Mineral adaptations following kidney transplantation

Klotho is predominantly expressed in the kidney and reported to have antioxidant and antifibrotic properties. Soluble Klotho (sKl), the circulating protein cleaved from membrane-bound Klotho, is reduced significantly with kidney disease and inversely associated with mortality. sKl has not been thoroughly evaluated prospectively after kidney transplantation. Incident kidney transplant recipients (KTRs) were prospectively evaluated pretransplantation, 1, 12 and 52 weeks post-transplantation. Basic biochemistry, sKl and intact FGF23 were measured. Within-subject comparisons were evaluated using repeat-measure anova or Friedman's analysis. Effects of immunosuppression and biochemical parameters on sKl and FGF-23 over time were analysed using mixed-effects modelling. Median serum creatinine (sCr) at 1 week was 116 (92-142) μmol/l, and at 52 weeks, all 29 KTRs had a functioning graft with median sCr of 111 (97-131) μmol/l. Compared with baseline, sKl was increased at 52 weeks following an initial decline at 1 week (P < 0.005 and P < 0.01, respectively), while FGF23 was considerably reduced at 52 weeks (P < 0.001). In a mixed-effects model, an increased sKl was not associated with reduction in immunosuppression or evaluated biochemical parameters. Modest increase in sKl is observed one-year postkidney transplantation with excellent early graft function suggesting factors beyond renal capacity may influence circulating sKl. FGF23 normalization was observed. Longer term evaluation in transplantation, specifically addressing the effects of immunosuppression, is required to understand the pathophysiology of the sKl/FGF23 axis and potential for modification.

Optimizing Outcomes in Pediatric Renal Transplantation Through the Australian Paired Kidney Exchange Program

Kidney paired donation (KPD) programs offer the opportunity to enable living kidney donation when immunological and other barriers prevent safe directed donation. Children are likely to require multiple transplants during their lifetime; therefore, high-level histocompatibility and organ quality matching are key priorities. Details are given for a cohort of seven pediatric renal transplantations performed through the Australian Kidney Exchange (AKX), including barriers to alternative transplantation and outcomes after KPD. Reasons for entering the KPD program were preformed donor-specific antibodies to their registered donor in five cases, ABO mismatch, and avoidance of the risk of exposure to hepatitis B virus. Four recipients were highly sensitized. All patients received transplants with organs of lower immunological risk compared with their registered donors. HLA eplet mismatch scores were calculated for donor-recipient pairs; three patients had improved eplet mismatch load with AKX donor compared with their registered donor. All grafts are functioning, with a mean estimated glomerular filtration rate of 77 mL/min/1.73 m² (range 46-94 mL) and a follow-up range of 8-54 months, and no patient experienced clinical or histological rejection. KPD is a viable strategy to overcome many barriers to living donation for pediatric patients who have an otherwise suitable donor and provides an opportunity to minimize immunological risks.

Use of Copy Number Deletion Polymorphisms to Assess DNA Chimerism

BACKGROUND

We describe a novel approach that harnesses the ubiquity of copy number deletion polymorphisms in human genomes to definitively detect and quantify chimeric DNA in clinical samples. Unlike other molecular approaches to chimerism analysis, the copy number deletion (CND) method targets genomic loci (&gt;50 base pairs in length) that are wholly absent from wild-type (i.e., self) background DNA sequences in a sex-independent manner.

METHODS

Bespoke quantitative PCR (qPCR) CND assays were developed and validated using a series of DNA standards and chimeric plasma DNA samples collected from 2 allogeneic kidney transplant recipients and 12 pregnant women. Assay performance and informativeness were assessed using appropriate statistical methods.

RESULTS

The CND qPCR assays showed high sensitivity, precision, and reliability for linear quantification of DNA chimerism down to 16 genomic equivalents (i.e., 106 pg). Fetal fraction (%) in 12 singleton male pregnancies was calculated using the CND qPCR approach, which showed closer agreement with single-nucleotide polymorphism–based massively parallel sequencing than the SRY (sex determining region Y) (Y chromosome) qPCR assay. The latter consistently underestimated the fetal fraction relative to the other methods. We also were able to measure biological changes in plasma nonself DNA concentrations in 2 renal transplant recipients.

CONCLUSIONS

The CND qPCR technique is suitable for measurement of chimerism for monitoring of rejection in allogeneic organ transplantation and quantification of the cell-free fetal DNA fraction in maternal plasma samples used for noninvasive prenatal genetic testing.

Mycophenolate mofetil substitution for cyclosporine-dependent myasthenia gravis and nephrotoxicity

Severe autoimmune myasthenia gravis is difficult to manage and may require immunosuppression with cyclosporine. However, cyclosporine dependency is associated with the risk of nephrotoxicity. Mycophenolate mofetil is a non-nephrotoxic alternative which should be considered to rescue cyclosporine-dependent, severe myasthenia gravis sufferers with renal impairment from progression to end-stage renal failure. However, the evidence is limited and studies have not assessed the outcome of a direct substitution in these cyclosporine-dependent patients. We study three such patients who successfully converted to mycophenolate mofetil, and briefly examine the evidence behind this option. We believe that total cyclosporine withdrawal is feasible, but strongly recommend overlapping mycophenolate mofetil treatment with cyclosporine.

