ESTRO 2024 - Abstract Book

S5190

Radiobiology - Immuno-radiobiology

ESTRO 2024

Results:

A total of 2834 original records were found of which 53 articles were included. The articles contained both patient studies and murine tumor models. Studies differed in cancer type or tumor model and treatment regimen. Despite these differences, it was found that neutrophil levels generally increase and reach maximal levels in the first few days after RT and remain elevated 2 weeks after RT. Treatment regimen seems to play an important role and hypofractionated RT resulted in a less immunosuppressive TME in some studies. Most studies describe the accumulation of immunosuppressive subsets of neutrophils. Furthermore, RT could upregulated Indoleamine 2,3 dioxygenase 1 and arginase 1 expression and neutrophil extracellular trap formation by neutrophils which all impair T cell anti-tumor immunity. However RT can also upregulate reactive oxygen species production by neutrophils which improved anti-tumor immunity. Most studies did report more immunosuppressive roles of neutrophils in the TME. Tumors with a more suppressive TME from the outset may convert neutrophils to a pro tumor phenotype. Furthermore, tumors already induce aberrant myelopoiesis and immune cell recruitment to the TME. RT induced inflammation may not be the direct cause, but a trigger which exacerbates immunosuppressive neutrophil recruitment to the TME. Multiple murine models do show improved RT efficacy when targeting immunosuppressive neutrophils, but this is not always the case.