Cytotoxic T cell responses to multiple conserved HIV epitopes in HIV-resistant prostitutes in Nairobi

Novel and promiscuous CTL epitopes in conserved regions of Gag targeted by individuals with early subtype C HIV type 1 infection from southern Africa

Characterization of optimal CTL epitopes in Gag can provide crucial information for evaluation of candidate vaccines in populations at the epicenter of the HIV-1 epidemic. We screened 38 individuals with recent subtype C HIV-1 infection using overlapping consensus C Gag peptides and hypothesized that unique HLA-restricting alleles in the southern African population would determine novel epitope identity. Seventy-four percent of individuals recognized at least one Gag peptide pool. Ten epitopic regions were identified across p17, p24, and p2p7p1p6, and greater than two-thirds of targeted regions were directed at: TGTEELRSLYNTVATLY (p17, 35%); GPKEPFRDYVDRFFKTLRAEQATQDV (p24, 19%); and RGGKLDKWEKIRLRPGGKKHYMLKHL (p17, 15%). After alignment of these epitopic regions with consensus M and a consensus subtype C sequence from the cohort, it was evident that the regions targeted were highly conserved. Fine epitope mapping revealed that five of nine identified optimal Gag epitopes were novel: HLVWASREL, LVWASRELERF, LYNTVATLY, PFRDYVDRFF, and TLRAEQATQD, and were restricted by unique HLA-Cw*08, HLA-A*30/B*57, HLA-A*29/B*44, and HLA-Cw*03 alleles, respectively. Notably, three of the mapped epitopes were restricted by more than one HLA allele. Although these epitopes were novel and restricted by unique HLA, they overlapped or were embedded within previously described CTL epitopes from subtype B HIV-1 infection. These data emphasize the promiscuous nature of epitope binding and support our hypothesis that HLA diversity between populations can shape fine epitope identity, but may not represent a constraint for universal recognition of Gag in highly conserved domains.

Multiple V1/V2 env variants are frequently present during primary infection with human immunodeficiency virus type 1

Human immunodeficiency virus type 1 (HIV-1) exists as a complex population of multiple genotypic variants in persons with chronic infection. However, acute HIV-1 infection via sexual transmission is a low-probability event in which there is thought to be low genetic complexity in the initial inoculum. In order to assess the viral complexity present during primary HIV-1 infection, the V1/V2 and V3 variable regions of the env gene were examined by using a heteroduplex tracking assay (HTA) capable of resolving these genotypic variants. Blood plasma samples from 26 primary HIV-1-infected subjects were analyzed for their level of diversity. Half of the subjects had more than one V1/V2 viral variant during primary infection, indicating the frequent transmission of multiple variants. This observation is inconsistent with the idea of infrequent transmission based on a small transmitting inoculum of cell-free virus. In chronically infected subjects, the complexity of the viral populations was even greater in both the V1/V2 and the V3 regions than in acutely infected subjects, indicating that in spite of the presence of multiple variants in acute infection, the virus does pass through a genetic bottleneck during transmission. We also examined how well the infecting virus penetrated different anatomical compartments by using the HTA. Viral variants detected in blood plasma were compared to those detected in seminal plasma and/or cerebral spinal fluid of six individuals. The virus in each of these compartments was to a large extent identical to virus in blood plasma, a finding consistent with rapid penetration of the infecting variant(s). The low-probability transmission of multiple variants could be the result of transient periods of hyperinfectiousness or hypersusceptibility. Alternatively, the inefficient transfer of a multiply infected cell could account for both the low probability of transmission and the transfer of multiple variants.

HIV-1 Env-specific cytotoxic T-lymphocyte responses in exposed, uninfected Kenyan sex workers: a prospective analysis

The prospective significance of HIV-specific cytotoxic T lymphocyte (CTL) responses in highly exposed, persistently seronegative populations is unknown. In 1996-1997 we screened for CTL responses against HIV clade B Env in 39 recently enrolled Kenyan female sex workers, and followed these women prospectively. Annual HIV incidence was 5.8%. CTL were independently associated with age and recent HIV-1 exposure,but were not prospectively associated with protection in a multivariable model that included HIV-1 exposure and duration of sex work.

Correlates of immune protection in HIV-1 infection: what we know, what we don't know, what we should know

The field of vaccinology began in ignorance of how protection was instilled in vaccine recipients. Today, a greater knowledge of immunology allows us to better understand what is being stimulated by various vaccines that leads to their protective effects: that is, their correlates of protection. Here we describe what is known about the correlates of protection for existing vaccines against a range of different viral diseases and discuss the correlates of protection against disease during natural infection with HIV-1. We will also discuss why it is important to design phase 3 clinical trials of HIV vaccines to determine the correlates of protection for each individual vaccine.

Full-length gag sequences of HIV type 1 subtype C recent seroconverters from Pune, India

Although HIV-1 subtype C is the most prevalent subtype worldwide, data on subtype C viruses are rather limited. Very little information is available on the complete HIV-1 subtype C gag sequences from India. We report full-length gag (p55) sequences from six Indian early seroconverters. The samples were collected within few weeks of seroconversion and may represent immunologically naive viruses. The comparison of p55 sequences with other Indian and non-Indian subtype C sequences as well as with nonsubtype C sequences obtained from the Los Alamos database revealed gag as a well-conserved region of the HIV genome (range: 84-95%). The phylogenetic tree indicated that the sequences compared here cluster together within clade C. Two epitopes in the p24 region of the gag gene were subtype C specific while many epitopes in the same region were also present in other clades. The data on HIV-1 subtype C full-length gag sequences would be useful in the design and evaluation of effective subtype C-based HIV vaccines.

Structures of HLA-A*1101 complexed with immunodominant nonamer and decamer HIV-1 epitopes clearly reveal the presence of a middle, secondary anchor residue

HLA-A*1101 is one of the most common human class I alleles worldwide. An increased frequency of HLA-A*1101 has been observed in cohorts of female sex workers from Northern Thailand who are highly exposed to HIV-1 and yet have remained persistently seronegative. In view of this apparent association of HLA-A*1101 with resistance to acquisition of HIV-1 infection, and given the importance of eliciting strong CTL responses to control and eliminate HIV-1, we have determined the crystal structure of HLA-A*1101 complexed with two immunodominant HIV-1 CTL epitopes: the nonamer reverse transcriptase(313-321) (AIFQSSMTK) and decamer Nef(73-82) (QVPLRPMTYK) peptides. The structures confirm the presence of primary anchor residues P2-Ile/-Val and P9-/P10-Lys, and also clearly reveal the presence of secondary anchor residues P6-Ser for reverse transcriptase and P7-Met for Nef. The overall backbone conformation of both peptides is defined as two bulges that are separated by a more buried middle residue. In this study, we discuss how this topology may offer functional advantages in the selection and presentation of HIV-1 CTL epitopes by HLA-A*1101. Overall, this structural analysis permits a more accurate definition of the peptide-binding motif of HLA-A*1101, the characterization of its antigenic surface, and the correlation of molecular determinants with resistance to HIV-1 infection. These studies are relevant for the rational design of HLA-A*1101-restricted CTL epitopes with improved binding and immunological properties for the development of HIV-1 vaccines.

