Achieving permanent survival of islet xenografts by independent manipulation of direct and indirect T-cell responses

Clinically available immunosuppression averts rejection but not systemic inflammation after porcine islet xenotransplant in cynomolgus macaques

A safe, efficacious, and clinically applicable immunosuppressive regimen is necessary for islet xenotransplantation to become a viable treatment option for diabetes. We performed intraportal transplants of wild-type adult porcine islets in 25 streptozotocin-diabetic cynomolgus monkeys. Islet engraftment was good in 21, partial in 3, and poor in 1 recipient. Median xenograft survival was 25 days with rapamycin and CTLA4Ig immunosuppression. Adding basiliximab induction and maintenance tacrolimus to the base regimen significantly extended median graft survival to 147 days (p < .0001), with three animals maintaining insulin-free xenograft survival for 265, 282, and 288 days. We demonstrate that this regimen suppresses non-Gal anti-pig antibody responses, circulating effector memory T cell expansion, effector function, and infiltration of the graft. However, a chronic systemic inflammatory state manifested in the majority of recipients with long-term graft survival indicated by increased neutrophil to lymphocyte ratio, IL-6, MCP-1, CD40, and CRP expression. This suggests that this immunosuppression regimen fails to regulate innate immunity and resulting inflammation is significantly associated with increased incidence and severity of adverse events making this regimen unacceptable for translation. Additional studies are needed to optimize a maintenance regimen for regulating the innate inflammatory response.

Immunogenetics of xenotransplantation

Xenotransplantation may become the highly desired solution to close the gap between the availability of donated organs and number of patients on the waiting list. In recent years, enormous progress has been made in the development of genetically engineered donor pigs. The introduced genetic modifications showed to be efficient in prolonging xenograft survival. In this review, we focus on the type of immune responses that may target xeno-organs after transplantation and promising immunogenetic modifications that show a beneficial effect in ameliorating or eliminating harmful xenogeneic immune responses. Increasing histocompatibility of xenografts by eliminating genetic discrepancies between species will pave their way into clinical application.

Nucleic acid-based theranostics in type 1 diabetes

Application of RNAi interference for type 1 diabetes (T1D) therapy bears tremendous potential. This review will discuss vehicles for oligonucleotide delivery, imaging modalities used for delivery monitoring, therapeutic targets, and different theranostic strategies that can be applied for T1D treatment.

Ex vivo-expanded baboon CD39 + regulatory T cells prevent rejection of porcine islet xenografts in NOD-SCID IL-2rγ-/- mice reconstituted with baboon peripheral blood mononuclear cells

BACKGROUND

A high immunosuppressive burden is required for long-term islet xenograft survival in non-human primates even using genetically modified donor pigs.

AIMS

We aimed to investigate the capacity of baboon regulatory T cells (Treg) to suppress islet xenograft rejection, thereby developing a potential immunoregulatory or tolerance therapy that could be evaluated in NHP models of xenotransplantation.

MATERIALS & METHODS

Baboon Treg expanded with stimulation by porcine peripheral blood mononuclear cells (PBMC) were characterized by cell phenotyping and suppressive activity assays in vitro. Their function in vivo was evaluated in neonatal porcine islet cell clusters (NICC) transplanted NOD-SCID IL-2rγ-/- (NSG) mice receiving baboon PBMC alone or with expanded autologous Treg.

RESULTS

The majority of expanded Treg coexpressed Foxp3 and CD39 and were highly suppressive of the baboon anti-pig xenogeneic T cell response in vitro. Reconstitution of mice with baboon PBMC alone resulted in NICC xenograft rejection within 35 days. Cotransfer with baboon PBMC and Treg prolonged islet xenograft survival beyond 100 days, correlating with Treg engraftment, intragraft CD39 and Foxp3 gene expression, and reduced graft infiltrating effector T cells and reduced interferon-γ production.

DISCUSSION & CONCLUSION

Our data supports the capacity of ex vivo expanded CD39+ baboon Treg to suppress islet xenograft rejection in primatized mice, suggesting it has potential as an adjunctive immunotherapy in preclinical NHP models of xenotransplantation.

