Immunotherapy of CT26 murine tumors is characterized by an oligoclonal response against the AH1 tumor rejection antigen

Abstract

The possibility to cure immunocompetent mice bearing murine CT26 colorectal tumors using cytokine-based therapeutics allows to study the tumor rejection process at a molecular level. Following treatment with L19-mIL12 or F8-mTNF, two antibody fusion proteins which preferentially concentrate a murine cytokine payload at the tumor site, CT26 tumors could be cured in a process that crucially relies on CD8+ T cells. In both settings, the AH1 peptide (derived from the gp70 envelop protein of murine leukemia virus) acted as the main tumor rejection antigen and ~50% of CD8+ T cells in the tumor mass are AH1-specific after therapy. In order to characterize the clonality of the T cell response after successful antibody-cytokine immunotherapy, we isolated CD8+ T cells from tumors and submitted them to T cell receptor (TCR) sequencing. As expected, different TCR sequences were found in different mice, as these molecules originate from a stochastic rearrangement process. CD8+ T cells featuring the ten most abundant TCR sequences represented more than 60% of total CD8+ T cell clones in the tumor mass, but less than 10% in the spleen. Looking at sorted CD8+ T cells from individual animals, AH1-specific TCRs were consistently found among the most abundant sequences. Collectively, these data suggest that the antitumor response driven by two different antibody-cytokine fusions proceeds through an oligoclonal expansion and activation of tumor-infiltrating CD8+ T cells.