FUSION PROTEINS FOR SELECTIVELY DEPLETING MuSK-SPECIFIC ANTIBODIES

Abstract

The present disclosure includes a fusion protein, called a "Macromolecule that targets MuSK-specific antibodies", including a targeting component that specifically binds to a cell surface receptor or other cell surface molecule, and an antigen component fused directly or indirectly to the targeting component. The antigen component is configured to specifically bind a target antigen-specific antibody. The present disclosure also includes a method of depleting a target antigen-specific antibody from a patient by administering to the patient a macromolecule that targets MuSK-specific antibodies having an antigen component configured to specifically bind the target antigen-specific antibody.

Description

[0001] FUSION PROTEINS FOR SELECTIVELY DEPLETING MuSK-SPECIFIC ANTIBODIES

[0002] CROSS REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to U.S. Provisional Application No. 63 / 748,048. filed 22 January 2025, which is hereby incorporated by reference herein in its entirety.

[0004] REFERENCE TO SEQUENCE LISTING SUBMITTED ELECTRONICALLY

[0005] This application contains a Sequence Listing, which is submitted electronically via EFS-Web as an XML Document formatted Sequence Listing with a file name ”206604-0003-00WO_SequenceListing” having a creation date of 13 January 2026 and having a size of 105,068 bytes. The Sequence Listing submitted via EFS-Web is part of the Specification and is herein incorporated by reference in its entirety.

[0006] TECHNICAL FIELD

[0007] This disclosure relates to molecules that selectively deplete antigen-specific antibodies from the body. The antigen-specific antibodies bind to the extracellular domains of a transmembrane protein called muscle-specific kinase (MuSK).

[0008] BACKGROUND

[0009] Antibodies are Y-shaped proteins present in blood and other body fluids of the human body and the bodies of mammals. Antibodies are a critical component of the body’s immune system. They function by recognizing a unique part of a foreign target, called the antigen. An antibody is able to selectively recognize and trigger an immune response to an antigen through its two antigen-binding sites. Each antigen-binding site is at the end of each upper tip of the antibody’s Y-shape. The target antigen may bind one or both antigen-binding sites. The base of an antibody’s Y-shape is called an Fc fragment. When an antibody binds to its target, the Fc region can bring about target clearance through antibody effector functions. Such responses can include cellular processes to destroy the antigen. In certain autoimmune diseases and other illnesses, pathogenic antibodies may be created that target self-antigens in the body,contributing to pathogenesis. An antibody may be in either of two physical forms, a soluble form that is secreted from the cell and is free in the blood serum, or a membrane-bound form that is attached to the outer-membrane of a B cell. The secreted antibodies cause pathology in diseases involving autoreactive antibodies. They can also contribute to transplant rejection or the elimination of protein-based therapeutics.

[0010] SUMMARY

[0011] The present disclosure includes fusion proteins or molecules, herein referred to as macromolecules that target MuSK-specific antibodies, that are configured to allow selective clearance of MuSK-specific antibodies that cause disease in myasthenia gravis associated with MuSK-specific antibodies (MuSK-MG). MuSK-MG is a rare orphan disease that is characterized by weakness and fatigability of the skeletal muscles, affects women more frequently than men and frequently presents in women during their 30s. The symptoms of this disease typically involve bulbar muscles, resulting in difficulty in speech, swallowing and chewing. Respiratory distress, that can be life-threatening, is observed in about one third of patients. Over time, patients develop muscle atrophy that can lead to long term disability’.

[0012] MuSK-MG requires a treatment that has a rapid mechanism of action to avoid severe symptoms, including respiratory distress, that can lead to death. Macromolecules that target MuSK-specific antibodies provide a potential treatment that removes the disease-causing antibodies and also has a fast onset of action.

[0013] A macromolecule that targets MuSK-specific antibodies includes a targeting component that is configured to specifically bind to an internalizing cell surface receptor or other internalizing cell surface molecule, and an antigen component that is configured to specifically bind to a MuSK-specific antibody or a variant thereof.

[0014] The targeting component of the macromolecule that targets MuSK-specific antibodies includes a protein, a protein fragment, a carbohydrate, a carbohydrate derivative or a small molecule that is configured to specifically bind to an internalizing cell surface receptor or other internalizing cell surface molecule. The antigen component of the macromolecule that targets MuSK-specific antibodies includes one or more molecules of an antigen or antigen fragment or antigen mimetic configured to specifically bind antibodies that recognize MuSK or domains thereof. Specifically, the antigen component of the macromolecule that targets MuSK-specific antibodies may include one or more extracellular domains of MuSK, or one or more fragmentsof MuSK or a MuSK mimetic. The antigen component may be fused directly or indirectly to the targeting component.

[0015] The extracellular region of MuSK comprises three immunoglobulin-like domains (Ig1-3) and a frizzled-like domain (Fz). Macromolecules comprising the following combinations of domains are selectively recognized by antibodies in serum samples of MuSK-MG patients but not in serum samples from healthy controls: Ig1, Ig1 + Ig2, Ig1 + Ig2 + Ig3 or Ig1 + Ig2 + Ig3 + Fz.

[0016] In one embodiment, therefore, the antigen component of the macromolecule comprises at least part of the Ig1 domain of MuSK.

[0017] In a further embodiment, the antigen component of the macromolecule comprises at least part of the Ig1 and Ig2 domains of MuSK.

[0018] In a further embodiment, the antigen component of the macromolecule comprises at least part of the Ig1, Ig2 and Ig3 domains of MuSK.

[0019] In a further embodiment, the antigen component of the macromolecule comprises the Ig1, Ig2, Ig3 and Fz domains of MuSK. The domains may be entire, or partial domains, such as truncated domains.

[0020] In a further embodiment, the antigen component of the macromolecule comprises substantially the entirety of said domains.

[0021] The antigen component may comprise a single polypeptide component including the foregoing domains. Alternatively, the antigen component may comprise two separate polypeptides, which may comprise the same or different domains of MuSK.

[0022] In a further embodiment, the domains may be comprised in three or more separate polypeptides of the antigen component.

[0023] In some embodiments of the present invention, the antigen component of the macromolecule does not consist of or comprise only Igl, Ig2 and Ig3 domains of MuSK alone, without also comprising the Fz domain.

[0024] In one embodiment, the Igl domain polypeptide which is comprised in the antigen component of the macromolecule comprises the sequence of SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7. SEQ ID NO: 8. SEQ ID NO: 10. SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 28, SEQ ID NO: 29, SEQ ID NO: 30, SEQ ID NO: 31, SEQ ID NO: 32, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, SEQ ID NO: 36, SEQ ID NO: 37, SEQ ID NO: 38, SEQ ID NO: 39, SEQ ID NO: 40, SEQ IDNO: 41, SEQ ID NO: 42, SEQ ID NO: 43, SEQ ID NO: 44, SEQ ID NO: 45, SEQ ID NO: 46, SEQ ID NO: 47, SEQ ID NO: 51, SEQ ID NO: 52 or SEQ ID NO: 53.

[0025] In one embodiment, the Ig2 domain polypeptide which is comprised in the antigen component of the macromolecule comprises the sequence of SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23. SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27. SEQ ID NO: 28, SEQ ID NO: 29, SEQ ID NO: 30, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, SEQ ID NO: 36, SEQ ID NO: 37, SEQ ID NO: 38, SEQ ID NO: 41, SEQ ID NO: 42, SEQ ID NO: 43, SEQ ID NO: 44, SEQ ID NO: 45, SEQ ID NO: 46, SEQ ID NO: 48, SEQ ID NO: 51, SEQ ID NO: 52 or SEQ ID NO: 53.

[0026] In one embodiment, the Ig3 domain polypeptide which is comprised in the antigen component of the macromolecule comprises the sequence of SEQ ID NO: 7, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 28, SEQ ID NO: 30, SEQ ID NO: 35, SEQ ID NO: 36, SEQ ID NO: 37, SEQ ID NO: 38, SEQ ID NO: 43, SEQ ID NO: 44, SEQ ID NO: 45, SEQ ID NO: 46, SEQ ID NO:49, SEQ ID NO: 52 or SEQ ID NO: 53.

[0027] In one embodiment, the Fz domain polypeptide which is comprised in the antigen component of the macromolecule comprises the sequence of SEQ ID NO: 7, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 28, SEQ ID NO: 37, SEQ ID NO: 38, SEQ ID NO: 45, SEQ ID NO: 46, SEQ ID NO: 50 or SEQ ID NO: 53.

[0028] The present disclosure also includes a method of depleting a target antigen-specific antibody from a patient by administering to the patient a macromolecule that targets MuSK-specific antibodies in an amount sufficient to remove at least 50% of the target antigen-specific antibody from the circulation or a target tissue in the patient.

[0029] The above macromolecule that targets MuSK-specific antibodies and methods may further include the following details, which may be combined with one another unless clearly mutually exclusive: i) the targeting component can bind to the internalizing cell surface receptor or internalizing cell surface molecule with a dissociation constant of less than 10 μM at near-neutral pH; ii) near-neutral pH may be greater than 6.8 and less than 7.5; iii) the macromolecule that targets MuSK-specific antibodies can comprise at least a first targetingcomponent and a second targeting component, wherein the protein or protein fragment of the first targeting component is configured to bind to a different cell surface receptor or a different cell surface molecule than the protein or protein fragment of the second targeting component; iv) the targeting component may include a heterodimer of two immunoglobulin Fc fragments in which one immunoglobulin Fc fragment of the heterodimer is fused to the antigen component and the other immunoglobulin Fc fragment may not be. or both Fc fragments may be fused to the same or different antigen components; v) the macromolecule that targets MuSK-specific antibodies may have substantially reduced binding or no detectable binding to Fc gamma receptors; vi) at least one of the immunoglobulin Fc fragments can be derived from an immunoglobulin class or isotype that does not bind to Fc gamma receptors and / or complement (C1q); vii) at least one of the immunoglobulin Fc fragments can be configured to bind to Fc gamma receptors, particularly to FcyRIIb; viii) at least one of the immunoglobulin Fc fragments can be modified to have a higher binding affinity for FcRn at near-neutral pH than an unmodified immunoglobulin Fc fragment; ix) the antigen component may be fused to one immunoglobulin Fc fragment at an N-terminus or a C-terminus of a hinge-CH2-CH3 domain of the immunoglobulin Fc fragment; x) the immunoglobulin Fc fragments may be modified to have no binding affinity for Fc gamma receptors and / or complement (C1q), or lower binding affinity for Fc gamma receptors and / or complement (C1q) than unmodified immunoglobulin Fc fragments; xi) the targeting component may comprise an immunoglobulin Fc fragment that is modified to bind with increased affinity to the inhibitory Fc gamma receptor, FcyRIIb; xii) the targeting component may include one or more antibody variable regions or fragments thereof that are configured to specifically bind to the internalizing cell surface receptor or the cell surface molecule; xiii) the antibody variable region or fragment thereof may include at least one nanobody; xiv) the nanobody may be a nanobody multimer in which one nanobody is fused to the antigen component and all other nanobodies in the nanobody multimer may not be fused to the antigen component; xv) the targeting component may dissociate from its target in early or late endosomes; xvi) the antigen component may be fused to an N-terminal location or a C-terminal location on the targeting component; xvii) the antigen component may be fused to a non-terminal location on the targeting component; xviii) the antigen component may be fused to the targeting component via a chemical reaction, through a linker, or during formation of a single combined antigen component-targeting component fusion protein; xix) the targeting component can be one or more albumin molecules, albumin fragments or mutated albumin variants that are configured to specifically bind to FcRn; xx) the targeting component caninclude one or more antibody variable domains or nanobodies that are configured to bind to a transferrin receptor; xxi) the targeting component can include one or more protein molecules or protein domains configured to bind to a transfenin receptor; xxii) the targeting component can include one or more antibody variable domains or nanobodies that are configured to bind to the asialoglycoprotein receptor (ASGPR); xxiii) the targeting component can include one or more protein molecules or protein domains, carbohydrates, carbohydrate derivatives or small molecules configured to bind to ASGPR; xxiv) the targeting component can include one or more antibody variable domains or nanobodies that are configured to bind to a mannose 6-phosphate receptor (M6PR) such as cation-independent M6PR (CI-M6PR); xxv) the targeting component can include one or more protein molecules or protein domains, carbohydrates, carbohydrate derivatives or small molecules configured to bind to a M6PR such as CI-M6PR; xxvi) the targeting component can include one or more protein molecules or protein domains, carbohydrates, carbohydrate derivatives or small molecules configured to bind to CD 163; xxvii) the targeting component can include one or more protein molecules or protein domains configured to bind to phosphatidylserine; xxviii) the targeting protein component can include one or more antibody variable domains or nanobodies configured to bind to phosphatidylserine; xxix) the one or more protein molecules or protein domains can be configured to bind the phosphatidylserine via a calcium-dependent mechanism; xxx) the targeting component can include a C2A domain of synaptotagmin 1; xxxi) the macromolecule that targets MuSK-specific antibodies can include at least a first antigen component and a second antigen component, wherein the one molecule of the antigen, antigen fragment or antigen mimetic of the first antigen component is different to the one molecule of the antigen molecule, antigen fragment or antigen mimetic of the second antigen component; xxxii) the macromolecule that targets MuSK-specific antibodies can include at least a first antigen component and additional antigen components, wherein the one molecule of the antigen, antigen fragment or antigen mimetic of the first antigen component is different to additional antigen molecules, antigen fragments or antigen mimetics of the additional antigen components; xxxiii) the method may include administering the macromolecule that targets MuSK-specific antibodies in amounts and at dosing frequencies sufficient to remove at least 50% of the target antigen-specific antibody from the circulation or from a tissue or organ in the patient; xxxiv) the method may include administering the macromolecule that targets MuSK-specific antibodies in amounts and at dosing frequencies sufficient to remove at least 80% of the target antigen-specific antibody from the circulation or from a tissue or organ in the patient; xxxv) the method mayinclude administering the macromolecule that targets MuSK-specific antibodies in amounts and at dosing frequencies sufficient to remove at least 90% of the target antigen-specific antibody from the circulation or from a tissue or organ in the patient; xxxvi) the macromolecule that targets MuSK-specific antibodies may remove less than 20% of non-target antibodies from the circulation or from a tissue or organ; xxxvii) the macromolecule that targets MuSK-specific antibodies may remove less than 10% of non-target antibodies from the circulation or from a tissue or organ; xxxviii) the macromolecule that targets MuSK-specific antibodies may remove less than 5% of non-target antibodies from the circulation or from a tissue or organ; xxxix) the macromolecule that targets MuSK-specific antibodies may cause degradation of the target antigen-specific antibody by a cell expressing the internalizing cell surface receptor or internalizing cell surface molecule; xl) the macromolecule that targets MuSK-specific antibodies may be administered to a patient with an autoimmune disease and the target antigenspecific antibody may specifically bind to an autoantigen; xli) the macromolecule that targets MuSK-specific antibodies may comprise at least one protein having at least one amino acid sequence of SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 8, SEQ ID NO: 9, SEQ ID NO: 10, SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 26, SEQ ID NO: 27. SEQ ID NO: 28. SEQ ID NO: 29. SEQ ID NO: 30. SEQ ID NO: 31. SEQ ID NO: 32, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, SEQ ID NO: 36, SEQ ID NO: 37, SEQ ID NO: 38, SEQ ID NO: 39, SEQ ID NO: 40, SEQ ID NO: 41, SEQ ID NO: 42, SEQ ID NO: 43, SEQ ID NO: 44, SEQ ID NO: 45, SEQ ID NO: 46, SEQ ID NO: 47, SEQ ID NO: 48, SEQ ID NO: 49, SEQ ID NO: 50. SEQ ID NO: 51. SEQ ID NO: 52. SEQ ID NO: 53, SEQ ID NO: 54, SEQ ID NO: 55, SEQ ID NO: 56, SEQ ID NO: 57, SEQ ID NO: 58, SEQ ID NO: 59, SEQ ID NO: 60, SEQ ID NO: 61, SEQ ID NO: 62, SEQ ID NO: 63, SEQ ID NO: 64, SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 67, SEQ ID NO: 68, SEQ ID NO: 69, SEQ ID NO: 70, SEQ ID NO: 71, SEQ ID NO: 72. SEQ ID NO: 73. SEQ ID NO: 74, SEQ ID NO: 75, SEQ ID NO: 76, SEQ ID NO: 77, SEQ ID NO: 78 or a homolog thereof; xlii) the macromolecule that targets MuSK-specific antibodies may include a heterodimer of proteins having amino acid sequences of SEQ ID NO: 2 plus SEQ ID NO: 4, SEQ ID NO: 1 plus SEQ ID NO: 5, SEQ ID NO: 2 plus SEQ ID NO: 6, SEQ ID NO: 2 plus SEQ ID NO: 7, SEQ ID NO: 2 plus SEQ ID NO: 8. SEQ ID NO: 9 plus SEQ ID NO: 10, SEQ ID NO: 11 plus SEQ ID NO: 12, SEQ ID NO: 13 plus SEQ ID NO: 14,SEQ ID NO: 15 plus SEQ ID NO: 17 plus SEQ ID NO: 19, SEQ ID NO: 15 plus SEQ ID NO: 18 plus SEQ ID NO: 19. SEQ ID NO: 16 plus SEQ ID NO: 17 plus SEQ ID NO: 19. SEQ ID NO: 16 plus SEQ ID NO: 18 plus SEQ ID NO: 19, SEQ ID NO: 3 plus SEQ ID NO: 20, SEQ ID NO: 2 plus SEQ ID NO: 21, SEQ ID NO: 2 plus SEQ ID NO: 22, SEQ ID NO: 2 plus SEQ ID NO: 23, SEQ ID NO: 2 plus SEQ ID NO: 24, SEQ ID NO: 2 plus SEQ ID NO: 25, SEQ ID NO: 26 plus SEQ ID NO: 27, SEQ ID NO: 1 plus SEQ ID NO: 28, SEQ ID NO: 1 plus SEQ ID NO: 29. SEQ ID NO: 1 plus SEQ ID NO: 30, SEQ ID NO: 16 plus SEQ ID NO: 39. SEQ ID NO: 16 plus SEQ ID NO: 40, SEQ ID NO: 16 plus SEQ ID NO: 41, SEQ ID NO: 16 plus SEQ ID NO: 42, SEQ ID NO: 16 plus SEQ ID NO: 43, SEQ ID NO: 16 plus SEQ ID NO: 44, SEQ ID NO: 16 plus SEQ ID NO: 45, SEQ ID NO: 16 plus SEQ ID NO: 46, any of the heterodimers described in Table 1. or homologs thereof.

