Cellular xenotransplantation of animal cells into people: benefits and risk.

The main benefit of xenotransplantation is its potential to overcome the worldwide organ shortage experienced in allotransplantation. Allogeneic transplantation is the only successful therapy for several life-threatening diseases, with cell, tissue or organ donation only partially meeting the demand and many patients dying while waiting for treatment. With supply falling short of demand, it is foreseen that the use of porcine material may at some stage overcome the existing gap between organ availability and clinical need. Recently, pig islet cells have been utilised in clinical trials, with safety being demonstrated. Indeed, pig-derived cells present several advantages: i) porcine cells have a stable function and differentiation pattern and are not tumorigenic; ii) pig cells have been shown to meet the physiological needs in large animal models; iii) the source of pig cells can be scaled up to meet demands in a highly standardised manner, and with respect to animal welfare regulations; iv) 'designated-pathogen-free' (DPF) pig lines can be produced, which could result in a higher safety profile than allotransplantation itself; v) the risk of zoonosis, which was raised years ago as the major hurdle, has been recently circumvented and is actually viewed as a controlled risk; and vi) immune risks are being circumvented via the use of genetically modified donor animals and encapsulation of porcine cells, particularly for the treatment of diabetes. Overall, the benefit appears to outweigh potential risks with respect to cellular xenotransplantation and this is discussed further in this review.

La xénotransplantation (ou hétérogreffe) a pour principal avantage de contourner le problème de la pénurie d'organes disponibles dans le monde pour réaliser des allogreffes. En effet, la transplantation allogénique est la seule thérapie qui permet de traiter avec succès certaines maladies potentiellement mortelles, mais les dons de cellules, de tissus et d'organes ne satisfont qu'une partie de la demande, de sorte que nombre de patients meurent dans l'attente d'un traitement. L'offre étant inférieure à la demande, on peut prévoir que le recours à des organes porcins puisse s'imposer dans un avenir plus ou moins proche afin de réduire l'écart entre les organes disponibles et les besoins cliniques. Récemment, des cellules d'îlots pancréatiques porcins ont été utilisées dans le cadre d'essais cliniques et leur innocuité a été démontrée. En effet, les cellules d'origine porcine présentent plusieurs avantages : i) les cellules porcines ont un fonctionnement et une différenciation cellulaires stables et ne sont pas tumorigènes ; ii) il a été démontré que les cellules porcines sont physiologiquement compatibles avec celles de modèles de grands animaux ; iii) le recours aux cellules porcines peut être échelonné en suivant des normes précises, en fonction de la demande et dans le respect de la réglementation applicable au bien-être animal ; iv) il est possible de produire des lignées cellulaires exemptes de microorganismes pathogènes spécifiques, ce qui offre encore plus de garanties de sécurité qu'une allogreffe ; v) le risque de zoonose, qui constituait le principal obstacle il y a quelques années a été récemment surmonté et on le considère aujourd'hui comme maîtrisé ; vi) les risques pour le système immunitaire du receveur ont été surmontés grâce à l'utilisation d'animaux génétiquement modifiés en tant que donneurs et à l'encapsulation des cellules porcines, en particulier pour les greffes destinées à des patients diabétiques. Les auteurs approfondissent l'examen des avantages de la xénotransplantation, qui l'emportent largement sur ses risques potentiels.

