Peripheral blood microchimerism in human liver and renal transplant recipients: rejection despite donor-specific chimerism

The Immunological Basis of Liver Allograft Rejection

Liver allograft rejection remains a significant cause of morbidity and graft failure in liver transplant recipients. Rejection is caused by the recognition of non-self donor alloantigens by recipient T-cells. Antigen recognition results in proliferation and activation of T-cells in lymphoid tissue before migration to the allograft. Activated T-cells have a variety of effector mechanisms including direct T-cell mediated damage to bile ducts, endothelium and hepatocytes and indirect effects through cytokine production and recruitment of tissue-destructive inflammatory cells. These effects explain the histological appearances of typical acute T-cell mediated rejection. In addition, donor specific antibodies, most typically against HLA antigens, may give rise to antibody-mediated rejection causing damage to the allograft primarily through endothelial injury. However, as an immune-privileged site there are several mechanisms in the liver capable of overcoming rejection and promoting tolerance to the graft, particularly in the context of recruitment of regulatory T-cells and promotors of an immunosuppressive environment. Indeed, around 20% of transplant recipients can be successfully weaned from immunosuppression. Hence, the host immunological response to the liver allograft is best regarded as a balance between rejection-promoting and tolerance-promoting factors. Understanding this balance provides insight into potential mechanisms for novel anti-rejection therapies.

Naturally acquired microchimerism: implications for transplantation outcome and novel methodologies for detection

Microchimerism represents a condition where one individual harbors genetically distinct cell populations, and the chimeric population constitutes <1% of the total number of cells. The most common natural source of microchimerism is pregnancy. The reciprocal cell exchange between a mother and her child often leads to the stable engraftment of hematopoietic and non-hematopoietic stem cells in both parties. Interaction between cells from the mother and those from the child may result in maternal immune cells becoming sensitized to inherited paternal alloantigens of the child, which are not expressed by the mother herself. Vice versa, immune cells of the child may become sensitized toward the non-inherited maternal alloantigens of the mother. The extent of microchimerism, its anatomical location, and the sensitivity of the techniques used for detecting its presence collectively determine whether microchimerism can be detected in an individual. In this review, we focus on the clinical consequences of microchimerism in solid organ and hematopoietic stem cell transplantation, and propose concepts derived from data of epidemiologic studies. Next, we elaborate on the latest molecular methodology, including digital PCR, for determining in a reliable and sensitive way the extent of microchimerism. For the first time, tools have become available to isolate viable chimeric cells from a host background, so that the challenges of establishing the biologic mechanisms and function of these cells may finally be tackled.

Effect of reverse chimerism on rejection in clinical transplantation

Chimerism may enable allografts to survive when immunosuppressive therapy is administered at low levels or is even absent. Reverse chimerism (RC) is focused on intragraft chimerism that repopulates the allograft with cells of recipient origin. We aimed to identify and analyze current clinical evidence on RC and the presence of endothelial RC and tissue-specific RC. A total of 33 clinical reports on cardiac, kidney, liver, and lung transplants published between 1972 and 2012 that focused on RC were included in a systematic review. Liver allografts presented with the highest percentage of endothelial RC and lung allografts by far the lowest. Tissue-specific RC was present in most of the recipients, but at very low levels. There were also cardiac and kidney allografts with chimerism, but the functionality of the cells of recipient origin was questionable. We were unable to determine whether RC was a trigger for or a result of acute rejection. Further clinical research should focus on outcomes to evaluate the clinical relevance of this form of chimerism in transplantation.

Beneficial effects of pretransplantation microchimerism on rejection-free survival in HLA-haploidentical family donor renal transplantation

BACKGROUND

Fetal-maternal microchimerism (MC) can develop during pregnancy and may persist for decades. Pretransplantation fetal-maternal MC may be present between mother and child and between siblings; however, its effect on renal transplantation is not known. We investigated the effects of pretransplantation MC on allograft outcomes in human leukocyte antigen (HLA)-haploidentical family donor transplantation.

METHODS

A total of 106 cases transplanted from 1996 to 2004 were retrospectively studied, with median follow-up of 96 months. The study and control groups included 63 and 43 cases of HLA-haploidentical and HLA-identical donor transplantations, respectively. MC against mismatched donor HLA-DRB1 allele was detected in the recipient's peripheral blood using nested polymerase chain reaction-single-strand conformation polymorphism method. The allograft outcomes of HLA-haploidentical MC (+) and (-) subgroups were compared with those of HLA-identical group.

RESULTS

Pretransplantation MC in the HLA-haploidentical recipients was detected in 22.2% (14 of 63). Compared with HLA-identical group, MC (-) subgroup showed significantly inferior allograft outcomes: higher acute rejection rate (11.6% vs. 42.9%; P=0.001), higher 5-year serum creatinine level (1.1 vs. 1.4 mg/dL; P=0.009), and lower 10-year rejection-free survival rate (83.7% vs. 54.5%; log-rank P=0.001). In contrast, MC (+) subgroup showed no significant differences from HLA-identical group in acute rejection rate (14.3%), 5-year serum creatinine level (1.1 mg/dL), and 10-year rejection-free survival rate (85.7%). Multivariate analysis revealed that pretransplantation MC is associated with a significantly lower risk of acute rejection (odds ratio=0.10; P=0.021).

CONCLUSION

Pretransplantation MC present in the recipient may have beneficial effects on rejection-free allograft survival in renal transplantation.

