Phenotypic and functional characterization of b-lineage cells associated with relapse and response to b-cell depletion therapy for rheumatoid arthritis

Background: Clinical response to therapeutic B-cell depletion by anti-CD20 antibody in rheumatoid arthritis (RA) is not associated with robust depletion of disease specific anti-citrullinated protein antibodies (ACPA). This suggests pathogenesis mediated predominantly by short-lived antibody secreting cells or an antibody independent role of B-cells or both in RA. The persistence of ACPA post B-cell depletion is consistent with secretion from long-lived plasma cells (PC) and could be linked to non-response to B-cell depletion. The aim of this thesis was to delineate populations of B-cells and plasma cells linked to RA disease activity. Results: Autoreactive citrullinated protein-specific B-cells were detected using ELISA from supernatants of B cell culture but not by flow cytometry or ELISpot. RA patients relapsing following B-cell depletion showed an increased proportion of a memory B-cell subset in the peripheral blood. The in vitro stage of B-cell differentiation closest to this relapse associated subset secreted multiple proinflammatory mediators. A novel mode of contact-dependent B-NK cell interaction was noted, likely to be due to EBV latency in B-cells or a novel mode of B-cell regulation by NK cells. CD19Neg PCs had a longer recovery time following depletion and had a longer life span in an in vitro PC differentiation model system but were generated early, which suggests that CD19 negativity is a marker for potential to be long-lived rather than PC age. Conclusions: Memory B-cell subset distribution is skewed during clinical relapse in RA which reflects on-going B-cell activity/differentiation generating inflammatory mediators or pathogenic short-lived antibody secreting cells which explains response to B-cell depletion or anti-TNF therapy. In those patients where B-cell depletion does not achieve clinical response, CD19Neg long-lived PCs may have a pathogenic role. Agents targeting certain stages of B-cell differentiation or long-lived PCs can be therapeutic options in carefully selected patients.