La principal ventaja del xenotrasplante reside en las posibilidades que ofrece para poner remedio a la penuria mundial de órganos destinados a alotrasplantes. El trasplante alogénico es la única terapia eficaz para muchas enfermedades potencialmente mortales, pero las donaciones de células, tejidos y órganos cubren solo una parte de la demanda y muchos pacientes mueren en espera de recibir tratamiento. Ante una oferta que no alcanza a cubrir la demanda, es previsible que en algún momento se recurra a material porcino como medio de subsanar el déficit de órganos disponibles para atender las necesidades clínicas existentes. En fechas recientes se han realizado ensayos clínicos con células de islote pancreático de cerdo y se ha demostrado que resultan seguras. De hecho, el uso de células de origen porcino presenta varias ventajas: i) las células porcinas tienen un patrón estable de funcionamiento y diferenciación y no son tumorígenas; ii) en modelos de animales de gran tamaño está demostrado que las células de cerdo responden a las necesidades fisiológicas; iii) es posible multiplicar las fuentes de células porcinas para responder a la demanda de modo sumamente normalizado y respetando las reglamentaciones de bienestar animal; iv) es posible generar linajes porcinos certificados como «exentos de patógenos¼, lo que podría ofrecer niveles de seguridad incluso mayores que los del propio alotrasplante; v) últimamente se ha podido conjurar el riesgo de zoonosis, que hace unos años parecía constituir el principal obstáculo y actualmente se considera un riesgo controlado; y vi) actualmente ya se evita el riesgo inmunitario gracias al uso de animales donantes genéticamente modificados y al encapsulamiento de las células porcinas, en especial para tratar la diabetes. Globalmente, por lo que respecta al xenotrasplante celular, los beneficios parecen pesar más que los eventuales riesgos, como indican los autores en su examen detallado.

Overexpression of Hypoxia-Inducible Factor-1α in Primary Graft Dysfunction Developing in an Orthotopic Lung Transplantation Rat Model.

BACKGROUND: Primary graft dysfunction (PGD) is the major cause of early morbidity and mortality after transplantation. A high rate of PGD is a frequent complication in orthotopic lung transplantation (OLT) models, which are currently used to investigate acute and chronic rejection pathways. Hypoxia-inducible factor (HIF)-1α is a heterodimeric αß transcription factor that mediates tissue response to hypoxia. In other solid organ transplantations, a significant correlation between HIF-1α expression and PGD was detected. To our knowledge no data are available on HIF-1α expression in PGD developing in lung transplantation. The aims of this study were to investigate HIF-1α expression (using immunohistochemistry) and correlate it to the main histological parameters related to ischemia-reperfusion (IR) injury, including terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) -positive apoptotic cells). METHODS: OLT was performed in 32 inbred rat strains and 11 of them died in the early postoperative period (from day 0-3) for IR injury. The histological and molecular evaluations were done in all lung tissues. Unimplanted donor rat lungs were used as controls. HIF-1α expression was correlated with all morphological parameters. RESULTS: Lung samples of animals with IR injury showed high scores of HIF-1α expression, edema, blood extravasation, granulocyte margination, apoptotic index, and necrosis in 91% of cases. Tissue overexpression of HIF-1α was detected in all lung samples with high scores of histological parameters and with high apoptotic indexes. CONCLUSION: Our data demonstrate that HIF-1α was overexpressed in more severe rat lung IR injury. The use of HIF-1α inhibitors could provide a translatable route into manipulating this complex system in vivo.

AAV9-mediated engineering of autotransplanted kidney of non-human primates.

Ex vivo gene transfer to the graft before transplantation is an attractive option for circumventing systemic side effects of chronic antirejection therapy. Gene delivery of the immunomodulatory protein cytotoxic T-lymphocyte-associated protein 4-immunoglobulin (CTLA4-Ig) prevented chronic kidney rejection in a rat model of allotransplantation without the need for systemic immunosuppression. Here we generated adeno-associated virus type 2 (AAV2) and AAV9 vectors encoding for LEA29Y, an optimized version of CTLA4-Ig. Both LEA29Y vectors were equally efficient for reducing T-cell proliferation in vitro. Serotype 9 was chosen for in vivo experiments owing to a lower frequency of preformed antibodies against the AAV9 capsid in 16 non-human primate tested sera. AAV9-LEA29Y was able to transduce the kidney of non-human primates in an autotransplantation model. Expression of LEA29Y mRNA by renal cells translated into the production of the corresponding protein, which was confined to the graft but not detected in serum. Results in non-human primates represent a step forward in maintaining the portability of this strategy into clinics.

Immediate and Catastrophic Antibody-Mediated Rejection in a Lung Transplant Recipient With Anti-Angiotensin II Receptor Type 1 and Anti-Endothelin-1 Receptor Type A Antibodies.

