Compositions and methods for treating infections of immune privileged organs comprising iga

Abstract

The inventions relates to Immunoglobulin A (IgA) or a pharmaceutical composition comprising IgA for use in the treatment of an infectious disease of or in an immune privileged organ, such as the eye, fetus, placenta, central nervous system (CNS) and / or testicles caused by a bacterial, fungal, viral or parasitic infection, in particular caused by bacteria of the human microbiome. IgA-coated pathogens can be addressed by FCAR+ and / or CD11c+ innate immune cells, for example by phagocytosis, or by activation of the complement system. The use of IgA or a pharmaceutical composition comprising IgA in immune privileged sites is advantageous because in contrast to IgG, IgA-coated pathogens do not trigger activation of C1q, a protein used for the controlled pruning of synapses. This prevents neuronal damage in said immune privileged organ(s), while at the same time allowing an antibody-mediated immune response in said organs.

Description

[0001] Compositions and methods for treating infections of immune privileged organs

[0002] Background of the invention

[0003] Certain sites of the mammalian body have immune privilege, meaning they are able to tolerate the introduction of antigens without eliciting an inflammatory immune response. Tissue grafts or allogeneic cells are normally recognized as foreign antigens by the body and attacked by the immune system. However, in immune privileged sites, tissue grafts can survive for extended periods of time without rejection occurring (HongS and Van Kaer L, 1999). immunologically privileged sites include, for example, the eyes, the placenta and fetus, the testicles, and the central nervous system.

[0004] immune privilege is thought to be an evolutionary adaptation to protect vital structures from the potentially damaging effects of an inflammatory immune response, inflammation in the brain or eye can lead to loss of organ function, while immune responses directed against a fetus can lead to miscarriage (Kent A., 2009).

[0005] The nature of isolation of immunologically privileged sites from the rest of the body’s immune system can cause them to become targets of autoimmune diseases or conditions, including sympathetic ophthalmia in the eye.

[0006] More seriously, the nature of isolation of immunologically privileged sites from the rest of the body’s immune system makes them also vulnerable to become targets of bacterial, viral or fungal infections or infections by parasites.

[0007] A a consequence the treatment of bacterial, viral, fungal or parasitic infections in immune-privileged organs such as the eye, the brain, the testicles or the fetus, in particular of bacterial eye infections such as endogenous endophthalmitis (infection of the inside of the eye by the body's own microbiome) is very difficult. Importantly, existing neuronal connections should not be destroyed during such treatment. Endophthalmitis is therefore treated by the systemic administration of antibiotics or antifungal agents. Nevertheless, patients often lose their sight even if treated.

[0008] The general concept of treating infectious diseases by administering antibodies directed against the causative pathogen is known in the art. WO2017 / 035154, which is entitled "MRKA polypeptides, antibodies and uses thereof", concerns antibodies and their medical use for treating syndromes associated with infections of Klebsiella pneumoniae, such as pyogenic liver abscesses (PL A), endophthalmitis, meningitis, and necrotizing meningitis.

[0009] However, the therapeutic outcome of classical antibody therapies in immune privilegedsites is unsatisfactory. For example, many patients lose their eyesight or die from encephalitis despite treatment. If patients still have eyesight after endophthalmitis or survive encephalitis, they often suffer irreversible damage, which is often caused by neuronal damage which occurred duringthe treatment.

[0010] Accordingly, there is a great need for new therapeutics for treating infections in immune privileged organs and tissues.

[0011] Summary of the invention

[0012] The present invention is based on a new insight into the mechanisms which provide immune protection of immuno-privileged sites against infections.

[0013] The inventions relates to Immunoglobulin A (IgA) or a pharmaceutical composition comprising IgA for use in the treatment of an infectious disease of or in an immune privileged organ, such as the eye, fetus, placenta, central nervous system (CNS) and / or testicles caused by a bacterial, fungal, viral or parasitic infection, in particular caused by bacteria of the human microbiome. IgA-coated pathogens can be attacked by FCAR+ and / or CD11 c+ innate immune cells, for example by phagocytosis, or by activation of the complement system. The use of IgA or a pharmaceutical composition comprising IgA in immune privileged sites is advantageous because in contrast to IgG, IgA-coated pathogens do not trigger activation of C1q, a protein used for the controlled pruning of synapses in neuron-rich immune privileged sites, such as the eye or the brain. This prevents neuronal damage in said immune privileged organ(s), while at the same time allowing an antibody-mediated immune response in said organs.

[0014] Briefly, it is suggested that local populations of IgA-producing B-cells protect immune privileged sites, in particular from infections by pathogens from the microbiome, by providing a local environment at the interface of the immune privileged site where soluble IgA, in particular against the pathogens from the microbiome, is present. Pathogens which cross this IgA-rich environment are then coated with IgA. If such IgA-coated pathogens then penetrate into the immune privileged site, IgA-dependent immune effector mechanisms, such as FCAR+ myeloid cells within the immune privileged site and / or IgA-dependent complement activation by the non-classical and / or lectin-pathway, assure that the infection is controlled by the immune system. This IgA-dependent protection mechanism for immune privileged sites has an important advantage over an IgG-based protection mechanism: in contrast to IgG, the classical, C1 Q-dependent pathway of complement activation is not engaged by IgA. This means that the complement system can be activated for the control of infection, such as in particular bacterial infection, without activation of C1 Q and thus without running the risk of undesired synapse pruning. This is because C1Q is a key mediator of controlled synapse pruning, and its activation in neuron-rich immune privileged sites, such as the eye or the brain, could lead to negative effects.Accordingly, it has been found that the administration of IgA to a subject, that is suffering from an infection of or in an immune privileged organ, contributes to the activation of innate immune cells, such as FCAR-expressing innate immune cells, at the site that is infected with pathogens, and initiates phagocytosis of said pathogens.

[0015] The technical problem to be solved by the invention is therefore the provision of therapies for the treatment of infection of or in an immune privileged organ, which treatment has the mentioned advantageous properties.

[0016] To solve this problem, the invention provides immunoglobulin A (IgA) or a pharmaceutical composition comprising IgA for use in methods of treating infectious diseases, of or in an immune privileged organ.

[0017] Said immune privileged organ is e.g. selected from the eye, fetus, placenta, central nervous system (CNS), and testicle, preferably selected from the eye and the brain.

[0018] Said infectious disease is e.g. selected from endophthalmitis, encephalitis, and sepsis, such as early onset sepsis.

[0019] The infection to be treated can be a bacterial, viral, fungal and / or parasitic infection, in particular it is the treatment of a bacterial infection.

[0020] Figures

[0021] Figure 1 - shows maternal B-cells with an IgA-type B-cell-receptor from human placenta identified by fluorescence-activated cell sorting (FACS)

[0022] Shown are representative FACS plots of lymphoid cells isolated from an HLA- A-type mismatched human term placenta, showing the expression of IgA within the CD19+ Lineage- (CD3, CD56, CD14) B-cell populations. The first plot shows the gating to separate maternal and fetal cells based on their HLA- A-type mismatch. Forthe sample shown, the maternal and fetal cells are HLA- A2- and HLA-A3, respectively.

[0023] The later plots show that 10.3% of all maternal B cells are IgA-positive, whereas IgA-positive B cells are absent within the fetal B cell population. Figure 2 - shows FCAR-positive myeloid cells from human placenta identified by FACS.

[0024] Shown are representative FACS plot showing the expression of CD89 within subsets of CD14+ lineage (CD3, CD56, CD19, CD66b) negative fetal myeloid cells, as defined by CD11c+ / -. Myeloid cells were isolated from HLA-A-type mismatched human term placentas, and maternal / fetal cells were separated based on the expression of HLA-A2 and / or HLA-A3. Bar graph shows the MFI (mean fluorescence intensity) of CD89 expression within the fetal CD14+CD11c± myeloid cell populations as analyzed by FACS (N=5). P-value was calculated by parametric unpaired t-test.

