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

Association of HLA Antigen Mismatch With Risk of Developing Skin Cancer After Solid-Organ Transplant

Importance

Risk factors for the development of skin cancer after solid-organ transplant can inform clinical care, but data on these risk factors are limited.

Objective

To study the association between HLA antigen mismatch and skin cancer incidence after solid-organ transplant.

Design, Setting, and Participants

This retrospective cohort study is a secondary analysis of the multicenter Transplant Skin Cancer Network study of 10 649 adults who underwent a primary solid-organ transplant between January 1, 2003, and December 31, 2003, or between January 1, 2008, and December 31, 2008. These participants were identified through the Scientific Registry of Transplant Recipients standard analysis files, which contain data collected mostly by the Organ Procurement and Transplantation Network. Participants were matched to skin cancer outcomes by medical record review. This study was conducted from August 1, 2016, to July 31, 2017.

Main Outcomes and Measures

The primary outcome was time to diagnosis of posttransplant skin cancer, including squamous cell carcinoma, melanoma, and Merkel cell carcinoma. The HLA antigen mismatch was calculated based on the 2016 Organ Procurement and Transplantation Network guidelines. Risk of skin cancer was analyzed using a multivariate Cox proportional hazards regression model.

Results

In total, 10 649 organ transplant recipients (6776 men [63.6%], with a mean [SD] age of 51 [12] years) contributed 59 923 years of follow-up. For each additional mismatched allele, a 7% to 8% reduction in skin cancer risk was found (adjusted hazard ratio [HR], 0.93; 95% CI, 0.87-0.99; P = .01). Subgroup analysis found the protective effect of HLA antigen mismatch to be statistically significant in lung (adjusted HR, 0.70; 95% CI, 0.56-0.87; P = .001) and heart (adjusted HR, 0.75; 95% CI, 0.60-0.93; P = .008) transplant recipients but not for recipients of liver, kidney, or pancreas. The degree of HLA-DR mismatch, but not HLA-A or HLA-B mismatch, was the most statistically significant for skin cancer risk (adjusted HR, 0.85; 95% CI, 0.74-0.97; P = .01).

Conclusions and Relevance

The HLA antigen mismatch appears to be associated with reductions in the risk of skin cancer after solid-organ transplant among heart and lung transplant recipients; this finding suggests that HLA antigen mismatch activates the tumor surveillance mechanisms that protect against skin cancer in transplant recipients and that skin cancer risk may be higher in patients who received a well-matched organ.

The Importance of HLA Assessment in "Off-the-Shelf" Allogeneic Mesenchymal Stem Cells Based-Therapies

The need for more effective therapies of chronic and acute diseases has led to the attempts of developing more adequate and less invasive treatment methods. Regenerative medicine relies mainly on the therapeutic potential of stem cells. Mesenchymal stem cells (MSCs), due to their immunosuppressive properties and tissue repair abilities, seem to be an ideal tool for cell-based therapies. Taking into account all available sources of MSCs, perinatal tissues become an attractive source of allogeneic MSCs. The allogeneic MSCs provide "off-the-shelf" cellular therapy, however, their allogenicity may be viewed as a limitation for their use. Moreover, some evidence suggests that MSCs are not as immune-privileged as it was previously reported. Therefore, understanding their interactions with the recipient's immune system is crucial for their successful clinical application. In this review, we discuss both autologous and allogeneic application of MSCs, focusing on current approaches to allogeneic MSCs therapies, with a particular interest in the role of human leukocyte antigens (HLA) and HLA-matching in allogeneic MSCs transplantation. Importantly, the evidence from the currently completed and ongoing clinical trials demonstrates that allogeneic MSCs transplantation is safe and seems to cause no major side-effects to the patient. These findings strongly support the case for MSCs efficacy in treatment of a variety of diseases and their use as an "off-the-shelf" medical product.

Degree of HLA class II eplet mismatch load improves prediction of antibody-mediated rejection in living donor kidney transplantation

BACKGROUND

HLA mismatching is a well known risk factor for worst outcomes in kidney transplantation.

METHODS

In the present study, HLA antigen and eplet mismatches were determined in 151 living donor-recipient pairs transplanted between 2007 and 2014 and rejection episodes and graft survival were evaluated.

