Intra-Tumoral Injection of Cytotoxic Chemotherapy-Treated Tumor Cells in Combination with Systemic Immune Checkpoint Blockade for Cancer Treatment

Although immune checkpoint blockade (ICB) has strong clinical benefit for treating some tumor types, it fails in others, indicating a need for additional modalities to enhance the ICB effect. Here, we identified one such modality by using DNA damage to create a live, injured tumor cell adjuvant. Using an optimized ex vivo co-culture system, we found that treating tumor cells with specific concentrations of etoposide, mitoxantrone, or doxorubicin markedly enhanced dendritic cell–mediated T cell activation. These immune-enhancing effects of DNA damage did not correlate with immunogenic cell death markers or with the extent of apoptosis or necroptosis; instead, these effects were mediated by live injured cells with activation of the DNA-PK, ATR, NF-κB, p38 MAPK, and RIPK1 signaling pathways. In mice, intra-tumoral injection of ex vivo etoposide–treated tumor cells in combination with systemic ICB (by anti-PD1 and anti-CTLA4 antibodies) increased the number of intra-tumoral CD103+ dendritic cells and circulating tumor-antigen–specific CD8+ T cells, decreased tumor growth, and improved survival. These effects were absent in Batf3−/− mice and in mice in which the DNA-damaging drug was injected directly into the tumor, due to DNA damage in the immune cells. The combination treatment induced complete tumor regression in a subset of mice that were then able to reject tumor re-challenge, indicating that the injured cell adjuvant treatment induced durable anti-tumor immunological memory. These results provide a strategy for enhancing the efficacy of immune checkpoint inhibition in tumor types that do not respond to this treatment modality by itself.