Soluble HLA antigens in the circulation of liver graft recipients

Mutual tolerance after liver and not after heart transplantation? Evaluation of patient-anti-donor and donor-anti-patient responses by mixed lymphocyte culture

The ultimate goal in organ transplantation is the induction of donor-specific transplantation tolerance. The fact that in some patients it is possible to withdraw immunosuppressive therapy completely, suggests that immunological adaptation or donor-specific nonresponsiveness can occur following transplantation. In earlier studies we have shown that after blood transfusion, the mixed lymphocyte reactivity of the donor against patient peripheral blood mononuclear lymphocytes taken after blood transfusion gradually decreased with time. This may reflect the induction of an immunoregulatory mechanism, which protects the recipient against an immune reaction of the donor, enhancing a state of mixed chimerism. A similar phenomenon might also play a role in the immunological mechanism leading to transplantation tolerance. Therefore, we studied responses in patients with a well-functioning liver and heart transplant using a primed lymphocyte test (PLT) and a mixed lymphocyte culture (MLC). Two years after liver transplantation the PLT and MLC responses of patient against donor were decreased significantly compared to the situation before transplantation. The response of donor against patient was also lower two years after transplantation. The decreased responses were donor-specific since responses to third-party cells generally remained unchanged. In heart transplant recipients we could not detect a donor-specific downregulation. The reversed response, of donor against patient, was not different from responses of third-party against patient cells. Therefore, we conclude that donor-specific nonresponsiveness is not induced in patients with well-functioning heart transplants. In contrast, after a successful liver transplantation the response of patient against donor is decreased, as is the reversed response. It may be valuable to test whether in liver transplant patients withdrawing or reducing of maintenance immunosuppression is permitted for patients who appear to have developed two-way donor-specific hyporeactivity.

The application of human monoclonal antibodies for monitoring donor derived soluble HLA class I molecules in the serum of heart transplant recipients

Increased levels of both donor and recipient derived HLA molecules can be found in serum and plasma of transplanted patients during rejection. Recent data suggest that levels of donor specific soluble HLA Class I (sHLA-1) correlate better with graft rejection than total sHLA Class I [1, 2]. Therefore, quantification of donor specific soluble counterparts of HLA Class I in the serum of the recipient may be a new way for non-invasive monitoring of rejection after organ transplantation. Up to now, only a limited number of mouse monoclonal antibodies (alpha HLA-A2, and alpha HLA-B7) has been used in enzyme linked immunosorbent assays (ELISAs) to detect donor specific HLA molecules in the plasma of transplant recipients. To monitor other donor-recipient combinations, we tested some of our HLA Class I specific human monoclonal antibodies, routinely used in complement dependent cytotoxicity, for their suitability in ELISA based assays. In the present model system, we used alpha HLA-A9 (BvK5C4) or alpha HLA-A3 (OK2F3) hybridoma-supernatant to set up a sHLA-A9 and sHLA-A3 specific ELISA. In a pilot study we show that these assays were sensitive enough to detect an increase of donor specific sHLA-I during rejection in the plasma of two heart transplant recipients. Use of a large set of human hybridoma's will enable monitoring most recipient/donor combinations in the near future.

Simultaneous heart and kidney transplantation as treatment for end-stage heart and kidney failure

BACKGROUND

The aim of the present analysis was to define the role of simultaneous heart and kidney transplantation (HNTX) using organs from the same donor by evaluation of clinical strategy and achieved outcome compared with a reference group of concurrently single heart transplant (HTX) and kidney transplant (NTX) recipients. Compared with other organ combinations (pancreas-kidney, heart-lung), HNTX has been performed infrequently and is reported mainly as case records in the literature. Because of expansion of recipient selection criteria for HTX and NTX, the number of patients requiring simultaneous replacement of both organs is increasing.

METHODS

Six HNTX recipients, three of them suffering from long-standing type I diabetes, received transplants between September 1990 and March 1996 and were analyzed in terms of clinical and immunological demographics and outcome. They were compared with 379 HTX and 769 NTX recipients operated upon within this period.

RESULTS

Survival for HNTX is 100% with a mean follow-up of 32.7+/-21.1 months. Cold ischemic time of the kidney was significantly shorter for HNTX than for NTX (6.5+/-1.0 hr vs. 22.1+/-6.8 hr, P<0.005). Although HNTX patients received HLA-unmatched grafts, no rejection of the kidney has been observed to date. There was no difference for rejection of the heart in HNTX compared to HTX recipients.

CONCLUSIONS

Satisfying results are obtained by HNTX and justify the use of two organs for one recipient. The favorable immunological behavior of the kidney despite use of HLA-unmatched grafts is most probably explained by higher immunosuppression and short cold ischemic time, although a combination effect cannot be excluded.

Soluble human leukocyte antigens, interleukin-6, and interferon-gamma during pregnancy

PROBLEM

Soluble human leukocyte antigens (sHLA), interferon-gamma (IFN-gamma), and interleukin-6 (IL-6) were studied during human pregnancy to test the hypothesis that sHLA concentrations are regulated by these specific cytokines.

METHOD OF STUDY

Enzyme-linked immunoadsorbent assays (ELISA) were used to measure sHLA I and II in maternal circulation, cord blood, and placenta effluents of pregnant and nonpregnant women; maternal serum cytokines were also determined.

RESULTS

sHLA in maternal and cord blood were equivalent to that in the placenta. By the third trimester, sHLA I concentrations in maternal plasma were significantly reduced compared to the first or second trimesters. sHLA II was increased during the second trimester relative to that postpartum. Maternal IL-6 and IFN-gamma concentrations were not statistically different throughout gestation or postpartum.

