Wharton Jelly Mesenchymal Stromal Cells as GVHD Prophylaxis

Despite progress in chemotherapy, targeted therapy and immunotherapy, allogeneic hematopoietic stem cell transplantation (allo-SCT) is still the only curative procedure for some hematological malignancies. The probability of finding a matched sibling donor (MSD) is estimated under the classical 30%, because of the age of patients and their relatives, and a matched unrelated donor (MUD) can take time to identify. Currently in France, 25% of the allo-SCT are performed with an haplo-identical related donor. The Baltimore group developed an approach using haploidentical related donors, RIC, T-replete bone marrow and post-transplant high dose cyclophosphamide (PTCy) in patients with advanced hematological malignancies. PTCy has shown to eradicate alloreactive donor and host T-cells, activated by respective antigens, thereby reducing the incidence of graft versus host disease (GvHD) but delaying hematopoietic recovery. Therefore, the main source of graft is peripheral blood stem cells (PBSC) mobilized by G-CSF in France. Unfortunately, with PBSC we observe a higher cumulative incidence of GvHD (around 50%) and a higher toxicity-related mortality (TRM), especially for recipients \>50 years old. The co-transplantation of Mesenchymal Stem Cells (MSC) at the time of transplantation has previously shown a double interest in GvHD immunomodulation and hematopoiesis support. Pre-clinical studies (in mice) have shown that mesenchymal stromal cells (MSCs) from Wharton's Jelly reduce the incidence of GvHD when the infusions are weekly repeated. We propose a phase I clinical trial to find the maximum tolerated dose (MTD) of a weekly infusion of WJ-MSC administered as GvHD prophylaxis and as a support for a faster hematological reconstitution after haplo-identical allo-SCT.