Single and serial measurements of cardiac troponin I in asymptomatic patients on chronic hemodialysis

AIMS

Coronary artery disease is the major cause of death in patients with end-stage renal failure on dialysis. This study aimed to assess the predictive value of a single cardiac troponin I (cTnI), and also the kinetics of serial values.

METHODS

Since cTnI is a potential biomarker of cardiac outcome, the present study examined single cTnI measurements (n = 88 patients) and its predictive value for future cardiac events, and a kinetic substudy of serial weekly cTnI measured for 8 weeks (n = 57) in a group of patients on hemodialysis.

RESULTS

Single cTnI measurements: 9 patients (10.2%) had a detectable cTnI at baseline and 79 patients (89.8%) had a negative baseline cTnI. There were no significant differences in age, sex, history of ischemic heart disease, diabetes, smoking or dyslipidemia between patients with detectable and negative cTnI. At the end of 9 months, the rate of combined primary endpoints, which included myocardial infarction, cardiac death and cardiac revascularization, was significantly higher in the patients with a detectable baseline cTnI (55.6%), compared to patients with a negative cTnI (6.3%) (p = 0.0007). Serial weekly cTnI measurements: significant fluctuations in cTnI were noted over time; 27% of patients with an undetectable cTnI measured at baseline had subsequent detectable levels in the serial follow-up.

CONCLUSION

A single detectable cTnI in asymptomatic patients on hemodialysis defines patients at high risk of future cardiac events. However, the incidence of detectable cTnI levels is markedly increased when serial weekly measurements are performed. The clinical significance of detectable serial measurements of cTnI is the focus of ongoing studies.

Increased expression of heparanase in puromycin aminonucleoside nephrosis

BACKGROUND

The beta-D-endoglycosidase heparanase has been proposed as an important contributor to loss of glomerular charge in proteinuria. Expression of heparanase was, therefore, determined in acute puromycin aminonucleoside (PAN) nephrosis.

METHODS

A rabbit polyclonal antibody was produced against a 17-amino acid peptide derived from the predicted amino acid sequence of heparanase. The antibody was validated by Western blot. Immunohistochemical staining and Western blotting were used to localize heparanase protein in normal kidneys and kidneys from rats with PAN nephrosis. Northern blot analysis was used to determine mRNA expression.

RESULTS

Immunohistochemical staining showed that heparanase protein was localized to tubular cells in the distal convoluted tubules, thick ascending limb of the loop of Henle, and transitional cell epithelium in normal kidney. Minimal expression was noted in normal glomeruli. Western blot analysis of protein from isolated normal glomeruli showed minimal expression of the 65 kD proheparanase protein. A marked increase in the staining for heparanase was found at day 5 of the PAN nephrosis model, at approximately the time of onset of proteinuria, and at day 14. Expression was predominantly seen in podocytes. At day 5, only the 65 kD proheparanase species was identified, but at day 14, mature 58 kD heparanase also was present. Northern blot analysis of sieved glomeruli at day 14 confirmed an increase in heparanase mRNA. The human podocyte cell line 56/10A1 also produced both proheparanase and mature heparanase, suggesting that podocytes can activate heparanase without other cell types.

CONCLUSION

The previously mentioned data confirm that the novel beta-D-endoglycosidase heparanase is up-regulated and activated in glomeruli from rats with proteinuria. Heparanase may be involved, therefore, in the loss of glomerular charge seen in proteinuria. Moreover, the presence of heparanase in normal tubules suggests that it may also be involved in cell migration or turnover.

Tolerance to limb tissue allografts between swine matched for major histocompatibility complex antigens

Transplantation of limb tissue allografts would greatly expand the realm of reconstructive surgery. However, the toxicity of chronic immunosuppression has adversely tilted the risk-benefit balance for clinical transplant. In this study, a procedure was sought to achieve host tolerance to limb tissue allografts through matching of the major histocompatibility complex (MHC) antigens between donor and host swine using only a 12-day course of cyclosporine. Massachusetts General Hospital (MGH) miniature swine were used as a large animal model with defined MHC, and musculoskeletal grafts from the donor hind limb were transplanted heterotopically to the recipient femoral vessels. Allografts from MHC-mismatched donors treated with cyclosporine (n = 4) were rejected in less than 6 weeks by gross inspection and histologic sections. Allografts from MHC-matched, minor antigen mismatched donors not treated with cyclosporine (n = 4) were rejected between 9 and 12 weeks. Allografts from similarly matched donors treated with 12 days of cyclosporine (n = 7) showed no evidence of rejection until sacrifice between 25 and 47 weeks. Thus allograft tolerance was achieved between MHC-matched swine using a limited course of cyclosporine. Demonstration of limb tissue allograft survival in a large animal model without long-term immunosuppression represents an important step toward clinical transplantation.

