A genome scale screen to identify regulators of PD-L1 in HNSCC

Abstract The immune checkpoint inhibitor Pembrolizumab was recently approved for the treatment of metastatic and recurrent HNSCC, but only 18% of patients in the initial trial responded to therapy, and it remains difficult to predict patients likely to experience benefit. We expect a broader understanding of checkpoint regulation in HNSCC to lead to improved response rates and identification of potential responders. To this end, we sought to identify targetable genetic factors modulating PD-L1, a molecule that serves to dampen the anti-tumor immune response. We developed a high throughput screen employing a Genome-scale CRISPR Knock-Out (GeCKO) library in HNSCC cell lines to identify targetable genes and pathways that may regulate PD-L1 expression. In UM-SCC-49, stable knockout pools with representation of approximately 300 gRNAs for each of over 20,000 target genes were expanded and serially sorted to create stable sub-populations with enhanced or diminished PD-L1 expression. These sub-populations were sequenced to identify gRNAs that increased or reduced PD-L1 expression, indicating that their genetic targets may function to regulate PD-L1. We observed 70% library coverage (44,900 gRNAs) in the initial population and 15% and 11% coverage in the sub-populations selected for high and low PD-L1 expression, respectively. We prioritized for validation 61 gRNAs that were enriched at least 2 fold in High or Low PDL1 pool over the control pool. Future experiments focus on validation of these targets in UM-SCC-49 and other cell lines. As we expand this screen and validate hits across multiple genetic backgrounds, we expect to reveal signaling networks promoting immune evasion and potential targets for combination immunotherapeutic protocols. Citation Format: Jacqueline Mann, Megan Ludwig, Aditi Kulkarni, Judy Kafelghazal, Julia Eisenberg, Rebecca Hoesli, Alexey Nesvizhskii, Chad Brenner. A genome scale screen to identify regulators of PD-L1 in HNSCC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3626.