Sculpting the tumour microenvironment by combining radiotherapy and ATR inhibition for curative-intent adjuvant immunotherapy

Results of combining radiotherapy/chemoradiotherapy and immune checkpoint blockade have been disappointing in patients with locally advanced head and neck squamous cell carcinoma (HNSCC). For such a potentially radiocurable disease, there remains an imperative to explore novel combination approaches. Here, we show that combining ATR inhibition with radiotherapy (ATRi/RT) increases the frequency of activated NKG2A/PD-1 double-positive T cells in animal models of HNSCC. Addition of dual anti-NKG2A/-PD-L1 blockade to ATRi/RT in the adjuvant, post-radiotherapy setting induces a robust antitumour response. Efficacy of the combination relies on CD40/CD40L costimulatory-mediated infiltration of activated/proliferative/memory CD8 and CD4 T cells with persistent or new T cell receptor (TCR) signalling, respectively. In this favourable therapeutic context, we reveal increased richness of the TCR repertoire and the emergence of numerous and large TCR clusters that share antigen specificity in response to combination therapy. Collectively, our data point towards promising combination approaches for future clinical testing in HNSCC.