Echchannaoui et al. analyzed the safety prolife of a high-affinity, single-chain mouse TCR specific for the HLA-A2.1-restricted, non-mutated human p53(264-272). The p53scTCR was created by covalently linking the variable TCRα and TCRβ domains and co-expressing them with a truncated constant TCRα domain to prevent TCR mispairing. Adoptive transfer of p53scTCR T cells to HLA-A2+ mice that lacked murine p53 or expressed wild-type human p53 did not induce autoimmune toxicities. In humanized syngeneic and xenograft mouse models, treatment led to tumor elimination and formation of an antigen-specific memory response.
Genetic engineering of T cells with a T cell receptor (TCR) targeting tumor antigen is a promising strategy for cancer immunotherapy. Inefficient expression of the introduced TCR due to TCR mispairing may limit the efficacy and adversely affect the safety of TCR gene therapy. Here, we evaluated the safety and therapeutic efficiency of an optimized single-chain TCR (scTCR) specific for an HLA-A2.1-restricted (non-mutated) p53(264-272) peptide in adoptive T cell transfer (ACT) models using our unique transgenic mice expressing human p53 and HLA-A2.1 that closely mimic the human setting. Specifically, we showed that adoptive transfer of optimized scTCR-redirected T cells does not induce on-target and off-target autoimmunity. Furthermore, ACT resulted in full tumor protection and led to a long-lived effective, antigen-specific memory T cell response in syngeneic and xenograft models. Taken together, the study demonstrated that our scTCR specific for the broadly expressed tumor-associated antigen p53(264-272) can eradicate p53(+)A2.1(+) tumor cells without inducing off-target or self-directed toxicities in mouse models of ACT. These data strongly support the improved safety and therapeutic efficacy of high-affinity p53scTCR for TCR-based immunotherapy of p53-associated malignancies.