CONCLUSIONS

These data do not suggest a role for maternal plasma IL-6 or IFN-gamma in regulation of systemic sHLA class I during pregnancy, but they do not address whether such events take place in local tissues of the maternal-fetal unit.

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.

Serum soluble human leucocyte antigen class I in paediatric liver transplantation with live, related donors

Serum soluble human leucocyte antigen (HLA) class-I is a useful marker for predicting immunological events in organ transplantation. In cadaver liver transplant cases it is especially the case that high amounts of soluble HLA-I are excreted from the grafts. In Japan, almost all liver transplants have been performed from living parent donors to their children. Therefore, it is interesting to know how soluble HLA-I changes in relation to clinical course. As part of this study we first examined serum concentrations of soluble HLA-I in 33 paediatric patients using enzyme-linked immunosorbent assay. Soluble HLA-I is composed of three different sized molecules (45, 39 and 34-36 kDa); then the change of distribution of these three molecules was demonstrated by Western blot analysis. When donor and recipient have different soluble HLA-I band patterns, the origin of the antigen can be assumed by this method. We found that in a comparison between pre- and post-transplants, the six out of eight (75%) patients that suffered episodes of acute rejection showed a significant elevation of soluble HLA-I, and all patients with infectious episodes had an elevated soluble HLA-I. Meanwhile, 10 out of 22 (45%) patients without any clinical complications still showed increased soluble HLA-I. The Western blot analysis showed that the soluble HLA-I molecules were considerably derived from the grafted liver, from one week to 24 months after grafting. In acute rejection, the band signals of donor origin were significantly increased. These signals were attenuated after immunosuppressive therapy. The grafted liver appears to contribute to the increase of soluble HLA-I following liver transplantation, and this increase is greater with the effects of the host immune system.

Soluble HLA class I antigens in patients with type I diabetes and their family members

Our objective was to study a possible contribution of MHC genes to S-HLA-I secretion in patients with Type I diabetes. Quantitatively, we used a highly sensitive enzyme-linked immunoassay to measure S-HLA-I in the serum of a total of 39 patients with Type I diabetes, as well as 36 kinships of 12 diabetic patients and 82 normal individuals with known HLA-phenotypes. S-HLA-I levels were abnormally elevated in patients or their non-diabetic relatives compared to normal controls (p < 0.0009). No complete HLA-haplotype had been identified to be correlated with high or low S-HLA-I secretion. Only the HLA-A23 or A24 (splits of HLA-A9) positive individuals sera were found to contain high S-HLA-I concentrations in all populations studied. The difference in S-HLA-I levels of HLA-A24 patients (n = 4) or their HLA-A24 positive non-diabetic relatives (n = 10) to the group of HLA-A24 normal controls (n = 15) was statistically highly significant (p < 0.0005 and p < 0.0009, respectively). The results suggests that HLA-A24 may confer additional independent risk for the disease expression in male children but not in female siblings. Nevertheless, the data implies that the patients or their non-diabetic relatives carrying the HLA-A24 have increased risk of developing ICA associated with high S-HLA-I levels compared to HLA-A24 negative probands or their kinships with low levels of S-HLA-I. This effect occurred irrespective to other diabetes related HLA-DR alleles. In summary, the results show a pronounced genetic heterogeneity of Type I diabetes with MHC control of the expression of S-HLA-I and possible involvement of hormonal factors that might potentiate a specific synthesis of S-HLA-I. The findings have implications for identifying individuals with a possible risk for developing the disease.

Serum concentrations of soluble HLA-class I and CD8 forms in patients with viral hepatic disorders

Soluble HLA-class I and CD8 molecules were determined by sandwich ELISA in patients with viral-induced hepatic disorders. As a whole, the patients with hepatic disorders (acute hepatitis: AH; chronic hepatitis: CH; liver cirrhosis: LC; hepatocellular carcinoma: HCC) showed higher sHLA-class I and sCD8 levels than normal controls (P < 0.001). AH patients had the highest sHLA-class I levels (mean, 3513 +/- 2112 ng/ml), followed by CH (2896 +/- 1290 ng/ml), LC (2293 +/- 1266 ng/ml), and HCC (2221 +/- 1212 ng/ml) sCD8 levels wer highest in AH, followed by HCC, LC, and CH, in that order. Among histologically defined C virus-positive patients, sHLA-I levels were higher in those with chronic active hepatitis (CAH) 2A (3802 +/- 1124 ng/ml) than in those with chronic persistent hepatitis (CPH; 2200 +/- 711 ng/ml; P < 0.01), the levels then decreased as the disease progressed (CAH2B, 3564 +/- 1783 ng/ml, LC, 2376 +/- 1265 ng/ml). In contrast, sCD8 values showed little difference among the disorders. sHLA-class I levels showed a positive correlation with sCD8 values both in whole patients and in patients with AH (P < 0.01), but no correlation was shown, in any patients, with biochemical parameters such as GPT and GOT. These findings, taken together, suggest that hepatic destruction is not the only cause of sHLA-class I production, but that sHLA-class I levels, together with sCD8 levels, may reflect immunological activity in hepatic disorders.

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.

