Donor regulatory T-cell therapy to prevent graft-versus-host disease

• Treg-engineered donor graft prevents acute and chronic GVHD.

• Patients treated with Treg-engineered graft who develop GVHD respond to primary corticosteroid therapy at a high rate.

Allogeneic hematopoietic cell transplantation is a curative therapy limited by graft-versus-host disease (GVHD). In preclinical studies and early-phase clinical studies, enrichment of donor regulatory T cells (Tregs) appears to prevent GVHD and promote healthy immunity. We enrolled 44 patients in an open-label, single-center, phase 2 efficacy study investigating if a precision selected and highly purified Treg therapy manufactured from donor-mobilized peripheral blood improves 1-year GVHD-free relapse-free survival (GRFS) after myeloablative conditioning. We compared this study arm with a concomitant standard-of-care (SOC) cohort. All donor Treg products were successfully manufactured and administered without cryopreservation within 72 hours. Participants had a 1-year incidence of acute grade 3 to 4 GVHD of 7%, moderate to severe chronic GVHD of 11%, and nonrelapse mortality rate of 4.5%. The primary end point of significantly improved 1-year GRFS was achieved at 64% evaluated against a predicted incidence of 40% (P = .002) with a realized incidence of 36% in the SOC comparator. For those trial patients who developed grade 2 to 4 acute GVHD, 91% responded to front-line corticosteroid therapy, whereas 50% responded in the SOC comparator group. Trial participants had a reduced incidence and burden of GVHD and improved GRFS, compared with rates common to highly variable unmanipulated donor grafts and multiagent immune suppression. This trial was registered at www.clinicaltrials.gov as #NCT01660607.