Interaction of allogeneic adipose tissue-derived stromal cells and unstimulated immune cells in vitro: the impact of cell-to-cell contact and hypoxia in the local milieu.

Multipotent mesenchymal stem cells (MSCs) are an attractive tool for cell therapy and regenerative medicine. Being applied in vivo, allogeneic MSCs are faced with both activated and unstimulated immune cells. The effects of MSCs on activated immune cells are well described and are mainly suppressive. Less is known about the interaction of MSCs with unstimulated immune cells. We evaluated the contribution of tissue-related O2 level ("physiological" hypoxia-5% O2) and cell-to-cell contact to the interaction between allogeneic adipose tissue-derived MSCs (ASCs) and unstimulated peripheral blood mononuclear cells (PBMCs). Under both O2 levels, ASCs affected the immune response by elevating the proportion of CD69+ T cells and modifying the functional activity of unstimulated PBMCs, providing a significant reduction of ROS level and activation of lysosome compartment. "Physiological" hypoxia partially attenuated the ASC modulation of PBMC function, reducing CD69+ cell activation and more significantly supressing ROS. In direct co-culture, the ASC effects were more pronounced. PBMC viability was preferentially maintained, and the lymphocyte subset ratio was altered in favour of B cells. Our findings demonstrate that allogeneic ASCs do not enhance the activation of unstimulated immune cells and can provide supportive functions. The "hypoxic" phenotype of ASCs may be more "desirable" for the interaction with allogeneic immune cells that may be required in cell therapy protocols.

Tissue-Related Hypoxia Attenuates Proinflammatory Effects of Allogeneic PBMCs on Adipose-Derived Stromal Cells In Vitro.

Human adipose tissue-stromal derived cells (ASCs) are considered a perspective tool for regenerative medicine. Depending on the application mode ASC/allogeneic immune cell interaction can occur in the systemic circulation under plenty high concentrations of O2 and in target tissues at lower O2 levels. Here we examined the effects of allogeneic PHA-stimulated peripheral blood mononuclear cells (PBMCs) on ASCs under ambient (20%) oxygen and "physiological" hypoxia (5% O2). As revealed with microarray analysis ASCs under 20% O2 were more affected by activated PBMCs, which was manifested in differential expression of more than 300 genes, whereas under 5% O2 only 140 genes were changed. Altered gene pattern was only partly overlapped at different O2 conditions. Under O2 ASCs retained their proliferative and differentiative capacities, mesenchymal phenotype, and intracellular organelle' state. ASCs were proinflammatory activated on transcription level that was confirmed by their ability to suppress activation and proliferation of mitogen-stimulated PBMCs. ASC/PBMCs interaction resulted in anti-inflammatory shift of paracrine mediators in conditioning medium with significant increase of immunosuppressive LIF level. Our data indicated that under both ambient and tissue-related O2 ASCs possessed immunosuppressive potential and maintained functional activity. Under "physiological" hypoxia ASCs were less susceptible to "priming" by allogeneic mitogen-activated PBMCs.