Cell migration and chimerism after whole-organ transplantation: the basis of graft acceptance

HLA and cross-reactive antigen group matching for cadaver kidney allocation

BACKGROUND

Allocation of cadaver kidneys by graded human leukocyte antigen (HLA) compatibility scoring arguably has had little effect on overall survival while prejudicing the transplant candidacy of African-American and other hard to match populations. Consequently, matching has been proposed of deduced amino acid residues of the individual HLA molecules shared by cross-reactive antigen groups (CREGs). We have examined the circumstances under which compatibility with either method impacted graft survival.

METHODS

Using Cox proportional hazards regression modeling, we studied the relationship between levels of conventional HLA mismatch and other donor and recipient factors on primary cadaver kidney survival between 1981 and 1995 at the University of Pittsburgh (n=1,780) and in the United Network for Organ Sharing (UNOS) Scientific Registry during 1991-1995 (n=31,291). The results were compared with those obtained by the matching of amino acid residues that identified CREG-compatible cases with as many as four (but not five and six) HLA mismatches.

RESULTS

With more than one HLA mismatch (> 85% of patients in both series), most of the survival advantage of a zero mismatch was lost. None of the HLA loci were "weak." In the UNOS (but not Pittsburgh) category of one-HLA mismatch (n=1334), a subgroup of CREG-matched recipients (35.3%) had better graft survival than the remaining 64.7%, who were CREG-mismatched. There was no advantage of a CREG match in the two- to four-HLA incompatibility tiers. Better graft survival with tacrolimus was observed in both the Pittsburgh and UNOS series.

CONCLUSIONS

Obligatory national sharing of cadaver kidneys is justifiable only for zero-HLA-mismatched kidneys. The potential value of CREG matching observed in the one-HLA-mismatched recipients of the UNOS (but not the Pittsburgh) experience deserves further study.

The lung as a source and a target organ for T- and B-lymphocytes

In lung transplantation, a substantial number of donor leukocytes are transferred from the donor to the recipient by the graft. Using a rat model, it was analyzed in this study to what extent leukocytes leave the lung, to which phenotype they belong, and to which organs they migrate. The model used was the orthotopic transplantation of the left lung of LEW.7B(RT7b) rats into LEW(RT7a) recipients. Lung allografts are not rejected in this strain combination, which differs only in the RT7 system, a genetic polymorphism of CD45. Using the RT7b marker (monoclonal antibody His41), the distribution of donor leukocytes passively transferred with the graft was studied by immunohistology 2 wk after transplantation. At this time, 2.9 +/- 0.1% (n = 6) of the peripheral blood leukocytes in the recipients were derived from the donor lung. The donor cell population detected in the blood consisted of T cells (59 +/- 4%), B cells (5.1 +/- 0.2%) and a surprisingly high fraction of natural killer (NK) cells (36 +/- 3%). No monocytes or granulocytes were found. In lymph nodes, spleen and thymus donor-derived T- and B-cells could be shown in typical T- and B-areas, respectively. Donor-derived leukocytes were found in the liver and the skin. In the tissue and the bronchoalveolar lavage (BAL) of the host lung, predominantly T cells were found. Furthermore, in the donor tissue and BAL more than 70% of T- and B-cells were host type, demonstrating that the donor lung had been repopulated to a great extent by host lymphocytes. This supports the relevance of BAL as a diagnostic tool in lung diseases. Thus, the lung is an immunologically important site, releasing lymphocytes which migrate to other organs and also attracting many lymphocytes from the circulation.

Serologic allogeneic chimerism

BACKGROUND

At least some transplanted livers secrete soluble human leukocyte antigens (sHLA) of donor phenotype into the body fluids of recipients. The individuals in whom this phenomenon occurs are by definition serologic allogeneic chimeras. Because an allogeneic transplanted liver may induce tolerance to itself and other organs in animals of the donor strain, and because maintenance of a soluble antigen in the circulation of any animal in sufficient quantity for a sufficient period generally leads to tolerance, this phenomenon may be biologically important. This study was performed to determine how common this phenomenon is and whether it occurs after transplantation of organs other than the liver.

METHODS

We studied 445 serum samples obtained from transplant recipients (liver, n=12; kidney, n=18; and heart, n=8) before and at various intervals after transplantation. All patients studied had allografts that had functioned for more than 1 year. We used an enzyme-linked immunosorbent assay to quantitate sHLA-A2 and sHLA-A1/A3/A11 (as a cross-reacting group). Donor and recipient combinations were selected in which measurable allotypes in donors were not present in recipients. In some instances, an additional allotype was present in a recipient but not in a donor.

RESULTS

All liver transplant recipients had detectable donor sHLA in their serum samples after transplantation. In 72% of kidney and 50% of heart transplant recipients, donor sHLA was found persistently in serum samples obtained after transplantation. Interestingly, all heart transplant recipients of HLA-A3, but none of HLA-A2, had detectable donor sHLA in their serum samples, a finding that may be due to technical reasons. High and stable serum concentrations of donor sHLA characterize long-term stable allograft function.

CONCLUSIONS

Donor sHLA is produced by all transplanted livers, most transplanted kidneys, and at least half of (but probably more) transplanted hearts. The hypothesis that donor sHLA may be tolerogenic to liver transplants can be expanded to include kidney and heart transplants.

