Common HLA Alleles Research Articles

Common HLA Alleles Associated with Health, but Not with Facial Attractiveness

Three adaptive hypotheses have been proposed to explain the link between the human leucocyte antigen (HLA) genes, health measures and facial attractiveness: inbreeding avoidance, heterozygote advantage and frequency-dependent selection. This paper reports findings that support a new hypothesis relating HLA to health. We suggest a new method to quantify the level of heterozygosity. HLA heterozygosity did not significantly predict health measures in women, but allele frequency did. Women with more common HLA alleles reported fewer cold and flu bouts per year, fewer illnesses in the previous year and rated themselves healthier than women with rare alleles. To our knowledge, this is the first study to show a positive correlation between HLA allele frequency and general health measures. We propose that certain common HLA alleles confer resistance to prevalent pathogens. Nevertheless, neither HLA heterozygosity nor allele frequency significantly predicted how healthy or attractive men rated the female volunteers. Three non-mutually exclusive explanations are put forward to explain this finding.

Clinical validation of the “ in silico” prediction of immunogenicity of a human recombinant therapeutic protein

Antibodies elicited by protein therapeutics can cause serious side effects in humans. We studied immunogenicity of a recombinant fusion protein (FPX) consisting of two identical, biologically active, peptides attached to human Fc fragment. EpiMatrix, an in silico epitope-mapping tool, predicted promiscuous T-cell epitope(s) within the 14-amino-acid carboxy-terminal region of the peptide portion of FPX. On administration of FPX in 76 healthy human subjects, 37% developed antibodies after a single injection. A memory T-cell response against the above carboxy-terminus of the peptide was observed in antibody-positive but not in antibody-negative subjects. Promiscuity of the predicted T-cell epitope(s) was confirmed by representation of all common HLA alleles in antibody-positive subjects. As predicted by EpiMatrix, HLA haplotype DRB1*0701/1501 was associated with the highest T-cell and antibody response. In conclusion, in silico prediction can be successfully used to identify Class II restricted T-cell epitopes within therapeutic proteins and predict immunogenicity thereof in humans.

Effect of HLA-compatibility in married couples on the development and severity of gestosis

We studied the effect of histocompatibility in married couples on the development and severity of gestosis. It was found that gestosis more often develops in women with two common HLA alleles of class II major histocompatibility complex with her husband. The greatest number of coincidences was detected in subgroups with medium and severe gestosis. Perinatal outcomes in women with medium-severe gestosis having HLA-alleles common with husbands are characterized by delivery of babies with lower body weight.

Identification of Vaccinia CD8 + T-Cell Epitopes Conserved among Vaccinia and Variola Viruses Restricted by Common MHC Class I Molecules, HLA-A2 or HLA-B7

Immunization with vaccinia virus results in long-lasting protection against smallpox and is an approach that has been successfully used to eliminate natural smallpox infections worldwide. Today, vaccinia virus is very important not only as a vaccine virus to protect human against smallpox, but also as an expression vector for immunization against other infectious diseases, such as HIV and cancer. In this article, we identify three new vaccinia human CD8 + T-cell epitopes conserved among vaccinia and variola viruses restricted by HLA-A2, HLA-B7, or HLA-B*3502, which belongs to the HLA-B7 supertype. Identification of these CD8 + T-cell epitopes restricted by common HLA alleles will help to quantitate human CD8 + T-cell responses to licensed and experimental smallpox vaccines and to vaccinia virus vectors. CD8 + T-cell responses specific to these epitopes can also be used to quantitate cellular immune responses, especially with new smallpox vaccines that do not induce a “take,” such as the modified vaccinia virus Ankara strain. Combined with previous reports by us and others, these results show that there are some vaccinia viral proteins containing multiple epitopes restricted by different MHC molecules of humans and mice.

