Identification of HLA-A11-restricted HIV-1-specific cytotoxic T-lymphocyte epitopes in China

To fully define HLA-A11-restricted HIV-1-specific cytotoxic T-lymphocyte epitopes in China, a method combining the enzyme-linked immunospot (ELISPOT) assay with intracellular gamma interferon staining (ICS) of peripheral blood mononuclear cells (PBMC) was used to map the optimal epitopes targeted by ELISPOT and then to define the HLA restriction of epitopes by ICS. A novel HLA-A11-restricted CTL epitope and five other published HLA-A11-restricted epitopes previously identified by reverse immunogenetics or other methods were defined. The approach of integrating ELISPOT with ICS is both convenient and useful for the characterization of CTL responses to HIV-1 infection; this method is practical for defining novel epitopes and facilitates in developing new strategies for future vaccine design in China and other Asian countries.     

Quantifiable cytotoxic T lymphocyte responses and HLA-related risk of progression to AIDS

There are significant associations between possession of certain HLA class I alleles and rate of progression to AIDS. Immunological data provide an explanatory mechanism for this relationship. Patients with HLA types associated with rapid disease progression recognize a significantly smaller fraction of their known repertoire of viral epitopes than do patients with HLA types associated with slow progression. Population frequency of HLA types (or supertypes) and their capacity to elicit cytotoxic T lymphocyte responses are also negatively correlated. These data provide an immunological mechanism to explain HLA-related risk of progression to AIDS and emphasize the central role of viral evolution in the pathogenesis of HIV.     

Cytolytic T lymphocytes (CTLs) from HIV-1 subtype C-infected Indian patients recognize CTL epitopes from a conserved immunodominant region of HIV-1 Gag and Nef

Analysis of the human immunodeficiency virus type 1 (HIV-1) cytolytic T lymphocyte (CTL) epitopes recognized by the targeted population is critical for HIV-1 vaccine design. Peripheral blood mononuclear cells from 47 Indian subjects at different stages of HIV-1 infection were tested for HIV-1 Gag-, Nef-, and Env-specific T cell responses by interferon (IFN)- gamma enzyme-linked immunospot (ELISPOT) assay, using pools of overlapping peptides. The Gag and Nef antigens were targeted by 83% and 36% of responders. Five immunodominant regions, 4 in Gag and 1 in Nef, were identified in the study; these regions are conserved across clades, including the African subtype C clade. Three antigenic regions were also found to be recognized by CTLs of the study participants. These regions were not identified as immunodominant regions in studies performed in Africa, which highlights the importance of differential clustering of responses within HIV-1 subtype C. Twenty-six putative epitopes--15 Gag (10 in p24 and 5 in p17), 10 Nef, and 1 Env (gp 41)--were predicted using a combination of peptide matrix ELISPOT assay and CTL epitope-prediction software. Ninety percent of the predicted epitopes were clustered in the conserved immunodominant regions of the Gag and Nef antigens. Of 26 predicted epitopes, 8 were promiscuous, 3 of which were highly conserved across clades. Three Gag and 4 Nef epitopes were novel. The identification of conserved epitopes will be important in the planning of an HIV-1 vaccine strategy for subtype C-affected regions.     

Relative dominance of Env-gp41-specific cytotoxic T lymphocytes responses in HIV-1 advanced infection

Human immunodeficiency virus type 1 (HIV-1)-specific cytotoxic T lymphocytes (CTL) responses provide an important defense in controlling HIV-1 replication, but they fail to control the progression of AIDS in advanced HIV-1 infection. To uncover the situation of these responses in patients with advanced HIV-1 infection, we assessed HIV-1-specific CTL responses in 20 individuals with advanced HIV-1 infection using 407 overlapping peptides spanning all expressed HIV-1 proteins using a gamma interferon-enzyme-linked immunospot (ELISpot) assay. In comparison to 20 individuals with moderately advanced HIV-1 infection, HIV-1-specific CTL responses were significantly decreased (P=0.044) and less peptides could be recognized (P=0.05) in advanced HIV-1 infection. Weakening of Env-gp120 and Gag-specific CTL responses contributed importantly to the decrease of CTL magnitude (P=0.042 and 0.078, respectively), while Env-gp41-specific CTL responses were relatively stronger during the end-stage of HIV-1 infection (P<0.001). Nef and Env-gp41 represented the most frequently targeted HIV-1 proteins in advanced HIV-1 infection. The entropy scores of peptides targeted in two groups were not significantly different. Only the breadth and magnitude of Env-gp41-specific CTL responses were positively correlated with viral loads in advanced HIV-1 infection (P=0.005 and 0.001, respectively). These findings suggest that progressive HIV-1 infection is associated with a weakening of Env-gp120- and Gag-specific CTL responses, and a simultaneous expansion of Env-gp41-specific CTL which is likely driven by high level viral replication.     