Low energy X-ray (grenz ray) treatment of purified islets prior to allotransplant markedly decreases passenger leukocyte populations

Grenz rays, or minimally penetrating X-rays, are known to be an effective treatment of certain recalcitrant immune-mediated skin diseases, but their use in modulating allograft rejection has not been tested. We examined the capacity of grenz ray treatment to minimize islet immunogenicity and extend allograft survival in a mouse model. In a preliminary experiment, 1 of 3 immunologically intact animals demonstrated long-term acceptance of their grenz ray treated islet allograft. Further experiments revealed that 28.6% (2 of 7) grenz ray treated islet allografts survived >60 d. A low dose of 20Gy, was important; a 4-fold increase in radiation resulted in rapid graft failure, and transplanting a higher islet mass did not alter this outcome. To determine whether increased islet allograft survival after grenz treatment would be masked by immunosuppression, we treated the recipients with CTLA-4 Ig, and found an additive effect, whereby 17.5% more animals accepted the graft long-term versus those with CTLA-4 Ig alone. Cell viability assays verified that islet integrity was maintained after treatment with 20Gy. As well, through splenocyte infiltration analysis, donor CD4+ T cell populations 24-hours after transplant were decreased by more than16-fold in recipients receiving irradiated islets compared with control. Donor CD8+ T cell populations, although less prevalent, decreased in all treatment groups compared with control. Our results suggest that brief treatment of isolated islets with low energy grenz rays before allotransplantation can significantly reduce passenger leukocytes and promote graft survival, possibly by inducing donor dendritic cells to differentiate toward a tolerogenic phenotype.

Preconditioning allows engraftment of mouse and human embryonic lung cells, enabling lung repair in mice

Repair of injured lungs represents a longstanding therapeutic challenge. We show that human and mouse embryonic lung tissue from the canalicular stage of development (20-22 weeks of gestation for humans, and embryonic day 15-16 (E15-E16) for mouse) are enriched with progenitors residing in distinct niches. On the basis of the marked analogy to progenitor niches in bone marrow (BM), we attempted strategies similar to BM transplantation, employing sublethal radiation to vacate lung progenitor niches and to reduce stem cell competition. Intravenous infusion of a single cell suspension of canalicular lung tissue from GFP-marked mice or human fetal donors into naphthalene-injured and irradiated syngeneic or SCID mice, respectively, induced marked long-term lung chimerism. Donor type structures or 'patches' contained epithelial, mesenchymal and endothelial cells. Transplantation of differentially labeled E16 mouse lung cells indicated that these patches were probably of clonal origin from the donor. Recipients of the single cell suspension transplant exhibited marked improvement in lung compliance and tissue damping reflecting the energy dissipation in the lung tissues. Our study provides proof of concept for lung reconstitution by canalicular-stage human lung cells after preconditioning of the pulmonary niche.

Local co-delivery of pancreatic islets and liposomal clodronate using injectable hydrogel to prevent acute immune reactions in a type 1 diabetes

PURPOSE

The purpose of this study was to investigate the effect of locally delivered pancreatic islet with liposomal clodronate (Clodrosome®) as an immunoprotection agent for the treatment of type 1 diabetes.

METHOD

The bio-distribution of liposomal clodronate in matrigel was checked by imaging analyzer. To verify the therapeutic efficacy of locally delivered islet with liposomal clodronate using injectable hydrogel, four groups of islet transplanted mice (n = 6 in each group) were prepared: 1) the islet group, 2) the islet-Clodrosome group, 3) the islet-Matrigel group, and 4) the islet-Matrigel-Clodrosome group. Immune cell migration and activation, and pro-inflammatory cytokine secretion was evaluated by immunohistochemistry staining and ELISA assay.

RESULTS

Cy5.5 labeled liposomes remained in the matrigel for over 7 days. The median survival time of transplanted islets (Islet-Matrigel-Clodrosome group) was significantly increased (>60 days), compared to other groups. Locally delivered liposomal clodronate in matrigel effectively inhibited the activation of macrophages, immune cell migration and activation, and pro-inflammatory cytokine secretion from macrophages.

CONCLUSIONS

Locally co-delivered pancreatic islets and liposomal clodronate using injectable hydrogel effectively cured type 1 diabetes. Especially, the inhibition of macrophage attack in the early stage after local delivery of islets was very important for the successful long-term survival of delivered islets.

Survival of free and encapsulated human and rat islet xenografts transplanted into the mouse bone marrow

Bone marrow was recently proposed as an alternative and potentially immune-privileged site for pancreatic islet transplantation. The aim of the present study was to assess the survival and rejection mechanisms of free and encapsulated xenogeneic islets transplanted into the medullary cavity of the femur, or under the kidney capsule of streptozotocin-induced diabetic C57BL/6 mice. The median survival of free rat islets transplanted into the bone marrow or under the kidney capsule was 9 and 14 days, respectively, whereas that of free human islets was shorter, 7 days (bone marrow) and 10 days (kidney capsule). Infiltrating CD8⁺ T cells and redistributed CD4⁺ T cells, and macrophages were detected around the transplanted islets in bone sections. Recipient mouse splenocytes proliferated in response to donor rat stimulator cells. One month after transplantation under both kidney capsule or into bone marrow, encapsulated rat islets had induced a similar degree of fibrotic reaction and still contained insulin positive cells. In conclusion, we successfully established a small animal model for xenogeneic islet transplantation into the bone marrow. The rejection of xenogeneic islets was associated with local and systemic T cell responses and macrophage recruitment. Although there was no evidence for immune-privilege, the bone marrow may represent a feasible site for encapsulated xenogeneic islet transplantation.