The Majority of Currently Circulating Human Immunodeficiency Virus Type 1 Clade B Viruses Fail To Prime Cytotoxic T-Lymphocyte Responses against an Otherwise Immunodominant HLA-A2-Restricted Epitope: Implications for Vaccine Design

Human immunodeficiency virus type 1 (HIV-1) mutates to escape immune selection pressure, but there is little evidence of selection mediated through HLA-A2, the dominant class I allele in persons infected with clade B virus. Moreover, HLA-A2-restricted responses are largely absent in the acute phase of infection as the viral load is being reduced, suggesting that circulating viruses may lack immunodominant epitopes targeted through HLA-A2. Here we demonstrate an A2-restricted epitope within Vpr (Vpr59-67) that is targeted by acute-phase HIV-1-specific CD8+ T cells, but only in a subset of persons expressing HLA-A2. Individuals in the acute stage of infection with viruses containing the most common current sequence within this epitope (consensus sequence) were unable to mount epitope-specific T-cell responses, whereas subjects infected with the less frequent I60L variant all developed these responses. The I60L variant epitope was a stronger binder to HLA-A2 and was recognized by epitope-specific T cells at lower peptide concentrations than the consensus sequence epitope. These data demonstrate that HLA-A2 is capable of contributing to the acute-phase cytotoxic T-lymphocyte response in infected subjects, but that most currently circulating viruses lack a dominant immunogenic epitope presented by this allele, and suggest that immunodominant epitopes restricted by common HLA alleles may be lost as the epidemic matures.

Identification of a beta-cell-specific HLA class I restricted epitope in type 1 diabetes.

Type 1 diabetes is an autoimmune disease in which pancreatic beta-cells are destroyed by cytotoxic T-cells that recognize peptide epitopes presented by HLA class I molecules. The identification of human beta-cell epitopes may significantly improve the prospects for immunodiagnosis and immunotherapy in type 1 diabetes. Using algorithms to predict nonameric beta-cell peptides that would bind to the common HLA allele, HLA-A*0201, we identified a potential epitope from the leader sequence of islet amyloid polypeptide (human islet amyloid polypeptide [IAPP] precursor protein [preproIAPP] 5-13: KLQVFLIVL). Peripheral blood mononuclear cells (PBMCs) were isolated from 18 HLA-A*0201 patients with type 1 diabetes (9 with recent-onset [<180 days; range, 1-120 days] and 9 with long-standing diabetes [>180 days; range, 183-3,273 days]) and 9 healthy, nondiabetic control subjects. PBMCs were screened for peptide recognition using interferon-gamma enzyme-linked immunospot (ELISpot) assays. Of the nine patients with recent-onset type 1 diabetes, six had ELISpot responses to preproIAPP 5-13 that were >3 SDs above the mean of the nondiabetic control subjects (P = 0.002). In contrast, no patients with type 1 diabetes for >180 days had a response above this threshold. In summary, preproIAPP 5-13 is a novel HLA class I epitope recognized by a significant proportion of cytotoxic T-cells from HLA-A*0201 patients with recent-onset type 1 diabetes and may prove to be a useful tool for the prediction and/or prevention of this disease.

Identification and characterization of HLA-A*3303-restricted, HIV type 1 Pol- and Gag-derived cytotoxic T cell epitopes.

HLA-A*3303 is one of the common HLA alleles in East and Southeast Asia. Identification of HLA-A*3303-restricted HIV-1 cytotoxic T lymphocyte (CTL) epitopes is therefore required to investigate the immunopathogenesis of AIDS and vaccine development in these areas, where AIDS is rapidly expanding. We attempted to identify HLA-A*3303-restricted CTL epitopes derived from relatively conserved proteins Pol, Gag, and Nef of HIV-1 clade B, using reverse immunogenetics. Ninety-nine 8-mer to 11-mer peptides corresponding to the HLA-A*3303-binding peptide motif were selected from the HIV-1 SF2 sequence. Fifty-two of these 99 peptides bound to HLA-A*3303. Six of these binding peptides induced peptide-specific CTLs in PBMCs from at least one of two HIV-1-seropositive individuals. CTL clones specific for three Pol peptides and one Gag peptide killed HLA-A*3303-restricted target cells infected with HIV-1 recombinant vaccinia, indicating that these peptides were naturally processed HLA-A*3303-restricted CTL epitopes. SF2-Pol 594-602 (FYVDGAANR) and SF2-Gag 144-152 (MVHQAISPR) induced specific CTLs in 5 and 4 of 10 chronically HIV-1-infected individuals, respectively, whereas SF2-Pol 60-70 (TLWQRPLVTIR) and SF2-Pol 934-943 (KIQNFRVYYR) induced specific CTLs in 2 and 1 of 10 chronically HIV-1-infected individuals, respectively. Thus, the former are immunodominant epitopes whereas the latter are not. These epitopes are useful for studies of AIDS immunopathogenesis and vaccine development.