Preexisting donor-specific anti-HLA antibodies (DSAs) have been associated with reduced survival of lung allografts. However, antibodies with specificities other than HLA may have a detrimental role on the lung transplant outcome. A young man with cystic fibrosis underwent lung transplantation with organs from a suitable deceased donor. At the time of transplantation, there were no anti-HLA DSAs. During surgery, the patient developed a severe and intractable pulmonary hypertension associated with right ventriular dysfunction, which required arteriovenous extracorporeal membrane oxygenation. After a brief period of clinical improvement, a rapid deterioration in hemodynamics led to the patient's death on postoperative day 5. Postmortem studies showed that lung specimens taken at the end of surgery were compatible with antibody-mediated rejection (AMR), while terminal samples evidenced diffuse capillaritis, blood extravasation, edema, and microthrombi, with foci of acute cellular rejection (A3). Immunological investigations demonstrated the presence of preexisting antibodies against the endothelin-1 receptor type A (ETA R) and the angiotensin II receptor type 1 (AT1 R), two of the most potent vasoconstrictors reported to date, whose levels slightly rose after transplantation. These data suggest that preexisting anti-ETA R and anti-AT1 R antibodies may have contributed to the onset of AMR and to the catastrophic clinical course of this patient.

Posttransplant Lymphoproliferative Disorders in Neuronal Xenotransplanted Macaques.

Posttransplant lymphoproliferative disorders (PTLDs) are a heterogeneous group of lymphoid proliferations that occur in the setting of depressed T-cell function due to immunosuppressive therapy used following solid organ transplantation, hematopoietic stem cell transplantation, and also xenotransplantation. In the present study, 28 immunosuppressed parkinsonian Macaca fascicularis were intracerebrally injected with wild-type or CTLA4-Ig transgenic porcine xenografts to identify a suitable strategy to enable long-term cell survival, maturation, and differentiation. Nine of 28 (32%) immunosuppressed primates developed masses compatible with PTLD, located mainly in the gastrointestinal tract and/or nasal cavity. The masses were classified as monomorphic PTLD according to the World Health Organization classification. Immunohistochemistry and polymerase chain reaction (PCR) analyses revealed that the PTLDs were associated with macaca lymphocryptovirus as confirmed by double-labeling immunohistochemistry for CD20 and Epstein-Barr nuclear antigen 2 (EBNA-2), where the viral protein was located within the CD20+ neoplastic B cells. In sera from 3 distinct phases of the experimental life of the primates, testing by quantitative PCR revealed a progression of the viral load that paralleled the PTLD progression and no evidence of zoonotic transmission of porcine lymphotropic herpesvirus through xenoneuronal grafts. These data suggest that monitoring the variation of macaca lymphocryptovirus DNA in primates could be used as a possible early diagnostic tool for PTLD progression, allowing preemptive treatment such as immunosuppression therapy reduction.

Cell Therapy for Parkinson's Disease: A Translational Approach to Assess the Role of Local and Systemic Immunosuppression.

Neural transplantation is a promising therapeutic approach for neurodegenerative diseases; however, many patients receiving intracerebral fetal allografts exhibit signs of immunization to donor antigens that could compromise the graft. In this context, we intracerebrally transplanted mesencephalic pig xenografts into primates to identify a suitable strategy to enable long-term cell survival, maturation, and differentiation. Parkinsonian primates received WT or CTLA4-Ig transgenic porcine xenografts and different durations of peripheral immunosuppression to test whether systemic plus graft-mediated local immunosuppression might avoid rejection. A striking recovery of spontaneous locomotion was observed in primates receiving systemic plus local immunosuppression for 6 mo. Recovery was associated with restoration of dopaminergic activity detected both by positron emission tomography imaging and histological examination. Local infiltration by T cells and CD80/86+ microglial cells expressing indoleamine 2,3-dioxigenase were observed only in CTLA4-Ig recipients. Results suggest that in this primate neurotransplantation model, peripheral immunosuppression is indispensable to achieve the long-term survival of porcine neuronal xenografts that is required to study the beneficial immunomodulatory effect of local blockade of T cell costimulation.

The immunological barriers to xenotransplantation.

