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, the dysregulation of interleukin-6 (IL-6) in the peritransplant 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-6 receptor (IL-6R) inhibition (tocilizumab [TCZ] or placebo) on a backbone of calcineurin inhibition and short-course methotrexate. We studied patients who did not develop acute GVHD (aGVHD) and included a placebo-treated group analyzed before the development of aGVHD. IL-6R inhibition promoted type I interferon-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, the genetic deletion of IL-6 signaling in donor T cells enhanced the expansion of cytolytic eomesodermin-positive (Eomes+) CD4+ regulatory T cell subsets and attenuated T helper 1 (Th1) and Th17 differentiation. Consistent with the promotion of this cytolytic CD4+ phenotype, antitumor 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 interferon programs and cytolytic CD4+ T-cell differentiation, including the Eomes+ fraction associated with favorable immunotherapy outcomes.