Differential effects of donor-specific HLA antibodies in living versus deceased donor transplant

The presence of donor-specific anti-HLA antibodies (DSAs) is associated with increased risk of graft failure after kidney transplant. We hypothesized that DSAs against HLA class I, class II, or both classes indicate a different risk for graft loss between deceased and living donor transplant. In this study, we investigated the impact of pretransplant DSAs, by using single antigen bead assays, on long-term graft survival in 3237 deceased and 1487 living donor kidney transplants with a negative complement-dependent crossmatch. In living donor transplants, we found a limited effect on graft survival of DSAs against class I or II antigens after transplant. Class I and II DSAs combined resulted in decreased 10-year graft survival (84% to 75%). In contrast, after deceased donor transplant, patients with class I or class II DSAs had a 10-year graft survival of 59% and 60%, respectively, both significantly lower than the survival for patients without DSAs (76%). The combination of class I and II DSAs resulted in a 10-year survival of 54% in deceased donor transplants. In conclusion, class I and II DSAs are a clear risk factor for graft loss in deceased donor transplants, while in living donor transplants, class I and II DSAs seem to be associated with an increased risk for graft failure, but this could not be assessed due to their low prevalence.

How can we reduce costs of solid-phase multiplex-bead assays used to determine anti-HLA antibodies?

Solid-phase multiplex-bead assays are widely used in transplantation to detect anti-human leukocyte antigen (HLA) antibodies. These assays enable high resolution detection of low levels of HLA antibodies. However, multiplex-bead assays are costly and yield variable measurements that limit the comparison of results between laboratories. In the context of a Dutch national Consortium study we aimed to determine the inter-assay and inter-machine variability of multiplex-bead assays, and we assessed how to reduce the assay reagents costs. Fifteen sera containing a variety of HLA antibodies were used yielding in total 7092 median fluorescence intensities (MFI) values. The inter-assay and inter-machine mean absolute relative differences (MARD) of the screening assay were 12% and 13%, respectively. The single antigen bead (SAB) inter-assay MARD was comparable, but showed a higher lot-to-lot variability. Reduction of screening assay reagents to 50% or 40% of manufacturers' recommendations resulted in MFI values comparable to 100% of the reagents, with an MARD of 12% or 14%, respectively. The MARD of the 50% and 40% SAB assay reagent reductions were 11% and 22%, respectively. From this study, we conclude that the reagents can be reliably reduced at least to 50% of manufacturers' recommendations with virtually no differences in HLA antibody assignments.

Diagnosis of early pancreas graft failure via antibody-mediated rejection: single-center experience with 256 pancreas transplantations

Early pancreas graft loss is usually attributed to technical failure while the possibility of antibody-mediated rejection (AMR) is generally overlooked. To investigate the role of AMR in early pancreas graft loss, we retrospectively assessed 256 patients with simultaneous pancreas-kidney transplantation (SPK) between 1985 and 2010 at our institute. We included 33 SPK patients who lost their pancreas graft <1 year after transplantation. AMR was diagnosed based on donor-specific antibodies, C4d and histology in 7 cases, 8 cases were suspicious for AMR and 18 pancreas graft losses were not due to AMR. Acute AMR occurred >1 month after transplantation in 6/7 cases, whereas all other causes typically led to loss <1 month after transplantation. Thrombotic lesions occurred equally among the 33 cases. In 12/18 concurrent kidney specimens, the diagnostic results paralleled those of the pancreas graft. All patients with acute AMR of the pancreas graft lost their renal grafts <1 year after transplantation. In the setting of a thrombotic event, histopathological analysis of early pancreas graft loss is advisable to rule out the possibility of AMR, particularly because a diagnosis of acute AMR has important consequences for renal graft outcomes.

Cross-validation of IFN-γ Elispot assay for measuring alloreactive memory/effector T cell responses in renal transplant recipients

Assessment of donor-specific alloreactive memory/effector T cell responses using an IFN-γ Elispot assay has been suggested to be a novel immune-monitoring tool for evaluating the cellular immune risk in renal transplantation. Here, we report the cross-validation data of the IFN-γ Elispot assay performed within different European laboratories taking part of the EU RISET consortium. For this purpose, development of a standard operating procedure (SOP), comparisons of lectures of IFN-γ plates assessing intra- and interlaboratory assay variability of allogeneic or peptide stimuli in both healthy and kidney transplant individuals have been the main objectives. We show that the use of a same SOP and count-settings of the Elispot bioreader allow low coefficient variation between laboratories. Frozen and shipped samples display slightly lower detectable IFN-γ frequencies than fresh samples. Importantly, a close correlation between different laboratories is obtained when measuring high frequencies of antigen-specific primed/memory T cell alloresponses. Interestingly, significant high donor-specific alloreactive T cell responses can be similarly detected among different laboratories in kidney transplant patients displaying histological patterns of acute T cell mediated rejection. In conclusion, assessment of circulating alloreactive memory/effector T cells using an INF-γ Elispot assay can be accurately achieved using the same SOP, Elispot bioreader and experienced technicians in kidney transplantation.

Immune mechanisms leading to drug-induced blood dyscrasias

Drug-induced blood dyscrasias may be due to toxicity of the drug, inborn errors of metabolism or immunological reactions. In the latter case, drug-induced antibodies are directed to specific target cells, such as platelets (thrombocytopenia) or granulocytes (agranulocytosis). Some of these immune mechanisms are based on the physical interaction between drug, antibody and target cells. A particular drug may bind to the surface of the blood cell which, as a carrier of the drug, will be destroyed as part of the immune reaction to the drug (hapten mechanism). Other drugs will form immune complexes with drug-specific antibodies. These immune complexes will bind to certain blood cells and destroy them as innocent bystanders (immune complex mechanism). In vitro assays are described which enable the offending drug to be detected by mimicking these immune mechanisms using patient serum, platelets or granulocytes, and the suspected drug. The diagnostic value of these in vitro assays is discussed.

Monitoring of cardiac graft recipients: comparison of in vivo activated, committed T lymphocytes in peripheral blood and in the graft

The proliferative and cytotoxic capacity of peripheral blood lymphocytes (PBL) and the cytotoxic activity of lymphocytes propagated from endomyocardial biopsies (EMB) towards donor cells was used to identify in vivo activated, committed T cells. A series of 39 PBL samples and 38 EMB simultaneously taken from 20 patients after heart transplantation was cultured in interleukin 2 (IL-2) conditioned medium. The cytotoxic capacity of these cultures against donor cells was tested in a 4-h chromium-51 release assay. From a comparable patient group, 224 samples were evaluated for donor reactivity by a primed lymphocyte test (PLT). Analysis showed that PBL cultures hardly ever contained committed cytotoxic T lymphocytes (cCTL, 2/39) or committed proliferative T lymphocytes (cPTL, 1/224). In contrast, significantly more EMB cultures (17/38, P < 0.001, chi2 test) demonstrated donor-directed cytotoxicity. This was especially found during rejection (11/17 vs 6/21 without rejection, P = 0.05). These results show that after heart transplantation, committed cells are mainly found in the graft.

