Efficacies of anti-CD20 antibody and Atacicept are differentially impacted by B Cell Maturation Antigen in neuro-autoimmunity

Abstract

Abstract B cells have emerged as a therapeutic target for multiple sclerosis (MS). Depleting B cells with anti-CD20 antibodies are effective in treating MS. Yet, TACI-Ig treatment, which blocks BAFF and APRIL (two cytokines important for B cell development and function), paradoxically increased disease activity in MS patients. The stark differences in clinical outcomes with these therapies demonstrate that B cells have both inflammatory and regulatory effects in MS. B cell Maturation Antigen (BCMA), a receptor that binds BAFF and APRIL, plays a prominent role in B cell function. The role BCMA plays in MS remains enigmatic and therefore we explored the impact BCMA deficiency has on the development and progression of the experimental autoimmune encephalomyelitis (EAE), a rodent model of MS. We found that EAE induced with MOG35–55 was severe in BCMA−/− mice compared to BCMA+/+ mice. The increased disease was associated with increased CNS inflammation and a skewing of B-cells toward a mature/inflammatory phenotype. Also, for the first time, we observed that BCMA deficiency directly affects the infiltration of inflammatory myeloid cells during EAE. We found that anti-CD20 treatment significantly reduced EAE in BCMA−/− mice but had no effect on BCMA+/+ mice. Conversely, we found that TACI-Ig treatment had no effect on BCMA−/− mice but did reduce EAE in BCMA+/+ mice. Our study demonstrates that BAFF and APRIL constrain the development and function of inflammatory B-cells through BCMA. We further demonstrate that BCMA inhibits inflammatory B cell responses, yet promotes inflammatory responses in macrophages. Finally, our data provide clues into the paradoxical results of clinical trials with anti-CD20 and TACI-Ig in MS patients.