Chimerism and tolerance in transplantation

Calcineurin inhibitor minimization in pediatric liver allograft recipients

The use of CNI in pediatric LTx has dramatically improved the outcome for children with end-stage liver disease by significantly reducing the rate of acute and chronic rejection. Long-term concerns about CNI-induced nephrotoxicity and other adverse effects remain an issue, particularly as the emphasis moves from short-term survival to long-term quality of life. This review summarizes lessons learnt from pediatric and adult solid organ transplantation in minimizing CNI use in immunosuppression protocols in children following LTx. There are three models for CNI minimization: dose reduction, withdrawal or avoidance, supplemented by the use of IL-2 receptor blocking antibodies in the peri-transplant period, and early transition to alternate drugs such as MMF or SRL. Prospective studies evaluating reduction or withdrawal protocols in adult and pediatric LTx indicate that rejection rates are comparable with traditional CNI-based immunosuppression and that two and five yr patient and graft survival are similar, with recovery in renal function. There are few studies evaluating complete avoidance of CNI, apart from that in renal transplantation, although the benefits of long-term reduction in cardiovascular, metabolic, and possibly neoplastic side effects may justify this approach. It is not clear yet how CNI minimization will affect the development of tolerance but experimental and preliminary clinical studies indicate that CNI and steroid avoidance or minimization in the peri-operative period may favor the development of long-term graft tolerance. In summary, CNI minimization may be safe and effective in the short term but large-scale pediatric randomized studies are required to evaluate the long-term efficacy of these regimes in the development of chronic rejection, PTLD, and graft tolerance.

Differential dynamics of donor DC and non-DC peripheral blood mononuclear cell microchimerism in lung transplantation

Donor cell microchimerism induces tolerance in animal models and may increase graft survival in man. Since dendritic cells (DC) are critical for induction of both tolerance and alloreactivity we developed a method to quantitate microchimerism in donor DC and non-DC in peripheral blood mononuclear cells (PBMC) after lung transplantation. Longitudinal analysis of donor cell microchimerism in eleven sex mismatched lung transplant recipients (LTR) up to 12 months post-transplant used Y chromosome based real-time PCR on sorted cells. Total DC or a proportion of DC subsets in PBMC did not change but there were heterogeneous and dynamic changes in microchimerism in DC and non-DC. Analysis of changes in DC using a mixed model analysis showed significantly less reduction in DC compared to non-DC over time (0.49, p=0.001). Preferential DC persistence compared to non-DC may indicate tolerance induction but future studies are required to determine if DC microchimerism after transplantation affects clinical outcomes.

Towards minimizing immunosuppression in pediatric liver transplant recipients

Immunosuppression regimens after liver transplantation focus mainly on preventing rejection and subsequent graft loss. However, in children, morbidity and mortality rates from infections exceed those from rejection after transplant, and immunosuppression can hinder growth, renal function, and graft tolerance. We hypothesized that early steroid withdrawal, with a primary aim of TAC monotherapy would yield no penalty in terms of rejection and graft loss, while reducing risks of infection and maximizing growth. We prospectively evaluated 64 consecutive pediatric liver transplant recipients. One yr patient/graft survival was 93/90%, respectively. At one yr post-transplant, 75.4% of patients were on TAC monotherapy. No deaths or graft losses were caused by infection. Sixty-one percent of patients had at least one episode of rejection, most within three months following transplant and 3.8% were treated for chronic rejection. One non-compliant adolescent died from chronic rejection. CMV, EBV, and lymphoproliferative disease rates were 3.1%, 5.3%, 1.8%, respectively. Pretransplant and one yr post-transplant glomerular filtration rates were unchanged. One yr improved catch-up growth was observed. We conclude that immunosuppression minimization after pediatric liver transplant yields no serious complications from rejection, and might confer advantages with respect to infection, renal function, growth, and is deserving of wider application and study.

A reply to Dembic: on an end to the beginning of misunderstanding the immune response

We all agree that dealing with the complexity and volume of the data necessitates the use of computer modelling. This in turn requires a heuristic conceptual framework to guide this modelling. The first attempt to do this by Cohn has been criticized by Dembic as being severely lacking. This commentary deals with his criticism of the framework to show why Cohn's postulates, in fact, remain unchallenged.