Immunomodulation by intrathymic injection of donor leukocytes in rhesus monkeys

BACKGROUND

Several studies have demonstrated that intrathymic injection of donor cells into adult rodents can result in long-term allograft survival. The rationale for using the intrathymic route of donor cell administration is that in the thymic environment immature T cells are educated to discriminate between self and non-self antigens. The validity of this approach was tested in non-human primates.

METHODS

The effect of the intrathymic injection of allogeneic donor cells was investigated in rhesus monkeys and compared with IV and intracutaneous administration of donor cells. Intrathymic injections were carried out without and with antithymocyte globulin. All animals received subsequently an allogeneic skin graft of the same donor and no immunosuppression post transplantation.

RESULTS

Skin graft survival was slightly shorter in animals treated with IC donor cell injections (mean survival time [MST]=8.9+/-0.52) than untreated control animals (MST=10.0+/-0.44), indicating that this route caused sensitisation. Intravenous donor cell injection showed prolongation of graft survival times (MST=11.6+/-1.69). Intrathymic donor cell injection resulted in a graft survival of 9.2+/-1.44 days although addition of antithymocyte globulin slightly prolonged graft survival to 10.3+/-2.84 (not significant). Whereas the cellular responses after intrathymic and intravenous donor cell injections increased, antithymocyte globulin treated animals did not show an increased cellular response. Recipients of intrathymic donor cells showed a significantly decreased humoral anti-donor response as compared to other groups.

CONCLUSIONS

Donor cell pretreatment alters the subsequent response to an allogeneic skin graft in monkeys and is dependent on the route of donor cell administration. This is also reflected in the alloantibody response and the in vitro cellular reactivity. Intrathymic administration of donor cells does not lead to prolonged skin graft acceptance.

The relevance of proficiency testing for laboratories involved in cadaveric organ transplantation and its consequences for graft survival

Organ exchange organizations such as Eurotransplant allocate organs on the basis of histocompatibility testing results. For this reason it is essential that all data reported by the affiliated laboratories are accurate and reliable. The Eurotransplant Reference Laboratory (ETRL) organizes proficiency testing schemes for the tissue-typing centers of the respective renal transplantation units participating in Eurotransplant. Each year, the ETRL sends out 8 peripheral blood samples of healthy blood donors for serological typing and crossmatching, 16 sera to screen for the presence and definition of HLA alloantibodies and 20 DNA samples for molecular typing to the 49 participating centers. The results are collected centrally and reported back to the participants in an open way. These exercises show that the quality of HLA typing, screening and crossmatching improved significantly over the years. In particular, the introduction of molecular typing for HLA-DR resulted in an increase of reliability. The clinical relevance of a reliable HLA typing was demonstrated in a selected group of transplants, the zero HLA-A,-B,-DR- mismatched group. After retyping the donors, 146 of the 3,458 matched transplants appeared to have a mismatch and those transplants had a significantly lower graft survival rate. A continuing problem, however, is the result of screening for panel reactive antibodies (PRA), where the percentage PRA reported for each serum varies significantly from center to center. The results indicate that the use of a PRA value for classification of patients and allocation of organs should be revisited.

Pretransplant donor-specific helper T cell reactivity as a tool for tailoring the individual need for immunosuppression

BACKGROUND

A reliable immunological assay for quantification of donor-specific alloreactivity to identify patients at risk for future allograft rejection would be a helpful tool in organ transplantation. Therefore, we questioned whether the T cell reactivity in patients measured before transplantation was predictive for the occurrence of acute rejection during the first year after kidney transplantation.

METHODS

The pretransplant T cell reactivity of peripheral blood mononuclear cells to donor and third-party antigens was tested in mixed lymphocyte cultures, and to tetanus toxoid. In addition, we measured the frequency of donor and third-party reactive helper T lymphocyte precursor and cytotoxic T lymphocyte precursors using limiting dilution analysis.

RESULTS

Patients who experienced acute rejection had significantly higher donor-specific mixed lymphocyte cultures responses (n=38; median stimulation index): 113 vs. 15, P=0.005) and helper T lymphocyte precursor frequency (n=37; median 194/106 vs. 62/106, P=0.009) measured before transplantation compared to patients without acute rejection. All patients with a low mixed lymphocyte culture response (stimulation index</=20; 13/13 vs. 12/25, P=0.001) and an undetectable helper T lymphocyte precursor frequency (<10/106 peripheral blood mononuclear cells; 7/7 vs. 17/30, P=0.04) before transplantation did not experience acute rejection. The donor-specific cytotoxic T lymphocyte precursor frequency (n=34; median 53/106 vs. 28/106, P=0.58) and tetanus toxoid-reactivity (n=38; median stimulation index: 53 vs.16, P=0.56) measured before transplantation did not correlate with acute rejection. No correlation between third-party reactivity and acute rejection was observed.

CONCLUSIONS

From these results we conclude that despite the current HLA matching criteria, undetectable helper T lymphocyte precursor frequency and low mixed lymphocyte culture responses against donor antigens measured before transplantation are predictive for a rejection-free first posttransplant year. These in vitro assays can be used to identify patients who require less immunosuppression after transplantation.

Permissible and immunogenic HLA-A mismatches: cytotoxic T-cell precursor frequencies reflect graft survival data

Analysis of the in vivo immunogenicity of single HLA mismatches, in the context of a patient's own human leukocyte antigen (HLA) phenotype, has been used to define permissible and immunogenic HLA mismatches. Kidney graft survival in the case of permissible mismatches was similar to that of completely HLA matched combinations, whereas immunogenic mismatches lead to a significantly poorer graft survival. The present study tested whether such permissible and immunogenic HLA mismatches are reflected in the in vitro cytotoxic T-lymphocyte (CTL) allorepertoire. Limiting dilution experiments were performed to analyze the number of precursor CTL directed against individual HLA class I antigens. In general, the frequency of CTLp directed against permissible HLA-A antigens (n = 70, mean frequency 27 CTLp per million peripheral blood lymphocytes [PBL]) was found to be significantly lower compared with the CTLp directed against immunogenic HLA-A antigens (n = 73, mean frequency 59 CTLp per million PBL). The difference was found both in healthy individuals and a population of renal transplant candidates. These results were confirmed by a retrospective analysis of CTLp frequencies performed between partly mismatched unrelated bone marrow donors and their potential recipients. In conclusion, on the population level the permissible and immunogenic HLA-A mismatches are indeed reflected in the CTL allorepertoire. However, due to the big overlap of the CTLp frequencies in these populations, the permissible or immunogenic nature of a mismatch for a particular patient should be determined on an individual basis.

