The role of dissolved oxygen levels on human Mesenchymal Stem Cell culture success, regulatory compliance and therapeutic potential

Most cells in the human body, including human mesenchymal stem cells (hMSCs), have evolved to survive and function in a low, physiological, oxygen (O₂) environment. Investigators have become increasingly aware of the effects of O₂ levels on hMSC biology and culture and are mimicking the natural niche of these cells in vitro to improve cell culture yields. This presents many challenges in relation to hMSC identity and function and in the maintenance of a controlled O₂ environment for cell culture. The aim of this review is to discuss a “hMSC checklist” as a guide to establishing which identity and potency assays to implement when studying hMSCs. The checklist includes markers, differentiation potential, proliferation & growth, attachment & migration, genomic stability and paracrine activity. Evidence drawn from the current literature demonstrates that low O₂ environments could improve most “hMSC checklist” attributes. However, there are substantial inconsistencies around both the terminology and the equipment used in low O₂ studies. Therefore, “hypoxia” as a term and as a culture condition are discussed. The biology of short (acute) vs long-term (chronic) hypoxia is considered and a nascent hypothesis to explain the behaviour of hMSCs in long-term hypoxia is presented. It is hoped that by establishing an ongoing discourse, and driving towards a regulatory recognisable “hMSC checklist”, we may be better able to provide the patient population with safe and efficacious regenerative treatments.