Methotrexate for immunosuppression in life-supporting pig-to-cynomolgus monkey renal xenotransplantation

Expression of recipient cytomegalovirus in immunosuppressed and xenotransplanted Macaca fascicularis may be related to more severe gastrointestinal lesions

BACKGROUND

Xenotransplantation is a potential answer to the current organ shortage, but the risk of infections related to overimmunosuppression is an important parameter that may predict the recipient's long-term survival. Cytomegalovirus (CMV) in xenotransplanted and immunosuppressed primates is a well-known cause of disease particularly affecting the gastrointestinal (GI) tract and a zoonotic concern.

METHODS

Post-mortem sera and tissues from 45 immunosuppressed and xenografted Macaca fascicularis were evaluated for CMV using antisera specific for the immediate early 1 (IE1), anti-RhCMV, and QPCR for virus.

RESULTS

Serological analysis showed 100% positivity for the presence of CMV antibodies following the application of a specific test designed for RhCMV. Five of 45 primates showed typical lesions of CMV infection in the GI tract, including neutrophilic enteritis and inclusion bodies. Molecular analysis confirmed the presence of recipient's CMV in the tissues with CMV histopathology. Porcine CMV from the donor animals was not found in any of the CMV-specific IHC-positive recipients.

CONCLUSION

The presence of active CMV infection in animals intended for xenograft experiments can lead to severe gastrointestinal lesions that could impact the overall aims of the study. In such cases, the animals should be investigated using appropriate (non-human primate-specific) diagnostic tools prior to use and treated aggressively with state-of-the-art antiviral therapy.

Progress in pig-to-non-human primate transplantation models (1998-2013): a comprehensive review of the literature

BACKGROUND

The pig-to-non-human primate model is the standard choice for in vivo studies of organ and cell xenotransplantation. In 1998, Lambrigts and his colleagues surveyed the entire world literature and reported all experimental studies in this model. With the increasing number of genetically engineered pigs that have become available during the past few years, this model is being utilized ever more frequently.

METHODS

We have now reviewed the literature again and have compiled the data we have been able to find for the period January 1, 1998 to December 31, 2013, a period of 16 yr.

RESULTS

The data are presented for transplants of the heart (heterotopic and orthotopic), kidney, liver, lung, islets, neuronal cells, hepatocytes, corneas, artery patches, and skin. Heart, kidney, and, particularly, islet xenograft survival have increased significantly since 1998.

DISCUSSION

The reasons for this are briefly discussed. A comment on the limitations of the model has been made, particularly with regard to those that will affect progression of xenotransplantation toward the clinic.

Thromboelastographic evaluation of coagulative profiles in pig-to-monkey kidney xenotransplantation

BACKGROUND

Activation of the clotting cascade is central in acute xenograft rejection (AHXR) that occurs when pig organs are transplanted into primates. The coagulopathy reported in this model is a very complex process that involves simultaneously coagulation factors, platelets and phospholipid-bearing cells (i.e., leukocytes, red blood cells, and endothelial cells). Choosing whole blood for coagulation analysis theoretically appears more favorable compared with plasma. Whole blood rotation thromboelastometry (ROTEM(®) ) is a point-of-care global coagulation analyzer able to evaluate the characteristics of clot formation and lysis by dynamic monitoring. The aim of this study was to record thromboelastographic profiles, performed by ROTEM(®) , in a series of immunosuppressed nephrectomized primates that received a life-supporting kidney.

METHODS

Of the eight primates, n = 4 received a pig kidney transgenic for human decay-accelerating factor (hDAF/Gal+); n = 2, an α 1,3-galactosyltransferase gene-knockout (GT-KO) pig kidney transgenic for human CD39, CD55, CD59 and fucosyltransferase (HTF); and n = 2, a GT-KO pig kidney transgenic for hDAF. Blood samples were collected before and at least once per week after transplantation till euthanasia. Intrinsic (INTEM) and extrinsic (EXTEM) coagulation pathways and the function of fibrinogen (FIBTEM) were evaluated. Thromboelastographic parameters considered were clotting time (CT, seconds) and clot formation time (CFT, seconds) in INTEM and EXTEM and maximum clot firmness (MCF, mm) in FIBTEM. The correlations between CT in INTEM and activated partial thromboplastin time (aPTT), CT in EXTEM and PT, CFT in INTEM and EXTEM, and platelet counts and MCF in FIBTEM and fibrinogen plasma levels were also considered.