Injection of allogeneic bone marrow cells into the portal vein of swine in utero

The ability to safely manipulate the immune system of the developing fetus carries the hope of effective treatment strategies for certain congenital disorders that can be diagnosed during gestation. One possible intervention is the induction of specific transplantation tolerance to an adult donor who could provide tissue after birth without the need for immunosuppression. Although the introduction of allogeneic stem cells to a developing immune system has been shown to result in hematopoietic chimerism, donor-specific transplantation tolerance has not been demonstrated in a large animal model. In previous reports of in utero stem-cell transplantation, the cells were injected into the fetus by an intraperitoneal route. We sought to improve upon this technique of cell transplantation by developing a method for the safe delivery of allogeneic stem cells directly into the hepatic circulation of fetal swine. In the second phase of our study, we determined if adult allogeneic bone marrow cells delivered to the fetus by this intravascular route could result in result in hematopoietic chimerism and donor-specific transplantation tolerance. A method of successful intravascular injection was designed in which a laparotomy was performed on a sow at midgestation (50-55 days) to administer 1 cc of inoculum into the portal vein of each fetus using transuterine ultrasound guidance and a 25-gauge spinal needle. In one sow, 10 piglets were injected with saline to test safety, and 8 piglets were born. For transplantation of stem cells to the fetuses, donor bone marrow was harvested from a genetically defined miniature swine. In one sow the marrow was injected without T-cell depletion resulting in abortion. In the third sow, the marrow was depleted of T-cells to less than 0.01% using magnetic beads conjugated to anti-CD3 monoclonal antibodies. No chimerism was detected in these offspring. Only in the fourth sow where the T-cell depletion was reduced to about 1% of the cells in the inoculum did one animal demonstrate chimerism. This piglet showed reproducible blood chimerism (0.95% donor cells) detected by flow cytometry measurement of monoclonal antibodies to the donor MHC. In addition, this animal demonstrated hyporesponsiveness to donor lymphocytes in an MLR assay while reacting strongly to third-party stimulator cells. A split-thickness skin graft from the donor was accepted, and a third-party graft was rapidly rejected.

Coagulation and thrombotic disorders associated with pig organ and hematopoietic cell transplantation in nonhuman primates

BACKGROUND

Efforts to achieve tolerance to transplanted pig organs in nonhuman primates by the induction of a state of mixed hematopoietic chimerism have been associated with disorders of coagulation and thrombosis. Activation of recipient vascular endothelium and platelets by porcine hematopoietic cells and/or activation of donor organ vascular endothelium and/or molecular differences between the species may play roles. Irradiation or drug therapy could possibly potentiate endothelial cell activation and/or injury.

METHODS

We have investigated parameters of coagulation and platelet activation in nonhuman primates after (1) a regimen aimed at inducing mixed hematopoietic chimerism and tolerance (TIR that included total body irradiation, T cell depletion, and splenectomy; (2) pig bone marrow or pig peripheral blood mobilized progenitor cell transplantation (PCTx); and/or (3) pig organ transplantation (POTx). Five experimental groups were studied. Baboons were the recipient subjects in all groups except Group 1. Gp 1 Cynomolgus monkeys (n=6) underwent TIR + allotransplantation of hematopoietic cells and a kidney or heart or TIR + concordant xenotransplantation (using baboons as donors) of cells and a kidney; Gp 2 Baboons (n=4) underwent TIR with or without (+/-) autologous hematopoietic cell infusion; Gp 3 (n=12) PCTx+/-TIR; Gp 4 (n=5) POTx+/-TIR; Gp 5 (n=4) TIR + PCTx + POTx. Platelet counts, with plasma prothrombin time, partial thromboplastin time, fibrinogen levels, fibrin split products and/or D-dimer were measured.

RESULTS

In the absence of a discordant (porcine) cellular or organ transplant (Groups 1 and 2), TIR resulted in transient thrombocytopenia only, in keeping with bone marrow depression from irradiation. PCTx alone (Group 3) was associated with the rapid development of a thrombotic thrombocytopenic (TTP)-like microangiopathic state, that persisted longer when PCTx was combined with TIR. POTx (+/-TIR) (Group 4) was associated with a gradual fall (over several days) in platelet counts and fibrinogen with disseminated intravascular coagulation (DIC); after graft excision, the DIC generally resolved. When TIR, PCTx and POTx were combined (Group 5), an initial TTP-like state was superseded by a consumptive picture of DIC within the first week, necessitating graft removal.

