HLA class I DNA typing of 215 "HLA-A, -B, -DR zero mismatched" kidney transplants

HLA typing by SSO and SSP methods

Human leukocyte antigen (HLA) typing, utilising the sequence-specific oligonucleotide (SSO) and sequence-specific primer (SSP) technologies, has been in routine use in many tissue typing laboratories worldwide for more than 20 years since the development of the polymerase chain reaction. Both methods are very useful for clinical and research purposes and can provide generic (low resolution) to allelic (high resolution) typing results. This chapter provides an overview of the SSO and SSP methods in relation to HLA typing.

[Discrepancies between human leukocyte antigen registry typing and confirmatory typing results of unrelated hematopoietic stem cell donors]

BACKGROUND

In unrelated hematopoietic stem cell transplantation, the accuracy of HLA registry typing (RT) of donors is important for timely search and coordination of HLA-matched donors. We analyzed discrepancies between HLA RT and confirmatory typing (CT) results of stem cell donors in Korean and foreign registries.

METHODS

We analyzed the HLA typing results of 834 donors for whom CT was performed at Seoul National University Hospital between April 1997 and March 2010. For CT, DNA typing was used in majority of the cases and HLA-A and HLA-B serological typing was used in some early cases. The discrepancies between the typing results were analyzed at the serological/generic level.

RESULTS

The overall discrepancy rate (RT error rate) was 3.2%, and the rate was similar in the Korean and foreign registries. The discrepancy rates in the Korean and foreign registries were more than 10% in the 1997-2001 searches, but decreased to less than 3% in the 2002-2010 searches. Analysis of 19 cases of RT errors in the Korean registry revealed 3 cases of sample switchover errors and 16 cases of typing errors in one of the HLA-A, HLA-B, or HLA-DR loci. The RT error rate in Japan Marrow Donor Program was lower than those in other foreign registries.

CONCLUSIONS

The error rate of HLA RT results of unrelated stem cell donors in the Korean registry was similar to those in the foreign registries, and has decreased in the recent searches following the change in the typing method from serological to DNA typing.

Strategies and technical challenges in allele level Class II typing in 2578 bone marrow transplantation donor-recipient pairs

Human leukocyte antigen typing of 2578 donor-recipient pairs whose transplantation was facilitated by the National Marrow Donor Program allowed for an in-depth analysis of the accuracy of high-volume allele level testing data. The methods employed provided allele level typing at DRB1/3/5, DQA1, DQB1, DPA1, and DPB1 using sequence-specific oligonucleotide probe hybridization (SSOPH), polymerase chain reaction (PCR) restriction fragment length polymorphism analysis, sequence specific PCR, and direct sequence-based typing (SBT). Each typing was independently tested by two laboratories in Phase 1, and in subsequent phases targeted samples were typed in duplicate by SBT to monitor typing quality. Comparison with prior transplant center typing was also evaluated. SSOPH detected discrepancies ranged from 0.6% at DPB1 to 5.1% at DQB1 in Phase 1. The majority of discrepancies, 62%, resulted from human error such as sample handling, result interpretation, or clerical errors. Alleles that are frequently discrepant have been identified in this predominantly white population.

Re-exposure to mismatched HLA class I is a significant risk factor for graft loss: multivariable analysis of 259 kidney retransplants

BACKGROUND

Kidney retransplants carry increased immunologic risk. One possible contributor to this risk may be re-exposure to human leukocyte antigens (HLA) common to a previous donor but foreign to the recipient. Conflicting publications have assessed this risk, so to examine our experience 259 kidney retransplants were analyzed.

METHODS

A retrospective cohort of retransplant patients from 1973 to 2005 with minimum 12 months follow up was examined. Using multivariable modeling, important confounders were controlled for identifying factors significantly affecting graft survival.