Immune escape mutations in HIV-1 sequence: the influence of HLA class I and II alleles in a host population on viral evolution

The selection in vivo of mutations in HIV-1 that allow viral escape from host HLA class I restricted cytotoxic T lymphocyte (CTL) responses has been documented in individuals. Recently we showed that the many HLA-A and -B allele-specific polymorphisms in HIV-1 reverse transcriptase (RT) suggested extensive CTLescape mutation at a population level. HLA class II restricted CD4 T helper responses have a central role in HIV-1 immunity and associations between HLA class II alleles and HIV-1 disease progression have been reported. However, CD4 T cell escape mutation in HIV-1 has not been proven. We sought to determine whether, as for CTLescape, CD4 T cell escape in HIV-1 was evident at a population level as HLA-DRB1 associated polymorphisms. We analysed the diversity of HIV-1 RT sequences in a large, well characterised cohort of HIV-1 infected patients over 2210 person-years of observation. We examined the relationship between the HLA-A, -B and -DRB1 alleles present in the cohort (as covariates) and polymorphism in HIV-1 RT (as the outcome) in multivariate logistic regression models. Each single residue in HIV-1 RT (positions 20-227) was examined in separate models sequentially. Power calculations and model selection steps were carried out to limit the number of comparisons, and final Bonferroni correction was made to mark out the most significant associations. Polymorphism in HIV-1 RT occurred at sites with least functional constraint against mutation. At these sites, we identified 64 characteristic polymorphisms associated with specific HLA-A or -B alleles (OR > 1, p 1, p < 0.05). Four of the 5 known T helper cell epitopes in HIV-1 RT encompassed sites of HLA-DRB1 allele-specific polymorphism found in our study. There were also 'negative associations' between polymorphism and common HLA alleles, suggesting that the HIV-1 consensus sequence could have been selected by the host population's dominant HLA. This novel, population-based approach shows that polymorphisms in HIV-1 sequence are characteristic for specific HLA class I and II alleles, in keeping with viral adaptation to both the CTLand CD4 T helper cell responses of a human host population. These findings suggest that HLA has a central role in HIV-1 primordial and contemporary evolution and has implications for epitope mapping and predicting HIV-1 dynamics in individuals.

A novel cytotoxic T-cell epitope presented by HLA-A24 molecule in hepatitis C virus infection

Background/Aims : It has been suggested that cytotoxic T lymphocytes (CTL) have crucial roles for the hepatocellular damage in hepatitis C virus (HCV) infection. A series of CTL epitopes located in the HCV protein have been identified. However, no CTL epitopes restricted by HLA-A24, a common HLA allele in humans, has been identified. Methods : Peripheral blood and liver infiltrating mononuclear cells from the patients with hepatitis C virus infection and healthy controls were stimulated with a series of peptides containing HLA-A24 binding motifs located in HCV protein. Results : An immunodominant HLA-A24 restricted CTL epitope (A24-4; AYSQQTRGL, amino acids 1031–1039) presented by HLA-A24 molecule was identified using a series of synthetic peptides containing the HLA-A24 binding motifs. The CTL activity against this peptide was induced both in peripheral blood and liver infiltrating mononuclear cells from HLA-A24-positive chronic hepatitis C patients, not from HLA-A24-negative patients and HLA-A24-positive healthy controls. CTL activity was blocked by anti-HLA-A24 and anti-CD8 antibodies, not by anti-CD4 antibody. Furthermore, the A24-4-specific CTL recognized the HCV gene transfected target cells. Conclusions : Because this peptide is presented by a common HLA class I molecule, it might be useful for protection against hepatocellular damage and vaccine development in large population of the HCV-infected patients.

HLA-A*01-restricted cytotoxic T-lymphocyte epitope from the Plasmodium falciparum circumsporozoite protein.

Here, we report the identification of a novel CD8+ cytotoxic T-lymphocyte epitope on the Plasmodium falciparum circumsporozoite protein (3D7; amino acids 310 to 319 [EPSDKHIKEY]) that is restricted by HLA-A*01 and is recognized by human volunteers immunized with irradiated P. falciparum sporozoites. HLA-A*01 is the second most common HLA allele among Caucasians.