The programmed death (PD)-1/PD-ligand 1 pathway regulates graft-versus-host-reactive CD8 T cells after liver transplantation

Acute graft-versus-host disease (aGVHD) is a life-threatening complication after solid-organ transplantation, which is mediated by host-reactive donor T cells emigrating from the allograft. We report on two liver transplant recipients who developed an almost complete donor chimerism in peripheral blood and bone marrow-infiltrating T cells during aGVHD. By analyzing these T cells directly ex vivo, we found that they died by apoptosis over time without evidence of rejection by host T cells. The host-versus-donor reactivity was selectively impaired, as anti-third-party and antiviral T cells were still detectable in the host repertoire. These findings support the acquired donor-specific allotolerance concept previously established in animal transplantation studies. We also observed that the resolution of aGVHD was not accompanied by an expansion of circulating immunosuppressive CD4/CD25/FoxP3-positive T cells. In fact, graft-versus-host-reactive T cells were controlled by an alternative negative regulatory pathway, executed by the programmed death (PD)-1 receptor and its ligand PD-L1. We found high PD-1 expression on donor CD4 and CD8 T cells. In addition, blocking PD-L1 on host-derived cells significantly enhanced alloreactivity by CD8 T cells in vitro. We suggest the interference with the PD-1/PD-L1 pathway as a therapeutic strategy to control graft-versus-host-reactive T cells in allograft recipients.

Prospective analysis between the therapy of immunosuppressive medication and allogeneic microchimerism after liver transplantation

After liver transplantation, migration of donor-derived hematopoietic cells to recipient can be detected in peripheral blood. This state is termed microchimerism. The aim of this study was to investigate prospectively the presence of allogeneic microchimerism, the occurrence of acute cellular rejection and the level of immunosuppression in transplanted patients. Microchimerism occurrence between 10 days and 12 months after liver transplantation was analyzed in 47 patients aged between 15 and 65 by a two-stage nested PCR/SSP technique to detect donor MHC HLA-DR gene specifically. A pre-transplant blood sample was collected from each patient to serve as individual negative control. Microchimerism was demonstrated in 32 (68%) of the 47 patients; of these, only 10 patients (31.2%) presented rejection. Early microchimerism was observed in 25 patients (78.12%) and late microchimerism in 7 patients (21.8%). Among the patients with microchimerism, 14 were given CyA and 18 were given FK506. In the group without microchimerism, 12 patients were given CyA and 03 were given FK506. There was a significant association between the presence of microchimerism and the absence of rejection (p=0.02) and also between microchimerism and the type of immunosuppression used. Our data indicate that microchimerism and probably differentiation of donor-derived leukocytes can have relevant immunologic effects both in terms of sensitization of recipient and in terms of immunomodulation toward tolerance induction.

Partial HLA matching and RH incompatibility resulting in graft versus host reaction and Evans syndrome after liver transplantation

We report a case of a 67-year-old male who underwent OLT from a deceased, sex-matched donor. Two months later he developed Evans syndrome and GVHD of the skin. Donor and recipient were matched for HLA-A and -B loci in the direction of rejection but mismatched in the direction of GVHD and fully mismatched for DRB1. These mismatches were permissible for engraftment of donor T-cells but led to GVHD. Chimerism appeared restricted to the T-cell compartment. In this case, partially matched passenger lymphocytes triggered a graft versus host reaction. In addition, alloantibodies caused cytopenias that improved after immunosuppression. HLA typing was critical in confirming this rare diagnosis and elucidating its cause. Recipients of solid organs from donors that are partially matched in the direction of rejection may need to be closely monitored for GVHD.

Composite tissue transplantation: a rapidly advancing field

Composite tissue allotransplantation (CTA) is emerging as a potential treatment for complex tissue defects. It is currently being performed with increasing frequency in the clinic. The feasibility of the procedure has been confirmed through 30 hand transplantation, 3 facial reconstructions, and vascularized knee, esophageal, and tracheal allografts. A major drawback for CTA is the requirement for lifelong immunosuppression. The toxicity of these agents has limited the widespread application of CTA. Methods to reduce or eliminate the requirement for immunosuppression and promote CTA acceptance would represent a significant step forward in the field. Multiple studies suggest that mixed chimerism established by bone marrow transplantation promotes tolerance resulting in allograft acceptance. This overview focuses on the history and the exponentially expanding applications of the new frontier in CTA transplantation: immunology associated with CTA; preclinical animal models of CTA; clinical experience with CTA; and advances in mixed chimerism-induced tolerance in CTA. Additionally, some important hurdles that must be overcome in using bone marrow chimerism to induce tolerance to CTA are also discussed.

Hematopoietic stem cell engraftment and seeding permits multi-lymphoid chimerism in vascularized bone marrow transplants