Prospects for an AIDS vaccine: three big questions, no easy answers

The unremitting devastation created by the AIDS pandemic will probably only be controlled when a vaccine is developed that is safe, effective, affordable, and simple enough to permit implementation in developing countries where the impact of AIDS is most severe. Although formidable practical, political, economic, social, and ethical challenges face the AIDS vaccine development effort, the most fundamental challenges now reside at the level of the basic biology of HIV-1 infection and pathogenesis. Of these biological considerations, three questions loom especially large: can we design immunogens that will elicit neutralising antibodies that are reactive against a wide variety of primary HIV isolates; will vaccine-elicited cytotoxic T cells be fundamentally better at controlling HIV-1 replication and ameliorating disease progression than those responses that arise during natural HIV infection; and to what extent will the tremendous global genetic diversity of HIV-1 compromise the breadth of vaccine-elicited protective immunity and the overall effectiveness of an AIDS vaccine? Although these are three exceptionally challenging questions, they are now being approached with clear hypotheses whose testing is being facilitated by an ever-improving array of technologies for vaccine design and immunological characterisation. The extent to which the field of AIDS vaccine research can now come together to answer these questions in the best coordinated, most efficient manner will probably be an important determinant of how and when an effective AIDS vaccine will be developed.

Human leukocyte antigen (HLA) B*18 and protection against mother-to-child HIV type 1 transmission

Human leukocyte antigen (HLA) molecules regulate the cellular immune system and may be determinants of infant susceptibility to human immunodeficiency virus type 1 (HIV-1) infection. Molecular HLA typing for class I alleles was performed on infants followed in a Kenyan perinatal cohort. Early HIV-1 infection status was defined as infection occurring at birth or month 1, while late infection via breast milk was defined as first detection of HIV-1 after 1 month of age. Likelihood ratio tests based on a proportional hazards model adjusting for maternal CD4 T cell count and HIV-1 viral load at 32 weeks of gestation were used to test associations between infant allelic variation and incident HIV-1 infection. Among 433 infants, 76 (18%) were HIV-1 infected during 12 months of follow-up. HLA B*18 was associated with a significantly lower risk of early HIV-1 transmission [relative risk (RR) = 0.26; 95% confidence interval (CI) 0.04-0.82], and none of the 24 breastfeeding infants expressing HLA B*18 who were uninfected at month 1 acquired HIV-1 late via breast milk. We observed a trend toward increased early HIV-1 acquisition for infants presenting HLA A*29 (RR = 2.0; 95% CI 1.0-3.8) and increased late HIV-1 acquisition via breast milk for both Cw*07 and Cw*08 (RR = 4.0; 95% CI 1.0-17.8 and RR = 7.2; 95% CI 1.2-37.3, respectively). HLA B*18 may protect breast-feeding infants against both early and late HIV-1 acquisition, a finding that could have implications for the design and monitoring of HIV-1 vaccines targeting cellular immune responses against HIV-1.

Potent neutralizing serum immunoglobulin A (IgA) in human immunodeficiency virus type 2-exposed IgG-seronegative individuals

The mechanisms behind the resistance to human immunodeficiency virus type 2 (HIV-2) infection are still not fully understood. In the present study, we explored the HIV-2-specific humoral serum immunoglobulin A (IgA) immune response in HIV-2-exposed IgG-seronegative (EGSN) individuals. Serum samples from heterosexual EGSN individuals and their known HIV-2-infected partners, as well as controls originating from Guinea-Bissau in Africa, were studied. Antibody reactivity to native and recombinant envelope glycoproteins was investigated, and the capacity of purified serum IgA to neutralize HIV-2(SBL6669) was tested. Our results showed that 16 of 25 EGSN samples exhibited reactivity against whole HIV-2 antigen, 6 of 25 samples reacted with recombinant gp36 (rgp36), and 3 of 25 samples were positive against HIV-2 rgp105; no reactivity to native HIV-2 gp125 was detected. Purified serum IgA antibodies from both EGSN and HIV-2-positive individuals, but not that from the negative controls, exhibited neutralization of HIV-2(SBL6669). The most potent neutralization activity was exhibited by IgA purified from EGSN compared to infected individuals' IgA. The antigenic pattern of the HIV-2-positive partners showed that all serum IgA samples were reactive to whole HIV-2 antigen, and 14 of 15 reacted with rgp36. For rgp105 and gp125, 5 of 15 and 4 of 15 samples exhibited binding, respectively. The serum of the EGSN group had a higher mean IgA concentration than that of the negative controls (P < 0.05). Thus, we describe HIV-2-specific serum IgA antigen reactivity and show a more potent serum IgA-mediated HIV-2-neutralizing activity in EGSN individuals than in HIV-2-infected patients.

HIV type 1-specific inter- and intrasubtype cellular immune responses in HIV type 1-infected Ugandans

Investigations concerning the extent and nature of subtype-specific and intersubtype immune responses in HIV-1-infected persons are necessary for the development of appropriate candidate vaccines. In the cross-sectional study described here, 26 HIV-1-positive Ugandan patients were tested for their ability to mount HIV antigen-specific cellular immune responses. Subjects were infected with either HIV-1 subtypes A, C, or D. Recombinant vaccinia virus (rVV)-based and peptide-based enzyme-linked immunospot (Elispot) assays were used to evaluate HIV-1-specific gamma-interferon (IFN-gamma) cellular responses. rVV expressing gag, pol, or env proteins derived from HIV-1 subtypes A, B, and D were evaluated for their ability to induce whole HIV-1-protein-specific IFN-gamma responses in 14 patients. A panel of previously identified HLA class I-restricted peptides based on representative sequences from HIV-1 subtypes A, B, C, and D and restricted through HLA-A2, -A29, -B42, -B53, and -B57 alleles were used to evaluate the presence of HIV-1-peptide-specific T cells in 19 patients. Using rVV, 27 of a possible 38 subtype-specific responses (71%) and 56 of a possible 110 intersubtype responses (51%) were observed. When appropriate peptides were used 18 of 39 (46.2%) subtype-specific and 13 of 39 (33.3%) intersubtype responses were observed. Peptide responses were higher quantitatively than those seen when rVV were used. In 7 patients, both rVV and specific peptides were evaluated; in 3 of 7 individuals, global responses were seen despite a lack of measurable HLA-restricted peptide-specific responses demonstrating the need to evaluate a broader range of HIV-specific immune responses.

Risk associated HIV-1 cross-clade resistance of whole peripheral blood mononuclear cells from exposed uninfected individuals with wild-type CCR5

Highly HIV exposed, persistently uninfected individuals (EUs) may hold clues to the generation of effective vaccine induced acquired immunity against HIV, and considerable effort has been devoted to detecting and characterizing HIV specific immune responses in EU cohorts. When searching for such clues, it is important to exclude individuals with genetically determined absence of receptors, as this protective mechanism could not be induced by HIV specific vaccines. Homozygosity for the DeltaC32 mutation of CCR5 prevents R5 HIV infection, independent of any virus-specific immune responses that may be acquired by exposure, while heterozygosity influences susceptibility to low level exposure. Reports on the in vitro susceptibility of EU cells compared to controls have been conflicting. Therefore, we studied 14 EUs with homozygous wild type CCR5, using a newly developed in vitro challenge assay (IVCA) to measure the magnitude and breadth of resistance to infection among EUs. CD8+ cells were relatively increased compared to controls, and were largely responsible for resistance to challenge, which depended on dose of virus inoculum, and extended across clades. Consistent with some EU cohort studies, resistance waned among individuals who reduced their high-risk behavior.