Mixed chimerism and split tolerance: mechanisms and clinical correlations

Establishing hematopoietic mixed chimerism can lead to donor-specific tolerance to transplanted organs and may eliminate the need for long-term immunosuppressive therapy, while also preventing chronic rejection. In this review, we discuss central and peripheral mechanisms of chimerism induced tolerance. However, even in the long-lasting presence of a donor organ or donor hematopoietic cells, some allogeneic tissues from the same donor can be rejected; a phenomenon known as split tolerance. With the current goal of creating mixed chimeras using clinically feasible amounts of donor bone marrow and with minimal conditioning, split tolerance may become more prevalent and its mechanisms need to be explored. Some predisposing factors that may increase the likelihood of split tolerance are immunogenicity of the graft, certain donor-recipient combinations, prior sensitization, location and type of graft and minimal conditioning chimerism induction protocols. Additionally, split tolerance may occur due to a differential susceptibility of various types of tissues to rejection. The mechanisms involved in a tissue's differential susceptibility to rejection include the presence of polymorphic tissue-specific antigens and variable sensitivity to indirect pathway effector mechanisms. Finally, we review the clinical attempts at allograft tolerance through the induction of chimerism; studies that are revealing the complex relationship between chimerism and tolerance. This relationship often displays split tolerance, and further research into its mechanisms is warranted.

Quantitative real-time ARMS-qPCR for mitochondrial DNA enables accurate detection of microchimerism in renal transplant recipients

The presence of microchimerism in peripheral blood of solid organ transplant recipients has been postulated to be beneficial for allograft acceptance. Kinetics of donor cell trafficking and accumulation in pediatric allograft recipients are largely unknown. In this study, we implemented SNPs of the HVRs I and II of mitochondrial DNA to serve as molecular genetic markers to detect donor-specific cell chimerism after pediatric renal transplantation. Serial dilution of artificial chimeric DNA samples showed a linear correlation coefficient of R > 0.98 and a detection sensitivity of 0.01% with high reproducibility. Longitudinal semiquantitative analysis of donor-specific SNPs was then performed in peripheral blood mononuclear cells samples up to two yr post-transplant. Quantity of donor-specific cell chimerism in peripheral blood was highest in the early post-transplant period reaching values of ~10% after liver-kidney and 2.8% after renal transplantation. From one wk after transplantation, renal transplant patients exhibited an amount of donor-specific mtDNA ranging from 0.01% to 0.1%. We developed a highly accurate, sensitive, and rapid real-time quantitative PCR method using sequence-specific primers and fluorescent hydrolysis probes for the detection of at least 0.01% donor-specific cells in the recipient's peripheral blood after renal transplantation.

Microchimerism in promoting graft acceptance in clinical transplantation

PURPOSE OF REVIEW

Infusions of bone marrow-derived cells together with 'space making' continue to be tested in clinical organ transplant tolerance protocols. These trials are based on the hypothesis that this might produce initial multilineage chimerism. There is some evidence that this in turn induces regulatory cells that control alloimmunity. Although a wealth of knowledge is available from animal models, this review deals with what we know or can speculate about donor bone marrow cells and chimerism in human organ transplantation.

RECENT FINDINGS

Calcineurin inhibitors are employed in most of these protocols to blunt the initial immune response. One protocol also has a stepwise regulatory cell generating treatment with sirolimus before total withdrawal. A number of donor chimeric lineages including stem cells, dendritic cells, myeloid precursors, and various lymphoid subpopulations have been described. Currently, it is recognized that the nature of cells that make up the chimerism could influence graft rejection versus acceptance. Tolerogenic donor chimeric cells may also generate regulatory subsets, thus controlling alloimmunity on two fronts.

SUMMARY

It might be speculated that prolonged and sustained regulation or possible anergy induced by chimerism may eventually lead to clonal deletion, thereby bringing about classical immunologic tolerance.

HLA-targeted flow cytometric sorting of blood cells allows separation of pure and viable microchimeric cell populations

Microchimerism is defined by the presence of low levels of nonhost cells in a person. We developed a reliable method for separating viable microchimeric cells from the host environment. For flow cytometric cell sorting, HLA antigens were targeted with human monoclonal HLA antibodies (mAbs). Optimal separation of microchimeric cells (present at a proportion as low as 0.01% in artificial mixtures) was obtained with 2 different HLA mAbs, one targeting the chimeric cells and the other the background cells. To verify purity of separated cell populations, flow-sorted fractions of 1000 cells were processed for DNA analysis by HLA-allele-specific and Y-chromosome-directed real-time quantitative PCR assays. After sorting, PCR signals of chimeric DNA markers in the positive fractions were significantly enhanced compared with those in the presort samples, and they were similar to those in 100% chimeric control samples. Next, we demonstrate applicability of HLA-targeted FACS sorting after pregnancy by separating chimeric maternal cells from child umbilical cord mononuclear cells. Targeting allelic differences with anti-HLA mAbs with FACS sorting allows maximal enrichment of viable microchimeric cells from a background cell population. The current methodology enables reliable microchimeric cell detection and separation in clinical specimens.

Should microchimerism turn into rejection prophylactics?

Non-self cells can circulate in the body of an individual after any sort of contact with an allogeneic source of cells, thus creating a situation of chimerism that can be transient or prolonged over time. This situation may appear after stem cell transplantation, pregnancy, transfusion or transplantation. Concerning transplantation, many hypotheses have been formulated regarding the existence, persistence and role of these circulating cells in the host. We will review the principal hypotheses that have been formulated for years since the first description of non-self circulating cells in mammals to the utilization of artificially induced chimerism protocols for the achievement of tolerance.

The combined organ effect: protection against rejection?

OBJECTIVES

To further our understanding of the potential protective effects of one organ allograft for another in combined organ transplants by comparing rejection-free survival and the 1-year rejection rate of each type of combined organ transplant.

SUMMARY BACKGROUND DATA

Liver allografts have been thought to be immunoprotective of other donor-specific allografts. Recent observations have extended this property to other organs.

METHODS

Analysis of data from the United Network of Organ Sharing included recipients 18 years or older (except those receiving intestinal transplants) transplanted between January 1, 1994, and October 6, 2005, and excluded those with a previous transplant (n = 45,306), live-donor transplant (n = 80,850), or insufficient follow-up (n = 4304). Patients were followed from transplant until death (n = 41,524), retransplantation (n = 4649), or last follow-up (n = 87,243).

