Soluble HLA antigens in the circulation of liver graft recipients

Impact of portal venous pancreas graft drainage on kidney graft outcome in simultaneous pancreas-kidney recipients reported to UNOS

Clinical data on the potential immunologic impact of portal (PD) vs. systemic (SD) venous pancreas graft drainage on outcome remains controversial. We reviewed the UNOS database to study the effect of PD vs. SD on the incidence of kidney graft rejection and survival in first cadaveric simultaneous pancreas-kidney (SPK) recipients transplanted 1994-2001. We studied three groups: all SPK (n=6629, 13% PD) (group I), SPK on tacrolimus (n=3563, 17% PD) (group II), and SPK on tacrolimus performed at centers with significant PD experience (n=948, 46% PD) (group III). The cumulative kidney graft rejection incidence for PD vs. SD was only significantly different in group I (for PD vs. SD, respectively: at 6 months, 31% vs. 36% [p=0.015]; at 1 year, 37% vs. 43% [p=0.006]). Kidney graft survival was similar in all groups for PD vs. SD. Multivariate analysis of group III showed only transplantation during the earlier era (1994-96), but not SD, to be an independent risk factor for kidney graft rejection. Portal venous pancreas graft drainage does not affect kidney graft rejection and survival in SPK recipients on tacrolimus. Our data suggests that the efficacy of current immunosuppressive protocols and increasing center experience are clinically much more relevant than any potential immunologic advantage of portal venous drainage in SPK recipients.

Immune regulation and graft survival in kidney transplant recipients are both enhanced by human leukocyte antigen matching

We hypothesized that donor/recipient sharing of the human leukocyte antigen (HLA) involved in allopeptide presentation to the T regulatory cell increases the incidence of immune regulation, thus contributing to long-term graft survival. Peripheral blood mononuclear cells (PBMC) were obtained from 40 living related donor (LRD) and 31 cadaver renal transplant recipients. The trans vivo delayed type hypersensitivity (DTH) assay was used to assign patients to regulator, nonregulator, and sensitized categories. In a large cohort (n=1934 patients), primary graft survival and rejection episodes were analyzed using a log rank test for comparison with the DTH results. The highest incidence of regulated anti-donor DTH was observed in the LRD HLA-identical group (6/6; 100%) followed by the LRD HLA 1 haplotype matched group (18/27; 67%). Within the cadaver population, two DR-matched recipients had a higher frequency of regulated anti-donor DTH (6/11; 55%) than 1 & 0 DR-matched recipients (3/18; 17%). In a multivariate model, matching for HLA-DR alone, or for DR plus DQ was significantly (p=0.045, p=0.041) correlated with DTH regulation. The better HLA-matched groups showed the highest incidence of DTH regulation and, in a larger retrospective analysis, displayed better graft survival and freedom from acute rejection (p<0.0001). HLA matching, and HLA-DR matching in particular, correlates with the incidence of immune regulation after kidney transplantation.

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IFN-gamma is an absolute requirement for spontaneous acceptance of liver allografts

Experimental liver allografts undergo spontaneous acceptance despite undergoing rejection during the first few weeks post transplant. We explored the role of interferon-gamma (IFN-gamma) in the spontaneous acceptance of mouse liver allografts. Strain of mouse (CBA) liver allografts transplanted into normal BALB/c mice developed histologic changes typical of rejection that spontaneously regressed, permitting long-term survival of these allografts similar to that of syngeneic grafts. In contrast, CBA liver allografts in IFN-gamma-deficient hosts manifested not only infiltration but also hemorrhage and necrosis, with no survival beyond 14 days. Despite differences in survival, local expression of cytotoxic T-cell genes in the transplant was not increased in IFN-gamma-deficient hosts, but livers in interferon-gamma-deficient mice (GKO) hosts displayed much less induction of major histocompatibility complex (MHC) class I and II expression. To determine whether the difference in survival was secondary to the direct effects of IFN-gamma on the liver, we transplanted livers from IFN-gamma-receptor-deficient mice into normal hosts. Liver allografts lacking IFN-gamma receptors also developed hemorrhage and necrosis with minimal induction of MHC expression. Thus IFN-gamma mediates a direct effect on rejecting liver allografts that reduces hemorrhage and necrosis, induces MHC expression, and is absolutely required for spontaneous acceptance.

Prolongation of long-term kidney graft survival by a simultaneous liver transplant: the liver does it, and the heart does it too

BACKGROUND

Whereas some authors reported that kidney transplants were protected from rejection by simultaneous liver grafts, other authors failed to obtain evidence for a kidney graft-protective role for the liver.

METHODS

The survival rate of 383 kidney grafts in recipients of combined kidney-liver transplants performed between 1985 and 2000 and reported to the international Collaborative Transplant Study (CTS) was analyzed and compared retrospectively with that of a matched group of control patients who were transplanted with kidneys only. In addition, 105 combined kidney-heart transplants performed during the same time period were analyzed.

RESULTS

At 1 year, the survival rate of kidney grafts in recipients of kidney-liver transplants was significantly lower than that in kidney only recipients (P<0.0001). Subsequently, however, kidneys in kidney-liver recipients fared much better so that the success rates were virtually identical after 8 years of follow-up (62.1+/-3.5% vs. 61.9+/-2.3%, P=ns). Half-life times after the first posttransplant year were 27.6 and 14.5 years for combined or single kidney grafts, respectively, and the projected 20-year graft survival rates were 46% and 35%, respectively. The 8-year survival rate of kidney grafts in recipients of combined kidney-heart recipients was 63.5+/-6.2%, the associated half-life time 31.6 years, and the projected 20-year graft survival rate 49%.

CONCLUSIONS

The long-term kidney graft survival rate is higher in recipients of combined kidney-liver transplants than in recipients of kidney grafts only. Because the success rate is equally high in recipients of combined kidney-heart transplants, it is necessary to reexamine the hypothesis that the liver possesses a unique capacity of protecting a simultaneous kidney graft from rejection.

Human liver allograft acceptance and the "tolerance assay". II. Donor HLA-A, -B but not DR antigens are able to trigger regulation of DTH

In our initial study of liver transplant recipients using the trans vivo delayed-type hypersensitivity (DTH) assay, we found that in donor derived B-LCL or sonicates of donor leukocytes triggered linked suppression of the response to recall antigens tetanus toxoid (TT) or Epstein-Barr virus (EBV). Since both donor antigen sources contain HLA class I and class II proteins, we wished to determine which donor HLA proteins were responsible for the linked suppression effect. PBMC from four liver transplant recipients with donor-specific DTH regulation were studied. Surprisingly, we found that single donor HLA-A or B antigens (4/4 patients) but not single HLA-DR (0/4) donor antigens triggered linked suppression of DTH. A dose response study of two patients revealed that donor-type HLA-DR antigens (0.5-500ng) were not capable of triggering any linked suppression; however, as little as 500pg of donor-type HLA-class I protein triggered linked suppression of DTH response to a recall antigen. These findings may have implications for the differential impacts of class I vs class II mismatching in organ transplantation. On a practical level, they indicate that soluble HLA-A and B antigens are the proper choice for detection of DTH regulation as part of a "tolerance assay" in human liver transplant recipients.

