Safe and Effective Adoptive T-Cell Receptor Transfer with a High Affinity Single Chain p53(264–272)-Specific TCR

Abstract 4226

Several studies have demonstrated the clinical efficacy of adoptive T cell therapy for targeting cancer. Using HLA-A2.1 transgenic mice, we have demonstrated the feasibility of T-cell receptor (TCR) gene transfer into T cells to circumvent self-tolerance to the widely expressed human p53(264–272) tumor-associated antigen and developed approaches to generate high-affinity CD8-independent TCR. A safety concern of TCR gene transfer is the pairing of endogenous and introduced TCR chains resulting in the potential generation of self-reactive T cells (off-target autoimmunity). Several strategies to favor matched TCR chains pairing and thus enhancing TCR cell surface expression, including optimization of TCR encoding nucleotide sequences, introduction of an additional inter-chain disulfide bond between the TCR α and β chain constant domains, coexpression of both TCR α and β encoding-genes using self-cleaving 2A virus peptide-based retroviral vectors have been applied. However, adoptive transfer of mouse T cells transduced with modified p53-specific TCRs into p53-deficient humanized (A2Kb) mice was inducing lethal autoimmunity due to the formation of self-reactive TCRs infiltrating vital organs, such as spleen, liver and bone marrow. Therefore, an optimized single chain (sc) p53-specific TCR was engineered to avoid the formation of mismatched TCR heterodimers. The safety and therapeutic efficiency of this approach were evaluated in humanized mouse models of adoptive T cell transfer and successfully demonstrated that optimized p53-specific scTCR-redirected T cells (i) do not induce OFF-target autoimmunity and (ii) mediate antitumor reactivity. Importantly, because the expression of p53 antigen on normal tissues raises the concern of potential on-target toxicity, we performed adoptive T cell transfer experiments in humanized mice expressing the Human p53 protein (Hupki mice) and did not observe any sign of TCR gene transfer-mediated GvHD in this model. In conclusion, these mouse studies suggest that the optimized p53(264–272)-specific scTCR could represent a safe and efficient approach for TCR-based gene therapy.