The availability of cells, tissues and organs from a non-human species such as the pig could, at least in theory, meet the demand of organs necessary for clinical transplantation. At this stage, the important goal of getting over the first year of survival has been reported for both cellular and solid organ xenotransplantation in relevant preclinical primate models. In addition, xenotransplantation is already in the clinic as shown by the broad use of animal-derived medical devices, such as bioprosthetic heart valves and biological materials used for surgical tissue repair. At this stage, however, prior to starting a wide-scale clinical application of xenotransplantation of viable cells and organs, the important obstacle represented by the humoral immune response will need to be overcome. Likewise, the barriers posed by the activation of the innate immune system and coagulative pathway will have to be controlled. As far as xenogeneic nonviable xenografts, increasing evidence suggests that considerable immune reactions, mediated by both innate and adaptive immunity, take place and influence the long-term outcome of xenogeneic materials in patients, possibly precluding the use of bioprosthetic heart valves in young individuals. In this context, the present article provides an overview of current knowledge on the immune processes following xenotransplantation and on the possible therapeutic interventions to overcome the immunological drawbacks involved in xenotransplantation.

Bortezomib, C1-inhibitor and plasma exchange do not prolong the survival of multi-transgenic GalT-KO pig kidney xenografts in baboons.

Galactosyl-transferase KO (GalT-KO) pigs represent a potential solution to xenograft rejection, particularly in the context of additional genetic modifications. We have performed life supporting kidney xenotransplantation into baboons utilizing GalT-KO pigs transgenic for human CD55/CD59/CD39/HT. Baboons received tacrolimus, mycophenolate mofetil, corticosteroids and recombinant human C1 inhibitor combined with cyclophosphamide or bortezomib with or without 2-3 plasma exchanges. One baboon received a control GalT-KO xenograft with the latter immunosuppression. All immunosuppressed baboons rejected the xenografts between days 9 and 15 with signs of acute humoral rejection, in contrast to untreated controls (n = 2) that lost their grafts on days 3 and 4. Immunofluorescence analyses showed deposition of IgM, C3, C5b-9 in rejected grafts, without C4d staining, indicating classical complement pathway blockade but alternate pathway activation. Moreover, rejected organs exhibited predominantly monocyte/macrophage infiltration with minimal lymphocyte representation. None of the recipients showed any signs of porcine endogenous retrovirus transmission but some showed evidence of porcine cytomegalovirus (PCMV) replication within the xenografts. Our work indicates that the addition of bortezomib and plasma exchange to the immunosuppressive regimen did not significantly prolong the survival of multi-transgenic GalT-KO renal xenografts. Non-Gal antibodies, the alternative complement pathway, innate mechanisms with monocyte activation and PCMV replication may have contributed to rejection.

Desensitization with plasmapheresis and anti-Cd20 for ABO incompatible kidney transplantation from living donor: experience of a single center in Italy.

OBJECTIVE: Blood group incompatibility in kidney transplants from a living donor can be successfully overcome by using various desensitization protocols: intravenous immunoglobulin, plasmapheresis (PP), immunoadsorption, and double filtration PP. PATIENTS AND METHODS: From July 2010 to October 2013, we performed 10 ABO incompatible kidney transplantation (KT) procedures from a living donor. The desensitization protocol was based on rituximab and PP+cytomegalovirus immune globulin. All patients received induction with basiliximab, except 1 case treated with Thymoglobuline® (ATG) for the simultaneous presence of donor-specific antibody. Tacrolimus and mycophenolate mofetil were initiated at the time of desensitization and continued after the transplant. RESULTS: After a mean follow-up of 11.6±10.4 months, all patients are alive with a functioning graft. The mean serum creatinine concentration at 1 month, 3 months, 6 months, and 1 year was 1.48±0.29, 1.47±0.18, 1.47±0.27, and 1.5±0.27 mg/dl. Three episodes of acute cellular rejection occurred in 2 patients. There was only 1 case of BK virus infection, treated with reduction of immunosuppressive therapy. The protocol biopsy specimens at 1, 3, and 6 months were C4d positive in the absence of acute rejection. CONCLUSIONS: Desensitization with rituximab, PP, and anti-cytomegalovirus immune globulin allowed us to perform transplants from living donors to ABO incompatible recipients with excellent results and reduced costs.