RESULTS

We found that high HLA-II eplet mismatch load (EpMM ≥ 13, versus low EpMM ≤ 5), was an independent predictor of AMR (adjusted HR = 14.839; P = 0.011), while HLA-II AgMM was not. We also showed that HLA-II EpMM load was a significant better predictor of AMR than AgMM (c-statistic = 0.064; P = 0.023). After discriminating HLA-II into HLA-DR and HLA-DQ loci we demonstrated that high versus low eplet mismatch load for HLA-DR (T3 ≥ 6 versus T = 0-1, p = 0.013) and HLA-DQ (T3 ≥ 7 versus T = 0-1, p = 0.009) are independent predictors for AMR. HLA-II EpMM increased discrimination performance of the classical HLA-II AgMM risk model (IDI, 0.061, 95%CI: 0.005-0.195) for AMR. Compared with AgMM, HLA-II eplet model adequately reclassified 13 of 17 patients (76.5%) with AMR and 92 of 134 patients (68.7%) without AMR (cfNRI, 0.785, 95%CI: 0.300-1.426).

CONCLUSIONS

Our study evidences that eplet-based matching is a refinement of the classical HLA antigen mismatch analysis in LDKT and is a potential biomarker for personalized assessment of alloimmune risk.

HLA Epitope Matching in Kidney Transplantation: An Overview for the General Nephrologist

Rapid changes in tissue-typing technology, including the widespread availability of highly specific molecular typing methods and solid-phase assays for the detection of allele-specific anti-HLA antibodies, make it increasingly challenging to remain up to date with developments in organ matching. Terms such as epitopes and eplets abound in the transplantation literature, but often it can be difficult to see what they might mean for the patient awaiting transplantation. In this review, we provide the historical context for current practice in tissue typing and explore the potential role of HLA epitopes in kidney transplantation. Despite impressive gains in preventing and managing T-cell-mediated rejection and the associated improvements in graft survival, the challenge of the humoral alloresponse remains largely unmet and is the major cause of late graft loss. Describing HLA antigens as a series of antibody targets, or epitopes, rather than based on broad seroreactivity patterns or precise amino acid sequences may provide a more practical and clinically relevant system to help avoid antibody-mediated rejection, reduce sensitization, and select the most appropriate organs in the setting of pre-existing alloantibodies. We explain the systems proposed to define HLA epitopes, summarize the evidence to date for their role in transplantation, and explore the potential benefits of incorporating HLA epitopes into clinical practice as this field continues to evolve toward everyday practice.

Ushering in the era of penile transplantation

Penile transplantation is a novel approach to management of penile loss in the developing field of composite tissue allotransplantation (CTA). Prior management for significant penile loss has been free flap phalloplasty with issues related to function, cosmesis, and functional loss from the location of flap harvest. Transplantation has been an evolving field with advancement in CTA over the past several decades leading to the option of penile transplant. Management of penile injury with replantation provided some preliminary groundwork on the technical aspects for penile transplantation. Additionally, penile transplantation raises many ethical, emotional, and psychological considerations with need for patience amidst ongoing advancement within the field.

Rethinking the advantage of zero-HLA mismatches in unrelated living donor kidney transplantation: implications on kidney paired donation

The OPTN/UNOS Kidney Paired Donation (KPD) Pilot Program allocates priority to zero-HLA mismatches. However, in unrelated living donor kidney transplants (LDKT)-the same donor source in KPD-no study has shown whether zero-HLA mismatches provide any advantage over >0 HLA mismatches. We hypothesize that zero-HLA mismatches among unrelated LDKT do not benefit graft survival. This retrospective SRTR database study analyzed LDKT recipients from 1987 to 2012. Among unrelated LDKT, subjects with zero-HLA mismatches were compared to a 1:1-5 matched (by donor age ±1 year and year of transplantation) control cohort with >0 HLA mismatches. The primary endpoint was death-censored graft survival. Among 32,654 unrelated LDKT recipients, 83 had zero-HLA mismatches and were matched to 407 controls with >0 HLA mismatches. Kaplan-Meier analyses for death-censored graft and patient survival showed no difference between study and control cohorts. In multivariate marginal Cox models, zero-HLA mismatches saw no benefit with death-censored graft survival (HR = 1.46, 95% CI 0.78-2.73) or patient survival (HR = 1.43, 95% CI 0.68-3.01). Our data suggest that in unrelated LDKT, zero-HLA mismatches may not offer any survival advantage. Therefore, particular study of zero-HLA mismatching is needed to validate its place in the OPTN/UNOS KPD Pilot Program allocation algorithm.

