Anti-Galalpha1-3Gal antibody levels in organ transplant recipients receiving immunosuppressive therapy

The effect of long-term pharmacologic immunosuppression (PI) on anti-Galalpha1-3Gal (alphaGal) antibody (Ab) levels has not been determined previously in humans. In this study, we measured alpha Gal Ab levels by ELISA in 14 healthy volunteers (controls) and in 70 patients with grafts (kidney, heart, liver) who had received different combinations of PI (including cyclosporine, tacrolimus, azathioprine, mycophenolate mofetil, and steroids) for >3 months. There was great variation in Gal IgM (<80-fold) and IgG (<160-fold). There was no difference in Gal IgM or Gal IgG between any one group and any other. In kidney patients with either high (mean 68%) or low (mean 6%) panel-reactive alloantibodies, there was no difference in alpha Gal Ab level or serum cytotoxicity to pig cells. In vitro immunoadsorption of alphaGal Ab from the serum did not change panel-reactive alloantibody positivity. Therapy with OKT3, a mouse product that might stimulate alphaGal Ab production, led to no significant change in patient Ab levels. We conclude that long-term (>3 months) PI does not reduce Gal Ab levels sufficiently to be of clinical value in xenotransplantation.

Venular thrombosis is the key event in the pathogenesis of antibody-mediated cardiac rejection

A review of the histopathologic features of serial biopsies and excised grafts of 117 experimental and clinical cardiac allografts and xenografts revealed a common sequence in the development of histopathologic changes in grafts showing antibody-mediated (hyperacute and acute vascular) rejection. Based on these observations, we propose the new concept that thrombosis of cardiac veins and venules is the initial key event in antibody-mediated rejection. This is followed by the development of congestion in the subtended venules and capillaries accompanied by interfascicular and, later, intermyocyte edema. Subsequently, focal or diffuse interstitial hemorrhage affecting the subendocardium, extending sometimes to involve the inner half of the ventricular myocardium, is observed. Antibody-mediated rejection therefore appears to be analogous to incomplete venous infarction of the heart. The observed histopathology (in which venular thrombosis plays a key role) favors a thrombogenic basis for the classical features of antibody-mediated rejection, namely edema, vascular thrombi and interstitial hemorrhage. A key role for venular thrombosis would explain the non-uniform distribution of the changes and may suggest new ways of preventing antibody-mediated xenograft rejection.

Decreased graft-versus-host disease after haplotype mismatched bone marrow allografts in miniature swine following interleukin-2 treatment

Graft-versus-host disease (GVHD) is an important complication of bone marrow transplantation after transplants between HLA-mismatched donor/recipient pairs. In mice, giving IL-2 post transplant decreases GVHD in this setting. We studied high-dose IL-2 therapy in pigs. Transplants were carried out after conditioning with fractionated total body radiation and cyclophosphamide. Fourteen pigs received a fully mismatched bone marrow transplant (six with IL-2; eight without IL-2), and six received a single haplotype class II mismatched transplant (three with IL-2; three without IL-2). GVHD was evaluated by skin histology. All fully mismatched recipients had severe GVHD (grade 2-3) and died within 13 to 51 days whether or not they received IL-2. Pigs receiving a one haplotype class II mismatched transplant without IL-2 developed severe skin GVHD lasting for 8-45 days; all died within 57 days. Similar pigs receiving IL-2 post transplant had no or only mild skin GVHD for less than 15 days; two are long-term survivors. Bone Marrow Transplantation (2000) 25, 47-52.

Peripheral blood progenitor cell mobilization and leukapheresis in pigs

BACKGROUND AND PURPOSE

The pig is being investigated as an organ donor for humans. Induction of immunologic tolerance to pig tissues in primates would overcome the major immunologic barriers to xenotransplantation. A proven method of inducing tolerance to allografts is by the induction of mixed hematopoietic chimerism by bone marrow transplantation. We are therefore investigating induction of mixed hematopoietic chimerism in the pig-to-baboon model.