Allogeneic class I MHC requirement for alloantigen-reactive helper T-lymphocyte responses in vivo. Evidence for indirect presentation of alloantigen

The mechanisms by which host T cells recognize transplant-associated alloantigens in vivo have not been established. Two alloantigen presentation pathways may be used: (1) allogeneic class I and class II MHC molecules may be recognized directly by host CD8+ and CD4+ cells, respectively, or (2) allogeneic MHC molecules may be processed as foreign peptide and presented by host antigen-presenting cells to CD4+ cells in the context of self class II proteins. In this study, the sponge matrix allograft model was used to examine the relative contributions of these alloantigen presentation pathways to CD4+ T-cell activation in vivo. Limiting dilution analysis was used to quantify the localization of interleukin-2-producing helper T lymphocytes (HTL) following implantation of sponge allografts. Allografts either were disparate at both class I and class 11, or were derived from beta2-microglobulin knockout (beta2M-/-) mice, which express class II but are deficient in class I. Two measures of in vivo HTL function were monitored: (1) the accumulation of HTL within the allograft (a process that is dependent upon antigen-driven cytokine production), and (2) the development of cytolytic alloantibodies. After implantation of sponge allografts expressing both class I and class II, HTL were readily detectable in the allograft, and cytolytic alloantibodies were present in the serum. When mice were implanted with beta2M-/- sponge allografts, HTL failed to infiltrate these class I-deficient allografts, and alloantibodies were not detectable in the sera of recipients of beta2M-/- sponge allografts. This in vivo requirement for class I expression was not reflected by traditional in vitro measures of HTL function; cells obtained from lymphoid tissues mounted a mixed lymphocyte response and produced interleukin-2 when stimulated with beta2M-/- splenocytes in vitro. One possible interpretation of these data is that in vivo HTL functions are dependent upon the presence of class I-reactive CD8+ T cells. However, HTL readily infiltrated grafts expressing both class I and class II when recipients depleted of CD8+ T cells, and alloantibodies were produced. These observations support the idea that indirect presentation of allogeneic class I molecules plays a critical role in regulating CD4+ HTL functions associated with allograft rejection in vivo.

Biochemical and immunological evaluation of donor-specific soluble HLA in the circulation of liver transplant recipients

MHC antigens, normally expressed as integral membrane proteins, are also present in soluble form in the peripheral circulation. These soluble human leukocyte antigens (sHLA) are found at elevated levels in patients with a variety of infections as well as in organ transplant recipients. In liver transplant recipients, however, most of the circulating sHLA are of donor phenotype, especially during the early posttransplant period. Here we report the purification and characterization of sHLA of both recipient and donor origin from liver transplant recipients. It was observed that sHLA consisted of four major polypeptides having molecular mass of 44, 41, 35-37, and 12 kD complexed with IgM and IgG antibodies. Further analysis revealed that these immunoglobulins contained anti-HLA antibodies. Analysis of the affinity-purified materials by a number of approaches failed to detect any other fragment(s) of HLA class I heavy chain polypeptides smaller than 12 kD. No significant difference was observed in the biochemical nature of the sHLA of donor and recipient origin and they were similar to those found in normal individuals. Affinity-purified HLA-A3 inhibited the cytolytic activity of an HLA-A3-specific CD8+ T cell line, whereas, purified sHLA-A2 failed to inhibit anti-HLA-A3 CTL activity. Further, the proliferation of the T cell line was not inhibited by sHLA-A3. Thus, the inhibitory activity shown by sHLA was antigen-specific and directed against a functional subset of T lymphocytes. These results support the notion that sHLA may play an important regulatory role in the immune response to allograft in humans.

The liver neither protects the kidney from rejection nor improves kidney graft survival after combined liver and kidney transplantation from the same donor

It has been proposed that the liver protects a simultaneously transplanted kidney from acute rejection. Using the United Network for Organ Sharing database, we compared the kidney allograft data from 248 combined liver and kidney transplants (LKT) with a control group comprising 206 contralateral kidney alone transplants (KAT) from the same donor. The LKT and KAT groups were identical with respect to most baseline parameters, save a greater degree of HLA matching in the KAT group. The overall 3-year graft survival rate was higher in the KAT group compared with the LKT group (80% vs 68%, P < 0.01). When these data were censored to remove death as a cause of graft loss and to minimize the matching effect, the 3-year survival rates were not statistically different (78% for KAT and 81% for LKT, P = NS). We conclude that the liver neither protects the kidney from rejection nor improves kidney allograft function or survival after LKT.

Small bowel transplantation. A life-saving option for selected patients with intestinal failure

Thirty-seven patients were listed for small bowel transplantation; 16 were transplanted and 15 died while waiting for a donor. Cyclosporine (N = 6) or tacrolimus (N = 10) were used for immune suppression. Graft rejection rates were lower in the combined liver/small bowel grafts than the isolated intestinal transplants (1/7 vs 5/7; P < 0.01) All of the cyclosporine group have died; the median survival was 25.7 months with two patients living more than five years. The tacrolimus group had fewer infections and a shorter hospital stay. All but two are alive with a median survival of 13 months. Seven of eight long-term survivors are off intravenous feedings. We conclude that small bowel transplantation is a life-saving option for patients with intestinal failure who cannot be maintained on total parenteral nutrition.

