Increased CD4+ T cell proliferation upon treatment correlates with improved overall survival of patients with metastatic melanoma upon anti-CTLA-4 therapy

Abstract

Abstract Blockade of cytotoxic T-lymphocyte antigen 4 (CTLA-4) augments anti-tumor immunity and has shown success in treating patients with metastatic melanoma. Mechanisms of anti-CTLA-4 efficacy have been proposed in animal models, yet the mechanisms in humans remain to be elucidated. Increased frequency of ICOS+ CD4+ T cells has been shown to be a marker of drug bioactivity, but discovery of prognostic indicators and baseline indicators of which patients are most likely to benefit from CTLA-4 blockade remains a priority. PBMCs from 29 metastatic melanoma patients in a multicenter compassionate use trial of anti-CTLA-4 antibody were evaluated using flow cytometry. At baseline and 12 weeks following initiation of treatment, CTLA-4, HLA-DR, ICOS, PD-L1, PD-1, and Ki-67 frequencies were assessed on CD4+ and CD8+ T cells, as well as CD3+CD4+ regulatory T cells. Independent of survival, anti-CTLA-4 treatment significantly increased the frequency of ICOS+ CD4+ T cells, corroborating previous findings. Interestingly, this increase was also observed in ICOS+ Tregs, but not in CD8+ T cells. Increased proliferative Ki67+ CD4+ T cells and Ki67+ Tregs upon CTLA-4 blockade were both associated with prolonged overall survival. Additionally, when the frequency of Ki67+ CD4+ T cells post-treatment was compared to the baseline frequency, patients with a ratio greater than 1.5 had greater overall survival. Increased post-treatment absolute lymphocyte count—a known prognostic biomarker—also correlated with clinical outcome. Our results suggest that anti-CTLA-4 therapy may be mediated by proliferation of CD4+ T cells, and we identify this proliferation as a novel prognostic biomarker in metastatic melanoma patients treated with anti-CTLA-4 antibody.