[0030] BRIEF DESCRIPTION OF THE DRAWINGS

[0031] For a more complete understanding of the present invention and its features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, which are not to scale, in which like numerals refer to like features, and in which:

[0032] FIGURE l is a schematic diagram of selected cellular events that lead to the degradation of MuSK-specific antibodies in the presence of a macromolecule that targets MuSK-specific antibodies;

[0033] FIGURE 2A is a schematic diagram of a macromolecule that targets MuSK-specific antibodies including an antigen fused to a N-terminal location of an Fc fragment. The antigen component of the macromolecule that targets MuSK-specific antibodies may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics;

[0034] FIGURE 2B is a schematic diagram of a macromolecule that targets MuSK-specific antibodies including an antigen fused to a C-terminal location of an Fc fragment. The antigen component of the macromolecule that targets MuSK-specific antibodies may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics;

[0035] FIGURE 2C is a schematic diagram of a macromolecule that targets MuSK-specific antibodies including an antigen fused to a non-terminal location of an Fc fragment. The antigencomponent of the macromolecule that targets MuSK-specific antibodies may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics;

[0036] FIGURE 2D is a schematic diagram of a macromolecule that targets MuSK-specific antibodies including two different antigens fused to the N-terminal locations of an Fc fragment. The antigen components of the macromolecule that targets MuSK-specific antibodies may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics;

[0037] FIGURE 2E is a schematic diagram of a macromolecule that targets MuSK-specific antibodies including two different antigens fused to the C-terminal locations of an Fc fragment. The antigen components of the macromolecule that targets MuSK-specific antibodies may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics;

[0038] FIGURE 2F is a schematic diagram of a macromolecule that targets MuSK-specific antibodies including two different antigens fused to the N- and C- terminal locations of the same Fc fragment. The two antigen components of the macromolecule that targets MuSK-specific antibodies are different and may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics;

[0039] FIGURE 2G is a schematic diagram of a macromolecule that targets MuSK-specific antibodies including two different antigens fused to the N- and C-terminal locations of different Fc fragments in an Fc heterodimer. Other embodiments can include three or four different antigen components fused to the N- and C-terminal locations. The two or more antigen components of the macromolecule that targets MuSK-specific antibodies are different and may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics;

[0040] FIGURE 2H is a schematic diagram of a macromolecule that targets MuSK-specific antibodies including an antigen fused to a terminal location of a protein or protein fragment that binds to a cell surface receptor or cell surface molecule. The protein or protein fragment can be albumin, an antibody single VHH domain, an antibody scFv fragment or an antibody Fab fragment. Alternatively, the protein or protein fragment can be replaced by a carbohydrate, carbohydrate derivative or small molecule that binds to a cell surface receptor or cell surface molecule. The antigen component of the macromolecule that targets MuSK-specific antibodiesmay include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics;

[0041] FIGURE 21 is a schematic diagram of a macromolecule that targets MuSK-specific antibodies including two different antigens fused to terminal locations of a protein or protein fragment that binds to a cell surface receptor or cell surface molecule. The protein or protein fragment can be albumin, an antibody single VHH domain, an antibody scFv fragment or an antibody Fab fragment. Alternatively, the protein or protein fragment can be replaced by a carbohydrate, carbohydrate derivative or small molecule that binds to a cell surface receptor or cell surface molecule. The two antigen components of the macromolecule that targets MuSK-specific antibodies are different and may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics;

[0042] FIGURE 2J is a schematic diagram of a macromolecule that targets MuSK-specific antibodies including an antigen fused to a non-terminal location of a protein or protein fragment that binds to a cell surface receptor or cell surface molecule. The protein or protein fragment can be albumin, an antibody single VHH domain, an antibody scFv fragment or an antibody Fab fragment. Alternatively, the protein or protein fragment can be replaced by a carbohydrate, carbohydrate derivative or small molecule that binds to a cell surface receptor or cell surface molecule. The antigen component of the macromolecule that targets MuSK-specific antibodies may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics;

[0043] FIGURE 2K is a schematic diagram of a macromolecule that targets MuSK-specific antibodies including an antigen fused to a C-terminal location of an antibody that binds to a cell surface protein or cell surface receptor. The antigen component of the macromolecule that targets MuSK-specific antibodies may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics;

[0044] FIGURE 2L is a schematic diagram of a macromolecule that targets MuSK-specific antibodies including an antigen fused to a C-terminal location of an antibody that binds to a cell surface protein or cell surface receptor. The targeting component is monovalent and comprises one Fab fragment per antibody molecule. The antigen component of the macromolecule that targets MuSK-specific antibodies may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics;FIGURE 2M is a schematic diagram of a macromolecule that targets MuSK-specific antibodies including an antigen fused to a N-terminal location of an Fc fragment and scFv fragments that bind to a cell surface protein or cell surface receptor to the C-termini of the Fc fragment. The antigen component of the macromolecule that targets MuSK-specific antibodies may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics;

[0045] FIGURE 2N is a schematic diagram of a macromolecule that targets MuSK-specific antibodies including an antigen fused to a C-terminal location of an Fc fragment and scFv fragments that bind to a cell surface protein or cell surface receptor to the N-termini of the Fc fragment. The antigen component of the macromolecule that targets MuSK-specific antibodies may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics;

[0046] FIGURE 20 is a schematic diagram of a macromolecule that targets MuSK-specific antibodies including two different antigens fused to C-terminal locations of an antibody that binds to a cell surface protein or cell surface receptor. The two antigen components of the macromolecule that target MuSK-specific antibodies are different and may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics;

[0047] FIGURE 2P is a schematic diagram of a macromolecule that targets MuSK-specific antibodies including two different antigens fused to C-terminal locations of an antibody that binds to a cell surface protein or cell surface receptor. The targeting component is monovalent and comprises one Fab fragment per antibody molecule. The two antigen components of the macromolecule that target MuSK-specific antibodies are different and may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics;

[0048] FIGURE 2Q is a schematic diagram of a macromolecule that targets MuSK-specific antibodies including two different antigens fused to the N- terminal locations of an Fc fragment and scFv fragments that bind to a cell surface protein or cell surface receptor to the C-termini of the Fc fragment. The two antigen components of the macromolecule that targets MuSK-specific antibodies are different and may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics;FIGURE 2R is a schematic diagram of a macromolecule that targets MuSK-specific antibodies including two different antigens fused to a C-terminal location of an Fc fragment and scFv fragments that bind to a cell surface protein or cell surface receptor to the N-termini of the Fc fragment. The two antigen components of the macromolecule that targets MuSK-specific antibodies are different and may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics;

[0049] FIGURE 2S is a schematic diagram of a macromolecule that targets MuSK-specific antibodies including an antigen fused to a N-terminal location of an Fc fragment and protein or protein fragments that bind to a cell surface protein or cell surface receptor to the C-termini of the Fc fragment. The antigen component of the macromolecule that targets MuSK-specific antibodies may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics;

[0050] FIGURE 2T is a schematic diagram of a macromolecule that targets MuSK-specific antibodies including an antigen fused to a C-terminal location of an Fc fragment and protein or protein fragments that bind to a cell surface protein or cell surface receptor to the N-termini of the Fc fragment. The antigen component of the macromolecule that targets MuSK-specific antibodies may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics;

[0051] FIGURE 2U is a schematic diagram of a macromolecule that targets MuSK-specific antibodies comprising two antigen molecules fused to the N-terminal locations of an Fc fragment. The antigen component of the macromolecule that targets MuSK-specific antibodies may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics; and

[0052] FIGURE 2V is a schematic diagram of a macromolecule that targets MuSK-specific antibodies comprising two antigen molecules fused to the N-terminal locations of an Fc fragment and protein or protein fragments that bind to a cell surface protein or cell surface receptor to the C-termini of the Fc fragment. The antigen components of the macromolecule that targets MuSK-specific antibodies may include one or more extracellular domains of MuSK. one or more fragments of MuSK or one or more MuSK mimetics.

[0053] FIGURE 3 is a schematic representation of the different extracellular domains (Ig1, Ig2, Ig3 and Fz) of MuSK that are connected to the transmembrane region and cytosolic tail (tyrosine kinase domain, TKD).FIGURES 4A, 4B, 4C and 4D show SDS-PAGE analyses of exemplary macromolecules that target MuSK-specific antibodies run under reducing and non-reducing conditions.

[0054] FIGURE 5 shows size exclusion analyses of exemplary macromolecules that target MuSK-specific antibodies.

[0055] FIGURE 6A shows the binding of an exemplary macromolecule that targets MuSK-specific antibodies to a recombinant (human IgGl / kappa) MuSK-specific antibody.

[0056] FIGURE 6B and 6C show the binding of an exemplary FcRn-targeting macromolecule that targets MuSK-specific antibodies to FcRn at pH 6.0 and pH 7.4.

[0057] FIGURES 7A, 7B and 7C show HPLC analyses of exemplary FcRn-targeting macromolecules that target MuSK-specific antibodies following incubation at 37°C for 5 or 14 days to evaluate their stability.

[0058] FIGURE 8A shows SDS-PAGE analyses of exemplary FcγRIIb-targeting macromolecules that target MuSK-specific antibodies run under reducing and non-reducing conditions.

[0059] FIGURE 8B shows size exclusion analyses of exemplary FcγRIIb-targeting macromolecules that target MuSK-specific antibodies.

[0060] FIGURE 9A shows graphs reporting exemplary data to demonstrate the effects of mutations that reduce binding to FcγRs on the interaction between exemplary FcRn-targeting macromolecules that target MuSK-specific antibodies and FcγRs.

[0061] FIGURE 9B shows graphs reporting exemplary data to demonstrate the effects of mutations that increase binding to the inhibitory receptor, FcγRIIb, on the interaction between exemplary FcγRIIb-targeting macromolecules that target MuSK-specific antibodies and FcγRIIb.

[0062] FIGURE 9C shows graphs reporting exemplary data to demonstrate the effects of mutations that reduce binding to complement C1q on the interaction between exemplary FcRn-targeting macromolecules that target MuSK-specific antibodies and C1q.

[0063] FIGURES 10A, 10B, 10C and 10D show graphs reporting exemplary data of the differential binding of MuSK-specific antibodies in serum samples of patients to different exemplary macromolecules that target MuSK-specific antibodies.FIGURES 11A, 11B, 11C, 11D, 11E, 11F, 11G and 11H show graphs reporting exemplary data to demonstrate the efficiency with which exemplary macromolecules that target MuSK-specific antibodies specifically deplete MuSK-specific antibodies from patient serum.

[0064] FIGURE 12 shows graphs reporting exemplary data to demonstrate that injection of an exemplary macromolecule that targets MuSK-specific antibodies into mice leads to the specific depletion of MuSK-specific antibodies from the serum.

[0065] FIGURE 13 shows a graph reporting exemplary data of the binding of exemplary FcγRIIb-targeting macromolecules that target MuSK-specific antibodies to MuSK-specific antibodies in serum samples of patients.

[0066] FIGURE 14 shows a graph reporting exemplary data to demonstrate the ability of exemplary FcyRIIb-targeting macromolecules that target MuSK-specific antibodies to deliver MuSK-specific antibodies to FcyRIIb-expressing cells.

[0067] FIGURE 15 shows a graph reporting exemplary data of the binding of an exemplary ASGPR-targeting macromolecule that targets MuSK-specific antibodies to recombinant ASGPR.

[0068] FIGURE 16 shows a graph reporting exemplary data to demonstrate the ability of an exemplary ASGPR-targeting macromolecule that targets MuSK-specific antibodies to deliver MuSK-specific antibodies to ASGPR-expressing cells.

[0069] FIGURE 17 shows exemplary monovalent, divalent and trival ent targeting components that bind to ASGPR.

[0070] FIGURE 18 shows exemplary targeting components that bind to ASGPR.

[0071] DETAILED DESCRIPTION

[0072] Various publications, articles and patents are cited or described in the background, summary and throughout the specification; each of these references is herein incorporated by reference in its entirety’. Discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is for the purpose of providing context for the disclosure provided herein. Such discussion is not an admission that any of these matters, singularly or in combination, form part of the prior art with respect to any disclosure provided herein.Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary’ skill in the art to which the disclosure provided herein pertains. Otherwise, certain terms used herein have the meanings as set forth in the specification.

[0073] This disclosure relates to engineered proteins or molecules, and more specifically, to macromolecules that target MuSK-specific antibodies, wherein such macromolecules are fusion proteins or molecules that are configured to selectively target MuSK-specific antibodies for depletion from the body. Macromolecules that target MuSK-specific antibodies cause the selective degradation of the targeted MuSK-specific antibodies by binding to the antigenspecific antibodies and directing them to late endosomes or lysosomes, which contain degradative enzymes. Macromolecules that target MuSK-specific antibodies are fusion proteins or molecules that include at least a targeting component and an antigen component. The targeting component includes a protein or protein fragment or other molecule such as a carbohydrate, carbohydrate derivative or small molecule that is configured to bind to a cell surface receptor or other cell surface molecule. The antigen component includes one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics that is / are recognized by the targeted antigen-specific antibody.

[0074] Upon binding of the antigen-specific antibody to the antigen component, a complex is formed comprising the macromolecule that targets MuSK-specific antibodies and the MuSK-specific antibody. The complex is also configured to bind to the cell surface receptor or other cell surface molecule, allowing cellular internalization of a complex that includes the macromolecule that targets MuSK-specific antibodies, the MuSK-specific antibody, and the targeted cell surface receptor or other cell surface molecule (see FIGURE 1). The targeted cell surface receptor or cell surface molecule may dissociate from the complex upon entry into the endosomes, due to acidic pH, low calcium concentrations and / or other conditions that distinguish the endosomal environment from the extracellular environment. Internalization into endosomes and lysosomal entry’ results in the selective degradation of the complex.

[0075] The term “antigen component” as used herein refers to an antigen, antigen fragment or antigen mimetic configured to specifically bind antibodies that recognize MuSK or domains thereof.

[0076] The term “MuSK-specific antibody” as used herein refers to an antibody or antibody fragment that binds to MuSK, MuSK fragment or MuSK mimetic.The term " MuSK fragment'’ as used herein refers to a part of MuSK that can be recognized by MuSK-specific antibodies.

[0077] The term '‘MuSK mimetic” as used herein refers to a protein, protein fragment, peptide or other molecule that has the same overall shape and properties as the part of the MuSK that is recognized by MuSK-specific antibodies.

[0078] The term “cell surface receptor" or “cell surface molecule” as used herein refers to a protein or other biological molecule (e.g., phospholipid, carbohydrate) that is exposed on the plasma membrane of a cell and also internalizes into the cell.

[0079] A macromolecule that targets MuSK-specific antibodies may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics fused to an Fc fragment of an IgG antibody (herein also referred to as “immunoglobulin Fc fragment”), an FcRn-specific nanobody, an FcRn-specific antibody that binds to FcRn through its variable region, an Fc fragment that binds with increased affinity to the inhibitory FcyRIIb. albumin or an albumin fragment, a PS-binding protein, a TfR-specific antibody, an ASGPR-binding protein or ligand, or other protein, protein fragment or other molecule such as a carbohydrate, carbohydrate derivative or small molecule that is configured to bind to a cell surface receptor or other cell surface molecule identifiable by skilled persons upon reading of the present disclosure.

[0080] Examples of macromolecules that target MuSK-specific antibodies described herein include targeting components that are configured to bind to cell surface molecules such as human FcRn, exposed phosphatidylserine (PS), the transferrin receptor (TfR), the asialoglycoprotein receptor (ASGPR) and the inhibitory Fc gamma receptor, FcyRIIb, and the scavenger receptor, CD163, with affinities (dissociation constants) of less than 10 M at near neutral pH.

[0081] FcRn, TfR, ASGPR, FcyRIIb, ASGPR and CD163 are proteins, and PS is a phospholipid that may be found on the surface and within different cell types within the body. This invention is not limited to targeting these receptors or cell surface molecules, and many other targets could be envisaged such as the low density lipoprotein receptor, high density lipoprotein receptor, T cell receptor, B cell receptor, G-protein coupled receptors, insulin receptor, glucagon receptors, galactose receptors, VEGF receptors, mannose receptors, mannose-6-phosphate receptors (e.g., cation-independent mannose 6-phosphate receptor, CI-M6PR), CD38, insulin growth factor receptor among others identifiable by those skilled in the art. Other targets can be identified in, for example, the following publications or databases:Cell surface receptor protein atlas (Bausch-Fluck, D., Hofmann, A., Bock, T., Frei, A. P., Cerciello, F., Jacobs. A., Moest, H., Omasits, U.. Gundry’, R. L., Yoon. C., Schiess, R., Schmidt, A., Mirkowska, P., Hartlova, A., Van Eyk, J. E., Bourquin, J-P., Aebersold, R., Boheler, K. R., Zandstra, P., Wollscheid, B. (2015) A mass spectrometric-derived cell surface protein atlas. PLoS One 10: e0121314), and the Human protein atlas (https: / / www.proteinatlas.org / humanproteome / secretome).

[0082] The targeting component can bind the cell surface receptor or other cell surface molecule with an affinity (dissociation constant) of less than 10 μM at near-neutral pH, which may be greater than 6.8 and less than 7.5.

[0083] Accordingly, the targeting component of a macromolecule that targets MuSK-specific antibodies can include any type of molecule that is configured to specifically bind to a cell surface receptor or other cell surface molecule. Such molecules can include proteins, protein fragments, polynucleotides such as ribonucleic acids or deoxyribonucleic acids, polypeptides, polysaccharides, lipids, amino acids, peptides, carbohydrates, carbohydrate derivatives and / or other small or large molecules and / or polymers identifiable by skilled persons in the art upon reading of the present disclosure. For example, the targeting component of a macromolecule that targets MuSK-specific antibodies can comprise a carbohydrate, carbohydrate derivative or other small molecule that is a ligand for a cellular receptor. Examples of such targeting components for ASGPR are described in the following: International Publication No. WO 2022 / 157626 Al, Degradation of extracellular targets, inventors: Allan, M., Bagdanoff, J., Bames, D. W., Blankenship, J., Bradner, J., Clairmont, K., Granda, B., Junge, G., Smith, T., Traggiai, E., Wamcke, M.; International Publication No. WO 2022 / 192478 Al, Bifunctional degraders of galactose-deficient immunoglobulins, inventors: Dubowchik, G. M., Spiegel, D., Caldwell, R. M.; US Patent No. 12,128,105 B2, Molecular degraders of extracellular proteins, inventors: Caianiello, D, Deramon, E., Spiegel, D.; International Publication No. WO 2025 / 035052 Al, Molecular degraders for the treatment of IgA nephropathy, inventors: Kazmierski, W., Pracitto, R., Dubowchik, G. M., Marcin, L. R., Bunin, A., Rossi, A. M., Iben, L. G.. McGrath, K., Lee. S.. Todd, M.; International Publication No. WO 2025 / 081173 A2, Bispecific molecular degraders of pathogenic proteins, inventors: Bunin, A., Car, B., Dow, M., Gardin, T., Lipson, S., Marcin, L. R., Mellott, D., Murray, S., Pirman, D., Velaparthi, U.; International Publication No. WO 2025 / 035040 Al, Lysosomal targeting bifunctional molecules for degradation of muscle-specific kinase autoantibodies, inventors: Chen. T., Iwig, J., Lewis, J. G., Lieser, R., Staben, S., Totten, S. M., Turtle, E. D.,. Examples of such targetingcomponents for mannose-6-phosphate receptor and insulin-like grow th factor 2 receptor are described in the following: International Publication No. WO 2022 / 157626 Al. Degradation of extracellular targets, inventors: Allan, M., Bagdanoff, J., Bames, D. W., Blankenship, J., Bradner, J., Clairmont, K., Granda, B., Junge, G., Smith, T., Traggiai, E., Wamcke, M.

[0084] The macromolecule that targets MuSK-specific antibodies can comprise at least a first targeting component and a second targeting component, wherein the protein, protein fragment or other molecule of the first targeting component is configured to bind to a different cell surface receptor or a different cell surface molecule than the protein, protein fragment or other molecule of the second targeting component.

[0085] The macromolecule that targets MuSK-specific antibodies can also comprise one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics that are attached at different positions such as the N- and C-termini of the targeting component.

[0086] As show n in FIGURE 1, a macromolecule that targets MuSK-specific antibodies binds selectively to MuSK-specific antibodies, but not antibodies that bind to other antigens, in the extracellular space. The macromolecule: MuSK-specific antibody complex (with one or two macromolecules bound to each antibody) is then internalized into cells due to binding of the macromolecule to an internalizing receptor such as FcRn. These MuSK-specific antibody macromolecule complexes enter lysosomes where the complexes are degraded. Through this mechanism of selective depletion, a macromolecule that targets MuSK-specific antibodies targets and selectively depletes MuSK-specific antibodies from the body without adversely affecting the levels of antibodies of non-targeted specificities.

[0087] In particular, a macromolecule that targets MuSK-specific antibodies as described herein can target and selectively deplete MuSK-specific antibodies from the body without having an adverse clinical effect in the patient due to depleting antibodies of non-targeted specificities. Such adverse clinical effects include, for example, immunosuppression, and symptoms thereof, such as pinkeye, bronchitis, ear infections, sinus infections, cold, diarrhea, pneumonia, yeast infection, meningitis, skin infections, and other opportunistic infections, particularly opportunistic infections normally controlled through antibody mediated immune responses, and blood disorders, such as low platelet counts or anemia, and hypogammaglobulinemia and symptoms thereof, such as abdominal pain, bloating, nausea, vomiting, diarrhea, or weight loss.In general, a macromolecule that targets MuSK-specific antibodies according to this disclosure is configured to specifically bind a cell surface receptor or molecule via a targeting component and also specifically bind to MuSK-specific antibodies at near-neutral pH via one or more antigen components that are fused directly or indirectly to the targeting component. The term “specifically bind” as used herein refers to a detectable selective intermolecular interaction between the targeting component and the cell surface receptor / molecule, or between the antigen component and the MuSK-specific antibody. For example, to specifically bind, the antigen needs to show a detectable interaction with the MuSK-antibodies that are being targeted, whilst not showing a detectable interaction with other antibodies that are specific for different antigens. Techniques for detecting specific binding are known within the art, such as ELISA, surface plasmon resonance and other methods identifiable by skilled persons.

[0088] Accordingly, a macromolecule that targets MuSK-specific antibodies allows at least a portion of the MuSK-specific antibody in the body of a patient to be internalized into cells that express the targeted cell surface receptor or targeted other cell surface molecule and thereafter intracellularly degraded.

