Abstract 6670: Association between circulating CD4 memory T cell levels and severe immune-related adverse events in melanoma patients treated with immune checkpoint blockade
Authors: Usmani Abul , Earland Noah , Zhang Wubing , Harris Peter K. , Bacchiocchi Antonietta , Nene Aishwarya , Chen David Y. , Sznol Mario , Halaban Ruth , Newman Aaron M. , Chaudhuri Aadel A. 
Published: April 2023

Abstract
Introduction: Severe immune-related adverse events (irAEs) occur in up to 60% of melanoma patients treated with immune checkpoint inhibitors (ICIs), causing substantial treatment-related morbidity and in the most severe cases, death. There is no clinical assay to predict who will develop severe ICI-induced irAEs and who will not. Using single-cell profiling assays applied to a retrospective melanoma cohort treated with ICIs, we recently showed that higher baseline levels of circulating CD4 effector memory T (TEM) cells were associated with severe irAE development, independent of the affected organ system (Lozano et al. Nature Medicine, 2022). As part of a prospective validation study of 100 melanoma patients, here we report our initial findings on the first 24 patients accrued to date.
Methods: We prospectively collected pre-ICI blood from 24 metastatic melanoma patients from two academic medical centers from February 2021 onward. Peripheral blood was collected pre-treatment on the day of immunotherapy (cycle 1 day 1). We then isolated peripheral blood mononuclear cells (PBMCs) and applied mass cytometry by time of flight (CyTOF) to profile 38 leukocyte markers including markers specific to CD4 TEM cells. Cellular subpopulations were quantified using Cytobank v9. Patients underwent routine medical oncology follow-up during and after ICI treatment including grading of irAEs using the Common Terminology Criteria for Adverse Events v5.
Results: Median follow-up time after pre-ICI blood collection was 9.1 months (range 2.6-18.5). Fifteen (63%) patients received combination (anti-PD1/anti-CTLA4) ICIs while the remainder received anti-PD1 monotherapy. Eight patients developed severe (grade 3+) irAEs at a median of 8.5 weeks (range 4-21) after treatment initiation, including 4 who developed life-threatening (grade 4) irAEs. Severe and life-threatening irAE development spanned 9 separate organ systems, most commonly gastrointestinal, dermatological, and hepatic. Using CyTOF, we found that circulating CD4 TEM cells were more abundant in patients who developed severe irAEs compared to those who did not (P = 0.01; AUC = 0.81), irrespective of the involved organ systems. Moreover, median-splitting the patient cohort into two groups based on pretreatment CD4 TEM levels revealed that patients with low CD4 TEMs had significantly longer freedom from severe irAE than those with high CD4 TEMs (not reached vs. 4.6 months; P = 0.013; HR = 6.7). There was no significant difference in pretreatment CD4 TEM levels between patients with and without durable clinical benefit to ICIs (P = 0.75).
Conclusion: Circulating CD4 TEM levels measured by CyTOF were associated with severe irAE development, independent of response status, in patients with advanced melanoma. These findings could form the basis for pretreatment ICI risk stratification in the future.
Citation Format: Abul Usmani, Noah Earland, Wubing Zhang, Peter K. Harris, Antonietta Bacchiocchi, Aishwarya Nene, David Y. Chen, Mario Sznol, Ruth Halaban, Aaron M. Newman, Aadel A. Chaudhuri. Association between circulating CD4 memory T cell levels and severe immune-related adverse events in melanoma patients treated with immune checkpoint blockade [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 6670.