Infusion of Mesenchymal Stem Cells Combined with Epithelial Progenitor Cells Promotes Injured Intestinal Repairing after Hematopoietic Cell Transplantation

Pre-transplant chemoradiotherapy can impair intestinal barrier function and disrupt immune homeostasis, and thus increase the incidence of infection and other related complications. Mesenchymal stem cells (MSCs) have the potential to rescue Inflammatory Bowel Disease and intestinal graft versus host disease owing to their immunosuppressive capabilities. However, limited studies regarding MSC administration has been reported to aggravate T cell-mediated tissue injury. Plus, endothelial progenitor cells (EPCs) could improve endothelium repair, facilitate hematopoietic reconstitution and alleviate complications associated with hematopoietic cell transplantation (HCT). The key goals of this study were to i) identify the role of MSC derived soluble and contact dependent factors and how these affect intestinal injury; ii) investigate the effect of MSC combined EPC therapy for repairing the injured intestine.

In this study, BALB/c mice were randomly divided into five groups, namely, total body irradiation only, bone marrow transplantation (BMT), MSC(BMT with 1 × 10⁶MSC infusion), EPC(BMT with 5 × 10⁵ EPCs infusion), and MSC+EPC (BMT with 1 × 10⁶ MSC and 5 × 10⁵ EPCs infusion). Results showed that the best performance of intestine was found in the MSC+EPC treated group, which showed more epithelial and goblet cells, and less apoptosis cells and adjacent crypts fusion in intestine morphology. EPC or MSC only group improved the intestinal injuries slightly compared with BMT group. The higher MECA-32 expression level was found in the intestinal tissue of MSC+EPC and MSC groups compared with other treated groups. The tight junction molecules occludin had highest expression level in the intestinal epithelial cells of MSC+EPC group, followed by MSC group and then EPC groups, but the expression level in BMT group was extremely low. Further study demonstrated that in MSC+EPC group the phosphorylated P38 enhanced heat shock protein HSP27 activation, which promoted cytoskeleton reconstruction and intestinal epithelial cells proliferation; and phosphorylated P38 also down-regulated the expression of apoptosis-related molecule caspase3.

Moreover, the multiple effects of MSCs on cellular immunity may reflect their diverse influences on the different T-cell subpopulations. MSC+EPC infusion increased the number of IL-17A secreting cells (Th17 and Tc17) in mesenteric lymph nodes early after HCT, and decreased Th1 cells at day 10 and delayed expanding of Tc1 from day 10 to day 15. The soluble IL-17A in intestinal tissue was significantly increased after MSC+EPC infusion in according with IL-17A secreting cells in mesenteric lymph nodes.

Furthermore, the gut bacterial information analyzed by high throughput sequencing uncovered that MSC and MSC+EPC groups had higher bacterial diversity and richness compared with other groups, and the bacterial community structures exhibited big changes regarding different treatment. Co-occurrence analysis demonstrated that the genus Akkermansia inducing PD-1 expression of T cells had significant correlation with phosphorylation of P38 and HSP27 in MSC+EPC and EPC treated groups, which indicated Akkermansia may be a key bacteria participanting the intestinal repairing in MSC and MSC+EPC groups.

In conclusion, this study confirmed that the MSC+EPC infusion can obviously repair injured intestine, and gut bacteria Akkermansia correlated with phosphorylation of P38 and HSP27 expression and participated in intestinal repairing.