Recognition of major histoincompatibilities after transplantation with marrow from HLA closely matched donors

Multiplex single nucleotide extension: a robust and high throughput method for HLA-A locus typing

This report describes a typing method that can identify all known human leukocyte antigen A (HLA-A) alleles by determining nucleotides present at polymorphic sites using single nucleotide extension. Allele specific primers are bound to capture oligonucleotides which allows for a multiplex approach during single nucleotide extension (SNE) reactions. Eleven group-specific polymerase chain reaction amplifications were performed to obtain the templates to be analyzed with sets of primers designed to investigate the polymorphisms. Extension of biotin-labeled ddNTPs onto allele-specific primers was catalyzed by a DNA polymerase and each primer was hybridized to a specific capture oligonucleotide covalently bound to a bead. After staining with streptavidin-PE, incorporated fluorescence was determined with a flow cytometer. Fluorescence intensities were interpreted by computer and the nucleotide sequence was translated into HLA-A genotypes. Group-specific amplification reactions and primer sets for SNE were validated with 42 reference samples of known HLA-A alleles. In addition, 296 samples from three populations (N. A. Caucasian, African-American, Terena S. A. Indian) were analyzed and results compared to previous typing by SSOP. Reproducibility between repeated typings was 100% and ambiguities were quite rare. The method has been found to be accurate, relatively simple to perform and fast. It is our method of choice for high resolution clinical HLA-A typing.

Selection of unrelated bone marrow donors by serology, molecular typing and cellular assays

As compared to hematopoietic stem cell transplantation (HSCT) with HLA genotypically identical donors, phenotypically matched unrelated HSCT is associated with lower survival. Serologically undisclosed HLA disparities account for the increased rate of post-transplant complications. With more than 1300 alleles currently identified, high-resolution molecular typing techniques have to be applied to distinguish the extensive degree of allelic polymorphism of the HLA system. Whereas a HLA-ABDR-serologically identical donor can be identified in the International Registry for >90% of the patients, only half of them can benefit of a highly compatible donor if donor selection is based on allele level matching for HLA-A/B/Cw/DRB1/B3/B5/DQB1 loci. During the last 10 years, we identified only approximately 20% of all known HLA alleles in the searches for our mainly Caucasoid patients. Rare alleles (i.e. alleles that represent <1% of a given serotype) do not have a major impact in patient/donor matching. Most of the incompatibilities are clustered in a limited number of serotypes that can be targeted first during the searches. However, due to linkage disequilibrium (e.g. B-Cw or DRB1-DQB1), incompatibilities at a given locus are often associated with disparities at adjacent loci. In vitro cellular assays such as the cytotoxic T-lymphocyte precursor frequency (CTLpf) analysis may contribute in discriminating functionally relevant HLA class I disparities, as well as minor antigen mismatches in case of sensitized donors. When a rare variant or an uncommon association in the patient's HLA haplotype has been found, the tissue typing laboratory may recommend considering a mismatched donor early in the search procedure instead of continuing a search with a low probability of success.

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.

Haploidentical transplantation. Importance of histocompatibility testing and chimerism studies in allogeneic bone marrow/stem cell transplantation

The transplantation of hematopoietic stem cells is sometimes the only treatment option for certain types of malignancies and hematological disorders. The best way to ensure a positive outcome from this type of procedure is to secure an identical human lymphocyte antigen-matched donor or use an autologous graft. This article reviews the indications for transplantation, the recipient and donor selection process, and posttransplant follow-up. The advantages of using haploidentical donors and the typing process also will be discussed.

A PCR-SSP method to specifically select HLA-A*0201 individuals for immunotherapeutic studies

HLA-A*0201 is an important restriction element for peptide presentation to T cells in disease and cancer. Mutation studies and analyses using cytotoxic T lymphocytes have shown the functional relevance of subtype-specific differences in HLA-A2 molecules for peptide binding and T-cell receptor recognition. Therefore, many immunotherapeutic studies need to accurately select HLA-A*0201-positive individuals. We designed an easy, robust approach based on the polymerase chain reaction using sequence-specific primers (PCR-SSP) to specifically distinguish A*0201-positive individuals from other HLA-A2 subtypes described to date. The first step includes reactions that give information whether the sample donor is HLA-A2 and, if so, whether the individual is homozygous or heterozygous for HLA-A2. Further, it is determined whether the sample has an HLA-A*0209 or an HLA-A*0201 sequence at the corresponding position in exon 4. Samples that may contain an HLA-A*0201 allele according to the results of this first step are subtyped in a second step nested PCR. Here the strategy is focussed on the discrimination of HLA-A*0201 from the other subtypes by considering divergent nucleotide positions in two ways. One SSP combination amplifies the HLA-A*0201 sequence while a corresponding SSP combination specifically amplifies the subtype or group of subtypes differing from HLA-A*0201 at this position. Thus, at relevant polymorphic nucleotide positions the HLA-A*0201 sequence is both directly and indirectly confirmed. This strategy strongly enhances the reliability of the subtyping and allows better verification of HLA-A*0201-positive patient selection for clinical studies.