Determination of the frequency of HLA antibody secreting B-lymphocytes in alloantigen sensitized individuals

Sera from prospective transplant patients are usually screened for HLA antibodies prior to transplantation, but presently available tests do not permit quantification of the humoral alloantigen directed response. We adapted a culture system for isolated human B-lymphocytes to assay the secretion of HLA-antibodies on a single cell basis. B-cell supernatants were screened for HLA antibodies by complement dependent cytotoxicity. The assay assigns precursor frequencies for HLA-alloantibody secreting B-lymphocytes (BCPFs), and simultaneously allows for dissection of the humoral alloantigen directed response into its monoclonal components. The lymphocytes of 15 HLA-seropositive multiparous women that were used to validate the assay, were found to contain HLA-BCPFs ranging from 0 to 123 per 10(6) B-lymphocytes (mean: 43 +/- 45 per 10(6) B-lymphocytes). The HLA-specificities of antibodies in the B-cell supernatants were in agreement with serum specificities. Genuine HLA reactivity of B-cell supernatants was confirmed using an ELISA with purified HLA class I antigens. When applied to lymphocytes of patients on transplant waiting lists, the present assay may enable the unraveling of serum specificities in their components, thus supplementing HLA antibody serum screening data.

Ultraviolet-B radiation induces modulation of antigen presentation of herpes simplex virus by human epidermal cells

Although ultraviolet (UV) B radiation is known to be immunosuppressive, there is little information regarding a relevant immunological endpoint to assess human subjects in vivo. Therefore, we have examined the effect of in vivo UV radiation on the ability of human epidermal cells (EC) to present herpes simplex virus (HSV) antigens to memory T cells. Human volunteers, who were seropositive for HSV, were exposed to one minimal erythemal dose (MED) for four consecutive days. EC, prepared from suction blister roofs, were co-cultured with autologous T cells in the presence of HSV. HSV antigen presentation by UV-exposed EC was increased compared with control, nonexposed EC. This up-regulation correlated with an influx of macrophages into the epidermis, which are considered to be associated with UV-induced tolerance. Altering the UV protocol to a sub-erythemal UV dose for four consecutive days or to a single high dose of 2 MED, resulted in suppressed HSV antigen presentation, without the influx of the UV-macrophages. One of the goals of the present study was to eventually use this HSV system to investigate sunscreen immunoprotection. A pilot study with a TiO2-containing sunscreen suggested that the endpoint for UV-induced immunosuppression presented here is promising to be used for human in vivo sunscreen immunoprotection studies.

Modulation of the alloimmune response by blood transfusions

Blood transfusions can induce both immune activation and immunosuppression. The former is expressed by the induction of HLA alloantibodies and T cell activation, while the latter is accompanied by enhanced graft survival in transfused versus non-transfused recipients. The immunological mechanism leading to downregulation of the alloimmune response has not yet been elucidated. Possible explanations include the induction of a Th2 response by non-professional antigen presentation by the transfused blood cells and blockage of alloreactive T cell reactivity by soluble HLA and soluble FasL in the supernatant of blood components. These mechanisms, however, do not explain the observations which have shown that the degree of HLA compatibility between the transfusion donor and patient is a determining factor. Transfusions in which the donor blood shares at least one HLA-DR antigen with the recipient induce tolerance, while fully HLA-DR mismatched transfusions lead to immunization. The importance of HLA-DR sharing suggests a central role for CD4+ regulatory T cells. In this case, indirect recognition of an allopeptide in the context of self-HLA-DR on the transfusion donor by CD4+ T cells of the recipient might be the clue to the induction of tolerance. Recent data from our laboratory in fact show that CD4+ T cells specific for an allopeptide in the context of self HLA-DR are able to downregulate the alloimmune response of autologous T cells. As these regulatory T cells produce IL-10, they may also be involved in the extension of tolerance via their modulatory effect on dendritic cells. It remains to be established whether these regulatory T cells are indeed responsible for the 'blood transfusion effect' in organ transplantation.

Differential inhibitory effects of intravenous immunoglobulin preparations on HLA-alloantibodies in vitro

BACKGROUND

Treatment of allosensitized patients with intravenously administered pooled immunoglobulin preparations (IVIG) may lead to a long-lasting reduction of anti-HLA alloantibody titers. An inhibitory response of IVIG preparations on lymphocytotoxicity is suggested to depend on IgG and to predict a successful reduction of anti-HLA alloantibodies upon the administration of high-dose IVIG in vivo.

METHODS

In this study, we evaluated different IVIG preparations for their in vitro inhibitory capacity on lymphocytotoxicity and binding of anti-HLA alloantibodies to purified HLA antigens. For that purpose sera from 24 highly sensitized patients awaiting kidney transplantation and serological HLA testing reagents were used. Panel-reactive antibody (PRA) determinations using standard complement-dependent cytotoxicity testing and anti-HLA alloantibody determination by ELISA were carried out in the presence and absence of 50% (v/v) IVIG.

RESULTS

The addition of IgG-containing IVIG preparations gave only a moderate inhibitory response judging from the average decrease of PRA levels (absolute DeltaPRA range: -2% to 16%), whereas the largest inhibition of lymphocytotoxicity was seen after the addition of IgM/IgA-containing IVIG preparations (absolute DeltaPRA range: 19% to 44%). For both IgG and IgM/IgA-containing IVIG preparations, the reduction of lymphocytotoxicity occurred in a dose-dependent fashion without a preference for particular anti-HLA class I antibody specificities. Significantly lower inhibitory effects on anti-HLA antibody reactivity were observed when the effects of IVIG preparations were monitored by ELISA (absolute DeltaPRA range: 7% to 22%).

CONCLUSIONS

Our data suggest that the immunomodulatory capacity is largely caused by the IgM/IgA fraction of IVIG when analyzed by lymphocytotoxicity. The different effect on ELISA versus complement-dependent cytotoxicity testing suggests that interactions of IVIG with complement rather than anti-idiotypic antibodies may contribute to the inhibitory effects of IVIG in vitro.

Acceptable HLA mismatches for highly immunized patients

Highly sensitized patients have developed antibodies against many different HLA antigens due to previous pregnancies, blood transfusions or failed transplants. These antibodies cause a positive crossmatch with almost all potential organ donors. As a positive crossmatch is a contra-indication for transplantation, highly sensitized patients have a low chance of transplantation unless special strategies are introduced. One such strategy is the acceptable mismatch program, which has led to transplantation of more than 300 of these highly sensitized patients within Eurotransplant. Centers are participating in the program on a voluntary basis. Before a patient can be included in this program, extensive antibody screening is necessary to define those HLA-A and -B antigens towards which the patient has never formed antibodies. Organ donor selection is based on complete compatibility with the patients own HLA antigens in combination with the acceptable mismatches. If such a combination is identified, mandatory exchange takes place. Despite the success of the acceptable mismatch program, about 25% of the patients will never receive a donor offer. These are patients with rare HLA antigens or rare combinations of HLA antigens. In the last few years, this group of patients has had the advantage of two additional programs running within Eurotransplant. In the HIT (highly immunized tray) program, sera of highly sensitized patients are sent to the different centers and crossmatched with all ABO compatible donors. In the case of a negative crossmatch, mandatory exchange takes place. Secondly, these patients can benefit from the extra points they receive for their waiting time, high antibody reactivity and rare HLA type in the standard Eurotransplant allocation system. We conclude that the application of these three strategies will lead to a significantly increased transplantation rate of highly sensitized patients.