Evidence for the presence of multilineage chimerism and progenitors of donor dendritic cells in the peripheral blood of bone marrow-augmented organ transplant recipients

We have postulated that the donor leukocyte microchimerism plays a seminal role in the acceptance of allografts by inducing and perpetuating variable degree of donor-specific nonreactivity in long-surviving organ recipients. Limited information is available, however, concerning the phenotype and function of these chimeric cells in humans. The unequivocal presence of donor dendritic cells (DCs), a prominent lineage in the microchimerism observed in rodents and clinical organ recipients, was difficult to demonstrate in bone marrow (BM)-augmented organ transplant recipients. This enigma was resolved by the recent description of a method for propagating circulating human DCs from their progenitors by culture in a medium enriched with granulocyte-macrophage colony-stimulating factor and interleukin 4, a condition known to inhibit outgrowth of monocytes, thus providing a selective growth advantage to committed progenitors of the myeloid lineage. Cells from BM-augmented organ recipients and normal control subjects harvested from 12- to 14-day cultures exhibited dendritic morphology and potent allostimulatory capacity. Using appropriate primers, the presence of donor DNA was verified by polymerase chain reaction within the lineage(null)/class II(bright) sorted DC. Phenotypic analysis of cultured DCs from BM-augmented patients, unlike that of controls, exhibited a marked down-regulation of B7-1 (CD80) while retaining normal levels of expression of B7-2 (CD86) cell surface molecules. The presence of donor DNA was also confirmed by polymerase chain reaction in individually sorted lineage+ (T, B, and NK) cells and macrophages, suggesting that the chimerism in BM-augmented patients is multilineage. The presence of progenitors of donor DCs in the peripheral blood of BM-augmented patients further substantiates the already convincing evidence of stem cell engraftment.

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

BACKGROUND

Development of donor-specific microchimerism (DSM) has been proposed as one of the possible mechanisms for induction and maintenance of allograft tolerance. The aim of this study was to determine: (1) the state of DSM in liver transplant (LTx) and renal transplant (RTx) recipients, (2) whether the persistent presence of an allograft is a requirement for maintenance of chimerism, and (3) whether donor-specific blood transfusions (DST) facilitate chimerism development in RTx recipients and whether this correlates with allograft function.

METHODS

Qualitative and quantitative analysis of DSM in peripheral blood of LTx and RTx recipients was assessed by polymerase chain reaction and competitive polymerase chain reaction using HLA-DR probes for mismatched antigens between the donor and recipient.

RESULTS

LTx recipients (11 of 12) who had or were having rejection were positive for DSM in circulation compared with 4 of 11 with normal allograft function (P<0.01). The number of donor cells did not correlate with allograft function. LTx recipients (4 of 4) who lost their first allograft and underwent retransplantation retained DSM for the first donors. RTx recipients who received DST (8 of 8) were positive for DSM compared with 6 of 12 of nontransfused recipients (P<0.045).

CONCLUSIONS

The results suggest that LTx and RTx recipients undergo rejection despite DSM. The development of DSM may not be a prerequisite for normal allograft function. Once DSM is established, the presence of the allograft is not required for maintenance of chimerism. DST facilitated the development of DSM in RTx recipients. Direct correlation was not observed between the development of DSM and allograft function in either DST or nontransfused RTx recipients.

A simultaneous negative and positive selection method that can detect chimerism at a frequency of 1 per 10,000 by flow cytometry

A three-color flow cytometric method with a simultaneous negative and positive selection (SNAPS) approach has been developed to detect blood chimerism using a FITC-conjugated recipient-specific HLA monoclonal antibody, a biotinylated donor-specific HLA monoclonal antibody and Cy5-PE-conjugated streptavidin and a PE-conjugated CD3 monoclonal antibody. Detection of simulated blood chimerism at a frequency of 0.01% was achieved by SNAPS. In contrast, by one-color flow cytometry methods, chimerism can be detected at only about 3-4% with the same donor-specific HLA monoclonal antibody. The percentages of donor CD3 cells detected by SNAPS are proportional to the percentages of donor CD3 cells counted. SNAPS method provides a fast, sensitive and reliable way to analyze trace amounts of donor cells in a recipient's blood.

Lung rejection occurs in lung transplant recipients with blood chimerism

BACKGROUND

It has been postulated that chimerism after transplantation might promote graft acceptance. In the present study, we prospectively assessed blood chimerism in 10 lung transplant recipients during the first posttransplant year and investigated whether chimerism was associated with an immunologically stable situation of the graft.

METHODS

The recipients' peripheral blood mononuclear cells were obtained before transplantation and at various time points during the first postoperative year. Donor cells were detected using nested polymerase chain reaction amplification of a donor-specific HLA-DRB1 allele. Clinical graft acceptance was determined by the number of rejection episodes.

RESULTS

The incidence of blood chimerism was high during the first 3 postoperative months and then decreased over time. All patients experienced at least one acute rejection episode, and three patients developed chronic rejection.

CONCLUSION

We, thus, conclude that rejection of the lung allograft may occur in the presence of blood chimerism.

