Tolerance of T-independent xeno-antibody responses in the hamster-to-rat xenotransplantation model is species-restricted but not tissue-specific

Anti-C5 Antibody Tesidolumab Reduces Early Antibody-mediated Rejection and Prolongs Survival in Renal Xenotransplantation

OBJECTIVE

Pig-to-primate renal xenotransplantation is plagued by early antibody-mediated graft loss which precludes clinical application of renal xenotransplantation. We evaluated whether temporary complement inhibition with anti-C5 antibody Tesidolumab could minimize the impact of early antibody-mediated rejection in rhesus monkeys receiving pig kidneys receiving costimulatory blockade-based immunosuppression.

METHODS

Double (Gal and Sda) and triple xenoantigen (Gal, Sda, and SLA I) pigs were created using CRISPR/Cas. Kidneys from DKO and TKO pigs were transplanted into rhesus monkeys that had the least reactive crossmatches. Recipients received anti-C5 antibody weekly for 70 days, and T cell depletion, anti-CD154, mycophenolic acid, and steroids as baseline immunosuppression (n = 7). Control recipients did not receive anti-C5 therapy (n = 10).

RESULTS

Temporary anti-C5 therapy reduced early graft loss secondary to antibody-mediated rejection and improved graft survival (P < 0.01). Deleting class I MHC (SLA I) in donor pigs did not ameliorate early antibody-mediated rejection (table). Anti-C5 therapy did not allow for the use of tacrolimus instead of anti-CD154 (table), prolonging survival to a maximum of 62 days.

CONCLUSION

Inhibition of the C5 complement subunit prolongs renal xenotransplant survival in a pig to non-human primate model.

Recombinant IL-33 prolongs leflunomide-mediated graft survival by reducing IFN-γ and expanding CD4(+)Foxp3(+) T cells in concordant heart transplantation

Interleukin (IL)-33 is a novel IL-1 family member, and its administration has been associated with promotion of T helper type-2 (Th2) cell activity and cytokines, particularly IL-4 and IL-5 in vivo. Recently, IL-33 was shown to increase CD4(+)Foxp3(+) regulatory T cells (Tregs) and to suppress levels of the Th1-type cytokine IFN-γ in allogeneic heart transplantation in mice. Therefore, we hypothesized that IL-33 and leflunomide (Lef) could prolong graft survival in the concordant mouse-to-rat heart transplantation model. In this model, xenografts undergo acute humoral xenograft rejection (AHXR) typically on day 3 or cell-mediated rejection approximately on day 7 if AHXR is inhibited by Lef treatment. Recipients were treated with Lef (n=6), IL-33 (n=6), IL-33 combined with Lef (n=6), or left untreated (n=6) for survival studies. Heart grafts were monitored until they stopped beating. Mouse heterotopic grafts were performed, and recipients were sacrificed on days 2 and 7 for histological and flow cytometric analyses. The combination of IL-33 and Lef significantly prolonged the grafts from 17.3±2.3 to 2.8±0.4 days, compared to untreated controls. IL-33 administration with Lef, while facilitating Th2-associated cytokines (IL-4 on day 2 but not day 7), also decreased IFN-γ on day 2 and day 7, compared with Lef treatment only. Furthermore, IL-33 with Lef administration caused an expansion of suppressive CD4(+)Foxp3(+) Tregs in rats. The IL-33 and Lef combination therapy resulted in significantly prolonged graft survival, associated with markedly decreased Th1 cells and increased IL-10 levels. In addition, the combination therapy significantly decreased the percentage of CD-45(+) B cells on days 2 and 7, compared with monotherapy. These findings reveal a new immunoregulatory property of IL-33. Specifically, it facilitates regulatory cells, particularly functional CD4(+)Foxp3(+) Tregs that underlie IL-33-mediated cardiac xenograft survival. Moreover, it can decrease Th1 cells and cytokine expression of Th1 T cells in xenograft recipients, for example IFN-γ.

Ischemic Preconditioning Can Overcome the Effect of Moderate to Severe Cold Ischemia on Concordant Mouse Xeno–Heart Transplants

PURPOSE

Concordant mouse xeno-heart transplants are relatively sensitive to ischemia-reperfusion injury. We investigated the effect of an ischemic preconditioning (IPC) protocol on the functional and biochemical outcome of mouse xenohearts transplanted to the Lewis rat.