[0089] A macromolecule that targets MuSK-specific antibodies according to this disclosure may avoid the elicitation of immune responses by the insertion of mutations to reduce or eliminate (activatory) FcyR binding and / or complement binding, which is expected to decrease the formation of potentially inflammatory immune complexes. A macromolecule that targets MuSK-specific antibodies may contain one molecule of antigen (i.e. one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics), whereas other macromolecules that target MuSK-specific antibodies according to the present disclosure can contain more than one molecule of an antigen, antigen fragment, or antigen mimetic. The bivalent nature of the antibodies that are bound by macromolecules that target MuSK-specific antibodies may result in complexes of two macromolecules that target MuSK-specific antibodies per antibody, which through target receptor dimerization is expected to increase the efficiency of lysosomal delivery of the macromolecule-antibody complexes.

[0090] A macromolecule that targets MuSK-specific antibodies according to the present disclosure can contain more than one molecule of an antigen, antigen fragment, or antigen mimetic. A macromolecule that targets MuSK-specific antibodies can comprise at least a first antigen component and a second antigen component, wherein the first antigen component (one or more extracellular domains of MuSK. one or more fragments of MuSK or one or more MuSK mimetics) are / is different to the second antigen component. Accordingly, amacromolecule that targets MuSK-specific antibodies comprising at least a first antigen component and a second antigen component allows clearance of MuSK-specific antibodies of more than one epitope specificity. Similarly, a macromolecule that targets MuSK-specific antibodies can also comprise more than two antigen components that are either the same or different.

[0091] In addition, a macromolecule that targets MuSK-specific antibodies may contain human or humanized proteins or protein fragments to avoid or decrease the possibility of an immune reaction to the macromolecule that targets MuSK-specific antibodies when administered to a human. The one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics may be a human protein or protein fragment for administration of the macromolecule that targets MuSK-specific antibodies to a human. The targeting component can also be a human protein or protein fragment, such as a human antibody fragment or human albumin or albumin fragment, or a humanized antibody or humanized antibody fragment for administration of the macromolecule that targets MuSK-specific antibodies to a human. If a macromolecule that targets MuSK-specific antibodies is developed for use in a non-human animal, then proteins or protein fragments derived from or engineered to be immunologically compatible with that animal may be used instead.

[0092] FIGURES 2A, 2B, 2C, 2D, 2E, 2F and 2G are schematics of macromolecules that target MuSK-specific antibodies including one or more antigen components fused to a targeting component comprising the Fc fragment of IgG. As understood by persons skilled in the art, the Fc fragment of an IgG is all of the lower base of the antibody’s Y-shape, which is the sulfhydryl-bridged hinge region and the CH2 and CH3 domains. Macromolecules that target MuSK-specific antibodies can comprise an Fc fragment that does not have the hinge region, or the hinge region does not have sulfhydryl bridges. The Fc fragment allows a macromolecule that targets MuSK-specific antibodies to bind an FcRn molecule on an FcRn-expressing cell. In the example shown in FIGURE 2A, 2B, 2D, 2E, 2F or 2G, one or more antigen components may be fused to Fc fragment at the N- or C-terminus of the hinge-CH2-CH3. When one or more antigen components are fused to the Fc fragment and the resulting antigen-Fc fragment dimerizes with another Fc fragment lacking an antigen or attached to different antigen components, using the knobs-into-holes strategy (for example, as described in Atwell, S., Ridgway, J. B. B., Wells, J. A., Carter, P (1997) Stable heterodimers from remodeling the domain interface of a homodimer using a phage display library. J. Mol. Biol., 270, 26-35; Moore. G. L., Bautista, C., Pong, E., Nguyen, D. H.. Jacinto, J.. Eivazi, A., Muchhal, U. S.,Karki, S., Chu, S. Y., Lazar, G. A. (2011). A novel bispecific antibody format enables simultaneous bivalent and monovalent co-engagement of distinct target antigens. MAbs 3, 546-557), a heterodimeric macromolecule that targets MuSK-specific antibodies as shown is produced. A macromolecule that targets MuSK-specific antibodies has an Fc fragment with a monomeric display of the antigen component, or of each antigen component if more than one antigen component is present. In addition to, or instead of, knobs-into-holes mutations, a macromolecule that targets MuSK-specific antibodies can comprise electrostatic steering mutations (for example, as described in Gunasekaran, K., Pentony, M., Shen, M., Garrett, L., Forte, C., Woodward, A., Ng, S. B., Bom, T., Retter, M., Manchulenko, K., Sweet, H., Foltz, I. N., Wittekind, M., Yan, W. (2010) Enhancing antibody Fc heterodimer formation through electrostatic steering effects: applications to bispecific molecules and monovalent IgG. J Biol Chem 285, 19637-19646) to promote heterodimer formation. Other approaches can also be used to generate heterodimers, such as the insertion of a (G4S)12(SEQ ID NO: 79) linker peptide between the C-terminus of the antigen-Fc fusion and N-terminus of a second Fc fragment (for example, as described in Zhou, L., Wang, H-Y., Tong, S., Okamoto, C. T., Shen, W-C., Zaro, J. L. (2016) Single chain Fc-dimer-human growth hormone fusion protein for improved drug delivery. Biomaterials, 117, 24-31). DNA and protein sequences of several examples of macromolecules that target MuSK-specific antibodies comprising knobs-into-holes mutations and mutations that reduce Fc gamma receptor and complement binding are presented in the Sequence Listing.

[0093] Examples of knobs-into-holes mutations include T366W: T366S / L368A / Y407V (for example as described in Atwell, S., Ridgway, J. B. B., Wells, J. A., Carter, P (1997) Stable heterodimers from remodeling the domain interface of a homodimer using a phage display library. J. Mol. Biol., 270, 26-35) or Y349T / T394F: S364H / F405A and Y349T / F405F: S364H / T394F (for example as described in Moore, G. L., Bautista, C., Pong, E., Nguyen, D. H., Jacinto, J.. Eivazi. A., Muchhal, U. S.. Karki, S., Chu, S. Y.. Lazar, G. A. (2011) A novel bispecific antibody format enables simultaneous bivalent and monovalent co-engagement of distinct target antigens. MAbs 3, 546-557) among others identifiable by persons skilled in the art. The residue numbering of these exemplary knobs into holes mutations refers to the EU antibody numbering system, as would be understood by persons skilled in the art.

[0094] Examples of electrostatic steering mutations include E356K / D399K: K392D / K409D and K409D / K370D: D357K / D399K (for example as described in Gunasekaran, K., Pentony,M., Shen, M., Garrett, L., Forte, C., Woodward, A., Ng, S. B., Bom, T., Retter, M., Manchulenko, K., Sweet, H., Foltz, I. N., Wittekind. M., Yan. W. (2010). Enhancing antibody Fc heterodimer formation through electrostatic steering effects: applications to bispecific molecules and monovalent IgG. J Biol Chem 285, 19637-19646) among others identifiable by persons skilled in the art. The residue numbering of these exemplary electrostatic steering mutations refers to the EU antibody numbering system, as would be understood by persons skilled in the art.

[0095] The Fc fragment may be modified to eliminate or substantially reduce the binding affinity for Fc gamma receptors, in particular for activatory FcyRs, and complement (Clq). This modification prevents inflammatory responses caused by the formation of multimeric immune complexes. For example, the following mutations can be inserted in the Fc fragment: L234S / L235T / G236R. L234A / L235A / D265S or G236R / L328R (for example as described in Wilkinson, I., Anderson, S., Fry, J., Julien, L. A., Neville, D., Qureshi, O., Watts, G., Hale, G. (2021) Fc-engineered antibodies with immune effector functions completely abolished. PLoS ONE, 16, e0260954; Kotanides, H., Li, Y., Malabunga, M., Carpenito, C., Eastman, S. W., Shen, Y.. Wang, G., Inigo, I., Surguladze. D.. Pennello, A. L., Persaud. K.. Hindi, S., Topper, M., Chen, X., Zhang, Y., Bulaon, D. K., Bailey, T., Lao, Y., Han, B., Torgerson, S., Chin, D., Sonyi, A., Haider, J. N., Novosaidly, R. D., Moxham, C. M., Plowman, G. D., Ludwig, D. L., Kalos, M. (2020) Bispecific targeting of PD-1 and PD-L1 enhances T-cell activation and antitumor immunity. Cancer Immunol. Res.. 8, 1300-1310; Horton, H. M., Bemett, M. J., Pong, E., Peipp, M., Karki. S., Chu, S. Y.. Richards, J. O.. Vostiar, L, Joyce, P. F.. Repp, R.. Desjarlais, J. R., Zhukosky, E. (2010) Potent in vitro and in vivo activity of an Fc-engineered anti-CD19 monoclonal antibody against lymphoma and leukemia. Cancer Res., 68, 8049-8057; Moore, G. L., Bautista, C., Pong, E., Nguyen, D. H., Jacinto, J., Eivazi, A., Muchhal, U. S., Karki, S., Chu, S. Y.. Lazar, G. A. (2011) A novel bispecific antibody format enables simultaneous bivalent and monovalent co-engagement of distinct target antigens. MAbs, 3, 546-557), N297A or N297Q (for example as described in Tao, M-H., Morrison, S. L. (1989) Studies of aglycosylated chimeric mouse-human IgG: role of carbohydrate in the structure and effector functions mediated by the human IgG constant region. J. Immunol., 143, 2595-2601; Lux, A., Yu. X., Scanlan, C. N., Nimmerjahn, F. (2013) Impact of immune complex size and glycosylation on IgG binding to human FcyRs. J. Immunol., 190, 4315-4323), D265A (for example as described in Lux, A., Yu, X., Scanlan, C. N., Nimmerjahn, F. (2013) Impact of immune complex size and glycosylation on IgG binding to human FcyRs. J. Immunol.. 190,4315-4323; Clynes, R. A., Towers, T. L., Presta, L. G., Ravetch, J. V. (2000) Inhibitory Fc receptors modulate in vivo cytotoxicity against tumor targets. Nat. Med. 6. 443-446), L234A / L235A (for example as described in Wines, B. D., Powell, M. S., Parren, P. W. H. I., Bames, N., Hogarth, P. M. (2000) The IgG Fc contains distinct Fc receptor (FcR) binding sites: the leukocyte receptors FcyRI and Fc / RIIa bind to a region in the Fc distinct from that recognized by neonatal FcR and protein A. J. Immunol., 164, 5313-5318), and L234A / L235A / P329G (for example as described in Schlothauer, T., Herter, S., Koller, C. F., Grau-Richards, S., Steinhart, V., Spick, C., Kubbies, M., Klein, C., Umana, P., Mossner, E. (2016) Novel human IgGl and IgG4 Fc-engineered antibodies with completely abolished effector functions. Prot. Eng. Des. Sei., 29, 457-466), among others identifiable by persons skilled in the art. The residue numbering of these exemplary mutations to reduce binding to Fc gamma receptors and complement (C 1 q) refers to the EU antibody numbering system, as would be understood by persons skilled in the art.

[0096] Other mutations to ablate FcyR and / or complement binding that target residues at, or in proximity to. the location of the FcyR and complement binding sites can be used. These sites on the Fc region of IgG have been localized (for example, as described in Jefferis, R., Lund, J. (2002) Interaction sites on human IgG-Fc for FcyR: current models. Immunol. Letts., 82, 57-65; Duncan, AR., Winter, G. (1988) The binding site for Clq on IgG. Nature, 332, 738-740; Idusogie. E. E.. Presta, L. G., Gazzano-Santoro, H., Totpal, K., Wong. P. Y.. Ultsch. M.. Meng, G., Mulkerrin, M G. (2000) Mapping of the Clq binding site on rituxan, a chimeric human antibody with a human IgGl Fc. J. Immunol., 164, 4178-4184; Hogarth, P. M., Anania, J., Wines, B. D. (2014) The FcyR of humans and non-human primates and their interaction with IgG: implications for induction of inflammation, resistance to infection and the use of therapeutic monoclonal antibodies. Curr. Top. Microbiol. Immunol., 382, 321-352).

[0097] A macromolecule that targets MuSK-specific antibodies may include Fc fragments derived from immunoglobulin classes or isotypes that do not bind, or have very weak binding, to Fc gamma receptors or complement such as human IgG2 or human IgG4.

[0098] The Fc fragment of a macromolecule that targets MuSK-specific antibodies may be modified to substantially increase its binding affinity for FcRn at near-neutral pH as compared to unmodified Fc fragments. For example, the dissociation constant between the Fc fragment and FcRn at a pH greater than 6.8 and less than 7.5 may be less than 10 pM as determined by surface plasmon resonance or other biophysical method. However, the Fc fragment may havea similar or increased affinity for FcRn as compared to an unmodified Fc fragment at acidic endosomal pH (about 6.0), or it may be modified to have a much lower or negligible binding affinity for FcRn at endosomal pH as compared to an unmodified Fc fragment. This increase in binding affinity for FcRn at near neutral pH allows each macromolecule that targets MuSK-specific antibodies to cause its bound target antigen-specific antibody to be efficiently internalized and trafficked into late endosomes or lysosomes in FcRn-expressing cells. Enhanced binding affinity of the Fc fragment for FcRn may be achieved by insertion of mutations. Naturally-occurring IgGs have a substantially higher binding affinity for FcRn at acidic pH levels as opposed to near-neutral pH. This property is essential for the recycling and transport of IgG within FcRn-expressing cells. In contrast, an increase in binding affinity for FcRn at pH 7.4, for example, results in receptor-mediated internalization into cells and lysosomal deliver}’. Further, for FcRn-targeting macromolecules that target MuSK-specific antibodies and comprise Fc fragments, linkage of the antigen component(s) to the C-terminus / termini (CH3 domain) of the Fc fragment, rather than to the N-terminus / termini, are exemplary embodiments.

[0099] In additional embodiments, the Fc fragment of the macromolecule that targets MuSK-specific antibodies can have mutations to enhance binding to the inhibitory Fc receptor, FcyRIIb. Such mutations include P238D, G237D / P271G / A330R, G237D / H268D / P271G / A330R, G236N / H268D / A330K or S267E / L328F (for example, as described in Mimoto, F., Katada, H., Kadono, S., Igawa, T., Kuramochi, T., Muraoka, M., Wada, Y., Haraya, K., Miyazaki, T., Hattori, K. (2013) Engineered antibody Fc variant with selectively enhanced FcyRIIb binding over both FcyRIla131'1and FcyRIIa11131. Prot. Eng. Des. Sei., 26, 589-598; Hori, Y., Ohmine, K, Katada. H., Noguchi, Y., Sato. K.. Nambu, T., Adeline, L. R., Wan, G. S., Haraya, K., Ozeki, K, Nanami, M., Tachibana, T., Sampei, Z., Kuramochi, T., Nezu, J., Hattori, K., Igawa, T. (2022) Elimination of serum soluble antigen in cynomolgus monkeys by combining pH-dependent antigen binding and novel Fc engineering. MAbs, 14:1, 2068213; Chu, S. Y.. Vostiar, I.. Karki, S., Moore, G. L., Lazar, G. A., Pong, E., Joyce, P. F., Szymkowski, D. E., Desjarlais, J. R. (2008) Inhibition of B cell receptor-mediated activation of primary human B cells by coengagement of CD19 and FcyRIIb with Fc-engineered antibodies. Mol. Immunol., 45, 3926-3933). The residue numbering of these exemplary mutations to enhance binding to FcyRIIb refers to the EU numbering system, as would be understood by persons skilled in the art. Additional mutations that enhance binding to FcyRIIb are described in: International Publication No. WO 2025 / 030003 A2, Molecules forcontrolling autoimmune response, inventors: Gutierrez, D. A., Logtenberg, M. E., Capilli, A. D. Further embodiments may comprise Fc fragments with mutations to increase the binding affinity for FcRn to lead to longer in vivo persistence. Such mutations are known to those with skill in the art (e.g., as described in Ramdani, Y., Lamamy, J., Watier, H, Gouilleux-Gruart, V. (2022) Monoclonal antibody engineering and design to modulate FcRn activities: a comprehensive review. Int. J. Mol. Sci., 23, 9604; Manso, T., Sanou, G., Nousias, C., Maalem, I., Boutin, F., Giudicelli, V., Duroux, P., Lefranc, M-P., Kossida, S. (2025) Identification of engineered IMGT Fc variants in IMGT / mAb-DB, a database of therapeutic antibodies and fusion proteins. MAbs, 17, 2594260).

[0100] As shown in FIGURE 2A, 2B and 2C, the antigen component may be attached to the Fc fragment at different terminal or non-terminal locations. Any location that does not prevent specific FcRn binding or binding to other target receptors such as FcyRIIb is suitable. For FcRn targeting, such locations include amino acid residues that are sufficiently distant from the FcRn interaction site (encompassing residues 252-256, 309-311, 433-436 at the CH2-CH3 domain interface). For FcyRIIb targeting, such locations include amino acid residues that are sufficiently distant from the FcyRIIb interaction site so as not to either directly or sterically reduce FcRn or FcyRIIb binding, as would be identifiable by skilled persons.

[0101] The antigen component may be fused to the Fc fragment in any suitable manner, including attachment via a chemical reaction, attachment through a linker, or during formation of a single combined antigen-Fc fragment protein. Examples of chemical coupling that could be used are: amine-to-amine (NHS esters), sulfhydryl-to-sulfhydryl (maleimide), amine-to-sulfhydryl (NHS ester / maleimide), sulfhydryl-to-carbohydrate (maleimide / hydrazide). or attachment via an unnatural amino acid with the desired chemical reactivity. This unnatural amino acid can be inserted during recombinant production of the Fc fragment and / or antigen. Polyethyleneglycol (PEG) spacers can also be inserted between the chemically conjugated proteins, protein fragments or other molecules. Possible linkers include repeats of glycineserine linker peptides, or other more rigid linker peptides, that are encoded in the recombinant expression plasmid for the antigen-Fc fusion. Linkage chemistry, sites of linkage and choice of peptide can be guided by molecular modeling, and can be designed to minimize loss of binding activity of the antigen or the protein / protein fragment targeting the cell surface molecule, as would be understood by skilled persons.

[0102] FIGURES 2D, 2E, 2F and 2G are schematic representations of macromolecules that target MuSK-specific antibodies and include tw o different antigen fusions fused to differentterminal locations in an Fc heterodimer. Macromolecules that target MuSK-specific antibodies could also include 3, 4 or more different antigen components attached to the N- and C-termini or non-terminal location(s) of the Fc fragment. The different antigen components may include one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics and can be linked to the Fc fragments using different linker sequences such as GGGGS (SEQ ID NO: 80), GS, or other linkers known to those with skill in the art.

[0103] FIGURE 2H, I and J are schematic representations of macromolecules that target MuSK-specific antibodies in which one or more antigen components are attached to albumin, an antibody variable region (single domain or nanobody), antibody scFv or Fab fragment. The antibody variable region specifically binds to a cell surface receptor or cell surface molecule such as FcRn, the transferrin receptor (TfR) or asialoglycoprotein receptor (ASGPR). Antibodies or antibody fragments that bind to FcRn and could comprise macromolecules that target MuSK-specific antibodies include SyntOOl (International Publication No. WO 2016 / 183352 Al, Humanized affinity-matured anti-FcRn antibodies, inventors: Blumberg, L. J, Blumberg, R. S., Jones, S. D., Roopenian, D., Holgate, R. G. E., Jones, T. D., Hearn, A. R.) and 1519 (WO 2106 / 180765 Al, Anti-FcRn antibodies, inventors: Bhatta, P., Dave, E., Heywood, S. P., Humphreys, D. P., Smith, B. J.). Antibodies or antibody fragments that bind to ASGPR and could comprise macromolecules that target MuSK-specific antibodies include 51A12 or affinity-matured (mutated) variants such as 51A12_A6 that have been described previously (International Publication No. WO 2014 / 023709 / A1; ASGPR antibodies and uses thereof; inventors: Hofer, T., Ji, C, Moessner, E., Umana, P). The antibody variable region that is used in a macromolecule to target MuSK-specific antibodies may be an entire variable region or a fragment thereof, so long as it can specifically bind to a cell surface receptor or cell surface molecule. The antibody variable region may include portions of a non-variable region of an antibody that is configured to bind to a cell surface receptor or cell surface molecule. For example, the antibody variable region may be a single-domain antibody (sdAb) or camelid-derived VHH domain (also commonly referred to as a nanobody). Such variable regions have the overall fold of an immunoglobulin domain, comprising two anti-parallel p-sheets, and can also include domains from other members of the immunoglobulin superfamily such as T cell receptor variable domains, constant region domains of antibodies or domains of the coreceptor, CD4, among others identifiable by persons skilled in the art. The antibody variable region may be present as a monomer as show n in FIGURE 2H, I or J, or as a multimer. For example, if the antibody variable region is present as a nanobody, it may be engineered with a linker peptidesuch as GSSGGSGGGGS (SEQ ID NO: 81) between the C-terminus of the first nanobody and the N-terminus of the second nanobody to form a dimer, resulting in increased binding avidity for target receptor / molecule. If the antibody variable region is a nanobody or another protein that is engineered to form multimers, variants without the antigen component may be included during generation of a macromolecule that targets MuSK-specific antibodies so that multimers contain only one copy of antigen. Alternatively the antibody variable regions can be attached to two or more different antigen components. Antibody variable regions can also include heterodimers of heavy chain variable (VH) domains linked by peptide linkers to light chain variable (VL) domains to form scFv fragments. The linker sequences that are used to link VH and VL domains are well known to those with skill in the art and include the GGGGSGGGGSGGGGS [(G4S)3] (SEQ ID NO: 82) sequence that connect the C-terminus of the VH domain to the N-terminus of the VL domain. In some embodiments, the C-terminus of the VL domain can be connected to the N-terminus of the VH domain with similar linker sequences. ScFvs that bind to a cell surface receptor or other cell surface molecule can be isolated from libraries of scFvs using phage display, yeast display or other antibody display approaches. The targeting protein component of a macromolecule that targets MuSK-specific antibodies could also include Fab fragments of an antibody that can be isolated from libraries of Fab fragments using phage display, yeast display etc. For nanobodies, scFvs and Fab fragments, affinities for binding to a cell surface receptor or cell surface molecule can be increased by randomly mutating residues in the complementarity determining regions (CDRs), or by using error-prone polymerase chain reaction, to generate libraries of mutated nanobodies or variable domains. Exemplary CDR residues that would be targeted are those in CDR3 of the light chain variable domain (residues 89-97; Kabat numbering) and CDR3 of the heavy chain variable domain (residues 95-102; Kabat numbering). These libraries can be displayed on phage or yeast and higher affinity variants selected using approaches known to those with skill in the art.

