Figure 2. The role of RT in induction of the antitumor immune response.

At baseline, both the tumor immune microenvironment and the poor antigenicity of the tumor allow it to escape immune recognition. Targeted RT can induce increased antigenic expression, release pro-inflammatory cytokines (e.g., CXCL16) that recruit immune cells, promote antigen cross-presentation (HMGB-1 via TLR4), and induce tumor expression of death receptors. Anti-CTLA4–targeted immunotherapy can enhance the adaptive immune component by promoting antigen cross-presentation and T cell activation. Used together, RT and immunotherapy may have synergistic effects and may shift the tumor immune system balance toward elimination.