MATERIAL AND METHODS

NMRI mice (30 to 40 g) were anesthetized, intubated, and mechanically ventilated. They were subjected either to a IPC protocol leading to an SaO(2) of 70% for 5 minutes followed by normoxia (defined as SaO(2) >90%) for 10 minutes (n = 9) or normoxia only (n = 11). The hearts were then heterotopically transplanted to Lewis rats (220 g). The frequencies of immediate onset and early dysfunction and late dysfunction were registered. The hearts surviving for 6 hours were explanted and the absolute concentrations of phosphocreatine and adenosine triphosphate (ATP) were determined in micromole per gram of heart tissue with high-pressure liquid chromatography. The phosphorylation ratio, PCr/ATP, a known correlate to biochemical and functional outcome, was calculated.

RESULTS

Four of 11 (36.4%) of control hearts experienced immediate onset and early dysfunction versus 0% (0/9) in M hearts subjected to IPC (P = .01). Furthermore, the IPC protocol increased the PCr concentration, 15.08 +/- 1.00 versus 9.04 +/- 2.04 micromol/g in controls (P = .01), and the PCr/ATP ratio, 1.80 +/- 0.17 versus 1.27 +/- 0.21 (NS; P = .06).

CONCLUSIONS

IPC provides a protective PCr overshoot overcoming the short-term effects of moderate to severe ischemic injury on mouse xeno-heart transplants.

Acute xenograft rejection, late xenograft rejection and long term survival xenografts in the hamster-to-rat heart transplantation model: histological characterisation under low-dose of FK506

BACKGROUND

Long-term survival studies have been conducted in hamster-to-rat cardiac models with a range of immunosuppressive treatments, but the histological pattern of Late Xenograft Rejection (LXR) has not been outlined. This study offers a detailed description of the histological changes in cardiac xenografts under three different immunological responses.

MATERIALS AND METHODS

Heterotopic hamster-to-Lewis rat cardiac transplant. Recipients were administered an antiproliferative drug (MMF, 25 mg/kg, or CyP, 10 mg/kg, from day -7 to +7 or from day 0 to +7, according to group) and FK506 (0.2 mg/kg; from day 0 to +30 or continuously). Unmodified recipients were used as controls. Conventional histology and indirect immunofluorescence of IgM, IgG and C3 deposits were performed.

RESULTS

In our study, xenografted rats that did not receive treatment developed a pattern of Acute Xenograft Rejection (AXR), with substantial tissue breakdown. Pretreated and treated animals until day 30 post-transplant developed LXR that may present two different histological patterns: one with vascular damage and predominant interstitial haemorrhage, and the other with extensive myocardial fibrosis. Long-term surviving rats (LTS) showed a morphology that was almost normal, with mild fibrosis and vascular endothelium preserved.

CONCLUSIONS

AXR, LXR and LTS in the hamster-to-rat heart transplantation model present a common humoral mechanism although their histopathological patterns are different depending on the length of immunosuppressive treatment but not on the type of antiproliferative drug administered. Pretreatment exerts an effect on fibrosis formation.

Heart and liver xenotransplantation under low-dose tacrolimus: graft survival after withdrawal of immunosuppression

BACKGROUND

The hamster-to-rat xenotransplantation model is a useful model to investigate the features of extended host response to long-surviving xenografts. Early xenoantibody responses are T-cell independent and resistant to tacrolimus. Treatment with the combination of mofetil mycophenolate plus FK506 avoids acute xenograft rejection completely, but after withdrawal of immunosuppression hamster grafts are rejected by a process called late xenograft rejection (LXR).

METHODS

Hamster hearts and livers were transplanted into Lewis rats. Grafted rats were treated with mofetil mycophenolate (25 mg/kg/day) for 8 days and FK506 (0.2 mg/kg/day) for 31 days. Serum IgM and IgG levels were determined by flow cytometry and interferon-gamma levels by ELISA. IgM, IgG, and C3 deposits were measured in tissue by immunofluorescence, and leukocyte infiltration was measured by immunoperoxidase staining. Results. Survival of heart and liver xenografts in the rats was 48+/-4 days and 63+/-8 days, respectively. After cessation of all immunosuppression, hearts were rejected in 18+/-4 days and livers in 33+/-8 days. Production sequences of xenoantibodies in the two organs differed substantially, especially 7 days after transplantation and at the moment of rejection. Quantification of interferon-gamma levels indicated that there were no significant changes after transplantation. Histological and immunohistochemical studies showed signs of humoral mechanism of LXR in rats undergoing heart transplantation and cellular mechanism of LXR in those that received a liver transplant. Conclusions. These observations suggest that rejection in the hamster-to-rat heart xenotransplantation model is mediated by a T cell-independent B-cell response to which a T cell-dependent B-cell response is added in LXR. In the liver xenotransplantation model, our hypothesis is that LXR is mediated by a mixed cell mechanism, involving lymphocytes CD4+ CD45RC+, macrophages, and cytotoxic T lymphocytes. In summary, we have demonstrated and compared the peculiar features of LXR in two different organs.