Dendritic cells: therapeutic potentials

Dendritic cells (DCs) are leukocytes that are specialized to capture antigens and initiate T-cell-mediated immune responses. After capture of antigens, DCs, then in an immature stage, leave their tissue of residence and migrate through the lymph/blood into secondary lymphoid organs where they differentiate into mature cells. Because DCs can prime animals in the absence of any other adjuvant, they have been termed 'nature's adjuvant'. Large numbers of DCs can now be generated from circulating monocytes or from CD34 hematopoietic progenitors in response to GM-CSF in combination with either IL4 or TNF alpha. In mice, tumor antigen loaded DCs have been shown to prevent the development of tumors and even to induce the regression of established tumors. DCs therapy represents a very promising approach to the treatment of cancer and infectious diseases. Early studies indicate the existence of DC populations that can induce tolerance and may prove useful in organ transplantation.

Autologous lymphokine-activated killer cell therapy of Epstein-Barr virus-positive and -negative lymphoproliferative disorders arising in organ transplant recipients

Lymphoreticular malignancies, collectively called posttransplant lymphoproliferative disorders (PTLD), eventually develop in 2-5% of organ transplant recipients. They frequently undergo regression when immunosuppression is reduced or stopped. This feature has been associated with a previous or de novo Epstein-Barr virus (EBV) infection. We herein describe immunotherapy with autologous lymphokine-activated killer (LAK) cells in seven patients with PTLD (four EBV-positive patients and three EBV-negative patients). Autologous peripheral blood mononuclear cells were obtained by leukapheresis, depleted of monocytes, and cultured in the presence of interleukin 2 for 10 to 11 days. A single dose of 5.2 x 10(9) to 5.6 x 10(10) LAK cells was given intravenously. Systemic interleukin 2 was not administered. The four patients with EBV+ PTLD had complete tumor regression; two of them developed controllable rejection. Three patients are well 13-16 months after treatment; the fourth patient died of pneumonia 41 days after infusion. Three patients with EBV- lymphomas had no response despite prior evidence that their tumors also were subject to immune surveillance. Two of these three patients died after being given other treatment, and the third patient has persistent tumor. In conclusion, autologous LAK cell infusion was effective for treatment of four EBV+ organ transplant recipients. LAK cell efficacy for three patients with EBV- PTLD was not evaluable under the management circumstances in which this treatment was utilized.

Striking augmentation of hematopoietic cell chimerism in noncytoablated allogeneic bone marrow recipients by FLT3 ligand and tacrolimus

The influence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and the recently identified hematopoietic stem-progenitor cell mobilizing factor flt3 ligand (FL) on donor leukocyte microchimerism in noncytodepleted recipients of allogeneic bone marrow (BM) was compared. B10 mice (H2b) given 50x10(6) allogeneic (B10.BR [H2k]) BM cells also received either GM-CSF (4 microg/day s.c.), FL (10 microg/day i.p.), or no cytokine, with or without concomitant tacrolimus (formerly FK506; 2 mg/kg) from day 0. Chimerism was quantitated in the spleen 7 days after transplantation by both polymerase chain reaction (donor DNA [major histocompatibility complex class II; I-E(k)]) and immunohistochemical (donor [I-E(k)+] cell) analyses. Whereas GM-CSF alone significantly augmented (fivefold) the level of donor DNA in recipients' spleens, FL alone caused a significant (60%) reduction. Donor DNA was increased 10-fold by tacrolimus alone, whereas coadministration of GM-CSF and tacrolimus resulted in a greater than additive effect (28-fold increase). A much more striking effect was observed with FL + tacrolimus (>125-fold increase in donor DNA compared with BM alone). These findings were reflected in the relative numbers of donor major histocompatibility complex class II+ cells (many resembling dendritic cells) detected in spleens, although quantitative differences among the groups were less pronounced. Evaluation of cytotoxic T lymphocyte generation by BM recipients' spleen cells revealed that FL alone augmented antidonor immunity and that this was reversed by tacrolimus. Thus, although FL may potentiate antidonor reactivity in nonimmunosuppressed, allogeneic BM recipients, it exhibits potent chimerism-enhancing activity when coadministered with recipient immunosuppressive therapy.

Microchimerism and rejection in clinical transplantation

BACKGROUND

Haemopoietic microchimerism has been identified in recipients of solid-organ transplants and is thought by some to be critical for the development and maintenance of immunological tolerance. The aim of this study was to correlate prospectively the persistence of donor cells with clinical outcome in recipients of kidney, kidney and pancreas, and liver transplants.

METHODS

Persistence of donor cells in recipient peripheral blood was assessed at 3 days, and at 1, 3, 6, and 12 months after transplantation by a two-stage nested PCR technique to detect donor MHC HLA DR gene specifically. A pretransplant blood sample was collected from each patient to serve as an individual negative control. Seven liver, six kidney and pancreas, and 17 kidney patients were enrolled. 12 of the 17 kidney patients and all of the kidney and pancreas, and liver recipients were suitable for analysis. Exact matches for donors and recipients at the HLA DR loci (n = 1) or inability to obain primer pair specificity among similar HLA DR types (n = 4), meant that we were unable to analyse five patients.

FINDINGS

Donor DNA was detected in 20 (80%) of 25, ten (40%) of 25, seven (30%) of 23, five (22%) of 23, and six (32%) of 19 recipients at 3 days, and 1, 3, 6 and 12 months post-transplant, respectively. Within individuals, the detection of donor DNA varied over time; only two patients had detectable donor DNA at all times. Analysis of the whole group of transplant patients showed a similar frequency and severity of rejection episodes in patients with and without microchimerism as defined by detectable donor DR genes.

