its side chain, such as cysteine; X23 can be Phe or any amino acid with a reactive group in its side chain, such as cysteine; X24 can be Phe or any amino acid with a reactive group in its side chain, such as cysteine; X25 can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X26 can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X27 can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X28 can be His or any amino acid with a reactive group in its side chain, such as cysteine X29 can be Leu or any amino acid with a reactive group in its side chain, such as cysteine X30 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine X31 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine X32 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine X33 can be Asn or any amino acid with a reactive group in its side chain, such as cysteine X34 can be Gly or any amino acid with a reactive group in its side chain, such as cysteine X35 can be Asp or any amino acid with a reactive group in its side chain, such as cysteine X36 can be Asn or any amino acid with a reactive group in its side chain, such as cysteine X37 can be Asp or any amino acid with a reactive group in its side chain, such as cysteine X38can be Ser or any amino acid with a reactive group in its side chain, such as cysteine X39can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X40can be Met or any amino acid with a reactive group in its side chain, such as cysteine; X41can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X42can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X43can be His or any amino acid with a reactive group in its side chain, such as cysteine; X44can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X45can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X46can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X47can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X48can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X49 can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X50can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X51can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X52 can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X53can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X54 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X55 can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X56 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X57 can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X58 can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X59 can be His or any amino acid with a reactive group in its side chain, such as cysteine; X60 can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X61 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X62 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X63 can be Val or any amino acid with a reactive group in its side chain, such as cysteine; X64 can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X65 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X66 can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X67 can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X68 can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X69 can be Val or any amino acid with a reactive group in its side chain, such as cysteine; X70can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X71can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X72can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X73can be Phe or any amino acid with a reactive group in its side chain, such as cysteine; X74can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X75can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X76can be Phe or any amino acid with a reactive group in its side chain, such as cysteine; X77can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X78can be Ile or any amino acid with a reactive group in its side chain, such as cysteine; X79can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X80can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X81 can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X82can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X83can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X84 can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X85can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X86 can be Ile or any amino acid with a reactive group in its side chain, such as cysteine; X87 can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X88 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine X89 is absent or Leu; X90 is absent or Cys, or a sequence which has 80% or more identity with SEQ ID NO.: 188, preferably a sequence which has 85% or more, 90% or more, 95% or more, 97% or more or 99% or more sequence identity with SEQ ID NO.: 188, provided that the building block has a globular 3D structure, is soluble, has a size (molecular mass) of about 2.5 to about 70 kDa, such as about 2.5 to about 50 kDa, such as about 2.5 to less than 50 kDa, more preferably of about 2.5 to about 30 kDa, such as about 2.5 to about 16 kDa, such as about 5 to about 16 kDa, or about 7 to about 16 kDa, or about 10 to about 16 kDa, and does not specifically bind to any human protein, as described herein, in particular does not specifically bind to human KRAS protein (GTPase KRas, EC:3.6.5.2, primary accession number P01116, see also Lim S., et al., “Exquisitely specific anti- KRAS biodegraders inform on the cellular prevalence of nucleotide-loaded states”, ACS Cent. Sci.2021, 7, 2, 274–291). In another embodiment, the at least one protein-based building block is a small globular human protein-based building bock, preferably derived from the polypeptide as defined in SEQ ID NO.: 190. SEQ ID NO.: 190 SHKQIYYSDKYDDEEFEYRHVMLPKDIAKLVPKTHLMSESEWRNLGVQQSQGWVHYMIHEPEPHILLFR RPLPKKPKK In one embodiment, the protein-based building block is a small globular human protein-based building bock which comprises, or alternatively, consists of, SEQ ID NO.: 191: X1X2X3X4IX5X6SX7X8X9X10X11X12X13X14X15X16X17X18VX19LPX20X21X22AX23X24VX25X23bX24bX25bX26MX27X28X29X30WX31X32LX33VX34QX35X36X37WX38HX39X40X41X42X43X44X45X46X47ILLFX48X49X50X51X52X53X 54X55X56X57, wherein X1 can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X2 can be His or any amino acid with a reactive group in its side chain, such as cysteine; X3 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X4 can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X5 can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X6 can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X7 can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X8 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X9 can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X10 can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X11 can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X12 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X13can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X14can be Phe or any amino acid with a reactive group in its side chain, such as cysteine; X15can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X16can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X17can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X18can be His or any amino acid with a reactive group in its side chain, such as cysteine; X19can be Met or any amino acid with a reactive group in its side chain, such as cysteine; X20can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X21can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X22can be Ile or any amino acid with a reactive group in its side chain, such as cysteine; X23can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X24 can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X25can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X23bcan be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X24b can be Thr or any amino acid with a reactive group in its side chain, such as cysteine; X25bcan be His or any amino acid with a reactive group in its side chain, such as cysteine; X26 can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X27 can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X28 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X29 can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X30 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X31 can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X32 can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X33 can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X34 can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X35 can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X36 can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X37 can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X38 can be Val or any amino acid with a reactive group in its side chain, such as cysteine; X39 can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X40 can be Met or any amino acid with a reactive group in its side chain, such as cysteine; X41 can be Ile or any amino acid with a reactive group in its side chain, such as cysteine; X42can be His or any amino acid with a reactive group in its side chain, such as cysteine; X43can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X44can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X45can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X46can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X47can be His or any amino acid with a reactive group in its side chain, such as cysteine; X48can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X49can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X50can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X51can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X52can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X53 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X54can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X55can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X56 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X57can be Lys or any amino acid with a reactive group in its side chain, such as cysteine, or a sequence which has 80% or more identity with SEQ ID NO.: 191, preferably a sequence which has 85% or more, 90% or more, 95% or more, 97% or more or 99% or more sequence identity with SEQ ID NO.: 191, provided that the building block has a globular 3D structure, is soluble, has a size (molecular mass) of about 2.5 to about 70 kDa, such as from about 2.5 to about 50 kDa, such as from about 2.5 to less than 50 kDa, more preferably of about 2.5 to about 30 kDa, such as about 2.5 to about 16 kDa, such as about 5 to about 16 kDa, or about 7 to about 16 kDa, or about 10 to about 16 kDa, and does not specifically bind to any human protein, as described herein. For instance, the at least one protein-based building block may be selected from SEQ ID NO.: 80-105, 175, 199, 208, 222-224. In one embodiment, the molecule of the present technology comprises at least one protein- based carrier building block as defined herein and at least one further moiety or cargo attached to the attachment point or conjugation site, wherein the at least one further moiety or cargo is selected from: a) a half-life extending (HLE) moiety, such as PEG, and / or b) a targeting moiety, such as an EGFR-targeting moiety, e.g., GE11 peptide or an anti-EGFR VHH; and / or c) a therapeutic moiety or precursor therefrom, e.g., such as an DR5-binding molecule; d) an imaging moiety, such as deferoxamine (DFO); e) a toxic moiety, such as DM4 or cryptophycin; f) nucleic acids such as siRNA; g) vitamins, such as folate; h) Toll-like receptor agonists, such as resiquimod; i) glycans, such as bis mannose 6 phosphate (bisM6P) or mannose 6 phosphate (M6P); and / or j) lipids, such as short-chain fatty acids. In one embodiment, the at least one half-life extending moiety is an albumin-binding ISVD, wherein the albumin-binding ISVD is preferably selected from SEQ ID NOs: 50-64 and 106, more preferably SEQ ID NO.: 63 or SEQ ID NO.: 106, or a sequence with at least 70%, preferably at least 80%, more preferably at least 90% and even more preferably at least 95% identity with SEQ ID NOs: 50-64 and / or 106. In a further embodiment, the at least one half-life extending moiety is a linear or branched polyethylene glycol moiety with a molecular weight of about 1- 60 kDa, preferably with a weight of about 1-15 kDa, such as about 14 or 15 kDa, or of about 1-10 kDa, such as 5 or 10 kDa. In one embodiment, the at least one protein-based carrier building block and the at least one further moiety or cargo are directly linked to each other. In a further embodiment, they are linked to each other through a peptide linker, preferably wherein the peptide linker is selected from SEQ ID NO.: 158-169 or 193-196, more preferably SEQ ID NO.: 163. Other linkers may be used, such as APN-maleimide linkers, as defined below and exemplified in the examples. For instance, the molecule of the present technology may comprise or, alternatively consist of, any one of SEQ ID NOs.: 107-127, SEQ ID NOs.: 170-174, 176 or 200. The present technology also provides a nucleic acid encoding the molecule of the present technology (or part of the molecule of the present technology). In addition, the present technology provides a vector comprising the nucleic acid of the present technology, and a composition comprising the molecule of the present technology, such as a pharmaceutical composition. Furthermore, the present technology relates to the molecule or composition of the present technology for use in medicine, in particular for use in the (prophylactic or therapeutic) treatment of diseases and or disorders, such as autoimmune / inflammatory diseases, cancer and / or infectious diseases. BRIEF DESCRIPTION OF THE FIGURES Figure 1. Amino acid sequence of ISVD RSV001A04 (SEQ ID NO.: 179). Figure 2. Amino acid sequence of K27m (without the C-terminal L), SEQ ID NO.: 68. Figure 3. Amino acid sequence of the CKS1-building block precursor (SEQ ID NO.: 190). Figure 4. Conjugation using an APN-maleimide ‘bifunctional’ linker. The carrier (protein-based building block comprised in the molecule) comprises at least one attachment point or conjugation site (represented as “-SH” in the figure). The APN-maleimide ‘bifunctional’ linker can be first attached to the conjugation site present in the carrier. Then, the cargo (represented as “DR5-SH” in the figure) can be attached to the other side of the APN- maleimide ‘bifunctional’ linker. Hence, the cargo has been attached or conjugated to the carrier through an APN-maleimide ‘bifunctional’ linker. Figure 5. Conjugability check of cysteine-engineered ISVDs-based carrier building blocks using Mass Spectrometry Deconvoluted Mass Spectrum of Mal-APN conjugation onto the molecule T028100075, comprising an ISVD-based carrier building block with one attachment point or conjugation site (“ISVD179-APN”, SEQ ID NO.: 176, Figure 5A) and onto the molecule T028100069, comprising an ISVD-based carrier building block with three attachment points or conjugation sites (“ISVD107-APN”, SEQ ID NO.: 107, Figure 5B). Mass Spec analysis was carried out using electrospray ionization (ESI) with online reverse phase column (RPC) for clean-up of the sample. Figure 6. Schematic representation of the molecules of Example 5. The figure shows the multivalent molecules comprising an HLE moiety (“ALB23”, which represents SEQ ID NO.: 106), a protein-based carrier building block (“CARRIER”, which represents SEQ ID NO.: 80) and three cargos (“DR5”) attached to three conjugation sites, which are three -SH groups of cysteines present at solvent-accessible positions. In Figure 6A, each cargo (“DR5”) is a DR5-GGC ISVD (“monovalent”, DR5-GGC, SEQ ID NO.: 177). In Figure 6B, each cargo (“DR5-DR5-DR5”) comprises three DR5 ISVDs (“trivalent”, DR5-DR5-DR5-GGC, SEQ ID NO.: 178). Figure 7. SDS-PAGE gel analysis of the conjugations performed in Example 5. Lane 3 shows the 3x conjugation status of the “trivalent” (DR5-DR5-DR5-GGC)cargo attached to the three conjugation sites on the building block as defined by SEQ ID NO.: 176. Lane 5 shown the 3x conjugation status of the “monovalent” (DR5-GGC) cargo attached to the three conjugation sites on the building block as defined by SEQ ID NO.: 176. The results of the control are not shown in the figure. Lane 4 is a protein ladder. Figure 8. Caspase 3 / 7 assay. Medium containing the indicated concentrations of DR5 agonists, as described below, was added, followed by 5 µM CellEvent™ Caspase-3 / 7 Green Detection Reagent. Real-time data acquisition and analysis were performed, and the caspase 3 / 7 signal was normalized for cell confluency at 24 h timepoint. “DR5 Trivalent format” refers to the trivalent DR5-GGC molecule as defined in SEQ ID NO.: 178; “DR5 Bivalent format” refers to the molecule as described in SEQ ID NO.: 207; “CARGO Nonavalent DR5” refers to a molecule comprising a HLE moiety (“ALB”, SEQ ID NO.: 106), an ISVD-based carrier building block (“CARRIER”, SEQ ID NO.: 107) with three conjugation sites (at positions 43, 100f and 105, according to Kabat) and three cargos attached via an APN-maleimide linker to the three conjugation sites, wherein each cargo comprises three DR5 ISVDs (SEQ ID NO.: 178); “CARGO Trivalent DR5” refers to a molecule comprising a HLE moiety (“ALB”, SEQ ID NO.: 106), an ISVD- based carrier building block (“CARRIER”, SEQ ID NO.: 107) with three conjugation sites (at positions 43, 100f and 105, according to Kabat) and three cargos attached via an APN- maleimide linker to the three conjugation sites, wherein each cargo comprises one DR5 ISVD (SEQ ID NO.: 177); “CARGO control” refers to the control molecule, which comprises a HLE moiety (“ALB”, SEQ ID NO.: 106), a control carrier building block (“RSV”, SEQ ID NO.: 176) with a C-terminal Cys to which a molecule comprising three DR5 ISVDs is attached via an APN- maleimide linker. Figure 9. siRNA conjugation using the molecule described in SEQ ID NO.: 108. “DOL3” refers to the molecule described in SEQ ID NO.: 108 with three siRNA molecules attached to the three conjugation sites comprised in the protein-based building block of this molecule. “DOL2” refers to the molecule described in SEQ ID NO.: 108 with two siRNA molecules attached to two conjugation sites, and “DOL1” refers to the molecule described in SEQ ID NO.: 108 with one siRNA molecule attached to one conjugation site. “T028100070” refers to the molecule described in SEQ ID NO.: 108 on its own, and “T028100070+TCEP” refers to the molecule described in SEQ ID NO.: 108 in its reduced form with TCEP. Figure 10. Combination of PEGylation (5, 10 or 20 kDa PEG) and radiolabeling (89Zn) of molecules as described in SEQ ID NO.: 108 (“ISVD108” in the figure). Concentration of the different molecules (marked as 1-4 in the figure) in blood over time is shown in this figure. Figure 11. HPLC / SEC analysis of Crypto / PEG conjugates onto molecules with SEQ ID NO.: 107 (Panel A) and SEQ ID NO.: 113 (Panels B and C). Samples: 5 µl injection; Column: TSK-GEL SW mAb HTP (Tosoh Bioscience) - 4 µm - 4.6 x 150 mm; Solvent: Isocratic with 100% SEC Buffer Kpi iPrOH 20% pH = 7 (Composition: KCl 1 M, 200 mL / KH2PO41 M, 52 mL / K2HPO41 M, 107 mL / MQ, 441 mL / iPrOH, 200 mL); Run: 15 min at 0.2 mL / min; V0=Exclusion volume, Vt= total volume of the column. Figure 12. Schematic representation of the cell-internalization assay used in Examples 11-14. Figure 13. Internalization of ALB-3C_K27m_w1 (SEQ ID NO.: 173) and ALB-5C_K27m_w1 (SEQ ID NO.: 174) molecules conjugated to GE11 peptide vs. alanine conjugation on NCI- H226 cells using HSA-pHAb, as described in Example 11. Figure 14. Preparation of tert-butyl (2S)-5-[2-(tert-butoxycarbonylamino)ethylamino]-2-(9H- fluoren-9-ylmethoxycarbonylamino)-5-oxo-pentanoate (intermediate 1). Figure 15. Preparation of tert-butyl (2S)-2-amino-5-[2-(tert- butoxycarbonylamino)ethylamino]-5-oxo-pentanoate (intermediate 2). Figure 16. Preparation of (2S)-5-(2-aminoethylamino)-2-[[4-[(2-amino-4-hydroxy-pteridin-6- yl)methylamino]benzoyl]amino]-5-oxo-pentanoic acid (intermediate 3). Figure 17. Preparation of (2S)-2-[[4-[(2-amino-4-oxo-1H-pteridin-6- yl)methylamino]benzoyl]amino]-5-[2-[3-(2,5-dioxopyrrol-1-yl)propanoylamino]ethylamino]- 5-oxo-pentanoic acid (folate-aminoethyl-maleimide). Figure 18. Internalization of Hela cell lines by the protein-based carrier molecules conjugated with folate. Protein-based carrier building blocks comprised in T028100070 and T028100075 have been conjugated either to maleimide-folate or to maleimide-Ala (negative control), as described in Example 12. Figure 19. Schema of the synthesis of the bisM6P ([(2S,3R,4R,5R)-6-[(3S,4S,5S,6R)-2- [[(2R,3S,4S,5S)-6-[[(2S,3S,4R,5R,6S)-4-[(3R,4R,5R,6S)-4,5-dihydroxy-6-(hydroxymethyl)-3- [(3R,4R,5R,6S)-3,4,5-trihydroxy-6-(phosphonooxymethyl)tetrahydropyran-2-yl]oxy- tetrahydropyran-2-yl]oxy-6-[4-[2-[3-[2-[2-[2-[2-(2,5-dioxopyrrol-1- yl)ethoxy]ethoxy]ethoxy]ethoxy]propanoyl]hydrazine]-4-oxo-butoxy]-3,5-dihydroxy- tetrahydropyran-2-yl]methoxy]-3,4,5-trihydroxy-tetrahydropyran-2-yl]methoxy]-4,5- dihydroxy-6-(hydroxymethyl)tetrahydropyran-3-yl]oxy-3,4,5-trihydroxy-tetrahydropyran-2- yl]methyl dihydrogen phosphate). Figure 20. Schematic representation of the cell-binding assay used in Examples 13 and 16. Figure 21. Binding of T028100069 (SEQ ID NO.: 107), T028100070 (SEQ ID NO.: 108) and T028100075 (SEQ ID NO.: 176) molecules conjugated with bis-M6P (diM6P) vs. Alanine on K- 562 cells in Flow Cytometry using HSA-biotin and Streptavidin-Phycoerythrin detection, as described in Example 13. An ISVD specifically binding M6PR (“ISVD specific for M6PR”) was used as positive control, and an ISVD which does not specifically bind M6PR (“ISVD no specific binding to M6PR”) was used as a further negative control. Figure 22. Internalization of T028100069 (SEQ ID NO.: 107), T028100070 (SEQ ID NO.: 108) and T028100075 (SEQ ID NO.: 176) CARGO conjugated with bis-M6P vs. Alanine on K-562 cells using HSA-pHAb for detection, as described in Example 13. An ISVD specifically binding M6PR (“ISVD specific for M6PR”) was used as positive control, and an ISVD which does not specifically bind M6PR (“ISVD no specific binding to M6PR”) was used as a further negative control. Figure 23. Lipidation QC via mass spec analysis of the DOL=0 (mal-ALA) and DOL 6 preparations confirms the conjugations for both batches. A near full conjugation of undecanoic acid and Alanine was observed. Figure 24. Internalization of ALB-RSV_c6 (T028100078, SEQ ID NO.: 113) with 11- Maleimidoundecanoic acid vs Alanine conjugation on BxPC-3 using HSA-pHAb for detection, as described in Example 14. Figure 25. (A) SEC analysis of the conjugation of the different mal-PEG molecules on the SH- groups of the side chains of the Cys present in the ISVD-derived building blocks of the different molecules (6x5 kDa, 5x5 kDa, 4x5 kDa and 1x30 kDa). (B) Size and Relative % of the different PEG-conjugated molecules analyzed by SEC. Figure 26. Measurement of ISVD-based carrier compound concentrations in rat serum. Figure 27: Non-reducing PAGE analysis of a partial CMA1 uploaded CKS-based carrier. DEFINITIONS Unless indicated or defined otherwise, all terms used have their usual meaning in the art, which will be clear to the skilled person. Reference is, for example, made to the standard handbooks, such as Sambrook et al., 1989 (Molecular Cloning: A Laboratory Manual, 2ndEd., Vols. 1-3, Cold Spring Harbor Laboratory Press), Ausubel et al., 1987 (Current protocols in molecular biology, Green Publishing and Wiley Interscience, New York), Lewin 1985 (Genes II, John Wiley & Sons, New York, N.Y.), Old et al., 1981 (Principles of Gene Manipulation: An Introduction to Genetic Engineering, 2ndEd., University of California Press, Berkeley, CA), Roitt et al., 2001 (Immunology, 6thEd., Mosby / Elsevier, Edinburgh), Roitt et al., 2001 (Roitt’s Essential Immunology, 10thEd., Blackwell Publishing, UK), and Janeway et al., 2005 (Immunobiology, 6thEd., Garland Science Publishing / Churchill Livingstone, New York), as well as to the general background art cited herein. Unless indicated otherwise, all methods, steps, techniques and manipulations that are not specifically described in detail herein can be performed and have been performed in a manner known per se, as will be clear to the skilled person. Reference is, for example, again made to the standard handbooks and the general background art mentioned herein and to the further references cited therein; as well as to for example the following reviews: Presta 2006 (Adv. Drug Deliv. Rev., 58: 640), Levin and Weiss 2006 (Mol. Biosyst., 2: 49), Irving et al., 2001 (J. Immunol. Methods, 248: 31), Schmitz et al., 2000 (Placenta 21 Suppl. A: S106), Gonzales et al., 2005 (Tumour Biol., 26: 31), which describe techniques for protein engineering, such as affinity maturation and other techniques for improving the specificity and other desired properties of proteins such as immunoglobulins. It must be noted that as used herein, the singular forms "a", "an", and "the", include plural references unless the context clearly indicates otherwise. Thus, for example, reference to "a reagent" includes one or more of such different reagents and reference to "the method" includes reference to equivalent steps and methods known to those of ordinary skill in the art that could be modified or substituted for the methods described herein. Unless otherwise indicated, the term "at least" preceding a series of elements is to be understood to refer to every element in the series. Those skilled in the art will recognize or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the technology described herein. Such equivalents are intended to be encompassed by the present technology. The term "and / or" wherever used herein includes the meaning of "and", "or" and "all or any other combination of the elements connected by said term". Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integer or step. When used herein the term "comprising" can be substituted with the term "containing" or "including" or sometimes when used herein with the term "having". The term “sequence” as used herein (for example in terms like “immunoglobulin sequence”, “antibody sequence”, “variable domain sequence”, “VHH sequence” or “protein sequence”), should generally be understood to include both the relevant amino acid sequence as well as nucleic acids or nucleotide sequences encoding the same, unless the context requires a more limited interpretation. Amino acid sequences are interpreted to mean a single amino acid or an unbranched sequence of two or more amino acids, depending on the context. Nucleotide sequences are interpreted to mean an unbranched sequence of 3 or more nucleotides. It is understood that any reference to the amino acid sequences is meant to encompass post- translational modifications of these sequences occurring in mammalian cells such as CHO cells, including, but not limited to, N-glycosylation, O-glycosylation, deamidation, Asp isomerization / fragmentation, pyro-glutamate formation, removal of C-terminal lysine, and Met / Trp oxidation. When a nucleotide sequence or amino acid sequence is said to “comprise” another nucleotide sequence or amino acid sequence, respectively, or to “essentially consist of” another nucleotide sequence or amino acid sequence, this may mean that the latter nucleotide sequence or amino acid sequence has been incorporated into the first mentioned nucleotide sequence or amino acid sequence, respectively, but more usually this generally means that the first mentioned nucleotide sequence or amino acid sequence comprises within its sequence a stretch of nucleotides or amino acid residues, respectively, that has the same nucleotide sequence or amino acid sequence, respectively, as the latter sequence, irrespective of how the first mentioned sequence has actually been generated or obtained (which may for example be by any suitable method described herein). Amino acids are organic compounds that contain amino[a] (−NH+3) and carboxylate (−CO−2) functional groups, along with a side chain (R group) specific to each amino acid. For instance, amino acids include those L-amino acids commonly found in naturally occurring proteins. “Amino acids”, in the context of the present technology, also include D-amino acids and non- natural, unusual or unnatural amino acids, as described below. Amino acid residues will be indicated according to the standard three-letter or one-letter amino acid code. Reference is made to Table A-2 on page 48 of WO 08 / 020079. Examples of amino acids commonly found in proteins and represented in the genetic code are listed in Table 1 below. Other common amino acids (excluding those listed in Table 1 below) are described on the table on p.624 of Pure & Appl. Chem., Vol. 56, No. 5, pp. 595—624, 1984, reproduced below as Table 2 for convenience. Table 1: Common amino acids (IUPAC) 1-Letter 3-Letter Code Code Name A Ala Alanine BAsxAspartic acid orAsparagineC Cys Cysteine D Asp Aspartic acid E Glu Glutamic acid F Phe Phenylalanine G Gly Glycine H His Histidine I Ile Isoleucine K Lys Lysine L Leu Leucine M Met Methionine N Asn Asparagine P Pro Proline Q Gln Glutamine R Arg Arginine S Ser Serine T Thr Threonine V Val Valine W Trp Tryptophan X XaaUncommon orUnspecifiedY Tyr Tyrosine ZGlxGlutamic acid orGlutamineTable 2. Further amino acids

