Anti-CTLA4 therapy leads to early expansion of a peripheral Th17 population and induction of Th1 cytokines

Abstract The systemic immunological effects of combining anti-CTLA4 therapy with PD-(L)1 blockade remain incompletely characterized, despite the widespread use of this combination in treating various solid tumors across multiple stages of disease. Herein, we investigated the additive impact of anti-CTLA4 on peripheral immune signatures in patients undergoing PD-(L)1 blockade, using blood samples from a cohort of patients receiving checkpoint inhibitor therapy for advanced solid tumors. We performed in-parallel analysis of peripheral blood mononuclear cells (PBMC) using Cytometry by Time-of-Flight (CyTOF) and plasma cytokines using Luminex immunoassay. Our study cohort included 104 patients, 54 who received anti-PD(L)1 alone and 50 who received anti-PD(L)1 in combination with anti-CTLA4. As compared to single-agent anti-PD(L)1, combination therapy was associated with a greater expansion of CD4+ T helper cell subsets, including Th17 (adjusted p=0.04) and regulatory T cells (Treg) (adjusted p=0.02), after multivariable and multiple testing adjustment. In patients receiving anti-CTLA4, examination of functional marker expression within the Th17 subset revealed an increase in expression of the Th1-related transcription factor TBET (p=0.003). Assessment of the peripheral cytokine signatures showed an increase in Th1-associated cytokines (p=0.002) in recipients of combination anti-PD(L)1 and anti-CTLA4, particularly the IFN-inducible cytokines MIG (adjusted p=0.05) and IP-10 (adjusted p=0.05). Our results confirm prior reports that anti-CTLA4 therapy is associated with augmentation of Th17 cell subsets, and they also show that anti-CTLA4 may reshape CD4+ T-cell responses through Th17-to-Th1 plasticity, revealing a potential mechanism for enhanced antitumor immunity with broader implications immune modulation in immunotherapy.