RANKL regulation of human B cell responses

PROJECT SUMMARY Improved understanding of B cell biology may uncover therapies that will restore immune tolerance in autoimmune disease with minimal safety risk. Tumor necrosis factor (TNF) superfamily members are key regulators of B cell biology, and blockade of several of these pathways has shown significant clinical benefit in autoimmunity with minimal infectious risk. For example, B cell activating factor (BAFF)-blockade provides benefit in lupus, a proliferation-inducing ligand (APRIL)-blockade provides benefit in IgA nephropathy, CD40L-blockade shows promise in Sjogren's disease, and all these therapies are well-tolerated. TNF superfamily member receptor activator of NF-κB (RANK), and its ligand RANKL, are highly expressed by memory B cell subsets. Human genetic variation in RANK is associated with the autoantibody-mediated disease myasthenia gravis. In mice, transient blockade of RANKL increases the quantity of antigen-specific vaccine titers. Yet, the impact of RANKL on human humoral immunity remains unknown. Understanding RANK-RANKL B cell control in humans may identify a new pathway to augment antibody responses to vaccination or dampen autoantibody responses in autoimmunity with limited safety risk. To address this gap in knowledge, I captured the in vivo human experiment by collecting plasma and peripheral blood mononuclear cells from individuals receiving denosumab, an FDA approved RANKL-blocking antibody commonly used in the treatment of osteoporosis, and matched controls following Covid-19 booster vaccination. I observed a significant increase in Covid-specific IgG responses, total IgG1, and autoantibody formation to numerous self-antigens in individuals receiving RANKL- blockade. As RANK signaling can induce FAS in osteoclasts and FAS expression in B cells is a critical negative regulator of T cell-dependent B cell responses, I hypothesize that blockade of RANKL broadly increases human B cell responses to vaccination and self-antigen by impairing B cell FAS-mediated apoptosis. This hypothesis will be tested through the following 3 aims: 1) Determine the impact of RANKL-blockade on humoral and cellular immunity to recent Covid and influenza vaccination versus remote tetanus vaccination, 2) Define the site of impaired B cell tolerance and the pattern of autoantibodies following RANKL-blockade, and 3) Test the impact of RANKL-blockade on FAS-mediated B cell survival in vitro and in vivo. Collectively, these studies will address the existing knowledge gap of RANKL control of human B cell responses and may provide the foundation to target RANK-RANKL to tune human humoral immunity.