METHODS

To obtain large numbers of pig hematopoietic cells, leukapheresis was used to collect blood cell products in miniature swine (n = 5) after progenitor cell mobilization by use of a course of hematopoietic growth factors (cytokines), consisting of porcine interleukin 3, porcine stem cell factor, and human granulocyte colony-stimulating factor.

RESULTS

Cytokine therapy and leukapheresis were well tolerated. Cytokine therapy increased the total white blood cell count and allowed large numbers of leukocytes (60 x 10(10)) to be obtained by apheresis, of which approximately 0.1% were granulocyte-erythrocyte-monocyte-megakaryocyte colony-forming units (CFU-GEMMs), which are considered to be representative of hematopoietic progenitors with multi-lineage potential.

CONCLUSIONS

The combination of cytokine therapy and leukapheresis enables hematopoietic progenitor cells to be obtained safely from miniature swine.

Pig xenogeneic antigen modification with green coffee bean alpha-galactosidase

Green coffee bean alpha-galactosidase can cleave the terminal alpha-galactose (alphaGal) on oligosaccharides that form the major antigen on pig endothelial cells recognized by primate-specific antibodies. Studies have been made of the conditions under which it is functional (e.g. temperature, pH) and of its biochemical and immunologic effects. Pig-to-rhesus monkey vein transplants were studied to identify the efficiency of the enzyme in delaying hyperacute rejection. When a graft became occluded, biopsies were taken for light microscopy (hematoxylin and eosin), scanning electron microscopy (SEM) and immunostaining with Griffonia simplicifolia IB4 lectin (GSIB4), and for IgM, IgG and C3. alpha-Galactosidase was stable for 72-96 h and was effective at 4 degrees C and pH 6.9 (conditions of human liver graft storage), although better function was obtained at 20 degrees C and pH 6.5. Using the porcine PK15 cell assay, the cytotoxicity of human serum was reduced after treatment of the pig cells with the enzyme. In vitro studies demonstrated that porcine veins treated with alpha-galactosidase lost endothelial expression of the Gal epitope within 30 min. SEM, however, demonstrated endothelial damage beginning within 2 h, probably caused by the alpha-galactosidase, as no damage was found in phosphate-buffered saline-treated veins, where the Gal epitope was preserved for >3 h. No change was found in either group on light microscopy. In vivo studies demonstrated that patency of the alpha-galactosidase-treated veins (mean 2.5 h) was longer than that of untreated veins (0.23 h) (P < 0.01). Biopsies showed no GSIB4 lectin staining for alpha-Gal epitopes and much less IgM and C3 deposition in the treated group. Light microscopy and SEM demonstrated more severe endothelial damage, hemorrhage, and fibrin formation in the untreated group. Galactosidase is effective in removing the terminal alphaGal and delays the onset of hyperacute rejection of pig veins transplanted into monkeys. However, its effect is temporary and, on its own, its use is unlikely to prolong survival of pig organs transplanted into primates sufficiently to be of clinical value.

Different responses of human anti-HLA and anti-alphagal antibody to long-term intravenous immunoglobulin therapy

Concentrated human immunoglobulin (IVIG) has been administered intravenously in the treatment of autoimmune disorders and to reduce anti-HLA antibodies in highly sensitized patients awaiting organ transplantation. It has also been shown, in experimental animals, to prevent the hyperacute rejection of discordant xenografts, possibly by anticomplement activity. The aim of the present study was to assess the effect of IVIG therapy on both acquired anti-HLA antibodies and natural antigalactose alpha1-3 galactose (alphaGal) antibodies in five patients awaiting heart transplantation. Five patients placed on mechanical circulatory support who had developed high HLA panel-reactive antibodies (PRA) or in whom the percentage of PRA was increasing rapidly were treated weekly with 500 mg/kg IVIG, which contained 1% of anti-alphaGal IgG. Levels of PRA, anti-alphaGal IgG and IgM, and serum cytotoxicity to pig cells were measured before, during, and after therapy. PRA percentages in the five patients were initially 85%, 53%, 23%, 19% and 19% (mean 39%). Mean PRA fell by 66% after 3 months of therapy (to a mean PRA of 14%), and by 96% after 6 months therapy (to a mean PRA of 2%). Anti-alphaGal antibody levels and serum cytotoxicity to pig aortic endothelial cells did not change significantly. These results confirm the effectiveness of IVIG therapy in reducing PRA in HLA highly sensitized patients. It is likely that IVIG does not contain the relevant anti-HLA antibody, resulting in an accelerated catabolism of native alloantibodies. However, as IVIG contains a normal level of anti-alphaGal IgG, catabolism of anti-alphaGal IgG is not modified, as it is being continuously replaced. To achieve a decrease in the anti-alphaGal IgG level it would be necessary to use IVIG depleted of this antibody.

