Immunotherapy of CT26 murine tumors is characterized by an oligoclonal response of tissue-resident memory T cells against the AH1 rejection antigen.

Abstract

Mice bearing CT26 tumors can be cured by administration of L19-mIL12 or F8-mTNF, two antibody fusion proteins which selectively deliver their cytokine payload to the tumor. In both settings, cancer cures crucially depended on CD8+ T cells and the AH1 peptide (derived from the gp70 protein of the murine leukemia virus) acted as the main tumor-rejection antigen, with ∼50% of CD8+ T cells in the neoplastic mass being AH1-specific after therapy. In order to characterize the clonality of the Tcell response, its phenotype, and activation status, we isolated CD8+ T cells from tumors and secondary lymphoid organs and submitted them to Tcell receptor (TCR) and total mRNA sequencing. We found an extremely diverse repertoire of more than 40000 unique TCR sequences, but the ten most abundant TCRs accounted for >60% of CD8+ T-cell clones in the tumor. AH1-specific TCRs were consistently found among the most abundant sequences. AH1-specific T cells in the tumor had a tissue-resident memory phenotype. Treatment with L19-mIL12 led to overexpression of IL-12 receptor and of markers of cell activation and proliferation. These data suggest that the antitumor response driven by antibody-cytokine fusions proceeds through an oligoclonal expansion and activation of tumor-infiltrating CD8+ T cells.