RESULTS

A total of 133,416 patients were analyzed. Rejection rates for allografts co-transplanted with donor-specific primary liver, kidney, and heart allografts are significantly lower than rejection rates for allografts transplanted alone. Allografts accompanying primary intestinal or pancreatic allografts did not have reduced rejection rates. A decreased rate of rejection was seen in interval kidney-heart transplants when allografts shared partial antigenic identity. Decreased rates of rejection were also seen in transplants of 2 donor-specific organs of the same type.

CONCLUSIONS

In combined simultaneous transplants, heart, liver, and kidney allografts are themselves protected and protect the other organ from rejection. Analysis of interval heart-kidney allografts suggests the need for partial antigenic identity between organs for the immunoprotection to take effect. This was not demonstrated in interval liver-kidney transplants. Increased antigen load of identical antigens, as seen in double-lung and double-kidney transplants, also offers immunologic protection against rejection.

Evaluation of the tolerogenic effects of donor bone marrow cells using a severe combined immunodeficient mouse-human islet transplant model

The immunoregulatory role of human donor bone marrow cells (DBMC) has been studied extensively in our laboratory using in vitro and ex vivo assays. However, new experimental systems that can overcome the limitations of tissue culture assays but with more clinical relevance than purely animal experimentation, needed to be generated. Therefore we have developed a new human peripheral blood lymphocyte (PBL) severe combined immunodeficient (SCID) mouse islet transplantation model without the occurrence of graft-versus-host disease (GvHD) and have used it to evaluate the tolerogenic effects of DBMC. Nonobese diabetogenic (NOD)-SCID mice were transplanted with human deceased donor islets and were reconstituted with human PBL (allogeneic to islets; denoted as recipient) with or without DBMC from the islet donor. It was observed that the most cellularly economical dose was 3000 islets per animal and that injection into the portal vein was better than implantation under the kidney capsule. Even though maximal lymphoid reconstitution was observed with 40-million fresh and anti-CD3 activated recipient PBL (conventional method), the mice developed severe graft GvHD. However, with the new method of reconstitution where animals were injected with 20-million anti-CD3-activated plus 40-million anti-donor-activated recipient PBL, no discernible GvHD was observed. More importantly, this latter method was associated with islet transplant rejection, which in turn could be abrogated by co-injection of the animals with DBMC. These in vivo results confirmed our previous in vitro observations that human DBMC have regulatory activity.

PCR-based methodology for molecular microchimerism detection and quantification

Peripheral blood microchimerism after pregnancy or solid organ transplantation has been widely studied, but a consensus on its detection has not yet been adopted. The objective of this study was to establish a panel of reproducible molecular polymerase chain reaction (PCR)-based methods for detection and quantification of foreign cells in an individual. We analyzed length polymorphisms generated by short tandem repeat (STR) and variable number tandem repeat (VNTR) markers. Human leukocyte antigen (HLA)-A and -B polymorphisms were detected by reference strand conformation analysis (RSCA). Class II polymorphisms on HLA-DRB1 locus were analyzed both by classical PCR-sequence-specific primers (SSP) and by quantitative PCR (Q-PCR). Also, sex-determining region-y gene (SRY) gene allowed specific male donor discrimination and quantification by Q-PCR in female recipients. Binomial statistical distribution analysis was used for each molecular technique to determine the number of PCR replicates of each sample. This analysis allowed the detection of the lowest detectable microchimerism level, when present. We could detect microchimerism in more than 96% and more than 86% of cases at levels as low as 1:10(5) and 1:10(6) donor per recipient cells (DPRC), respectively, using Q-PCR for SRY or for nonshared HLA-DRB1 alleles. These techniques allowed as low as 1 genome-equivalent cell detection. Lower levels (nanochimerism) could be detected but not quantified because of technique limitations. However, classical PCR methods allowed detection down to 1:10(4) DPRC for HLA-DRB1 PCR-SSP. The clinical application of these techniques in solid organ transplanted recipients showed microchimerism levels ranging from 1:10(4) to 1:10(6) DPRC after kidney or heart transplantation, and 1 log higher (1:10(3) to 1:10(6) DPRC) after liver transplantation. In conclusion, the standardization of molecular microchimerism detection techniques will allow for comparable interpretation of results in microchimerism detection for diagnostic or research studies.

Chimerism and tolerance in a recipient of a deceased-donor liver transplant

Complete hematopoietic chimerism and tolerance of a liver allograft from a deceased male donor developed in a 9-year-old girl, with no evidence of graft-versus-host disease 17 months after transplantation. The tolerance was preceded by a period of severe hemolysis, reflecting partial chimerism that was refractory to standard therapies. The hemolysis resolved after the gradual withdrawal of all immunosuppressive therapy.

Chimerism and bone marrow based therapies in transplantation

Composite tissue allotransplantation holds a great potential for providing increased knowledge of anatomy and microsurgical experience for life-enhancing reconstructions. Many transplant cases around the world have made this a clinical reality at the present time. Composite tissue allotransplants contain multiple tissue types, including bone, muscle, vessels, nerves, skin, and immune cells and bear a huge antigenic load. Although immunosuppressive drugs are applied successfully to prevent allograft rejection, their side effects pose a barrier to worldwide use. Bone marrow therapy in many tolerance induction protocols, therefore, provides a guide to reaching the target of permanent immunotolerance. Multiple studies suggest that bone marrow is immunomodulatory and may facilitate allograft acceptance. In this review, bone marrow based therapy protocols of clinical and experimental models are presented in two major categories: solid organ and composite tissue transplantation.

Outcomes 18 months after the first human partial face transplantation

BACKGROUND

We performed the first human partial face allograft on November 27, 2005. Here we report outcomes up to 18 months after transplantation.

METHODS

The postsurgical induction immunosuppression protocol included thymoglobulins combined with tacrolimus, mycophenolate mofetil, and prednisone. Donor hematopoietic stem cells were infused on postoperative days 4 and 11. Sequential biopsy specimens were taken from a sentinel skin graft, the facial skin, and the oral mucosa. Functional progress was assessed by tests of sensory and motor function performed monthly. Psychological support was provided before and after transplantation.