Vascularized bone marrow transplantation (VBMT) across a MHC barrier under a 7-day alphabeta-TCR mAb and CsA protocol facilitated multiple hematolymphoid chimerism via trafficking of the immature (CD90) bone marrow cells (BMC) between donor and recipient compartments. Early engraftment of donor BMC [BN(RT1(n))] into the recipient BM compartment [LEW(RT1(l))] was achieved at 1 week posttransplant and this was associated with active hematopoiesis within allografted bone and correlated with high chimerism in the hematolymphoid organs. Two-way trafficking between donor and recipient BM compartments was confirmed by the presence of recipient MHC class I cells (RT1(l)) within the allografted bone up to 3 weeks posttransplant. At 10 weeks posttransplant, decline of BMC viability in allografted bone corresponded with bone fibrosis and lack of hematopoiesis. In contrast, active hematopoiesis was present in the recipient bone as evidenced by the presence of donor-specific immature (CD90/RT1(n)) cells, which correlated with chimerism maintenance. Clonogenic activity of donor-origin cells (RT1(n)) engrafted into the host BM compartment was confirmed by colony-forming units (CFU) assay. These results confirm that hematolymphoid chimerism is developed early post-VBMT by T-cell lineage and despite allografted bone fibrosis chimerism maintenance is supported by B-cell linage and active hematopoiesis of donor-origin cells in the host BM compartment.

Circulating nucleic acids in plasma/serum

Since the discovery of circulating nucleic acids in plasma in 1948, many diagnostic applications have emerged. For example, diagnostic and prognostic potentials of circulating tumour-derived DNA have been demonstrated for many types of cancer. The parallel development of fetal-derived DNA detection in maternal plasma has opened up the possibility of non-invasive prenatal diagnosis and monitoring of many pregnancy-associated disorders. In this regard, non-invasive fetal rhesus blood group genotyping has already been translated to clinical practice. Other applications of circulating DNA in traumatology and transplant monitoring have also been reported. The more recent discoveries of circulating tumour-derived RNA and fetal-derived RNA have proven to be equally important as their DNA counterparts. Successful prenatal diagnosis of Down's syndrome by fetal RNA analysis has recently been reported. However, the definite origin and release mechanisms of circulating nucleic acids have remained incompletely understood, with cell death being suggested to be associated with such nucleic acid release. Pre-analytical standardisation will become increasingly relevant when comparing data from different laboratories. In conclusion, studies of circulating nucleic acids have promised exciting developments in molecular diagnostics in the years to come.

Short-Term Anti-CD4 Plus Anti-TNF-α Receptor Treatment in Allogeneic Small Bowel Transplantation Results in Long-Term Survival

BACKGROUND

Despite improved immunosuppression, intestinal transplantation is still complicated by severe rejection episodes. To further improve immunosuppressive concepts, we evaluated an anti-CD4 antibody and an anti-tumor necrosis factor (TNF)-alpha monoclonal antibody for their immunosuppressive efficacy in the standard rat model of intestinal transplantation.

METHODS

Intestinal transplantation was performed in the DA to Lewis combination, and recipients were treated perioperatively with either the anti-CD4 antibody RIB5/2 (day -1, 0, postoperative days 1, 2, 4, 7, 10, 14, 17, and 21), the anti-TNF antibody etanercept (60 min before reperfusion, postoperative days 3, 6, and 9) or a combination of both. Survival, histology and expression of immunologic mediator genes on days 3 and 4 after transplantation were investigated.

RESULTS

Treatment with anti-CD4 antibody alone (19.71+/-5.94) and the antibody combination (171.58+/-122.76) prolonged survival. The chemokine MIP-1alpha was significantly decreased in both anti-CD4 antibody treatment groups, possibly indicating an additional effect of the TNF-alpha blockade on the immune modulation by RIB5/2.

CONCLUSIONS

Our study demonstrated long-term graft survival in short-term treatment with a combination of an anti-CD4 antibody and a TNF-alpha antibody in more than 50% of the recipients of intestinal grafts. Such a combined approach could also be useful in clinical small bowel transplantation.

Fully MHC-Disparate Mixed Hemopoietic Chimeras Show Specific Defects in the Control of Chronic Viral Infections

The establishment of mixed allogeneic chimerism can induce donor-specific transplantation tolerance across full MHC barriers. However, a theoretical disadvantage of this approach is the possibility that the state of mixed chimerism might negatively affect the recipient's immune competence to control pathogens. Previous studies using murine models have not supported this hypothesis, because they indicate that acute viral infections are cleared by chimeric animals with similar kinetics to that of unmanipulated controls. However, chronic or persistent viral infections often require a more complex and sustained response with cooperation between CD4 Th cells, CTL, and B cells for effective control. The current study indicates that profound defects become manifest in the control of chronic pathogenic infections in MHC-disparate mixed allogeneic chimeric mice. Furthermore, we show that ineffective priming of the donor-restricted CTL response leads to virus persistence, as well as severe T cell exhaustion. Our results further suggest that either T cell adoptive immunotherapy or selected MHC haplotype matching partially restore immune competence. These approaches may facilitate the translation of mixed chimerism therapeutic regimens.