[0104] FIGURES 2H and 21 illustrate the antigen component at a terminal location of antibody variable region, scFv or Fab fragment, optionally it may be located at a non-terminal location (FIGURE 2J). The antigen component may be fused to albumin, the antibody variable region, scFv or Fab fragment in any suitable manner, including attachment via a chemical reaction, attachment through a linker, or during formation of a single combined antigen-antibody variable region, scFv or Fab fragment fusion protein.A macromolecule that targets MuSK-specific antibodies may also contain an antigen component fused to a targeting component that includes a protein other than an antibody or antibody fragment such as albumin, providing that this protein is configured to bind to a cell surface receptor or other cell surface molecule. Albumin is known to bind to FcRn (Chaudhury, C., Mehnaz, S., Robinson, J. M., Hayton, W. L., Pearl, D. K., Roopenian, D. C., Anderson, C. L. (2003) The major histocompatibility complex-related Fc receptor for IgG (FcRn) binds albumin and prolongs its lifespan. J. Exp. Med., 197, 315-322; Sand. K. M. K., Bern, M., Nilsen, J., Noordzij, H. T., Sandlie, I., Andersen, J. T. (2015) Front. Immunol., 5, Article 582). For example, a macromolecule that targets MuSK-specific antibodies includes the antigen component fused to albumin or an albumin fragment able to bind FcRn. The albumin or albumin fragment may be mutated or modified so that it binds with increased affinity to FcRn. For example, mutations can be inserted into the FcRn binding domain (Dill) of (human serum) albumin using error prone PCR followed by display of libraries of mutated albumin variants on yeast or phage, and selection of higher affinity variants. Alternatively, higher affinity variants can be generated by mutating residues at or near the albumimFcRn interface and either selecting or screening for albumin variants with increased binding affinity (for example, using approaches described in: US patent 8,748,380 B2, Albumin variants, inventors: Plumridge, A., Sleep, D., Cameron, J., Sandlie, I., Andersen, J. T., Friis., E. P.; Bern, M., Nilsen, J., Ferrarese, M., Sand, K. M. K., Gjolberg, T. T., Lode, H. E., Davidson, R. J., Camire, R. M., Baekkevold, E. S., Foss, S., Grevys, A., Dalhus, B., Wilson, J.. Hoydahl, L. S.. Christianson. G. J., Roopenian, D C., Schlothauer, T., Michaelson, T. E., Moe, M. C., Lombardi, S., Pinotti, M., Sandlie, I., Branchini, A. Andersen, J. T. (2020) An engineered human albumin enhances half-life and transmucosal delivery when fused to protein-based biologies. Sci. Transl. Med., 14, eabb0580). Although the antigen component can be attached at a non-terminal location of albumin or an albumin fragment, it may instead be located at a terminal location. The antigen component may be fused to albumin or the albumin fragment in any suitable manner, including attachment via a chemical reaction, attachment through a linker, or during formation of a single combined antigen-FcRn-binding protein.

[0105] Similarly, the targeting component can be a carbohydrate, a carbohydrate derivative or small molecule that binds to ASGPR or mannose 6-phosphate receptor (e.g. CI-M6PR) that is attached to the antigen component using chemical methods known to those with skill in the art. In further embodiments, the antigen component can be expressed as a fusion protein and chemically conjugated to the carbohydrate, carbohydrate derivative or small molecule.Examples of such targeting components include, but are not limited to, those described previously in: International Publication No. WO 2022 / 157626 Al. Degradation of extracellular targets, inventors: Allan, M., Bagdanoff, J., Barnes, D. W., Blankenship, J., Bradner, J., Clairmont, K., Granda, B., Junge, G., Smith, T., Traggiai, E., Wamcke, M.; International Publication No. WO 2020 / 132100 Al, Bifunctional molecules for lysosomal targeting and related composition and methods, inventors: Bertozzi. C.. Banik, S., Pedram, K., Ahn, G.; International Publication No. WO 2022 / 192478 Al, Bifunctional degraders of galactose-deficient immunoglobulins, inventors: Dubowchik, G. M., Spiegel, D., Caldwell, R. M.; US PatentNo. 12,128,105 B2, Molecular degraders of extracellular proteins, inventors: Caianiello, D., Deramon, E.. Spiegel, D.; International Publication No. WO 2025 / 035052 Al. Molecular degraders for the treatment of IgA nephropathy, inventors: Kazmierski, W., Pracitto, R., Dubowchik, G. M., Marcin, L. R., Bunin, A., Rossi, A. M., Iben, L. G., McGrath, K., Lee, S., Todd, M.; International Publication No. WO 2025 / 081173 A2, Bispecific molecular degraders of pathogenic proteins, inventors: Bunin, A., Car, B., Dow, M., Gardin, T., Lipson, S., Marcin, L. R., Mellott, D., Murray. S., Pirman, D., Velaparthi, U.; International Publication No. WO 2025 / 035040 Al, Lysosomal targeting bifunctional molecules for degradation of musclespecific kinase autoantibodies, inventors: Chen, T., Iwig, J., Lewis, J. G., Lieser, R., Staben, S., Totten, S. M., Turtle, E. D.

[0106] FIGURE 2K, 2L are schematic representations of exemplary macromolecules that target MuSK-specific antibodies including an antigen component attached to the C-terminus of an antibody with one or two Fab fragments that bind to a cell surface protein or cell surface molecule. The Fc fragment (Fc) in the antibody can be engineered to bind to FcRn with increased affinity and may be mutated so that it binds to Fc gamma receptors, particularly to activatory FcyRs, and complement with very low or no detectable binding affinity. In order to avoid antibody homodimers in which both Fc fragments have a fused antigen component, the macromolecules that target MuSK-specific antibodies as shown in FIGURE 2K, 2L are designed with knobs-into-holes mutations and / or electrostatic steering mutations to promote heterodimer formation, so there is only one antibody heavy chain per antibody molecule with the attached antigen component. FIGURES 2M and 2N are schematic representations of exemplary macromolecules that comprise scFv fragments that bind to a cell surface protein or cell surface receptor and are attached to the C- or N-termini of the Fc fragment, and the antigen component is attached to the N- or C-termini, respectively, of the Fc fragment.For the embodiments shown in FIGURES 20, 2P, 2Q and 2R, two different antigen components could be attached to the N- or C-termini of the Fc fragment, or if only one Fab fragment or scFv fragment is present, three different antigen components could be attached. For the embodiments shown in FIGURES 2K, 2M, 2N, 20, 2Q and 2R both Fab fragments or scFv fragments may bind to the same cell surface protein or other cell surface molecule; alternatively, they could bind to two or more different cell surface proteins or molecules.

[0107] FIGURE 2S is a schematic representation of an exemplary macromolecule that targets MuSK-specific antibodies including an antigen component attached to the N-terminus of an Fc fragment. In the example show n in FIGURE 2S, protein or protein fragments that bind to a cell surface receptor or cell surface molecule are attached to the C-terminus of the Fc fragment. For example, the protein or protein fragment may be the C2A domain of synaptotagmin that binds to phosphatidylserine (PS). The Fc fragment can also be engineered to bind to FcRn or inhibitory Fc RIIb with increased affinity and may be mutated so that it binds to activatory Fc gamma receptors and complement with reduced binding affinity. The macromolecule that targets MuSK-specific antibodies as shown in FIGURE 2S is designed with knobs-into-holes mutations and / or electrostatic steering mutations to promote heterodimer formation, so there is only one Fc with one Fc-antigen. In FIGURE 2S, both Fc fragments have proteins or protein fragments that bind to the cell surface protein or other cell surface molecule fused to them; alternatively, only one such protein or protein fragment may be present. In the exemplary macromolecule that targets MuSK-specific antibodies shown in FIGURE 2T, the antigen component and protein or protein fragments that bind to a cell surface receptor or cell surface molecule are fused to the C- and N-termini of the Fc fragments, respectively. The Fc component is similar to that described for the exemplary macromolecule that targets MuSK-specific antibodies shown in FIGURE 2S.

[0108] As shown in FIGURE 2U, in an exemplary7macromolecule that targets MuSK-specific antibodies, two molecules of the same antigen component may be attached to the Fc fragment at N-terminal or other locations. This exemplary macromolecule that targets MuSK-specific antibodies is a homodimer that contains mutations to enhance binding to FcRn or FcyRIIb, and does not contain knobs-into-holes and / or electrostatic steering mutations.

[0109] FIGURE 2V is a schematic representation of an exemplary macromolecule that targets MuSK-specific antibodies comprising two molecules of the same antigen component attached to the N-termini of an Fc fragment. In the exemplary embodiment shown in FIGURE 2V,protein or protein fragments that bind to a cell surface receptor or cell surface molecule are attached to the C-terminus of the Fc fragment. This exemplary macromolecule that targets MuSK-specific antibodies is a homodimer and does not contain knobs-into-holes and / or electrostatic steering mutations. In FIGURE 2V, the homodimeric Fc fragment has proteins or protein fragments that bind to the cell surface protein or other cell surface molecule fused to both polypeptide chains, but in other embodiments, only one such protein or protein fragment may be present.

[0110] For macromolecules that target MuSK-specific antibodies, similar principles to those used in the examples shown in FIGURES 2A, 2B, 2C, 2D, 2E, 2F, 2G, 2H, 2I, 2J, 2K, 2Q, 2R, 2S, 2T, 2U and 2V may be applied to other macromolecules. In the examples shown in FIGURES 2A. 2B, 2C, 2K, 2L. 2M, 2N, 2S and 2T the macromolecule that targets MuSK-specific antibodies has two antibody Fc fragments that are engineered with knobs-into-holes mutations and / or electrostatic steering mutations to drive the formation of heterodimers comprising one antigen linked to one Fc fragment and one Fc fragment with no antigen attached. Other embodiments shown in FIGURES 2D, 2E, 2F, 2G, 21, 20, 2P, 2Q, 2R, 2U and 2V can include two or more antigen components that may be different or the same. The Fc fragment can be further engineered to bind to FcRn with increased affinity at near neutral pH (FIGURES 2 A, 2B, 2C, 2E, 2F, 2G, 2U and 2V) or connected to one or more proteins, scFv fragments, Fab fragments or other molecules, including a small molecule or carbohydrate, that target one or more cell surface receptors or molecules (FIGURES 2H. 21 and 2J). The Fc fragments in the examples shown in FIGURES 2K, 2L, 2M, 2N, 20, 2P, 2Q, 2R, 2S and 2T can also be engineered to bind with higher affinity to FcRn so that they target both FcRn and one or more cell surface receptors or molecules.

[0111] Albumin binds more strongly to FcRn at acidic pH than at neutral pH. However, albumin molecules may also be modified to alter their binding affinities at near-neutral or endosomal pH to encourage degradation of the target antigen-specific antibody. Similarly, antibody variable region FcRn-binding proteins may be affected by pH in a manner specific to that protein, but they may still be modified to alter their binding affinities at near-neutral or endosomal pH to encourage degradation of the target antigen-specific antibody. These FcRn-binding proteins can be isolated from libraries of immunoglobulin variable domains, scFv (VH: VL heterodimers in which VH and VL domains are connected to each other by linker peptides such as GGGGSGGGGSGGGGGS; SEQ ID NO: 82) or Fab fragments using phage display, yeast display or other technologies known to those with skill-in-the-art. These librariescan either be derived from naturally occurring antibody variable genes, or can be generated using approaches that result in ‘semi-synthetic' libraries wherein complementarity’ determining regions (CDRs) are produced using randomized oligonucleotide sequences. Further increases to their affinities can be achieved by, for example, inserting random mutations in the CDRs using error-prone PCR followed by selection using phage display or yeast display. Exemplary CDR residues that would be targeted are those in CDR3 of the light chain variable domain (residues 89-97; Kabat numbering) and CDR3 of the heavy chain variable domain (residues 95-102; Kabat numbering). Similar methods can be used to isolate antibody-based proteins or scaffold-based proteins that bind to other cell surface receptors / molecules.

[0112] A macromolecule that targets MuSK-specific antibodies may include any targeting component that is configured to specifically bind to a receptor or other molecule on the cell surface. The targeting component is fused directly or indirectly (e.g., via a linker) to an antigen component (i.e. one or more extracellular domains of MuSK, one or more fragments of MuSK or one or more MuSK mimetics), where the antigen component binds to a MuSK-specific antibody. Accordingly, a macromolecule that targets MuSK-specific antibodies can include more than one antigen component. If the targeting protein contains an immunoglobulin-derived Fc fragment, the Fc region can be mutated so that it does not bind, or binds at substantially reduced levels, to Fc gamma receptors (particularly activatory FcyRs) and complement, or binds with increased affinity to the inhibitory receptor, FcyRIIb. Several different possible configurations of a macromolecule that targets MuSK-specific antibodies are shown in FIGURE 2A-V; these are shown as examples and are not limiting, since multiple other configurations can also be envisaged by those with skill-in-the-art.

[0113] For example, a macromolecule that targets MuSK-specific antibodies can have variations in the number of targeting domains or antibody fragments (e.g.. Fab fragments or scFv fragments) (FIGURE 2). These targeting domains or antibody fragments can be linked to immunoglobulin Fc fragments, whereas in others, the targeting domains or antibody fragments may be linked to each other; the antigen and antibody fragments can be fused to Fc fragments or each other in different onentations (FIGURE 2); a macromolecule that targets MuSK-specific antibodies can include linker sequences that vary in length and composition between the fusion proteins, domains or fragments e.g., IEGRMD (SEQ ID NO: 83), GS, or GGGGS (SEQ ID NO: 80) or 2-3 repeats of this linker; antigen mimetics such as small molecules or peptides can be used; the Fc fragment in a macromolecule that targets MuSK-specific antibodies may be mutated so that it has substantially reduced binding affinity for (activatory)Fc gamma receptors, complement, and increased affinity for binding to FcRn; the Fc may be mutated so that it has increased affinity for the inhibitory Fc receptor, FcyRIIb. The Fc fragments of a macromolecule that targets MuSK-specific antibodies may have mutations such as knobs-into-holes and / or electrostatic steering mutations so that heterodimers of Fc fragments are formed.

[0114] Additional embodiments can comprise targeting components that are polynucleotides such as ribonucleic acids or deoxyribonucleic acids, polypeptides, polysaccharides, lipids, amino acids, peptides, carbohydrates, carbohydrate derivatives and / or other small or large molecules and / or polymers identifiable by skilled persons in the art upon reading of the present disclosure. Such targeting components can be connected to the antigen component of the macromolecule that targets MuSK-specific antibodies using methods known to those with skill in that art that are, for example, described in the following: International Publication No. WO 2022 / 157626 Al, Degradation of extracellular targets, inventors: Allan, M., Bagdanoff, J., Barnes, D. W., Blankenship, J., Bradner, J., Clairmont, K., Granda, B., Junge. G.. Smith, T., Traggiai. E., Wamcke, M.; International Publication No. WO 2022 / 192478 Al. Bifunctional degraders of galactose-deficient immunoglobulins, inventors: Dubowchik, G. M., Spiegel, D., Caldwell, R. M.; US Patent No. 12,128,105 B2, Molecular degraders of extracellular proteins, inventors: Caianiello, D., Deramon, E., Spiegel, D.; International Publication No. WO 2025 / 035052 Al, Molecular degraders for the treatment of IgA nephropathy, inventors: Kazmierski, W., Pracitto, R., Dubowchik, G. M., Marcin, L. R., Bunin, A., Rossi, A. M., Iben, L. G., McGrath, K., Lee, S., Todd, M.; International Publication No. WO 2025 / 081173 A2, Bispecific molecular degraders of pathogenic proteins, inventors: Bunin, A., Car, B., Dow, M., Gardin, T.. Lipson, S., Marcin. L. R., Mellott, D.. Murray, S., Pirman, D., Velaparthi, U.; International Publication No. WO 2025 / 035040 Al, Lysosomal targeting bifunctional molecules for degradation of muscle-specific kinase autoantibodies, inventors: Chen, T., Iwig, J., Lewis, J. G., Lieser, R., Staben, S., Totten, S. M., Turtle, E. D.

[0115] In several examples described herein, the macromolecule that targets MuSK-specific antibodies can be a heterodimer of proteins comprising the amino acid sequences SEQ ID NO: 2 plus SEQ ID NO: 4, SEQ ID NO: 1 plus SEQ ID NO: 5, SEQ ID NO: 2 plus SEQ ID NO: 6, SEQ ID NO: 2 plus SEQ ID NO: 7, SEQ ID NO: 2 plus SEQ ID NO: 8, SEQ ID NO: 9 plus SEQ ID NO: 10, SEQ ID NO: 11 plus SEQ ID NO: 12, SEQ ID NO: 13 plus SEQ ID NO: 14, SEQ ID NO: 15 plus SEQ ID NO: 17 plus SEQ ID NO: 19, SEQ ID NO: 15 plus SEQ ID NO: 18 plus SEQ ID NO: 19, SEQ ID NO: 16 plus SEQ ID NO: 17 plus SEQ ID NO: 19, SEQ IDNO: 16 plus SEQ ID NO: 18 plus SEQ ID NO: 19, SEQ ID NO: 3 plus SEQ ID NO: 20, SEQ ID NO: 2 plus SEQ ID NO: 21, SEQ ID NO: 2 plus SEQ ID NO: 22, SEQ ID NO: 2 plus SEQ ID NO: 23, SEQ ID NO: 2 plus SEQ ID NO: 24, SEQ ID NO: 2 plus SEQ ID NO: 25, SEQ ID NO: 26 plus SEQ ID NO: 27, SEQ ID NO: 1 plus SEQ ID NO: 28, SEQ ID NO: 1 plus SEQ ID NO: 29, SEQ ID NO: 1 plus SEQ ID NO: 30, SEQ ID NO: 16 plus SEQ ID NO: 39, SEQ ID NO: 16 plus SEQ ID NO: 40, SEQ ID NO: 16 plus SEQ ID NO: 41, SEQ ID NO: 16 plus SEQ ID NO: 42. SEQ ID NO: 16 plus SEQ ID NO: 43. SEQ ID NO: 16 plus SEQ ID NO: 44. SEQ ID NO: 16 plus SEQ ID NO: 45, SEQ ID NO: 16 plus SEQ ID NO: 46, any of the heterodimers described in Table 1, or homologs thereof.