The problem of anti-pig antibodies in pig-to-primate xenografting: current and novel methods of depletion and/or suppression of production of anti-pig antibodies

The role of antibodies directed against Galalpha1-3Gal (alpha-Gal) epitopes in porcine-to-primate xenotransplantation has been widely studied during the past few years. These antibodies (anti-alpha-Gal) have been associated with both hyperacute rejection and acute vascular rejection of vascularized organs. Depletion and (temporary or permanent) suppression of production of anti-alpha-Gal seem to be essential to the long-term survival of these organs, even when the ultimate aim is accommodation or tolerance. Although more than 95% depletion of anti-alpha-Gal can be achieved by the use of immunoaffinity column technology, to date no regimen has been successful in preventing the return of anti-alpha-Gal (from continuing production). In this review, we discuss current and novel methods for achieving depletion or inhibition (i.e. extracorporeal immunoadsorption, anti-idiotypic antibodies, the intravenous infusion of immunoglobulin or oligosaccharides) and suppression of production (i.e. irradiation, pharmacologic agents, specific monoclonal antibodies, immunotoxins) of anti-alpha-Gal antibodies.

Major carbohydrate epitopes in tissues of domestic and African wild animals of potential interest for xenotransplantation research

We investigated the main glycotopes expressed on the tissues of 44 animal species, including primates, nonprimate mammals, marsupials, birds, and a reptile. Paraffin-embedded tissue sections of kidney, heart, liver, pancreas, lung, brain and intestine of 24 domestic animal species were stained with seven fluorescent-labeled lectins. Testis sections of 20 African wild animal species were tested with the same lectins. Overall, three main immunofluorescence patterns were found in the vascular compartment. First, humans and Old World monkeys express genetically polymorphic ABH antigens and do not express alphaGal. Second, New World monkeys, other mammals, and marsupials do not express ABH antigens, but have large amounts of a genetically monomorphic alphaGal. Third, birds and reptiles do not express either ABH or alphaGal, but have monomorphic betaGal, probably different from the lactosamine precursor of ABH and alphaGal. Epithelial cells producing exocrine secretions also expressed carbohydrate epitopes. The fluorescence patterns of the cells of the exocrine compartment are similar, but not identical, to those expressed in the vascular compartment. All the animals tested have some ABH and betaGal in exocrine tissues, but New World monkeys and lower mammals are the only ones expressing alphaGal in exocrine tissues.

Transfer of swine major histocompatibility complex class II genes into autologous bone marrow cells of baboons for the induction of tolerance across xenogeneic barriers

BACKGROUND

The present study examined the potential role of gene therapy in the induction of tolerance to anti-porcine major histocompatibility complex (SLA) class II-mediated responses after porcine renal or skin xenografts.

METHODS

Baboons were treated with a non-myeloablative or a myeloablative preparative regimen before bone marrow transplantation with autologous bone marrow cells retrovirally transduced to express both SLA class II DR and neomycin phosphotransferase (NeoR) genes, or the NeoR gene alone. Four months or more after bone marrow transplantation, the immunological response to a porcine kidney or skin xenograft was examined. Both the renal and skin xenografts were SLA DR-matched to the transgene, and recipients were conditioned by combinations of complement inhibitors, adsorption of natural antibodies, immunosuppressive therapy, and splenectomy.