Repeat HLA-B and -DR loci mismatching at second liver transplantation improves patient survival

The role of HLA matching in liver transplantation remains uncertain, and the effect of HLA mismatches on the outcome of second transplants has not been studied. In renal transplantation, if HLA mismatches are repeated in the second graft there is a greatly increased risk of immunological graft failure. In the present study, 78 patients who had received second liver transplants were studied. HLA typing was performed using standard complement-dependent microcytotoxicity for class I (A and B) antigens, and a combination of restriction fragment length polymorphism and serology for HLA-DR. Patient survival at follow-up for those with a repeat B locus mismatch was improved (79% compared with 43%, P < 0.02), and a similar effect was noted for repeat DR mismatches (67% vs. 47%, P = 0.06). In the subgroup of patients who received a second transplant for graft rejection, 90% of patients with a repeat B mismatch were alive at follow-up compared with 46% without B mismatches (P = 0.02). This improvement in patient survival was evident during the first 2 months after the second transplant. In this study, repeat HLA-B and -DR mismatching improves survival after second transplantation.

HLA-derived peptides which inhibit T cell function bind to members of the heat-shock protein 70 family

Synthetic peptides corresponding to sequences of HLA class I molecules have inhibitory effects on T cell function. The peptides investigated in this study have sequences corresponding to the relatively conserved region of the alpha 1 helix of HLA class I molecules that overlaps the "public epitope" Bw4/Bw6. These HLA-derived peptides exhibit inhibitory effects on T lymphocytes and have beneficial effects on the survival of allogenic organ transplants in mice and rats. Peptides corresponding to the Bw4a epitope appear most potent as they inhibit the differentiation of T cell precursors into mature cytotoxic T lymphocytes (CTL) and target cell lysis by established CTL lines and clones. To elucidate the mechanism through which these peptides mediate their inhibitory effect on T lymphocytes, peptide binding proteins were isolated from T cell lysates. We show that the inhibitory Bw4a peptide binds two members of the heat-shock protein (HSP) 70 family, constitutively expressed HSC70 and heat-inducible HSP70. Peptide binding to HSC/HSP70 is sequence specific and follows the rules defined by the HSC70 binding motif. Most intriguing, however, is the strict correlation of peptide binding to HSC/HSP70 and the functional effects such that only inhibitory peptides bind to HSC70 and HSP70 whereas noninhibitory peptides do not bind. This correlation suggests that small molecular weight HLA-derived peptides may modulate T cell responses by directly interacting with HSPs. In contrast to numerous reports of HSP70 expression at the surface of antigen-presenting cells and some tumor cells, we find no evidence that HSC/HSP70 are expressed at the surface of the affected T cells. Therefore, we believe that the peptides' immunodulatory effects are not mediated through a signaling event initiated by interaction of peptide with surface HSP, but favor a model similar to the action of other immunomodulatory compounds, FK506 and cyclosporin A, with a role for HSC/HSP70 similar to that for immunophilins, FKBPs and CyP40.

Indirect T cell recognition in allograft rejection

Allograft rejection has been attributed predominantly to alloreactive T cells which recognize intact allogeneic MHC on donor antigen presenting cells (APC). Following transplantation, T cells may also recognize donor derived MHC antigens which have been processed and presented as antigenic peptides in the context of self-MHC by recipient APC--so called indirect allorecognition. This article discusses the possible role of indirect T cell recognition in the graft rejection response with particular emphasis on recent experimental data obtained from in vivo transplant models. Although the relative contribution of indirect allorecognition to the rejection process remains unclear the available evidence suggests that the contribution of self-MHC restricted T cells to graft rejection may have been underestimated.

T cell receptor (TCR) repertoire in alloimmune responses

A large number of alloantigenic determinants could be generated by both the direct and indirect alloantigen presentation pathways. Hence, a heterogeneous population of T cells expressing a wide variety of receptors would be expected to respond to this diverse array of alloantigenic determinants. However, T cells expressing highly restricted T cell receptor (TCR) variable genes have been reported in a variety of alloimmune responses. A similar phenomenon has been observed in a wide variety of other immune responses, from those induced by superantigens, to very specific responses induced by a single peptide presented by a single MHC molecule. Given this scenario, the limited number of T cell clones which dominate an allograft rejection response, or for that matter an autoimmune response or a tumor specific response, could be therapeutically targeted by virtue of the selected TCR expression.

Variable chimerism, graft-versus-host disease, and tolerance after different kinds of cell and whole organ transplantation from Lewis to brown Norway rats

The bidirectional paradigm of tolerance involving reciprocal host vs. graft and graft vs. host reactions was examined after Lewis (LEW)-->Brown Norway (BN) transplantation of different whole organs (liver, intestine, heart, and kidney) or of 2.5 x 10(8) LEW leukocytes obtained from bone marrow, spleen, lymph nodes, and thymus. The experiments were performed without immunosuppression or under 14 daily doses of postoperative tacrolimus, which were continued in weekly doses to 100 days in a "continuous treatment" subgroup, and to 27 days in a short treatment group. Without immunosuppression, all organs and cell suspensions failed to engraft or were acutely rejected. GVHD (usually fatal) was always caused when either the long or short treatment was used for recipients of intestinal grafts and cell suspensions of spleen and lymph nodes. In contrast, both immunosuppressive protocols allowed engraftment of bone marrow cells, liver, heart, and kidney without clinical GVHD, whereas thymus cell suspensions and small doses of whole blood neither engrafted nor caused GVHD. At 100 days, now drug-free for 73 days, the liver, bone marrow, and heart recipients were tolerant in that they accepted all challenge LEW heart and/or liver grafts for 100 more days despite in vitro evidence of donor-specific reactivity (split tolerance). At 200 days, histopathologic studies of the challenge livers were normal no matter what the priming graft. However, the still-beating challenge hearts had a spectrum from normal to severe chronic rejection that defined the tolerogenicity of the original primary grafts: liver best-->bone marrow next-->heart least. Both the GVHD propensity and tolerogenicity in these experiments were closely associated with recipient tissue chimerism 30 and 100 days after the experiments began. The tissue chimerism was invariably multilineage, but the GVHD outcome was associated with T cell over-representation. These observations provide guidelines that should be considered in devising leukocyte augmentation protocols for human whole organ recipients. The results are discussed in relation to the historical tolerance studies of Billingham, Brent, and Medawar; Good; Monaco; and Calne.