Protective and susceptible HLA polymorphisms in IgA nephropathy patients with end-stage renal failure

Idiopathic immunoglobulin A (IgA) nephropathy is characterised by an extreme variability in clinical course, leading to end-stage renal failure in 15-20% of adults. This subgroup of patients with IgA nephropathy is usually included in the waiting lists of organ exchange organisations. The frequency of HLA-A,B,DR antigens of this subset of IgA nephropathy patients was calculated and compared to controls. The antigens HLA-B35 and DR5 were significantly increased in the patients with relative risk values of 1.385 and 1.487, respectively. The antigens HLA-B7, B8, DR2, and DR3 were found in a significantly lower frequency in the patients as compared to the controls. The relative risk (RR) values ranged between 0.695 and 0.727. Consequently, the haplotypes HLA-A1, B8, DR3, HLA-A3, B7, DR2, HLA-A2, B7, DR2 together with HLA-A1, B15, DR4, HLA-A9, B12, DR7, and HLA-A10, B18, DR2 were found to be protective with RR values ranging from 0.309 to 0.587. The only susceptible haplotype observed was HLA-A2-B5, DR5 (RR=2.990).

REJECTION OF A KIDNEY TRANSPLANT DOES NOT ALWAYS LEAD TO PRIMING OF CYTOTOXIC T CELLS AGAINST MISMATCHED DONOR HLA CLASS I ANTIGENS1

BACKGROUND

Previous studies showed that graft rejection is often associated with the presence of primed cytotoxic T cells (CTLs) with a high avidity for donor cells. Similar high avidity CTLs have been found in individuals who have formed IgG anti-HLA antibodies. The presence of such CTLs to a specific HLA mismatch is therefore considered to be a reflection of an activated immune system, and a contraindication for retransplantation with a donor sharing this particular HLA class I mismatch.

METHODS

In our study we investigated whether patients have always primed CTLs against all individual HLA class I mismatches present on a rejected graft. Therefore, 14 patients who had undergone transplantectomy after irreversible kidney graft rejection were analyzed with respect to donor-specific CTLp frequencies and the presence or absence of high avidity CTLs directed against HLA class I mismatches present on the rejected graft.

RESULTS

Patients, who have not formed anti-HLA antibodies against the donor have mainly naive CTLs. Most of the patients, that have developed IgG anti-HLA antibodies against a donor mismatch, have primed CTLs directed against that particular mismatch. However, patients with IgM anti-HLA antibodies only, and patients with IgG anti-HLA antibodies in historical sera but no IgG anti-HLA antibodies in current sera, have mainly naive CTLs against the donor HLA mismatch.

CONCLUSION

Our results suggest that it is not always necessary to exclude repeated HLA class I mismatches for a subsequent transplantation. In addition to good anti-HLA antibody screening, the CTLp-assay may be a useful tool for donor-selection in retransplant candidates.

Pregnancy can induce long-persisting primed CTLs specific for inherited paternal HLA antigens

Previous studies showed that pregnancy can prime the maternal cellular immune response directed against paternal HLA antigens. Primed CTLs specific for inherited paternal HLA antigens (IPA) were found in women who had formed HLA allo antibodies, whereas naive CTLs were present in women who did not form antibodies against the paternal HLA antigens. As HLA allo antibodies may disappear in time, it is not clear which women on the waiting list for transplantation have been sensitized to paternal HLA antigens and are at risk for graft rejection if paternal HLA antigens are shared by the donor organ. The presence of primed CTLs specific for a particular antigen is considered to be a reflection of sensitization.In the present study we investigated whether these primed CTLs persist in women who had been pregnant and had formed antibodies against the inherited paternal HLA class I antigens. For this purpose 14 women who had their last pregnancy 10 years ago were analyzed with respect to IPA-specific CTLp frequencies and the presence of high avidity CTLs directed against inherited paternal HLA class I antigens. Although primed CTLs specific for IPA's were found more frequently in women with persisting alloantibodies, they still can be detected when the antibodies have disappeared. The current data show that primed CTLs directed against inherited paternal HLA antigens towards which antibodies have been formed in the past can persist for more than 10 years after pregnancy. The cellular test used in our study can be useful to detect presensitization in women with a history of pregnancy, who enter the waiting list for transplantation.

HLA-C expression on platelets: studies with an HLA-Cw1-specific human monoclonal antibody

BACKGROUND AND OBJECTIVES

The expression of HLA-C on the surface of platelets is rarely studied due to the lack of proper alloantisera. We addressed this question using an IgM human monoclonal antibody directed against HLA-Cw1 (VP6G3).

MATERIAL AND METHODS

Both flow cytometry and complement dependent cytotoxicity studies were used in the current analysis.

RESULTS

The expression of the HLA-Cw1 antigen on platelets is lower than on peripheral blood lymphocytes as shown by flow cytometry. Variation in expression levels between individuals is also observed. Using this antibody in a complement-dependent cytotoxicity assay, we did not observe lysis using platelets as targets, whereas peripheral blood lymphocytes of the same blood donors were adequately lysed.

CONCLUSIONS

These results confirm that platelets indeed express HLA-C. Furthermore, the results support the insignificant role of HLA-C in immunological platelet refractoriness.

Immunomodulation by blood transfusions

Blood transfusions can affect the immune response in two opposite ways. They may either lead to immunization or to tolerance induction. Immunization is reflected by the induction of HLA alloantibodies and T cell activation while the induction of tolerance is suggested by the enhanced graft survival in transfused versus non-transfused recipients. The immunological mechanism leading to downregulation of the alloimmune response is not clear. One possible explanation is the induction of a Th2 response by non-professional antigen presentation by the transfused blood cells. On the other hand, evidence is accumulating that the degree of HLA compatibility between transfusion donor and patient is a determining factor. Transfusions sharing at least one HLA-DR antigen with the recipient induce tolerance while fully HLA-DR mismatched transfusions lead to immunization. The importance of the degree of HLA-DR sharing suggests a central role for CD4+ regulatory T cells. We hypothesize that indirect recognition of an allopeptide in the context of self-HLA-DR on the transfusion donor by CD4+ T cells of the recipient might be the clue to tolerance induction. Preliminary data show indeed that CD4+ T cells specific for an allopeptide in the context of self HLA-DR are able to downregulate the alloimmune response of autologous T cells. Further analysis of transplanted patients, who have received an HLA-DR shared transfusion, should reveal whether such CD4+ regulatory T cells are indeed responsible for the beneficial effect of pretransplant blood transfusions.

Clinical significance of leukoreduktion of blood components

The clinical significance of leukocyte reduction of all blood components must be deducted from patients transfused in the surgical setting. Under these circumstances many factors contribute to morbidity and mortality, while such factors can be candidates for confounders. Moreover, to investigate effects on infrequent events such as post-operative mortality and multiple organ dysfunction syndrome, large patient cohorts must be studied. Our studies suggest that leukocytes or leukocyte aggregates in red cell transfusions indeed may be harmful if larger dosages are administered under certain clinical circumstances. A critical leukocyte load seems to start with approximately 2.5 x 10(9). Reducing the leukocyte contamination of red cell components, not necessarily by filtration, may benefit patients who require multiple transfusions within a short time interval.

