T028: Single-cell RNA sequencing reveals the interplay between circulating CD4 T cells, B cells and cancer-associated monocytes in classic Hodgkin lymphoma treated with PD-1 blockade

Abstract

Classic Hodgkin lymphoma (cHL) is a largely MHC class I-negative tumor with recurrent 9p24.1/ PD-L1/ PD-L2 copy gains and the highest reported response rates to PD-1 blockade. In cHL, the efficacy of PD-1 blockade is closely associated with Hodgkin and Reed-Sternberg (HRS) cell expression of MHC class II, highlighting the potential role of CD4+ T-cell effectors and additional non-MHC class I-mediated mechanisms of tumor cell killing. We utilized scRNA sequencing to characterize the peripheral immune response to PD-1 blockade and more broadly define non-CD8+ dependent mechanisms of immune evasion in cHL. Peripheral blood mononuclear cells were obtained from 20 patients with relapsed/refractory (R/R) cHL treated with PD-1 blockade (nivolumab) on the CheckMate 205 clinical trial (cycle 1 day 1 [C1D1] and cycle 4 day 1 [C4D1]), 11 patients with newly diagnosed, previously untreated cHL and 13 healthy donors. Unlike healthy donors, all evaluated patients with cHL had circulating IFN stimulated adaptive and innate populations, including several distinct CD4+ T-cell effectors and an NK cell subset with reduced cytotoxic potential, and decreased numbers of B cells at all stages of differentiation. Patients with the most favorable responses to PD-1 blockade had: 1) significantly increased CD4+ T-cell receptor diversity and more abundant naïve/ central memory subsets; and 2) significantly higher B-cell receptor diversity and increased numbers of circulating B cells. The most abundant circulating CD3- population in patients with cHL was a newly identified monocyte subset with increased expression of multiple immunosuppressive and tumorigenic cytokines and chemokines, PD-L1 and SIRPa. This newly identified monocytic population was virtually absent from the blood of healthy donors. RNAscope analysis of the intact tumor microenvironment localized these tumor-infiltrating monocytes/macrophages to the immediate proximity of HRS cells. Monocytes from patients whose disease progressed following PD-1 blockade expressed significantly higher levels of immunosuppressive cytokine/chemokine signature which led to the development of a predictive transcriptional assay. We identified a comparable circulating monocyte population and transcriptional signature associated with unresponsiveness to PD-1 blockade in an additional solid tumor underscoring the broad-based significance of these findings.