[0025] Figure3: shows that opsonization by IgA enhances phagocytic uptake of E. coli particles by placental CD11c+ CD89+ macrophages. (A) Phagocytosis of pHrodo E. coli BioParticles by CD11 c+ CD89+ macrophages from a human placenta, upon opsonization with varying concentrations of monomeric human serum IgA (pg / ml, as indicated). Data represented as Median Fluorescent Intensity (MFI) values normalized to non-opsonized E. coli control. Bars denote the median across biological replicates. (B) Quantification of the percentage of pHrodo E. coli positive cells within human placental CD11 c+ CD89+ macrophages upon phagocytosis of E. coli particles opsonized with 1500 pg / ml monomeric human serum IgA; ***, p < 0.001, paired t test. (C) Phagocytosis of pHrodo E. coli BioParticles opsonized with monomeric serum IgA (1500 pg / ml) by CD11c+ CD89+ macrophages from 3 human placentae. Top: representative plots. Bottom: fold change Median Fluorescent Intensity (MFI) quantification, normalized to non-opsonized E. coli control. Samples at 4°C and in the presence of cytochalasin D are shown as negative controls, as actin and energy metabolism are required for active phagocytosis.

[0026] Figure 4 - sows that PIGR, the polymeric immunoglobuline transporter, is not expressed in placenta.

[0027] Figure 5 - shows that FCAR(CD89)- expressing macrophages are also present in the trabecular meshwork of the eye

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[0056] Detailed description of the invention

[0057] Definitions

[0058] As used herein the term “immunoglobulin A” or “IgA” refersto the A isotype of antibodies. Immunoglobulin A is known to play a role in the immune function of mucous membranes, where it is predominantly present as a dimer of IgA, joined by a protein called J-Chain. In blood plasma IgA is predominantly monomeric. In human beings, IgA differs from other antibody isotypes, such as IgG, IgD, IgE or IgM, by having a different heavy chain.

[0059] The term “lgA1 ” denotes a subclass of IgA and is the predominant IgA subclass found in serum. Most lymphoid tissues show a predominance of lgA1 among IgA-producing cells. The heavy chain of lgA1 is, in humans, encoded by gene IGHA1.

[0060] The term “lgA2” denotes another subclass of IgA. In secretory lymphoid tissues (e.g., gut-associated lymphoid tissue, or GALT), the share of lgA2 production is larger than in the non-secretory lymphoid organs (e.g. spleen, peripheral lymph nodes). In lgA2, the heavy and light chains are not linked with disulfide, but with non-covalent bonds. The heavy chain of lgA2 is, in humans, encoded by gene IGHA2.

[0061] The term “serum IgA” refers to the form of IgA that is found in the blood serum. Serum IgA consists mainly of IgA in its monomeric form.

[0062] IgA can interact with an Fc receptor called FCAR (or CD89), which is expressed on immune effector cells and can initiate inflammatory reactions. Ligation of FCAR by IgA containing immune complexes causes antibody-dependent cell-mediated cytotoxicity(ADCC), degranulation of eosinophils and basophils, phagocytosis by monocytes, macrophages, and neutrophils, and triggering of respiratory burst activity by polymorphonuclear leukocytes.

[0063] The term “secretory IgA” or “slgA” refers to the form of IgA that is found in mucosal areas as a result of a cooperation between plasma cells that produce polymeric IgA (plgA), and mucosal epithelial cells that express polymeric immunoglobulin receptor (plgR). Polymeric IgA (mainly the secretory dimer) is produced by plasma cells, for example in the lamina propria adjacent to mucosal surfaces. slgA primarily acts by blockading epithelial receptors (e.g. by binding their ligands on pathogens), by sterically hindering attachment to epithelial cells, and by immune exclusion. slgA is the main immunoglobulin found in mucous secretions, including tears, saliva, sweat, colostrum and secretions from the genitourinary tract, gastrointestinal tract, prostate and respiratory epithelium. It is also found in small amounts in blood. The secretory component of slgA protects the immunoglobulin from being degraded by proteolytic enzymes; thus, slgA can survive in the harsh gastrointestinal tract environment and provide protection against microbes that multiply in body secretions.

[0064] The aforementioned lgA1 and lgA2 subclasses can be produced as a monomeric as well as a dimeric form.

[0065] The term "antibody" is used in the broadest sense and specifically covers intact monoclonal antibodies, polyclonal antibodies, multispecific antibodies (e.g. bispecific antibodies) formed from at least two intact antibodies, and antibody fragments so long as they exhibit the desired biological activity.

[0066] "Antibody fragments" comprise a portion of an intact antibody, generally the antigen binding or variable region of the intact antibody. Examples of antibody fragments include Fab, Fab', F(ab')2, and Fv fragments: diabodies; single-chain antibody molecules; and multispecific antibodies formed from antibody fragments.

[0067] The term "monoclonal antibody" as used herein refers to an antibody obtained from a population of substantially homogeneous antibodies, i.e. the individual antibodies comprisingthe population are identical except for possible naturally occurring mutations that may be present in minor amounts. Monoclonal antibodies are highly specific, being directed against a single antigenic site. Furthermore, in contrast to "polyclonal antibody" preparations which typically include different antibodies directed against different determinants (epitopes), each monoclonal antibody is directed against a single determinant on the antigen. In addition to their specificity, the monoclonal antibodies can frequently be advantageous in that they are synthesized by the hybridoma culture, uncontaminated by other immunoglobulins. The "monoclonal" indicates the character of the antibody as being obtained from a substantially homogeneous population of antibodies, and is not to be construed as requiring production of the antibody by anyparticular method. For example, the monoclonal antibodies to be used in accordance with the present invention may be made by the hybridoma method first described by Kohler et al., Nature, 256:495 (1975), or may be made by generally well-known recombinant DNA methods. The "monoclonal antibodies" may also be isolated from phage antibody libraries using the techniques described in Clackson et al., Nature, 352:624-628 (1991 ) and Marks et al., J. Mol. Biol., 222:581-597 (1991 ), for example. The monoclonal antibodies herein specifically include chimeric antibodies (immunoglobulins) in which a portion of the heavy and / or light chain is identical with or homologous to corresponding sequences in antibodies derived from a particular species or belonging to a particular antibody class or subclass, while the remainder of the chain(s) is identical with or homologous to corresponding sequences in antibodies derived from another species or belonging to another antibody class or subclass, as well as fragments of such antibodies, so long as they exhibit the desired biological activity. An "isolated" antibody is one which has been identified and separated and / or recovered from a component of its natural environment. Contaminant components of its natural environment are materials which would interfere with diagnostic or therapeutic uses for the antibody, and may include enzymes, hormones, and other proteinaceous or non-proteinaceous solutes. In preferred embodiments, the antibody will be purified (1) to greater than 95% by weight of antibody as determined by the Lowry method, and most preferably more than 99% by weight, (2) to a degree sufficient to obtain at least 15 residues of N-terminal or internal amino acid sequence by use of a spinning cup sequenator, or (3) to homogeneity by SDS-PAGE under reducing or nonreducing conditions using Coomassie blue or, preferably, silver stain. Isolated antibody includes the antibody in situ within recombinant cells since at least one component of the antibody's natural environment will not be present. Ordinarily, however, isolated antibody will be prepared by at least one purification step.

[0068] The receptor for the Fc fragment of IgA or “FCAR” as used herein is, in human beings, encoded by the gene FCAR. FCAR encodes the transmembrane receptor FcaRI, also known as “CD89” (Cluster of Differentiation 89). FcaRI binds the heavy-chain constant region of Immunoglobulin A (IgA) antibodies. FcaRI is, for example, present on the cell surface of myeloid lineage cells, including neutrophils, monocytes, macrophages, and eosinophils.

