Isolation of mitochondrial mutation-specific T cell receptors.

Neoantigen-specific T cells play a major role in cancer immunotherapy. Mutated proteins derived from non-synonymous mutations in tumor genomic DNA are the major source of neoantigens. It is conceivable that non-synonymous mutations found in tumor mitochondrial DNA (mtDNA) can also generate neoantigens that can be recognized by T cell receptors (TCRs). However, no tumor mitochondrial mutation-specific TCRs have been reported. As a proof-of-concept study, we obtained 3,798 non-synonymous single-nucleotide mutations across 38 tumor types through The Cancer Mitochondria Atlas project. These mutations were subjected to an epitope prediction algorithm to predict binding affinities for HLA-A*0201. The top 300 candidate peptides were synthesized and screened against 10 healthy donors with homozygous HLA-A*0201 alleles. Mutation-reactive T cells were subjected to single-cell sequencing to identify TCR sequences, followed by validations. Here, four MT-ND2 (A103T) mutation-specific TCRs were isolated from a donor. These TCRs interacted with HLA-A*0201-restricted IMMAMTMKL peptide. Additionally, through a single-cell sequencing approach, we demonstrated that a non-synonymous mutation, MT-CO1 (V274I), could be detected in nearly all tumor cells in a colorectal tumor specimen, whereas other mutations in 2 out of 4 tumors were detected in subclonal populations. This study suggests that isolating tumor mitochondrial mutation-specific TCRs is possible, but some biological barriers need to be considered.