Introduction: Islet transplantation is a minimally invasive treatment for type 1 diabetes. However, several problems remain, such as early graft damage. Early graft damage prevents the achievement of insulin withdrawal with single islet transplantation. Stem cell-islet co-transplantation has attracted attention as one method to improve islet engraftment. Human amniotic epithelial cell (hAEC), one of the perinatal stem cells, could be a promising candidate as a cell source. Angiogenesis-promoting, anti-inflammatory, and immunomodulatory effects have been reported in this stem cell. We hypothesized that these characteristics would improve the islet engraftment and planned this study to overcome early islet damage with hAEC-islet co-transplantation.
Methods: Human amniotic membrane (hAM) was collected from delivered placentas with the consent of pregnant women who underwent an elective cesarean section at full term. hAECs were immediately isolated from collected hAM and cryopreserved in liquid nitrogen.
In an in vivo study, diabetes was induced in Lewis rats with streptozotocin 7–8 days before transplantation. 600 IEQs syngeneic islets isolated from Lewis rats were transplanted alone or mixed with 1.0×10⁶ hAECs via the portal vein. Blood glucose levels were measured periodically after transplantation. Serum samples were collected early after transplantation, and inflammatory cytokines in the serum were quantified by a multiplex assay. In addition, thrombin antithrombin (TAT) levels in the plasma were analyzed to examine the influence of hAEC on instant blood-mediated inflammatory reaction (IBMIR). After the observation completed, the liver was removed and subjected to immunohistochemical staining.
An in vitro study was also performed to investigate the mechanisms of action of hAEC-islet co-transplantation. The co-cultured supernatants were collected and analyzed using a multiplex assay.
Results: The blood glucose levels were significantly low in the co-transplantation group (p = 0.041). The cure rate of diabetes was significantly high in the co-transplantation group (p < 0.01).
Results of serum inflammatory cytokine quantification in the co-transplantation group showed significantly lower C-X-C motif chemokine ligand 1 (CXCL1), interleukin-4 (IL-4), interleukin-5 (IL-5), and interleukin-12p70 (IL-12p70) than in the control group. Plasma TAT levels trended to be lower in the co-transplantation group, though the difference did not reach statistical significance. Histological findings revealed that no obvious hAEC accumulation or angiogenesis promotion around the islets was observed in the co-transplantation group.
The co-cultured supernatant also showed significant suppression of CXCL1 in the co-culture group.
Conclusions: This study showed that hAEC-islet co-transplantation promoted islet engraftment. The main mechanism of this effect was suggested to be the suppression of inflammatory cell migration induced by chemokines, rather than the suppression of IBMIR.