Potential applications and prospects for cardiac xenotransplantation

Leflunomide Inhibits rat-to-Mouse Cardiac Xenograft Rejection by Suppressing Adaptive Immune Cell Response and NF-κB Signaling Activation

Xenotransplantation is a potential solution for the severe shortage of human donor organs and tissues. The generation of humanized animal models attenuates strong innate immune responses, such as complement-mediated hyperacute rejection. However, acute vascular rejection and cell mediated rejection remain primary barriers to xenotransplantation, which limits its clinical application. In this study, we systematically investigated the immunosuppressive effect of LEF using a rat-to-mouse heart xenotransplantation model. SD rat xenogeneic hearts were transplanted into C57BL/6 mice, and survived 34.5 days after LEF treatment. In contrast, BALB/c allogeneic hearts were transplanted into C57BL/6 mice, and survived 31 days after LEF treatment. Compared to normal saline treatment, LEF treatment decreased xenoreactive T cells and CD19⁺ B cells in recipient splenocytes. Most importantly, LEF treatment protected myocardial cells by decreasing xenoreactive T and B cell infiltration, inflammatory gene expression, and IgM deposition in grafts. In vivo assays revealed that LEF treatment eliminated xenoreactive and alloreactive T and B lymphocytes by suppressing the activation of the NF-κB signaling pathway. Taken together, these observations complement the evidence supporting the potential use of LEF in xenotransplantation.

Upregulation of α-enolase in acute rejection of cardiac transplant in rat model: implications for the secretion of interleukin-17

Acute allograft rejection remains a major problem in solid organ transplantation. The enzyme α-enolase has been shown to induce an immune response in cardiac transplantation. In this study, we investigated the role of α-enolase in acute allograft rejection in a rat model of heart transplantation. Hearts from either (WF: RT1(u) ) or (Lew: RT1(1) ) rats were transplanted into (Lew: RT1(1) ) rats. No rejection occurred in the isograft group, for which the median survival time was >168 days, whereas the median survival time of the allograft group was significantly less at 10 ± 2.1 days (n = 8 per group, p < 0.001). Increased inflammation was observed in allografts, including increased α-enolase expression and increased numbers of infiltrating CD4(+) T cells (p < 0.05). By immunohistochemical staining, we confirmed that α-enolase was expressed not only in myocardial cells but also in the infiltrating lymphocytes. However, on the fifth day after transplantation, α-enolase expression was no longer observed in the lymphocytes (n = 3, p < 0.001). In contrast, no lymphocytes were found in isografts after transplantation (n = 3, p < 0.001). α-enolase expression was increased in lymphocytes, which are implicated in the acute rejection of cardiac transplants. Intragraft α-enolase inhibition may be useful as an adjuvant therapy to systemic immunosuppression in heart transplantation.

CD4 T cells mediate cardiac xenograft rejection via host MHC Class II

BACKGROUND

Previous studies have shown that acute CD4 T-cell-mediated cardiac allograft rejection requires donor major histocompatibility complex (MHC) Class II expression and can be independent of "indirect" antigen presentation. However, other studies suggested that indirect antigen presentation to CD4 T cells may play a primary role in cellular xenograft immunity. Thus, the relative roles of direct/indirect CD4 T cell reactivity against cardiac xenografts are unclear. In this study we set out to determine the role for indirect CD4 T cell reactivity in cardiac xenograft rejection.

METHODS

Rat hearts were transplanted heterotopically into wild-type and immunodeficient mice. Recipients were untreated, treated with depleting antibodies, or reconstituted with wild-type cells.

RESULTS

Antibody depletion confirmed that rat heart xenograft rejection in C57Bl/6 mice was CD4 T-cell-dependent. Also, heart xenografts survived long term in B6 MHC Class II (C2D)-deficient mice. Graft acceptance in C2D mice was not secondary to CD4 T cell deficiency alone, because transferred B6 CD4 T cells failed to trigger rejection in C2D hosts. Furthermore, purified CD4 T cells were sufficient for acute rejection of rat heart xenografts in immune-deficient B6rag1(-/-) recipients. Importantly, CD4 T cells did not reject rat hearts in C2Drag1(-/-) hosts, in contrast to results using cardiac allografts. "Direct" xenoreactive CD4 T cells were not sufficient to mediate rejection despite vigorous reactivity to rat stimulator cells in vitro.