Broad-spectrum sunscreens offer protection against urocanic acid photoisomerization by artificial ultraviolet radiation in human skin

Cis-urocanic acid (UCA) has been indicated as an important mediator of ultraviolet (UV)-induced immunosuppression. In this study we describe a rapid, noninvasive method for the determination of the protective capacity of various sunscreens against the UV-induced isomerization of trans-UCA into its cis form. For this purpose we applied sunscreens prior to in vivo exposure of human volunteers with single or repeated broadband UVB irradiations of 100 mJ per cm2. We found significant but different levels of protection against UCA photoisomerization by all sunscreens that correlated with the sun protection factor. A comparison of various sunscreens with a sun protection factor of 10, showed that the best protection was offered by the sunscreens (containing organic UV filters or TiO2) with broad absorption spectra. The ability to inhibit cis-UCA formation was not influenced by the penetration characteristics of sunscreens, as determined by application of the sunscreen on quartz glass that was placed on the skin, preventing penetration of sunscreen in the skin. In addition ex vivo UV exposure of human skin was employed to permit other tests of immunomodulation, in this case the mixed epidermal cell lymphocyte reaction. The advantage of this ex vivo method is that there is no need to take biopsies from volunteers. Ex vivo irradiation of human skin with a single dose of 200 mJ per cm2 resulted in similar protection by the sunscreens against cis-UCA formation as in the in vivo system. Furthermore, the mixed epidermal cell lymphocyte reaction data correlated with the cis-UCA findings. We conclude that UCA isomerization is an excellent method to determine sunscreen efficacy and that broad-spectrum sunscreens offer good immunoprotection.

In vitro CTL precursor frequencies do not reflect a beneficial effect of cross-reactive group (CREG) matching

Adjustment of histocompatibility-based allocation criteria in kidney transplantation from HLA matching to matching on the basis of cross-reactive groups (CREG), was recently suggested to be a good alternative to transplant with more "well-matched" kidneys, without negatively influencing graft survival. Because graft rejection is often mediated by cytotoxic T cells (CTLs), we investigated whether a beneficial effect of CREG matching is reflected in vitro by lower CTL precursor frequencies (CTLpf). Therefore, CTLpf were determined in a group of healthy individuals and analyzed with respect to the number of HLA and CREG mismatches. A clear correlation was found between the number of HLA mismatches and the CTLpf, that is, the lowest mean frequency in case of 0 HLA-A, B mismatches (66 CTL precursors per 10(6) cells) and the highest in combinations with 4 HLA mismatches (mean = 303 CTLp/10(6) cells). The situation was different in the case of CREG mismatches. Although the highest frequency was found in the group of 4 CREG mismatches, no significant differences were observed between 0, 1, and 2 CREG mismatches. High CTLpf, up to 430/10(6), were even seen in the case of 0 CREG mismatches. Also within a well-defined group of single HLA-A or HLA-B mismatches no difference in CTLpf were observed between the subgroups with 0 vs. 1 CREG mismatches. The present study showed that in vitro the CTLpf correlates better with HLA than with CREG matching. These data are consistent with findings reported by several groups that matching for the CREG does not benefit transplant outcome.

Beneficial effect of HLA-DR matching on the survival of corneal allografts

BACKGROUND

Although HLA typing and matching have been used for 3 decades, that practice has been poorly implemented in corneal transplantation, mainly because of inconclusive or contradictory analytical results. Consequently, we studied the immune response of corneal transplant recipients to HLA histoincompatibilities in a large homogeneous study.

METHODS

All corneal transplantations performed by a single surgeon between 1976 and 1996 were studied. HLA-AB matching was used for recipient selection. All HLA typings were performed by a single experienced laboratory. Population genetic techniques were used to assess the validity of the HLA typings. Mono- and multivariate analyses were performed to identify the factors which significantly influence the survival of corneal allografts. Simulation studies were carried out to demonstrate the effects of mis-typed donor and recipient HLA-DR typings on analytical results.

RESULTS

Retransplantation, degree of vascularization, HLA-AB and DR matching, endothelial cell count, graft size, recipient gender, and storage method were identified as significant factors by our monovariate analyses. A Cox proportional hazards survival analysis model identified degree of vascularization and HLA-AB and DR matching as significant prognostic factors when all immunological rejection episodes were used, P=0.000001. When only irreversible immunological rejection episodes were used, panel reactive antibodies, retransplantation, and number of rejection events were also identified, P=0.000001. Simulation studies showed that the effects of HLA-DR matching are abrogated by poor HLA-DR typings.

CONCLUSIONS

Corneal allograft recipients have a normal alloimmune response to histoincompatibilities. Demonstration of that fact requires accurate HLA typings.

Further evidence for an association of HLA-DR7 with basal cell carcinoma on the tropical island of Saba

OBJECTIVE

To establish the association of HLA alleles (ie, HLA-DR1, HLA-DR4, and HLA-DR7) with individuals with skin cancer on the tropical island of Saba. This island was chosen because most of the white population has fair skin and excessive exposure to sunlight, which results in a high prevalence of skin cancer.

DESIGN

HLA typing was performed in 124 white individuals with histologically proven basal cell and/or squamous cell carcinoma and in control subjects. Skin type, the presence of freckling, and the number of actinic keratoses were determined.

SETTING

Population-based study.

SUBJECTS

Inhabitants of Saba with and without skin cancer.

MAIN OUTCOME MEASURE

Presence of HLA-DR1, HLA-DR4, and HLA-DR7 alleles.

RESULTS

Associations of HLA alleles with basal cell and squamous cell carcinoma have been reported. The presence of the HLA-DR7 allele was positively associated with the development of basal cell carcinoma (odds ratio, 3.8; 95% confidence interval, 1.1-13.4). Adjustment for skin type, which is a potentially confounding factor for the association between HLA alleles and skin cancer, did not substantially alter this association. No other associations between HLA alleles and skin cancer were found, possibly because of the small size of the study population.

CONCLUSION

This study presented further evidence for an association between HLA-DR7 and basal cell carcinoma. Arch Dermatol. 2000;136:1019-1022

Permanent detrimental effect of nonimmunological factors on long-term renal graft survival: a parsimonious model of time-dependency

PURPOSE

We attempted to model and test the pattern of effects of prognostic factors on renal graft survival during the posttransplantation time course.

PATIENTS AND METHODS

Patients who received a cadaveric kidney-only transplant between January 1990 and December 1995 in Eurotransplant, who received cyclosporine as induction therapy, and who had a complete follow-up at the time of analysis were included in the study (n= 10614). An index summarizing all covariate information was calculated and used for modeling the time-dependent effects with relation to graft failure.

RESULTS

The immunological factors (HLA mismatch and % panel-reactive antibody) were seen to have a slowly decreasing negative effect on renal graft survival. The cold ischemic trauma (>24 hr) exerted a permanent detrimental effect on the grafts. The use of organs obtained from old donors was associated with a constant higher risk of graft loss.

