"Leveraging CAR T cells to Achieve Desensitization and Enable Transplantation"

Zheng Zhang, Caroline Markmann, Ming Yu, Susan Rostami, Wei Wang, Trini Ochoa, Kalpana Parvathaneni, Xiaoming Xu, John Scholler, Michael Milone, Ali Naji, David Allman and Vijay Bhoj

Alloantibodies against MHC present a major barrier to transplantation. Donor-specific alloantibodies preclude transplant due to the risk of hyperacute graft rejection. Highly-sensitized patients experience prolonged wait times and high mortality rates while awaiting a compatible organ. Current desensitization approaches are ineffective as they do not adequately deplete allo-specific B cells and plasma cells (PCs). We hypothesize that stringent depletion of these cells is required to eliminate pre-existing alloantibodies. We leverage the exquisite ability of CAR T cells to eliminate target cells to desensitize transplant candidates. 

We constructed CARs targeting mCD19 or mBCMA, which, together, are expressed across the entire B cell-PC developmental continuum. We evaluated the function of optimized CAR T cells against B cells and PCs in vitro using cytotoxicity assays. To construct a murine model of allo-sensitization, C57Bl/6 mice were sensitized with two serial BALB/c skin grafts.  After skin rejection, sensitized mice received total body irradiation followed by treatment with either control T cells, CART-19 T cells, or a combination of CART-19 and CART-BCMA T cells (combo-CART). Alloantibodies, total immunoglobulins, and B cells were measured over 13 weeks. Functional desensitization was then assessed by induction of diabetes using streptozotocin followed by Balb/c-derived islet cell transplant and blood glucose measurements to assess graft survival.

CD19- and BCMA-targeted CARs induced antigen-specific T cell responses and effectively depleted primary B cells and PCs in vitro and in vivo. Whereas control and CART-19 T cells were ineffective at desensitizing mice, combo-CART treatment resulted in significant decrease of alloantibodies. Islet cell grafts succumbed to hyperacute rejection in the 80% of control and CART-19 treated mice. However, combo-CART treatment resulted in prolonged graft survival in all mice (mean 35 days, range 16-60). Thus, CAR T cells targeting B cell and PC antigens represent a promising approach to desensitization and could enable life-saving transplantation.