INTERPRETATION

These data suggest that a significant percentage of the recipients had persistent donor class II DNA in the peripheral circulation for at least 1 year after transplantation. We showed that a pretransplant blood sample is critical to avoid a false-positive result, and suggest that detectable chimerism may vary over time in individual patients. Therefore, analysis of microchimerism with a single, post-transplant analysis may not help in making clinical decisions for individual patients.

Epstein-Barr virus-associated post-transplant lympho-proliferative disease of donor origin in liver transplant recipients

BACKGROUND/AIMS

Post-transplant lymphoproliferative disease, a potential complication of solid organ transplantation, occurs in about 3% of orthotopic liver transplant recipients. We report the genetic and virological characterization of two cases of post-transplant lymphoproliferative disease that occurred early (4 and 6 months) after orthotopic liver transplant as large-cell non-Hodgkin's lymphomas located at the hepatic hilum.

METHODS

Lymphomatous tissues were analyzed for clonality and presence of Epstein-Barr virus (EBV) sequences by Southern blot, polymerase chain reaction, and in situ hybridization techniques.

RESULTS

The tumors in both cases were sustained by a clonal proliferation of B lymphocytes containing type A EBV DNA. Moreover, in situ hybridization with a digoxigenin-labeled EBV-specific probe evidenced a strong nuclear signal in most of the neoplastic cells. DNA microsatellite analysis at three different loci detected alleles of donor origin in both tumor samples, suggesting that the neoplastic B cells were of donor origin.

CONCLUSIONS

EBV-infected donor B lymphocytes might be responsible for intragraft post-transplant lymphoproliferative disease in orthotopic liver transplant recipients. As 20 to 30% of post-transplant lymphomas involve the graft itself, donor-derived post-transplant lymphoproliferative disease might be more frequent than presently appreciated. Prospective studies are needed to assess its real incidence and identify possible risk factors.

Modulatory effects of human donor bone marrow cells on allogeneic cellular immune responses

BACKGROUND

In order to evaluate whether immunoregulatory mechanisms are brought about by human donor bone marrow cell infusions accompanying organ transplantation, we established in vitro culture systems analogous to the transplant model.

METHODS

Cell-mediated lympholysis (CML) and mixed lymphocyte culture (MLC) responses of peripheral blood lymphocytes or spleen cells stimulated with irradiated cadaver donor spleen cells in the presence of specific donor vertebral-body bone marrow cell (DBMC) modulators were tested.

RESULTS

When compared with spleen cells as modulator controls, DBMC inhibited both the proliferative and cytotoxic responses in a dose-dependent manner. Use of unirradiated and T cell-depleted DBMC was required for detection of the inhibitory activity. Furthermore, DBMC had to be added within the first 2 days after the initiation of the cultures for the down-regulation of CML (MLC) to occur. The down-regulation of MLC responses could not be shown to be antigen (donor) specific. Physical separation of DBMC from the responder-stimulator cells using the transwell system abrogated modulation of the CML (and MLC) reactions, suggesting the requirement of cell-cell contact for modulatory effect. The inhibitory activity by DBMC could not be overcome by addition of up to 200 U/ml of exogenous recombinant interleukin 2 to the cultures. However, it could be abrogated by restimulation with donor spleen cells, indicating that donor reactive cells were not deleted by DBMC in short-term cultures.

CONCLUSIONS

These results showed a regulatory role for DBMC in cellular immune responses against donor cell alloantigens, supporting the rationale for DBMC for facilitating clinical allograft acceptance.

The future of transplantation: with particular reference to chimerism and xenotransplantation

The assumption for the last third of a century that stem cell-driven hematolymphopoietic chimerism was irrelevant to successful conventional whole organ transplantation has prompted alternative inadequate explanations of organ allograft acceptance. This assumption clouded the biologic meaning of successful organ as well as bone marrow transplantation, and precluded the development of a cardinal principle that accommodated all facets of transplantation. Recognition of this error and the incorporation of the chimerism factor into a two-way paradigm have allowed previous enigmas of organ as well as bone marrow engraftment to be explained. No credible evidence has emerged to interdict this interactive concept. If the two-way paradigm is correct, it will allow the remarkable advances that have been made in basic immunology to be more meaningfully exploited for transplantation, including that of xenografts.

Rejection of spontaneously accepted rat liver allografts with recipientinterleukin-2 treatment or donor irradiation