RESULTS

Re-exposure to HLA class I (HLA-A or B) antigens, peak panel reactive antibodies and donor source were the most important determinants of allograft survival, despite a negative conventional or anti-human globulin-augmented T cell crossmatch. We failed to demonstrate that recipient re-exposure to HLA class II (HLA-DR) or positive B cell crossmatch were associated with adverse outcomes. Sample size and molecular versus serologic methods may have influenced the former, while inability to determine antibody specificities may have influenced the latter. Controlling for other variables, the adjusted risk of graft loss associated with re-exposure to HLA class I increased by 71% (P=0.006) and occurred early, consistent with recall of memory cytotoxic T lymphocyte or antibody responses.

CONCLUSIONS

Kidney recipients re-exposed to mismatched HLA class I antigens appear to be at heightened risk of early graft loss. Such patients may benefit from pretransplant identification of donor specific antibodies using solid phase methods and heightened vigilance for acute rejection. Future studies may indicate whether more intensive immunosuppression for these patients is warranted.

Assessment of differences in HLA-A, -B, and -DRB1 allele mismatches among African-American and non-African-American recipients of deceased kidney transplants

Among recipients of deceased donor kidney transplants, African-Americans experience a more rapid rate of kidney allograft loss than non-African-Americans. The purpose of this study was to characterize and quantify the HLA-A, -B, and -DRB1 allele mismatches and amino acid substitutions at antigen recognition sites among African-American and non-African-American recipients of deceased donor kidney transplants matched at the antigen level. In recipients with zero HLA antigen mismatches, the degree of one or two HLA allele mismatches for both racial groups combined was 47%, 29%, and 11% at HLA-DRB1, HLA-B, and HLA-A, respectively. There was a greater number of allele mismatches in African-Americans than non-African-Americans at HLA-A (P < .0001), -B (P = .096), and -DRB1 loci (P < .0001). For both racial groups, the HLA allele mismatches were predominantly at A2 for HLA-A; B35 and B44 for HLA-B; but multiple specificities for HLA-DRB1. The observed amino acid mismatches were concentrated at a few functional positions in the antigen binding site of HLA-A and -B and -DRB1 molecules. Future studies are ongoing to assess the impact of these HLA mismatches on kidney allograft loss.

Impact of Donor-Recipient MHC Matching on Experimental Islet Allotransplant Survival in Naïve and Presensitized Lewis Rats

In human islet transplantation (ITX), the impact of donor-recipient major histocompatibility complex (MHC) matching on transplant survival is currently unknown. Utilizing defined MHC mismatches, we have investigated the outcome of ITX in naïve and presensitized congenic Lewis rats. ITX into streptozotocin diabetic Lewis rats was performed under the kidney capsule. Presensitization by skin transplantation was performed on days 1, 28, and 56, followed by ITX on day 84. Survival was greatest in isolated MHC class I mismatches, followed by isolated MHC class II mismatches. The shortest transplant survival was observed following full MHC mismatched ITX (P<0.05 vs. isolated MHC class I or II). Following recipient presensitization, islets in general showed reduced survival compared to naïve recipients. In this congenic rat model, islet transplant survival was significantly influenced by the degree of donor-recipient MHC matching, as well as by recipient presensitization. These data suggest that MHC matching might be useful in human islet transplantation.

Quality control of a national bone marrow donor registry: results of a pilot study and proposal for a standardized approach

