Co-Transplantation of HLA-Haploidentical, Bone Marrow Derived Mesenchymal Stem Cells Prevents Graft Failure and Improves Hematological Recovery in T-Cell Depleted Haploidentical Stem Cell Transplantation.

Haploidentical CD34⁺ purified peripheral blood stem cell transplantation (PBSCT) is associated with an increased risk of graft failure/rejection. Animal models suggest that MSCs may promote engraftment after hematopoietic stem cell transplanation (HSCT) but there role in overcoming graft failure in human HSCT is still unclear. We recently reported our initial findings in 13 children receiving MSCs in conjunction with haplo-PBSCT. Here we report our extended series of 20 patients, now including those with MDS known to have an increased risk of rejection. MSCs were isolated from marrow of PBSCT donors and expanded under GMP conditions using same batch FCS containing medium and a standardized protocol, approximately 4–5 weeks before transplantation. MSCs (fresh or cryopreserved) were administered i.v. 4 hours before the allograft. Conditioning depended on underlying disease. No pharmacological GvHD prophylaxis was given after PBSCT. Characteristics of the patients and results are summarized in table 1. In comparison to historical controls (20% graft failure), all patients given MSCs showed successful and stable engraftment (p=0.03). Hematological recovery was accelerated (see table 2). Viral reactivations did not differ between patients and controls. MSC use was feasible and safe without infusion toxicities. In contrast to our initial findings, our extended analysis shows a statistically significant reduction in graft failure rates for patients cotransplanted with MSCs. Moreover, MSC cotransplantation may also prevent graft rejection in patients with MDS. In view of these findings, cotransplantation of MSCs could become standard practice for optimizing the outcome of children given this type of allograft.