Use of an adenoviral vector to express soluble donor-major histocompatibility complex molecules capable of suppressing the immune response in rat transplant recipients

There is an accumulating body of evidence indicating that soluble major histocompatibility complex (sMHC) molecules have donor-specific immunosuppressive properties. One classic, but still unproven, theory is that production of sMHC by liver transplants induces a potent immunosuppressive effect. To mimic this possible effect, we have developed a replication deficient adenovirus (Ad-RQ) to express high levels of donor sMHC class I molecules (sRT1.A(a)) in the liver. Ad-RQ produced sRT1.A(a) was measured by enzyme-linked immunosorbent assay (ELISA) after in vitro infection of Lewis (RT1(l)) hepatocytes, and in vivo following intravenous virus injection into Lewis rats. Results indicated high sRT1.A(a) expression in Lewis hepatocyte cultures and, in vivo, high expression was also demonstrated and maintained for at least 1 week. A strong immunosuppressive potential of sMHC in vivo was revealed by prolongation of cardiac (ACI, RT1(a)) heart allograft survival in high-responder Lewis rat recipients treated with Ad-RQ alone. Furthermore, limiting dilution cytotoxic T-lymphocyte precursor (CTLp) analysis of lymphocytes from Ad-RQ-treated Lewis recipients receiving an ACI heart transplant indicated a marked decrease in antidonor CTLp frequency. In conclusion, our results demonstrate that viral vectors can be used effectively to express high levels of sMHC molecules, and their immunosuppressive effect, without concurrent immunosuppression, is sufficiently potent to prolong heart transplant survival.

Is presensitization relevant to liver transplantation outcome?

The impact of anti-HLA antibodies and crossmatch (CM) on liver transplantation (LT) outcome is still controversial. In this retrospective study we analyzed LT outcome according to pretransplant pre-formed anti-HLA antibodies and CM status. Serum anti-HLA antibodies were screened by ELISA assay, utilizing One Lambda antigen tray-mixed (LAT-M). CMs were performed by the complement dependent cytotoxicity test using Dithiotreitol treated sera. Anti-HLA antibodies were studied in 80 recipients; 56/80 had positive LAT-M tests (PLAT-M), whereas the remaining 24 recipients tested negative for both classes I and II (NLAT-M). Rejection episodes were more frequent in PLAT-M compared with NLAT-M group in post-LT intervals of <1 week (p = 0.05), 1 week-3 months (p = 0.035), and 3-12 months (p = 0.076). Graft and patient survival rates were better, albeit not significantly, in the NLAT-M compared with PLAT-M recipients. CM status was investigated in 62/80 recipients, 18/62 recipients had positive CM (PCM), and 44 had negative CM (NCM). Five of 18 PCM recipients (28%) experienced early graft loss compared with 1/44 (2%) with NCM (p = 0.006). Rejection episodes were more frequent within first 3 months post-LT in PCM recipients compared with NCM (p = 0.015). One-year graft survival rate was better in NCM, compared with PCM recipients (graft loss of 2/44 vs 5/18). NCM PLAT-M had a higher incidence of rejection episodes compared with the NCM NLAT-M group (p = 0.031). The presence of anti-HLA antibodies suggests a deleterious effect on LT outcome, and was associated with an increased incidence of early graft loss and rejection episodes.

The role of passenger leukocyte genotype in rejection and acceptance of rat liver allografts

BACKGROUND

Although graft-resident passenger leukocytes are known to mediate acute rejection by triggering direct allorecognition, they may also act in an immunomodulatory fashion and play an important role in tolerance induction. Our purpose in the current study was to utilize rat bone marrow chimeras to evaluate the role of the genotype of passenger leukocytes in both acute rejection and tolerance of liver allografts.

METHODS

The fate of livers bearing donor-type, recipient-type, and third-party passenger leukocytes was evaluated in the MHC class I and II mismatched rejector combination ACI-->LEW and the acceptor combination PVG-->DA.

RESULTS

We report that although treatment of ACI liver donors with lethal irradiation does not lead to prolongation of graft survival in the ACI-->LEW strain combination, ACI livers bearing recipient-type (LEW) or third-party passenger leukocytes (BN) are rejected at a significantly slower rate. We confirm that lethal irradiation of PVG donor animals leads to abrogation of tolerance induction with acute rejection of their livers by DA recipients. However, the majority of PVG livers carrying donor-type (PVG), recipient-type (DA), or third-party (LEW) passenger leukocytes are accepted for >100 days. These DA recipients develop immune tolerance to the donor parenchyma (PVG).

CONCLUSIONS

Our findings demonstrate that long-term acceptance of liver allografts and tolerance induction is not dependent on the presence of donor-type passenger leukocytes and can be achieved with organs carrying donor-type, recipient-type, or third-party passenger leukocytes. The importance of the MHC framework on the surface of passenger leukocytes as a critical regulator of the immune response after transplantation of chimeric organs is substantiated by the delayed tempo of rejection of ACI livers bearing recipient-type or third-party passenger leukocytes in the ACI-->LEW strain combination.

Identification of patients best suited for combined liver-kidney transplantation: part II

Liver-kidney transplantation (LKT) should be reserved for those recipients with primary disease affecting both organs. However, increasing transplant list waiting times have increased the development and duration of acute renal failure before liver transplantation. Furthermore, the need for posttransplant calcineurin inhibitors can render healing from acute renal failure difficult. Because of the increasing requests for and controversy over the topic of a kidney with a liver transplant (OLT) when complete failure of the kidney is not known, the following article will review the impact of renal failure on liver transplant outcome, treatment of peri-OLT renal failure, rejection rates after LKT, survival after LKT, and information on renal histology and progression of disease into the beginnings of an algorithm for making a decision about combined LKT.

Spontaneous acceptance of liver transplants in rodents: evidence that liver leucocytes induce recipient T-cell death by neglect

In many animal models transplanted livers are not rejected, even when there is a complete MHC mismatch between the donor and recipient and the recipient is not immunosuppressed. This distinguishes liver transplants from other organs, such as kidneys and hearts, which are rapidly rejected in mismatched individuals. Acceptance of transplanted livers in a rat model is not due to the absence of an immune response to the liver and there is a rapid, abortive response that is ultimately exhausted. Donor leucocytes transferred with the liver appear to be responsible for both liver acceptance and the abortive activation of the recipient's T cells. The immune mechanism of liver transplant acceptance appears to be due to 'death by neglect' in which T cells are activated to express IL-2 and IFN-gamma mRNA in the recipient lymphoid tissues, but not at adequate levels within the graft. Subsequently the activated T cells die leading to specific clonal deletion of liver donor-reactive T cells. These findings have important implications for liver transplant patients as immunosuppressive drugs that are given to prevent rejection can also interfere with this form of tolerance. In addition, it might be possible to modify the immunosuppressive drug treatment of transplant patients to promote the process of death by neglect of recipient alloreactive T cells.

