T cell states, repertoire and function in classical Hodgkin lymphoma revealed through single-cell analyses
The classical Hodgkin lymphoma (cHL) environment is comprised of a rich and varied immune cell infiltrate that is co-opted to support the survival and growth of malignant Hodgkin-Reed-Sternberg (HRS) cells. Several lines of evidence support the notion that, despite the immune suppressive environment that characterizes this disease, HRS cells are actively surveilled by endogenous T cells. For instance, HRS cells recurrently acquire genetic lesions associated with impaired antigen presentation and PD-L1 upregulation. Moreoever, cHL is particularly vulnerable to anti-PD-1/PD-L1 immunotherapy, which indicates that T cells can recognize and eliminate HRS cells when dominant immune checkpoints are disabled. However, the T cells that drive responses to anti-PD-1 therapy in cHL have not been defined. Furthermore, there is a paucity of data linking phenotypic and functional T cell states with clonality at the single cell level in cHL. To address this knowledge gap, we performed paired single cell RNA and T cell receptor sequencing (scRNA/TCR-seq) on 14 cHL and 5 reactive lymphoid tissue (RLT) specimens. Recurrent and significant clonal expansion within effector and exhausted CD8+ T cell and regulatory T (TREG) cell clusters was uniquely observed in most cHL specimens. Surprisingly, CD8+ T cells exhibiting transcriptional features of exhaustion were relatively uncommon in cHL specimens. Multi-plex flow cytometric analysis revealed maintained effector cytokine secretion by most conventional lymphoma-infiltrating T cells upon ex vivo restimulation, which argued against a profound T cell dysfunctional state in cHL, and suggested that lymphoma-iniltrating T cells, when removed from the immune suppressive cHL environment, are capable of exerting effector functions. Finally, these results raise new questions about the nature of the T cells that mediate response to PD-1 blockade therapy in patients with cHL. Overall design: Single cell RNA and TCR sequencing analysis of 14 Hodgkin lymphoma samples and 5 reactive lymph tissue samples.