Ex-vivo Expansion of Bone Marrow-derived Mesenchymal Stromal Cells for Clinical Use: the Starting Platelet Concentration of Human Platelet Lysate Affects Cell Proliferation, Senescence and Phenotype

Abstract

Abstract Background: In the last decades the replacement of fetal bovine serum (FBS) with human Platelet Lysate (hPL) for ATMPs expansion has been for a long time investigated to overcome FBS-related issues. Despite several studies confirming hPL safety and efficacy in Mesenchymal Stromal Cell (MSC) expansion, there are still gaps in the knowledge of hPL as a supplement, like the composition and release criteria. As growth factors are released after thrombocytes lysis during hPL production, starting platelet concentration may affect hPL quality. This study aimed to investigate hPL starting platelet concentration effects on bone marrow-derived MSC (BM-MSC) ex-vivo expansion. Methods: MSC were isolated from the bone marrow (BM) of 7 donors and cultured from passage 1 to 5 in 4 different conditions: DMEM 10% FBS and DMEM 5% hPL varying starting platelet concentration. Particularly hPL was produced by in-hospital Transfusion Service, in three different starting platelet concentrations (sPLTC): high (4x109 PLTS/ml), medium (2x109 PLTS/ml) and low (1x109 PLTS/ml). The study focused on the analysis of parameters that are mostly affected by hPL such as cell proliferation, immunophenotype, telomeric length, differentiation and senescence. Results: Evaluation of proliferation indexes (PDT and PD) underlined dose-dependent effects of sPLTC, also confirmed by flow cytometry cell cycle analysis. Immunophenotype seems not to be affected by sPLTC. Differences were instead detected by adhesion molecules markers CD10, CD106, CD166, and CD146 expression, as their expression showed a dose-dependent downregulation, based on the sPLTC. Differentiation potential seems to be unaffected by different sPLTC as all cell batches differentiated into osteoblasts, adipocytes and chondrocytes. On the contrary senescence and relative telomeric length RTL (detected by SA-β-GAL activity and PNA-FITC flow cytometry) are strongly affected by sPLTC, in a dose-dependent manner. Particularly high sPLTC results in cell senescence associated with decreased RTL. Conclusions: our data showed that sPLTC affects some BM MSCs properties, underlying its importance during hPL preparation. According to this study, we suggest a medium sPLTC for hPL preparation, as the best compromise between the increase in proliferation index and effects on senescence.