DRG2 is required for cell surface localization of PD-L1 in melanoma cells and optimum response to anti-PD-1 immune checkpoint blockade [bulk RNA-seq]

Tumors expressing high level of programmed cell death-1 (PD-1) ligand 1 (PD-L1) are more likely to respond to immune checkpoint blockers (ICBs) targeting PD-1 or PD-L1. However, more than half of tumor patients with high PD-L1 expression does not respond to ICBs and the underlying mechanisms are yet to be clarified. Here we show that depletion of developmentally regulated GTP-binding protein 2 (DRG2) inhibited recycling of endosomal PD-L1 and reduced surface PD-L1 level in melanoma cells. DRG2-depleted cells showed decreased binding with recombinant PD-1. Although DRG2-depleted cells expressed high levels of PD-L1, anti-PD-1 ICB did not activate T cells within DRG2-depleted tumors and failed to improve the survival of DRG2-depleted tumor-bearing mice. Cohort analysis of melanoma patients under anti-PD-1 treatment revealed that patients bearing tumors with high DRG2 protein level were more sensitive to PD-1 anti-PD-1 ICBs. These findings identify DRG2 as a regulator of recycling of endosomal PD-L1 and a key determinant for response to anti-PD-1 ICB and provide insights into how to increase the correlation between PD-L1 expression and response to ICB. We performed RNA-Seq on total RNA samples (RIN above 8.5) from B16F10-pLKO and B16F10-shDRG2 cells stimulated with 5 ng/ml recombinant mouse IFN-γ (PeproTech, 315-05) for 24 h.