Multicenter randomized prospective clinical evaluation of meloxicam administered via transmucosal oral spray in client-owned dogs.

The clinical safety and efficacy of a transmucosal oral spray (TMOS) formulation of meloxicam was evaluated for the control of pain and inflammation associated with osteoarthritis in dogs. A total of 280 client-owned dogs were enrolled at fourteen veterinary clinics: there were 187 dogs in the meloxicam TMOS group and 93 in the placebo control group. Dogs received placebo or treatment spray once daily for twenty-eight days. Improvement in signs of osteoarthritis was measured using client-specific outcome measures (CSOM) made at days 14 and 28 and veterinary assessments of lameness and pain on palpation made at day 28. A significantly higher number of dogs in the meloxicam TMOS group were treatment successes at 28 days (72.6%) compared with the placebo group (46.9%), based on CSOM scores. Total CSOM scores were significantly lower in the meloxicam TMOS-treated group compared with the placebo group at both 14 and 28 days. Differences between treatment groups were not observed in veterinary assessments. Gastrointestinal effects of meloxicam were observed in some animals. Meloxicam TMOS was found to be safe and effective in dogs for the control of pain and inflammation associated with osteoarthritis.

Bioequivalence in dogs of a meloxicam formulation administered as a transmucosal oral mist with an orally administered pioneer suspension product.

A mucosal mist formulation of meloxicam, administered as a spray into the mouth (test article), was compared for bioequivalence to a pioneer meloxicam suspension for oral administration (reference article). Pharmacokinetic profiles and average bioequivalence were investigated in 20 dogs. The study design comprised a two-period, two-sequence, two-treatment cross-over design, with maximum concentration (C(max)) and area under plasma concentration-time curve to last sampling time (AUC(last)) used as pivotal bioequivalence variables. Bioequivalence of the products was confirmed, based on relative ratios of geometric mean concentrations (and 90% confidence intervals within the range 0.80-1.25) for C(max) of 101.9 (97.99-106.0) and for AUC(last) of 97.24 (94.44-100.1). The initial absorption of meloxicam was more rapid for the test article, despite virtually identical C(max) values for the two products. Mean elimination half-lives were 29.6 h (test article) and 30.0 h (reference article). The meloxicam plasma concentration-time profiles were considered in relation to published data on the inhibition of the cyclooxygenase-1 (COX-1) and COX-2 isoenzymes by meloxicam.

Glomerular c4d immunoreactivity in acute rejection biopsies of renal transplant patients.

In renal transplant patients, glomerulitis may be present in all types of acute rejection, often accompanied by diffuse C4d staining of peritubular capillaries: C4d3 positivity in more than 50% of peritubular capillaries. It may progress to chronic transplant glomerulopathy, characterized by capillary basement membrane multilayering, proteinuria, and progressive loss of renal function. While C4d3 is a recognized marker of an antibody-mediated reaction, the significance of glomerular C4d (GlC4d) staining is unknown. The aim of this study was to evaluate GlC4d immunoreactivity and its correlation with C4d3 in acute rejection biopsies. Paraffin-embedded acute rejection biopsies from 90 renal transplant patients were evaluated according to the Banff classification. Biopsies showing C4d-positive endothelial cells in more than 50% of glomeruli were considered GlC4d-positive. C4d3-positive staining prevalence was 23%. GlC4d-positive staining showed an 89% concordance rate (r = 0.81, P < .0001; Cohen's k = 0.80, P < .0001). GlC4d detection sensitivity was 0.80 and specificity 0.97. C4d3 and GlC4d immunoreactivity was significantly associated with glomerulitis (P < .006 and P < .03, respectively) and with proteinuria at the time of biopsy (P < .03 and P < .01, respectively). Interestingly, GlC4d positivity correlated better than C4d3 positivity with the presence of posttransplant circulating anti-human leukocyte antigen alloantibodies (P < .04 and P = .7, respectively). Patients with C4d3- or GlC4d-positive acute rejections underwent graft loss due to interstitial fibrosis and tubular atrophy more frequently than those with C4d0- or GlC4d-negative rejections (P < .0001 and P < .005, respectively), whereas no differences were observed in graft loss due to death. In conclusion, C4d3 and GlC4d stains showed a high correlation rate. Compared with C4d3, GlC4d staining demonstrated good sensitivity and excellent specificity. Our results suggested that GlC4d staining may indicate glomerular endothelial damage and be of prognostic value.