Frontiers in nephrology: immune tolerance to allografts in humans

Vascularized allografts are rejected unless some indefinite modification to the recipient's immune system is made. This modification is typically achieved through the long-term administration of immunosuppressive drugs. Patients thus trade their end-stage organ failure for dependence on daily drug therapy and the accompanying chronic condition of immunodeficiency. However, it is clear from studies in experimental animals that rejection can be prevented through the use of several therapeutic approaches, including donor hematopoietic cell infusion, chimerism, T cell depletion, and/or co-stimulation blockade. Successfully treated animals avoid rejection beyond the period of therapy without a phenotype of chronic immunosuppression and are thus considered to be tolerant of their grafts. Although intriguing, this success in animals has yet to be reproducibly translated to the clinic, and human transplant recipients remain tethered to immunosuppressive drugs with rare exceptions. This article provides an overview of the existing, largely anecdotal, clinical experience with organ allograft tolerance. It reviews the various approaches that are being applied in pilot human trials and suggests avenues for future clinical investigation.

Allosuppressive Donor CD4+CD25+ Regulatory T Cells Detach from the Graft and Circulate in Recipients after Liver Transplantation

Organ transplantation (Tx) results in a transfer of donor leukocytes from the graft to the recipient, which can lead to chimerism and may promote tolerance. It remains unclear whether this tolerance involves donor-derived regulatory T cells (Tregs). In this study, we examined the presence and allosuppressive activity of CD4+CD25+Foxp3+ Tregs in perfusates of human liver grafts and monitored the cells presence in the circulation of recipients after liver Tx. Vascular perfusions of 22 liver grafts were performed with University of Wisconsin preservation and albumin solutions. Flow cytometric analysis revealed that perfusate T cells had high LFA-1 integrin expression and had a reversed CD4 to CD8 ratio compared with control blood of healthy individuals. These findings indicate that perfusate cells are of liver origin and not derived from residual donor blood. Further characterization of perfusate mononuclear cells showed an increased proportion of CD4+CD25+CTLA4+ T cells compared with healthy control blood. Increased percentages of Foxp3+ cells, which were negative for CD127, confirmed the enrichment of Tregs in perfusates. In MLR, CD4+CD25+ T cells from perfusates suppressed proliferation and IFN-gamma production of donor and recipient T cells. In vivo within the first weeks after Tx, up to 5% of CD4+CD25+CTLA4+ T cells in recipient blood were derived from the donor liver. In conclusion, a substantial number of donor Tregs detach from the liver graft during perfusion and continue to migrate into the recipient after Tx. These donor Tregs suppress the direct pathway alloresponses and may in vivo contribute to chimerism-associated tolerance early after liver Tx.

Donor B cells in splenic follicles of experimental pulmonary allograft recipients

BACKGROUND

After transplantation, passenger leukocytes move to lymphoid organs of the recipient. These cells appear to initiate allograft rejection, but they also might be involved in tolerance induction.

MATERIALS AND METHODS

Orthotopic left lung transplantation was performed in the Dark Agouti to Lewis rat strain combination with no immunosuppression. Recipient spleens were removed at intervals of 24 h until day 6 after transplantation. For comparison, spleens from renal allograft recipients were analysed. Donor-derived major histocompatibility complex (MHC) class II antigens were detected by monoclonal antibody OX76. In double-staining experiments with antibodies specific for leukocyte subpopulations, their localisation and identity was analysed.

RESULTS

OX76-positive leukocytes were already detected in recipient spleens on day 1 post-transplantation. They increased in number until day 3 and decreased in number thereafter. Most of them were localised in splenic follicles and expressed the B cell variant of CD45R and IgG. Cell surface antigens typical for other leukocyte subpopulations were not detected. In the spleens of renal allograft recipients, only few donor-derived cells were seen.

CONCLUSION

After lung transplantation, numerous MHC class II-positive B cells migrate to the splenic follicles of the recipient. These cells might, in part, be responsible for immunologic differences observed between renal and pulmonary allografts.

Applications of bilateral vascularized femoral bone marrow transplantation for chimerism induction across the major histocompatibility (MHC) barrier: part II

Bilateral vascularized bone marrow transplant (VBMT) model was designed to induce chimerism across the major histocompatibility (MHC) barrier under combined alphabeta T-cell receptor monoclonal antibody and cyclosporine A (alphabeta-TCRmAb/CsA) protocol. Seventeen transplants were performed between BN(RT1) donors and Lewis(RTI) recipients. Group I, isograft controls; Group II, allografts rejection controls; Group III, allografts under 7-day protocol of alphabeta-TCRmAb/CsA. Donor bilateral femoral bones were bilaterally anastomosed to the abdominal aorta and inferior vena cava of recipient. At day 7 posttransplantation, all bone flaps were viable. Groups I and III survived without signs of rejection. In Group III, peak level of chimerism in peripheral blood was evaluated at day 21 (24.2%), at day 63 declined to 1.5%, and was maintained at this level thereafter. Donor-derived cells were present in the bone marrow of recipients at 28.2% at day 21 posttransplant. Histology confirmed viability of bone marrow cells in isograft during the entire follow-up and up to 35 days in treatment Group III. Bilateral VBMT induced donor-specific chimerism across the MHC barrier under the immunomodulatory protocol of alphabeta-TCRmAb/CsA.

