Polysialic acid as an antigen for monoclonal antibody HIgM12 to treat multiple sclerosis and other neurodegenerative disorders

Abstract

CNS regeneration is a desirable goal for diseases of brain and spinal cord. Current therapeutic strategies for the treatment of multiple sclerosis (MS) aim to eliminate detrimental effects of the immune system, so far without reversing disability or affecting long-term prognosis in patients. Approachable molecular targets that stimulate CNS repair are not part of the clinical praxis or have not been identified yet. The purpose of this study was to identify the molecular target of the human monoclonal antibody HIgM12. HIgM12 reverses motor deficits in chronically demyelinated mice, a model of MS. Here we identified polysialic acid (PSA) attached to the Neural Cell Adhesion Molecule (NCAM) as the antigen for HIgM12 by using different NCAM knockout strains and through PSA removal from the NCAM protein core. Antibody binding to CNS tissue and primary cells, antibody-mediated cell adhesion and neurite outgrowth on HIgM12-coated nitrocellulose was detected only in the presence of PSA as assessed by Western blotting, immunoprecipitation, immunocytochemistry and histochemistry. We conclude that HIgM12 mediates it's in vivo and in vitro effects through binding to PSA and has the potential to be an effective therapy for MS and neurodegenerative diseases.

Antibody Binding Specificity for Kappa (Vκ) Light Chain-containing Human (IgM) Antibodies: Polysialic Acid (PSA) Attached to NCAM as a Case Study

“…This anti-PSA IgG antibody detects PSA on SynCAM and NCAM on different CNS cell types including microglial cells 41 . In contrast to the anti-PSA IgG antibody, human IgM antibodies HIgM12, HIgM42 and the anti-PSA mouse IgM (clone 2-2B) are unable to target PSA on SynCAM (but on NCAM) at various embryonic and early postnatal stages in mice, while non-polysialylated SynCAM is easily detectable 15 . The IgM antibodies used are also not able to detect PSA on microglial cells (Figures 3 + 4).…”

“…This protocol describes the identification of PSA-NCAM as the antigen for the regenerative human IgM antibody HIgM12, effective in animal models of MS and ALS [15][16][17][18] . The methodology used is principally applicable to all human antibodies with specific Vκ light chains VκI, VκIII and VκIV and mouse antibodies with VκI light chains, irrespective of the antibody's isotype.…”

“…Antibody HIgM12 was identified from patients with Waldenstrom's macroglobulinemia, stimulates neurite outgrowth in vitro [12][13][14] and targets polysialic acid (PSA) attached to the neural cell adhesion molecule (PSA-NCAM) 15,16 . The three major NCAM isoforms termed NCAM180, NCAM140, and NCAM120, are alternative splice variants of a primary transcript that vary only in their cytoplasmic domain.…”

Treatment with a recombinant human IgM that recognizes PSA-NCAM preserves brain pathology in MOG-induced experimental autoimmune encephalomyelitis

“…In contrast, rHIgM12 binds to neurons and protects against axonal injury in chronic TMEV murine model and ALS model [12]. The binding of this antibody to PSA-NCAM and gangliosides of glia and neurons results in neurite extension in vitro and neurite outgrowth [11].…”

“…A neuron-binding, recombinant human immunoglobulin M (rHIgM12), promotes neurite outgrowth and preserves motor deficits in a chronic inflammatory demyelinating murine model [11]. rHIgM12 binds to the surface of neurons, oligodendrocyte progenitors and a population of astrocytes by recognizing polysialic acid (PSA) attached to neural cell adhesion molecule (NCAM) and to gangliosides GD1a and GT1b [11,12].…”