HIV-1-specific CD8 T cell responses in a pediatric slow progressor infected as a premature neonate

We describe the long-term survival of an individual infected with HIV-1 during extrauterine life as a premature newborn. In the absence of viral attenuation in the Nef/LTR structure or significant co-receptor polymorphisms, slow progression was associated with the strong HIV-1-specific broadly cross-reactive CD8 T cell responses. HIV-1 infection as early as 25 weeks' gestation may thus results in the development of immune responses that control viral replication and lead to prolonged survival.     

Direct visualization of HIV-1-specific cytotoxic T lymphocytes during primary infection

OBJECTIVE: HIV-specific cytotoxic T lymphocytes (CTL) are believed to play an important role in containing viral replication throughout HIV-1 infection. Previous studies have attempted to quantify the HIV-1-specific CTL precursor frequency during primary HIV infection by using limiting dilution analysis, which almost certainly underestimates the true CTL frequency. Here we use a relatively new technique to quantify HIV-specific CD8 T cells in primary HIV infection. METHODS: We have used soluble tetrameric complexes of HLA class I molecules complexed with HIV epitope peptides to study the dynamics and frequency of HIV-specific CD8 T cells in relation to plasma viral load in early HIV infection, in three patients with a highly focused HIV-specific CTL response. RESULTS: We show that the frequencies of HIV-1-specific CD8 T cells in acute infection are significantly higher than previously documented and can be demonstrated well before full seroconversion. These studies also confirm the immunodominance of the B27-restricted response in HIV infection and demonstrate a close temporal relationship between the numbers of circulating HIV-specific CD8 T cells and viral load. CONCLUSIONS: These findings strongly suggest that HIV-1-specific CD8 T cells are responding directly to the level of viral replication in early HIV infection and are a major factor in its control. In addition, the data indicate that immunodominance for CD8 T-cell responses is established in the acute phase of HIV infection.     

Identification of immunodominant hepatitis C virus (HCV)-specific cytotoxic T-cell epitopes by stimulation with endogenously synthesized HCV antigens

Hepatitis C virus (HCV)-specific CD8(+) cytotoxic T lymphocytes (CTL) are believed to play an important role in the pathogenesis of liver cell injury and viral clearance in HCV infection. Because HCV does not efficiently infect human cells in vitro and primary infected hepatocytes cannot be used as stimulator/target cells for CTL analysis, development of efficient systems to activate and expand CTL in vitro, reproducing antigen presentation to CTL occurring during natural infection, is mandatory to study CTL activity and to define the hierarchy of immunodominance of CTL epitopes. To achieve this goal, 5 different defective adenoviruses carrying structural and nonstructural HCV genes (core, core-E1-E2, E2, NS3-NS4A, NS3-NS5A) were used to induce the endogenous synthesis of HCV proteins in human adherent mononuclear cells in vitro and to allow their entry into the HLA class I cytosolic pathway of antigen processing. The cytolytic activity of peripheral blood lympho-mononuclear cells (PBMC) from HLA-A2(+) HCV-infected patients stimulated with recombinant adenovirus-infected cells was tested against target cells either pulsed with a panel of synthetic peptides containing the HLA-A2 binding motif or infected with recombinant vaccinia viruses carrying HCV genes. Our study defines a reproducible system to stimulate and expand HCV-specific CTL in vitro that mimics the conditions of antigen encounter in vivo. By this approach, we have identified several HLA-A2-restricted epitopes that should correspond to immunodominant HCV sequences recognized by CTL during natural infection. Therefore, these amino acid sequences represent ideal candidates for the design of therapeutic vaccines for chronic HCV infection.     

