Interrogating the interleukin-6 (IL-6)/IL-23/T-helper (Th)17 axis in immunotherapy toxicity: Mechanistic insights and therapeutic implications.

12134 Background: Immune checkpoint inhibitors (ICIs) have transformed cancer therapy, but grade ≥ 3 immune-related adverse events (irAEs) affect 60% of patients. The mechanisms driving irAEs remain poorly understood, hindering the development of strategies to mitigate toxicity without compromising efficacy. Methods: We analyzed biomarkers from an ongoing phase I/II trial (NCT04940299) evaluating tocilizumab (IL-6R blockade) in two regimens; 162 mg subcutaneously weekly (regular dose, RD) or bi-weekly (dose-dense, DD), combined with ipilimumab (3 mg/kg) and nivolumab (1 mg/kg) up to 12 weeks as front-line therapy for advanced melanoma. Longitudinal analyses of blood, tumor, and inflamed tissue biopsies were performed to identify biomarkers for risk stratification and to elucidate the immunobiology of irAEs and antitumor responses across four patient subgroups, categorized by tumor response and the presence or absence of grade ≥ 3 irAEs. Results: A total of 35 patients were treated with the triplet and followed for up to 15 months. By week 12 after treatment initiation, grade ≥ 3 irAEs occurred in 15 patients (43%), with similar frequencies in the RD (44%) and the DD (40%) cohorts. Within 90 days after last tocilizumab dose, the incidence of grade ≥ 3 irAEs increased to 56% in the RD cohort but remained unchanged in the DD cohort, resulting in an overall incidence of 51%. The best overall response rate (ORR) was 66%, with 64% in the RD cohort and 70% in the DD cohort. NanoString analysis of tumor biopsies identified 31 upregulated genes in patients with grade ≥ 3 irAEs compared to those without, including RORC, a key regulator of Th17 differentiation, which was significantly elevated in longitudinal biopsies (pre: n = 8; post: n = 6) of patients with high-grade irAEs. IL-17, IL-1, and TNF signaling pathways were significantly decreased after tocilizumab treatment in the subgroup of patients without the grade ≥ 3 irAEs (pre: n = 14, post: n = 9). LunaPhore-COMET analysis showed elevated Th17 and γδ T-cell subsets (CD4+ and CD8+) in inflamed tissues compared to matched healthy or tumor tissues. CyTOF profiling of blood showed higher γδ T-cell levels at baseline in patients with grade ≥ 3 irAEs (n = 6), which remained elevated following tocilizumab treatment. Conclusions: These findings underscore the pivotal role of Th17 cells in the development of irAEs and suggest that current tocilizumab regimens may provide insufficient IL-6 blockade or require combination strategies, such as concurrent IL-23 inhibition, to more effectively target Th17 cells expansion and maintenance. Notably, this study is the first to identify γδ T-cells as potential predictive biomarkers for irAEs, yet their utility requires further validation. A randomized phase II trial exploring these mechanisms is underway. Clinical trial information: NCT04940299 .