HLA epitopes as viewed by antibodies: what is it all about?

The need for new approaches to define HLA antibodies, in the context of organ transplantation, is intensely debated among HLA professionals. In this review, we sought to provide background and perspective to current understanding of the immunogenicity of HLA mismatches with respect to the humoral alloimmune response and the definition of B cell epitopes. Initial data suggest that epitope matching not only assists in defining better matches for the current transplant, but also minimizes the risk of developing de novo HLA-donor-specific-antibodies posttransplant. In other words, other than lowering the risk of current graft rejection, epitope matching is likely to lower overall future sensitization levels and thus increases the likelihood of finding a compatible donor when the need for a retransplantation arises. More detailed knowledge of epitopes makes it possible to investigate what constitutes permissible versus non-permissible HLA mismatches. The currently available evidence suggest that epitope matching is the most rational way to decrease the risk of HLA-linked transplant rejection. This review is aimed at stimulating further and more intense collaborative effort in this field.

HLA mismatching within or outside of cross-reactive groups (CREGs) is associated with similar outcomes after unrelated hematopoietic stem cell transplantation

The National Marrow Donor Program maintains a registry of volunteer donors for patients in need of a hematopoietic stem cell transplantation. Strategies for selecting a partially HLA-mismatched donor vary when a full match cannot be identified. Some transplantation centers limit the selection of mismatched donors to those sharing mismatched antigens within HLA-A and HLA-B cross-reactive groups (CREGs). To assess whether an HLA mismatch within a CREG group ("minor") may result in better outcome than a mismatch outside CREG groups ("major"), we analyzed validated outcomes data from 2709 bone marrow and peripheral blood stem cell transplantations. Three-hundred and ninety-six pairs (15%) were HLA-DRB1 allele matched but had an antigen-level mismatch at HLA-A or HLA-B. Univariate and multivariate analyses of engraftment, graft-versus-host disease, and survival showed that outcome is not significantly different between minor and major mismatches (P = .47, from the log-rank test for Kaplan-Meier survival). However, HLA-A, HLA-B, and HLA-DRB1 allele-matched cases had significantly better outcome than mismatched cases (P < .001). For patients without an HLA match, the selection of a CREG-compatible donor as tested does not improve outcome.

Influence of Mismatching of HLA Cross-Reactive Groups on Cadaveric Kidney Transplantation

Finding fully HLA-matched recipients for a given donor is not practical due to the allelic diversity of the loci. Cross-reactive group (CREG) matching has been considered a feasible alternative to HLA matching. However, the true efficacy of CREG matching in cadaveric kidney transplantation is controversial. Using conventional HLA and CREG classifications proposed by Rodey and McKenna, we counted the number of mismatches for 319 patients who received cadaver kidney transplants between 1992 and 2003 at Asan Medical Center in Korea. When we compared transplants with four or fewer HLA-A, -B, and -DR antigen mismatches with those with five or more, we observed a significant difference in 5-year survival rate (88.5% versus 78.6%; P = .0189). Transplants with no or one HLA-DR mismatch had a significantly better 5-year survival rate than those with two HLA-DR mismatches (87.9% versus 80.0%; P = .0469). Among transplants with one or two HLA-DR mismatches, transplants with zero or one CREG mismatch showed better 5-year graft survival rate than those with two or more CREG mismatches (89.4% versus 79.8%; P = .0415) only in McKenna's CREG classification. These results suggest that the impact of CREG mismatches on graft survival may depend on CREG classification and on the distribution of HLA-DR mismatches.

When Race Matters

Several widely held assumptions shape end-of-life discussion in the United States. They are embedded in mainstream bioethics and biomedical discourse, debate, and discussion, as well as in the popular media. We have come to regard them as the conventional wisdom. Despite their apparent reasonableness, the assumptions are not held universally by all US citizens, particularly those of color. They hold contradictions that partially explain why fewer African Americans than whites complete advance directives, and why African Americans tend to desire aggressive care at the end of life. This article considers some of these assumptions. It then considers a case and an approach to care that seeks to resolve potential conflicts proactively.