Antigenic load and peripheral chimeric levels in entire and partial liver allograft recipients

Orthotopic partial liver transplantation (PLT) models were developed in rats to explore the unique role of the liver in transplant tolerance. In PVG rats, syngeneic PLT established that surgical reduction to one-third of the liver and orthotopic transplantation permitted survival. Allogeneic PLT in the PVG to DA liver-tolerant model, both 50% and 33%, did not affect the tolerogeneic property of the liver, with all PLT recipients surviving indefinitely. Blood samples taken at various time points for detection of donor cells using flow cytometry showed a steady increase in donor cell chimerism in both PLT and whole liver transplantation (WLT) recipients that persisted throughout the 3-month observation period. At each time point, the level of donor cell chimerism in PLT was higher than that in WLT. We conclude that transplantation of one-third of the liver is compatible with survival in rats. Reduction of antigenic load by means of hepatectomy does not affect the tolerogenic effect of the liver in the PVG to DA LT model because of the remarkable regeneration capability of the liver. Peripheral chimeric levels increase progressively after WLT, suggesting that this is an ongoing immunological phenomenon. The earlier and increased chimerism after PLT may be associated with liver regeneration.

Il-12 antagonism enhances apoptotic death of T cells within hepatic allografts from Flt3 ligand-treated donors and promotes graft acceptance

Mouse livers are accepted across MHC barriers and induce donor-specific tolerance without immunosuppressive therapy. By contrast, livers from donors treated with Flt3 ligand, which dramatically increases hepatic interstitial dendritic cells, are rejected acutely (median survival time 5 days). This switch from tolerance to rejection is associated with a marked reduction in apoptotic activity of graft-infiltrating cells. We hypothesized that IL-12 production by enhanced numbers of donor APC might inhibit apoptosis, promote expansion of Th1 cells, and play a key role in liver rejection. Therefore, C3H (H2(k)) recipients of liver grafts from Flt3 ligand-treated B10 donors were given neutralizing anti-IL-12 mAb (200 or 500 microg) on days 0 and 2 after transplant. Graft survival was markedly prolonged at the higher mAb dose, with 50% of grafts surviving >100 days. This effect was associated with reductions in IFN-gamma gene transcripts within the graft-infiltrating cell population and with reductions in circulating IFN-gamma and IL-10 levels, donor-specific CTL and NK cell activities, and circulating alloantibody levels. At the same time, there were marked increases in apoptotic (TUNEL(+)) CD4(+) and especially CD8(+) cells, both within the grafts and in spleens of anti-IL-12 mAb-treated mice. In vitro, exogenous IL-12 inhibited apoptotic death induced in naive allogeneic T cells by liver nonparenchymal cells. These findings suggest that suppression of rejection by IL-12 antagonism, linked to restoration of apoptotic activity within the peripheral alloreactive T cell population, is important for liver allograft survival and tolerance induction.

Rapid decreases in donor-specific cytotoxic T lymphocyte precursor frequencies and graft outcome after liver and lung transplantation

BACKGROUND

A decrease in donor-specific T cell precursor frequencies as seen late, one or more years, after transplantation is assumed to reflect transplantation tolerance, a condition important for long term acceptance of the allograft. However, such late decreases also occur in recipients that developed chronic transplant dysfunction questioning its relevance in transplantation tolerance. We investigated whether early, i.e., the first 6 months, decreases in donor-specific T cell precursor frequencies reflect transplantation tolerance and predict graft outcome after liver and lung transplantation.

METHODS

Donor and third party specific cytotoxic (CTLp) and helper T lymphocyte precursor (HTLp) frequencies were analyzed in pretransplant and 1 (or 2) and 6-month blood samples taken from liver and lung recipients and were correlated with graft outcome.

RESULTS

In liver allograft recipients with good graft function (n=7), mean donor-specific CTLp frequencies decreased as early as 1 month after transplantation and remained low thereafter. In contrast, mean CTLp frequencies did not decrease in liver allograft recipients with chronic transplant dysfunction (n=6). In lung allograft recipients, donor-specific CTLp frequencies remained relatively high and frequencies were not different between recipients without (n=6) or with (n=6) chronic transplant dysfunction. Donor-specific HTLp frequencies did not change significantly after liver or lung transplantation and did not differ between recipients without or with chronic transplant dysfunction.

CONCLUSIONS

An early decrease in donor-specific CTLp correlates with good graft outcome after liver transplantation. Such rapid decreases in alloreactivity do not occur after lung transplantation illustrating the unique capacity of liver allografts to induce transplantation tolerance.

Immune activation is required for the induction of liver allograft tolerance: implications for immunosuppressive therapy

Liver transplants in many animal models are unusual because often they are not rejected even when transplanted across complete major histocompatibility complex barriers without immunosuppression. Their paradoxical behavior is even more obvious when the immune mechanism of acceptance is examined. Instead of acceptance resulting from a lack of immune response to the graft, the opposite occurs, and there is an unusual extensive increase in immune activation in acceptance compared with rejection. This abnormal extensive immune activation is driven by donor leukocytes transferred with the liver and results in death of the recipient cells that would normally reject the transplant. Some forms of immunosuppression inhibit this activation-associated liver transplant tolerance. The significance of these findings and possible means to design future treatment protocols for clinical transplantation that optimize management of liver transplant recipients are discussed.

Soluble donor HLA class I and beta 2m-free heavy chain in serum of lung transplant recipients: steady-state levels and increases in patients with recurrent CMV infection, acute rejection episodes, and poor outcome

We determined the concentration of donor sHLA/beta(2)m and total beta(2)m-free heavy chain (HC) in the serum of lung transplant recipients with ELISA assays. While we were unable to detect specific donor beta(2)m-free HCs due to a lack of available antibodies, we could determine if events that led to an increase in the release of beta(2)m-free HC also led to an increase in the release of donor sHLA/beta(2)m, particularly the 36 kDa, proteolytically cleaved form. We found that lung transplants constituitively release donor sHLA/beta(2)m at ng/ml levels. The levels (both of donor sHLA/beta(2)m and total beta(2)m-free HC) were significantly increased in CMV-sero-negative recipients (but not in CMV-sero-positive recipients) at the onset of post-transplant CMV disease. Acute rejection episodes were also associated with an increased release of donor sHLA/beta(2)m, but not of beta(2)m-free HC. However, in patients with particularly poor outcome (i.e., graft loss within 1 year) there was a significant release of beta(2)m-free HC. Analysis of one such patient showed a predominance of 36 kDa forms of donor-sHLA/beta(2)m. Our data are consistent with the hypothesis that the metalloproteinase that cleaves beta(2)m-free HC is active during uncontrolled CMV infection and acute rejection. However, recall responses to CMV and controlled immune responses to donor may result in little or no activation of sHLA class I release.

Soluble HLA class I and Fas ligand molecules in blood components and their role in the immunomodulatory effects of blood transfusions

It has been known for many years that blood transfusions may have immunomodulatory effects, however an ultimate explanation of this phenomenon is lacking. In the present paper we report that the concentrations of soluble HLA class I (sHLA-I) and soluble Fas ligand (sFasL) molecules in supernatants of blood components which contain elevated numbers of residual donor leukocytes, like red blood cells and random-donor platelets, are significantly higher than in other blood components. Elevated amounts of sFasL molecules are also found in some commercial immunoglobulin preparations. sHLA-I and sFasL molecules in blood components and in immunoglobulin preparations are biologically active in vitro as they inhibit mixed lymphocyte responses and cytotoxic T cell activity in allogeneic and autologous combinations and induce apoptosis in Fas-positive cells. If these results are paralleled in vivo the amount of sHLA-I and sFasL molecules should be taken into account in clinical practice in order to select the blood component and the immunoglobulin preparation which could induce the desired immunomodulatory effect in the recipient.