Molecular Typing Shows a High Level of HLA Class I Incompatibility in Serologically Well Matched Donor/Patient Pairs: Implications for Unrelated Bone Marrow Donor Selection

In comparison with HLA-matched sibling bone marrow transplants, unrelated donor transplants are associated with increased graft-versus-host disease and graft failure. This is likely in part due to HLA incompatibilities not identified by current matching strategies. High resolution DNA-based typing methods for HLA class II loci have improved donor selection and treatment outcome in unrelated donor bone marrow transplantation. By using DNA-based typing methods for HLA-A and -B on a cohort of 100 potential bone marrow donor/patient pairs, we find that serological typing for HLA class I is limited in its ability to identify incompatibilities in unrelated pairs. Furthermore, the incompatibilities identified are associated with the presence at high frequency of alloreactive cytotoxic T-lymphocyte precursors. DNA typing also indicates that HLA-C mismatches are common in HLA-A and -B serologically matched pairs. Such mismatches appear to be significantly less immunogenic with respect to cytotoxic T-lymphocyte recognition, but are expected to influence natural killer cell activity. Thus, improved resolution of HLA class I shows many previously undisclosed mismatches that appear to be immunologically functional. Use of high resolution typing methods in routine matching is expected to improve unrelated donor selection and transplant outcome.

Molecular Typing Shows a High Level of HLA Class I Incompatibility in Serologically Well Matched Donor/Patient Pairs: Implications for Unrelated Bone Marrow Donor Selection

In comparison with HLA-matched sibling bone marrow transplants, unrelated donor transplants are associated with increased graft-versus-host disease and graft failure. This is likely in part due to HLA incompatibilities not identified by current matching strategies. High resolution DNA-based typing methods for HLA class II loci have improved donor selection and treatment outcome in unrelated donor bone marrow transplantation. By using DNA-based typing methods for HLA-A and -B on a cohort of 100 potential bone marrow donor/patient pairs, we find that serological typing for HLA class I is limited in its ability to identify incompatibilities in unrelated pairs. Furthermore, the incompatibilities identified are associated with the presence at high frequency of alloreactive cytotoxic T-lymphocyte precursors. DNA typing also indicates that HLA-C mismatches are common in HLA-A and -B serologically matched pairs. Such mismatches appear to be significantly less immunogenic with respect to cytotoxic T-lymphocyte recognition, but are expected to influence natural killer cell activity. Thus, improved resolution of HLA class I shows many previously undisclosed mismatches that appear to be immunologically functional. Use of high resolution typing methods in routine matching is expected to improve unrelated donor selection and transplant outcome.

HA-1 and the SMCY-derived peptide FIDSYICQV (H-Y) are immunodominant minor histocompatibility antigens after bone marrow transplantation

BACKGROUND

Allogeneic bone marrow donors can be incompatible at different levels. Even HLA-identical pairs will be still incompatible for numerous minor histocompatibility antigens (mHag). Nevertheless, some incompatibilities are found to be associated with an increased risk of graft-versus-host disease (GVHD), which could be related to the way the immune system recognizes these antigens.

METHODS

We determined the specificity of cytotoxic T-cell clones isolated during acute GVHD or during bone marrow graft rejection in patients (n=14) transplanted with marrow from donors who were histoincompatible for different minor and/or major histocompatibility antigens.

RESULTS

We found a clear hierarchy among the different types of histoincompatibilities. In three combinations mismatched for a class I allele, all 27 clones isolated during GVHD were specific for the incompatible HLA molecule. In the 11 class I-identical combinations, 14 different mHags were recognized. The mHag HA-1, known to have a significant impact on the development of GVHD, was recognized in the two HA-1-incompatible combinations. In one of these combinations, which was sex mismatched, all 56 clones analyzed were directed against HA-1, demonstrating the dominance of this mHag. In the four HA-1-compatible, sex-mismatched combinations, the anti-H-Y response was directed against one immunodominant epitope rather than against multiple Y-chromosome-encoded epitopes. All male specific cytotoxic T lymphocytes (n=15) recognized the same high-performance liquid chromatography-purified peptide fraction presented by T2 cells. Moreover, all cytotoxic T lymphocytes tested (n=6) were specific for the SMCY-derived peptide FIDSYICQV, originally described as being the H-Y epitope recognized in the context of HLA-A*0201.

CONCLUSIONS

Some histocompatibility antigens are recognized in an immunodominant fashion and will therefore be recognized in the majority of mismatched combinations. Only for such antigens, correlations between mismatches and the occurrence of GVHD or graft rejections will be found.

Sequence-Based Typing Provides a New Look at HLA-C Diversity

Although extensive HLA-A and HLA-B polymorphism is evident, the true diversity of HLA-C has remained hidden due to poor resolution of HLA-C Ags. To better understand the polymorphic nature of HLA-C molecules, 1823 samples from the National Marrow Donor Program research repository in North America have been typed by DNA sequencing and interpreted in terms of HLA-C diversification. Results show that HLA-Cw*0701 was the most common allele with a frequency of 16%, whereas 28% of the alleles typed as Cw12-18 (serologic blanks). The frequency of homozygotes was 9.8% as compared with previous studies of 18% for sequence-specific primers and 50% for serology. Most startling was the frequency at which new alleles were detected; 19 new HLA-C alleles were detected, representing a rate of ∼1 in 100 samples typed. These new HLA-C alleles result from 29 nucleotide substitutions of which 4 are silent, such that coding substitutions concentrated about the Ag-binding groove predominate. Polymorphism at the HLA-C locus therefore resembles that at the HLA-A and HLA-B loci more than previously believed, indicating that antigenic stress is driving HLA-C evolution. However, sequence conservation in the α-helix of the first domain and a clustering of unique amino acids around the B pocket indicate that HLA-C alleles respond to antigenic pressures differently than HLA-A and HLA-B. Finally, because the samples characterized were predominantly from Caucasians, we hypothesize that HLA-C polymorphism will equal or exceed that of the HLA-A and -B loci as DNA sequence-based typing is extended to include more non-Caucasian individuals.