CONCLUSIONS

Taken together, our results show that CD4 T cells are both necessary and sufficient for acute cardiac xenograft rejection and that host MHC Class II is critical in this process.

Managing drugs and devices in patients with permanent ventricular assist devices

Patients will be considered for destination mechanical circulatory support device (MCSD) implantation when all other organ-saving treatment options have failed and they are not eligible for heart transplantation. Current medical evidence suggests that only for those patients who are inotrope-dependent and therefore likely have a 1-year survival probability without MCSD implantation of less than 50%, MCSD intervention will add to survival and quality-of-life benefit. Suitable candidates for MCSD are those patients who have a high risk of dying from heart failure but acceptable noncardiac risk. Evaluation of patients for MCSD requires a systematic and critical review of all organ systems and of the psychosocial situation. Specifically, right ventricular function and risk of right ventricular failure should be evaluated before planning destination MCSD implantation. Treatment will focus on prompt recovery from MCSD implantation, maintaining optimal treatment for heart failure, and preventing/treating MCSD complications, including infection, bleeding, coagulopathy, right heart failure, and device dysfunction. MCSD programs should be organized as an advanced heart failure center directed by specialized heart failure cardiologists, surgeons expert at implant and management of MCSD, specialized nurses, social workers, psychologists, financial experts, and physical therapists. MCSD practice is based on a patient-centered theory, with an appropriate understanding of the respective roles of the physician and the patient during their iterative encounters in which the patient is an autonomous person making responsible personal health decisions while the health care team is providing continued expert and empathic counseling about various options, based on systematic outcomes research (eg, by participation in the Interagency Registry for Mechanically Assisted Circulatory Support - MCSD database ).

Comparison of propofol and isoflurane anesthesia in orthotopic pig-to-baboon cardiac xenotransplantation

BACKGROUND

Orthotopic pig-to-baboon xenogeneic heart transplantation (oXHTx) is the only accepted preclinical animal model for cardiac xenotransplantation. We compared the hemodynamic stability of a propofol- and isoflurane-based anesthetic regimen during oXHTx.

METHODS

Hearts from 12 hDAF or hCD46 transgenic pigs (Sus scrofa; body weight 7 to 32 kg) were transplanted into baboons (Papio anubis and Papio hamadryas; body weight 9 to 26 kg) in the orthotopic life-supporting position. Animals received a propofol-based intravenous regimen or inhalation anesthesia with isoflurane. Analgesia was achieved with fentanyl in both groups. Systemic hemodynamic variables were measured before, during and after cardiopulmonary bypass (CPB) and the need for inotropic or vasoactive pharmacological support was compared before and after CPB.

RESULTS

Global hemodynamic variables [i.e. heart rate, mean arterial pressure (MAP) and cardiac output] were not significantly different in propofol-anesthetized baboons compared to baboons anesthetized with isoflurane. Baboons anesthetized with isoflurane showed a trend towards less pharmacological support required to achieve an adequate MAP of >60 mmHg after CPB (propofol: epinephrine 0.13 [0.05; 0.16] and norepinephrine 0.15 [0.02; 0.16] microg/kg/min vs. isoflurane: epinephrine 0.05 [0.02; 0.08] and norepinephrine 0.06 [0.02; 0.19] microg/kg/min; no significant difference).

CONCLUSIONS

Propofol and isoflurane appear to provide equal hemodynamic stability in orthotopic cardiac pig-to-baboon xenotransplantation prior to the start of CPB. The trend of a reduced catecholamine support needed after CPB, however, suggests that isoflurane may be the preferred drug for maintenance of anesthesia in this primate model.

Differences in activities of the enzymes of nucleotide metabolism and its implications for cardiac xenotransplantation

Xenotransplantation is one be possible solution for a severe shortage of human organs available for transplantation. However, only a few studies addressed metabolic compatibility of transplanted animal organs. Our aim was to compare activities of adenosine metabolizing enzymes in the heart of different species that are relevant to clinical or experimental xenotransplantation. We noted fundamental differences: ecto-5' nucleotidease (E5' N) activity was 4-fold lower in pig and baboon hearts compared to the human hearts while mouse activity was compatible with human and rat activity was three times higher than human. There also were significant differences in AMP-deaminase (AMPD), adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP) activities. We conclude that differences in nucleotide metabolism may contribute to organ dysfunction after xenotransplantation.

