Unravelling an HLA-DR association in childhood acute lymphoblastic leukemia. (1/27)

Genetic and environmental factors play an interactive role in the development of childhood acute lymphoblastic leukemia (ALL). Since the demonstration of a major histocompatibility complex (MHC) influence on mouse leukemia in 1964, an HLA association has been considered as a possible genetic risk factor. Despite extensive efforts, however, no strong evidence comparable to the H-2(k) influence on mouse leukemia has been shown. The number of negative serological studies resulted in a loss of interest and consequently, no molecular HLA-DR association study has been published to date. We reconsidered the HLA-DR association in childhood ALL in 114 patients from a single center and 325 local newborn controls by polymerase chain reaction (PCR) analysis of the HLA-DRB1/3/4/5 loci. With conventional analysis, there was a moderate allelic association with the most common allele in the HLA-DR53 group, HLA-DRB1*04, in the whole group that was stronger in males (P =.0005, odds ratio = 2.9). When the other expressed HLA-DRB loci were examined, homozygosity for HLA-DRB4*01, encoding the HLA-DR53 specificity, was increased in patients (21.1% v 8.3%; odds ratio = 2.9, P =.0005). Consideration of gender showed that all of these associations were reflections of a male-specific increase in homozygosity for HLA-DRB4*01 (32.8% v 4. 0%; odds ratio = 11.7, 95% confidence interval [CI] = 4.9 to 28.0; P = 3 x 10(-8)). This highly significant result provided the long-suspected evidence for the HLA-DR influence on the development of childhood ALL while confirming the recessive nature of the MHC influence on human leukemogenesis as in experimental models. The cross-reactivity between HLA-DR53 and H-2Ek, extensive mimicry of the immunodominant epitope of HLA-DR53 by several carcinogenic viruses, and the extra amount of DNA in the vicinity of the HLA-DRB4 gene argue for the case that HLA-DRB4*01 may be one of the genetic risk factors for childhood ALL.  (+info)

Identification of NY-ESO-1 epitopes presented by human histocompatibility antigen (HLA)-DRB4*0101-0103 and recognized by CD4(+) T lymphocytes of patients with NY-ESO-1-expressing melanoma. (2/27)

NY-ESO-1 is a member of the cancer-testis family of tumor antigens that elicits strong humoral and cellular immune responses in patients with NY-ESO-1-expressing cancers. Since CD4(+) T lymphocytes play a critical role in generating antigen-specific cytotoxic T lymphocyte and antibody responses, we searched for NY-ESO-1 epitopes presented by histocompatibility leukocyte antigen (HLA) class II molecules. Autologous monocyte-derived dendritic cells of cancer patients were incubated with recombinant NY-ESO-1 protein and used in enzyme-linked immunospot (ELISPOT) assays to detect NY-ESO-1-specific CD4(+) T lymphocyte responses. To identify possible epitopes presented by distinct HLA class II alleles, overlapping 18-mer peptides derived from NY-ESO-1 were synthetized and tested for recognition by CD4(+) T lymphocytes in autologous settings. We identified three NY-ESO-1-derived peptides presented by DRB4*0101-0103 and recognized by CD4(+) T lymphocytes of two melanoma patients sharing these HLA class II alleles. Specificity of recognition was confirmed by proliferation assays. The characterization of HLA class II-restricted epitopes will be useful for the assessment of spontaneous and vaccine-induced immune responses of cancer patients against defined tumor antigens. Further, the therapeutic efficacy of active immunization using antigenic HLA class I-restricted peptides may be improved by adding HLA class II-presented epitopes.  (+info)

T-cell reactivity against streptococcal antigens in the periphery mirrors reactivity of heart-infiltrating T lymphocytes in rheumatic heart disease patients. (3/27)