Increased beta2-microglobulin-free HLA class I heavy chain serum levels in the course of immune responses to viral antigens and to mismatched HLA antigens

Besides being present in serum in association with beta2-mu, HLA class I heavy chains are also present in serum as beta2-micro-free moieties. The increase in serum levels of beta2-micro-associated HLA class I heavy chains in conditions associated with an activation of the immune system have prompted us to measure the serum levels of beta2-mu-free HLA class I heavy chains in the course of immune responses to viral antigens and to mismatched histocompatibility antigens. The serum level of beta2-mu-free HLA class I heavy chains, like that of beta2-mu-associated HLA class I heavy chains was significantly increased in patients affected by advanced HIV-1 infection or by chronic hepatitis C (CHC). In the latter group of patients an association was found between a reduction in the beta2-mu-free HLA class I heavy chain serum level and response to therapy with interferon alpha and ribavirin. Moreover, the beta2-mu-free HLA class I heavy chain serum level was increased more than that of beta2-mu-associated HLA class I heavy chains during episodes of liver ischemia following liver transplantation and in the course of acute graft rejection and of acute graft-versus-host-disease (GVHD) after allogeneic bone marrow transplantation (BMT). These results suggest that the serum levels of beta2-mu-free and beta2-mu-associated HLA class I heavy chains are independently regulated. Furthermore, beta2-mu-free HLA class I heavy chain serum level may be a useful marker to monitor response to therapy in CHC patients and the clinical course of liver and bone marrow grafts.

Donor-derived soluble HLA plasma levels can not be used to monitor graft rejection in heart transplant recipients

OBJECTIVE

Increased levels of both donor- and recipient-derived HLA class I molecules (sHLA-I) can be found in serum or plasma of transplanted patients during rejection. Earlier data indicate that levels of donor-derived sHLA-I (dsHLA-I) correlate better with graft rejection than total sHLA Class I (Zavazava N, Kraatz E, Gassel AM, Muller-Ruchholtz W. Plasma MHC class I expression in cardiac graft patients: donor-specific soluble antigen in a pre-sensitized graft patient. Transplant Proc 1991;23:2258-2260; Claas FHJ, Jankowska-Gan E, DeVito LD, et al. Monitoring of heart transplant rejection using a donor-specific soluble HLA class I ELISA. Hum Immunol 1993;37:121). Therefore, quantifying donor-derived soluble counterparts of HLA Class I (sHLA-I) in the plasma of the recipient may offer a new possibility for non-invasive monitoring of rejection after organ transplantation.

METHODS

In an extended study with 34 heart transplant recipients, we used sHLA-I specific ELISAs to monitor donor-derived soluble sHLA-A2, -A3, -A9, -B7, -B12 and B51.

RESULTS

The assays were sensitive enough to detect dsHLA Class I in plasma of the recipients. However, the levels of sHLA were not found to be a useful tool for monitoring rejection. Rejection was often associated with low levels of donor sHLA. The recent finding that antibodies can inhibit the detection of sHLA molecules might explain this discrepancy. In order to test this hypothesis, patient sera were screened for the presence of anti-HLA antibodies and the results were related to the donor-derived sHLA levels. Only in four out of 34 patients HLA Class I specific antibodies could explain the low sHLA levels during rejection.

CONCLUSIONS

In heart transplantation increased donor-derived sHLA levels are not a suitable marker for rejection and that antibody formation can not explain these results. Therefore, monitoring rejection episodes on the basis of donor-derived soluble HLA molecules is not a realistic approach to decrease the number of biopsies after heart transplantation.

Sensitization of tumour cells to lysis by virus-specific CTL using antibody-targeted MHC class I/peptide complexes

A number of cell surface molecules with specificity to tumour cells have been identified and monoclonal antibodies (mAb) to some of these antigens have been used for targeting tumour cells in vivo. We have sought to link the powerful effector mechanisms of cytotoxic T-cells with the specificity of mAb, by targeting recombinant HLA class I molecules to tumour cells using an antibody delivery system. Soluble recombinant MHC class I/peptide complexes including HLA-A2.1 refolded around an immunodominant peptide from the HIV gag protein (HLA-A2/gag) were synthesized, and the stability of these complexes at 37 degrees C was confirmed by enzyme-linked immunosorbent assay using a conformation-specific antibody. MHC class I-negative lymphoma cells (Daudi) were labelled with a biotinylated mAb specific for a cell surface protein (anti-CD20) then linked to soluble biotinylated HLA-A2/gag complexes using an avidin bridge. Flow cytometry revealed strong labelling of lymphoma cells with HLA-A2/gag complexes (80-fold increase in mean channel fluorescence). CTL specific for HLA-A2/gag efficiently lysed complex-targeted cells, while control CTL (specific for an HLA-A2.1-restricted epitope of melan-A) did not. Similarly, SK-mel-29 melanoma cells were also efficiently lysed by HLA-A2/gag-specific CTL when HLA-A2/gag complexes were linked to their surface via the HMW-MAA specific anti-melanoma antibody 225.28s. With further consideration to the in vivo stability of the MHC class I/peptide complexes, this system could prove a new strategy for the immunological therapy of cancer.

Liver transplant recipient sera derived soluble HLA mediates allele specific CTL apoptosis

BACKGROUND

Significant levels of donor soluble human leukocyte antigen (HLA) class I (sHLA) are present in patients after transplants. We investigated the possibility that sHLA may inhibit cytolytic T lymphocyte (CTL) activity by inducing apoptosis of the CTL, thereby serving as a mechanism for specific tolerance.

METHODS

sHLA-A2 and A3 were isolated from the sera of liver transplant recipients by affinity chromatography. T cell bulk lines directed against HLA-A2 and HLA-A3 were generated by stimulation with HLA-A2, A3+ peripheral blood leukocytes and B-lymphoblastoid cells. Induction of T cell apoptosis by sHLA was analyzed by adding sHLA to allospecific CTL 4 or for 24 hr before flow cytometric analysis of propidium iodide and fluorescein isothiocyanate-conjugated annexin V stained cells. T cell receptor (TCR) engagement by sHLA was demonstrated using a monoclonal antibody specific for the TCR.

RESULTS

sHLA-A3 inhibited CTL activity of a HLA-A3 T cell line by 53%, whereas sHLA-A2 had no effect. sHLA-A3 also increased T cell death by 77% over the control, whereas sHLA-A2 had no significant effect. However, sHLA-A2 induced 21% apoptosis of an anti-HLA-A2 T cell line, whereas sHLA-A3 caused only 3% apoptosis. The antibody complexed form of sHLA was ineffective in the induction of apoptosis. Preincubation of the T cells with anti-T cell receptor monoclonal antibody protected the T cells from sHLA-induced apoptosis, indicating that sHLA-TCR engagement is necessary for this process to occur.

CONCLUSION

TCR-mediated apoptosis of alloreactive CTL may serve as a mechanism by which sHLA can modulate the immune response.