Manufacturing porcine islets: culture at 22 °C has no advantage above culture at 37 °C: a gene expression evaluation

BACKGROUND

The manufacturing process of islets includes a culture step which was originally introduced to ease the logistics of procedures in preparing the graft and transplant recipient. It has been suggested that culture at room temperature has an advantage over culture at 37 °C, in part by reducing immunogenicity via preferential elimination of contaminating cells (such as passenger leukocytes) within islets. We investigated this using islets isolated from pancreata of adult pigs.

METHODS

Porcine islets were isolated from three donors and cultured at 37 °C for 1 day, and then under three different conditions: 37 °C for 6 days (condition A); 22 °C for 6 days (condition B); or 22 °C for 5 days followed by 37 °C for 1 day (condition C). Recovery was assessed by DNA measurement, viability by oxygen consumption rate normalized for DNA (OCR/DNA), and gene expression by RT-PCR for a series of 9 lymphocyte markers, 11 lymphokines and chemokines, and 14 apoptotic and stress markers.

RESULTS

Post-culture islet recoveries were similar for the three culture conditions. Average OCR/DNA values were 129-159 nmol/min·mgDNA before culture, and 259-291, 204-212, and 207-228 nmol/min·mgDNA, respectively, for culture under conditions A, B, and C, respectively. Irrespective of culture condition, examined gene expression in all three series of lymphocyte markers, lymphokines and chemokines, and apoptotic and stress markers manifested a statistically significant decrease upon culture for 7 days. This decrease was most dramatic for condition A: in particular, most of lymphocyte markers showed a >10-fold reduction and also six markers in the lymphokine and chemokine series; these reductions are consistent with the elimination of immune cells present within islets during culture. The reduction was less for apoptotic and stress markers. For culture under condition B, the reduction in gene expression was less, and culture under condition C resulted in gene expression levels similar to those under condition A: this indicates that 24 h at 37 °C is sufficient to re-equilibrate gene expression levels from those in islets cultured at 22 °C to those in islets cultured at 37 °C. Results were consistent among the preparations from the three donors.

CONCLUSIONS

Culture of porcine islets at 37 °C provides benefits over culture at 22 °C with respect to OCR/DNA outcomes and reduced expression of genes encoding lymphocyte markers, lymphokines and chemokines, and markers for apoptosis and stress.

Alternative immunomodulatory strategies for xenotransplantation: CD80/CD86-CTLA4 pathway-modified immature dendritic cells promote xenograft survival

Background

Xenotransplantation is a promising approach to circumventing the current organ shortage. However, T-cell-dependent anti-xenoresponses are a major challenge to successful xenografts. Given the advantages of the use of CTLA4-Ig in the survival of allografts, the purpose of the study was to investigate the therapeutic potential of CTLA4-IgG4 modified immature dendritic cells (imDCs) in the prevention of islets xenograft rejection.

Methods

CTLA4-IgG4 was constructed by the fusion of the extracellular regions of porcine CTLA4 to human the hIgG4 Fc region. The imDCs were induced and cultured from porcine peripheral blood mononuclear cells (PBMC). The CTLA4-IgG4 modified imDCs were delivered via the portal vein to the liver of diabetic mice (insulin-dependent diabetes mellitus) before islet xenografting, and mCTLA4-Ig was administered intravenously after xenotransplantation.

Results

The xenograft survival of mice receiving unmodified imDCs was approximately 30 days. However, following administration of CTLA4-IgG4 modified imDCs before grafting and mCTLA4-Ig after grafting, xenografts survived for more than 100 days. Flow cytometric analysis showed that the CD4⁺CD25⁺Foxp3⁺ Treg population was increased in spleens. The efficacy of donor CTLA4-IgG4 modified imDCs correlated partially with the amplification of Tregs.

Conclusions

These results confirm that selective inhibition of the direct and indirect pathways of T-cell activation by donor CTLA4-IgG4 modified imDCs and receptor CTLA4-Ig is a highly effective strategy to promote survival of xenografts.

Potential of T-regulatory cells to protect xenografts

PURPOSE OF REVIEW

Immunological barriers still preclude clinical xenotransplantation. The protective role of CD4(+)CD25(+)Foxp3(+) T-regulatory cells (Treg) in allotransplantation is well described and, therefore, could represent a promising therapeutical tool for xenotransplantation. This review addresses the latest findings on Treg in xenotransplantation research.