Unrelated hematopoietic stem cell transplantation (HSCT) is a recognized therapy for hematological diseases and over 8 million HLA-typed donors are ready to donate. Increased international exchanges and rapid requests through the Bone Marrow Donor Worldwide (BMDW) ask for standardized quality assurance. Since no such standards have been established to date, we tested a pilot program in order to evaluate donor availability and quality of HLA typing of the Swiss Registry. The 18500 donors of the registry have been analyzed by serology for HLA-AB and by molecular typing for HLA-DR. Through three successive annual quality control (QC) exercises, a total of 114 donor requests were sent to 13 blood transfusion centers responsible for donor recruitment asking for a blood sample. Donors were randomly selected according to recruitment periods (1988-1993; 1994-1997; 1998-2000), and to homozygosity for HLA-A and/or -B antigens. An additional 80 frozen blood samples from the repository corresponding to the three periods (n=26) and to the 2001 period (n=54) were also included in the HLA study. HLA-AB typings were done by polymerase chain reaction-sequence specific primers (PCR-SSP) and all discrepancies were retyped. The results showed that 79 samples provided by 69.3% of the requested donors were received within 14 days, and 19 samples (16.7%) were received in >14 days. Altogether, an 86% rate of donor availability was observed, independent of the recruitment period. Among the requested donors, 16 (14%) were not available: for medical reasons (two), for personal reasons (eight), for loss (one), and for an unknown reason (five). The HLA-A/B DNA typing results of 166 homozygous and 12 heterozygous blood samples showed that 437/439 (99.5%) of the assigned A/B antigens were correct. However in 36/178 donors (20.2%) an HLA-A or -B antigen had been missed (34 donors) or misassigned (two donors) by serology, with a decreasing discrepancy rate of 30% (1988-1993) to 18.5% in 2001. Assuming that HLA-A or -B homozygotes are found in 10-15% of the donors and that correct assignments have been observed in nearly 100% of the donors, an overall error rate of 4-5% would be expected for the national registry HLA-AB typing. These data show that standardized quality control for donor availability and HLA typing is feasible, and we propose that this model could be applied to the registries participating in bone marrow donor worldwide.

Molecular basis of HLA polymorphism: implications in clinical transplantation

Polymorphism of the human leukocyte antigens (HLA) represents a major barrier to organ and hematopoietic stem cell (HSC) transplantation. The cloning and sequencing of HLA class I and II genes has not only provided a clear picture of the molecular basis of allelic polymorphism, but also allowed the development of a variety of PCR-based DNA typing techniques. Such methods are now progressively replacing serological typing for assessing donor/recipient HLA compatibility in clinical transplantation. The 100 serological HLA-A,B,Cw,DR,DQ,DP specificities now comprise more than 1300 alleles defined at the DNA sequence level. Most of the serotypes are subdivided into numerous allelic subtypes in worldwide populations (up to 50 alleles in some cases), although a limited number of alleles are detected in a given population group. In organ transplantation application of HLA molecular typing allowed to improve typing quality, leading to a more precise matching assessment with better clinical results. Knowledge of the molecular basis of class I gene polymorphisms also led to the development of new matching algorithms such as HLA-Matchmaker, based on immunogenic amino acid triplets localized on antibody-accessible external domains of class I antigens. The most impressive impact of novel DNA typing methods concerns matching for allogeneic HSC transplantation because subtle serologically silent sequence differences between allelic subtypes are efficiently recognized by alloreactive T-cells with potentially serious consequences for graft outcome. High resolution HLA class I and II matching has contributed to improve patients survival after unrelated HSC transplantation, although the relative importance of individual loci remains to be elucidated. Donor matching criteria should take into account parameters such as the time frame allowed by the patient's disease and the probability to identify a well matched donor based on the patient's HLA phenotype.

HLA Class I typing of volunteers for a bone marrow registry: QC analysis by DNA-based methodology identifies serological typing discrepancies in the assignment of HLA-A and B antigens

Until recently, the majority of newly recruited volunteer donors were typed for HLA-A and -B by serology onto the National Marrow Donor Program Registry. Quality control of this serological typing performed by contracted laboratories was carried out by retesting approximately 1% of each laboratory's test volume utilizing DNA-based techniques (SSOP). The criteria used for selection included samples presumed to be homozygotes, samples with split antigen specificities and samples with antigens considered to be difficult to define. Out of 1983 samples analyzed, 156 HLA-A (3.9%) and 265 HLA-B (6.7%) locus discrepancies were identified. Review of these discrepancies by both the serological and QC laboratory revealed that the majority of discrepancies were due to errors in serological typing. Serological discrepancies were categorized as follows: blank antigens identified (36.8%) and misassignments (63.2%). Misassignments were defined as either the incorrect assignment of antigens within a group ("wrong split"), or a complete misassignment. Antigens reported as blanks most frequently belonged to the A19 and A28 groups and to the B70, 46 and 40 groups. The most frequent misassignments within groups were the A19 and A10 groups, and the B40 and B15 groups. Other HLA-A misassignments included A2 vs A28 or A2 vs A69, while other HLA-B misassignments included B35 and B70. This QC analysis showed that serological typing of class I antigens for the purposes of NMDP registry typing is prone to a significant error rate. Careful evaluation and selection of contracted laboratories by the NMDP suggests methodological limitations rather than poor performance as the main cause of these observations.

