HIV-specific cytotoxic T-cells in HIV-exposed but uninfected Gambian women

Comparison of sexual behavior and HIV risk between two HIV-1 serodiscordant couple cohorts: the CHAVI 002 study

BACKGROUND

The CHAVI002 study was designed to characterize immune responses, particularly HIV-specific T-cell responses, amongst 2 cohorts of HIV-exposed seronegative (HESN) individuals. The absence of a clear definition of HESNs has impaired comparison of research within and between such cohorts. This report describes two distinct HESN cohorts and attempts to quantify HIV exposure using a 'HIV risk index' (RI) model.

METHODS

HIV serodiscordant couples (UK; 24, Uganda; 72) and HIV unexposed seronegative (HUSN) controls (UK; 14, Uganda; 26 couples, 3 individuals) completed sexual behavior questionnaires every 3 months over a 9 month period. The two cohorts were heterogeneous, with most HESNs in the UK men who have sex with men (MSM), while all HESNs in Uganda were in heterosexual relationships. Concordance of responses between partners was determined. Each participant's sexual behavior score (SBS) was estimated based on the number and type of unprotected sex acts carried out in defined time periods. Independent HIV acquisition risk factors (partner plasma viral load, STIs, male circumcision, pregnancy) were integrated with the SBS, generating a RI for each HESN.

RESULTS

96 HIV serodiscordant couples completed 929 SBQs. SBSs remained relatively stable amongst the UK cohort, whilst decreasing from Visit 1 to 2 in the Ugandan cohort. Compared to the Ugandan cohort, SBSs and RIs in the UK cohort were lower at visit 1, and generally higher at later visits. Differences between the cohorts, with lower rates of ART use in Uganda and higher risk per-act sex in the UK, had major impacts on the SBSs and RIs of each cohort. There was one HIV transmission event in the UK cohort.

CONCLUSIONS

Employment of a risk quantification model facilitated quantification and comparison of HIV acquisition risk across two disparate HIV serodiscordant couple cohorts.

Anti-HPV16 E2 protein T-cell responses and viral control in women with usual vulvar intraepithelial neoplasia and their healthy partners

T-cell responses (proliferation, intracellular cytokine synthesis and IFNγ ELISPOT) against human papillomavirus 16 (HPV16) E2 peptides were tested during 18 months in a longitudinal study in eight women presenting with HPV16-related usual vulvar intraepithelial neoplasia (VIN) and their healthy male partners. In six women, anti-E2 proliferative responses and cytokine production (single IFNγ and/or dual IFNγ/IL2 and/or single IL2) by CD4+ T lymphocytes became detectable after treating and healing of the usual VIN. In the women presenting with persistent lesions despite therapy, no proliferation was observed. Anti-E2 proliferative responses were also observed with dual IFNγ/IL2 production by CD4+ T-cells in six male partners who did not exhibit any genital HPV-related diseases. Ex vivo IFNγ ELISPOT showed numerous effector T-cells producing IFNγ after stimulation by a dominant E2 peptide in all men and women. Since the E2 protein is absent from the viral particles but is required for viral DNA replication, these results suggest a recent infection with replicative HPV16 in male partners. The presence of polyfunctional anti-E2 T-cell responses in the blood of asymptomatic men unambiguously establishes HPV infection even without detectable lesions. These results, despite the small size of the studied group, provide an argument in favor of prophylactic HPV vaccination of young men in order to prevent HPV16 infection and viral transmission from men to women.

PREDICTING THE PROBABILITY OF PERSISTENCE OF HIV INFECTION WITH THE STANDARD MODEL

It is not well understood why the transmission of HIV may have a small probability of occurrence despite frequent high risk exposures or ongoing contact between members of a discordant couple. We explore the possible contributions made by distributions of system parameters beginning with the standard three-component differential equation model for the growth of a HIV virion population in an infected host in the absence of drug therapy. The overall dynamical behavior of the model is determined by the set of values of six parameters, some of which describe host immune system properties and others which describe virus properties. There may be one or two critical points whose natures play a key role in determining the outcome of infection and in particular whether the HIV population will persist or become extinct. There are two cases which may arise. In the first case, there is only one critical point P1at biological values and this is an asymptotically stable node. The system ends up with zero virions and so the host becomes HIV-free. In the second case, there are two critical points P1and P2at biological values. Here P1is an unstable saddle point and P2is an asymptotically stable spiral point with a non-zero virion level. In this case the HIV population persists unless parameters change. We let the parameter values take random values from distributions based on empirical data, but suitably truncated, and determine the probabilities of occurrence of the various combinations of critical points. From these simulations the probability that an HIV infection will persist, across a population, is estimated. It is found that with conservatively estimated distributions of parameters, within the framework of the standard 3-component model, the chances that a within-host HIV population will become extinct is between 0.6% and 6.9%. With less conservative parameter estimates, the probability is estimated to be as high as 24%. The many complicating factors related to the transmission and possible spontaneous elimination of the virus and the need for experimental data to clarify whether transient infections may occur are discussed. More realistic yet complicated higher dimensional models are likely to yield smaller probabilities of extinction.

Dissecting the HIV-specific immune response: a systems biology approach

PURPOSE OF REVIEW

Several unique HIV-infected or HIV-resistant cohorts have been studied over the years to try and delineate the correlates of protection. Although several mechanisms have been put forward, studies aiming to integrate the different mechanisms into a comprehensive model are still lacking. Current systems biology approaches emphasize the importance of unifying independent datasets, provide tools that facilitate hypothesis formulation and testing, and direct us toward uncovering novel therapeutic targets by defining molecular networks perturbed during disease. This review will focus on the current findings that utilized systems biology techniques in order to identify correlates of protection from HIV disease progression and resistance to infection in unique cohorts of individuals as well as in nonhuman primate models of SIV infection.

RECENT FINDINGS

Using systems biology technologies and data analysis tools, the studies described herein have found that pathways implicated in survival, cell cycling, inflammation, and oxidative stress work in unison to limit pathology caused by chronic immune activation. This situation favors the survival of effector lymphocytes and limits the dissemination of viral particles in HIV elite controllers, exposed-uninfected individuals, and natural hosts of SIV infection.

SUMMARY

Systems and computational biology tools have clearly expanded our understanding of HIV pathogenesis by unifying independent observations and by giving us novel molecular targets to pursue. These molecular signatures have the potential to uncover correlates of protection in HIV disease and, in the era of personalized medicine, to determine predictive signatures of treatment efficacy and/or failure.

Microarray analysis of HIV resistant female sex workers reveal a gene expression signature pattern reminiscent of a lowered immune activation state

To identify novel biomarkers for HIV-1 resistance, including pathways that may be critical in anti-HIV-1 vaccine design, we carried out a gene expression analysis on blood samples obtained from HIV-1 highly exposed seronegatives (HESN) from a commercial sex worker cohort in Nairobi and compared their profiles to HIV-1 negative controls. Whole blood samples were collected from 43 HIV-1 resistant sex workers and a similar number of controls. Total RNA was extracted and hybridized to the Affymetrix HUG 133 Plus 2.0 micro arrays (Affymetrix, Santa Clara CA). Output data was analysed through ArrayAssist software (Agilent, San Jose CA). More than 2,274 probe sets were differentially expressed in the HESN as compared to the control group (fold change ≥1.3; p value ≤0.0001, FDR <0.05). Unsupervised hierarchical clustering of the differentially expressed genes readily distinguished HESNs from controls. Pathway analysis through the KEGG signaling database revealed a majority of the impacted pathways (13 of 15, 87%) had genes that were significantly down regulated. The most down expressed pathways were glycolysis/gluconeogenesis, pentose phosphate, phosphatidyl inositol, natural killer cell cytotoxicity and T-cell receptor signaling. Ribosomal protein synthesis and tight junction genes were up regulated. We infer that the hallmark of HIV-1 resistance is down regulation of genes in key signaling pathways that HIV-1 depends on for infection.