[0069] Likewise, a “FCAR-expressing cell” is a cell, for example of a myeloid lineage, including neutrophils, monocytes, macrophages, and eosinophils, which expresses FCAR on the cell surface.

[0070] “Recruitment” of cells, such as FCAR-expressing cells, to an infection site can be tested in a mouse model, for example a humanized mouse model, by extracting the cell mass from an infection site, separating the cells and analyzing, for example by FACS afterappropriate staining, the number of FCAR-expressing cells associated with the cell mass of the infection site. A treatment that is able to recruit said cells to the infection site (such as the administration of IgA according to the invention) will over time lead to a situation where these cells make up a higher percentage in terms of cell numbers of the analyzed cell mass from the infection site when compared to appropriate controls without said treatment.

[0071] The “complement component 1 q” (or simply “C1 q”) is a protein complex involved in the complement system, which is part of the innate immune system. C1 q together with C1 r and Cisforms theC1 complex. C1q itself is a complex, and the individual proteins of said complex, in human beings, are encoded by the genes C1QA, C1QB and C1QC. Antibodies of the adaptive immune system can bind antigen, forming an antigen-antibody complex. When C1q binds antigen-antibody complexes, the C1 complex becomes activated. Activation of the C1 complex initiates the classical complement pathway of the complement system.

[0072] C1 q is also involved in synapse pruning, for example in the brain.

[0073] The terms "phagocytic cells" and "phagocytes" are used interchangeably herein to refer to a cell that is capable of phagocytosis. There are different main categories of professional phagocytes: mononuclear phagocytes, comprising macrophages sensu strictu, monocytes and dendritic cells as well as polymorphonuclear leukocytes (neutrophils). However, there are also "non-professional" phagocytic cells known to participate in efferocytosis, efferocytosis being the process by which professional and nonprofessional phagocytes dispose of apoptotic cells in a rapid and efficient manner. Preferred according to the invention are FCAR-expressing phagocytic cells, such as FCAR-expressing myeloid cells, in particular FCAR-expressing macrophages.

[0074] The term “activation” as used herein relates to the phenomenon that external stimuli can induce changes to cell, thereby activating it. Macrophages, for example, can be activated by cytokines such as interferon-gamma (IFN-gamma) and bacterial endotoxins, such as lipopolysaccharide (LPS). Activated macrophages undergo many changes which allow them to kill invading bacteria or infected cells. They release toxic chemicals and proteins which have toxic effects on other cells. Activated macrophages have altered metabolism, increased levels of lysosomal proteins, and a greater ability to phagocytosis and kill microbes. Activated macrophages also release proteases, chemotatic factors for other leukocytes; reactive oxygen species such as nitric oxide and superoxide; cytokines such as tumor necrosis factor-alpha (TNF-alpha), interleukin one and eight (IL-1 and IL-8), eicosanoids, as well as growth factors. These products of activated macrophages can result in the kind of tissue destruction which is a hallmark of inflammation. Preferred according to the invention is the activation of the phagocytotic activity of FCAR-expressing cells, such as FCAR-expressing myeloid cells, in particular FCAR-expressing macrophages.“CD11 c”, also known as Integrin, alpha X (complement component 3 receptor 4 subunit) (ITGAX), is an integrin alpha X chain protein. Integrins are heterodimeric integral membrane proteins composed of an alpha chain and a beta chain. This protein plays a role in the adherence of neutrophils and monocytes to stimulated endothelium cells, and in the phagocytosis of complement coated particles. CD11 c is a type I transmembrane protein found at high levels on most human dendritic cells, but also on monocytes, macrophages, neutrophils, and some B cells that induces cellular activation and helps trigger neutrophil respiratory burst; expressed in hairy cell leukemias, acute nonlymphocytic leukemias, and some B-cell chronic lymphocytic leukemias.

[0075] The ’’innate immune system” or nonspecific immune system is one of the two main immunity strategies (the other being the adaptive immune system) in vertebrates. The innate immune system is an alternate defense strategy and is the dominant immune system response found in plants, fungi, prokaryotes, and invertebrates The major functions of the innate immune system are to:

[0076] • recruit immune cells to infection sites by producing chemical factors, including chemical mediators called cytokines

[0077] • activate the complement cascade to identify bacteria, activate cells, and promote clearance of antibody complexes or dead cells

[0078] • identify and remove foreign substances present in organs, tissues, blood and lymph, by specialized white blood cells

[0079] • activate the adaptive immune system through antigen presentation

[0080] • act as a physical and chemical barrier to infectious agents; via physical measures such as skin and mucus, and chemical measures such as clottingfactors and host defense peptides.

[0081] “Innate immune cells” as used herein refer to cells that are part of the innate immune system. “Innate immune cells” according to invention are preferably "phagocytic cells" as defined hereinabove, more preferably FCAR-expressing phagocytic cells, such as FCAR-expressing myeloid cells, in particular FCAR-expressing macrophages.

[0082] As used herein, the term "subject" denotes a mammal, preferably a human being.

[0083] In the context of the invention, the term "treating" or "treatment", as used herein, means reversing, alleviating, inhibiting the progress of, or preventing the disease or condition to which such term applies, or one or more symptoms of such disease or condition.

[0084] The term “ex-vivo” as used herein means outside of a living body.

[0085] The term “in-vitro” as used herein means outside of a living body and within a laboratory environment. For example, cells which are cultured “in-vitro” are cultured in controlled, and often artificial, culture media.As used herein „allogeneic“ is a term referring to human material, such as human cells or human protein compositions, that are not derived from the individual which is to be treated. For example, an allogeneic stem cell transplant is different from an autologous stem cell transplant, which uses stem cells from the patient's own body.

[0086] As used herein „autologous“ is a term referring to human material, such as human cells or human protein compositions derived from an individual's own cells. For example, in autologous blood transfusions, the patient's own blood is collected and reinfused into the body.

[0087] “Antibody opsonization” as generally defined is a process by which a pathogen is marked for phagocytosis through coating of a target cell with antibodies. Immunoglobulins participate in molecular tagging of pathogens which display antigens recognized by their specific paratope. The binding of antibodies enhances pathogen identification and recruitment of immune effector cells, ultimately accelerating microbial clearance through phagocytic destruction or antibody-dependent cellular cytotoxicity.

[0088] “Opsonization” as specifically used herein relates to marking of pathogens and other particles as part of the late-stage adaptive immune response, by immunoglobulin antibodies, such as IgA. These antibodies can interact with Fc receptors, such as FCAR, on myeloid cells, such as macrophages and neutrophils resulting in phagocytosis.

[0089] “Endophthalmitis” or endophthalmia, is an inflammation of the interior cavity of the eye, usually caused by an infection. It is a possible complication of all intraocular surgeries, particularly cataract surgery, and can result in loss of vision or loss of the eye itself. Infection can be caused by bacteria or fungi, and is classified as “exogenous endophthalmitis” (infection introduced by direct inoculation as in surgery or penetrating trauma), or “endogenous endophthalmitis” (organisms carried by blood vessels to the eye from another site of infection) and is more common in people who have an immunocompromised state.

[0090] “Encephalitis” is inflammation of the brain. The severity can be variable with symptoms including reduction or alteration in consciousness, headache, fever, confusion, a stiff neck, and vomiting. Complications may include seizures, hallucinations, trouble speaking, memory problems, and problems with hearing. Causes of encephalitis include viruses such as herpes simplex virus and rabies virus as well as bacteria, fungi, or parasites. Risk factors include a weak immune system. Diagnosis is typically based on symptoms and supported by blood tests, medical imaging, and analysis of cerebrospinal fluid.