While MHC incompatible DA (RTl(a)) to Lewis (RT1(1), LEW) rat liver allografts are acutely rejected, the reciprocal LEW to DA liver grafts are spontaneously accepted. The mechanism of this acceptance remains unclear. We evaluated the effect of donor treatment with total body irradiation (TBI) or gadolinium chloride (GdCl3), and recipient treatment with exogenous IL-2 after transplantation on the survival of the spontaneously accepted liver grafts. Male LEW and DA rats were used as donors and recipients for orthotopic liver allo- or iso-graft transplants. The LEW liver donor was treated by TBI (10 gray) 7 days before transplantation, or LEW donor Kupffer cell phagocytosis was blocked with GdCl3 (7 mg/kg) on days -2 and -1 pretransplant. In an attempt to reverse LEW liver graft acceptance, 180,000 units human IL-2 (hIL-2) were administered daily IP to the DA liver recipients from days 1 to 7 after liver grafting. While untreated LEW recipients rejected DA liver grafts within 13 days, DA recipients accepted LEW livers indefinitely (>302 days). In contrast, irradiation of the LEW liver donor prevented the spontaneous acceptance by DA recipients, and resulted in acute rejection of the liver grafts in 9-20 days. However, spontaneous graft tolerance was restored by parking the irradiated LEW donor liver in naive LEW rats for 48 hr before retransplantation to DA recipients (>50 days). When LEW donors were treated with GdCl3, which is known to block Kupffer cell phagocytosis and antigen processing, the spontaneous acceptance of the LEW liver grafts by DA recipients was unaffected. However, when exogenous rhIL-2 was given daily, LEW liver allografts were rejected by the DA recipients. The resulting liver failure correlated with a progressive increase in serum bilirubin and the development of a predominantly lymphocytic portal tract infiltration, bile duct epithelial damage, and portal vein endothelitis, which is consistent with acute allograft rejection. LEW and DA recipients of liver isografts developed no toxicity and survived indefinitely (>100 days) when treated with the same dose of IL-2. These results indicate that spontaneous rat liver allograft acceptance is associated with the presence of radiosensitive cells in the donor liver that may interact with recipient T cells to inhibit (Th1) production of IL-2.

Weaning of immunosuppression in liver transplant recipients

Immunosuppression has been sporadically discontinued by noncompliant liver allograft recipients for whom an additional 4 1/2 years of follow-up is provided. These anecdotal observations prompted a previously reported prospective drug withdrawal program in 59 liver recipients. This prospective series has been increased to 95 patients whose weaning was begun between June 1992 and March 1996, 8.4+/-4.4 (SD) years after liver replacement. A further 4 1/2 years follow-up was obtained of the 5 self-weaned patients. The prospectively weaned recipients (93 livers; 2 liver/kidney) had undergone transplantation under immunosuppression based on azathioprine (AZA, through 1979), cyclosporine (CsA, 1980-1989), or tacrolimus (TAC, 1989-1994). In patients on CsA or TAC based cocktails, the adjunct drugs were weaned first in the early part of the trial. Since 1994, the T cell-directed drugs were weaned first. Three of the 5 original self-weaned recipients remain well after drug-free intervals of 14 to 17 years. A fourth patient died in a vehicular accident after 11 years off immunosuppression, and the fifth patient underwent retransplantation because of hepatitis C infection after 9 drug-free years; their allografts had no histopathologic evidence of rejection. Eighteen (19%) of the 95 patients in the prospective series have been drug free for from 10 months to 4.8 years. In the total group, 18 (19%) have had biopsy proved acute rejection; 7 (7%) had a presumed acute rejection without biopsy; 37 (39%) are still weaning; and 12 (13%, all well) were withdrawn from the protocol at reduced immunosuppression because of noncompliance (n=8), recurrent PBC (n=2), pregnancy (n=1), and renal failure necessitating kidney transplantation (n=1). No patients were formally diagnosed with chronic rejection, but 3 (3%) were placed back on preexisting immunosuppression or switched from cyclosporine (CsA) to tacrolimus (TAC) because of histopathologic evidence of duct injury. Two patients with normal liver function died during the trial, both from complications of prior chronic immunosuppression. No grafts suffered permanent functional impairment and only one patient developed temporary jaundice. Long surviving liver transplant recipients are systematically overimmunosuppressed. Consequently, drug weaning, whether incomplete or complete, is an important management strategy providing it is done slowly under careful physician surveillance. Complete weaning from CsA-based regimens has been difficult. Disease recurrence during drug withdrawal was documented in 2 of 13 patients with PBC and could be a risk with other autoimmune disorders.

Sequential measurement of peripheral blood allogeneic microchimerism levels and association with pulmonary function

We have shown in lung recipients that high levels of peripheral blood allogeneic microchimerism at 12 to 18 months posttransplant correlated with donor antigen-specific hyporeactivity (i.e., decreased proliferative response to donor antigen in MLC while response to 3rd-party cells remains unchanged); both parameters correlated with an obliterative bronchiolitis (OB)-free state. We have expanded these studies to determine any association of sequential microchimerism levels with concomitant clinical events. In this preliminary study of 7 lung recipients, we used limiting-dilution PCR to quantify peripheral blood microchimerism at serial timepoints ranging from 3 to >48 months posttransplant. These levels were compared with a variety of immunologic and clinical parameters: acute rejection, CMV infection, OB, donor antigen-specific hyporeactivity, and pulmonary function. Pulmonary function was measured per the International Society of Heart and Lung Transplantation: "current FEV1/ baseline FEV1" (FEV1: forced expiratory volume in 1 second). Of the clinical parameters, the association between microchimerism and pulmonary function was the most striking. We observed dynamic patterns of peripheral microchimerism, which reflected the general rise and fall of FEV1. In all 7 recipients, chimerism and FEV1 were high very early posttransplant, then dropped at various rates and to various degrees. After its initial decline, microchimerism increased with FEV1 for the 1 hyporesponsive recipient; for the other 6 recipients, both values declined. These results illustrate, for the first time, that the fluctuation of peripheral blood microchimerism levels is associated with the recipient's clinical condition.