The case to abandon human leukocyte antigen matching for kidney allocation: would it be wise to throw out the baby with the bathwater?

Since major histocompatibility (MHC) antigen matching was introduced in the early 1970s as the key factor determining kidney transplant allocation, several studies, mainly arising from organ-sharing organizations in the United States and Europe, have debated this complex issue. The first fundamental concern is the interaction of human leukocyte antigen matching with other transplant outcome risk factors, for example, prolongation of ischemia and matching for age. Much concordant data advocate restraining MHC antigen-based allocation in terms of space and time limits. The second fundamental concern is the balancing of the advantages of better antigen matching in terms of improved graft survival and the improved transplantation rate in immunologically high-risk patients with the major drawback of inequitable access for ethnic minorities and patients with rare MHC haplotypes. These issues have led to considering renewed kidney allocation rules, discarding human leukocyte antigen matching from algorithms, or modifying the specificity allocation level by using cross-reactive group matching or class II MHC antigen matching. The evolving concepts in the field of histocompatibility support the need for periodically updated, flexible, and hybrid allocation systems, as designed in France by the Etablissement français des Greffes.

No impact of cross-reactive group human leucocyte antigen class I matching on long-term kidney graft survival

The aim was to elucidate the effect of matching for the broad human leucocyte antigen (HLA)-A and -B cross-reactive groups (CREGs) of major histocompatibility complex (MHC) class I on long-term kidney graft survival.

MATERIAL AND METHODS

1304 patients transplanted at Rigshospitalet between 1968 and 1999 with a cadaver kidney and followed until 2000. The definition of CREGs based on amino acid residues was according to United Network for Organ Sharing (UNOS) (1996). Graft-survival analyses (Kaplan Meier) were performed for all cases and for cases censored for death with functioning grafts.

RESULTS

Univariate analysis showed no effect of any specific donor or recipient CREG on graft survival. Contrary to some reports in the literature, the absolute and relative number of CREG shares and of CREG mismatches had no effect on graft survival even when censored for graft loss because of death. However, graft survival was dependent on DR shares (P < 0.05), indicating that matching for MHC class II seems to be more important than that for the broad MHC class I phenotype represented by CREG.

HLAmatchmaker: a molecularly based algorithm for histocompatibility determination. IV. An alternative strategy to increase the number of compatible donors for highly sensitized patients

BACKGROUND

HLAMatchmaker is a computer algorithm that determines human leukocyte antigen (HLA) compatibility at the level of polymorphic amino acid triplets in antibody-accessible sequence positions. Recent studies have shown that HLA-DR-matched kidney transplant recipients with zero to two triplet mismatches had almost identical graft survival rates as those with zero HLA-A,B,DR antigen mismatches. This report describes how HLAMatchmaker can be used to identify more compatible donors for highly sensitized patients.

METHODS

The HLAMatchmaker program was used to calculate the probability of finding a donor (PFD) with zero, one, or two triplet mismatches for 54 highly sensitized patients waiting for a kidney transplant and having panel reactive antibody (PRA) values greater than 85% and 50 randomly selected nonsensitized patients with PRA values less than 3%.

RESULTS

There was a wide variability for PFD values for the two patient cohorts. If only donors with zero HLA-A,B mismatches were deemed acceptable for recipients, the median PFD of a zero-antigen mismatch was 0.046% for nonsensitized patients and 0.009% for highly sensitized patients (P=0.007). Half of the highly sensitized patients had a PFD below 0.01%, or fewer than 1 in 10,000 donors would have zero antigen mismatches. Application of HLAMatchmaker identified additional HLA antigens with zero-triplet mismatches for 27 patients, resulting in a 1.8-fold increase in PFD. Considering additional antigens with one-triplet or two-triplet mismatches increased the PFD by an additional 3.8-fold and 13.7-fold, respectively. Acceptable antigen mismatches for 37 of the 54 highly sensitized patients were identified by consistently negative reactions in serum screens, and their addition resulted in a 12.7-fold increase of the PFD to a median of 0.141%. Applying these acceptable antigens to the HLAMatchmaker algorithm identified additional antigens with zero or acceptable triplet mismatches and their inclusion increased the PFD by 3.3-fold to 0.347%.

