Background
Bone tissue engineering using combinations of adult mesenchymal stem cells (MSCs), growth factors and/or biomaterial scaffolds, is emerging as a promising alternative to autologous and allogeneic bone grafting. Although, fetal bovine serum (FBS) is still the most commonly used supplement for ex vivo expansion of human MSCs, it is important to substitute animal-derived products for clinical applications, according to current Good Manufacturing Practices (cGMP). Human platelet-derivatives (PDs) represent optimal FBS-substitutes due to the nature and range of the released growth factors (GF).
Aim/Hypothesis
(1) To systematically review the literature to identify different types of PDs, and (2) to refine the protocols for preparation of optimal platelet-derived supplements in terms of (a) GF concentrations, and (b) human MSC expansion and differentiation. The overall aim was to optimize the preparation of a cGMP-compliant platelet GF concentrate for large-scale MSC expansion.
Material and Methods
A systematic literature review was performed to compare the efficacy of different PDs. PDs were categorized as platelet ‘releasates’ (PR) or ‘lysates’ (PL) depending on the method of GF release, i.e. via chemical activation with thrombin (or calcium), or via mechanical lysis via freezing and thawing, respectively. Based on the review, selected protocols for preparation of PR and PL, using platelet concentrates pooled from 5 donors, were systematically tested and compared, in terms of (a) ELISA-based GF concentrations [platelet-derived growth factor (PDGF)-BB, transforming growth factor (TGF)- μ 946,1, and vascular endothelial growth factor (VEGF)], and (b) in vitro proliferation, colony-formation, surface marker expression (flow cytometry), and osteogenic differentiation assays of human gingiva-derived MSCs. Cells cultured in 10% FBS were used as the control. Experiments were performed in triplicates, using cells from three donors, and data were statistically analysed.
Results
A number of protocols were identified for preparation of PR and PL, varying in the nature and concentrations of activators (thrombin/calcium), and number and duration of freezing/thawing cycles, respectively. Few studies directly compared PR and PL, and a trend for superior cell proliferation with PL was observed. Based on the review, four different protocols were selected and adapted for preparation of PR and PL. For in vitro MSC experiments, PR/PL concentrations of 5% and 10% were tested. Consistent with results of the review, higher concentrations of GFs (PDGF-BB, TGF- μ 946,1, VEGF) were identified in PL vs. PR. Moreover, proliferation of MSCs was higher in PL vs. PR, in some donors, proliferation was higher in 5% PL vs. 10% PL, suggesting that 5% may be the optimal concentration when using this method of PL preparation. Comparable surface marker expression (stromal phenotype) was observed in MSCs expanded in PL vs. FBS. Significantly higher proliferation (population doubling-time) and colony-formation, and comparable osteogenic differentiation, of MSCs was observed in 5% PL vs. 10% FBS.
Conclusions and Clinical Implications
Human PL prepared from pooled platelet concentrates by a simple, economical and cGMP-compliant method, represents the optimal GF-supplement and FBS-substitute, while maintaining the key properties of MSCs, i.e., stromal phenotype, proliferation and osteogenic differentiation potential, for clinical bone tissue engineering applications.
John Wiley & Sons, 2017. Vol. 28, no S14, p. 57-57
26th Annual Scientific Meeting of the European Association for Osseointegration, Madrid, Spain (5-7 October, 2017)