Checkpoint-blocker induced autoimmunity is associated with pretreatment T cell expression profiles and favourable outcome in melanoma

11.1 BackgroundImmune checkpoint blockers (ICBs) activate CD8+ T cells to elicit anti-cancer activity but frequently lead to immune-related adverse events (irAEs). The relationship of irAE with baseline parameters and clinical outcome is unclear. We investigated associations between irAE development, CD8+ T cell receptor diversity and expression and clinical outcome in a non-trial setting. 1.2 MethodsPatients [&ge;]18 years old with metastatic melanoma (MM) receiving combination ICB (ipilimumab plus nivolumab - cICB, n=60) or single-agent ICB (nivolumab/pembrolizumab - sICB, n=78) were prospectively recruited. We retrospectively evaluated the impact of irAEs on survival. This analysis was repeated in an independent cohort of MM patients treated at a separate institution (n=210, cICB:74, sICB:136). We performed RNA sequencing of CD8+ T cells isolated from patients prior to treatment, analysing T cell receptor clonality differential transcript expression according to irAE development. 1.3 Results48.6% of patients experienced treatment-related irAEs within the first 5 cycles of treatment. Development of irAE prior to the 5th cycle of ICB was associated with longer progression-free and overall survival (PFS, OS) in the primary cohort (log-rank test, PFS: P=0.00034; OS: P<0.0001), replicated in the secondary cohort (OS: P=0.00064). Across cohorts median survival for those patients not experiencing irAE was 14.4 (95% CI:9.6-19.5) months vs not-reached (95% CI:28.9 - Inf), P=3.0x10-7. Pre-treatment performance status and neutrophil count, but not BMI, were additional predictors of clinical outcome. Analysis of CD8+ T cells from 128 patients demonstrated irAE development was associated with increased T cell receptor diversity post-treatment (P=4.3x10-5). Development of irAE in sICB recipients was additionally associated with baseline differential expression of 224 transcripts (FDR<0.1), enriched in pro-inflammatory pathway genes including CYP4F3 and PTGS2. 1.4 ConclusionsEarly irAE development post-ICB is strongly associated with favourable survival in MM and increased diversity of peripheral CD8+ T cell receptors after treatment. irAE post-sICB is associated with pre-treatment upregulation of inflammatory pathways, indicating irAE development may reflect baseline immune activation states. Key messageImmune-related adverse events (irAEs) commonly occur in patients with metastatic melanoma treated with immune checkpoint blockade (ICB) therapy. In real world setting we find development of early irAEs post-ICB treatment is associated with survival benefit, indicative of a shared mechanism with anti-tumour efficacy. CD8+ T cells from patients who develop irAE show increased receptor diversity, and pre-treatment samples from patients who develop irAE post single-agent anti-PD1 show over-expression of inflammatory pathways, indicating baseline immune state can determine irAE development.