[0002] D-amino acids are also encompassed by the definition of “amino acid”. As used herein, the term “D-amino acid” refers to amino acids where the stereogenic carbon alpha to the amino group has the D-configuration. Unusual, unnatural or non-natural amino acids are also encompassed by the definition of “amino acid”. As used herein, the term "unnatural amino acid" or “non-canonical amino acid” or “non-natural amino acid” or “novel amino acid” (or the like) refers to an amino acid that is not one of the twenty amino acids commonly found in peptides synthesized in nature, and known by the one letter abbreviations A, R, N, C, D, Q, E, G, H, I, L, K, M, F, P, S, T, W, Y and V. Exemplary unnatural amino acids are described in Young et al., “Beyond the canonical 20 amino acids: expanding the genetic lexicon,” J. of Biological Chemistry, 285(15): 11039- 11044 (2010), the disclosure of which is incorporated herein by reference. Alexander R. Nödling et al. (“Using genetically incorporated unnatural amino acids to control protein functions in mammalian cells”, Essays Biochem, 3 July 2019; 63 (2): 237–266), the disclosure of which is incorporated herein by reference, provides an overview of unnatural amino acids that have been successfully incorporated into proteins in mammalian cells, see, e.g., Table 1 starting on p.240. Non-limiting examples of unnatural amino acids include: p-acetyl-phenylalanine, O-4-allyl-L- tyrosine, 4-propyl-L-tyrosine, L-Dopa, p-azido-phenylalanine, N6-(propargyloxy)-carbonyl-L- lysine (PrK), azido-lysine (N6-azidoethoxy-carbonyl-L-lysine, AzK). In some embodiments, the unnatural amino acid comprises a selective reactive group, or a reactive group for site- selective labeling or conjugation of a moiety or cargo. In some instances, the chemistry is a biorthogonal reaction (e.g., biocompatible and selective reactions). In some cases, the chemistry is a Cu(I)-catalyzed or “copper-free” alkyne-azide triazole-forming reaction, the Staudinger ligation, inverse-electron-demand Diels-Alder (IEDDA) reaction, “photo-click” chemistry, or a metal-mediated process such as olefin metathesis and Suzuki-Miyaura or Sonogashira cross-coupling. For further examples of unnatural amino acids, we refer to WO 2021 / 072167, the disclosure of which is incorporated herein by reference. The terms "protein", "peptide", "protein / peptide", and "polypeptide" are used interchangeably throughout the present disclosure, and each has the same meaning for purposes of this disclosure. Each term refers to an organic compound made of a linear chain of two or more amino acids. The compound may have ten or more amino acids; twenty-five or more amino acids; fifty or more amino acids; one hundred or more amino acids, two hundred or more amino acids, and even three hundred or more amino acids. The skilled artisan will appreciate that polypeptides generally comprise fewer amino acids than proteins, although there is no art-recognized cut-off point of the number of amino acids that distinguish a polypeptide and a protein; that polypeptides may be made by chemical synthesis or recombinant methods; and that proteins are generally made in vitro or in vivo by recombinant methods as known in the art. By convention, the amide bond in the primary structure of polypeptides is in the order that the amino acids are written, in which the amine end (N-terminus) of a polypeptide is always on the left, while the acid end (C-terminus) is on the right. Any amino acid sequence that contains post-translationally modified amino acids may be described as the amino acid sequence that is initially translated using the symbols shown in Table 1 with the modified positions; e.g., hydroxylations or glycosylations, but these modifications shall not be shown explicitly in the amino acid sequence. Any peptide or protein that can be expressed as a sequence modified linkages, cross links and end caps, non-peptidyl bonds, etc., is embraced by this definition. In the context of the present technology, the terms “specificity”, “binding specifically” or “specific binding” refer to the number of different target molecules, such as antigens, to which a particular binding unit can bind with sufficiently high affinity (see below). “Specificity”, “binding specifically” or “specific binding” are used interchangeably herein with “selectivity”, “binding selectively” or “selective binding”. Generally, binding units, such as binding ISVDs, specifically bind to their designated targets. The specificity / selectivity of a binding unit can be determined based on affinity. The affinity denotes the strength or stability of a molecular interaction. The affinity is commonly given by the KD, or dissociation constant, which has units of mol / litre (or M). The affinity can also be expressed as an association constant, KA, which equals 1 / KD and has units of (mol / litre)-1(or M-1). The affinity is a measure for the binding strength between a moiety and a binding site on a target molecule: the lower the value of the KD, the stronger the binding strength between a target molecule and a targeting moiety. The KD-value characterizes the strength of a molecular interaction also in a thermodynamic sense as it is related to the change of free energy (DG) of binding by the well-known relation DG=RT.ln(KD) (equivalently DG=-RT.ln(KA)), where R equals the gas constant, T equals the absolute temperature and ln denotes the natural logarithm. The KDmay also be expressed as the ratio of the dissociation rate constant of a complex, denoted as koff, to the rate of its association, denoted kon(so that KD=koff / konand KA= kon / koff). The off-rate koffhas units s-1(where s is the SI unit notation of second). The on-rate konhas units M-1s-1. The on-rate may vary between 102M-1s-1to about 107M-1s-1, approaching the diffusion-limited association rate constant for bimolecular interactions. The off-rate is related to the half-life of a given molecular interaction by the relation t1 / 2=ln(2) / koff. The off-rate may vary between 10-6s-1(near irreversible complex with a t1 / 2 of multiple days) to 1 s-1(t1 / 2=0.69 s). The measured KD may correspond to the apparent KD if the measuring process somehow influences the intrinsic binding affinity of the implied molecules for example by artefacts related to the coating on the biosensor of one molecule. Also, an apparent KD may be measured if one molecule contains more than one recognition sites for the other molecule or molecules. In such situation the measured affinity may be affected by the avidity of the interaction by the two molecules. The dissociation constant (KD) may be the actual or apparent dissociation constant, as will be clear to the skilled person. Methods for determining the KD will be clear to the skilled person, and for example include the techniques mentioned below. In this respect, it will also be clear that it may not be possible to measure dissociation constants of more than 10-4moles / litre or 10-3moles / litre (e.g., of 10-2moles / litre). Optionally, as will also be clear to the skilled person, the (actual or apparent) KD may be calculated on the basis of the (actual or apparent) association constant (KA), by means of the relationship (KD = 1 / KA). KA = 1 / KD --> KA= [AB] / [A].[B]. The term “about” used in the context of the parameters or parameter ranges of the provided herein shall have the following meanings. Unless indicated otherwise, where the term “about” is applied to a particular value or to a range, the value or range is interpreted as being as accurate as the method used to measure it. If no error margins are specified in the application, the last decimal place of a numerical value indicates its degree of accuracy. Where no other error margins are given, the maximum margin is ascertained by applying the rounding-off convention to the last decimal place, e.g., for a pH value of about pH 2.7, the error margin is 2.65-2.74. However, for the following parameters, the specific margins shall apply: a temperature specified in °C with no decimal place shall have an error margin of ± 1°C (e.g., a temperature value of about 50°C means 50°C ± 1°C); a time indicated in hours shall have an error margin of 0.1 hours irrespective of the decimal places (e.g., a time value of about 1.0 hours means 1.0 hours ± 0.1 hours; a time value of about 0.5 hours means 0.5 hours ± 0.1 hours). In the present application, any parameter indicated with the term “about” is also contemplated as being disclosed without the term “about”. In other words, embodiments referring to a parameter value using the term “about” shall also describe an embodiment directed to the numerical value of said parameter as such. For example, an embodiment specifying a pH of “about pH 2.7” shall also disclose an embodiment specifying a pH of “pH 2.7” as such; an embodiment specifying a pH range of “between about pH 2.7 and about pH 2.1” shall also describe an embodiment specifying a pH range of “between pH 2.7 and pH 2.1”, etc. For the purposes of comparing two or more nucleotide sequences, the percentage of “sequence identity” between a first nucleotide sequence and a second nucleotide sequence may be calculated by dividing [the number of nucleotides in the first nucleotide sequence that are identical to the nucleotides at the corresponding positions in the second nucleotide sequence] by [the total number of nucleotides in the first nucleotide sequence] and multiplying by [100%], in which each deletion, insertion, substitution or addition of a nucleotide in the second nucleotide sequence – compared to the first nucleotide sequence – is considered as a difference at a single nucleotide (position). Alternatively, the degree of sequence identity between two or more nucleotide sequences may be calculated using a known computer algorithm for sequence alignment such as NCBI Blast v2.0, using standard settings. Some other techniques, computer algorithms and settings for determining the degree of sequence identity are for example described in WO 04 / 037999, EP 0967284, EP 1085089, WO 00 / 55318, WO 00 / 78972, WO 98 / 49185 and GB 2357768. Usually, for the purpose of determining the percentage of “sequence identity” between two nucleotide sequences in accordance with the calculation method outlined hereinabove, the nucleotide sequence with the greatest number of nucleotides will be taken as the “first” nucleotide sequence, and the other nucleotide sequence will be taken as the “second” nucleotide sequence. For the purposes of comparing two or more amino acid sequences, the percentage of “sequence identity” between a first amino acid sequence and a second amino acid sequence (also referred to herein as “amino acid identity”) may be calculated by dividing [the number of amino acid residues in the first amino acid sequence that are identical to the amino acid residues at the corresponding positions in the second amino acid sequence] by [the total number of amino acid residues in the first amino acid sequence] and multiplying by [100%], in which each deletion, insertion, substitution or addition of an amino acid residue in the second amino acid sequence – compared to the first amino acid sequence – is considered as a difference at a single amino acid residue (position), i.e., as an “amino acid difference” as defined herein. Alternatively, the degree of sequence identity between two amino acid sequences may be calculated using a known computer algorithm, such as those mentioned above for determining the degree of sequence identity for nucleotide sequences, again using standard settings. Usually, for the purpose of determining the percentage of “sequence identity” between two amino acid sequences in accordance with the calculation method outlined hereinabove, the amino acid sequence with the greatest number of amino acid residues will be taken as the “first” amino acid sequence, and the other amino acid sequence will be taken as the “second” amino acid sequence. Also, in determining the degree of sequence identity between two amino acid sequences, the skilled person may take into account so-called “conservative” amino acid substitutions, which can generally be described as amino acid substitutions in which an amino acid residue is replaced with another amino acid residue of similar chemical structure and which has little or essentially no influence on the 3D structure, function, activity, or other biological properties of the polypeptide. Such conservative amino acid substitutions are well known in the art, for example from WO 04 / 037999, GB 335768, WO 98 / 49185, WO 00 / 46383, and WO 01 / 09300; and (preferred) types and / or combinations of such substitutions may be selected on the basis of the pertinent teachings from WO 04 / 037999 as well as WO 98 / 49185 and from the further references cited therein. Such conservative substitutions preferably are substitutions in which one amino acid within the following groups (a) – (e) is substituted by another amino acid residue within the same group: (a) small aliphatic, nonpolar or slightly polar residues: Ala, Ser, Thr, Pro and Gly; (b) polar, negatively charged residues and their (uncharged) amides: Asp, Asn, Glu and Gln; (c) polar, positively charged residues: His, Arg and Lys; (d) large aliphatic, nonpolar residues: Met, Leu, Ile, Val and Cys; and (e) aromatic residues: Phe, Tyr and Trp. Particularly preferred conservative substitutions are as follows: Ala into Gly or into Ser; Arg into Lys; Asn into Gln or into His; Asp into Glu; Cys into Ser; Gln into Asn; Glu into Asp; Gly into Ala or into Pro; His into Asn or into Gln; Ile into Leu or into Val; Leu into Ile or into Val; Lys into Arg, into Gln or into Glu; Met into Leu, into Tyr or into Ile; Phe into Met, into Leu or into Tyr; Ser into Thr; Thr into Ser; Trp into Tyr; Tyr into Trp; and / or Phe into Val, into Ile or into Leu. Amino acid sequences and nucleic acid sequences are said to be “exactly the same” if they have 100% sequence identity (as defined herein) over their entire length. When comparing two amino acid sequences, the term “amino acid difference” refers to an insertion, deletion or substitution of a single amino acid residue on a position of the first sequence, compared to the second sequence; it being understood that two amino acid sequences may contain one, two or more such amino acid differences. According to the present description, “protein solubility” is a thermodynamic parameter defined as the concentration of protein in a saturated solution that is in equilibrium with a solid phase, either crystalline or amorphous, under a given set of conditions (see, e.g., Kramer RM. et al., “Toward a molecular understanding of protein solubility: increased negative surface charge correlates with increased solubility”, Biophys J., 2012, 102(8):1907-15). PROTEIN-BASED BUILDING BLOCK The molecule of the present technology comprises, or alternatively, consists of, at least one protein-based carrier building block (also referred herein as “carrier building block”, “protein- based building block”, or simply “building block” or “carrier”), as defined herein. For instance, the molecule of the present technology may comprise or, alternatively, consist of, a single protein-based carrier building block. In other embodiments, the molecule comprises more than one protein-based building blocks, such as two, three, four, five, six or more carrier building blocks. The protein-based carrier building block comprises (and, preferably, consists of) at least part of a protein or a whole structured protein, i.e., the protein-based carrier building block is preferably a polypeptide. The protein-based carrier building block is designed as a “carrier” or “delivery” moiety, with at least one attachment point or conjugation site, preferably with at least two attachment points or conjugation sites, for conjugation or attachment of cargos, as defined in detail below. Suitable cargos include proteins, peptides, toxic payloads, nucleic acids, oligonucleotides, fluorophores, glycans, chelators for / and radio-isotopes, polyethylene glycol (PEG) molecules, vitamins (such as biotin or folate), etc. Specific non-limiting examples of suitable cargos are depicted below in the present description. An attachment point or conjugation site, in the context of the present technology, refers to any group comprised in the protein-based building block which is suitable for attaching or conjugating a cargo to it. The attachment point or conjugation site is preferably present at a solvent-accessible position in the protein-based building block, as explained in detail below. An attachment point or conjugation site may be a reactive group present in the side chain of any amino acid in the protein-based carrier building block, preferably an amino acid present at a solvent-accessible position in the protein-based carrier building block, or may be the N- terminal primary amine, and / or the C-terminal carboxylic group of the protein-based building block. The attachment point / conjugation site allows the formation of a covalent bond with a group present in the cargo to be conjugated and / or attached to the protein-based carrier building block. In a preferred embodiment, the attachment point or conjugation site is a reactive group present in the side chain of an amino acid in the protein-based carrier building block, preferably present at a solvent-accessible position in the protein-based carrier building block, which allows the formation of a covalent bond with a group present in the cargo to be conjugated and / or attached to the protein-based carrier building block. In another embodiment, two of the conjugation sites or attachment points of the protein-based building block are reactive groups present in the side chain of two amino acids present in the protein- based carrier building block, preferably two amino acid presents at solvent-accessible positions in the protein-based carrier building block. In another embodiment, all of the conjugation sites or attachment points of the protein-based building block are reactive groups present in the side chain of amino acids present in the protein-based carrier building block, preferably amino acid presents at solvent-accessible positions in the protein-based carrier building block. Globular three dimensional (3D) structure The protein-based carrier building block of the present technology has a globular three- dimensional (3D) structure, i.e., it is or comprises a structured protein with a globular 3D structure. Globular proteins have approximately spherical shape. Nearly all globular proteins contain substantial numbers of α-helices and / or β-sheets folded into a compact structure that is stabilized by both polar and nonpolar interactions. The globular 3D structure forms naturally and often involves interactions mediated by the side chains of the amino acids. Most often, the hydrophobic amino acid side chains are buried, closely packed, in the interior of a globular protein, out of contact with water. Hydrophilic amino acid side chains lie on the surface of the globular proteins exposed to the water. Consequently, globular proteins are usually very soluble in aqueous solutions (from “Gene Expression: Translation of the Genetic Code”, Chang-Hui Shen, in Diagnostic Molecular Biology, 2019). In the context of the present technology, a protein or part of a protein with globular 3D structure can be defined as a protein or part of it which comprises at least one α-helix and / or at least one β-sheet as part of its secondary structure. From a simple sequence of amino acids to its final 3D structure, a protein passes through four levels of structuring known as primary, secondary, tertiary, and quaternary. At the end of these stages the protein begins to fold up into a stable 3D structure that will allow it to fulfil its proper function. Hence, the amino acid sequence of a protein is known as the “primary structure” of that protein. The “secondary structure” can be defined as the arrangement of a polypeptide chain into more or less regular hydrogen-bonded structures, and it has two basic elements: o Alpha helix - spiral configuration of a polypeptide chain with 3.6 residues (amino acids) per turn. The helix may be left-handed or right-handed, and the latter is more common. o Beta strand (or beta-sheet) - two adjacent polypeptide strands that are bonded together. Two or more strands may interact to form a beta sheet. Finally, the “tertiary structure” can be defined as the level of protein structure at which an entire polypeptide chain has folded into a 3D structure. In multi-chain proteins, the term tertiary structure applies to the individual chains. See Smith, A.D., et al., eds.1997, Oxford Dictionary of Biochemistry and Molecular Biology, New York: Oxford University Press. The three-dimensional structure of a protein can be determined by techniques such as X-ray crystallography, nuclear magnetic resonance (NMR), cryo-electron microscopy (EM) or circular dichroism (CD). X-ray crystallography is a common technique used to determine 3D protein structure, but also NMR (suited for small proteins) and cryo-EM (suited for large proteins) can provide information about a protein's tertiary structure. Circular dichroism is an excellent method for rapidly evaluating the secondary structure, folding and binding properties of proteins, see, e.g., Jones, C. (“Circular dichroism of biopharmaceutical proteins in a quality-regulated environment”, J Pharm Biomed Anal., 2022, 219:114945). Because the CD spectra of proteins are so dependent on their conformation, CD can be used to estimate the structure of unknown proteins and monitor conformational changes due to temperature, mutations, heat, denaturants or binding interactions. For instance, α-helical proteins have negative bands at 222 nm and 208 nm and a positive band at 193 nm. Proteins with well- defined antiparallel β-pleated sheets (β-helices) have negative bands at 218 nm and positive bands at 195 nm, while disordered proteins have very low ellipticity above 210 nm and negative bands near 195 nm. See Greenfield NJ., “Using circular dichroism spectra to estimate protein secondary structure”, Nat Protoc., 2006, 1(6):2876-90 for further details. Hence, the protein-based carrier building block of the present technology comprises at least one α-helix and / or at least one β-sheet as part of its secondary structure, preferably more than one α-helix and / or more than one β-sheet as part of its secondary structure, leading to a globular 3D tertiary structure. This allows the engineering of site- and stereospecific- conjugation sites or attachment points, as described in detail in this specification. The presence of at least one α-helix and / or at least one β-sheet in a certain polypeptide or protein can be determined by known techniques, as explained above, such as, e.g., CD. Solubility The protein-based carrier building block of the present technology is soluble. In the context of the present technology, a soluble building block means that the building block has a solubility of 10 mg / mL or more, preferably of 20 mg / mL, preferably of 50 mg / mL or more, and even more preferably of 100 mg / mL or more, measured in water or a suitable buffer or solvent (e.g., an aqueous solution, or a physiological buffer, such as a buffer which is amenable for parenteral administration) at room temperature (RT). In a preferred embodiment, the solubility of the protein-based carrier building block is measured in water or in a suitable buffer at RT, more preferably in a buffer such as citrate buffer (e.g., citrate buffer 5 mM) or PBS, at pH 7.0 or 7.4, at RT. Other preferred suitable buffers which are suitable for measuring the solubility of the protein-based carrier building block are Dulbecco’s phosphate buffered saline (DPBS, which is a balanced salt solution containing potassium chloride, monobasic potassium phosphate, sodium chloride, and dibasic sodium phosphate, e.g., 2.7 mM KCl, 1.5 mM KH2PO4, 136.9 mM NaCl, 8.9 mM Na2HPO4•7H2O, pH7.0-7.3, commercially available from GIBCO (Nr14190-094)), preferably pH 7.0 or 7.3 or 7.4, at RT, or histidine buffer at pH 6.5, at RT (comprising histidine (10 mM to 100 mM, such as 10 mM), sucrose (1% to 10%, such as 10%) and, optionally, Tween 80 (0.001% to 1%, such as 0.01%)), or phosphate buffer pH 7.0, at RT (comprising NaH2PO4 / Na2HPO4 (10 and 50 mM, such as 10 mM), sodium chloride (NaCl) (100-150 mM, such as 130 mM NaCl) and, optionally, Tween 80 (0.001% to 1%, such as 0.01%)). The skilled person is aware of methods to measure the solubility of a protein solution. For instance, the supplementary material of Kramer RM. et al., “Toward a molecular understanding of protein solubility: increased negative surface charge correlates with increased solubility”, Biophys J., 2012, 102(8):1907-15) describes solubility measurements of folded proteins. Additionally or alternatively, solubility measurements can be performed as follows. The protein solution (e.g., in citrate buffer 5 mM, pH 7.0, or in PBS pH 7.4, or in water, or in any of the suitable buffers described above) is concentrated by ultrafiltration (e.g., via tangential flow filtration (TFF)) until some cloudiness appears in the solution. Then, the solution is spined at high speed or 0.22 µm filtered to remove any non-soluble material, and the OD280of the supernatant is measured. Using the molar extinction coefficient of the specific protein, the protein concentration of the supernatant (and, thus, the concentration of the protein in a saturated solution that is in equilibrium with a solid phase, i.e., the protein solubility) is obtained. For instance, in the context of the present technology, physiological buffers suitable for parenteral administration can include the following components: Glutamate, Tartrate, Lactate, Citrate, Malate, Gluconate, Ascorbate, Maleate, Phosphate, Succinate, Acetate, Bicarbonate, Aspartate, Histidine, Benzoate, Tromethamine, Diethanolamine, Ammonium or Glycine. The most common buffers used in parenteral formulations are based on histidine, citrate, phosphate, and acetate (see, e.g., Broadhead J, Gibson M., “Parenteral dosage forms”, in: Gibson M., editor, “Pharmaceutical preformulation and formulation”, New York: Informa healthcare; 2009, p.325–47). Preferably, the protein-based carrier building block of the present technology is soluble in reduced state, i.e., it is soluble when the -SH groups (e.g., in the side chain of one or more Cys) present at solvent accessible positions in its amino acid sequence, if any, is(are) in a reduced form (as “-SH”), and not oxidized. For instance, a protein-based carrier building block may be reduced when subjected to reducing conditions for enough time. For instance, reducing conditions may mean using beta-mercaptoethanol (2-ME), dithiothreitol (DTT) or and TCEP (Tris (2-carboxyethyl) phosphine). Size (molecular mass)The protein-based carrier building block of the present technology has a size (molecular mass) of about 2.5 to about 70 kDa, such as about 2.5, 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, 65 or about 70 kDa. Preferably, the building block is a small building block with a size of about 2.5 to about 50 kDa, such as of about 2.5 to about less than 50 kDa, such as about 2.5 to about 40 kDa, or about 2.5 to about 35 kDa, more preferably of about 2.5 to about 30 kDa, such as about 5 to about 30 kDa, or about 7 to about 30 kDa, or about 10 to about 30 kDa, or about 2.5 to about 25 kDa, or about 5 to about 25 kDa, or about 7 to about 25 kDa, or about 10 to about 25 kDa, or about 2.5 to about 20 kDa, or about 5 to about 20 kDa, or about 7 to about 20 kDa, or about 10 to about 20 kDa, or about 2.5 to about 18 kDa, or about 5 to about 18 kDa, or about 7 to about 18 kDa, or about 10 to about 18 kDa. More preferably, the building block of the present technology has a size of about 2.5 to about 16 kDa, such as about 5 to about 16 kDa, or about 7 to about 16 kDa, or about 10 to about 16 kDa, or such as about 2.5, 3, 5, 6.5, 7, 10, 11, 12, 13, 14, 15 or 16 kDa. For instance, the protein-based building block may have a size (molecular mass) of about 6 kDa, or of about 7 kDa, or of about 15 kDa, or of about 16 kDa. In an even more preferred embodiment, the protein-based carrier building block has a size of about 15 kDa. Non-functionality The protein-based carrier building block of the present technology does not specifically bind to any human protein. If the building block shows any interaction with one or more human proteins, such interaction is characterized by low specificity and / or low affinity, as defined herein. For instance, the protein-based carrier building block of the present technology does not specifically bind crystallizable fragment (Fc) receptors (FcRs), Fc-binding proteins or Fc- sensors. For instance, the protein-based carrier building block does not specifically bind C- type lectin receptors (CLRs). All antibodies possess two functional domains — one that confers antigen specificity, known as the antigen-binding fragment (Fab), and another that drives antibody function, known as the crystallizable fragment (Fc). The specific effector functions that are triggered by antibodies are determined by the receptors to which the antibody Fc domain binds and the specific innate immune cells on which these FcRs are expressed. These sensors include both classical FcRs and non-classical C-type lectin receptors (CLRs), see Lu, L. et al., “Beyond binding: antibody effector functions in infectious diseases”, Nat Rev Immunol, 2018, 18, 46–61. Table 1 of Lu, L. et al provides non-limiting examples of Fc domain sensors (e.g., Fcγ or FcRn) to which the protein-based carrier building block of the present technology do not specifically bind. Consequently, the protein-based carrier building block of the present technology does not show effector functions of conventional antibodies mediated by the Fc domain. In another embodiment, the protein-based carrier building block and / or the molecule does not specifically bind crystallizable fragment (Fc) receptors (FcRs), Fc-binding proteins or Fc-sensors. For instance, the protein-based carrier building block and / or the molecule does not specifically bind C-type lectin receptors (CLRs). Hence, in one embodiment, none of the components comprised in the molecule of the present technology (e.g., at least one protein-based carrier building block and / or at least one cargo attached or conjugated to it) specifically bind crystallizable fragment (Fc) receptors (FcRs), Fc-binding proteins, Fc- sensors and / or CLRs. In another embodiment, the protein-based building block and / or the molecule of the present technology does not show effector functions of conventional antibodies mediated by the Fc domain, i.e., none of the components comprised in the molecule of the present technology show effector functions of conventional antibodies mediated by the Fc domain. In one embodiment, the molecule of the present technology does not include conventional VH-VLpairing / interaction and / or does not include CL-CH1 pairing such as CL-CH1 binding disulphide bridges. In another embodiment, the protein-based carrier building block of the present technology does not specifically bind the variable domain of the light chain (VL) and / or the variable domain of the heavy chain (VH) of an antibody, such as the VL and / or the VH of a monoclonal antibody (mAb). In another embodiment, the protein-based carrier building block does not specifically bind the first constant domain of the heavy chain (CH1) of an antibody, such as the CH1 of a mAb. In another embodiment, the protein-based carrier building block does not specifically bind the constant domain of the light chain (CL) of an antibody, such as the CL of a mAb. In another embodiment, the protein-based carrier building block does not specifically bind the third constant domain of the heavy chain (CH3) of an antibody, such as the CH3 of a mAb. In another embodiment, the protein-based carrier building block does not specifically bind the second constant domain of the heavy chain (CH2) of an antibody, such as the CH2 of a mAb. In one embodiment, the molecule and / or the building block of the present technology is not a Fab fragment from an antibody, such as from a mAb. In one embodiment, the molecule and / or the building block of the present technology is not a CH, preferably is not a CH1 fragment from an antibody, such as from a mAb. The molecule and / or the building block of the present technology is not an antibody, such as a mAb, is not a Fc fragment, or a Fv fragment. The protein-based carrier building block of the present technology may derive from a target- binding protein (such as an ISVD, a DARPin, an affibody or an affitin) (the “protein-based carrier building block precursor”). In the context of the present technology, a “protein-based carrier building block precursor” or “building block precursor” is a protein-based moiety which may be modified to generate the protein-based carrier building block comprised in the molecule of the present technology. In the context of the present technology, the “protein-based carrier building block precursor” is a protein which is modified (e.g., by point mutations and / or by addition / deletion of amino acids to its sequence) to generate the protein-based carrier building block of the present technology. For instance, the “protein-based carrier building block precursor” is modified so that it no longer specifically binds any human protein, preferably so that it also does not specifically bind any (non-human) molecule (including non-human biomolecule) and / or any non-protein (human) molecule (including biomolecule), in particular any molecule (including biomolecule) to which the precursor specifically binds. In addition, if necessary, the “protein- based carrier building block precursor” is modified so that it incorporates one or more attachment points or conjugation sites as described herein. The “protein-based carrier building block precursor” has a sequence identity of at least 60%, such as at least 70%, or at least 75%, preferably of at least 80% with the protein-based carrier building block derived from it. For instance, the “protein-based carrier building block precursor” has a sequence identity of at least 85%, such as at least 90%, such as at least 91%, such as at least 92%, such as at least 93%, such as at least 94%, such as at least 95%, such as at least 96%, such as at least 97%, such as at least 98%, such as at least 99%, or more with the protein-based carrier building block derived from it. For instance, the “protein-based carrier building block precursor” may share the whole amino acid sequence with protein-based carrier building block derived from it with the exception of at least one, such as one, two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, fifteen, twenty or more amino acids. Of course, the protein-based carrier building block derived from a protein-based carrier building block precursor has a globular 3D structure, is soluble, has a size (molecular mass) of about 2.5 to about 70 kDa, such as about 2.5 to about 50 kDa, such as of about 2.5 to less than 50 kDa, more preferably of about 2.5 to about 30 kDa, such as about 2.5 to about 16 kDa, such as about 5 to about 16 kDa, or about 7 to about 16 kDa, or about 10 to about 16 kDa, does not specifically bind any human protein and preferably does not specifically bind any protein or non-protein molecule to which the precursor specifically binds. Preferably, the carrier building block of the present technology does also not specifically bind to any non-protein molecule (including non-protein biomolecules, such as nucleic acids, e.g., DNA and / or RNA, lipids (e.g., phosphatidylserine (PS)) or glycans), e.g., to any non-protein human molecule (including biomolecule), such as human nucleic acids, e.g., human DNA and / or human RNA, human lipids (e.g., such as phosphatidylserine (PS)) or human glycans, e.g., human glycoplipids. In particular, preferably, the carrier building block does also not specifically bind to any non-protein molecule (including biomolecules) (such as nucleic acids such as DNA and / or RNA, lipids (e.g., such as phosphatidylserine (PS)) or glycans), e.g., to any non-protein human molecule (including biomolecules), such as human nucleic acids, e.g.,human DNA and / or human RNA, human lipids (e.g., phosphatidylserine (PS)) or human glycans, e.g., human glycoplipids to which the protein-based carrier building block precursor specifically binds (i.e., the protein-based building block preferably does also not specifically bind to the precursor’s target, e.g., a non-protein molecule (including biomolecules) or a non- human protein). In another preferred embodiment, the protein-based building block of the present technology does also not specifically bind to any (non-human) molecule (including biomolecules) which the protein-based carrier building block precursor specifically binds to (i.e., the protein-based building block preferably does also not specifically bind to the precursor’s target, e.g., a non- human protein or a non-protein molecule (including biomolecules)), or binds to any (non- human) molecule which the protein-based carrier building block precursor specifically binds to (i.e., the protein-based building