HIV-1-specific cellular immune responses among HIV-1-resistant sex workers

Comparison of the Biological Basis for Non-HIV Transmission to HIV-Exposed Seronegative Individuals, Disease Non-Progression in HIV Long-Term Non-Progressors and Elite Controllers

HIV-exposed seronegative individuals (HESIs) are a small fraction of persons who are multiply exposed to human immunodeficiency virus (HIV), but do not exhibit serological or clinical evidence of HIV infection. In other words, they are groups of people maintaining an uninfected status for a long time, even after being exposed to HIV several times. The long-term non-progressors (LTNPs), on the other hand, are a group of HIV-infected individuals (approx. 5%) who remain clinically and immunologically stable for an extended number of years without combination antiretroviral therapy (cART). Meanwhile, elite controllers are comprise a much lower number (0.5%) of HIV-infected persons who spontaneously and durably control viremia to below levels of detection for at least 12 months, even when using the most sensitive assays, such as polymerase chain reaction (PCR) in the absence of cART. Despite the fact that there is no universal agreement regarding the mechanisms by which these groups of individuals are able to control HIV infection and/or disease progression, there is a general consensus that the mechanisms of protection are multifaceted and include genetic, immunological as well as viral factors. In this review, we analyze and compare the biological factors responsible for the control of HIV in these unique groups of individuals.

Needle-Free Devices and CpG-Adjuvanted DNA Improve Anti-HIV Antibody Responses of Both DNA and Modified Vaccinia Ankara-Vectored Candidate Vaccines

The combination of mosaic Gag and CAP256 envelope in an HIV vaccine regimen comprising DNA prime and modified vaccinia Ankara (MVA) boost followed by protein boost has previously been shown to generate robust autologous Tier 2 neutralizing antibodies (nAbs) in rabbits. Further refinements of this strategy have been investigated to improve antibody responses. The delivery of both DNA and recombinant MVA vaccines with a needle-free device was compared to delivery by injection, and the effect of formulating the DNA vaccine with adjuvant CpG ODN 1826 was determined. The Pharmajet Stratis^® needle-free injection device (PharmaJet, Golden, CO, USA) improved binding antibody responses to the DNA vaccine as well as both binding and neutralizing antibody responses to the MVA vaccines. Formulation of the DNA vaccines with CpG adjuvant further improved the antibody responses. A shortened vaccination regimen of a single DNA inoculation followed by a single MVA inoculation did not elicit Tier 1B nor Tier 2 neutralization responses as produced by the two DNA, followed by two MVA vaccination regimen. This study showed the immunogenicity of HIV DNA and MVA vaccines administered in a DDMM regimen could be improved using the PharmaJet Stratis needle-free injection device and formulation of the DNA vaccines with CpG adjuvant.

Natural Immunity against HIV-1: Progression of Understanding after Association Studies

Natural immunity against HIV has been observed in many individuals in the world. Among them, a group of female sex workers enrolled in the Pumwani sex worker cohort remained HIV uninfected for more than 30 years despite high-risk sex work. Many studies have been carried out to understand this natural immunity to HIV in the hope to develop effective vaccines and preventions. This review focuses on two such examples. These studies started from identifying immunogenetic or genetic associations with resistance to HIV acquisition, and followed up with an in-depth investigation to understand the biological relevance of the correlations of protection, and to develop and test novel vaccines and preventions.

Transient Increases in Inflammation and Proapoptotic Potential Are Associated with the HESN Phenotype Observed in a Subgroup of Kenyan Female Sex Workers

Interferon (IFN) -stimulated genes (ISGs) are critical effectors of IFN response to viral infection, but whether ISG expression is a correlate of protection against HIV infection remains elusive. A well-characterized subcohort of Kenyan female sex workers, who, despite being repeatedly exposed to HIV-1 remain seronegative (HESN), exhibit reduced baseline systemic and mucosal immune activation. This study tested the hypothesis that regulation of ISGs in the cells of HESN potentiates a robust antiviral response against HIV. Transcriptional profile of a panel of ISGs with antiviral function in PBMC and isolated CD4+ T cells from HESN and non-HESN sex worker controls were defined following exogenous IFN-stimulation using relative RT-qPCR. This study identified a unique profile of proinflammatory and proapoptotic ISGs with robust but transient responses to exogenous IFN-γ and IFN-α2 in HESN cells. In contrast, the non-HESN cells had a strong and prolonged proinflammatory ISG profile at baseline and following IFN challenge. Potential mechanisms may include augmented bystander apoptosis due to increased TRAIL expression (16-fold), in non-HESN cells. The study also identified two negative regulators of ISG induction associated with the HESN phenotype. Robust upregulation of SOCS-1 and IRF-1, in addition to HDM2, could contribute to the strict regulation of proinflammatory and proapoptotic ISGs in HESN cells. As reducing IRF-1 in the non-HESN cells resulted in the identified HESN ISG profile, and decreased HIV susceptibility, the unique HESN ISG profile could be a correlate of protection against HIV infection.

Elevated Numbers of HIV-Specific Poly-Functional CD8+ T Cells With Stem Cell-Like and Follicular Homing Phenotypes in HIV-Exposed Seronegative Individuals

HIV-specific CD8⁺ T cells are known to play a key role in viral control during acute and chronic HIV infection. Although many studies have demonstrated the importance of HIV-specific CD8⁺ T cells in viral control, its correlation with protection against HIV infection remains incompletely understood. To better understand the nature of the immune response that contributes to the early control of HIV infection, we analyzed the phenotype, distribution and function of anti-viral CD8⁺ T cells in a cohort of HIV-exposed seronegative (HESN) women, and compared them with healthy controls and HIV-infected individuals. Further, we evaluated the in vitro viral inhibition activity of CD8⁺ T cells against diverse HIV-1 strains. We found that the HESN group had significantly higher levels of CD8⁺ T cells that express T-stem cell-like (TSCM) and follicular homing (CXCR5⁺) phenotype with more effector like characteristics as compared to healthy controls. Further, we observed that the HESN population had a higher frequency of HIV-specific poly-functional CD8⁺ T cells with robust in vitro virus inhibiting capacity against different clades of HIV. Overall, our results demonstrate that the HESN population has elevated levels of HIV-specific poly-functional CD8⁺ T cells with robust virus inhibiting ability and express elevated levels of markers pertaining to TSCM and follicular homing phenotype. These results demonstrate that future vaccine and therapeutic strategies should focus on eliciting these critical CD8⁺ T cell subsets.