An HLA-directed molecular and bioinformatics approach identifies new HLA-A11 HIV-1 subtype E cytotoxic T lymphocyte epitopes in HIV-1-infected Thais.

Only limited cytotoxic T lymphocyte (CTL) epitope mapping has been done in nonsubtype B HIV-infected persons. We used molecular immunogenetic tools to determine HIV-specific CTL responses in HIV-1 Env subtype E-infected female sex workers (FSWs) from northern Thailand, where more than 50% of the population is HLA-A11 positive. EpiMatrix, a computer-based T cell epitope prediction algorithm, and a manual editing approach were used to predict 77 possible HLA-A11 CTL epitopes in HIV-1, some of which were conserved between subtypes B and E. MHC binding of these peptides was determined in an HLA-A11 stabilization assay, and binding peptides were tested for CTL recognition in eight HLA-A11-positive FSWs. Subtype E versions of known HLA-A2 subtype B HIV epitopes were also tested in four HLA-A2 positive FSWs. CTL responses were detected in all HLA-A11-positive and in three of four HLA-A2-positive persons. Among the 12 FSWs responses to peptides were found to Pol in 9 (75%), Env in 7 (58%), Nef in 5 (42%), and Gag in 5 (42%), and to conserved epitopes in 8 (67%). To identify HLA-A11 CTL epitopes in the absence of prediction tools, it would have been necessary to test almost 3000 10-mer peptides. EpiMatrix and manual predictions reduced this number to 77, of which 26 were MHC binding and 12 were CTL epitopes. Six of these HLA-A11 CTL epitopes have not been previously reported and are located in RT, gp120, and gp41. This report of CTL responses in subtype E-infected individuals defines epitopes that may be useful in HIV pathogenesis or vaccine studies.     

Inter-clade cross-reactivity of HIV-1-specific T cell responses in human immunodeficiency virus type 1 infection in China

To determine the degree of HIV-1-specific cytotoxic-T-lymphocyte (CTL) cross-responses to the clade B and C consensus sequences at the single peptide level. We assessed CTL responses in 46 HIV-1 clade B chronically infected individuals using an interferon-gamma Elispot assay with a total of 826 overlapping peptides spanning HIV-1 clade B and C consensus sequences. In general, 583 peptides were recognized by HIV-1-specific T cells in the study subjects (292 clade B, 291 clade C respectively), of which 204 peptides in both clades were recognized simultaneously. The HIV-1-specific CTL responses to both clade peptides contributed 54.23% (954/1759) to the total responses. No significant difference was observed between the overall magnitude or frequency of CTL responses to clade B proteins and those to clade C proteins. According to the profiles of CTL magnitude and CTL frequency, the top 44 and 35 synthetic peptides were identified as immunodominant regions in the clade B and C consensus sequences respectively and 27 corresponding peptides in two immunodominant regions were cross-reactive. These peptides with cross-reactivity had a significantly higher ability to elicit CTL responses (P< 0.01) and preferentially had a trend of lower entropy and higher inter-clade homology. A wide degree of cross-clade reactivity of HIV-1-specific T cells exist in clade B and clade C variants. Most of immunodominant peptides with cross-reactivity are vigorous to elicit CTL responses and preferentially be conservative. This result may make future HIV-1 vaccines including multiple copies of CTL epitopes in these immunodominant peptides effective for this population.     