Frontiers of immunological tolerance

Herein, we succinctly review mechanisms underlying self-tolerance and the roles of dendritic leukocytes (DCs) in T-cell tolerance to self and foreign antigens. We also consider the properties of naturally arising and other populations of regulatory T cells (Treg), together with growing evidence that interplay between DCs and Treg cells can sustain antigen-specific tolerance. B-cell tolerance and the role of hematopoietic cell chimerism in the induction and maintenance of tolerance are also discussed, as is the impact of cosignaling pathway manipulation on tolerance induction. This overview also surveys prospects for technological advances in the monitoring and prediction of tolerance and the application of genomic and proteomic analysis. In addition, we consider potential novel therapeutic targets for promotion of tolerance induction.

???Prope??? Tolerance in a Noncompliant Living Related Small Bowel Transplant Recipient After Severe Rejection

Advances in immunosuppression and surgical technique have greatly improved patient outcomes after intestinal transplantation. However, the procedure remains one of the most challenging among solid organ transplantation as a result of the high rate of acute rejection, sepsis, and posttransplantation lymphoproliferative disorder. Recently, clinical trials to explore tolerance protocols in humans have been initiated, including small bowel transplant recipients, with results not always reproducible. The concept of operational tolerance is more meaningful in the clinical setting when physiological stability of graft function is achieved in the absence of maintenance immunosuppression. We report the intriguing case of a living related small bowel transplant recipient who developed clinical "prope" tolerance to the graft after treatment of severe acute rejection despite continuous noncompliance with immunosuppressive therapy.

Acquired immunologic tolerance: with particular reference to transplantation

The first unequivocally successful bone marrow cell transplantation in humans was recorded in 1968 by the University of Minnesota team of Robert A. Good (Gatti et al. Lancet 2: 1366-1369, 1968). This achievement was a direct extension of mouse models of acquired immunologic tolerance that were established 15 years earlier. In contrast, organ (i.e. kidney) transplantation was accomplished precociously in humans (in 1959) before demonstrating its feasibility in any experimental model and in the absence of a defensible immunologic rationale. Due to the striking differences between the outcomes with the two kinds of procedure, the mechanisms of organ engraftment were long thought to differ from the leukocyte chimerism-associated ones of bone marrow transplantation. This and other concepts of alloengraftment and acquired tolerance have changed over time. Current concepts and their clinical implications can be understood and discussed best from the perspective provided by the life and times of Bob Good.

Cell migration from baby to mother

Fetal cells migrate into the mother during pregnancy. Fetomaternal transfer probably occurs in all pregnancies and in humans the fetal cells can persist for decades. Microchimeric fetal cells are found in various maternal tissues and organs including blood, bone marrow, skin and liver. In mice, fetal cells have also been found in the brain. The fetal cells also appear to target sites of injury. Fetomaternal microchimerism may have important implications for the immune status of women, influencing autoimmunity and tolerance to transplants. Further understanding of the ability of fetal cells to cross both the placental and blood-brain barriers, to migrate into diverse tissues, and to differentiate into multiple cell types may also advance strategies for intravenous transplantation of stem cells for cytotherapeutic repair. Here we discuss hypotheses for how fetal cells cross the placental and blood-brain barriers and the persistence and distribution of fetal cells in the mother.

Predictors of organ allograft tolerance following hematopoietic cell transplantation

Using the miniature swine large animal model we have attempted to determine the relationship between tolerance and the presence of donor cells in the bone marrow, thymus and lineages of peripheral blood in a series of hematopoietic cell transplant recipients receiving delayed donor allografts without immunosuppression. Twenty-two animals receiving hematopoietic cell transplantation and a delayed organ allograft were analyzed. Assays for presence of donor CFUs in bone marrow (by PCR), thymic chimerism (by FACS and PCR/Southern Blot), peripheral blood chimerism (by FACS), and in vitro responsiveness to donor MHC were performed. Presence of donor BM CFUs, thymic chimerism and multilineage peripheral blood chimerism at the time of organ transplantation all correlated precisely with subsequent allograft tolerance (p < 0.001, p < 0.001, p < 0.005 respectively). These parameters were therefore accurate predictors (Positive Predictive Value (PPV) = 100% in all) of tolerance. In vitro assays of responsiveness were also highly associated (p < 0.002, p < 0.002 respectively), but were not as accurate predictors of subsequent organ tolerance (CML PPV = 80%). Engraftment, as indicated by the presence of donor derived CFU in the bone marrow, detectable thymic chimerism and multilineage peripheral blood chimerism are reliable predictors of subsequent donor allograft acceptance in hematopoietic cell transplant recipients.

