A major goal of immunotherapy remains the control of pathogenic T cell responses that drive autoimmunity and allograft rejection. Adherent progenitor cells, including mesenchymal stromal cells (MSCs) and multipotent adult progenitor cells (MAPCs), represent attractive immunomodulatory cell therapy candidates currently active in clinical trials. MAPCs can be distinguished from MSCs on the basis of cellular phenotype, size, transcriptional profile, and expansion capacity. However, despite their ongoing evaluation in autoimmune and allogeneic solid organ transplantation settings, data supporting the immune regulatory potential of clinical-grade MAPCs are limited. In this study, we used allogeneic islet transplantation as a model indication to assess the ability of clinical-grade MAPCs to control T cell responses that drive immunopathology in human autoimmune disease and allograft rejection. MAPCs suppressed T cell proliferation and Th1 and Th17 cytokine production while increasing secretion of IL-10 and were able to suppress effector functions of bona fide autoreactive T cells from individuals with type 1 diabetes mellitus, including killing of human islets. Furthermore, MAPCs favored the proliferation of regulatory T cells during homeostatic expansion driven by γ-chain cytokines and exerted a durable, yet reversible, control of T cell function. MAPC suppression required licensing and proceeded via IDO-mediated tryptophan catabolism. Therefore, the common immune modulatory characteristics of clinical-grade MAPCs shown in this study suggest that they can be regarded as an alternative source of adult progenitor cells with similar clinical usefulness to MSCs. Taken collectively, these findings may guide the successful deployment of both MSCs and MAPCs for the amelioration of human autoimmunity and allograft rejection.

Multipotent adult progenitor cells (MAPCs) are bone marrow-derived nonhematopoietic stem cells with a broad differentiation potential and extensive expansion capacity. A comparative study between human mesenchymal stem cells (hMSCs) and human MAPCs (hMAPCs) has shown that hMAPCs have clearly distinct phenotypical and functional characteristics from hMSCs. In particular, hMAPCs express lower levels of MHC class I than hMSCs and cannot only differentiate into typical mesenchymal cell types but can also differentiate in vitro and in vivo into functional endothelial cells. The use of hMSCs as cellular immunomodulatory stem cell products gained much interest since their immunomodulatory capacities in vitro became evident over the last decade. Currently, the clinical grade stem cell product of hMAPCs is already used in clinical trials to prevent graft-versus-host disease (GVHD), as well as for the treatment of acute myocardial infarct, ischemic stroke, and Crohn's disease. Therefore, we studied the immune phenotype, immunogenicity, and immunosuppressive effect of hMAPCs in vitro. We demonstrated that hMAPCs are nonimmunogenic for T-cell proliferation and cytokine production. In addition, hMAPCs exert strong immunosuppressive effects on T-cell alloreactivity and on T-cell proliferation induced by mitogens and recall antigens. This immunomodulatory effect was not MHC restricted, which makes off-the-shelf use promising. The immunosuppressive effect of hMAPCs is partially mediated via soluble factors and dependent on indoleamine 2,3-dioxygenase (IDO) activity. At last, we isolated hMAPCs, the clinical grade stem cell product of hMAPCs, named MultiStem, and hMSCs from one single donor and observed that both the immunogenicity and the immunosuppressive capacities of all three stem cell products are comparable in vitro. In conclusion, hMAPCs have potent immunomodulatory properties in vitro and can serve as a valuable cell source for the clinical use of immunomodulatory cellular stem cell product.