RESULTS

Although the long-term presence of the SLA transgene was detected in the peripheral blood and/or bone marrow cells of all baboons, the transcription of the transgene was transient. Autopsy tissues were available from one animal and demonstrated expression of the SLA DR transgene in lymphohematopoietic tissues. After kidney and skin transplantation, xenografts were rejected after 8-22 days. Long-term follow-up of control animals demonstrated that high levels of induced IgG antibodies to new non-alphaGal epitopes developed after organ rejection. In contrast, induced non-alphaGal IgG antibody responses were minimal in the SLA DR-transduced baboons.

CONCLUSIONS

Transfer and expression of xenogeneic class II DR transgenes can be achieved in baboons. This therapy may prevent late T cell-dependent responses to porcine xenografts, which include induced non-alphaGal IgG antibody responses.

Long-term discordant xenogeneic (porcine-to-primate) bone marrow engraftment in a monkey treated with porcine-specific growth factors

BACKGROUND

Mixed allogeneic hematopoietic chimerism has previously been reliably achieved and shown to induce tolerance to fully MHC-mismatched allografts in mice and monkeys. However, the establishment of hematopoietic chimerism has been difficult to achieve in the discordant pig-to-primate xenogeneic model.

METHODS

To address this issue, two cynomolgus monkeys were conditioned by whole body irradiation (total dose 300 cGy) 6 and 5 days before the infusion of pig bone marrow (BM). Monkey anti-pig natural antibodies were immunoadsorbed by extracorporeal perfusion of monkey blood through a pig liver, immediately before the intravenous infusion of porcine BM (day 0). Cyclosporine was administered for 4 weeks and 15-deoxyspergualin for 2 weeks. One monkey received recombinant pig cytokines (stem cell factor and interleukin 3) for 2 weeks, whereas the other received only saline as a control.

RESULTS

Both monkeys recovered from pancytopenia within 4 weeks of whole body irradiation. Anti-pig IgM and IgG antibodies were successfully depleted by the liver perfusion but returned to pretreatment levels within 12-14 days. Methylcellulose colony assays at days 180 and 300 revealed that about 2% of the myeloid progenitors in the BM of the cytokine-treated recipient were of pig origin, whereas no chimerism was detected in the BM of the untreated control monkey at similar times. The chimeric animal was less responsive by mixed lymphocyte reaction to pig-specific stimulators than the control monkey and significantly hyporesponsive when compared with a monkey that had rejected a porcine kidney transplant.

CONCLUSION

To our knowledge, this is the first report of long-term survival of discordant xenogeneic BM in a primate recipient.

Xenotransplantation--state of the art--update 1999

Organ transplantation is limited by the number of cadaveric human donor organs that become available. Xenotransplantation - the transplantation of organs and tissues between animal species - would supply an unlimited number of organs and offer many other advantages. The pig has been identified as the most suitable donor animal. Pig organs, when transplanted into humans or nonhuman primates, are, however, rejected hyperacutely within minutes by antibody-mediated complement activation. Human anti-pig antibodies have been identified as being directed against galactose alpha 1-3galactose (alpha Gal) epitopes on pig vascular endothelium. Methods have been successfully developed to prevent hyperacute rejection. These include (i) depletion or inhibition of recipient antibodies or complement and (ii) development of transgenic pigs that express a human complement-regulatory protein (e.g. hDAF). The persistence or return of anti-pig antibody, however, even following the use of hDAF pig organs, eventually leads to what has been variously termed "acute vascular rejection" or "delayed xenograft rejection", which is again believed to be largely antibody-dependent. Nevertheless, experimental pig-to-primate organ xenotransplantation now results in transplant function for days and weeks rather than minutes. Little is yet known of the nature of the acute cellular rejection response that is anticipated to follow, and of any subsequent chronic rejection that may develop. Tolerance to both the alpha Gal epitope and to swine leukocyte antigens (SLA) is being explored using gene therapy techniques and by the induction of hematopoietic cell chimerism. The development of genetically engineered pigs that do not express the alpha Gal epitope is also being pursued. Considerable progress has been made in recent years, but experimental results do not yet warrant the initiation of a clinical trial of organ xenotransplantation. However, trials are already underway of pig cell transplants in patients with diabetes and neurodegenerative conditions, such as Parkinson's disease.

