INTRODUCTION: Haploidentical transplantation, with extensive T cell depletion to prevent GvHD, is associated with a high incidence of infection-related deaths. The key challenge is to improve immune recovery with allogeneic donor T cells without triggering GvHD. As T regulatory cells (Tregs) controlled GvHD in pre-clinical studies, the present study evaluated the impact of an infusion of donor CD4/CD25 + Tregs, followed by an inoculum of donor mature T cells (Tcons) and positively immunoselected CD34 + cells in the setting of haploidentical stem cell transplantation. PATIENTS AND METHODS: Twenty-eight patients were enrolled in this study (22 AML; 5 ALL; 1 NHL). All received immunoselected Tregs (CliniMACS, Miltenyi Biotec) followed by positively immunoselected CD34 + cells together with Tcons 4 days later. No GvHD prophylaxis was administered. RESULTS: 26/28 patients engrafted. No acute GvHD developed in 24/26 patients; 2 developed ≥ grade II acute GvHD. No patient has developed chronic GvHD. CD4 and CD8 counts rapidly increased after transplant. Episodes of CMV reactivation were significantly fewer than in controls. CONCLUSIONS: In the setting of haploidentical transplantation infusion of Tregs makes administration of a high dose of T cells feasible. This strategy provides a long-term protection from GvHD and robust immune reconstitution.