block preferably does also not specifically bind to the precursor’s target, e.g., a non-human protein or a non-protein molecule) with a KD value greater than 5x10-4mol / litre, as described herein. For example, if the precursor of the protein-based carrier building block is an anti-RSV (respiratory syncytial virus) ISVD (i.e., it specifically binds one or more proteins of RSV, such as protein F of RSV), the protein-based carrier building block derived from it preferably does not specifically bind those RSV proteins (or binds those proteins, such as protein F of RSV preferably with a KDvalue greater than 5x10-4mol / litre, as described herein). For example, if the precursor of the protein-based carrier building block specifically binds to virus (e.g., it is an anti-viral ISVD, an anti-viral DARPin, an anti-viral affitin, an anti-viral affibody, or the like) and / or to viral molecules (e.g., it specifically binds one or more viral biomolecules, e.g., viral proteins, viral nucleic acids, viral lipids or viral glycans), the protein- based carrier building block derived from it preferably does not specifically bind those virus and / or viral molecules (or binds those virus and / or viral molecules preferably with a KDvalue greater than 5x10-4mol / litre, as described herein). In other embodiments, the protein-based carrier building block specifically binds to virus (e.g., it is an anti-viral ISVD, an anti-viral DARPin, an anti-viral affitin, an anti-viral affibody, or the like) and / or to viral molecules (e.g., it specifically binds one or more viral biomolecules, e.g., viral proteins, viral nucleic acids, viral lipids or viral glycans), as its precursor does, but the specific binding is eliminated when at least a cargo is attached to the protein-based building block. Example of viruses which the protein-based building block precursor (and / or protein-based building block of the present technology) may specifically bind are the following: RSV, influenza virus, rabies virus, potyvirus, bacteriophage, rotavirus, HIV protein, Hepatitis B virus, Hepatitis C virus, norovirus, Shiga toxins from lambdoid prophages, Herpes simplex virus, Grapevine fanleaf virus (GFLV), Ebola, Middle East respiratory syndrome (MERS) virus, acute respiratory syndrome (SARS) virus, SARS-COV2, Vibrio or a White Spot Syndrome virus, cytomegalovirus, parvovirus, ZIKA virus, Chikungunya Virus (CHIKV). Hence, in one embodiment, the protein-based building block precursor, e.g., an ISVD, may specifically bind to one or more of these viruses (or molecules, including biomolecules, comprised therein). The resulting protein-based building block may not specifically bind to the virus (or molecules, including biomolecules, comprised therein) to which the precursor binds. If the protein-based building block of the present technology shows specific binding towards one or more of these viruses (or molecules, including biomolecules, comprised therein), that specific binding as described herein is lost when at least a cargo is attached to the at least one conjugation site comprised therein. For example, if the precursor of the protein-based carrier building block specifically binds to protozoa (a microorganism, unicellular eukaryote) (e.g., it is an anti-protozoa ISVD, an anti- protozoa DARPin, an anti-protozoa affitin, an anti-protozoa affibody, or the like) and / or to protozoa molecules (e.g., it specifically binds one or more protozoa biomolecules, e.g., protozoa proteins, protozoa nucleic acids, protozoa lipids or protozoa glycans), the protein- based carrier building block derived from it preferably does not specifically bind those protozoa and / or protozoa molecules (or binds those protozoa and / or protozoa molecules preferably with a KDvalue greater than 5x10-4mol / litre, as described herein). In other embodiments, the protein-based carrier building block specifically binds to protozoa (e.g., it is an anti-protozoa ISVD, an anti-protozoa DARPin, an anti-protozoa affitin, an anti-protozoa affibody, or the like) and / or to protozoa molecules (e.g., it specifically binds one or more protozoa biomolecules, e.g., protozoa proteins, protozoa nucleic acids, protozoa lipids or protozoa glycans), as its precursor does, but the specific binding is eliminated when at least a cargo is attached to the protein-based building block. Examples of protozoa and protozoa molecules to which the protein-based building block precursor (and / or protein-based building block of the present technology) may specifically bind are the following: Trypanosoma evansi, Eimeria stiedae, Variant surface glycoprotein (VSG). Hence, in one embodiment, the protein- based building block precursor, e.g., an ISVD, may specifically bind to one or more of these protozoa (or molecules, including biomolecules, comprised therein). The resulting protein- based building block may not specifically bind to the protozoa (or molecules, including biomolecules, comprised therein) to which the precursor binds. If the protein-based building block of the present technology shows specific binding towards one or more of these protozoa (or molecules, including biomolecules, comprised therein), that specific binding as described herein is lost when at least a cargo is attached to the at least one conjugation site comprised therein. For example, if the precursor of the protein-based carrier building block specifically binds to mammalian proteins (e.g., it is an anti-mammalian protein ISVD, an anti-mammalian protein DARPin, an anti-mammalian protein affitin, an anti-mammalian protein affibody, or the like), the protein-based carrier building block derived from it preferably does not specifically bind those mammalian proteins (or binds those mammalian proteins preferably with a KD value greater than 5x10-4mol / litre, as described herein). In other embodiments, the protein-based carrier building block specifically binds to mammalian proteins, as its precursor does, but the specific binding is eliminated when at least a cargo is attached to the protein-based building block. Example of a mammalian protein to which the protein-based building block precursor (and / or protein-based building block of the present technology) may specifically bind is bovine serum albumin. Hence, in one embodiment, the protein-based building block precursor, e.g., an ISVD, may specifically bind to this mammalian protein. The resulting protein-based building block may not specifically bind to the mammalian protein to which the precursor binds. If the protein-based building block of the present technology shows specific binding towards this mammalian protein, that specific binding as described herein is lost when at least a cargo is attached to the at least one conjugation site comprised therein. For example, if the precursor of the protein-based carrier building block specifically binds to avian proteins (e.g., it is an anti-avian protein ISVD, an anti-avian protein DARPin, an anti-avian protein affitin, an anti-avian protein affibody, or the like), the protein-based carrier building block derived from it preferably does not specifically bind those avian proteins (or binds those avian proteins preferably with a KDvalue greater than 5x10-4mol / litre, as described herein). In other embodiments, the protein-based carrier building block specifically binds to avian proteins, as its precursor does, but the specific binding is eliminated when at least a cargo is attached to the protein-based building block. Example of an avian protein to which the protein-based building block precursor (and / or protein-based building block of the present technology) may specifically bind is Ovalbumin (chicken). Hence, in one embodiment, the protein-based building block precursor, e.g., an ISVD, may specifically bind to this avian protein. The resulting protein-based building block may not specifically bind to the avian protein to which the precursor binds. If the protein-based building block of the present technology shows specific binding towards this avian protein, that specific binding as described herein is lost when at least a cargo is attached to the at least one conjugation site comprised therein. For example, if the precursor of the protein-based carrier building block specifically binds to yeast and / or moulds proteins (e.g., it is an anti-yeast and / or anti-moulds protein ISVD, an anti- yeast and / or moulds protein DARPin, an anti-yeast and / or moulds protein affitin, an anti-yeast and / or moulds protein affibody, or the like), the protein-based carrier building block derived from it preferably does not specifically bind those yeast and / or moulds proteins (or binds those yeast and / or moulds proteins preferably with a KD value greater than 5x10-4mol / litre, as described herein). In other embodiments, the protein-based carrier building block specifically binds to yeast and / or moulds proteins, as its precursor does, but the specific binding is eliminated when at least a cargo is attached to the protein-based building block. Examples of yeast and moulds proteins to which the protein-based building block precursor (and / or protein-based building block of the present technology) may specifically bind are yeast extract, inactivated yeast, Candida. Hence, in one embodiment, the protein-based building block precursor, e.g., an ISVD, may specifically bind to one or more of these yeast and / or moulds proteins. The resulting protein-based building block may not specifically bind to at least one of these yeast and / or moulds proteins to which the precursor binds. If the protein-based building block of the present technology shows specific binding towards these yeast and / or moulds proteins, that specific binding as described herein is lost when at least a cargo is attached to the at least one conjugation site comprised therein. For example, if the precursor of the protein-based carrier building block specifically binds to plant proteins (e.g., it is an anti-plant protein ISVD, an anti-plant protein DARPin, an anti-plant protein affitin, an anti-plant protein affibody, or the like), the protein-based carrier building block derived from it preferably does not specifically bind those plant proteins (or binds those plant proteins preferably with a KD value greater than 5x10-4mol / litre, as described herein). In other embodiments, the protein-based carrier building block specifically binds to plant proteins, as its precursor does, but the specific binding is eliminated when at least a cargo is attached to the protein-based building block. Examples of plant proteins to which the protein- based building block precursor (and / or protein-based building block of the present technology) may specifically bind are Starch Branching Enzyme II (maize), polyphenol, Linoic acid (Sunflower, maize), plant seed. Hence, in one embodiment, the protein-based building block precursor, e.g., an ISVD, may specifically bind to one or more of these plant proteins. The resulting protein-based building block may not specifically bind to at least one of these plant proteins to which the precursor binds. If the protein-based building block of the present technology shows specific binding towards these plant proteins, that specific binding as described herein is lost when at least a cargo is attached to the at least one conjugation site comprised therein. For example, if the precursor of the protein-based carrier building block specifically binds to fungi proteins (e.g., it is an anti-fungi protein ISVD, an anti-fungi protein DARPin, an anti-fungi protein affitin, an anti-fungi protein affibody, or the like), the protein-based carrier building block derived from it preferably does not specifically bind those fungi proteins (or binds those fungi proteins preferably with a KDvalue greater than 5x10-4mol / litre, as described herein). In other embodiments, the protein-based carrier building block specifically binds to fungi proteins, as its precursor does, but the specific binding is eliminated when at least a cargo is attached to the protein-based building block. Examples of fungi proteins to which the protein- based building block precursor (and / or protein-based building block of the present technology) may specifically bind are Cutinase, chitin, fungus sphingolipids. Hence, in one embodiment, the protein-based building block precursor, e.g., an ISVD, may specifically bind to at least one of these fungi proteins. The resulting protein-based building block may not specifically bind to the at least one of these fungi protein to which the precursor binds. If the protein-based building block of the present technology shows specific binding towards at least one of these fungi proteins, that specific binding as described herein is lost when at least a cargo is attached to the at least one conjugation site comprised therein. For example, if the precursor of the protein-based carrier building block specifically binds to bacteria (e.g., it is an anti-bacterial ISVD, an anti-bacterial DARPin, an anti-bacterial affitin, an anti-bacterial affibody, or the like) and / or to bacterial molecules (e.g., it specifically binds one or more bacterial biomolecules, e.g., bacterial proteins, bacterial nucleic acids, bacterial lipids or bacterial glycans), the protein-based carrier building block derived from it preferably does not specifically bind those bacteria and / or bacterial molecules (or binds those bacteria and / or bacterial molecules preferably with a KD value greater than 5x10-4mol / litre, as described herein). In other embodiments, the protein-based carrier building block specifically binds to bacteria (e.g., it is an anti-bacterial ISVD, an anti-bacterial DARPin, an anti-bacterial affitin, an anti-bacterial affibody, or the like) and / or to bacterial molecules (e.g., it specifically binds one or more bacterial biomolecules, e.g., bacterial proteins, bacterial nucleic acids, bacterial lipids or bacterial glycans), as its precursor does, but the specific binding is eliminated when at least a cargo is attached to the protein-based building block. Examples of bacteria and bacterial molecules to which the protein-based building block precursor (and / or protein-based building block of the present technology) may specifically bind are the following: Beta-lactamase, tetanus toxin, Lactate Oxidase, Salmonella typhimurium, Helicobacter pylori, Mycobacterium tuberculosis, Clostridium difficile (toxin A and B), Pseudomonas aeruginosa, Bacillus anthracis, Botulinum Neurotoxin, Treponema pallidum, Chlamydia trachomatis, Escherichia coli, Campylobacter jejuni (flagella), Salmonella enterica, Bordetella pertussis (toxin), Shigella spp, Streptomyces venezuelae, chloramphenicol. Hence, in one embodiment, the protein-based building block precursor, e.g., an ISVD, may specifically bind to one or more of these bacteria (or their molecules, including biomolecules). The resulting protein-based building block may not specifically bind to the bacteria (or their molecules, including biomolecules) to which the precursor binds. If the protein-based building block of the present technology shows specific binding towards one or more of these bacteria (or molecules, including biomolecules, comprised therein), that specific binding as described herein is lost when at least a cargo is attached to the at least one conjugation site comprised therein. For example, if the precursor of the protein-based carrier building block specifically binds to non-human animal proteins, such as snake proteins (e.g., it is an anti-snake protein ISVD, an anti-snake protein DARPin, an anti-snake protein affitin, an anti-snake protein affibody, or the like), the protein-based carrier building block derived from it preferably does not specifically bind those snake proteins (or binds those snake proteins preferably with a KD value greater than 5x10-4mol / litre, as described herein). In other embodiments, the protein-based carrier building block specifically binds to snake proteins, as its precursor does, but the specific binding is eliminated when at least a cargo is attached to the protein-based building block. Example of a snake protein to which the protein-based building block precursor (and / or protein-based building block of the present technology) may specifically bind is Cobra toxin. Hence, in one embodiment, the protein-based building block precursor, e.g., an ISVD, may specifically bind to this snake protein. The resulting protein-based building block may not specifically bind to the snake protein to which the precursor binds. If the protein-based building block of the present technology shows specific binding towards this snake protein, that specific binding as described herein is lost when at least a cargo is attached to the at least one conjugation site comprised therein. For example, if the precursor of the protein-based carrier building block specifically binds to green fluorescent protein (GFP), which is a protein from Jellyfish (sea jellies) and corals, sea anemones, zoanithids, copepods and lancelets (e.g., it is an anti-GFP ISVD, an anti-GFP DARPin, an anti-GFP affitin, an anti-GFP affibody, or the like), the protein-based carrier building block derived from it preferably does not specifically bind GFP (or binds GFP preferably with a KDvalue greater than 5x10-4mol / litre, as described herein). In other embodiments, the protein- based carrier building block specifically binds to GFP, as its precursor does, but the specific binding is eliminated when at least a cargo is attached to the protein-based building block. Hence, in one embodiment, the protein-based building block precursor, e.g., an ISVD, may specifically bind to GFP. The resulting protein-based building block may not specifically bind to GFP to which the precursor binds. If the protein-based building block of the present technology shows specific binding towards GFP, that specific binding as described herein is lost when at least a cargo is attached to the at least one conjugation site comprised therein. For example, if the precursor of the protein-based carrier building block specifically binds to insect proteins (e.g., it is an anti-insect protein ISVD, an anti-insect protein DARPin, an anti- insect protein affitin, an anti-insect protein affibody, or the like), the protein-based carrier building block derived from it preferably does not specifically bind those insect proteins (or binds those insect proteins preferably with a KDvalue greater than 5x10-4mol / litre, as described herein). In other embodiments, the protein-based carrier building block specifically binds to insect proteins, as its precursor does, but the specific binding is eliminated when at least a cargo is attached to the protein-based building block. Examples of insect proteins to which the protein-based building block precursor (and / or protein-based building block of the present technology) may specifically bind are Androctonus autralis hecor toxins, chitin, chitin binding domain (CBD), V-ATPase subunit C, trehalase, cytochrome p450 monooxygenase, chitin deacetylase, chitin synthase and NPC1 sterol transporter. Hence, in one embodiment, the protein-based building block precursor, e.g., an ISVD, may specifically bind to at least one of these insect proteins. The resulting protein-based building block may not specifically bind to the at least one of these insect proteins to which the precursor binds. If the protein-based building block of the present technology shows specific binding towards at least one of these insect proteins, that specific binding as described herein is lost when at least a cargo is attached to the at least one conjugation site comprised therein. For example, if the precursor of the protein-based carrier building block specifically binds to chitin, which is a crustaceans protein (e.g., it is an anti-chitin ISVD, an anti-chitin DARPin, an anti-chitin affitin, an anti-chitin affibody, or the like), the protein-based carrier building block derived from it preferably does not specifically bind chitin (or binds chitin preferably with a KDvalue greater than 5x10-4mol / litre, as described herein). In other embodiments, the protein- based carrier building block specifically binds to chitin, as its precursor does, but the specific binding is eliminated when at least a cargo is attached to the protein-based building block. Hence, in one embodiment, the protein-based building block precursor, e.g., an ISVD, may specifically bind to chitin. The resulting protein-based building block may not specifically bind to chitin to which the precursor binds. If the protein-based building block of the present technology shows specific binding towards chitin, that specific binding as described herein is lost when at least a cargo is attached to the at least one conjugation site comprised therein. Hence, preferably, the protein-based carrier building block does not specifically bind to the precursor’s target, should the protein-based carrier building block precursor have a target and should this be a non-human molecule (including biomolecules), such as a non-human protein. Hence, in one embodiment, the at least one protein-based building block comprised in the molecule of the present technology does not specifically bind any RSV protein, such as protein F of RSV, or binds any RSV protein, such as protein F of RSV, with a KD (KD value) greater than 5x10-4mol / litre, as described herein. WO 2009 / 147248, Tables A-1 and A-2, provide examples of F-protein sequences. In one embodiment, the at least one protein-based building block comprised in the molecule of the present technology does not comprise / does not consist of an amino acid sequence selected from SEQ ID NO.: 1-34 as depicted on Tables A-1 and A-2 of WO 2016 / 055656. In another embodiment, the at least one protein-based building block comprised in the molecule of the present technology does not comprise / does not consist of the amino acid sequence as defined in SEQ ID NO.: 214. In a further preferred embodiment, the protein-based building block of the present technology, when it has at least one cargo (such as a “model cargo”, e.g. a maleimide-modified alanine) attached to it (via the at least one conjugation sites or attachment points comprised therein) does not specifically bind to any molecule (including biomolecules) which the protein- based carrier building block precursor specifically binds to (i.e., the protein-based building block, with at least a cargo attached to it, preferably does not specifically bind to the precursor’s target, e.g., a non-human protein or a non-protein molecule (including biomolecules)), or binds to any (non-human) molecule (including biomolecules) which the protein-based carrier building block precursor specifically binds to (i.e., the protein-based building block, with a cargo attached to it, preferably does also not specifically bind to the precursor’s target, e.g., a non-human protein or a non-protein molecule) with a KDvalue greater than 5x10-4mol / litre, as described herein. Hence, in a preferred embodiment, if the protein based carrier building block of the present technology shows any specific binding towards a specific target, such as towards a molecule (including biomolecules, e.g., human, non-human animal, plant, microbial, viral, etc.), or towards a cell (e.g., animal, human, plant cell), microorganisms, virus, etc., that specific binding is eliminated when at least a cargo is attached to at least one attachment point or conjugation site comprised in the protein-based building block. In this specific embodiment, the cargo attached to the protein-based building block may of course show specific binding towards a target (including biomolecules, as described herein), but the protein-based building block does no longer specifically binds its target. In a further preferred embodiment, the protein-based carrier building block of the present technology does not specifically bind to any human or non-human (e.g., non-human animal, plant, yeast, etc.) cell and / or cell type. If the building block shows any interaction with one or more human or non-human cells and / or cell types, such interaction is characterized by low specificity and / or low affinity, as defined herein. In particular, preferably, the carrier building block does also not specifically bind to any human or non-human cell and / or cell type to which the protein-based carrier building block precursor specifically binds (i.e., the protein-based building block preferably does also not specifically bind to the precursor’s target, e.g., a non- protein molecule or a protein present on the surface of a human cell). The lack of binding to any human or non-human cell and / or cell type can for example be assessed with the “cell binding assay” as described below (see also, e.g., Hunter SA and Cochran JR, “Cell-binding assays for determining the affinity of protein-protein interactions: technologies and considerations”, Methods Enzymol., 2016, 580:21-44). In another embodiment, the the protein-based carrier building block of the present technology does not specifically bind to any microorganism such as bacteria, fungi, protists, yeast and / or virus, or to any microbial or viral molecule (including biomolecules). If the building block shows any interaction with one or more microorganisms and / or virus, or with any microbial or viral molecule (including biomolecules), such interaction is characterized by low specificity and / or low affinity, as defined herein. In particular, preferably, the carrier building block does also not specifically bind to any microorganism and / or virus (or to any microbial or viral molecule (including biomolecules)) to which the protein-based carrier building block precursor specifically binds (i.e., the protein-based building block preferably does also not specifically bind to the precursor’s target, e.g., a virus, a microorganism, a non- protein molecule (including biomolecules) or a protein present on the surface of a microorganism and / or virus). The lack of binding to any microorganism, or virus, or microbial molecule, or viral molecule can for example be assessed with the “cell binding assay” and / or SPR as described herein. In another embodiment, the protein-based carrier building block of the present technology does not specifically bind to any microorganism such as bacteria, fungi, protists, yeast and / or virus (and / or to any microbial or viral molecule or biomolecule, such as microbial or viral proteins, nucleic acids, lipids, glycans, etc.) when it has at least one cargo (such as a “model cargo”, e.g. a maleimide-modified alanine) attached or conjugated to it (via the at least one attachment point or conjugation sites comprised therein). If the building block comprising the cargo attached to it shows any interaction with one or more microorganisms and / or virus (or with any microbial or viral molecule or biomolecule, such as microbial or viral proteins, nucleic acids, lipids, glycans, etc.), such interaction is characterized by low specificity and / or low affinity, as defined herein. In particular, preferably, the carrier building block does also not specifically bind to any microorganism and / or virus (or to any microbial or viral molecule or biomolecule, such as microbial or viral proteins, nucleic acids, lipids, glycans, etc.) to which the protein-based carrier building block precursor specifically binds when the protein-based carrier building block has at least one cargo attached or conjugated to it (i.e., the protein- based building block preferably does also not specifically bind to the precursor’s target , e.g., a non-protein molecule or biomolecule or a protein present on the surface of a microorganism and / or virus, or present in the microorganism or virus, when it has at least one cargo attached or conjugated to it). For instance, the protein-based building block of the present technology does not specifically bind to any viruses and / or viral proteins, such as RSV and / or one or more proteins of RSV, such as protein F of RSV, when the building block has at least a cargo attached or conjugated to it. Hence, for instance, the protein-based carrier building block (e.g., a DARPin-based carrier building block) may show specific binding towards a microorganism and / or a virus, such as RSV and / or RSV proteins, such as protein F of RSV, but the specific binding (as defined herein), if any, is lost when at least one cargo is attached or conjugated to the protein-based building block. The lack of specific binding to any microorganism can for example be assessed with the “cell binding assay” as described herein. The lack of specific binding to viruses, microbial and / or viral molecules or biomolecules can, for example, be assessed by surface plasmon resonance, as described herein. In another embodiment, the protein-based carrier building block of the present technology does not specifically bind to any molecule, including biomolecules, including human molecules and non-human molecules (including human and non-human biomolecules, e.g., human and / or non-human proteins, human and / or non-human nucleic acids such as DNA and / or RNA, human and / or non-human lipids (e.g., such as phosphatidylserine (PS)) or non-human glycans),or binds to any molecule, including bio molecules, including human molecules and non-human molecules (including human and non-human biomolecules, e.g., human and / or non-human proteins, nucleic acids such as DNA and / or RNA, lipids (e.g., such as phosphatidylserine (PS)) or glycans) with a KD (KD value) greater than 5x10-4mol / litre, as described herein. For instance, the protein-based carrier building block does not specifically bind to any human and / or non-human animal biomolecule (e.g., human and / or non-human animal proteins, human and / or non-human nucleic acids such as DNA and / or RNA, human and / or non-human lipids (e.g., such as phosphatidylserine (PS)) or human and / or non-human glycans), or binds to any human and / or non-human animal biomolecule with a KD (KD value) greater than 5x10-4mol / litre, as described herein. For instance, the protein-based carrier building block does not specifically bind to any bacterial molecule (including bacterial biomolecules, e.g., bacterial proteins, nucleic acids such as DNA and / or RNA, lipids (e.g., such as phosphatidylserine (PS)) or glycans), or binds to any bacterial molecule, as defined above, with a KD (KD value) greater than 5x10-4mol / litre, as described herein. For instance, the protein-based carrier building block of the present technology does not specifically bind to any viral molecule (including biomolecules, e.g., viral proteins, nucleic acids such as DNA and / or RNA, lipids (e.g., such as phosphatidylserine (PS)) or glycans), or binds to any viral molecule, as defined herein, with a KD(KDvalue) greater than 5x10-4mol / litre, as described herein. For instance, the protein-based carrier building block does not specifically bind to any fungi molecule (including biomolecules, e.g., fungi proteins, nucleic acids such as DNA and / or RNA, lipids (e.g., such as phosphatidylserine (PS)) or glycans), or binds to any fungi molecule, as defined herein, with a KD(KDvalue) greater than 5x10-4mol / litre, as described herein. For instance, the protein-based carrier building block does not specifically bind to any yeast molecule (including biomolecules, e.g., yeast proteins, nucleic acids such as DNA and / or RNA, lipids (e.g., such as phosphatidylserine (PS)) or glycans), or binds to any yeast molecule, as described herein, with a KD(KDvalue) greater than 5x10-4mol / litre, as described herein. For instance, the protein-based carrier building block does not specifically bind to any plant molecule (including biomolecules, e.g., plant proteins, nucleic acids such as DNA and / or RNA, lipids (e.g., such as phosphatidylserine (PS)) or glycans), or binds to any plant molecule, as defined herein, with a KD(KDvalue) greater than 5x10-4mol / litre, as described herein. For instance, the protein-based carrier building block does not specifically bind to any mammalian molecule (including mammalian biomolecules, e.g., mammalian proteins, nucleic acids such as DNA and / or RNA, lipids (e.g., such as phosphatidylserine (PS)) or glycans), or binds to any mammalian molecule, as defined herein, with a KD (KD value) greater than 5x10-4mol / litre, as described herein. In the context of the present technology, the term “biomolecule” or “biological molecule” refers to molecules present in organisms, including animals, plants, microorganisms that play a role in one or more biological processes, such as cell division, morphogenesis, or development. Biomolecules are the building blocks of life and perform important functions in living organisms. Biomolecules include the primary metabolites which are large macromolecules such as proteins, carbohydrates (glycans), lipids (e.g., such as PS), and nucleic acids (such as DNA, RNA), as well as small molecules such as vitamins and hormones. The four major types of biomolecules are carbohydrates (glycans), lipids, nucleic acids, and proteins. In a further preferred embodiment, the protein-based carrier building block of the present technology does not specifically bind any non-human protein and / or any non-protein molecule (including biomolecule) when at least one cargo (such as a “model cargo”, e.g. a maleimide-modified alanine) is conjugated to the at least one attachment point or conjugation site on the protein-based carrier building block, preferably it does not specifically bind any non-human protein and / or any non-protein molecule (including biomolecule) to which the protein-based carrier building block precursor specifically binds, or binds to them with a KD(KDvalue) greater than 5x10-4mol / litre, as described herein. Hence, in one embodiment, the present technology provides a molecule comprising at least one protein-based carrier building block as described in the present technology, wherein the protein-based carrier building block has at least a cargo (such as a “model cargo”, e.g. a maleimide-modified alanine) attached or conjugated to it (via the at least one attachment point or conjugation site comprised in the protein-based carrier building block), and wherein the protein-based carrier building block does not specifically bind to any molecule (including biomolecules) and / or organisms (such as cells, microorganisms, virus, etc.). Hence, in one embodiment, the protein-based building block, when at least a cargo is conjugated to it, loses its target binding specificity. For instance, the protein-based building block, comprising a cargo attached to it, does not specifically bind to any molecule (including biomolecules) and / or organisms (such as cells, microorganisms, virus, etc.) which the protein-based carrier building block precursor specifically binds (i.e., the protein-based building block, with at least a cargo attached to it, preferably does not specifically bind to the precursor’s target, or binds to any (non-human) molecule (including biomolecules) and / or organisms (such as cells, microorganisms, virus, etc.) which the protein-based carrier building block precursor specifically binds to (i.e., the protein-based building block, with a cargo attached to it, preferably does also not specifically bind to the precursor’s target) with a KD value greater than 5x10-4mol / litre, as described herein. The skilled person is aware of means for reducing and / or eliminating specific binding of a protein-based carrier building block precursor to proteins and / or non-protein molecules (including biomolecules). For instance, mutations may be performed in the amino acid sequence of the precursor building block so that it no longer specifically binds to human proteins, or to any non-human protein, or to non-protein molecules (including biomolecules), or binds to them with a KD (KD value) greater than 5x10-4mol / litre, as described herein. The affinity of a molecular interaction between two molecules (e.g., of two biomolecules) can be measured via different techniques known per se, such as the well-known surface plasmon resonance (SPR) biosensor technique (see for example Ober et al.2001, Intern. Immunology 13: 1551-1559, in particular section “Surface plasmon resonance (SPR) experiments” starting on p.1552, which describes conditions for measuring the affinity of a molecular interaction between two molecules, or the explanations provided herein in this description). The term "surface plasmon resonance", as used herein, refers to an optical phenomenon that allows for the analysis of real-time biospecific interactions by detection of alterations in protein concentrations within a biosensor matrix, where one molecule is immobilized on the biosensor chip and the other molecule is passed over the immobilized molecule under flow conditions yielding kon, koffmeasurements and hence KD(or KA) values. This can for example be performed using the well-known BIAcore® system (BIAcore International AB, a Cytiva lifesciences company, Uppsala, Sweden and Piscataway, NJ). For further descriptions, see Jonsson et al. (1993, Ann. Biol. Clin.51: 19-26), Jonsson et al. (1991 Biotechniques 11: 620- 627), Johnsson et al. (1995, J. Mol. Recognit. 8: 125-131), and Johnnson et al. (1991, Anal. Biochem. 