Immunogenicity of multiple gene and clade human immunodeficiency virus type 1 DNA vaccines

The ability to elicit an immune response to a spectrum of human immunodeficiency virus type 1 (HIV-1) gene products from divergent strains is a desirable feature of an AIDS vaccine. In this study, we examined combinations of plasmids expressing multiple HIV-1 genes from different clades for their ability to elicit humoral and cellular immune responses in mice. Immunization with a modified Env, gp145DeltaCFI, in combination with a Gag-Pol-Nef fusion protein plasmid elicited similar CD4(+) and CD8(+) cellular responses to immunization with either vector alone. Further, when mice were immunized with a mixture of Env from three clades, A, B, and C, together with Gag-Pol-Nef, the overall potency and balance of CD4(+)- and CD8(+)-T-cell responses to all viral antigens were similar, with only minor differences noted. In addition, plasmid mixtures elicited antibody responses comparable to those from individual inoculations. These findings suggest that a multigene and multiclade vaccine, including components from A, B, and C Env and Gag-Pol-Nef, can broaden antiviral immune responses without immune interference. Such combinations of immunogens may help to address concerns about viral genetic diversity for a prospective HIV-1 vaccine.

HIV type 1 antigen-responsive CD4+ T-lymphocytes in exposed yet HIV Type 1 seronegative Ugandans

CD4(+) T cell help is important for the functionality of CD8(+) cytotoxic T-lymphocytes (CTLs) in limiting viral replication and may contribute to mediation of apparent resistance to HIV-1 infection in exposed seronegative (ESN) individuals. Using five HIV-1 antigens in an intracellular cytokine assay, the presence of specific antigen-responsive interferon- gamma-positive (IFN-gamma(+)) CD69(+) CD4(+) T-lymphocytes was evaluated in ESNs, their seropositive partners, and unexposed seronegative controls. Ten ESNs (five females, five uncircumcised males) were identified from 10 HIV-1 serodiscordant couples with a history of frequent unprotected sexual intercourse. All ESNs and controls were negative on two EIAs and for HIV-1 proviral DNA. The frequency of ESNs with antigen-responsive IFN-gamma(+) CD69(+) CD4(+) T-lymphocytes ranged from three to five of eight for the different HIV-1 antigens. Six of eight ESNs tested had a positive response to at least one of the five antigens. Responses were on average 3.5 times higher among seropositives compared to ESNs and absent in the five unexposed controls. A negative correlation was noted between responses in ESNs and the plasma viral load of their seropositive spouse. Clade-specific and cross-clade reactivity were noted in both ESNs and seropositive partners tested. The findings confirm that ESNs are in a state of HIV-1-specific immune activation and suggest that HIV-1-specific IFN-gamma(+) CD69(+) CD4(+) T-lymphocytes in addition to HIV-1-specific CD8(+) CTLs already described by others are potential immunological correlates of protection from persistent HIV-1 infection.

The HIV-1 chimeric protein CR3 expressed by poxviral vectors induces a diverse CD8+ T cell response in mice and is antigenic for PBMCs from HIV+ patients

Recombinant avipoxvirus vectors are attractive for vaccination against human immunodeficiency virus type 1 (HIV-1), where induction of a cytotoxic CD8(+) T cell (CTL) response seems to be an important component of protective immunity. We expressed the chimeric protein CR3, composed by CTL epitopes rich regions from, RT, Gag and Nef and conserved Th cell epitopes from gp120, gp41 and Vpr of HIV-1 in a fowlpox virus (FWPV) vector (FPCR3), and used this vector to induce HIV-specific CTL responses in mice. Mice immunised twice intraperitoneally with FPCR3, developed a CD8(+) T cell response measured as production of IFN-gamma by splenocytes in response to stimulation with P815 cells infected with recombinant vaccinia viruses (rVV) expressing CR3, Gag and Nef. The number of IFN-gamma secreting cells was markedly higher when a P815 cell line constitutively expressing CR3 was used as target cells for Enzyme-linked-immunospot (ELISPOT). CR3 epitopes were also specifically recognised by human PBMCs from three HIV(+) patients with different haplotypes. These results confirm the potential of FWPV vectors expressing these novel HIV-1 chimeric proteins to induce a simultaneous CD8(+) T cell response against conserved viral targets and early expressed regulatory proteins.

Evidence for Gag p24-specific CD4 T cells with reduced susceptibility to R5 HIV-1 infection in a UK cohort of HIV-exposed-seronegative subjects

AIM

To characterize HIV-1 Gag p24-specific CD4 cell responses in HIV-exposed-seronegative (ES) individuals.

METHODOLOGY

Twelve ES individuals, of diverse ethnicity and wild type for the CCR5 Delta-32 mutation, were identified. Controls were HIV-negative blood donors. Gag p24-specific and total Vbeta+ CD4 cells that expressed MIP-1beta, IFN-gamma and IL-2 were enumerated by intracytoplasmic cytokine staining. beta-Chemokine expression was correlated with susceptibility to R5 HIV-1 infection, as measured by polymerase chain reaction for integrated HIV-1 and by p24 enzyme-linked immunosorbent assay.

RESULTS

Similar numbers of mitogen-stimulated and Vbeta+ MIP-1beta+, IFN-gamma+ and IL-2+ T cells were found in ES and HIV-negative control subjects. However, all ES subjects tested had an HIV Gag p24-specific MIP-1beta+, IFN-gamma+ and IL-2+ CD4 T-cell response that was rare in controls. p24-Specific cells of all ES but no control subjects could be expanded by in-vitro Ag/IL-2 stimulation, and when re-stimulated with an overlapping peptide series showed evidence of a broad CD4 cell memory response directed against multiple regions of Gag p24. Mitogen-stimulated ES CD4 cells were as susceptible to HIV infection as those from control subjects, but p24-specific IFN-gamma+ CD4 cells of six out of seven ES subjects tested were less susceptible to R5 HIV-1 infection than the counterpart fraction depleted of p24-specific IFN-gamma+ cells. The addition of blocking anti-beta-chemokine antibodies did not promote R5 HIV-1 infection of p24-specific IFN-gamma+ cells.

CONCLUSION

Specific CD4 cell immunity, characterized by a broadly directed memory Gag-p24 CD4 cell response and reduced susceptibility of specific CD4 cells to R5 HIV-1 infection, is a likely correlate of non-transmission.

Functional human immunodeficiency virus type 1 (HIV-1) Gag-Pol or HIV-1 Gag-Pol and env expressed from a single rhabdovirus-based vaccine vector genome

Recombinant rabies virus (RV) vaccine strain-based vectors have been successfully developed as vaccines against other viral diseases (J. P. McGettigan et al., J. Virol. 75:4430-4434, 2001; McGettigan et al., J. Virol. 75:8724-8732, 2001; C. A. Siler et al., Virology 292:24-34, 2002), and safety concerns have recently been addressed (McGettigan et al., J. Virol. 77:237-244, 2003). However, size limitations of the vectors may restrict their use for development of vaccine applications that require the expression of large and multiple foreign antigens. Here we describe a new RV-based vaccine vehicle expressing 4.4 kb of the human immunodeficiency virus type 1 (HIV-1) Gag-Pol precursor Pr160. Our results indicate that Pr160 is expressed and processed, as demonstrated by immunostaining and Western blotting. Electron microscopy studies showed both immature and mature HIV-1 virus-like particles (VLPs), indicating that the expressed HIV-1 Gag Pr55 precursor was processed properly by the HIV-1 protease. A functional assay also confirmed the cleavage and functional expression of the HIV-1 reverse transcriptase (RT) from the modified RV genome. In the next step, we constructed and recovered a new RV vaccine strain-based vector expressing a chimeric HIV-1(89.6P) RV envelope protein from an additional RV transcription unit located between the RV nucleoprotein (N) and phosphoprotein (P) in addition to HIV-1 Pr160. The 2.2-kb chimeric HIV-1/RV envelope protein is composed of the HIV-1 Env ectodomain (ED) and transmembrane domain (TD) fused to RV glycoprotein (G) cytoplasmic domain (CD), which is required for efficient incorporation of HIV-1 Env into RV particles. Of note, the expression of both HIV-1 Env and HIV-1 Pr160 resulted in an increase in the rhabdoviral genome of >55%. Both rhabdovirus-expressed HIV-1 precursor proteins were functional, as indicated by RT activity and Env-based fusion assays. These findings demonstrate that both multiple and very large foreign genes can be effectively expressed by RV-based vectors. This research opens up the possibility for the further improvement of rhabdovirus-based HIV-1 vaccines and their use to express large foreign proteins, perhaps from multiple human pathogens.

