New HLA-A2 variants defined by monoclonal antibodies and cytotoxic T lymphocytes

Oligotyping of HLA-A2, -A3, and -B44 subtypes. Detection of subtype incompatibilities between patients and their serologically matched unrelated bone marrow donors

We have set up a simple PCR-SSO oligotyping procedure that is able to discriminate ten HLA-A2 (2 PCR/11 probes), two HLA-A3 (1 PCR/1 probe), and two HLA-B44 subtypes (1 PCR/2 probes). The frequency of these subtypes has been determined in a large panel of local blood donors and leukemic patients in combination with their unrelated potential donors. A*0201 and A*0301 were the predominant subtypes (> 95%) for A2 and A3, respectively. B*4402 occurred twice as frequently as B*4403. A2 and B44 subtype mismatches were analyzed in a group of 30 patients and their 116 unrelated potential donors who were matched serologically (low-stringency matching: AB without splits, DR1-10). For seven patients (23%) at least one A2- or B44-subtype-mismatched donor was found. For two of these patients (7%), the subtype-mismatched donor would have been considered as compatible on the basis of high stringency matching (AB splits, DRB1 subtypes, DRB3/B5). For one patient of Mediterranean origin, all five donors recruited from a north European registry (matched with high stringency) appeared to be subtype incompatible (A*0201/A*0205). The rather low percentage of A2- and B4-subtype mismatches in DRB1/B3/B5 matched combinations confirms the significance of linkage disequilibria of HLA antigens. Because unrelated donor selection is done through international registries, however, class I subtyping might be necessary when individuals originate from different geographic areas.

DNA typing for HLA class I alleles: I. Subsets of HLA-A2 and of -A28

A group of HLA-A locus alleles known to be comprised of approximately 14 closely related variants are collectively called HLA-A2 and -A28. Variations among these alleles are given by differences in only a few codons, and in the case of A*6901, elements of A*6801 (exons 1 and 2) and of A*0201 are combined. The purpose of these experiments was to determine the possibility of designing oligonucleotide probes to identify and develop a typing method for all or most of the A2 and A28 variants. Because the regions of interest are also shared by alleles of other groups, allele-specific or group-specific primers were needed to amplify only the alleles under study. HLA-A2-specific amplification of exon 2 and selective amplification of portions of exon 3 of the A2-A28 group were accomplished with sequence-specific primers and after appropriate adjustments of the PCR conditions. Hybridization patterns using products of four PCR reactions with our set of probes distinguished 11 alleles. Two other alleles might be recognized with the reagents used, but were not found in the panels in this study. A*0201 and A*0209, which are different in exon 4, were not resolved because exon 4 was not tested. A new variant of Aw68, defined by a hybridization pattern obtained with our probes, was different from A*6801 only in that it was negative with probe A6. It was called A*68.3. Population studies were performed in North American whites, blacks, and Indians and in a sample of subjects from North China. HLA-A*0201 was the most frequent allele. A*0202 was found only in blacks, and A*0203 and A*0207 were found only in Chinese. Among the A28-positive subjects, Caucasoids were predominantly A*6801 or A*68.3; A*6802 was the most frequent subtype in American blacks; among American Indians the predominant type was A*68.3. The two A28-positive Chinese subjects studied had A*6901. The results obtained demonstrate that DNA typing is an efficient method for determining these alleles. The methodology should be applicable to other class I groups and should be useful for more extensive population studies, for matching for bone marrow transplantation, and for investigation of certain diseases associated with HLA class I alleles.

Techniques used to define human MHC antigens: monoclonals, class I and class II biochemistry

A variety of straightforward biochemical techniques have been applied to the analysis of HLA molecules. These techniques centre largely on two components: monoclonal antibodies (mAbs) and gel analysis systems. Although only the basic applications are discussed here, the techniques have broad applications. Monoclonal-gel systems may be used for the characterisation of polymorphisms in HLA class I alpha chains or class II alpha and beta chains. This requires the use of mAbs which are locus-specific and monomorphic. Alternatively, B lymphoblastoid cell lines (B-LCL) whose HLA antigen mobilities are known in advance may be used for screening uncharacterised monoclonals for locus specificity.

HLA typing with monoclonal antibodies: evaluation of 356 HLA monoclonal antibodies including 181 studied during the 10th International Histocompatibility Workshop

