Spontaneous acceptance or rejection of orthotopic liver transplants in outbred and partially inbred miniature swine

Effects of Subnormothermic Perfusion Before Transplantation for Liver Grafts from Donation After Cardiac Death: A Simplified Dripping Perfusion Method in Pigs

BACKGROUND

Liver transplantation from donors after cardiac death (DCD) provides a solution to the donor shortage. However, DCD liver grafts are associated with a high incidence of primary graft nonfunction. We investigated the effectiveness of subnormothermic porcine liver perfusion, before transplantation from DCD, on graft viability.

METHODS

Landrace pigs (25-30 kg) were randomly allocated to 3 groups (5 per group): heart-beating (HB) graft, transplanted after a 4-hour period of cold storage (CS); DCD graft, retrieved 20 minutes after apnea-induced cardiac arrest (respiratory withdrawal) and transplanted after a 4-hour period of CS; and subnormothermic ex vivo liver perfusion (SELP) graft, retrieved in the same manner as the DCD graft but perfused with a subnormothermic oxygenated Krebs-Henseleit buffer (21-25°C, 10-15 cm H₂O) for 30 minutes in a simplified dripping manner, without a machine perfusion system, after the 4-hour period of CS, and subsequently transplanted.

RESULTS

Although all animals in the HB group survived for >7 days, all animals in the DCD group died within 12 hours after transplantation. In the SELP group, 2 recipients survived for >7 days and another 2 recipients were killed on day 5. The survival rate was significantly better for SELP than for DCD grafts (P = .0016). The values of tumor necrosis factor α were not significantly different between the SELP and HB groups. Preserved structure of the parenchyma was observed in the SELP group on histologic examination.

CONCLUSIONS

A simplified subnormothermic perfusion before liver transplantation is expected to improve graft viability and survival.

Recurrence and rejection in liver transplantation for primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) is a chronic progressive inflammatory disease affecting the bile ducts, leading to fibrosis and eventually cirrhosis in most patients. Its etiology is unknown and so far no effective medical therapy is available. Liver transplantation (LTX) is the only curative treatment and at present PSC is the main indication for LTX in the Scandinavian countries. Close to half of the PSC patients experience one or more episodes of acute cellular rejection (ACR) following transplantation and approximately 1/5 of the transplanted patients develop recurrent disease in the graft. In addition, some reports indicate that ACR early after LTX for PSC can influence the risk for recurrent disease. For these important post-transplantation entities affecting PSC patients, we have reviewed the current literature on epidemiology, pathogenesis, treatment and the possible influence of rejection on the risk of recurrent disease in the allograft.

Hematopoietic cell transplantation for tolerance induction: animal models to clinical trials

The induction of donor-specific immune tolerance is the "holy grail" of transplantation, as it would avoid the toxicities of chronic immunosuppressive therapies while preventing acute and chronic graft rejection. A large number of approaches to tolerance induction have been described in the experimental literature, but only hematopoietic cell transplantation has shown preliminary success for intentional tolerance induction in pilot clinical trials. This review summarizes the conditions that allow progress to be made in moving strategies for tolerance induction from the bench to the bedside and discuss the mechanisms by which tolerance may be achieved through hematopoietic cell transplantation.

The persistence of regulatory cells developing after rat spontaneous liver acceptance

BACKGROUND

We have previously reported that the spontaneous acceptance of Lewis (LEW, RT1(l)) to Dark Agouti (DA, RT1(a)) rat orthotopic liver transplant (OLT) is eliminated by donor gamma-irradiation. The acceptance of the irradiated LEW liver is also reestablished in a naïve rat after the adoptive transfer of T regulatory (T-reg) cells from a LEW to a DA liver-tolerant long-term (>60 days) survivor (LTS) into a naïve DA rat. However, little is known about the growth conditions required to maintain T-reg function. In this study, we examined the need for continued donor-specific alloantigen stimulation for the maintenance and function of T-reg cells.

METHODS

Splenocytes (SCs; 1.5 x 10(8) cells) from a LEW liver allograft-tolerant LTS DA recipient were adoptively transferred fresh or after in vitro stimulation into another naive DA rat on day 1, 4, or 7 before an irradiated (1000R) LEW liver transplant. For in vitro alloantigen stimulation, SCs from LEW to DA LTS were co-cultured with mitomycin-C (MMC)-treated naïve LEW (donor alloantigen-specific) or Brown Norway (BN) (RT1(n); third party) SCs for 72 hours. Graft rejection, as defined by death of the recipient, was confirmed histologically.

