Humoral response to Epstein-Barr virus in patients with multiple sclerosis treated with B cell depletion therapy

Background: B cell depletion therapy is highly effective in relapsing‐remitting multiple sclerosis (RRMS). However, the precise underlying mechanisms of action for its biological effects in MS have still not been clarified. Epstein‐Barr virus (EBV) is a known risk factor for MS and seems to be a prerequisite for disease development. EBV resides latently in the memory B cells, and may not only increase the risk of developing MS, but also contribute to disease activity and disability progression. Therefore, the effects of B cell depletion in MS could be associated with the depletion of EBV‐infected cells and the altered immune response to the virus. In this study, we investigate the impact of B cell depletion on the humoral immune response specific to EBV in patients with MS. Methods: Newly diagnosed, treatment‐naïve patients with RRMS were followed up to 18 months after initiation of B‐cell depletion therapy in the Overlord‐MS study, a phase III trial (NCT04578639). We analyzed serum sampled before treatment and after 3, 6, 12 and 18 months for immunoglobulin γ (IgG) against Epstein‐Barr nuclear antigen 1 (EBNA1) and Epstein‐Barr viral capsid antigen (VCA). We analyzed antibodies to cytomegalovirus (CMV) and total IgG in serum, as controls for viral and overall humoral immunity. The risk allele, HLA‐DRB1*15:01, and the protective allele, HLA‐A*02:01, were determined in all participants. In addition, polymerase chain reaction (PCR) for circulating EBV‐DNA was performed in the first 156 samples drawn. The associations between time on B cell‐depletion therapy and serum anti‐EBV antibody levels were estimated using linear mixed‐effects models. Results: A total of 290 serum samples from 99 patients were available for analysis. After 6, 12 and 18 months, the EBNA1 IgG levels decreased by 12.7 % (95 % CI ‐18.8 to ‐6.60, p < 0.001), 12.1 % (95 % CI ‐19.8 to ‐3.7, p = 0.006) and 14.6 % (95 % CI to ‐25.3 to ‐2.4, p = 0.02) respectively, compared to baseline level. Carriers of the HLA‐DRB1*15:01 allele had higher EBNA1 IgG levels at baseline (p = 0.02). The VCA IgG levels significantly increased by 13.7 % (95 % CI 9.4 to 18.1, p < 0.001) after 3 months, compared to baseline, and persisted at this level throughout the follow‐up. CMV IgG levels decreased, but to a lesser extent than the decrease of EBNA1 IgG, and total IgG levels decreased during therapy. Circulating EBV‐DNA was found in only three of 156 samples from 64 patients. Conclusions: EBNA1 IgG levels decreased, while VCA IgG levels increased, during B cell depletion therapy. This supports the hypothesis that the mechanism of action for B cell depletion therapy might be mediated by effects on EBV infection, which, in turn, mitigate immune cross‐reactivity and disease perpetuation.