Transplantation of Haplo-Identical Bone Marrow-Derived Mesenchymal Stem Cells Together with Hematopoietic Stem Cells To Promote Engraftment in Children. A Phase I/II Multicenter Study.

Graft failure or rejection is an identified problem in haplo-identical or second attempt transplantation. In the bone marrow, mesenchymal stem cells (MSCs) have been identified and shown in animal models to enhance hematopoietic stem cell (HSC) engraftment. Advances in techniques and higher quality culture components have allowed the development of an MSC expansion procedure resulting in sufficient MSCs for clinical application. Adult studies have suggested that co-transplantation of MSCs and HSCs in the HLA-identical setting, is feasible and safe.

Here we present the first combined clinical experience within the EBMT MSC expansion consortium with respect to co-transplantation of haplo-identical MSCs in the pediatric allogeneic transplantation setting.

Six weeks before the SCT, 50 cc of bone marrow are sampled under sterile conditions. Density gradient-separated MNCs are plated into tissue culture flasks in low-glucose DMEM supplemented with 10% fetal calf serum and incubated at 37⁰C with 5% CO₂. At 70% confluence, the cells are trypsinized and re-plated at 4x10³ cells/ cm² until the target dose of 1–2 x10⁶/kg recipient body weight is obtained. Enrichment and expansion of MSCs is performed under GMP conditions in nationally accredited laboratories. MSCs (either fresh or cryopreserved) are administered i.v. 4 hours before infusion of donor HSCs. To date 4 children have undergone co-transplantation. Patient characteristics are summarized in the table. All toxicities associated with the procedure were documented, as were the engraftment kinetics and immune recovery. The study was carried out with approval of the respective local ethical committees.

The data indicate that expansion and co-transplantation of MSCs is feasible and well tolerated. While the study is ongoing initial engraftment and immune recovery data (compared to historical data) is encouraging and to date there have been no episodes of graft rejection or severe adverse events related to this treatment.