Human amniotic fluid-derived stem cells are rejected after transplantation in the myocardium of normal, ischemic, immuno-suppressed or immuno-deficient rat

Human amniotic fluid-derived stem (AFS) cells, similarly to embryonic stem cells, could possess privileged immunological characteristics suitable for a successful transplantation even in a discordant xenograft system. We investigated whether AFS cells could be fruitfully used in a rat model of myocardial infarction. c-kit immunomagnetic-sorted AFS cells were characterized by flow cytometric analysis and cytospins as well as reverse-transcription polymerase chain reaction, Western blotting and immunocytochemistry for cardiovascular differentiation markers. In vitro, AFS cell phenotypic conversion was assayed by cardiovascular-specific induction media or co-cultured with rat neonatal cardiomyocytes. AFS cells showed mRNAs and/or protein for endothelial (angiopoietin, CD146) and smooth muscle (smoothelin) cells, and cardiomyocyte (Nkx2.5, MLC-2v, GATA-4, beta-MyHC) markers. Acquisition of a cardiomyocyte-like phenotype in rare AFS cells could be seen only in co-cultures with rat neonatal cells. In vivo, AFS cells xenotransplantated in a rat model of myocardial infarction, with or without cyclosporine treatment, or in intact heart from immuno-competent or immuno-deficient animals were acutely rejected due to the different recruitment of recipient CD4(+), CD8(+) T and B lymphocytes, NK cells and macrophages. This reaction is most likely to be linked to expression of B7 co-stimulatory molecules CD80 and CD86 as well as macrophage marker CD68 on AFS cells. Xenotransplanted AFS cells gave also rise in some animals to cell masses in the subendocardium and myocardium suggestive of a process of chondro-osteogenic differentiation. Despite AFS cells in vitro can differentiate to some extent to cells of cardiovascular lineages, their in vivo use in xenotransplantation for cell therapy of myocardial infarction is hampered by their peculiar immunogenic properties and phenotypic instability.

Correction of hemophilia as a proof of concept for treatment of monogenic diseases by fetal spleen transplantation

Previous clinical attempts to correct genetic deficiencies such as hemophilia or Gaucher disease by transplantation of allogeneic spleen were associated with aggressive graft versus host disease, mediated by mature T cells derived from the donor spleen. We show that a fetal pig spleen harvested at the embryonic day 42 stage, before the appearance of T cells, exhibited optimal growth potential upon transplantation into SCID mice, and the growing tissue expressed factor VIII. Transplantation of embryonic day 42 spleen tissue into hemophilic SCID mice led to complete alleviation of hemophilia within 2-3 months after transplant, as demonstrated by tail bleeding and by assays for factor VIII blood levels. These results provide a proof of principle to the concept that transplantation of a fetal spleen, obtained from a developmental stage before the appearance of T cells, could provide a novel treatment modality for genetic deficiencies of an enzyme or a factor that can be replaced by the growing spleen tissue.

The physiologic basis for the management of ventricular assist devices

Mechanical ventricular assist devices are now approved as destination therapy for terminal heart failure. It is the purpose of this review to discuss the physiology of this technology that is considered in outpatient care. The currently available pulsatile devices are solely dependent of preload volume and, when placed in the automatic mode, can maintain physiologic cardiac outputs with exercise. However, because of their dependence on preload volume, there are unique physiologic consequences; device bradycardia represents volume depletion, device tachycardia reflects volume overload. The differential diagnosis of left ventricular assist device dysfunction includes native right ventricular failure, native left ventricular recovery, or other technical considerations. The management of biventricular mechanical support as well as arrhythmia management and the role of echocardiographic assessment in this unique patient population will be discussed. Expertise in outpatient management of such devices is now a requisite for subspecialists in heart failure, In the future, technical innovations may simplify management for professionals, patients, and their families.

Embryonic pig pancreatic tissue transplantation for the treatment of diabetes

BACKGROUND

Transplantation of embryonic pig pancreatic tissue as a source of insulin has been suggested for the cure of diabetes. However, previous limited clinical trials failed in their attempts to treat diabetic patients by transplantation of advanced gestational age porcine embryonic pancreas. In the present study we examined growth potential, functionality, and immunogenicity of pig embryonic pancreatic tissue harvested at different gestational ages.

