The therapeutic effect of mesenchymal stromal cells (MSCs) following myocardial infarction (MI) is small. This may be due to differences in cellular sources and donor age, route of administration, in vitro cellular manipulations and the short time course of follow up in many animal studies. Here, we compared MSCs from two different sources (adult bone marrow or Wharton's jelly from umbilical cord) for their long-term therapeutic effect following MI in a rat model to evaluate the effect of donor age. MSCs (or control infusions) were given intravenously 24-48 hr after myocardial ischemia (MI) induced by coronary artery ligation. Cardiac function was assessed by ultrasound at time points starting from before MSC infusion through 68 weeks after MI. A significant improvement in ejection fraction was seen in animals that received MSCs in time points 25 to 31 wks after treatment (p < 0.01). These results support previous work that show that MSCs can cause improvement in cardiac function and extend that work by showing that the beneficial effects are durable. To investigate MSCs' cardiac differentiation potential, Wharton's jelly MSCs were co-cultured with fetal or adult bone-derived marrow MSCs. When Wharton's jelly MSCs were co-cultured with fetal MSCs, and not with adult MSCs, myotube structures were observed in two-three days and spontaneous contractions (beating) cells were observed in fiveseven days. The beating structures formed a functional syncytium indicated by coordinated contractions (beating) of independent nodes. Taken together, these results suggest that MSCs given 24-48 hr after MI have a significant and durable beneficial effect more than 25 weeks after MI and that MSC treatment can home to damaged tissue and improve heart function after intravenous infusion 24-48 hrs after MI, and that WJCs may be a useful source for off-the-shelf cellular therapy for MI.

Abstract:Isolates of mesenchymal stromal cells (MSCs) contain a mixed cell population of stem cells, multipotent and unipotent progenitors, and differentiated cells. It is speculated that the useful subpopulation for tissue engineering and cell therapy will be the multipotent progenitor cells or the stem cells. The colony forming unit-fibroblast (CFU-F) assay is an in vitro assay for clonogenicity, which is one property of the stem/progenitor cell population of MSCs. Our goal was to generate standard protocols that would permit the expansion and maintenance of CFU-F. Previous work reported that low plating density and/or exposure to 5% oxygen vs. 21% oxygen increased proliferation rate and enhanced expansion of MSCs. Here, we characterized the effect of both plating density and oxygen concentration on MSCs derived from Wharton's jelly (WJCs). We found that reducing oxygen concentration from 21% (room air) to 5% during expansion increased cell yield and maintained CFU-F, without affecting the expression of surface markers or the differentiation capacity of WJCs. In addition, reducing plating density from 100 cells/cm 2 to 10 cells/cm 2 increased CFU-F frequency. Therefore, plating density and oxygen concentration are two important variables that affect the expansion rate and frequency of CFU-F of WJCs. These results suggest that these two variables might be used to produce different input populations for tissue engineering or cellular therapy.

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