[0091] “Sepsis” is a potentially life-threatening condition that arises when the body's response to infection causes injury to its own tissues and organs. Sepsis is caused by many organisms including bacteria, viruses and fungi. Common locations for the primaryinfection include the lungs, brain, urinary tract, skin, and abdominal organs. Risk factors include being very young or old, a weakened immune system from conditions such as cancer or diabetes, major trauma, and burns.

[0092] “Early onset sepsis” or “neonatal sepsis” refers in common clinical usage to a bacterial blood stream infection in the first month of life, typically an infection with fungi, viruses, or parasites. The leading causes of early onset sepsis are infections caused by Streptococcus agaiactiae or Escherichia coii.

[0093] As used herein, the term “pharmaceutically acceptable carrier” refers to a diluent, adjuvant, excipient, orvehicle with which plasma-derived IgA of the present invention can be administered. Such carriers can be sterile liquids, such as water and oils, including those of petroleum, animal, vegetable or synthetic origin, such as peanut oil, soybean oil, mineral oil, sesame oil and the like, polyethylene glycols, glycerin, propylene glycol or other synthetic solvents. Saline solutions and aqueous dextrose and glycerol solutions can also be employed as liquid carriers, particularly for injectable solutions. Non-limiting examples of suitable excipients include starch, glucose, lactose, sucrose, gelatin, silica gel, sodium stearate, glycerol monostearate, talc, sodium chloride, glycerol, propylene glycol, water, ethanol and the like. Excipients may also include wetting or emulsifying agents, or pH buffering agents such as acetates, citrates or phosphates; antibacterial agents such as benzyl alcohol or methyl parabens; antioxidants such as ascorbic acid or sodium bisulfite; chelating agents such as ethylenediaminetetraacetic acid; and agents for the adjustment of tonicity such as sodium chloride or dextrose.

[0094] The phrases "parenteral administration" and "administered parenterally" as used herein means modes of administration otherthan enteral and topical administration, usually by injection, and include epidermal, intravenous, intramuscular, intraarterial, intrathecal, intracapsular, intraorbital, intracardiac, intradermal, intraperitoneal, intratendinous, transtracheal, subcutaneous, subcuticular, intraarticular, subcapsular, subarachnoid, intraspinal, intracranial, intrathoracic, epidural and intrasternal injection and infusion. It is to be understood that this invention is not limited to the particular materials and methods described herein. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments and is not intended to limit the scope of the present invention, which will be limited only by the appended claims. As used herein, the singular forms "a", "an", and "the" include plural reference unless the context clearly indicates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The following references provide one of skill with a general definition of many of the terms used in this invention - unless defined otherwise herein - and ranked in increasing order of priority: Singleton et al., Dictionary of Microbiology and Molecular Biology (3rd ed. 2006); The Glossary of Genomics Terms (JAMA. 2013; 309(14):1533-1535), Janeway’s Immunobiology, 9thedition and “PracticalFlow Cytometry”, 4thedition by H.M. Shapiro.

[0095] All publications mentioned herein are cited for the purpose of describing and disclosing the cell lines, protocols, reagents and vectors which are reported in the publications and which might be used in connection with the invention. Nothing herein is to be construed as an admission that the invention is not entitled to antedate such disclosure by virtue of prior invention.

[0096] Detailed description

[0097] The human placenta is an example of an immune-privileged site. In a single cell dataset enriched for human immune cells it was noted that FCAR-expressing myeloid cells were present on the fetal side (i.e. within the immune privileged site), while IGHA1 -expressing B-cells were present on the maternal side (i.e. just outside of the immune privileged site). The presence of both cell types was then confirmed in FACS-experiments (see figures 1 and 2). In available online datasets this spatial arrangement of IgA-expressing B-cells and FCAR-expressing myeloid cells, was also found for other immune privileged organs, such as the brain and the eye.

[0098] It was then found, for example in example 3 (see also figure 3), discussed in detail below, that upon opsonization with varying amounts of human serum IgA, there was a concentration-dependent increase in phagocytic activity of placental CD11c+ CD89+ macrophages (Fig. 3A). At the highest concentration of 1.5 mg / ml IgA, a consistent increase in the proportion of placental CD11c+ CD89+ macrophages was found that could phagocytose the opsonized E. coli particles (Fig. 3B, 3C). The proportion of cells unable to phagocytose E. coli particles nearly halved upon opsonization with IgA (Fig.4B). Overall, these results indicate an enhanced bacterial clearance potential for placental CD11c+ CD89+ macrophages upon IgA-opsonization of the bacteria. This finding in combination with the spatial arrangement of IgA-expressing B-cells and FCAR-expressing myeloid cells which is found for several immune privileged sites, makes it plausible that the body uses IgA for protection of its immune privileged sites.

[0099] Accordingly, these data make it plausible that the administration of IgA to a subject, that is suffering from an infection of or in an immune privileged organ, contributes to the recruitment and activation of innate immune cells, such as FCAR-expressing innate immune cells to the site that is infected with pathogens, and initiates phagocytosis of said pathogens. Accordingly, the invention provides immunoglobulin A (IgA) or a pharmaceutical composition comprising IgA for use in methods of treating infectious diseases, of or in an immune privileged organ.

[0100] In some embodiments, said immune privileged organ is selected from the group consisting of the eye, fetus, placenta, central nervous system (CNS) and the testicles.In some embodiments, said immune privileged organ is the eye.

[0101] In some embodiments, said immune privileged organ is the fetus.

[0102] In some embodiments, said immune privileged organ is the placenta.

[0103] In some embodiments, said immune privileged organ is the central nervous system, and in particularthe brain.

[0104] In some embodiments, said immune privileged organ are the testicles.

[0105] In some embodiments said innate immune cells are "phagocytic cells" as defined hereinabove, more preferably FCAR-expressing phagocytic cells, such as FCAR-expressing myeloid cells, in particular FCAR-expressing macrophages.

[0106] In some embodiments said innate immune cells are "phagocytic cells" as defined hereinabove, that express FCAR and that additionally express CD11c, i.e. that are CD11c+ and FCAR+ phagocytic cells, such as CD11c+ and FCAR+ myeloid cells, in particular CD11 c+ and FCAR+ expressing macrophages.

[0107] It has also been found that there is a link between IgA-deficiency and the incidence of sepsis, in particular early onset sepsis. Accordingly, the invention provides immunoglobulin A (IgA) or a pharmaceutical composition comprising IgA for use in methods of treating sepsis, preferably early onset sepsis.

[0108] In some embodiments, said infectious disease is selected from the group consisting of endophthalmitis, encephalitis, and early onset sepsis, preferably endogenous endophthalmitis.

[0109] In some embodiments, said infectious disease is endophthalmitis.

[0110] In some embodiments, said infectious disease is encephalitis.

[0111] In some embodiments, said infectious disease is early onset sepsis.

[0112] In a preferred embodiment of the invention, said infectious disease is endophthalmitis. In a more preferred embodiment of the invention, said infectious disease is endogenous endophthalmitis.

[0113] In further embodiments, said infectious disease is selected from the group consisting of a bacterial, viral, fungal and / or parasitic infection.

[0114] In a preferred embodiment of the invention, said infectious disease is an infection with a microorganism of a mammalian microbiome, such as the human microbiome.In a preferred embodiment of the invention, said infectious disease is a bacterial infection, such as a bacterial infection with a bacterium of the human microbiome.