Serum levels of beta-2-microglobulin-free heavy chain of HLA class I antigen in healthy individuals: relationship to their class I allotype

An ELISA-based double determinant immunoassay has been established to measure the soluble beta2-microglobulin (beta2m)-free heavy chain (FHC) of the HLA-B, -C (and HLA-A3, -A28 and -A30) class I molecular complex in sera from 212 HLA-typed healthy unrelated individuals. FHC was calculated by means of a standard curve constructed using serial concentrations of beta2m-associated HLA-class I heavy chain (HLA-I)/FHC purified from cultured human lymphoid cell C1R-sB7-supernatant. The mean FHC concentration (+/-SD) was 0.25 mg/l (+/-0.2). Its median concentration did not statistically differ between males and females, though the male/female ratio was greater in the high secretor (FHC >0.45 mg/l; mean + 1SD) than in the low secretor group (FHC < 0.05 mg/l; mean - 1SD). FHC < 0.05 mg/l was statistically (Fisher's exact test) associated with HLA-B17 (p = 0.003); FHC > 0.45 mg/l was statistically associated with HLA-B35 (p = 0.003) and -Cw4 (p = 0.002). None of these allele-positive groups showed a mean FHC concentration 1.5 times higher than that of the corresponding allele-negative ones. This allotype-dependent HLA-B and C FHC enhancement was less marked than that previously reported for HLA-I in individuals carrying HLA-A9 (and its splits). These results indicate that FHC could be a more valuable marker when its levels are compared among individuals carrying different allotypes. Moreover the lack of correlation between FHC and HLA-I levels measured in 52 HLA-A3, -A28 or -A30 positive individuals suggests that the two molecules may be regulated by different metabolic pathways and their serum expression may have a different biological significance.

Implication of soluble and membrane HLA class I and serum IL-10 in liver graft acceptance

Membrane HLA class-I expression (mHLA-I), soluble HLA class-I antigens (sHLA-I) and interleukin (IL)-10 are different factors implicated in the special acceptance of liver allograft. In this study, pre- and post-operative levels of mHLA-I in peripheral blood lymphocytes (PBL) and serum sHLA-I were analyzed in 86 liver transplants, immunosuppressed with Cyclosporine-A, methylprednisolone and azathioprine, and classified into acute-rejection (AR, n = 28) and non-acute-rejection (NAR, n = 58) groups. Serum IL-10 was studied in 47 recipients (AR-group, n = 16 and NAR-group, n = 31). Pre-transplant values of mHLA-I and sHLA-I showed a bimodal distribution (high/low) in NAR-recipients, but in AR-patients were mainly included in the low expression/secretion zone (mHLA-I, p < 0.02 and sHLA-I, p < 0.05). Consequently, average pre-transplant mHLA-I (868 +/- 109 versus 998 +/- 123, p < 0.05) and sHLA-I (1.3 +/- 0.4 versus 2.02 +/- 0.7 microg/ml, p < 0.01) was lower in the AR- than in the NAR-group. After transplant both parameters decreased in the NAR-group, but increased in AR-recipients previous to and on rejection diagnosis day. Additionally, serum IL-10 levels were significantly higher (p < 0.01) in the NAR than in the AR-group during the first 24 h post-transplant. In conclusion, low pre-transplant mHLA-I and sHLA-I levels pre-dispose liver recipients to acute rejection, whereas early post-transplant increases of serum IL-10 appear to be related to a good liver allograft acceptance.

Specific sHLA in healthy donors and donor-specific sHLA in renal transplant patients

We studied cadaver kidney transplant recipients to determine if their serum levels of donor-specific class I sHLA correlated with graft outcome. Testing of sHLA was performed by an ELISA sandwich assay using allospecific monoclonal trapping antibodies and anti-beta2-mu detecting antibody. Sufficient sHLA sensitivity (<1 ng/ml) was achieved by using two synergistic trapping antibodies. Suitable antibodies were available for A2 and B7, and data were collected for these two antigens. Stability of these sHLA was determined in plasma and serum as were ranges of normal and background levels. Background levels varied substantially. Five A2- recipients of A2+ grafts and 5 B7- recipients of B7+ grafts were studied with appropriate sHLA levels measured pre-transplant and at intervals post-transplant. Graft outcome was assessed by serum creatinines, renal biopsies and/or therapy for rejection. In the 5 patients (3 A2- and 2 B7-) whose post-transplant donor-specific sHLA never exceeded immunological complications (e.g., post-operative ATN, ureteral obstruction) did not affect the correlation. In the 5 patients with post-transplant levels exceeding pre-transplant levels, subsequent evidence of rejection was observed. Periodic measurement of donor-specific sHLA should be a useful instrument for monitoring renal allograft rejection.

Monitoring of soluble HLA class I size variants after liver transplantation

To monitor soluble HLA class I (sHLA-I) and their size variants after liver transplantation (LTX) plasma samples from 22 LTX patients were studied by sHLA-I ELISA, SDS-PAGE, and densitometry. Samples collected were classified into three groups: Group 1 comprised samples taken during episodes without complications, group 2 during episodes of cholangitis/cholestasis (CC), and group 3 during episodes of acute rejection (AR). Compared to group 1 (0.27 +/- 0.03 SEM microg/ml) mean sHLA-I increments in groups 2 and 3 were with 0.53 +/- 0.05 SEM microg/ml and 0.47 +/- 0.04 SEM microg/ml increased (p < 0.001). The same samples were studied by SDS-PAGE and the 43, 39, and 35 kD sHLA-I variants were quantified densitometrically. In samples of group 1 ratios of 43 vs. 39 kD bands revealed a mean of 2.1 +/- 0.3, whereas in group 2 and 3 these were only 0.8 +/- 0.1 SEM and 0.9 +/- 0.1 SEM, respectively, (p < 0.001). For the relation between 43 and 35 kD variants a reduced ratio of 1.1 +/- 0.2 SEM was confined to group 3 samples (p < 0.001), as groups 1 and 2 had ratios of 13.4 +/- 2.3 SEM and 8.4 +/- 2.9 SEM, respectively. This indicates that elevated sHLA-I levels during CC or AR are mainly caused by increases of 39 and/or 35 kD sized molecules. Therefore, our study demonstrates, that after LTX the contribution of sHLA-I size variants to total sHLA-I amounts changes drastically during immune activation pointing to different mechanisms of sHLA-I release.

Anti-HLA antibodies interfere in the detection of soluble HLA class I molecules

Heart transplant rejection is routinely defined by histological evaluation of endomyocardial biopsies (EMB). As elevated levels of donor derived sHLA (dsHLA) can be detected in the serum of transplanted patients just before or during rejection, quantification of donor specific soluble counterparts of HLA Class I (sHLA-I) in the serum of the recipient may be a new way for non-invasive monitoring of graft rejection. However, not all patients show an increase of dsHLA at time of rejection. A reason for this might be that anti-donor-HLA antibodies, which are formed by the patient, form complexes with donor sHLA-I molecules. This masking or blocking of sHLA-I binding sites might cause false-negative results of tests detecting donor specific sHLA. Using HLA-antigen specific ELISA tests we could demonstrate that most anti-HLA antibodies block the detection of sHLA antigens in plasma, even in high dilutions of the antibody when the antibodies were not detectable in a CDC test. In general, HLA-antigen specific antibodies block the detection of sHLA molecules, while broadly-reactive antibodies, recognizing another epitope on the molecule, do not. The implication of these findings is that more than one dsHLA allotype within one patient should be tested to monitor graft rejection. In addition, sHLA monitoring must be combined with an HLA-antibody screening.