HLA-AB typing by polymerase-chain reaction with sequence-specific primers: more accurate, less errors, and increased resolution compared to serological typing

Until recently, serological typing has been the primary technique used for HLA class I analysis. But because of limitations, molecular-typing techniques have replaced or supplemented the microlymphocytotoxicity test. It has been assumed that HLA class I serological typing was more accurate than serological HLA-DR typing; the latter has been shown to have 10-25% errors. But several studies have shown that HLA-AB typing was poorer than expected, and error frequencies between 5-25% were reported. This study systematically investigated the accuracy of HLA class I serological AB typing in healthy, bone-marrow registry donors, necrokidney donors, kidney-transplantation patients (on waiting lists), and haematological disorder patients. Genomic HLA class I typing, which uses polymerase-chain reaction with sequence-specific primers (PCR-SSP), gave discrepant results in 3-24% of the patients, compared to serological typings. The highest error rate (24%) was found among haematological disorder patients. Among the kidney waiting-list patients and necrokidney donors, 11% discrepancies were found. In the consecutively typed bone-marrow donors group, 3% errors were found. But among those with only one detected HLA-A specificity, 12% discrepancies were found, and among donors with only one detected HLA-B specificity, 19% errors were found. Based on these results, we recommend that patients with haematological disorders should be typed using genomic techniques. In investigations of bone-marrow registry donors and kidney patients, in which only one serological specificity is found, additional typing by genomic methods should be done.

Why do we reject grafts?

One of the puzzles in clinical and experimental organ and tissue transplantation has been why it is that, with the exception of transplantation between genetically identical twin pairs, transplantation results in a rapidly progressing immune response to the point of tissue necrosis in a matter of a few days, even though the recipient has not been immunized to the donor. Indeed, the numbers of T lymphocytes predetermined to react against grafts are relatively abundant compared to those that recognize microbial antigens. Cellular, molecular, and genetic studies are now revealing the nature of T-cell recognition, and why it is that we cannot freely exchange tissue grafts.

The influence of conventional and cross-reactive group HLA matching on cardiac transplant outcome: an analysis from the United Network of Organ Sharing Scientific Registry

BACKGROUND

The short tolerable cold ischemia time and the importance of other risk factors have generally superseded the role of HLA matching in the allocation of donor hearts. Recent advances in the accuracy and time required to perform HLA typing and crossmatching, however, have led us to re-examine the United Network of Organ Sharing Transplant Registry for the effects of the HLA incompatibility on outcome in relation to other possible risk factors.

METHODS

These include conventional HLA-A, -B, and cross-reactive group (CREG) mismatching (mm), HLA-DR mm, pretransplantation panel-reactive antibody (PRA), recipient and donor race and donor age, cold ischemia time, and the pretransplantation use of either a left ventricular assist device or an intra-aortic balloon pump.

