Predictive and pharmacodynamic biomarkers for combination therapy in stage III-IV melanoma: A Simon phase II trial (NCT03999749).

222 Background: The evaluation of biomarkers that predict response and immune-related adverse events (irAEs) is crucial for optimizing melanoma treatment with Immune checkpoint inhibitors (ICIs). We report predictive and pharmacodynamic biomarkers for response and irAEs using high-dimensional flow cytometry in a phase II trial combining nivolumab (3 mg/kg), ipilimumab (1 mg/ml), and the IL-6 receptor inhibitor tocilizumab (4 mg/kg) in unresectable/advanced melanoma patients. Methods: We analyzed serum and blood from melanoma patients at baseline, weeks 7 and 37, categorized them by irAE severity and clinical response. Patients were categorized based on the severity of irAEs (grades 3-5) (TOX), the absence of toxicity or grades 1-2 irAE (NT), clinical benefit (CB), and non-clinical benefit (NCB). Immune monitoring regimen included ELISA for IL-6, gp130, IL-23, osteopontin, and Luminex oncological panel (LXSAHM-22). We employed multi-parametric flow cytometry panels to examine myeloid cells, cytotoxic T cells, and checkpoint protein expression on immune cells. We processed ~1 million PBMCs per sample using various antibodies, with data acquisition performed via Sony’s ID7000 cytometer. The data underwent quality control, normalization PBMCs per patient, concatenation, dimensionality reduction, and clustering in FlowJo. Results: Among the 70 patients administered treatment, we observed a best overall response rate of 57%. Grade 3-5 irAEs occurred in 22% of patients by week 24. Patients manifesting irAEs exhibited notably higher baseline Th17 cell counts (NT=181±18 vs. Tox=311±49, p<0.01) and CD26+ Naive CD4 T-cell populations (NT=5838±801 vs. Tox=9632±1343, p<0.04), suggesting their potential role as predictive markers for toxicity. Additionally, in vitro investigations led us to identify CD26 co-stimulation as a preliminary step in TH17 cell differentiation. Key pharmacodynamic markers included a significant elevation in Treg cells (NCB=1286±71 vs. CB=1492±95, p=0.02) and reduction in serum gp130 levels (NCB=104±5 vs. CB=83±5 ng/ml, p<0.01) at week 7 in addition to IL-6 (NCB=7.5±1.5 vs. CB=4.6±1.1 pg/ml, p<0.01) and osteopontin (NCB=95±15 vs. CB=25±3 ng/ml, p<0.01) by week 37 when compared to baseline. Conclusions: Our findings suggest that Th17 cells can serve as a toxicity biomarker for combination therapy with ipilimumab, nivolumab and tocilizumab. Circulating Treg cells and serum osteopontin have emerged as promising pharmacodynamic biomarkers. Clinical trial information: NCT03999749 .