Beneficial effects of the transgenic expression of human sTNF-αR-Fc and HO-1 on pig-to-mouse islet xenograft survival.

Both human soluble tumor necrosis factor-α receptor-Fc (sTNF-αR-Fc) and heme oxygenase-1 (HO-1) transgenic pigs have been generated previously for xenotransplantation. Here, we investigated whether overexpression of sTNF-αR-Fc or HO-1 in pig islets prolongs islet xenograft survival. Adult porcine islets were isolated from human sTNF-αR-Fc or HO-1 transgenic and wild type pigs, and were transplanted into diabetic nude mice. Effects of the expression of both genes on islet apoptosis, chemokine expression, cellular infiltration, antibody production, and islet xenograft survival were analyzed. Human sTNF-αR-Fc transgenic pigs successfully expressed sTNF-αR-Fc in the islets; human HO-1 transgenic pigs expressed significant levels of HO-1 in the islets. Pig-to-mouse islet xenograft survival was significantly prolonged in both the sTNF-αR-Fc and HO-1 groups compared with that in the wild type group. Both the sTNF-αR-Fc and HO-1 groups exhibited suppressed intragraft expression of monocyte chemoattractant protein-1 (MCP-1) and decreased perigraft infiltration of immune cells. However, there was no difference in the anti-pig antibody levels between the groups. Apoptosis of islet cells during the early engraftment was suppressed only in the HO-1 group. Porcine islets from both sTNF-αR-Fc and HO-1 transgenic pigs prolonged xenograft survival by suppressing islet cell apoptosis or secondary inflammatory responses following islet death, indicating that these transgenic pigs might have applications in successful islet xenotransplantation.

Roles of islet Toll-like receptors in pig to mouse islet xenotransplantation.

Although innate immunity plays important roles in xenograft rejection, there have been few studies on the role of toll-like receptors (TLRs) in xenotransplantation. Furthermore, most studies focused on the recipient's TLRs. Therefore, we investigated whether TLRs in porcine islets can contribute to islet xenograft rejection. Adult porcine islets were isolated and stimulated by polyinosinic/polycytidylic acid (poly I:C) or lipopolysaccharide (LPS). Both poly I:C and LPS stimulation in porcine islets induced expression of chemokines (RANTES, MCP-1, IP-10, and IL-8), cytokines (IL-6 and type I interferons), and adhesion molecules (VCAM-1 and ICAM-1). Porcine islet supernatants stimulated by TLR agonists induced chemotaxis of human leukocytes. They also induced procoagulant activation (tissue factor and fgl-2). However, TLR stimulation did not influence insulin secretion. When porcine MyD88 was knocked down using shRNA lentivirus, TLR-mediated induction of proinflammatory mediators and procoagulants was attenuated. When LPS was injected to MyD88 or TLR4 knockout mice after porcine islet transplantation, LPS stimulation on donor islets interfered with islet xenograft tolerance induction by anti-CD154 antibodies. Inflammatory cell infiltration and expression of proinflammatory chemokines and cytokines in islet xenografts also increased. In conclusion, TLR activation in porcine islets induced both a proinflammatory and procoagulant response and thereby contributed to xenograft rejection.

Roles of Toll-like receptors in allogeneic islet transplantation.

BACKGROUND: Toll-like receptors (TLRs) are involved in the rejection of solid organ allografts. However, the roles of TLRs in islets are still controversial. We investigated the roles of TLRs in donor islets together with those in recipients in allogeneic islet transplantation. METHODS: To assess the roles of TLRs in either donor islets or recipients, allogeneic islet transplantation was performed using myeloid differentiation factor 88 (MyD88)-knockout (KO), TLR4-KO, or Toll/interleukin-1 receptor domain-containing adaptor-inducing interferon-ß (TRIF)-KO mice. RESULTS: Both polyriboinosinic polyribocytidylic acid and lipopolysaccharide (LPS) stimulation induced the mRNA expression of regulated and normal T cell expressed and secreted, interferon-γ-inducible protein-10, monocyte chemotactic protein-1, interleukin-8, and inducible nitric oxide synthase in murine islets, whereas the induction was attenuated in TRIF-KO, interferon-ß promoter stimulator-1-KO, and TLR4-KO mice. When islets from MyD88-KO, TLR4-KO, or TRIF-KO C57BL/6 mice were transplanted to BALB/c recipients, graft survival was not better than that of wild-type (WT) islets. However, the survival of the MyD88-KO islet allograft was significantly prolonged when combined with anti-CD40L. In parallel, LPS stimulation in donor islets interfered with anti-CD40L blockade-mediated long-term survival of islet allografts in TLR4-KO recipients. LPS stimulation increased the perigraft infiltration of both T cells and macrophages. Then again, when islets from WT BALB/c mice were transplanted to MyD88-KO, TRIF-KO, or WT C57BL/6 mice, there was no difference in graft survival, although some of the MyD88-KO recipients obtained long-term graft survival. However, anti-CD40L prolonged graft survival significantly in MyD88-KO recipients. The absence of MyD88 in either donors or recipients decreased the perigraft infiltration of inflammatory cells when combined with anti-CD40L. CONCLUSIONS: TLRs in both donor islets and recipients are involved in islet allograft rejection.