198: 268-277). For instance, the affinity (KD) of a molecular interaction between two molecules can be determined via SPR on a ProteOn XPR36 instrument (Bio-Rad Laboratories). The experiment can be performed at 25°C, and as assay buffer PBS pH7.4 containing 0.005% Tween 20 (Bio-Rad Laboratories) can be used. Targets such as human proteins or non-protein molecules (biomolecules), or non-human biomolecules, as described herein, such as nucleic acids (e.g., DNA, RNA), lipids (e.g., such as phosphatidylserine (PS)) or glycans can be immobilized onto different ligand lanes from a GLC sensorchip (Bio-Rad Laboratories), e.g., with the ProteOn Amine Coupling Kit (Bio-Rad Laboratories) according to the manufacturer’s instructions. The protein-based building blocks of the present technology can be captured on the target immobilized ligand lanes. One ligand lane can serve as a reference surface and no protein-based building block is captured on the surface. Different concentrations (e.g., ranging from 300 nM to 1.2 nM) diluted in running buffer can be flowed over the respective protein-based building blocks and reference surface in multi-cycle kinetics for 2 minutes, followed by a constant flow of the assay buffer for 15 minutes. Between the different injections, the surfaces can be regenerated with 3 M MgCl2 (Cytiva), or with 10 mM Glycine pH 1.5 (Cytiva). Several buffer blanks can be injected for double referencing. Data can be analyzed, e.g., with the ProteOn Manager 3.1.0 software (Bio-Rad Laboratories). The kinetic rate constants (ka and kd) can be calculated by fitting the sensorgrams via the Langmuir 1:1 interaction ligand binding model. The equilibrium dissociation constant KDcan be calculated as the kd / ka ratio. See also, e.g., https: / / nicoyalife.com / wp- content / uploads / 2023 / 02 / characterization-of-Influenza-using-Alto.pdf. Another well-known biosensor technique to determine affinities of biomolecular interactions is bio-layer interferometry (BLI) (see for example Abdiche et al.2008, Anal. Biochem.377: 209- 217). The term “bio-layer Interferometry” or “BLI”, as used herein, refers to a label-free optical technique that analyzes the interference pattern of light reflected from two surfaces: an internal reference layer (reference beam) and a layer of immobilized protein on the biosensor tip (signal beam). A change in the number of molecules bound to the tip of the biosensor causes a shift in the interference pattern, reported as a wavelength shift (nm), the magnitude of which is a direct measure of the number of molecules bound to the biosensor tip surface. Since the interactions can be measured in real-time, association and dissociation rates and affinities can be determined. BLI can for example be performed using the well-known Octet® Systems (ForteBio, a division of Pall Life Sciences, Menlo Park, USA). Alternatively, affinities can be measured in Kinetic Exclusion Assay (KinExA) (see for example Drake et al., “Characterizing high-affinity antigen / antibody complexes by kinetic- and equilibrium-based methods”, Anal. Biochem., 2004, 328: 35-43), using the KinExA® platform (Sapidyne Instruments Inc, Boise, USA). The“term "KinExA", as used herein, refers to a solution-based method to measure true equilibrium binding affinity and kinetics of unmodified molecules. Equilibrated solutions of a binding unit / target complex, such as an antibody / antigen complex, are passed over a column with beads precoated with antigen (or antibody), allowing the free antibody (or antigen) to bind to the coated molecule. Detection of the antibody (or antigen) thus captured is accomplished with a fluorescently labeled protein binding the antibody (or antigen). Further, the GYROLAB® immunoassay system provides a platform for automated bioanalysis and rapid sample turnaround (Fraley et al., “The Gyrolab™ immunoassay system: a platform for automated bioanalysis and rapid sample turnaround”, Bioanalysis 2013, 5: 1765-74). Further, the affinity of a molecular interaction between two molecules (e.g., between two biomolecules such as between two proteins), or between one biomolecule such as one protein and one cell, can be measured using flow cytometry to analyze ligand binding to antigens such as proteins, lipids (e.g., such as phosphatidylserine (PS)), sugars, etc. presented on the surface of a cell (“cell binding assay”). The skilled person is familiar with cell-binding assays to determine the affinity of a certain soluble molecule (such as the molecule of the present technology) and a binding partner present on the surface of a cell, such as a human cell. For instance, Hunter S. A. and Cochran J. R. (“Cell-binding assays for determining the affinity of protein–protein interactions: technologies and considerations”, Methods Enzymol.2016, 580: 21–44), present a practical guide for measuring binding events between soluble ligands and binding partners expressed on the surface of, inter alia, mammalian cells. For instance, as shown in the examples, the cell binding assay can be carried out as follows: a. Adding a fixed number of (human or non-human) cells to a 96-well V-bottom plate (e.g., 50 μL human cell suspension (e.g., 5E+04 / 96-well), or to tubes, such as Eppendorf tubes, in cold fluorescence-activated cell sorting (FACS) buffer (e.g., consisting of D-PBS, 2% heat inactivated fetal bovine serum (HI FBS) and 0.05% Sodium Azide); b. Optionally performing a washing step; c. Adding the soluble molecule, e.g., the molecule of the present technology, or the protein-based building block of the present technology, preferably marked, such as with a fluorescent label or an epitope tag, and incubate for a certain amount of time, until the reaction has come to equilibrium, generally a number of hours, e.g., for about 3h, at low temperature, typically 4°C while shaking; d. Evaluating the binding of the soluble molecule to the human cells by flow cytometry, e.g., by FACS. Hence, the cell-binding assay can be performed by adding a number of cells (human or non- human, such as non-human animal, plant, microorganisms, etc.) to a recipient (e.g., 96-well V-bottom plate or tubes, as described above), preferably in a physiological buffer, adding the molecule which binding is to be assessed (e.g., the molecule of the present technology, or the protein-based building block of the present technology), which is preferably marked, and incubate it with the cells for an amount of time, e.g., when the reaction has come to equilibrium, generally a number of hours, e.g., for about 3h, preferably at low temperature, typically 4°C, preferably while shaking, and finally evaluating the binding of the soluble molecule to the human cells by flow cytometry, e.g., by FACS. In order to calculate the binding affinities (e.g., KDand / or EC50) between a soluble molecule, e.g., the molecule of the present technology, and a human cell, the soluble molecule in step c. above may be added to each well / tube at varying concentrations, spanning two orders of magnitude above and below the anticipated KDand / or EC50. Binding values can be determined from the average signal value (e.g., average fluorescence value) of each sample, plotting the fraction bound vs. ligand concentration (log scale) and fitting a sigmoidal curve using nonlinear regression analysis. The ligand concentration at half the fraction bound, also referred to as EC50, will be a first approximation of the equilibrium dissociation constant (KD). The skilled person is able to determine whether a molecule is able to specifically bind human proteins, as defined in the context of the present technology. For instance, the skilled person may make use of commercially available protein arrays to determine the binding affinity of a certain molecule (protein) towards human proteins. For instance, the skilled person may make use of the commercially available Proteome Profiler™ Antibody Arrays, which allows for the semiquantitative measurement of more than 100 proteins in a single sample. Alternatively or additionally, the skilled person may make use of, for example, HuProt™ assay, such as the version v4.0, which consists of >21,000 unique human proteins, isoform variants, and protein fragments – covering 16,794 unique genes. This includes 15,889 of the 19,613 canonical human proteins described in the Human Protein Atlas, with broad coverage across protein subclasses. The skilled person can also use commercially available cell arrays, such as human, non-human animal, plant, bacteria, yeast, etc. arrays to determine the binding affinity (e.g., KD and / or EC50) of a certain molecule (protein) towards human cells. See also, e.g., Example 16. Similarly, the skilled person is able to determine whether a molecule is able to specifically bind a non-human protein, such as a bacterial or viral protein. For instance, the skilled person may make use of protein-binding assays to determine the binding affinity of a certain molecule (e.g., a protein) towards non-human (such as bacterial or viral) proteins. Similarly, the skilled person is able to determine whether a molecule (e.g., a protein) is able to specifically bind a non-protein molecule, e.g., a human non-protein molecule, such as human DNA, human RNA, human lipids (e.g., such as phosphatidylserine (PS)) or human glycans, see, e.g., Campanero- Rhodes MA et al., “Microarray strategies for exploring bacterial surface glycans and their interactions with glycan-binding proteins”, Front Microbiol. 2020, 10:2909. For instance, as described above, the binding affinity of a molecular interaction between two molecules (such as two proteins, or a protein and a non-protein molecule) can be measured by SPR. SPR allows for the determination of the KDof a potential interaction between two molecules, as described in detail above. As it will be evident to the skilled person, the at least one carrier building block comprised in the molecule of the present technology may show non-specific binding with one or more human proteins (and / or with one or more non-human proteins, and / or with one or more non- protein molecules, such as human non-protein molecules, and / or with one or more human cell types as described above). This is because there may be molecular forces between the at least one carrier building block of the present technology and one or more human proteins (and / or one or more non-human proteins, and / or one or more non-protein molecules, such as human non-protein molecules, and / or one or more human cells, as described above), e.g., in the form of hydrophobic interactions, hydrogen bonding, Van der Waals interactions, and other nonspecific interactions. Hence, if this happens, the at least one carrier building block comprised in the molecule of the present technology may non-specifically bind to one or more human proteins (and / or to one or more non-human proteins, and / or to one or more non- protein molecules, such as human non-protein molecules, and / or to one or more human cells, if this is the case, as described above). In the context of the present technology, any KD value greater than 5x10-4mol / litre (or any KA value lower than 2x103litres / mol) is generally considered to represent “non-specific binding”. Hence, the building block may bind to any human protein (or non-human protein, and / or to any human cell, if this is the case, as explained above) with a KD (KD value) greater than 5x10-4mol / litre (or with a KA value lower than 2x103litres / mol), such as with a KD (KD value) greater than 5.5x10-4mol / litre (or with a KA value lower than 1.8x103litres / mol), or with a KD (KD value) greater than 6x10-4mol / litre (or with a KA value lower than 1.7x103litres / mol). In addition, in the context of the present technology, in a preferred embodiment, the carrier building block may bind to any non-protein molecule, such as to any human non-protein molecule (e.g., DNA, RNA, lipids (e.g., such as phosphatidylserine (PS)), glycans) with a KD(KDvalue) greater than 5x10-4mol / litre (or with a KAvalue lower than 2x103litres / mol), such as with a KD(KDvalue) greater than 5.5x10-4mol / litre (or with a KAvalue lower than 1.8x103litres / mol), or with a KD(KDvalue) greater than 6x10-4mol / litre (or with a KAvalue lower than 1.7x103litres / mol). In addition, in the context of the present technology, the building block may bind to any human cell with a KD(KDvalue) greater than 5x10-4mol / litre (or with a KAvalue lower than 2x103litres / mol), such as with a KD(KDvalue) greater than 5.5x10-4mol / litre (or with a KAvalue lower than 1.8x103litres / mol), or with a KD(KDvalue) greater than 6x10-4mol / litre (or with a KAvalue lower than 1.7x103litres / mol). In the context of the present technology, this binding affinity is considered to be “non-specific binding”. In one embodiment, the protein-based carrier building block of the present technology is not derived from the crystallizable fragment of an antibody (Fc, which contains two CH2 and two CH3 domains) such as the Fc fragment of a monoclonal antibody (mAb). In another embodiment, the protein-based carrier building block of the present technology is not derived from the CH2 and / or the CH3 domains of the Fc fragment. In another embodiment, the protein-based carrier building block of the present technology is not derived from a CH1 and / or the CL domains comprised in the antigen-binding fragment (Fab) of an antibody, such as the CH1 and / or the CL domains comprised in the Fab of a mAb. In one embodiment, the molecule of the present technology is not (or is not derived from) a crystallizable fragment (Fc) of an antibody, such as a mAb. In another embodiment, the molecule of the present technology is not (or is not derived from) the Fab of an antibody, such as a mAb. In one embodiment, the molecule of the present technology does not comprise VH-VL pairs or, e.g., it does not comprise at least one VH and at least one VL which interact (are bound to) with each other, such as in an antibody. In another embodiment, the molecule of the present technology does not comprise CL-CH1 conjugates, e.g., it does not comprise at least one CL and at least one CH1 which are linked to each other, e.g., through a disulphide bridge. Attachment points or conjugation sites As mentioned above, the carrier building block present in the molecule of the present technology has at least one attachment point (also referred to as conjugation site in the present disclosure), preferably at a solvent-accessible position, as defined further below. Preferably, the at least one protein-based carrier building block comprises more than one attachment points or conjugation sites, preferably at solvent-accessible positions. In a preferred embodiment, the protein-based carrier building block comprises at least two attachment points or conjugation sites. In another embodiment, the protein-based building block comprises three conjugation sites or more, such as six or nine conjugation sites. For instance, the protein-based carrier building block may have two, three, four, five, six, seven, eight, nine, ten conjugation sites or more. In one embodiment, if more than one, the conjugation sites present in the carrier building block are different from each other. For instance, if the carrier building block comprises two conjugation sites, these conjugation sites may be functionally / chemically different from each other, i.e., each conjugation site or attachment point is chemically different from each other (e.g., if there are two conjugation sites, one conjugation site may be a -SH group present in the side chain of a cysteine located in a solvent-accessible position, and the other conjugation site may be a -NH2group present in the side chain of a lysine located in a solvent-accessible position). If the building block has more than two conjugation sites (e.g., at least three conjugation sites, such as three, four, five, six, seven, eight, nine, ten, etc.), there may be at least two types of conjugation sites among the at least three conjugation sites present in the building block. In another embodiment, if the building block has three conjugation sites, each conjugation site is functionally different from each other. In another embodiment, if the building block has three conjugation sites, two conjugation sites are the same and one conjugation site is functionally different from the other two conjugation sites. In another embodiment, all conjugation sites present in the building block are functionally different from each other. In another embodiment, all conjugation sites present in the carrier building block are the same. For instance, the protein- based building block may comprise one, two, three, four, five, six, seven, eight, nine, ten or more conjugation sites which are all the same, e.g., which are all -SH groups present in the side chain of cysteines located at solvent-accessible positions in the protein-based building block. In another embodiment, alternatively or additionally, if there is more than one conjugation site, the conjugation sites are spatially distant from each other (spatially separated from each other). The skilled person will appreciate that the minimal distance between conjugation sites will be dictated by the nature of the cargos (and linkers, if used) which are to be attached or conjugated to the attachment points or conjugation sites in the protein-based carrier building block. For larger cargos (e.g., ISVDs), the minimal distance can still be kept small when used in combination with long linkers, which add the needed flexibility and the envisaged target binding. A short distance between conjugation sites, combined with short linkers, if any, will likely limit the target binding of larger cargos, and result in restricted engagement (e.g., increased cell specificity). In addition, the solubility of the molecule may be decreased (i.e., the molecule may be more prone to aggregation). On the other hand, if the cargos to be attached are rather small (e.g., radioactive isotopes), the minimal distance can be kept small even in the absence of linkers, see, e.g., Example 5 below. Hence, the skilled person will be able to select the location of the specific conjugation sites and the length and flexibility of the linkers, if any, depending on the nature of the cargos which are to be attached or conjugated to the protein-based carrier building block. A “conjugation site” or “attachment point” may be a reactive group in the side chain of a natural or a non-natural (also referred to as “noncanonical”, “unnatural” or “unusual”, as described above) amino acid preferably located at a solvent-accessible position in the protein- based carrier building block. It may also be the C-terminal and / or N-terminal reactive group (-COOH and -NH2 groups, respectively) of the protein-based carrier building block. In the context of the present technology, a “reactive group in the side chain of an amino acid” (either natural or non-natural, as defined above) refers to any chemical group present in the side chain of an amino acid which is capable of forming a covalent bond. For instance, if the amino acid is lysine (or ornithine (Orn), or Diaminopropionic acid (Dap), or Diaminobutyric acid (Dab)), the reactive group present on its side chain is a primary amine. For example, if the amino acid is cysteine, the reactive group present on its side chain is a thiol group. For example, if the amino acid is aspartic or glutamic acid, the reactive group present in their side chain is a carboxylic group. For example, if the amino acid is tyrosine, the reactive group present on its side chain is a phenolic hydroxyl group. For example, if the amino acid is arginine, the reactive group present on its side chain is a guanidino group. For example, if the amino acid is methionine, the reactive group present on its side chain is a thioether group. In the context of the present technology, the “C-terminal or N-terminal reactive group of the protein-based carrier building block” refers to the -COOH and -NH2reactive groups present in the C- and N-terminal amino acid of the protein-based carrier building block. If the carrier building block does not have a free C- and / or N-terminal end (e.g., because the carrier building block is C- and / or N-terminal linked to another protein-based building block, or to another peptide or protein, or because the N-terminal is amidated, or because the C-terminal is acetylated, etc.), then the N- and C-terminal ends of the carrier building block are not suitable as attachment points or conjugation sites as defined herein. In some embodiments the “conjugation site” or “attachment point” is not the C-terminal or N-terminal reactive group of the protein-based carrier building block. The at least one conjugation site or attachment point present in the building block of the present technology may be already present in the building block precursor (e.g., the -NH2group in the side chain of a lysine present in the building block precursor, preferably at a solvent-accessible position) or may be engineered. Preferably, at least one or more of the attachment points or conjugation sites of the protein-based building block are engineered. In the context of the present technology, an “engineered” attachment point or conjugation site means a conjugation site or attachment point which is present in the protein-based carrier building block but which was not present in its precursor at the same or corresponding position. For instance, the protein-based building block precursor may be modified to introduce one or more attachment points or conjugation sites, as described in detail below. A non-limiting example of an engineered attachment point or conjugation site is a reactive group present in the side chain of an amino acid in the protein-based carrier building block which amino acid was not present at the same or equivalent position in the building block precursor. For instance, if the building block precursor has a serine at a certain position X (which is preferably a solvent-accessible position) in the building block precursor, and that serine is mutated to a cysteine in the carrier building block, the -SH group of that cysteine would be an engineered attachment point or conjugation site. For instance, if an amino acid (e.g., a Cys, or a Tyr) is added at the N- or C-terminal end of the building block precursor, the reactive group present in the side chain of that newly added amino acid in the carrier building block would be an engineered attachment point or conjugation site. Hence, in a preferred embodiment, the protein-based carrier building block of the present technology has at least two conjugation sites or attachment points, wherein at least one, preferably at least two of them are engineered attachment points or conjugation sites, i.e., they were not present in the building block precursor at the same or corresponding position. In another preferred embodiment, all of the conjugation sites or attachment points present in the protein-based building block are engineered attachment points or conjugation sites, i.e., they were not present in the building block precursor at the same or corresponding position. In one embodiment, the carrier building block has two or more engineered attachment points or conjugation sites, such as three, four, five, six, seven, eight, nine, ten or more engineered attachment points or conjugation sites. As used herein a residue position in one polypeptide sequence “corresponds to” a residue position in another polypeptide sequence if it exists in an equivalent position in the polypeptide sequence, as indicated, e.g., by primary sequence homology or functional equivalence or Kabat numbering. A corresponding position may be identified by alignment of the two polypeptide sequences. The alignment used to identify a corresponding position or corresponding region may be obtained using a conventional alignment algorithm such as Blast (Altschul et al., “Basic local alignment search tool”, J Mol Biol., 1990, 215(3):403-10). The at least one conjugation site present in the carrier building block of the present technology may be free (i.e., ready for reaction) or capped / protected. Hence, the α-amino group, the carboxylic acid terminus, or the reactive groups present in the side chain of one or more amino acids of the carrier building block (e.g., amines, carboxylic acids, alcohols, thiols) may be capped or protected with a protecting group, e.g., to prevent polymerization of the amino acids, to minimize undesirable side reactions during the synthesis of the building block or to selectively attach different cargos, for example. Of course, if the at least one conjugation site is capped or protected, it has to be de-capped or deprotected before attaching or conjugating a cargo to it, as described in detail below. Thus, the at least one conjugation site present in the protein-based carrier building block of the present technology may be (non-limiting) a primary amine, a thiol group, a hydroxyl group, a guanidino group, a carboxyl group or a thioether group. For instance, the conjugation site may be a free or capped (protected) thiol group. Hence, in some embodiments, the at least one conjugation site present in the protein-based carrier building block of the present technology may be a primary amine present in the side chain of a lysine (or ornithine (Orn), or Diaminopropionic acid (Dap), or Diaminobutyric acid (Dab)) in the protein-based building block, preferably located at a solvent-accessible position. In other embodiments, the conjugation site is a thiol group present in the side chain of a cysteine in the protein-based building block, preferably located at a solvent-accessible position in the protein-based building block. In other embodiments, the conjugation site is a carboxylic group present in the side chain of an aspartic or glutamic acid in the protein-based building block, preferably located at a solvent-accessible position in the protein-based building block. In other embodiments, the conjugation site is a guanidino group present the side chain of an arginine in the protein-based building block, preferably located at a solvent-accessible position in the protein-based building block. In other embodiments, the conjugation site is a thioether group present the side chain of a methionine in the protein-based building block, preferably located at a solvent-accessible position in the protein-based building block. In other embodiments, the conjugation site is the phenolic OH-group of a tyrosine in the protein- based building block, preferably located at a solvent-accessible position in the protein-based building block. In one embodiment, the tyrosine is preferably located at the N- or C-terminal end of the protein-based carrier building block of the molecule. In other embodiments, the conjugation site is the N-terminal primary amine of the carrier building block, if this is free and preferably solvent-accessible. In other embodiments, the conjugation site is the C-terminal carboxyl group of the carrier building block, if this is free and preferably solvent-accessible. As described above, the conjugation sites may be free or protected. For instance, as already described above, if the conjugation site is a thiol group (e.g., from a cysteine in the protein- based building block, preferably located at a solvent-accessible position in the protein-based building block), the thiol group may be free (-SH) or protected / capped. A capped thiol group refers to a thiol group which is (reversibly) protected with a protecting group (e.g., with another cysteine, with glutathione (GSH), with cysteamine or with protecting groups such as Benzyl (Bzl, Bn), Trityl (Trt), Diphenylmethyl (Dpm, Bzh, Bh), Tetrahydropyranyl (Thp), tert- Butyl (tBu), etc.). Spears, R., et al., (“Cysteine protecting groups: applications in peptide and protein science”, Chem. Soc. Rev., 2021, 50, 11098) provides a review on the different cysteine protecting groups. In addition, Isidro-Llobet, A., et al., (“Amino acid-protecting groups”, Chem Rev., 2009, 109(6):2455-504) provides a review of different amino acid protecting groups. In one embodiment, the protein-based carrier building block of the present technology comprises at least two attachment points or conjugation sites which are two reactive groups present in the side chain of two amino acids (which may be natural or a non-natural) in the protein-based building block, preferably located at solvent-accessible positions in the protein- based carrier building block. For instance, in one embodiment, the protein-based carrier building block comprises at least two attachment points or conjugation sites which are two reactive groups present in the side chain of two natural amino acids (e.g., two Cys) in the protein-based building block, preferably located at solvent-accessible positions in the protein- based carrier building block. In one embodiment, at least one of the attachment points or conjugation sites present in the protein-based building block is linked (directly or via a linker) to a cargo, as defined herein. In a preferred embodiment, the molecule of the present technology comprises at least one protein-based carrier building block and at least one cargo, wherein the at least one cargo is attached or conjugated to the at least one protein-based carrier building block through the at least one attachment point or conjugation site. A “cargo” may be any molecule which is / may be attached or conjugated to the protein-based carrier building block through the attachment point(s) or conjugation site(s) present therein. For instance, cargos which may be attached or conjugated to the protein-based carrier building block of the present technology are proteins, peptides, ISVDs (such as VHH, VL or VH), polyethylene glycol (PEG), small molecules (such as, e.g., cryptophycin, DM4), glycans (such as, e.g., M6P), lipids, chelators, fluorophores, radio isotopes, vitamins (such as folic acid or biotin), nucleic acids such as oligonucleotides or siRNA, etc. The cargo may have different functionalities. For instance, the at least one cargo may be a half-life extending (HLE) molecule, a targeting molecule, a therapeutic molecule or precursor thereof, an imaging molecule, a toxic molecule, an agonist (such as a Toll-like receptor (TLR) agonist), a T-cell engagement molecule, a sweeping / degrader molecule, a cell-penetrating molecule, a nuclear localization molecule, a blood brain barrier (BBB) shuttle, a radiotherapeutic molecule or an imaging probe. Hence, in another embodiment, the molecule of the present technology comprises at least one protein-based carrier building block and at least one cargo, wherein the cargo is attached or conjugated to the at least one protein-based carrier building block through the at least one attachment point or conjugation site, and wherein the cargo is a HLE molecule, such as an albumin-binding ISVD (as described herein, e.g., as defined in Table 8, such as SEQ ID NO.: 63 or 106) or a PEG molecule, or ELNN polypeptides, as described herein. In another embodiment, the molecule of the present technology comprises at least one protein-based carrier building block and at least one cargo, wherein the cargo is attached or conjugated to the at least one protein-based carrier building block through the at least one attachment point or conjugation site, and wherein the cargo is a targeting moiety and / or a therapeutic moiety as described herein. In a further embodiment, the molecule of the present technology comprises at least one protein-based carrier building block and at least two cargos, wherein the cargos are attached or conjugated to the at least one protein-based carrier building block through at least two attachment points or conjugation sites, wherein the at least two cargos are one HLE molecule, as described herein, and one therapeutic and / or targeting moiety, as described herein. In one embodiment, the at least one protein-based carrier building block comprised in the molecule of the present technology comprises at least two cysteines, preferably located at solvent accessible positions, such as three cysteines, or six cysteines, or nine cysteines, preferably located at solvent accessible positions, with free or capped thiol groups that are the at least two, such as three, or six, or nine, conjugation sites as defined herein. In one embodiment, the at least one protein-based carrier building block comprised in the molecule of the present technology comprises three cysteines, preferably located at solvent accessible positions, with free or capped thiol groups that are the three conjugation sites as defined herein. In one embodiment, the protein-based carrier building block does not comprise any other cysteine at solvent accessible positions besides the three cysteines at solvent-accessible positions which bear the three conjugation sites (free or capped thiol groups) (but may comprise one or more cysteines at positions which are not solvent-accessible). In another embodiment, the at least one protein-based carrier building block comprised in the molecule of the present technology comprises four, five, six, seven, eight, nine, ten or more cysteines, preferably located at solvent accessible positions, with free or capped thiol groups that are the four, five, six, seven, eight, nine, ten or more conjugation sites as defined herein. In one embodiment, the protein-based carrier building block does not comprise any other cysteine at solvent accessible positions besides the four, five, six, seven, eight, nine, ten or more cysteines which bear the four, five, six, seven, eight, nine, ten or more conjugation sites (free or capped thiol groups) and which are located at solvent-accessible positions in the building block. In other embodiments, the at least one protein-based building block comprised in the molecule of the present technology comprises at least one amino acid, such as one, two, three, four, five, six, seven, eight, nine, ten or more, which may be natural or non-natural, preferably located at solvent accessible positions, which comprises a reactive group on its side chain which is the conjugation site as defined herein. In another embodiment, the at least one protein-based building block comprised in the molecule of the present technology comprises at least two conjugation sites, one of which is a (free or protected) thiol group from a cysteine preferably located at a solvent-accessible position in the protein-based carrier building block, and the other one is a -OH group from a tyrosine preferably located at a solvent-accessible position in the protein-based carrier building block, preferably from a N- or C-terminally exposed tyrosine. In another embodiment, the at least one protein-based building block comprised in the molecule of the present technology comprises at least two conjugation sites, one of which is a (free or protected) thiol group from a cysteine preferably located at a solvent-accessible position in the protein-based carrier building block, and the other one is a reactive group from a non-natural amino acid preferably located at a solvent- accessible position in the protein-based carrier building block. In one embodiment, a conjugation site or attachment point in the protein-based building block is a selenol (-HSe) group from a selenocysteine (Sec or U), which may be located, e.g., in the C-terminal of the protein-based carrier building block. In another embodiment, a conjugation site or attachment point in the protein-based building block is a keto group of a p- acetylphenylalanine (pAcPhe), that can be selectively coupled to an alkoxyamine derivatized cargo, see, e.g., Jun Y. Axup et al., “Synthesis of site-specific antibody-drug conjugates using unnatural amino acids”, PNAS, 2012, 109 (40) 16101-16106. The skilled person is aware of ways of incorporating one or more unnatural amino acids in the at least one protein-based building block comprised in the molecule of the present technology, if this is the case. For instance, WO 2021 / 050554, the content of which is herewith incorporated by reference, describes in detail how to incorporate one or more unnatural amino acid(s) in a protein. In one embodiment, the conjugation site is a free or capped thiol group in the side chain of a cysteine, preferably present at a solvent-accessible position in the building block. Cysteine is often the site of choice when it comes to the site-specific modification of proteins, also known as bioconjugation, owing to its favourable properties (nucleophilic profile of the thiol at neutral / near-neutral pH, low natural abundance, general ease of incorporation into proteins via site-directed mutagenesis) (from Spears R. J. et al., “Cysteine protecting groups: applications in peptide and protein science”, Chem. Soc. Rev., 2021, 50, 11098-11155). In a preferred embodiment, the at least one conjugation site or attachment point is selected from: a thiol group (-SH, free or capped) present in the side chain of a cysteine preferably located at a solvent-accessible position in the protein-based carrier building block, -NH2 (primary amine, either from the N-terminal end of the protein-based building block or present in the side chain of an amino acid, such as lysine or ornithine), -OH present in the side chain of a tyrosine (either a C-terminal tyrosine, N-terminal tyrosine or a tyrosine preferably present at any other solvent-accessible position in the protein-based carrier building block), C-terminal -COOH and azido group present in the side chain of non-natural amino acids (such as azidolysine). More preferably, the at least one conjugation site or attachment point is a thiol group (free or capped) present in the side chain of a cysteine preferably located at a solvent- accessible position in the protein-based building block. In one embodiment, the protein-based building block of the present technology comprises six attachment points or conjugation sites, wherein three of them are -SH groups present in the side chain of three Cys, preferably located at solvent-accessible positions, and wherein three of them are -NH2 present in the side chain of three Lys, preferably located at solvent-accessible positions in the protein-based building block. Hence, the at least one conjugation site present in the at least one building block comprised in the molecule of the present technology allows for conjugation of different cargos (directly or by means of a linker, as it will be clear to the skilled person and described in detail below). The skilled person is aware of ways of attaching cargos to the conjugation site(s) present in the building block. For instance, Spicer C. D. et al. (“Achieving controlled biomolecule- biomaterial conjugation”, Chem Rev. 2018, 118(16):7702-7743), the content of which is herewith incorporated by reference, provides a review on the chemistry of biomolecule conjugation and provide a comprehensive overview of the key strategies for achieving controlled functionalization. For instance, if a conjugation site is a -SH group (free or capped) present in the side chain of a cysteine preferably located at a solvent-accessible position in the protein-based carrier building block, the cargo can be attached or conjugated to the building block (directly or by means of a linker) by alkylation, metal-assisted arylation, disulphide exchange or addition to a maleimide Michael acceptor. It can also be attached or conjugated using the so-called “PODS-based conjugation, see, e.g., Davydova M. et al., ”Synthesis and bioconjugation of thiol-reactive reagents for the creation of site-selectively modified immunoconjugates”, J Vis Exp., 2019, 145:10.3791 / 59063. These different methods provide a high level of chemoselectivity for cysteine (see, e.g., D. Alvarez Dorta, et al., Chem. Eur. J.2020, 26, 14257). If at least one conjugation site is a -SH group (free or capped) present in the side chain of a cysteine preferably located at a solvent-accessible position in the protein-based carrier building block, the cargo can be attached or conjugated to it through addition to a maleimide Michael acceptor. Maleimide present in the cargo will specifically react with the at least one free thiol to form a thioether bond, generally at pH 6.5 to 7.5. Of course, if the -SH group is capped or protected, it should first decapped or deprotected (e.g., reduced with reducing reagent, such as dithiothreitol (DTT) or tris(2-carboxyethyl)phosphine (TCEP)), and then the cargo can be attached to it. For instance, an APN-maleimide ‘bifunctional’ linker (see Formula I in the Examples), also known as 3-(4-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1- yl)phenyl)propiolonitrile), can be used to attach or conjugate a cargo to a -SH attachment point present in the side chain of a cysteine preferably located at a solvent-accessible position in the protein-based carrier building block. For instance, a bis-maleimido-PEG3-linker (1,11- bismaleimido-triethyleneglycol) can be used to attach or conjugate a cargo to a -SH attachment point present in the side chain of a cysteine preferably located at a solvent- accessible position in the protein-based carrier building block. In addition, maleimide- modified cargos (see, e.g., PEG-maleimide, N-ethylmaleimide, maleimido-PEG-acid, Resiquimod (R-848)-maleimide, cryptophycin-PEG-maleimide) can be attached to the -SH attachment point present in the side chain of a cysteine preferably located at a solvent- accessible position in the protein-based carrier building block, see also the examples. For instance, if a conjugation site is a -OH group of a tyrosine preferably located at a solvent- accessible position in the protein-based carrier building block, the cargo can be attached or conjugated to the building block (directly or by means of a linker) by several chemical methods such as cross-linking via catalytic tyrosine mono electronic oxidation, three-component Mannich-type tyrosine conjugation, conjugation via sulphur fluoride exchange chemistry (SuFEx), transition-metal complexes for tyrosine conjugation, diazonium coupling reaction, reactions with triazolinediones, etc. (for a review, see, e.g., D. Alvarez Dorta et al., Chem. Eur. J., 2020, 26, 14257). Alternatively or additionally, if the conjugation site is the -OH group of an N- and / or C-terminal tyrosine, the cargo can be attached or conjugated to the building block (directly or by means of a linker) enzymatically as described, e.g., in Alan M. Marmelstein et al., Journal of the American Chemical Society, 2020, 142 (11), 5078-5086. As described therein, if conjugation of at least one cargo to a N- and / or C-terminal tyrosine is to be performed, the protein-based building block may preferably be extended with flexible (GG) or (G4S1)1-3GG tags (sequences) in order to facilitate the enzymatic addition, as described in Alan M. Marmelstein et al., cited above. In this case, tyrosinase from Agaricus bisporus (abTYR), a copper-dependent enzyme that functions to convert tyrosine into melanin via an o-quinone intermediate, may be used. Alternatively, the much smaller Bacillus megaterium tyrosinase (bmTYR) may be used to catalyze the reaction. For instance, if the conjugation site is the N-terminal primary amine of the protein-based carrier building block and / or the primary amine present in the side chain of an amino acid preferably located at a solvent-accessible position in the protein-based carrier building block (e.g., Lys, Orn, or any non-natural amino acid with a primary amine on its side chain), the cargo may be attached or conjugated to the carrier building block (directly or by means of a linker) by reaction of a group present in the cargo / linker (e.g., isothiocyanates, isocyanates, acyl azides, NHS esters, sulfonyl chlorides, aldehydes, glyoxals, epoxides, oxiranes, carbonates, aryl halides, imidoesters, carbodiimides, anhydrides, or fluorophenyl esters) and the primary amine. See, e.g., Bioconjugate Techniques (Third edition), 2013, Chapter 3 – “The reactions of bioconjugation”, Greg T.Hermanson. For instance, if the building block comprises at least two conjugation sites which include a - OH from a tyrosine and a -SH from a cysteine preferably located at a solvent-accessible positions in the protein-based carrier building block, thiol nucleophiles can be conveniently capped through disulfide formation with Ellman’s reagent. Following the coupling reaction in the -OH from the tyrosine, the thiol groups can be de-capped through brief exposure to an appropriate reducing agent, as described in Alan M. Marmelstein et al., mentioned above. Another option to attach or conjugate a cargo to an attachment point or conjugation site in the protein-based building block (directly or by means of a linker) is the use of sortase- mediated transpeptidation reactions. Sortases allow functionalization of the N-, C-terminus and the creation of non-natural fusions (i.e., N-N or C-C chimeras) via the installation of click handles, see, e.g., Guimaraes C. P. et al. (“Site-specific C-terminal and internal loop labelling of proteins using sortase-mediated reactions”, Nature Protocols, 2013, 8(9): 1787-1799). As described in this protocol, sortase-mediated reactions are applicable to any protein of interest (e.g., to the protein-based carrier building block of the present technology), provided it contains (i) an LPXTG motif (where X can be any amino acid and glycine cannot be a free carboxylate) as the sortase target or (ii) a suitably exposed glycine residue to serve as the incoming nucleophile. The natural nucleophile of sortase can be replaced by any peptide / protein with an oligoglycine (Gly1−5) at the N-terminus (in many cases a single glycine suffices). In turn, the peptides can be decorated with any cargo molecule (e.g., fluorophores, biotin, cross-linkers, lipids, carbohydrates, nucleic acids), provided that a free N-terminal glycine remains available on the peptide used as the incoming nucleophile. Thus, incubation of sortase, LPXTG-containing protein and nucleophile leads to the covalent attachment of that nucleophile to the protein of interest in a site-specific manner. Guimaraes C. P. et al., mentioned above, provides a protocol that allows the functionalization of any given protein at its C-terminus. The target protein is engineered with a sortase-recognition motif (LPXTG). Upon recognition, sortase cleaves the protein between the threonine and glycine residues, facilitating the attachment of an exogenously added oligoglycine (Gly1−5) peptide modified with the functional group of choice (e.g., the cargo to be attached to the protein-based carrier building block). Theile C. S. et al. (“Site-specific N-terminal labeling of proteins using sortase- mediated reactions”, Nature Protocols, 2013, 8(9): 1800-1807) describes the use of sortase- mediated reactions to label the N-terminus of any given protein of interest. As described in this protocol, the protein to be labeled is engineered with an exposed stretch of glycines or alanines at its N-terminus when using sortase A from S. aureus or S. pyogenes, respectively. A peptide decorated with a functional group of choice (fluorophores, biotin, lipids, nucleic acids, carbohydrates and so on) and comprising a sortase recognition motif LPXTG / A sequence (X being any amino acid, as stated above) at its C terminus (e.g., the cargo) is then added to the reaction together with sortase. Sortase A cleaves between the threonine and glycine / alanine residues, forming a thioester intermediate with the peptide probe. Nucleophilic attack by the N-terminally modified protein of interest resolves the intermediate, resulting in the formation of a covalent bond between the peptide probe (e.g., the cargo) and the N terminus of the protein (see Fig.1 of Theile C. S. et al., mentioned above). Alternatively, depsi-peptides can be used for N-terminal labeling, see Theile C. S. et al., mentioned above. Finally, Witte M. D. et al. (“Production of unnaturally linked chimeric proteins using a combination of sortase- catalyzed transpeptidation and click chemistry”, Nature Protocols, 2013, 8(9): 1808-1819) describes a procedure for the production of N-to-N and C-to-C fusion proteins. By equipping the N-terminus or C-terminus of the proteins of interest with a set of click handles using sortase A, followed by a strain-promoted click reaction, unnatural N-to-N and C-to-C linked (hetero) fusion proteins are established. As described in Witte M. D. et al., peptides for creating C-to-C linked proteins are synthesized with an N-terminal triglycine motif and an azide or cyclooctyne (DIBAC) at the C-terminus (see also Fig.2 of this document). The proteins of interest are engineered with C-terminal LPXTG sequences. To prepare N-to-N linked proteins, the authors of this protocol synthesize peptides containing the LPXTGG sortase A recognition sequence at the C-terminus (X can be any residue, but the authors prefer a polar residue, such as a glutamic acid, to aid precipitation of the peptide after cleavage from the resin and to increase the solubility of the peptide in water) and an azido or a cyclooctyne group at the N- terminus of the probe. The proteins to be linked should comprise 1-5 Gly at the N-terminus. The final step of the procedure is fusing the click handle–containing proteins, see Fig. 1 of Witte M. D. et al. In view of the above, it is possible to attach or conjugate cargos to the protein-based carrier building block (directly or by means of a linker) using sortases, as described in detail in Guimaraes C. P. et al., Theile C. S. et al. and Witte M. D. et al., the content of which is incorporated herewith by reference. The cargos may be attached or conjugated (directly or by means of linkers) at conjugation sites or attachment points in the protein-based carrier building block, which are either the N- or C-terminus of the protein-based building block using the above-described sortase methodology. Hence, if the conjugation site or attachment point of the protein-based carrier building block is the C-terminal end of the building block, a cargo may be attached or conjugated to it using sortase, provided that the C-terminal end of the building block comprises a sortase-recognition motif (LPXTG) and the cargo comprises a oligoglycine ((Gly)1-5) modified peptide at the N-terminal (see Fig.2 of Guimaraes C. P. et al.). If the conjugation site or attachment point of the protein-based carrier building block is the N-terminal end of the building block, a cargo may be attached or conjugated to it using sortase, provided that the N-terminal end of the building block comprises a (Gly)1-5 tag sequence and the cargo comprises a sortase-recognition motif (LPXTG / A) at the C-terminal (see Fig.1 of Theile C. S. et al.). In addition, protein or peptide cargos can be attached to the N / C-terminal end of the protein-based carrier building block in a N-to-N and / or C-to-C manner, as described in detail in Witte M. D. et al. Hence, by selecting appropriate (possibly initially capped) conjugation sites, the skilled person is able to attach or conjugate different cargos to the building block. Solvent-accessible positions As described above, the at least one conjugation site or attachment point present in the protein-based carrier building block is preferably located at solvent-accessible positions in the building block. The skilled person is able to identify “solvent-accessible positions” in the carrier building block precursor. This can be performed in silico by means of computer modelling. For instance, the skilled person can make use of readily available software tools such as MAESTRO (Schrödinger, LLC, New York, NY, 2021), a multi-agent prediction system, based on statistical scoring functions (SSFs) and different machine learning approaches, see, e.g., Laimer et al. BMC Bioinformatics (2015) 16:116. In addition, the skilled person can also make use of readily available software tools such as YASARA (www.yasara.org), for identifying at least potential solvent-accessible positions for the at least one conjugation site of the building block. With the help of in silico tools such as MAESTRO or YASARA, the skilled person is able to identify solvent-accessible positions that are potentially suitable for engineering conjugations sites as defined above. Hence, with the help of tools such as MAESTRO or YASARA, potentially suitable conjugation sites are identified. An example of how to identify solvent-accessible positions that are potentially suitable for engineering conjugations sites as defined above is provided in the examples of this application (e.g., Examples 1-3). As described therein, a protein is selected as starting point for developing the protein-based carrier building block (the so-called “building block precursor”). Using, e.g., MAESTRO, residues in the building block precursor with a Solvent-Accessible Surface Area (SASA) greater than or equal to, e.g., 27 Å2(square angstrom) can be considered to be solvent-accessible. The stability (∆G in solvent) of the mutation of each of the identified residues (e.g., to a cysteine residue) can then be calculated, see, e.g., Laimer J. et al, “MAESTRO--multi agent stability prediction upon point mutations”, BMC Bioinformatics, 2015, 16:116, for further details. Destabilizing mutations (e.g., mutations for which the calculated ∆G in solvent is higher) are generally not further considered as potential positions for conjugation sites or attachment points. Hence, once potentially suitable conjugation sites are identified with the help of tools such as MAESTRO or YASARA, the stability (∆G in solvent) of the mutation of each of the identified residues (e.g., to a cysteine residue) is calculated. Those residues with lower calculated ∆G in solvent would be preferably further selected as potential positions for conjugation sites or attachment points. For instance, ∆G values in the range of -20 to +5 can be considered as non-destabilizing mutations. The skilled person will understand that the ∆G value for each of the mutations of the identified residues may vary depending on the specific protein and / or the specific mutations considered. The skilled person will also understand that the preferred mutations are those whose ∆G values are the lowest. Depending on these ∆G values, the number of conjugation sites and the type of cargo that will be conjugated, the skilled person will further select certain positions over others among the ones initially identified as potentially solvent- accessible with the help of tools such as MAESTRO or YASARA. Alternatively or additionally, the skilled person can use hydrogen / deuterium exchange mass spectrometry (HDX-MS) to determine at least potential solvent-accessible positions in a protein. HDX-MS reports on the local chemical environment and solvent accessibility of the protein backbone by monitoring the exchange of peptide bond amide protons with the deuterons of a D2O solvent. The rate of hydrogen-deuterium exchange is dependent on the solvent accessibility and folded state of the protein (see Englander SW. et al., “Hydrogen exchange: the modern legacy of Linderstrøm-Lang”, Protein Sci., 1997, 6(5):1101-9). If the identified solvent-accessible position is to be occupied by a certain amino acid with a reactive group in its side chain, (e.g., by a cysteine), the in silico modelling (e.g., with MAESTRO) will also take into account the potential interactions of the reactive group of that amino acid (e.g., the -SH present in the side chain of the cysteine) with other reactive groups present in the side chain of other amino acids present in the protein-based carrier building block (e.g., with other -SH groups present in the protein, if any). Additionally or alternatively, the “solvent-accessible positions” can be identified and / or verified empirically. For instance, the “solvent-accessible positions” theoretically identified using available in silico software tools such as MAESTRO, as described above, may preferably be empirically confirmed by manufacturability. Formulation and process stability of potential building block candidates help narrow down lead candidates at an early stage, prior to large- scale manufacturing (see the examples and also, e.g., Ramachander, R., Rathore, N. (2013), ”Molecule and manufacturability assessment leading to robust commercial formulation for therapeutic proteins” in: Kolhe, P., Shah, M., Rathore, N. (eds) Sterile Product Development, AAPS Advances in the Pharmaceutical Sciences Series, vol 6. Springer, New York, NY). Hence, once potential suitable solvent-accessible positions have been theoretically identified in the protein-based building block precursor, expression levels, conjugation efficiency, formulation, quality control, solubility, process stability, etc., of the resulting protein-based carrier building block should preferably be evaluated. Solvent-accessible positions which lead to building blocks excelling in expression yield, manufacturability, solubility and / or stability are preferred, see the Examples for further details. For instance, once suitable solvent-accessible positions have been theoretically identified in the building block precursor, protein expression of the selected variants (i.e., the resulting protein-based building blocks with amino acid(s) bearing the conjugation site(s) in the theoretically-selected solvent-accessible position(s)) may take place. In this step it can be asserted whether the introduction of the specific amino acids at the theoretically-identified solvent accessible positions (e.g., point mutations, addition of amino acids at the N- and / or C- terminal of the protein, etc.) has a negative impact on, e.g., the synthesis, expression levels, conjugation efficiency or 3D globular structure of each specific variant. In addition, the minimal required solubility and lack of specific binding to human proteins (and, optionally, to non-protein molecules and / or non-human proteins, preferably to the precursor’s target), as described in detail above, can be assessed. Possible changes in 3D structure could be assessed, for example, by CD (circular dichroism) spectrum analysis, as described in detail above. In addition, the stability of the resulting variants can also be confirmed with a Thermal Shift Assay. This assay detects protein melting temperatures (Tm) and can thus be used to check protein stability. It can be used to characterize the stability / folding of a protein’s 3D structure. SYPRO® Orange is a naturally quenched dye that interacts with the hydrophobic core of proteins which becomes visible following thermal denaturation. As a result, the temperature in the middle of the thermal denaturation process is labelled as melting temperature Tm. This is a way of assessing the stability of the resulting variants or mutants. In addition, “model cargos” can be attached or conjugated to the selected variants, in order to quantify the extent of conjugation (conjugation efficiency), i.e., to ascertain whether the resulting protein-based building block with the conjugation sites at the selected solvent- accessible positions will in practice be suitable for the attachment or conjugation of the desired cargos. A “model cargo” may be any molecule with a molecular weight higher than, e.g., 100 Da. For instance, if a potential conjugation site is a thiol group, a “model cargo” may be a maleimide-modified alanine (e.g., N-Maleoyl-β-alanine), or a biotin-maleimide, as described in Junutula, J. et al. (“Site-specific conjugation of a cytotoxic drug to an antibody improves the therapeutic index”, Nat Biotechnol, 26, 925–932 (2008)). For instance, if the conjugation of the “model cargo(s)” results in a stable conjugate (protein-based building block with one or more model cargos conjugated to it), with an acceptable extent of conjugation (to be decided on a case-by-case basis, for example ≥90% conjugation efficiency, such as 90% conjugation efficiency, or 95% conjugation efficiency, or 97% conjugation efficiency, or 99% conjugation efficiency or more), allowing a standard PK in vivo, preserving its globular 3D structure and the conjugation status in vivo, etc., those solvent-accessible positions should be preferred for cargo conjugation, and conjugation of the desired cargo(s) may take place, see also the examples below. Point mutations In one embodiment, the at least one conjugation site present in the building block may be generated by introducing specific point mutations at solvent-accessible positions in the peptide sequence of the building block precursor. For instance, point mutations may be introduced at solvent-accessible positions in the building block precursor in order to generate the protein-based building block comprised in the molecule of the present technology, which comprises at least one conjugation site or attachment point at defined solvent-accessible positions, as described herein. For instance, the conjugation sites may be generated by mutating specific amino acids preferably at solvent-accessible positions of a building block precursor to cysteine (“Cys- mutations”). Alternatively or additionally, the conjugation sites may be generated by mutating specific amino acids preferably at solvent-accessible positions of a building block precursor to natural or non-natural amino acids with a reactive group in its side chain. Amino acid distribution data of occurrence at certain positions (e.g., Cys, Ser) in the building block precursor can also be used to guide the design and introduction of conjugation sites. Additionally or alternatively, the building block precursor may be modified by adding one or more amino acids at the N- and / or C-terminal of the protein sequence, to introduce at least one conjugation site or attachment point preferably at a solvent-accessible position, as described herein, to generate the protein-based building block of the present technology. In another embodiment, the at least one conjugation site may be already present preferably at solvent-accessible positions in the protein-based building block precursor, and there is no need of generating it. This is the case for the primary amine at the N-terminal of the building block, the -COOH at the C-terminal or in the side chain of the building block, the primary amine in the side chain of, e.g., a lysine preferably already present at a solvent-accessible position in the building block precursor or the thiol group in the side chain of a cysteine preferably already present at a solvent-accessible position in the building block precursor. If the building block comprises more than one conjugation sites, these can be generated by introducing, e.g., specific point mutations preferably at solvent-accessible positions in the peptide sequence of the building block precursor. Additionally or alternatively, other suitable conjugation sites or attachment points may be already present preferably at solvent- accessible positions in the building bock precursor, i.e., there is no need of generating these conjugation sites by introducing, e.g., specific point mutations and / or adding one or more amino acids at the N- and / or C-terminal of the building bock precursor. The skilled person will decide on the number and position of the attachment point(s) or conjugation site(s) based on the protein-based building block and the cargo(s) to be attached to it, directly or by means of a linker, as described herein. As described in detail above, preferably, the point mutations are non-destabilizing point mutations. Stability of mutants can be calculated with different methods which predict the impact of mutations on protein stability, e.g., based on artificial intelligence (AI). For instance, stability of mutants can be calculated with MAESTRO, as defined above and explained in detail in the examples, and can also be confirmed empirically by manufacturability (including but not limited to expression level and stability assessment, as described above). In a preferred embodiment, the point mutations are mutations of amino acids preferably located at solvent-accessible positions in the building block precursor to cysteines. In another embodiment, the point mutation consists of the replacement of a serine residue preferably in a solvent-accessible position of the building block precursors by a cysteine. In another embodiment, the point mutations are mutations of preferably solvent-accessible amino acids in the building block precursor to lysines. In another embodiment, the point mutations are mutations of preferably solvent-accessible amino acids in the building block precursor to tyrosines. In another embodiment, the point mutations are mutations of preferably solvent- accessible amino acids in the building block precursor to a natural or non-natural amino acid, as described above. Addition of a C- or N- natural and / or non-natural amino acid with a reactive group in its side chain For instance, the conjugation sites may be generated by adding, in the building block precursor, one or more C- or N-terminal natural and / or one or more C- or N-terminal non- natural amino acid(s) with a reactive group in its side chain. Preferably, if present, the one or more terminal natural or non-natural amino acid is added at the C-terminus of the building block precursor. For instance, one or more of the conjugation sites is(are) generated by adding a N- or C- terminal cysteine, a N- or C- terminal tyrosine and / or a N- or C-terminal non-natural amino acid to the protein-based building block precursor. Preferably, at least one of the conjugation sites is generated by adding a N- or C- terminal tyrosine to the protein-based building block precursor, preferably a C-terminal tyrosine. In a preferred embodiment, the N- and / or C-terminal Tyr is preceded / followed by flexible (GG) or ((G4S1)1-3GG) sequences (e.g. - GGY, -(G4S1)1-3GGY, YGG-, Y(G4S1)1-3GG-, YGG(S1G4)1-3-, or YGG(G4S1)1-3-), as described in detail in Alan M. Marmelstein et al., Journal of the American Chemical Society, 2020, 142 (11), 5078- 5086. Hence, the at least one protein-based carrier building block comprised in the molecule of the present technology may comprise a N- and / or C-terminal Cys, Tyr, and / or non-natural amino acid, for instance a C-terminal Tyr, as in a -GGY or -(G4S1)1-3GGY tag (sequence). In addition, the at least one protein-based carrier building block of the present technology may comprise a N- and / or C-terminal conjugation site or attachment point suitable for conjugation with sortase, as described above. In these cases, the protein-based carrier building block should be engineered to comprise a C-terminal sortase recognition motif (LPXTG, where X can be any amino acid), a N-terminal polygly ((Gly)1-5) tag or both. In addition, if N-to-N and / or C-to-C attachments or conjugations are desired, the protein-based carrier building block should be engineered to comprise a C-terminal sortase recognition motif (for C-to-C attachments) or a N-terminal polygly ((Gly)1-5) tag (for N-to-N attachments), as described in detail above. See in particular Guimaraes C. P. et al., Theile C. S. et al. and Witte M. D. et al., listed above. Finally, as described above, the conjugation sites may be generated by combinations of the above mechanisms, e.g., the at least one conjugation site can be obtained by performing point mutations (e.g., Ser to Cys at a solvent-accessible position of the building block, as described above), or by adding a C- and / or N- terminal amino acid, such as cysteine, or tyrosine, or a non-natural amino acid, or a sortase recognition motif, or a polygly ((Gly)1-5) tag to the protein- based building block precursor, as described above. Examples of building blocks Small globular non-human proteins-based building blocks The protein-based carrier building block(s) of the present technology may be based on a small globular non-human protein. In the context of the present technology, a “small globular non- human protein” refers to a non-human protein which has a size (molecular mass) of about 2.5 to about 70 kDa, preferably of about 2.5 to about 50 kDa, such as about 2.5 to less than 50 kDa, more preferably of about 2.5 to about 30 kDa, even more preferably of about 2.5 to about 16 kDa, as described herein and which has a globular three-dimensional (3D) structure, as described herein. In addition, the at least one non-human protein-based carrier building block does not specifically bind to any human protein, as defined in this specification, preferably it also does not specifically bind to any non-protein molecule (such as nucleic acids (e.g., DNA, RNA), glycans, lipids (e.g., such as phosphatidylserine (PS)), etc.), such as any human non-protein molecule (biomolecule) (such as human DNA, human RNA, human glycans, human lipids (e.g., such as phosphatidylserine (PS)), etc.), preferably it also does not specifically bind to any non-protein molecule (such as nucleic acids (DNA, RNA), glycans, lipids (e.g., such as phosphatidylserine (PS)), etc.), to which the building block precursor binds specifically, if any, and preferably it also does not specifically bind to any non-human protein (e.g., a bacterial and / or viral protein) to which the building block precursor binds specifically, if any. Further, preferably, the at least one non-human protein-based carrier building block (i) does not specifically bind to any human cell and / or cell type, or binds to a human cell and / or cell type with a KD (KD value) greater than 5x10-4mol / litre, preferably as determined by cell- binding assay, (ii) does not specifically bind any microorganism such as bacteria, fungi, protists, yeast and / or to any virus, or binds to a microorganism such as bacteria, fungi, protists, yeast and / or to virus with a KD(KDvalue) greater than 5x10-4mol / litre, preferably as determined by cell-binding assay and / or SPR, as described herein, and / or (iii) does not specifically bind to any biomolecule, including human biomolecules and non-human biomolecules, such as plant biomolecules, virus biomolecules and / or microorganism biomolecules (such as bacteria, fungi, protists and / or yeast), or binds to biomolecules, including human biomolecules and non- human biomolecules, with a KD(KDvalue) greater than 5x10-4mol / litre, preferably as determined by cell-binding assay and / or SPR, as described herein. In a preferred embodiment, the protein-based carrier building block does not specifically bind any non-human protein and / or non-protein molecule, preferably the precursor’s target, when a cargo is conjugated to the at least one attachment point or conjugation site on the protein- based carrier building block, as described above. Hence, in a preferred embodiment, the molecule of the present technology, which comprises at least one protein-based building block and at least one cargo attached to the at least one protein-based building block through the at least one conjugation site or attachment point, does not specifically bind any non- human protein or non-protein molecule, such as any human non-protein molecule, as described herein, in particular it does not specifically bind any protein or non-protein molecule to which the building block precursor binds, if any. As described above, in the context of the present technology, if the protein-based building block or molecule of the present technology shows any interaction with one or more human protein (or non-human protein, or non-protein molecule, as described above), such interaction is characterized by low specificity and / or low affinity, as described in detail above. A human protein is a protein present in the human body. The Human Protein Atlas (HPA, https: / / www.proteinatlas.org) is a Swedish-based program initiated in 2003 with the aim to map all the human proteins in cells, tissues, and organs. Small globular non-human proteins, in the context of the present technology, include proteins which are derived from human proteins, but which have been modified so that they are no longer human proteins. Examples of small globular non-human proteins are ISVDs, such as “human ISVDs” (e.g., VH, VL) and “non-human ISVDs” (e.g., VHH, non-human VH, VLor engineered ISVDs), DARPins (derived from ankyrin repeat proteins), affibodies or affitins. The small globular non-human proteins may have a therapeutic or targeting activity. Immunoglobulin single variable domains (ISVDs)-based building blocks In one embodiment, the at least one protein-based carrier building block of the present technology is based on a polypeptide which comprises or, alternatively, consists of, at least one immunoglobulin single variable domain (ISVD), such as an ISVD derived from VHor VHH(a heavy-chain ISVD). As described above, the protein-based carrier building block of the present technology has a globular 3D structure, is soluble, has a size (molecular mass) of about 2.5 to about 70 kDa, such as about 2.5 to about 50 kDa, such as about 2.5 to less than 50 kDa, more preferably of about 2.5 to about 30 kDa, such as about 2.5 to about 16 kDa, such as about 5 to about 16 kDa, or about 7 to about 16 kDa, or about 10 to about 16 kDa. In addition, the at least one building block comprised in the molecule of the present technology does not specifically bind to any human protein, as defined in this specification, preferably it also does not specifically bind to any non-protein molecule (such as DNA, RNA, glycans, lipids (e.g., such as phosphatidylserine (PS)), etc.), such as any human non-protein molecule (such as human DNA, human RNA, human glycans, human lipids (e.g., such as phosphatidylserine (PS)), etc.), preferably it also does not specifically bind to any non-protein molecule (such as DNA, RNA, glycans, lipids (e.g., such as phosphatidylserine (PS)), etc.), to which the building block precursor binds specifically, if any, and preferably it also does not specifically bind to any non-human protein (e.g., a bacterial and / or viral protein) to which the building block precursor binds specifically, if any. In a preferred embodiment, the protein-based carrier building block does not specifically bind any non-human protein and / or non-protein molecule, preferably the precursor’s target, when a cargo is conjugated to the at least one attachment point or conjugation site on the protein- based carrier building block, as described above. Hence, in a preferred embodiment, the molecule of the present technology, which comprises at least one protein-based building block and at least one cargo attached to the at least one protein-based building block through the at least one conjugation site or attachment point, does not specifically