A phase 1 study of donor regulatory T-cell infusion plus low-dose interleukin-2 for steroid-refractory chronic graft-vs-host disease.

Chronic graft-versus-host disease (cGVHD) remains a frequent cause of non-relapse morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Despite recent advances, options for steroid-refractory (SR) cGVHD are limited. In previous trials of low-dose interleukin-2 (LD IL-2), the immunomodulatory properties of regulatory T cells (Tregs) have been harnessed to treat SR-cGVHD safely and effectively. In the present study, we combined a single infusion of Treg-enriched lymphocytes (Treg DLI) from the original stem cell donor with in vivo Treg expansion using LD IL-2 (1 x 106 IU/m2/day for 8 weeks) in 25 adult patients with SR-cGVHD. Treg were not expanded ex vivo. Treg DLI was initiated at 0.1 x 106 cells/kg patient and escalated to a maximum dose of 1 x 106 cells/kg. Treg DLI plus LD IL-2 was well-tolerated and led to partial responses (PR) in 5 of 25 patients (20%) after 8 weeks of therapy. Ten additional patients (40%) had stable disease with minor responses not meeting PR criteria. Patients at all dose levels had similar Treg expansion without significant changes in CD4+ conventional T cells or CD8+ T cells. High-throughput sequencing of the T-cell receptor β locus showed selective improvement of Treg diversity. A subset of DLI-derived Treg clones showed preferential expansion at week 8 and long-term persistence 1-year post-infusion. We demonstrate for the first time that infusion of polyclonal healthy donor Tregs followed by expansion with LD IL-2 is safe in patients with SR-cGVHD, thus establishing a foundation for future adoptive Treg therapies in the post-transplant setting. This trial is registered at www.clinicaltrials.gov as NCT01937468.