Abscopal effects observed in cancer radiation therapy and oncolytic virotherapy: an overview

Immunoglobulin-mediated suppression of immune checkpoint pathways may lead to a considerable activation of host immune responses against malignancies. Substantial therapeutic benefits were reported among patients who participated in cancer immunotherapy clinical trials which utilized monoclonal antibodies against cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), programmed cell death protein 1 (PD-1) and programmed cell death 1 ligand 1 (PD-L1). In a subsequent stage, immune checkpoint inhibitors were used in various clinical trials in combination with other therapeutic agents, such as immunomodulatory factors, chemotherapeutics, oncolytic viruses and radiation therapy. Interestingly, local antitumor interventions based either on radiation therapy or oncolytic viruses resulted in systemic immune responses in a number of oncological patients. The elimination of untreated cancer tissues that may follow a localized therapeutic intervention was termed abscopal effect, which represents a major achievement in the field of cancer therapy.