Metronomic Radiotherapy Reverses Tumor Immune Desertification and Resistance to Immunotherapy

The development of approaches for inflaming cold tumors is critical for increasing response to immunotherapy (IMT) reliant upon the re-invigoration of T cells for tumor control. Here we report, in a pre-clinical advanced ID8 ovarian cancer model, that metronomic low-dose radiotherapy (LDRT; 1 Gy) promotes T-cell infiltration and enables responsiveness to treatment including low-dose cyclophosphamide (CP), and combinatorial IMT comprising immune checkpoint blockade (ICB) targeting PD-1 and CTLA-4, and anti-CD40 agonist antibody, for significant tumor control and survival. Responses to this radio-combinatorial immunotherapy (RACIM) relied upon re-programming of both innate and adaptive immunity. We further identified RACIM-induced intratumoral dendritic cell states with co-stimulatory capacity and expressing the stress ligand RAE1, as well as of polyfunctional NKG2D+TCF1-PD1+CD4+T cells. We further report major tumor regressions in a subset of advanced cancer patients for which cold tumors were treated with LDRT, CP, aspirin, and ICB (NCT03728179). Unbiased analyses of biopsies revealed T-cell infiltration, up-regulation of type I IFN, and Th1 signatures as well as down-regulation of M2 macrophage and epithelial to mesenchymal transition gene-signatures, and a more oligoclonal TCR repertoire after RACIM, in responding patients. Evaluation of the impact on immune cells of low dose whole abdominal radiotherapy in orthotopic ovarian cancer. In this experiments, mice were injected ID8 ovarian cancer cells (5 million). 21 days later mice were treated: 1) control/NT, cyclophophamide(CP)+ aPD1+aCTLA4+aCD40ag (IT), or CP + IT + low-dose Rx (1 gray each) 8 days later, a second round. 5 days later mice were sacrificed and tumors processed.