Blood group chimerism

PURPOSE OF REVIEW

With improved methods for detecting chimeras and growing numbers of stem cell transplantations, blood group and other forms of chimerism are observed with increasing frequency. This review will focus on the state of science and new insights into the multifaceted subject of blood group chimerism.

RECENT FINDINGS

Recognition that the immune system tolerates chimeric cells under certain conditions has led to efforts to elucidate related immune-modulating processes. The chimeric state following transplantation of hematopoietic stem cells, as well as after solid organ transplantation, is of special interest. Also, chimerism is considered to be a potential trigger for certain autoimmune diseases. Natural chimerism is more frequent than previously recognized. Using improved laboratory techniques, investigators can often trace chimeric tissues to their origin. New therapeutic strategies have been applied after stem cell transplantation depending on the chimeric state. Also, recent research has resulted in methods for determining chimerism in maternal peripheral blood that reflect fetal blood type and certain congenital diseases.

SUMMARY

The subject of human chimerism has evolved from a curiosity of nature to an important field of research and, potentially, holds the key to advancing our understanding of the fundamental mechanisms of immune tolerance.

Modeling CTLA4-linked autoimmunity with RNA interference in mice

The CTLA4 gene is important for T lymphocyte-mediated immunoregulation and has been associated with several autoimmune diseases, in particular, type 1 diabetes. To model the impact of natural genetic variants of CTLA4, we constructed RNA interference (RNAi) "knockdown" mice through lentiviral transgenesis. Variegation of expression was observed in founders but proved surmountable because it reflected parental imprinting, with derepression by transmission from male lentigenics. Unlike the indiscriminate multiorgan autoimmune phenotype of the corresponding knockout mice, Ctla4 knockdown animals had a disease primarily focused on the pancreas, with rapid progression to diabetes. As with the human disease, the knockdown phenotype was tempered by genetic-modifier loci. RNAi should be more pertinent than gene ablation in modeling disease pathogenesis linked to a gene-dosage variation.

Presence of donor-and-recipient-derived DNA microchimerism in the cell-free blood samples of renal transplantation recipients associates with the acceptance of transplanted kidneys

AIM

To examine whether the existence of the donor-and recipient-derived DNA chimerism in recipient's plasma can be a predictive marker for the status of transplanted organ.

METHODS

One hundred and twenty-six female patients who had been transplanted with male kidneys were enrolled in the present study. In these female recipients, the SRY(1), DYZ(1)(1st) and DYZ(1)(2nd) genes on the Y chromosome from the plasma were prospectively examined using reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

SRY, DYZ(1)(1st) and DYZ(1)(2nd) sequences were detected in the cell-free blood (plasma) of 97 (77%) of 126 female patients with male kidney. The average time that the transplanted kidneys functioned was 8.7 years and 5.4 years among microchimerism-positive and microchimerism-negative recipients, respectively. The frequency of the patients who had acute rejection after renal transplantation was approximately 10% and 28% in microchimerism-positive and microchimerism-negative recipients, respectively. Serum creatinine levels in microchimerism-positive patients were significantly lower than those in microchimerism-negative patients.

CONCLUSION

These results suggest that plasma DNA microchimerism present in certain patients following renal transplantation and measurement of plasma DNA microchimerism using quantitative RT-PCR might be a useful predictor for the acceptance of transplanted kidneys.

The last 5 years of basic science investigation in transplant immunology

Many new insights have been gained over the past 5 years into the mechanisms that regulate immune reactivity to cell and organ transplants. This new knowledge is being applied to the development of innovative experimental strategies that may soon be evaluated in the clinic.

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.

Immune-privileged embryonic Swiss mouse STO and STO cell-derived progenitor cells: major histocompatibility complex and cell differentiation antigen expression patterns resemble those of human embryonic stem cell lines