[0116] The macromolecule that targets MuSK-specific antibodies can be a fusion protein comprising an amino acid sequence having at least 50% identity with SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 8, SEQ ID NO: 9, SEQ ID NO: 10, SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22. SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 26, SEQ ID NO: 27, SEQ ID NO: 28, SEQ ID NO: 29, SEQ ID NO: 30, SEQ ID NO: 31, SEQ ID NO: 32, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, SEQ ID NO: 36, SEQ ID NO: 37, SEQ ID NO: 38, SEQ ID NO: 39, SEQ ID NO: 40, SEQ ID NO: 41, SEQ ID NO: 42, SEQ ID NO: 43, SEQ ID NO: 44. SEQ ID NO: 45, SEQ ID NO: 46, SEQ ID NO: 47, SEQ ID NO: 48, SEQ ID NO: 49, SEQ ID NO: 50, SEQ ID NO: 51, SEQ ID NO: 52, SEQ ID NO: 53, SEQ ID NO: 54, SEQ ID NO: 55, SEQ ID NO: 56, SEQ ID NO: 57, SEQ ID NO: 58, SEQ ID NO: 59, SEQ ID NO: 60, SEQ ID NO: 61, SEQ ID NO: 62, SEQ ID NO: 63, SEQ ID NO: 64, SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 67, SEQ ID NO: 68, SEQ ID NO: 69, SEQ ID NO: 70, SEQ ID NO: 71, SEQ ID NO: 72, SEQ ID NO: 73, SEQ ID NO: 74, SEQ ID NO: 75, SEQ ID NO: 76, SEQ ID NO: 77 or SEQ ID NO: 78.

[0117] As used herein, "sequence identity" or "identity" in the context of two nucleic acid or polypeptide sequences makes reference to the nucleotide bases or residues in the two sequences that are the same when aligned for maximum correspondence over a specified comparison window. When percentage of sequence identity or similarity is used in reference to proteins, it is recognized that residue positions which are not identical often differ by conservative amino acid substitutions, where amino acid residues are substituted with a functionally equivalent residue of the amino acid residues with similar physiochemical properties and therefore do not change the functional properties of the molecule.A functionally equivalent residue of an amino acid used herein typically refers to other amino acid residues having physiochemical and stereochemical characteristics substantially similar to the original amino acid. The physiochemical properties include water solubility (hydrophobicity or hydrophilicity), dielectric and electrochemical properties, physiological pH, partial charge of side chains (positive, negative or neutral) and other properties identifiable to a person skilled in the art. The stereochemical characteristics include spatial and conformational arrangement of the amino acids and their chirality. For example, glutamic acid is considered to be a functionally equivalent residue to aspartic acid in the sense of the current disclosure. Tyrosine and tryptophan are considered as functionally equivalent residues to phenylalanine. Arginine and lysine are considered as functionally equivalent residues.

[0118] A person skilled in the art would understand that similarity between sequences is ty pically measured by a process that includes the steps of aligning the two polypeptide or polynucleotide sequences to form aligned sequences, then detecting the number of matched characters, i.e. characters similar or identical between the two aligned sequences, and calculating the total number of matched characters divided by the total number of aligned characters in each polypeptide or polynucleotide sequence, including gaps. The similarity result is expressed as a percentage of identity.

[0119] As used herein, "percentage of sequence identity" means the value determined by comparing two optimally aligned sequences over a comparison window, wherein the portion of the polynucleotide sequence in the comparison window may include additions or deletions (gaps) as compared to the reference sequence (which does not include additions or deletions) for optimal alignment of the two sequences. The percentage is calculated by determining the number of positions at which the identical nucleic acid base or amino acid residue occurs in both sequences to yield the number of matched positions, dividing the number of matched positions by the total number of positions in the window of comparison, and multiplying the result by 100 to yield the percentage of sequence identity.

[0120] As used herein, "reference sequence" is a defined sequence used as a basis for sequence comparison. A reference sequence may be a subset or the entirety of a specified sequence; for example, as a segment of a full-length protein or protein fragment. A reference sequence can be, for example, a sequence identifiable in a database such as GenBank and UniProt and others identifiable to those skilled in the art.

[0121] As understood by those skilled in the art, determination of percent identity between any two sequences can be accomplished using a mathematical algorithm. Computerimplementations of suitable mathematical algorithms can be utilized for comparison of sequences to determine sequence identity. Such implementations include, but are not limited to: CLUSTAL, ALIGN, GAP, BESTFIT, BLAST, FASTA, among others identifiable by skilled persons.

[0122] For example, a macromolecule that targets MuSK-specific antibodies according to the present disclosure can have an amino acid sequence having at least 50% sequence identity, at least 80%, at least 90%, at least 95% sequence identity compared to SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 8, SEQ ID NO: 9, SEQ ID NO: 10, SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22. SEQ ID NO: 23. SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 26, SEQ ID NO: 27, SEQ ID NO: 28, SEQ ID NO: 29, SEQ ID NO: 30, SEQ ID NO: 31, SEQ ID NO: 32, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, SEQ ID NO: 36, SEQ ID NO: 37, SEQ ID NO: 38, SEQ ID NO: 39, SEQ ID NO: 40, SEQ ID NO: 41, SEQ ID NO: 42, SEQ ID NO: 43, SEQ ID NO: 44. SEQ ID NO: 45, SEQ ID NO: 46, SEQ ID NO: 47, SEQ ID NO: 48, SEQ ID NO: 49, SEQ ID NO: 50, SEQ ID NO: 51, SEQ ID NO: 52, SEQ ID NO: 53, SEQ ID NO: 54, SEQ ID NO: 55, SEQ ID NO: 56, SEQ ID NO: 57, SEQ ID NO: 58, SEQ ID NO: 59, SEQ ID NO: 60, SEQ ID NO: 61, SEQ ID NO: 62, SEQ ID NO: 63, SEQ ID NO: 64, SEQ ID NO: 65, SEQ ID NO: 66. SEQ ID NO: 67, SEQ ID NO: 68, SEQ ID NO: 69, SEQ ID NO: 70, SEQ ID NO: 71, SEQ ID NO: 72, SEQ ID NO: 73, SEQ ID NO: 74, SEQ ID NO: 75, SEQ ID NO: 76, SEQ ID NO: 77 or SEQ ID NO: 78.

[0123] As shown in the examples below, a macromolecule that targets MuSK-specific antibodies is able to selectively deplete MuSK-specific antibodies with specificity for their fused antigen. As shown in the examples below, a macromolecule that targets MuSK-specific antibodies is able to selectively deplete the target MuSK-specific antibodies without adversely affecting the levels of antibodies of other specificities or eliciting an adverse immune reaction. These findings stand in contrast to other approaches, in which treatment results in depletion of total IgGs, through the use of FcRn inhibitors or antibodies that destroy B cells. Such approaches adversely affect antibodies of non-targeted specificities or B cell function because they lack the selectivity provided by the macromolecule that targets MuSK-specific antibodies.

[0124] A macromolecule that targets MuSK-specific antibodies may be administered in any way able to deliver them to cells expressing the receptor or other molecule on the cell surface that is being targeted, such as via injection, particularly intravenous, subcutaneous orintramuscular injection, or injection into a tissue targeted by the antigen-specific antibody that is to be depleted. A macromolecule that targets MuSK-specific antibodies can also be expressed in cells that have been genetically engineered to contain expression constructs encoding the macromolecule. In particular, cells can be genetically engineered by introducing expression constructs that encode the macromolecule that targets MuSK-specific antibodies that include proteins or peptides that allow secretion of the macromolecule from the engineered cells in situ.

[0125] A macromolecule that targets MuSK-specific antibodies may be administered in an amount that does not block every targeted receptor / cell surface molecule, and therefore does not adversely affect the function of the cell surface receptor / molecule. The dose of the macromolecule that targets MuSK-specific antibodies used may be similar to the amount of MuSK-specific antibody being targeted for clearance. In addition, macromolecules that target MuSK-specific antibodies can be designed so that they do not compete with the natural ligand of the cell surface receptor or cell surface molecule for binding, for example, by using nanobodies (VHH) that bind to FcRn at a site that does not overlap with the IgG binding site (for example as described in Andersen, J. T., Gonzalez-Pajuelo, M., Foss, S., Landsverk, O. J. B., Pinto, D., Szyroki, A., de Haard. H. J.. Saunders, M.. Vanlandshoot. P., Sandlie, I. (2012) Selection of nanobodies that target human neonatal receptor. Sci. Rep., 3, 1118). In addition, the macromolecule that targets MuSK-specific antibodies may remove less than 10%, less than 5%, less than 1%, or less than 0.1% of non-targeted antibodies in the circulation or in a tissue targeted by the antigen-specific antibody that is to be depleted. Retention of non-targeted antibodies during and after treatment with the macromolecule may be important in normal immune function and the avoidance of infections, among other effects as described herein.

[0126] A macromolecule that targets MuSK-specific antibodies may be repeatedly dosed at, for example, daily, twice weekly, or weekly intervals to achieve the desired lowering of MuSK-specific antibody levels. The levels of MuSK-specific antibody in the circulation of a patient can be determined by using enzyme-linked immunosorbent assays (ELISAs) or cell binding assays to analyze serum (or plasma) samples. Alternatively, other methods that are well known to those with skill in the art for determining antigen-specific antibodies can be used.

[0127] A macromolecule that targets MuSK-specific antibodies may be administered in an amount sufficient to deplete at least 50%, at least 80% or at least 90% of the concentration of the MuSK-specific antibody in the circulation or in a tissue recognized by the MuSK-specificantibody within one hour, two hours, five hours, 24 hours or 48 hours or longer of administration. The persistence of the macromolecule that targets MuSK-specific antibodies in the body will be a determinant of how long it has activity in depleting MuSK-specific antibody. A macromolecule that targets MuSK-specific antibodies can be designed to have different in vivo half-lives by the behavior of the cell surface receptor or cell surface molecule that they target. The affinity of the macromolecule that targets MuSK-specific antibodies for this cell surface receptor or cell surface molecule can also be modified using mutagenesis and approaches known to those with skill in the art, to result in a macromolecule that targets MuSK-specific antibodies that have different persistence in the circulation and / or tissues. In particular, the macromolecule that targets MuSK-specific antibodies may be administered in an amount roughly equimolar with the amount of MuSK-specific antibody to be depleted.

[0128] A macromolecule that targets MuSK-specific antibodies may also be administered in combination with other treatments used to treat MuSK-MG. These include plasmapheresis, the delivery of intravenous immunoglobulin (IVIG), or B-cell depletion using approaches such as B-cell specific antibodies or chimeric antigen receptor (CAR) T cells.

[0129] EMBODIMENTS

[0130] The following clauses describe particular Embodiments of the invention.

[0131] 1. A macromolecule that depletes muscle-specific kinase specific (MuSK-specific) antibodies from the serum or tissue of a subject, said macromolecule comprising a targeting component that is configured to specifically bind to a cell surface receptor or other cell surface molecule, and a first antigen component that is configured to specifically bind to a MuSK-specific antibody or a variant thereof, wherein the first antigen component comprises at least part of the Ig1 domain of MuSK.

[0132] 2. The macromolecule according to embodiment 1, wherein the macromolecule comprises substantially the entire Igl domain of MuSK.

[0133] 3. The macromolecule according to embodiment 1, wherein the first antigen component of the macromolecule comprises at least part of the Ig1 and Ig2 domains of MuSK.4. The macromolecule according to embodiment 1, wherein the first antigen component of the macromolecule comprises at least part of the Ig1, Ig2 and Ig3 domains of MuSK.

[0134] 5. The macromolecule according to embodiment 1, wherein the first antigen component of the macromolecule comprises at least part of the Igl, Ig2. Ig3 and Fz domains of MuSK.

[0135] 6. The macromolecule according to any preceding embodiment, wherein the first antigen component of the macromolecule comprises substantially the entirety of said domains.

[0136] 7. The macromolecule according to any preceding embodiment, wherein the first antigen component comprises a single polypeptide component including said domains.

[0137] 8. The macromolecule according to any one of embodiments 1 to 6, wherein the first antigen component comprises two or more separate polypeptides, each of which comprises the same or different domains of MuSK.

[0138] 9. The macromolecule according to embodiment 8, wherein the domains are comprised in three or more separate polypeptides of the antigen component.

[0139] 10. The macromolecule of any preceding embodiment, wherein the targeting component comprises an immunoglobulin Fc fragment.

[0140] 11. The macromolecule of embodiment 10, wherein the immunoglobulin Fc fragment is modified to have substantially reduced binding affinity for Fc gamma receptors compared to an unmodified immunoglobulin Fc fragment.

[0141] 12. The macromolecule of embodiment 11, wherein the immunoglobulin Fc fragment comprises L234S / L235T / G236R mutations according to EU numbering.

[0142] 13. The macromolecule of embodiment 10. wherein the immunoglobulin Fc fragment is modified to have substantially reduced binding affinity' for complement Clq compared to an unmodified immunoglobulin Fc fragment.14. The macromolecule of embodiment 10, wherein the immunoglobulin Fc fragment is modified to have a higher binding affinity for FcRn at near-neutral pH than an unmodified immunoglobulin Fc fragment.

[0143] 15. The macromolecule of embodiment 14, wherein the immunoglobulin Fc fragment comprises M252Y / S254T / T256E / H433K / N434F mutations according to EU numbering.

[0144] 16. The macromolecule of embodiment 10, wherein the immunoglobulin Fc fragment is modified to have increased binding affinity for FcyRIIb compared to an unmodified immunoglobulin Fc fragment.

[0145] 17. The macromolecule of embodiment 16, wherein the immunoglobulin Fc fragment comprises mutations selected from the group consisting of P238D, G237D / P271G / A330R, G237D / H268D / P271G / A330R, G236N / H268D / A330K, and S267E / L328F according to EU numbering.

[0146] 18. The macromolecule of any one of embodiments 10-17, wherein the targeting component comprises a heterodimer of two immunoglobulin Fc fragments.

[0147] 19. The macromolecule of embodiment 18, wherein one immunoglobulin Fc fragment of the heterodimer is fused to the antigen component and the other immunoglobulin Fc fragment is not fused to the antigen component.

[0148] 20. The macromolecule of embodiment 18 or 19, wherein the heterodimer comprises knobs-into-holes mutations.

[0149] 21. The macromolecule of embodiment 20, wherein the knobs-into-holes mutations comprise T366W in one Fc fragment and T366S / L368A / Y407V in the other Fc fragment according to EU numbering.22. The macromolecule of any one of embodiments 10-21. wherein the first antigen component is fused to an N-terminus of the immunoglobulin Fc fragment.

[0150] 23. The macromolecule of any one of embodiments 10-21, wherein the first antigen component is fused to a C-terminus of the immunoglobulin Fc fragment.

[0151] 24. The macromolecule of any preceding embodiment, wherein the targeting component comprises albumin or an albumin fragment.

[0152] 25. The macromolecule of embodiment 24, wherein the albumin or albumin fragment is configured to specifically bind to FcRn.

[0153] 26. The macromolecule of any one of embodiments 1-23, wherein the targeting component comprises one or more antibody variable regions configured to specifically bind to the cell surface receptor or cell surface molecule.

[0154] 27. The macromolecule of embodiment 26, wherein the one or more antibody variable regions comprise at least one nanobody.

[0155] 28. The macromolecule of any preceding embodiment, wherein the cell surface receptor or cell surface molecule is FcRn.

[0156] 29. The macromolecule of embodiment 28, wherein the targeting component can bind to FcRn with a dissociation constant of less than 10 μM at near-neutral pH.

[0157] 30. The macromolecule of any one of embodiments 1-27. wherein the cell surface receptor or cell surface molecule is a transferrin receptor.

[0158] 31. The macromolecule of any one of embodiments 1-27, wherein the cell surface receptor or cell surface molecule is an asialoglycoprotein receptor (ASGPR).32. The macromolecule of embodiment 31, wherein the targeting component comprises an antibody or antibody fragment that specifically binds to ASGPR.

[0159] 33. The macromolecule of any one of embodiments 1-27, wherein the cell surface receptor or cell surface molecule is FcyRIIb.

[0160] 34. The macromolecule of any one of embodiments 1-27, wherein the cell surface receptor or cell surface molecule is CD 163.

[0161] 35. The macromolecule of any one of embodiments 1-27. wherein the cell surface receptor or cell surface molecule is a mannose 6-phosphate receptor.

[0162] 36. The macromolecule of any one of embodiments 1-27, wherein the cell surface receptor or cell surface molecule is phosphatidylserine.

[0163] 37. The macromolecule of embodiment 36, wherein the targeting component comprises a C2A domain of synaptotagmin 1.

[0164] 38. The macromolecule of any preceding embodiment, wherein the targeting component comprises a carbohydrate or carbohydrate derivative configured to specifically bind to the cell surface receptor or cell surface molecule.

[0165] 39. The macromolecule of any preceding embodiment wherein the targeting component comprises a small molecule configured to specifically bind to the cell surface receptor or cell surface molecule.

[0166] 40. The macromolecule of any preceding embodiment, w herein the first antigen component is fused to the targeting component via a linker.

[0167] 41. The macromolecule of embodiment 40, wherein the linker comprises a glycine-serine linker, optionally a glycine-glycine-glycine-glycine-serine (GGGGS; SEQ ID NO: 80) linker peptide.42. The macromolecule of any preceding embodiment, further comprising a second antigen component that is different from the first antigen component.

[0168] 43. The macromolecule of embodiment 42, wherein the second antigen component comprises one or more domains of MuSK different from those in the first antigen component.

[0169] 44. The macromolecule of embodiment 43, wherein the first antigen component is linked to the N- or C-terminus of an Fc polypeptide and the second antigen component is linked to the C- or N-terminus, respectively, of the same Fc polypeptide.

[0170] 45. The macromolecule of embodiment 43, wherein the second antigen component is linked to the N- or C-terminus of a different Fc polypeptide in an Fc heterodimer compared with the first antigen component.

[0171] 46. The macromolecule according to any preceding embodiment, wherein the first or second antigen component comprises an Igl domain polypeptide comprising the sequence of SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 8. SEQ ID NO: 10. SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 28. SEQ ID NO: 29, SEQ ID NO: 30, SEQ ID NO: 31, SEQ ID NO: 32, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, SEQ ID NO: 36, SEQ ID NO: 37, SEQ ID NO: 38, SEQ ID NO: 39, SEQ ID NO: 40, SEQ ID NO: 41, SEQ ID NO: 42, SEQ ID NO: 43, SEQ ID NO: 44, SEQ ID NO: 45, SEQ ID NO: 46, SEQ ID NO: 47, SEQ ID NO: 51, SEQ ID NO: 52 or SEQ ID NO: 53.

[0172] 47. The macromolecule according to any preceding embodiment, wherein the first or second antigen component comprises an Ig2 domain polypeptide comprising the sequence of SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 28, SEQ ID NO: 29, SEQ ID NO: 30, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, SEQ ID NO: 36, SEQ ID NO: 37, SEQ IDNO: 38, SEQ ID NO: 41, SEQ ID NO: 42, SEQ ID NO: 43, SEQ ID NO: 44, SEQ ID NO: 45, SEQ ID NO: 46, SEQ ID NO: 48, SEQ ID NO: 51, SEQ ID NO: 52 or SEQ ID NO: 53.

[0173] 48. The macromolecule according to any preceding embodiment, wherein the first or second antigen binding component comprises an Ig3 domain polypeptide comprising the sequence of SEQ ID NO: 7, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 28, SEQ ID NO: 30, SEQ ID NO: 35, SEQ ID NO: 36, SEQ ID NO: 37, SEQ ID NO: 38, SEQ ID NO: 43, SEQ ID NO: 44, SEQ ID NO: 45, SEQ ID NO: 46, SEQ ID NO:49, SEQ ID NO: 52 or SEQ ID NO: 53.

[0174] 49. The macromolecule according to any preceding embodiment, wherein the first or second antigen component comprises an Fz domain polypeptide comprising the sequence of SEQ ID NO: 7, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 28, SEQ ID NO: 37, SEQ ID NO: 38, SEQ ID NO: 45, SEQ ID NO: 46, SEQ ID NO: 50 or SEQ ID NO: 53.

[0175] 50. The macromolecule of any preceding embodiment, wherein the macromolecule comprises an amino acid sequence having at least 90% sequence identity to a sequence selected from the group consisting of SEQ ID NO: 1 through SEQ ID NO: 78.

[0176] 51. A method of treating MuSK-associated myasthenia gravis in a subject, comprising:

[0177] (a) administering to the subject an effective amount of the macromolecule of any preceding embodiment; and

[0178] (b) monitoring the subject for a reduction in MuSK-specific antibodies,

[0179] wherein the macromolecule removes at least 50% of circulating MuSK-specific antibodies within 24 hours of administration.52. The method of embodiment 51, wherein the macromolecule is administered in an amount sufficient to remove at least 80% of the MuSK-specific antibodies from the circulation in the subject.