RESULTS

Sensitivity to light touch, as assessed with the use of static monofilaments, and sensitivity to heat and cold had returned to normal at 6 months after transplantation. Motor recovery was slower, and labial contact allowing complete mouth closure was achieved at 10 months. Psychological acceptance of the graft progressed as function improved. Rejection episodes occurred on days 18 and 214 after transplantation and were reversed. A decrease in inulin clearance led to a change in immunosuppressive regimen from tacrolimus to sirolimus at 14 months. Extracorporeal photochemotherapy was introduced at 10 months to prevent recurrence of rejection. There have been no subsequent rejection episodes. At 18 months, the patient is satisfied with the aesthetic result.

CONCLUSIONS

In this patient who underwent the first partial face transplantation, the functional and aesthetic results 18 months after transplantation are satisfactory.

Immunologic approaches to composite tissue allograft

This article discusses the immunologic principles and the most promising immunologic approaches for composite tissue allograft tolerance. We have previously reviewed some of the pharmacologic approaches for composite tissue allo-transplantation. In this review, we will summarize the range of options that may address the challenge of transplantation in reconstructive surgery.

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.

The difficulty of eliminating donor leukocyte microchimerism in rat recipients bearing established organ allografts

BACKGROUND

Unequivocal eradication of donor leukocyte microchimerism from recipients of long-surviving organ transplants has never been reported. Here we describe a drastic attempt to accomplish this objective.

METHODS

In control experiments, a rank order of microchimerism and of associated donor specific nonreactivity was produced in Brown-Norway (BN) rats by transplantation of Lewis (LEW) liver, bone marrow cell (BMC) and heart allografts under a brief course of tacrolimus. The degree of microchimerism at 60 and 110 days was estimated with semiquanitative immunocytochemical and PCR techniques. Tolerance at 110 days was assessed in the different control groups by challenge transplantation of naïve LEW hearts. In parallel experimental groups, an attempt was made to eliminate microchimerism from the BN recipients. The animals were submitted at 60 days to 9.5-Gy total body irradiation (TBI), reconstituted immediately with naïve BN BMC, and tested for donor specific nonreactivity by LEW heart transplantation at 110 days.

RESULTS

After the TBI-reconstitution at 60 days, microchimerism was undetectable in BMC recipients at 110 days, significantly reduced in heart recipients, and least affected in liver recipients. Except in liver recipients, abrogation of LEW-specific nonreactivity was demonstrated by rejection of the priming grafts, or by rejection of the challenge heart grafts, and by in vitro immune assay.

CONCLUSIONS

It is difficult to eliminate microchimerism in organ recipients once the donor cells have settled into tissue niches.

Stem cells and cancer: Evidence for bone marrow stem cells in epithelial cancers

Cancer commonly arises at the sites of chronic inflammation and infection. Although this association has long been recognized, the reason has remained unclear. Within the gastrointestinal tract, there are many examples of inflammatory conditions associated with cancer, and these include reflux disease and Barrett’s adenocarcinoma of the esophagus, Helicobacter infection and gastric cancer, inflammatory bowel disease and colorectal cancer and viral hepatitis leading to hepatocellular carcinoma. There are several mechanisms by which chronic inflammation has been postulated to lead to cancer which includes enhanced proliferation in an endless attempt to heal damage, the presence of a persistent inflammatory environment creating a pro-carcinogenic environment and more recently a role for engraftment of circulating marrow-derived stem cells which may contribute to the stromal components of the tumor as well as the tumor mass itself. Here we review the recent advances in our understanding of the contributions of circulating bone marrow-derived stem cells to the formation of tumors in animal models as well as in human beings.

Bone marrow-induced tolerance in the era of pancreas and islets transplantation

Enormous progress has been made in the field of solid organ adaptation recently because of the improvement in immunosuppression. Although powerful immunosuppressive drugs decrease the rate of acute rejection significantly, the long-term functional graft survival and tolerance induction remains poor. Chronic rejection is the main cause of graft failure. An electronic search was performed for articles on chimerism, tolerance, and immunologic perspectives of islet and pancreas transplantation along with referrals to our experience. Infusion of donor bone marrow-derived cells to create a chimeric state continue to be tested in clinical protocols intended to induce specific immunologic tolerance. The proposed mechanisms of immunologic engagement and the emergence of a tolerant state through mixed chimerism include central depletion of alloreactive cells, induction of T-cell anergy, and generation of suppressor cells by interactions between donor and host cells. In this setting, depletion of recipient T cells by different strategies and subsequent repopulation by donor hematopoietic cells after donor bone marrow infusion are prerequisites for tolerance induction. Many efforts have aimed to establish mixed chimerism along with tolerance in solid organ transplantation including pancreas and islets to facilitate engraftment. A review of the more important advances in the field and the future prospects combined with our experience to induce tolerance in the clinic and the laboratory is presented in this article.

Bone marrow cells as the origin of stomach cancer

Cells derived from bone marrow are pluripotent, with the ability to differentiate into multiple cell types. Environmental cues dictate differentiation decisions. It should not be surprising then, that abnormal cell environments lead to abnormal differentiation of these cells, and in some cases, malignant transformation. Identifying a role for bone marrow-derived cells in the initiation and progression of cancer allows a dramatic change in the way in which cancer is viewed. Identifying the cell responsible for initiating a tumor offers the exciting possibility of specifically targeting unique aspects of these cells and altering signaling properties for more effective therapeutic approaches.

Influence des antigènes de groupes sanguins en transplantation

Blood group antigens seem to be implied in the mechanisms of tissue and cell rejection. All erythrocyte blood groups are not only demonstrated on red cells. Some of them can be observed on several tissues of the body, particularly antigens of ABO, Hh, Lewis and I(i) systems... These ubiquitory antigens, called "histo-antigens" are developed very early at the various embryofetal stages depending on the tissues. The ABO system plays a fundamental role in graft and transplant. If the ABO compatibility is fundamental for the prognosis of a kidney, liver and heart transplantation, it has only a minor effect on the marrow, bone or cornea transplantation. The physiopathologic mechanisms are known, for the main points, and in connection with ABH antigens presence. Recent works show that systems RH, FY and JK could play a role in the process of graft rejection.