Alteration of CD8+ T cell effector diversity during HIV-1 infection with discordant normalization in effective antiretroviral therapy

BACKGROUND

Although the impairment of HIV-specific T lymphocytes is evident during chronic HIV-infection, it is unclear whether the increased CD8+ T cells associates with either selective or overall change of effector functional phenotype. Instead of study on HIV-specific T cells only, analyzing bulk T cell populations represent a neglected area of T cell impairment, which go far beyond HIV-specific T cells.

METHODS

In this study, we determined the diversity of CD8+ T cells in term of cytolytic molecule expression (perforin, granzyme A, and granzyme B) and cytokine production ability (IFN-gamma, TNF-alpha, and IL-2) using intracellular staining and flow cytometry technique. The results were compared between healthy individuals, untreated, and antiretroviral therapy (ART) treated HIV infected patients.

RESULTS

We demonstrated the presence of four different subsets of CD8+ T cells that expressed different combinations of cytolytic molecules. We also identified seven different subsets of cytokine producing cells based on different combination of IFN-gamma, TNF-alpha, and IL-2. Results showed significant alterations of these cell subsets that expressed different combination of cytolytic effector molecules or cytokines in HIV infected patients. Furthermore, cytolytic molecule expressing cell subsets are not normalized in effective ART treated patients, whereas the selective population of cytokine producing cells returned to normal value.

CONCLUSIONS

The effector diversity of CD8+ T cells changed in HIV infected patients. Although effective ART altered functional diversity of these cells, long-term suppression of viral replication may be required to normalize the selected CD8+ T cell effector phenotype in HIV infected patients.

Effect of multiple infection of cells on the evolutionary dynamics of HIV in vivo: implications for host adaptation mechanisms

The dynamics between human immunodeficiency virus type 1 and the immune system have been studied both experimentally and mathematically, exploring aspects of host adaptation and viral mechanisms to escape host control. The majority of this work, however, has been performed assuming that any cell can only be infected by one copy of the virus. In recent years, it has become clear that multiple copies of the virus can infect the same cell, a process we refer to as co-infection. Here, we review this topic and discuss how immune control of the infection and the ability of the virus to escape immune control is affected by co-infection.

Phylogenetic analysis consistent with a clinical history of sexual transmission of HIV-1 from a single donor reveals transmission of highly distinct variants

BACKGROUND

To combat the pandemic of human immunodeficiency virus 1 (HIV-1), a successful vaccine will need to cope with the variability of transmissible viruses. Human hosts infected with HIV-1 potentially harbour many viral variants but very little is known about viruses that are likely to be transmitted, or even if there are viral characteristics that predict enhanced transmission in vivo. We show for the first time that genetic divergence consistent with a single transmission event in vivo can represent several years of pre-transmission evolution.

RESULTS

We describe a highly unusual case consistent with a single donor transmitting highly related but distinct HIV-1 variants to two individuals on the same evening. We confirm that the clustering of viral genetic sequences, present within each recipient, is consistent with the history of a single donor across the viral env, gag and pol genes by maximum likelihood and bayesian Markov Chain Monte Carlo based phylogenetic analyses. Based on an uncorrelated, lognormal relaxed clock of env gene evolution calibrated with other datasets, the time since the most recent common ancestor is estimated as 2.86 years prior to transmission (95% confidence interval 1.28 to 4.54 years).

CONCLUSION

Our results show that an effective design for a preventative vaccine will need to anticipate extensive HIV-1 diversity within an individual donor as well as diversity at the population level.

The nonnucleoside reverse transcriptase inhibitor MIV-150 in carrageenan gel prevents rectal transmission of simian/human immunodeficiency virus infection in macaques

Development of a microbicide that prevents rectal transmission of human immunodeficiency virus (HIV) is a vital component in reducing HIV spread. We recently demonstrated that a formulation of the nonnucleoside reverse transcriptase inhibitor (NNRTI) MIV-150 in carrageenan reduced vaginal infection of macaques with simian immunodeficiency virus SIVmac239 with HIV-1(HxB2) reverse transcriptase (SHIV-RT). Herein, we performed the first testing of MIV-150-carrageenan against rectal infection. Rhesus macaques were treated rectally with MIV-150-carrageenan or methyl cellulose (MC) placebo gel up to 4 h prior to rectal challenge with 10³ or 10(4) 50% tissue culture infective doses (TCID₅₀) of SHIV-RT. Infection was assessed by measuring plasma virus RNA as well as T and B cell responses. MIV-150-carrageenan protected all animals challenged with 10³ TCID(₅₀ when gel was applied either 30 min or 4 h prior to challenge, while 100% of the MC-treated animals became infected (n = 4 each; P < 0.03). Partial protection (2 of 4 animals) by MIV-150-carrageenan was observed for rectal challenge with 10-fold more virus applied 4 h after the gel. Sequencing of the RT gene from plasma virus RNA isolated at peak viremia confirmed that both of these animals (like infected MC controls) were infected with wild-type virus. Infection correlated with the development of SIV-specific T and B cell responses. MIV-150 was detected in the rectal fluids and tissues 4 h after gel application but was not detected in the blood at any time (0.5 to 24 h). These data are promising for the development of NNRTI-containing gels to prevent rectal HIV transmission.

Quantifying sexual exposure to HIV within an HIV-serodiscordant relationship: development of an algorithm

BACKGROUND

The risk of acquiring HIV from a single sexual contact varies enormously reflecting biological and behavioural characteristics of both infected and uninfected partners. Accurate information on HIV transmission risk is required to construct evidence-based risk reduction practices for individuals, to direct the provision of prevention strategies at the population level, and enable the definition, quantification and comparison of true exposure in individuals termed 'exposed uninfected' within clinical trials.

METHODS

Following a systematic review of current literature on HIV transmission estimates, an HIV risk score was developed, incorporating weighted risk factors into a Bernoulli mathematical model, allowing quantification of overall risk of HIV acquisition within HIV-serodiscordant partnerships.

RESULTS

The HIV risk score enumerates the relative risk of HIV acquisition from HIV-positive partners incorporating the type and frequency of specific sex acts, the index case HIV plasma viral load and stage of disease, and the presence of genital ulcer disease in either partner and pregnancy, HSV-2 seropositivity, and circumcision status (men only) in the HIV-negative partner.

CONCLUSION

Key determinants of HIV exposure risk can be incorporated into a mathematical model in order to quantify individual relative risks of HIV acquisition. Such a model can facilitate comparisons within clinical trials of exposed uninfected individuals and facilitate interventions to reduce HIV transmission.

Differences in HIV-specific T cell responses between HIV-exposed and -unexposed HIV-seronegative individuals

HIV-1-specific T lymphocyte responses in individuals exposed to HIV-1 but who remain persistently seronegative (HESNs) have been reported in some but not all previous studies. This study was designed to resolve unequivocally the question of whether HESNs make HIV-1-specific T cell responses. We performed a blind investigation to measure HIV-1-specific T cell responses in both HIV-1-serodiscordant couples and HIV-1-unexposed seronegative controls (HUSNs). We found low-frequency HIV-1-specific T cells in both HESNs and HUSNs but show that the response rates were higher over time in the former (P = 0.01). Furthermore, the magnitudes of the HIV-1-specific T cell responses were significantly higher among responding HESNs than among HUSNs over time (P = 0.002). In both groups, responses were mediated by CD4 T cells. The responses were mapped to single peptides, which often corresponded to epitopes restricted by multiple HLA-DR types that have previously been detected in HIV-1-infected patients. HIV-1-specific T cell responses in HUSNs and some HESNs likely represent cross-reactivity to self or foreign non-HIV-1 antigens. The significantly greater T cell responses in HESNs, including in two who were homozygous for CCR5Δ32, demonstrates that HIV-1-specific T cell responses can be induced or augmented by exposure to HIV-1 without infection.