[0180] 53. The method of embodiment 51 or 52. wherein the MuSK-specific antibodies are specific for the Igl, Ig2, Ig3 or Fz domain of MuSK.

[0181] 54. A method of treating MuSK-associated myasthenia gravis in a subject, comprising administering to the subject an effective amount of the macromolecule of any one of embodiments 1-50 in combination with a therapy selected from the group consisting of plasmapheresis, intravenous immunoglobulin, a B-cell depleting antibody or aB-cell depleting CAR T cell.

[0182] EXAMPLES

[0183] The following examples are provided to further illustrate specific embodiments of the disclosure. They are not intended to disclose or describe each and every aspect of the disclosure in complete detail and should be not be so interpreted. Unless otherwise specified, designations of compositions are used consistently throughout these examples.

[0184] A summary' of exemplary' macromolecules that target MuSK-specific antibodies, including their SEQ ID NOs, is presented in Tables 2 and 3.

[0185] Example 1; Expression, purification and characterization of exemplary macromolecules that bind to FcRn with increased affinity and target MuSK-specific antibodies Embodiments of exemplary macromolecules that bind to FcRn with increased affinity and target MuSK-specific antibodies comprising one or more antigen components are shown in FIGURE 2A, 2B, 2C, 2D, 2E, 2F and 2G. These macromolecules comprise heterodimeric Fc fragments with mutations to eliminate interactions with human FcyRs and to enhance the binding affinity' to FcRn at near-neutral pH. Heterodimer formation of the two Fc fragments is achieved by inserting ’knobs-mto-holes’ mutations in the CH3 domains.

[0186] FIGURE 3 shows a schematic representation of the domains of MuSK, with the extracellular domains (Igl, Ig2, Ig3 and Fz) and transmembrane region.Expression constructs to generate exemplary macromolecules that target MuSK-specific antibodies (SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 8, SEQ ID NO: 9, SEQ ID NO: 10, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 28, SEQ ID NO: 29, SEQ ID NO: 30, SEQ ID NO: 54 or SEQ ID NO: 58) that bind to FcRn with increased affinity were made as follows: to express the polypeptide chain with one or more extracellular domains, or parts of domains, of MuSK fused to an engineered Fc fragment, codons encoding one or more extracellular domains of MuSK were linked in frame to codons encoding linker peptides (e.g. GS, G4S, SEQ ID NO: 80) to codons encoding the C-terminus of the CH3 domain, or N-terminus of the hinge region, of a human IgGl -derived Fc fragment using standard molecular biology techniques (thereby encoding SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 28, SEQ ID NO: 29 or SEQ ID NO: 30). Mutations to ablate binding to FcyRs (L234S / L235T / G236R; L234A / L235A / D265S or L234A / L235A / P329G can be used as alternatives; EU numbering used for mutations), enhance binding to FcRn (MST-HN; M252Y / S254T / T256E / H433K / N434F; EU numbering) and generate ‘knobs-into-holes’ (T366W; EU numbering) were inserted into the Fc fragment gene (thereby encoding SEQ ID NO: 4, SEQ ID NO: 5. SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 8. SEQ ID NO: 10. SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 28, SEQ ID NO: 29 or SEQ ID NO: 30). Codons encoding the mouse Ig leader peptide MGWSCIILFLVATATGVHS (SEQ ID NO: 84) were appended to the N-terminus of the Fc fragment gene, or of the antigen gene segment for antigens fused to the N-terminus of the Fc fragment gene. Alternatively, other leader peptides known to persons skilled in the art could be used.

[0187] For expression as heterodimers, Fc fragment genes with FcRn-enhancing mutations and mutations to ablate FcyR binding (L234S / L235T / G236R or L234A / L235A / P329G; alternatively L234A / L235A / D265S can be used; EU numbering used for mutations) were generated with complementary knobs-into-holes mutations (T366S / L368A / Y407V; EU numbering) (thereby encoding SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 9, SEQ ID NO: 54 or SEQ ID NO: 58).

[0188] Further embodiments for exemplary FcRn-targeting macromolecules that target MuSK-specific antibodies are shown in Table 1. These embodiments can be made by combining theFcRn-targeting components (SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 9, SEQ ID NO: 54, SEQ ID NO: 58, SEQ ID NO: 63, SEQ ID NO: 64, SEQ ID NO: 68, SEQ ID NO: 71, SEQ ID NO: 72, SEQ ID NO: 76) with one or more domains of MuSK (SEQ ID NO: 47, SEQ ID NO: 48, SEQ ID NO: 49, SEQ ID NO: 50, SEQ ID NO: 51, SEQ ID NO: 52, SEQ ID NO: 53) as N- or C-terminal fusion proteins, with different linkers (e.g. G4S, SEQ ID NO: 80) using analogous methods to those described above. The Fc-antigen fusions can be coexpressed with Fc fragments or Fc-antigen fusion proteins to generate heterodimers comprising one or more antigen components, as exemplified in FIGURE 2. For expression of two or more MuSK domains that are not contiguous in the natural MuSK sequence, the domains can be linked by, for example, GS or G4S (SEQ ID NO: 80) linkers.

[0189] Recombinant proteins were expressed in ExpiCHO (Life Technologies) cells following transient transfection with the Gibco expression system kit (Life Technologies). The proteins were purified using protein A-Sepharose followed by size exclusion chromatography (SEC) in phosphate buffered saline (PBS). SDS-PAGE analyses for exemplary' macromolecules that target MuSK-specific antibodies (MMG_027 + MMG_068, MMG_027 + MMG_135, MMG 027 + MMG 137 and MMG_027 + MMG_138; see Table 2 for corresponding SEQ ID NOs) are shown in FIGURES 4A, 4B, 4C and 4D. FIGURE 5 shows size exclusion analyses using a Superdex 200 Increase column for several of the exemplary' macromolecules that target MuSK-specific antibodies (MMG_027 + MMG_068, MMG_027 + MMG_135 and MMG_027 + MMG 137; see Table 2 for corresponding SEQ ID NOs).

[0190] The FcRn-targeting macromolecules that target MuSK-specific antibodies bind to recombinant (human IgGl / kappa) MuSK-specific antibodies and maintain a significantly higher binding affinity for FcRn at neutral pH and at an acidic pH due to the presence of the MST-HN mutations (M252Y, S254T, T256E, H433K, N434F; EU numbering).

[0191] Surface plasmon resonance experiments to analyze the interactions of recombinant macromolecules with a MuSK-specific antibody and human FcRn were carried out using a BIAcore T200 (GE Healthcare). For example, the binding of a macromolecule that targets MuSK-specific antibodies to a recombinant MuSK-specific antibody generated using standard methods as a human IgGl / kappa antibody (MMG Tracer l ) comprising the VH and VL domain sequences of antibody 11-3F6 (SEQ ID NO: 17 and SEQ ID NO: 21, respectively in: WO 2020 / 055240 Al, MuSK inhibition, inventors: van der Maarel, S. M., Verschuuren, J. J. G. M., Huijbers, M. G. M., Plomp, J. J.) was analyzed by injecting a range of concentrations (0.5-350 nM of macromolecule over immobilized antibody (coupled at ~ 616 RU on a flow cell of aCM5 sensor chip) in PBS (pH 7.4) plus 0.01% v / v Tween-20 at a flow rate of 10 pl / minute. Flow cells were regenerated following each injection and dissociation phase using 10 mM glycine-HCL pH 1.5. Data were zero-adjusted and background-subtracted (background obtained by injection over a flow cell coupled with buffer only during coupling reaction). FIGURE 6A shows representative sensorgrams for the binding of a macromolecule that targets a MuSK-specific antibody (MMG_027 + MMG_137; see Table 2 for corresponding SEQ ID NOs) to antibody 11-3F6. The equilibrium dissociation constant for the interaction is 20.6 nM.

[0192] Binding of an exemplary macromolecule that targets MuSK-specific antibodies to recombinant human FcRn was analyzed by injecting a range of concentrations (0.1-200 nM or 0.5-500 nM for pH 6.0 or pH 7.4, respectively) of macromolecule over immobilized FcRn (coupled at ~ 1499 or 441 RU on flow cells of CM5 sensor chips) in PBS (pH 6.0 or pH 7.4) plus 0.01 % v / v Tween-20 at a flow rate of 10 pl / minute. Flow cells were regenerated following each injection and dissociation phase using 0.1 M NaCl, 0.1 M sodium bicarbonate, pH 8.5. Data were zero- adjusted and background-subtracted (background obtained by injection over a flow cell coupled with buffer only during coupling reaction). FIGURES 6B and 6C show sensorgrams for the binding of a macromolecule that targets MuSK-specific antibodies (MMG_027 + MMG_137; see Table 2 for corresponding SEQ ID NOs) to FcRn at pH 6.0 and pH 7.4. The equilibrium dissociation constants for the interactions are ~1.5 nM (pH 6.0) or -10.5 nM (pH 7.4) (note that these are apparent dissociation constants due to avidity effects with immobilized FcRn), indicating much stronger binding to human FcRn than observed for human IgGl or Fc fragments that are not engineered for increased affinity for human FcRn (for example, see Zhou, J., Mateos, F., Ober, R. J., Ward, E. S. (2005) Conferring the binding properties of the mouse MHC class I-related receptor, FcRn, onto the human ortholog by sequential rounds of site-directed mutagenesis. J. Mol. Biol., 345, 1071-1081).

[0193] Mutations to increase the affinity for FcRn such as MST-HN were identified using the following approach: residues in proximity to amino acids (e.g. 253, 435) that are known to be essential for FcRn binding were randomly mutated in an Fc fragment gene and the libraries of mutated Fc fragments displayed on phage. Fc fragments with increased binding affinity for FcRn were selected using phage display technology (Ghetie, V., Popov, S., Borvak, J., Radu, C., Matesoi, D., Medesan, C., Ober, R. J., Ward, E. S. (1997) Increasing the serum persistence of an IgG fragment by random mutagenesis, Nature Biotech., 15, 637-640; Dall’Acqua, W. F., Woods, R. M., Ward, E. S., Palaszynski, S. R., Patel, N. K., Brewah, Y. A., Wu, H., Kiener, P A., Langermann. S. (2001) Increasing the affinity of a human IgGl for the neonatal receptor:biological consequences, J. Immunol., 169, 5171-5180). Alternatively, these residues can be mutated to every other possible amino acid and Fc fragments with higher affinity for FcRn identified using methods such as ELISA or surface plasmon resonance binding analyses.

[0194] Size exclusion analyses indicate that exemplar}' recombinant macromolecules that target MuSK-specific antibodies (MMG_027 + MMG_068, MMG_027 + MMG_135 and MMG_027 + MMG_137) have favorable behavior following incubation in phosphate buffered saline when incubated for 5 or 14 days at 37°C (FIGURES 7A, 7B and 7C).

[0195] Example 2: Design and construction of macromolecules that target MuSK-specific antibodies and the internalizing receptors, FcyRIIb and ASGPR

[0196] Expression constructs to generate the exemplary macromolecules that target MuSK-specific antibodies and bind with increased affinity’ to the inhibitor7receptor, FcyRIIb, were made as follows: to express the polypeptide chain with one or more extracellular domains of MuSK. or a peptide thereof, fused to an engineered Fc fragment, the genes encoding the Igl, Ig2, Ig3 and Fz domains of MuSK were linked in frame to codons encoding linker peptides (e.g. GS, G4S, SEQ ID NO: 80; other linker sequences can also be used) to codons encoding the C-terminus of the CH3 domain of a human IgGl-derived Fc fragment using standard molecular biology techniques: (thereby encoding SEQ ID NO: 12, SEQ ID NO: 14 or SEQ ID NO: 27). Mutations to enhance binding to FcyRIIb (G236N / H268D / A330K; S267E / L328F, P238D; EU numbering) and generate ‘knobs-into-holes’ (T366W; EU numbering) were inserted into the Fc fragment gene. Codons encoding the mouse Ig leader peptide MGWSCIILFLVATATGVHS (SEQ ID NO: 84) were appended to the N-terminus of the Fc fragment gene. For expression as heterodimers, Fc fragment genes with FcyRIIb-enhancing mutations were generated with complementary’ knobs-into-holes mutations (T366S / L368A / Y407V; EU numbering) (thereby encoding SEQ ID NO: 11, SEQ ID NO: 13 or SEQ ID NO: 26).

[0197] Further embodiments for exemplary FcyRIIb-targeting macromolecules that target MuSK-specific antibodies are shown in Table 1. These embodiments can be made by combining FcyRIIb-targeting components (SEQ ID NO: 11. SEQ ID NO: 13, SEQ ID NO: 26, SEQ ID NO: 55, SEQ ID NO: 56, SEQ ID NO: 57, SEQ ID NO: 59, SEQ ID NO: 60, SEQ ID NO: 61, SEQ ID NO: 62, SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 67, SEQ ID NO: 69, SEQ ID NO: 70, SEQ ID NO: 73, SEQ ID NO: 74, SEQ ID NO: 75, SEQ ID NO: 77, SEQ ID NO: 78) with one or more domains of MuSK (SEQ ID NO: 47, SEQ ID NO: 48, SEQ ID NO:49, SEQ ID NO: 50, SEQ ID NO: 51, SEQ ID NO: 52, SEQ ID NO: 53) as N- or C-terminal fusion proteins, with different linkers (e.g. G4S. SEQ ID NO: 80) using analogous methods to those described above. In addition, half-life extending mutations that increase the binding affinity for FcRn and prolong in vivo persistence can be inserted into the Fc fragment. Such mutations are known to those with skill in the art (e.g., see Ramdani, Y., Lamamy, J., Watier, H, Gouilleux-Gruart, V. (2022) Monoclonal antibody engineering and design to modulate FcRn activities: a comprehensive review. Int. J. Mol. Sci., 23, 9604; Manso, T., Sanou, G., Nousias, C., Maalem, I., Boutin, F., Giudicelli, V., Duroux, P, Lefranc, M-P., Kossida, S. (2025) Identification of engineered IMGT Fc variants in IMGT / mAb-DB, a database of therapeutic antibodies and fusion proteins. MAbs, 17, 2594260). The Fc-antigen fusions can be co-expressed with Fc fragments or Fc-antigen fusion proteins to generate heterodimers comprising one or more antigen components, as exemplified in FIGURE 2. For expression of two or more MuSK domains that are not contiguous in the natural MuSK sequence, the domains can be linked by, for example, GS or G4S (SEQ ID NO: 80) linkers.

[0198] To generate a macromolecule that targets MuSK-specific antibodies that binds to ASGPR, the following expression constructs were made: to express the polypeptide chain with one or more extracellular domains of MuSK, or a peptide thereof, the gene encoding the Igl, Ig2, Ig3 and Fz domains of MuSK was linked in frame with codons encoding linker peptides (e.g. GS, G4S, SEQ ID NO: 80) to the C-terminal codon of the CH3 region of a human IgGl / kappa antibody (SEQ ID NO: 19) comprising VH and VL domain genes of the 51A12_A6 antibody (the variable domain gene sequences are described as SEQ ID NO: 4 for VH and SEQ ID NO: 44 for VL in: International Publication No. WO 2014 / 023709 / A1; ASGPR antibodies and uses thereof; inventors: Hofer, T., Ji, C., Moessner, E., Umana, P) (thereby encoding, for example, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 18 or SEQ ID NO: 19). Mutations to ablate binding to FcyRs (L234S / L235T / G236R, L234A / L235A / D265S or L234A / L235A / P329G; EU numbering) and generate ‘knobs-into-holes’ (T366W; EU numbering) were inserted into the Fc fragment of the MuSK-heavy chain fusion (thereby encoding SEQ ID NO: 19). For expression as heterodimers, heavy chain or Fc fragment genes with mutations to ablate FcyR binding (L234S / L235T / G236R; L234A / L235A / D265S or L234A / L235A / P329G can be used as alternatives; EU numbering) were generated with complementary knobs-into-holes mutations (T366S / L368A / Y407V; EU numbering) (thereby encoding SEQ ID NO: 15 or SEQ ID NO: 16). For additional embodiments, genes encoding one or more extracellular domains of MuSK that are different to those appended to the firstCH3 domain are linked in frame with codons encoding linker peptides (e.g. GS, G4S, SEQ ID NO: 80) to the sequence encoding the second CH3 domain of the antibody.

[0199] Recombinant proteins were expressed in ExpiCHO (Life Technologies) cells following transient transfection with the Gibco expression system kit (Life Technologies). The proteins were purified using protein A-Sepharose followed by size exclusion chromatography (SEC) in PBS (Lonza). SDS-PAGE analyses for exemplary macromolecules that target MuSK-specific antibodies (MMG_232 + MMG_233 and MMG_248 + MMG_343; see Table 2 for corresponding SEQ ID NOs) are shown in FIGURE 8A. FIGURE 8B shows size exclusion analyses using a Superdex 200 Increase column for several of the exemplary macromolecules that target MuSK-specific antibodies (MMG_232 + MMG_233 and MMG_248 + MMG_343; see Table 2 for corresponding SEQ ID NOs).

[0200] Example 3; Effects of Fc mutations on FcyR and Clq binding of exemplary macromolecules that target MuSK-specific antibodies

[0201] The effects of mutations to alter binding to FcyRs and complement Clq of exemplary macromolecules that target MuSK-specific antibodies are shown in FIGURES 9A, 9B and 9C. To analyze the binding of FcyRs, wells of ELISA plates were coated with macromolecule or, as a control, wild type human IgGl. Following washing with PBS containing 0.05% v / v Tween 20 (PBST) and PBS, wells were incubated in 4% (w / v) skimmed milk in PBS. Wells were then washed in PBST and PBS, and pre-incubated mixtures of biotinylated FcyR (CD16a, CD32a, CD32b or CD64; from Sino Biological) with neutravidin-horse radish peroxidase (HRP) to form multivalent complexes in 1% (w / v) skimmed milk in PBST were added to the wells. Following incubation, wells were washed with PBST followed by PBS. This was followed by addition of TMB substrate (e.g. BioFX® TMB One Component HRP Microwell Substrate) to detect bound neutravidin-HRP.

[0202] To assess binding of the macromolecules that target MuSK-specific antibodies to complement Clq, wells of ELISA plates were coated with macromolecule or, as a control, wild type human IgGl. Following washing with phosphate buffered saline (PBS) containing 0.05% v / v Tween 20 (PBST) and PBS, wells were incubated in 1% (w / v) skimmed milk in PBS. Wells were then washed with PBST and PBS, and 0.2 pg / ml complement Clq conjugated to HRP in 1 % (w / v) skimmed milk in PBS was added. Following washing with PBST and MilliQ water, TMB substrate (e.g. BioFX® TMB One Component HRP Microwell Substrate) was added to detect bound HRP.The results presented in FIGURE 9A shows that an exemplary macromolecule that targets MuSK-specific antibodies with mutations to reduce binding to FcyRs (MMG_027 + MMG 137; see Table 2 for corresponding SEQ ID NOs) has levels of binding that are close to background signal, indicating effective removal of FcyR binding. By contrast, data shown in FIGURE 9B demonstrates that exemplary FcyRIIb (CD32b)-targeting macromolecules that target MuSK-specific antibodies with mutations to increase affinity for FcyRIIb (MMG_232 + MMG_233 and MMG_248 + MMG 343; see Table 2 for corresponding SEQ ID NOs) bind to this FcyR.

[0203] In addition, exemplary molecules that target MuSK-specific antibodies with mutations to reduce binding to complement Clq (MMG_027 + MMG_068, MMG_027 + MMG_135 and MMG_027 + MMG_137; see Table 2 for corresponding SEQ ID NOs) show levels of binding to this protein at background levels (FIGURE 9C).

[0204] Example 4; Binding of MuSK-specific autoantibodies to exemplary macromolecules that target MuSK-specific antibodies

[0205] To analyze the binding of macromolecules that target MuSK-specific antibodies to autoantibodies in serum samples of MuSK-MG patients, wells of ELISA plates were coated with purified macromolecule, washed with PBS containing 0.05% v / v Tween 20 (PBST), followed by PBS only, and then incubated with blocking buffer. As controls, an Fc fusion comprising an irrelevant antigen component (MMG_Controll or MMG_Control2) or PBS (labeled PBS) were used to coat wells, followed by washes as above and treatment with blocking buffer. Following washing with PBST and PBS, dilutions (200-fold) of serum samples from MuSK-MG patients were added to each well. As a control, serum from healthy controls (HC serum) was used. Following incubation and washing with PBST followed by PBS, wells were incubated with biotinylated anti-human CHI (IgG)-specific antibody followed by neutravidin conjugated to horse-radish peroxidase (HRP). The wells were then washed with PBST followed by PBS, and TMB substrate (e g. BioFX® TMB One Component HRP Micro well Substrate) added to detect bound HRP conjugate.