Inflammation, HIV, and Immune Quiescence: Leveraging on Immunomodulatory Products to Reduce HIV Susceptibility

The relationship between inflammation and HIV has been a focus of research over the last decade. In HIV-infected individuals, increased HIV-associated immune activation significantly correlated to disease progression. While genital inflammation (GI) has been shown to significantly increase the risk of HIV acquisition and transmission, immune correlates for reduced risk remain limited. In certain HIV-exposed seronegative individuals, an immune quiescent phenotype characterized reduced risk. Immune quiescence is defined by specific, targeted, highly regulated immune responses that hinder overt inflammation or immune activation. Targeted management of inflammation, therefore, is a plausible strategy to mitigate HIV risk and slow disease progression. Nonsteroidal anti-inflammatory drugs (NSAIDs) such as hydroxychloroquine and aspirin have shown encouraging preliminary results in low-risk women by reducing systemic and genital immune activation. A topical NSAID, containing ibuprofen, is effective in treating vulvovaginal inflammation. Additionally, the glucocorticoids (GCs), prednisolone, and dexamethasone are used to treat HIV-associated immune activation. Collectively, these data inform on immune-modulating drugs to reduce HIV risk. However, the prolonged use of these pharmaceutical drugs is associated with adverse effects, both systemically and to a lesser extent topically. Natural products with their reduced side effects coupled with anti-inflammatory properties render them viable options. Lactic acid (LA) has immunomodulatory properties. LA regulates the genital microbiome by facilitating the growth of Lactobacillus species, while simultaneously limiting bacterial species that cause microbial dysbiosis and GI. Glycerol monolaurate, besides being anti-inflammatory, also inhibited SIV infections in rhesus macaques. The proposed pharmaceutical and natural products could be used in combination with either antiretrovirals for treatment or preexposure prophylaxis for HIV prevention. This review provides a summary on the associations between inflammation, HIV risk, and disease progression. Furthermore, we use the knowledge from immune quiescence to exploit the use of pharmaceutical and natural products as strategic interventions to manage inflammation, toward mitigating HIV infections.

Natural Immunity to HIV: A Template for Vaccine Strategies

Africa accounts for the majority of global human immunodeficiency virus (HIV) infections, most of which affect women through heterosexual intercourse. Currently, there is no cure for HIV and the development of vaccines and microbicides remains the best solution to eradicate the pandemic. We and others have identified HIV highly-exposed seronegative (HESN) individuals among African female commercial sex workers (CSWs). Analyses of genital samples from HESNs have demonstrated potent innate and anti-inflammatory conditions, HIV-specific CD4⁺ and CD8⁺ T-cells as well as immunoglobulins (Igs), and increased regulatory cell populations, all of which support a delicate balance between strength and control against HIV intrusion. Moreover, we have recently shown that frequencies of innate marginal zone (MZ) B-cells are decreased in the blood of HESNs when compared to HIV-uninfected non-CSW women, suggesting their recruitment to peripheral sites. This coincides with the fact that levels of B lymphocyte stimulator (BLyS/BAFF), known to shape the MZ pool and whose overexpression leads to MZ deregulation in HIV-infected progressors, are significantly lower in the blood of HESNs when compared to both HIV-infected CSWs and HIV-uninfected non-CSW women. Interestingly, MZ B-cells can bind HIV gp120 and produce specific IgG and IgA, and have a propensity for B regulatory potential, which could help both the fight against HIV and maintenance of low inflammatory conditions in HESNs. HESN individuals provide an exceptional opportunity to identify important clues for the development of protective devices, and efforts should aim at soliciting immune responses observed in the context of their natural immunity to HIV.

Brief Report: HIV-1 gp120 T-Cell Responses Correspond to Infection Outcomes in the Global iPrEx Chemoprophylaxis Trial

Association of HIV-1–specific T-cell responses to infection risk in seronegative individuals is controversial. We quantified and phenotypically characterized gp120-specific T-cell responses in HIV-1 exposed, but uninfected subjects enrolled in the global Pre-exposure Prophylaxis Initiative (iPrEx) chemoprophylaxis trial. IFNγ ELISpot responses were detected in 24% of subjects irrespective of infection outcome. HIV-1 gp120 envelope-specific T-cell responses were more uniformly IFN-γ+TNF-α+Mip-1β+ in persistently seronegative subjects relative to subjects who later seroconverted (median frequency of 76.5% and 66.5%, respectively). IFNγ responses targeted the V2 loop for subjects who remained seronegative. HIV-1 gp120 envelope V2 loop-specific CD8⁺ T-cell responses may help to protect against HIV-1 acquisition.

Blood B Lymphocyte Stimulator (BLyS)/BAFF levels may reflect natural immunity to HIV in highly exposed uninfected Beninese Commercial Sex Workers

We have previously shown that excess B lymphocyte Stimulator (BLyS)/BAFF in plasma and on surface of blood dendritic cells (DC) of HIV-infected progressors coincides with B-cell dysregulations and increased frequencies of "precursor" innate marginal zone (MZ)-like B-cells. In contrast, both blood BLyS levels and frequencies of this population remained unaltered in HIV elite-controllers. Based on these observations, we hypothesized that control of BLyS and innate B-cell status could be associated with natural immunity against HIV infection. Therefore, we assessed blood BLyS levels and B-cell status in HIV highly-exposed commercial sex workers (CSWs) from Benin. We found blood BLyS levels of HIV-uninfected CSWs were lower than those observed in both HIV-infected CSW and HIV-uninfected non-CSW groups. Furthermore, levels of BLyS expression on blood T-cells and monocytes were lower in HIV-uninfected CSWs when compared to HIV-infected CSWs, but higher than those observed for HIV-uninfected non-CSWs. Concomitantly, HIV-infected CSWs presented a dysregulated blood B-cell compartment, characterized by increased total IgG1, increased frequencies of populations presenting immature and/or innate profiles and a higher ratio of IgG(+)/IgA(+) plasmablasts. In contrast, relatively low levels of BLyS in the blood of HIV-uninfected CSWs coincided with a rather preserved B-cell compartment.