RESULTS

In all animals, thromboelastographic profiles showed progressive prolongation of CT (activation of coagulative cascade) in INTEM. A close correspondence was observed between (i) the prolongation of the CFT values (propagation of clot formation), both in INTEM and EXTEM, and the decrease in platelet counts; (ii) the reduction in MCF values (clot firmness) ​​in FIBTEM and the decrease in fibrinogen plasma levels. No concordance between CT in INTEM and aPTT and between CT in EXTEM and PT was observed.

CONCLUSIONS

Our study demonstrated that ROTEM(®) analyzer could be a useful and complementary tool to study the consumptive coagulopathy, either "compensated" or "non-compensated," that takes place when transgenic pig kidneys are transplanted into primates. Larger and prospective studies are needed to confirm our results and to evaluate the role of ROTEM(®) to guide the management of consumptive coagulopathy in order to prolong the survival of the transplanted organ.

Effects of long-term administration of recombinant human protein C in xenografted primates

BACKGROUND

The role potential of recombinant human activated protein C (rhaPC), a recently developed molecule with anticoagulant and antiinflammatory properties, in prolonging survival in immunosuppressed primate recipients of porcine renal xenografts has been evaluated.

METHODS

rhaPC was administered daily for 5 days (24 μg/kg/hr; group A; n = 3) or throughout the postoperative period (8-24 μg/kg/hr; group B; n = 2; or 24-48 μg/kg/hr; group C; n = 4). Animals in group D (n = 2) received rhaPC daily (24 μg/kg/hr) combined with recombinant human antithrombin (84 U/kg every 8 hr). Two animals served as control (group E).

RESULTS

The results indicate that rhaPC is protective against fibrin deposition early after transplantation but does not prevent fibrin deposition and the occurrence of acute humoral xenograft rejection (AHXR) later on. Animals in the study survived between 8 and 55 days. At the dose used, rhaPC is able to prevent fibrin deposition in the graft in the first 2 weeks after xenotransplantation, except when it is administered in conjunction with antithrombin. However, rhaPC did not prevent the eventual occurrence of AHXR in primate recipients of porcine xenografts.

CONCLUSIONS

In this pig to primate model, rhaPC confers a short advantage in the prevention of early perioperative xenograft damage but does not represent an effective strategy for preventing AHXR.

Prolonged survival of renal allograft in rats by methotrexate-albumin conjugates as immunosuppressive therapy

Methothrexate (MTX) causes unwanted adverse events by affecting gastrointestinal and bone marrow cells when used as an immunosuppressant. Our aim was to reduce those side effects by covalent binding of methothrexate to human serum albumin (HSA) targeting rapidly proliferating lymphocytes, which are known to ingest albumin as an energy source. Twenty-one rats received a kidney transplant. Group A (n = 5) received standard immunosupression (free MTX); group B (n = 9), albumin-MTX conjugates; and group C (n = 7) albumin control. The primary endpoint of this animal study was transplant survival, which was evaluated as death due to uremia. The study was terminated on day 100. Placebo-treated rat recipients (group C) rejected their grafts at a median of 8 days, which was prolonged to 17 days in standard immunosuppressed rats (group A), resulting in doubling transplant survival compared to nonimmunosuppressed animals. However, the same dose given as HSA-conjugated MTX prolonged the median survival time to 43 days. (group B). Hence, the administration of conjugated methotrexate appeared to result in a doubling of transplant survival compared with standard immunosuppression. Moreover, two animals receiving MTX-HSA became long-term survivors without additional immunosuppression. Further studies should be performed to evaluate the significance of these findings in larger animals and possibly in clinical studies.

Histopathological findings in the gastrointestinal tract of primate recipients of porcine renal xenografts following different immunosuppressive regimens

BACKGROUND

Cyclophosphamide (CYP) and methotrexate (MTX) have been used as immunosuppressants in induction or maintenance protocols in a large variety of xenotransplantation models. Combining the use of transgenic porcine organs expressing human decay-accelerating factor (hDAF) with immunosuppressive therapy that included the use of CYP or MTX, survival of primate recipients of life-supporting renal xenografts has been prolonged. However, both drugs can cause significant systemic toxicity and, in particular, gastrointestinal (GI) toxicity. To date only limited data have been reported on the histopathological features deriving from the use of such agents in non-human primates.