Common HLA alleles, rather than rare mutants, confer susceptibility to coeliac disease

Coeliac Disease (CD) is a gluten sensitive enteropathy characterised by villous atrophy and crypt cell hyperplasia. It has a very strong HLA class II association to the DQ locus. The nature of the involvement of the DQ locus in the susceptibility to CD has been examined by tissue culture experiments, association and peptide binding studies. We examined the role of the DQ molecules in the pathogenesis from the perspective of a genetic family study. Using flanking microsatellite markers to the class II region of the MHC to establish the parental origin of the susceptibility DQ alleles, we have evidence suggesting that the HLA association is probably due to the necessity to have these DQ alleles in order to express CD and there is no support for the presence of a rare mutation within the DQ alleles nor any rare HLA-linked gene nearby in linkage disequilibrium with the DQ locus. This approach is applicable to other diseases demonstrating strong association with common alleles, and can be used to predict whether screening the region for rare mutations is likely to be worthwhile.

Protection from Plasmodium berghei infection by priming and boosting T cells to a single class I-restricted epitope with recombinant carriers suitable for human use.

The desirability of inducing cytotoxic T cell responses to defined epitopes in humans has led to the development of a variety of recombinant delivery systems. Recombinant protein particles derived from a yeast retrotransposon (Ty) and the modified Ankara vaccinia (MVA) virus can deliver large epitope strings or even whole proteins. Both have previously been administered safely in humans. Immunization with recombinant Ty and MVA containing a single Plasmodium berghei class I-binding epitope provided 95% sterile protection against malaria in mice. The sequence of immunization, Ty followed by MVA, was critical to elicit high levels of IFN-gamma-producing cells and protection. The reciprocal sequence (MVA/TY) or homologous boosting was not protective. Both constructs (Ty and MVA) contain the H-2Kd-restricted pb9 CTL epitope from the circumsporozoite protein of P. berghei among a string of 8-15 human P. falciparum-derived CTL epitopes restricted through 7 common HLA alleles as well as widely recognized CD4 T cell epitopes. Thus, the novel recombinant Ty/MVA prime/boost combination with these constructs provides a safe alternative for evaluation for human vaccination against P. falciparum malaria.

Naturally occurring IgG anti-HLA alloantibody does not correlate with HIV type 1 resistance in Nairobi prostitutes.

In an effort to identify an immunological basis for natural resistance to HIV-1 infection, we have examined serum antibody responses to HLA class I antigens in female prostitutes of the Nairobi Sex Workers Study. Anti-HLA antibodies are known to block HIV infectivity in vitro and can be protective against SIV challenge in macaques immunized with purified class I HLA. Thus, it was postulated that broadly cross-reactive alloantibodies recognizing common HLA alleles in the client population might contribute to the prevention of heterosexual transmission of HIV. In fact, 12% of the women were found to have serum IgG antibodies against class I alloantigens. However, this alloantibody did not correlate with the HIV status of the women and was found in a similar proportion of HIV-positive and HIV-resistant women. The observed levels of alloantibody did not increase with HIV infection in susceptible individuals, suggesting that potential antigenic mimicry between HIV and host HLA class I antigens does not significantly increase levels of anti-class I antibodies. The lack of correlation between serum anti-allo-class I HLA antibodies and the risk of sexual transmission indicates that this humoral immune response is unlikely to be the natural mechanism behind the HIV-resistance phenotype of persistently HIV-seronegative women. This result, however, does not preclude the further investigation of alloimmunization as an artificial HIV immunization strategy.

The Multi-epitope Approach for Immunotherapy for Cancer: Identification of Several CTL Epitopes from Various Tumor-Associated Antigens Expressed on Solid Epithelial Tumors

ABSTRACT: One approach to development of specific cancer immunotherapy relies on the induction of cytotoxic T lymphocytes (CTL) specific for tumor-associated antigens (TAA). Induction of TAA-specific CTL could be used towards the eradication of established tumors, or to prevent their dissemination or recurrence after primary treatment. The present study identifies a set of CTL epitopes from TAA frequently found on solid epithelial tumors such as breast, lung and gastro-intestinal tumors. Specifically, HLA-A2.1 binding peptides from the MAGE2, MAGE3, HER-2/ neu and CEA antigens were tested for their capacity to elicit in vitro anti-tumor CTL using lymphocytes from normal volunteers and autologous dendritic cells as antigen-presenting cells. A total of 6 new epitopes (MAGE2[10 157], MAGE3[9 112], CEA[9 691], CEA[9 24], HER2[9 435] and HER2[9 5]) were identified which were capable of specifically recognizing tumor cell lines expressing HLA-A2.1 and the corresponding TAA. In one case (CEA[9 24]), induction of vigorous anti-tumor CTL responses required epitope engineering to increase HLA-A2.1 binding affinity. Finally, most of the newly identified epitopes (5 out of 6) were found to be highly crossreactive with other common HLA alleles of the A2 supertype (A2.2, A2.3, A2.6 and A6802), thus demonstrating their potential in providing broad and non-ethnically biased population coverage. The results are discussed in the context of the development of multi-epitope-based therapies with broad applicability for patients suffering from commonly found tumors.

