Tissue culture prevents hyperacute rejection of islet xenografts

Reversal of diabetes in non-immunosuppressed rhesus macaques by intraportal porcine islet xenografts precedes acute cellular rejection

BACKGROUND

The functional response and immunobiology of primarily non-vascularized islet cell xenografts remain poorly defined in non-human primates.

METHODS

We transplanted 20,000 adult porcine islet equivalents/kg (purified and cultured for 48-h) intraportally into six streptozotocin-diabetic and two non-diabetic rhesus macaques. Two recipients were killed at various intervals post-transplant for histologic examination of livers bearing xenografts.

RESULTS

Plasma glucose levels in diabetic recipients averaged 94 mg/dl at 12 h, 92 mg/dl at 24 h, 147 mg/dl at 48 h, and 157 mg/dl at 72 h post-transplant. Serum porcine C-peptide was present in eight of eight recipients at 12 h, in five of six at 24 h, in four of four at 48 h, and in one of two at 72 h post-transplant. C3a and SC5b-9 plasma levels increased at 12 h post-transplant and returned to pre-transplant levels by 24 h. IgG, IgM anti-pig and anti-Gal IgG serum antibody levels did not increase post-transplant. Rejection was initiated by IgM and complement deposition on islets. Neutrophils dominated the cellular infiltrate at 12 h; CD4+ and CD8+ T cells were the main infiltrating cells at 24, 48, and 72 h; and macrophages increasingly infiltrated xenografts starting at 24 h post-transplant. Numerous xenoislets were present at all time points; their proportion without intraislet infiltrates decreased from 65% at 24 h to 17% at 72 h post-transplant.

CONCLUSIONS

Pig-to-primate intraportal islet xenografts reverse diabetes and the majority of intraportally transplanted xenogeneic islets are not subject to hyperacute rejection. They undergo acute cellular rejection mediated by CD4+- and CD8+ T cells and macrophages.

Damage to porcine islets of Langerhans after exposure to human blood in vitro, or after intraportal transplantation to cynomologus monkeys: protective effects of sCR1 and heparin

BACKGROUND

Porcine islets offer an attractive alternative to human islets in clinical islet transplantation. The preferred method of islet transplantation is intra-portal injection into the liver. We have recently shown, both in vitro with human islets and in vivo with porcine islets, that islets exposed to allogeneic blood trigger an injurious inflammatory reaction characterized by activation of both coagulation and the complement systems. We have now tested whether a similar reaction is triggered when xenogeneic porcine islets are exposed to human blood in vitro and after intraportal transplantation into primates. Furthermore, we investigated the effect of inhibiting the complement and coagulation systems.

METHOD

Islets isolated from adult and fetal porcine pancreas were perfused with fresh human blood in surface heparinized PVC tubings for 5-60 min. Blood cell counts and parameters related to coagulation and the complement system were analyzed, and islets were retrieved after the perifusion was examined by immunohistochemical method. Heparin and soluble complement receptor 1 (sCR1; TP10, 100 microg/ml) were added to the system in some experiments. Furthermore, adult porcine islets were transplanted intraportally into untreated and sCR1- (40 mg/kg BW i.v.) treated cynomolgus monkeys, and plasma insulin concentration was monitored during 60 min after transplantation.

RESULTS

Porcine islets perifused with human blood triggered an immediate inflammatory reaction, characterized by a rapid consumption and activation of platelets, consumption of neutrophils and monocytes, activation of the coagulation and complement systems, and release of large amounts of insulin. Islet morphologic analysis revealed damaged islets embedded in clots and infiltrated with CD11+ leukocytes. C3a and C5b-9 was deposited on the islet surface, but human immunoglobulin was not. Complement inhibition with sCR1 reduced insulin release significantly. Intraportal islet transplantation into untreated cynomolgus monkeys resulted in a marked and rapid increase in plasma insulin concentration indicative of islet damage. Pretreatment of the monkeys with sCR1 resulted in significantly less insulin release than in untreated control monkeys.

CONCLUSION

Exposure of isolated xenogeneic islets of Langerhans to blood, both in vitro and in vivo, resulted in acute islet damage. Complement and platelets seem to have a central role in the reactions described. Strategies to efficiently inhibit these reactions will be crucial for clinical intraportal islet xenotransplantation to be successful.

Posttransplant nonfunction of canine islets in PVG rats deficient in complement component C6

BACKGROUND

Discordant islet xenografts are immediately nonfunctional in nonimmunosuppressed recipients other than the mouse, a process called primary nonfunction. Although at present it is unknown whether complement is involved, complement might participate in the induction of primary nonfunction through a number of mechanisms. We investigated the potential role of the membrane attack complex of complement in primary nonfunction of transplanted xenoislets.

METHODS

Canine islets were transplanted into both nonimmunosuppressed and immunosuppressed normocomplementemic and C6-deficient (C6D) PVG rats. Cyclosporine, rapamycin, deoxyspergualin, and mycophenolate mofetil were used for immunosuppression from day -3 to cessation of islet cell function. Serum glucose was measured at 6 hr after transplant and daily thereafter. Xenograft tissue sections were obtained at various times after transplant and stained for inflammatory cells and insulin.

RESULTS

Canine islets grafted in nonimmunosuppressed C6D rats and normocomplementemic rats underwent primary nonfunction in all animals. The incidence of primary nonfunction in animals receiving a four-drug immunosuppressive regimen was 33% in the normocomplementemic rats but only 10% in the C6D rats. The mean functional islet survival time was 1.57+/-0.33 days in the normocomplementemic group and 2.70+/-0.67 days in the C6D group (P=0.38). The islet xenografts showed little difference in degree and composition of cell infiltration between normocomplementemic and C6D rats.

CONCLUSION

The membrane attack complex does not appear to play a major role in primary nonfunction of canine islet xenografts in nonimmunosuppressed PVG rats. However, there was a lower incidence of primary nonfunction and a longer posttransplant survival time in immunosuppressed C6D rats, suggesting the membrane attack complex may play a minor role in recipients that are heavily immunosuppressed.