T-cell molecular mimicry between streptococcal and heart proteins has been proposed as the triggering factor leading to autoimmunity in rheumatic heart disease (RHD). We searched for immunodominant T-cell M5 epitopes among RHD patients with defined clinical outcomes and compared the T-cell reactivities of peripheral blood and intralesional T cells from patients with severe RHD. The role of HLA class II molecules in the presentation of M5 peptides was also evaluated. We studied the T-cell reactivity against M5 peptides and heart proteins on peripheral blood mononuclear cells (PBMC) from 74 RHD patients grouped according to the severity of disease, along with intralesional and peripheral T-cell clones from RHD patients. Peptides encompassing residues 1 to 25, 81 to 103, 125 to 139, and 163 to 177 were more frequently recognized by PBMC from RHD patients than by those from controls. The M5 peptide encompassing residues 81 to 96 [M5(81-96) peptide] was most frequently recognized by PBMC from HLA-DR7+ DR53+ patients with severe RHD, and 46.9% (15 of 32) and 43% (3 of 7) of heart-infiltrating and PBMC-derived peptide-reactive T-cell clones, respectively, recognized the M5(81-103) region. Heart proteins were recognized more frequently by PBMC from patients with severe RHD than by those from patients with mild RHD. The similar pattern of T-cell reactivity found with both peripheral blood and heart-infiltrating T cells is consistent with the migration of M-protein-sensitized T cells to the heart tissue. Conversely, the presence of heart-reactive T cells in the PBMC of patients with severe RHD also suggests a spillover of sensitized T cells from the heart lesion.  (+info)

Identification of helper T-cell epitopes that encompass or lie proximal to cytotoxic T-cell epitopes in the gp100 melanoma tumor antigen. (4/27)

The melanocyte-associated antigen gp100 constitutes one of the most attractive targets for T-cell-based immunotherapy against malignant melanoma. Although several MHC class I-restricted epitopes have been identified for CTLs, thus far, only one MHC class II T helper epitope (restricted by HLA-DR4) has been described in the literature. Using an algorithm to identify promiscuous helper T-cell epitopes, here we describe three additional MHC class II-restricted epitopes from gp100. Whereas one T helper epitope, gp100(175-189), was restricted by the HLA-DR53 and DQw6 alleles, the T-cell responses to two other epitopes, gp100(74-89) and gp100(576-590), were restricted by HLA-DR7. Most interestingly, the newly identified helper T lymphocyte epitopes encompass or lie proximal to previously described CTL epitopes for this tumor-associated antigen. Together with the previously described HLA-DR4-restricted epitope, these T helper epitopes offer coverage for the majority of the human population. Moreover, the use of peptide vaccines containing both CTLs and T helper epitopes could offer therapeutic advantages over current approaches that focus solely on eliciting antitumor CTL responses.  (+info)

Increased heterozygosity for MHC class II lineages in newborn males. (5/27)

In plants, fungi and marine invertebrates, there are genetic compatibility systems to ensure diversity in the offspring. The importance of genetic compatibility in gametic union and selective abortion in vertebrate animals has also been appreciated recently. There have been suggestions that the major histocompatibility complex (HLA in humans) may be a compatibility system in vertebrates. HLA class II haplotypes often contain a second expressed DRB locus which can be either DRB3, DRB4 or DRB5. These encode the supertypical specificities and mark the ancestral lineages. The members of each lineage have related DNA sequences at the main class II locus HLA-DRB1. We analysed 415 newborns at all expressed DRB loci by PCR analysis to seek evidence for sex-specific prenatal selection events. While there was no significant change in heterozygosity rates between males and females at DRB1, the proportion of males carrying two DRB1 specificities from different ancestral lineages was significantly increased (53.7% in males vs 39.3% in females, P = 0.003). The genotypes consisting of phylogenetically most distinct ones, namely the DRB3 and DRB4 haplotypes, showed the most striking difference between sexes (P = 0.007). These results suggested a more favourable outcome for male concepti heterozygous for supertypical haplotypes. Heterozygosity for most divergent haplotypical families ensures the highest degree of functional heterozygosity at the main HLA class II locus DRB1 while increasing the likelihood of heterozygosity also at other MHC loci. Our observations agree with the previously reported heterozygote excess in male newborn rats and mice. Correlations between MHC class II heterozygosity and advertised male quality in deer and pheasant as well as increased reproductive success in MHC class II heterozygous male macaques are examples of postnatal benefits of heterozygosity in males that may be behind the development of prenatal selection mechanisms. The MHC-mediated prenatal selection of males may also be one of the selective events suggested by the very high primary (male-to-female) sex ratio at fertilization reaching close to unity at birth in humans. These results provide an appealing working hypothesis for further studies in humans and other vertebrates.  (+info)

CD4+ T-cell clones specific for wild-type factor VIII: a molecular mechanism responsible for a higher incidence of inhibitor formation in mild/moderate hemophilia A. (6/27)

