A stromal-free, serum-free system to expand ex vivo hematopoietic stem cells from mobilized peripheral blood of patients with hematologic malignancies and healthy donors

Background aims: The number of hematopoietic stem cells (HSCs) is critical for transplantation. The ex vivo expansion of mobilized peripheral blood (MPB) HSCs is of clinical value for reconstitution to meet clinical need. Methods: This study proposed a simple, defined, stromal-free and serum-free culture system (SF-HSC medium) for clinical use, which is composed of Iscove's modified Dulbecco's medium, cytokine cocktails and serum substitutes. This study also characterized the cellular properties of expanded MPB CD133⁺ HSCs from patients with hematologic malignancies and healthy donors by surface antigen, colony-forming cell, long-term culture-initiating cell, gene expression and in vivo engraftment assays. Results: The expanded fold values of CD45⁺ white blood cells and CD34⁺, CD133⁺, CD34⁺CD38^-, CD133⁺CD38^-, CD34⁺CD133⁺, colony-forming and long-term culture-initiating cells at the end of 7-day culture from CD133⁺ MPB of hematologic malignancies were 9.4-fold, 5.9-fold, 4.0-fold, 35.8-fold, 21.9-fold, 3.8-fold, 11.8-fold and 6.7-fold, and values from healthy donor CD133⁺ MPB were 20.7-fold, 14.5-fold, 8.5-fold, 83.8-fold, 37.3-fold, 6.2-fold, 19.1-fold and 14.6-fold. The high enrichment of CD38^- cells, which were either CD34⁺ or CD133⁺, sustained the proliferation of early uncommitted HSCs. The expanded cells showed high levels of messenger RNA expression of HOBX4, ABCG2 and HTERT and had the in vivo ability to re-populate NOD/SCID mice. Conclusions: Our results demonstrated that an initial, limited number of MPB CD133⁺ HSCs could be expanded functionally in SF-HSC medium. We believe that this serum-free expansion technique can be employed in both basic research and clinical transplantation.