HIV-1 and hijacking of the host immune system: the current scenario

Human immunodeficiency virus (HIV) infection is a major health burden across the world which leads to the development of acquired immune deficiency syndrome (AIDS). This review article discusses the prevalence of HIV, its major routes of transmission, natural immunity, and evasion from the host immune system. HIV is mostly prevalent in Sub-Saharan Africa and low income countries. It is mostly transmitted by sharing syringe needles, blood transfusion, and sexual routes. The host immune system is categorized into three main types; the innate, the adaptive, and the intrinsic immune system. Regarding the innate immune system against HIV, the key players are mucosal membrane, dendritic cells (DCs), complement system, interferon, and host Micro RNAs. The major components of the adaptive immune system exploited by HIV are T cells mainly CD4+ T cells and B cells. The intrinsic immune system confronted by HIV involves (apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like 3G) APOBEC3G, tripartite motif 5-α (TRIM5a), terherin, and (SAM-domain HD-domain containing protein) SAMHD1. HIV-1 efficiently interacts with the host immune system, exploits the host machinery, successfully replicates and transmits from one cell to another. Further research is required to explore evasion strategies of HIV to develop novel therapeutic approaches against HIV.

Cellular immune correlates analysis of an HIV-1 preexposure prophylaxis trial

HIV-1-specific T-cell responses in exposed seronegative subjects suggest that a viral breach of the exposure site is more common than current transmission rates would suggest and that host immunity can extinguish subsequent infection foci. The Preexposure Prophylaxis Initiative (iPrEx) chemoprophylaxis trial provided an opportunity to rigorously investigate these responses in a case-control immunology study; 84 preinfection peripheral blood mononuclear cell samples from individuals enrolled in the iPrEx trial who later seroconverted were matched with 480 samples from enrolled subjects who remained seronegative from both the placebo and active treatment arms. T-cell responses to HIV-1 Gag, Protease, Integrase, Reverse Transcriptase, Vif, and Nef antigens were quantified for all subjects in an IFN-γ enzyme-linked immunospot (ELISpot) assay. IFN-γ responses varied in magnitude and frequency across subjects. A positive response was more prevalent in those who remained persistently HIV-1-negative for Gag (P = 0.007), Integrase (P < 0.001), Vif (P < 0.001), and Nef (P < 0.001). When correlated with outcomes in the iPrEx trial, Vif- and Integrase-specific T-cell responses were associated with reduced HIV-1 infection risk [hazard ratio (HR) = 0.36, 95% confidence interval (95% CI) = 0.19-0.66 and HR = 0.52, 95% CI = 0.28-0.96, respectively]. Antigen-specific responses were independent of emtricitabine/tenofovir disoproxil fumarate use. IFN-γ secretion in the ELISpot was confirmed using multiparametric flow cytometry and largely attributed to effector memory CD4+ or CD8+ T cells. Our results show that HIV-1-specific T-cell immunity can be detected in exposed but uninfected individuals and that these T-cell responses can differentiate individuals according to infection outcomes.

Maternal plasma and breastmilk viral loads are associated with HIV-1-specific cellular immune responses among HIV-1-exposed, uninfected infants in Kenya

Infants exposed to maternal HIV-1 provide an opportunity to assess correlates of HIV-1-specific interferon (IFN)-γ responses and may be informative in the development of HIV-1 vaccines. HIV-1-infected women with CD4 counts 200-500 cells/mm(3) were randomized to short-course zidovudine/nevirapine (ZDV/NVP) or highly active anti-retroviral therapy (HAART) between 2003 and 2005. Maternal plasma and breastmilk HIV-1 RNA and DNA were quantified during the first 6-12 months postpartum. HIV-1 gag peptide-stimulated enzyme-linked immunospot (ELISPOT) assays were conducted in HIV-1-exposed, uninfected infants (EU), and correlates were determined using regression and generalized estimating equations. Among 47 EU infants, 21 (45%) had ≥1 positive ELISPOT result during follow-up. Infants had a median response magnitude of 177 HIV-1-specific spot-forming units (SFU)/106 peripheral blood mononuclear cells (PBMC) [interquartile range (IQR)=117-287] directed against 2 (IQR = 1-3) gag peptide pools. The prevalence and magnitude of responses did not differ by maternal anti-retroviral (ARV) randomization arm. Maternal plasma HIV-1 RNA levels during pregnancy (P=0.009) and breastmilk HIV-1 DNA levels at 1 month (P=0.02) were associated with a higher magnitude of infant HIV-1-specific ELISPOT responses at 1 month postpartum. During follow-up, concurrent breastmilk HIV-1 RNA and DNA (cell-free virus and cell-associated virus, respectively) each were associated positively with magnitude of infant HIV-1-specific responses (P=0.01). Our data demonstrate the importance of antigenic exposure on the induction of infant HIV-1-specific cellular immune responses in the absence of infection.

Resistance to hepatitis C virus: potential genetic and immunological determinants

Studies of individuals who were highly exposed but seronegative (HESN) for HIV infection led to the discovery that homozygosity for the Δ32 deletion mutation in the CCR5 gene prevents viral entry into target cells, and is associated with resistance to infection. Additionally, evidence for protective immunity has been noted in some HESN groups, such as sex workers in The Gambia. Population studies of individuals at high risk for hepatitis C virus infection suggest that an HESN phenotype exists. The body of evidence, which suggests that protective immunity allows clearance of hepatitis C virus without seroconversion is growing. Furthermore, proof-of-principle evidence from in-vitro studies shows that genetic polymorphisms can confer resistance to establishment of infection. This Review discusses the possibility that genetic mutations confer resistance against hepatitis C virus, and also explores evidence for protective immunity, including via genetically programmed variations in host responses. The data generally strengthens the notion that investigations of naturally arising polymorphisms within the hepatitis C virus interactome, and genetic association studies of well characterised HESN individuals, could identify potential targets for vaccine design and inform novel therapies.