CONCLUSIONS

Both PCTx and POTx lead to profound alterations in hemostasis and coagulation parameters that must be overcome if discordant xenotransplantation of hematopoietic cells and organs is to be fully successful. Disordered thromboregulation could exacerbate vascular damage and potentiate activation of coagulation pathways after exposure to xenogeneic cells or a vascularized xenograft.

Acute humoral xenograft rejection: destruction of the microvascular capillary endothelium in pig-to-nonhuman primate renal grafts

The major cause of xenograft loss beyond hyperacute rejection is a form of injury, traditionally termed delayed xenograft rejection (DXR), whose pathogenesis is unknown. Here we analyze the immunologic and morphologic features of DXR that develops in pig kidney xenografts transplanted into nonhuman primates. Kidneys from miniature swine were transplanted into cynomolgus monkeys (n = 14) or baboons (n = 11) that received regimens aimed to induce mixed chimerism and tolerance. No kidney was rejected hyperacutely. Morphologic and immunohistochemical studies were performed on serial biopsies, and an effort was made to quantify the pathologic features seen. The early phase of DXR (Days 0-12) was characterized by focal deposition of IgM, IgG, C3, and scanty neutrophil and macrophage infiltrates. The first abnormality recognized was glomerular and peritubular capillary endothelial cell death as defined by in situ DNA nick-end labeling (TUNEL). Damaged endothelial cells underwent apoptosis and, later, frank necrosis. The progressive phase developed around Day 6 and was characterized by progressive deposition of IgM, IgG, C3, and prominent infiltration of cytotoxic T cells and macrophages, with a small number of NK cells. Thrombotic microangiopathy developed in the glomeruli and peritubular capillaries with TUNEL+ endothelial cells, platelet aggregation, and destruction of the capillary network. Only rare damaged arterial endothelial cells and tubular epithelial cells were observed, with rare endothelialitis and tubulitis. In the advanced phase of DXR, interstitial hemorrhage and infarction occurred. During the development of DXR, the number of TUNEL+ cells increased, and this correlated with progressive deposition of antibody. The degree of platelet aggregation correlated with the number of TUNEL+ damaged endothelial cells. We conclude that peritubular and glomerular capillary endothelia are the primary targets of renal DXR rather than tubular epithelial cells or arterial endothelium and that the earliest detectable change is endothelial cell death. DXR was characterized by progressive destruction of the microvasculature (glomeruli and peritubular capillaries) and formation of fibrin-platelet thrombi. Both cytotoxic cells and antibodies potentially mediate the endothelial damage in DXR; however, in this model, DXR is largely humorally mediated and is better termed "acute humoral xenograft rejection."

Thymic transplantation in miniature swine. II. Induction of tolerance by transplantation of composite thymokidneys to thymectomized recipients

Previous studies in our laboratory have demonstrated that the presence of the thymus is essential for rapid and stable tolerance induction in allotransplant models. We now report an attempt to induce tolerance to kidney allografts by transplanting donor thymic grafts simultaneously with the kidney in thymectomized recipients. Recipients were thymectomized 3 wk before receiving an organ and/or tissues from a class I-mismatched donor. Recipients received 1) a kidney allograft alone, 2) a composite allogeneic thymokidney (kidney with vascularized autologous thymic tissue under its capsule), or 3) separate kidney and thymic grafts from the same donor. All recipients received a 12-day course of cyclosporine. Thymectomized animals receiving a kidney allograft alone or receiving separate thymic and kidney grafts had unstable renal function due to severe rejection with the persistence of anti-donor cytotoxic T cell reactivity. In contrast, recipients of composite thymokidney grafts had stable renal function with no evidence of rejection histologically and donor-specific unresponsiveness. By postoperative day 14, the thymic tissue in the thymokidney contained recipient-type dendritic cells. By postoperative day 60, recipient-type class I positive thymocytes appeared in the thymic medulla, indicating thymopoiesis. T cells were both recipient and donor MHC-restricted. These data demonstrate that the presence of vascularized-donor thymic tissue induces rapid and stable tolerance to class I-disparate kidney allografts in thymectomized recipients. To our knowledge, this is the first evidence of functional vascularized thymic grafts permitting transplantation tolerance to be induced in a large animal model.

Thymic transplantation in miniature swine. I. Development and function of the "thymokidney"

BACKGROUND

Previous studies in our laboratory have demonstrated the importance of the thymus for rapid and stable tolerance induction in an allotransplant model. The focus of the present study was to explore the feasibility of autologous thymic transplantation to produce a new transplantable organ (thymokidney) and to examine the function of subsequent vascularized thymokidney transplants in T cell development.

MATERIALS AND METHODS

Eight juvenile swine received autologous thymic grafts under the renal capsule. Thymic tissue was obtained through a partial (n=6) or complete (n=2) thymectomy, and growth of the autologous thymic graft was compared between partially and completely thymectomized animals. Two of the partially thymectomized animals received irradiated (1000 cGy) as well as non-irradiated autologous thymic grafts. Graft survival, growth and evidence of thymocyte development was determined by (a) macroscopic examination of the implanted tissue, (b) histological examination, and (c) flow cytometry. Naive CD4 SP T cells were identified by CD45RA-expression.