CONCLUSIONS

HLAMatchmaker offers a valuable strategy for identifying more suitably HLA-matched donors and has the potential for alleviating the problem of accumulation of highly sensitized patients on the transplant waiting list.

HLAmatchmaker: a molecularly based algorithm for histocompatibility determination. III. Effect of matching at the HLA-A,B amino acid triplet level on kidney transplant survival

BACKGROUND

HLAMatchmaker is a recently developed computer-based algorithm to determine donor-recipient HLA compatibility at the molecular level. Originally designed for highly alloimmunized patients, this algorithm is based on the concept that immunogenic epitopes are represented by amino acid triplets on exposed parts of protein sequences of HLA-A, -B, and -C chains accessible to alloantibodies. Donor HLA compatibility is determined by intralocus and interlocus comparisons of triplets in polymorphic sequence positions. For most patients, HLAMatchmaker can identify certain mismatched HLA antigens that are zero-triplet mismatches to the patient's HLA phenotype and should, therefore, be considered fully histocompatible. The present study was designed to determine how class I HLA matching at the triplet level affects kidney transplant outcome.

METHODS

We analyzed two multicenter databases of zero-HLA-DR-mismatched kidneys transplanted from 1987 to 1999. One database consisted of 31,879 primary allografts registered by U.S. transplant centers in the United Network for Organ Sharing database and the other consisted of 15,872 transplants in the Eurotransplant program.

RESULTS

HLA-A,B mismatched kidneys that were compatible at the triplet level exhibited almost identical graft survival rates as the zero-HLA-A,B antigen mismatches defined by conventional criteria. This beneficial effect of triplet matching was seen for both nonsensitized and sensitized patients and also for white and nonwhite patients.

CONCLUSIONS

These findings suggest that the application of HLAMatchmaker will increase the number of successful transplants, at least in the HLA-DR match combinations.

HLA matching and the United Network for Organ Sharing Allocation System: impact of HLA matching on African-American recipients of cadaveric kidney transplants

BACKGROUND

A recent proposal supports the elimination of allocation points for human leukocyte antigen (HLA) mismatches (MM) in cadaveric kidney transplantation. The intent is to increase access for some racial groups that might be disadvantaged by the representation of race-specific HLA in a largely white donor pool. We report our experience from two transplant centers that serve a large African American (AA) patient population.

METHODS

All cadaveric transplants into AA recipients from 1994 to 2000 (n=162) were included in a retrospective review.

RESULTS

Superior graft survival was observed in AA recipients of 0 MM transplants. When induction therapy was used, the graft survival at 3 years for the human leukocyte antigen (HLA)-BDR MM grades given allocation points (0,1,2 MM) was 82% versus only 49% for BDR MM grades not given points (3,4 MM: =0.0022).

CONCLUSIONS

Our collective experience demonstrates that AA patients having HLA-BDR MM grades given allocation points had better graft survival. Removing points for HLA from the national allocation system may result in significantly poorer outcome in AA kidney recipients.

Definition of permissible and immunogenic HLA antigens based on epitope analysis of the HLA specific antibodies produced in sensitized patients

The goal of this study was to develop an accurate protocol whereby detection of acceptable HLA-A and -B mismatches is based on epitope analysis of HLA class I specific antibodies detected in the serum of highly sensitized patients awaiting a kidney retransplant. A total of 400 serum samples from 44 highly sensitized patients with panel reactive antibodies (PRA) of > or = 60% were collected during a 3-year follow-up period. All patients had been sensitized from a previous graft. In order to define the specificities of the HLA class I specific antibodies, two techniques were used in parallel: the antihuman globulin augmented complement-dependent cytotoxicity (CDC) technique and an enzyme-linked immunoabsorbent assay (ELISA) technique. Epitope identification was based on class I HLA antigen sequencing, where the unique epitope configuration on one HLA antigen represented the private epitope of the specific HLA antigen, and epitopes shared by more than one HLA antigen represented public determinants. The epitope prediction for the immunogenic HLA epitopes was based on an MHC database. For each highly sensitized patient, antibody specificities against actual and 'at risk' epitopes were defined. Following epitope analysis, all HLA antigens that did not express the actual and/or 'at risk' immunogenic epitopes were considered as acceptable mismatches of epitope analysis. The cytotoxicity of highly sensitized patients was determined using two different panels of selected, separated T lymphocytes. HLA class I specific IgG antibodies against 69 actual and 86 'at risk' epitopes were detected. In all patients, a large number of acceptable mismatches were defined. These included a large number of HLA antigens, corresponding to both HLA-A and -B loci. Our study introduces an accurate protocol for the detection of acceptable mismatches in highly sensitized patients. According to this protocol, the detailed description of immunogenic HLA specific epitope targets, against which HLA class I specific antibodies are directed, is a useful tool for the detection of acceptable mismatches in highly sensitized patients. This may lead to reduced production of HLA class I specific antibodies and, consequently, improved graft survival.