CONCLUSIONS

An analysis of determinants of human allograft dysfunction should also study the interaction between the effects and time. Nonimmunological factors had a constant detrimental effect on graft failure, whereas the impact of the immunological factors--although remaining important for late graft loss--very slowly decreased. In the context of marginal transplants, clustering of unfavorable factors should be avoided to prevent late graft losses.

Cross-reactive group matching does not lead to a better allocation and survival of donor kidneys

BACKGROUND

In cadaveric renal transplantation HLA-A, -B, -DR matching of donor and recipient is beneficial for graft survival. However, allocation based on HLA matching seems to favor recipients with more frequently occurring HLA antigens. In this study we investigated whether matching on the basis of cross-reactive groups (CREGs), defined according to the United Network for Organ Sharing (UNOS), would be a good alternative for the allocation of kidneys without negatively influencing graft survival. Theoretically, this approach would provide more recipients with an immunologically well-matched donor organ.

METHODS

The influence of CREG matching on graft survival was studied in univariate analyses using the Eurotransplant database.

RESULTS

No beneficial effect of CREG matching was observed, whereas a significant HLA matching effect was observed in the 0 CREG mismatched donor/ recipient combinations. Only in the small subgroup with 1 MM for HLA-A, -B and 0 MM for HLA-DR, a significantly better survival was observed, when this mismatch belonged to the 0 or 1 MM CREG group versus two or more MM CREG group. However, this subgroup concerns only 8% of the transplants performed.

CONCLUSIONS

In contrast to other reports, our study showed that HLA matching is by far more beneficial than CREG matching. In the homogenous Eurotransplant population, adjusting the matching criteria toward CREG matching would not lead to an improved graft survival.

Survival of donor cells 25 years after intrauterine transfusion

Persistence of donor leukocytes in the circulation of recipients of intrauterine transfusion (IUT) has been observed up to 5 years after birth. The aim of this study was to determine whether transfusions with nonirradiated, nonleukocyte-depleted donor blood during the fetal period resulted in long-term immunomodulation of the recipient. Twenty-four surviving IUT recipients between 1966 and 1976 were tested for autoimmune disease and autoantibodies at follow-up. Ten had sex-mismatched donors and were therefore informative for chimerism studies using fluorescence in situ hybridization (FISH). Seven female recipients could be tested for chimerism using a Y- chromosome-specific polymerase chain reaction (PCR) because they received at least 1 IUT from a male donor. Nine recipients could be studied for cytotoxic T-lymphocyte precursor (CTLp) and helper T-lymphocyte precursor (HTLp) frequencies because the original donors were available for testing. All surviving IUT recipients were in good health at the time of the examination, and routine laboratory testing revealed no abnormalities. None of the IUT recipients were chimeric as determined by FISH analysis, but Y-chromosome-specific sequences were detected by PCR in 6 of the 7 women. However, the CTLp and HTLp frequencies of the IUT recipients against the donors were comparable to those of the controls. The current study provides evidence that IUT can result in the persistence of donor cells in the recipient for a period longer than 20 years but that it is not associated with immunotolerance or with signs of chronic antigenic stimulation. (Blood. 2000;95:2709-2714)

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.

High frequency of allele-specific down-regulation of HLA class I expression in uveal melanoma cell lines

Uveal melanoma is the most common primary intra-ocular tumor in adults and has a high mortality rate due to liver metastases, for which no effective treatment is available. To investigate whether immunotherapy might be feasible in uveal melanoma, the HLA class I surface expression of 6 uveal melanoma cell lines was analyzed by flow cytometry using a broad panel of allele-specific monoclonal antibodies. To up-regulate HLA expression, cells were also cultured with IFN-alpha or -gamma. In general, expression of HLA-A alleles was high (except for cell line EOM-3) and could be further up-regulated by both IFN-alpha and -gamma. In cell line EOM-3, IFN-gamma treatment resulted in significant HLA-A expression while IFN-alpha treatment did not. Expression of HLA-B alleles was low or even negative. Variable effects were observed after IFN treatment. In 3 cell lines, expression of some HLA-B alleles could not be induced by IFN-alpha or -gamma: HLA-B44 in cell line 92-1, HLA-B15 in cell line OCM-1 and HLA-B5 in cell line MEL-202. The other B alleles of these cell lines showed enhanced expression levels upon IFN stimulation. In OMM-1 cells, IFN-alpha and -gamma increased the expression of HLA-A but did not induce expression of the 2 B alleles, indicating an HLA-B locus-specific loss. We thus found a high frequency of allele-specific and locus-specific down-regulation of HLA expression in uveal melanoma cell lines. Some of these defects were not restored by IFN-alpha or -gamma treatment. The lack of HLA expression may explain why uveal melanoma cells escape immune surveillance by cytotoxic T cells and complicate the development of immunotherapy in uveal melanoma.

Immunological tolerance in an HLA non-identical chimeric twin

Blood group chimeric twins offer a unique opportunity to study immunological tolerance in humans. Although this condition is not as rare as previously considered, detailed immunological studies of blood group chimeras are lacking. We describe here a case of secondary chimerism in a dizygotic twin of opposite gender. The karyotypes of the cultured fibroblast confirmed the sex of each twin, all cells in the boy were 46, XY and all cells in the girl were 46, XX. Molecular HLA typing on fibroblasts revealed HLA-DR, DQ and DP disparities between the two siblings. Mixed lymphocyte culture (MLC) revealed a mutual absence of alloreactivity.

Correlation between oral sex and a low incidence of preeclampsia: a role for soluble HLA in seminal fluid?

The involvement of immune mechanisms in the aetiology of preeclampsia is often suggested. Normal pregnancy is thought to be associated with a state of tolerance to the foreign antigens of the fetus, whereas in preeclamptic women this immunological tolerance might be hampered. The present study shows that oral sex and swallowing sperm is correlated with a diminished occurrence of preeclampsia which fits in the existing idea that a paternal factor is involved in the occurrence of preeclampsia. Because pregnancy has many similarities with transplantation, we hypothesize that induction of allogeneic tolerance to the paternal HLA molecules of the fetus may be crucial. Recent data suggest that exposure, and especially oral exposure to soluble HLA (sHLA) or HLA derived peptides can lead to transplantation tolerance. Similarly, sHLA antigens, that are present in the seminal plasma, might cause tolerance in the mother to paternal antigens. In order to test whether this indeed may be the case, we investigated whether sHLA antigens are present in seminal plasma. Using a specific ELISA we detected sHLA class I molecules in seminal plasma. The level varied between individuals and was related to the level in plasma. Further studies showed that these sHLA class I molecules included classical HLA class I alleles, such as sHLA-A2, -B7, -B51, -B35 and sHLA-A9. Preliminary data show lower levels of sHLA in seminal plasma in the preeclampsia group, although not significantly different from the control group. An extension of the present study is necessary to verify this hypothesis.