[0115] When said infectious disease is a bacterial infection, said bacterial infection may be an infection with at least one bacterium selected from the group consisting of Staphylococcus spec, such as Staphylococcus aureus, Staphylococcus saprophyticus, Staphylococcus lugdunensis, Staphylococcus schleiferi, Staphylococcus caprae or Staphylococcus epidermidis; Streptococcus spec, such as Streptococcus pneumoniae, Streptococcus pyogenes, Streptococcus agalactiae, Streptococcus dysgalactiae, Streptococcus gallolyticus, Streptococcus aginosus, Streptococcus suis, Streptococcus mitis or Streptococcus mutans; Klebsiella spec, such as Klebsiella pneumoniae, Klebsiella oxytoca or Klebsiella variicola, and Clostridium spec, such as Clostridium difficile or Clostridium botulinum.

[0116] Streptococcus agalactiae for example is the human pathogen causing more than half of the cases of early onset sepsis in term newborns (de Goffau, Lager et al. 2019, Stoll, Puopolo et al. 2020). It is interesting that clinical isolates of Streptococcus agalactiae are among the few bacterial pathogens expressing a protein that can bind to the Fc part of IgAs (Schalen 1993), the Cbeta protein Bac, and this binding blocks the interaction of human IgAs with the IgA Fc alpha receptor FCAR (Woof 2002). Streptococcus agalactiae also causes endogeneous endophthalmitis in adults (Yoshida, Yokokura et al. 2020, Ishikawa, Uchida et al. 2021) as well as neonatal (Tavares, Pinho et al. 2022) and adult meningitis (Oordt-Speets, Bolijn et al. 2018). Without wishing to be bound by theory, it might not be a coincidence that a pathogen with an efficient mechanism to evade IgA / FCAR based protection - by sequestering the Fc part of IgAs and thereby preventing its identification by FCAR-expressing immune effector cells - is prominent among infections of immune privileged sites.

[0117] Also Streptococcus pneumoniae is a prominent pathogen for endogeneous endophthalmitis (Chen, Chong et al. 2021) and meningitis (Koelman, Brouwer et al.

[0118] 2020). And like Streptococcus agalactiae it is equipped with a mechanism that interferes with the hosts IgA-mediated immune defense, namely its lgA1 protease (Chi, Rahkola et al. 2017). These observations in the literature also support the concept of a protective function of IgA for immune privileged sites.

[0119] In a preferred embodiment of the invention, said infectious disease is a fungal infection. When said infectious disease is a fungal infection, said fungal infection is an infection with at least one fungus selected from the group consisting of Candida spec, such as Candida albicans; or Fusarium spec, such as Fusarium solani, Fusarium oxysporum, Fusarium verticillioides, or Fusarium proliferatum, most preferably with Candida albicans.In a preferred embodiment of the invention, said infectious disease is a viral infection. When said infectious disease is a viral infection, said viral infection is an infection with a virus such as a Herpes virus, preferably the Herpes simplex virus.

[0120] In a preferred embodiment of the invention, said infectious disease is a parasitic infection.

[0121] When said infectious disease is a parasitic infection, said parasitic infection is an infection with at least one parasite selected from the group consisting of Toxoplasma gondii, and Toxocara spec, such as Toxocara canis, Toxocara cati, Toxocara leonina, Toxocara malayasiensis, or Toxocara vitulorum.

[0122] In some embodiments said IgA is a mammalian IgA selected from serum or secretory IgA.

[0123] In some embodiments said IgA is human IgA selected from serum or secretory IgA.

[0124] In some embodiments said IgA is human serum IgA.

[0125] In some embodiments said IgA is selected from monomeric IgA and polymeric IgA, such as dimeric IgA.

[0126] In some embodiments said IgA is dimeric IgA.

[0127] Preferably, said IgA is monomeric IgA.

[0128] Most preferably, said IgA is human monomeric serum IgA.

[0129] In some embodiments said IgA is selected from lgA1 or lgA2.

[0130] Preferably, said IgA is selected from monomeric lgA1 or lgA2.

[0131] Preferably, said IgA is monomeric lgA1.

[0132] More preferably, said IgA is human monomeric lgA1.

[0133] Most preferably, said IgA is human monomeric serum lgA1.

[0134] In some embodiments, said IgA is provided as monoclonal antibody or a fragment thereof. In some embodiments, said IgA is provided as isolated antibody.

[0135] In further embodiments said IgA for use comprises the administration of a pathogenspecific IgA to a mammalian subject, when the species of the infectious bacterium, fungus, virus or parasite is known.When the nature of an infectious agent, for example an infectious agent causing endogenous endophthalmitis, is not known, a mix of IgAs may be preferable. The invention therefore also relates to a pharmaceutical composition comprising a collection of at least 3 types of IgA with different binding specificities for use in human and / or in veterinary medicine, in particular for use in a method of treating an infectious disease, in particular an infectious disease of the CNS or the eye, or an infectious disease of the newborn baby, for example an infectious disease which manifests itself until day 10 after birth, such as early onset sepsis. For example, said collection of at least 3 types of IgA may be mammalian IgA obtainable from serum or secretory IgA, in particular wherein said IgA is obtainable from human serum IgA.

[0136] The reasoning behind such an approach, without wishing to be bound by theory, is as follows. For example, endogenous endophthalmitis is usually caused by commensal bacteria found in the gut. An individual's serum contains a cocktail of IgAs against these intestinal bacteria. Therefore, if the type of bacterium causing endophthalmitis is unknown, an IgA mix can be isolated from the patient's own blood (autologous approach), which is very likely to contain IgAs that are specific to the pathogen. Since many species of bacteria are common in the microbiome of people, also an IgA mixobtained from other people can be used (allogenic approach). This IgA mix can then be injected into the infected eye.

[0137] In some embodiments, the present invention therefore relates to the use of mammalian, such as human, IgA obtainable from serum for use in autologous or in allogeneic administration, such as for the treatment of an infection.

[0138] When said serum IgA is for use in allogenic administration, then said IgA is preferably pooled from at least 3 donors, such as from 3 to 5 donors, from 3 to 10 donors or the like. It has further been found that treatment of a subject that is suffering from an infectious disease in an immune privileged organ with IgA protects said immune privileged organ(s) against neuronal damage, e.g. by avoiding ectopically triggered C1q activation. Advantageously, the invention therefore provides immunoglobulin A (IgA) or a pharmaceutical composition comprising IgA for use in methods of treating infectious diseases, of or in an immune privileged organ, such as the eye, fetus, placenta, central nervous system (CNS) and testicles, wherein neuronal damage is prevented, i.e. wherein existing neurons in these immune privileged organs are protected against neuronal damage, preferably by avoiding ectopically triggered C1 q activation.

[0139] It has further been found that treatment of a subject that is suffering from an infectious disease in an immune privileged organ with IgA, leads to the recruitment and activation of FCAR-expressing innate immune cells to the infection site and the phagocytosis of the pathogens by said FCAR-expressing innate immune cells; or to activation of the complement system via the non-classical pathways. Accordingly, the invention providesimmunoglobulin A (IgA) or a pharmaceutical composition comprising IgA for use in methods of treating infectious diseases, of or in an immune privileged organ, such as the eye, fetus, placenta, central nervous system (CNS) and testicles, wherein FCAR-expressing innate immune cells are recruited to and activated at the infection site and phagocytosis of the pathogens is initiated; or wherein the complement system is activated via the non-classical pathways.

[0140] An embodiment of the present invention provides a composition comprising, consisting essentially of, or consisting of IgA as described hereinabove and optionally one or more excipients in a pharmaceutical carrier and the use of said composition for treating infectious diseases in immune privileged organs as described hereinabove.

[0141] For the avoidance of doubt the aspects and embodiments for IgA and the uses thereof described hereinabove apply similarly to the composition comprising said IgA, which is preferably a pharmaceutical composition.

