No increased trapping of multipotent mesenchymal stromal cells in bone marrow filters compared with other bone marrow cells

Background Multipotent mesenchymal stromal cells (MSc) are candidates for cellular therapy in regenerative medicine and as treatment of graft-verfus-host-disease (GvHD) after hematopoietic stem cell (HSC) transplantation. It has been suggested that MSC may be trapped in bone marrow (BM) filters during the stem cell procurement and lost from the HSC graft. Methods We investigated filtered BM and filters from six HSC donors. MSC were expanded from the two sources and investigated by flow cytometry, doubling capacity, differentiation ability and suppression in mixed lymphocyte cultures. Results A range of 0.3-3.4% cells was trapped in the filters. By flow cytometry, there was no difference in the proportions of different cell types between the filter-retrieved and filtered BM cells. The phenotype, immunosuppressive capacity, differentiation and growth were equal in MSC expanded from the two cell sources. Discussion Given the low number of trapped cells, filters do not appear to be a good source of MSC When intended for clinical transplantation, MSC need to be expanded ex vivo to achieve sufficient doses for a clinical effect.