Skin carcinoma arising from donor cells in a kidney transplant recipient

The incidence of skin cancer is increased in transplant recipients. UV radiation, papillomaviruses, and immunosuppression participate in the pathogenesis of these tumors. In addition, donor cells may leave the grafted organ, reach peripheral tissues and either induce immune phenomena or possibly take part in tissue remodeling. Herein, we investigated the possible involvement of donor cells in the development of skin tumors in kidney allograft recipients. We analyzed a series of 48 malignant and benign cutaneous tumors developing in 14 females who had been grafted with a male kidney. The number of male cells was measured on microdissected material by quantitative PCR for Y chromosome. In the samples with high levels of male cells, fluorescent in situ hybridization (FISH) with X and Y probes and/or immuno-FISH with anticytokeratin antibodies were carried out. Male cells were detected in 5/15 squamous cell carcinomas and Bowen disease (range 4-180 copies), 3/5 basal cell carcinomas (91-645), 6/11 actinic keratosis (7-102), 2/4 keratoacanthoma (22-41), and 2/5 benign cutaneous lesions (14-55). In a basal cell carcinoma specimen with a high number of male cells, FISH showed that most cells within the tumoral buds were XY. In this lesion, immuno-FISH showed the presence of XY cytokeratin-positive cells indicating that the tumor nests contained male keratinocytes. In contrast, in other female transplants, male cells present in the tumors were not epithelial. In conclusion, stem cells originating from a grafted kidney may migrate to the skin, differentiate, or fuse as keratinocytes that could, rarely, undergo cancer transformation.

Donor bone marrow transplantation: chimerism and tolerance

Infusion of donor bone marrow (DBM)-derived cells continue to be tested in clinical protocols intended to induce specific immunologic tolerance. Central clonal deletion of donor-specific alloreactive cells associated with mixed chimerism reliably produced long-term graft tolerance. In this setting, depletion of recipient T cells by antilymphocyte antibodies and subsequent repopulation by donor hematopoietic cells after donor bone marrow infusion (DBMI) are prerequisites for tolerance induction. Major advances have been made in animal models and in pilot clinical trials and the key questions with the future perspectives are presented in this article.

Tolerance induction in clinical transplantation

Introduction of modern immunosuppressive agents has led to great success of allotransplantation in humans, and survival rates for all solid organs have been dramatically improved. However, a constant proportion of organs is lost every year due to chronic allograft rejection and immunosuppressive drug toxicity. This has led to a situation where, despite the of donor organ shortage, about one third of the patients on the kidney transplant waiting list are listed for a retransplant. The induction of donor-specific tolerance has the potential of at least partially resolving this problem, since it might prevent chronic rejection and drug toxicity at the same time. For a variety of protocols, successful tolerance induction has been demonstrated in rodent models. However, translation of such protocols to large animal models and on clinical trials has turned out to be very difficult. This review briefly describes mechanisms and barriers to transplantation tolerance, and then focuses on pre-clinical and clinical studies in non-human primates and humans. We have divided the strategies into two groups, based on the principle mechanisms of tolerance induction: the first group are protocols not using hematopoietic stem cell transplantation (HCT) as part of there regimen. They rely mainly on intensive T cell depletion (either by total body irradiation, total lymphoid irradiation or treatment with T cell-depleting agents such as anti-thymocyte globulin, anti-CD52 antibody or CD3 immunotoxin), which have been combined with costimulatory blockade, signaling blockade or donor antigen infusion. The second group are HCT-based protocols combining HCT with T cell-depleting agents and cytoreductive treatment. So far, only two protocols (one with total lymphoid irradiation and anti-thymocyte globulin, but no HCT; one with HCT, cyclophosphamide, anti-thymocyte globulin and thymic irradiation) have been translated into successful human studies. We summarize and discuss the results of these trials and suggest goals for further studies for the development tolerance protocols applicable for a broad population of allograft recipients.

The concept of “partial” clinical tolerance

The status of "partial" tolerance to organ allografts versus the status of complete tolerance is the main topic of this paper. Progress made in immunosuppression, particularly by use of various lymphocyte depleting agents for "induction therapy", seems to favor the subsequent development of T cells with suppressor/regulatory properties. The effective deletion of alloreactive T helper and cytotoxic cells in conjunction with the expansion of antigen-specific suppressor (CD8 + CD28 - FOXP3+) and regulatory (CD4 + CD25+ FOXP3+) T cells creates a milieu in which the graft is well tolerated under an "umbrella" of low dosage immunosuppression. The most effective induction treatment is Campath-1H, although ATGAM at high dosage is also widely used. Total lymphoid irradiation (TLI) is another very effective pretreatment strategy in spite of the risks which are associated with it. The induction of "partial" tolerance is a step in the right direction for exploring strategies that may lead to the induction of complete tolerance. It is safe for the patients and can prolong significantly the function of the graft, preventing the onset of chronic rejection.

Crossing the bridge: large animal models in translational transplantation research

Many methods for reducing the immunosuppressive requirements of allotransplantation have been proposed based on a growing understanding of physiological and allospecific immunity. As these regimens are developed for clinical application, they require validation in models that are reasonably predictive of their performance in humans. This article provides an overview of the large animal models commonly used to test immunomodulatory organ transplant protocols. The rationale for the use of large animals and the effects of common immunosuppressants in the dog, pig, and non-human primate are reviewed. Promising methods for the induction of allospecific tolerance are surveyed with references to early human trials where appropriate.