Suppression of HIV-1 Replication by HIV-1-Irrelevant CD8+Cytotoxic T Lymphocytes Resulting in Preservation of Persistently HIV-1-Infected CellsIn Vitro

CD8+ cells of asymptomatic HIV-1 carriers (AC) contain HIV-1-specific cytotoxic T lymphocytes (CTLs) but suppress HIV-1 replication in a class I major histocompatibility complex (MHC-I)-unrestricted manner. In order to selectively investigate the HIV-1-suppressive function of CTLs apart from HIV-1-specific cytotoxicity, HIV-1-irrelevant allo-specific CTLs were established from an HIV-1-uninfected individual and their HIV-1-suppressive activity against autologous CD4+ peripheral blood mononuclear cells (PBMC) was examined. We found that these CTLs significantly suppressed both R5 and X4-HIV-1 replication in either acutely or persistently infected autologous PBMC. Although these CTLs partially killed HIV-1-infected PBMC through Fas ligand, CTLs still suppressed late steps of HIV-1 replication in the presence of neutralizing antibodies to Fas ligand. HIV-1 replication in PBMC that had been suppressed by CTLs was reversible following depletion of CTLs from culture, analogous to the previous observation for CD8+ cell-depleted PBMC of AC. Induction of HIV-1 replication by CTL-depletion was amplified by addition of newly prepared CD4+ cells or activation with staphylococcal enterotoxin B. Our results indicate that CTLs can suppress HIV-1 replication in PBMC in an antigen-nonspecific manner and preserve infected cells in a state capable of restarting HIV-1 replication and transmission.

Most highly exposed seronegative men lack HIV-1-specific, IFN-gamma-secreting T cells

Naturally acquired cellular immunity in individuals who have been exposed to HIV-1 but have remained uninfected may hold clues for the design of an effective HIV vaccine. To determine the presence and nature of such an HIV-1-specific immune response, we evaluated the quantity and fine specificity of HIV-1-reactive IFN-gamma-secreting T cells in a group of highly exposed seronegative men having sex with men. All 46 ES reported frequent unprotected anal sex with known HIV-1-infected partners at enrollment, and high risk activities continued in at least one-half of the volunteers for up to >6 years of observation. Despite the high frequency of unprotected anal intercourse and potential HIV-1 exposure, the vast majority of individuals demonstrated no or very low numbers of HIV-1-specific, IFN-gamma-secreting T cells. Even when HIV-1 epitopes were presented by peptide-pulsed autologous dendritic cells in 15 of the highest risk volunteers, HIV-1-specific T cells remained infrequent, and the proportion of responders was not significantly different from that in a lower risk seronegative control cohort. Only PBMC from two individuals who have remained uninfected to date exhibited distinctly positive responses. However, these responses rarely persisted over time, single epitope specificities were identified in only one volunteer, and HIV-1-specific memory T cell clones did not expand in vitro. HIV-1-specific, IFN-gamma-secreting T cells are thus unlikely to substantially contribute to resistance against infection in most exposed seronegative men having sex with men.

Cross-reactive CD8+ T cell epitopes identified in US adolescent minorities

Vaccines designed to bring forth CD8+ T cell responses in different racial and ethnic groups will require inclusion of T cell epitopes presented by various MHC class I molecules. This study was designed to identify new CD8+ T cell epitopes in HIV-infected African American and Hispanic youth as well as to determine the frequency of responses to both novel and previously described HIV-1 epitopes in a cohort of racially and ethnically diverse individuals. We found 8 MHC class I-restricted CD8+ T cell epitopes that had not been previously described, another 8 epitopes that were restricted by class I alleles not previously associated with these epitopes, and 8 additional epitopes that have been described previously. In a larger cohort, we demonstrated that 11 (69%) of these 16 newly described immunogens were recognized by individuals of different race or ethnicity. Most HIV-1-specific CD8+ T cell epitopes identified were either novel or restricted by alternative MHC class I alleles. Frequent recognition of several of these CTL epitopes in persons of diverse racial backgrounds bodes well for the development of a broadly reactive HIV-1 vaccine.

HIV vaccines 1983-2003

Twenty years after the discovery of HIV, there is still no vaccine. This year, an envelope vaccine aimed at stimulating neutralizing antibodies was unable to protect against infection in phase 3 trials. But more than 20 HIV vaccines designed to stimulate T-cell responses are being developed. Will any of them work?

The influence of HLA genotype on AIDS

Genetic resistance to infectious diseases is likely to involve a complex array of immune-response and other genes with variants that impose subtle but significant consequences on gene expression or protein function. We have gained considerable insight into the genetic determinants of HIV-1 disease, and the HLA class I genes appear to be highly influential in this regard. Numerous reports have identified a role for HLA genotype in AIDS outcomes, implicating many HLA alleles in various aspects of HIV disease. Here we review the HLA associations with progression to AIDS that have been consistently affirmed and discuss the underlying mechanisms behind some of these associations based on functional studies of immune cell recognition.

Expression and immunogenicity of sequence-modified human immunodeficiency virus type 1 subtype B pol and gagpol DNA vaccines

Control of the worldwide AIDS pandemic may require not only preventive but also therapeutic immunization strategies. To meet this challenge, the next generation of human immunodeficiency virus type 1 (HIV-1) vaccines must stimulate broad and durable cellular immune responses to multiple HIV antigens. Results of both natural history studies and virus challenge studies with macaques indicate that responses to both Gag and Pol antigens are important for the control of viremia. Previously, we reported increased Rev-independent expression and improved immunogenicity of DNA vaccines encoding sequence-modified Gag derived from the HIV-1(SF2) strain (J. zur Megede, M. C. Chen, B. Doe, M. Schaefer, C. E. Greer, M. Selby, G. R. Otten, and S. W. Barnett, J. Virol. 74: 2628-2635, 2000). Here we describe results of expression and immunogenicity studies conducted with novel sequence-modified HIV-1(SF2) GagPol and Pol vaccine antigens. These Pol antigens contain deletions in the integrase coding region and were mutated in the reverse transcriptase (RT) coding region to remove potentially deleterious enzymatic activities. The resulting Pol sequences were used alone or in combination with sequence-modified Gag. In the latter, the natural translational frameshift between the Gag and Pol coding sequences was either retained or removed. Smaller, in-frame fusion gene cassettes expressing Gag plus RT or protease plus RT also were evaluated. Expression of Gag and Pol from GagPol fusion gene cassettes appeared to be reduced when the HIV protease was active. Therefore, additional constructs were evaluated in which mutations were introduced to attenuate or inactivate the protease activity. Nevertheless, when these constructs were delivered to mice as DNA vaccines, similar levels of CD8(+) T-cell responses to Gag and Pol epitopes were observed regardless of the level of protease activity. Overall, the cellular immune responses against Gag induced in mice immunized with multigenic gagpol plasmids were similar to those observed in mice immunized with the plasmid encoding Gag alone. Furthermore, all of the sequence-modified pol and gagpol plasmids expressed high levels of Pol-specific antigens in a Rev-independent fashion and were able to induce potent Pol-specific T- and B-cell responses in mice. These results support the inclusion of a gagpol in-frame fusion gene in future HIV vaccine approaches.