Molecular HLA typing--the brave new world.

Molecular HLA typing--the brave new world.

Natural inactivation of a common HLA allele (A*2402) has occurred on at least three separate occasions.

HLA-A*2402 is common and widely distributed in human populations. Several individuals were identified who type genotypically for A*2402, but are serologically null for the HLA-A24 Ag. Sequencing and transfection of genomic DNA fragments containing null and wild-type A*2402 alleles, and the related A*2301 allele, revealed three different null alleles (A*2409N, A*2411N, and A*2402(low)), each of which differs from A*2402 by a single nucleotide change within the 6.7-kb sequence. The A*2301 and A*2402 sequences differ by no substitutions additional to those previously determined for the 1.1-kb cDNA. In exon 4, A*2409N has an in-frame stop codon, while A*2411N has a nucleotide insertion that alters the reading frame, causing premature termination. A*2402(low) has a nucleotide substitution near the splice acceptor site for intron 2 that impairs the production of correctly spliced mRNA. For A*2409N and A*2411N, mRNA is undetectable by Northern analysis, whereas A*2402(low) produces a low level of mRNA and a concomitant amount of normal A*2402 protein at the cell surface. The protein expressed from the A*2402(low) allele is sufficient to stimulate an alloreactive T cell response. On a background of unexpected sequence homogeneity, the single nucleotide changes in the A*2409N, A*2411, and A*2402(low) alleles have dramatic effects upon gene expression and are of likely importance for HLA matching in clinical transplantation. Segregation of at least three independently inactivated A*2402 alleles in human populations raises the possibility that loss of A*2402 may be the result of natural selection.

Conserved CTL epitopes within EBV latent membrane protein 2: a potential target for CTL-based tumor therapy.

In healthy virus carriers, EBV is subject to strong CTL responses that principally target the EBV nuclear Ag (EBNA) 3A, 3B, 3C subset of virus proteins. In vitro-reactivated CTLs of this kind have proved very effective in treating EBV-positive immunoblastic lymphoma, a malignancy that expresses the full range of virus proteins. However, targeting other EBV-positive tumors will require CTLs that recognize some of the subdominant viral Ags since in nasopharyngeal carcinoma and EBV-positive Hodgkin's disease, EBNA1, latent membrane protein (LMP) 1, and LMP2 are the only virus proteins present. Studying healthy virus carriers (Caucasian and Chinese), we identified five CTL target epitopes in LMP2 restricted through HLA alleles particularly common in the southern Chinese population, which is most at risk for nasopharyngeal carcinoma (HLA-A2, 50%; A11, 50%; A24, 30%; and B40, 32%). Furthermore, we analyzed the effect of HLA subtype polymorphism, especially in the context of A2 for which four subtypes are present at significant frequency in the Chinese population. As to virus polymorphism, LMP2 epitope sequences (in contrast to EBNA 3A, 3B, and 3C epitopes) were shown to be antigenically conserved among EBV isolates from different world populations, including viruses present in nasopharyngeal carcinoma and Hodgkin's disease biopsy samples. Thus, nasopharyngeal carcinoma and Hodgkin's disease are predicted to express LMP2 proteins that contain conserved CTL target epitopes restricted through common HLA alleles; boosting responses to these epitopes could form the basis of a CTL-based therapy for these malignancies.

Precursor frequency analysis of cytotoxic T lymphocytes to pre-erythrocytic antigens of Plasmodium falciparum in West Africa.

