Impact of humanised isolation and culture conditions on stemness and osteogenic potential of bone marrow derived mesenchymal stromal cells

Therapeutic potential of human bone marrow stromal/stem cells (hBMSC) must be developed using well defined xenogenic-free conditions. hBMSC were isolated from healthy donors (n = 3) using different isolation and expansion methods. Donor I was isolated and expanded by either bone marrow directly seeded and cells expanded in 10% AB human serum (AB) + 5 ng/ml fibroblast growth factor-2 (FGF2) [Direct(AB + FGF(low))] or Ammonium-Chloride-Potassium Lysing Buffer was used before the cells were expanded in 10% AB + 5 ng/ml FGF-2 [ACK(AB + FGF(low))] or Lymphoprep density gradient medium was used before the cells were expanded in 10% AB + 5 ng/ml FGF2 [Lympho(AB + FGF(low))] or bone marrow directly seeded and cells expanded in 10% pooled platelet lysate plasma (PL) + heparin (2 I/U/mL) [Direct(PL)]. Groups for donors II and III were: Direct(AB + FGF(low)) or 10% AB + 10 ng/ml FGF2 [Direct(AB + FGF(high))] or Direct(PL). HBMSCs were assessed for viability, multi-potency, osteogenic, inflammatory response and replicative senescence in vitro after 1 and 3 weeks. Pre-selected culture conditions, Direct(AB + FGF(high)) or Direct(PL), were seeded on biphasic calcium phosphate granules and subcutaneously implanted in NOD/SCID mice. After 1 and 11 weeks, explants were analysed for inflammatory and osteogenic response at gene level and histologically. To identify implanted human cells, in situ hybridisation was performed. hBMSC from all conditions showed in vitro multi-lineage potency. hBMSCs expanded in PL expressed stemness markers in vitro at significantly higher levels. Generally, cells expanded in AB + FGF2 conditions expressed higher osteogenic markers after 1 week both in vitro and in vivo. After 11 weeks in vivo, Direct(AB + FGF(high)) formed mature ectopic bone, compared to immature mineralised tissues formed by Direct(PL) implants. Mouse responses showed a significant upregulation of IL-1 alpha and IL-1 beta expression in Direct(PL). After 1 week, human cells were observed in both groups and after 11 weeks in Direct(AB + FGF(high)) only. To conclude, results showed a significant effect of the isolation methods and demonstrated a relatively consistent pattern of efficacy from all donors. A tendency of hBMSC expanded in PL to retain a more stem-like phenotype elucidates their delayed differentiation and different inflammatory expressions.