bind any non- human protein or non-protein molecule, such as any human non-protein molecule, as described herein, in particular it does not specifically bind any protein or non-protein molecule to which the building block precursor binds, if any. As described above, in the context of the present technology, if the protein-based building block or molecule of the present technology shows any interaction with one or more human protein (or non-human protein, or non-protein molecule, as described above), such interaction is characterized by low specificity and / or low affinity, as described in detail above. Hence, in the specific embodiment where the at least one protein-based building block is based on an ISVD, preferably a heavy-chain ISVD, the resulting ISVD-based building block does not specifically bind to any human protein. In addition, as explained above, it is preferred that the ISVD-based building block does not specifically bind to any non-protein molecule, such as any human non-protein molecule. Furthermore, it is also preferred that the ISVD-based building block does not specifically bind to any non-human protein or non-protein molecule to which the protein-based carrier building block precursor specifically binds, if any, as described above. In the context of the present technology, an “ISVD-based building block” refers to a protein- based building block which derives from an ISVD, i.e., which is structurally similar to an ISVD but does not specifically bind to any human protein, preferably does not specifically bind to any target to which the ISVD specifically binds. For instance, the ISVD-based building block has a sequence identity of at least 60%, or 70%, or 80% with an ISVD, e.g., with its ISVD precursor. For instance, the ISVD-based building block has a sequence identity of at least 85%, such as at least 90%, such as at least 91%, such as at least 92%, such as at least 93%, such as at least 94%, such as at least 95%, such as at least 96%, such as at least 97%, such as at least 98%, such as at least 99%, or more with an ISVD, e.g., with its ISVD precursor. For instance, an ISVD-based building block may share the whole amino acid sequence with its ISVD precursor with the exception of at least one, such as one, two, three, four, five, six, seven, eight, nine, ten, fifteen, eighteen, twenty, twenty-five, thirty or more amino acids. In addition, the ISVD-based building block has a globular 3D structure, is soluble, has a size (molecular mass) of about 2.5 to about 70 kDa, such as about 2.5 to about 50 kDa, or of about 2.5 to less than 50 kDa, more preferably of about 2.5 to about 30 kDa, such as about 2.5 to about 16 kDa, such as about 5 to about 16 kDa, or about 7 to about 16 kDa, or about 10 to about 16 kDa, and does not specifically bind any human protein and preferably does not specifically bind any protein or non-protein molecule to which the precursor specifically binds. The skilled person is aware of means for eliminating the specific binding properties of a certain ISVD precursor, e.g., by performing mutations in the amino acids responsible for the binding of the ISVD to the target (e.g., in one or more of the amino acids conforming the CDRs of the ISVD), by adding amino acids and / or by deleting amino acids from the precursor’s sequence. The term “immunoglobulin single variable domain” (ISVD), interchangeably used with “single variable domain”, defines immunoglobulin molecules wherein the antigen binding site is present on, and formed by, a single immunoglobulin domain. This sets ISVDs apart from “conventional” immunoglobulins (e.g., monoclonal antibodies) or their fragments (such as Fab, Fab’, F(ab’)2, scFv, di-scFv), wherein two immunoglobulin domains, in particular two variable domains, interact to form an antigen binding site. Typically, in conventional immunoglobulins, a heavy chain variable domain (VH) and a light chain variable domain (VL) interact to form an antigen binding site. In this case, the complementarity determining regions (CDRs) of both VH and VL will contribute to the antigen binding site, i.e., a total of 6 CDRs will be involved in antigen binding site formation. In view of the above definition, the antigen-binding domain of a conventional 4-chain antibody (such as an IgG, IgM, IgA, IgD or IgE molecule; known in the art) or of a Fab fragment, a F(ab')2 fragment, an Fv fragment such as a disulphide linked Fv or a scFv fragment, or a diabody (all known in the art) derived from such conventional 4-chain antibody, would normally not be regarded as an ISVD as, in these cases, binding to the respective epitope of an antigen would normally not occur by one single immunoglobulin domain but by a pair of associating immunoglobulin domains such as light and heavy chain variable domains, i.e., by a VH-VL pair of immunoglobulin domains, which jointly bind to an epitope of the respective antigen. In contrast, generally, ISVDs are capable of specifically binding to an epitope of the antigen without pairing with an additional immunoglobulin variable domain. The binding site of an ISVD is formed by a single VH, a single VHHor single VLdomain. In the context of the present technology, in the specific embodiment where the at least one protein-based building block is based on an ISVD, the ISVD building block precursor may be a light chain variable domain sequence (e.g., a VL-sequence) or a suitable fragment thereof; or a heavy chain variable domain sequence (e.g., a VH-sequence or VHHsequence) or a suitable fragment thereof; as long as the resulting building block has a globular 3D structure, has a size (molecular mass) of about 2.5 to about 70 kDa, such as about 2.5 to about 50 kDa, or of about 2.5 to less than 50 kDa, more preferably of about 2.5 to about 30 kDa, such as about 2.5 to about 16 kDa, such as about 5 to about 16 kDa, or about 7 to about 16 kDa, or about 10 to about 16 kDa, and is soluble, as defined in detail above. An ISVD which may preferably be the precursor of the protein-based building block comprised in the molecule of the present technology can for example be a heavy chain ISVD, such as a VH, VHH, including a camelized VH or humanized VHH. In one embodiment, the protein-based building block precursor is a VHH, including a camelized VH or humanized VHH, as long as the resulting protein-based building block is soluble, has a globular 3D structure, has a size (molecular mass) of about 2.5 to about 70 kDa, such as about 2.5 to about 50 kDa, or of about 2.5 to less than 50 kDa, more preferably of about 2.5 to about 30 kDa, such as about 2.5 to about 16 kDa, such as about 5 to about 16 kDa, or about 7 to about 16 kDa, or about 10 to about 16 kDa, and does not specifically bind to human proteins. In addition, preferably, the resulting building block does not specifically bind to any non-protein molecule, such as DNA, RNA, lipids (e.g., such as phosphatidylserine (PS)) or glycans, e.g., glycoplipids. Furthermore, preferably, the resulting building block does also not specifically bind to any non-human protein to which the protein- based carrier building block precursor specifically binds, if any, as described above. Heavy chain ISVDs can be derived from a conventional four-chain antibody or from a heavy chain antibody. For example, the ISVD precursor may be a single domain antibody (or an amino acid sequence that is suitable for use as a single domain antibody), a "dAb" or dAb (or an amino acid sequence that is suitable for use as a dAb) or a Nanobody® ISVD (as defined herein, and including but not limited to a VHH); other single variable domains, or any suitable fragment of any one thereof, as long as the resulting protein-based building block is soluble, has a globular 3D structure and does not specifically bind to human proteins, preferably does not specifically bind to any non-protein (human) molecule, such as DNA, RNA, lipids (e.g., such as phosphatidylserine (PS)) or glycans, e.g., glycoplipids, and, preferably, does also not specifically bind to any non-human protein to which the protein-based carrier building block precursor specifically binds, if any, as described above. Preferably, the ISVD precursor is a VH, a humanized VH, a human VH, a VHH, a humanized VHHor a camelized VH. More preferably, the ISVD precursor is a Nanobody® ISVD (such as a VHH, including a humanized VHHor camelized VH) or a suitable fragment thereof, as long as the protein-based building block is soluble, has a globular 3D structure and does not specifically bind to human proteins, preferably does not specifically bind to any non-protein (human) molecule, such as DNA, RNA, lipids (e.g., such as phosphatidylserine (PS)) or glycans, e.g., glycoplipids, and, preferably, does also not specifically bind to any non-human protein to which the protein-based carrier building block precursor specifically binds, if any, as described above. Nanobody® is a registered trademark from Ablynx N.V. “VHH domains”, also known as VHHs, VHH antibody fragments, and VHH antibodies, have originally been described as the antigen binding immunoglobulin variable domain of “heavy chain antibodies”; i.e., of “antibodies devoid of light chains”, see Hamers-Casterman et al., Nature, 363: 446-448, 1993. The term “VHH domain” has been chosen in order to distinguish these variable domains from the heavy chain variable domains that are present in conventional 4-chain antibodies, which are referred to herein as “VH domains”, and from the light chain variable domains that are present in conventional 4-chain antibodies, which are referred to herein as “VL domains”. For a further description of VHH’s, reference is made to the review article by Muyldermans (“Single domain camel antibodies: current status”, J Biotechnol., 2001, 74: 277-302). VHH domains can be obtained from heavy chain-only antibodies (HCAbs) that are circulating in Camelidae, see e.g., Muyldermans S., “A guide to: generation and design of nanobodies”, FEBS J., 2021, 288(7):2084-2102. Hence, in a preferred embodiment, the ISVD-based building block has a sequence identity of at least 80% with a VHH (such as a humanized VHH or camelized VH), e.g., its VHH precursor. For instance, the ISVD- based building block has a sequence identity of at least 60%, or at least 70%, or 80%, or at least 85%, such as at least 90%, such as at least 91%, such as at least 92%, such as at least 93%, such as at least 94%, such as at least 95%, such as at least 96%, such as at least 97%, such as at least 98%, such as at least 99%, or more with a VHH, e.g., its VHHprecursor. For instance, the ISVD-based building block may share the whole amino acid sequence with its VHHprecursor with the exception of at least one, such as one, two, three, four, five, six, seven, eight, nine, ten, fifteen, eighteen, twenty, twenty-five, thirty or more amino acids, which are different in the protein-based carrier building block. Typically, the generation of immunoglobulins involves the immunization of experimental animals, fusion of immunoglobulin producing cells to create hybridomas and screening for the desired specificities. Alternatively, immunoglobulins can be generated by screening of naïve, immune, or synthetic libraries, e.g., by phage display. The generation of immunoglobulin sequences, such as VHHs, has been described extensively in various publications, among which WO 94 / 04678, Hamers-Casterman et al.1993 (“Naturally occurring antibodies devoid of light chains”, Nature, 363: 446-448, 1993) and Muyldermans et al. 2001 (“Single domain camel antibodies: current status”, J Biotechnol., 2001, 74: 277- 302) can be exemplified. In these methods, camelids are immunized with the target antigen in order to induce an immune response against said target antigen. The repertoire of VHHs obtained from said immunization is further screened for VHHs that bind (or not) a target antigen. In the context of the present technology, immunoglobulin sequences of different origin may be used, comprising mouse, rat, rabbit, donkey, human and camelid immunoglobulin sequences. In the context of the present technology, fully human, humanized or chimeric sequences are also included. In the context of the present technology, camelid immunoglobulin sequences and humanized camelid immunoglobulin sequences, or camelized domain antibodies, e.g. camelized dAb as described by Ward et al. (Nature, 341: 544, 1989) (see for example WO 94 / 04678 and Davies and Riechmann, “'Camelising' human antibody fragments: NMR studies on VH domains”, Febs Lett., 339:285-290, 1994 and “Single antibody domains as small recognition units: design and in vitro antigen selection of camelized, human VH domains with improved protein stability”, Prot. Eng., 1996, 9(6):531-537) are also included. A “humanized VHH” comprises an amino acid sequence that corresponds to the amino acid sequence of a naturally occurring VHHdomain, but that has been “humanized” , i.e., by replacing one or more amino acid residues in the amino acid sequence of said naturally occurring VHHsequence (and in particular in the framework sequences) by one or more of the amino acid residues that occur at the corresponding position(s) in a VHdomain from a conventional 4-chain antibody from a human being (e.g., indicated above). This can be performed in a manner known per se, which will be clear to the skilled person, for example on the basis of the further description herein and the prior art (e.g., WO 2008 / 020079). Again, it should be noted that such humanized VHHs can be obtained in any suitable manner known per se and thus are not strictly limited to polypeptides that have been obtained using a polypeptide that comprises a naturally occurring VHHdomain as a starting material. Preferably, if the building block of the present technology is a VHH, the VHH is a humanized VHH. A “camelized VH” comprises an amino acid sequence that corresponds to the amino acid sequence of a naturally occurring VH domain, but that has been “camelized”, i.e., by replacing one or more amino acid residues in the amino acid sequence of a naturally occurring VH domain from a conventional 4-chain antibody by one or more of the amino acid residues that occur at the corresponding position(s) in a VHH domain of a heavy chain antibody. This can be performed in a manner known per se, which will be clear to the skilled person, for example on the basis of the further description herein and the prior art (e.g. WO 2008 / 020079). Such “camelizing” substitutions are usually inserted at amino acid positions that form and / or are present at the VH-VL interface, and / or at the so-called Camelidae hallmark residues, as defined herein (see for example WO 94 / 04678 and Davies and Riechmann, 1994 and 1996, supra). In one embodiment, the VH sequence that is used as a starting material or starting point for generating or designing the camelized VH is a VH sequence from a mammal, or the VH sequence of a human being, such as a VH3 sequence. However, it should be noted that such camelized VH can be obtained in any suitable manner known per se and thus are not strictly limited to polypeptides that have been obtained using a polypeptide that comprises a naturally occurring VH domain as a starting material. The structure of an ISVD sequence can be considered to be comprised of four framework regions (“FRs”), which are referred to in the art and herein as “Framework region 1” (“FR1”); as “Framework region 2” (“FR2”); as “Framework region 3” (“FR3”); and as “Framework region 4” (“FR4”), respectively; which framework regions are interrupted by three complementary determining regions (“CDRs”), which are referred to in the art and herein as “Complementarity Determining Region 1” (“CDR1”); as “Complementarity Determining Region 2” (“CDR2”); and as “Complementarity Determining Region 3” (“CDR3”), respectively. Also, as further described in paragraph q) on pages 58 and 59 of WO 2008 / 020079, the amino acid residues of an ISVD are numbered according to the general numbering for VHdomains given by Kabat et al. (“Sequence of proteins of immunological interest”, US Public Health Services, NIH Bethesda, MD, Publication No.91), as applied to VHHdomains from Camelids in the article of Riechmann and Muyldermans, 2000 (J. Immunol. Methods, 240 (1-2): 185-195; see for example Figure 2 of this publication). It should be noted that - as is well known in the art for VHdomains and for VHHdomains - the total number of amino acid residues in each of the CDRs may vary and may not correspond to the total number of amino acid residues indicated by the Kabat numbering. That is, one or more positions according to the Kabat numbering may not be occupied in the actual sequence, or the actual sequence may contain more amino acid residues than the number allowed for by the Kabat numbering. This means that, generally, the numbering according to Kabat may or may not correspond to the actual numbering of the amino acid residues in the actual sequence. The total number of amino acid residues in a VH domain and a VHH domain will usually be in the range of from 110 to 120, often between 112 and 115. It should however be noted that smaller and longer sequences may also be suitable for the purposes described herein. In the present application CDR sequences may also be described according to Kabat numbering with AbM CDR annotation, as described in Kontermann and Dübel (Eds. 2010, Antibody Engineering, vol 2, Springer Verlag Heidelberg Berlin, Martin, Chapter 3, pp.33-51). According to this method, FR1 comprises the amino acid residues at positions 1-25, CDR1 comprises the amino acid residues at positions 26-35, FR2 comprises the amino acids at positions 36-49, CDR2 comprises the amino acid residues at positions 50-58, FR3 comprises the amino acid residues at positions 59-94, CDR3 comprises the amino acid residues at positions 95-102, and FR4 comprises the amino acid residues at positions 103-113. Determination of CDR regions may also be done according to different methods. In the CDR determination according to Kabat, FR1 of an ISVD comprises the amino acid residues at positions 1-30, CDR1 of an ISVD comprises the amino acid residues at positions 31-35, FR2 of an ISVD comprises the amino acids at positions 36-49, CDR2 of an ISVD comprises the amino acid residues at positions 50-65, FR3 of an ISVD comprises the amino acid residues at positions 66-94, CDR3 of an ISVD comprises the amino acid residues at positions 95-102, and FR4 of an ISVD comprises the amino acid residues at positions 103-113. In such an immunoglobulin sequence, the framework sequences may be any suitable framework sequences, and examples of suitable framework sequences will be clear to the skilled person, for example on the basis the standard handbooks and the further disclosure and prior art mentioned herein. The framework sequences are a suitable combination of immunoglobulin framework sequences or framework sequences that have been derived from immunoglobulin framework sequences, for example by humanization or camelization. For example, the framework sequences may be framework sequences derived from a light chain variable domain (e.g. a VL- sequence) and / or from a heavy chain variable domain (e.g. a VH-sequence or VHH sequence). In one aspect, the framework sequences are either framework sequences that have been derived from a VHH-sequence in which said framework sequences may optionally have been partially or fully humanized or are conventional VH sequences that have been camelized (as defined herein). In particular, the framework sequences present in the ISVD sequences referred to in the present technology may contain one or more of Hallmark residues (as defined herein), such that the ISVD sequence is a Nanobody® ISVD, such as, e.g., a VHH, including a humanized VHH or camelized VH. Some non-limiting examples of suitable combinations of such framework sequences will become clear from the further disclosure herein. However, it should be noted that, in the context of the present technology, the origin of the ISVD sequence or the origin of the nucleotide sequence used to express it is not limited, nor as to the way that the ISVD sequence or nucleotide sequence is or has been generated or obtained. Thus, the ISVD sequences may be naturally occurring sequences (from any suitable species) or synthetic or semi-synthetic sequences. In a specific but non-limiting aspect, the ISVD sequence is a naturally occurring sequence (from any suitable species) or a synthetic or semi-synthetic sequence, including but not limited to “humanized” (as defined herein) immunoglobulin sequences (such as partially or fully humanized mouse or rabbit immunoglobulin sequences, and in particular partially or fully humanized VHHsequences), “camelized” (as defined herein) immunoglobulin sequences, as well as immunoglobulin sequences that have been obtained by techniques such as affinity maturation (for example, starting from synthetic, random or naturally occurring immunoglobulin sequences), CDR grafting, veneering, combining fragments derived from different immunoglobulin sequences, PCR assembly using overlapping primers, and similar techniques for engineering immunoglobulin sequences well known to the skilled person; or any suitable combination of any of the foregoing. Similarly, nucleotide sequences may be naturally occurring nucleotide sequences or synthetic or semi-synthetic sequences, and may for example be sequences that are isolated by PCR from a suitable naturally occurring template, e.g., DNA or RNA isolated from a cell, nucleotide sequences that have been isolated from a library (and in particular, an expression library), nucleotide sequences that have been prepared by introducing mutations into a naturally occurring nucleotide sequence (using any suitable technique known per se, such as mismatch PCR), nucleotide sequence that have been prepared by PCR using overlapping primers, or nucleotide sequences that have been prepared using techniques for DNA synthesis known per se. As described above, the ISVD precursor is preferably a VHH, including a humanized VHH or camelized VH, or a suitable fragment thereof, more preferably a humanized VHH or a suitable fragment thereof. The resulting protein-based building block should be soluble, have a globular 3D structure and not specifically bind to human proteins, preferably should also not specifically bind to any non-protein molecule and preferably should also not specifically bind to any non-human protein to which the VHHprecursor specifically binds, if any, as described above. Preferably, as described above, the molecule comprising at least one VHH(including humanized VHHor camelized VH)-derived protein-based building block and at least one cargo attached to it through the at least one conjugation site or attachment point, does not specifically bind to any non-protein molecule and / or does not specifically bind to any non- human protein to which the VHH(including humanized VHHor camelized VH) precursor specifically binds. Further, preferably, the at least one ISVD-based carrier building block (i) does not specifically bind to any human cell and / or cell type, or binds to a human cell and / or cell type with a KD(KDvalue) greater than 5x10-4mol / litre, preferably as determined by cell-binding assay, (ii) does not specifically bind any microorganism such as bacteria, fungi, protists, yeast and / or to any virus, or binds to a microorganism such as bacteria, fungi, protists, yeast and / or to virus with a KD(KDvalue) greater than 5x10-4mol / litre, preferably as determined by cell-binding assay and / or SPR, as described herein, and / or (iii) does not specifically bind to any biomolecule, including human biomolecules and non-human biomolecules, such as plant biomolecules, virus biomolecules and / or microorganism biomolecules (such as bacteria, fungi, protists and / or yeast), or binds to biomolecules, including human biomolecules and non-human biomolecules, with a KD (KD value) greater than 5x10-4mol / litre, preferably as determined by cell-binding assay and / or SPR, as described herein. As described above, the ISVD precursor is preferably a VHH, humanized VHH or camelized VH, such as a Nanobody® ISVD, or a suitable fragment thereof, more preferably a humanized Nanobody® ISVD or a suitable fragment thereof. The resulting protein-based building block should be soluble, have a globular 3D structure and not specifically bind to human proteins, preferably should also not specifically bind to any non-protein molecule and preferably should also not specifically bind to any non-human protein to which the VHH, humanized VHH or camelized VH, such as Nanobody® ISVD, precursor specifically binds, if any, as described above. Preferably, as described above, the molecule comprising at least one VHH, humanized VHH or camelized VH, such as Nanobody® ISVD-derived protein-based building block and at least one cargo attached to it through the at least one conjugation site or attachment point, does not specifically bind to any non-protein molecule and / or does not specifically bind to any non-human protein to which the VHH, humanized VHH or camelized VH, such as Nanobody® ISVD precursor specifically binds. For a general description of Nanobody® ISVDs, reference is made to the present description, as well as to the prior art cited herein. In this respect, it should however be noted that this description and the prior art mainly described Nanobody® ISVDs of the so-called “VH3 class”, i.e. Nanobody® ISVDs with a high degree of sequence homology to human germline sequences of the VH3 class such as DP-47, DP-51 or DP-29. It should however be noted that the present technology in its broadest sense can generally use any type of Nanobody® ISVD, and for example also uses the Nanobody® ISVDs belonging to the so-called “VH4 class”, i.e. Nanobody® ISVDs with a high degree of sequence homology to human germline sequences of the VH4 class such as DP-78, as for example described in WO 2007 / 118670. In one embodiment, the at least one protein-based carrier building block comprised in the molecule of the present technology is derived from a Nanobody® ISVD belonging to the so- called “VH3 class”, i.e. a Nanobody® ISVDs with a high degree of sequence homology to human germline sequences of the VH3 class such as DP-47, DP-51 or DP-29, as long as the protein- based building block is soluble, has a globular 3D structure and does not specifically bind to human proteins, preferably does not specifically bind to any non-protein human molecule and preferably does also not specifically bind to any non-human protein to which the ISVD precursor specifically binds, as described above. Generally, Nanobody® ISVDs (in particular VHH sequences, including (partially) humanized VHH sequences and camelized VH sequences) can be characterized by the presence of one or more “Hallmark residues” (as described herein) in one or more of the framework sequences (again as further described herein). Generally, a Nanobody® ISVD can be defined as an immunoglobulin sequence with the (general) structure FR1 - CDR1 - FR2 - CDR2 - FR3 - CDR3 - FR4 in which FR1 to FR4 refer to framework regions 1 to 4, respectively, and in which CDR1 to CDR3 refer to the complementarity determining regions 1 to 3, respectively, and in which one or more of the Hallmark residues are as further defined herein. In particular, a Nanobody® ISVD can be an immunoglobulin sequence with the (general) structure FR1 - CDR1 - FR2 - CDR2 - FR3 - CDR3 - FR4 in which FR1 to FR4 refer to framework regions 1 to 4, respectively, and in which CDR1 to CDR3 refer to the complementarity determining regions 1 to 3, respectively, and in which the framework sequences are as further defined herein. More in particular, a Nanobody® ISVD can be an immunoglobulin sequence with the (general) structure FR1 - CDR1 - FR2 - CDR2 - FR3 - CDR3 - FR4 in which FR1 to FR4 refer to framework regions 1 to 4, respectively, and in which CDR1 to CDR3 refer to the complementarity determining regions 1 to 3, respectively, and in which: one or more of the amino acid residues at positions 11, 37, 44, 45, 47, 83, 84, 103, 104 and 108 according to the Kabat numbering are chosen from the Hallmark residues mentioned in Table 3 below. Table 3: Hallmark Residues in Nanobody® ISVDs (according to Kabat numbering) Position Human VH3 Hallmark Residues 11 L, V; predominantly L L, S, V, M, W, F, T, Q, E, A, R, G, K, Y, N, P, I; preferably L 37 V, I, F; usually V F(1), Y, V, L, A, H, S, I, W, C, N, G, D, T, P, preferably F(1)or Y 44(8)G E(3), Q(3), G(2), D, A, K, R, L, P, S, V, H, T, N, W, M, I; preferably G(2), E(3)or Q(3);most preferably G(2)or Q(3). 45(8)L L(2), R(3), P, H, F, G, Q, S, E, T, Y, C, I, D, V; preferably L(2)or R(3) 47(8)W, Y F(1), L(1)or W(2)G, I, S, A, V, M, R, Y, E, P, T, C, H, K, Q, N, D; preferably W(2), L(1)or F(1)83 R or K; usually R R, K(5), T, E(5), Q, N, S, I, V, G, M, L, A, D, Y, H; preferably K or R; most preferably K 84 A, T, D; predominantly A P(5), S, H, L, A, V, I, T, F, D, R, Y, N, Q, G, E; preferably P 103 W W(4), R(6), G, S, K, A, M, Y, L, F, T, N, V, Q, P(6), E, C; preferably W 104 G G, A, S, T, D, P, N, E, C, L; preferably G 108 L, M or T; predominantly Q, L(7), R, P, E, K, S, T, M, A, H; preferably Q or L(7)L Notes:(1)In particular, but not exclusively, in combination with KERE or KQRE at positions 43-46.(2)Usually as GLEW at positions 44-47.(3)Usually as KERE or KQRE at positions 43-46, e.g. as KEREL, KEREF, KQREL, KQREF, KEREG, KQREW or KQREG at positions 43-47. Alternatively, also sequences such as TERE (for example TEREL), TQRE (for example TQREL), KECE (for example KECEL or KECER), KQCE (for example KQCEL), RERE (for example REREG), RQRE (for example RQREL, RQREF or RQREW), QERE (for example QEREG), QQRE, (for example QQREW, QQREL or QQREF), KGRE (for example KGREG), KDRE (for example KDREV) are possible. Some other possible, but less preferred sequences include for example DECKL and NVCEL. (4) With both GLEW at positions 44-47 and KERE or KQRE at positions 43-46. (5) Often as KP or EP at positions 83-84 of naturally occurring VHHdomains. (6) In particular, but not exclusively, in combination with GLEW at positions 44-47. (7) With the proviso that when positions 44-47 are GLEW, position 108 is always Q in (non- humanized) VHHsequences that also contain a W at 103. (8) The GLEW group also contains GLEW-like sequences at positions 44-47, such as for example GVEW, EPEW, GLER, DQEW, DLEW, GIEW, ELEW, GPEW, EWLP, GPER, GLER and ELEW. Thus, a Nanobody® ISVD can be defined as an amino acid sequence with the (general) structure FR1 - CDR1 - FR2 - CDR2 - FR3 - CDR3 - FR4 in which FR1 to FR4 refer to framework regions 1 to 4, respectively, and in which CDR1 to CDR3 refer to the complementarity determining regions 1 to 3, respectively, and in which one or more of the amino acid residues at positions 11, 37, 44, 45, 47, 83, 84, 103, 104 and 108 according to the Kabat numbering are chosen from the Hallmark residues mentioned in Table 3. For instance, when the protein-based building block of the present technology is based on an ISVD, it may derive from anti-viral ISVDs, such as from anti-viral VHHor Nanobody® ISVDs. For instance, the building block of the present technology may derive from a functional ISVD (i.e., an ISVD which specifically binds to human proteins, and / or to non-human proteins, such as viral proteins and / or bacterial proteins, and / or to non-protein molecules, such as human non- protein molecules) which has been engineered / modified so that it no longer specifically binds to any human protein, preferably which has been engineered / modified so that it also no longer specifically binds to any non-human protein to which it originally bound, such as bacterial and / or viral proteins, as described in detail above and / or preferably which has been engineered / modified so that it also no longer specifically binds to any non-protein molecule to which it originally bound, if any. In a further preferred embodiment, the ISVD-based building block of the present technology derives from an ISVD, such as from a heavy-chain ISVD, preferably from a Nanobody® ISVD, which has been further engineered / modified to include mutations which prevent / remove binding by pre-existing antibodies / factors. Examples of such mutations are described, e.g., in WO 2012 / 175741 and WO 2015 / 173325. For instance, to prevent / remove binding by pre-existing antibodies / factors, the amino acid at position 11 (according to Kabat) may be Val or Leu, preferably Val; and / or the amino acid at position 89 (according to Kabat) may be preferably Val, Thr or Leu, preferably Leu; and / or the amino acid at position 110 (according to Kabat) may be preferably Thr, Lys or Gln, preferably Thr; and / or the amino acid at position 112 (according to Kabat) may be Ser, Lys or Gln, preferably Ser; and / or the ISVD-based building block may contain a C-terminal extension of 1- 5 amino acids chosen from any naturally occurring amino acid. The resulting ISVD-based building block may be derived from a variant from an anti-hRSV ISVD, such as, e.g., variants from the anti-hRSV ISVDs depicted on Table A-2 starting on p. 69 of WO 2018 / 099968. In a preferred embodiment, the resulting ISVD-based building block is derived from a variant from ISVD RSV001A04, SEQ ID NO.: 179 in the present description, and also referred to as RSV001A04, and described in detail in SEQ ID NO.: 5 on Table A-1, page 388 of WO 2010 / 139808 (referred therein to as NC41)). In this specific embodiment, the protein- based carrier building block derived from RSV001A04 does not specifically bind any human protein. In this embodiment, the “building block precursor” (or “ISVD precursor”) is RSV001A04, SEQ ID NO.: 179: EVQLVESGGGLVQAGGSLSISCAASGGSLSNYVLGWFRQAPGKEREFVAAINWRGDITIGPPNVEGRFTI SRDNAKNTGYLQMNSLAPDDTAVYYCGAGTPLNPGAYIYDWSYDYWGRGTQVTVSS. Once an ISVD is selected as starting point (as “ISVD precursor”, see above), residues preferably located at solvent-accessible positions should be identified to generate the at least one conjugation site, as described in detailed above in this description. Additionally or alternatively, the conjugation site(s) may already be in the ISVD precursor, either as reactive groups in the side chain of amino acids preferably located at solvent-accessible positions or as free N-terminal primary amine and / or free C-terminal carboxylic acid. For instance, one or more of the identified residues, preferably located at solvent-accessible positions in the amino acid sequence of the ISVD precursor are replaced by a cysteine, a lysine, a tyrosine and / or a non-natural amino acid. In one embodiment, the at least one protein-based building block comprised in the molecule of the present technology is derived from an ISVD, such as an ISVD belonging to the so-called “VH3 class”, wherein the resulting building block comprises at least one cysteine, at least one lysine, at least one non-natural amino acid and / or at least one tyrosine, preferably located at one or more solvent-accessible positions. In another embodiment, the at least one protein- based building block comprised in the molecule of the present technology is derived from an ISVD, such as an ISVD belonging to the so-called “VH3 class”, wherein the resulting building block comprises at least one engineered cysteine, at least one engineered lysine, at least one non-natural amino acid and / or at least one engineered tyrosine, preferably located at one or more solvent-accessible positions. Preferably, the building block of the molecule of the present technology, when it is derived from an ISVD, preferably from a VHH(including humanized VHHor camelized VH) or Nanobody® ISVD, as described above, comprises a leucine at position 108 (according to Kabat numbering). In other embodiments, the building block of the molecule of the present technology, when it is derived from an ISVD, as described above, comprises a valine at position 11, a leucine at position 89 and / or a leucine at position 108 (according to Kabat numbering). In one embodiment, the at least one protein-based carrier building block present in the molecule of the present technology comprises, or alternatively, consists of, SEQ ID NO.: 186: X1VX2LX3EX4X5GX6X7X8X9X10X11GX12X13X14IX15CX16AX17X18X19X20LX21X22X23VLGWFRX24AX25X26X2 7X28X29X30FVAAINX31X32X33X34X35X36X37X38PX39X40VX41X42X43FX44IX45X46X47X48X49X50X51TGX52LX5 3MX54X55LX56X57X58DX59AX60YX61CGAGX62PX63X64X65X66AYX67X68X69X70SYX71X72X73GX74X75TX76V X77VX78X79X80X81X82, wherein X1 (position 1 according to Kabat numbering) can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X2 (position 3 according to Kabat numbering) can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X3 (position 5 according to Kabat numbering) can be Val or any amino acid with a reactive group in its side chain, such as cysteine; X4 (position 7 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X5 (position 8 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X6(position 10 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X7(position 11 according to Kabat numbering) can be Leu, Val Ser, Met, Trp, Phe, Thr, Gln, Glu, Ala, Arg, Gly, Lys, Tyr, Asn, Pro or Ile, preferably Leu or Val or any amino acid with a reactive group in its side chain, such as cysteine; X8(position 12 according to Kabat numbering) can