Embryonic mouse STO (S, SIM; T, 6-thioguanine resistant; O, ouabain resistant) and 3(8)21-enhanced green fluorescent protein (EGFP) cell lines exhibit long-term survival and hepatic progenitor cell behaviour after xenogeneic engraftment in non-immunosuppressed inbred rats, and were previously designated major histocompatibility complex (MHC) class I- and class II-negative lines. To determine the molecular basis for undetectable MHC determinants, the expression and haplotype of H-2K, H-2D, H-2L and I-A proteins were reassessed by reverse transcriptase-polymerase chain reaction (RT-PCR), cDNA sequencing, RNA hybridization, immunoblotting, quantitative RT-PCR (QPCR), immunocytochemistry and flow cytometry. To detect cell differentiation (CD) surface antigens characteristic of stem cells, apoptotic regulation or adaptive immunity that might facilitate progenitor cell status or immune privilege, flow cytometry was also used to screen untreated and cytokine [interferon (IFN)-gamma]-treated cultures. Despite prior PCR genotyping analyses suggestive of H-2q haplotypes in STO, 3(8)21-EGFP and parental 3(8)21 cells, all three lines expressed H-2K cDNA sequences identical to those of d-haplotype BALB/c mice, as well as constitutive and cytokine-inducible H-2K(d) determinants. In contrast, apart from H-2L(d[LOW]) display in 3(8)21 cells, H-2Dd, H-2Ld and I-Ad determinants were undetectable. All three lines expressed constitutive and cytokine-inducible CD34; however, except for inducible CD117([LOW]) expression in 3(8)21 cells, no expression of CD45, CD117, CD62L, CD80, CD86, CD90.1 or CD95L/CD178 was observed. Constitutive and cytokine-inducible CD95([LOW]) expression was detected in STO and 3(8)21 cells, but not in 3(8)21-EGFP cells. MHC (class I(+[LOW])/class II-) and CD (CD34+/CD80-/CD86-/CD95L-) expression patterns in STO and STO cell-derived progenitor cells resemble patterns reported for human embryonic stem cell lines. Whether these patterns reflect associations with mechanisms that are regulatory of immune privilege or functional tissue-specific plasticity is unknown.

Antilymphoid antibody preconditioning and tacrolimus monotherapy for pediatric kidney transplantation

OBJECTIVE

Heavy post-transplant immunosuppression may contribute to long-term immunosuppression dependence by subverting tolerogenic mechanisms; thus, we sought to determine if this undesirable consequence could be mitigated by pretransplant lymphoid depletion and minimalistic post-transplant monotherapy.

STUDY DESIGN

Lymphoid depletion in 17 unselected pediatric recipients of live (n = 14) or deceased donor kidneys (n = 3) was accomplished with antithymocyte globulin (ATG) (n = 8) or alemtuzumab (n = 9). Tacrolimus was begun post-transplantation with subsequent lengthening of intervals between doses (spaced weaning). Maintenance immunosuppression, morbidity, graft function, and patient/graft survival were collated.

RESULTS

Steroids were added temporarily to treat rejection in two patients (both ATG subgroup) or to treat hemolytic anemia in two others. After 16 to 31 months (mean 22), patient and graft survival was 100% and 94%, respectively. The only graft loss was in a nonweaned noncompliant recipient. In the other 16, serum creatinine was 0.85 +/- 0.35 mg/dL and creatinine clearance was 90.8 +/- 22.1 mL/1.73 m2. All 16 patients are on monotherapy (15 tacrolimus, one sirolimus), and 14 receive every other day or 3 times per week doses. There were no wound or other infections. Two patients developed insulin-dependent diabetes.

CONCLUSION

The strategy of lymphoid depletion and minimum post-transplant immunosuppression appears safe and effective for pediatric kidney recipients.

Soluble HLA-G in heart transplantation: their relationship to rejection episodes and immunosuppressive therapy

The aims of this study were to quantify the level of soluble HLA-G in heart transplant patients, to determine the relationship between the sHLA-G levels and the appearance of acute rejection episodes, and to identify the influence of immunosuppressive therapy on sHLA-G levels. Analysis of sHLA-G, measured by enzyme-linked immunosorbent assay in the transplant patients, revealed the existence of two similarly sized groups of patients. One group displayed a significant increase (p < 0.001) in sHLA-G during the first month after transplantation while the other group maintained low levels of the molecule (0-30 ng/ml) throughout the study. The latter group displayed a high incidence of recurrent severe rejection. A significant increase (p < 0.01) in sHLA-G 2 hours after administration of immunosuppressive treatment (mycophenolate mofetil, cyclosporine A/FK506, corticoids) was found. These results suggest that sHLA-G participates in the induction of certain levels of immunological tolerance in these recipients.

Frequency of Recipient-Derived Chimerism and Relationship With Acute Rejection and HLA Tissue Typing in Transplanted Livers

BACKGROUND

We sought to determine the extent and time course of recipient-derived chimerism after transplantation and the relationship with acute rejection episodes (ARE) and HLA typing in hepatic allograft patients.

PATIENTS AND METHODS

We studied 18 needle liver biopsy specimens from patients who had undergone orthotopic liver transplantation. Fluorescent in situ hybridization (FISH) analysis for X and Y chromosomes was performed in all cases with a sex mismatch. To evaluate the HLA matching, we used serological and polymerase chain reaction (PCR) methodology.

RESULTS

There was a sex mismatch between the recipients and donors in all cases. X and Y chromosome chimerism was detected in 14 of 18 (83%; 31.14 +/- 27.4) patients. Also, no statistical association was found between the presence and the extent of chimerism and clinicopathological parameters (P < .05).

