Expansion of human cardiac stem cells in physiological oxygen improves cell production efficiency and potency for myocardial repair

Aims The ex vivo expansion of cardiac stem cells from minimally invasive human heart biopsies yields tens of millions of cells within 3-4 weeks, but chromosomal abnormalities were frequently detected in preliminary production runs. Here we attempt to avoid aneuploidy and improve cell quality by expanding human cardiac stem cells in physiological low-oxygen (5 O₂) conditions, rather than in traditional culture in a general CO₂ incubator (20 O₂).Methods and results Human heart biopsies (n=16) were divided and processed in parallel to expand cardiac stem cells under 5 or 20 O₂. Compared with 20 O₂, 5 O₂ culture doubled the cell production and markedly diminished the frequency of aneuploidy. Cells expanded in 5 O₂ showed lower intracellular levels of reactive oxygen species, less cell senescence, and higher resistance to oxidative stress than those grown in 20 O₂, although the expression of stem cell antigens and adhesion molecules was comparable between groups, as was the paracrine secretion of growth factors into conditioned media. In vivo, the implantation of 5 O₂ cells into infarcted hearts of mice resulted in greater cell engraftment and better functional recovery than with conventionally cultured cells. Conclusion The expansion of human adult cardiac stem cells in low oxygen increased cell yield, and the resulting cells were superior by various key in vitro and in vivo metrics of cell quality. Physiological oxygen tensions in culture facilitate the ex vivo expansion of healthy, biologically potent stem cells.