Intracellular expression of a chimeric antigen reverses resistance to cancer immunotherapy

The interaction of frameshift mutation-derived cancer neoantigens and cancer immunotherapy remains unknown. We found that live cell adjuvant or cDNA transfection in the muscle, which express MHC-class I and class II-restricted non-self-peptides, generated broad-spectrum anti-tumor immunity. Such chimeric peptides did not need to be tumor-neoantigens, but must be in a single chain (complete T cell antigen: CTA). Long product of frameshift mutation frequently contained CTA and the colon cancer patients with the long frameshift products (>120 amino acids) showed a good prognosis. Mechanistically, live cell adjuvant expressing CTA strengthened crosstalk between dendritic cells and CD8+ T cells in a CD4+ T cells-dependent manner. This cross talk suppressed CD8+ T cell exhaustion and produced stem-cell like progenitor CD8+ T cells in vivo. Combination of the live cell adjuvant conversed unresponsive tumors to responsive to PD-1 blockade therapy. Together, our findings provide a new broad-spectrum cancer immunotherapy, and clarify the type of frameshift neoantigens controlling the efficacy.