Tolerance to rat liver allografts: IV. Acceptance depends on the quantity of donor tissue and on donor leukocytes

Liver allografts in some rat strains are often spontaneously accepted across a complete major histocompatibility barrier without the requirement for immunosuppression while other nonliver allografts are rejected. In previous studies, we have shown that spontaneous acceptance is dependent on liver passenger leukocytes. Depletion of passenger leukocytes by donor irradiation allows rejection, with DA recipients of irradiated PVG livers having a median survival time (MST) of 16 days. Here we show that, in this model, spontaneous acceptance is reconstituted by intravenous injection of donor leukocytes. Intravenous injection of 3-5x10(7) PVG liver leukocytes significantly prolonged DA survival time (MST=96 days, P=0.026), as did 5x10(7) spleen leukocytes (MST>100 days, P=0.002). Deletion of T cells from the reconstituting inoculum reduced survival time (MST=78 days, P=0.039), whereas deletion of B cells or monocytes/macrophages had no effect on survival time. In contrast, PVG hearts are regularly rejected by DA recipients, and PVG liver or spleen leukocytes, even at doses of greater than 3x10(8) cells/recipient, were unable to induce heart acceptance. To investigate the possibility that acceptance of the irradiated liver but not the heart might be due to the large mass of the liver, two kidneys and two hearts of PVG origin were transplanted to each DA recipient together with 1.5x10(8) PVG leukocytes. These organs survived for greater than 200 days, thereby showing that a large mass of donor tissue, in association with donor leukocytes, leads to acceptance of organs that are rejected if transplanted singly. It appears likely that spontaneous liver transplant tolerance is a high-dose or activation-associated immune phenomenon.

The lost chord: microchimerism and allograft survival

Recent evidence suggests that passenger leukocytes migrate after organ transplantation and produce persistent chimerism, which is essential for sustained survival of the allografts. Here, Thomas Starzl and colleagues argure that this hematolymphopoietic chimerism provides an important framework for the interpretation of basic and therapeutically oriented transplantataion research.

Routine use of the piggyback technique in pediatric orthotopic liver transplantation

The theoretical advantages of the piggyback technique over conventional orthotopic liver transplantation are as follows. (1) Continuous venous decompression during the anhepatic phase is provided without venovenous bypass. (2) Warm ischemia time can be shortened because there is no need for the infrahepatic vena cava anastomosis. The following report is a review of the authors' experience with this method in children during the past year at their institution. Analyses of intraoperative hemodynamics and blood loss, postoperative renal function, patient and graft survival, and length of hospital stay have shown excellent results. There were no intraoperative deaths, and causes of death and graft loss were not related to the technique. The authors conclude that children who undergo liver transplantation can be very satisfactorily managed with the piggyback operation, and this technique may be more advantageous than the conventional method.

Complete lymphoid chimerism and chronic graft-versus-host disease in an infant recipient of a hepatic allograft from an HLA-homozygous parental living donor

Living-related donor liver transplantation (LDLT) is an accepted approach to pediatric liver transplantation. Parental donation imposes a significant risk of chimerism with graft-versus-host disease (GVHD) because donors homozygous at all HLA loci (1.6% of the population) present no mismatched HLA antigens to be recognized by their offspring's immune system. The case of a 9-month-old who underwent LDLT with her 23-year-old HLA-homozygous mother as a donor demonstrates the consequences of this occurrence. The patient developed GVHD with aplastic anemia; the patient's nucleated peripheral blood elements were shown to be entirely derived from the donor. Later, after some marrow recovery, the patient's circulating lymphocytes had a donor origin, while the marrow-derived neutrophils had a recipient origin. The patient suffers from chronic GVHD and debilitating skin disease several years posttransplant. Our current protocol calls for HLA typing to eliminate parents who are homozygous at all HLA loci as donors of hepatic allografts to their children.

An assessment of the effects of cadaver donor bone marrow on kidney allograft recipient blood cell chimerism by a novel technique combining PCR and flow cytometry

A new technique, the PCR-flow assay is described that has allowed for the serial identification and quantitation of discrete mononuclear cell subsets of donor (or recipient) bone marrow derived cells in cadaver kidney transplant recipients infused postoperatively with donor vertebral body bone marrow cells. With fixed permeabilized cells in flow cytometry the amplification power of the polymerase chain reaction (PCR), using fluorescent-labeled primers to identify single copy HLA class II DRbeta1 genes of either donor or recipient origin, is combined with multi-color fluorochrome-labeled CD epitope-specific monoclonal antibodies. The details of the methodology are described; these support the utility of the assay. Initial observations were made on the chimeric makeup of the peripheral blood as well as iliac crest bone marrow between six months and one year posttransplantation in recipients serially followed weekly and then monthly, concomitantly compared with a control group of stable kidney transplant recipients using similar therapeutic protocols, who did not receive cadaver bone marrow. Several findings are of note. In 14 recipients of two bone marrow infusions totalling a mean of 6.29+/-2.18x10(10) cells, donor CD34 positive (+) (immature) cells were fourteen times as numerous in peripheral blood six months postoperatively as in six recipients given half as many bone marrow cells in one infusion (averaging 3.02+/-0.5x10(10)). These donor CD34+ cells unexpectedly averaged 36+/-7% of the total (donor plus recipient) CD34+ subset counted. Moreover, iliac crest bone marrow aspirates contained an average of thirteen times this number of CD34+ cells than in the peripheral blood, supporting the notion of engraftment. Of additional interest, between six months and one year posttransplant although no donor cells could be detected in peripheral blood of the controls there was an identifiable presence of donor CD34+ cells in their iliac crest bone marrow, albeit 10-fold less than the marrow-infused patients. In the clinical follow-up, although there were three unrelated mortalities, there were no additional kidney losses with current serum creatinine concentrations averaging 1.3+/-0.06 mg/dl. In conclusion, the PCR-flow assay presents the possibility of identifying discrete subsets of donor or recipient cells that may have an immunoregulatory function.

