LAUSR

Objectives: The number of Mesenchymal Stem/Stromal Cells (MSCs) in the human bone marrow (BM) is small compared to other cell types, estimated at 0.01-0.02%. Bone marrow aspirate concentration (BMAC) may be used to increase numbers of MSCs, but the efficacy of BMAC, as well as the composition of MSC subpopulations after processing, is currently unknown. The purpose of this descriptive laboratory study is to assess the enrichment of MSC subpopulations in bone marrow aspirate by two different BMAC devices versus standard BM aspiration from single donors. Methods: 120 mL of BM was aspirated from multiple punctures of the iliac crest in 9 human male donors. Each sample was divided into 3 partitions and processed by 2 different commercially available systems Harvest BMAC or Emcyte PureBMC, and compared to untreated BM aspirate as an internal control. Samples were quantitatively analyzed with multicolor flow cytometry for cellular viability and expression of hematopoietic and MSC subpopulation markers. Colony-forming unit-fibroblasts (CFU-F) assays were performed to estimate the number of functional progenitor cells. Results: Cell viability after processing was over 90% in all groups without significant differences, and hematopoietic cell content was lower in BMAC where, in contrast, non-hematopoietic stem cell subpopulations were significantly enriched. Specifically, BMAC from Harvest BMAC contained more CD45-CD73+CD90+ (11.44 fold vs control, p = 0.01), CD45-CD10+ (3.68 fold vs control, p = 0.01), CD45-CD29+ (1.54 fold vs control, p = 0.03), and CD45-CD119+ (5.52 fold vs control, p = 0.02) cells, whereas Emcyte PureBMC concentrated more CD45-CD73+ cells (13.90 fold vs control, p = 0.04). Both BMAC devices mainly enriched the CD45-CD90+CD271+ MSC subpopulation (Harvest BMAC: 13,011.84 fold vs control, p = 0.001; Emcyte PureBMC: 10,669.11 fold vs control, p = 0.02) compared to other MSC subpopulations. Both BMAC systems significantly increased progenitor colonies (Harvest BMAC: 2692 CFU-F/mL; Emcyte PureBMC: 4336 CFU-F/mL) verses control BM aspiration (183 CFU-F/mL), p<0.05. Conclusion: BMAC devices lead to: 1) enrichment of functional mesenchymal stem cell subpopulations with distinct phenotypes, 2) no increase in hematopoietic stem cell concentration, and 3) no significant loss of cell viability.