[0142] In further embodiments, the invention relates to the use of IgA or a composition comprising said IgA, for the preparation of a medicament for the treatment of infectious diseases of or on immune privileged organs, as described herein.

[0143] In further embodiments, the invention relates to a method of treating infectious diseases of or on immune privileged organs, said method comprising administering a therapeutically effective amount of IgA or a composition comprising said IgA as described herein, to a subject in need thereof.

[0144] Said IgA or said composition comprising said IgA is suitable for application in human or veterinary medicine, preferably in human medicine.

[0145] Preferably, the composition has at least 90% (w / v) of IgA purity, more preferably at least 95% of IgA purity. In a most preferred embodiment, the composition has a 95% (w / v) of IgA purity.

[0146] The actual dosage levels of the IgA in the pharmaceutical composition of the present invention may be varied so as to obtain an amount of said IgA which is effective to achieve the desired therapeutic response for a particular patient, composition, and mode of administration. The selected dosage level will depend upon a variety of pharmacokinetic factors, the route of administration, the time of administration, the rate of excretion of the IgA being employed, the duration of the treatment, other drugs, compounds and / or materials used in combination with the particular compositions employed, the age, sex, weight, condition, general health and prior medical history of the patient being treated, and like factors well known in the medical arts.

[0147] The dose to be administered of the composition is preferably from 75 mg IgA / kg body weight to 1 g IgA / kg body weight, more preferably from 75 mg IgA / kg body weight to 600mg IgA / kg body weight and, most preferably, from 75 mg IgA / kg body weight to 300 mg IgA / kg body weight. In addition, the composition is preferably provided or administered at least once a week or every other day or thrice weekly or on a daily basis.

[0148] In further embodiments, an exemplary, non-limiting range for a therapeutically effective amount of the IgA of the present invention is about 0.1 -10 mg IgA / kg body weight, such as about 0.1-5 mg IgA / kg body weight, for example about 0.1-2 mg IgA / kg body weight, such as about 0.1-1 mg IgA / kg body weight, for instance about 0.15, about 0.2, about 0.5, about 1 , about 1.5 or about 2 mg IgA / kg body weight

[0149] The pharmaceutical composition may be administered by any suitable route and mode. Suitable routes of administering an IgA of the present invention in vivo and in vitro are well known in the art and may be selected by those of ordinary skill in the art.

[0150] In one embodiment, a pharmaceutical composition of the present invention is administered parenterally.

[0151] In one embodiment that pharmaceutical composition is administered by intravenous or subcutaneous injection or infusion.

[0152] The mode of administration is advantageously adapted to the infection to be treated. For example, in the case of endophthalmitis, a preferred mode of administration is intraocular injection. In the case of an infection of the CNS, a preferred mode of administration is an intracranial or an intracerebral injection. In the case of early-onset sepsis of a newborn, a preferred mode of administration is intravenous injection.

[0153] In some embodiments, said IgA can be recombinant, plasma-derived, cell culture-derived, transgenic or chemically synthesized.

[0154] If said IgA is recombinant, it can be obtained according to any technique known in the field of expression, production and purification of proteins. For example, IgA nucleic acid sequence can be inserted in any vector suitable for expression in the elected host cell, e.g. bacteria (Escherichia coii, Bacillus subtilis, Salmonella typhimurium, Pseudomonas spec., Streptomyces spec, and Staphylococcus spec.), yeast (Saccharomyces spec., Pichia spec, or Kluyveromyces spec.), insect cells (Bombyx mori, Mamestra brassicae, Spodoptera frugiperda, Trichoplusia ni or Drosophila melanogaster) or mammalian cells (HeLa cells, baby hamster kidney (BHK) cells, monkey kidney cells (COS-1), human hepatocellular carcinoma cells (e.g., Hep G2), human adenovirus transformed 293 cells, mouse L-929 cells, HaK hamster cell lines, murine 3T3 cells derived from Swiss, Balb-c or NIH mice, CV-1 cell line, cell strains derived from in vitro culture of primary tissue or primary explants.

[0155] Cell culture-derived IgA can be produced through any method or procedure known in the state of the art, for example, the hybridoma method.Transgenic and chemically synthesized IgA can be produced through any method or procedure known in the state of the art.

[0156] In a preferred embodiment, said IgA is serum-derived IgA, isolated from a suitable fraction of blood, with methods that are known in the art.

[0157] According to particular embodiments, it is contemplated that the composition comprising IgA is administered alone.

[0158] In another embodiment, the composition comprising IgA is administered together with one or more other compositions or molecules. Said other compositions or molecules are preferably selected from anti-inflammatory molecules, antibiotics (for example, small molecule antibiotics, molecules that are antimicrobial in nature, natural or synthetic peptide antimicrobials and / or proteins with antimicrobial properties), other immunomodulators or combinations thereof. Suitable other compositions or molecules are vancomycin, meropenem, lactoferrin or combinations thereof. The administration of the composition comprising IgA together with one or more other compositions or molecules as mentioned above includes the administration at the same time of all the compositions or molecules or the administration one after the other of the compositions or molecules to be provided.

[0159] Examples

[0160] Example 1 : Single cell data

[0161] A preparation of cells from term placenta was prepared for single cell RNAseq, as described in detail in WO2023094436A1 , which is herein incorporated by reference. The cells were enriched for cells of the adaptive and innate immune system. Within the scRNAseq dataset, FCAR-expressing myeloid cells and IGHA1 -expressing B-cells could be identified.

[0162] Example 2: IgA-expressing B-cells within the placenta

[0163] A preparation of cells from term placenta was prepared for FACS. The cells were enriched for cells of the adaptive and innate immune system, as described in Example 3. Within this cell population, FCAR-expressing myeloid cells (figure 2) and IGHA1 -expressing B-cells (figure 1) could be identified.

[0164] Example 3: Examination of the role of IgA on bacterial phagocytosis Experimental description

[0165] To examinethe role of IgA on bacterial phagocytosis, there was performed a phagocytosis assay with pH-sensitive pHrodo-labelled E. coli particles. Upon opsonization with varying amounts of human serum IgA, there was a concentration-dependent increase inphagocytic activity of placental CD11c+ CD89+ macrophages (Fig. 3A). At the highest concentration of 1.5 mg / ml IgA, a consistent increase in the proportion of placental CD11 c+ CD89+ macrophages was found that could phagocytose the opsonized E. coli particles (Fig. 3B, 3C). The proportion of cells unable to phagocytose E. coli particles nearly halved upon opsonization with IgA (Fig. 3B). Overall, these results indicate an enhanced bacterial clearance potentialfor placental CD11 c+ CD89+ macrophages upon IgA-opsonization of the bacteria.

[0166] Materials and Methods

[0167] Isolation of placental B-cells

[0168] Term placentas were processed immediately after acquisition from Cesarean section deliveries. The decidua basalis was removed using scissors and forceps, and the villous tissue up to the chorionic membrane was collected in 50 ml tubes containing PBS. The tissue was minced with scissors and washed in PBS until the suspension was clear. The tissue was digested with 0.25% Trypsin-EDTA (Gibco, 25200072) supplemented with 0.1 mg / ml DNAse I (Sigma-Aldrich, DN25) at 37 °C with agitation for 10 mins. The digested sample was washed with wash media (RPMI-1640 [Gibco, 31870025] supplemented with 10% NCS [Gibco, 26010074] and 0.1 mg / ml DNAse I) over a cell dissociation sieve (Sigma-Aldrich, CD1 -1 KT) to stop the digestion. The undigested tissue was then washed with PBS and digested with 1 mg / ml Collagenase IV (Sigma-Aldrich, C5138) supplemented with 1 mg / ml DNAse I for 75 mins with agitation at 37 °C. The resulting cell suspension was washed with wash media and passed through the cell dissociation sieve. The digest was then serially passed through 100 pm and 70 pm filters. The filtered cell suspension was washed and resuspended in RPMI. The cells were layered onto a Percoll gradient (Sigma-Aldrich, GE17-0891 -01) in a 50 ml tube with the following layers: 70% Percoll with RPMI, 50% Percoll with PBS, 25% Percoll with RPMI and cell suspension, and 1 x PBS on top. The gradient was spun at 800 RCF (-2000 RPM) without break for 30 mins. The topmost cell layer was carefully removed using sterile transfer pipette, and the lymphoid cell layer between 50% and 70% Percoll was collected. These cells were washed with PBS, RBC-lysed (Morphisto, 12146.005), washed again with PBS, and resuspended in cold PBS. The isolated placental lymphoid cells were then blocked with human FcR blocking reagent (Miltenyi, 130-059-901) and proceeded immediately with FACS staining under cold conditions for analysis using a Cytek Aurora analyzer.