RESULTS

Growth of transplanted thymic tissue was demonstrated in all thymic graft recipients. No difference was seen between partially and completely thymectomized animals. By POD 60, the thymic grafts exhibited normal macroscopic and microscopic structure, and normal thymocyte composition. Irradiated thymic tissue displayed a similar pattern of development, but growth was markedly delayed. To evaluate thymic function of the graft, a composite thymokidney was transplanted into a recipient which had previously been thymectomized, had few circulating CD4-single positive cells and had lost MLR reactivity. The number of CD4+/CD45RA+ cells in this animal increased steadily from POD 30 to POD 150, indicating that the thymus of the composite thymokidney allograft was functional; in addition, MLR assays demonstrated that the recipient recovered immunocompetence.

CONCLUSIONS

The establishment of a thymokidney by thymic autografting to the renal subcapsular space results in normal thymic growth and function, and may provide a valuable tool for studying the role of the thymus in tolerance induction. As far as we are aware, we provide the first evidence of functional vascularized thymic graft reconstituting T cells and leading to a return of a immunocompetence in a large animal model.

Role of the thymus in transplantation tolerance in miniature swine. III. Surgical manipulation of the thymus interferes with stable induction of tolerance to class I-mismatched renal allografts

BACKGROUND

Previous studies have demonstrated that long-term tolerance of class I mismatched renal allografts in miniature swine is induced by a short course of cyclosporine (CyA), and that a total thymectomy 21 days before transplantation abrogates the induction of stable tolerance. We have now examined the effects of surgical manipulation of the thymus, with or without a reduction in the thymic volume, on the induction of tolerance.

MATERIALS AND METHODS

Miniature swine receiving a transplant of a class I-mismatched renal allograft and 12 days of CyA underwent either (1) a partial thymectomy 21 days before kidney transplantation (day -21), (2) serial thymic biopsies (to evaluate the effect of surgical trauma and reduction in volume of the thymus) or serial incisions of the thymus thymus (to evaluate the effect of surgical trauma without changes in thymic volume), (3) a sham thymectomy on day -21, or serial sham thymic surgery on the same POD as the thymic biopsies and incisions (control animals).

RESULTS

Control animals had a stable plasma creatinine, had donor-specific unresponsiveness in cell-mediated lympholysis (CML) assays, had absence of rejection in kidney biopsy specimens, and did not develop anti-donor class I immunoglobulin (Ig)G alloantibodies. Animals undergoing a partial thymectomy on day -21 or serial thymic biopsies showed severe renal dysfunction, histological evidence of rejection in kidney biopsy specimens and anti-donor reactivity in CML assays; all but one animal developed anti-donor class I IgG alloantibodies. Serial incisions of the thymus induced an increase in plasma creatinine and histological rejection in 1 of 3 animals and anti-donor cytotoxic T cells in vitro in all 3 animals.

CONCLUSIONS

A partial thymectomy or serial thymic biopsies markedly interfere with the induction of tolerance to renal allografts. Serial thymic incisions also interfere with the induction of tolerance, but to a lesser degree. These studies may have implications for tolerance-inducing protocols that involve thymic manipulation.

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.

Role of the thymus in transplantation tolerance in miniature swine: II. Effect of steroids and age on the induction of tolerance to class I mismatched renal allografts

BACKGROUND

Recent studies in young (5-7 months) miniature swine have demonstrated that the thymus is involved in the rapid induction of stable tolerance to class I mismatched renal allografts after a 12-day course of Cyclosporine (CyA). Because both steroids and age are known to influence the structure and function of the thymus, we have now studied the effects of these two parameters on tolerance induction in this model.

MATERIALS AND METHODS

In young swine, the administration of methylprednisolone (MP) during the standard tolerance-inducing regimen (a 12-day course of CyA) produced severe renal dysfunction and acute cellular rejection histologically. However, the renal allografts recovered and were accepted for >100 days with histological evidence of chronic rejection. To test the effect of age, two relatively old swine (55 and 71 months) received transplants of class I mismatched renal allografts and the standard 12-day course of CyA. One animal rejected the allograft acutely on postoperative day 22, and the second also rejected, but more slowly, with manifestations of chronic rejection.

CONCLUSION

These findings suggest that both MP and old age interfere with the induction of stable tolerance in a fashion similar to the previously described effect of thymectomy. These results may have important implications for the mechanism of thymic-dependent tolerance, for the use of steroids in clinical protocols for the induction of allograft tolerance, and for the application of such protocols to adult patients.