Refinement of a macaque transplantation model: application of a subcutaneous port as a means for long-term enteral drug administration and nutritional supplementation.

A new application of a device enabling the long-term enteral administration of drugs or nutritional supplementation was developed for implementing in research entailing the use of macaques (Macaca fascicularis). After implanting a subcutaneous port, a surgically-placed gastrostomy (SPG) was completed to afford access to the gastric lumen and enable the administration of substances. In this study, the device was left in place for a period ranging between two and 12 months in macaques (n= 16). In five cases, the SPG was used successfully for 8-12 months, until the experimental endpoint was reached. In six cases, the SPG had to be removed earlier due to local infection at the implant site, which promptly regressed after the SPG was removed and antibiotic treatment was administered. One SPG-implanted macaque was euthanized for reasons unrelated to the SPG or the xenotransplantation procedure. In four cases, the SPG was implanted without any complications but has yet to be used to administer substances to the animals. From an ethical standpoint, the SPG device described here minimizes the forced handling of macaques otherwise needed for the oral administration of viscous or unpalatable substances by gavage. The device thus represents an effective refinement that fully complies with the tenet of the '3 Rs' that should be considered by primate centres exposing non-human primates to the long-term daily administration of substances by oral gavage.

Xenotransplantation of galactosyl-transferase knockout, CD55, CD59, CD39, and fucosyl-transferase transgenic pig kidneys into baboons.

Galactosyl-transferase knockout (GT-KO) pigs represent the latest major progress to reduce immune reactions in xenotransplantation. However, their organs are still subject to rapid humoral rejection involving complement activation requiring the ongoing development of further genetic modifications in the pig. In a pig-to-baboon renal transplantation setting, we have used donor pigs that are not only GT-KO, but also transgenic for human CD55 (hCD55), hCD59, hCD39, and fucosyl-transferase (hHT). We studied kidney xenograft survival, physiological and immunologic parameters, xenogeneic rejection characteristics, as well as viral transmission aspects among two groups of baboons: control animals (n = 2), versus those (n = 4) treated with a cocktail of cyclophosphamide, tacrolimus, mycophenolate mofetil, steroids, and a recombinant human C1 inhibitor. Whereas control animals showed clear acute humoral rejection at around day 4, the treated animals showed moderately improved graft survival with rejection at around 2 weeks posttransplantation. Biopsies showed signs of acute vascular rejection (interstitial hemorrhage, glomerular thrombi, and acute tubular necrosis) as well as immunoglobulin (Ig)M and complement deposition in the glomerular and peritubular capillaries. The low level of preformed non-Gal-α1.3Gal IgM detected prior to transplantation increased at 6 days posttransplantation, whereas induced IgG appeared after day 6. No porcine endogenous retrovirus (PERV) transmission was detected in any transplanted baboon. Thus, surprisingly, organs from the GT-KO, hCD55, hCD59, hCD39, and hHT transgenic donors did not appear to convey significant protection against baboon anti-pig antibodies and complement activation, which obviously continue to be significant factors under a suboptimal immunosuppression regimen. The association, timing, and doses of immunosuppressive drugs remain critical. They will have to be optimized to achieve longer graft survivals.

Experimental hepatology applied to stem cells.