Serum cytotoxicity to pig cells and anti-alphaGal antibody level and specificity in humans and baboons

BACKGROUND

Removal and/or "neutralization" of anti-Gal alpha1-3Gal (alphaGal) antibodies can prevent or delay the hyperacute rejection of pig organs transplanted into primates.

AIM

To determine variations in (1) cytotoxicity to pig kidney (PK15) cells, (2) anti-alphaGal antibody level, and (3) specificity in adult human (n=46) and baboon (n=38) sera.

METHODS

Cytotoxicity to PK15 cells was determined by adding rabbit complement to heat-inactivated serum, using a two-color fluorescent dye to distinguish live and dead cells. Anti-alphaGal antibody level was determined by ELISA using alphaGal trisaccharide type 2-BSA glycoconjugate as antigen target. Specificity determined by ELISA using four different alphaGal-BSA glycoconjugates: (disaccharide, trisaccharides type 2 and 6, and pentasaccharide).

RESULTS

Cytotoxicity of human AB sera varied from 30-100% PK15 relative cell damage (%RCD), although that of baboon sera of all blood groups varied from 35-100% RCD. In human AB sera, anti-alphaGal antibody level (at a dilution of 1:80) varied from undetectable to 0.75 (OD at 405 nm), although in baboon sera of all blood groups, anti-alphaGal antibody level varied from undetectable to >2.0. There was no correlation between anti-alphaGal antibody level and serum cytotoxicity in either species. Specificity varied among individuals in both human and baboon sera.

CONCLUSIONS

These studies have demonstrated (1) considerable variation in cytotoxicity and anti-alphaGal antibody level in human and baboon sera, but a lack of correlation between these two parameters; (2) considerable variation in the specificity of anti-alphaGal antibodies; (3) blood group B human and baboon sera have lower levels of anti-alphaGal antibodies; (4) no relation between blood group and specificity of anti-alphaGal antibodies. Although there are minor differences in the parameters measured, baboons would appear to be suitable surrogates for humans in the pig-to-primate xenograft model.

Effect of pig-specific cytokines on mobilization of hematopoietic progenitor cells in pigs and on pig bone marrow engraftment in baboons

Mixed hematopoietic chimerism has been found to be a requirement for achieving specific immunologic hyporesponsiveness. Some of the requirements for in vitro and in vivo coexistence of discordant hematopoietic systems in the pig-to-baboon (or human) model have been investigated. We have tested the efficacy of pig-specific cytokines (PSC) (IL3, SCF, GM-CSF) in the mobilization of porcine bone marrow (BM) progenitors in vivo (i) in the pig and (ii) in baboons that underwent a conditioning regimen and porcine BM transplantation. In a preliminary in vitro study, porcine BM cells were incubated in various media to assess the effect of human plasma on pig progenitors in a colony-forming unit (CFU) assay. In in vivo studies, four pigs received PSC and one control pig did not. Six baboons underwent natural antibody removal, with subsequent pig BM transplantation. Four of these six underwent nonmyeloablative (n=2) or myeloablative (n=2) conditioning and all received PSC treatment. Two baboons did not receive PSC, one of which underwent a nonmyeloablative regimen. Sequential blood samples and BM biopsies in pigs and baboons were analyzed by CFU assay for the detection of porcine cells. Baboon samples were analyzed by polymerase chain reaction (PCR) to detect porcine DNA. In the case of the in vitro tests, colony forming by porcine progenitors was not inhibited by media containing human plasma and for the in vivo tests, PSC increased the number of progenitors in pig BM; mobilization of progenitors into the peripheral blood was observed. PSC-treated baboons which experienced transient depletion of leukocytes < 1,000/ml (as an effect of the conditioning regimen) had porcine BM cells detectable by PCR for as long as day 316 after BM transplantation. In conclusion we found that: (i) under the conditions of these studies, in vitro porcine progenitor cell growth was not inhibited by human plasma containing natural antibody and complement; (ii) PSC treatment led to an increased number of progenitors in pig BM and peripheral blood; (iii) the combination of an effective conditioning regimen and treatment with PSC was capable of inducing long-term survival of pig progenitors in baboons, although only a low level of engraftment was achieved.