During the 10th International Histocompatibility Workshop (10th WS), 181 HLA MoAbs were studied using lymphocytotoxicity micro-technique (LCT) and/or enzyme immuno-assay (EIA), and their capacity to serve as typing reagents was evaluated. 129 MoAbs were tested by both techniques. Results obtained with 92 class I and 86 class II polymorphic MoAbs (10th WS) were compared to published data concerning 180 class I and 176 class II polymorphic MoAbs, listed in an HLA-MoAbs Register maintained in our laboratory. The following conclusions can be proposed: 1/HLA-A, B typing by LCT with MoAbs is possible for about 14 specificities. Some specificities are clearly recognized (HLA-A3, B8, B13, Bw4, Bw6), others are recognized as cross-reacting groups (B7+27+w22+40), others are not currently recognized by any MoAb with restricted specificity (B5, B15). Several MoAbs confirmed the existence of shared epitopes between products from a single locus (A2-A28, A25-A32), or from A and B loci (A2-B17, Bw4-A9-A32). A single HLA-Cw MoAb has been described. 2/HLA class II typing by LCT with MoAbs is more difficult than class I typing. DR2, DR3, DR4, DR5 and DR7 as well as DRw52 and DRw53 are well defined; other DR specificities are poorly or not at all defined. Particular associations (DR1+DR4, DR3+DRw6, all DR except DR7) are recognized by several MoAbs. All DQw specificities are well recognized, including new specificities defined only by MoAbs: WA (DQw4), TA10 (DQw7), 2B3 (DQw6+w8+w9). Only two HLA-DP MoAbs have been described. 3/Satisfactory results, similar to those of LCT, were obtained with EIA using lymphoid cell lines as targets. 4/Human MoAbs (12 in the Register) are satisfactory typing reagents. They could represent in the future a significant contribution to HLA typing with MoAbs.

HLA-B27 and HLA-A2 subtypes: structure, evolution and function

Beyond the resolution of tissue typing serology, HLA class I antigens display a certain level of structural microheterogeneity, that allows their subdivision into subtypes. The structure of these subtypes shows that multiple mechanisms operate in the generation of HLA polymorphism and suggests possible evolutionary pathways for subtype diversification. In addition, subtype polymorphism critically affects cellular allorecognition and antigen presentation to self-restricted T cells. These properties are used to define the structure and diversity of T-cell epitopes. In this review, José López de Castro discusses the nature and evolution of this polymorphism and its modulation of antigen recognition by cytolytic T lymphocytes.

Biochemical HLA typing: a population study in 112 Caucasians

In order to define frequencies and associations of biochemically defined HLA-A and -B specificities and their variants and subtypes in a Caucasian population, biochemical HLA typing was performed in a panel of 112 Austrians. Already known rare variants of HLA-A2, A3, A30, Aw33 and B39 and the more frequent subtypes of HLA-B27, B35, B44 and, in addition, a so far unknown variant of HLA-B18 were present in the panel. Family segregation analyses of the biochemically defined HLA class I variants revealed that they could be found only in certain rare haplotypes, most of them in high linkage disequilibrium. The basic variant of HLA-A30, for example, obviously occurred only in the HLA-A30, B49, Cw7 haplotype, similar to the Aw33 acidic variant, which was exclusively found in the Aw33, Bw58, Cw3 haplotype. None of the biochemical variants was found in frequent common haplotypes.

Molecular analysis of HLA-A2.4 functional variant KLO: close structural and evolutionary relatedness to the HLA-A2.2 subtype

The structure of an HLA-A2.4 functional variant (A2.4c) expressed on donor KLO has been examined by comparative peptide mapping with other HLA-A2 antigens of known structure and radiochemical sequencing. All the peptide differences between A2.4c and A2.1 could be accounted for by five amino acid changes at positions 9, 43, 66, 95, and 156. The nature of residues 9, 43, and 95 in A2.4c was determined by sequencing to be identical to those in A2.2Y. The nature of residue 156 in A2.4c was also assigned as identical to that in A2.2Y on the basis of the identity of the corresponding peptide in its chromatographic comparison with A2.2Y. Position 66 was unique to A2.4c. It was determined to be an Asn residue instead of the Lys present in all other HLA-A2 antigens of known structure. This was the only detected amino acid difference between A2.4c and A2.2Y. The results indicate that, from a structural point of view, A2.4c is most closely related to the A2.2 subtype antigens and not to other A2.4 antigens. The data are compatible with the assumption that A2.4c was derived from A2.2Y by a single point mutation event.

Functional analysis of the HLA-A2/Aw68 recombinant molecule HLA-Aw69: Epstein-Barr virus specific cytotoxic T cells restricted through Aw69 can utilise restricting determinants on Aw68 but not on A2

Epstein-Barr virus-specific cytotoxic T cell lines, expanded in interleukin 2-conditioned medium, have been generated in vitro from virus-immune individuals bearing either the common HLA-A2 antigen (A2.1), a variant A2 antigen (A2.2) or a novel antigen Aw69 which is a recombinant molecule having identity with HLA-Aw68 in the alpha 1 domain and with HLA-A2 in the alpha 2 and alpha 3 domains. Virus-specific cytotoxic T cells restricted through A2.1 or A2.2 only recognised targets bearing the identical sub-type of A2 molecules and showed no cross-recognition of other A2 sub-types, of Aw68 or of Aw69. In contrast, virus-specific cytotoxic T cells restricted through the Aw69 antigen showed a significant cross-recognition of restricting determinants on Aw68 but not on A2 molecules. The results suggest that the alpha 1 extracellular domain of the HLA-Aw69 molecule plays a predominant role in the formation of T cell restricting determinants.