RECENT FINDINGS

In vivo, costimulation blockade-based strategies including anti-CD154 monoclonal antibodies (mAbs) in combination with rapamycin or anti-LFA-1 mAb prolonged both concordant and discordant islets xenografts survival in a Treg-dependent manner. In vitro, IL-10 secretion was shown to be critical for the suppression of xenogeneic responses mediated by Treg. Moreover, transgenic expression of inducible costimulator-immunoglobulin or PD-L1 on porcine endothelial cells inhibited human T-cell proliferation in vitro and was associated with the induction of Treg and IL-10 secretion. CXCR3 mediated the recruitment of Treg to pig endothelium. Finally, the recruitment of human Treg was enhanced by the immobilization of human CCL17 on pig endothelium.

SUMMARY

There is increasing evidence for the potential of CD4(+)CD25(+)Foxp3(+) Treg to protect xenografts. Induction of Treg in recipients and/or recruitment of human Treg to pig endothelium may represent novel strategies to prevent cell-mediated rejection in pig-to-human xenotransplantation.

Therapeutic effect of cytotoxic T lymphocyte antigen 4/immunoglobulin on a murine model of primary biliary cirrhosis

Collectively, the data in both humans and murine models of human primary biliary cirrhosis (PBC) suggest that activated T cells, particularly CD8 T cells, play a critical role in biliary cell destruction. Under physiological conditions, T-cell activation involves two critical signals that involve the major histocompatibility complex and a set of costimulatory molecules, which include a receptor on T cells termed cytotoxic T lymphocyte antigen 4 (CTLA-4). Germane to the studies reported herein, signaling by CTLA-4 has the potential to modulate costimulation and induce inhibitory signals. In this study, we have taken advantage of our well-defined murine model of PBC, in which mice are immunized with 2-octynoic acid coupled to bovine serum albumin (2OA-BSA), leading to the production of high-titer antimitochondrial autoantibodies (AMAs) and portal cellular infiltrates. To investigate the potential of CTLA-4-Ig (immunoglobulin) as an immunotherapeutic agent, we treated mice both before and after induction of autoimmune cholangitis. First, we demonstrate that CTLA-4-Ig treatment, begun 1 day before 2OA-BSA immunization, completely inhibits the manifestations of cholangitis, including AMA production, intrahepatic T-cell infiltrates, and bile duct damage. However, and more critically, treatment with CTLA-4-Ig, initiated after the development of autoimmune cholangitis in previously immunized mice, also resulted in significant therapeutic benefit, including reduced intrahepatic T-cell infiltrates and biliary cell damage, although AMA levels were not altered.

CONCLUSION

These data suggest that an optimized regimen with CTLA-4-Ig has the potential to serve as an investigative therapeutic tool in patients with PBC.

A theranostic small interfering RNA nanoprobe protects pancreatic islet grafts from adoptively transferred immune rejection

Islet transplantation has recently emerged as an acceptable clinical modality for restoring normoglycemia in patients with type 1 diabetes mellitus (T1DM). The long-term survival and function of islet grafts is compromised by immune rejection-related factors. Downregulation of factors that mediate immune rejection using RNA interference holds promise for improving islet graft resistance to damaging factors after transplantation. Here, we used a dual-purpose therapy/imaging small interfering (si)RNA magnetic nanoparticle (MN) probe that targets β(2) microglobulin (B2M), a key component of the major histocompatibility class I complex (MHC I). In addition to serving as a siRNA carrier, this MN-siB2M probe enables monitoring of graft persistence noninvasively using magnetic resonance imaging (MRI). Human islets labeled with these MNs before transplantation into B2M (null) NOD/scid mice showed significantly improved preservation of graft volume starting at 2 weeks, as determined by longitudinal MRI in an adoptive transfer model (P < 0.05). Furthermore, animals transplanted with MN-siB2M-labeled islets demonstrated a significant delay of up to 23.8 ± 4.8 days in diabetes onset after the adoptive transfer of T cells relative to 6.5 ± 4.5 days in controls. This study demonstrated that our approach could protect pancreatic islet grafts from immune rejection and could potentially be applied to allotransplantation and prevention of the autoimmune recurrence of T1DM in islet transplantation or endogenous islets.

Blockade of both B7-H4 and CTLA-4 co-signaling pathways enhances mouse islet allograft survival

Costimulation blockade is an effective way to prevent allograft rejection. In this study, we tested the efficacy of two negative co-signaling molecules in protecting islet allograft function. We used local expression of B7-H4 by adenoviral transduction of islets (Ad-B7-H4) and systemic administration of CTLA-4.Ig to investigate the outcomes of allograft survival. Five groups of streptozotocin-induced diabetic C57BL/6 mice received 400 islets each from BALB/c donors. The groups consisted of control (G1); CTLA-4.Ig (G2); Ad-LacZ (G3); Ad-B7-H4 (G4); and Ad-B7-H4 and CTLA-4.Ig combined (G5). G1 and G3 developed graft failure on average of two weeks. G2, G4 and G5 survived for 43.8 ± 34.8, 54.7 ± 31.2 and 77.8 ± 21.5 d, respectively. Activated T and B cells in the lymph nodes were significantly controlled by CTLA-4.Ig treatment. Significantly reduced infiltrates were also detected in the allografts of G2 compared with G1. By contrast, B7-H4 significantly inhibited Th1-associated IFN-gamma secretion in the early stage and increased Foxp3 (+) T cells in the long-term surviving allografts. Our study suggests that CTLA-4 and B7-H4 inhibit alloimmune responses through distinct mechanisms, and that combination therapy which activates two negative co-signaling pathways can further enhance islet allograft survival.