HIV-1 adaptation to HLA: a window into virus-host immune interactions

HIV-1 develops specific mutations within its genome that allow it to escape detection by human leukocyte antigen (HLA) class I-restricted immune responses, notably those of CD8(+) cytotoxic T lymphocytes (CTL). HLA thus represents a major force driving the evolution and diversification of HIV-1 within individuals and at the population level. Importantly, the study of HIV-1 adaptation to HLA also represents an opportunity to identify what qualities constitute an effective immune response, how the virus in turn adapts to these pressures, and how we may harness this information to design HIV-1 vaccines that stimulate effective cellular immunity.

The rise and fall of HIV in high-prevalence countries: a challenge for mathematical modeling

Several countries with generalized, high-prevalence HIV epidemics, mostly in sub-Saharan Africa, have experienced rapid declines in transmission. These HIV epidemics, often with rapid onsets, have generally been attributed to a combination of factors related to high-risk sexual behavior. The subsequent declines in these countries began prior to widespread therapy or implementation of any other major biomedical prevention. This change has been construed as evidence of behavior change, often on the basis of mathematical models, but direct evidence for behavior changes that would explain these declines is limited. Here, we look at the structure of current models and argue that the common “fixed risk per sexual contact" assumption favors the conclusion of substantial behavior changes. We argue that this assumption ignores reported non-linearities between exposure and risk. Taking this into account, we propose that some of the decline in HIV transmission may be part of the natural dynamics of the epidemic, and that several factors that have traditionally been ignored by modelers for lack of precise quantitative estimates may well hold the key to understanding epidemiologic trends.

Association between cellular immune activation, target cell frequency, and risk of human immunodeficiency virus type 1 superinfection

We performed a case-control study of women at risk of HIV-1 superinfection to understand the relationship between immune activation and HIV-1 acquisition. An increase in the frequency of HIV-1 target cells, but not in other markers of T cell activation, was associated with a 1.7-fold increase in the odds of superinfection. This suggests that HIV-1 acquisition risk is influenced more by the frequency of target cells than by the generalized level of immune activation.

Immune quiescence: a model of protection against HIV infection

Aberrant immune activation is a strong correlate of HIV disease progression, but little is known about how immune activation alters susceptibility to HIV infection. Susceptibility to HIV infection varies between individuals, but the immunological determinants of HIV transmission are not well understood. Here, we present evidence from studies of HIV transmission in the context of clinical trials and HIV-exposed seronegative (HESN) cohorts that implicates elevated immune activation as a risk factor for acquiring HIV. We propose a model of protection from infection based on a phenotype of low baseline immune activation referred to as immune quiescence. Immune quiescence is evidenced by reduced expression of T cell activation markers, low levels of generalized gene transcription and low levels of proinflammatory cytokine and chemokine production in the periphery and genital mucosa of HESN. Since HIV preferentially replicates in activated CD4+ T cells, immune quiescence may protect against infection by limiting HIV target cell availability. Although the determinants of immune quiescence are unclear, several potential factors have been identified that may be involved in driving this phenotype. HESN were shown to have elevated proportions of regulatory T cells (Tregs), which are known to suppress T cell activation. Likewise, proteins involved in controlling inflammation in the genital tract have been found to be elevated in HESN. Furthermore, expression of interferon regulatory factor 1 (IRF-1) is reduced in HESN as a consequence of genetic polymorphisms and differential epigenetic regulation. Since IRF-1 is an important regulator of immune responses, it may play a role in maintaining immune quiescence. Based on this model, we propose a novel avenue for HIV prevention targeted based on reducing host mucosal immune activation.

HIV exposed seronegative individuals show antibodies specifically recognizing native HIV envelope glycoprotein

BACKGROUND

Susceptibility to HIV transmission by sexual intercourse has been associated with cellular anti-HIV responses. We aimed to also evaluate potential systemic humoral responses against HIV in a group of HIV-exposed seronegative individuals (HESN) in stable relationship with HIV-infected partners.

METHODS

We recruited 27 serodiscordant couples. HESN were classified according to HIV exposure into very low/low and moderate/high risk. Plasma from HESN and HIV partners were tested for neutralizing capacity and for the recognition of cell-surface expressed and recombinant forms of HIV envelope glycoproteins (Env). Healthy individuals (healthy control, n=11) were used as controls.

RESULTS

Recognition of cell-surface expressed Env by both immunoglobulin (Ig)G and IgA was higher in plasma samples from HESN than in healthy controls (P=0.0062 and P=0.0144, respectively). IgG binding to Env was significantly increased in HESN after unmasking CD4-induced epitopes (P=0.001), suggesting a wide range of targeted epitopes. Remarkably, ELISA assays using trimeric gp140 or monomeric gp120 failed to detect significant differences in reactivity between groups. Neutralization analysis showed residual activity in only three HESN samples (11%), whereas 70% of HIV-infected partners showed neutralizing activity. Although anti-Env humoral responses were found in 85% of HESN, their magnitude was not associated with the estimated level of exposure or the detection of HIV-specific cellular immune responses.

CONCLUSION

A high proportion of HESN show detectable plasma IgG or IgA recognizing different exposed and cryptic Env native epitopes unrelated to neutralizing capacity. Therefore, low but persistent HIV exposure induces new virus-specific systemic humoral responses or boosts preexisting natural antibodies.

Correlates and characteristics of hepatitis C virus-specific T-cell immunity in exposed uninfected high-risk prison inmates

Some hepatitis C (HCV)-uninfected, high-risk individuals have HCV-specific cellular immunity without viraemia or seroconversion. The characteristics of these responses and the risk behavioural associations were studied in 94 subjects in a prospective cohort of recently seronegative prisoners reporting injecting drug use (IDU). Detailed behavioural data were collected. HCV antibody and PCR testing were performed. ELISpot assays for HCV-induced interferon (IFN)-γ and interleukin (IL)-2 production by T lymphocytes, as well as multiplex in vitro cytokine production assays, were performed. Seventy-eight subjects remained antibody and PCR negative and 16 seroconverted. Of the seronegative group, 22 (28%) had IFN-γ ELISpot responses in comparison with 13 of the 16 seroconverters (82%). This seronegative immune status was associated positively with injecting anabolic steroids and negatively with a recent break from IDU. The IFN-γ ELISpot responses involved both CD4 and CD8 T lymphocytes and were comparable in magnitude, but narrower in specificity, in uninfected subjects than in seroconverters. A subset of seronegative subjects had HCV-induced cytokine production patterns comparable with the seroconverters with increased production of IFN-γ, IL-2 and tumour necrosis factor (TNF)-α and reduced IL-10 in response to nonstructural peptides. In conclusion, comparable patterns of HCV-specific cellular immunity are found in recently infected subjects and in a minority of high-risk, uninfected subjects. Further characterization of these responses and their protective efficacy will inform HCV vaccine development.