[0169] Isolation of placental myeloid cells

[0170] Term placentas were processed immediately after acquisition from Cesarean section deliveries. The decidua basalis was removed using scissors and forceps, and the villous tissue up to the chorionic membrane was collected in 50 ml tubes containing PBS. The tissue was minced with scissors and washed in PBS until the suspension was clear. The tissue was digested with 0.25% Trypsin-EDTA (Gibco, 25200072) supplemented with 0.1mg / ml DNAse I (Sigma-Aldrich, DN25) at 37 °C with agitation for 10 mins. The digested sample was washed with wash media (RPMI-1640 [Gibco, 31870025] supplemented with 10% NCS [Gibco, 26010074] and 0.1 mg / ml DNAse I) over a cell dissociation sieve (Sigma-Aldrich, CD1 -1 KT) to stop the digestion. The undigested tissue was then washed with PBS and digested with 1 mg / ml Collagenase IV (Sigma-Aldrich, C5138) supplemented with 1 mg / ml DNAse I for 75 mins with agitation at 37 °C. The resulting cell suspension was washed with wash media and passed through the cell dissociation sieve. The digest was then serially passed through 100 pm and 70 pm filters. The filtered cell suspension was washed and resuspended in RPMI. The cells were layered onto a Percoll gradient (Sigma-Aldrich, GE17-0891 -01) in a 50 ml tube with the following layers: 70% Percoll with RPMI, 50% Percoll with PBS, 25% Percoll with RPMI and cell suspension, and 1 x PBS on top. The gradient was spun at 800 RCF (-2000 RPM) without break for 30 mins. The topmost cell layer was carefully removed using sterile transfer pipette, and the myeloid cell layer between 25% and 50% Percoll was collected. These cells were washed with PBS, RBC-lysed (Morphisto, 12146.005), washed again with PBS, and resuspended in cold RPMI or PBS, depending on the experiment.

[0171] For FACS the isolated placental myeloid cells were blocked with human FcR blocking reagent (Miltenyi, 130-059-901) and proceeded immediately with FACS staining under cold conditions for analysis using a Cytek Aurora analyzer.

[0172] For the phagocytosis assay the isolated placental myeloid cells were then counted and resuspended in cold cell culture media (RPMI 1640 [Gibco, 31870025] supplemented with 2mM GlutaMAX [Thermo Scientific, 35050038] and 10% Fetal Bovine Serum [Gibco 10500064]) and immediately used for the phagocytosis assay.

[0173] Phagocytosis assay

[0174] A 1:50 dilution of 1 mg / ml pHrodo™ Deep Red E. coli BioParticles™ (Invitrogen, P35360) was used for phagocytosis assays with 180k placental myeloid cells in a final assay volume of 180 pl. Prior to phagocytosis, an equivalent amount of bacterial particles (e.g.: 3.6 pl bacterial particles for a final assay volume of 180 pl) were incubated with varying concentrations (as indicated) of human serum IgA (MP Biomedical, SKU: 0855906) in 70 pl 1 x PBS in a V-bottom 96-well plate for 30 minutes at room temperature (RT) in the dark for opsonization. Simultaneously, 180k placental myeloid cells were seeded in F-bottom 96-well plate in cell culture media (RPMI 1640 [Gibco, 31870025] supplemented with 2mM GlutaMAX [Thermo Scientific, 35050038] and 10% Fetal Bovine Serum [Gibco 10500064]) and incubated for 30 minutes at 37 ° C. Control cells were either treated with 10 pM Cytochalasin D at 37 ° C or incubated at 4 ° C for 30 minutes. After opsonization, bacterial particles were washed twice with cell culture media at 3200g for 5 mins at RT to remove excess unbound IgA. For phagocytosis, the opsonized bacterial particles were incubated with the seeded placental myeloid cells for 30 minutes at 37 °C (except for the 4 °C control). The 96-well assay plate was then transferred on ice and proceededimmediately with FACS staining under cold conditions for analysis using a Cytek Aurora analyzer.

[0175] DISCUSSION

[0176] Immune cells in the placenta were studied and maternal B-cells were found that express both IGHA1 and JCHAIN in the sc dataset described in WO2023094436A1 , which is herein incorporated by reference. Those maternal B-cells with an IgA-type B-cell-receptor could also be identified by FACS (Figure 1). Thus, it is suggested that the maternal / fetal interface in the placenta is lined by IgA-producing B-cells.

[0177] There were further identified FCAR-expressing fetal myeloid cells in the single-cell dataset, have confirmed the presence of FCAR-positive fetal myeloid cells in the term placenta by FACS (Figure 2). Said cells were isolated. The isolated FCAR-positive myeloid cells were tested, they phagocytosed bacteria in an FCAR-mediated manner and Phagocytosis was greatly increased by opsonization with IgA (Figure 3).

[0178] The fetal immune system does not contain IgA-producing plasma cells (Hayward 1983). Thus, any IgA for opsonization of bacteria entering the fetal side of the placenta is likely of maternal origin, and opsonization would happen on the maternal side of the maternal / fetal interface, since, in contrast to IgG, IgA is not actively transported from the mother to the fetus via FcRn (Roopenian and Akilesh 2007). Furthermore, the IgA binding polymeric immunoglobuline transporter PIGR is not expressed in placenta as indicate by available data from the Human Protein Atlas (Uhlen, Fagerberg et al. 2015) and shown in Figure 4.

[0179] Based on these findings, the invention suggests a model for how immune privileged organs, such as the fetus, the eye and the brain, are protected.

[0180] Commensal bacteria residing in the gut are the most likely candidates to contaminate the maternal blood stream and therefore need to be prevented from reaching other parts of the body, and in particular the fetus. IgA-producing B cells reside in the gut and secrete IgA specific for commensal bacteria into the lumen of the gut, coating the bacteria of the microbiome.

[0181] In order to access the fetus, an immune privileged site, bacteria would have to pass the placenta as the barrier tissue protecting the immune privileged site. They would meet a wall of local, soluble IgA, produced by local gut-trained IgA-producing plasma cells, which would coat them with IgA specific against commensal bacteria (Fitzpatrick, Frazer et al. 2020). If the so coated bacteria should then pass the placenta, they would be recognized by the CD89 / FCAR-expressing cells of the innate immune system in the fetus - macrophages, monocytes and neutrophils - which could eliminate them.This mechanism would allow the fetus, an example of an immune privileged site where soluble IgA is typically absent under homeostatic conditions (Sheth 1971, Hayward 1983), to harness the power and specificity of the adaptive immune systems indirectly -via FCAR, the corresponding Fc-receptor on the effector cells of the innate immune system.