HLAMatchmaker: a molecularly based algorithm for histocompatibility determination. I. Description of the algorithm

This report describes an algorithm for identifying acceptable HLA antigens for highly alloimmunized patients without the need for extensive serum screening. This algorithm is based on the concept that immunogenic epitopes are represented by amino acid triplets on exposed parts of protein sequences of human leukocyte antigen chains (HLA-A, HLA-B, and HLA-C) accessible to alloantibodies. A computer program (HLAMatchmaker) has been developed to determine class I HLA compatibility at the molecular level. It makes intralocus and interlocus comparisons of polymorphic triplets in sequence positions to determine the spectrum of non-shared triplets on donor HLA antigens. In most cases is it possible to identify certain mismatched HLA antigens that share all their polymorphic triplets with the patient's HLA antigens and could therefore, be considered fully compatible. HLAMatchmaker permits also the identification of additional mismatches that are acceptable as determined from the triplet information on HLA-typed panel cells that do not react with patient's serum.HLAMatchmaker provides an assessment of donor-recipient HLA compatibility at the structural level and this algorithm is different from conventional methods based on the mere counting of numbers of mismatched HLA antigens or CREGs. This donor selection strategy is suitable especially for allosensitized patients in need of a compatible transplant or platelet transfusion.

Characterization of HLA class I specific antibodies by ELISA using solubilized antigen targets: II. Clinical relevance

Until recently, the nature of humoral sensitization to HLA has been characterized by data from lymphocyte-based assays, predominantly cytotoxicity tests. We have examined the characteristics, determined by enzyme-linked immunosorbent assay (ELISA), of sera from 191 subjects known to have produced HLA-specific antibody. We found that ELISA detected higher frequencies compared with cytotoxicity of many (74.5%), but not all, HLA-specific antibodies; in many cases (42.6%) the frequencies of these antibodies were higher than predicted from population frequencies whereas some antibodies (23.4%) occurred with lower than expected frequencies. Some of the increase in frequencies can be accounted for by crossreactivity, i.e., sensitization to epitopes shared among two or more allelic products. The presence of epitopes shared between a recipient's antigen and a mismatched antigen in a donor also tended to narrow the specificity of antibody produced. However the data also indicate differences in immunogenicity among different antigens suggesting that crossreactive group matching would be beneficial in some but not all cases. Finally, we present case studies to illustrate the value of ELISA in predicting humoral rejection episodes and in monitoring the efficacy of rejection therapies.

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.

History of clinical transplantation

The emergence of transplantation has seen the development of increasingly potent immunosuppressive agents, progressively better methods of tissue and organ preservation, refinements in histocompatibility matching, and numerous innovations in surgical techniques. Such efforts in combination ultimately made it possible to successfully engraft all of the organs and bone marrow cells in humans. At a more fundamental level, however, the transplantation enterprise hinged on two seminal turning points. The first was the recognition by Billingham, Brent, and Medawar in 1953 that it was possible to induce chimerism-associated neonatal tolerance deliberately. This discovery escalated over the next 15 years to the first successful bone marrow transplantations in humans in 1968. The second turning point was the demonstration during the early 1960s that canine and human organ allografts could self-induce tolerance with the aid of immunosuppression. By the end of 1962, however, it had been incorrectly concluded that turning points one and two involved different immune mechanisms. The error was not corrected until well into the 1990s. In this historical account, the vast literature that sprang up during the intervening 30 years has been summarized. Although admirably documenting empiric progress in clinical transplantation, its failure to explain organ allograft acceptance predestined organ recipients to lifetime immunosuppression and precluded fundamental changes in the treatment policies. After it was discovered in 1992 that long-surviving organ transplant recipients had persistent microchimerism, it was possible to see the mechanistic commonality of organ and bone marrow transplantation. A clarifying central principle of immunology could then be synthesized with which to guide efforts to induce tolerance systematically to human tissues and perhaps ultimately to xenografts.

