LAUSR

Background: Immune checkpoint inhibitors (ICI) have proven to be game-changing treatments for mucosal head and neck squamous cell cancer (HNSCC). Emerging successes with anti-PD-1/PD-L1 therapy have led to durable responses and prolonged survival in both human papillomavirus-positive (HPV+) and negative (HPV-) patients. There is now a need for predictive biomarkers to guide patient selection for highly targeted ICI therapies as currently available diagnostic biomarkers have a limited value. The tumor microenvironment (TME) composition, contexture, and cellular architecture are now recognized as key to understanding immune responsive and resistant phenotypes. Here, we are using a spatial biology approach to explore the TME in metastatic/recurrent HNSCC tumors treated with Pembrolizumab/Nivolumab. Methods: In this study, we used single cell, multiomic spatial phenotyping utilizing the PhenoCycler-Fusion spatial biology platform to characterize the TME of HNSCC tumors from a cohort of n=40 patients. The discovery cohort consisted of patients who had complete vs. partial vs. stable vs. progressive responses to ICI therapy. We first analyzed tissues using an ultrahigh-plex antibody panel of >60 antibodies that label immune cell lineages, checkpoints, activation markers as well as tissue structure and the stroma. We then conducted whole-slide, single cell resolution RNA detection with complementary markers on serial sections from the same tissue blocks; the combination of these data allowed us to obtain multiomic spatial signatures that offered uniquely comprehensive insight into the TME of our tissue cohorts. Results: Our study identified highly resolved tissue immune contexture analysis and metabolic tissue signatures associated with resistance and sensitivity to immunotherapy. Most notably, multiomic profiling of HNSCC tumours provided deeper insights into ICI therapy resistance than the single omics based approaches alone. Conclusions: Our study demonstrates the power of unbiased, multiomic spatial phenotyping with whole-slide imaging to identify biomarkers associated with response to ICI therapy in HNSCC. Citation Format: HaYeun Ji, Niyati Jhaveri, Ning Ma, Bassem B. Cheikh, Aditya Pratapa, James Monkman, Ken O’Byrne, Brett Hughes, Arutha Kulasinghe, Oliver Braubach. Single cell, multiomic spatial phenotyping of immunotherapy responses in head and neck cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5647.