Effects of MHC class I on HIV/SIV disease in primates

Data indicate that resistance to HIV-1 disease involves an array of contrasting HLA genotypic effects that are subtle, but significant, particularly when these genetic effects are considered as a whole. Numerous reports attributing a role for HLA genotype in AIDS outcomes have been reported, and a few of these have been affirmed in multiple studies. Functional studies of immune cell recognition have provided clues to the underlying mechanisms behind some of the strongest HLA associations, suggesting the means by which relative resistance or susceptibility to the virus may occur. SIV infection in non-human primates has served as an invaluable model for understanding AIDS pathogenesis (in rhesus monkeys) and viral resistance (in chimpanzee). The effect of rhesus MHC class I molecules on the evolution of SIV has been convincingly described [19], and a recent study in humans has suggested that selection pressure conferred by HLA molecules is responsible for specific genetic variation in HIV-1 [114]. HIV-1 may eventually have conspicuous evolutionary effects on HLA and other AIDS restriction genes, a prolonged process that could have occurred in chimpanzee [92]. To prevent such an outcome, it will be necessary to approach the disease from many perspectives, andapply comprehensively the knowledge gained to the successful control of the virus.

Interleukin 12-augmented T cell proliferation of peripheral blood mononuclear cells from HIV-seropositive individuals is associated with interleukin 12 receptor beta 2 upregulation

Interleukin 12 (IL-12) production is believed to be impaired in individuals with HIV infection and this impairment manifests early in disease, when the CD4(+) cell counts are within normal values. The reduced antigen-specific and mitogen-stimulated T cell-proliferative responses that occur in HIV infection can be corrected by the addition of recombinant human interleukin 12 (rhIL-12). As the IL-12 receptor (IL-12R) is central to the IL-12 signaling pathway, we examined whether the augmentation of antigen-specific proliferation of HIV(+) peripheral blood mononuclear cells (PBMCs) related to altered IL-12R expression. rhIL-12 augmented antigen-specific proliferation of HIV(+) PBMCs but not of HIV(-) PBMCs. Examination of resting PBMCs from HIV(+) and HIV(-) donors showed that neither of these populations expressed IL-12R beta 1 or IL-12R beta 2 chains on their cell surface as detected by flow cytometry. However, examination of mRNA showed that both IL-12R beta 1 and IL-12R beta 2 mRNAs were markedly reduced in HIV(+) PBMCs when compared with HIV(-) PBMCs. After mitogen activation there was an increase in IL-12R beta 1 expression on the cell surface of HIV(+) and HIV(-) PBMCs and this level was not altered by coculture with rhIL-12 or interferon gamma (IFN-gamma). However, coculture of phytohemagglutinin (PHA)-activated HIV(+) or HIV(-) PBMCs with rhIL-12 (but not IFN-gamma) increased IL-12R beta 2 expression on the cell surface of both populations. Examination at the message level showed a correction of IL-12R beta 1 to normal levels with activation that was further enhanced by rhIL-12 coculture for both the HIV(+) and HIV(-) PBMCs. However, although the level of IL-12R beta 2 for the HIV(+) PBMCs was normalized by PHA, rhIL-12 caused a further augmentation. This information provides a strong link between IL-12R upregulation, and the significant improvement in antigen-specific HIV-proliferative responses seen with the addition of rhIL-12. It also reveals that the dysfunction in IL-12R expression seen in cells from HIV(+) patients occurs at the transcriptional level. In addition, we provide further evidence that IL-12R beta 1 and IL-12R beta 2 regulation in human PBMCs is independent of IFN-gamma.

Vaccine for AIDS and Ebola virus infection

Ebola virus and HIV present challenges for vaccine development because natural immunity to these viruses is difficult to find, and there are no immune correlates of protection in humans. Modern molecular genetic, virologic and immune analyses have been used to rationally identify promising approaches based on animal model and human clinical studies. Improved vaccine candidates have been defined for HIV, and a promising Ebola vaccine have conferred protection in non-human primates. Further evaluation in humans will allow an assessment of their potential efficacy and point the way to the development of more successful vaccines.

HIV-1 vaccines: the search continues

This article gives an overview about the development of an HIV-1 vaccine. Tremendous numbers of papers have been published on this topic during the last 10 years, and this article can only touch on the different directions taken toward the development of an HIV-1 vaccine, and not give a complete overview of the entire field.

Repetitive and consistent cervicovaginal exposure to certain viral pathogens appears to protect against their sexual acquisition in some women: potential mechanisms

Several groups have proposed that human female promiscuity or polyandry, with repetitive and consistent cervicovaginal exposure to human immunodeficiency virus type 1 (HIV-1), can lead to protection against sexual acquisition of HIV-1 in some of these women. The mechanism of this phenomenon, the highly exposed persistently HIV-seronegative (HEPS) state, is unknown. Thus far, it has been correlated with viral epitope-specific immune responses in only about half of the women evaluated. But when present, these responses decline rapidly following interruption of pathogen exposure, and correlate with prompt acquisition of HIV. I have extended the concept of HEPS to another sexually transmitted viral pathogen, human papillomavirus (HPV). Supporting clinical and immunological information were identified from a literature search using PubMed as well as several sets of epidemiological data, including longitudinal surveys of HIV-1 incidence among female commercial sex workers (CSWs) in Africa and Thailand, and follow-up of a Danish cohort of CSWs and a large group of Brazilian women, both at high risk for HPV infection. These studies suggest that male-to-female penile-vaginal transmission of at least two viruses, HIV-1 and HPV, is blocked by local mucosal responses, immunologic or otherwise, which require repetitive, uninterrupted exposure to pathogen. Exploration of the mechanisms underlying such ostensibly protective responses may facilitate development of STD vaccines.

Characterization and selection of HIV-1 subtype C isolates for use in vaccine development

HIV-1 genetic diversity among circulating strains presents a major challenge for HIV-1 vaccine development, particularly for developing countries where less sequence information is available. To identify representative viruses for inclusion in candidate vaccines targeted for South Africa, we applied an efficient sequence survey strategy to samples from recently and chronically infected persons residing in potential vaccine trial sites. All 111 sequences were subtype C, including 30 partial gag, 26 partial pol, 27 V2-V3 env, and 28 V5-partial gp41 sequences. Of the 10 viruses cultured from recently infected individuals, 9 were R5 and 1 was R5X4. Two isolates, Du151 and Du422, collected within 2 months of infection, were selected as vaccine strains on the basis of their amino acid similarity to a derived South African consensus sequence The selection of recently transmitted R5 isolates for vaccine design may provide an advantage in a subtype C R5-dominant epidemic. The full-length Du422 gag and Du151 pol and env genes were cloned into the Venezuelan equine encephalitis (VEE) replicon particle (VRP) expression system. Du422 Gag protein expressed from the VRP accumulated to a high level and was immunogenic as demonstrated by cytotoxic T lymphocyte responses in mice vaccinated with gag-VRPs. Optimization of codon use for VRP expression in human cells did not enhance expression of the gag gene. The cloned Du151 env gene encoded a functional protein as demonstrated by fusion of VRP-infected cells with cells expressing CD4 and CCR5. Genes identified in this study have been incorporated into the VEE VRP candidate vaccines targeted for clinical trial in South Africa.

Demystified. Human endogenous retroviruses

Human endogenous retroviruses (HERVs) are a family of viruses within our genome with similarities to present day exogenous retroviruses. HERVs have been inherited by successive generations and it is possible that some have conferred biological benefits. However, several HERVs have been implicated in certain cancers and autoimmune diseases. This article demystifies these retroviruses by providing an insight into HERVs, their means of classification, and a synopsis of HERVs implicated in cancer and autoimmunity. Furthermore, the biological roles of HERVs are explored.