Intravenous synthetic alphaGal saccharides delay hyperacute rejection following pig-to-baboon heart transplantation

Several oligosaccharides containing the terminal structure Gal(alpha)1-3Gal (alphaGal) and different side chains were tested in vitro for their ability to block natural anti(alpha)Gal antibodies. A di-and a trisaccharide (di(alpha)Gal and tri(alpha)Gal) were selected. A blood group B baboon, having IgG and IgM natural antipig titers of 1:256 and 1:1024 and a hemolytic titer (to pig red blood cells, RBCs) of 1:8, was chosen to measure pharmacokinetic parameters of the saccharides and to assess the extent of in vivo neutralization of the antibodies. Three grams each of the di(alpha)Gal and the tri(alpha)Gal dissolved in saline were administered by bolus intravenous (i.v.) injection. Blood samples were collected at various times and urine was collected at 8 and 24 h. Plasma and urine concentrations of the alphaGal saccharides were estimated by an ELISA specially developed for this study. A fast distribution phase followed by equilibrium and excretion phases were observed, indicating a T1/2 in the order of 1 h. Fifty-eight per cent of the saccharides were recovered in the urine within 24 h. Determination of antipig antibody binding by FACS analysis and of serum cytotoxicity titers for pig endothelial cells demonstrated that a 70% reduction in binding and cytotoxicity could be achieved with plasma saccharide levels of 300-400 microg/ml. Six months later, a pig heart was transplanted heterotopically into the baboon. A 3-g bolus of the saccharide mixture (1.5 g of each saccharide) was given i.v. before allowing blood reperfusion of the transplanted heart, followed by an i.v. infusion of 1 g/hr for 1 hr and 0.5 g/hr for the 3 succeeding hours. Blood concentrations of the saccharides, CH50, hematology and cytotoxicity for PK15 cells were estimated in blood samples taken at various times. Heart function was observed to be satisfactory for 8 h, but was found to have ceased at 18 h. Myocardial biopsies taken at 3 and 5 h showed congestion only, suggestive of minimal vascular rejection, but by 18 h demonstrated severe vascular rejection. In conclusion, alphaGal saccharide therapy given for a period of 4 h delayed, but did not totally prevent, the development of vascular rejection in the pig-to-baboon heart transplant model. alphaGal saccharide therapy may be one of several useful approaches for the prevention of hyperacute rejection in pig-to-primate organ transplantation.

Lack of variation in alphaGal expression on lymphocytes in miniature swine of different genotypes

BACKGROUND

Gal(alpha)1-3Gal epitopes (alphaGal) have been demonstrated to be present on tissues of all pig breeds tested to-date and are the major target for human anti-(alpha)galactosyl (alphaGal) antibodies. We investigated members of an MHC-inbred miniature swine herd to assess whether there was an association between genotype and expression of alphaGal. Identification of a low expressor genotype would potentially enable selective breeding of pigs that might prove beneficial as donors in clinical xenotransplantation.

METHODS

we measured alphaGal expression on various pig cells by use of fluorescent-activated cell sorter (FACS) using (i) purified human anti-alphaGal antibody and (ii) the isolectin GS-I-B4. Initial studies were on porcine peripheral blood mononuclear cells (PBMCs) and subsequent studies on lymphocytes, platelets, and T cell subsets (CD4+ and CD8+ cells).

