Adoptive In Situ Vaccination with Cyclical Intermittent Stereotactic Body Radiotherapy (SBRT) and Immunotherapy – a Review and Proposed Strategy

Immunotherapy with stereotactic body radiotherapy (SBRT), low-dose antiangiogenics, immune adjuvants, nanomedicine, or other combinations will likely play a lead role in managing malignancies soon. Presently, its benefit extends to about 12% to 20% of patients, in the background of possible recurrence eventually and the toxicities, including in non-responders. Stereotactic body radiotherapy (SBRT) not only eliminates the indexed lesions, but recently, the evidence is accumulating about its systemic abscopal effects. It needs to be evolved to a dependable in situ therapeutic vaccine production and to activate short- and long-term memory immune lymphocytes. The in-situ immune cascade happens with the ability of SBRT to generate Tumor-specific neoantigens and neoepitopes, which enhance the activation of antigen-presenting cells, invoke and restore the competence of Tumor-infiltrating lymphocytes, resulting in cancer cell lysis. This cell lysis, in turn, can generate further neoantigens and epitopes, imparting a virtuous cycle that is the hallmark of effective vaccines. Additionally, SBRT can synergistically enhance the other in situ vaccination strategies, concurrent in vitro vaccines or nanomedicines, making it a primary tool for sensitizing even the “cold” tumors for immunotherapy. The present proposed hypotheses, primarily based on a preclinical literature review, focus on the critical aspects of the in-situ vaccination generation capability of SBRT when used in pulsed, cyclical, or intermittent endothelial-sparing single dose schedules along with immunotherapy and other supportive measures. This schedule is categorized as in situ vaccine dose (ISVD) radiotherapy (RT) (distinguishable from the standard therapeutic SBRT schedule) in metastatic cancer settings after standard /first-line therapies.