Delayed revascularization of islet after transplantation by IL-6 blockade in pig to nonhuman primate islet xenotransplantation model

Abstract

Background

Pancreatic islet transplantation is currently proven as a promising treatment for type 1 diabetes patients with labile glycemic control and severe hypoglycemia unawareness. Upon islet transplantation, revascularization is essential for proper functioning of the transplanted islets. As IL-6 is important for endothelial cell survival and systemic inflammation related to xenograft, the effect of IL-6 receptor antagonist, tocilizumab on revascularization of the transplanted islets was examined in pig to nonhuman primate islet xenotransplantation model. Also, the endothelial cell origin in a new vessel of the transplanted pig islets was determined.

Methods

Pig islets were isolated from designated pathogen-free (DPF) SNU miniature pigs and transplanted via portal vein into five streptozotocin-induced diabetic monkeys. One group (n=2, basal group) was treated with anti-thymoglobulin (ATG), anti-CD40 antibody (2C10R4), sirolimus and tacrolimus and the other group was additionally given tocilizumab on top of basal immunosuppression (n=3, Tocilizumab group). To confirm IL-6 blocking effect, C-reactive protein (CRP) levels and serum IL-6 concentration were measured. Scheduled biopsy of the margin of the posterior segment right lobe inferior of the liver was performed at three weeks after transplantation to assess the degree of revascularization of the transplanted islets. Immunohistochemical staining using anti-insulin, anti-CD31 antibodies and lectin IB4 was conducted to find the origin of endothelial cells in the islet graft.

Results

CRP significantly increased at 1~2 days after transplantation in Basal group, but not in Tocilizumab group and higher serum IL-6 concentration was measured in latter group, showing the biological potency of tocilizumab. In Basal group, well-developed endothelial cells were observed on the peri- and intra islet area, whereas the number of CD31 ⁺ cells in the intra-islet space was significantly reduced in Tocilizumab group. Finally, new endothelial cells in the pig islet graft was positive for CD31, but not for lectin IB4, suggesting that they are originated from the recipient monkey.

Conclusions

our results demonstrated that tocilizumab can delay revascularization of the transplanted islet, although this effect had no significant correlation to the overall islet graft survival. In the pig to NHP islet xenotransplantation model, the endothelial cells from recipient monkey form new blood vessels in and around pig islets.