RESULTS

there was considerable day-to-day variation in alphaGal expression on PBMCs from the same pig. When only lymphocytes were examined, there was a high degree of reproducibility, and no significant difference in alphaGal expression was detected between representative pairs of animlas of three different genotypes. Purified anti-alphaGal antibody bound to different sites on the alphaGal epitope than did Griffonia (Bandeiraea) simplicifolia I-B4 (GS-I-B4). Lectin binding was significantly reduced in the absence of divalent cations. When CD4+ and CD8+ T cells were examined for alphaGal expression, two distinct populations of each type of cell were observed, with larger cells expressing a higher level of alphaGal.

CONCLUSIONS

although the number of pigs of different genotypes studied was small, on the basis of this limited study, pigs of a low alphaGal expressor genotype that could be selectively bred for use in clinical xenotransplantation were not identified.

Porcine kidney and heart transplantation in baboons undergoing a tolerance induction regimen and antibody adsorption

BACKGROUND

Xenotransplantation would provide a solution to the current shortage of organs for transplantation. Our group has been successful in inducing tolerance in mice and monkey models of allogeneic transplantation. The present study attempts to extend the same tolerance-inducing regimen to a pig-to-baboon organ transplantation model.

METHODS

Nine baboons underwent a conditioning regimen (consisting of nonmyeloablative or myeloablative whole body and thymic irradiation, splenectomy, antithymocyte globulin, pharmacologic immunosuppression and porcine bone marrow transplantation [BMTx]), which has previously been demonstrated to induce donor-specific allograft tolerance in monkeys. In addition, immunoadsorption of anti-alphaGal antibody (Ab) was performed. Four of the nine baboons received pig kidney transplants (KTx), and one also underwent repeat transplantation with an SLA-matched kidney. Two received heterotopic pig heart transplants (HTx). Three baboons underwent conditioning without organ transplantation for long-term studies of natural Ab kinetics.

RESULTS

In the three baboons that received the conditioning regimen without an organ transplant, immunoadsorption reduced Ab by approximately 90%, but recovery of Ab to pretreatment level or higher occurred within 7 days. In contrast, the level of Ab remained low after organ transplant. No Ab to pig antigens other than alphaGal was detected in any baboon before or after BMTx, KTx, or HTx. No graft succumbed to hyperacute rejection. KTx function began to deteriorate within 3-6 days, with oliguria and hematuria progressing to anuria, and the kidneys were excised after 3, 6, 9, 11, and 14 days, respectively. One HTx ceased functioning at 8 days; the second baboon died with a contracting HTx at 15 days. Features of coagulopathy and thrombocytopenia developed in all six transplanted baboons (high D-dimer, prolonged prothrombin time and partial thromboplastin time, and falling fibrinogen) resulting in serious bleeding complications in two baboons, one of which died on day 9. Donor organs showed progressive acute humoral rejection with deposits of IgM, IgG, and complement; a focal mononuclear cellular infiltrate was also observed. The ureter was the earliest structure of the KTx affected by rejection, with progression to necrosis.

CONCLUSIONS

This conditioning regimen prevented hyperacute rejection but was ineffective in preventing the return of Ab, which was associated with the development of acute humoral rejection with features of coagulopathy. No baboon developed anti-pig Ab other than alphaGal Ab. Further modifications of the protocol directed toward suppression of production of Ab are required to successfully induce tolerance to pig organs in baboons.

A reliable, rapid and inexpensive two-color fluorescence assay to monitor serum cytotoxicity in xenotransplantation