Induction of a strong HIV-specific CD8+ T cell response in mice using a fowlpox virus vector expressing an HIV-1 multi-CTL-epitope polypeptide

Recombinant avipoxvirus vectors are attractive candidates for use in vaccination strategies for infections such as human immunodeficiency virus type 1 (HIV-1), where induction of a CD8+ T cell response is thought to be an important component of protective immunity. Here, we report the expression of a multiepitope polypeptide (TAB9) composed of the central 15 amino acids of the V3 loop from six different isolates of HIV-1 in a fowlpox virus (FWPV) vector, and the use of this vector (FPTAB9LZ) to induce strong HIV-specific CD8+ T cell responses in mice. In animals immunized twice intravenously with FPTAB9LZ, almost 2% of the CD8+ T cells in the spleen were shown to produce IFN-gamma in response to stimulation with HIV-1 peptides 1 week after the second immunization. The most dominant response was to the HIV-1 IIIB peptide. A strong HIV-specific response was also induced by intraperitoneal immunization of mice with FPTAB9LZ, whilst subcutaneous immunization elicited a weaker response. Intraperitoneal immunization with FPTAB9LZ was also shown to provide protection against challenge with a recombinant vaccinia virus expressing antigens, including those in TAB9. These results confirm the potential of FWPV vectors for use in HIV vaccination strategies.

Epitope-vaccine strategy against HIV-1: today and tomorrow

Vaccines play important roles in preventing infectious diseases caused by different pathogens. However, some pathogens such as HIV-1 challenge current vaccine strategy. Poor immunogenicity and the high mutation rate of HIV-1 make great difficulties in inducing potent immune responses strong enough to prevent infection via vaccination. Epitope-vaccine, which could intensively enhance predefined epitope-specific immune responses, was suggested as a new strategy against HIV-1 and HIV-1 mutation. Epitope-vaccines afford powerful approaches to elicit potent, broad and complete immune protection against not only primary homologous viral isolates but also heterologous viral mutants. Although most studies are still preliminary now, epitope-vaccine as a novel strategy against the AIDS epidemic has great developmental potential. To trigger T-cell-dependent IgG antibody responses and improve affinities of the epitope-specific antibodies, approaches such as recombinant multi-epitope-vaccination and prime-boosting vaccination were suggested. Cellular immune responses, especially CTL responses, could also be elicited and enhanced in addition to humoral immune responses. Developed epitope-vaccines activating both arms of the immune system would benefit prevention and immunotherapy not only against HIV but also other chronic infections.

A review of vaccines for HIV prevention

HIV/AIDS has become the most devastating pandemic in recorded history. It has killed 40 million people in the last 20 years and the World Health Organisation estimated that at least 14,000 new infections occurred daily in 2001. There will be up to 100 million new infections in the next 10 years (for current updates, visit http://www.unaids.org/epidemic_update/). Most HIV infections occur in the developing world, and the adverse social and economic impact of the HIV/AIDS pandemic, particularly in the developing world, is unprecedented. Highly active antiretroviral therapy (HAART) has had significant effects on HIV/AIDS in the developed world. The drugs have acted to prolong survival, reduce the viral load, and to alleviate suffering. However, the incidence of side effects and resistance is high and the drugs are unaffordable and unavailable in the developing world. HAART regimens are difficult to comply with. Public health efforts to modify the behaviour, attitude and culture that accelerate the spread of HIV/AIDS have had only modest success. There is urgent need for a prophylactic and/or therapeutic HIV vaccine. This is a review of the obstacles and current trends in HIV vaccine development.

Evaluation of FIV protein-expressing VEE-replicon vaccine vectors in cats

Venezuelan equine encephalitis (VEE) virus-replicon particles (VRP) were used to generate feline immunodeficiency virus (FIV) Gag- and ENV-expressing vaccine vectors. Serum and mucosal FIV-specific antibody was detected in cats immunized subcutaneously, once monthly for 5 months, with FIV-expressing VRP. Expansion of the CD8+ L-selectin negative phenotype and transient CD8+ noncytolytic suppressor activity were seen in cats immunized with FIV-expressing or control VRP. Despite induction of FIV-specific immune responses and nonspecific suppressor responses, all cats became infected following vaginal challenge with high dose, pathogenic cell-associated FIV-NCSU(1) although relative early maintenance of CD4+ cells was seen in FIV-immunized cats.

Neutralizing antibodies mechanism of neutralization and protective activity against HIV-1

The role of the humoral immune response in prevention against HIV-1 infection is still incompletely understood. However, neutralizing antibodies to certain epitopes on HIV-1 envelope glycoproteins inhibit HIV-1 infection in vitro and in vivo. Passive administration of these antibodies by themselves or in combination completely protected hu-PBL-SCID mice or macaques from intravenous, vaginal, as well as maternal-fetal mucosal transmission. All these studies provide direct experimental evidence that neutralizing antibodies are potent enough to prevent HIV infection, and strongly suggest that neutralizing-antibody-based vaccines could provide effective protection against HIV-1, despite the potent action of CTLs. Some neutralizing epitopes have been defined in vitro and in vivo. Unfortunately, none of the neutralizing-antibody-based candidate vaccines has been demonstrated to induce enough protective activity. Weak antigenicity and immunogenicity of neutralizing epitopes on native or recombinant proteins and other factors made it difficult to induce neutralizing-epitope-specific antibody responses in vivo enough to prevent against primary isolates. Recent studies indicated that HIV-1 variations resulted in escape from neutralization or the CTL responses, which may be the principal challenge for HIV-1 prevention. Epitope vaccine as a new strategy activating both arms of the immune system, namely, using the "principal neutralizing epitopes" and the CTL epitopes in combination, should provide new hope for developing an effective vaccine to halt the HIV-1 epidemic.

Polymorphisms of cytotoxic T-lymphocyte (CTL) and T-helper epitopes within reverse transcriptase (RT) of HIV-1 subtype C from Ethiopia and Botswana following selection of antiretroviral drug resistance

Drug resistance is the major limiting factor in the effective therapeutic management of HIV infection with antiretroviral drugs (ARVs). In developing countries, where access to ARVs may be limited, therapeutic vaccine protocols designed to restrict the advent of drug resistance may be of interest. Whereas the immunodominant regions of HIV-1 clade B RT peptides have been well characterized, little is known about potential divergence among RTs of other HIV-1 subtypes. In this study, RT sequence polymorphisms were ascertained in phylogenetically classified subtype C isolates from treatment-nai;ve Ethiopian (n = 5) and Botswanian persons (n = 9). There were clusters of variability in some RT epitopes associated with cytotoxic T lymphocyte (CTL) and helper T cell function within subtype C viruses, although other epitopes remained conserved among subtype C and B viruses. Subtype C mutations associated with drug resistance were identified in vitro, using increasing concentrations of non-nucleoside RT inhibitors (NNRTIs) and nucleoside RT inhibitors (NRTIs). Mutations within immunogenic regions of clade C RT were noted during drug selection of subtype C isolates with nevirapine (S98I, Y181C, V108I and K103N), delavirdine, (A62V, V75E, L100I, K103T, V108I, Y181C), efavirenz (K103E, V106M, V179D, Y188C/H, G190A), lamivudine (M184I, M184V), and zidovudine (K70R), respectively. Further characterization of predicted CTL and T-helper anchor motifs and ARV-induced mutations in HIV-1 non-B subtype RTs is warranted.