METHODS

Cyclophosphamide or MTX was used as part of the immunosuppressive regimen in 15 bilaterally nephrectomized non-human primate (Macaca fascicularis) recipients of a life-supporting hDAF porcine kidney. At post-mortem, a detailed analysis of the GI tract in animals receiving either CYP or MTX was performed. Paraffin-embedded sections of each portion of the GI tract were prepared and stained with hematoxylin and eosin (H&E). In some animals, additional investigations by immunohistochemistry (CD3, CD5, CD20, CD79 alpha cy, lambda, and kappa light chains) and by in situ hybridization for EBV encoded RNA (EBER) were undertaken.

RESULTS

The xenografted animals from the CYP group had a mean survival of 31 days (range: 0 to 90 days); animals from the MTX group survived a median of 14 days (range: 0 to 39 days). GI complications were the most frequent cause of euthanasia after renal failure. In CYP-treated animals GI-tract lesions were primarily characterized by diffuse, severe lymphoplasmocytic mucosal inflammatory infiltrate. Variable degrees of villi atrophy and fusion, gut-associated lymphoid tissue (GALT) and goblet cell hyperplasia were also observed. In MTX-treated primates, findings were consistent with severe villi atrophy associated with mild-to-moderate disseminated lymphoplasmocytic infiltration.

CONCLUSIONS

In conclusion, GI tract lesions are an early and consistent finding when CYP or MTX are used as induction agents in this model. The two compounds induce different types of GI tract damage, however, in agreement with their different mechanisms of action. Whilst CYP primarily determines inflammatory lesions, MTX leads to a degenerative type of damage. This study indicates that immunosuppressive drugs can cause severe GI tract damage in primate recipients of renal xenografts and may be responsible for life-threatening lesions.

Effects of Long-term Administration of High-dose Recombinant Human Antithrombin in Immunosuppressed Primate Recipients of Porcine Xenografts

BACKGROUND

Fibrin deposition is central to the acute humoral rejection process occurring in the presence of consumptive coagulopathy when pig organs are transplanted into primates.

METHODS

To assess whether strategies aimed at preventing fibrin formation may extend xenograft survival, we administered high daily doses of recombinant human antithrombin (rhAT) (500 U/kg twice daily) to obtain both anticoagulant and anti-inflammatory effects in immunosuppressed primate recipients of porcine kidneys.

RESULTS

Some degree of consumptive coagulopathy developed in both rhAT-treated (n=3) and untreated (n=3) primates. No major differences in the coagulation parameters analyzed were observed between the 2 groups. Similarly, no difference in survival was seen between rhAT-treated (20.6+/-4 days; range: 15-23 days) and untreated animals (17.3+/-11.6 days; range: 7-30 days), although the rhAT-treated primates had a higher bleeding tendency. Despite the high daily dose of rhAT, considerable fibrin deposition was observed in the graft as early as 2 weeks after transplantation.

CONCLUSIONS

These results suggest that a high daily dose of rhAT fails to influence survival or prevent fibrin formation and deposition in the graft in our pig-to-primate model. However, the potential role of rhAT administered in combination with heparins or other clotting inhibitor concentrates in this model remains to be determined.

Tolerability of cyclosphosphamide and methotrexate induction immunosuppression in nonhuman primates

Transplantation in nonhuman primates, in particular using solid organs from porcine donors, requires an efficacious induction immunosuppression. Besides biologicals, the low molecular weight drugs used include cyclophosphamide (CyP) and methotrexate (MTX). As these compounds generally have a narrow therapeutic window, we performed tolerability studies in baboons and cynomolgus monkeys, with/without maintenance immunosuppressants such as cyclosporine A, everolimus, mycophenolate sodium and FTY720. In both species, a four-dose CyP regimen of 40, 20, 30 and 30 mg/kg i.v. on days 1, 2, 4 and 6 is not tolerated, but the regimen is tolerated upon individual adjustment of the third and fourth dose to 18-25 and 8-20mg/kg, respectively, based on white blood cell count. In cynomolgus monkeys, a 5-day course of MTX i.v. at 0.5 mg/(kg d) is well tolerated, but not MTX at 1.0 mg/(kg d); in combination with maintenance immunosuppression, the 0.5mg/(kg d) dose can cause adverse effects. Combinations of CyP and MTX are tolerated using the 5-day course of MTX at 0.25 mg/(kg d) and a four-dose regimen of CyP at 10, 2.5, 7.5 and 7.5 mg/kg. These regimens are tolerated in combination with maintenance immunosuppressants. The data provide base values for investigators using nonhuman primates in experimental studies, particularly in xenotransplantation requiring effective induction immunosuppression that is close to maximum tolerated dose levels.