RESULTS

All LEW liver grafts were accepted spontaneously by DA recipients for more than 60 days (n=32), while all irradiated LEW livers were acutely rejected (n=9; mean survival time [MST]=12.8 +/- 4.0 days). When LTS DA SCs were adoptively transferred into a naive DA rat 1 day before OLT, all irradiated LEW grafts were accepted greater than 60 days (n=9). However, when fresh LTS DA SCs were transferred to a new naïve DA rat on 4 or 7 days before OLT, all irradiated LEW liver grafts were acutely rejected (MST=10.2 +/- 0.5 days [n=4] and MST=13.5 +/- 5.0 days [n=4], respectively). When LTS DA SCs were stimulated in vitro before adoptive transfer, irradiated LEW liver grafts after 4 days (n=5) were then accepted. In vitro culture of LTS DA SCs with MMC-treated BN SCs (third-party) for 72 hours before adoptive transfer resulted in 3 of 5 irradiated LEW livers at day 4 being accepted (n=5).

CONCLUSIONS

The maintenance of T-reg function requires continuous LEW donor-specific alloantigen stimulation.

Early biological and immune response to semi-identical liver or kidney allograft in miniature swine

In inbred miniature swine, semi-identical liver allograft recipients survive up to 3 months without immunosuppression, whereas similarly mismatched kidney allografts are uniformly rejected within 2 weeks. The early biological and immunological events were assessed in this unique model. SLA(d/d) pigs (MGH, Harvard Medical School, Boston, MA, USA) received liver or kidney allograft from heterozygous SLA(c/d) miniature swine. Survival, graft function, histology, intragraft cytokines, peripheral lymphocyte and platelet count, plasma cortisol level and cellular/humoral anti-donor immune response were assessed. Kidney allografts were uniformly rejected within 2 weeks, whereas liver allografts survived for up to 87 days. After both liver and kidney transplantation, the peripheral lymphocyte count decreased during the first week concomitantly to a significant elevation of plasma cortisol level. Early decrease of peripheral platelet count was observed after liver but not renal transplantation. Up-regulation of transforming growth factor beta1 (TGF-beta1) and interferon-gamma (IFN-gamma) was observed during the first postoperative week in semi-identical liver allografts and IFN-gamma as well as IL-10 in kidney allografts. In liver recipients, labelled autologous lymphocytes accumulated in the liver graft and native spleen, whereas after renal allograft, lymphocytes accumulated in the native spleen and liver but never in the kidney allograft. Specific cellular anti-donor unresponsiveness was observed from the first post-transplant day in both liver and kidney recipients, while the humoral anti-donor response remained intact. In semi-identical liver allograft, recipient rejection is milder and slower than in similarly matched kidney allograft. The intragraft up-regulation of TGF-beta1 in semi-identical liver allograft might be one mediator to explain the modulation of rejection after liver transplant. The rapid, nonspecific accumulation of recipient lymphocytes in the liver allograft but not in kidney allograft might also play a role in the different survival time in this model.

Mini-pig fresh osteochondral allografts deteriorate after 1 week of cold storage

As a well-defined animal transplantation model, the mini-pig potentially is well-suited for large animal studies of fresh osteochondral allograft transplantation. This study was done to determine the histologic characteristics and function of proteoglycan synthesis of mini-pig articular cartilage after refrigeration in basal media for as much as 6 weeks. Osteochondral sections of 10 mini-pig knees were refrigerated in various media at 4 degrees C for 1 to 42 days after slaughter. Four hundred twenty samples were evaluated by 35S uptake and 260 samples by histologic evaluations. Proteoglycan synthesis declined by 7 days to 21% of the level measured on Day 1 and was undetectable at 42 days. Histologic evaluation revealed progressive degeneration. Mankin scores rose from 3.69 +/- 0.27 on Day 1 to 6.40 +/- 0.18 on Day 7, and logarithmically increased to 10.83 +/- 0.07 on Day 42. These results indicate that the metabolic characteristics of porcine articular cartilage were not retained after refrigeration in basal media for 7 days. Optimum cold storage of porcine osteochondral allografts for cartilage transplantation research may be less than 7 days. Because osteochondral grafts for clinical use currently are stored for greater than 7 days, similar studies of the viability of human articular cartilage are needed.

Crossing the bridge: large animal models in translational transplantation research

Many methods for reducing the immunosuppressive requirements of allotransplantation have been proposed based on a growing understanding of physiological and allospecific immunity. As these regimens are developed for clinical application, they require validation in models that are reasonably predictive of their performance in humans. This article provides an overview of the large animal models commonly used to test immunomodulatory organ transplant protocols. The rationale for the use of large animals and the effects of common immunosuppressants in the dog, pig, and non-human primate are reviewed. Promising methods for the induction of allospecific tolerance are surveyed with references to early human trials where appropriate.