Transplantation is an accepted treatment today for many people suffering from organ failure. More and more patients are referred for transplant surgery, and the waiting lists are growing longer because not enough organs and tissues are donated for transplantation. This has led to several potentially viable alternatives being considered, including bio-artificial support devices, the transplantation of mature cells or stem/progenitor cells and the potential transplantation of xenogenic organs and cells [Burra P, Samuel D, Wendon J, Pietrangelo A, Gupta S. Strategies for liver support: from stem cells to xenotransplantation. J Hepatol 2004;41:1050-9]. Numerous investigators around the world are engaged in these investigations and the pace of discovery has begun to accelerate in recent years. To take stock of the achievements of recent years, the AISF sponsored a Single-Topic Conference, held in Padua on 26-27 May, 2006, with the participation of many leading investigators from various parts of Italy and Europe. This present paper summarizes the content of the Conference. Different issues were analysed, from the biology of stem cells to the possible use of gene therapy. The speakers were clinicians and scientists interested in diseases not only of the liver but also of other organs such as the kidney or heart. The fact that numerous specialties were represented helped the audience to understand the stem cell research area from different standpoints, and what research has achieved so far.

Refinement of a transplantation project in the non-human primate by the use of a humane endpoint.

An assessment scheme was developed to establish a humane endpoint in a pig-to-primate renal xenotransplantation project, with a view to minimizing and controlling any pain or suffering conditions in the animals involved while still achieving the scientific objective. In particular, the assessment criteria for identifying the earliest endpoint are described, bearing in mind both the researcher's need to obtain top-quality data and the ethical need to safeguard the animals. The scheme should also be applicable to other experiments involving non-human primates (e.g. allotransplantation, survival after major surgery, pharmacological safety tests) because it considers reproducible general parameters together with aspects specific to each experimental model.

An update on xenotransplantation.

Xenotransplantation is one of the possible avenues currently being explored to address the shortage problem of human organs. With this in mind, this article will briefly review the current situation with respect to the immunological, physiological and biosafety aspects related to the transplantation of pig organs into primates. Acute humoral xenograft rejection (AHXR) currently remains the central immunological obstacle and the development of strategies for both a better control of the elicited anti-pig humoral immune response or the prevention of the onset of coagulation disorders that accompany AHXR are the two primary focuses of research. To date, porcine xenografts have been shown to sustain the life of nonhuman primates for several months. Such preclinical studies have also demonstrated the absence of insurmountable physiological incompatibilities between pig and primate. In addition, reassuring findings regarding biosafety aspects have been generated and pro-active research aimed at the identification of an organ source with a higher safety profile is also underway. These advancements, in conjunction with ongoing research in pig genetic engineering, immunosuppression and tolerance are expected to further extend the survival of porcine xenografts transplanted into primates. However, until further physiological, efficacy and safety data are generated in relevant primate models, clinical xenotransplantation should not be considered.

Liver repopulation with bone marrow derived cells improves the metabolic disorder in the Gunn rat.

BACKGROUND: Reversible ischaemia/reperfusion (I/R) liver injury has been used to induce engraftment and hepatic parenchymal differentiation of exogenous beta2-microglubulin(-)/Thy1(+) bone marrow derived cells. AIM: To test the ability of this method of hepatic parenchymal repopulation, theoretically applicable to clinical practice, to correct the metabolic disorder in a rat model of congenital hyperbilirubinaemia. METHODS AND RESULTS: Analysis by confocal laser microscopy of fluorescence labelled cells and by immunohistochemistry for beta2-microglubulin, 72 hours after intraportal delivery, showed engraftment of infused cells in liver parenchyma of rats with I/R, but not in control animals with non-injured liver. Transplantation of bone marrow derived cells obtained from GFP-transgenic rats into Lewis rats resulted in the presence of up to 20% of GFP positive hepatocytes in I/R liver lobes after one month. The repopulation rate was proportional to the number of transplanted cells. Infusion of GFP negative bone marrow derived cells into GFP positive transgenic rats resulted in the appearance of GFP negative hepatocytes, suggesting that the main mechanism underlying parenchymal repopulation was differentiation rather than cell fusion. Transplantation of wild type bone marrow derived cells into hyperbilirubinaemic Gunn rats with deficient bilirubin conjugation after I/R damage resulted in 30% decrease in serum bilirubin, the appearance of bilirubin conjugates in bile, and the expression of normal UDP-glucuronyltransferase enzyme evaluated by polymerase chain reaction. CONCLUSIONS: I/R injury induced hepatic parenchymal engraftment and differentiation into hepatocyte-like cells of bone marrow derived cells. Transplantation of bone marrow derived cells from non-affected animals resulted in the partial correction of hyperbilirubinaemia in the Gunn rat.

