Gvhd Increases Apoptosis of CD8⁺, but Not CD4⁺, T Cells Expanded by Vaccines but Is Not Dependent on Fas Ligand

Abstract 2098

Donor lymphocyte infusions (DLIs) administered following allogeneic blood and marrow transplantation (alloBMT) can enhance T cell reconstitution through homeostatic peripheral expansion (HPE), but can also cause graft-versus-host-disease (GVHD). Vaccines are a strategy to skew T cells toward a “third-party” tumor antigen, but it is not clear if the effects of GVHD on vaccine-responding T cells is equivalent to the effects on alloantigen-reactive polyclonal T cells. Previous work by others has demonstrated “bystander” effects of GVHD causing activation-induced cell death through the Fas pathway on polyclonal T cells; however, the impact of GVHD on T cells expanded by a vaccine expressing a third-party nonalloantigen remains unclear. T cell depleted (TCD) minor histocompatibility antigen (mHA)-mismatched alloBMT (CD45.1⁺ B6 –> CD45.1⁺/CD45.2⁺ B6 × C3H.SW) was followed by a CD45.1⁺ B6 DLI on day +14 to induce GVHD. CD45.2⁺ B6 Rag2^-/- T cell receptor transgenic (TCRTg) CD4⁺ or CD8⁺ T cells specific for epitopes derived from the male histocompatibility antigen complex (HY) were administered on day +28 with an HY-expressing male dendritic cell vaccine to determine the impact of the allogeneic environment on the persistence, proliferation and survival of vaccine-responding T cells. Despite the fact that syngeneic and allogeneic recipients had similar degrees of lymphopenia, the absolute number of CD4⁺ and CD8⁺ TCRTg T cells was decreased 5 and 7 days respectively after adoptive transfer and vaccination in alloBMT recipients compared to syngeneic recipients (p < 0.05). To determine the mechanism of decreased persistence of the TCRTg T cells, proliferation was measured by assessing dilution of CFSE and apoptosis was measured by FACS analysis for Annexin V. Importantly, since both the CD4⁺ and CD8⁺ TCRTg T cells do not undergo HPE, all proliferation has to be antigen-driven. Neither CD4⁺ nor CD8⁺ TCRTg T cells proliferated in the absence of HY vaccine following alloBMT, confirming lack of bystander proliferation. Interestingly, both CD4⁺ (p < 0.01) and CD8⁺ (p < 0.05) TCRTg T cells undergo less vaccine-induced proliferation after alloBMT compared to syngeneic recipients. The amount of CD8⁺ TCRTg T cell apoptosis following vaccination was higher in allogeneic recipients (p < 0.05), but there was no difference in CD4⁺ TCRTg T cell apoptosis. Surprisingly, using a DLI from Fas ligand-deficient B6 (gld) donors on day +14 was sufficient to induce GVHD but did not prevent CD8⁺ TCRTg T cell apoptosis. Thus, diminished vaccine responses during GVHD appear to result in part from impaired CD8⁺ and CD4⁺ T cell vaccine-driven proliferation, but there is an additional contribution on CD8⁺ T cell apoptosis that is not dependent on recognition of alloantigen or the Fas-Fas ligand pathway.