"Infectious tolerance" develops after the spontaneous acceptance of Lewis-to-Dark Agouti rat liver transplants

BACKGROUND

After monoclonal antibody or donor-specific transfusion treatment, infectious tolerance to rat or mouse heart or skin transplants can be passed on to naive recipients by adoptive transfer of tolerant lymphocytes. We examined whether similar regulatory cells develop after the spontaneous acceptance of Lewis-to-Dark Agouti (DA) rat liver transplants without immunomodulating agents.

METHODS

After Lewis-to-DA rat liver transplantation, 100 x 10(6) splenocytes were harvested and adoptively transferred into a 450 rad-irradiated naive DA rat 24 hours before Lewis heart transplantation. Adoptive transfer of CD4+ or CD8+ T cells was also examined. In some experiments, splenocytes from recipients with long-term accepted Lewis hearts induced by adoptive transfer were serially transferred to multiple generations of recipients before Lewis rat heart transplantation. In vitro mixed lymphocyte culture response and cytotoxic T lymphocyte generation were measured.

RESULTS

When splenocytes from a DA rat recipient >60 days after Lewis rat liver acceptance were transferred into irradiated DA rat recipients, all Lewis rat hearts were accepted, whereas third-party Brown-Norway rat hearts were rejected. However, splenocytes from DA rat recipients 30 days after liver transplantation did not prolong Lewis rat heart survival. Adoptive transfer of 40 x 10(6) CD4+, 10 x 10(6) CD4+ or 10 x 10(6) CD8+ cells from a DA rat bearing Lewis rat liver >60 days resulted in acceptance of 88%, 80%, or 57% acceptance of Lewis rat hearts, respectively. Serial second and third adoptive transfer of long-term survivor splenocytes resulted in the acceptance of all Lewis rat hearts. In mixed lymphocyte culture, splenocytes from a naive DA rat and a DA rat accepting a Lewis rat liver transplant for >60 days showed similar proliferative responses to both Lewis and Brown-Norway rat stimulators. An equivalent level of indirect cytotoxic T lymphocyte activity was exhibited by splenocytes from both a naive DA and a DA rat accepting a Lewis rat liver transplant for >60 days.

CONCLUSIONS

Regulatory cells developing after the spontaneous acceptance of a Lewis to DA liver transplant can serially adoptively transfer the acceptance of a Lewis rat cardiac graft in spite of the presence of in vitro antidonor reactivity. Both CD4+ and CD8+ populations have this regulatory activity, although the CD4+ population plays the dominant role.

Swine composite tissue allotransplant model for preclinical hand transplant studies

Our laboratory previously developed and used an orthotopic radial forelimb osteomyocutaneous flap in the pig as a preclinical composite tissue allograft (CTA) model. To ensure that it mimicked the clinical situation as closely as possible we developed this model taking many immunologic and reconstructive considerations into account. While our original pig CTA model was ideal for studying the methods of preventing skin, muscle, bone, vessel and nerve rejection, and systemic toxicity, it did not include specialized tissues/structures of a joint and digit. Therefore, we were unable to evaluate rejection of these specialized tissues and their functional properties. Recognizing the importance of assessing joint rejection and function in hand transplantation research we developed a new swine forelimb CTA model that included the animal's medial digit. The present study describes the anatomy and the transplantation technique used in this new preclinical CTA model. We transplanted a radial osteomyocutaneous flap that included the medial digit between two size- (17-21 kg) and age- (6-8-week) matched farm pigs. We removed the digit from the recipient pig's forelimb in continuity with a section of the radial bone and replaced it with the same structure transplanted from a donor pig. After transplantation, a full-length cast was placed on the recipient pig's operated limb and changes in flap color, temperature and the presence of edema were monitored continuously for 6 h, and then regularly at predetermined intervals over 4 days. No weight bearing restrictions were placed on the animal's operated limb. After 4 days, the animal was euthanized. Direct visual monitoring of the allograft during 4 days revealed it was viable with no signs of graft failure due to technical complications associated with the transplant procedure. Upon waking from anesthesia, the animal stood and wandered freely about its cage with no apparent difficulty. Based on the animal's high level of activity at this time, we concluded that the procedure caused it minimal morbidity. At 4 days after the operation, early signs of rejection (skin erythema and edema) were observed. By incorporating a digit into our original CTA pig forelimb model we have made it a better model for performing preclinical hand transplant studies. The added advantage of being able to assess methods of preventing rejection in the specialized joint/digital tissues (articular cartilage, digital flexor and extensor systems, the nail complex) and assess long-term function of these structures is important. The fact that the procedure does not cause major morbidity to the animal makes it possible to conduct long-term graft survival and functional studies.