Natural Immunity to HIV: a delicate balance between strength and control

Understanding how the mucosal immune system in the human female reproductive tract might prevent or facilitate HIV infection has important implications for the design of effective interventions. We and others have established cohorts of highly-exposed, HIV-seronegative individuals, such as HIV-uninfected commercial sex workers, who have remained HIV-negative after more than 5 years of active prostitution. Observations obtained in studies of such individuals, who represent a model of natural immunity to HIV, indicate that HIV resistance may be associated with the host's capacity to preserve systemic integrity by constraining immune activity and controlling inflammatory conditions at the mucosal point of entry. This likely necessitates the orchestration of balanced, first-line and adaptive immune responses.

[Factors involved in resistance to human immunodeficiency virus infection]

Repeated exposure to human immunodeficiency virus (HIV) is not always associated with infection and a subset of individuals remains persistently as HIV-seronegative despite multiple episodes of HIV exposure. These individuals are called HIV-exposed seronegatives (ESN). Several genetic and immunological factors have been involved in this resistance to HIV acquisition. Genetic factors have been linked to genes encoding chemokine receptors and their natural ligands as well as genes of the major histocompatibility complex. Immunological factors include both innate and adaptive immunity. The study of ESN provides a unique opportunity to unveil the mechanisms of natural protection against viral infection. Their better understanding may lead to novel preventive and immune-therapeutic approaches, including vaccines.

Computational analysis of HIV-1 resistance based on gene expression profiles and the virus-host interaction network

A very small proportion of people remain negative for HIV infection after repeated HIV-1 viral exposure, which is called HIV-1 resistance. Understanding the mechanism of HIV-1 resistance is important for the development of HIV-1 vaccines and Acquired Immune Deficiency Syndrome (AIDS) therapies. In this study, we analyzed the gene expression profiles of CD4+ T cells from HIV-1-resistant individuals and HIV-susceptible individuals. One hundred eighty-five discriminative HIV-1 resistance genes were identified using the Minimum Redundancy-Maximum Relevance (mRMR) and Incremental Feature Selection (IFS) methods. The virus protein target enrichment analysis of the 185 HIV-1 resistance genes suggested that the HIV-1 protein nef might play an important role in HIV-1 infection. Moreover, we identified 29 infection information exchanger genes from the 185 HIV-1 resistance genes based on a virus-host interaction network analysis. The infection information exchanger genes are located on the shortest paths between virus-targeted proteins and are important for the coordination of virus infection. These proteins may be useful targets for AIDS prevention or therapy, as intervention in these pathways could disrupt communication with virus-targeted proteins and HIV-1 infection.

HIV vaccines: current status worldwide and in Africa

Since HIV-1 was identified, development of a preventive vaccine has been a major goal. Significant progress toward that goal has been made by 2010. In macaques, a vigorous T effector cell response has protected some animals from disease caused by simian immunodeficiency virus (SIV). Broadly, neutralizing human anti-HIV antibodies have been isolated and their structures, and targets are rapidly being elucidated. For the first time an AIDS vaccine has shown modest protective efficacy in a human clinical trial. To reach the final goal, there is a need for a coordinated global effort, including a range of approaches including novel high-throughput screening techniques, X-ray crystallography, and monoclonal antibody isolation, analysis of T cell responses and their impact on disease progression, human epidemiology, as well as targeted studies in nonhuman primates. African research teams as well as cohorts of healthy volunteers and HIV-infected individuals have contributed to HIV vaccine research and development in many important ways. It is essential that this work continue to speed the development and deployment of a vaccine suitable for African populations.

HIV viral set point and host immune control in individuals with HIV-specific CD8+ T-cell responses prior to HIV acquisition

OBJECTIVE

Vaccine-induced CD8(+) T-cell responses in primates have been associated with a reduced simian immunodeficiency virus plasma viral load and enhanced T-cell responses, but cellular vaccines have shown limited success in human trials. We previously described HIV-specific T-cell responses in two groups of highly exposed, persistently seronegative Kenyan female sex workers, and a subset of these participants have subsequently acquired HIV. We examined the impact of pre-existing CD8(+) T-cell responses on post-acquisition outcomes.

DESIGN AND METHODS

HIV-specific CD8(+) T-cell responses had been examined in highly exposed, persistently seronegative participants from the Pumwani and Kibera cohorts, using a combination of virus-specific lysis, proliferation, interferon-gamma production, or all. Plasma viral load set point and HIV-specific T-cell proliferation and cytokine production were now examined post hoc by blinded investigators in the subset of participants who acquired HIV.

RESULTS

Pre-acquisition cellular immune assays and post-infection viral load were available for 46 participants, and HIV-specific CD8(+) T-cell responses had been detected in 25 of 46 (54%) participants. Pre-acquisition CD8(+) T-cell responses were associated with a lower post-acquisition HIV viral load set point in both cohorts (pooled analysis, 3.1 vs. 4.1 log(10) RNA copies/ml; P=0.0002) and with enhanced post-acquisition HIV-specific CD8(+) T-cell proliferation (3.8 vs. 1.0%, P=0.03), but with a trend to reduced post-acquisition CD8(+) T-cell interferon-gamma responses.

CONCLUSION

HIV-specific CD8(+) T-cell responses prior to HIV acquisition were associated with a lower HIV viral load and an altered functional profile of post-acquisition CD8(+) T-cell responses.