Detection and characterization of HLA class I molecules in the supernatant of an hepatocarcinoma cell line and of EBV-transformed B cell lines

Human leukocyte antigens (HLA) class I molecules can be detected in "soluble" form in the supernatant of cultured cell lines and in serum and plasma of humans. These "soluble" HLA class I molecules are assumed to play a role in liver transplantation. In order to define the nature and composition of HLA class I molecules found in solution, we studied the HLA class I production of an hepatoma carcinoma cell line (HepG2) and of EBV-transformed B-cell lines. Based on molecular weight (MW) analysis, it was demonstrated that different forms of HLA class I molecules were produced by HepG2 cells and EBV B-cells. Monoclonal antibodies (mAbs) specific for HLA class I alleles were able to recognize the mature 45 kDa form, but failed to interact with the 42 kDa and 39 kDa MW forms of HLA class I. Of these different MW forms of HLA class I molecules the mature 45 kDa product was found predominantly to be associated with subcellular vesicles whereas the alternative MW forms of 42 kDa and 39 kDa exist as truly free entities in supernatants.

Soluble HLA Class I, HLA Class II, and Fas Ligand in Blood Components: A Possible Key to Explain the Immunomodulatory Effects of Allogeneic Blood Transfusions

The immunomodulatory effect of allogeneic blood transfusions (ABT) has been known for many years. However, a complete understanding of the effects of ABT on the recipient’s immune system has remained elusive. Soluble HLA class I (sHLA-I), HLA class II (sHLA-II), and Fas ligand (sFasL) molecules may play immunoregulatory roles. We determined by double-determinant immunoenzymatic assay (DDIA) sHLA-I, sHLA-II, and sFasL concentrations in different blood components. sHLA-I and sFasL levels in red blood cells (RBCs) stored for up to 30 days and in random-donor platelets are significantly (P < .001) higher than in other blood components and their amount is proportionate to the number of residual donor leukocytes and to the length of storage. Blood components with high sHLA-I and sFasL levels play immunoregulatory roles in vitro as in allogeneic mixed lymphocyte responses (MLR) and antigen-specific cytotoxic T-cell (CTL) activity, and induce apoptosis in Fas-positive cells. These data suggest that soluble molecules in blood components are functional. If these results are paralleled in vivo, they should be taken into account in transfusion practice. Blood components that can cause immunosuppression should be chosen to induce transplantation tolerance, whereas blood components that lack immunosuppressive effects should be preferred to reduce the risk of postoperative complications and cancer recurrence.

Beta2-micro-free HLA class I heavy chain levels in sera of healthy individuals. Lack of association with beta2-micro-associated HLA class I heavy chain levels and HLA phenotype

We have applied a double-determinant immune assay (DDIA) to measure soluble beta2-microglobulin (beta2-micro)-free HLA class I heavy chains in serum. The mean concentration of beta2-micro-free HLA class I heavy chains in serum from 120 healthy subjects was 0.21+/-0.24 microg/ml. The individual serum levels of beta2-micro-free HLA class I heavy chains had a wide distribution, did not seem to be related with HLA phenotype, were stable over time and did not change with age. The serum levels of soluble beta2-micro-free HLA class I heavy chains did not correlate with those of soluble beta2-micro-associated HLA class I heavy chains, suggesting that their release is independently regulated. Three forms of soluble beta2-micro-free HLA class I heavy chains, with apparent molecular masses of 44, 39 and 37-35 kD, respectively, circulate in human serum. These results provide a useful background to assess the serum level of soluble beta2-micro-free HLA class I heavy chains in pathological conditions and to evaluate their putative immunoregulatory function.

Pediatric liver transplantation with cadaveric or living related donors: comparative results in 90 elective recipients of primary grafts

STUDY DESIGN

Between July 1993 and March 1997, 110 children were listed for primary elective liver transplantation with cadaveric (Cad: n = 68) or living-related (LR: n = 42) donors. Pregraft mortality, post-transplant survival, and surgical and immunologic complications were retrospectively compared in both groups.

RESULTS

The pregraft mortality rate was 10 (15%) of 68 versus 1 (2%) of 42 in the Cad and LR groups, respectively (P =.049). Postliver transplantation 1-year patient and graft survival rates were 87% and 75% in the Cad group (n = 49) versus 92% and 90% in the LR group (n = 41), respectively (NS). The incidence of post-transplant complications was as follows: hepatic artery thrombosis (Cad: 16%; LR: 0%, P =.020), portal vein thrombosis (Cad: 8%; LR: 2%, NS), and biliary complications (Cad: 14%; LR: 34%, P =.044). The overall incidence of acute rejection was similar in both groups; however, a lower incidence of acute rejection occurred in LR graft recipients treated with tacrolimus.

CONCLUSIONS

The introduction of an LR donor liver transplantation program allowed a significant decrease in the pretransplant mortality rate, with a consequent overall improvement in patient survival compared with the Cad series. The incidence of biliary complications was higher in the LR series, whereas better human leukocyte antigen matching in this subgroup did not result in a lower rejection incidence.

Soluble HLA Class I, HLA Class II, and Fas Ligand in Blood Components: A Possible Key to Explain the Immunomodulatory Effects of Allogeneic Blood Transfusions

The immunomodulatory effect of allogeneic blood transfusions (ABT) has been known for many years. However, a complete understanding of the effects of ABT on the recipient’s immune system has remained elusive. Soluble HLA class I (sHLA-I), HLA class II (sHLA-II), and Fas ligand (sFasL) molecules may play immunoregulatory roles. We determined by double-determinant immunoenzymatic assay (DDIA) sHLA-I, sHLA-II, and sFasL concentrations in different blood components. sHLA-I and sFasL levels in red blood cells (RBCs) stored for up to 30 days and in random-donor platelets are significantly (P &lt; .001) higher than in other blood components and their amount is proportionate to the number of residual donor leukocytes and to the length of storage. Blood components with high sHLA-I and sFasL levels play immunoregulatory roles in vitro as in allogeneic mixed lymphocyte responses (MLR) and antigen-specific cytotoxic T-cell (CTL) activity, and induce apoptosis in Fas-positive cells. These data suggest that soluble molecules in blood components are functional. If these results are paralleled in vivo, they should be taken into account in transfusion practice. Blood components that can cause immunosuppression should be chosen to induce transplantation tolerance, whereas blood components that lack immunosuppressive effects should be preferred to reduce the risk of postoperative complications and cancer recurrence.