Determination of acceptable HLA mismatches in highly sensitized patients by soluble HLA class I ELISA inhibition

BACKGROUND

Acceptable HLA mismatches for highly sensitized patients are determined so as to increase their chances of receiving transplants. The disadvantage of the current procedures is that the antibody reactivity of the patients' sera is tested against HLA antigens expressed on cells or HLA antigens isolated from cell lysates. Therefore, two (homozygous for HLA-A and -B) to four (heterozygous for HLA-A and -B) different HLA class I antigens are present in the test. This might cause reactivity toward nonacceptable mismatches to mask the determination of acceptable mismatches.

METHODS

Recently we observed that the detection of soluble HLA class I antigens is inhibited by HLA-specific antibodies. In the present study, inhibition of soluble HLA-specific ELISAs (anti-soluble HLA-A2, -B7, -B12) was evaluated as a tool used to determine acceptable mismatches. The results were compared with current determination of acceptable mismatches (which is by complement-dependent cytotoxicity and/or fluorescence-activated cell sorter analysis).

RESULTS

In the case of acceptable mismatches determined by conventional methods, sera from the patients were not interfering in these ELISAs, whereas in the case of nonacceptable mismatches (thus specific antibodies), significant inhibition was observed in most instances. Among the nonacceptable mismatches, the test showed significant inhibition in 20 of 24 cases, whereas among acceptable mismatches, no inhibition was observed (in eight of eight), indicating the lack of specific antibodies.

CONCLUSIONS

In highly sensitized patients, the introduction of soluble HLA-specific ELISAs is of additional and confirmatory value for the determination of acceptable mismatches. The major advantage of this approach is that antibody reactivity is tested against single antigens only.

The importance of H2 haplotype sharing in the induction of specific unresponsiveness by pretransplant blood transfusions

BACKGROUND

The beneficial effect on graft survival achieved by pretransplant blood transfusions is well established. Previous studies have shown that the degree of major histocompatibility complex (MHC) (mis)-match between the transfusion donor and the recipient plays a determining role. However, other factors are also involved. In this study, we explored the hypothesis that, in addition to sharing of MHC antigens between the transfusion donor and the recipient, the MHC type of the organ donor is also of importance.

METHODS

To mimic the human situation, F1 mice, rather than inbred strains, were pretreated with haplotype-shared allogeneic whole blood transfusions and transplanted with hearts of organ donors with different matched or mismatched H2 haplotypes.

RESULTS

When a heart was transplanted 1 week after donor-specific transfusion (DST; blood transfusion donor=organ donor), an excellent prolongation of graft survival was obtained (median survival time: 77 days vs. 9 days in untreated mice). However, this was only the case when a haplotype was shared with the recipient; a DST given with no match between organ donor (=BT donor) and recipient did not induce any prolongation. Furthermore, in order to obtain the optimal beneficial effect of a haplotype-shared blood transfusion, the other haplotype of the transfusion donor had to be mismatched with the recipient. The immunogenetic studies showed that haplotype-shared blood transfusions in combinations where the H2 type of the organ donor differed from that of the transfusion donor are less efficient in inducing prolongation of graft survival.

CONCLUSIONS

These results demonstrate that haplotype-shared blood transfusions can induce a significantly prolonged survival of cardiac allografts in F1 mice. The immunogenetic studies suggest that presentation of alloantigen-derived peptides in the context of self MHC (the indirect pathway of allorecognition) is essential for the beneficial effect of haplotype-shared blood transfusions.

T helper frequencies in peripheral blood reflect donor-directed reactivity in the graft after clinical heart transplantation

We describe the usefulness of a fast (48-h) limiting dilution assay (LDA) for the enumeration of human alloreactive helper T lymphocytes (HTL) in the peripheral blood, in relation to histologically defined rejection grades after heart transplantation. HTL frequencies (HTLf) in pretransplant samples varied from patient to patient, ranging from 106 to 625 HTL/106 peripheral blood mononuclear cells (PBMC). In the first week after heart transplantation (HTx), when immunosuppression was instituted, HTLf were significant lower (range 30-190 HTL/106). The level of HTL in the first week after HTx when rejection grade was 0 or 1A (ISHLT score) was considered to be the baseline frequency. This frequency did not correlate with the number of subsequent rejection episodes. During rejection (grade 3), donor-specific HTLf were increased above their baseline frequencies (P = 0.01). Expressed as percentage of baseline frequencies, HTLf increased significantly during acute rejection (AR) compared with 1-2 weeks before rejection (P = 0.003). The increase was specific, since viral infections did not result in a rise of donor-specific HTL, while also HTLf specific for third party HLA antigens were not elevated during rejection. Monitoring HTLf in peripheral blood with a shortened (48-h) assay may serve as a non-invasive method for detecting intragraft immunological reactivity. Demonstrating absence of donor-specific reactivity may limit the number of invasive endomyocardial biopsy (EMB) procedures and allow tapering of immunosuppressive treatment.

Isolation of broadly reactive, tumor-specific, HLA Class-I restricted CTL from blood lymphocytes of a breast cancer patient

Blood lymphocytes of a HLA-A2 positive breast cancer patient were stimulated with either MCF-7 or MDA-MB-231, i.e., HLA-A2-matched allogeneic breast carcinoma cell lines. Several CD8+ CTL clones with reactivity against the stimulator cells but not against K562 were generated. Reactivity could be blocked with monoclonal antibody (mAb) W6/32, MA2.1, and/or BB7.2, indicating that the clones are HLA-class I and HLA-A2 restricted. The CTL clones generated following stimulation with MCF-7, recognized various other allogeneic HLA-A2+ tumor cell lines, including breast carcinoma, renal cell carcinoma, and melanoma cell lines, but not HLA-A2 tumor cell lines. The CTL clones did not recognize normal HLA-A2+ cells including breast epithelial cells, renal proximal tubular epithelial cells (PTEC), or EBV-transformed B cells including the autologous EBV cell line. In contrast to the CTL clones induced with MCF-7, the reactivity of the clones stimulated with MDA-MB-231, was limited to the stimulator cell MDA-MB-231. Cytotoxicity assays utilizing T2 cells loaded with peptides as target cells indicated that none of the examined CTL-epitopes derived from HER-2/neu, Muc-1, Ep-CAM-1, and p53 were recognized by the CTL clones generated. Our findings underscore that breast cancer is an immunogenic tumor and that HLA-class I-matched allogeneic tumor cells can be used as stimulator cells to generate tumor-specific CTL from peripheral blood of a breast cancer patient with specificity for an antigenic determinant that is broadly expressed on tumor cells from various origins or with specificity limited to the breast cancer stimulator cell.

In vitro reactivity of allospecific cytotoxic T lymphocytes does not explain the taboo phenomenon

Matching for human leucocyte antigens (HLA) is important for graft survival in kidney transplantation. Nevertheless, most patients receive a kidney graft with multiple HLA mismatches. Some of these mismatches seem to be more harmful than others. By studying the effect of single HLA mismatches in the context of the patients' own HLA, we have previously identified donor/recipient combinations with a significantly higher incidence of early graft failure, the so-called taboo combinations. In the present study we investigated whether a higher cytotoxic T lymphocyte (CTL) response towards taboo mismatches may be involved in this phenomenon. CTL reactivity was determined both in taboo and control combinations by in vitro CTL precursor assays, using peripheral blood mononuclear cells and proximal tubular epithelial cells as target cells. Inhibition studies with CD8-antibody as well as Cyclosporin A were performed to identify high avidity and primed CTLs. Furthermore, in committed CTLp assays indirect recognition of the taboo mismatch was tested using synthetic peptides. The CTL precursor frequencies in taboo combinations were always lower than the CTL precursor frequencies in control combinations. No difference in avidity and activation status of the CTLs could be detected when taboo combinations were compared with the controls. In the committed CTLp assays no reactivity towards any of the synthetic peptides was observed. The significantly poorer graft survival of taboo combinations cannot be explained by a higher number of donor-specific CTLs. Furthermore, the avidity or activation status of these CTLs does not provide a clue to the taboo phenomenon.

