Sharon Freshour is a PhD candidate in the Human and Statistical Genetics program at Washington University School of Medicine in St. Louis. She graduated from St. Edward’s University in 2016 with a B.S. in Mathematics. She is interested in utilizing next generation sequencing and bioinformatic analysis to understand the genomic landscape of cancer and how it relates to treatment response. Her current research topics include using whole genome sequencing to explore copy number alterations in childhood brain tumors and using single cell RNA sequencing to understand mechanisms of response to checkpoint inhibitor treatment in a mouse model of bladder cancer.
Sharon Freshour, Bryan Fisk, Timothy Chen, Haolin Shen, Matthew Mosior, Zachary Skidmore, Catrina Fronick, Jennifer Bolzenius, Obi Griffith, Vivek Arora, Malachi Griffith
Washington University School of Medicine, St. Louis, MO, United States
Bladder cancer is the tenth most common cancer worldwide, accounting for over 500,000 new cancer cases and 200,000 cancer-related deaths per year. In recent years, use of immune checkpoint blockade (ICB) treatments for bladder cancer has become more common and several PD-1/PD-L1 inhibitors have been approved by the FDA for treatment of bladder cancer. However, clinical trials of PD-1/PD-L1 monotherapy show response rates of only ~30%, indicating many patients are not receiving benefit from ICB treatments. Thus, a deeper understanding of ICB treatment response is needed to improve responses and identify patients who will benefit most from treatment. To explore mechanisms of response to combined PD-1/CTLA-4 ICB treatment in individual cell types, we generated scRNA-seq using a mouse model of invasive urothelial carcinoma with three conditions: untreated tumor, treated tumor, and tumor treated after CD4+ T cell depletion. After classifying tumor cells based on detection of somatic variants and assigning non-tumor cell types using SingleR, we performed differential expression analysis, overrepresentation analysis, and gene set enrichment analysis (GSEA) within each cell type. GSEA revealed that endothelial cells were enriched for upregulated IFN-g response genes when comparing treated cells to both untreated cells and cells treated after CD4+ T cell depletion. Functional analysis showed that knocking out IFNgR1 in endothelial cells inhibited treatment response. Together, these results indicated that IFN-g signaling in endothelial cells is a key mediator of ICB induced anti-tumor activity.