Effect of combined OX40Ig and CTLA4Ig gene local transfer on allograft rejection and the underlying mechanisms

BACKGROUND

OX40Ig and CTLA4Ig fusion proteins have been suggested to induce immune tolerance and prevent rejection in allografts. The present study aims to investigate and compare the effects of ex vivo combined OX40Ig and CTLA4Ig lentivirus-mediated gene transfer on the long-term survival of the graft, as well as potential underlying mechanisms.

METHODS

We ex vivo transferred Brown Norway rats' superficial groin free flap with lentivirus vectors expressing OX40Ig or CTLA4Ig, or OX40Ig and CTLA4Ig combined, and transplanted the free flaps to Lewis rats. Short-course rapamycin was administered after transfection and transplantation. RT-PCR and Western blot were employed to evaluate expression of OX40Ig and CTLA4Ig. We assessed the survival time of the grafts and the degree of acute graft rejection after indicated treatment. Mixed lymphocyte reaction, flow cytometry, and ELISA were also used to evaluate systemic immune reactions.

RESULTS

Ex vivo transfer of OX40Ig or CTLA4Ig lentivirus vectors led to local expression of corresponding mRNA and proteins in the donor flap without affecting other organs of the recipient. The graft survival time was significantly expanded and rejection was markedly attenuated after transfection. Mixed lymphocyte reaction, flow cytometry (CD4(+) and CD8(+) T lymphocyte proportions), and serum ELISA analysis (IL-2, IFN-γ, IL-4, and IL-10) also showed decreased immune response following transfection. Combined OX40Ig and CTLA4Ig transfer exerted superior effect on improving graft survival and preventing graft rejection, inhibiting the immune response and decreasing the production of proinflammatory cytokines, compared with singular transfer of either OX40Ig or CTLA4Ig.

CONCLUSION

Combined ex vivo transfer of OX40Ig and CTLA4Ig lentivirus vectors provided superior benefits on long-term survival and restoration of the graft through inhibiting immune response and decreasing the production of proinflammatory cytokines.

Adoptive transfer with in vitro expanded human regulatory T cells protects against porcine islet xenograft rejection via interleukin-10 in humanized mice

T cell-mediated rejection remains a barrier to the clinical application of islet xenotransplantation. Regulatory T cells (Treg) regulate immune responses by suppressing effector T cells. This study aimed to determine the ability of human Treg to prevent islet xenograft rejection and the mechanism(s) involved. Neonatal porcine islet transplanted NOD-SCID IL2rγ(-/-) mice received human peripheral blood mononuclear cells (PBMC) with in vitro expanded autologous Treg in the absence or presence of anti-human interleukin-10 (IL-10) monoclonal antibody. In addition, human PBMC-reconstituted recipient mice received recombinant human IL-10 (rhIL-10). Adoptive transfer with expanded autologous Treg prevented islet xenograft rejection in human PBMC-reconstituted mice by inhibiting graft infiltration of effector cells and their function. Neutralization of human IL-10 shortened xenograft survival in mice receiving human PBMC and Treg. In addition, rhIL-10 treatment led to prolonged xenograft survival in human PBMC-reconstituted mice. This study demonstrates the ability of human Treg to prevent T-cell effector function and the importance of IL-10 in this response. In vitro Treg expansion was a simple and effective strategy for generating autologous Treg and highlighted a potential adoptive Treg cell therapy to suppress antigraft T-cell responses and reduce the requirement for immunosuppression in islet xenotransplantation.

Relative efficiency of porcine and human cytotoxic T-lymphocyte antigen 4 immunoglobulin in inhibiting human CD4+ T-cell responses co-stimulated by porcine and human B7 molecules