[0206] The ELISA analyses demonstrate specific binding of exemplary macromolecules that target MuSK-specific antibodies and comprise different MuSK domains (Igl, MMG_027 + MMG_068; Igl + Ig2, MMG_027 + MMG_135; Igl + Ig2 + Ig3 + Fz, MMG_027 + MMG 137; see Table 2 for corresponding SEQ ID NOs) to autoantibodies in serum samplesfrom MuSK-MG patients (FIGURES 10A, 10B, IOC and 10D). The analyses demonstrate that for some serum samples (e.g. serum samples 010, 017, 025), binding to an exemplary macromolecule with four ECDs of MuSK (MMG_027 + MMG_137) is higher than that to exemplary macromolecules comprising subsets of these domains (MMG_027 + MMG_068 and MMG_027 + MMG_135).

[0207] Example 5: Ability of exemplary macromolecules that target MuSK-specific antibodies to deplete MuSK-specific antibodies in serum

[0208] To analyze the depletion of MuSK-specific antibodies from patient serum samples by macromolecules that target MuSK-specific antibodies, wells of ELISA plates were coated with purified macromolecules (MuSK-specific), a control macromolecule comprising an irrelevant antigen or blocking buffer, washed with phosphate buffered saline (PBS) containing 0.05% v / v Tween 20 (PBST), followed by PBS only, and then incubated with blocking buffer. Dilutions (100-300 fold) of serum samples in PBS were then added to wells, incubated ('panned') for one hour at room temperature and then transferred to a second well. This serial incubation was repeated for each sample for a total of six wells. Following the incubations, the presence of MuSK-specific antibodies in the samples that bind to various macromolecules comprising different domains of MuSK were analyzed using the same protocol as in Example 4.

[0209] The results presented in FIGURES 11 A. 11B. 11C. 11D. HE. 11F. 11G and 11H demonstrate that exemplary macromolecules (MMG_027 + MMG_068, MMG_027 + MMG_135 and MMG_027 + MMG_137; see Table 2 for corresponding SEQ ID NOs) that target MuSK-specific antibodies specifically deplete antibodies specific for MuSK in patient serum samples. To demonstrate the specificity of depletion, the reduction of MuSK-specific antibodies is also significantly greater following incubation of serum samples with wells coated with macromolecules that target MuSK-specific antibodies compared with wells coated with blocking buffer or with a control macromolecule (comprising an irrelevant antigen; MMG_Control 1. that as shown on the left side of each panel, is effective in depleting antibodies specific for this irrelevant antigen). By comparing the behavior of an exemplary macromolecule that comprises Igl, Ig2, Ig3 and Fz domains (MMG_027 + MMG_137) with macromolecules that comprise subsets of these domains (MMG_027 + MMG_068 and MMG_027 + MMG_135), the results demonstrate that for a subset of serum samples (e.g. 003, 010, 017). all four ECDs of MuSK are required to efficiently remove MuSK-specificantibodies. By contrast, for other serum samples (e.g. 001, 002, 016), the ability of macromolecules with Igl (MMG_027 + MMG_068) or Igl and Ig2 (MMG_027 + MMG_135) have activity that is similar to that of MMG_027 + MMG 137 comprising Igl, Ig2, Ig3 and Fz domains.

[0210] Example 6: Ability of exemplary macromolecules that target MuSK-specific antibodies to deplete MuSK-specific antibodies in mice

[0211] To determine the ability of macromolecules that target MuSK-specific antibodies to specifically deplete MuSK-specific antibodies in vivo, C57BL / 6J mice were injected with 25 pg MuSK-specific antibody (n = 3 mice / group). The recombinant human IgGl / kappa antibody (MMG Tracer 1) was generated using standard methods comprising the VH and VL domain sequences of the 11 3F6 antibody (SEQ ID NO: 17 and SEQ ID NO: 21, respectively in: International Publication No. WO 2020 / 055240 Al, MuSK inhibition, inventors: van der Maarel, S. M., Verschuuren, J. J. G. M., Huijbers, M. G. M., Plomp, J. J.). Three days later, mice were injected with a 4-fold molar excess of an exemplary macromolecule that targets MuSK-specific antibodies or a control macromolecule comprising an irrelevant antigen (MMG_Control2) via intravenous injection. Blood samples were taken from mice prior to and following antibody and macromolecule injections (see plots for sampling times) and levels of MuSK-specific antibodies in serum determined using ELISA.

[0212] The data shown in FIGURE 12 demonstrate that, compared with the effect of the control macromolecule (MMG_Control2), an exemplary macromolecule that targets MuSK-specific antibodies (MMG_027 + MMG 137; see Table 2 for corresponding SEQ ID NOs) induces a rapid and substantial decrease in MuSK-specific antibody in the circulation of mice.

[0213] Example 7; Binding of MuSK-specific autoantibodies to exemplary FcyRIIb-targeting macromolecules that target MuSK-specific antibodies

[0214] To analyze the binding of FcyRIIb-targeting macromolecules that target MuSK-specific antibodies to autoantibodies in serum samples of MuSK patients, w ells of ELISA plates were coated with purified macromolecule, washed with PBS containing 0.05% v / v Tween 20 (PBST), followed by PBS only, and then incubated with blocking solution. As controls, an Fc fusion comprising an irrelevant antigen component (MMG_Control3) or PBS (labeled PBS) were used to coat wells, followed by washing as above and treatment with blocking buffer.Following washing with PBST and PBS. 200-fold dilutions of serum samples from MuSK patients were added to each well. As controls, serum from healthy controls (HC serum) was used. Following incubation and washing with PBST followed by PBS, wells were incubated with anti-human F(ab’)2-specific antibody conjugated to horse-radish peroxidase (HRP). The wells were then washed with PBST followed by PBS, and TMB substrate (e.g. BioFX® TMB One Component HRP Microwell Substrate) was added to detect bound HRP conjugate.

[0215] The ELISA analyses shown in FIGURE 13 demonstrate specific binding of antibodies in serum samples of MuSK-MG patients to exemplary FcyRIIb-targeting macromolecules that target MuSK-specific antibodies and comprise Igl, Ig2, Ig3 and Fz domains of MuSK (MMG 232 + MMG_233 and MMG_248 + MMG 343; see Table 2 for corresponding SEQ ID NOs).

[0216] Example 8: Ability of exemplary FcyRIIb-targeting macromolecules that target MuSK-specific antibodies to lead to accumulation of MuSK-specific antibodies in FcyRIIb-expressing cells

[0217] To analyze the ability of FcyRIIb-targeting macromolecules that target MuSK-specific antibodies to result in accumulation of MuSK-specific antibodies in FcyRIIb-expressing cells, the following assay was carried out: CH0-K1 cells expressing FcyRIIb (Promega) were seeded at a density of 0.25 x 106cells per well in 96 well plates and incubated for 16-18 hours in a 37°C incubator with 5% CO2. Cells were incubated with FcyRIIb-targeting macromolecule (MMG_232 + MMG_233 and MMG_248 + MMG_343; see Table 2 for corresponding SEQ ID NOs) premixed at a fourfold molar excess (200 nM: 50 nM) with Alexa Fluor 647-conjugated MuSK-specific antibody (MMG_Tracer2) for 60 minutes in a 37°C incubator with 5% CO2. MMG-Tracer2 is a MuSK-specific, recombinant human IgGl / lambda antibody that was generated using standard methods and comprises the VH and VL domain sequences of the 13-3B5 antibody (SEQ ID NO: 29 and SEQ ID NO: 33, respectively in: International Publication No. WO 2020 / 055240 Al, MuSK inhibition, inventors: van der Maarel, S. M., Verschuuren, J. J. G. M., Huijbers, M. G. M., Plomp, J. J.). As controls, Alexa Fluor 647-conjugated MuSK-specific antibody (MMG_Tracer2) was mixed with vehicle (PBS) or with an FcyRIIb-targeting macromolecule comprising an irrelevant antigen (MMG Control4). Following the incubation, cells were washed, detached from the plate wells by trypsinization,washed and analyzed by flow cytometry.

[0218] The results presented in FIGURE 14 demonstrate that incubation of exemplary FcγRIIb-targeting macromolecules that target MuSK-specific antibodies (MMG_232 + MMG 233 and MMG_248 + MMG_343; see Table 2 for corresponding SEQ ID NOs) with a MuSK-specific antibody (MMG_Tracer2) leads to the accumulation of the antibody in FcyRIIb-expressing cells (labeled +MMG_232 + MMG_233 and +MMG_248 + MMG_343). The specificity of this accumulation is demonstrated by incubating the cells with MuSK-specific antibody alone (MMG_Tracer2), or MMG_Tracer2 mixed with an FcyRIIb-targeting macromolecule comprising an irrelevant antigen (i.e. not MuSK or MuSK domains; MMG_Control4) (FIGURE 14).

[0219] Example 9; Binding of exemplary ASGPR-targeting macromolecules that target MuSK-specific antibodies to ASGPR

[0220] To assess the binding of an exemplary ASGPR-targeting macromolecule that targets MuSK-specific antibodies to ASGPR, wells of ELISA plates were coated with recombinant ASGPR (5 pg / ml), washed with PBS containing 0.05% v / v Tween 20 (PBST), followed by PBS only, and then incubated with blocking solution (3% w / v bovine serum albumin, BSA, in PBS). Following washing with PBST and PBS, an ASGPR-targeting macromolecule (MMG_214 + MMG_217 + MMG 235; see Table 2 for corresponding SEQ ID NOs) or control macromolecule (MMG_027 + MMG_137, that is not expected to bind to ASGPR; see Table 2 for corresponding SEQ ID NOs) were added at a concentration of 33 nM. Following incubation and washing with PBST followed by PBS, wells were incubated with anti-human Fc-specific antibody conjugated to horse-radish peroxidase (HRP). The wells were then washed with PBST followed by PBS, and TMB substrate (e.g. BioFX® TMB One Component HRP Microwell Substrate) added to detect bound HRP conjugate.

[0221] The results presented in FIGURE 15 demonstrate that an exemplary ASGPR-targeting macromolecule that targets MuSK-specific antibodies (MMG_214 + MMG_217 + MMG_235; see Table 2 for corresponding SEQ ID NOs) binds specifically to recombinant ASGPR.

[0222] Example 10: Ability of exemplary ASGPR-targeting macromolecules that target MuSK-specific antibodies to lead to accumulation of MuSK-specific antibodies in ASGPR-expressing cells

[0223] To analyze the ability of ASGPR-targeting macromolecules that target MuSK-specific antibodies to result in accumulation of MuSK-specific antibodies in ASGPR-expressing cells, the following assay was carried out: Hep G2 cells (ATCC, HB-8065) were seeded at a density of 0.25 x 106cells per well in 96 well plates and incubated for 16-18 hours in a 37°C incubator with 5% CO2. Cells were incubated with ASGPR-targeting macromolecule (MMG_214 + MMG_217 + MMG_235; see Table 2 for corresponding SEQ ID NOs) premixed at a fourfold molar excess (200 nM: 50 nM) with Alexa Fluor 647-conjugated MuSK-specific antibody (MMG_Tracer2) for 60 minutes in a 37°C incubator with 5% CO2. As a control, Alexa Fluor 647-conjugated MuSK-specific antibody (MMG_Tracer2) was mixed with vehicle (PBS). Following the incubation, cells were washed, detached from the plate wells by trypsinization, washed and analyzed by flow cytometry.

[0224] The results presented in FIGURE 16 demonstrate that incubation of an exemplary ASGPR-targeting macromolecule that targets MuSK-specific antibodies (MMG_214 + MMG_217 + MMG_235; see Table 2 for corresponding SEQ ID NOs) with an MuSK-specific antibody (MMG_Tracer2) leads to the accumulation of the antibody in ASGPR-expressing cells (labeled +MMG_214 + MMG_217 + MMG_235). The specificity of this accumulation is demonstrated by incubating the cells with MuSK-specific antibody alone (MMG_Tracer2) (FIGURE 16).

[0225] Example 11: Generation of macromolecules that target MuSK-specific antibodies and comprise targeting components that bind to the internalizing receptor ASGPR

[0226] To generate exemplary macromolecules that target MuSK-specific antibodies by binding through their targeting component to ASGPR, the following approaches can be used: the genes encoding one or more of the Igl, Ig2, Ig3 or Fz domains of MuSK can be linked to the N- or C-termini of human serum albumin (HSA) or the Dill domain of HSA via linkers such as G4S or (G4S)₃ (SEQ ID NOs: 80 or 82, respectively) (thereby encoding SEQ ID NO: 31, SEQ ID NO: 32, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, SEQ ID NO: 36, SEQ ID NO: 37 or SEQ ID NO: 38). In some embodiments, one or more domains of MuSK can be linked to the N-terminus of HSA or the Dill domain via linkers such as G4S or (G4S)3 (SEQ ID NOs: 80 or 82, respectively), and different domains (one or more) can be linked to the C-terminus of HSA or the Dill domain via linkers such as G4S or (G4S)₃ (SEQ ID NOs: 80 or 82, respectively). The corresponding proteins can be expressed in transfected CHO cells, or other suitable expression host, and purified. The design of these constructs is similar to that shown in FIGURES 2H and 21. Following size exclusion purification, recombinant fusion proteins can be conjugated to targeting molecules that bind to ASGPR (monovalent, divalent or bivalent; FIGURE 17) via Cys34 on HSA, or via Lys residues in the HSA-fusion constructs, to generate conjugates with multiple (e.g. 1-6) ligands attached. As examples, a phenyl maleimide group or pentafluorophenyl (PFP; -C(O)O-pentafluorophenyl) group attached via a linker to the (branched) ASGPR-targeting molecule can be used to conjugate to Cys or Lys residues, respectively. The chemical synthesis of the ASGPR-targeting molecules and conjugation chemistry can be carried out using methods known to those with skill in the art and, for example, are described in the following: International Publication No. WO 2023 / 288033 Al, ASGPR cell surface receptor binding compounds and conjugates, inventors: Bush, B. B., Ernst, J. T., Packard, G. K., Lewis, J. G., Turtle, E. D.; International Publication No. WO 2025 / 035040 Al, Lysosomal targeting bifunctional molecules for degradation of musclespecific kinase autoantibodies, inventors: Chen, T., Iwig, J., Lewis, J. G., Lieser, R., Staben, S., Totten, S. M., Turtle, E. D.

[0227] Additional exemplary embodiments include those in which HSA is replaced by an immunoglobulin Fc fragment (e.g., SEQ ID NO: 39, SEQ ID NO: 40, SEQ ID NO: 41, SEQ ID NO: 42, SEQ ID NO: 43, SEQ ID NO: 44, SEQ ID NO: 45 or SEQ ID NO: 46). Mutations (L234S / L235T / G236R, L234A / L235A / P329G or L234A / L235A / D265S; EU numbering) to ablate binding to FcyRs can be inserted into the Fc fragment genes, that can also have knobs-into-holes mutations (e.g. T366W) to drive heterodimer formation. For expression as heterodimers, Fc fragment genes with FcyR-ablating mutations (L234S / L235T / G236R, L234A / L235A / P329G or L234A / L235A / D265S; EU numbering) (thereby encoding, for example, SEQ ID NO: 16), in some cases with additional antigen components comprising MuSK domains attached to theN- or C-terminus, can be generated with complementary knobs-into-holes mutations (e.g., T366S / L368A / Y407V; EU numbering). The design of these constructs is similar to that shown in FIGURES 2A, 2B, 2C, 2D, 2E, 2F and 2G, and can also include the insertions of mutations (e.g., M252Y / S254T / T256E; EU numbering) to increase binding to FcRn.Additional embodiments for macromolecules comprising targeting components that bind to ASGPR can be made by the generation of expression constructs for one or more of the Igl, Ig2, Ig3 or Fz domains of MuSK (e.g., SEQ ID NO: 47, SEQ ID NO: 48, SEQ ID NO: 49, SEQ ID NO: 50, SEQ ID NO: 51, SEQ ID NO: 52, or SEQ ID NO: 53). For expression of two or more MuSK domains, domains that are not contiguous in the natural MuSK sequence can be linked by, for example, GS or G4S (SEQ ID NO: 80) linkers. Recombinant MuSK proteins can be expressed and purified from transfected CHO cells or other suitable expression host. Alternatively, the domains can be expressed as separate constructs comprising one or more of the following domains: Igl, Ig2, Ig3 or Fz (e.g. SEQ ID NO: 47, SEQ ID NO: 48, SEQ ID NO: 49, SEQ ID NO: 50, SEQ ID NO: 51, SEQ ID NO: 52, or SEQ ID NO: 53). Following size exclusion purification, the MuSK proteins can be conjugated via Cys or Lys residues using methods known to those with skill the art to targeting molecules that bind to ASGPR (e.g., FIGURE 18). Additional embodiments can include one or more MuSK domains expressed as fusion proteins with immunoglobulin Fc fragments, as described above (SEQ ID NO: 39, SEQ ID NO: 40, SEQ ID NO: 41, SEQ ID NO: 42, SEQ ID NO: 43, SEQ ID NO: 44, SEQ ID NO: 45, or SEQ ID NO: 46), followed by conjugation to ASGPR-targeting molecules. Exemplary ASGPR-targeting molecules are described in the following: US patent 12,128,105 B2, Molecular degraders of extracellular proteins, inventors: Caianiello, D., Deramon, E., Spiegel, D.; International Publication No. WO 2022 / 192478 Al, Bifunctional degraders of galactose-deficient immunoglobulins, inventors. Dubowchik, G.M., Spiegel, D., Caldwell, R.M.; International Publication No. WO 2025 / 035052 Al, Molecular degraders for the treatment of IgA nephropathy, inventors: Kazmierski, W., Pracitto, R., Dubowchik, G. M., Marcin, L. R., Bunin, A., Rossi, A. M., Iben, L. G., McGrath, K., Lee, S., Todd, M.; International Publication No. WO 2025 / 081173 A2, Bispecific molecular degraders of pathogenic proteins, inventors: Bunin, A., Car, B., Dow, M., Gardin, T., Lipson, S., Marcin, L. R., Mellott, D., Murray, S., Pirman, D., Velaparthi.