An enzyme immunoassay for rat soluble MHC class I molecules (RT1a) and the release of soluble class I from mitogenically stimulated mononuclear cells

Soluble MHC class I antigens can be detected in the serum of humans and various animals and appear in the circulation shortly after liver transplantation. The precise role of these antigens is currently uncertain, but soluble MHC class I may be involved in immunomodulation. We have developed an enzyme linked immunosorbent assay for soluble rat MHC class I (RT1a) molecules and monitored the kinetics of antigen release following in vitro stimulation of splenic mononuclear cells. A 4 day DA splenocyte Con A supernatant provided a source of soluble class I antigens and was arbitrarily assigned a concentration of 1000 units/ml. Ninety six well plates were coated with a rat RT1a-specific mAb (MN4-91-6) and soluble class I binding was detected using a biotinylated mAb reactive with a monomorphic region of the rat MHC class I molecule (OX18) followed by a streptavidin-alkaline phosphatase conjugate and substrate. The intra- and interassay variations were typically less than 5% and 10% respectively, to give a working range for the assay of between 62.5 and 1000 units/ml. Mitogenic stimulation led to a progressive increase in soluble class I levels in culture supernatants. This assay will be valuable in differentiating recipient and graft responses following experimental organ transplantation.

Increased serum concentration of soluble HLA-DR antigens in HIV infection and following transplantation

HLA class I and class II antigens circulate in serum as soluble molecules. Increased concentrations of soluble HLA class I molecules have been demonstrated in viral diseases, in rejection episodes following organ transplantation and in graft versus host disease. To explore the possibility of a variation of the serum concentrations of soluble HLA class II molecules in the same pathologic conditions we developed a double determinant immune assay that detects whole soluble HLA-DR molecules (sHLA-DR). The mean level of sHLA-DR antigens in sera from 23 healthy individuals was 0.64 +/- 0.72 microgram/ml. Elevated serum concentrations of sHLA-DR molecules were detected in sera from HIV infected patients in CDC2/3 and in CDC4 C1 stages (2.0 +/- 1.7 micrograms/ml and 4.6 +/- 1.7 micrograms/ml, respectively), in sera from patients affected by acute rejection after liver transplantation (5.3 +/- 3.7 micrograms/ml) and in sera from patients affected by severe acute graft versus host disease following bone marrow transplantation (8.8 +/- 3.1 micrograms/ml). The increase of sHLA-DR molecules in these sera significantly correlated with the elevation of soluble HLA class I antigens (P = 0.0004). The reported data suggest that both soluble HLA class I and class II molecules serum levels increase during viral infections and strong immune reactions and could suggest the involvement of these molecules in immunoregulation.

Variable chimerism, graft-versus-host disease, and tolerance after different kinds of cell and whole organ transplantation from Lewis to brown Norway rats

The bidirectional paradigm of tolerance involving reciprocal host vs. graft and graft vs. host reactions was examined after Lewis (LEW)-->Brown Norway (BN) transplantation of different whole organs (liver, intestine, heart, and kidney) or of 2.5 x 10(8) LEW leukocytes obtained from bone marrow, spleen, lymph nodes, and thymus. The experiments were performed without immunosuppression or under 14 daily doses of postoperative tacrolimus, which were continued in weekly doses to 100 days in a "continuous treatment" subgroup, and to 27 days in a short treatment group. Without immunosuppression, all organs and cell suspensions failed to engraft or were acutely rejected. GVHD (usually fatal) was always caused when either the long or short treatment was used for recipients of intestinal grafts and cell suspensions of spleen and lymph nodes. In contrast, both immunosuppressive protocols allowed engraftment of bone marrow cells, liver, heart, and kidney without clinical GVHD, whereas thymus cell suspensions and small doses of whole blood neither engrafted nor caused GVHD. At 100 days, now drug-free for 73 days, the liver, bone marrow, and heart recipients were tolerant in that they accepted all challenge LEW heart and/or liver grafts for 100 more days despite in vitro evidence of donor-specific reactivity (split tolerance). At 200 days, histopathologic studies of the challenge livers were normal no matter what the priming graft. However, the still-beating challenge hearts had a spectrum from normal to severe chronic rejection that defined the tolerogenicity of the original primary grafts: liver best-->bone marrow next-->heart least. Both the GVHD propensity and tolerogenicity in these experiments were closely associated with recipient tissue chimerism 30 and 100 days after the experiments began. The tissue chimerism was invariably multilineage, but the GVHD outcome was associated with T cell over-representation. These observations provide guidelines that should be considered in devising leukocyte augmentation protocols for human whole organ recipients. The results are discussed in relation to the historical tolerance studies of Billingham, Brent, and Medawar; Good; Monaco; and Calne.