Absence of reproducibly detectable low-level HIV viremia in highly exposed seronegative men and women

OBJECTIVE

Transient HIV infections have been invoked to account for the cellular immune responses detected in highly virus-exposed individuals who have remained HIV-seronegative. We tested for very low levels of HIV RNA in 524 seronegative plasma samples from 311 highly exposed women and men from three longitudinal HIV cohorts.

DESIGN

Two thousand and seventy-three transcription-mediated amplification (TMA) HIV RNA tests were performed for an average of 3.95 TMA assays per plasma sample. Quadruplicate TMA assays, analyzing a total of 2 ml of plasma, provided an estimated sensitivity of 3.5 HIV RNA copies/ml.

RESULTS

Four samples from individuals who did not seroconvert within the following 6 months were positive for HIV RNA. For one sample, human polymorphism DNA analysis indicated a sample mix-up. Borderline HIV RNA detection signals were detected for the other three positive samples but further replicate TMA testing yielded no positive results. Nested PCR assays (n = 254) for HIV proviral DNA in peripheral blood mononuclear cells (PBMCs) from these three individuals were negative.

CONCLUSION

Transient viremia was not reproducibly detected in highly HIV-exposed seronegative men and women. If transient infections do occur, plasma HIV RNA levels may remain below the detection limits of the sensitive assay used here, be of very short duration, or viral replication may be restricted to mucosal surfaces or their draining lymphoid tissues.

A phase I trial of preventive HIV vaccination with heterologous poxviral-vectors containing matching HIV-1 inserts in healthy HIV-uninfected subjects

We evaluated replication-defective poxvirus vectors (modified vaccinia Ankara [MVA] and fowlpox [FPV]) in a homologous and heterologous vector prime-boost vaccination regimen containing matching HIV inserts (MVA-HIV and FPV-HIV) given at months 0, 1, 3, 5 and 7 in 150 healthy HIV-negative vaccinia-naïve participants. FPV-HIV alone was poorly immunogenic, while the high dose (10(9)pfu/2 ml) of MVA-HIV alone elicited maximal responses after two injections: CD4+ and CD8+ T-cell responses in 26/55 (47.3%) and 5/60 (8.3%) of participants, respectively, and IFN-γ ELISpot responses in 28/62 (45.2%). The infrequent CD8+ T-cell responses following MVA-HIV priming were boosted only by the heterologous (FPV-HIV) construct in 14/27 (51.9%) of participants post 4th vaccination. Alternatively, HIV envelope-specific binding antibodies were demonstrated in approximately two-thirds of recipients of the homologous boosting regimen, but in less than 20% of subjects after the heterologous vector boost. Thus, a heterologous poxvirus vector prime-boost regimen can induce HIV-specific CD8+ T-cell and CD4+ T-cell responses, which may be an important feature of an optimal regimen for preventive HIV vaccination.

Living in a house of cards: re-evaluating CD8+ T-cell immune correlates against HIV

The Merck STEP and the Thai RV144 human immunodeficiency virus (HIV) vaccine trials confirmed that we still have a long way to go before developing a prophylactic HIV vaccine. The main issue at hand is that we have yet to identify an immunological correlate of protection against HIV. While many question the T-cell-based approach towards vaccine development, it is likely that T cells will be a necessary part of any vaccine strategy. CD8(+) T cells remain an attractive option because of their ability to specifically recognize and eliminate virally infected host cells. In this review, we recapitulate the evidence for CD8(+) T cells as an immunological correlate against HIV, but more importantly, we assess the means by which we evaluate their antiviral capacity. To achieve a breakthrough in the domain of T-cell-based HIV vaccine development, it has become abundantly clear that we must overhaul our system of immune monitoring and come up with a 'rational' tactic to evaluate the efficacy of HIV-specific CD8(+) T cells.

CD26/dipeptidyl peptidase IV (CD26/DPPIV) is highly expressed in peripheral blood of HIV-1 exposed uninfected female sex workers

Background

Design of effective vaccines against the human immunodeficiency virus (HIV-1) continues to present formidable challenges. However, individuals who are exposed HIV-1 but do not get infected may reveal correlates of protection that may inform on effective vaccine design. A preliminary gene expression analysis of HIV resistant female sex workers (HIV-R) suggested a high expression CD26/DPPIV gene. Previous studies have indicated an anti-HIV effect of high CD26/DPPIV expressing cells in vitro. Similarly, high CD26/DPPIV protein levels in vivo have been shown to be a risk factor for type 2 diabetes. We carried out a study to confirm if the high CD26/DPPIV gene expression among the HIV-R were concordant with high blood protein levels and its correlation with clinical type 2 diabetes and other perturbations in the insulin signaling pathway.

Results

A quantitative CD26/DPPIV plasma analysis from 100 HIV-R, 100 HIV infected (HIV +) and 100 HIV negative controls (HIV Neg) showed a significantly elevated CD26/DPPIV concentration among the HIV-R group (mean 1315 ng/ml) than the HIV Neg (910 ng/ml) and HIV + (870 ng/ml, p < 0.001). Similarly a FACs analysis of cell associated DPPIV (CD26) revealed a higher CD26/DPPIV expression on CD4+ T-cells derived from HIV-R than from the HIV+ (90.30% vs 80.90 p = 0.002) and HIV Neg controls (90.30% vs 82.30 p < 0.001) respectively. A further comparison of the mean fluorescent intensity (MFI) of CD26/DPPIV expression showed a higher DPP4 MFI on HIV-R CD4+ T cells (median 118 vs 91 for HIV-Neg, p = 0.0003). An evaluation for hyperglycemia, did not confirm Type 2 diabetes but an impaired fasting glucose condition (5.775 mmol/L). A follow-up quantitative PCR analysis of the insulin signaling pathway genes showed a down expression of NFκB, a central mediator of the immune response and activator of HIV-1 transcription.

Conclusion

HIV resistant sex workers have a high expression of CD26/DPPIV in tandem with lowered immune activation markers. This may suggest a novel role for CD26/DPPIV in protection against HIV infection in vivo.

Effective recognition of HIV-1-infected cells by HIV-1 integrase-specific HLA-B∗4002-restricted T cells

HLA-B∗4002 is one of the common HLA-B alleles in the world. All 7 reported HLA-B∗4002-restricted HIV epitopes are derived from Gag, Nef, and Vpr. In the present study we sought to identify novel HLA-B∗4002-restricted HIV epitopes by using overlapping 11-mer peptides of HIV-1 Nef, Gag, and Pol, and found that 6 of these 11-mer Pol peptides included HLA-B∗4002-restricted epitopes. Analysis using truncated peptides of these 6 peptides defined 4 optimal Pol (integrase) epitopes. All epitopes previously reported had Glu at position 2 (P2), suggesting that Glu at P2 is the anchor residue for HLA-B∗4002; whereas only 2 of the integrase epitopes that we here identified had Glu at P2. CTL clones specific for the 2 epitopes effectively recognized HIV-1-infected cells whereas those for other 2 epitopes only weakly recognized them. The antigen sensitivity of the former clones for the epitope peptide was much higher than that of the latter clones, suggesting 2 possibilities: 1) the former T cells have high-affinity TCRs and/or 2) the epitope peptides recognized by the former T cells are highly presented by HLA-B∗4002 in HIV-1-infected cells. These integrase-specific T cells with high antigen sensitivity may contribute to the suppression of HIV-1 replication in HIV-1-infected HLA-B∗4002+ individuals.