Simplified technique of orthotopic liver transplantation in pigs

BACKGROUND

Pig models have become common in transplantation immunological research. However, in pigs, clamping of the venous splanchnic system during orthotopic liver transplantation (OLT) is responsible for high morbidity and mortality rates; therefore, the use of venovenous bypass (VVB) is advocated. Because venous bypass can also cause specific complications, a simplified method for OLT in pigs has been developed and evaluated in terms of morbidity and mortality.

METHODS

Twenty-three OLTs were performed between pairs of inbred miniature swine. Donor and recipient pairs (weighing 20-35 kg) were selected at 3-6 months of age. In the donor, the portal vein, infrahepatic vena cava, and suprahepatic vena cava were dissected, whereas the hepatic artery was preserved in continuity with the coeliac trunk and the abdominal aorta up to the iliac bifurcation. In situ cold perfusion was then performed. The recipient was prepared simultaneously by another surgical team. After total hepatectomy and complete portal and caval clamping, the suprahepatic vena cava and portal vein were sutured; VVB was not used. After completion of both venous sutures, the liver graft was reperfused. The infrahepatic vena cava was then anastomosed and unclamped. The donor aorta conduit was implanted end-to-side to the recipient infrarenal aorta, and the biliary reconstruction consisted of a cholecystojejunostomy with a Roux-Y loop.

RESULTS

Twenty of 23 (87%) animals survived more than 1 week (7-483 days). The mean anhepatic time was 29.6+/-4.12 min. Although severe hypotension was noted during the anhepatic phase, the hemodynamic status rapidly recovered and stabilized after graft reperfusion.

CONCLUSION

Simplified technique without VVB is appropriate for successfully achieving OLT in pigs.

A 12-day course of FK506 allows long-term acceptance of semi-identical liver allograft in inbred miniature swine

BACKGROUND

Spontaneous tolerance to liver allograft has been reported previously in outbred pig models, but the lack of genetic background did not allow to analyze the impact of the major histocompatibility complex (MHC) on tolerance induction. A model of semi-identical liver allograft was therefore developed in inbred miniature swine in order to mimic the clinical situation of living related liver transplant (parent into infant) and to study a protocol for inducing tolerance to liver allograft.

METHODS

SLAdd (class Id/d, class IId/d) pigs received orthotopic liver allograft from heterozygous SLAcd (class Ic/d, class IIc/d) miniature swine. Eight animals did not receive immunosuppression. Fourteen SLAdd animals had a 12-day course of FK506 and were divided in two subgroups. In subgroup FK-1, six pigs received a daily intramuscular injection of FK506 at 0.1-0.4 mg/kg, in order to reach daily trough levels between 7 and 20 ng/ml; in subgroup FK-2, eight additional animals received two daily injections of FK506 at 0.05 mg/kg regardless of the daily trough levels. Graft survival, liver biological tests, histology, cellular and humoral immune responses, as well as detection of microchimerism were assessed in all groups.

RESULTS

All untreated animals rejected their allograft and died within 28.1 +/- 9.5 days. These rejector animals developed a significant anti-donor cellular and humoral immune response. No peripheral or lymphoid tissue microchimerism was detected in this group. In contrast, long-term survival was obtained in five FK-treated animals (112, 154, 406, 413, and 440 days), whereas several pigs died with a normal allograft function from either overimmunosuppression or intercurrent causes. All FK-treated pigs developed a specific anti-donor unresponsiveness in both cell mediated lymphocytotoxicity and mixed lymphocyte reaction and did not develop anti-donor alloantibodies. The study of the anti-donor immune response by mixed lymphocyte reaction, during the first postoperative week, demonstrated a specific anti-donor unresponsiveness in the peripheral blood from the first posttransplant day. Although microchimerism was detectable in the peripheral blood for several postoperative weeks (maximum 10 weeks) in FK-treated animals, donor cells or DNA were not detected during the long-term follow-up in peripheral blood or lymphoid tissues.

CONCLUSIONS

Spontaneous tolerance to semi-identical orthotopic liver allograft did not occur, whereas a 12-day course of FK506 allowed long-term graft acceptance. All FK-treated animals developed in vitro signs of specific immune unresponsiveness and transient peripheral microchimerism. The specific anti-donor cellular unresponsiveness occurred on the first postoperative day after surgery and was of long-term duration. The study of the early immunological events in this model could be of major importance regarding clinical living related liver transplantation.