Translational frontiers and clinical opportunities of immunologically-fitted radiotherapy.

Ionising radiations can have a wide range of impacts on tumour-immune interactions, which are being studied with the greatest interest and at an accelerating pace by the medical community. Despite its undeniable immunostimulatory potential, it clearly appears that radiotherapy as it is prescribed and delivered nowadays often alters the host's immunity towards a suboptimal state. This may impair the full recovery of a sustained and efficient anti-tumour immunosurveillance post-treatment. An emerging concept is arising from this awareness and consists in re-considering the way of designing radiation treatment plannings, notably by taking into account the individualised risks of deleterious radio-induced immune alteration that can be deciphered from the planned beam trajectory through lymphocyte-rich organs. In this review, we critically appraise key aspects to consider while planning immunologically-fitted radiotherapy, including the challenges linked to the identification of new dose constraints to immune-rich structures. We also discuss how pharmacological immunomodulation could be advantageously used in combination with radiotherapy to compensate for the radio-induced loss, for example with (i) agonists of interleukin (IL)-2, IL-4, IL-7, IL-9, IL-15 or IL-21, similarly to G-CSF being used for the prophylaxis of severe chemo-induced neutropenia, or with (ii) myeloid-derived suppressive cells (MDSC) blockers.