An HIV-1 clade A/E DNA prime, recombinant fowlpox virus boost vaccine is safe, but non-immunogenic in a randomized phase I/IIa trial in Thai volunteers at low risk of HIV infection

BACKGROUND

Previously demonstrated safe and highly immunogenic in non-human primates, this study assessed DNA (pHIS-HIV-AE) prime, recombinant fowlpox (rFPV-HIV-AE) boost vaccines in humans.

RESULTS

Eight participants (6 active vaccine, 2 placebo) received all vaccinations; local and systemic reactions were mild to moderate. The percentage CD4(+) and CD8(+) T cells responding to HIV-1 Gag antigens by ICS (mean ± SD) was 0.16 ± 0.12 and 0.10 ± 0.12 for active and 0.01 ± 0.01 and 0.00 ± 0.00 for placebo vaccine respectively. The percentage of T cells responding did not reach pre-defined thresholds to be considered positive responses. Consequently, the Data Safety Monitoring Board recommended cessation of further recruitment. Existing volunteers were followed to 52 weeks.

METHODS

Vectors expressing homologous HIV-1 clade A/E gag, pol, env and regulatory genes or matched placebo were administered intramuscularly at weeks 0, 4, 8 (6 mg pHIS-HIV-AE) and week 12 (3.0 x 10(8) pfu rFPV-HIV-AE) in this randomized, double-blind, placebo-controlled phase I/IIa study in healthy Thai adults at low risk of HIV infection. Immunogenicity was determined by interferon-gamma and IL-2 expression using intracellular cytokine staining assay (ICS), 13 weeks after randomization. Interim analysis was performed when eight volunteers reached 16 weeks follow-up.

CONCLUSIONS

Vaccine candidates were generally well tolerated, but showed limited immunogenicity. Better vaccines and delivery systems are required.

New approaches to design HIV-1 T-cell vaccines

PURPOSE OF REVIEW

Following the evidence that T-cell responses are crucial in the control of HIV-1 infection, vaccines targeting T-cell responses were tested in recent clinical trials. However, these vaccines showed a lack of efficacy. This review attempts to define the qualitative and quantitative features that are desirable for T-cell-induced responses by vaccines. We also describe strategies that could lead to achievement of this goal.

RECENT FINDINGS

Using the yellow fever vaccine as a benchmark of an efficient vaccine, recent studies identified factors of immune protection and more importantly innate immune pathways needed for the establishment of long-term protective adaptive immunity.

SUMMARY

To prevent or control HIV-1 infection, a vaccine must induce efficient and persistent antigen-specific T cells endowed with mucosal homing capacity. Such cells should have the capability to counteract HIV-1 diversity and its rapid spread from the initial site of infection. To achieve this goal, the activation of a diversified innate immune response is critical. New systems biology approaches will provide more precise correlates of immune protection that will pave the way for new approaches in T-cell-based vaccines.

HBV-specific T-cell responses in healthy seronegative sexual partners of patients with chronic HBV infection

The hepatitis B virus (HBV) is frequently transmitted by sexual intercourse. Thus, HBV-guidelines recommend vaccination. However, we have identified healthy hepatitis B surface antigen and anti-HBc-negative unvaccinated sexual partners of patients with chronic hepatitis B. We investigated whether HBV-specific cellular immune responses were present that could explain the apparent protection against HBV infection. In six anti-HBc-negative HBV-exposed sexual partners, HBV-specific T-cell responses were studied by proliferation assay and cytometric bead array after stimulation with 74 overlapping peptides spanning the HBV core, pre-S and S-encoding regions. Eleven HBV-unexposed individuals served as negative controls. HBV-DNA was undetectable in serum and peripheral blood mononuclear cells in all cases. HBV-specific cytokine secretion was observed in 4/6 seronegative partners, but only in 1/11 controls. Proliferative responses were detectable in 5/6 partners and 0/11 controls. HBV-specific cytokine secretion exists in healthy seronegative virus-exposed individuals. HBV core-directed immune responses indicate past, but controlled viral replication. T-cell immunity may prevent clinical manifestation of HBV infection in the absence of humoral immunity.

Influence of HLA class I and HLA-KIR compound genotypes on HIV-2 infection and markers of disease progression in a Manjako community in West Africa

Overall, the time to AIDS after HIV-2 infection is longer than with HIV-1, and many individuals infected with HIV-2 virus remain healthy throughout their lives. Multiple HLA and KIR gene products have been implicated in the control of HIV-1, but the effect of variation at these loci on HIV-2 disease is unknown. We show here for the first time that HLA-B*1503 is associated significantly with poor prognosis after HIV-2 infection and that HLA-B*0801 is associated with susceptibility to infection. Interestingly, previous data indicate that HLA-B*1503 is associated with low viral loads in HIV-1 clade B infection but has no significant effect on viral load in clade C infection. In general, alleles strongly associated with HIV-1 disease showed no effect in HIV-2 disease. These data emphasize the unique nature of the effects of HLA and HLA/KIR combinations on HIV-2 immune responses relative to HIV-1, which could be related to their distinct clinical course.

The most common Chinese rhesus macaque MHC class I molecule shares peptide binding repertoire with the HLA-B7 supertype

Of the two rhesus macaque subspecies used for AIDS studies, the Simian immunodeficiency virus-infected Indian rhesus macaque (Macaca mulatta) is the most established model of HIV infection, providing both insight into pathogenesis and a system for testing novel vaccines. Despite the Chinese rhesus macaque potentially being a more relevant model for AIDS outcomes than the Indian rhesus macaque, the Chinese-origin rhesus macaques have not been well-characterized for their major histocompatibility complex (MHC) composition and function, reducing their greater utilization. In this study, we characterized a total of 50 unique Chinese rhesus macaques from several varying origins for their entire MHC class I allele composition and identified a total of 58 unique complete MHC class I sequences. Only nine of the sequences had been associated with Indian rhesus macaques, and 28/58 (48.3%) of the sequences identified were novel. From all MHC alleles detected, we prioritized Mamu-A1*02201 for functional characterization based on its higher frequency of expression. Upon the development of MHC/peptide binding assays and definition of its associated motif, we revealed that this allele shares peptide binding characteristics with the HLA-B7 supertype, the most frequent supertype in human populations. These studies provide the first functional characterization of an MHC class I molecule in the context of Chinese rhesus macaques and the first instance of HLA-B7 analogy for rhesus macaques.

Highly avid, oligoclonal, early-differentiated antigen-specific CD8+ T cells in chronic HIV-2 infection

HIV-1-specific CD8(+) T cells are present in most HIV-1-infected people and play an important role in controlling viral replication, but the characteristics of an effective HIV-specific T-cell response are largely unknown. The majority of HIV-2-infected people behave as long-term non-progressors while those who progress to AIDS do so in a manner indistinguishable from HIV-1. A detailed study of HIV-2 infection may identify protective immune responses. Robust gag p26-specific T-cell responses are elicited during HIV-2 infection and correlate with control of viremia. In this study, we analyzed features of an HLA-B 3501-restricted T-cell response to HIV-2 p26 that may contribute to virus control. In contrast to HIV-1, HIV-2-specific T cells are at an early stage of differentiation (CD27(+)CD28(+)), a finding that relates directly to CD4(+) T-cell levels and inversely to immune activation. The cells demonstrate IFN-gamma secretion, oligoclonal T-cell receptor Vbeta gene segment usage, exceptional avidity and secretion of pro-inflammatory cytokines. Despite the potentially strong selection pressure imposed on the virus by these cells, there was no evidence of HIV-2 sequence evolution. We propose that in chronic HIV-2 infection, the maintenance of early-differentiated, highly avid CD8(+) T cells could account for the non-progressive course of disease. Such responses may be desirable from an HIV vaccine.