Phosphatidylinositol transfer proteins (PITPs) regulate the interface between signal transduction, membrane-trafficking, and lipid metabolic pathways in eukaryotic cells. The best characterized mammalian PITPs are PITP␣ and PITP␤, two highly homologous proteins that are encoded by distinct genes. Insights into PITP␣ and PITP␤ function in mammalian systems have been gleaned exclusively from cell-free or permeabilized cell reconstitution and resolution studies. Herein, we report for the first time the use of genetic approaches to directly address the physiological functions of PITP␣ and PITP␤ in murine cells. Contrary to expectations, we find that ablation of PITP␣ function in murine cells fails to compromise growth and has no significant consequence for bulk phospholipid metabolism. Moreover, the data show that PITP␣ does not play an obvious role in any of the cellular activities where it has been reconstituted as an essential stimulatory factor. These activities include protein trafficking through the constitutive secretory pathway, endocytic pathway function, biogenesis of mast cell dense core secretory granules, and the agonist-induced fusion of dense core secretory granules to the mast cell plasma membrane. Finally, the data demonstrate that PITP␣-deficient cells not only retain their responsiveness to bulk growth factor stimulation but also retain their pluripotency. In contrast, we were unable to evict both PITP␤ alleles from murine cells and show that PITP␤ deficiency results in catastrophic failure early in murine embryonic development. We suggest that PITP␤ is an essential housekeeping PITP in murine cells, whereas PITP␣ plays a far more specialized function in mammals than that indicated by in vitro systems that show PITP dependence.

Mesenchymal stromal cells (MSCs) are multipotent stem cells with immunosuppressive and trophic support functions. While MSCs from different sources frequently display a similar appearance in culture, they often show differences in their surface marker and gene expression profiles. Although bone marrow is considered the "gold standard" tissue to isolate classical MSCs (BM-MSC), MSC-like cells are currently also derived from more easily accessible extra-embryonic tissues such as the umbilical cord. In this study, we defined the best way to isolate MSCs from the Wharton's jelly of the human umbilical cord (WJ-MSC) and assessed the mesenchymal and immunological phenotype of BM-MSC and WJ-MSC. Moreover, the gene expression profile of established WJ-MSC cultures was compared to two different bone marrow-derived stem cell populations (BM-MSC and multipotent adult progenitor cells or MAPC). We observed that explant culturing of Wharton's jelly matrix is superior to collagenase tissue digestion for obtaining mesenchymal-like cells, with explant isolated cells displaying increased expansion potential. While being phenotypically similar to adult MSCs, WJ-MSC show a different gene expression profile. Gene ontology analysis revealed that genes associated with cell adhesion, proliferation, and immune system functioning are enriched in WJ-MSC. In vivo transplantation confirms their immune modulatory effect on T cells, similar to BM-MSC and MAPC. Furthermore, WJ-MSC intrinsically overexpress genes involved in neurotrophic support and their secretome induces neuronal maturation of SH-SY5Y neuroblastoma cells to a greater extent than BM-MSC. This signature makes WJ-MSC an attractive candidate for cell-based therapy in neurodegenerative and immune-mediated central nervous system disorders such as multiple sclerosis, Parkinson's disease, or amyotrophic lateral sclerosis.

The last decade has seen much progress in adjunctive cell therapy for immune disorders. Both corporate and institutional Phase III studies have been run using mesenchymal stromal cells (MSC) for treatment of Graft versus Host Disease (GvHD), and product approval has been achieved for treatment of pediatric GvHD in Canada and New Zealand (Prochymal®; Osiris Therapeutics). This effectiveness has prompted the prophylactic use of adherent stem cells at the time of allogeneic hematopoietic stem cell transplantation (HSCT) to prevent occurrence of GvHD and possibly provide stromal support for hematopoietic recovery. The MultiStem® product is an adult adherent stem cell product derived from bone marrow which has significant clinical exposure. MultiStem cells are currently in phase II clinical studies for treatment of ischemic stroke and ulcerative colitis, with Phase I studies completed in acute myocardial infarction and for GvHD prophylaxis in allogeneic HSCT, demonstrating that MultiStem administration was well tolerated while the incidence and severity of GvHD was reduced. In advancing this clinical approach, it is important to recognize that alternate models exist based on clinical manufacturing strategies. Corporate sponsors exploit the universal donor properties of adherent stem cells and manufacture at large scale, with many products obtained from one or limited donors and used across many patients. In Europe, institutional sponsors often produce allogeneic product in a patient designated context. For this approach, disposable bioreactors producing <10 products/donor in a closed system manner are very well suited. In this review, the use of adherent stem cells for GvHD prophylaxis is summarized and the suitability of disposable bioreactors for MultiStem production is presented, with an emphasis on quality control parameters, which are critical with a multiple donor approach for manufacturing.