RESULTS

Three-year survival was clearly inferior in non-white (0.6921) as compared with white (0.7632) recipients, but this difference could not be accounted for by the degree of donor-recipient HLA mm that had occurred by chance. Nevertheless, the degree of mm that did occur seemed to have an impact on survival. The importance of HLA-DR mm was confirmed, and it ranked only behind the use of an assist device and recipient race in the multivariate analysis. HLA-A and B mm exerted an additional effect, but this was only true in white recipients. Of these, HLA-A achieved statistical significance as an independent risk factor. In general, CREG mm was not a significant variable. However, more than twice as many 0-1 or 0-2 CREG, 0 DR mm as compared with 0-1 or 0-2 A,B, 0 DR mm transplants enjoyed approximately equal and very good 1- and 3-year survival. Assuming no change is cold ischemia time, the potential number of 0 CREG, 0 DR mm, ABO-compatible transplants that could be achieved when an Organ Procurement Organization had 50-100 patients on their waiting list was calculated. The surprisingly high frequency of approximately 24-36% suggests that this favorable match could be considered along with other important factors in the local allocation process. When pretransplantation PRA was analyzed as a continuous variable from 0 to 100%, it was a highly significant risk factor, but this effect was more strikingly evident when the PRA was analyzed in 20% increments above zero. Recently, left ventricular assist device usage has become increasingly common, and it has been associated with strikingly increased pretransplantation PRA levels. When they occur together, the data indicates that these patients are at a very high risk for graft failure.

CONCLUSIONS

We believe that newer typing and crossmatching techniques make it possible to add HLA criteria to the allocation protocol of donor cardiac organs and would lead to improved long-term survival.

HLA-B22 diversity including a novel B54 variant (B*5507) in the Korean population

Diversity in the HLA-B22 group was investigated in the Korean population using PCR-SSOP and DNA sequencing analyses. Allelic typing of the B22 gene was performed by gene amplification of the polymorphic exons 2 and 3 of the HLA-B genes from 91 B22 positive individuals followed by a hybridization assay using 63 digoxigenin-labelled probes. Five different SSOP patterns including an unexpected pattern were identified and correlated well with the observed serologic types and with data obtained from DNA sequencing analyses. Novel allele, B*5507, was identified from two unrelated individuals who exhibited standard B54 serologic reactivity but an unexpected SSOP pattern. The DNA sequence of B*5507 is identical to B*5502 in exons 2 and 3 except for a single nucleotide substitution at codon 45 (GAG-->GGG) altering glutamic acid to glycine. Among the already known B molecules, this substitution has been observed only in the B54 molecule encoded by B*5401 allele. This is the evidence that Gly-45 is a crucial site forming the B54 serologic epitope. Interestingly, both alleles (B*5401 and B*5507) exhibit strong association with Cw*0102. Along with previous data, B22 appears to be a very diverse group in the Korean population consisting of at least seven different alleles. B*5401, B*5502, and B*5601 are the most frequent alleles. B*5507, B*5501, B*5504, and B*5604 appear at lower frequencies. Data obtained from this study will be useful in hematopoietic stem cell donor searches as well as in determination of a typing strategy for the HLA-B22 types in this population.

A special report: histocompatibility testing guidelines for hematopoietic stem cell transplantation using volunteer donors. Quality Assurance and Donor Registries Working Groups of the World Marrow Donor Association

The World Marrow Donor Association has formulated guidelines for establishing the extent and quality of histocompatibility testing for unrelated donor registries, umbilical cord blood banks, and transplant centers involved in international exchange of hematopoietic stem cells for allogeneic transplantation. Registry and cord blood bank guidelines suggest that, at a minimum, initial HLA typing should be performed for three HLA loci, HLA-A, -B, and -DR, at low resolution/split antigen level. DNA-based testing methods should be utilized for HLA-DR typing. DNA-based testing for HLA-A and -B should replace serologic testing of new volunteer donors and cord blood units as robust protocols and reagents become available to the laboratories. Transplant center guidelines for typing of patient, family and to confirm the HLA types of potential unrelated donors should include, at the minimum, typing HLA-A, B, and -DR loci using primarily DNA-based testing methods at allele level resolution for DRB1 and low resolution/split antigen level for HLA-A and -B. It is strongly recommended that the typing of a patient and the selected donor be performed using the same set of reagents, methodology, and interpretation criteria with fresh tissue samples to ensure HLA identity. Guidelines for laboratory accreditation, approaches to quality assurance and quality control for HLA testing, and suggestions for the format of the HLA database of donor types are also outlined.

