Potent Antitumor T-Cell Memory Is Generated by Curative Viral Oncolytic Immunotherapy But Not Curative Chemotherapy.

BACKGROUND: Late developing breast cancer metastases are common and lethal despite treatment with adjuvant chemotherapy at the time of primary tumor excision. Stimulation of an antitumor immune response is an alternative strategy for preventing this devastating development.

MATERIALS AND METHODS: A mouse model of the human epidermal growth factor receptor 2 (HER2/neu)-positive mammary cancer was used to compare the antitumor memory T-cell response following tumor cure by viral oncolytic immunotherapy, chemotherapy, surgical excision, or surgical excision plus virus infection. Memory T-cell response was assessed by functional in vivo assays.

RESULTS: Antitumor T-cell memory was generated most powerfully by curative viral oncolytic immunotherapy and poorly by curative chemotherapy. Cure by surgical excision generated an immune antitumor response which was increased by neo-adjuvant virus infection. CD4 memory T-cells were most potent.

CONCLUSION: Virus infection of tumor generates an antitumor memory immune response and chemotherapy suppresses this response. Clinical trials testing adjuvant immune stimulation instead of chemotherapy may be worth exploring because memory antitumor T-cells have the unique potential to find and eliminate small nests of metastatic cancer cells in sanctuary sites and prevent emergence of tumors from dormant cancer cells.