Differences between T cell epitopes recognized after immunization and after infection

Evidence suggests that cellular immune responses play a crucial role in the control of HIV and SIV replication in infected individuals. Several vaccine strategies have therefore targeted these CD8(+) and CD4(+) responses. Whether vaccination induces the same repertoire of responses seen after infection is, however, a key unanswered question in HIV vaccine development. We therefore compared the epitope specificity induced by vaccination to that present postchallenge in the peripheral blood. Intracellular cytokine staining of PBMC stimulated with overlapping 15/20-mer peptides spanning the proteins of SIV were measured after DNA/modified vaccinia Ankara vaccination of eight rhesus macaques. Lymphocytes from 8 animals recognized a total of 39 CD8 epitopes and 41 CD4 epitopes encoded by the vaccine. T cell responses were again monitored after challenge with SIVmac239 to investigate the evolution of these responses. Only 57% of all CD8(+) T cell responses and 19% of all CD4(+) T cell responses present after vaccination were recalled after infection as measured in the peripheral blood. Interestingly, 29 new CD8 epitopes and 5 new CD4 epitopes were recognized by PBMC in the acute phase. These new epitopes were not detected after vaccination, and only some of them were maintained in the chronic phase (33% of CD8 and no CD4 responses). Additionally, 24 new CD8 epitopes and 7 new CD4 epitopes were recognized by PBMC in the chronic phase of infection. The repertoire of the immune response detected in the peripheral blood after immunization substantially differed from the immune response detected in the peripheral blood after infection.

Sustained peptide-specific gamma interferon T-cell response in rhesus macaques immunized with human immunodeficiency virus gag DNA vaccines

We examined the influence of dose and method of antigen delivery on the dynamics and durability of T-cell responses to candidate human immunodeficiency virus (HIV) vaccines. Codon-optimized sequences from the HIV gag gene were inserted into alternative DNA vaccine vectors to express the coding sequence with or without the tissue plasminogen activator leader sequence. We delivered the vaccines by intramuscular injection as plasmid DNA without adjuvant or as plasmid DNA formulated with a novel block copolymer adjuvant (CRL8623) and then monitored the ensuing T-cell responses by using a gamma interferon enzyme-linked immunospot assay. We demonstrated persistence of the cell-mediated immune (CMI) response in rhesus macaques for at least 18 months following a four-dose vaccination regimen. The plasmid vaccine, with or without CRL8623, was immunogenic in macaques; however, the form coadministered with adjuvant exhibited improved T-cell responses, with a bias toward more antigen-specific CD8(+) T cells. Finally, we examined the fine specificity of the T-cell response to the gag vaccines by testing the response of 23 vaccinated macaques to individual Gag 20-mer peptides. Collectively, the monkeys responded to 25 epitopes, and, on average, each monkey recognized a minimum of 2.7 epitopes. The results indicate that a broad and durable CMI response to HIV DNA vaccines can be induced in a relevant nonhuman primate model.

Magnitude and frequency of cytotoxic T-lymphocyte responses: identification of immunodominant regions of human immunodeficiency virus type 1 subtype C

A systematic analysis of immune responses on a population level is critical for a human immunodeficiency virus type 1 (HIV-1) vaccine design. Our studies in Botswana on (i) molecular analysis of the HIV-1 subtype C (HIV-1C) epidemic, (ii) frequencies of major histocompatibility complex class I HLA types, and (iii) cytotoxic T-lymphocyte (CTL) responses in the course of natural infection allowed us to address HIV-1C-specific immune responses on a population level. We analyzed the magnitude and frequency of the gamma interferon ELISPOT-based CTL responses and translated them into normalized cumulative CTL responses. The introduction of population-based cumulative CTL responses reflected both (i) essentials of the predominant virus circulating locally in Botswana and (ii) specificities of the genetic background of the Botswana population, and it allowed the identification of immunodominant regions across the entire HIV-1C. The most robust and vigorous immune responses were found within the HIV-1C proteins Gag p24, Vpr, Tat, and Nef. In addition, moderately strong responses were scattered across Gag p24, Pol reverse transcriptase and integrase, Vif, Tat, Env gp120 and gp41, and Nef. Assuming that at least some of the immune responses are protective, these identified immunodominant regions could be utilized in designing an HIV vaccine candidate for the population of southern Africa. Targeting multiple immunodominant regions should improve the overall vaccine immunogenicity in the local population and minimize viral escape from immune recognition. Furthermore, the analysis of HIV-1C-specific immune responses on a population level represents a comprehensive systematic approach in HIV vaccine design and should be considered for other HIV-1 subtypes and/or different geographic areas.

HLA typing in a Kenyan cohort identifies novel class I alleles that restrict cytotoxic T-cell responses to local HIV-1 clades

OBJECTIVES

To investigate HLA class I allele frequencies in a Kenyan commercial sex worker (CSW) cohort, and to examine HIV-1 specific cytotoxic T lymphocyte (CTL) responses directed against epitopes derived from locally prevalent clade A virus.

METHODS

PCR-single strand polymorphism HLA class I typing. Sequencing of novel alleles and examination of their distribution in the CSW cohort, and a low risk HIV uninfected cohort. The peptide-binding motif of a novel class I allele was predicted, and a panel of candidate CTL epitopes was synthesized whose functional significance was examined using ELISpot and Cr release assays.

RESULTS

Class I HLA-A and B frequencies within the cohort are presented. Two novel class I alleles were found, HLA-B*4415 and HLA-Cw*0407. These two class I alleles were relatively common, both in the CSW cohort (2.1% and 3.3% respectively) and in a cohort of lower risk women (1.9% and 3.8% respectively). Allele HLA-B*4415 restricted CTL responses against a novel epitope (EEKAFSPEV) derived from p24 of clade A HIV-1, and HLA-Cw0407 restricted CTL against a predefined HLA-Cw*0401 gp120 epitope.

CONCLUSIONS

Multi-epitope vaccine design requires knowledge of HLA class I distribution and HIV CTL epitope characterization in potential target populations. The description of two novel HLA class I alleles at high frequency in this high risk Kenyan CSW cohort suggests that HLA mapping of vaccine cohorts and subsequent characterization of local CTL epitopes will be warranted prior to vaccine trials.

Boosting of SIV-specific T cell responses in rhesus macaques that resist repeated intravaginal challenge with SIVmac251

Despite repeated high-risk exposure to infectious HIV-1, some individuals remain HIV-1 seronegative and apparently uninfected. The use of nonhuman primate model systems to study SIVmac transmission may help to elucidate the factors responsible for protection in exposed, seronegative (ESN) humans. In an earlier vaccination study, three control rhesus macaques that were exposed to three sequential intravaginal challenges with pathogenic SIVmac251 failed to show evidence of infection after 5 years of observation. 51Cr release assay results suggested that these animals had low-level cytotoxic T lymphocyte responses to SIVmac proteins. We hypothesized that these responses might be an important component of protection from mucosal challenge. We performed an additional intravaginal challenge of all three macaques and monitored SIV-specific T cell responses in peripheral blood, using the sensitive enzyme-linked immunospot (ELISpot) assay. After the fourth challenge, one animal became infected; this animal did not mount a strong SIV-specific T cell response. Two other macaques remained uninfected as determined by peripheral blood mononuclear cell (PBMC) coculture, polymerase chain reaction (PCR), and branched DNA (bDNA) analysis of peripheral blood and lymphoid tissues, but demonstrated boosting of SIV-specific T cell responses after challenge. These results support a protective role for SIVmac-specific T cells in repeatedly exposed, persistently seronegative rhesus macaques.

