Abstract
The combination of immunotherapy and radiotherapy has demonstrated synergistic potential, especially when a combination of immune checkpoint inhibitors (ICIs) is administered. Cytotoxic T-Lymphocyte-Associated Protein-4 (CTLA-4) inhibitors and Programmed Death-Ligand 1 (PD-L1) inhibitors or Programmed Cell Death Protein 1 (PD-1) inhibitors have been assessed in both clinical and preclinical studies; the addition of radiotherapy activates immunomodulatory mechanisms materialized by an effect similar to "in situ" vaccination or the "abscopal" distant response of lesions outside the irradiation field. The new therapeutic targets (T cell immune-receptor with Ig and ITIM domains (TIGIT), Lymphocyte activating gene 3 (LAG-3), and T cell Ig- and mucin-domain-containing molecule-3 (TIM-3)) associated with traditional ICIs and radiotherapy open new perspectives to the concept of immuno-radiotherapy. The dynamic evaluation of T lymphocyte expression involved in the antitumor immune response, both in the tumor microenvironment (TME) and in the tumor itself, could have biomarker value in assessing the response to combination therapy with traditional and new ICIs in association with irradiation. Preclinical data justify the initiation of clinical trials in various tumor pathologies to explore this concept.