Immune responses and their regulation by donor bone marrow cells in clinical organ transplantation

Infusions of donor bone marrow derived cells (DBMC) continue to be tested in clinical protocols intended to induce specific immunologic tolerance of solid organ transplants based on the observations that donor-specific tolerance is induced this way in animal models. We studied the immunological effects of human DBMC infusions in renal transplantation using modifications in lymphoproliferation (MLR) and cytotoxicity (CML) assays. The salient observations and tentative conclusions are summarized in this review. Among many types of organs transplanted using DBMC at this center, it was found that the cadaver renal recipients (CAD) had significantly decreased chronic rejection and higher graft survival when compared to equivalent non-infused controls. DBMC infusion was also associated with a marginal and non-specific immune depression. It was also observed that the number of chimeric donor cells gradually increased in the iliac crest bone marrow compartment with a concomitant decrease in the peripheral blood and that the increase was more rapid in living-related donor (LRD)-kidney/DBMC recipients in spite of a lower number of DBMC infused (<25%) than in the CAD-kidney/DBMC group. In the LRD recipients with residual anti-donor responses, purified chimeric cells of either donor or recipient inhibited recipient immune responses to the donor significantly more strongly than the freshly obtained bone marrow from the specific donor or volunteer suggesting an active regulatory role for chimeric cells. A number of (non-chimeric) subpopulations of bone marrow cells including CD34(+) stem cells and the CD34(-) early progeny like CD38(+), CD2(+), CD5(+) and CD1(+) lymphoid cells as well as CD33(+) (but CD15(-)) myeloid cells down-regulated the MLR and CML responses of allogeneic PBMC stimulated with (autologous) donor spleen cells. These regulatory effects appeared to be refractory to the action of commonly used immunosuppressive drugs and occurred during the early phase of the immune response through cell-cell interactions. Most of these DBMC sub-populations had stimulatory capabilities, albeit markedly lower than donor spleen cells, but only through the indirect antigen presentation pathway. When co-cultured with allogeneic stimulators, purified CD34(+) cells were found to give rise both to CD3(-) TCRalphabeta(+), as well as CD3(+) TCRalphabeta(+) cells and, thereby, responded in MLR to allogeneic stimulation (but did not generate cytotoxic effector cells). Also, a number of DBMC subpopulations inhibited the CML and to a lesser extent the MLR, of autologous post-thymic responding T cells stimulated with allogeneic irradiated cells, mediated through soluble factors. Finally, non-chimeric DBMC also inhibited the proliferative and cytotoxic responses of autologous T cells to EBV antigens, inducing T suppressor cells, which in turn could inhibit autologous anti-EBV CTL generation and B cell anti-CMV antibody production. These studies all suggested a strong inhibitory property of a number of DBMC sub-populations in vitro and in vivo with the notion that they promote unresponsiveness.

Human donor bone marrow cells induce in vitro "suppressor T cells" that functionally suppress autologous B cells

We have reported a beneficial effect of donor vertebral body bone marrow cells (DBMC) infusions in cadaver renal allograft recipients in a 6-year follow-up, but with a transient increase in early (6 month) postoperative CMV infections and concomitant suppressed immunoglobulins (Ig) production. We also found that although there was no difference between the DBMC-infused and non-infused (control) groups in the development of donor-specific antibody, we now describe an additional difference seen in the percent reactive antibody (PRA) reactivity against a panel of HLA antigens that developed postoperatively. We hypothesize that (allogeneic) antigen presenting cells in the DBMC, systemically infused, caused the generation of recipient T suppressor (T4-suppressor) cells, thereby "inducing" a negative influence on B cell Ig production. We tested this notion in vitro by incubating PBL from CMV IgG positive laboratory volunteers with either (allogeneic) T-cell depleted DBMC or donor spleen cells (DSPC) from (the same) cadaver donors. After 7 days, the (responding) T cells were collected using magnetic beads and placed in culture with purified B cells freshly obtained from the same (autologous) CMV positive volunteer. To these cultures were added either media or 40 ng of CMV antigen. After 3, 5, 7, and 9 days, the expression of surface anti-CMV Ig was measured by flow cytometry using a panel of fluorescent markers double-labeled for activated B cells (CD20, CD19, and HLA DRw) and CMV-FITC. We also determined the phenotype of the cultured T cells using anti-CD3, CD4, and CD62L specific monoclonal antibodies. B cells that had been in contact with autologous T cells derived from DBMC cultures (TBM) were less likely to express anti-CMV surface Ig than those cultured with DSPC (TSP). The flow cytometry analysis revealed an increase in the number of T4 suppressor cells (CD3+, CD4+, CD62L+) in the TBM group, whereas the T4 helper phenotype (CD3+, CD4+, CD62L-) predominated in the TSP group. These in vitro findings support the notion that (allogeneic) DBMC infusions can induce a T4 suppressor (regulatory) influence and thereby indirectly affect B-cell function.

Outpatient allografting in hematologic malignancies and nonmalignant disorders--applying lessons learned in the canine model to humans

The novel allogeneic transplant approach outlined in this chapter proposes the dual concepts that currently used intensive cytoreductive conditioning programs can be successfully replaced by nonmyeloblative immunosuppression and that stem cell grafts create marrow space for engraftment through subclinical GVH reactions. Immunosuppression can be conceptually divided into two parts, one targeted exclusively towards host cells before transplantation, and the other aimed at both host and donor T lymphocytes after transplantation. The resultant effect is to either establish mutual graft-host tolerance as reflected by stable mixed donor-host chimerism or accomplish complete donor chimerism. Preclinical studies have demonstrated the feasibility of this new approach in the context of MHC-identical transplants in young canines. Early data from the dog model of severe hereditary hemolytic anemia suggest that mixed chimerism can partially correct the phenotypic expression of disease, but that complete chimerism will be necessary to halt the continued hemolytic process of the host type minority red blood cell population. In contrast, mixed chimerism would be expected to correct disease manifestations of other severe hereditary red blood cell disorders such as sickle cell disease. The early results in human patients with hematological malignancies have demonstrated the feasibility of establishing hematopoietic engraftment using a nonmyeloblative conditioning regimen. Using this regimen, transplants were performed in the outpatient setting, and the need for transfusion support was minimal. Preliminary information suggests that mixed chimerism does not appear to be stable in this older patient population, with most patients progressing to full donor chimerism and a small minority rejecting. Complete disease responses and molecular remissions have been observed in a significant proportion of patients, suggesting that adoptive immunotherapy may not be necessary in most cases. However, in those patients that engraft with at least mixed chimerism and develop progression of the underlying malignancy, DLIs can be used for subsequent adoptive immunotherapy. The feasibility and safety of the outpatient approach for MHC-nonidentical transplantation has been demonstrated. Graft rejection appears to have been corrected by the addition of fludarabine to the nonmyeloablative conditioning regimen for the recipients of HLA-identical sibling allografts. Despite most recipients of MHC-nonidentical transplantation having sustained engraftment, some rejections have been observed. Studies are ongoing to identify the risk factors for rejection after unrelated HSCT to ensure uniform engraftment in future studies.

