Mesenchymal stem/progenitor cells (MSCs) were reported to enhance the survival of cellular and organ transplants. However, their mode of action was not established. We here used a mouse model of corneal allotransplantation and demonstrated that peri-transplant intravenous (i.v.) infusion of human MSCs (hMSCs) decreased the early surgically induced inflammation and reduced the activation of antigen-presenting cells (APCs) in the cornea and draining lymph nodes (DLNs). Subsequently, immune rejection was decreased, and allograft survival was prolonged. Quantitative assays for human GAPDH revealed that <10 hMSCs out of 1 × 10(6) injected cells were recovered in the cornea 10 hours to 28 days after i.v. infusion. Most of hMSCs were trapped in lungs where they were activated to increase expression of the gene for a multifunctional anti-inflammatory protein tumor necrosis factor-α stimulated gene/protein 6 (TSG-6). i.v. hMSCs with a knockdown of TSG-6 did not suppress the early inflammation and failed to prolong the allograft survival. Also, i.v. infusion of recombinant TSG-6 reproduced the effects of hMSCs. Results suggest that hMSCs improve the survival of corneal allografts without engraftment and primarily by secreting TSG-6 that acts by aborting early inflammatory responses. The same mechanism may explain previous reports that MSCs decrease rejection of other organ transplants.

y These authors contributed equally to this project and should be considered co-first authors.The porcine cornea may be a good solution for the shortage of human donor corneas because its size and refractive properties are comparable to those of the human cornea. However, antigenic differences need to be overcome to apply xenocorneal transplantation in actual clinical practice. We aimed to investigate the feasibility of full-thickness porcine corneas as human corneal substitutes using a CD40-CD154 costimulatory pathway blocking strategy in a clinically applicable pigto-nonhuman primate corneal transplantation model. As a result, the mean survival time of the xenocorneal grafts in recipients who received anti-CD154 antibodybased immunosuppressants (POD318 (n ¼ 4); >933, >243, 318 and >192) was significantly longer than that in controls (POD28 (n ¼ 3); 21, 28 and 29; p ¼ 0.010, logrank test). Administration of anti-CD154 antibodies markedly reduced inflammatory cellular infiltrations (predominantly CD8 T cells and macrophages) into the xenocorneal grafts and almost completely blocked xenoantigen-triggered increases in Th1-associated cytokines, chemokines and C3a in the aqueous humor. Moreover, systemic expansion of memory T cells was effectively controlled and responses of anti-Gal/donor pig-specific antibodies were considerably diminished by programmed injection of anti-CD154 antibodies. Consequently, porcine corneas might be promising human corneal substitutes when the transplantation is accompanied by potent immunosuppression such as a CD40-CD154 costimulatory pathway blockade.

Exogenously administered mesenchymal stem/stromal cells (MSCs) suppress autoimmunity despite transient engraftment. However, the mechanism is unclear. In this study, we report a novel mechanism by which MSCs modulate the immune system by recruiting myeloid-derived suppressor cells in a mouse model of experimental autoimmune uveitis (EAU). Intravenous infusion of MSCs blocked EAU development and reduced Th1 and Th17 responses. Time course analysis revealed an increase of MHC class IIloLy6G−Ly6ChiCD11b+ cells in draining lymph nodes by MSCs. These Ly6ChiCD11b+ cells suppressed CD4+ cell proliferation and Th1/Th17 differentiation and induced CD4+ cell apoptosis. Adoptive transfer of Ly6ChiCD11b+ cells ameliorated EAU, whereas depletion of Ly6ChiCD11b+ cells abrogated the effects of MSCs. 1.8% of MSCs were present in draining lymph nodes 1 d after infusion, and MSCs with CCL2 knockdown did not increase MHC class IIloLy6G−Ly6ChiCD11b+ cells and failed to attenuate EAU. Therefore, our findings demonstrate that MSCs suppress autoimmunity by recruiting myeloid-derived suppressor cells into sites of inflammation in a CCL2-dependent manner.

Dry eye syndrome (DES) is one of the most common ocular diseases affecting nearly 10% of the US population. Most of the currently available treatments are palliative, and few therapeutic agents target biological pathway of DES. Although DES is a multifactorial disease, it is well-known that inflammation in the ocular surface plays an important role in the pathogenesis of DES. Mesenchymal stem/stromal cells (MSCs) have been shown to repair tissues by modulating excessive immune responses in various diseases. Therefore, we here investigated the therapeutic potential of MSCs in a murine model of an inflammation-mediated dry eye that was induced by an intraorbital injection of concanavalin A. We found that a periorbital administration of MSCs reduced the infiltration of CD4(+) T cells and the levels of inflammatory cytokines in the intraorbital gland and ocular surface. Also, MSCs significantly increased aqueous tear production and the number of conjunctival goblet cells. Subsequently, corneal epithelial integrity was well-preserved by MSCs. Together, the results demonstrate that MSCs protect the ocular surface by suppressing inflammation in DES, and suggest that MSCs may offer a therapy for a number of ocular surface diseases where inflammation plays a key role.

Increased numbers of macrophages in rejected corneal allografts implicate that these cells might contribute to the immunopathogenesis of corneal graft rejection.