α1,3-Galactosyltransferase gene-knockout pigs transgenic for porcine cytotoxic T-lymphocyte antigen 4 immunoglobulin (pCTLA4-Ig) have been produced to reduce T-cell-mediated rejection following xenotransplantation. The level of soluble pCTLA4-Ig in their blood was greatly in excess of the therapeutic level in patients, rendering the pigs immune-incompetent. Soluble pCTLA4-Ig produced by these transgenic pigs was evaluated for binding to porcine and human (h) B7 molecules, and for its inhibitory effect on allogeneic and xenogeneic human T-cell responses. Porcine CTLA4-Ig-expressing peripheral blood mononuclear cells (PBMCs) and aortic endothelial cells (AECs) were evaluated for their direct inhibitory effect on hCD4+ T-cell responses. Soluble pCTLA4-Ig and purified hCTLA4-Ig showed similar binding to pB7 molecules, but pCTLA4-Ig showed significantly less binding to hB7 molecules. The pCTLA4-Ig and hCTLA4-Ig inhibited the response of hCD4+ T cells to pAECs equally, but pCTLA4-Ig was less successful in inhibiting the human allogeneic response. The hCD4+ T-cell response to PBMCs from pCTLA4-Ig pigs was significantly lower than that of non-pCTLA4-Ig pigs. Although pCTLA4-Ig was detected in the cytoplasm of pCTLA4-Ig-expressing pAECs, only a minimal level of soluble pCTLA4-Ig was detected in the supernatant during culture, and pCTLA4-Ig-expressing pAECs did not inhibit the xenogeneic direct human T-cell response. High-level tissue-specific production of pCTLA4-Ig may be required for sufficient immunosuppression for organ or cell (e.g., islets) transplantation.

Porcine CTLA4-Ig prolong islet xenografts in rats by downregulating the direct pathway of T-cell activation

AIM

Porcine pancreatic islets fused with pCTLA4-Ig were transplanted into diabetic rats. Xenografts survival was observed, and the underlying immunological rejection mechanisms were investigated.

METHODS

Control porcine islets, empty vector (Adv-GFP)-transfected, and gene-modified porcine islets were transplanted into the renal capsule of diabetic rats. The survival rates of the xenografts were observed. Changes in serum levels of IL-4 and γ-IFN in the recipients were assessed.

RESULTS

The survival time of xenografts in the gene-modified porcine islets group was 34.50 ± 4.14 days, which was longer than those in the control group (34.50 ± 4.14 days vs. 7.43 ± 1.72 days and 7.22 ± 1.72 days; P < 0.01). Changes in the serum levels of IL-4 and γ-IFN between the groups of rats post-transplantation indicated the differentiation bias of T helper cells.

CONCLUSIONS

The donor-originated pCTLA-IgG4 fusion protein inhibits the direct pathway of recipient T-cell priming, which might prolong xenograft survival.

Pancreatic-derived pathfinder cells enable regeneration of critically damaged adult pancreatic tissue and completely reverse streptozotocin-induced diabetes

We demonstrate that intravenous delivery of human, or rat, pancreas-derived pathfinder (PDP) cells can totally regenerate critically damaged adult tissue and restore normal function across a species barrier. We have used a mouse model of streptozotocin (STZ)-induced diabetes to demonstrate this. Normoglycemia was restored and maintained for up to 89 days following the induction of diabetes and subsequent intravenous delivery of PDP cells. Normal pancreatic histology also appeared to be restored, and treated diabetic animals gained body weight. Regenerated tissue was primarily of host origin, with few rat or human cells detectable by fluorescent in situ hybridization (FISH). Crucially, the insulin produced by these animals was overwhelmingly murine in origin and was both types I and II, indicative of a process of developmental recapitulation. These results demonstrate the feasibility of using intravenous administration of adult cells to regenerate damaged tissue. Critically, they enhance our understanding of the mechanisms relating to such repair and suggest a means for novel therapeutic intervention in loss of tissue and organ function with age.

Overcoming the barriers to xenotransplantation: prospects for the future

Cross-species transplantation (xenotransplantation) has immense potential to solve the critical need for organs, tissues and cells for clinical transplantation. The increasing availability of genetically engineered pigs is enabling progress to be made in pig-to-nonhuman primate experimental models. Potent pharmacologic immunosuppressive regimens have largely prevented T-cell rejection and a T-cell-dependent elicited antibody response. However, coagulation dysfunction between the pig and primate is proving to be a major problem, and this can result in life-threatening consumptive coagulopathy. This complication is unlikely to be overcome until pigs expressing a human 'antithrombotic' or 'anticoagulant' gene, such as thrombomodulin, tissue factor pathway inhibitor or CD39, become available. Progress in islet xenotransplantation has been more encouraging, and diabetes has been controlled in nonhuman primates for periods in excess of 6 months, although this has usually been achieved using immunosuppressive protocols that might not be clinically applicable. Further advances are required to overcome the remaining barriers.

