The present study shows that human UCX® cells are a homogenous population of stem cells that comply with the current definition of mesenchymal stromal cell (MSC) as established by the International Society for Cellular Therapy (ISCT)  namely, cells adhere to a plastic surface, at least 95% of UCX® cells in the population are consistently positive for the cell surface markers CD44, CD73, CD90 and CD105 and less than 2% positive for CD14, CD19, CD31, CD34, CD45 and HLA-DR, and cells are capable of undergoing tri-lineage differentiation into adipocytes, chondrocytes and osteoblasts. More importantly, UCX® cells have the capacity to inhibit human T-cell proliferation, and concomitantly induce the conversion of T-cells to the Treg sub-type of regulatory cells. Our results showed that such capacity is more evident in UCX® cells than in BM-MSCs, sometimes considered the gold standard for MSC therapy applications.
Our results also showed that, in a xenogeneic setting, human UCX® cell immunosuppression properties can result in arthritic anti-inflammatory activity in vivo, both in acute and chronic arthritis animal models. UCX® cells administered in a rat CarrIA model strongly attenuated hind paw inflammation, protecting against acute edema formation in a cell-specific fashion. Furthermore, UCX® action in vivo was dependent on cell viability. The anti-inflammatory effect was not observed when using human BM-MSCs in the same acute model, in accordance to the lower immunosuppressive capacity observed in vitro. The differences in anti-inflammatory behavior between UCX® cells and BM-MSCs, as seen in a CarrIA model, agree with previous studies where UC-MSCs have proven effective in treating collagen-induced arthritis in mice , while BM-MSCs have been shown to be ineffective in AIA rats . These different observations also show that MSCs from different tissue sources should not be treated as equal in terms of their immunosuppressive and anti-inflammatory activities and should therefore be discussed and evaluated as separate treatment strategies.
In fact, a comparative study between BM-MSCs and Wharton’s Jelly-derived UC-MSCs, primed with key pro-inflammatory cytokines IFN-γ and TNF-α, showed that the extent of immunosuppression was more accentuated with UC-MSCs than with BM-MSCs in both cases . Furthermore, priming BM-MSCs with IFNγ enhanced suppression of mitogen-driven lymphocyte proliferation only, whereas IFN-γ primed UC-MSCs were better suppressors in MLRs, in agreement with our observations using UCX® cells. Additionally, PHA-stimulated lymphocytes in co-cultures of primed/unprimed UC-MSCs and BM-MSCs showed that UC-MSCs resulted in an early activation of a negative co-stimulatory molecule, CTLA4, which was not evident with BM-MSCs . In summary, different expression patterns indicated that UC-MSCs were less immunogenic, more immunosuppressive and more inflammatory than BM-MSCs .
More recently, the observations described above have been further consubstantiated. High throughput gene expression analysis using microarrays (GeneShip® from Affymetrix) have shown that UCX® cells express significantly higher levels of IL-8, IL1β, LIF and TGFβ when compared with BM-MSCs. The receptors for pro-inflammatory cytokines such as IFN-γ, TNFα and IL-1β were also found substantially expressed in UCX® cells, which is consistent with the reported ability of these cells to home to inflammation sites and become immunosuppressive in response to inflammatory signals (results to be published elsewhere). The expression of LIF and TGF-β are particularly relevant for this study since both have been directly implicated in Treg induction [36, 37].
Finally, the combined immunosuppressive and anti-inflammatory capabilities of human UCX® cells were successfully applied to the treatment of AIA in vivo. treated animals, through an i.a. mode of administration, presented full recovery of both local and systemic AIA signs, as well as local motor hindrance. Overall, the results suggest that UCX® cells have been successful in protecting against the development of more severe manifestations of arthritis, from a period with already observable manifestations at day 13 (AI of 4) up to day 38 after induction, when Sham controls and untreated animals developed clearly more severe conditions. Additional to this protective effect, both i.p. and i.a.- administered UCX® cells were able to promote regression of arthritic manifestations, reducing all measurable and observable IA parameters. To our knowledge, this study presents the first evidence of successful treatment of chronic adjuvant-induced arthritis (AIA) where MSC-type cells have been administered after the appearance of clear AIA manifestations.
Human UC-MSCs have been shown previously to suppress the various inflammatory effects of FLSs and T-cells of RA in vitro, and to attenuate the development of collagen-induced arthritis (CIA) in mice. In addition, the immunosuppressive activity of UC-MSCs was prolonged by the participation of Tregs . Tregs modulate a variety of immune functions from initial T-cell and B-cell activation to effector function in the target tissue, and appear to play a critical role in the maintenance of self-immune tolerance in RA [28, 38]. Some authors consider that CD4+CD25+ cells in PBMCs contain a mixture of both thymic natural Tregs (nTregs) and periphery induced Tregs (iTregs). The generation of iTregs is dependent upon the presence of both TGF-β and TGF-β receptor signals. Furthermore, iTregs are known to be superior to nTregs in ameliorating established CIA, as well as other types of ongoing autoimmunities . We would like to propose that the use of UCX® cells is an effective and promising new approach for treating autoimmune-derived inflammatory arthritis symptoms by a mechanism involving homing to inflammation sites and immunosuppression via a two-way pathway: 1- repression of T-cell proliferation and 2- TGF-β-dependent paracrine promotion of iTreg conversion. The beneficial effects can be extended to the systemic nature of autoimmune inflammatory arthritis disorders, such as RA.