Development of Th1 imprints to rBCG expressing a foreign protein: implications for vaccination against HIV-1 and diverse influenza strains

We demonstrate here that immunizing naïve mice with low numbers of recombinant Bacille Calmette-Guérin (rBCG) expressing β-galactosidase (β-gal) generates predominant Th1 responses to both BCG and β-gal whereas infection with high numbers generates a mixed Th1/Th2 response to both BCG and β-gal. Furthermore, the Th1 response to both BCG and β-gal is stable when mice, pre-exposed to low numbers of rBCG, are challenged four months later with high numbers of rBCG. Thus the Th1/Th2 phenotypes of the immune responses to β-gal and to BCG are “coherently” regulated. Such rBCG vectors, encoding antigens of pathogens preferentially susceptible to cell-mediated attack, may be useful in vaccinating against such pathogens. We discuss vaccination strategies employing rBCG vectors that are designed to provide protection against diverse influenza strains or numerous variants of HIV-1 and consider what further experiments are essential to explore the possibility of realizing such strategies.

Association and impact of XPG Asp 1104 His gene polymorphism in HIV 1 disease progression to AIDS among north Indian HIV seropositive individuals

Various efforts made to stop the deadly epidemic of HIV since its discovery in 1983 remain unsuccessful and this virus still continues to claim the lives of millions of individuals every year. The viral effect in the cell is complicated and the overall disease outcome is the result of interaction between a few viral proteins and complex host immune response. Because it has been reported that XPG (Xeroderma pigementesum group G) gene does play a role in reducing UV induced apoptosis and participate in Nucleotide Excision Repair (NER) process of DNA damage, it was hypothesized that polymorphism in this gene may have a role in HIV 1 disease progression to AIDS. The aim of the present study, therefore, was to find out the association between XPG gene polymorphism and its effect on the rate of HIV 1 disease progression to AIDS. 300 HIV seropositive cases and an equal number of age and sex matched controls were recruited for the study from north Indian population. The PCR-RFLP method was utilized to genotype 600 study subject for the XPG Asp (1104) His gene polymorphism. There was significant difference in the frequency of the His/His variant genotype (OR 1.95, 95% CI = 1.93-3.63, P = 0.04) between cases and controls indicating a probable role of this gene in host viral interactions.

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.

Imbalance of naive and memory T lymphocytes with sustained high cellular activation during the first year of life from uninfected children born to HIV-1-infected mothers on HAART

The immune consequences of in utero HIV exposure to uninfected children whose mothers were submitted to highly active antiretroviral therapy (HAART) during gestation are not well defined. We evaluated 45 HIV-exposed uninfected (ENI) neonates and 45 healthy unexposed control (CT) neonates. All HIV-infected mothers received HAART during pregnancy, and the viral load at delivery was <50 copies/mL for 56.8%. Twenty-three ENI neonates were further evaluated after 12 months and compared to 23 unexposed healthy age-matched infants. Immunophenotyping was performed by flow cytometry in cord and peripheral blood. Cord blood lymphocyte numbers did not differ between groups. However, ENI neonates had a lower percentage of naive T cells than CT neonates (CD4+, 76.6 vs 83.1%, P < 0.001; CD8+, 70.9 vs 79.6%, P = 0.003) and higher percentages of central memory T cells than CT neonates (CD4+, 13.9 vs 8.7%, P < 0.001; CD8+, 8.6 vs 4.8%, P = 0.001). CD38 mean fluorescence intensity of T cells was higher in ENI neonates (CD4+, 62.2 vs 52.1, P = 0.007; CD8+, 47.7 vs 35.3, P < 0.001). At 12 months, ENI infants still had higher mean fluorescence intensity of CD38 on T cells (CD4+, 34.2 vs 23.3, P < 0.001; CD8+, 26.8 vs 19.4, P = 0.035). Despite effective maternal virologic control at delivery, HIV-exposed uninfected children were born with lower levels of naive T cells. Immune activation was present at birth and remained until at least 12 months of age, suggesting that in utero exposure to HIV causes subtle immune abnormalities.

Viral fitness implications of variation within an immunodominant CD8+ T-cell epitope of HIV-1

Cytotoxic T-lymphocyte (CTL) epitopes within the HIV genome are subject to negative and positive selective pressures, the balance of which influences CTL escape at a given epitope. We investigated whether viral fitness requirements dictate conservation of the HLA-A2 restricted immunodominant epitope SLYNTVATL (SL9). Viral clones incorporating changes throughout the SL9 epitope region were compared to consensus SL9 virus in terms of replication kinetics and relative viral fitness. Constructs recapitulating in vivo SL9-CTL escape variants showed markedly little effect on replication and fitness, as did non-natural conservative mutations targeting immunologically relevant positions of the epitope. Although certain residues of the epitope were constrained by viral requirements, our research reveals that there are multiple SL9 variants that are well tolerated virologically but fail to arise in vivo. In light of this data, assumptions regarding the balance of immune and viral selective pressures on this immunodominant epitope sequence need to be reassessed.

High prevalence of genetically similar HIV-1 recombinants among infected sex workers in Nairobi, Kenya

HIV-1, a highly diverse infectious agent, shows the greatest sequence diversity in highly exposed individuals, including greater levels of recombination. HIV-1 diversity in Nairobi, Kenya was examined in 240 individuals, including both those with high and low exposure to HIV. Sequence analysis of a 590 nucleotide proviral region encompassing vpu and part of env revealed that most viruses were clade A1 (70%), while both clade D (9%) and clade C (6%) virus were also observed, as was recombinant virus (15%). Participation in sex work was significantly associated with clade: these subjects had a lower likelihood of infection with clade C virus and a higher likelihood of infection with a recombinant isolate (p = 0.038). Interestingly, most of the recombinants formed distinct groups based on shared recombination breakpoints between common clades (n = 33/37). This study shows the value of continued HIV sequence analysis to examine and monitor viral genetic variability.