Cellular HIV-1 restriction factors: a new avenue for AIDS therapy?

The lack of an efficacious HIV-1 vaccine and the continued emergence of drug-resistant HIV-1 strains have pushed the research community to explore novel avenues for AIDS therapy. Over the last decade, one new avenue that has been realized involves cellular HIV-1 restriction factors, defined as host cellular proteins or factors that restrict or inhibit HIV-1 replication. Many of these factors are interferon-induced and inhibit specific stages of the HIV-1 lifecycle that are not targeted by current AIDS therapies. Our understanding of the molecular mechanisms underlying HIV-1 restriction is far from complete, but our current knowledge of these factors offers hope for the future development of novel therapeutic ideas.

Prior mucosal exposure to heterologous cells alters the pathogenesis of cell-associated mucosal feline immunodeficiency virus challenge

BACKGROUND

Several lines of research suggest that exposure to cellular material can alter the susceptibility to infection by HIV-1. Because sexual contact often includes exposure to cellular material, we hypothesized that repeated mucosal exposure to heterologous cells would induce an immune response that would alter the susceptibility to mucosal infection. Using the feline immunodeficiency virus (FIV) model of HIV-1 mucosal transmission, the cervicovaginal mucosa was exposed once weekly for 12 weeks to 5,000 heterologous cells or media (control) and then cats were vaginally challenged with cell-associated or cell-free FIV.

RESULTS

Exposure to heterologous cells decreased the percentage of lymphocytes in the mucosal and systemic lymph nodes (LN) expressing L-selectin as well as the percentage of CD4+ CD25+ T cells. These shifts were associated with enhanced ex-vivo proliferative responses to heterologous cells. Following mucosal challenge with cell-associated, but not cell-free, FIV, proviral burden was reduced by 64% in cats previously exposed to heterologous cells as compared to media exposed controls.

CONCLUSIONS

The pathogenesis and/or the threshold for mucosal infection by infected cells (but not cell-free virus) can be modulated by mucosal exposure to uninfected heterologous cells.

Dual infection with HIV-1 and HIV-2: double trouble or destructive interference?

HIV-1 and HIV-2 are two related retroviruses and, in regions where both infections are endemic, HIV-1/2 dual infection can occur. Several important questions arise about the interplay between these two viruses in a single host, including: what is the potential for HIV-1–HIV-2 recombinants to form, are there synergistic or inhibitory mechanisms that result in distinct viral replication dynamics when compared with HIV-1 or HIV-2 monoinfected individuals and what are the factors to consider when choosing antiretroviral regimes in HIV-1/2 dual-infected individuals? We summarize the relevant evidence to answer these questions, as well as indentify trends in prevalence and how the natural history of HIV-1/2 dual infection differs from that of HIV-1 or HIV-2 monoinfection. The epidemiological and in vitro evidence pertaining to the question of whether HIV-2 infection may protect against HIV-1 superinfection will also be addressed.

Selection of extreme phenotypes: the role of clinical observation in translational research

Systematic collection of phenotypes and their correlation with molecular data has been proposed as a useful method to advance in the study of disease. Although some databases for animal species are being developed, progress in humans is slow, probably due to the multifactorial origin of many human diseases and to the intricacy of accurately classifying phenotypes, among other factors. An alternative approach has been to identify and to study individuals or families with very characteristic, clinically relevant phenotypes. This strategy has shown increased efficiency to identify the molecular features underlying such phenotypes. While on most occasions the subjects selected for these studies presented harmful phenotypes, a few studies have been performed in individuals with very favourable phenotypes. The consistent results achieved suggest that it seems logical to further develop this strategy as a methodology to study human disease, including cancer. The identification and the study with high-throughput techniques of individuals showing a markedly decreased risk of developing cancer or of cancer patients presenting either an unusually favourable prognosis or striking responses following a specific treatment, might be promising ways to maximize the yield of this approach and to reveal the molecular causes that explain those phenotypes and thus highlight useful therapeutic targets. This manuscript reviews the current status of selection of extreme phenotypes in cancer research and provides directions for future development of this methodology.

Human leukocyte antigen class I supertypes and HIV-1 control in African Americans

The role of human leukocyte antigen (HLA) class I supertypes in controlling human immunodeficiency virus type 1 (HIV-1) infection in African Americans has not been established. We examined the effects of the HLA-A and HLA-B alleles and supertypes on the outcomes of HIV-1 clade B infection among 338 African American women and adolescents. HLA-B58 and -B62 supertypes (B58s and B62s) were associated with favorable HIV-1 disease control (proportional odds ratio [POR] of 0.33 and 95% confidence interval [95% CI] of 0.21 to 0.52 for the former and POR of 0.26 and 95% CI of 0.09 to 0.73 for the latter); B7s and B44s were associated with unfavorable disease control (POR of 2.39 and 95% CI of 1.54 to 3.73 for the former and POR of 1.63 and 95% CI of 1.08 to 2.47 for the latter). In general, individual alleles within specific B supertypes exerted relatively homogeneous effects. A notable exception was B27s, whose protective influence (POR, 0.58; 95% CI, 0.35 to 0.94) was masked by the opposing effect of its member allele B*1510. The associations of most B supertypes (e.g., B58s and B7s) were largely explained either by well-known effects of constituent B alleles or by effects of previously unimplicated B alleles aggregated into a particular supertype (e.g., B44s and B62s). A higher frequency of HLA-B genotypic supertypes correlated with a higher mean viral load (VL) and lower mean CD4 count (Pearson's r = 0.63 and 0.62, respectively; P = 0.03). Among the genotypic supertypes, B58s and its member allele B*57 contributed disproportionately to the explainable VL variation. The study demonstrated the dominant role of HLA-B supertypes in HIV-1 clade B-infected African Americans and further dissected the contributions of individual class I alleles and their population frequencies to the supertype effects.

Preclinical evaluation of the immunogenicity of C-type HIV-1-based DNA and NYVAC vaccines in the Balb/C mouse model

As part of a European initiative (EuroVacc), we report the design, construction, and immunogenicity of two HIV-1 vaccine candidates based on a clade C virus strain (CN54) representing the current major epidemic in Asia and parts of Africa. Open reading frames encoding an artificial 160-kDa GagPolNef (GPN) polyprotein and the external glycoprotein gp120 were fully RNA and codon optimized. A DNA vaccine (DNA-GPN and DNA-gp120, referred to as DNA-C), and a replication-deficient vaccinia virus encoding both reading frames (NYVAC-C), were assessed regarding immunogenicity in Balb/C mice. The intramuscular administration of both plasmid DNA constructs, followed by two booster DNA immunizations, induced substantial T-cell responses against both antigens as well as Env-specific antibodies. Whereas low doses of NYVAC-C failed to induce specific CTL or antibodies, high doses generated cellular as well as humoral immune responses, but these did not reach the levels seen following DNA vaccination. The most potent immune responses were detectable using prime:boost protocols, regardless of whether DNA-C or NYVAC-C was used as the priming or boosting agent. These preclinical findings revealed the immunogenic response triggered by DNA-C and its enhancement by combining it with NYVAC-C, thus complementing the macaque preclinical and human phase I clinical studies of EuroVacc.

Construction and immunogenicity of Salmonella vaccine vector expressing HIV-1 antigen and MCP3

This study aims to determine the efficacy of Salmonella enterica serovar Typhimurium STM-1 bearing MCP-3 gene as a delivery vehicle for the HIV gag gene (in particular p24 gene) and HIV env gene. The STM1 delivery HIV-p24 vaccination was carried out in the form of a recombinant or a DNA vaccine whereas only a DNA vaccine was used for HIV env . Naked DNA vaccination was also tested and immune responses were evaluated following immunisation in mouse model.

