Summary:The best strategies for haploidentical stem cell transplants are not known. We used a standard myeloablative pretransplant conditioning regimen (30 mg/kg VP-16, 120 mg/kg cyclophosphamide, and 12 Gy of TBI in six fractions), an increased peripheral stem cell dose of Ͼ10 ؋ 10 6 CD34 ؉ cells/kg, T cell depletion (with CD34 Recently, data from animal experiments and in vitro studies 13,14 and from human transplantation [1][2][3][4]6,[15][16][17] have addressed the impact of stem cell dose. Previously, the achievable stem cell dose was limited by the amount of bone marrow that could be harvested. This has changed in the current era of allogeneic peripheral blood stem cell transplantation. 18 It was hypothesized, that a higher stem cell dose, as achieved by mobilizing peripheral blood stem cells may promote engraftment, and immune reconstitution and maintain graft-versus-leukemia effects despite extensive T cell depletion. We planned to test this hypothesis by using a protocol of an increased peripheral stem cell dose, a standard myeloablative conditioning regimen, T cell depletion, and a short course of post-transplant cyclosporine to promote engraftment. We report our initial experience with this protocol.؉
Patients and methods
MethodsPeripheral stem cells were mobilized by daily subcutaneous injection of 10 g/kg of G-CSF. Donors underwent 15-25 l apheresis on days 5-8 of G-CSF mobilization. The goal was to collect Ͼ10 ϫ 10 6 CD34 ϩ cells/kg. Allowing for a 50% loss during T cell depletion, Ͼ20 ϫ 10 6 CD34 ϩ cells/kg were collected. If this goal could not be reached, a second mobilization was planned. 19 The apheresis product was T cell-depleted using CD34 ϩ positive selection followed by CD4/CD8 depletion steps (Isolex 300i; Baxter, Deerfield, IL, USA) to achieve Ͻ1 ϫ 10 5 CD3 ϩ cells/kg. The transplants were cryopreserved using 10% DMSO as cryoprotectant and stored in the vapor phase of a liquid nitrogen tank at Ϫ196°C. Pretransplant conditioning was our standard regimen of 30 mg/kg VP-16, 120 mg/kg cyclophosphamide and TBI, 12 Gy in six fractions or busulphan 16 mg/kg and cyclophosphamide 120 mg/kg for patients who had undergone prior irradiation. The transplants were thawed at the bedside and infused rapidly on day 0. Cyclosporine was used for post-transplant immune suppression, tapered rapidly after day 14. Engraftment was defined as reaching 0.5 ϫ 10 9 /l neutrophils stable over 3 days, after a period of aplasia. The modified Glucksberg criteria were used to score acute graft-versus-host disease (GVHD). Prophylaxis of infectious complications included cotrimoxazole, acyclovir, fluconazole and weekly CMV antigenemia