A new bioartificial pancreas utilizing amphiphilic membranes for the immunoisolation of porcine islets: a pilot study in the canine

We have developed a replaceable bioartificial pancreas to treat diabetes utilizing a unique cocontinous amphiphilic conetwork membrane created for macroencapsulation and immunoisolation of porcine islet cells (PICs). The membrane is assembled from hydrophilic poly(N,N-dimethyl acrylamide) and hydrophobic/oxyphilic polydimethylsiloxane chains cross-linked with hydrophobic/oxyphilic polymethylhydrosiloxane chains. Our hypothesis is that this membrane allows the survival of xenotransplanted PICs in the absence of prevascularization or immunosuppression because of its extraordinarily high-oxygen permeability and small hydrophilic channel dimensions (3-4 nm). The key components are a 5-10 microm thick semipermeable amphiphilic conetwork membrane reinforced with an electrospun nanomat of polydimethylsiloxane-containing polyurethane, and a laser-perforated nitinol scaffold to provide geometric stability. Devices were loaded with PICs and tested for their ability to maintain islet viability without prevascularization, prevent rejection, and reverse hyperglycemia in three pancreatectomized dogs without immunosuppression. Tissue tolerance was good and there was no systemic toxicity. The bioartificial pancreas protected PICs from toxic environments in vitro and in vivo. Islets remained viable for up to 3 weeks without signs of rejection. Neovascularization was observed. Hyperglycemia was not reversed, most likely because of insufficient islet mass. Further studies to determine long-term islet viability and correction of hyperglycemia are warranted.

Current status of xenotransplantation and prospects for clinical application

Xenotransplantation is one promising approach to bridge the gap between available human cells, tissues, and organs and the needs of patients with diabetes or end-stage organ failure. Based on recent progress using genetically modified source pigs, improving results with conventional and experimental immunosuppression, and expanded understanding of residual physiologic hurdles, xenotransplantation appears likely to be evaluated in clinical trials in the near future for some select applications. This review offers a comprehensive overview of known mechanisms of xenograft injury, a contemporary assessment of preclinical progress and residual barriers, and our opinions regarding where breakthroughs are likely to occur.

Recent advances in pig-to-human organ and cell transplantation

Xenotransplantation using pigs offers the prospect of an unlimited number of organs and cells for clinical transplantation. A major step forward has been achieved with the introduction of pigs homozygous for alpha1,3-galactosyltransferase gene-knockouts that do not express the major antigenic target for primate antipig antibodies (i.e., Galalpha1,3Gal). Heterotopic heart transplants have survived for 2-6 months in baboons. However, other immune and pathophysiologic barriers remain, including: i) anti-non-Gal antibodies and cells of the innate immune system; and ii) thrombogenesis associated with incompatibilities in the coagulation-anticoagulation systems of pig and primate. Further genetic modification of the organ-source pig to overcome these barriers is being undertaken.

Alpha1,3-galactosyltransferase gene-knockout pigs for xenotransplantation: where do we go from here?

The ability to genetically engineer pigs that no longer express the Galalpha1,3Gal (Gal) oligosaccharide has been a significant step toward the clinical applicability of xenotransplantation. Using a chronic immunosuppressive regimen based on costimulatory blockade, hearts from these pigs have survived from 2 to 6 months in baboons. Graft failure was predominantly from the development of a thrombotic microangiopathy. Potential contributing factors include the presence of preformed anti-nonGal antibodies or the development of low levels of elicited antibodies to nonGal antigens, natural killer (NK) cell or macrophage activity, and inherent coagulation dysregulation between pigs and primates. The breeding of pigs transgenic for an "anticoagulant" gene, such as human tissue factor pathway inhibitor, hirudin, or CD39, or lacking the gene for the prothrombinase, fibrinogen-like protein-2, is anticipated to inhibit the change in the endothelium to a procoagulant state that takes place in the pig organ after transplantation. The identification of the targets for anti-nonGal antibodies and/or human macrophages might allow further genetic modification of the pig, and xenogeneic NK cell recognition and activation may be inhibited by the transgenic expression of human leukocyte antigen molecules and/or by blocking the function of activating NK receptors. The ultimate goal of induction of T-cell tolerance may be possible only if these hurdles in the coagulation system and innate immunity can be overcome.

Pig-to-non-human primate heart transplantation: immunologic progress over 20 years

The major developments in pig-to-non-human primate heart xenotransplantation during the past 20 years are summarized, largely through the experience of one investigator. Genetic modifications to organ-source pigs have been important steps in increasing heart xenograft survival from a few minutes in 1986 to 2 to 6 months in 2005.

Xenotransplantation of purified pre-natal porcine beta cells in mice normalizes diabetes when a short anti-CD4-CD8 antibody treatment is combined with transient insulin injections

BACKGROUND

Pre-natal porcine endocrine islet cell grafts were recently shown to contain immature beta cells with a marked potential for growth and differentiation following transplantation, and hence for a progressive and long-term correction of diabetes in immune-incompetent mice. The present study investigates whether these grafts are also capable of correcting hyperglycemia in immune-competent mice receiving a short treatment with anti-CD4-CD8 antibodies.