be Val or any amino acid with a reactive group in its side chain, such as cysteine; X9(position 13 according to Kabat numbering) can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X10(position 14 according to Kabat numbering) can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X11 (position 15 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X12(position 17 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X13(position 18 according to Kabat numbering) can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X14 (position 19 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X15: (position 21 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X16: (position 23 according to Kabat numbering) can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X17: (position 25 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X18: (position 26 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X19: (position 27 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X20: (position 28 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X21: (position 30 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X22: (position 31 according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X23: (position 32 according to Kabat numbering) can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X24: (position 39 according to Kabat numbering) can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X25: (position 41 according to Kabat numbering) can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X26: (position 42 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X27: (position 43 according to Kabat numbering) can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X28: (position 44 according to Kabat numbering) can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X29: (position 45 according to Kabat numbering) can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X30: (position 46 according to Kabat numbering) can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X31: (position 52a according to Kabat numbering) can be Trp or any amino acid with a reactive group in its side chain, such as cysteine; X32: (position 53 according to Kabat numbering) can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X33: (position 54 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X34: (position 55 according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X35: (position 56 according to Kabat numbering) can be Ile or any amino acid with a reactive group in its side chain, such as cysteine; X36: (position 57 according to Kabat numbering) can be Thr or any amino acid with a reactive group in its side chain, such as cysteine; X37: (position 58 according to Kabat numbering) can be Ile or any amino acid with a reactive group in its side chain, such as cysteine; X38: (position 59 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X39: (position 61 according to Kabat numbering) can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X40: (position 62 according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X41: (position 64 according to Kabat numbering) can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X42: (position 65 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X43: (position 66 according to Kabat numbering) can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X44: (position 68 according to Kabat numbering) can be Thr or any amino acid with a reactive group in its side chain, such as cysteine; X45: (position 70 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X46: (position 71 according to Kabat numbering) can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X47: (position 72 according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X48: (position 73 according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X49: (position 74 according to Kabat numbering) can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X50: (position 75 according to Kabat numbering) can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X51: (position 76 according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X52: (position 79 according to Kabat numbering) can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X53: (position 81 according to Kabat numbering) can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X54: (position 82a according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X55: (position 82b according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X56: (position 83 according to Kabat numbering) can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X57: (position 84 according to Kabat numbering) can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X58: (position 85 according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X59: (position 87 according to Kabat numbering) can be Thr or any amino acid with a reactive group in its side chain, such as cysteine; X60: (position 89 according to Kabat numbering) can be Leu, Val, Ser, Met, Trp, Phe, Thr, Gln, Glu, Ala, Arg, Gly, Lys, Tyr, Asn, Pro or Ile; preferably Leu, Val, Ser or Glu, more preferably Leu or Val or any other amino acid with a reactive group in its side chain, such as cysteine; X61: (position 91 according to Kabat numbering) can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X62: (position 96 according to Kabat numbering) can be Thr or any amino acid with a reactive group in its side chain, such as cysteine; X63: (position 98 according to Kabat numbering) can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X64: (position 99 according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X65: (position 100 according to Kabat numbering) can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X66: (position100a according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X67: (position100d according to Kabat numbering) can be Ile or any amino acid with a reactive group in its side chain, such as cysteine; X68: (position100e according to Kabat numbering) can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X69: (position 100f according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X70: (position 100g according to Kabat numbering) can be Trp or any amino acid with a reactive group in its side chain, such as cysteine; X71: (position 101 according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X72: (position 102 according to Kabat numbering) can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X73: (position 103 according to Kabat numbering) can be Trp or any amino acid with a reactive group in its side chain, such as cysteine; X74: (position 105 according to Kabat numbering) can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X75: (position 106 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X76: (position 108 according to Kabat numbering) can be Gln, Leu, Arg, Pro, Glu, Lys, Ser, Thr, Met, Ala or His; preferably Gln or Leu, or any other amino acid with a reactive group in its side chain, such as cysteine; X77: (position 110 according to Kabat numbering) can be Thr or any amino acid with a reactive group in its side chain, such as cysteine; X78: (position 112 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X79: (position 113 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X80: is absent or Gly; X81: is absent or Gly; X82: is absent or Cys, or a sequence which has 80% or more identity with SEQ ID NO.: 186, preferably a sequence which has 85% or more, 90% or more, 95% or more, 97% or more or 99% or more sequence identity with SEQ ID NO.: 186, provided that the building block has a globular 3D structure, is soluble, has a size (molecular mass) of about 2.5 to about 70 kDa, such as about 2.5 to about 50 kDa, or of about 2.5 to less than 50 kDa, more preferably of about 2.5 to about 30 kDa, such as about 2.5 to about 16 kDa, such as about 5 to about 16 kDa, or about 7 to about 16 kDa, or about 10 to about 16 kDa, and does not specifically bind to any human protein, preferably does not specifically binds to any non-human protein to which it originally bound, such as bacterial and / or viral proteins, as described in detail above and / or preferably does not specifically binds to any non-protein molecule to which it originally bound, if any, all as described in detail above. Preferably, as described above, the molecule comprising at least one such ISVD-derived protein-based building block and at least one cargo attached to it through the at least one conjugation site or attachment point, does not specifically bind to any non-protein molecule and / or does not specifically bind to any non-human protein to which the ISVD precursor specifically binds. Preferably, the protein-based carrier building block of the present technology comprises, or alternatively, consists of, SEQ ID NO.: 186 as defined above, wherein one or more of the amino acid residues at positions 11, 37, 44, 45, 47, 83, 84, 103, 104 and 108 according to Kabat numbering are chosen from the Hallmark residues mentioned in Table 3 above. In a further preferred embodiment, additionally or alternatively, the protein-based carrier building block of the present technology comprises, or alternatively, consists of, SEQ ID NO.: 186 as defined above, wherein SEQ ID NO.: 186 has been further engineered / modified to include mutations which prevent / remove binding by pre-existing antibodies / factors. Examples of such mutations are described, e.g., in WO 2012 / 175741 and WO 2015 / 173325. For instance, to prevent / remove binding by pre-existing antibodies / factors, the amino acid at position 11 (according to Kabat) in SEQ ID NO.: 186 is preferably Val, and / or the amino acid at position 89 (according to Kabat) in SEQ ID NO.: 186 is preferably Thr or Leu and / or the amino acid at position 110 (according to Kabat) in SEQ ID NO.: 186 is preferably Lys or Gln and / or the amino acid at position 112 (according to Kabat) in SEQ ID NO. 186 is preferably Lys or Gln and / or SEQ ID NO 186 contains a C-terminal extension of 1-5 amino acids chosen from any naturally occurring amino acid. Hence, the present technology provides a polypeptide which comprises, or alternatively, consists of, SEQ ID NO.: 186 as defined above. Preferably, the polypeptide comprises, or alternatively, consists of, SEQ ID NO.: 186 as defined above, wherein one or more of the amino acid residues at positions 11, 37, 44, 45, 47, 83, 84, 103, 104 and 108 according to Kabat numbering are chosen from the Hallmark residues mentioned in Table 3 above. In a further embodiment, additionally or alternatively, the polypeptide comprises, or alternatively, consists of, SEQ ID NO.: 186 as defined above, wherein SEQ ID NO.: 186 has been further engineered / modified to include mutations which prevent / remove binding by pre-existing antibodies / factors. Examples of such mutations are described, e.g., in WO 2012 / 175741 and WO 2015 / 173325. For instance, to prevent / remove binding by pre-existing antibodies / factors, the amino acid at position 11 (according to Kabat) in SEQ ID NO.: 186 is preferably Val, and / or the amino acid at position 89 (according to Kabat) in SEQ ID NO.: 186 is preferably Thr or Leu and / or the amino acid at position 110 (according to Kabat) in SEQ ID NO.: 186 is preferably Lys or Gln and / or the amino acid at position 112 (according to Kabat) in SEQ ID NO.186 is preferably Lys or Gln and / or SEQ ID NO 186 contains a C-terminal extension of 1-5 amino acids chosen from any naturally occurring amino acid. In one embodiment, the at least one protein-based carrier building block present in the molecule of the present technology comprises, or alternatively, consists of, SEQ ID NO.: 206: X1aVQLVEX1GGGZ1VX2AGGX3LX4IX5CX6AX7X7bGX7cLSX8YVLGWFRQAPGX9X10REFVAAINWRGX11I TIGPPX12VEX13RFX14IX15RX16NX17X18NTGYLQMNX19LAPX19bDTAZ2YYCGAGTPLNPX20AYIYX21WS YDYWGX22GTZ3VTVX23SX24X25X26 wherein X1a (position 1 according to Kabat numbering) can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X1 (position 7 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; Z1 (position 11 according to Kabat numbering) can be Leu, Val, Ser, Met, Trp, Phe, Thr, Gln, Glu, Ala, Arg, Gly, Lys, Tyr, Asn, Pro or Ile; preferably Leu, Val, Ser or Glu, more preferably Leu or Val; X2(position 13 according to Kabat numbering) can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X3(position 17 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X4(position 19 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X5: (position 21 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X6: (position 23 according to Kabat numbering) can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X7: (position 25 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X7b: (position 26 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X7c: (position 28 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X8: (position 31 according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X9: (position 43 according to Kabat numbering) can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X10: (position 44 according to Kabat numbering) can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X11: (position 55 according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X12: (position 62 according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X13: (position 65 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X14: (position 68 according to Kabat numbering) can be Thr or any amino acid with a reactive group in its side chain, such as cysteine; X15: (position 70 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X16: (position 72 according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X17: (position 74 according to Kabat numbering) can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X18: (position 75 according to Kabat numbering) can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X19: (position 82b according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X19b: (position 85 according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; Z2: (position 89 according to Kabat numbering) can be Leu, Val, Ser, Met, Trp, Phe, Thr, Gln, Glu, Ala, Arg, Gly, Lys, Tyr, Asn, Pro or Ile; preferably Leu, Val, Ser or Glu, more preferably Leu or Val; X20: (position100a according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X21: (position 100f according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X22: (position 105 according to Kabat numbering) can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; Z3: (position 108 according to Kabat numbering) can be Gln, Leu, Arg, Pro, Glu, Lys, Ser, Thr, Met, Ala or His; preferably Gln or Leu; X23: (position 112 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X24: is absent or Gly; X25: is absent or Gly; X26: is absent or Cys, or a sequence which has 80% or more identity with SEQ ID NO.: 206, preferably a sequence which has 85% or more, 90% or more, 95% or more, 97% or more or 99% or more sequence identity with SEQ ID NO.: 206, provided that the building block has a globular 3D structure, is soluble, has a size (molecular mass) of about 2.5 to about 70 kDa, such as about 2.5 to about 50 kDa, or of about 2.5 to less than 50 kDa, more preferably of about 2.5 to about 30 kDa, such as about 2.5 to about 16 kDa, such as about 5 to about 16 kDa, or about 7 to about 16 kDa, or about 10 to about 16 kDa, and does not specifically bind to any human protein, preferably does not specifically binds to any non-human protein to which it originally bound, such as bacterial and / or viral proteins, as described in detail above and / or preferably does not specifically binds to any non-protein molecule to which it originally bound, if any, all as described in detail above. Preferably, as described above, the molecule comprising at least one such ISVD-derived protein-based building block and at least one cargo attached to it through the at least one conjugation site or attachment point, does not specifically bind to any non-protein molecule and / or does not specifically bind to any non-human protein to which the ISVD precursor specifically binds. Preferably, the protein-based carrier building block of the present technology comprises, or alternatively, consists of, SEQ ID NO.: 206, as defined above, wherein one or more of the amino acid residues at positions 11, 37, 44, 45, 47, 83, 84, 103, 104 and 108 according to Kabat numbering are chosen from the Hallmark residues mentioned in Table 3 above. In a further preferred embodiment, additionally or alternatively, the protein-based carrier building block of the present technology comprises, or alternatively, consists of, SEQ ID NO.: 206 as defined above, wherein SEQ ID NO.: 206 has been further engineered / modified to include mutations which prevent / remove binding by pre-existing antibodies / factors. Examples of such mutations are described, e.g., in WO 2012 / 175741 and WO 2015 / 173325. For instance, to prevent / remove binding by pre-existing antibodies / factors, the amino acid at position 11 (according to Kabat) in SEQ ID NO.: 206 is preferably Val, and / or the amino acid at position 89 (according to Kabat) in SEQ ID NO.: 206 is preferably Thr or Leu and / or the amino acid at position 110 (according to Kabat) in SEQ ID NO.: 206 is preferably Lys or Gln and / or the amino acid at position 112 (according to Kabat) in SEQ ID NO.: 206 is preferably Lys or Gln and / or SEQ ID NO 206 contains a C-terminal extension of 1-5 amino acids chosen from any naturally occurring amino acid. Hence, the present technology provides a polypeptide which comprises, or alternatively, consists of, SEQ ID NO.: 206, as defined above. Preferably, the polypeptide comprises, or alternatively, consists of, SEQ ID NO.: 206, as defined above, wherein one or more of the amino acid residues at positions 11, 37, 44, 45, 47, 83, 84, 103, 104 and 108 according to Kabat numbering are chosen from the Hallmark residues mentioned in Table 3 above. In a further embodiment, additionally or alternatively, the polypeptide comprises, or alternatively, consists of, SEQ ID NO.: 206 as defined above, wherein SEQ ID NO.: 206 has been further engineered / modified to include mutations which prevent / remove binding by pre-existing antibodies / factors. Examples of such mutations are described, e.g., in WO 2012 / 175741 and WO 2015 / 173325. For instance, to prevent / remove binding by pre-existing antibodies / factors, the amino acid at position 11 (according to Kabat) in SEQ ID NO.: 206 is preferably Val, and / or the amino acid at position 89 (according to Kabat) in SEQ ID NO.: 206 is preferably Thr or Leu and / or the amino acid at position 110 (according to Kabat) in SEQ ID NO.: 206 is preferably Lys or Gln and / or the amino acid at position 112 (according to Kabat) in SEQ ID NO.: 206 is preferably Lys or Gln and / or SEQ ID NO.: 206 contains a C-terminal extension of 1-5 amino acids chosen from any naturally occurring amino acid. In one embodiment, the at least one protein-based carrier building block present in the molecule of the present technology comprises, or alternatively, consists of, SEQ ID NO.: 185: EVQLVEX1GGGZ1VX2AGGX3LX4IX5CX6AX7GGSLSX8YVLGWFRQAPGX9X10REFVAAINWRGX11ITIGP PX12VEX13RFX14IX15RX16NX17X18NTGYLQMNX19LAPDDTAZ2YYCGAGTPLNPX20AYIYX21WSYDYWG X22GTZ3VTVX23SX24X25X26 wherein X1 (position 7 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; Z1 (position 11 according to Kabat numbering) can be Leu, Val, Ser, Met, Trp, Phe, Thr, Gln, Glu, Ala, Arg, Gly, Lys, Tyr, Asn, Pro or Ile; preferably Leu, Val, Ser or Glu, more preferably Leu or Val; X2 (position 13 according to Kabat numbering) can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X3 (position 17 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X4(position 19 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X5: (position 21 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X6: (position 23 according to Kabat numbering) can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X7: (position 25 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X8: (position 31 according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X9: ( position 43 according to Kabat numbering) can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X10: (position 44 according to Kabat numbering) can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X11: (position 55 according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X12: (position 62 according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X13: (position 65 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X14: (position 68 according to Kabat numbering) can be Thr or any amino acid with a reactive group in its side chain, such as cysteine; X15: (position 70 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X16: (position 72 according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X17: (position 74 according to Kabat numbering) can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X18: (position 75 according to Kabat numbering) can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X19: (position 82b according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; Z2: (position 89 according to Kabat numbering) can be Leu, Val, Ser, Met, Trp, Phe, Thr, Gln, Glu, Ala, Arg, Gly, Lys, Tyr, Asn, Pro or Ile; preferably Leu, Val, Ser or Glu, more preferably Leu or Val; X20: (position100a according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X21: (position 100f according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X22: (position 105 according to Kabat numbering) can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; Z3: (position 108 according to Kabat numbering) can be Gln, Leu, Arg, Pro, Glu, Lys, Ser, Thr, Met, Ala or His; preferably Gln or Leu; X23: (position 112 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X24: is absent or Gly; X25: is absent or Gly; X26: is absent or Cys, or a sequence which has 80% or more identity with SEQ ID NO.: 185, preferably a sequence which has 85% or more, 90% or more, 95% or more, 97% or more or 99% or more sequence identity with SEQ ID NO.: 185, provided that the building block has a globular 3D structure, is soluble, has a size (molecular mass) of about 2.5 to about 70 kDa, such as about 2.5 to about 50 kDa, or of about 2.5 to less than 50 kDa, more preferably of about 2.5 to about 30 kDa, such as about 2.5 to about 16 kDa, such as about 5 to about 16 kDa, or about 7 to about 16 kDa, or about 10 to about 16 kDa, and does not specifically bind to any human protein, preferably does not specifically binds to any non-human protein to which it originally bound, such as bacterial and / or viral proteins, as described in detail above and / or preferably does not specifically binds to any non-protein molecule to which it originally bound, if any, all as described in detail above. Preferably, as described above, the molecule comprising at least one such ISVD-derived protein-based building block and at least one cargo attached to it through the at least one conjugation site or attachment point, does not specifically bind to any non-protein molecule and / or does not specifically bind to any non-human protein to which the ISVD precursor specifically binds. Preferably, the protein-based carrier building block of the present technology comprises, or alternatively, consists of, SEQ ID NO.: 185, as defined above, wherein one or more of the amino acid residues at positions 11, 37, 44, 45, 47, 83, 84, 103, 104 and 108 according to Kabat numbering are chosen from the Hallmark residues mentioned in Table 3 above. In a further preferred embodiment, additionally or alternatively, the protein-based carrier building block of the present technology comprises, or alternatively, consists of, SEQ ID NO.: 185 as defined above, wherein SEQ ID NO.: 185 has been further engineered / modified to include mutations which prevent / remove binding by pre-existing antibodies / factors. Examples of such mutations are described, e.g., in WO 2012 / 175741 and WO 2015 / 173325. For instance, to prevent / remove binding by pre-existing antibodies / factors, the amino acid at position 11 (according to Kabat) in SEQ ID NO.: 185 is preferably Val, and / or the amino acid at position 89 (according to Kabat) in SEQ ID NO.: 185 preferably Thr or Leu and / or the amino acid at position 110 (according to Kabat) in SEQ ID NO.: 185 is preferably Lys or Gln and / or the amino acid at position 112 (according to Kabat) in SEQ ID NO.: 185 is preferably Lys or Gln and / or SEQ ID NO.: 185 contains a C-terminal extension of 1-5 amino acids chosen from any naturally occurring amino acid. Hence, the present technology provides a polypeptide which comprises, or alternatively, consists of, SEQ ID NO.: 185, as defined above. Preferably, the polypeptide comprises, or alternatively, consists of, SEQ ID NO.: 185, as defined above, wherein one or more of the amino acid residues at positions 11, 37, 44, 45, 47, 83, 84, 103, 104 and 108 according to Kabat numbering are chosen from the Hallmark residues mentioned in Table 3 above. In a further embodiment, additionally or alternatively, the polypeptide comprises, or alternatively, consists of, SEQ ID NO.: 185 as defined above, wherein SEQ ID NO.: 185 has been further engineered / modified to include mutations which prevent / remove binding by pre-existing antibodies / factors. Examples of such mutations are described, e.g., in WO 2012 / 175741 and WO 2015 / 173325. For instance, to prevent / remove binding by pre-existing antibodies / factors, the amino acid at position 11 (according to Kabat) in SEQ ID NO.: 185 is preferably Val, and / or the amino acid at position 89 (according to Kabat) in SEQ ID NO.: 185 is preferably Thr or Leu and / or the amino acid at position 110 (according to Kabat) in SEQ ID NO.: 185 is preferably Lys or Gln and / or the amino acid at position 112 (according to Kabat) in SEQ ID NO.185 is preferably Lys or Gln and / or SEQ ID NO 18 contains a C-terminal extension of 1-5 amino acids chosen from any naturally occurring amino acid. In one embodiment, the protein-based carrier building block comprises at least one amino acid with a reactive group in its side chain, such as a cysteine, or a lysine, or a tyrosine, or a non-natural amino acid, preferably a cysteine, in at least one of the following solvent- accessible positions, such as three amino acids with a reactive group in its side chain, such as three cysteines, or three lysines, or three tyrosines, or three non-natural amino acids, preferably three cysteines, in the following solvent-accessible positions in SEQ ID NO.: 179 according to Kabat numbering: * 43, 100f, 105; or * 43, 75, 100a; or * 21, 68, 100f; or * 7, 44, 55; or * 13, 72, 100a; * 13, 31, 100f; or * C-terminal Cys (-GGC), even more preferably in at least one of the following solvent-accessible positions in SEQ ID NO.: 179 (according to Kabat numbering): * 43, 100f, 105; or * 43, 75, 100a. Hence, in one embodiment, the protein-based building block of the present technology comprises, or alternatively, consists of, one of the following sequences: *SEQ ID NO.: 185, wherein X1: (position 7 according to Kabat numbering) is Ser; Z1: (position 11 according to Kabat numbering) is Leu or Val; X2: (position 13 according to Kabat numbering) is Gln; X3: (position 17 according to Kabat numbering) is Ser; X4: (position 19 according to Kabat numbering) is Ser; X5: (position 21 according to Kabat numbering) is Ser; X6: (position 23 according to Kabat numbering) is Ala; X7: (position 25 according to Kabat numbering) is Ser; X8: (position 31 according to Kabat numbering) is Asn; X9: (position 43 according to Kabat numbering) can be any amino acid with a reactive group in its side chain, such as a cysteine, or a lysine, or a tyrosine, or a non-natural amino acid, preferably a cysteine; X10: (position 44 according to Kabat numbering) is Glu; X11: (position 55 according to Kabat numbering) is Asp; X12: (position 62 according to Kabat numbering) is Asn; X13: (position 65 according to Kabat numbering) is Gly; X14: (position 68 according to Kabat numbering) is Thr; X15: (position 70 according to Kabat numbering) is Ser; X16: (position 72 according to Kabat numbering) is Asp; X17: (position 74 according to Kabat numbering) is Ala; X18: (position 75 according to Kabat numbering) is Lys; X19: (position 82b according to Kabat numbering) is Ser; Z2: (position 89 according to Kabat numbering) is Val or Leu; X20: (position100a according to Kabat numbering) is Gly; X21: (position 100f according to Kabat numbering) can be any amino acid with a reactive group in its side chain, such as a cysteine, or a lysine, or a tyrosine, or a non-natural amino acid, preferably a cysteine; X22: (position 105 according to Kabat numbering) can be any amino acid with a reactive group in its side chain, such as a cysteine, or a lysine, or a tyrosine, or a non-natural amino acid, preferably a cysteine; Z3: (position 108 according to Kabat numbering) is Gln or Leu; X23: (position 112 according to Kabat numbering) is Ser; X24: is absent; X25: is absent; X26: is absent, or * SEQ ID NO.: 185, wherein X1: (position 7 according to Kabat numbering) is Ser; Z1: (position 11 according to Kabat numbering) is Leu or Val; X2: (position 13 according to Kabat numbering) is Gln; X3: (position 17 according to Kabat numbering) is Ser; X4: (position 19 according to Kabat numbering) is Ser; X5: (position 21 according to Kabat numbering) is Ser; X6: (position 23 according to Kabat numbering) is Ala; X7: (position 25 according to Kabat numbering) is Ser; X8: (position 31 according to Kabat numbering) is Asn; X9: (position 43 according to Kabat numbering) can be any amino acid with a reactive group in its side chain, such as a cysteine, or a lysine, or a tyrosine, or a non-natural amino acid, preferably a cysteine; X10: (position 44 according to Kabat numbering) is Glu; X11: (position 55 according to Kabat numbering) is Asp; X12: (position 62 according to Kabat numbering) is Asn; X13: (position 65 according to Kabat numbering) is Gly; X14: (position 68 according to Kabat numbering) is Thr; X15: (position 70 according to Kabat numbering) is Ser; X16: (position 72 according to Kabat numbering) is Asp; X17: (position 74 according to Kabat numbering) is Ala; X18: (position 75 according to Kabat numbering) can be any amino acid with a reactive group in its side chain, such as a cysteine, or a lysine, or a tyrosine, or a non-natural amino acid, preferably a cysteine; X19: (position 82b according to Kabat numbering) is Ser; Z2: (position 89 according to Kabat numbering) is Val or Leu; X20: (position100a according to Kabat numbering) can be any amino acid with a reactive group in its side chain, such as a cysteine, or a lysine, or a tyrosine, or a non-natural amino acid, preferably a cysteine; X21: (position 100f according to Kabat numbering) is Asp; X22: (position 105 according to Kabat numbering) is Arg; Z3: (position 108 according to Kabat numbering) is Gln or Leu; X23: (position 112 according to Kabat numbering) is Ser; X24: is absent; X25: is absent; X26: is absent, or * SEQ ID NO.: 185, wherein X1: (position 7 according to Kabat numbering) is Ser; Z1: (position 11 according to Kabat numbering) is Leu or Val; X2: (position 13 according to Kabat numbering) is Gln; X3: (position 17 according to Kabat numbering) is Ser; X4: (position 19 according to Kabat numbering) is Ser; X5: (position 21 according to Kabat numbering) can be any amino acid with a reactive group in its side chain, such as a cysteine, or a lysine, or a tyrosine, or a non-natural amino acid, preferably a cysteine; X6: (position 23 according to Kabat numbering) is Ala; X7: (position 25 according to Kabat numbering) is Ser; X8: (position 31 according to Kabat numbering) is Asn; X9: (position 43 according to Kabat numbering) is Lys; X10: (position 44 according to Kabat numbering) is Glu; X11: (position 55 according to Kabat numbering) is Asp; X12: (position 62 according to Kabat numbering) is Asn; X13: (position 65 according to Kabat numbering) is Gly; X14: (position 68 according to Kabat numbering) can be any amino acid with a reactive group in its side chain, such as a cysteine, or a lysine, or a tyrosine, or a non-natural amino acid, preferably a cysteine; X15: (position 70 according to Kabat numbering) is Ser; X16: (position 72 according to Kabat numbering) is Asp; X17: (position 74 according to Kabat numbering) is Ala; X18: (position 75 according to Kabat numbering) is Lys; X19: (position 82b according to Kabat numbering) is Ser; Z2: (position 89 according to Kabat numbering) is Val or Leu; X20: (position100a according to Kabat numbering) is Gly; X21: (position 100f according to Kabat numbering) can be any amino acid with a reactive group in its side chain, such as a cysteine, or a lysine, or a tyrosine, or a non-natural amino acid, preferably a cysteine; X22: (position 105 according to Kabat numbering) is Arg; Z3: (position 108 according to Kabat numbering) is Gln or Leu; X23: (position 112 according to Kabat numbering) is Ser; X24: is absent; X25: is absent; X26: is absent, or * SEQ ID NO.: 185, wherein X1:(position 7 according to Kabat numbering) can be any amino acid with a reactive group in its side chain, such as a cysteine, or a lysine, or a tyrosine, or a non-natural amino acid, preferably a cysteine; Z1: (position 11 according to Kabat numbering) is Leu or Val; X2: (position 13 according to Kabat numbering) is Gln; X3: (position 17 according to Kabat numbering) is Ser; X4: (position 19 according to Kabat numbering) is Ser; X5: (position 21 according to Kabat numbering) is Ser; X6: (position 23 according to Kabat numbering) is Ala; X7: (position 25 according to Kabat numbering) is Ser; X8: (position 31 according to Kabat numbering) is Asn; X9: (position 43 according to Kabat numbering) is Lys; X10: (position 44 according to Kabat numbering) can be any amino acid with a reactive group in its side chain, such as a cysteine, or a lysine, or a tyrosine, or a non-natural amino acid, preferably a cysteine; X11: (position 55 according to Kabat numbering) can be any amino acid with a reactive group in its side chain, such as a cysteine, or a lysine, or a tyrosine, or a non-natural amino acid, preferably a cysteine; X12: (position 62 according to Kabat numbering) is Asn; X13: (position 65 according to Kabat numbering) is Gly; X14: (position 68 according to Kabat numbering) is Thr; X15: (position 70 according to Kabat numbering) is Ser; X16: (position 72 according to Kabat numbering) is Asp; X17: (position 74 according to Kabat numbering) is Ala; X18: (position 75 according to Kabat numbering) is Lys; X19: (position 82b according to Kabat numbering) is Ser; Z2: (position 89 according to Kabat numbering) is Val or Leu; X20: (position100a according to Kabat numbering) is Gly; X21: (position 100f according to Kabat numbering) is Asp; X22: (position 105 according to Kabat numbering) is Arg; Z3: (position 108 according to Kabat numbering) is Gln or Leu; X23: (position 112 according to Kabat numbering) is Ser; X24: is absent; X25: is absent; X26: is absent, or * SEQ ID NO.: 185, wherein X1: (position 7 according to Kabat numbering) is Ser; Z1: (position 11 according to Kabat numbering) is Leu or Val; X2: (position 13 according to Kabat numbering) can be any amino acid with a reactive group in its side chain, such as a cysteine, or a lysine, or a tyrosine, or a non-natural amino acid, preferably a cysteine; X3: (position 17 according to Kabat numbering) is Ser; X4: (position 19 according to Kabat numbering) is Ser; X5: (position 21 according to Kabat numbering) is Ser; X6: (position 23 according to Kabat numbering) is Ala; X7: (position 25 according to Kabat numbering) is Ser; X8: (position 31 according to Kabat numbering) is Asn; X9: (position 43 according to Kabat numbering) is Lys; X10: (position 44 according to Kabat numbering) is Glu; X11: (position 55 according to Kabat numbering) is Asp; X12: (position 62 according to Kabat numbering) is Asn; X13: (position 65 according to Kabat numbering) is Gly; X14: (position 68 according to Kabat numbering) is Thr; X15: (position 70 according to Kabat numbering) is Ser; X16: (position 72 according to Kabat numbering) can be any amino acid with a reactive group in its side chain, such as a cysteine, or a lysine, or a tyrosine, or a non-natural amino acid, preferably a cysteine; X17: (position 74 according to Kabat numbering) is Ala; X18: (position 75 according to Kabat numbering) is Lys; X19: (position 82b according to Kabat numbering) is Ser; Z2: (position 89 according to Kabat numbering) is Val or Leu; X20: (position100a according to Kabat numbering) can be any amino acid with a reactive group in its side chain, such as a cysteine, or a lysine, or a tyrosine, or a non-natural amino acid, preferably a cysteine; X21: (position 100f according to Kabat numbering) is Asp; X22: (position 105 according to Kabat numbering) is Arg; Z3: (position 108 according to Kabat numbering) is Gln or Leu; X23: (position 112 according to Kabat numbering) is Ser; X24: is absent; X25: is absent; X26: is absent, or * SEQ ID NO.: 185, wherein X1: (position 7 according to Kabat numbering) is Ser; Z1: (position 11 according to Kabat numbering) is Leu or Val; X2: (position 13 according to Kabat numbering) can be any amino acid with a reactive group in its side chain, such as a cysteine, or a lysine, or a tyrosine, or a non-...