Soluble HLA-G molecule. An alternatively spliced HLA-G mRNA form candidate to encode it in peripheral blood mononuclear cells and human trophoblasts

The HLA-G nonclassic MHC class I gene expressed at the maternal-fetal interface may be involved in cell protection against NK cell lysis. HLA-G mRNA is observed in different adult or fetal human cells and exhibits four alternative forms: HLA-G1, HLA-G2, HLA-G3, and HLA-G4 lacking, respectively, exon 7; exons 7 and 3, exons 7, 3, and 4; exons 7 and 4. Because exon 5 encodes the transmembrane domain of the HLA-G antigen, none of these transcripts could give a soluble form as detected in supernatant of trophoblasts. In this report, we describe an additional alternatively spliced for of HLA-G transcript (HLA-G5) present in adult PBMCs and first-trimester trophoblasts that contains intron 4. Moreover, as with all other transcripts, HLA-G5, is devoid of exon 7. Its relative frequency is, respectively, approximately 1:8 and approximately 1:26 in adult PBMCs and first-trimester trophoblasts. The presence of intron 4 generates a stop codon that excludes transmembrane region (exon 5) of the HLA-G molecule and therefore might produce a soluble antigen. These results are discussed with regard to data on soluble forms of classic HLA antigens and the possible role of HLA-G.

Isolation of a 40 kDa immunoinhibitory protein induced by rat liver transplantation

In certain combinations of donor and recipient rat strains, such as DA (RT1a) donors into PVG (RT1c) recipients, rejection after orthotopic liver transplantation (OLT) is overcome without immunosuppressive drugs, although other organs transplanted between these combinations are promptly rejected. The mechanisms involved in achieving drug-free liver allograft tolerance still remain poorly understood. In the present study, OLT (DA into PVG) serum from various postoperative times was analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis and two unique proteins of 40 kDa and 37 kDa were found to be in large concentrations in 60 day post-OLT serum. These proteins could only be detected at specific times after OLT in the DA into PVG combination and could not be detected in the serum of syngenically transplanted animals (DA into DA) and (PVG into PVG), rejector combinations (DA into LEW) requiring immunosuppressive treatment or induced by other organ transplants. When these proteins were purified and sequenced they were found to have an identical N-terminal sequence which is not listed in sequence databases. Mixed lymphocyte assays revealed that only the 40 kDa protein has a immunosuppressive capability which additionally appears to be donor specific. The 40 kDa protein will aid further in the understanding of how drug-free tolerance is attained in certain liver allografts and may also act as a marker of when treatment with conventional immunosuppressive drugs can be stopped in clinical OLT providing a homologue of the molecule can be found. This possibility appears likely as case reports already exist of patients who have successfully been able to cease treatment with such drugs.

The essential roles of parenchymal tissues and passenger leukocytes in the tolerance induced by liver grafting in rats

Liver allografts in pigs and rodents are uniquely capable of inducing tolerance to themselves and to other grafts of donor tissues, instead of succumbing to the acute rejection that follows transplantation of other allogeneic tissues. We demonstrate here, using normal and chimaeric rat liver grafts, that both the allogeneic liver parenchyma and the intrahepatic leukocytes of donor type contribute to the establishment of long-term tolerance, each component being essential and complementary. The essential role of hepatic parenchyma may be related to its continuous release of soluble transplantation antigens that facilitate tolerogenesis. We suggest that clinical attempts at tolerance induction by the infusion of donor bone marrow-derived leukocytes may likewise be facilitated by the coadministration of soluble transplantation antigens of donor type.

Allogeneic lymphocyte chimerism after clinical lung transplantation

Donor lungs contain large amounts of passenger leukocytes which are transferred to the recipient by organ transplantation. In this study we have analysed the fate of these cells and have studied the populations of donor leucocytes detectable in the blood circulation of ten lung transplanted patients during the first postoperative weeks. To this aim we have applied immunocytological as well as flow cytometric analyses using monoclonal antibodies against polymorphic HLA class I antigens that differed between donor and recipient as well as antibodies against cell differentiation markers. The results demonstrate that donor cells can be detected in the circulation of all lung transplanted patients but there is a considerable interindividual variability between 0.9% and 17.5% (mean 5.1%) on postoperative day 3. Cells were usually detectable for 2-4 weeks and had disappeared in all patients after 1 month. The circulating donor cells consisted exclusively of lymphocytes. T cells were the predominant population, most of which seemed to be CD45R0+, but B and NK (natural killer) cells were also present. Probably due to the small numbers of patients studied no correlation between clinical parameters and the extent of donor lymphocyte persistence; there were no clinical graft-versus-host reactions. The findings demonstrate the regular existence of a transient (macro)chimerism due to passenger lymphocytes in the early phase after lung transplantation. The immunological function and the relation between this phenomenon and the long-term microchimerism which frequently develops after solid organ transplantation remain unclear.

Production of soluble HLA-class-I molecules by IFN-gamma-induced colon-adenocarcinoma cells

High levels of soluble HLA-class-I molecules (sHLA) were found to be produced in a time- and dose-dependent manner by colon-adenocarcinoma Colo205 cells in response to IFN-gamma stimulation. Among other cytokines tested, only IL-6, TNF, IFN-alpha and IFN-beta showed weak inducibility. IFN-gamma-induced production of sHLA was synergistically enhanced by IL-1 alpha, IL-6 or TNF, and combined treatment with TNF and IL-6 exhibited an additive to synergistic induction. Expression of sHLA is unlikely to result from IFN-gamma-induced enhancement of overall HLA-class-I expression, as at low concentrations IFN-alpha, IFN-beta and IFN-gamma stimulated increased expression of cell membrane HLA-class-I molecules in Colo205 cells with almost equal efficiency, whereas only IFN-gamma induced high level production of sHLA. Immunoblotting with a monoclonal antibody recognizing beta 2-microglobulin-free HLA-class-I heavy chain revealed 3 major forms of sHLA heavy chain, i.e., 45/43-, 37- and 33-kDa molecules, in the culture supernatants of IFN-gamma-induced Colo205 cells. The 45/43-kDa proteins can be partitioned into Triton X-114, representing intact HLA-class-I heavy chains shed from the cell membrane. The hydrophilic 37- and 33-kDa heavy chain, which remained almost exclusively in the aqueous phase after extraction with Triton X-114, could well be due to alternative RNA splicing, with deletion of exon 5 encoding the hydrophobic transmembrane region of membrane-anchored HLA-class-I heavy chain.

