Decidual stromal cells support tolerance at the human foetal-maternal interface by inducing regulatory M2 macrophages and regulatory T-cells.

During pregnancy, the semi-allogeneic nature of the foetus requires maternal immune adaption and acquisition of tolerance at the foetal-maternal interface. Macrophages with regulatory properties and regulatory T (Treg) cells are central in promoting foetal tolerance and are enriched in the decidua (the uterine endometrium during pregnancy). Although tissue-resident decidual stromal cells (DSC) have been implicated in regulatory functions, it is not known if they are able to induce the regulatory phenotype of macrophages and T-cells. In this study we report that maternally derived DSC are able to induce homeostatic M2 macrophages and Treg cells. CD14+ monocytes and CD4+ T-cells from healthy non-pregnant women were cultured in the presence or absence of conditioned medium (CM) from DSC isolated from 1st trimester and term placentas. DSC-CM alone was able to promote the survival of macrophages and to induce a regulatory CD14brightCD163+CD209+CD86dim phenotype, typical for decidual macrophages and similar to that induced by M-CSF. Interestingly, DSC-CM was also able to overrule the pro-inflammatory effects of GM-CSF by upregulating CD14, CD163 and CD209. Protein-profiling showed that M-CSF was secreted by DSC, and blocking of M-CSF partially reversed the M2 phenotype and reduced viability. DSC-CM also expanded CD25brightFoxp3+ Treg cells, an expansion that was abolished by a SMAD3-inhibitor, indicating the contribution of TGF-ß signaling. In conclusion, our findings collectively emphasize the role of tissue-resident stromal cells in shaping the tolerogenic environment at the foetal-maternal interface.

Superselective intra-arterial umbilical cord blood administration to BM in experimental animals.

Umbilical cord blood (UCB) as a source of hematopoietic stem cells for transplantation is limited by the low number of cells and delayed engraftment. UCB cells are infused i.v. for transplantation, although only a proportion of the cells reach the BM. We investigated whether UCB could be administered safely using superselective intra-arterial (i.a.) injection. We injected human UCB (5 × 10(6)) into the aorta in rats, into the iliac artery in mice and into the femoral nutrient artery (FNA) in rabbits. We used angiography, immunohistochemistry, intravital microscopy and qPCR to assess safety end points and the distribution of injected cells. All animals showed normal behavior. No evidence of organ infarction was noted. UCB injected into the FNA of rabbits did not change the flow rates, measured by angiography. By qPCR, we found significantly higher fold-change values in the injected BM compared with i.v. injection (P=0.0087). Using intravital microscopy we visualized the mouse capillary bed during i.a. injection without cellular congestion. In summary, we show that i.a. infusion of UCB is safe and reaches an eightfold increase in engraftment in the BM compared with i.v. infusion. These studies lay the foundation for clinical trials.

Stromal cells-are they really useful for GVHD?

Mesenchymal stromal cells (MSCs) have immunomodulatory effects and are increasingly being used for the treatment of acute and chronic GVHD. Although they seem immuno-privileged, they induce alloresponses, but the risk of immunization is poorly characterized. After infusion, they first reach the lungs, liver and spleen, and are then difficult to trace. Several mechanisms are involved in stromal cells suppressing alloreactivity, such as induction of regulatory T cells, but whether or not this will also affect leukemic relapse or increase infections is not known. Although several encouraging pilot studies have been published, there have been few prospective randomized trials. There may be a bias in the literature, as negative results are seldom published, and there have been few comparative studies with other immunosuppressive regimens. Most animal models have failed to show any effect on GVHD. Several questions remain to be answered for optimization of stromal cell therapy. Which source is optimal-BM, fat, cord or decidua? Can stromal cells be replaced by exosomes, which culture conditions are most appropriate and at what passage and how frequently should cells be administered? More research is required to move stromal cell therapy forward to become an established treatment for acute and chronic GVHD.