B Cells and CD40/CD154 Interactions Are Required for CD8 T Cell Recovery Following Antibody-Mediated Lymphoablation.

Abstract

Antibody-meditaed lymphoablation is commonly used as an induction therapy in transplant patients. However, recipients eventually reconstitute their T cell repertoire, develop anti-donor immune responses and reject transplanted organ. The goal of this study was to investigate the requirements for T cell recovery following lymphoablation in a mouse model of heterotopic cardiac transplantation. We previously reported that memory CD4 T cells are less susceptible to depletion by murine antithymocyte globulin (mATG) than CD8 T cells. Additional CD4 T cell depletion impaired CD8 T cell recovery after mATG treatment in B6 recipients of BALB/c heart allografts (0.2% vs 3-5% of spleen CD8 T cells recovered by d. 10 posttransplant) and in non-transplanted B6 mice. Analogous findings were made in recipients treated with anti-CD8 ± anti-CD4 mAbs demonstrating that the requirement for CD4 cell help is a common feature of antibody-mediated lymphoablation. In addition, memory CD8 T cell reconstitution depended on CD4 T cell help in non-transplanted B6 mice and in B6 isograft recipients treated with mATG. Treatment with blocking anti-CD154 mAb plus mATG inhibited memory CD8 T cell recovery in B6 heart allograft recipients similar to the levels observed after CD4 T cell depletion. Conversely, agonistic anti-CD40 mAb restored expansion of memory CD8 T cells following mATG treatment of CD4 T cell depleted heart allograft recipients. To test whether B cells are required for CD8 T cell recovery, we used B6.huCD20tg mice. Treatment with anti-human CD20 mAb depleted >90% of peripheral B cells and markedly inhibited CD8 T cell expansion in huCD20tg recipients compared to B cell-sufficient mice. Next, B cells were isolated from mATG treated recipients with or without CD4 depletion. In the absence of CD4 T cells, B cells expressed lower levels of MHC class I, CD80, CD86, and TNFa suggesting that both cognate interactions and cytokines promote CD8 T cell expansion. Our results show that CD4 T cell help mediated through B cells and CD40/CD154 interactions drives CD8 T cell reconstitution following antibody-mediated depletion. These findings may be used to improve the efficiency of lymphoablation in sensitized transplant recipients.