Peripheral tolerance to class I mismatched renal allografts in miniature swine: donor antigen-activated peripheral blood lymphocytes from tolerant swine inhibit antidonor CTL reactivity

Studies utilizing partially inbred miniature swine have demonstrated that a short course of cyclosporin A leads to indefinite survival of two haplotype class I mismatched renal allografts. In the present study, we have examined peripheral regulatory mechanisms that may be involved in maintenance of tolerance by coculturing PBL from long-term tolerant animals with naive recipient-matched PBL in cell-mediated lympholysis assays. We show that PBL from tolerant animals, primed in vitro with donor Ag, suppress antidonor CTL reactivity by naive recipient-matched PBL. Suppression was not observed when PBL from naive animals, primed with donor-matched PBL, were cocultured with PBL from a second naive animal, nor did PBL from either tolerant or naive recipient-matched control animals, primed with third-party Ag, suppress the generation of anti-third-party CTL by a second naive animal. The suppression was cell dose-dependent, radiation-sensitive, required cell-to-cell contact not reversed by the provision of exogenous IL-2, and associated with lower levels of IL-2R expression on the suppressive effector group (particularly the CD8 single positive cells) when compared with the control effector group. These data indicate an association between the presence of peripheral regulatory cells demonstrable in vitro and the maintenance of tolerance to renal allografts.

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.

Mechanism of tolerance to class I-mismatched renal allografts in miniature swine: regulation of interleukin-2 receptor alpha-chain expression on CD8 peripheral blood lymphocytes of tolerant animals

BACKGROUND

Donor-specific tolerance to renal allografts in miniature swine is uniformly induced across a two-haplotype class I plus minor histocompatibility antigen disparity by a 12-day course of cyclosporine. Recent studies have demonstrated that the thymus is essential for rapid and stable tolerance induction, because either prior thymectomy or a series of thymic biopsies induce a spontaneously reversible rejection crisis after the 12-day course of cyclosporine. The present study examined the peripheral cellular mechanisms of tolerance by analyzing cytotoxic effector pathways in peripheral blood lymphocytes (PBL) of tolerant animals.

METHODS

The phenotype and cytotoxic T lymphocyte response of alloantigen-activated PBL cultures using cells from a series of tolerant animals with stable renal function (no thymic manipulation), or during a rejection crisis (induced by thymic biopsies), were studied. The in vitro findings were correlated with the in vivo clinical course of experimental animals.

RESULTS

The data demonstrated that in vivo and in vitro tolerance was associated with a specific deficiency of interleukin-2 receptor (IL-2R) alpha-chain up-regulation on CD8 single-positive (SP) T cells expressing high levels of CD8 (CD8high) when PBL from tolerant animals are stimulated with donor class I alloantigen. Stimulation by third party class I alloantigen, or by donor antigen during a rejection crisis, produced efficient cytotoxic T lymphocyte responses and expression of IL-2Ralpha on CD8high SP cells.

CONCLUSION

Antigen-specific regulation of the IL-2Ralpha expression on CD8high SP PBL is a principal event associated with and potentially involved in the mechanism of tolerance in this preclinical large animal model.

Depletion of anti-Gal(alpha)1-3Gal antibody in baboons by specific alpha-Gal immunoaffinity columns

Ongoing studies at our center on facilitating transplantation of discordant xenogeneic organs are focused on tolerance induction. To abrogate hyperacute rejection, we have used adsorption methods to eliminate natural anti-Gal(alpha)1-3Gal (alphaGal) antibodies from the circulation of baboons. We have analyzed data concerning antibody removal in baboons that were 1) immunologically naive, 2) receiving conventional pharmacologic immunosuppressive therapy (IS), and 3) treated with a conditioning regimen for tolerance induction. We compared the efficiency of removing alphaGal antibody 1) by perfusion of whole blood through an alphaGal affinity column (CP; n=5) with 2) perfusion of plasma (separated from cellular components by apheresis) through an alphaGal column (CPA; n=39). Our studies demonstrate that 1) CP and CPA are equally effective in removing anti-alphaGal antibody, 2) CPA is the method of choice if multiple adsorptions are required, 3) CPA in naive animals transiently affects levels of total IgG and IgM, 4) four CPAs repeated at 2-4 day intervals in association with heavy IS reduce the pool of anti-alphaGal antibody and total Ig, and 5) splenectomy and/or IS delay the return of anti-alphaGal antibody.

