T-cell receptor sequencing reveals selected donor-reactive CD8+ T cell clones resist antithymocyte globulin depletion after kidney transplantation

High frequencies of donor-reactive memory T cells in the periphery of transplant candidates prior to transplantation are linked to the development of post-transplant acute rejection episodes and to reduced allograft function. Rabbit anti-thymocyte globulin (rATG) effectively depletes naïve CD4+ and CD8+ T cells for > 6 months post-transplant, but rATG's effects on human donor-reactive T cells have not been carefully determined. To address this, we performed T cell receptor beta chain sequencing (TCRseq) on PBMC aliquots collected pre-transplant and serially post-transplant in seven kidney transplant recipients who received rATG as induction therapy. We tracked the evolution of the donor-reactive CD4+ and CD8+ T cell repertoires, identified stimulated pre-transplant, CTV-(surface dye)-labeled, PBMC from each patient with donor cells or third-party cells. Our analyses showed that while rATG depleted CD4+ T cells in all tested subjects, a subset of donor-reactive CD8+ T cells that were present at high frequencies pre-transplant, consistent with expanded memory cells, resisted rATG depletion, underwent post-transplant expansion and were functional. Together, our data support the conclusion that a subset of human memory CD8+ T cells specifically reactive to donor antigens expand in vivo despite induction therapy with rATG and thus have the potential to mediate allograft damage.