Differences in immunoregulatory cytokine expression patterns in the systemic and genital tract compartments of HIV-1-infected commercial sex workers in Benin

Initial exposure to human immunodeficiency virus type 1 (HIV-1) during heterosexual transmission occurs in the genital tract. Although much of the literature on the immune response to HIV-1 infection is based on studies performed at the systemic level, our understanding of tissue-specific immunity is lacking. Levels of both genital mucosal and blood interleukin (IL)-2, IL-4, IL-6, IL-10, tumor necrosis factor (TNF)-alpha, and interferon (IFN)-gamma production were compared between 57 HIV-1-uninfected and 52 HIV-1-infected female commercial sex workers (CSWs) as well as 73 HIV-1-uninfected non-CSW control women at low risk for exposure. HIV-1-infected CSWs had significantly higher genital mucosal levels of TNF-alpha and IFN-gamma compared with those in both the HIV-uninfected CSW and non-CSW groups. In contrast, the serum levels of all the cytokines tested were lower in HIV-1-infected CSWs compared with those in the other groups. The increased production of genital mucosal pro-inflammatory cytokines in HIV-1-infected CSWs possibly reflects susceptibility to HIV-1 infection and disease progression/perpetuation at the initial site of exposure.

Human immunodeficiency virus (HIV) type 1 proviral hypermutation correlates with CD4 count in HIV-infected women from Kenya

APOBEC3G is an important innate immune molecule that causes human immunodeficiency virus type 1 (HIV-1) hypermutation, which can result in detrimental viral genome mutations. The Vif protein of wild-type HIV-1 counteracts APOBEC3G activity by targeting it for degradation and inhibiting its incorporation into viral particles. Additional APOBEC cytidine deaminases have been identified, such as APOBEC3F, which has a similar mode of action but different sequence specificity. A relationship between APOBEC3F/G and HIV disease progression has been proposed. During HIV-1 sequence analysis of the vpu/env region of 240 HIV-infected subjects from Nairobi, Kenya, 13 drastically hypermutated proviral sequences were identified. Sequences derived from plasma virus, however, lacked hypermutation, as did proviral vif. When correlates of disease progression were examined, subjects with hypermutated provirus were found to have significantly higher CD4 counts than the other subjects. Furthermore, hypermutation as estimated by elevated adenine content positively correlated with CD4 count for all 240 study subjects. The sequence context of the observed hypermutation was statistically associated with APOBEC3F/G activity. In contrast to previous studies, this study demonstrates that higher CD4 counts correlate with increased hypermutation in the absence of obvious mutations in the APOBEC inhibiting Vif protein. This strongly suggests that host factors, such as APOBEC3F/G, are playing a protective role in these patients, modulating viral hypermutation and host disease progression. These findings support the potential of targeting APOBEC3F/G for therapeutic purposes.

Full-length HIV type 1 proviral sequencing of 10 highly exposed women from Nairobi, Kenya reveals a high proportion of intersubtype recombinants

Phylogenetic analysis has revealed that the current HIV/AIDS pandemic consists of a multitude of different viral clades and recombinant viruses. The predominant circulating HIV-1 clade in Kenya is A1; however, Kenya borders countries where different subtypes are prominent, making Kenya a likely location for recombination. Previous studies have reported significant differences in the proportions of sequences in Kenya that are intersubtype recombinants. Studies that performed sequence-based typing on multiple HIV-1 genomic regions or full-length sequences found higher rates of recombination than those that examined a single gene or gene fragment. In this study, we describe full-length HIV-1 proviral sequence-based genotyping after limited peripheral blood mononuclear cell (PBMC) coculture. Ten subjects from a highly exposed cohort located in Nairobi, Kenya were examined. Pairwise comparison found minimal difference between sequences generated directly from patient PBMC DNA compared to sequences from cocultured PBMC DNA. Of the 10 full-length HIV-1 sequences examined, five were nonrecombinant clade A1, while the other five were unique intersubtype recombinants. Although this frequency of recombination is higher than previously described in Kenya, this finding is in agreement with previous full-length sequence data. Interestingly, although all the nonrecombinant sequences were clade A1, not all the recombinant sequences contained a clade A1 sequence.

Human leukocyte antigen-DQ alleles and haplotypes and their associations with resistance and susceptibility to HIV-1 infection

OBJECTIVES

To determine the association of DQ antigens with resistance and susceptibility to HIV-1.

DESIGN

Despite repeated exposure to HIV-1, a subset of women in the Pumwani Sex Worker cohort established in Nairobi, Kenya in 1985 have remained HIV-1 negative for at least 3 years and are classified as resistant. Differential susceptibility to HIV-1 infection is associated with HIV-1 specific CD4 and CD8 T cell responses. As human leukocyte antigen-DQ antigens present viral peptides to CD4 cells, we genotyped human leukocyte antigen -DQ alleles for 978 women enrolled in the cohort and performed cross-sectional and longitudinal analyses to identify associations of human leukocyte antigen -DQ with resistance/susceptibility to HIV-1.

METHODS

DQA1 and DQB1 were genotyped using taxonomy-based sequence analysis. SPSS 13.0 was used to determine associations of DQ alleles/haplotypes with HIV-1 resistance, susceptibility, and seroconversion rates.

RESULTS

Several DQB1 alleles and DQ haplotypes were associated with resistance to HIV-1 infection. These included DQB1*050301 (P = 0.055, Odds Ratio = 12.77, 95% Confidence Interval = 1.44-112), DQB1*0603 and DQB1*0609 (P = 0.037, Odds Ratio = 3.25, 95% Confidence Interval = 1.12-9.47), and DQA1*010201-DQB1*0603 (P = 0.044, Odds Ratio = 17.33, 95% Confidence Interval = 1.79-168). Conversely, DQB1*0602 (P = 0.048, Odds Ratio = 0.68, 95% Confidence Interval = 0.44-1.05) and DQA1*010201-DQB1*0602 (P = 0.039, Odds Ratio = 0.64, 95% Confidence Interval = 0.41-1.03) were overrepresented in the HIV-1 infected population. DQA1*0504-DQB1*0201, DQA1*010201-DQB1*0201, DQA1*0402-DQB1*0402 and DQA1*0402-DQB1*030101 genotypes were only found in HIV-1 positive subjects (Odds Ratio = 0.30-0.31, 95% Confidence Interval = 0.03-3.70), and these women seroconverted rapidly. The associations of these DQ alleles and haplotypes with resistance and susceptibility to HIV-1 were independent of the previously reported human leukocyte antigen-DRB*01, human leukocyte antigen A2/6802, and human leukocyte antigen-A*2301.