Flow cytometric "rare event analysis": a standardized approach to the analysis of donor cell chimerism

Lack of standardization of methods and detection limits contributes to the controversial results regarding microchimerism after organ transplantation and has prompted the development of a standardized, reproducible, "easy-to-use" flow cytometric method for this type of "rare event analysis".EDTA-blood of healthy, HLA-typed donors was stained simultaneously with FITC- and biotin-labeled HLA-class I antibodies (One Lambda) as well as Cy5-PE-labeled CD45 (Medac, Hamburg) according to a standard protocol and analysed on a Coulter EPICS XL Flow cytometer (FCM). An absolute range of positivity (mean MESF+/- 1 STD) was determined for 22 HLA-specific antibodies. The range of positivity ranged between 5000 and 20,000 MESF (anti-A23, 24(9) FITC) and 40,000-140,000 (anti-Bw6 FITC). The frequency of nonspecific positive signals using nonstained cells, isotype-controls and irrelevant HLA antibodies was between 0.01% and about 0.5%, in some samples up to 1.4%, with an MESF between 8000 and 150,000, thus interfering clearly with the defined positive range of most antibodies tested. Using an "HLA antibody cocktail", combining FITC- and PE-labeled antibodies for different HLA specificities and thereby creating an internal control, the identification of donor cells was improved but was only rarely applicable. Due to the lack of highly reactive antibodies, FCM analysis was not suitable for the reliable identification of very low numbers of donor hematopoetic cells despite the theoretical advantages of flow cytometric detection of rare events. The single parameter approach was hampered by a significant frequency of nonspecific positive signals, which were easily mistaken as specific (true) positive signals, whereas the multiparameter approach could only be used in selected cases.

Mixed chimerism and transplantation tolerance

Achieving transplantation tolerance is an important goal in the effort to reduce long-term morbidity and mortality in organ transplant recipients. Robust, lifelong, donor-specific tolerance can be reliably achieved by induction of mixed chimerism in various animal models. To date, the clinical application of these proto-cols has been impeded partly by the potential toxicity of the required host conditioning regimens and the lack of successful studies in large animals. This article reviews the progress achieved in recent years in developing considerably milder conditioning protocols in rodents, and in extending some of these models to achieve permanent mixed chimerism and tolerance in large animals. Advances in the induction of xenogeneic tolerance through mixed chimerism are also discussed.

T cell mixed chimerism is significantly correlated to a decreased risk of acute graft-versus-host disease after allogeneic stem cell transplantation

BACKGROUND

It has been debated whether mixed chimerism (MC) is correlated to a decreased incidence of graft-versus-host disease (GVHD) after allogeneic stem cell transplantation (SCT).

METHODS

Between September 1996 and April 1999 we analyzed 102 patients for MC in the T-cell fraction post allogeneic SCT, using PCR amplification of variable numbers of tandem repeat (VNTR) loci. All samples, taken regularly post SCT, were cell separated using anti-CD3 immunomagnetic beads.

RESULTS

T-cell mixed chimerism was detected in 58 out of 102 patients (57%). Patient characteristics were comparable in the T-cell MC- and donor chimeric-group (DC). The median follow-up time for the MC group was 714 days (range 58 - 1248) as compared to 427 days (range 45 - 1042) for the DC group. Overall probability of acute GVHD grades II-IV was significantly higher in the DC group as compared to the MC group (52% vs. 5%, P<0.001). In multivariate analysis T-cell DC proved to be the most significant risk factor for acute GVHD grades II-IV. The cumulative incidence of relapse, among patients with malignant disease, did not show any statistical difference between the T-cell MC patients and the DC-group. There was a tendency for better overall survival in the T-cell MC group compared to the DC group (2 yrs; 73% vs. 54%, P=0.06). Among DC patients, 14/20 (70%) deaths were due to GVHD versus none in the MC-group(P<0.001).

CONCLUSION

T-cell mixed chimerism was significantly correlated to a decreased risk of moderate to severe acute GVHD and death by GVHD.

Analysis of alloreactivity and intragraft cytokine profiles in living donor liver transplant recipients with graft acceptance

Although some previous studies have indicated the possibility of immunosuppression withdrawal in clinical liver transplantation, the mechanism of graft acceptance is not clear. The aim of this study is to elucidate the alloreactivity against the donor and intragraft cytokine profiles in living donor liver transplant (LDLT) recipients with graft acceptance. In October 1999, we had 23 patients who survived without immunosuppression after LDLT with a median drug-free period of 25 months (range: 3-69 months). They consisted of six patients who were electively weaned by an elective weaning protocol and 17 either forcibly or accidentally weaned patients due to various causes but mainly due to infection. We evaluated the alloreactivity against the donor in these patients by a mixed lymphocyte reaction and intragraft cytokine profiles by real-time reverse transcriptase-polymerase chain reaction. The development of donor-specific hyporeactivity was observed in the patients with graft acceptance. The cytokine pattern in the supernatant of the culture medium revealed a down regulation of T helper (Th) 1 cytokine INF gamma against the donor while no significant difference was seen in Th2 cytokine IL-10. Regarding the intragraft cytokine profiles, we could find no amplification of Thl cytokines (IL-2, INF y) and IL-4 while some of the patients revealed a gene expression of IL-10 with no significant difference from that of the normal, untransplanted liver specimen. In addition, no difference was observed in any other cytokines (IL-1beta, IL-8, IL-15, TNFalpha) compared with those of the normal controls. We propose that the down regulation of Th1 cytokine is one possible mechanism of graft acceptance in LDLT recipients.

