Myasthenia gravis (MG) is an autoimmune neuromuscular disorder caused by autoantibodies that disrupt components of neuromuscular junctions, such as the acetylcholine receptor (AChR, 90% of patients). Rituximab (RTX) is a B cell depleting agent used in the management of an increasingly wide range of autoimmune diseases; many AChR MG patients achieve remission after RTX but relapse following treatment cessation is common. The thymus is a known reservoir of B cells that can produce pathogenic anti-AChR antibodies and resection of the thymus has long been known to improve MG symptoms; however, many patients also fail to achieve complete remission after thymectomy. In both cases, we conclude that the failed depletion of B cells relevant to disease may be driving poor responses. Developing systemic immunotherapy to better target B cells that escape depletion is therefore of critical importance for effective MG treatment. Characterizing the features of B cells that re-emerge after RTX depletion in MG would further the development of more effective treatments for MG and lead to a deeper understanding of the immuno-pathophysiology behind the disorder. The overall goal of this project is to characterize the transcriptional features of disease-relevant B cells from patients who experienced poor outcomes from two randomized clinical trials on the use of rituximab and thymectomy for the treatment of AChR MG. Our laboratory recently developed a method called single cell tracing of adaptive immune repertoires (STAIR) that allows for the unbiased identification and transcriptional characterization of autoantigen-specific B cells that escape RTX depletion by combining high-depth bulk repertoire sequencing methods with single cell gene expression and repertoire analysis. For this proposal, I will apply this approach to investigate the single cell gene expression characteristics of B cells from the thymus that persist in the circulation of patients who underwent thymectomy (Goal 1), and the characteristics of B cells associated with poor clinical responses to RTX (Goal 2). We will test the hypothesis that B cells shared with the thymus will have a similar single cell transcriptional identity as those that fail to be depleted by RTX: we expect that they will be clonally expanded IgG-switched ASCs with specificity for autoantigen. This fellowship integrates a training plan that will include invaluable learning experiences in machine learning and the latest NGS technology This training plan will enhance the applicant's goal of becoming a physician scientist at the interface of clinical medicine and science.
Rituximab (RTX) is a B cell depleting therapy approved for the treatment of an increasing number of autoimmune disorders; however, we observed that a significant fraction of myasthenia gravis (MG) patients relapsed despite early remission with RTX, a phenomenon observed in the context of other RTX-treated autoimmune disorders as well. This proposal will investigate the mechanism of relapse after B cell depleting therapy in MG by using novel single-cell tracing of adaptive immune repertoire (STAIR) analysis to study samples from two completed randomized clinical trials (BeatMG, MGTX). This experience will also provide invaluable computational and experimental training and new learning for the applicant.