[0228] SEQUENCE LISTING

[0229] Table 1: Sequence identifiers of targeting and antigen components that can be combined with each other to generate macromolecules that target MuSK-specific antibodies

[0230] | FcRn targeting component | Antigen component

[0231]

[0232] SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID SEQ ID NO: 47, SEQ ID NO: 48, SEQ ID NO: 49, NO: 9, SEQ ID NO: 54, SEQ ID NO: 58, SEQ ID NO: 63, SEQ ID NO: 50, SEQ ID NO: 51, SEQ ID NO: 52, SEQ ID NO: 64, SEQ ID NO: 68, SEQ ID NO: 71, SEQ ID SEQ ID NO: 53

[0233] NO: 72, SEQ ID NO: 76

[0234] FcyRllb targeting component Antigen component

[0235] SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 26, SEQ ID SEQ ID NO: 47, SEQ ID NO: 48, SEQ ID NO: 49, NO: 55, SEQ ID NO: 56, SEQ ID NO: 57, SEQ ID NO: SEQ ID NO: 50, SEQ ID NO: 51, SEQ ID NO: 52, 59, SEQ ID NO: 60, SEQ ID NO: 61, SEQ ID NO: 62, SEQ ID NO: 53

[0236] SEQ ID NO: 65, SEQ ID NO: 66, SEQ ID NO: 67, SEQ ID

[0237] NO: 69, SEQ ID NO: 70, SEQ ID NO: 73, SEQ ID NO:

[0238]

[0239] 74, SEQ ID NO: 75, SEQ ID NO: 77, SEQ ID NO: 78

[0240] Table 2; Sequence identifiers and properties of exemplary' molecules that target MuSK-specific antibodies

[0241] Identifier Amino acid ID MuSK domains present

[0242] MMG_022 SEQ ID NO: 1 None; Fc only

[0243] MMG_027 SEQ ID NO: 2 None; Fc only

[0244] MMG_061 SEQ ID NO: 3 None; Fc only

[0245] MMG 068 SEQ ID NO: 4 Igl with Fc

[0246] MMG_069 SEQ ID NO: 5 Igl with Fc

[0247] MMG_135 SEQ ID NO: 6 Igl, Ig2 with Fc

[0248] MMG_137 SEQ ID NO: 7 Igl, Ig2, Ig3, Fz with Fc

[0249] MMG_138 SEQ ID NO: 8 Igl, Ig2, Ig3 with Fc

[0250] MMG 223 SEQ ID NO: 9 None; Fc only

[0251] MMG_225 SEQ ID NO: 10 Igl, Ig2, Ig3, Fz with Fc

[0252] MMG_232 SEQ ID NO: 11 None; Fc only

[0253] MMG_233 SEQ ID NO: 12 Igl, Ig2, Ig3, Fz with Fc

[0254] MMG_229 SEQ ID NO: 13 None; Fc only

[0255] MMG 234 SEQ ID NO: 14 Igl, Ig2, Ig3, Fz with Fc

[0256] MMG_214 SEQ ID NO: 15 Heavy chain only (ASGPR-specific antibody)

[0257] MMG_215 SEQ ID NO: 16 None; Fc only

[0258] MMG_217 SEQ ID NO: 17 Light chain only (ASGPR-specific antibody)

[0259] MMG_218 SEQ ID NO: 18 Light chain only (ASGPR-specific antibody)

[0260] MMG_235 SEQ ID NO: 19 Igl, Ig2, Ig3, Fz with heavy chain (ASGPR- specific antibody)

[0261] MMG 236 SEQ ID NO: 20 Igl, Ig2, Ig3, Fz with Fc

[0262] MMG_237 SEQ ID NO: 21 Igl, Ig2, Ig3, Fz-Fz with Fc

[0263] MMG_238 SEQ ID NO: 22 Igl, Ig2, Ig3, Fz-Fz with Fc

[0264] MMG_189 SEQ ID NO: 23 Igl, Ig2, Ig3, Fz (partial) with Fc

[0265] MMG_239 SEQ ID NO: 24 Igl, Ig2, Ig3, Fz (partial) with Fc

[0266] MMG 240 SEQ ID NO: 25 Igl, Ig2, Ig3, Fz (partial) with Fc

[0267] MMG_248 SEQ ID NO: 26 None; Fc only

[0268] MMG_343 SEQ ID NO: 27 Igl, Ig2, Ig3, Fz with Fc

[0269]

[0270] MMG_273 SEQ ID NO: 28 Igl, Ig2, Ig3, Fz with FcMMG_362 SEQ ID NO 29 Igl, Ig2 with Fc MMG_363 SEQ ID NO 30 Igl, Ig2, Ig3 with Fc MMG_364 SEQ ID NO 31 Igl with albumin MMG_365 SEQ ID NO 32 Igl with albumin MMG 366 SEQ ID NO 33 Igl, Ig2 with albumin MMG_367 SEQ ID NO 34 Igl, Ig2 with albumin MMG_368 SEQ ID NO 35 Igl, Ig2, Ig3 with albumin MMG_369 SEQ ID NO 36 Igl, Ig2, Ig3 with albumin MMG_370 SEQ ID NO 37 Igl, Ig2, Ig3, Fz with albumin MMG 371 SEQ ID NO 38 Igl, Ig2, Ig3, Fz with albumin MMG_372 SEQ ID NO 39 Igl with Fc

[0271] MMG_373 SEQ ID NO 40 Igl with Fc

[0272] MMG_374 SEQ ID NO 41 Igl, Ig2 with Fc MMG_375 SEQ ID NO 42 Igl, Ig2 with Fc MMG 376 SEQ ID NO 43 Igl, Ig2, Ig3 with Fc MMG_377 SEQ ID NO 44 Igl, Ig2, Ig3 with Fc MMG_378 SEQ ID NO 45 Igl, Ig2, Ig3, Fz with Fc MMG_379 SEQ ID NO 46 Igl, Ig2, Ig3, Fz with Fc MMG_380 SEQ ID NO 47 Igl

[0273] MMG_381 SEQ ID NO 48 Ig2

[0274] MMG_382 SEQ ID NO 49 Ig3

[0275] MMG_383 SEQ ID NO 50 Fz

[0276] MMG_384 SEQ ID NO 51 Igl, Ig2

[0277] MMG_385 SEQ ID NO 52 Igl, Ig2, Ig3

[0278] MMG_386 SEQ ID NO 53 Igl, Ig2, Ig3, Fz MMG_088 SEQ ID NO 54 None; Fc only MMG_316 SEQ ID NO 55 None; Fc only MMG_317 SEQ ID NO 56 None; Fc only MMG_318 SEQ ID NO 57 None; Fc only MMG_319 SEQ ID NO 58 None; Fc only MMG_320 SEQ ID NO 59 None; Fc only MMG_321 SEQ ID NO 60 None; Fc only MMG_110 SEQ ID NO 61 None; Fc only MMG_112 SEQ ID NO 62 None; Fc only MMG_322 SEQ ID NO 63 None; Fc only MMG_323 SEQ ID NO 64 None; Fc only

[0279] MMG_324 SEQ ID NO 65 None; Fc only MMG_325 SEQ ID NO 66 None; Fc only MMG_326 SEQ ID NO 67 None; Fc only MMG_327 SEQ ID NO 68 None; Fc only MMG_328 SEQ ID NO 69 None; Fc only MMG_329 SEQ ID NO 70 None; Fc only MMG_330 SEQ ID NO 71 None; Fc only MMG_331 SEQ ID NO 72 None; Fc only MMG_332 SEQ ID NO 73 None; Fc only

[0280]

[0281] MMG_333 SEQ ID NO 74 None; Fc onlyMMG_334 SEQ ID NO: 75 None; Fc only

[0282] MMG_335 SEQ ID NO: 76 None; Fc only

[0283] MMG_336 SEQ ID NO: 77 None; Fc only

[0284]

[0285] MMG_337 SEQ ID NO: 78 None; Fc only

[0286] Table 3: Sequence identifiers and receptor targets of exemplary macromolecules that target MuSK-specific antibodies

[0287] Identifier Amino acid ID Receptor target

[0288] MMG_022 SEQ ID NO 1 FcRn

[0289] MMG 027 SEQ ID NO 2 FcRn

[0290] MMG_061 SEQ ID NO 3 FcRn

[0291] MMG_068 SEQ ID NO 4 FcRn

[0292] MMG_069 SEQ ID NO 5 FcRn

[0293] MMG_135 SEQ ID NO 6 FcRn

[0294] MMG_137 SEQ ID NO 7 FcRn

[0295] MMG_138 SEQ ID NO 8 FcRn

[0296] MMG_223 SEQ ID NO 9 FcRn

[0297] MMG_225 SEQ ID NO 10 FcRn

[0298] MMG_232 SEQ ID NO 11 FcyRllb

[0299] MMG_233 SEQ ID NO 12 FcyRllb

[0300] MMG_229 SEQ ID NO 13 FcyRllb

[0301] MMG_234 SEQ ID NO 14 FcyRllb

[0302] MMG_214 SEQ ID NO 15 ASG PR

[0303] MMG_215 SEQ ID NO 16 ASG PR

[0304] MMG_217 SEQ ID NO 17 ASG PR

[0305] MMG_218 SEQ ID NO 18 ASG PR

[0306] MMG_235 SEQ ID NO 19 ASG PR

[0307] MMG_236 SEQ ID NO 20 FcRn

[0308] MMG_237 SEQ ID NO 21 FcRn

[0309] MMG_238 SEQ ID NO 22 FcRn

[0310] MMG_189 SEQ ID NO 23 FcRn

[0311] MMG_239 SEQ ID NO 24 FcRn

[0312] MMG_240 SEQ ID NO 25 FcRn

[0313] MMG_248 SEQ ID NO 26 FcyRllb

[0314] MMG_343 SEQ ID NO n FcyRllb

[0315] MMG_273 SEQ ID NO 28 FcRn

[0316] MMG_362 SEQ ID NO 29 FcRn

[0317] MMG_363 SEQ ID NO 30 FcRn

[0318] MMG_364 SEQ ID NO 31 ASG PR

[0319] MMG_365 SEQ ID NO 32 ASG PR

[0320] MMG_366 SEQ ID NO 33 ASG PR

[0321] MMG_367 SEQ ID NO 34 ASG PR

[0322] MMG_368 SEQ ID NO 35 ASG PR

[0323]

[0324] MMG_369 SEQ ID NO 36 ASG PRMMG_370 SEQ ID NO 37 ASG PR MMG_371 SEQ ID NO 38 ASG PR MMG_372 SEQ ID NO 39 ASG PR MMG_373 SEQ ID NO 40 ASG PR MMG 374 SEQ ID NO 41 ASG PR MMG_375 SEQ ID NO 42 ASG PR MMG_376 SEQ ID NO 43 ASG PR MMG_377 SEQ ID NO 44 ASG PR MMG_378 SEQ ID NO 45 ASG PR MMG 379 SEQ ID NO 46 ASG PR MMG_380 SEQ ID NO 47 FcRn, FcyRllb, ASGPR MMG_381 SEQ ID NO 48 FcRn, FcyRllb, ASGPR MMG_382 SEQ ID NO 49 FcRn, FcyRllb, ASGPR MMG_383 SEQ ID NO 50 FcRn, FcyRllb, ASGPR MMG 384 SEQ ID NO 51 FcRn, FcyRllb, ASGPR MMG_385 SEQ ID NO 52 FcRn, FcyRllb, ASGPR MMG_386 SEQ ID NO 53 FcRn, FcyRllb, ASGPR MMG_088 SEQ ID NO 54 FcRn

[0325] MMG_316 SEQ ID NO 55 FcyRllb MMG_317 SEQ ID NO 56 FcyRllb MMG_318 SEQ ID NO 57 FcyRllb MMG_319 SEQ ID NO 58 FcRn

[0326] MMG_320 SEQ ID NO 59 FcyRllb MMG_321 SEQ ID NO 60 FcyRllb MMG_110 SEQ ID NO 61 FcyRllb MMG_112 SEQ ID NO 62 FcyRllb MMG_322 SEQ ID NO 63 FcRn

[0327] MMG_323 SEQ ID NO 64 FcRn

[0328] MMG_324 SEQ ID NO 65 FcyRllb MMG_325 SEQ ID NO 66 FcyRllb MMG_326 SEQ ID NO 67 FcyRllb MMG_327 SEQ ID NO 68 FcRn

[0329] MMG_328 SEQ ID NO 69 FcyRllb MMG_329 SEQ ID NO 70 FcyRllb MMG_330 SEQ ID NO 71 FcRn

[0330] MMG_331 SEQ ID NO 12 FcRn

[0331] MMG_332 SEQ ID NO 73 FcyRllb MMG_333 SEQ ID NO 74 FcyRllb MMG_334 SEQ ID NO 75 FcyRllb MMG_335 SEQ ID NO 76 FcRn

[0332] MMG_336 SEQ ID NO 77 FcyRllb

[0333]

[0334] MMG_337 SEQ ID NO 78 FcyRllbThe above disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments which fall within the true spirit and scope of the present disclosure. Thus, to the maximum extent allowed by law, the scope of the present disclosure is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.

Claims

CLAIMS1. A macromolecule that depletes muscle-specific kinase specific (MuSK-specific) antibodies from the serum or tissue of a subject, said macromolecule comprising a targeting component that is configured to specifically bind to a cell surface receptor or other cell surface molecule, and a first antigen component that is configured to specifically bind to a MuSK-specific antibody or a variant thereof, wherein the first antigen component comprises at least part of the Ig1 domain of MuSK.

2. The macromolecule according to claim 1, wherein the macromolecule comprises substantially the entire Igl domain of MuSK.

3. The macromolecule according to claim 1, wherein the first antigen component of the macromolecule comprises at least part of the Ig1 and Ig2 domains of MuSK.

4. The macromolecule according to claim 1, wherein the first antigen component of the macromolecule comprises at least part of the Ig1, Ig2 and Ig3 domains of MuSK.

5. The macromolecule according to claim 1, wherein the first antigen component of the macromolecule comprises at least part of the Igl, Ig2, Ig3 and Fz domains of MuSK.

6. The macromolecule according to any preceding claim, wherein the first antigen component of the macromolecule comprises substantially the entirety of said domains.

7. The macromolecule according to any preceding claim, wherein the first antigen component comprises a single polypeptide component including said domains.

8. The macromolecule according to any one of claims 1 to 6, wherein the first antigen component comprises two or more separate polypeptides, each of which comprises the same or different domains of MuSK.

9. The macromolecule according to claim 8, wherein the domains are comprised in three or more separate polypeptides of the antigen component.

10. The macromolecule of claim 1, wherein the targeting component comprises an immunoglobulin Fc fragment.

11. The macromolecule of claim 10, wherein the immunoglobulin Fc fragment is modified to have substantially reduced binding affinity for Fc gamma receptors compared to an unmodified immunoglobulin Fc fragment.

12. The macromolecule of claim 11, wherein the immunoglobulin Fc fragment comprises L234S / L235T / G236R mutations according to EU numbering.

13. The macromolecule of claim 10, wherein the immunoglobulin Fc fragment is modified to have substantially reduced binding affinity for complement Clq compared to an unmodified immunoglobulin Fc fragment.

14. The macromolecule of claim 10, wherein the immunoglobulin Fc fragment is modified to have a higher binding affinity’ for FcRn at near-neutral pH than an unmodified immunoglobulin Fc fragment.

15. The macromolecule of claim 14, wherein the immunoglobulin Fc fragment comprises M252Y / S254T / T256E / H433K / N434F mutations according to EU numbering.

16. The macromolecule of claim 10, wherein the immunoglobulin Fc fragment is modified to have increased binding affinity for FcyRIIb compared to an unmodified immunoglobulin Fc fragment.

17. The macromolecule of claim 16, wherein the immunoglobulin Fc fragment comprises mutations selected from the group consisting of P238D, G237D / P271G / A330R,G237D / H268D / P271G / A330R, G236N / H268D / A330K, and S267E / L328F according to EU numbering.

18. The macromolecule of claim 10, wherein the targeting component comprises a heterodimer of two immunoglobulin Fc fragments.

19. The macromolecule of claim 18, wherein one immunoglobulin Fc fragment of the heterodimer is fused to the antigen component and the other immunoglobulin Fc fragment is not fused to the antigen component.

20. The macromolecule of claim 18, wherein the heterodimer comprises knobs-into-holes mutations.

21. The macromolecule of claim 20, wherein the knobs-into-holes mutations comprise T366W in one Fc fragment and T366S / L368A / Y407V in the other Fc fragment according to EU numbering.

22. The macromolecule of claim 10, wherein the first antigen component is fused to an N-terminus of the immunoglobulin Fc fragment.

23. The macromolecule of claim 10. wherein the first antigen component is fused to a C-terminus of the immunoglobulin Fc fragment.

24. The macromolecule of claim 1, wherein the targeting component comprises albumin or an albumin fragment.

25. The macromolecule of claim 24, wherein the albumin or albumin fragment is configured to specifically bind to FcRn.

26. The macromolecule of claim 1, wherein the targeting component comprises one or more antibody variable regions configured to specifically bind to the cell surface receptor or cell surface molecule.

27. The macromolecule of claim 26, wherein the one or more antibody variable regions comprise at least one nanobody.

28. The macromolecule of claim 1, wherein the cell surface receptor or cell surface molecule is FcRn.

29. The macromolecule of claim 28, wherein the targeting component can bind to FcRn with a dissociation constant of less than 10 μM at near-neutral pH.

30. The macromolecule of claim 1, wherein the cell surface receptor or cell surface molecule is a transferrin receptor.

31. The macromolecule of claim 1, wherein the cell surface receptor or cell surface molecule is an asialoglycoprotein receptor (ASGPR).

32. The macromolecule of claim 31, wherein the targeting component comprises an antibody or antibody fragment that specifically binds to ASGPR.

33. The macromolecule of claim 1, wherein the cell surface receptor or cell surface molecule is FcyRIIb.

34. The macromolecule of claim 1, wherein the cell surface receptor or cell surface molecule is CD163.

35. The macromolecule of claim 1, wherein the cell surface receptor or cell surface molecule is a mannose 6-phosphate receptor.

36. The macromolecule of claim 1, wherein the cell surface receptor or cell surface molecule is phosphatidylserine.

37. The macromolecule of claim 36, wherein the targeting component comprises a C2A domain of synaptotagmin 1.

38. The macromolecule of claim 1, wherein the targeting component comprises a carbohydrate or carbohydrate derivative configured to specifically bind to the cell surface receptor or cell surface molecule.

39. The macromolecule of claim 1. wherein the targeting component comprises a small molecule configured to specifically bind to the cell surface receptor or cell surface molecule.

40. The macromolecule of claim 1, wherein the first antigen component is fused to the targeting component via a linker.

41. The macromolecule of claim 40, wherein the linker comprises a glycine-serine linker, optionally a glycine-glycine-glycine-glycine-serine (GGGGS: SEQ ID NO: 80) linker peptide.

42. The macromolecule of claim 1. further comprising a second antigen component that is different from the first antigen component.

43. The macromolecule of claim 42, wherein the second antigen component comprises one or more domains of MuSK different from those in the first antigen component.

44. The macromolecule of claim 43, wherein the first antigen component is linked to the N- or C -terminus of an Fc polypeptide and the second antigen component is linked to the C- or N-terminus, respectively, of the same Fc polypeptide.

45. The macromolecule of claim 43, wherein the second antigen component is linked to the N-or C-terminus of a different Fc polypeptide in an Fc heterodimer compared with the first antigen component.

46. The macromolecule according to any preceding claim, wherein the first or second antigen component comprises an Igl domain polypeptide comprising the sequence of SEQ ID NO: 4, SEQ ID NO:

5. SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO:

8. SEQ ID NO:

10. SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQID NO:

23. SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 28, SEQ ID NO: 29, SEQ ID NO: 30, SEQ ID NO: 31, SEQ ID NO: 32, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO:

35. SEQ ID NO:

36. SEQ ID NO:

37. SEQ ID NO: 38, SEQ ID NO: 39, SEQ ID NO: 40, SEQ ID NO: 41, SEQ ID NO: 42, SEQ ID NO: 43, SEQ ID NO: 44, SEQ ID NO: 45, SEQ ID NO: 46, SEQ ID NO: 47, SEQ ID NO: 51, SEQ ID NO: 52 or SEQ ID NO: 53.

47. The macromolecule according to any preceding claim, wherein the first or second antigen component comprises an Ig2 domain polypeptide comprising the sequence of SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO:

22. SEQ ID NO:

23. SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 28, SEQ ID NO: 29, SEQ ID NO: 30, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, SEQ ID NO: 36, SEQ ID NO: 37, SEQ ID NO: 38, SEQ ID NO: 41, SEQ ID NO: 42, SEQ ID NO: 43, SEQ ID NO: 44, SEQ ID NO: 45, SEQ ID NO: 46, SEQ ID NO: 48, SEQ ID NO: 51, SEQ ID NO: 52 or SEQ ID NO: 53.

48. The macromolecule according to any preceding claim, wherein the first or second antigen component comprises an Ig3 domain polypeptide comprising the sequence of SEQ ID NO: 7, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 28, SEQ ID NO: 30, SEQ ID NO: 35, SEQ ID NO: 36, SEQ ID NO: 37, SEQ ID NO: 38, SEQ ID NO: 43, SEQ ID NO: 44, SEQ ID NO: 45, SEQ ID NO: 46, SEQ ID NO:49, SEQ ID NO: 52 or SEQ ID NO: 53.

49. The macromolecule according to any preceding claim, wherein the first or second antigen component comprises an Fz domain polypeptide comprising the sequence of SEQ ID NO: 7, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 28, SEQ ID NO: 37, SEQ ID NO: 38, SEQ ID NO: 45, SEQ ID NO: 46, SEQ ID NO: 50 or SEQ ID NO: 53.

50. The macromolecule of claim 1, wherein the macromolecule comprises an amino acid sequence having at least 90% sequence identity to a sequence selected from the group consisting of SEQ ID NO: 1 through SEQ ID NO: 78.

51. A method of treating MuSK-associated myasthenia gravis in a subject, comprising:(a) administering to the subject an effective amount of the macromolecule of claim 1; and(b) monitoring the subject for a reduction in MuSK-specific antibodies,wherein the macromolecule removes at least 50% of circulating MuSK-specific antibodies within 24 hours of administration.

52. The method of claim 51, wherein the macromolecule is administered in an amount sufficient to remove at least 80% of the MuSK-specific antibodies from the circulation in the subject.

53. The method of claim 51, wherein the MuSK-specific antibodies are specific for the Igl, Ig2, Ig3 or Fz domain of MuSK.

54. The method of claim 52, wherein the MuSK-specific antibodies are specific for the Igl, Ig2, Ig3 or Fz domain of MuSK.

55. A method of treating MuSK-associated myasthenia gravis in a subject, comprising administering to the subject an effective amount of the macromolecule of claim 1 in combination with a therapy selected from the group consisting of plasmapheresis, intravenous immunoglobulin, a B-cell depleting antibody or a B-cell depleting CAR T cell.

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