Fluorotyping of HLA-DRB by sequence-specific priming and fluorogenic probing

Similar to our recently described HLA-A and -C fluorotyping strategies, the aim of this study was to develop a sequence-specific primed polymerase chain reaction (PCR-SSP)-based fluorotyping method for HLA-DRB. Applying the fluorogenic 5' nuclease assay, it is possible to increase the sample throughput rate by abolishing all labor-intensive post-amplification steps. Additionally, problems related to contamination are eliminated. The method relies on the 5'-3' exonuclease activity of the Taq-DNA Polymerase which cleaves a target-specific and individually labelled fluorogenic probe during successful PCR. Different labelled probes specific for different targets can be applied in a single PCR, allowing independent detection of the specific HLA and the internal control product. The probe used to detect the HLA-DRB specific amplicons was labeled at its 5' end with FAM as the reporter and further 3' with TAMRA as the quencher. The probe hybridized within the 2nd exon to a conserved region which was covered by all primer mixes. In case of amplification, the cleavage of the fluorogenic probe led to an interruption of the TAMRA-mediated quenching effect and generated a significant increase of the FAM fluorescence. The HLA-DRB fluorotyping information was based on the FAM fluorescence released by 24 individual primer mixes. A TET-TAMRA-labelled probe was used to indicate amplification of the internal control sequence in each PCR reaction. So far, 170 PCR typed clinical samples representing all serologically defined HLA-DRB specificities were analyzed using this fluorotyping method. The results were 100% concordant with those obtained by conventional agarose gel detection.

DNA Typing for HLA-A and HLA-B Identifies Disparities Between Patients and Unrelated Donors Matched by HLA-A and HLA-B Serology and HLA-DRB1

High incidences of graft failure and graft-versus-host disease in the recipients of bone marrow transplantations (BMT) from unrelated donors (URD) may reflect the existence of allelic disparities between the patient and the URD despite apparent HLA identity at HLA-A, HLA-B, and HLA-DRB1 loci. To identify the extent and pattern of allelic disparities at HLA-A and HLA-B loci, 128 patients and 484 potential URD were evaluated by DNA typing. DNA typing for HLA-A, HLA-B, and HLA-DRB1 was performed at Memorial Sloan Kettering Cancer Center. HLA-A and HLA-B serotyping on URD was provided by the registries. By original typing (serology for HLA-A and HLA-B; DNA typing for DRB1) 187, 164, and 133 URD were 6/6, 5/6, and 4/6 matches, respectively. Following DNA typing, however, only 52.9% of the originally 6/6 matched URD remained 6/6, while 38.5%, 7.5%, and 1.1% were found to be 5/6, 4/6, and 3/6 matches. The level of disparity was higher in the originally 5/6 (P&lt; .01) and 4/6 (P &lt; .01) matched URD. A higher level of disparity was seen for HLA-B as compared to HLA-A. In addition, a serotype related variation was also noticed. For example, 24.1% of HLA-A2 and 60.1% of HLA-B35 seromatched URD were genotypically disparate, but no disparities were seen for HLA-A1 and HLA-B8. A higher percentage of HLA-A (67.4%) compared with HLA-B (35.4%) serologic homozygous URD remained genotypically homozygous (P = .01). The level of allelic disparity was lower (P &lt; .01 for 6/6; P = .02 for 5/6) if the patient had one of the 15 most common haplotypes (A1B8DR3, A2B7DR15, A3B7DR15, etc) in comparison to the rest of the group. Outcome studies will answer the question whether these disparities are associated with a higher rate of immunological complications seen with URD-BMT.