RESULTS

vaccination cellular immune responses induced by recombinant p24 STM1 (STM1/pHly-p24) were greater than those elicited by the p24 DNA vaccine in STM1 (STM1/VR-p24), (but statistically not significant) than those induced by oral vaccination. However, IgA responses induced by oral vaccination with either a recombinant or DNA vaccine of p24 in STM1 are higher than those induced by IP vaccination. In addition, the numbers of cells secreting IL4 are reduced after oral vaccination with STM1/VR-p24/MCP3. However, for the HIV p24 antigen, STM1/MCP3 preferentially induces IFNgamma-secreting splenocytes.

CONCLUSIONS

This result confirms other studies that Salmonella was able to deliver HIV antigens to the immune system and induced specific immune responses to the HIV antigen and for the HIV p24 antigen, STM1/MCP3 induces secretion of IFNgamma.

Recombinant pro-apoptotic Mycobacterium tuberculosis generates CD8+ T cell responses against human immunodeficiency virus type 1 Env and M. tuberculosis in neonatal mice

Mycobacterium bovis BCG is an attractive vaccine vector against breast milk HIV transmission because it elicits Th1-type responses in newborns. However, BCG causes disease in HIV-infected infants. Genetically attenuated Mycobacterium tuberculosis (Mtb) mutants represent a safer alternative for immunocompromised populations. In the current study, we compared the immunogenicity in mice of three different recombinant attenuated Mtb strains expressing an HIV envelope (Env) antigen construct. Two of these strains (DeltalysA DeltapanCD Mtb and DeltaRD1 DeltapanCD Mtb) failed to induce significant levels of HIV Env-specific CD8(+) T cell responses. In striking contrast, an HIV-1 Env-expressing attenuated DeltalysA Mtb containing a deletion in secA2, which encodes a virulence-related secretion system involved in evading adaptive immunity, generated consistently measurable Env-specific CD8(+) T cell responses that were significantly greater than those observed after immunization with BCG expressing HIV Env. Similarly, another strain of DeltalysA DeltasecA2 Mtb expressing SIV Gag induced Gag- and Mtb-specific CD8(+) T cells producing perforin or IFNgamma, and Gag-specific CD4(+) T cells producing IFNgamma within 3 weeks after immunization in adult mice; in addition, IFNgamma-producing Gag-specific CD8(+) T cells and Mtb-specific CD4(+) T cells were observed in neonatal mice within 1 week of immunization. We conclude that DeltalysA DeltasecA2 Mtb is a promising vaccine platform to construct a safe combination HIV-TB vaccine for use in neonates.

The molecular mechanism of human resistance to HIV-1 infection in persistently infected individuals--a review, hypothesis and implications

Resistance to HIV-1 infection in Europeans is associated with a mutation in the gene that codes for the CCR5 protein that is present in Th2 cells and serves as a coreceptor for HIV-1 R5 strain. A deletion of 32 amino acids from the cytokine receptor prevents infection. This mutation prevails in Europeans and is absent in Africans. However, duplication of a gene that codes for a chemokine that binds to the CCR5 was discovered in Africans (mean gene copy 6 while in non-Africans the mean gene copy is 3). Higher expression of these genes protects T cells against HIV-1 infection in vitro. It should be noted that resistance to HIV-1 R5 variant does not protect against HIV-1 R4 variant. It was reported that a minority of highly HIV-1 exposed African professional sex workers (APSW) were resistant to the virus infection during a 10 years period. Recently, the analysis of the cytokines in the serum of the persistently infected seronegative women revealed that the latter hypo-expresses the cytokine IL-4. Since the molecular events during HIV-1 infection are associated with a marked increase in the levels of IL-4 and IgE in the sera of the infected individuals, it suggests that AIDS is an allergy. Thus, a very low level of IL-4 production may abrogate the virus infection. Studies on the human IL-4 gene revealed that together with the IL-4 mRNA a spliced variant with a deletion of exon 2 is synthesized. The latter is a natural antagonist of IL-4 and when expressed in an individual at a level higher than IL-4, the person will resist a microbial infection (e.g. Mycobacterium tuberculosis) or asthma. The present hypothesis suggests that the HIV-1 resistant APSWs produce more IL-4 delta 2 molecules than IL-4 molecules. The binding of IL-4 delta 2 to IL-4 receptors on T and B cells prevents their functions and the infection by HIV-1. The implications of these studies are that treatment of HIV-1 infected people with drugs that will block the IL-4 receptors will stop HIV-1 infections and the determination of the levels of IL-4 and IL-4 delta 2 in the sera of HIV-1+ patients will enable to identify the individuals that have a natural resistance to HIV-l/AIDS and those who need treatments.

Preinfection human immunodeficiency virus (HIV)-specific cytotoxic T lymphocytes failed to prevent HIV type 1 infection from strains genetically unrelated to viruses in long-term exposed partners

Understanding the mechanisms underlying potential altered susceptibility to human immunodeficiency virus type 1 (HIV-1) infection in highly exposed seronegative (ES) individuals and the later clinical consequences of breakthrough infection can provide insight into strategies to control HIV-1 with an effective vaccine. From our Seattle ES cohort, we identified one individual (LSC63) who seroconverted after over 2 years of repeated unprotected sexual contact with his HIV-1-infected partner (P63) and other sexual partners of unknown HIV-1 serostatus. The HIV-1 variants infecting LSC63 were genetically unrelated to those sequenced from P63. This may not be surprising, since viral load measurements in P63 were repeatedly below 50 copies/ml, making him an unlikely transmitter. However, broad HIV-1-specific cytotoxic T-lymphocyte (CTL) responses were detected in LSC63 before seroconversion. Compared to those detected after seroconversion, these responses were of lower magnitude and half of them targeted different regions of the viral proteome. Strong HLA-B27-restricted CTLs, which have been associated with disease control, were detected in LSC63 after but not before seroconversion. Furthermore, for the majority of the protein-coding regions of the HIV-1 variants in LSC63 (except gp41, nef, and the 3' half of pol), the genetic distances between the infecting viruses and the viruses to which he was exposed through P63 (termed the exposed virus) were comparable to the distances between random subtype B HIV-1 sequences and the exposed viruses. These results suggest that broad preinfection immune responses were not able to prevent the acquisition of HIV-1 infection in LSC63, even though the infecting viruses were not particularly distant from the viruses that may have elicited these responses.

Impact of intrinsic cooperative thermodynamics of peptide-MHC complexes on antiviral activity of HIV-specific CTL

The antiviral activity of HIV-specific CTL is not equally potent but rather is dependent on their specificity. But what characteristic of targeted peptides influences CTL antiviral activity remains elusive. We addressed this issue based on HLA-B35-restricted CTLs specific for two overlapping immunodominant Nef epitopes, VY8 (VPLRPMTY) and RY11 (RPQVPLRPMTY). VY8-specific CTLs were more potently cytotoxic toward HIV-infected primary CD4(+) cells than RY11-specific CTLs. Reconstruction of their TCR revealed no substantial difference in their functional avidity toward cognate Ags. Instead, the decay analysis of the peptide-MHC complex (pMHC) revealed that the VY8/HLA-B35 complex could maintain its capacity to sensitize T cells much longer than its RY11 counterpart. Corroboratively, the introduction of a mutation in the epitopes that substantially delayed pMHC decay rendered Nef-expressing target cells more susceptible to CTL killing. Moreover, by using differential scanning calorimetry and circular dichroism analyses, we found that the susceptible pMHC ligands for CTL killing showed interdependent and cooperative, rather than separate or sequential, transitions within their heterotrimer components under the thermally induced unfolding process. Collectively, our results highlight the significant effects of intrinsic peptide factors that support cooperative thermodynamics within pMHC on the efficient CTL killing of HIV-infected cells, thus providing us better insight into vaccine design.