Small bowel transplantation

The small bowel, the largest lymphoid organ in the body and host to a myriad of foreign antigens has presented a formidable challenge for transplantation. In the past 5 years, small bowel transplantation has become a viable clinical entity. Successful transplantation of the small bowel has been achieved as part of multivisceral grafting, combined small bowel and liver grafts and even as isolated small bowel grafts. Allograft rejection remains an important post-transplantation problem, although graft versus host disease has been less of a clinical problem than initially feared. Markers that may serve to predict early rejection have been identified and include: assessment of endoscopic biopsies for enterocyte Class II antigen expression and for mucosal T cell and macrophage infiltration, bowel permeability studies, and measurement of changes in transepithelial potential difference. Earlier detection of rejection and more potent therapy for rejection episodes will be necessary to further improve outcomes.

Effect of crossmatching on outcome in organ transplantation

The complement-dependent cytotoxicity (CDC) crossmatch and the flow cytometry crossmatch (FCXM) are both used prospectively in renal transplantation, and their use is under evaluation in other types of major organ transplantation. The FCXM is the more sensitive method and better predicts outcome in second and subsequent renal allografts. Improved survival has unmasked the detrimental effect of a positive crossmatch on outcome in liver transplantation. Because of the urgent need of liver transplant candidates, it is unrealistic to defer transplantation until a crossmatch-negative donor is found; however, additional therapeutic measures may be taken to improve outcome for crossmatch-positive liver recipients. Some reports suggest that prospective crossmatching may improve outcome for sensitized heart recipients, and, additionally, recent studies have demonstrated that HLA compatibility between donor and recipient is an independent variable affecting survival after heart transplantation, prompting a reassessment of the current practice of transplanting hearts without consideration of the HLA match.

Detection efficacy of soluble HLA-A, B antigens using 1D-IEF

Soluble HLA class I alloantigens (sHLA class I) can be typed according to their isoelectric points (IEP) after immunoprecipitation by w6/32 monoclonal antibody (mAb) coupled to immunomagnetic beads and focusing. In order to prove the large scale efficacy of this methodology, EDTA-plasma samples from 344 probands HLA-A, B typed by serology were analysed by one-dimensional isoelectric focusing and HLA class I specific Westernblot (1D-IEF). In addition, detergent solubilized HLA class I membrane molecules from approximately one half of the probands were studied too. Soluble HLA-A24,B7,B18,B62 antigens were identified in nearly all experiments, whereas A28, B13, and B51 could be detected in about 50%. A third group of HLA antigens (A26, B8, B44) could be visualized rarely. The difficulties of detection might be due to the different affinity of mAb w6/32 to certain sHLA class I gene products or to variable amounts of sHLA class I in the plasma specimens. Some modifications of the antigen capture technique have already led to a slightly better degree of antigen recognition in 25 probands tested. Thus, HLA-A, B typing using sHLA molecules and 1D-IEF in the assay format presented does not yet seem to be a definitive alternative for HLA class I serology or biochemistry of membrane-bound HLA class I molecules but it should be a promising technique if no cells are available or donor-derived sHLA allotypes are to be monitored after HLA mismatched organ transplantation.

Prospects for induction of tolerance in renal transplantation

Immunological tolerance is the ultimate goal of transplantation immunobiology. Current therapies involve nonspecific immunosuppression with concomitant risks for infection, malignancy, and drug-specific side effects. By inducing specific immune unresponsiveness to the graft it should be possible to maintain transplants without the need for chronic drug administration and without the risk of nonspecific immunosuppression. This review highlights recent progress in the understanding of immunological tolerance, with special attention to the long-term prospects for successful induction of tolerance in renal transplant patients.

The history and development of organ transplantation: biology and rejection

In this chapter I have tried to survey organ transplantation from the point of view of a researcher who has been involved in the field since 1959. I have traced the two different lines of research--one, immunological and the other, surgical. To a large extent the surgical problems of transplantation have now been solved but rejection remains the main stumbling block to long-term survival of organ allografts. Immunological tolerance and defining rejection as an immune mechanism provided a background which was considered by immunologists to be hopeless from the point of view of clinical application. Surgeons, however, demonstrated the successful grafting of kidneys in identical twins. Then surgical observations clarified the different susceptibility of individual tissues to rejection, the liver being less likely to be rejected of the vital vascularized organs. An analysis of this phenomenon has been presented together with data on new powerful immunosuppressive drugs. Work in progress world wide is directed to the eventual establishment of tolerance in the clinic so that recipients of organ grafts will not have to submit to a lifetime of potentially toxic drug dosage. A shortage of organs for transplantation and the ethical dilemmas make organ transplantation an unusual and worrying field of medicine. Perhaps we will find salvation in transplanting organs from animals, although this achievement would seem to be some way off.