Human immunodeficiency virus (HIV-1) gp160-specific lymphocyte proliferative responses of mononuclear leukocytes from HIV-1 recombinant gp160 vaccine recipients

The lymphocyte proliferative responses were studied of 12 volunteers enrolled in a phase I trial of a baculovirus-expressed recombinant human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (rgp160) vaccine. Six subjects received rgp160 and three subjects each received recombinant hepatitis B vaccine or placebo at 0, 1, and 6 months. rgp160 and a control preparation, baculovirus-expressed recombinant HIV-1 p24, were used as in vitro antigens. At day 56, all rgp160 recipients had stimulation indexes (rgp160/rp24) greater than 3.0, and five of six had differences in counts per minute (cpm) greater than 1000. Stimulation indexes were less than 2.0 and cpm differences were less than 150 in all six who did not receive rgp160. Lymphocyte proliferative responses were first noted 2 weeks to 5 months before initial Western blot reactivity and persisted for greater than or equal to 540 days, even among subjects who lost detectable antibody. Thus, the HIV-1 rgp160 vaccine induces persistent cellular immune recognition as demonstrated by lymphocyte proliferation.     

Augmentation of HIV-1-specific T helper cell responses in chronic HIV-1 infection by therapeutic immunization

OBJECTIVE: To determine whether therapeutic immunization with a whole inactivated HIV-1 immunogen augments HIV-1-specific T helper cell responses in chronically infected individuals receiving suppressive antiretroviral therapy (ART). DESIGN: An investigator-initiated, single center, double-blind, placebo-controlled, randomized trial. METHODS: Subjects selected for study were HIV-1-infected adults on ART with an HIV-1-RNA plasma viral load of less than 500 copies/ml for at least 6 months, and a CD4 cell count greater than 250 cells/mm3 before starting ART. Study subjects were randomly assigned to receive either immunogen (inactivated envelope-depleted HIV-1 coupled with incomplete Freund's adjuvant; IFA), versus placebo (IFA alone). The primary outcome was significant CD4 cell lymphoproliferative responses to HIV-1 proteins. Secondary endpoints included HIV-1-specific CD8 T cell responses, CD4 cell count/percentage, HIV-1-RNA plasma viral load, and delayed-type hypersensitivity (DTH) responses. RESULTS: The augmentation of HIV-1-specific T helper cell responses was achieved in five out of five vaccine recipients and none out of four controls (P = 0.008, Fisher's exact test). There were no significant changes in the breadth or magnitude of cytotoxic T lymphocyte responses, CD4 cell count/percentages, or DTH test responses. CONCLUSION: HIV-1-specific T helper cell responses can be successfully increased by therapeutic immunization in individuals with chronic infection on suppressive ART. Further studies will be needed to determine whether the augmentation of these responses correlate with long-term clinical benefits.     

Relationship between human immunodeficiency virus type 1 (HIV-1)-specific memory cytotoxic T lymphocytes and virus load after recent HIV-1 seroconversion.

Human immunodeficiency virus type 1 (HIV-1)-specific memory, or precursor, cytotoxic T lymphocytes (CTL) in 14 subjects who had recently experienced seroconversion were evaluated with respect to virus set point, defined as plasma HIV-1 RNA level 6 months after seroconversion. Env-, Gag-, Pol-, and Nef-specific precursor CTL were detected in (51)Cr-release assays, using antigen-stimulated peripheral blood mononuclear cells as effectors and B cell lines infected with HIV-1-vaccinia recombinants as targets. All subjects tested had precursor CTL specific to at least 2 HIV-1 antigens. Detection of Env-specific precursor CTL was associated with a high set point (P=.0221). The number of antigens recognized tended to be greater in subjects with higher set points (rho=.45621; P=.1171). Gag-specific precursor CTL frequency correlated inversely with set point (rho=-.8478; P=.0003). Two heterozygotes for a 32-bp deletion in CCR5 had the lowest set points (P=.0220) and highest Gag precursor CTL frequencies (P=.0128). These data suggest that host factors that restrict viral replication may be important determinants of the level of HIV-1-specific precursor CTL.     

