Abstract 2138: Immune features of irAEs and aPD1 response in urothelial cancer patients of the RADIOHEAD study, as detected in blood by mass cytometry immune profiling
Authors: Healy Connor P. , Sweere Johanna M. , Liang Samantha I. , Sigal Natalia , Enrico Elizabeth , Cheng Li-Chun , Lucas Anastasia , Thompson Marshall A. , Da Silva Diane M. , Jarrell Justin A. , Srinivasan Ramji , Spitzer Matthew H. , Nguyen Ngan , Spencer Christine N. 
Published: April 2023

Abstract
Checkpoint immunotherapies (CPI) have resulted in long lasting clinical responses; however, CPI treatment comes with the risk of immune-related adverse events (irAEs). Previous reports have established a correlation between irAE occurrence and better CPI patient outcomes, yet these correlations and their underlying biological mechanisms are poorly understood. To better understand the immunological mechanisms behind the correlation of irAE presentation and response, we performed immune profiling on 40 urothelial carcinoma (UC) patients receiving aPD-1 as part of the RADIOHEAD study (Lucas et al. SITC 2022, abstract #1256). A 44-marker mass cytometry panel was used to profile pretreatment and early on-treatment PBMCs to capture cell subsets and functional states across innate and adaptive immune cells. We performed analysis on gated immune cell populations and through unsupervised clustering. Group comparisons were made by adjusted Kruskal-Wallis test, whereas survival correlates were assessed through univariate Cox regression analysis. For clinical outcome analyses, we defined responders as patients who had overall survival greater than 12 months (n=26) and noted 8 patients developed irAEs. Several immune features early on-treatment were associated with overall survival. KLRG1+ naive and HLA-DR+ CD38+ central memory CD8 T cells were negatively correlated with survival, whereas Treg and TIM-3+ classical monocytes were positively associated (HR= 2.6, 3.2, 0.4, 0.05; p=0.0002, 0.00005, 0.01,0.009 respectively). Next, we classified patients into the following groups: responders with irAE (R-irAE, n=5), responders without irAE (n=21), non-responders with irAE (n=3) and non-responders without irAE (n=10). We found that several immune features were unique to R-irAE patients early on aPD-1 treatment. R-irAE patients had up to 30% more CD74+ cDCs, up to 4-fold more TIM-3+ classical monocytes, and had a greater fold decrease in CD16+ NK cells from baseline compared to other patients (p&lt;0.005, 0.001,0.008 respectively). They also had up to 2-fold more Treg cells early on treatment, including a subset of activated Tregs marked by expression of CD38, CTLA-4, ICOS and TIGIT (p=0.05) which trended up to significance at pretreatment (p=0.075). In this study, we demonstrate that high-dimensional immune profiling by mass cytometry can detect novel blood-based biomarkers associated with clinical outcomes. Although CPI response and irAE incidence both require activation of a patient’s immune system, different mechanisms likely apply. Based on our findings, there are markers associated with responders broadly, as well as specific to R-irAE patients. We plan to validate these findings and identify additional markers and mechanisms of response and irAE with immune profiling on more RADIOHEAD indications.
Citation Format: Connor P. Healy, Johanna M. Sweere, Samantha I. Liang, Natalia Sigal, Elizabeth Enrico, Li-Chun Cheng, Anastasia Lucas, Marshall A. Thompson, Diane M. Da Silva, Justin A. Jarrell, Ramji Srinivasan, Matthew H. Spitzer, Ngan Nguyen, Christine N. Spencer. Immune features of irAEs and aPD1 response in urothelial cancer patients of the RADIOHEAD study, as detected in blood by mass cytometry immune profiling [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 2138.