Expression of CTLA-4 in nonhuman primate lymphocytes and its use as a potential target for specific immunotoxin-mediated apoptosis: results of in vitro studies.

T-cell-mediated immunoregulation is one of the main mechanisms implicated in induction and maintenance of transplantation tolerance. In this regard, deletion or modulation of xeno/alloantigen-specific T cells, as well as blocking of their interactions with other cell populations, are currently being pursued for tolerance induction in humans as well as nonhuman primates. In order to investigate whether cytotoxic T-lymphocyte antigen-4 (CTLA-4) may represent a suitable target for a T cell depletion approach in nonhuman primate models, we analysed CTLA-4 expression in peripheral blood mononuclear cells (PBMCs) from nonhuman primates and the potential role of two anti-CTLA-4 saporin-conjugated immunotoxins. The analysis was performed in PBMCs from 8 cynomolgus monkeys from Philippines and from Mauritius both at protein level by flow cytometry and at transcriptional level by RT-PCR. In addition, the apoptotic role of the immunotoxins was investigated. The results showed that CTLA-4 was expressed at variable levels depending on the origin of the cynomolgus monkeys and the resting or activated cell condition. CTLA-4 was not expressed on resting Mauritius PBMCs and showed a lower up-regulation upon PMA/PHA activation compared to the Philippines PBMCs that expressed CTLA-4 also before activation. Two CTLA-4 RNA transcripts (672 and 550 bp) were detected with levels variations after cell stimulation. Two anti-CTLA-4 immunotoxins induced in vitro apoptosis of activated PBMCs from both sources of cynomolgus monkeys. This is the first report that documents CTLA-4 expression both at protein and transcriptional level by nonhuman primate PBMCs and provides novel perspectives of xeno/allograft rejection immunotherapy based on CTLA-4 targeting.

Hyperacute lung rejection in the pig-to-human model. 2. Synergy between soluble and membrane complement inhibition.

BACKGROUND: The role of complement in hyperacute lung xenograft rejection has not been elucidated. The present study evaluates the effect of complement (C) C3/C5 convertase inhibition on hyperacute rejection of pig lung by human blood. METHODS: In an established ex-vivo model, lungs from pigs heterozygous for human decay accelerating factor (hDAF), non-transgenic littermate control pigs, or farm-bred pigs were perfused with fresh human blood that was either unmodified or treated with soluble complement receptor type 1 (sCR1: TP10, 100 microg/ml). RESULTS: Non-transgenic lungs from littermate controls had a median survival time of 35 min (range 5 to 210; P = 0.25 vs. farm-bred piglets: median 5 min, range 5 to 10). Lungs expressing hDAF survived for a median of 90 min (range 10 to 161; P = 0.5 and 0.01 vs. littermate and farm-bred controls, respectively), with sCR1, whereas hDAF (-) lungs failed by 35 min (range 6 to 307), hDAF (+) lungs survived for 330 min (range 39 to 577) [P = 0.002 vs. farm-bred; P = 0.08 vs. hDAF (-); P = 0.17 vs. sCR1/hDAF (-)]. The rise in pulmonary vascular resistance (PVR) at 5 min was blunted only by hDAF (+) with sCR1 (0.26 +/- 0.2 vs. 0.5 to 0.7 mmHg/ml/min for other groups). Plasma C3a and sC5b-9 and tissue deposition of C5b-9 were dramatically diminished using sCR1, and further decreased in association with hDAF. Histamine and thromboxane were produced rapidly in all groups. CONCLUSION: Complement plays an important role in lung HAR. However, even potent inhibition of C3/C5 convertase, both membrane bound in lung and by a soluble-phase inhibitor in the blood, does not prevent activation of inflammatory responses known to be particularly injurious to the lung. Our findings implicate a role for innate immune pathways resistant to efficient complement regulation. The role of anti-species antibody, coagulation pathway dysregulation, and additional environmental or genetic influences remain to be defined.