Adoptive transfer of allogeneic regulatory T cells into patients with chronic graft-versus-host disease

Background aims. Mouse models indicate that adoptive transfer of regulatory T cells (Treg) may suppress graft-versus-host-disease (GvHD) while preserving graft-versus-leukemia reactions. We aimed to develop a protocol for the efficient isolation and in vitro expansion of donor-derived Treg and to establish the proof-of-concept for the clinical application of ex vivo generated Treg preparations in five patients with otherwise treatment-refractory chronic GvHD (cGvHD). Methods. Allogeneic Treg were isolated from unstimulated leukapheresis products of the corresponding human leukocyte antigen matched donors by use of clinical-grade magnetic-activated bead sorting. To increase the amount and purity, Treg were cultivated for 7-12 days and infused after a median time of 35 months after allogeneic hematopoietic cell transplantation. Results. Final products contained Treg with a median purity of 84.1% CD4(+)CD25(high)CD127(low)FOXP3(+) of CD45(+) cells and a mean quantity of 2.4 x 10(6) Treg per kg body wt. All isolated cell products showed in vitro suppressive activity. On transfusion, two of five patients showed a clinical response with improvement of cGvHD symptoms. The other three patients showed stable cGvHD symptoms for up to 21 months. In four of five patients, increased counts of Treg were detectable on Treg transfusion, immunosuppressive treatment could be reduced and suppression of CD69 activation marker expression on T-effector cells was observed. However, one patient had development of malignant melanoma and another patient had Bowen skin cancer 4 months and 11 months after Treg transfusion, respectively. Conclusions. We demonstrate a feasible and reproducible approach of isolating functional Treg in high quantity and purity for clinical application and show opportunities and risks of adoptive Treg transfer into patients with cGvHD.