Regulatory function of human CD4+ cytolytic T lymphocytes

Allograft rejection is mediated by both CD4+ and CD8+ T cells. The lytic function of the classic CD8+ cytolytic T lymphocytes (CTL) occurs through recognition of allogeneic major histocompatibility complex (MHC) class I on the surface of the graft. CD4+ CTL recognize MHC class II through a direct recognition pathway or an indirect pathway where MHC peptides are presented in the context of self MHC class II. Lytic CD4+ cells may destroy graft tissue or, we hypothesize, the indirect CD4+ T cell may down regulate CD8+ CTL by recognition of donor MHC peptides presented by self MHC class II expressed on CD8+ T cells. To define the role of CD4+ CTL in allograft outcome we used a CD4+ CTL that is MHC class II restricted, recognizing human leucocyte antigen (HLA)-A1 and HLA-B8 peptides in the context of HLA-DR4. This line (MDSxA1/B8) will lyse DR4+ B lymphoblastoid cells (LCL) pulsed with HLA-A1/B8 peptides (amino acids 60-84 of the alpha1 domain of the MHC class I molecule). These T cells will also lyse peptide-pulsed antigen-specific T cell clones, both CD4+ and CD8+, that express HLA-DR4. These clones must process and present the MHC class I peptides for recognition and lysis to occur. These results suggest a possible mechanism to explain allograft tolerance. Lytic CD4+ T cells, that recognize donor HLA peptides through an indirect antigen presentation pathway, down-regulate donor-specific CTL through peptide-specific lysis resulting in graft tolerance.

Soluble HLA-I in rheumatic diseases

OBJECTIVE

To study serum levels of Class I soluble HLA (sHLA-I) in patients with systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), polymyositis or dermatomyositis (PM/DM) or scleroderma and to assess the possible influence of ethnic factors on concentration in each disease group.

METHODS

Solid-phase enzyme linked immunoassay was used to measure sHLA-I in the serum of 385 patients with varied ethnic backgrounds (American-Caucasians, African-Americans, Georgian-Caucasians) with rheumatic diseases. Studies on patients were compared to similar measurements of 189 healthy individuals.

RESULTS

Mean sHLA-I levels were significantly higher in patients with SLE than those observed in healthy individuals or other rheumatic diseases. Highest concentrations were present in Georgian-Caucasian patients with SLE. American-Caucasian patients with RA or scleroderma had higher sHLA-I levels than normal Caucasian individuals. The majority of patients with PM/DM in all ethnic subgroups were low secretors of sHLA-I.

CONCLUSION

Mechanisms underlying the secretion of sHLA-I appear to differ among the rheumatic diseases studied and various ethnic groups. These genetic differences in sHLA-I secretion could be associated with ethnic and pathophysiologic differences among these rheumatic diseases.

Allogeneic hepatocyte transplantation: Contribution of Fas-Fas ligand interaction to allogeneic hepatocyte rejection

Hepatocyte transplantation is a potential therapeutic modality for overcoming the shortage of liver donors, and the clinical application of allogeneic hepatocyte transplantation has been considered. However, there are two major problems with allogeneic hepatocyte transplantation: protection of transplanted hepatocytes from rejection and stimulation of the rapid proliferation of surviving cells. Without immunosuppression, allogeneic hepatocytes are rapidly rejected within a few days after transplantation, even though it is relatively easy to induce immunotolerance after allogeneic whole liver transplantation. Accordingly, different rejection mechanisms seem to operate after allogeneic hepatocyte transplantation and whole liver transplantation. To overcome the rejection of transplanted hepatocytes, induction of donor-specific unresponsiveness to graft without compromising the host immune system would be ideal. We previously reported that the Fas-Fas ligand system plays a critical role in the CD28-independent pathway of hepatocyte rejection. Therefore, blockade of rejection using CTLA4 immunoglobulin (CTLA4Ig) or anti-CD80/86 monoclonal antibodies and anti-FasL monoclonal antibody may prolong the survival of transplanted allogeneic hepatocytes. Furthermore, administration of hepatocyte growth factor (HGF) can promote the proliferation of allogeneic hepatocytes and this may lead to the development of a functioning liver substitute.

Combined liver-kidney transplantation in patients with cirrhosis and renal failure: effect of a positive cross-match and benefits of combined transplantation

Patients with renal failure after liver transplantation have a particularly poor prognosis. Therefore, in the setting of end-stage renal disease requiring dialysis or severe renal insufficiency that will not improve after liver replacement, combined liver-kidney transplantation (LKT) is the preferred approach. We have adopted a policy of LKT in patients with end-stage liver disease and renal insufficiency undergoing dialysis or with a creatinine clearance less than 35 mL/min and evidence of chronic renal dysfunction. Since 1991, we have performed 208 orthotopic liver transplantations. Fourteen patients (8%) have undergone combined LKT, including 6 patients undergoing hemodialysis. Cytotoxic cross-matches (modified Amos technique and antihuman globulin method) were performed on 13 of 14 patients and were positive in 3 patients. Two patients died less than 4 months after LKT and 12 patients are alive and well. Graft survival censored for patient death was 100% for liver allografts and 93% for renal allografts, with a mean follow-up of 39 +/- 24 months. The most recent serum creatinine level in the patients with the 11 functioning grafts was 1.1 +/- 0.6 mg/dL. Biopsy-proven acute rejection occurred in 50% of simultaneous liver allografts. By contrast, only a single episode (6%) of renal allograft dysfunction was attributable to acute rejection. All rejection episodes occurred in the first 90 days after transplantation and were steroid sensitive. Three of 14 combined procedures were performed in the setting of a positive cytotoxic cross-match. In 2 recent patients, the results were confirmed by positive cross-matches to the donor's T and B cells by flow cytometry. Flow cytometric cross-matches reverted to negative 1 hour after liver transplantation and several hours before the administration of antithymocyte globulin. The cross-matches remained negative on postoperative days 1 and 7. Presently, all 3 patients with a positive cross-match enjoy normal hepatic and renal function at 631, 706, and 2275 days follow-up. Renal scans were performed in 4 LKT recipients not previously undergoing hemodialysis and indicated varying and unpredictable degrees of function in the native and transplanted kidneys. In conclusion, combined LKT can be performed safely and is associated with a low rate of acute rejection, even in the setting of a positive cross-match. Predicting which patients with renal insufficiency will benefit from LKT remains challenging; however, these results suggest that LKT should be encouraged in patients with evidence of irreversible renal insufficiency who require liver transplantation.

Donor-specific hyporeactivity after liver transplantation: prominent decreases in donor-specific cytotoxic T lymphocyte precursor frequencies independent of changes in helper T lymphocyte precursor frequencies or suppressor cell activity

BACKGROUND

The development of immunological donor-specific hyporeactivity may account for the low incidence of chronic rejection after clinical liver transplantation. We investigated whether hyporeactivity commonly develops after liver transplantation by analyzing precursor frequencies of donor-reactive cytotoxic (CTLp) and helper (HTLp) T lymphocytes and mixed lymphocyte culture (MLC) reactivity in liver allograft recipients. We further studied whether CTLp hyporeactivity correlated with changes in donor-specific HTLp frequencies or suppressor cell activity.

METHODS

CTLp and HTLp frequencies and MLC reactivity against donor and third-party spleen cells were determined in pre- and posttransplantation peripheral blood samples from 18 recipients with good graft function 2 years after transplantation. By mixing posttransplantation samples (with "putative" suppressor cell activity) with pretransplantation samples (in which normal CTL activity with no suppressor cell activity is expected), the presence of suppressor cell activity in peripheral blood was analyzed.

