Discarded fraction from bone marrow erythrocyte depletion procedure is a good source of multipotent mesenchymal stromal cells

Multipotent mesenchymal stromal cells (MSCs) (1) are a promising source for cell therapy (2). They can be isolated from various adult human tissues, but procurement is difficult and often achieved through invasive procedures (3). Therefore, research has focused on finding new, more convenient sources. A number of bone marrow (BM) processing and manipulation techniques have been developed to improve the outcome of hematopoietic stem cell transplantation. Among the available methodologies to enrich stem cells from large BM volumes and to prevent transplant complications, BM erythrocyte depletion circumvents problems associated with donor/recipient incompatibility for ABO blood group antigens. This procedure inevitably involves a loss of stem cells (4). A frequently used method to remove erythrocytes from BM consists in gravity sedimentation. The erythrocyte portion (EP), which may contain a viable number of stem cells (4), is subsequently discarded. In the present correspondence, we report on the feasibility of expanding MSCs from the erythrocyte fraction obtained after BM erythrocyte depletion. To this aim, after obtaining written informed consent, we sampled BM from four HLA-identical sibling donors, manipulated (red blood celle depleted) for ABO blood group antigen incompatibility. BMwas centrifuged at 1500 rpm for 15minutes at þ4 C to produce a buffy-coat containing