Whole genome CRISPR screening identifies molecular mechanisms of PD-L1 expression in Adult T-cell leukemia/lymphoma.

Adult T-cell leukemia/lymphoma (ATLL) is an aggressive T-cell malignancy with a poor prognosis and limited treatment options. Programmed cell death ligand 1(PD-L1) is recognized to be involved in the pathobiology of ATLL. However, what molecules control PD-L1 expression and whether genetic or pharmacological intervention might modify PD-L1 expression in ATLL cells is still unknown. In order to comprehend the regulatory mechanisms of PD-L1 expression in ATLL cells, we performed unbiased genome-wide clustered regularly interspaced short palindromic repeat (CRISPR) screening in this work. In ATLL cells, we discovered that the neddylation-associated genes NEDD8, NAE1, UBA3, and CUL3 negatively regulated PD-L1 expression while STAT3 positively did so in ATLL cells. We verified, in line with the genetic results, that treatment with the JAK1/2 inhibitor ruxolitinib or the neddylation pathway inhibitor pevonedistat resulted in a decrease in PD-L1 expression in ATLL cells or an increase in it. It is significant that these results held true regardless of whether ATLL cells had the PD-L1 3' structural variant, a known genetic anomaly that promotes PD-L1 overexpression in certain primary ATLL patients. Pevonedistat alone showed cytotoxicity for ATLL cells, but compared to each single modality, pevonedistat improved the cytotoxic effects of the anti-PD-L1 monoclonal antibody Avelumab and chimeric antigen receptor T-cells targeting PD-L1 in vitro. As a result, our work provided insight into a portion of the complex regulatory mechanisms governing PD-L1 expression in ATLL cells and demonstrated the in vitro preliminary preclinical efficacy of PD-L1-directed immunotherapies by using pevonedistat to upregulate PD-L1 in ATLL cells.