Immune checkpoint therapy is an effective strategy to enhance the anti-tumor activity of T-cells and has led to significant and durable responses in a subset of cancer patients. Identification of the T-cell receptors and relevant cancer antigens that drive these positive anti-tumor responses are of great interest as they could then be developed into TCR-T cell therapy candidates, thus extending these anti-tumor benefits to patients that share the same tumor antigens.

Using a proprietary genome-wide screen termed ‘TargetScan’, we interrogated patient-derived TCRs that underwent clonal expansion in response to immune checkpoint therapy. In one screen in which ten expanded TCRs obtained from a Head and Neck cancer patient who exhibited substantial tumor reduction were evaluated, a cancer testis antigen, MAGEA1, was identified as a target. Deconvolution studies revealed that two distinct TCR clonotypes recognized the same novel C*07:02-restricted epitope, suggesting that a polyclonal response to MAGEA1 may have contributed to the tumor reduction of this patient. Engineered T-cells expressing each TCR exhibited significant activation, cytokine production and cytotoxicity against a panel of HLA-C*07:02-positive cancer cell lines expressing variable levels of MAGEA1.

To ensure these TCRs do not exhibit problematic off-target recognition, each TCR was individually screened against a genome-wide library comprising sequences from every protein in the entire human proteome, identifying TCR-41 as a suitable TCR for clinical development. Additional safety assessments revealed no allo-reactivity relative to a panel of 110 HLA-I molecules, and no discernable recognition of a diverse collection of C*07:02-positive primary normal cells. To further enhance the activity of T cells engineered with this TCR, a transposon-based vector was developed that delivers the TCR gene, along with the genes for CD8 and a dominant-negative form of TGFbR2, into both CD4+ and CD8+ T cells. This therapeutic candidate, term TSC-204-C07, has been advanced to IND-enabling studies to prepare for clinical testing. Overall, these results substantiate the approach of using TargetScan to identify relevant tumor antigens and TCRs from the expanded T cell repertoires of patients exhibiting exceptional responses to immune checkpoint blockade.

• By interrogating cancer patients who are responding to immune checkpoint blockade therapy, we successfully identified TCR and relevant antigens that drive positive clinical response. One such TCR is a high-affinity TCR against an HLA-C07:02 restricted MAGE-A1 epitope. This TCR demonstrates robust cancer cell killing, minimal off-target and allo-reactivity effects, and is under IND-enabling studies for future clinical testing.