Costimulatory molecule-deficient dendritic cell progenitors (MHC class II+, CD80dim, CD86-) prolong cardiac allograft survival in nonimmunosuppressed recipients

We have shown previously that granulocyte-macrophage colony-stimulating factor-stimulated mouse bone marrow-derived MHC class II+ dendritic cell (DC) progenitors that are deficient in cell surface expression of the costimulatory molecules B7-1 (CD80) and B7-2 (CD86) can induce alloantigen-specific T-cell anergy in vitro. To test the in vivo relevance of these findings, 2 x 10(6) B10 (H2b) mouse bone marrow-derived DC progenitors (NLDC 145+, MHC class II+, B7-1dim, B7-2-/dim) that induced T-cell hyporesponsiveness in vitro were injected systemically into normal C3H (H2k) recipients. Seven days later, the mice received heterotopic heart transplants from B10 donors. No immunosuppressive treatment was given. Median graft survival time was prolonged significantly from 9.5 to 22 days. Median graft survival time was also increased, although to a lesser extent (16.5 days), in mice that received third-party (BALB/c; H2d) DC progenitors. Ex vivo analysis of host T-cell responses to donor and third-party alloantigens 7 days after the injection of DC progenitors (the time of heart transplant) revealed minimal anti-donor mixed leukocyte reaction and cytotoxic T lymphocyte reactivity. These responses were reduced substantially compared with those of spleen cells from animals pretreated with "mature" granulocyte-macrophage colony-stimulating factor + interleukin-4-stimulated DC (MHC class IIbright, B7-1+, B7-2bright), many of which rejected their heart grafts in an accelerated fashion. Among the injected donor MHC class II+ DC progenitors that migrated to recipient secondary lymphoid tissue were cells that appeared to have up-regulated cell surface B7-1 and B7-2 molecule expression. This observation may explain, at least in part, the temporary or unstable nature of the hyporesponsiveness induced by the DC progenitors in nonimmunosuppressed recipients.

An examination of tissue chimerism in the ACI to Lewis rat cardiac transplant model

While the existence of chimeric cells in host tissue following organ transplantation is well documented, its distribution, temporal evolution and relationship to allograft survival is less clear. To explore this phenomenon, Lewis recipients of ACI cardiac allografts representing a wide range of immunosuppressive protocols and graft survival times were examined for the presence of chimerism using a sensitive polymerase chain reaction assay. Four groups of animals were examined: untransplanted animals receiving donor specific transfusion (DST)/cyclosporine A (CsA); allograft recipients with no treatment; recipients treated with DST/CsA/supplementary immunosuppression with rejection at 21-183 days; and recipients sacrificed with functioning allografts, treated with DST/CsA/supplementary immunosuppression and surviving > 200 days. To elucidate variations in the tissue distribution of chimeric cells, bone marrow, skin, liver, spleen, and thymus were examined in each animal. Untransplanted animals receiving DST/CsA displayed no evidence of chimerism. In animals receiving a cardiac allograft but no treatment, there was extensive evidence of chimerism in four of five animals. Chimerism was also detected in seven of nine animals with intermediate graft survival at the time of rejection. In animals with long-term graft survival, only four of eight displayed chimerism. These results suggest that, without immunosuppression, early chimerism does not lead to prolonged graft survival and that, even when graft survival is moderately prolonged, these cells are not sufficient to prevent rejection. In conclusion, chimerism appears to be a common phenomenon following transplantation, is not a result of DST, and may not be necessary for maintenance of long-term graft survival.

Liver allograft rejection in rats depleted of CD8+ cells

The mechanism(s) of rejection or tolerance induction is a competitive, complex process that presumably involves interactions between multiple subpopulations of T lymphocytes. We investigated the roles of CD8+ cytolytic and CD4+ helper T cells in rat strains that tolerate liver allografts and that differ at both the major histocompatibility complex (MHC) (RT1) and minor histocompatibility genes. Orthotopic liver transplantation (OLT) with arterial reconstruction was performed with Brown Norway (BN) (RT1n) donors and Lewis (RT1(1)) recipients, some of which were untreated, others treated with anti-CD8 antibody, and still others treated with anti-CD4 antibody. Liver graft rejection was monitored for 28 days on the basis of two criteria: (1) serum levels of AST enzyme at 3-day intervals and (2) liver biopsies at weekly intervals and at the time of sacrifice at the end of the study period. In the untreated control group, an elevation of AST was found to peak at day 6 after grafting, and it remained elevated until day 28 (AST 542 +/- 72 U/l). Histologically, signs of severe rejection were first observed on day 9; these changed to moderate rejection about day 21 and to mild rejection by day 28, when the animals were sacrificed. Recipients pre-treated with anti-CD8 demonstrated a significant elevation of AST within 6 days that, unlike in the control recipients, continued to rise sharply through the observation period (AST 1127 +/- 181 U/l, P = 0.009 vs control group). Liver biopsies showed mild rejection at day 9 and moderate rejection at days 21 through 28. Recipients pretreated with anti-CD4 showed a time course of enzyme elevation and severity of rejection that was not significantly different from that observed in the control group. However, anti-CD4 treatment resulted in only 75% depletion of CD4+ cells in peripheral blood as compared to complete elimination of CD8+ cells following anti-CD8 treatment. Functional studies of spleen and liver-infiltrating lymphocytes obtained after 28 days showed low proliferative response in mixed lymphocyte culture with both BN and PVG stimulator spleen and lymph node cells. These results suggest that in this donor/recipient combination, removal of CD8+ cells increases the severity of rejection as demonstrated by a progressive rise in AST and histology. Moreover, OLT in this combination results in a profound, nonspecific inhibition of proliferative T-cell responses to MHC alloantigens.