A limited number of HLA epitopes are recognized from HLA class I-specific antibodies detected in the serum of sensitized patients

The goal of this study was to evaluate the epitope specificity of HLA class I-specific antibodies detected in the serum of sensitized patients awaiting retransplantation. The study group consisted of 22 sensitized from previous graft patients, who produced stable IgG HLA class I-specific antibodies. A total of 60 serum samples were screened and analyzed by two techniques in parallel: the antihuman globulin augmented CDC (AHG-CDC) technique and an ELISA technique. All recipients and donors were typed for class I HLA antigens by a standard lymphocytotoxicity technique. The epitope identification was based on class I HLA antigens sequencing, where the multiple immunogenic epitopes are differentially shared among various HLA antigens. The unique epitope configuration on one HLA antigen represents the private epitope of the specific HLA antigen while epitopes shared by more than one HLA antigen represent public determinants. In some HLA antigens (HLA-A1), more than one private epitope has been defined, while in others (HLA-B35, -B51), the private epitopes are not yet known. In a total of 36 antibody reactivity patterns, the majority of the definable IgG HLA class I-specific antibodies corresponded to the A-locus (75%), and only 25% had specificities against the B-locus antigens, although the number of incompatibilities concerning both loci were almost identical (29 for the HLA antigens of the A-locus and 26 for those of B-locus). All patients produced HLA class I-specific antibodies with specificities against the private epitopes of the immunogenic mismatched HLA antigen(s). In 6/21 cases (28.6%), HLA class I alloreactivity spreading to nongraft HLA antigens was detected and 9 public (shared) immunogenic alloepitopes were recognized. In conclusion, appling the epitope analysis of HLA class I-specific antibodies produced by sensitized from previous graft patients, we were able to define the immunogenic alloepitopes. We consider that the immunogenic alloepitopes, during transplantation course, are mainly private epitopes of mismatched HLA antigens and, in certain cases, shared epitopes between the donor alloantigens and other HLA antigens. This knowledge may offer the potential of transplanting sensitized patients through improved donor selection.

Posttransplant lymphoproliferative disorders in adult and pediatric renal transplant patients receiving tacrolimus-based immunosuppression

Between March 27, 1989 and December 31, 1997, 1316 kidney transplantations alone were performed under tacrolimus-based immunosuppression at our center. Posttransplant lymphoproliferative disorders (PTLD) developed in 25 (1.9%) cases; the incidence in adults was 1.2% (15/1217), whereas in pediatric patients it was 10.1% (10/99; P<.0001). PTLD was diagnosed 21.0+/-22.5 months after transplantation, 25.0+/-24.7 months in adults and 14.4+/-18.2 months in pediatric patients. Of the 4 adult cases in whom both the donor and recipient Epstein Barr virus (EBV) serologies were known, 2 (50%) were seropositive donor --> seronegative recipient. Of 7 pediatric cases in whom both the donor and recipient EBV serologies were known, 6 (86%) were EBV seropositive donor --> seronegative recipient. Acute rejection was observed before the diagnosis of PTLD in 8 (53%) of 15 adults and 3 (30%) of 10 pediatric patients. Initial treatment of PTLD included a marked decrease or cessation of immunosuppression with concomitant ganciclovir therapy; two adults and two pediatric patients required chemotherapy. With a mean follow-up of 24.9+/-30.1 months after transplantation, the 1- and 5-year actuarial patient and graft survival rates in adults were 93% and 86%, and 80% and 60%, respectively. Two adults died, 3.7 and 46.2 months after transplantation, of complications related to PTLD, and 10 (including the 2 deaths) lost their allograft 3.7-84.7 months after transplantation. In children, the 1- and 5-year actuarial patient and graft survival rates were 100% and 100%, and 100% and 89%, respectively. No child died; one child lost his allograft 41.3 months after transplantation. One child had presumed recurrent PTLD that responded to discontinuation of tacrolimus and reinitiation of antiviral therapy. The mean serum creatinine level in adults was 2.5+/-1.2 mg/dl, and in children, it was 1.3+/-0.6 mg/ dl. Under tacrolimus-based immunosuppression, PTLD is less common after renal transplantation in adults than in children, but PTLD in children is associated with more favorable outcomes than in adults.