Role of the thymus in transplantation tolerance in miniature swine. I. Requirement of the thymus for rapid and stable induction of tolerance to class I-mismatched renal allografts

The almost uniform failure in transplant patients of tolerance-inducing regimens that have been found to be effective in rodents, has made it necessary to examine large animal models before testing of new approaches clinically. Miniature swine have been shown to share many relevant immunologic parameters with humans, and because of their reproducible genetics, have proved extremely useful in providing such a large animal model. We have previously shown that indefinite systemic tolerance to renal allografts in miniature swine is induced in 100% of cases across a two-haplotype class I plus minor histocompatibility antigen disparity by a 12-d course of Cyclosporine A (CyA), in contrast to irreversible rejection observed uniformly without CyA treatment. In the present study, we have examined the role of the thymus during the induction of tolerance by performing a complete thymectomy 21 d before renal transplantation. This analysis demonstrated a striking difference between thymectomized and nonthymectomized animals. Thymectomized swine developed acute cellular rejection characterized by a T cell (CD25(+)) infiltrate, tubulitis, endothelialitis and glomerulitis, and anti-donor CTL reactivity in vitro. Nonthymectomized and sham thymectomized animals had a mild T cell infiltrate with few CD25(+) cells and no anti-donor CTL response in vitro. These results indicate that the thymus is required for rapid and stable induction of tolerance.

Characterization of FcR Ig-binding sites and epitope mapping

The low-affinity receptor for IgG, Fc gamma RII, and the high-affinity receptor for IgE, Fc epsilon RI, are functionally distinct but structurally homologous receptors. These characteristics have been exploited using a chimeric receptor strategy to examine segments of human Fc gamma RII for IgG-binding function. A series of chimeric receptors was generated by exchanging coding regions of the extracellular ligand-binding regions between Fc gamma RII and the Fc epsilon RI alpha chain using splice overlap extension by the polymerase chain reaction. The expression of these chimeric receptors in COS-7 cells and analysis of their IgG/IgE binding capacities have enabled the Ig-binding region of Fc gamma RII to be localized to a subregion of the second extracellular domain. The localization of the Ig-binding region of Fc gamma RII has provided the opportunity of performing site-directed mutagenesis to determine the key amino acids involved in the interaction of the receptor with IgG. These findings demonstrate that the chimeric receptor approach is a powerful technique for the dissection of structure/function relationships of structurally related yet functionally different molecules.

Recombinant soluble human Fc gamma RII: production, characterization, and inhibition of the Arthus reaction

A recombinant soluble form of human Fc gamma RII (rsFc gamma RII) was genetically engineered by the insertion of a termination codon 5' of sequences encoding the transmembrane domain of a human Fc gamma RII cDNA. Chinese hamster ovary cells were transfected with the modified cDNA and the secreted rsFc gamma RII purified from the tissue culture supernatant (to > 95%, assessed by SDS-PAGE) using heat aggregated human immunoglobulin G (IgG) immunoaffinity chromatography. The IgG-purified rsFc gamma RII was relatively homogeneous (approximately 31,000 M(r)) whereas the total unpurified rsFc gamma RII secreted into the tissue culture supernatant was heterogeneous relating to N-linked glycosylation differences. Functional in vitro activity of the rsFc gamma RII was demonstrated by: (a) ability to bind via the Fc portion of human IgG and mouse IgG (IgG2a > IgG1 > > IgG2b); (b) complete inhibition of binding of erythrocytes sensitized with rabbit IgG to membrane-bound Fc gamma RII on K562 cells; and (c) inhibition of the anti-Leu4-induced T cell proliferation assay. Blood clearance and biodistribution studies show the rsFc gamma RII was excreted predominantly through the kidney in a biphasic manner, with an alpha-phase (t1/2 approximately 25 min) and a beta-phase (t1/2 approximately 4.6 h); the kidneys were the only organs noted with tissue-specific accumulation. In vivo, the administration of rsFc gamma RII significantly inhibited the immune complex-mediated inflammatory response induced by the reversed passive Arthus reaction model in rats. There was a specific and dose-dependent relationship between the amount of rsFc gamma RII administered, and the reduction in the size and severity of the macroscopic inflammatory lesion. Histological analysis of the skin showed a diffuse neutrophil infiltrate in both control and rsFc gamma RII-treated rats, however the perivascular infiltrate and the red cell extravasation was less intense in the rsFc gamma RII-treated group. It is likely that complement activation leads to neutrophil chemotaxis, but neutrophil activation via Fc gamma RII, which results in inflammatory mediator release, is inhibited. The data indicate that rsFc gamma RII is a potential therapeutic agent for the treatment of antibody or immune complex-mediated tissue damage.

Mapping epitopes of human Fc gamma RII (CDw32) with monoclonal antibodies and recombinant receptors

