Regimen-Dependent Anti-Cytokine and Immune-Checkpoint Autoantibodies Are Associated with Immunotherapy Toxicity and Response in Melanoma

Immune checkpoint inhibitor (ICI) efficacy and immune-related adverse events (irAEs) in melanoma are influenced by the pre-treatment immune state. We investigated whether baseline autoantibodies directed against cytokines, chemokines, cytokine receptors, and immune-checkpoint/costimulatory proteins were associated with outcome in a regimen-dependent manner. Baseline sera from patients with metastatic melanoma were profiled on a multiplex bead array of 86 cytokine, chemokine, cytokine-receptor and immune-checkpoint antigens, and associations with best overall response and irAE development were assessed within pre-specified treatment strata by label-permutation testing with Benjamini–Hochberg false-discovery-rate control (SAM as a sensitivity analysis). Associations differed by ICI regimen. Anti-IL17A and anti-CCL2 reactivity was higher in patients developing irAEs under ipilimumab monotherapy (both p = 0.003) and shifted in the opposite direction under pembrolizumab without prior CTLA-4 therapy. Higher anti-PD-L1/CD274 and anti-CCL5 and lower anti-KIT reactivity were associated with response to pembrolizumab without prior CTLA-4 therapy (p = 0.025, p = 0.002, p = 0.006), and lower anti-MCAM and anti-CSF3 reactivity with response under ipilimumab/nivolumab (p = 0.001 and p = 0.002). No association survived false-discovery-rate correction, so all findings are exploratory and hypothesis-generating; higher baseline anti-IL10 reactivity was a leading irAE signal under pembrolizumab without prior CTLA-4 therapy (p = 0.027). These regimen-dependent humoral markers warrant prospective, regimen-stratified validation.