Removal and/or neutralization of preformed anti-pig antibodies in non-human primate blood have been shown to prevent the hyperacute rejection of transplanted pig organs. The purpose of this study was to establish a suitable in vitro method that would allow for screening and comparison of various agents and methods potentially useful in the prevention of hyperacute rejection. The pig kidney cell line (PK15), pig aortic endothelial cell line (AG08472), and a primary culture of endothelial cells explanted from a pig aorta were incubated with either human or baboon sera. Complement-dependent cytotoxic activity of human and baboon sera was determined on all three types of pig cells using a two-color fluorescence assay and compared with the conventional 51Chromium (51Cr)-release assay. The assay was also performed on PK15 cells as a 2-chambered slide assay and compared with a microcytotoxicity assay performed in Terasaki trays. Using the microcytotoxicity assay, a 1-step assay utilizing endogenous complement was compared with a 2-step assay where rabbit complement was added. Of the three types of cells studied, PK15 cells were the most sensitive to cytotoxic injury, followed by AG cells and the primary endothelial culture. Good correlation between the 51Cr-release and the two-color fluorescence method was documented. There was good agreement between the results obtained using the 2-chambered slide method and the microcytotoxicity assay, as there was between the 1- and the 2-step assays. The 1- and 2-step assays provided information on the level and efficacy of endogenous complement. We conclude that the two-color fluorescence assay is suitable for the rapid and inexpensive screening of therapeutic interventions that might be useful in the prevention of hyperacute xenograft rejection, and that PK15 cells are suitable for use in this assay.

Disseminated intravascular coagulation in association with the delayed rejection of pig-to-baboon renal xenografts

BACKGROUND

Intravascular fibrin deposition and platelet sequestration occur with porcine xenograft rejection by baboons. Disseminated intravascular coagulopathy may arise either as a direct consequence of the failure to fully deplete xenoreactive natural antibodies and block complement, or because of putative cross-species molecular incompatibilities in this discordant species combination.

METHODS

Three baboons were conditioned with retrovirally transduced autologous bone marrow to induce tolerance to swine antigens. Xenoreactive natural antibodies and complement were depleted by plasmapheresis and the use of Gal alpha1-3Gal column adsorptions; baboons were then splenectomized and underwent renal xenografting from inbred, miniature pigs. Soluble complement receptor type-1 with protocol immunosuppression (mycophenolate mofetil, 15-deoxyspergualin, steroids, and cyclosporine) was administered.

RESULTS

A bleeding diathesis was clinically evident from days 5 to 12 after transplantation in two baboons. Low levels of circulating C3a, C3d, and iC3b were measured despite the absence of functional circulating complement components. Profound thrombocytopenia with abnormalities in keeping with disseminated intravascular coagulopathy were observed. Prolongation of prothrombin and partial thromboplastin times was accompanied by evidence for tissue factor-mediated coagulation pathways, high levels of thrombin generation (prothrombin fragment F(1+2) production and thrombin-antithrombin complex formation), fibrinogen depletion, and production of high levels of the fibrin degradation product D-dimer. Importantly, these disturbances resolved rapidly after the excision of the rejected xenografts in two surviving animals. Histopathological examination of the rejected xenografts confirmed vascular injury, fibrin deposition, platelet deposition, and localized complement activation.

CONCLUSIONS

Systemic coagulation disturbances are associated with delayed xenograft rejection.

Personal social networks and HIV status among women on methadone

This objective of this study was to examine the association between a women's HIV status and specific (IDUs) characteristics of her social networks with respect to (1) number of injection drug users (2) number of drug partners and (3) number of HIV-positive contacts in her personal networks, after controlling for the respondent's demographic characteristics and drug use. Participants were recruited through posted announcements in three methadone clinics in Harlem, New York City. Individuals were considered eligible if they were enrolled as patients in one of the clinics for at least three months. A social network questionnaire modeled after the General Social Survey network section was developed by the investigators. Face-to-face interviews were conducted by trained interviewers and included demographics, drug use, self-reported HIV status of the woman and her network members, and the social network structures. Univariate analyses found that HIV-positive and HIV-negative women had different network profiles. HIV-positive women were more likely to associate with a higher number of current drug users, injection drug users, injection drug users who were HIV-positive, drug partners, drug partners who used injection drugs, and drug partners who were HIV-positive. Multivariate analyses indicated that HIV-positive respondents were more likely to associate with HIV-positive network members than their HIV-negative counterparts. The findings suggest that to better understand the spread of HIV among female drug users and to design more effective HIV/AIDS prevention programmes, efforts should move beyond focusing on individual attributes to address the contextual dynamics of social networks.