Global phenotypic characterisation of human platelet lysate expanded MSCs by high-throughput flow cytometry.

Mesenchymal stromal cells (MSCs) are a promising cell source to develop cell therapy for many diseases. Human platelet lysate (PLT) is increasingly used as an alternative to foetal calf serum (FCS) for clinical-scale MSC production. To date, the global surface protein expression of PLT-expended MSCs (MSC-PLT) is not known. To investigate this, paired MSC-PLT and MSC-FCS were analysed in parallel using high-throughput flow cytometry for the expression of 356 cell surface proteins. MSC-PLT showed differential surface protein expression compared to their MSC-FCS counterpart. Higher percentage of positive cells was observed in MSC-PLT for 48 surface proteins, of which 13 were significantly enriched on MSC-PLT. This finding was validated using multiparameter flow cytometry and further confirmed by quantitative staining intensity analysis. The enriched surface proteins are relevant to increased proliferation and migration capacity, as well as enhanced chondrogenic and osteogenic differentiation properties. In silico network analysis revealed that these enriched surface proteins are involved in three distinct networks that are associated with inflammatory responses, carbohydrate metabolism and cellular motility. This is the first study reporting differential cell surface protein expression between MSC-PLT and MSC-FSC. Further studies are required to uncover the impact of those enriched proteins on biological functions of MSC-PLT.

Enumeration of circulating endothelial cell frequency as a diagnostic marker in aortic valve surgery - a flow cytometric approach.

BACKGROUND: The frequency of circulating endothelial cells (CEC) in patients' peripheral blood can be assessed as a direct marker of endothelial damage. However, conventional enumeration methods are extremely challenging. We developed a novel, automated approach to determine CEC frequencies and tested this method on two groups of patients undergoing conventional (CAVR) versus trans-catheter aortic valve implantation (TAVI). METHODS: CEC frequencies were assessed by a flow cytometric approach, including automated pre-enrichment of CD34 positive blood cell subpopulation and isotype controls. The efficacy and reproducibility of the CEC enumeration method was validated by spiking blood samples of healthy control donors with defined numbers of endothelial cells. RESULTS: CEC frequencies were significantly higher in the TAVI group before (9.8 ± 4.1 vs. 5.5 ± 2.2, p = 0.019) and 1 h after surgery (13.4 ± 5.1 vs. 8.2 ± 4.1, p = 0.030) corresponding to higher Euroscore, STS score in higher risk patients from the TAVI group. Five days after surgery, CEC frequencies became significantly higher in the more invasive CAVR group (39.0 ± 13.0 vs. 14.3 ± 4.4, p < 0.001) compared to minimally invasive TAVI approach. CONCLUSIONS: The new flow cytometric approach might be a robust and reliable method for CEC enumeration. Initial results show that CEC frequency is a valid clinical marker for the assessment of pre-operative risk, invasiveness of surgical procedure and clinical outcome. Further studies are necessary to validate the practical clinical usefulness and the potential superiority compared to conventional markers.

Three specific antigens to isolate endothelial progenitor cells from human liposuction material.

BACKGROUND AIMS: Human endothelial progenitor cells (EPC) play an important role in regenerative medicine and contribute to neovascularization on vessel injury. They are usually enriched from peripheral blood, cord blood and bone marrow. In human fat tissue, EPC are rare and their isolation remains a challenge. METHODS: Fat tissue was prepared by collagenase digestion, and the expression of specific marker proteins was evaluated by flow cytometry in the stromal vascular fraction (SVF). For enrichment, magnetic cell sorting was performed with the use of CD133 microbeads and EPC were cultured until colonies appeared. A second purification was performed with CD34; additional isolation steps were performed with the use of a combination of CD34 and CD31 microbeads. Enriched cells were investigated by flow cytometry for the expression of endothelial specific markers, by Matrigel assay and by the uptake of acetylated low-density lipoprotein. RESULTS: The expression pattern confirmed the heterogeneous nature of the SVF, with rare numbers of CD133+ detectable. EPC gained from the SVF by magnetic enrichment showed cobblestone morphology of outgrowth endothelial cells and expressed the specific markers CD31, CD144, vascular endothelial growth factor (VEGF)R2, CD146, CD73 and CD105. Functional integrity was confirmed by uptake of acetylated low-density lipoprotein and the formation of tube-like structures on Matrigel. CONCLUSIONS: Rare EPC can be enriched from human fat tissue by magnetic cell sorting with the use of a combination of microbeads directed against CD133, an early EPC marker, CD34, a stem cell marker, and CD31, a typical marker for endothelial cells. In culture, they differentiate into EC and hence could have the potential to contribute to neovascularization in regenerative medicine.