Abstract 1167: Prospective analysis of pretreatment circulating CD4 memory T cell features associated with severe immunotherapy toxicity

Abstract Introduction: Immune checkpoint inhibitors (ICIs) have revolutionized melanoma treatment, significantly improving outcomes. Nevertheless, too many melanoma patients undergoing ICI treatment experience severe and often debilitating immune-related adverse events (irAEs). In a retrospective melanoma cohort treated with ICIs, we previously found that elevated baseline levels of circulating CD4 effector memory T (TEM) cells were associated with the development of severe irAEs, irrespective of the affected organ system (Lozano et al. , Nature Medicine, 2022). Here, we present data from an extended prospective validation cohort from 47 patients across two academic medical centers. Methods: Of 47 patients, 26 received combination anti-PD1/anti-CTLA4 ICIs, 3 combination anti-PD1/anti-LAG3 ICIs, 17 anti-PD1 ICI, and 1 anti-CTLA4 ICI. Peripheral blood mononuclear cells (PBMCs) were prepared from pretreatment (Cycle 1 Day 1) blood samples obtained from all patients. We performed mass cytometry (CyTOF) on PBMCs using a 38-marker panel to deeply profile immune subsets. We further leveraged bulk RNA-seq from 24 patients to (i) deconvolve CD4 memory T cell abundance using CIBERSORTx and (ii) determine T cell receptor (TCR) diversity using Shannon entropy following MiXCR clonotype assembly. irAEs were graded on a 5-point scale using the Common Terminology Criteria for Adverse Events v5. Results: After treatment initiation, 14 patients experienced severe irAEs (grade 3+) at a median of 12. 1 weeks (range 4-54), including 4 with life-threatening (grade 4) irAEs. CyTOF revealed elevated circulating CD4 TEM cells in patients that developed severe irAEs (P0. 0001; AUC=0. 87), including those treated with combination ICIs (P=0. 0001; AUC=0. 89). We further observed a continuous relationship between increasing CD4 TEM levels and irAE grade (P=3e-6, Jonckheere-Terpstra test). We then combined CD4 memory T cell abundance and TCR diversity derived from bulk RNA-seq on 24 of these patients using logistic regression (trained on data from Lozano et al. ) to yield a composite model score. The pretreatment composite model score was strongly associated with severe irAE development (P=0. 0009, AUC=0. 88), and in a median split, identified patients with shorter time to severe irAE development (3 months vs. not reached; P=0. 006; HR=10. 5). Notably, composite model features and the overall score had no significant association with immunotherapy benefit. Conclusion: In this prospective study, both circulating CD4 TEM levels determined by CyTOF and a composite model score measured by RNA-seq were strongly associated with severe irAE development, independent of response status. These findings hold promise for future pretreatment risk stratification of ICI therapy. Citation Format: Abul Usmani, Noah Earland, Wubing Zhang, Peter K. Harris, Antonietta Bacchiocchi, Chloe M. Sachs, Aishwarya Nene, David Y. Chen, Mario Sznol, Ruth Halaban, Aaron M. Newman, Aadel A. Chaudhuri. Prospective analysis of pretreatment circulating CD4 memory T cell features associated with severe immunotherapy toxicity abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 1167.