562. Human T-Cells Modified as Antigen Presenting Cells Are Superior to Professional APC in Stimulating T-Cell Responses

Abstract

Adoptive transfer of T-cells expressing herpes simplex thymidine kinase (HSV-TK) induces an immune response against the transgene in HIV patients and in allogeneic stem cell transplant recipients' resulting in eradication of transferred cells. The elimination of transferred cells is mediated by HSV-TK-specific CD8+ T-cells. As a vigorous T-cell response to the modified T-cells has been detected in clinical trials we reason that genetically modified human T-cells may represent a novel class of antigen presenting cells for eliciting CD8+ T-cell responses. In the current study human T-cells are oncoretrovirally transduced with a model antigen, CMV tegument pp65 protein. The ability of these genetically modified cells to function as antigen presenting cells (T-cellAPC) was investigated. Both CD4+ and CD8+ T-cells genetically modified with CMV pp65 gene can stimulate CMV-specific T cells as determined by IFN-γ production of activated T-cells. Furthermore, the potential of T-cellAPC to induce and expand CMV pp65-specific CTLs was addressed and compared to CD40-B–mediated CTL expansion. Both CD40-B and T-cellAPC induced and expanded simultaneously antigen-specific CTLs in vitro to more than one epitope with different HLA restriction alleles from healthy CMV seropositive donors. After only one round of seven days in vitro stimulation with T-cellAPC, CMV pp65-restricted T-cells were expanded up to 97-fold as determined with tetramer staining. In contrast, CTL cultures stimulated with autologous CD40-BAPC expanded only up to 41-fold. The observed difference in expansion potential mediated either with T-cellAPC or CD40-BAPC could result in phenotypic functional differences in the Ag-specific CTL populations. To address this issue the expression of co stimulation and chemokine receptors on tetramer positive cells was determined. Despite differential expression profile of costimulatory ligands on T-cellAPC and CD40-BAPC, both expanded CTL populations are of effector/memory phenotype and efficiently kill CMV-infected fibroblasts. Thus, T-cells transduced with oncoretroviral vectors to express full-length antigens are potent APC and can potentially be utilized as a new vaccine strategy in vivo against viral pathogens and cancer.