Donor bone marrow-derived chimeric cells present in renal transplant recipients infused with donor marrow. I. Potent regulators of recipient antidonor immune responses

BACKGROUND

Even though a number of transplant centers have adopted donor-specific bone marrow cell (DBMC) infusions to enhance donor cell chimerism, to date there has been no direct evidence linking chimerism with tolerance induction in human organ transplant recipients.

METHODS

Cells of donor phenotype were isolated 1 year postoperatively from the peripheral blood lymphocytes and iliac crest bone marrow of 11 living-related-donor (LRD) renal transplant recipients, who had received perioperative donor bone marrow cell infusions. These recipient-derived donor (RdD) cells were characterized phenotypically by flow cytometric analysis and functionally as modulators in mixed lymphocyte reaction (MLR) and cell-mediated lympholysis (CML) assays.

RESULTS

The yield of RdD cells ranged from 0.1 to O.9% of the starting material with the majority being TcRalphabeta, CD3 positive T cells, a substantial percentage of which coexpressed CD28. At 1 year posttransplant almost 50% of the LRD-kidney/DBMC recipients tested so far exhibited donor-specific unresponsiveness in MLR (7/17) and CML (6/13) reactions and this trend was further enhanced at 23 years. In the recipients with residual positive antidonor immune responses, the RdD cells inhibited recipient antidonor MLR and CML responses significantly more strongly than freshly isolated and similarly treated iliac crest bone marrow cells from the donor. RdD cells also inhibited the MLR of the recipient to third party allogeneic stimulator cells; however, this nonspecific effect was significantly weaker than specific inhibition. We also established long-term bone marrow cultures stimulated every 2 weeks with irradiated alogeneic feeder cells, that had similar functional properties thus possibly providing us with an in vitro correlate the RdD cells.

CONCLUSIONS

These results clearly support the notion that the infused donor cells play a positive role in the induction and/or maintenance of transplant tolerance.

Involvement of multiple subpopulations of human bone marrow cells in the regulation of allogeneic cellular immune responses

BACKGROUND

The identity of the cells in the human bone marrow that function as effective regulators of in vitro and possibly in vivo cellular immune responses is not well established.

METHODS

Cell subpopulations were isolated from cadaver donor vertebral-body bone marrow cells (DBMC) by using immuno-magnetic microbeads and were tested as inhibitors (modulators) in cell-mediated lympholysis (CML) and mixed lymphocyte reaction (MLR) responses of normal peripheral blood lymphocytes stimulated with irradiated cadaver donor spleen cells.

RESULTS

Compared with spleen cells as controls, un-irradiated T-cell depleted DBMC inhibited both the MLR and CML responses of allogeneic responder cells in a dose dependent manner (as in our previous reports). The inhibition was also mediated by a number of purified subpopulations including pluripotent CD34+ stem cells, and their CD34 negative early progeny of both lymphoid and myeloid lineages. These included DBMC enriched for non-T-cell lymphoid precursors (NT-LP/DBMC; i.e., DBMC depleted of CD3, CD15, and glycophorin-A positive cells) and DBMC positively selected for CD38+, CD2+, CD5+, and CD1+ lymphoid cells (all were depleted of CD3+ cells) as well as CD33+ (but CD15 negative) myeloid precursors. However, positively selected CD19+ B-cells and CD15+ myeloid cells did not inhibit the MLR and CML responses. The NT-LP/DBMC that had been repeatedly stimulated with irradiated allogeneic peripheral blood lymphocytes caused the strongest inhibition of the MLR and CML responses of the same allogeneic cells with 200 times fewer modulator cells needed than uncultured DBMC (P<0.001). Flow cytometric analysis revealed that majority of cells in these cell lines had become CD3+ TcR-alphabeta+ CD4+ and CD28+ cells.

CONCLUSION

A variety of less differentiated cells of various lineages residing in the human bone marrow are immunoregulatory in vitro. Among them, there is at least one subset that can undergo differentiation in vitro into regulatory T cells that can be maintained in long-term cultures.

Chimerism in peripheral blood of sensitized patients waiting for renal transplantation: clinical implications

BACKGROUND

Potential renal transplant recipients with preformed antibodies to HLA resulting from previous transplants, pregnancy, and/or transfusions are unlikely to receive an allograft. The factors contributing to the long-term maintenance of antibody titers in these individuals are still unknown. In the present study, we sought to determine whether chimerism in the blood correlates with maintenance of HLA sensitization in highly sensitized patients.

METHODS

Qualitative analysis of chimerism in blood of sensitized patients was assessed by polymerase chain reaction-sequence specific oligonucleotide probes (PCR-SSOP) to HLA-DR. PCR single-strand conformation polymorphism (PCR-SSCP) was used to confirm the extra HLA-DR antigens detected by PCR-SSOP.

RESULTS

Fourteen of 36 patients (38.9%) were positive for more than two HLA-DR indicative of chimerism. The presence of extra HLA-DR was confirmed by PCR-SSCP. When patients were analyzed on the basis of their panel-reactive antibody (PRA) status, 10 of 15 (66.7%) were positive for chimerism in the sensitized group, compared with only two of eight (25%) in the unsensitized group. Of the five males in the sensitized group who had received a blood transfusion but not a transplant, three were positive for chimerism. An association was observed between chimerism and maintenance of sensitization. None of the eight normal subjects studied demonstrated chimerism.

CONCLUSIONS

The results obtained with sensitized patients suggest an association between blood chimerism and maintenance of HLA sensitization. We speculate that chimerism may lead to long-term maintenance of anti-HLA antibody titers. This finding implies that abolition of chimerism could result in the eventual elimination of antigenic stimuli for antibody production against HLA antigens.