LAUSR

Previous research into B cell biomarkers of poor response to the anti-CD20 drug rituximab in autoimmune disease relates to insufficient B cell depletion. Expansion of memory B cell (MBC) subsets were also associated with poorer response. We investigated whether the relative expression of the target antigen CD20 on B cell subpopulations could also contribute to drug resistance. Peripheral blood samples from 6 rituximab naïve (RTX-N) patients with autoimmune rheumatic diseases (active systemic lupus erythematosus and rheumatoid arthritis), 6 patients previously treated with rituximab (RTX-T), and 6 healthy controls (HC) were obtained. B cell subpopulations were defined using the relative expression of IgD and CD27 using flow cytometry. Patients in the RTX-N group had significantly higher frequency of CD19+CD20- B cells (median=25.9% of total B cells, compared to 1.26% in HC), p = 0.0022. CD19+CD20-B cells were predominantly switched MBC (IgD-CD27+) and double negative (IgDCD27-) MBC cells. All patients in the RTX-T group (median 22 months post-rituximab) had detectable CD19+CD20- B cells (median=52.25% of total B cells), of which the majority were switched MBC (median=4.54%, range 0.23-74%) and DN B cells (median=53.5%, range 11.6-98.1%). Collectively, we noted that the frequency of CD19+CD20- B cells in peripheral circulation was higher in RTX-T>RTX-N>HC. Our preliminary results have identified greater frequency of CD19+CD20- population of B cells in peripheral blood of patients with autoimmune disease, particularly after treatment with rituximab, suggesting that they evade rituximab. These are predominantly of the switched MBC and DN B cell subpopulations. Given the potential of these cells to contribute to disease activity in autoimmune disease, alternative strategies targeting CD19 may help overcome rituximab resistance. Disclosure K. Shah: Grants/research support; Roche Glycart. C. Klein: Corporate appointments; Roche Glycart. Shareholder/stock ownership; Roche. G. Cambridge: None. D. Sen: None. M. Castelino: None. A. Akbar: None. D.A. Isenberg: None. M. Leandro: None. V.R. Reddy: Grants/research support; Roche Glycart, BRC UCLH.