TGF-beta 1 pretreatment impairs the allostimulatory function of human bone marrow-derived antigen-presenting cells for both naive and primed T cells

Transforming growth factor-beta (TGF-beta) exhibits strong antiproliferative effects upon lymphocytes and inhibits many of the effector functions of activated immune cells. However, its influence on the inductive phase of immune responses, and in particular its effect on antigen-presenting cells (APC), has not been well studied. In this investigation, we examined the influence of human TGF-beta 1 on the antigen-presenting function of human bone marrow (BM)-derived APC propagated in liquid culture for 11-17 days in response to granulocyte/macrophage colony-stimulating factor (GM-CSF). These cells were predominantly macrophages, accompanied by a minor population of dendritic cells. TGF-beta 1 had no effect upon the allostimulatory function of vertebral body whole BM cells cultured for 3-5 days in GM-CSF. However, it markedly reduced the allostimulatory capacity of BM-derived APC exposed to the cytokine for the last 3 days of culture. This inhibitory action could not be ascribed to cytokine 'carry-over', or to any consistent changes in the expression of cell surface molecules implicated in antigen presentation (HLA-DR), intercellular adhesion (ICAM-1; CD54), or costimulatory activity (B7-1; CD80). Mechanisms that may underlie the inhibitory action of TGF-beta on APC function and the immunologic and possible clinical implications of the findings are discussed.

Detection of circulating donor deoxyribonucleic acid by microsatellite analysis in a liver transplant recipient

The diagnosis of graft-versus-host disease following liver transplantation may be delayed because the clinical and pathological features are nonspecific. We report the use of microsatellites to support a diagnosis of GVHD in a patient who developed fever and a skin rash 28 days after liver transplantation. The pattern of microsatellite alleles amplified from the peripheral blood on day 51 posttransplant indicated that recipient and donor DNA were present in approximately equal proportions. Microsatellite typing is a simple and rapid method to identify high levels of circulating donor DNA to support a diagnosis of GVHD following liver transplantation.

Prevention of Transplant Rejection: Can Tolerance be Achieved with Immunosuppressive Treatment?

Successful solid organ transplantation is generally attributed to the increasingly precise ability of drugs to control rejection. However, it was recently shown that a few donor haematolymphoid cells can survive for decades in recipients of successful organ allografts, a phenomenon called microchimaerism. The association for decades of haematolymphoid chimaerism with allograft tolerance in experimental transplantation suggests that immunosuppressive drugs merely create a milieu that enables an allograft and its complement of passenger leucocytes to prime the recipient for graft acceptance.Exploitation of this concept requires a fundamental shift in the classical view of passenger leucocytes only as initiators of rejection. Microchimaerism has taught us that solid organ transplantation involves the transfer of two donor organ systems to the recipient: the allograft parenchyma and the donor haematolymphoid system in the form of donor stem cells contained within the passenger leucocyte compartment. Each has the potential to integrate with the corresponding recipient system and carry out normal physiological functions, such as immunological self definition. Resistance to initial integration by mature T cells requires some form of immunosuppression, but maintenance of donor immune system function will depend on renewable supply of cells, which can be provided by engrafted progenitors. Successful clinical application will depend on the development of low morbidity methods to enhance engraftment of donor haemopoietic stem cells.

Complete withdrawal of immunosuppression in allograft recipients. A study in rhesus monkeys

The influence of pretransplant blood transfusions on kidney allograft survival after cessation of immunosuppressive treatment was studied in 11 rhesus monkeys. The animals were conditioned by three pretransplant blood transfusions. After an induction treatment with cyclosporine (CsA), the immunosuppression was stopped and the natural course of the graft was followed. In two monkeys long-term graft survival without immunosuppression was obtained (2.5 and 4.25 years). In a third monkey, permanent allograft acceptance was achieved after complete cessation of immunosuppression. The monkey is still alive with a well-functioning graft for more than 13 years after cessation of immunosuppression. This monkey had received CsA for 12 months, two MHC DR-matched blood transfusions, and no repeated mismatches between graft and blood transfusion donors. We speculate that blood transfusions may influence allograft function in two opposite ways. As reported previously in man, MHC class-II-matched transfusions appear to beneficially influence allograft survival. This effect seems to be negated by a mismatched MHC class II antigen in the blood transfusion donor which is also present in the organ donor -- a so-called repeated mismatch. Further studies in rhesus monkeys are required to confirm and extend these results. In the future, these observations might help in developing a protocol that opens up the possibility of cessation of immunosuppression in transplant patients.