The ELISPOT assay: an easily transferable method for measuring cellular responses and identifying T cell epitopes

Characterization of human leukocyte antigen (HLA) class I restricted epitopes derived from viral pathogens is imperative for formulating therapeutic interventions, as well as for vaccine design and monitoring. Sensitive, easy and cost-effective assays that measure the frequency of antigen-specific T lymphocytes are crucial for evaluating and improving vaccines and therapies. This paper reviews the ELISPOT technique that allows for quantifying HIV-specific T lymphocytes at the single cell level from peripheral blood by detection of antigen-induced cytokine secretion. The assay can be used successfully to quantify T cell immune responses in humans infected with different pathogens and to assess T cell immunogenicity of vaccines in phase I/II and III clinical trials. This review focuses on the ELISPOT methodology and discusses how it can be standardized and potentially used by multiple international laboratories attached to clinical trial sites.

CD8+ T-cell immunity to HIV infection

Fifteen years after the first, definitive reports of HIV-1-specific, CD8+ T cells [147,148], there is ample evidence for the importance of these cells in control of HIV-1 infection. As much is known of their role in the natural history of HIV-1 infection and their cellular and molecular mechanisms of reactivity than of T-cell responses to any other human virus. Indeed, HIV-1-related research has led the scientific field in revealing many new, fundamental principles of cellular immunity in the last 15 years. From these data, there are multiple, posited mechanisms for loss of CD8+ T-cell control of HIV-1 infection. These include both intrinsic defects in T-cell function and loss of T-cell recognition of HIV-1 because of its extraordinary genetic diversity and disruption of antigen presentation. Efforts have begun on devising approaches to reverse these immune defects in infected individuals and develop vaccines that induce T-cell immunity for protection from infection. Combination antiretroviral drug regimens now provide exceptional, long-lasting control of HIV-1 infection, even though they do not restore anti-HIV-1 T-cell immunity fully in persons with chronic HIV-1 infection. Very encouraging results show that such treatment can maintain normal T-cell reactivity specific for this virus in some persons with early HIV-1 infection. Unfortunately, the antiviral treatment does not cure the host of this persistent, latent virus. This has led to new strategies for immunotherapeutic intervention to enhance the level and breadth of the T-cell repertoire specific for the host's residual virus in persons with chronic HIV-1 infection. Although the principles of immunotherapy stem from early in the last century, modern era approaches are integrating highly sophisticated, molecular and cell biology reagents and methods for control of HIV-1 infection. The most promising immunotherapies are autologous virus activated in vivo by STI or administered in autologous DC that have been engineered ex vivo. There are also compelling rationales supported by animal models and early clinical trials for use of cytokines and chemokines as recombinant proteins or DNA to augment anti-HIV-1 T-cell reactivity and trafficking of T cells and APC to tissue sites of infection. For prevention of HIV-1 infection, the discouragingly poor results of vaccine development in the late 1980s and early 1990s have led to very encouraging, recent studies in monkeys that show partially protective and possibly sterilizing immunity. Finally, clinical trials of new-generation DNA and live vector vaccines already have indications of improved induction of HIV-1-specific T-cell responses. Knowledge of HIV-1-specific T-cell immunity and its role in protection from HIV-1 infection and disease must continue to expand until the goal of complete control of HIV-1 infection is accomplished.

HIV-specific CD8 T-cell activity in uninfected injection drug users is associated with maintenance of seronegativity

OBJECTIVES

To determine whether HIV-exposed, uninfected subjects (EUs) having HIV-specific effector activity are at a reduced risk for seroconverting compared with EUs with no HIV-specific effector responses.

DESIGN

Twenty-eight intravenous drug users (IVDU) with documented risk for HIV infection over a 1-year period were screened for the presence of HIV-specific CD8+ effector cell activity. Group I included 18 IVDUs who remained seronegative despite exposure to HIV through needle sharing with partner(s) known to be HIV infected. Group II included 10 IVDUs who seroconverted after similar HIV exposure.

METHODS

The enzyme-linked immunospot (ELIspot; Mabtech AB, Nacka, Sweden) assay was used to measure the frequency of HIV-specific interferon-gamma secreting cells. Peripheral blood mononuclear cells (PBMC) were stimulated with a panel of synthetic HIV peptides in a major histocompatibility complex class I antigen-restricted fashion. PBMC from group II were obtained from timepoints 7 months or less before seroconversion.

RESULTS

Twelve of 18 (66.7%) persistently seronegative subjects versus none of 10 seroconverters exhibited detectable HIV-specific effector responses at the sampling date (P < 0.001; Fisher's exact test). This represents an odds ratio of 40.38 (95% confidence intervals 2.95 to > 3000).

CONCLUSION

EUs who have developed HIV-specific effector responses are at a reduced risk for seroconversion compared with EUs who do not develop this type of immunity. This observation supports the hypothesis that HIV-specific effector responses are a correlate of immune protection from HIV infection.

High HIV-1 genetic diversity in Cuba

BACKGROUND

HIV-1 subtype B is largely predominant in the Caribbean, although other subtypes have been recently identified in Cuba.

OBJECTIVES

To examine HIV-1 genetic diversity in Cuba.

METHODS

The study enrolled 105 HIV-1-infected individuals, 93 of whom had acquired the infection in Cuba. DNA from peripheral blood mononuclear cells was used for polymerase chain reaction amplification and sequencing of pol (protease-reverse transcriptase) and env (V3 region) segments. Phylogenetic trees were constructed using the neighbour-joining method. Intersubtype recombination was analysed by bootscanning.

RESULTS

Of the samples, 50 (48%) were of subtype B and 55 (52%) of diverse non-B subtypes and recombinant forms. Among non-B viruses, 12 were non-recombinant, belonging to six subtypes (C, D, F1, G, H and J), the most frequent of which was subtype G (n = 5). The remaining 43 (78%) non-B viruses were recombinant, with 14 different forms, the two most common of which were Dpol/Aenv (n = 21) and U(unknown)pol/Henv (n = 7), which grouped in respective monophyletic clusters. Twelve recombinant viruses were mosaics of different genetic forms circulating in Cuba. Overall, 21 genetic forms were identified, with all known HIV-1 group M subtypes present in Cuba, either as non-recombinant viruses or as segments of recombinant forms. Non-B subtype viruses were predominant among heterosexuals (72%) and B subtype viruses among homo- or bisexuals (63%).

CONCLUSION

An extraordinarily high diversity of HIV-1 genetic forms, unparalleled in the Americas and comparable to that found in Central Africa, is present in Cuba.

Molecular epidemiology of HIV-1 genetic forms and its significance for vaccine development and therapy

Since their initial expansion in human beings roughly seven decades ago in central Africa, the HIV-1 pandemic strains have diversified extensively through mutation and recombination. 24 circulating genetic forms of the main HIV-1 group are presently recognised, including 11 subtypes or sub-subtypes and 13 circulating recombinant forms. New genetic forms are being introduced in different areas of the world, changing the molecular epidemiology of the infection. It is generally agreed that the control of the HIV-1 pandemic requires the development of vaccines that efficiently protect against the range of HIV-1 genetic forms. The introduction of effective antiretroviral therapies in areas of high HIV-1 prevalence may also contribute to the control of the pandemic, as has been documented in developed countries. Efficient targeting of the extensive genetic diversity of HIV-1 constitutes one of the major challenges in present efforts against the pandemic, although the significance of HIV-1 genetic forms for vaccine development and therapy remains to be defined.

HIV Vaccines: Biological and Clinical Considerations

The discovery of an HIV-1 vaccine is a high priority. Recent advances in HIV vaccine development include an improved understanding about virus biology and structure, and the development of quantitative techniques that enable a detailed analysis of vaccine-induced immune responses in humans. The preclinical vaccine pipeline looks healthy, and a common feature of the new vaccine strategies is their ability to attenuate clinical disease rather than prevent HIV infection in nonhuman primates. Human clinical trials to evaluate the safety and immunogenicity of these vaccine candidates and strategies are being actively pursued.