IL-6 receptor inhibition promotes expansion of cytolytic CD4+ T cells after cellular immunotherapy.

Graft-versus-host disease (GVHD) remains a major barrier to the success of allogeneic hematopoietic stem cell transplantation (HSCT). In preclinical models, dysregulation of IL-6 in the peri-transplant period promotes GVHD via STAT3-dependent T cell differentiation and monocyte activation but the nature of immunological effects invoked in patients remains unclear. To advance our understanding of IL-6 signaling in humans during HSCT, we performed single-cell RNA sequencing on circulating CD14+ monocytes and CD4+ T cells from patient samples within a clinical trial of IL-6R inhibition (tocilizumab (TCZ) or placebo) on a backbone of calcineurin inhibition (CNI) and short-course methotrexate. We studied patients who did not develop acute GVHD and included a placebo-treated group analyzed prior to the development of acute GVHD. IL-6R inhibition promoted Type-I IFN-associated transcriptional programs in both CD4+ T cells and CD14+ monocytes. Surprisingly, IL-6R-inhibition with TCZ profoundly enhanced cytolytic CD4+ T cell differentiation. In experimental HSCT and chimeric antigen receptor T cell systems, genetic deletion of IL-6 signaling in donor T cells enhanced the expansion of cytolytic Eomes+ CD4+ regulatory T cell subsets whilst attenuating Th1 and Th17 differentiation. Consistent with the promotion of this cytolytic CD4+ phenotype, anti-tumor effects were improved in the absence of IL-6 signaling. In summary, these data demonstrate that IL-6R inhibition during cell therapy imprints Type-I IFN programs and cytolytic CD4+ T cell differentiation, including the Eomes+ fraction associated with favorable immunotherapy outcomes.