New high resolution typing strategy for HLA-A locus alleles based on dye terminator sequencing of haplotypic group-specific PCR-amplicons of exon 2 and exon 3

In this study, a new sequencing-based typing strategy for the HLA-A locus is presented which involves group-specific separate amplification of exon 2 and 3 of HLA-A alleles in a first step. Conserved HLA-A locus-specific primers of intron 1 or 3 were combined in 10 primer-mixes with group-specific primers hybridizing to the 5'- or 3'-end of exon 3 or 2 for pre-typing of the HLA-A alleles in 14 allelic groups. Maximally four overlapping short amplicons are produced under identical polymerase chain reaction (PCR) conditions with individual separate amplification of exon 2 and exon 3 of the haplotypic alleles in most heterozygous combinations. Time- and money-saving one-directional Big Dye Terminator cycle sequencing is shown to provide reliable high resolution typing of the HLA-A alleles, even in a few cases of two amplicons in one primer reaction mixture. In comparison, to other sequencing-based typing (SBT) techniques the applied typing strategy minimizes the risk of unequal amplification or of drop-outs of one of the haplotypic alleles and allows unequivocal definition of the cis/ trans linkage of polymorphic positions of the complete exon 2 and exon 3 in most heterozygous cells. This also includes detection of new alleles differing in the polymorphic template generating primer annealing sites as well as in unusual combinations of known exon 2 and 3 sequences. With 10 primer sets working under identical conditions for pre-grouping and separate amplification of the haplotypic alleles our SBT procedure also could be implemented in clinical settings of large-scale stem cell donor histocompatibility testing for fast molecular HLA-A matching.

DNA Typing for HLA-A and HLA-B Identifies Disparities Between Patients and Unrelated Donors Matched by HLA-A and HLA-B Serology and HLA-DRB1

High incidences of graft failure and graft-versus-host disease in the recipients of bone marrow transplantations (BMT) from unrelated donors (URD) may reflect the existence of allelic disparities between the patient and the URD despite apparent HLA identity at HLA-A, HLA-B, and HLA-DRB1 loci. To identify the extent and pattern of allelic disparities at HLA-A and HLA-B loci, 128 patients and 484 potential URD were evaluated by DNA typing. DNA typing for HLA-A, HLA-B, and HLA-DRB1 was performed at Memorial Sloan Kettering Cancer Center. HLA-A and HLA-B serotyping on URD was provided by the registries. By original typing (serology for HLA-A and HLA-B; DNA typing for DRB1) 187, 164, and 133 URD were 6/6, 5/6, and 4/6 matches, respectively. Following DNA typing, however, only 52.9% of the originally 6/6 matched URD remained 6/6, while 38.5%, 7.5%, and 1.1% were found to be 5/6, 4/6, and 3/6 matches. The level of disparity was higher in the originally 5/6 (P< .01) and 4/6 (P < .01) matched URD. A higher level of disparity was seen for HLA-B as compared to HLA-A. In addition, a serotype related variation was also noticed. For example, 24.1% of HLA-A2 and 60.1% of HLA-B35 seromatched URD were genotypically disparate, but no disparities were seen for HLA-A1 and HLA-B8. A higher percentage of HLA-A (67.4%) compared with HLA-B (35.4%) serologic homozygous URD remained genotypically homozygous (P = .01). The level of allelic disparity was lower (P < .01 for 6/6; P = .02 for 5/6) if the patient had one of the 15 most common haplotypes (A1B8DR3, A2B7DR15, A3B7DR15, etc) in comparison to the rest of the group. Outcome studies will answer the question whether these disparities are associated with a higher rate of immunological complications seen with URD-BMT.