Multiple HIV-1 infection of cells and the evolutionary dynamics of cytotoxic T lymphocyte escape mutants

Cytotoxic T lymphocytes (CTL) are an important branch of the immune system, killing virus-infected cells. Many viruses can mutate so that infected cells are not killed by CTL anymore. This escape can contribute to virus persistence and disease. A prominent example is HIV-1. The evolutionary dynamics of CTL escape mutants in vivo have been studied experimentally and mathematically, assuming that a cell can only be infected with one HIV particle at a time. However, according to data, multiple virus particles frequently infect the same cell, a process called coinfection. Here, we study the evolutionary dynamics of CTL escape mutants in the context of coinfection. A mathematical model suggests that an intermediate strength of the CTL response against the wild-type is most detrimental for an escape mutant, minimizing overall virus load and even leading to its extinction. A weaker or, paradoxically, stronger CTL response against the wild-type both lead to the persistence of the escape mutant and higher virus load. It is hypothesized that an intermediate strength of the CTL response, and thus the suboptimal virus suppression observed in HIV-1 infection, might be adaptive to minimize the impact of existing CTL escape mutants on overall virus load.

Distribution of CCR5 genotypes and HLA Class I B alleles in HIV-1 infected and uninfected injecting drug users from Rio de Janeiro, Brazil

Host genetic factors play an important role in the HIV epidemic dynamics, and have been considered in studies assessing susceptibility/resistance to HIV-1 infection as well as clinical evolution. Class I and Class II HLA alleles have been associated with the heterogeneity of HIV-1 infection susceptibility, as protective or risk factors for HIV-1 transmission. Moreover, a 32-base pair deletion in the HIV-1 CCR5 gene-coding region confers resistance to HIV-1 infection in homozygous individuals for the deleted allele. In this study, DNA samples from HIV-1 infected and uninfected injecting drug users (IDUs) from Rio de Janeiro were PCR amplified to determine CCR5 genotypes based on the presence of the CCR5Delta32 mutation and typed for the HLA-B locus, in an attempt to assess possible associations between these genetic factors and susceptibility/resistance to HIV-1 infection. The distribution of CCR5 genotypes between the two IDU groups did not differ. The homozygous mutant genotype Delta32/Delta32 was not found in this study. Except for HLA-B*45 (4.0% vs. 3.0%; p=0.04) and for B*51 (12.1% vs. 4.4%; p=0.002), no statistically significant differences were made evident when analyzing the frequencies of each HLA-B allele between Caucasian and non-Caucasian IDUs. The most frequent HLA-B alleles were B*15; B*35; B*44 and B*51. Although some differences in the allele frequencies could be observed between the two IDU groups, none of these was statistically significant. Therefore, no putative association between these genetic markers and susceptibility/resistance to HIV-1 infection could be made evident in the present study. So far, the assessment of genetic markers among the IDU population has been restricted to North American, European, and Asian studies and this report represents a pioneer descriptive study of the distribution of CCR5 genotypes and HLA-B alleles in Rio de Janeiro, Brazil.

Hepatitis C virus (HCV)--specific T cell responses in injection drug users with apparent resistance to HCV infection

BACKGROUND

Injection drug users (IDUs) are at risk of acquiring hepatitis C virus (HCV) infection. We have identified a cohort of long-term IDUs who remain uninfected by HCV despite high-risk behavior. We have categorized these subjects as "exposed uninfected" and have sought immunological correlates with this apparent resistance.

METHODS

We studied 40 exposed uninfected subjects testing negative for both HCV antibody and HCV RNA. Details of injection behavior were ascertained by questionnaire. In vitro interferon (IFN)-gamma production by T cells in response to HCV proteins (core, E1, NS3, NS4, and NS5) was quantified by enzyme-linked immunospot assay, and findings were compared with those in 21 healthy control subjects.

RESULTS

All exposed uninfected subjects reported sharing needles or other injection paraphernalia on multiple occasions. The mean duration of injecting was 9.3 years (range, 0.5-26 years), with a median estimated number of injection episodes of 8760. IFN-gamma production in response to HCV proteins was found in 23 (58%) of 40 exposed uninfected subjects versus 4 (19%) of 21 control subjects (P = .004), with 14 exposed uninfected subjects responding to multiple antigens, compared with none of the control subjects (P = .001).

CONCLUSIONS

The majority of long-term IDUs who remain uninfected by HCV despite their high-risk behavior have HCV-specific T cell responses. These responses were frequently found for multiple HCV proteins, making cross-reactivity to other homologous antigens unlikely. These responses may represent an immunological footprint of HCV exposure that has not resulted in viremia or HCV antibody seroconversion. The potential role played by these responses in protection from HCV infection is of clinical importance.

Novel mouse models for understanding HIV-1 pathogenesis

Small animal models in which in vivo HIV-1 infection, pathogenesis, and immune responses can be studied would permit both basic research on the biology of the disease, as well as a system to rapidly screen developmental therapeutics and/or vaccines. To date, the most widely-used models have been the severe combined immunodeficient (SCID)-hu (also known as the thy/liv SCID-hu) and the huPBL-SCID mouse models. Recently three new models have emerged, i.e., the intrasplenic huPBL/SPL-SCID model, the NOD/SCID/IL2Rgamma(null) mouse model, and the Rag2(-/-)gamma(c) (-/-) mouse model. Details on the construction, maintenance and HIV-1 infection of these models are discussed.

Deficiency of HIV-Gag-specific T cells in early childhood correlates with poor viral containment

Perinatal HIV infection is characterized by a sustained high-level viremia and a high risk of rapid progression to AIDS, indicating a failure of immunologic containment of the virus. We hypothesized that age-related differences in the specificity or function of HIV-specific T cells may influence HIV RNA levels and clinical outcome following perinatal infection. In this study, we defined the HIV epitopes targeted by 76 pediatric subjects (47 HIV infected and 29 HIV exposed, but uninfected), and assessed the ability of HIV-specific CD8 and CD4 T cells to degranulate and produce IFN-gamma, TNF-alpha, and IL-2. No responses were detected among HIV-uninfected infants, whereas responses among infected subjects increased in magnitude and breadth with age. Gag-specific responses were uncommon during early infancy, and their frequency was significantly lower among children younger than 24 mo old (p = 0.014). Importantly, Gag responders exhibited significantly lower HIV RNA levels than nonresponders (log viral load 5.8 vs 5.0; p = 0.005). Both the total and Gag-specific T cell frequency correlated inversely with viral load after correction for age, whereas no relationship with targeting of other viral proteins was observed. Functional assessment of HIV-specific T cells by multiparameter flow cytometry revealed that polyfunctional CD8 cells were less prevalent in children before 24 mo of age, and that HIV-specific CD4 cell responses were of universally low frequency among antiretroviral-naive children and absent in young infants. These cross-sectional data suggest that qualitative differences in the CD8 response, combined with a deficiency of HIV-specific CD4 cells, may contribute to the inability of young infants to limit replication of HIV.