Quantification of serum-soluble HLA class I antigens in patients with gastric cancer

The amount of sHLA-I in serum was examined in 74 patients with gastric cancer and 15 normal healthy controls. For mAbs, W6/32 specific for HLA-A, -B, -C, and biotin IOT2 specific for HLA class I associated with beta 2 microglobulin, were used to determine the values of sHLA-I using an ELISA. The patients in stage-IV gastric cancer showed lower values of sHLA-I (445.4 +/- 247.1 ng/ml) than those in stage I (725.9 +/- 575.8 ng/ml), stage II (752.8 +/- 255.0 ng/ml), and normal controls (868.9 +/- 715.0 ng/ml) (P < 0.05). In analysis of the patients with HLA-A24, the allele that has been reported to secrete more sHLA-I than other alleles, the results were nearly the same. These results suggest that the secretion of sHLA-I is low in patients with very advanced cancer. However, there was no correlation between the sHLA-I level and the metastasis or prognosis in longitudinal studies in 11 patients.

Monitoring of kidney and simultaneous pancreas-kidney transplantation rejection by release of donor-specific, soluble HLA class I

Using an HLA-A2-specific ELISA we monitored daily pretransplantation and posttransplantation sera from five kidney and eight simultaneous pancreas-kidney HLA-A2-negative recipients of HLA-A2-positive transplants during hospitalization. We found that, unlike liver transplants, neither kidney nor simultaneous pancreas-kidney transplants continuously secreted donor HLA proteins. However, three of four rejection episodes in kidney recipients and seven of seven rejection episodes in simultaneous pancreas-kidney recipients were accompanied by elevated serum levels of donor sHLA-A2 (> 5 ng/ml). In only one kidney patient was there a release of donor antigen without evidence of rejection, but in the simultaneous pancreas-kidney group most patients had at least one time point of detectable sHLA-A2 without strong evidence of kidney rejection. While total sHLA levels were also elevated during rejection, the rise in donor-specific sHLA was more dramatic when compared to pretransplantation background levels. We hypothesized that the release of donor sHLA class I proteins by transplanted organs might be a systemic indication of rejection in both pancreas and kidney allografts. The detection of donor sHLA in recipient sera could be an important noninvasive monitor of rejection, especially in the pancreas, which is currently difficult to monitor as a single-organ transplant.

Assessment of three methods of evaluating soluble class I HLA molecules in cell culture supernatants and serum samples from the second international workshop on soluble human leukocyte antigens

Three methodologies were compared in assessing sHLA specificities in cell culture supernatants and serum specimens from the Second International Workshop on sHLA: CDC inhibition, FC inhibition, and cellular ELISA inhibition. Initially, the CDC inhibition assay used polyclonal antisera in commercial HLA-phenotyping trays to confirm known specificities and screen for unknown specificities in 31 specimens. Although partly successful, critical limits were imposed by the variable antiserum titers. Thus, using pools of these same antisera and renal transplant recipient antisera, the FC inhibition assay was employed to determine the endpoint serum titers before confirming the known sHLA specificities. Of 25 specimens, four were not confirmed and five gave weak inhibitory reactions. The cellular ELISA inhibition assay, incorporating patient sera and mAbs toward three HLA, successfully confirmed all three known specificities in eight selected workshop specimens. Each methodology had advantages and disadvantages, but all three methods were successful in detecting and identifying sHLA class I specificities. Success, however, was dependent on the initial characterization (specificity and titer) and titration to end point (appropriate for each method's sensitivity) of each antibody preparation.

Soluble form of an HLA-B7 class I antigen specifically suppresses humoral alloimmunization

A soluble HLA-B7 molecule, designated sB7 and generated by genetically engineering the B7 gene to remove the transmembrane and cytoplasmic domains, was tested as a tolerogen. Supernatants from cultures of C1R cells transfected with the gene for sB7 were harvested and concentrated, as were control supernatants. From days -17 to -1, C57Bl/6 mice were pretreated with a total of 11 intraperitoneal doses of 1.0 microgram each of sB7 or appropriate control supernatant, and then were challenged intraperitoneally on each of days 0, 7, and 14 with 10(6) C1R-B7 cells (expressing surface HLA-B7). Antibody kinetics revealed (1) anti-B7 was not induced after sB7 pretreatment; (2) the anti-B7 response of sB7-pretreated mice was marginal and of apparent low avidity compared with the brisk anti-B7 response of control mice; (3) none of the mice made antibody to a control HLA antigen, A24; (4) all mice made strong antibody responses to the non-B7 surface antigens of C1R; (5) free sB7 did not appear in the blood of the treated mice; and (6) all mice appeared to be generally healthy. These data show soluble B7 antigen is not immunogenic and appears to specifically block humoral immune response to cell membrane-bound HLA-B7 in a nontoxic manner.

HLA class-I-soluble antigen serum levels in liver transplantation. A predictor marker of acute rejection

The serum levels of sHLA-I have been determined in 16 patients following liver transplantation. sHLA-I levels did not show remarkable variations in six patients without evidence of transplant-related complications. sHLA-I levels strongly increased in 10 patients undergoing acute rejection episodes. In these patients, an average 20% daily increase of sHLA-I levels was detected on the 6 days preceding and on the 2 days following the rejection episode. A fast decrease of sHLA-I levels was observed in seven patients following treatment of acute rejection with anti-CD3 mAb. The serum level of sHLA-I antigens positively correlated with ALT serum level and inversely correlated with PT. The determination of sHLA-I in serum may therefore be proposed as a useful marker in the monitoring of patients following liver transplantation. The increase of sHLA-I antigens may predict the onset of acute rejection whereas their decrease may be related to a good response of acute rejection to immunosuppressive treatment.