METHODS

Pure endocrine islet cell grafts with 0.5 to 1.0 million beta cells were prepared from pre-natal pigs and transplanted under the kidney capsule of alloxan-diabetic CBA/Ca mice. Survival, growth and function of implanted beta cells were followed by measuring plasma porcine C-peptide and glucose, and graft insulin content at start and at post-transplant (PT) week 35. The effect was studied of a 5-day treatment with non-depleting anti-CD4 YTS177 and depleting anti-CD8 YTS169 antibody, either without or with transient insulin injections.

RESULTS

Without antibody treatment, all graft recipients remained porcine C-peptide negative and died. Antibody treatment decreased CD4-expression and percentage CD8 cells for 10 and 18 weeks respectively. It resulted in a 30 week-survival of nine out of 14 graft recipients; all nine had progressively become C-peptide positive but only one proceeded to normoglycemia. When antibody treatment was combined with transient insulin injections, 11 out of 14 graft recipients survived long-term, eight became C-peptide positive and six were normoglycemic at PT week 30. In both groups, surviving recipients exhibited a graft insulin content that was 6- to 9-fold higher than at implantation.

CONCLUSIONS

Pre-natal porcine beta cells grow and differentiate when transplanted in diabetic immune-competent mice that have been transiently immune suppressed with anti-CD4 and anti-CD8 monoclonal antibodies. They develop metabolic control when recipients are also transiently treated with insulin injections.

Gal knockout and beyond

Recently, Galalpha1-3Galbeta1-4GlcNAc (Gal) knockout (k/o) pigs have been developed using genetic cloning technologies. This remarkable achievement has generated great enthusiasm in xenotransplantation studies. This review summarizes the current status of nonhuman primate experiments using Gal k/o pig organs. Briefly, when Gal k/o pig organs are transplanted into primates, hyperacute rejection does not occur. Although graft survival has been prolonged up to a few months in some cases, the overall results were not better than those using Gal-positive pig organs with human complement regulatory protein transgenes. Gal k/o pig kidneys rapidly developed rejection which was associated with increased anti-non-Gal antibodies. Although the precise mechanisms of Gal k/o pig organ rejection are not clear, it could result from incomplete deletion of Gal, up-regulation of new antigen (non-Gal antigen) and/or production of non-Gal antibodies. Future work in xenotransplantation should place emphasis on further modification of donors, such as combining human complement regulatory genes with Gal k/o, deleting non-Gal antigens and adding protective/surviving genes or a gene that inhibits coagulation. Induction of donor-specific T- and B-cell tolerance and promotion of accommodation are also warranted.

Avenues for immunomodulation and graft protection by gene therapy in transplantation

Organ transplantation represents the only definitive therapy for many causes of end-organ failure. However, the universal success of this therapy is limited by chronic allograft rejection, the side effects of chronic immunosuppressive therapy, and a severe shortage of donor organs. Presently, the success of solid-organ transplantation depends on the continuous administration of toxic and nonspecific immunosuppressive agents, therapies that present risks for opportunistic infection, malignancy, and a variety of agent-specific side effects. To promote the use of transplantation with limited risk of long-term sequelae, three dominant research challenges emerge: (i) elimination of the need for exogenous immunosuppression by immunological tolerance induction; (ii) prevention of chronic rejection/graft dysfunction; and (iii) expansion of available organs for transplantation. Gene therapy may provide significant advances and solutions in each of these areas. Rejection of the graft in the immediate post-transplant period has been attacked through the transfer of immunomodulatory molecules in addition to tolerance inducing approaches. Chronic graft rejection may be similarly addressed through permanent tolerance induction or alternatively through the introduction of molecules to resist chronic graft damage. Genetic manipulation of stem cells may ultimately produce transgenic animals to serve as tissue donors to overcome the limited donor organ supply. This review will highlight ongoing developments in the translation of gene therapy approaches to the challenges inherent in transplantation.

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.

Nomenclature for factors of the swine leukocyte antigen class II system, 2005

A systematic nomenclature for the genes and alleles of the swine major histocompatibility complex (MHC) is essential to the development and communication of research in swine immunology. The Swine Leukocyte Antigen (SLA) Nomenclature Committee of the International Society for Animal Genetics (ISAG) has reviewed all of the DNA-sequence information for MHC class II genes, available in GenBank/EMBL/DDBJ databases, and the associated published reports to develop such a systematic nomenclature. This article summarizes the proposed nomenclature, which parallels the World Health Organization's nomenclature for factors of the human MHC. The SLA class II genes expressed on the cell membrane will be noted as SLA-DRA, SLA-DRB1, SLA-DQA, and SLA-DQB1. Nomenclature assignments for all SLA class II GenBank sequences are now noted. The committee will add new SLA class II allele designations, as they are discovered, and will maintain a publicly available list of all recognized genes and alleles using the Immuno Polymorphism Database (IPD). The sequences will be available from the IPD-MHC section of the database which contains non-human MHC sequences (http://www.ebi.ac.uk/ipd/mhc/sla/).