Cross-reactive cytotoxic T lymphocytes against a HIV-1 p24 epitope in slow progressors with B*57

OBJECTIVES: To determine whether CD8 T lymphocytes from HIV-1-infected patients expressing B*5701 and B*5703 show broad cross-reactivity against different variants of a conserved p24 epitope, which might account for the good prognosis of HIV-1-infected individuals with HLA-B*57. DESIGN: B*5701+ and B*5703+ were recruited from Nairobi, Kenya and from Oxford, UK. All patients had been HIV positive for at least 8 years and could be categorized as slow progressors. METHODS: CD8 cytotoxic T cell clones were generated from B*5701+ and B*5703+ donors and tested for their ability to recognize clade variants of an index p24 epitope in standard cytolytic assays. Cross-reactive responses in freshly isolated peripheral blood mononuclear cells (PBMC) were assessed by interferon-gamma (IFNgamma) production and tetramer binding. RESULTS: Broad cross-clade reactivity for both cytolysis and tetramer binding was observed in CD8 T cell clones from patients harbouring the index epitope sequence. Patterns of cross-reactivity were similar in freshly isolated PBMC but varied between individuals in terms of strength and breath of responses generated. One common variant induced an unusual response with tetramer binding but often failed to induce IFNgamma production, and another was a weak stimulator of both IFNgamma and cytolytic activity. CONCLUSION: B*5701+ and B5703+ donors demonstrate broad functional cross-reactivity to both common and rare variants of a dominant p24 epitope, which could be relevant to the association of B*57 alleles with slow progression to AIDS.     

Sex-based differences in T lymphocyte responses in HIV-1-seropositive individuals

Sex-based differences in the levels of human immunodeficiency virus 1 (HIV-1) RNA in plasma could be associated with differences in the strength of HIV-1-specific CD8(+) T cell responses. CD8(+) effector responses in 18 men and 15 women were measured 0-2 years (time A) and 5-7 years (time B) after seroconversion. CD8(+) effector responses were seen in 7 (39%) of 18 men and 2 (13%) of 15 women at time A (P=.13) and in 12 (67%) of 18 men and 10 (67%) of 15 women at time B (P=.99). At time B, the strength of CD8(+) effector responses correlated with the number of CD4(+) lymphocytes in women ( rho =-0.68; P=.005) but not in men ( rho =-0.14; P=.58). The level of HIV-1 RNA was not associated with the strength of CD8(+) effector responses according to sex, but there was a sex-based difference in the correlation between the strength of CD8(+) effector response and the number of CD4(+) lymphocytes.     

Prevalence and magnitude of human immunodeficiency virus (HIV) type 1-specific lymphocyte responses in breast milk from HIV-1-seropositive women

Human immunodeficiency virus (HIV) type 1-specific cell-mediated immunity of breast milk may influence the likelihood of mother-to-child transmission of HIV-1 via breast-feeding. In breast-milk specimens collected during the first month postpartum from HIV-1-seropositive women in Nairobi, HIV-1 gag-specific cellular responses were detected in 17 (47%) of 36, and env-specific cellular responses were present in 20 (40%) of 50. Peripheral blood lymphocyte responses against either gag or env were detected in 35 (66%) of the 53 subjects, 18 (51%) of whom had positive gag or env responses in their breast milk. In paired analyses of blood and breast milk, the mean magnitude of responses to env or gag stimulation in breast milk was significantly higher than that in blood and remained higher in breast milk after normalization of responses according to CD8+ lymphocyte count. These results suggest that CD8+ lymphocytes present in breast milk have the capacity to recognize HIV-1-infected cells and may be selectively transported to breast milk to reduce either viral replication or transmission in breast milk.     

Higher frequency of HIV-1-specific T cell immune responses in African American children vertically infected with HIV-1

The progression of human immunodeficiency virus (HIV) disease and plasma levels of HIV may differ between racial groups. We compared HIV-specific T cell responses between vertically HIV-1-infected Hispanic and African American children. Subjects were matched for sex, age, viral load, and CD4(+) cell count in 18 pairs; T cell responses were measured by cytokine-enhanced interferon- gamma assay. Peripheral blood mononuclear cells were stimulated with HIV consensus peptides from Gag, Nef, and Tat. The influence of ethnicity, sex, age, viral load, and CD4(+) cell count on T cell responses was determined through linear regression analyses. After adjustment for CD4(+) count, age, and log(10) viral load, African American children demonstrated significantly higher Gag responses (average, 486 spot-forming cells higher; P=.01) than Hispanic children; this was significantly driven by robust responses in African American girls near the age of puberty, many of whom carried the human leukocyte antigen class I B*58 allele.