Skin graft of double transgenic pigs of N-acetylglucosaminyltransferase III (GnT-III) and DAF (CD55) genes survived in cynomolgus monkey for 31 days

BACKGROUND

Our previous study reported that cynomolgus monkey did not hyperacutely reject a skin xenograft from a N-acetylglucosaminyltransferase III (GnT-III) transgenic pig. In the present study, we reported on the survival time of skin xenografts in GnT-III, DAF (CD55), and double (D/G) transgenic pigs, and the effect of FK506 thereon.

MATERIAL AND METHODS

Skin from GnT-III, DAF and D/G transgenic pigs were transplanted to cynomolgus monkeys. Under general anesthesia, full thickness skin defects (1.5 x 1.5 cm each) were made on the back of the monkey. Pig abdominal skin, obtained using an electric dermatome, was cut into pieces and transplanted onto the monkey wounds and fixed. In addition, skins of GnT-III and D/G pigs were also transplanted to cynomolgus monkeys that had been treated intramuscularly with FK506 at a dose of 0.5 mg/kg/day for 14 days after transplantation. Grafts were observed and photographed each day and skin graft biopsies were done on days 3, 5, 7, 10, 11, 14, 21, 28 and 31 after transplantation. Graft rejection was assessed histologically, based on our previous criteria for skin allografts.

RESULTS

Even in the immuno-suppressive drug free condition, skin xenografts of GnT-III, DAF and D/G transgenic pigs were not hyperacutely rejected in early phase after transplantation by the cynomolgus monkey. The pattern of these xenograft rejections was histologically similar to those for rat allograft rejections. Most of the GnT-III, DAF and D/G pig skin grafts remained nearly intact up to day 5, but slight lymphocyte infiltration was noted on day 7 (grade 1). On day 9, while the GnT-III skin showed moderate lymphocyte and eosinophilic infiltration, the DAF and D/G pig skin grafts showed complete epidermal separation (grade 3). On the other hand, in the case of cynomolgus monkeys treated with FK506, the GnT-III skin showed complete epidermal separation (grade 3) on day 21. In addition, one of the D/G skin graft was intact on day 21 and moderate lymphocyte infiltration and intraepidermal blister formation (grade 1) was finally seen on day 31.

CONCLUSION

Our data show the possibility that both the DAF and GnT-III double transgenic pig skin xenografts can be used in place of human skin allografts in cases of severe burns.

Ureteral stenosis in HDAF pig-to-primate renal xenotransplantation: a phenomenon related to immunological events?

The aim of this study was to analyze the incidence of ureteral stenosis in a life-supporting human decay-accelerating factor (hDAF) transgenic pig-to-cynomolgus monkey kidney transplantation model and determine the role of possible immunological events in its pathogenesis. Thirty consecutive bi-nephrectomized cynomolgus monkeys received a kidney from hDAF transgenic pigs with or without a ureteral stent. Four monkeys were euthanized prematurely after transplantation. In the remaining 26 cases, the mean survival was 24 +/- 19 days. Except in one case, there was a close relationship between ureter and kidney in terms of type and severity of rejection. There were six ureteral stenoses; five were repaired by stent positioning and resurgery extended survival for an additional 16 +/- 10 days. The stenotic ureters showed diffuse acute humoral xenograft rejection (AHXR), while all cases with no or only focal signs of ureteral rejection never revealed ureteral obstruction. Use of a ureteral stent extends the survival of a xenografted primate, thereby helping to clarify the immunological events surrounding the onset of AHXR in kidneys in long-term xenograft recipients.