Improved suppression of circulating complement does not block acute vascular rejection of pig-to-rhesus monkey cardiac transplants.

At present, acute vascular rejection (AVR) remains a primary obstacle inhibiting long-term graft survival in the pig-to-non-human primate transplant model. The present study was undertaken to determine whether repetitive injection of low dose Yunnan-cobra venom factor (Y-CVF), a potent complement inhibitor derived from the venom of Naja kaouthia can completely abrogate hemolytic complement activity and subsequently improve the results in a pig-to-rhesus monkey heterotopic heart transplant model. Nine adult rhesus monkeys received a heterotopic heart transplant from wild-type pigs and the recipients were allocated into two groups: group 1 (n = 4) received repetitive injection of low dose Y-CVF until the end of the study and group 2 (n = 5) did not receive Y-CVF. All recipients were treated with cyclosporine A (CsA), cyclophosphamide (CyP) and steroids. Repetitive Y-CVF treatment led to very dramatic fall in CH50 and serum C3 levels (CH50 < 3 units/C3 remained undetectable throughout the experiment) and successfully prevented hyperacute rejection (HAR), while three of five animals in group 2 underwent HAR. However, the continuous suppression of circulating complement did not prevent AVR and the grafts in group 1 survived from 8 to 13 days. Despite undetectable C3 in circulating blood, C3 deposition was present in these grafts. The venular thrombosis was the predominant histopathologic feature of AVR. We conclude that repetitive injection of low dose Y-CVF can be used to continuously suppress circulating complement in a very potent manner and successfully prevent HAR. However, this therapy did not inhibit complement deposition in the graft and failed to prevent AVR. These data suggest that using alternative pig donors [i.e. human decay accelerating factor (hDAF)-transgenic] in combination with the systemic use of complement inhibitors may be necessary to further control complement activation and improve survival in pig-to-non-human primate xenotransplant model.

[Study the mechanisms and inducing transplantation immune tolerance of FTY720].

OBJECTIVE: To explore the operational mechanisms and potential approach to inducing transplantation immune tolerance of FTY720. METHODS: Mouse splenocytes were incubated with FTY720, then the DNA was extracted and analyzed using gel electrophoresis. Hearts of inbred BALB/c (H-2(d)) mice were transplanted heterotopically in C57BL/6 (H-2b) mice. Recipients were randomly divided into six groups. Group-1 (n = 6) was the nil-treated control. Groups-2, 3 and 4 were given FTY720 at the dose of 3 mg.kg(-1) by oral gavage once a day with different time courses. Group-2 (n = 14) were administrated from 3 days before transplantation (day-3) to the 11th day after the transplantation (day 11); Group-3 (n = 6) from day 0 to day 14; Group-4 (n = 6) from day-3 to day 0. Group-5 (n = 5) and 6 (n = 5) were treated with Cyclosporine A (10 mg.kg(-1)) and 40-O-(2-hydroxyethyl)-rapamycin (RAD) (3 mg.kg(-1)) respectively by daily gavage from day 3 to day 11. The long survivors (> 100 d) in Group-2 were detected with their IL-4 and IFN-gamma levels and their tolerant state was challenged with second graft: the donor type skin. RESULTS: Apoptosis changes of the mouse splenocytes incubated with FTY720 was showed by typical DNA ladders. The median survival time (MST) of Group-1 was 8 d. MST of Group-2 was 55 d and grafts in six mice survived more than 100 d. MST of Group-3 was 16.5 d. Group-4 has a MST of 14 d with one case exceeded 100 d. MST of Group-5 and 6 were 10 d and 13 d respectively. Long survivors of Group-2 can accept donor-type skin graft and the level of IL-4 in their serum is up-regulated while IFN-gamma remained stable. CONCLUSIONS: Pretreatment of FTY720 bring about effect on the early events of transplantation immune responses. This effect might be mediated by apoptosis induction in lymphocytes using this drug. We originally designed the regime of FTY720 monotherapy, which started pre-operationally and maintained for a short period of time, and induced stable tolerance the allo-graft in mouse.