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.

Evaluation of HLA matching for CREG antigens in Europe

BACKGROUND

In North America, cross-reactive antigen group (CREG) matching was introduced recently for cadaver kidney allocation. This is expected to result in improved graft outcome and an increased number of transplants for patients with rare HLA antigens.

METHODS

We analyzed the impact of CREG matching using the data of the Collaborative Transplant Study for 59,516 first cadaver transplants performed in Western Europe. The 10 HLA class I CREGs described by Takemoto et al. were used for a comparison with the conventional HLA-A+B mismatching scheme.

RESULTS

Transplant outcome depends primarily on the number of HLA-A+B mismatches and not on the CREG match grades. In a retrospective analysis, CREG mismatches correlated with the number of HLA-A+B mismatches. However, in computer simulations, we found that prospective CREG matching is not associated with beneficial HLA-A+B matching.

CONCLUSION

The positive CREG matching effect observed in retrospective analyses is caused by the underlying effects of conventional HLA-A+B matching. CREG-oriented cadaver kidney allocation in Europe would, therefore, be inferior to the current conventional HLA-A+B+DR allocation.

Differences in anti-CREG antibody formation between transplanted and nontransplanted renal patients

BACKGROUND

The aim of this study was investigation of the HLA-I cross-reactive group (CREG)-specific antibodies (Abs) in sera from patients with a failed renal transplant and from nontransplanted patients.

METHODS

A total of 5292 sera from 570 patients awaiting kidney transplantation were screened for the presence of HLA-I CREG-specific Abs. Patients who had never received a transplant (group A), and those with a previous transplant and Abs either not related (group B) or related to donor specificities (group C) were studied. A further division was made for Abs directed against specificities either included in (intra-CREG) or not included in patients' HLA-CREG (extra-CREG).

RESULTS

Twelve of 24 (50%) Abs produced in response to mismatched donor HLA specificities after a failed graft were intra-CREG Abs, compared to 7 of 39 (18%) Abs that were not transplant-related.

CONCLUSIONS

Renal grafts showed a stronger immunogenicity than other sources of allosensitization. Our data also suggest that CREG matching may not be useful for renal allocation.

Matching for private or public HLA epitopes reduces acute rejection episodes and improves two-year renal allograft function

BACKGROUND

The current role of HLA matching in renal transplantation is controversial. Public HLA epitope matching has been suggested to be as advantageous as private HLA matching, with the added benefit of increasing recipients' access to well-matched grafts.

METHODS

In this single-center study of 105 renal transplant recipients, we examined the association of HLA matching with early (0-3 months) and late (4-6 months) rejection episodes (RE), as well as renal allograft function up to 2 years after transplant.

RESULTS

Poor HLA-DR, but not HLA-A or -B, matching was associated with early RE (0 DR matches, RE=2.7+/-0.19, 1 DR match, RE=2.37+/-0.18, vs. 2 DR matches, RE=1.5+/-0.38; P < 0.01). In contrast, poor HLA-B, but not HLA-A or -DR, matching was associated with late rejections (0 HLA-B matches, RE=1.1+/-0.51 vs. 1-2 HLA-B matches, RE=0.51+/-0.1; P < 0.004). HLA-B matching was also associated with a significantly lower serum creatinine (SCr) level at 24 months (0 HLA-B matches, SCr=178+/-20 micromol/L vs. SCr=132+/-6 micromol/L for 1-2 HLA-B matches; P < 0.025). Matching for 10 supertypic HLA-A and -B cross-reactive groups was associated with reduced late graft rejection (0-2 residue matches, RE=1.15+/-0.18 vs. RE=0.62+/-0.12 for 3 to 7 residue matches; P < 0.013) as well as a significantly lower SCr level at 24 months (0-2 residue matches, SCr=205+/-29 micromol/L vs SCr=131+/-6 micromol/L for 3 to 7 residue matches; P < 0.001) after transplantation.

CONCLUSIONS

HLA-DR matching was associated with a reduced frequency of early rejection episodes, whereas HLA-B or residue/cross-reactive group matching was associated with a reduced frequency of late rejection episodes and improved graft function at 2 years.