[0182] This spatial arrangement of B-cells and myeloid cells in the placenta is similar to the situation in the brain, where gut-trained IgA producing plasma cells provide a firewall of IgA (Fitzpatrick, Frazer et al. 2020) and are located in the meningeal venous sinuses (Fitzpatrick, Frazer et al. 2020), another interface with an immune privileged site. It is interesting to note that microglia cells, the macrophages inside the brain parenchyme, are similar to the placenta-resident monocyte-derived cells in that they express significant levels of CD89 / FCAR (Galatro, Holtman et al. 2017, Ayana, Singh et al. 2018). Furthermore, there is evidence for a similar spatial arrangement of immune cells also in the eye. The presence of IgA in tears is well established (Allansmith 1973), and is produced by local B cells of the eye-associated lymphoid tissue (Knop, Knop et al. 2008). A search in the cell atlas of the human ocular anterior segment identified FCAR-expressing macrophages in the trabecular meshwork and thus clearly within the immune privileged part of the eye (Figure 5) (van Zyl, Yan et al. 2022).

[0183] Based on these findings a common concept for the immune privileged sites placenta, brain and eye is suggested: IgA-secreting B cells at the outside of the barrier towards the immune privileged site, and CD89 / FCAR expressing myeloid cells behind this barrier and / or within the immune privileged site that are capable of protecting these organs from a possible infection.

[0184] It is further suggested that there is also evidence for a second mechanisms that makes IgA particularly useful for the treatment of infectious disease in immune privileged sites, particularly the nervous system and the eyellnlike IgG and IgM, Human IgA activates IgA has been described as non-inflammatory (Russell, Sibley et al. 1997), yet it can activate the complement system(Roos, Bouwman et al. 2001 ), but it does so via the non-classical mannan-binding lectin pathway (Maillard, Wyatt et al. 2015) and not via he classical pathway involving C1q, as does IgM and IgG. It is suggested that it is this pathway specificity of IgA that makes it uniquely suitable for protecting the brain and the eye. This is because in both, eye and brain, C1 Q is used for synapse pruning (Stevens, Allen et al.

[0185] 2007), and activation of the classical C1 Q pathway is associated with neurodegenerative diseases in the brain (Hong, Beja-Glasser et al. 2016) and in the eye (Yednock, Fong et al.

[0186] 2022; Grover, Sankaranarayanan et al. 2023). It is therefore plausible that an immune response, which was triggered by lgG1 / C1Q complexes likely interferes with the proper control of C1 Q’s role in synapse pruning in the brain and eye. One reason for this might be C1Qs ability to activate other C1Qs in an intermolecular process (Reid 2018, Ugurlar, Howes et al. 2018). The benefit of avoiding ectopically triggered C1 Q activation has beenshown by the ability of C1 q-blocking antibodies to protect from the neuronal damage associated with sepsis-associated encephalopathy (Chung, Wickel et al. 2023), suggestingthat neuronal damage is not mainly driven by inflammation as such, but by the activation of C1Q resultingfrom the inflammatory response. The use of IgA instead of lgG1 should therefore help in minimizing potentially detrimental effects of an active pathogen control on neuronal plasticity in the central nervous system.

[0187] In summary, we suggest a mechanism for how gut-educated IgA-producing B-cells at the interface to immune privileged sites can protect the eye, the brain, the placenta, and by extension, the fetus. IgA is a non-essential, but effective element in these mechanisms. It does so by engaging at least two effector pathways: the specific IgA receptor FCAR and the non-classical pathways of complement activation.

Claims

Claims1. Immunoglobulin A (IgA) or a pharmaceutical composition comprising IgA for use in the treatment of an infectious disease of or in an immune privileged organ.

2. The IgA or the pharmaceutical composition for use according to claim 1 , wherein said immune privileged organ is selected from the eye, fetus, placenta, central nervous system (CNS) and testicle, preferably from the eye and central nervous system.

3. The IgA or the pharmaceutical composition for use according to claim 1 or 2, wherein the infectious disease is selected from endophthalmitis, encephalitis, sepsis such as early onset sepsis, preferably wherein the infectious disease is endogenous endophthalmitis.

4. The IgA or the pharmaceutical composition for use according to any one of the preceding claims, wherein said infectious disease is selected from bacterial, viral, fungal and / or parasitic infection, in particular wherein said infectious disease is a bacterial infection.

5. The IgA or the pharmaceutical composition for use according to any one of the preceding claims, wherein said infectious disease is caused by a microorganism of a mammalian microbiome, such as the human microbiome.

6. The IgA or the pharmaceutical composition for use according to any one of the preceding claims, wherein said infectious disease is an infection with at least one bacterium selected from the group consisting of Staphylococcus spec, such as Staphylococcus aureus, Staphylococcus saprophyticus, Staphylococcus lugdunensis, Staphylococcus schleiferi, Staphylococcus caprae or Staphylococcus epidermidis; Streptococcus spec, such as Streptococcus pneumoniae, Streptococcus pyogenes, Streptococcus agalactiae, Streptococcus dysgalactiae, Streptococcus gallolyticus, Streptococcus aginosus, Streptococcus suis, Streptococcus mitis or Streptococcus mutans; Klebsiella spec, such as Klebsiella pneumoniae, Klebsiella oxytoca or Klebsiella variicola, and Clostridium spec, such as Clostridium difficile or Clostridium botulinum;or wherein said infectious disease is an infection with at least one fungus selected from the group consisting of Candida spec, such as Candida albicans; and Fusarium spec, such as Fusarium solani, Fusarium oxysporum, Fusarium verticillioides, or Fusarium proliferatum;or wherein said infectious disease is a viral infection with a Herpes virus, such as the Herpes simplex virus,or wherein said infectious disease is a parasitic infection with at least one parasite selected from the group consisting of Toxoplasma gondii, and Toxocara spec, such as Toxocara canis, Toxocara cati, Toxocara leonina, Toxocara malayasiensis, or Toxocara vitulorum.

7. The pharmaceutical composition for use according to any one of the preceding claims, wherein said IgA is monomeric IgA.

8. The IgA or the pharmaceutical composition for use according to any one of the preceding claims, wherein said IgA is lgA1 or lgA2, preferably monomeric lgA1 or lgA2, most preferably monomeric lgA1.

9. A pharmaceutical composition comprising a collection of at least 3 types of IgA with different binding specificities for use in human and / or in veterinary medicine, in particular for the use according to any one of claims 1 to 8.

10. The pharmaceutical composition for use according to claim 9, wherein said collection of at least 3 types of IgA is mammalian IgA obtainable from serum or secretory IgA.

11. The pharmaceutical composition for use according to any one of claims 9 or 10, wherein said IgA is obtainable from human serum IgA.

12. The pharmaceutical composition for use according to any one of claims 9 to 11 for use in autologous or in allogeneic administration, wherein said IgA for use in allogeneic administration is pooled from at least 3 donors.

13. The IgA or the pharmaceutical composition for use according to any one of the preceding claims wherein said use comprises- when the identity of the disease-causing pathogen is known: the administration of a pathogen-specific IgA or a pharmaceutical composition comprising said pathogen-specific IgA according to any one of claims 1 to 8 to a mammalian subject;or- when the identity of the disease-causing pathogen is unknown: the administration of a pharmaceutical composition according to any one of claims 9 to 12 to a mammalian subject.

14. The IgA or the pharmaceutical composition for use according to any one of the preceding claims, wherein the administration of said IgA or pharmaceutical composition comprising said IgA leads to the recruitment of FCAR+ and / or CD11 c+ innate immune cells to the infection site and the phagocytosis of the pathogens bysaid FCAR+ and / or CD11 c+ innate immune cells.

15. The IgA or the pharmaceutical composition for use according to any one of the preceding claims, wherein the administration of said IgA or pharmaceutical composition comprising said IgA activates the complement system via the non- classical and / or the lectin-pathway, thereby preventing synapse pruning.

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