RESULTS

Two years after transplantation, all but one (94%) of the recipients had developed CTLp hyporeactivity as evidenced by reduced donor-specific CTLp frequencies. The development of hyporeactivity was not specific for any particular underlying disease. The occurrence of HTL hyporeactivity, however, was less frequent: 38% and 20% of recipients were HTLp and MLC hyporeactive, respectively. Decreases in CTLp frequencies did not correlate with decreased donor-specific HTL function or suppressor cell activity in peripheral blood samples.

CONCLUSIONS

Donor-specific CTLp hyporeactivity can develop in the majority of liver allograft recipients, irrespective of underlying disease. Donor-specific HTL hyporeactivity, however, occurs infrequently. A reduction in donor-specific CTLp frequencies was found to be independent of changes in donor-specific HTLp or suppressor cell activity, suggesting that other mechanisms (e.g., clonal deletion) are operative in the reduction of donor-specific CTLp after liver transplantation.

Two distinct forms of soluble MHC class I molecules synthesized by different mechanisms in normal rat cells in vitro

Rat soluble MHC class I synthesis was studied at both RNA and protein levels to determine whether multiple forms of soluble MHC class I molecules are produced by different mechanisms. RT-PCR and sequencing of MHC class I transcripts identified an alternatively spliced nonclassical MHC class I gene product, lacking both exon 5 and 6, in both spleen and liver. Immunoprecipitation and SDS-PAGE identified two distinct soluble MHC class I proteins in both splenocyte- and hepatocyte-culture supernatants. The 36Kd classical soluble MHC class I protein (RT1.Aa) was precipitated by both allele-specific (MN4.91.6, R3/13, R2/15S) and pan-reactive (OX18) mAbs. The 39Kd non-RT1.A soluble MHC class I protein was precipitated only by OX18. The production of soluble RT1.Aa was inhibited by a metalloproteinase inhibitor, but not by serine/thiol protease inhibitors. None of these protease inhibitors interfered with the soluble non-RT1.A production, suggesting that it might be derived from an alternatively spliced MHC class I transcript. The soluble non-RT1.A was always associated with beta2m. However, soluble RT1.Aa molecule was cleaved in beta2m-free form and was reassociated with beta2m in culture supernatants. Thus two soluble MHC class I molecules, classical (36Kd RT1.Aa) and nonclassical (the alternatively spliced transcript), were produced from rat cells. Alternative splicing led to the nonclassical soluble MHC class I synthesis. Proteolytic cleavage by metalloproteinase led to the classical soluble MHC class I synthesis.

Flow cytometric analysis of chimerism in the rat tolerant to a renal allograft

BACKGROUND

Chimerism, produced by the two-way migration of cells between graft and host, is a proposed mechanism by which tolerance occurs. The appearance of donor/recipient chimeras in tolerant ACI to Lewis rat heterotopic renal transplants was assessed in peripheral blood leukocytes using flow cytometry after staining with monoclonal antibodies.

MATERIALS AND METHODS

ACI and Lewis rats were used as donor and recipient, respectively, after Rapamycin and Cyclosporin immunosuppression with or without donor blood or bone marrow transfusion. ACI and Lewis animals were also used for isograft and single-kidney controls. Animals were sacrificed at various time points after initial operation. Flow cytometry was performed on isolated peripheral blood leukocytes at sacrifice. Histologic and functional data were also obtained. The monoclonal antibody panel included RT1(a) (ACI, MHC I) combined with CD2, CD4, CD8, CD16, and CD25 or RT1(a,c) (bone marrow chimeras).

RESULTS

RT1(a)+, CD8+ cells were transiently present in the peripheral blood leukocytes of Lewis recipients with the exception of allogeneic bone marrow recipients. No significant number of RT1(a)+, CD16+ ("dendritic" cell-line) chimeras was seen. Veto cells (RT1(a,c)+) were transiently present in the bone marrow recipients, but they did not lead to improved outcome. Furthermore, no correlation was made between histologic tolerance and any of these donor-derived cells.

CONCLUSION

Donor/recipient chimerism, and the veto cell phenomenon are not operational tolerance mechanisms in this stringent model of ACI to Lewis rat renal transplantation.

Immunologic suppression mediated by genetically modified hepatocytes expressing secreted allo-MHC class I molecules

Studies suggest that immunosuppression associated with liver transplantation may be related to the secretion of MHC class I antigen (Ag) by hepatocytes. To investigate this possibility, we developed a culture system whereby naive Lewis (RT1.A1) splenocytes were cocultured with autologous hepatocytes transfected with plasmids encoding either the membrane-bound or secreted allogeneic MHC class I Ag, RT1.Aa. Cytotoxic T lymphocyte (CTL) and helper T lymphocyte (HTL) limiting dilution assays were subsequently performed on preconditioned lymphocytes. Lymphocytes preconditioned with hepatocytes secreting RT1.Aa showed an alloantigen specific inhibition of CTL precursors (CTLp). In contrast, exposure of splenocytes to hepatocyte-expressed membrane-bound RT1.Aa resulted in Ag-specific CTLp priming. This CTLp priming effect by hepatocyte-expressed membrane-bound Ag could be effectively blocked when splenocytes were first preincubated with hepatocytes secreting RT1.Aa, before being exposed to hepatocytes expressing membrane-bound RT1.Aa. In contrast to CTLp, HTLp frequency, as determined by IL-2 production, was unaffected by either hepatocyte-expressed membrane-bound or secreted RT1.Aa. Further studies on splenocytes conditioned with hepatocytes expressing secreted allo-MHC Ag suggest the possibility of suppressor cell development. This was demonstrated by prolongation of ACI (RT1a) heart allograft survival in Lewis recipients following adoptive transfer of splenocytes that were preconditioned in vitro with hepatocytes secreting alloantigen.

Defining the outcome of immunosuppression withdrawal after liver transplantation

Successful immunosuppression withdrawal should benefit the natural history of organ transplantation patients. To identify the clinical hazards of removing drug treatment and possible characteristics that predict a favorable outcome in long-term liver recipients, immunosuppression was withdrawn completely and the clinicopathological outcome documented in 18 liver recipients. Indication for transplantation, HLA matching, early rejection history, and presence of microchimerism were examined as predictors of outcome. Chimerism was determined by polymerase chain reaction-based examination for donor-specific HLA-DRB1 alleles and Y-gene-specific nucleotide sequences. At 3 years, 5 patients (28%) remained completely off immunosuppression; 12 patients (67%) experienced histological graft changes: acute rejection in 4, portal tract inflammation/hepatitis in 7, and necrosis in 1. Hepatitis B or C viral infections did not account for the nonrejection patterns. Unmasking of systemic disorders occurred. Chimerism, demonstrated in 7 patients (39%), with skin the optimal tissue, was not associated with tolerance. Parameters associated with successful drug withdrawal were transplantation for non-immune-mediated liver disorders, fewer donor-recipient HLA A, B, and DR mismatches, and a low incidence of early rejection. Immunosuppression withdrawal is a feasible option in a proportion of selected liver recipients, but identification of tolerant patients remains imprecise.