METHODS AND FINDINGS

Implantation of embryonic pig pancreatic tissues of different gestational ages in SCID mice reveals that embryonic day 42 (E42) pig pancreas can enable a massive growth of pig islets for prolonged periods and restore normoglycemia in diabetic mice. Furthermore, both direct and indirect T cell rejection responses to the xenogeneic tissue demonstrated that E42 tissue, in comparison to E56 or later embryonic tissues, exhibits markedly reduced immunogenicity. Finally, fully immunocompetent diabetic mice grafted with the E42 pig pancreatic tissue and treated with an immunosuppression protocol comprising CTLA4-Ig and anti-CD40 ligand (anti-CD40L) attained normal blood glucose levels, eliminating the need for insulin.

CONCLUSIONS

These results emphasize the importance of selecting embryonic tissue of the correct gestational age for optimal growth and function and for reduced immunogenicity, and provide a proof of principle for the therapeutic potential of E42 embryonic pig pancreatic tissue transplantation in diabetes.

hDAF porcine cardiac xenograft maintains cardiac output after orthotopic transplantation into baboon - a perioperative study

BACKGROUND

Only limited data are available on the physiological functional compatibility of cardiac xenografts after orthotopic pig to baboon transplantation (oXHTx). Thus we investigated hemodynamic parameters including cardiac output (CO) before and after oXHTx.

METHODS

Orthotopic xenogeneic heart transplantation from nine hDAF transgeneic piglets to baboons was performed. We used femoral arterial thermodilution for the invasive assessment of CO and stroke volume.

RESULTS

Baseline CO of the baboons after induction of anesthesia was 1.36 (1.0-1.9) l/min. 30 to 60 min after termination of the cardiopulmonary bypass, CO of the cardiac xenograft was significantly increased to 1.72 (1.3-2.1) l/min (P < 0.01). The stroke volumes of the baboon heart before transplantation and the cardiac xenograft was comparable [14.9 (11-26) vs. 11.8 (10-23) ml]. Thus the higher CO was achieved by an increase in heart rate after oXHTx [75.0 (69-110) vs. 140.0 (77-180)/min; P < 0.01]. Despite the increased CO, oxygen delivery was reduced [256 (251-354) vs. 227 (172-477) ml/min; P < 0.01] due to the inevitable hemodilution during the cardiopulmonary bypass and the blood loss caused by the surgical procedures.

CONCLUSION

Our results demonstrate that in the early phase after orthotopic transplantation of hDAF pig hearts to baboons, cardiac function of the donor heart is maintained and exceeds baseline CO. However, in the early intraoperative phase this was only possible by using inotropic substances and vasopressors due to the inevitable blood loss and dilution by the priming of the bypass circuit.

Transplantation of cardiac-committed mouse embryonic stem cells to infarcted sheep myocardium: a preclinical study

BACKGROUND

Heart failure develops after myocardial infarction and is a major cause of morbidity and mortality. The ability to direct differentiation of embryonic stem cells (ESC) towards a cardiomyogenic phenotype makes them an attractive therapeutic option for cardiac repair, but species-specific and individual-specific immunological imprinting remains a hurdle. Our aim was to ascertain whether the purported immune privilege of ESC allows for their cross-species engraftment in a clinically relevant large-animal model.

METHODS

We studied engraftment and differentiation of cardiac-committed mouse ESC in 18 sheep in which a myocardial infarction had been induced; nine controls received medium and nine sheep (five of which were immunosuppressed) received ESC. The gain in myocardial function was measured by echocardiography 1 month after cell transplantation.

FINDINGS

Cardiac-committed murine ESC engrafted in infarcted myocardium of immunosuppressed and immunocompetent sheep, and differentiated into mature cardiomyocytes that expressed connexins. Colonisation of the scar area by ESC was accompanied by a functional benefit of the damaged myocardium. Left-ventricular ejection fraction deteriorated in the control group by a median of 9.9% (range -20 to 0.3) relative to baseline (p=0.011) whereas in the treated group it improved by 6.6% (-5.7 to 50.8; comparison between groups p=0.002).

INTERPRETATION

These findings obtained in a clinically relevant large-animal model of heart failure strengthen the potential therapeutic use of ESC to regenerate the severely dysfunctional myocardium and bring additional evidence for an immune privilege of these cells.