Characterization and comparison of bone marrow and peripheral blood mononuclear cells used for cellular therapy in critical leg ischaemia: towards a new cellular product

Autologous transplantation of either bone marrow (BM) or peripheral blood (PB) mononuclear cells (MNC) induces therapeutic angiogenesis in patients with peripheral arterial occlusive disease. Yet, the precise nature of the cellular product obtained from BM or PB and used in these therapeutic strategies remains unclear. We have analysed the characteristics of BM-MNC and PB-MNC collected without mobilization and implanted in patients with critical limb ischaemia in a clinical trial of cellular therapy including 16 individuals treated by BM-MNC and eight by PB-MNC. These MNCs were characterized by cell counts, viability assessment and enumeration of leucocyte subsets, CD34 stem and endothelial progenitor cells (EPCs) (CD34+/CD133+/VEGF-R2+) by flow cytometry. Mean fluorescence intensity ratios were determined for CD34, CD133 and VEGF-R2 markers. All analyses were simultaneously performed in two laboratories. Accuracy and reliability between both laboratories were achieved. BM-MNCs and PB-MNCs were quantitatively and qualitatively heterogeneous and quite different from each other. Stem cells and EPCs were significantly more present in BM- compared to PB-cell products, but with similar mean fluorescence intensity ratios. A weakly positive correlation was observed between CD34+ cell counts and EPCs levels, confirming the specificity of cell identification. A great variability was observed in cell product characteristics according to their origin and also between individuals. These data stress the necessity of optimal characterization of cell products especially in multicentric clinical trials.