Mild/moderate hemophilia A patients carrying certain mutations in the C1 domain of factor VIII (FVIII) have a higher risk of inhibitor occurrence. To analyze the mechanisms responsible for inhibitor development in such patients, we characterized FVIII-specific CD4(+) T-cell clones derived from a mild hemophilia A patient carrying an Arg2150His substitution in the C1 domain and who presented with a high titer inhibitor toward normal but not self-FVIII. All T-cell clones recognized synthetic peptides encompassing Arg2150. The peptides were presented to the T-cell clones by DRB1*0401/DRB4*01 or DRB1*1501/DRB5*01. Interestingly, the latter haplotype was previously reported as being associated with an increased incidence of inhibitor formation. Peptide I2144-T2161 also bound to other DR molecules such as DRB1*0101 and DRB1*0701, indicating that the peptide binds to major histocompatibility complex (MHC) class II molecules expressed in more than 60% of the population. None of the T-cell clones recognized recombinant FVIII carrying the substitution Arg2150His, even when FVIII was presented by an FVIII-specific B-cell line. The mutation likely alters T-cell recognition of the mutated peptide associated to MHC molecules, because the mutated peptide bound to immunopurified DR molecules nearly as effectively as the native peptide. These observations demonstrate that T cells of this patient with mutation Arg2150His distinguish between self- and wild-type FVIII and provide a plausible mechanism for the frequent occurrence of an inhibitor in patients carrying this substitution. A similar phenomenon may occur with other mutations associated to an increased incidence of inhibitor formation.  (+info)

Systematic analysis of the combinatorial nature of epitopes recognized by TCR leads to identification of mimicry epitopes for glutamic acid decarboxylase 65-specific TCRs. (7/27)

Accumulating evidence indicates that recognition by TCRs is far more degenerate than formerly presumed. Cross-recognition of microbial Ags by autoreactive T cells is implicated in the development of autoimmunity, and elucidating the recognition nature of TCRs has great significance for revelation of the disease process. A major drawback of currently used means, including positional scanning synthetic combinatorial peptide libraries, to analyze diversity of epitopes recognized by certain TCRs is that the systematic detection of cross-recognized epitopes considering the combinatorial effect of amino acids within the epitope is difficult. We devised a novel method to resolve this issue and used it to analyze cross-recognition profiles of two glutamic acid decarboxylase 65-autoreactive CD4(+) T cell clones, established from type I diabetes patients. We generated a DNA-based randomized epitope library based on the original glutamic acid decarboxylase epitope using class II-associated invariant chain peptide-substituted invariant chains. The epitope library was composed of seven sublibraries, in which three successive residues within the epitope were randomized simultaneously. Analysis of agonistic epitopes indicates that recognition by both TCRs was significantly affected by combinations of amino acids in the antigenic peptide, although the degree of combinatorial effect differed between the two TCRs. Protein database searching based on the TCR recognition profile proved successful in identifying several microbial and self-protein-derived mimicry epitopes. Some of the identified mimicry epitopes were actually produced from recombinant microbial proteins by APCs to stimulate T cell clones. Our data demonstrate the importance of the combinatorial nature of amino acid residues of epitopes in molecular mimicry.  (+info)

Identification of HLA-DR1 beta chain residues critical for binding staphylococcal enterotoxins A and E. (8/27)

Superantigens are thought to make external contacts with major histocompatibility complex (MHC) class II molecules and with the V beta portion of a T cell antigen receptor (TCR), thereby stimulating entire families of T cells. The precise mapping of superantigen binding sites on class II molecules may provide valuable information on how TCR and MHC molecules interact. Two bacterial superantigens, staphylococcal enterotoxins A and E (SEA/SEE) bind well to most HLA-DR alleles, but poorly to HLA-DRw53. The sequences responsible for this binding were localized to the putative alpha helix of the DR beta chain by measuring toxin binding to a panel of chimeric class II molecules expressed on transfected cells. Binding of SEA/SEE to the DRw14 (Dw9) molecule suggested that the conserved histidine 81 in the beta chain of most DR molecules was important, whereas the tyrosine 81 in the DRw53 beta chain was detrimental for high-affinity binding. To prove this, reciprocal point mutations were introduced in the DR1 and DRw53 beta chains. Mutation of histidine 81 in the DR1 beta chain to tyrosine reduced SEA/SEE binding, but did not prevent recognition of two DR1-restricted peptides by six of eight antigen-specific T cell lines. Conversely, introduction to histidine at position 81 in the DRw53 beta chain restored normal levels of SEA/SEE binding. These data suggest that a binding site of SEA and SEE lies on the outer face of the beta chain alpha helix, pointing away from the antigen-binding groove.  (+info)