Some individuals living in malaria-endemic areas have CTL to Plasmodium falciparum liver stage Ags. We have quantified these CTL responses using limiting dilution analysis studies on the peripheral blood cells of naturally exposed Gambian donors. CTL precursor frequencies were determined to a wide range of epitopes derived from different liver stage Ags (liver stage protein 1, circumsporozoite protein, thrombospondin-related anonymous protein, and sporozoite threonine/asparagine-rich protein) restricted through common HLA alleles present in this population (HLA-A2.1, -A2.2, -B7, -B8, -B35, and B53). Precursor frequencies were between 17 and 98/million PBMC and correlated with the levels of specific lysis in parallel bulk cultures. The quantitative nature of limiting dilution assay analysis revealed varying degrees of immunodominance in the CTL responses to different epitopes within single proteins (thrombospondin related anonymous protein: tr42, tr43, tr26, tr29, and tr39; circumsporozoite protein: cp6, cp26, and cp29) and within individual donors. The temporal stability of some of these CTL responses was determined over a 4-yr period. This is the first quantitative study of CTL specific for any plasmodial species or nonviral pathogen in humans and provides a basis for a multiepitope approach to malaria vaccination.

The Association Between Immunodeficiency and the Development of Autoimmune Disease

There is a paradoxical relationship between immunodeficiency diseases and autoimmunity. While not all individuals with immunodeficiency develop autoimmunity, nor are all individuals with autoimmunity immunodeficient, defects within certain components of the immune system carry a high risk for the development of autoimmune disease. Inherited deficiencies of the complement system have a high incidence of systemic lupus erythematosus (SLE), glomerulonephritis, and vasculitis. Carrier mothers of children with chronic granulomatous disease, an X-linked defect of phagocytosis, often develop discoid lupus. Several antibody deficiencies are associated with autoimmune disease. Autoimmune cytopenias are commonly observed in individuals with selective IgA deficiency and common variable immune deficiency. Polyarticular arthritis can be seen in children with X-linked agammaglobulinemia. Combined cellular and antibody deficiencies, such as Wiskott-Aldrich syndrome, carry an increased risk for juvenile rheumatoid arthritis and autoimmune hemolytic anemia. Several hypothetical mechanisms have been proposed to explain the associations between autoimmunity and immunodeficiency. Immunologic defects may result in a failure to exclude microbial antigens, resulting in chronic immunologic activation and autoimmune symptoms. There may be shared genetic factors, such as common HLA alleles, which predispose an individual to both autoimmunity and immunodeficiency. Defects within one component of the immune system may alter the way a pathogen induces an immune response and lead to an inflammatory response directed at self-antigens. An understanding of the immunologic defects that contribute to the development of autoimmunity will provide an insight into the pathogenesis of the autoimmune process.

HLA A2.1-restricted cytotoxic T cells recognizing a range of Epstein-Barr virus isolates through a defined epitope in latent membrane protein LMP2

Cytotoxic T-lymphocyte (CTL) responses induced by persistent Epstein-Barr virus (EBV) infection in normal B-lymphoid tissues could potentially be directed against EBV-positive malignancies if expression of the relevant viral target proteins is maintained in tumor cells. For malignancies such as nasopharyngeal carcinoma and Hodgkin's disease, this will require CTL targeting against the nuclear antigen EBNA1 or the latent membrane proteins LMP1 and LMP2. Here we analyze in detail a B95.8 EBV-reactivated CTL response which is specific for LMP2 and restricted through a common HLA allele, A2.1. We found that in vitro-reactivated CTL preparations from several A2.1-positive virus-immune donors contained detectable reactivity against A2.1-bearing target cells expressing either LMP2A or the smaller LMP2B protein from recombinant vaccinia virus vectors. Peptide sensitization experiments then mapped the A2.1-restricted response to a single epitope, the nonamer CLGGLLTMV (LMP2A residues 426 to 434), whose sequence accords well with the proposed peptide binding motif for A2.1. Most Caucasian and African virus isolates (whether of type 1 or type 2) were identical in sequence to B95.8 across this LMP2 epitope region, although 2 of 12 such isolates encoded a Leu-->Ile change at epitope position 6. In contrast, most Southeast Asian and New Guinean isolates (whether of type 1 or type 2) constituted a different virus group with a Cys-->Ser mutation at epitope position 1. CTLs raised against the B95.8-encoded epitope were nevertheless able to recognize these variant epitope sequences in the context of A2.1 whether they were provided exogenously as synthetic peptides or generated endogenously in B cells transformed with the variant viruses. A CTL response of this kind could have therapeutic potential in that it is directed against a protein expressed in many EBV-positive malignancies, is reactive across a range of virus isolates, and is restricted through a relatively common HLA allele.