Background

B cell depleting therapies are highly effective treatments for multiple sclerosis (MS). B cells are more numerous in active than inactive lesions, and their intrathecal clonal expansion and oligoclonal band production are hallmarks of MS. B cells also present antigens to T cells and secrete inflammatory cytokines. The antigenic specificity of individual B cells in cerebrospinal fluid (CSF) obtained from patients with early MS may help further clarify the role of B cells in MS biology.

Objectives

To determine the viral and autoantigen repertoire of CSF-derived, class-switched B cells from untreated, early MS patients.

Methods

We performed single cell immunoglobulin sequencing on CSF plasma cells, plasmablasts, and class switched memory B cells from 9 untreated patients: five with relapsing remitting MS (RRMS) and four with clinically isolated syndrome (CIS). The interval between the first attack and lumbar puncture ranged from 1 - 222 days (median 67 days). Brain and spinal cord MRIs performed concurrently with lumbar punctures revealed 5/9 patients with gadolinium enhancing lesions.

Using paired heavy and light chain immunoglobulin sequences, we generated 75 monoclonal antibodies (mAbs) and screened them on a suite of unbiased antigen discovery platforms: 1) mouse brain tissue staining, 2) whole human proteome programmable phage display, 3) pan-viral programmable phage display, 4) mouse and human brain immunoprecipitation mass spectrometry.

Results

The mAbs showed diverse antigen specificities. Candidate antigens were primarily ubiquitously expressed, intracellular proteins; however, a minority were macromolecules associated with the plasma membrane and/or enriched in brain tissue. Shared antigenic targets were occasionally identified within subjects but were rarely identified across subjects, with the latter including cytoskeletal proteins. For two mAbs, high-confidence antigens with prima facie relevance to MS were identified: 1) a white matter-restricted lipid species, and 2) an Epstein-Barr virus-interacting host protein.

Conclusions

Using our panel of 75 mAbs derived from plasma cells, plasmablasts, and class-switched memory B cells found in the CSF of early, untreated RRMS/CIS patients, we identified a diverse repertoire of antigenic targets, with a majority comprised of intracellular host proteins.