CONCLUSIONS

Our results suggest that chimerism was frequently seen in liver allografts, but it did not influence the occurrence of ARE, tissue compatibility, or histopathological changes in the posttransplantation period. The clinical, immunological, and histopathological relevance of chimerism remain unclear. These results may relate to the small number of patients and disproportion of chimerism-positive versus-negative cases. Further prospective studies will be required to clarify these findings in a larger population of liver transplant patients.

Complete differentiation of CD8+ T cells activated locally within the transplanted liver

The transplanted liver elicits systemic tolerance, and the underlying mechanism may also account for the persistence of liver infections, such as malaria and viral hepatitis. These phenomena have led to the hypothesis that antigen presentation within the liver is abortive, leading to T cell tolerance or apoptosis. Here we test this hypothesis in an optimized orthotopic liver transplantation model. In direct contradiction to this model, the liver itself induces full CD8+ T cell activation and differentiation. The effects of microchimerism were neutralized by bone marrow transplantation in the liver donor, and the lack of liver-derived antigen-presenting cells was documented by eight-color flow cytometry and by sensitive functional assays. We conclude that local antigen presentation cannot explain liver tolerance. On the contrary, the liver may be an excellent priming site for naive CD8+ T cells.

Microchimerism and Skin Disease: True-True Unrelated?

Microchimerism, the stable presence of foreign cells in an individual, may result from trafficking during pregnancy or from organ or hematopoietic transplantation, and has been hypothesized to cause autoimmunity and certain skin diseases. Yet microchimeric cells are found in normal individuals and may be important to tissue repair. Thus microchimerism may be common, and finding microchimeric cells in diseased as well as normal tissue may be a "true-true unrelated" situation.

Microchimerism maintains deletion of the donor cell-specific CD8+ T cell repertoire

Rare cases of stable allograft acceptance after discontinuation of immunosuppression are often accompanied by macrochimerism (> 1% donor cells in blood) or microchimerism (< 1% donor cells in blood). Here, we have investigated whether persistence of donor cells is the cause or the consequence of long-lasting CTL unresponsiveness. We found that engraftment of splenocytes bearing a single foreign MHC class I-restricted epitope resulted in lifelong donor cell microchimerism and specific CTL unresponsiveness. This status was reversed in a strictly time- and thymus-dependent fashion when the engrafted cells were experimentally removed. The results presented herein show that microchimerism actively maintains CTL unresponsiveness toward a minor histocompatibility antigen by deleting the specific repertoire and thus excluding dominant, T cell extrinsic mechanisms of CTL unresponsiveness independent of systemically persisting donor cell antigen.

Prognostic assays for rejection and tolerance in organ transplantation

In this review, I have summarised our understanding of acute rejection of organ transplants, and for convenience I have identified three processes, recognition, rejection and regulation. In stark contrast to this text-book picture of acute rejection, I have drawn attention to some of the clinical realities, where processes are altered by powerful immunosuppressive drugs, and where many transplant recipients are pre-sensitised to transplantation antigens prior to engraftment. The ultimate goal is to encourage the emergence of a utopian immunological state, wherein patients tolerate organ transplants for life after being weaned from all immunosuppressive drugs. Assays that may be used in the future to reliably monitor this process are still at a very exciting stage of development.

Progress in heart transplantation

The field of heart transplantation was built upon the discoveries of immunity and tolerance by Landsteiner, Medawar, Burnet, and others, as well as technical advancements in surgical technique by Carrel. Since the first successful human heart transplant performed by Christiaan Barnard in 1967, there has been substantial progress in the field of heart transplantation, especially over the last several decades. With advances in immunosuppression and surgical techniques, the rates of acute rejection and infection leading to graft failure have declined. However, the detection of acute and chronic allograft rejection remains one of the most important yet unsettled matters. As such, many new horizons exist for further advancement of the field of heart transplantation and for improving the outcomes of the patients we serve.

Color-engineered rats and luminescent LacZ imaging: a new platform to visualize biological processes

The rat represents an excellent mammalian model for broadening medical knowledge, and a wealth of information on its physiology has been obtained from its use as an experimental organism. Furthermore, its ample body size allows various surgical manipulations that cannot be performed on a mouse. Many rat models mimic human diseases and have therefore been used in a variety of biomedical studies, including physiology, pharmacology, and transplantation. In an effort to create specifically designed rats for new biomedical research and the field of regenerative medicine, we develop an engineered rat system on the basis of transgenic technology and succeed in establishing unique rats that possess genetically encoded color probes: green fluorescent protein (GFP), DsRed2 (red liver), Cre/LoxP (red to green), and LacZ (blue and luminescence). In this work, we highlight their characteristics and describe recent applications for tissue engineering and regeneration. Coupled with recent progress in modern imaging systems, these transgenic rats are providing powerful tools for the elucidation of many cellular processes in biomedical science, and may lead to innovative medical treatments.