Sharing cross-reactive groups of MHC class I improves long-term graft survival

BACKGROUND

Renal transplant loss from chronic rejection remains substantial. To increase our understanding of this syndrome, we identified risk factors predicting late graft loss, with a special emphasis on the impact of human lymphocyte antigen (HLA) matching.

METHODS

We studied all 654 cadaveric kidney transplants performed in our center between 1983 and 1996 that had survived for more than six months. Eighty-two transplants, lost because of chronic rejection, were used as the outcome variable. The influence of HLA mismatches and shares on long-term graft survival was evaluated at the level of private antigens and cross-reactive groups (CREG) of multiple histocompatibility complex (MHC) class I. HLA and other recipient, donors and transplant parameters were studied using univariate and multivariate Cox regression analysis.

RESULTS

The cohort had a mean number of 1.9 HLA mismatches. Because of the homozygosity of HLA antigens, HLA mismatches were not reciprocal to shares. CREG and HLA-A-B mismatches had a relative risk for graft loss of 1.19 (95% CI, 0.97 to 1.45) and 1.05 (0.84 to 1.32) per mismatch. In contrast, the relative risk per shared CREG and broad HLA-A-B antigen was 0.76 (0.63 to 0.92) and 0.79 (0.61 to 1.03). Multivariate analysis revealed that individuals sharing less than four CREGs had a relative risk of 2.13 (1.29 to 3.75) for late graft loss. Other independent predictors were a recipient age of less than 50 years, relative risk 1.95 (1.02 to 3.71); a donor age of more than 50 years, relative risk 1.68 (1.01 to 2.80); acute rejection (vascular vs. no rejection), relative risk 3.52 (1.72 to 7.18); proteinuria (dipstick > 1+ vs. negative), relative risk 2.86 (1.29 to 6.35); and a serum creatinine concentration of more than 150 micromol/liter at six months, relative risk 3.41 (1.96 to 5.94).

CONCLUSION

We identified several coexisting recipient-, donor-, and transplant-related risk factors for graft loss from chronic rejection. In this well-matched group of renal transplants, HLA mismatches and shares had a nonreciprocal relationship. Sharing of HLA antigens, especially CREG of MHC class I, was associated with improved long-term survival.

The impact of special programs for kidney transplantation of highly sensitized patients in Eurotransplant

Highly immunized patients will continue to accumulate on the waiting list of many registries unless special allocation programs are introduced. In Eurotransplant such patients can benefit from 2 programs, the Acceptable Mismatch (AM) and the Highly Immunized Tray (HIT) programs. Kidney exchange is mandatory in these programs. In addition, highly immunized patients who do not participate in these programs profit from additional points in the allocation procedure (ET-HI). In the past 18 months the 3 programs have run in parallel. Here, we show that the AM and HIT programs are highly effective with respect to increasing the patient's chance of finding a crossmatch negative donor in an adequate time course. Furthermore, the transplantation results of AM and HIT are at least comparable to those of the ET-HI. The main gain at present seems to be the significantly shorter waiting time in the AM and HIT programs.

Genotyping for human platelet-specific antigens HPA-1, -2, -3, -4 and -5 in the Slovenian population reveals a slightly increased frequency of HPA-1b and HPA-2b as compared to other European populations

Typing of human platelet alloantigens (HPA) is necessary in various clinical situations. The purpose of this study was to type a random sample of the Slovenian population for HPA alleles, in order to obtain genetic population data. A total of 152 unrelated Slovenian blood donors were genotyped for HPA-1, -2, -3, -4 and -5 alleles using a simple method that enables simultaneous and complete determination of HPA genotypes. Ten different polymerase chain reactions employing sequence-specific priming (PCR-SSP), which worked in identical cycling conditions, were used. The allele frequencies were 0.809 for HPA-1a, 0.191 for HPA-1b, 0.891 for HPA-2a, 0.109 for HPA-2b, 0.591 for HPA-3a, 0.407 for HPA-3b, 0.997 for HPA-4a, 0.00 for HPA-4b, 0.934 for HPA-5a and 0.066 for HPA-5b. When compared to results of studies of various other Caucasian populations, our population displayed a slightly but not significantly higher proportion of the HPA-1b and 2b alleles.

Human bone allografts can induce T cells with high affinity for donor antigens

We analysed the cellular immune response in ten transplantations of different massive bone allografts, of which five had a poor clinical outcome. Cytotoxic T lymphocytes (CTL) and T helper lymphocytes (TH) against mismatched donor antigens were found in all patients. More importantly, CTL with a high affinity for donor antigens were found in five cases. High-affinity CTL need no CD8 molecule to stabilise the antigen binding and are strongly associated with rejection of heart and corneal transplants. Even after removal of most of the bone-marrow cells, we found high-affinity CTL and high TH frequencies. This T-cell response could be detected over a period of years. We conclude that frozen bone allografts can induce high-affinity donor-specific CTL. The present assay allows qualification and quantification of the levels of CTL and TH in the blood. This approach may be helpful in studying the effect of the immune response on the outcome of the graft.

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.

Auto- and alloimmune reactivity to human islet allografts transplanted into type 1 diabetic patients

Allogeneic islet transplantation can restore an insulin-independent state in C-peptide-negative type 1 diabetic patients. We recently reported three cases of surviving islet allografts that were implanted in type 1 diabetic patients under maintenance immune suppression for a previous kidney graft. The present study compares islet graft-specific cellular auto- and alloreactivity in peripheral blood from those three recipients and from four patients with failing islet allografts measured over a period of 6 months after portal islet implantation. The three cases that remained C-peptide-positive for >1 year exhibited no signs of alloreactivity, and their autoreactivity to islet autoantigens was only marginally increased. In contrast, rapid failure (<3 weeks) in three other cases was accompanied by increases in precursor frequencies of graft-specific alloreactive T-cells; in one of them, the alloreactivity was preceded by a sharply increased autoreactivity to several islet autoantigens. One recipient had a delayed loss of islet graft function (33 weeks); he did not exhibit signs of graft-specific alloimmunity, but developed a delayed increase in autoreactivity. The parallel between metabolic outcome of human beta-cell allografts and cellular auto- and alloreactivity in peripheral blood suggests a causal relationship. The present study therefore demonstrates that T-cell reactivities in peripheral blood can be used to monitor immune mechanisms, which influence survival of beta-cell allografts in diabetic patients.