Editorial Volume 7, Issue 3 pp 144—145

Figure 1. Potential mechanism of action of combined radiotherapy and immunotherapy. Antigen presenting cells (APC) take up tumor antigens released from tumor cells destroyed by radiotherapy to activate CD8 T cells. The antitumor function of activated CD8 T cells (CTL) are suppressed by regulatory T cells (Treg), checkpoint molecules expressed by T cells (CTLA-4 and PD-1) and by tumor cells (PD-L1 /B7-H1). Immunotherapy with antibodies blocking the immune suppression function of Treg cells and checkpoint molecules restores the antitumor activity of CTLs capable of rejecting tumor cells that are not in the radiation field ( an abscopal effect).