CD25 Blockade Delays Regulatory T Cell Reconstitution and Does Not Prevent Graft-versus-Host Disease After Allogeneic Hematopoietic Cell Transplantation

•It was believed that daclizumab would prevent acute graft-versus-host disease (GVHD) by blocking T cell activation.•A trial of daclizumab after allogeneic transplantation did not decrease aGVHD.•Follow-up showed that anti-CD25 therapy delayed regulatory T cell (Treg) repopulation after transplantation.•Transient Treg reduction may have long-term effects on chronic GVHD and relapse risk.•Antibody-mediated CD25 blockade may be useful in promoting antitumor immunity.