Elimination of alloantibody responses using chimeric HLA-II antibody receptor T cells

Abstract Introduction Anti-HLA antibodies (alloantibodies) pose challenges in the setting of organ or bone marrow transplantation. The presence of pre-existing alloantibodies, which may occur as a result of prior pregnancy, transfusion, or transplantation, can present a barrier to finding a compatible transplant donor, especially in highly-sensitized patients. Additionally, solid organ transplant recipients can form de novo donor-specific alloantibodies (DSAs) after transplantation and these may lead to allograft rejection. Current strategies aimed at eliminating pre-existing alloantibodies (desensitization) such as intravenous immunoglobulin (IVIG), plasmapheresis, rituximab, proteasome inhibitors, and imlifidase have demonstrated inconsistent efficacy or fail to produce sustained reductions in alloantibodies. Moreover, they target circulating antibodies or B cells without specificity, highlighting the need for therapies that can durably and selectively deplete HLA-specific B cells and, in turn, alloantibodies. To this end, T cell engineered to express Chimeric HLA Antibody Receptors (CHARs) have demonstrated efficacy in targeting specific anti-HLA class I-producing B cell clones. However, alloantibodies to HLA class II molecules represent a significant unaddressed challenge. Here, we developed a targeted therapy for anti-HLA class II desensitization by generating T cells expressing class II CHARs (CHAR-II). Methods and Results We expressed the extracellular domains of HLA-DQ or -DR molecules coupled with the 4-1BBζ/CD3ζ domains into human T cells and evaluated them in vitro. Receptor structure optimization studies yielded CHAR-II T cells with high level and stable expression of CHARs. Optimized CHAR-II T cells were effectively activated by immobilized monoclonal antibodies targeting the specific HLA-II molecules and by B cell hybridomas expressing HLA-II-specific B cell receptors, as evidenced by the upregulation of T cell activation markers and cytokine secretion. Next, we assessed the cytotoxic potential of the CHAR-II T cells against B cell hybridomas and demonstrated dose-dependent, antigen-specific target cell lysis. To determine the potential of CHAR-II T cells to target clinically-relevant alloantibodies, we employed serum adsorption assays using sera from sensitized transplant candidates. CHAR-II T cells selectively depleted alloantibodies that were specific or cross-reactive to the HLA alleles expressed on the CHARs. Finally, we modeled targeting of patient's alloantibody-specific B cells in vitro and confirmed that CHAR-II T cells eliminate primary B cell clones, and HLA class-II alloantibodies, with high specificity. Conclusion Overall, our findings provide proof of concept for the use of the CHAR-II platform as an efficient and selective therapeutic strategy for desensitization or treatment of antibody-mediated rejection in the context of transplantation.