Claims

CLAIMS 1. A molecule comprising at least one protein-based building block, wherein the at least one protein-based building block: a) comprises at least two conjugation sites or attachment points; b) has a molecular mass of about 2.5 to about 70 kDa; c) has a globular three-dimensional (3D) structure; d) has a solubility of 10 mg / mL or more, measured in an aqueous solution at room temperature, wherein the aqueous solution is citrate buffer or PBS, at pH 7.0 or 7.4; e) does not specifically bind to any human protein or binds one or more human proteins with a KD value greater than 5x10-4mol / litre, as determined by surface plasmon resonance, for instance as described in Ober et al. 2001, Intern. Immunology 13: 1551-1559; and f) does not comprise or consists of an amino acid sequence selected from SEQ ID NO.: 1-34 as depicted on Tables A-1 and A-2 of WO 2016 / 055656 and / or SEQ ID NO.: 1- 12 as depicted on Table A-1 of WO 2010 / 139808.

2. The molecule of claim 1, wherein one of the at least two, preferably the at least two conjugation site(s) or attachment point(s) are present at a solvent-accessible positions in the protein-based building block.

3. The molecule of any of claims 1 to 2, wherein at least one of the attachment points or conjugation sites, preferably at least two attachment points or conjugation sites, more preferably all of the attachment points or conjugation sites, is(are) an engineered attachment point or conjugation site.

4. The molecule of any of claims 1 to 3, wherein the at least two attachment points or conjugation sites are reactive groups present in the side chain of any amino acid in the protein- based carrier building block, preferably reactive groups present in the side chain of a cysteine and / or in the side chain of a tyrosine, and / or in the side chain of a lysine, and / or in the side chain of a non-natural amino acid.

5. The molecule of any of claims 1 to 4, wherein the at least two conjugation sites are selected from a primary amine, a thiol group, a hydroxyl group, a guanidino group, a carboxyl group and / or a thioether group, preferably from a primary amine and / or a thiol group, more preferably a thiol group.

6. The molecule of any of claims 1 to 5, wherein the at least one protein-based building block does not specifically bind to any non-protein molecule, such as DNA, RNA, lipids or glycans, or binds one or more non-protein molecules with a KDvalue greater than 5x10-4mol / litre.

7. The molecule of any of claims 1 to 6, wherein the at least one protein-based building block comprises at least one cargo attached to at least one of the attachment points or conjugation sites.

8. The molecule of any of claims 1 to 7, wherein the protein-based building block is a small globular non-human protein-based building block or a small globular human protein- based building block, preferably wherein small globular non-human protein-based building block is an immunoglobulin single variable domain (ISVD)-based building block, a DARP-in- based building block, an affibody-based building block or an affitin-based building block and wherein the small globular human protein-based building block is a cyclin-dependent kinase subunit 1 (CKS1) protein-based building block.

9. The molecule of claim 8, wherein the ISVD-based building block is derived from a VH, a humanized VH, a human VH, a VHH, a humanized VHH or a camelized VH (derived from a heavy- chain ISVD), preferably derived from an ISVD belonging to the “VH3 class”.

10. The molecule of any of claims 8 to 9, wherein the ISVD-derived building block is derived from RSV001A04 (SEQ ID NO.: 179).

11. The molecule of any of claims 8 to 10, wherein the ISVD-derived building block comprises or, alternatively, consists of SEQ ID NO.: 186:X1VX2LX3EX4X5GX6X7X8X9X10X11GX12X13X14IX15CX16AX17X18X19X20LX21X22X23VLGWFRX24AX25X26X27X28X29X30FVAAINX31X32X33X34X35X36X37X38PX39X40VX41X42X43FX44IX45X46X47X48X49X50X51TGX52LX53MX54X55LX56X57X58DX59AX60YX61CGAGX62PX63X64X65X66AYX67X68X69X70SYX71X72X73GX74X75TX76V X77VX78X79X80X81X82wherein X1(position 1 according to Kabat numbering) can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X2(position 3 according to Kabat numbering) can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X3 (position 5 according to Kabat numbering) can be Val or any amino acid with a reactive group in its side chain, such as cysteine; X4(position 7 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X5(position 8 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X6 (position 10 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X7 (position 11 according to Kabat numbering) can be Leu, Val Ser, Met, Trp, Phe, Thr, Gln, Glu, Ala, Arg, Gly, Lys, Tyr, Asn, Pro or Ile, preferably Leu or Val or any amino acid with a reactive group in its side chain, such as cysteine; X8 (position 12 according to Kabat numbering) can be Val or any amino acid with a reactive group in its side chain, such as cysteine; X9 (position 13 according to Kabat numbering) can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X10 (position 14 according to Kabat numbering) can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X11 (position 15 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X12 (position 17 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine;X13(position 18 according to Kabat numbering) can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X14(position 19 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X15: (position 21 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X16: (position 23 according to Kabat numbering) can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X17: (position 25 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X18: (position 26 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X19: (position 27 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X20: (position 28 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X21: (position 30 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X22: (position 31 according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X23: (position 32 according to Kabat numbering) can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X24: (position 39 according to Kabat numbering) can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X25: (position 41 according to Kabat numbering) can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X26: (position 42 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X27: (position 43 according to Kabat numbering) can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X28: (position 44 according to Kabat numbering) can be Glu or any amino acid with a reactive group in its side chain, such as cysteine;X29: (position 45 according to Kabat numbering) can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X30: (position 46 according to Kabat numbering) can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X31: (position 52a according to Kabat numbering) can be Trp or any amino acid with a reactive group in its side chain, such as cysteine; X32: (position 53 according to Kabat numbering) can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X33: (position 54 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X34: (position 55 according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X35: (position 56 according to Kabat numbering) can be Ile or any amino acid with a reactive group in its side chain, such as cysteine; X36: (position 57 according to Kabat numbering) can be Thr or any amino acid with a reactive group in its side chain, such as cysteine; X37: (position 58 according to Kabat numbering) can be Ile or any amino acid with a reactive group in its side chain, such as cysteine; X38: (position 59 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X39: (position 61 according to Kabat numbering) can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X40: (position 62 according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X41: (position 64 according to Kabat numbering) can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X42: (position 65 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X43: (position 66 according to Kabat numbering) can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X44: (position 68 according to Kabat numbering) can be Thr or any amino acid with a reactive group in its side chain, such as cysteine;X45: (position 70 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X46: (position 71 according to Kabat numbering) can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X47: (position 72 according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X48: (position 73 according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X49: (position 74 according to Kabat numbering) can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X50: (position 75 according to Kabat numbering) can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X51: (position 76 according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X52: (position 79 according to Kabat numbering) can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X53: (position 81 according to Kabat numbering) can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X54: (position 82a according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X55: (position 82b according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X56: (position 83 according to Kabat numbering) can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X57: (position 84 according to Kabat numbering) can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X58: (position 85 according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X59: (position 87 according to Kabat numbering) can be Thr or any amino acid with a reactive group in its side chain, such as cysteine;X60: (position 89 according to Kabat numbering) can be Leu, Val, Ser, Met, Trp, Phe, Thr, Gln, Glu, Ala, Arg, Gly, Lys, Tyr, Asn, Pro or Ile; preferably Leu, Val, Ser or Glu, more preferably Leu or Val or any other amino acid with a reactive group in its side chain, such as cysteine; X61: (position 91 according to Kabat numbering) can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X62: (position 96 according to Kabat numbering) can be Thr or any amino acid with a reactive group in its side chain, such as cysteine; X63: (position 98 according to Kabat numbering) can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X64: (position 99 according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X65: (position 100 according to Kabat numbering) can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X66: (position100a according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X67: (position100d according to Kabat numbering) can be Ile or any amino acid with a reactive group in its side chain, such as cysteine; X68: (position100e according to Kabat numbering) can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X69: (position 100f according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X70: (position 100g according to Kabat numbering) can be Trp or any amino acid with a reactive group in its side chain, such as cysteine; X71: (position 101 according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X72: (position 102 according to Kabat numbering) can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X73: (position 103 according to Kabat numbering) can be Trp or any amino acid with a reactive group in its side chain, such as cysteine; X74: (position 105 according to Kabat numbering) can be Arg or any amino acid with a reactive group in its side chain, such as cysteine;X75: (position 106 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X76: (position 108 according to Kabat numbering) can be Gln, Leu, Arg, Pro, Glu, Lys, Ser, Thr, Met, Ala or His; preferably Gln or Leu, or any other amino acid with a reactive group in its side chain, such as cysteine; X77: (position 110 according to Kabat numbering) can be Thr or any amino acid with a reactive group in its side chain, such as cysteine; X78: (position 112 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X79: (position 113 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X80: is absent or Gly; X81: is absent or Gly; X82: is absent or Cys, or a sequence which has 80% or more identity with SEQ ID NO.: 186, preferably a sequence which has 85% or more, 90% or more, 95% or more, 97% or more or 99% or more sequence identity with SEQ ID NO.: 186, provided that the building block has a globular 3D structure, is soluble, has a size (molecular mass) of about 2.5 to about 70 kDa, such as about 2.5 to about 50 kDa, or of about 2.5 to less than 50 kDa, more preferably of about 2.5 to about 30 kDa, such as about 2.5 to about 16 kDa, such as about 5 to about 16 kDa, or about 7 to about 16 kDa, or about 10 to about 16 kDa, and does not specifically bind to any human protein.

12. The molecule of any of claims 8 to 11, wherein the ISVD-derived building block comprises or, alternatively, consists of SEQ ID NO.: 206: X1aVQLVEX1GGGZ1VX2AGGX3LX4IX5CX6AX7X7bGX7cLSX8YVLGWFRQAPGX9X10REFVAAINWRGX11I TIGPPX12VEX13RFX14IX15RX16NX17X18NTGYLQMNX19LAPX19bDTAZ2YYCGAGTPLNPX20AYIYX21WS YDYWGX22GTZ3VTVX23SX24X25X26 whereinX1a(position 1 according to Kabat numbering) can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X1(position 7 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; Z1(position 11 according to Kabat numbering) can be Leu, Val, Ser, Met, Trp, Phe, Thr, Gln, Glu, Ala, Arg, Gly, Lys, Tyr, Asn, Pro or Ile; preferably Leu, Val, Ser or Glu, more preferably Leu or Val; X2(position 13 according to Kabat numbering) can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X3(position 17 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X4(position 19 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X5: (position 21 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X6: (position 23 according to Kabat numbering) can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X7: (position 25 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X7b: (position 26 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X7c: (position 28 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X8: (position 31 according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X9: ( position 43 according to Kabat numbering) can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X10: (position 44 according to Kabat numbering) can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X11: (position 55 according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine;X12: (position 62 according to Kabat numbering) can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X13: (position 65 according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X14: (position 68 according to Kabat numbering) can be Thr or any amino acid with a reactive group in its side chain, such as cysteine; X15: (position 70 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X16: (position 72 according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X17: (position 74 according to Kabat numbering) can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X18: (position 75 according to Kabat numbering) can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X19: (position 82b according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X19b: (position 85 according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; Z2: (position 89 according to Kabat numbering) can be Leu, Val, Ser, Met, Trp, Phe, Thr, Gln, Glu, Ala, Arg, Gly, Lys, Tyr, Asn, Pro or Ile; preferably Leu, Val, Ser or Glu, more preferably Leu or Val; X20: (position100a according to Kabat numbering) can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X21: (position 100f according to Kabat numbering) can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X22: (position 105 according to Kabat numbering) can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; Z3: (position 108 according to Kabat numbering) can be Gln, Leu, Arg, Pro, Glu, Lys, Ser, Thr, Met, Ala or His; preferably Gln or Leu; X23: (position 112 according to Kabat numbering) can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X24: is absent or Gly;X25: is absent or Gly; X26: is absent or Cys, or a sequence which has 80% or more identity with SEQ ID NO.: 206, preferably a sequence which has 85% or more, 90% or more, 95% or more, 97% or more or 99% or more sequence identity with SEQ ID NO.: 206, provided that the building block has a globular 3D structure, is soluble, has a size (molecular mass) of about 2.5 to about 70 kDa, such as about 2.5 to about 50 kDa, or of about 2.5 to less than 50 kDa, more preferably of about 2.5 to about 30 kDa, such as about 2.5 to about 16 kDa, such as about 5 to about 16 kDa, or about 7 to about 16 kDa, or about 10 to about 16 kDa, and does not specifically bind to any human protein.

13. The molecule of claim 8, wherein the DARPin-based building block is derived from the polypeptide as defined in SEQ ID NO.:

187.

14. The molecule of claim 13, wherein at least one protein-based building block comprises, or alternatively, consists of, SEQ ID NO.: 188: X1X2GX3X4LLX5AAX6X7X8X9X10X11X12VX13X14LMX15X16X17AX18VX19AX20X21X22X23GX24TPLHLAAX25 X26X27X28X29X30IVX31VLLX32X33X34AX35VX36AX37DX38X39GATPLHLAAX40X41X42X43X44X45IVX46VLLX4 7X48X49AX50VX51AX52DX53X54GATPLHX55AAX56X57X58X59X60X61IVX62X63LX64X65X66X67AX68X69X70AX 71DX72X73X74X75TAX76X77ISX78X79X80X81X82X83X84LAX85X86LX87X88X89X90, wherein X1 can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X2 can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X3 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X4 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X5 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X6 can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X7 can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X8 can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X9 can be Gln or any amino acid with a reactive group in its side chain, such as cysteine;X10can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X11can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X12can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X13can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X14can be Ile or any amino acid with a reactive group in its side chain, such as cysteine; X15can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X16can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X17can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X18can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X19can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X20can be His or any amino acid with a reactive group in its side chain, such as cysteine; X21 can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X22can be Thr or any amino acid with a reactive group in its side chain, such as cysteine; X23can be Phe or any amino acid with a reactive group in its side chain, such as cysteine; X24 can be Phe or any amino acid with a reactive group in its side chain, such as cysteine; X25can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X26 can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X27 can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X28 can be His or any amino acid with a reactive group in its side chain, such as cysteine X29 can be Leu or any amino acid with a reactive group in its side chain, such as cysteine X30 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine X31 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine X32 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine X33 can be Asn or any amino acid with a reactive group in its side chain, such as cysteine X34 can be Gly or any amino acid with a reactive group in its side chain, such as cysteine X35 can be Asp or any amino acid with a reactive group in its side chain, such as cysteine X36 can be Asn or any amino acid with a reactive group in its side chain, such as cysteine X37 can be Asp or any amino acid with a reactive group in its side chain, such as cysteine X38 can be Ser or any amino acid with a reactive group in its side chain, such as cysteine X39 can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X40 can be Met or any amino acid with a reactive group in its side chain, such as cysteine; X41 can be Arg or any amino acid with a reactive group in its side chain, such as cysteine;X42can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X43can be His or any amino acid with a reactive group in its side chain, such as cysteine; X44can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X45can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X46can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X47can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X48can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X49can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X50can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X51can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X52can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X53 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X54can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X55can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X56 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X57can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X58 can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X59 can be His or any amino acid with a reactive group in its side chain, such as cysteine; X60 can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X61 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X62 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X63 can be Val or any amino acid with a reactive group in its side chain, such as cysteine; X64 can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X65 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X66 can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X67 can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X68 can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X69 can be Val or any amino acid with a reactive group in its side chain, such as cysteine; X70 can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X71 can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X72 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X73 can be Phe or any amino acid with a reactive group in its side chain, such as cysteine;X74can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X75can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X76can be Phe or any amino acid with a reactive group in its side chain, such as cysteine; X77can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X78can be Ile or any amino acid with a reactive group in its side chain, such as cysteine; X79can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X80can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X81can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X82can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X83can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X84can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X85 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X86can be Ile or any amino acid with a reactive group in its side chain, such as cysteine; X87can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X88 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X89can be absent or Leu; X90 can be absent or Cys or a sequence which has 80% or more identity with SEQ ID NO.: 188, preferably a sequence which has 85% or more, 90% or more, 95% or more, 97% or more or 99% or more sequence identity with SEQ ID NO.: 188, provided that the building block has a globular 3D structure, is soluble, has a size (molecular mass) of about 2.5 to about 70 kDa, such as about 2.5 to about 50 kDa, or of about 2.5 to less than 50 kDa, more preferably of about 2.5 to about 30 kDa, such as about 2.5 to about 16 kDa, such as about 5 to about 16 kDa, or about 7 to about 16 kDa, or about 10 to about 16 kDa, and does not specifically bind to any human protein.

15. The molecule of any of claims 13 to 14, wherein the at least one protein-based building block comprises, or alternatively, consists of, SEQ ID NO.: 189, DLGKX1LLEAARAGQDDEVRILMANGADVNAHDTFGFTPLHLAALYGHLX2IVEVLLKNGAX3VNAX4DSY GATPLHLAAMRGHLX5IVX6VLLKYGAX7VX8AX9DEX10GATPLHLAAKAGHLX11IVEVLLKNGAX12VNAQ DKFGKTAFDISIX13NGNEX14LAEILQX15X16X17,wherein X1can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X2can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X3can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X4can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X5can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X6can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X7can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X8can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X9can be Ala or any amino acid with a reactive group in its side chain, such as cysteine; X10 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X11can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X12can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X13 can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X14can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X15 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X16 can be absent or Leu; X17 can be absent or Cys, or a sequence which has 80% or more identity with SEQ ID NO.: 189, preferably a sequence which has 85% or more, 90% or more, 95% or more, 97% or more or 99% or more sequence identity with SEQ ID NO.: 189, provided that the building block has a globular 3D structure, is soluble, has a size (molecular mass) of about 2.5 to about 70 kDa, such as about 2.5 to about 50 kDa, or of about 2.5 to less than 50 kDa, more preferably of about 2.5 to about 30 kDa, such as about 2.5 to about 16 kDa, such as about 5 to about 16 kDa, or about 7 to about 16 kDa, or about 10 to about 16 kDa, and does not specifically bind to any human protein.

16. The molecule of claim 8, wherein the CSK1-derived building block is derived from the polypeptide as defined in SEQ ID NO.: 190.

17. The molecule of claim 16, wherein the at least one protein-based building block comprises, or alternatively, consists of, SEQ ID NO.: 191: X1X2X3X4IX5X6SX7X8X9X10X11X12X13X14X15X16X17X18VX19LPX20X21X22AX23X24VX25X23bX24bX25bX26MX27X28X29X30WX31X32LX33VX34QX35X36X37WX38HX39X40X41X42X43X44X45X46X47ILLFX48X49X50X51X52X53X54X55X56X57, wherein X1can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X2can be His or any amino acid with a reactive group in its side chain, such as cysteine; X3can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X4can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X5 can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X6can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X7can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X8 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X9can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X10 can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X11 can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X12 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X13 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X14 can be Phe or any amino acid with a reactive group in its side chain, such as cysteine; X15 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X16 can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X17 can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X18 can be His or any amino acid with a reactive group in its side chain, such as cysteine; X19 can be Met or any amino acid with a reactive group in its side chain, such as cysteine; X20 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X21 can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X22 can be Ile or any amino acid with a reactive group in its side chain, such as cysteine; X23 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X24 can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X25 can be Pro or any amino acid with a reactive group in its side chain, such as cysteine;X23bcan be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X24bcan be Thr or any amino acid with a reactive group in its side chain, such as cysteine; X25bcan be His or any amino acid with a reactive group in its side chain, such as cysteine; X26can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X27can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X28can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X29can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X30can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X31can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X32can be Asn or any amino acid with a reactive group in its side chain, such as cysteine; X33can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X34 can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X35can be Ser or any amino acid with a reactive group in its side chain, such as cysteine; X36can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X37 can be Gly or any amino acid with a reactive group in its side chain, such as cysteine; X38can be Val or any amino acid with a reactive group in its side chain, such as cysteine; X39 can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X40 can be Met or any amino acid with a reactive group in its side chain, such as cysteine; X41 can be Ile or any amino acid with a reactive group in its side chain, such as cysteine; X42 can be His or any amino acid with a reactive group in its side chain, such as cysteine; X43 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X44 can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X45 can be Glu or any amino acid with a reactive group in its side chain, such as cysteine; X46 can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X47 can be His or any amino acid with a reactive group in its side chain, such as cysteine; X48 can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X49 can be Arg or any amino acid with a reactive group in its side chain, such as cysteine; X50 can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X51 can be Leu or any amino acid with a reactive group in its side chain, such as cysteine; X52 can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X53 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X54 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine;X55can be Pro or any amino acid with a reactive group in its side chain, such as cysteine; X56can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X57can be Lys or any amino acid with a reactive group in its side chain, such as cysteine, or a sequence which has 80% or more identity with SEQ ID NO.: 191, preferably a sequence which has 85% or more, 90% or more, 95% or more, 97% or more or 99% or more sequence identity with SEQ ID NO.: 191, provided that the building block has a globular 3D structure, is soluble, has a size (molecular mass) of about 2.5 to about 70 kDa, such as about 2.5 to about 50 kDa, or of about 2.5 to less than 50 kDa, more preferably of about 2.5 to about 30 kDa, such as about 2.5 to about 16 kDa, such as about 5 to about 16 kDa, or about 7 to about 16 kDa, or about 10 to about 16 kDa, and does not specifically bind to any human protein.

18. The molecule of any of claims 16 to 17, wherein the at least one protein-based building block comprises, or alternatively, consists of, SEQ ID NO.: 205: SHKQIYYSX1X2X3X4X5EEFEYRHVX6LPKDIAKLVPX7THLMSESEWRNLGVQQSX8GWVHYX9IHEPEPHI LLFRRPLPKKPKX10, wherein X1 can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X2 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X3 can be Tyr or any amino acid with a reactive group in its side chain, such as cysteine; X4 can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X5 can be Asp or any amino acid with a reactive group in its side chain, such as cysteine; X6 can be Met or any amino acid with a reactive group in its side chain, such as cysteine; X7 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine; X8 can be Gln or any amino acid with a reactive group in its side chain, such as cysteine; X9 can be Met or any amino acid with a reactive group in its side chain, such as cysteine; X10 can be Lys or any amino acid with a reactive group in its side chain, such as cysteine, or a sequence which has 80% or more identity with SEQ ID NO.: 205, preferably a sequence which has 85% or more, 90% or more, 95% or more, 97% or more or 99% or more sequenceidentity with SEQ ID NO.: 205, provided that the building block has a globular 3D structure, is soluble, has a size (molecular mass) of about 2.5 to about 70 kDa, such as about 2.5 to about 50 kDa, or of about 2.5 to less than 50 kDa, more preferably of about 2.5 to about 30 kDa, such as about 2.5 to about 16 kDa, such as about 5 to about 16 kDa, or about 7 to about 16 kDa, or about 10 to about 16 kDa, and does not specifically bind to any human protein.

19. The molecule of any of claims 1 to 18, wherein the at least one protein-based building block comprises or consist of a polypeptide selected from SEQ ID NO.: 80-105, 175, 199, 208 and / or 222-224.

20. The molecule of any of claims 1 to 19, wherein the molecule comprises at least one protein-based building block and at least one further moiety or cargo, preferably wherein the at least one further moiety or cargo is selected from a) a half-life extending (HLE) moiety, and / or b) a targeting moiety, preferably an EGFR-targeting moiety such as GE11 peptide; and / or c) a therapeutic moiety or precursor therefrom; d) an imaging moiety; e) a toxic moiety; f) siRNA; g) vitamins, preferably folate; h) Toll-like receptor agonists; i) glycans, preferably bis mannose 6 phosphate (bisM6P) or mannose 6 phosphate (M6P); and / or j) lipids, preferably short-chain fatty acids.

21. The molecule of claim 20, wherein the at least one cargo is directly attached to the at least one protein-based building block, or wherein the at least one cargo is attached to the at least one protein-based building block through a linker.

22. The molecule of any of claims 20 to 21, wherein the cargo is an (in vivo) half-life extending moiety, preferably a PEG molecule, preferably a 1-20 kDa pEG molecule, morepreferably a 1-10 kDa PEG molecule, even more preferably a 1-5 kDa PEG molecule, an ELNN polypeptide or an albumin-binding polypeptide.

23. The molecule of claim 22, wherein the albumin-binding polypeptide is an albumin- binding ISVD, wherein preferably the albumin-binding ISVD comprises or, alternatively consists of, a polypeptide as defined in any one of SEQ ID NOs.: 50-64 or 106, preferably SEQ ID NOs.: 63 or 106.

24. The molecule of any of claims 1 to 23, wherein the molecule comprises or, alternatively consists of, a polypeptide as defined in any one of SEQ ID NOs.: 107-127, 170-174, 176 or 200.

25. A nucleic acid encoding the molecule as defined in any one of claims 1 to 24, part of the molecule as defined in any one of claims 1 to 24 and / or the protein-based building block as defined in any one of claims 1-19.

26. A vector comprising the nucleic acid as defined in claim 25.

27. A composition comprising the molecule as defined in any one of claims 1 to 24, such as a pharmaceutical composition.

28. A method for producing the molecule as defined in any one of claims 1 to 24, wherein the method comprises: a) expressing, in a suitable host cell or host organism or in another suitable expression system, a nucleic acid sequence encoding the at least one protein-based carrier building block and / or the molecule or part of the molecule as defined in any one of claims 1 to 24; b) optionally isolating and / or purifying the at least one protein-based carrier building block and / or the molecule or part of the molecule expressed in a); c) optionally conjugating one or more (further) cargos to the attachment point(s) or conjugation sites(s) of the protein-based carrier building block.

29. A method for producing the molecule as defined in any one of claims 1 to 24, wherein the method comprises: a) chemically synthesizing the at least one protein-based carrier building block and / or the molecule or part of the molecule as defined in any one of claims 1 to 24, preferably by using solid-phase peptide synthesis; b) optionally isolating and / or purifying the at least one protein-based carrier building block and / or the molecule or part of the molecule synthesized in a); c) optionally conjugating one or more (further) cargos to the attachment point(s) or conjugation sites(s) of the protein-based carrier building block.

30. The molecule according to any one of claims 1 to 24 or the composition according to claim 27 for use in medicine.

31. The molecule according to any one of claims 1 to 24 or the composition according to claim 27 for use in the prophylactic and / or therapeutic treatment of an autoimmune / inflammatory disease, an infectious disease and / or cancer, such as hematological (blood) and solid tumor cancer disease.

32. The molecule according to any one of claims 1 to 24 or the composition according to claim 27 for use as a vaccine.

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