Fluorotyping of HLA-A by sequence-specific priming and fluorogenic probing

The aim of our study was to develop a fluorotyping strategy for the HLA-A locus. In contrast to conventional sequence-specific primed PCR (PCR-SSP), which is based on an agarose gel electrophoresis, fluorotyping eliminates the drawback of low sample throughput, low potential for automation and problems related to contamination. Additionally, fluorotyping is capable of delivering quantitative results depending on the system set-up. The fluorescence-based PCR-SSP assay relies on target-specific and individually labeled fluorogenic probes allowing a simultaneous and differential detection of the specific HLA and the internal control product. The probe used to detect the HLA-A specific amplicons was labeled at its 5' end with 6-carboxyfluorescein (FAM) as the reporter and at its 3' end with 6-carboxy-tetramethylrhodamine (TAMRA) as the quencher. The probe hybridized within the 2nd intron to a conserved region which was found to be identical in all HLA-A alleles and was covered by all primer mixes. During successful PCR the cleavage of the FAM-labeled probe through the 5'-3' exonuclease activity of the Taq DNA-polymerase led to an interruption of the TAMRA-mediated quenching effect and generated a significant increase of the FAM fluorescence. The specific HLA-A typing information was based on the FAM fluorescence released by 24 individual PCR primer mixes. The internal control amplicon was detected with a tetrachloro-6-carboxyfluorescein-TAMRA-labeled fluorogenic probe. Since the HLA-A amplicons had to include the 2nd intron as the target for the fluorogenic probe, the sequence motifs which could be used as priming sites were limited. Therefore, some primer mixes covered more than one specificity resulting in ambiguous amplification patterns in 31 of 231 possible allele or group combinations of HLA-A1-A80. These ambiguities, which all involved the inability to discriminate a particular heterozygous genotype from a homozygous genotype, may be resolved by the quantitative data revealed by fluorotyping. This feature is also helpful to detect new alleles which are not amplified by the current primer mixes.

A strong impact of matching for a limited number of HLA-DR antigens on graft survival and rejection episodes: a single-center study of first cadaveric kidneys to nonsensitized recipients

BACKGROUND

A single-center study of 655 nonsensitized recipients of primary cadaveric kidney grafts is presented.

RESULTS

Graft survival in serologically HLA-DR 1-10 antigen-matched grafts to nonsensitized recipients at 1 year was 90%, compared with 82% (P=0.004) and 73% (P=0.001) in one and two DR antigen-mismatched grafts. The corresponding figures at 5 years were 76%, 62%, and 56%, respectively. Matching for the DR antigens 11-14, or for some DR alleles only detectable by genomic typing, further improved graft survival, but the differences did not reach statistical significance. Matching also for the serologically defined HLA-A and -B antigens did not significantly further improve overall graft survival, but some effects for grafts surviving at least 1 year were observed. Among recipients of grafts mismatched for zero, one, or two HLA-DR antigens, acute rejection episodes were experienced in 48%, 64% (P<0.001), and 82% (P<0.001), respectively, within the first 3 months. HLA-A and -B mismatches showed no significant correlation to acute rejection episodes.

CONCLUSION

Matching for the DR antigens 1-10 significantly secures and prolongs the survival of first cadaveric renal grafts. Our results also show that DR 1-10 antigen-matched combinations can often be obtained even in rather small recipient pools, when actively sought for.

Comparison of serological and DNA PCR-SSP typing results for HLA-A and HLA-B in 421 Black individuals: a Collaborative Transplant Study report

In a recent study, we observed a discrepancy rate of 8.5% between the results of molecular and serological HLA class I typing in Caucasian kidney donors and recipients. In the present study we addressed the question how often black individuals are mistyped using the serological technique. 421 Blacks whose HLA typing results were reported to the Collaborative Transplant Study (CTS) were typed retrospectively for HLA-A and -B using a PCR-SSP method. 78 of the 421 individuals (18.5%) showed a discrepancy for HLA-A and 107 individuals (25.4%) for HLA-B. 36.3% of all individuals tested showed either an HLA-A or an HLA-B discrepancy. 13.1% of the discrepancies at the HLA-A locus were due to antigen misassignments and 4.8% were due to missed antigens. HLA-B discrepancies were caused in 15.7% by antigen misassignments and in 10.5% by missed antigens. These results demonstrate an impressive advantage of the PCR-SSP method for HLA-A and HLA-B locus typing over serological typing in black individuals. The high typing discrepancy rate observed in Blacks provides a strong argument for replacing serological typing by the DNA method. It is likely that this will improve the HLA matching correlation in clinical transplantation in Blacks.