IL2/anti-IL2 complex combined with CTLA-4, but not PD-1, blockade rescues antitumor NK cell function by regulatory T-cell modulation.

High-dose IL2 immunotherapy can induce long-lasting cancer regression but is toxic and insufficiently efficacious. Improvements are obtained with IL2/anti-IL2 complexes (IL2Cx) which re-direct IL2 action to CD8+ T and NK cells. Here, we evaluated the efficacy of combining IL2Cx with blockade of inhibitory immune pathways. In an autochthonous lung adenocarcinoma model, we show that the IL2Cx/anti-PD-1 combination increases CD8+ T-cell infiltration of the lung and controls tumor growth. In the B16-OVA model, which is resistant to checkpoint inhibition, combination of IL2Cx with PD-1 or CTLA-4 pathway blockade reverses that resistance. Both combinations work by reinvigorating exhausted intratumoral CD8+ T cells and by increasing the breadth of tumor-specific T-cell responses. However, only the IL2Cx/anti-CTLA-4 combination is able to rescue NK cell antitumor function by modulating intratumoral regulatory T cells. Overall, association of IL2Cx with PD-1 or CTLA-4 pathway blockade acts by different cellular mechanisms, paving the way for the rational design of combinatorial antitumor therapies.