Comprehensive analysis of HIV Gag-specific IFN-gamma response in HIV-1- and HIV-2-infected asymptomatic patients from a clinical cohort in The Gambia

Majority of HIV-2-infected individuals meet the criteria of long-term non-progressors. This has been linked to superior qualitative HIV-2-specific cellular immune responses that correlate with viral control. However, it is unknown whether this is due to frequent targeting of immunodominant Gag epitopes in HIV-2 than HIV-1 infection. We describe a comprehensive comparison of the magnitude, breadth and frequency of Gag responses and the degree of cross-recognition of frequently targeted, immunodominant Gag peptides in a cross-sectional study of asymptomatic HIV-1- and HIV-2-infected individuals. Fresh PBMC from 20 HIV-1- and 20 HIV-2-infected patients with similar CD4(+) T-cell counts (p=0.36) were stimulated with pools of HIV-1 and/or HIV-2 Gag peptides in an IFN-gamma ELISPOT assay. We found no difference in the cumulative magnitude of IFN-gamma responses (p=0.75) despite significantly lower plasma viral loads in HIV-2-infected people (p<0.0001). However, Gag211-290 was targeted with significantly higher magnitude in HIV-2-infected subjects (p=0.03) although this did not correlate with viral control. There was no difference in frequently targeted Gag peptides, the breadth, immunodominance or cross-recognition of Gag peptide pools between the two infections. This suggests that other factors may control viral replication in HIV-2 infection.

Scientific consultation on cell mediated immunity (CMI) in dengue and dengue vaccine development

Dengue is a re-emerging arboviral disease of great public health importance. Limited understanding of protective immune responses against dengue has hampered advancement of dengue vaccine candidates. Demonstrating an immunological correlate of protection has been limited to associating quantitative neutralizing antibody titers with clinical outcomes following infection. There have been a number of studies investigating the role of cell mediated immunity (CMI) in natural infections and these have demonstrated roles in both virus clearance and potentiating disease. Vaccine developers have extended the exploratory study of CMI in natural infection to the study of dengue vaccine recipients. Primary infections and monovalent vaccine administration generates dengue type-specific T-cell responses. Secondary infection, vaccination of flavivirus primed individuals, or administration of multivalent vaccine candidates results in broad, cross-reactive T-cell responses, similar to the broadening of antibody patterns. However, the precise function of CMI in protection or disease pathology remains ill-defined and, at present, there is no evidence to suggest that CMI can be utilized as a correlate of protection. Nonetheless, the study of CMI in natural infection and following vaccine administration should continue in an attempt to improve the understanding of dengue immunopathology, vaccine candidate immunogenicity, and potential correlates of protection.

Impaired viral entry cannot explain reduced CD4+ T cell susceptibility to HIV type 1 in certain highly exposed individuals

Rare individuals report repeated unprotected HIV-1 sexual exposures, yet remain seronegative for years. We investigated the possibility that reduced in vitro CD4(+) T cell susceptibility to HIV-1 infection protects such highly exposed seronegative (ES) individuals. Susceptibility to three R5-tropic HIV-1 isolates, regardless of inoculating dose, was remarkably similar between 81 ES and 33 low-risk controls. In 94% (99/105) of donors, we observed a 1.36 log-unit range in HIV-1(JR-CSF) production, with similar results for HIV-1(1192). The median frequency of intracellular Gag(+) T cells after single-round infection was similar in ES (5.2%) and controls (7.2%), p = 0.456. However, in repeated testing, CD4(+) T cells from two controls (6.1%) and four ES (4.9%) exhibited a 10- to 2500-fold reduction in HIV-1 production and required 5- to 12-fold greater HIV-1(1192) and HIV-1(JR-CSF) inocula to establish infection (TCID(50)). Reduced viral entry cannot explain the low producer phenotype; no differences in CCR5 receptor density or beta-chemokine production were observed. In conclusion, we have identified a remarkably narrow range of HIV-1 susceptibility in seronegative donors regardless of risk activity, which can be applied as a benchmark to assess vaccine-induced antiviral effector activities. However, CD4(+) T cells from a subset of individuals demonstrated reduced HIV-1 susceptibility unexplained by impaired entry, lending support to the possibility that cellular restriction of HIV-1 may account for continued seronegativity in some of those having repeated sexual exposure. Identifying the host-virus interactions responsible for diminished in vitro susceptibility may contribute to the development of novel therapeutic strategies.

Effects of recombinant human growth hormone on HIV-1-specific T-cell responses, thymic output and proviral DNA in patients on HAART: 48-week follow-up

BACKGROUND

Efficacious immune-based therapy in treated chronic HIV-1 infection requires the induction of virus-specific CD4+ T cells and subsequent maturation and maintenance of specific memory CD8+ T cells. Concomitant daily administration of recombinant human growth hormone (rhGH) with highly active antiretroviral therapy (HAART) was used in chronically infected patients with lipodystrophy in an attempt to reconstitute these virus-specific T-cell responses.

METHODS

Individuals with chronic HIV-1 infection on HAART were enrolled on a randomized, double-blinded, placebo-controlled study to receive rhGH therapy. We assessed HIV-1-specific proliferative CD4+ and interferon-gamma (IFN-gamma)-producing CD8+ T-cell responses, quantified thymic output and proviral HIV-1 DNA at the following time points: baseline; after 12 weeks of rhGH therapy; at 24 weeks, after randomization into three groups [placebo weeks 12-24 (Group A), alternate-day dosing weeks 12-24 (Group B), and twice-per-week dosing weeks 12-24 (Group C)]; and at 48 weeks after all patients had received HAART alone for the final 24 weeks.

RESULTS

We found significant increases in both proliferative CD4+ and IFN-gamma-producing CD8+ HIV-1-specific T-cell responses after daily administration of rhGH. This increase was focused on HIV-1 Gag-specific T-cell responses. Following subsequent randomisation into different dosing regimens, HIV-1-specific proliferative CD4+ T-cell responses declined in patients receiving less frequent dosing of rhGH, while virus-specific IFN-gamma-producing CD8+ T-cell responses were maintained for longer periods of time. There was no significant change in thymic output and the cell-associated HIV-1 DNA remained stable in most patients. An increased anti-HIV-1 Nef-specific CD4+ T-cell proliferative response was correlated to a decrease in proviral load, and an increased HIV-1 Gag-specific IFN-gamma-producing CD8+ T-cell response correlated with an increase in proviral load.

CONCLUSION

The implication of these data is that daily dosing of rhGH with HAART, in addition to improving HIV-1-associated lipodystrophy, may reverse some of the T-lymphocyte dysfunction seen in most treated HIV-1-positive patients, in a dose-dependent manner. Such immune-based therapeutic strategies used in treated, chronic HIV-1 infection may enable the induction of virus-specific CD4+ T cells essential for the subsequent 'kick-start' and expansion of virus-specific CD8+ T cells.

TRIAL REGISTRATION

GH in Lipoatrophy IMP22350.

A common human leucocyte antigen-DP genotype is associated with resistance to HIV-1 infection in Kenyan sex workers

Human leucocyte antigen-DP presents peptides to CD4 T cells and plays an important role in parasitic infections and autoimmune diseases, yet its influence on HIV-1 susceptibility has not been well studied. Here, we report several human leucocyte antigen-DP genotypes associated with HIV-1 susceptibility in Kenyan sex workers. Among these, one common genotype stands out. DPA1*010301 (frequency = 60.4%) was associated with HIV-1 resistance (P = 0.033, odds ratio = 1.585, 95% confidence interval = 1.036-2.425) and slower seroconversion (P = 0.001, log rank = 0.595, 95% confidence interval = 0.433-0.817). The discovery of common human leucocyte antigen-DP genotypes contributing to HIV-1 immunity may help overcome difficulties encountered with highly polymorphic human leucocyte antigens.

Potentially exposed but uninfected individuals produce cytotoxic and polyfunctional human immunodeficiency virus type 1-specific CD8(+) T-cell responses which can be defined to the epitope level

We measured CD8(+) T-cell responses in 12 potentially exposed but uninfected men who have sex with men by using cytokine flow cytometry. Four of the individuals screened exhibited polyfunctional immune responses to human immunodeficiency virus type 1 Gag or Vif. The minimum cytotoxic T lymphocyte epitope was mapped in one Gag responder.