Fc gamma RII is a low affinity FcR for IgG with two Ig-like extracellular domains (D1 gamma and D2 gamma), a transmembrane domain, and a cytoplasmic domain. The production, characterization, and epitope analysis of four anti-human Fc gamma RII mAb (8.2, 8.7, 8.26, and 7.30) are detailed, and the mAb are compared with two defined CDw32 mAb, IV.3 and CIKM5. Reactivity of all mAb with Fc gamma RII was demonstrated by (a) specific binding to Fc gamma RII+ L cells (produced after transfection of L cells with human Fc gamma RIIa cDNA, HFc3.0), by using flow cytometry, (b) inhibition of the binding of SRBC sensitized with rabbit antibody (EA) to Fc gamma RII+ L cells, and (c) immunoprecipitation and SDS-PAGE, which detected a 42-kDa protein on K562 and U937 cells and a single 45-kDa protein on Fc gamma RII+ L cells. The mAb were able to detect different forms of Fc gamma RII, by flow cytometry, on Daudi cells (8.7 and 7.30) and U937 cells (8.2, IV.3, and CIKM5); 8.26 stained Daudi cells with intermediate fluorescence and U937 cells with the highest fluorescence, relative to the remaining mAb. Binding to transiently expressed isoforms of Fc gamma RII (a and b1) and four allelic variants of Fc gamma RIIa in COS-7 cells did not distinguish the mAb epitopes. Further mapping of the mAb epitopes was determined by (a) EA inhibition assays, (b) mAb blocking studies, and (c) the binding of the mAb to segments of human Fc gamma RIIa by using genetically engineered chimeric receptors. Chimeric receptors expressing either D1 gamma linked to domain 2 of Fc epsilon RI or domain 1 of Fc epsilon RI linked to D2 gamma were produced by exchanging homologous, but antigenically different, regions of Fc gamma RIIa and the high affinity receptor for IgE. Four clusters of mAb were identified, each mapping to discrete epitopes of Fc gamma RII. Cluster I (mAb 8.2 and CIKM5) defines a combinatorial epitope with determinants in D1 gamma and D2 gamma distant from the IgG Fc binding site, inasmuch as F(ab')2 fragments of 8.2 and CIKM5 do not inhibit the binding of EA to Fc gamma RII. The epitopes of clusters 2 (mAb 8.26), 3 (mAb IV.3), and 4 (mAb 8.7 and 7.30) are located entirely in D2 gamma and all involve the IgG Fc binding region, because F(ab')/F(ab')2 fragments of the mAb inhibit EA binding to Fc gamma RII. Thus, all mAb that inhibit the binding of EA map totally to D2 gamma; it is likely the IgG Fc binding region is also contained in D2 gamma.

Mapping epitopes of human Fc gamma RII (CDw32) with monoclonal antibodies and recombinant receptors

Fc gamma RII is a low affinity FcR for IgG with two Ig-like extracellular domains (D1 gamma and D2 gamma), a transmembrane domain, and a cytoplasmic domain. The production, characterization, and epitope analysis of four anti-human Fc gamma RII mAb (8.2, 8.7, 8.26, and 7.30) are detailed, and the mAb are compared with two defined CDw32 mAb, IV.3 and CIKM5. Reactivity of all mAb with Fc gamma RII was demonstrated by (a) specific binding to Fc gamma RII+ L cells (produced after transfection of L cells with human Fc gamma RIIa cDNA, HFc3.0), by using flow cytometry, (b) inhibition of the binding of SRBC sensitized with rabbit antibody (EA) to Fc gamma RII+ L cells, and (c) immunoprecipitation and SDS-PAGE, which detected a 42-kDa protein on K562 and U937 cells and a single 45-kDa protein on Fc gamma RII+ L cells. The mAb were able to detect different forms of Fc gamma RII, by flow cytometry, on Daudi cells (8.7 and 7.30) and U937 cells (8.2, IV.3, and CIKM5); 8.26 stained Daudi cells with intermediate fluorescence and U937 cells with the highest fluorescence, relative to the remaining mAb. Binding to transiently expressed isoforms of Fc gamma RII (a and b1) and four allelic variants of Fc gamma RIIa in COS-7 cells did not distinguish the mAb epitopes. Further mapping of the mAb epitopes was determined by (a) EA inhibition assays, (b) mAb blocking studies, and (c) the binding of the mAb to segments of human Fc gamma RIIa by using genetically engineered chimeric receptors. Chimeric receptors expressing either D1 gamma linked to domain 2 of Fc epsilon RI or domain 1 of Fc epsilon RI linked to D2 gamma were produced by exchanging homologous, but antigenically different, regions of Fc gamma RIIa and the high affinity receptor for IgE. Four clusters of mAb were identified, each mapping to discrete epitopes of Fc gamma RII. Cluster I (mAb 8.2 and CIKM5) defines a combinatorial epitope with determinants in D1 gamma and D2 gamma distant from the IgG Fc binding site, inasmuch as F(ab')2 fragments of 8.2 and CIKM5 do not inhibit the binding of EA to Fc gamma RII. The epitopes of clusters 2 (mAb 8.26), 3 (mAb IV.3), and 4 (mAb 8.7 and 7.30) are located entirely in D2 gamma and all involve the IgG Fc binding region, because F(ab')/F(ab')2 fragments of the mAb inhibit EA binding to Fc gamma RII. Thus, all mAb that inhibit the binding of EA map totally to D2 gamma; it is likely the IgG Fc binding region is also contained in D2 gamma.