Dual immune checkpoint blockade induces analogous alterations in the dysfunctional CD8+ T cell and activated Treg compartment

Immune checkpoint blockade has shown clinical activity in a range of cancer types. To dissect the effect of neoadjuvant PD-1 and CTLA4 blockade on intratumoral T cells in treatment-naïve head and neck squamous cell carcinoma, we analyzed immune infiltrates in tumor biopsies from responding and non-responding patients. At baseline, a higher ratio between active (4-1BB/OX-40+) and inactive regulatory CD4+ T cells was associated with response to therapy. Furthermore, upon therapy, this active Treg population showed a profound decrease in responding patients. In an analogous process, the intratumoral dysfunctional CD8+ T cell compartment displayed a decrease in the expression of activity and dysfunction-related genes in responding patients, while in clinically non-responding patients, NK cells showed an increased cytotoxic transcriptional profile early upon treatment. These data reveal the immunological changes in response to dual PD-1 and CTLA4 blockade, including a parallel remodeling of presumed tumor-reactive T cell compartments in responding patients, and indicate that the presence of an activated Treg compartment at baseline may be associated with response. We performed single cell RNA and TCR sequencing (10x Genomics) on immune infiltrates (CD45+ cells) from 18 HNSCC patients enrolled in the IMCISION trial (Vos et al. 2021). Viable immune cells were isolated from pre-treatment and on-treatment primary tumor biopsies of 10 patients responding (1 partial pathological response and 9 major pathological responses) and 7 patients non-responding to anti-PD-1 and anti-CTLA4 combination immunotherapy. One patient treated with anti-PD-1 monotherapy (1 major pathological response) was included in the dataset. *** Raw sequencing data will be deposited on EGA. ***