CONCLUSION

The associations of DQ alleles and haplotypes with resistance and susceptibility to HIV-1 emphasize the importance of human leukocyte antigen-DQ and CD4 in anti-HIV-1 immunity.

Effects of chronic alcohol drinking on receptor-binding, internalization, and degradation of human immunodeficiency virus 1 envelope protein gp120 in hepatocytes

Although alcohol drinking increases susceptibility to human immunodeficiency virus (HIV) infection, possible mechanisms underlying the effects of alcohol are not yet known. Since the HIV envelope protein gp120 plays a key role in progression of HIV infection, the aim of the present study was to evaluate the toxicity and degradation of gp120 in hepatocytes isolated from liver of alcohol-preferring rats drinking either 15% ethanol in water or pure water for 70 days. The hypothesis was that alcohol drinking augmented the toxicity, but suppressed degradation of gp120. Hepatocytes from water-drinking rats (C-cells) or ethanol-drinking rats (Et-cells) were treated with laptacystin, anti-CD4 antibodies, CCR5 antagonist, or mannose, followed by [(125)I]gp120 or native gp120. At predetermined intervals, control (C) and ethanol exposed (Et) cells were analyzed for toxicity and degradation of gp120. In C-cells, [(125)I]gp120 binding and internalization peaked within 5-45 min and remained elevated for up to 10h and then decreased gradually. In Et-cells, [(125)I]gp120 binding peaked comparably to C-cells, but the binding remained to the peak level throughout the experimental period. C-cells exhibited the lysosomal/ubiquitin-mediated degradation of intracellular gp120, resulting in released gp120 fragments into the incubation medium that suppressed gp120-CD4 binding, improved cell viability, and inhibited gp120-induced apoptosis. Ethanol drinking suppressed gp120 degradation in and release of gp120 fragments from hepatocytes. The incubation medium of Et-cells did not suppress gp120-CD4 binding or the gp120-mediated apoptosis in hepatocytes. Thus, chronic alcohol drinking augmented the adverse effects of gp120 possibly by suppressing its degradation in hepatocytes. The present observation also suggests that a number of CCR5 or ubiquitin-based therapeutic drugs may not be effective in suppressing HIV infection in alcohol-drinking subjects.

Human T cell reconstitution in DiGeorge syndrome and HIV-1 infection

The thymus is essential for proper development and maintenance of a broad T cell repertoire capable of recognizing a wide-range of foreign antigens. Recent advances in multicolor flow cytometry, non-invasive imaging techniques, and molecular assessments of thymic function have enabled a more comprehensive characterization of human thymic output in clinical settings than in the past. These techniques have been particularly valuable in monitoring human T cells after therapeutic thymic grafting for complete DiGeorge syndrome and during HIV-1 infection and AIDS. By defining the degree and mechanisms of T cell reconstitution in these settings, clinical investigators and primary caregivers have been able to better diagnose, treat and care for individuals with congenital or acquired immune deficiencies associated with loss of thymic function.

Sharing the benefits of genetic resources: from biodiversity to human genetics

Benefit sharing aims to achieve an equitable exchange between the granting of access to a genetic resource and the provision of compensation. The Convention on Biological Diversity (CBD), adopted at the 1992 Earth Summit in Rio de Janeiro, is the only international legal instrument setting out obligations for sharing the benefits derived from the use of biodiversity. The CBD excludes human genetic resources from its scope, however, this article considers whether it should be expanded to include those resources, so as to enable research subjects to claim a share of the benefits to be negotiated on a case-by-case basis. Our conclusion on this question is: 'No, the CBD should not be expanded to include human genetic resources.' There are essential differences between human and non-human genetic resources, and, in the context of research on humans, an essentially fair exchange model is already available between the health care industry and research subjects. Those who contribute to research should receive benefits in the form of accessible new health care products and services, suitable for local health needs and linked to economic prosperity (e.g. jobs). When this exchange model does not apply, as is often the case in developing countries, individually negotiated benefit sharing agreements between researchers and research subjects should not be used as 'window dressing'. Instead, national governments should focus their finances on the best economic investment they could make; the investment in population health and health research as outlined by the World Health Organization's Commission on Macroeconomics and Health; whilst international barriers to such spending need to be removed.

Characterization of CD8 T-cell responses in HIV-1-exposed seronegative commercial sex workers from Nairobi, Kenya

CD8+ T-lymphocyte responses are crucial to the control of HIV-1; therefore, studying the CD8+ immune response in a naturally resistant population could provide valuable insights into an effective anti-HIV response in healthy uninfected individuals. Approximately 5-10% of the women in the Pumwani Commercial Sex Worker cohort in Nairobi, Kenya, have been highly exposed to HIV-1 yet remain HIV-IgG-seronegative and HIV-PCR negative (HIV(ES)). As IFN-gamma production correlates to cytotoxic function, the CD8+ T-lymphocyte IFN-gamma response to HIV p24 peptides was compared in HIV(ES) and HIV-infected (HIV+) individuals. Almost 40% of the HIV(ES) had a CD8+ IFN-gamma+ response that was five times lower in magnitude than that of the HIV+ group. The breadth of the response in HIV(ES) was very narrow and focused primarily on one peptide that is similar to the protective KK10 peptide. In the HIV+ group, low peripheral CD4+ counts negatively influenced the number of CD8+ cells producing IFN-gamma, which may undermine the ability to control HIV. Overall, many of the HIV(ES) women possess a HIV-1 p24-specific CD8+ IFN-gamma response, providing evidence to the specificity needed for an effective HIV vaccine.

Protective immunity against hepatitis C virus infection

There is increasing evidence that a small percentage of individuals exposed to the hepatitis C virus have the capacity to generate a strong cellular immune response against the virus and avoid persistent infection, and perhaps do so repeatedly after re-exposure. This article reviews the evidence that the responses identified in this unique group of individuals represent the protective immunity that will need to be elicited by hepatitis C virus vaccines.

Reduced CD4 T cell activation and in vitro susceptibility to HIV-1 infection in exposed uninfected Central Africans

BACKGROUND

Environmentally driven immune activation was suggested to contribute to high rates of HIV-1 infection in Africa. We report here a study of immune activation markers and susceptibility to HIV-1 infection in vitro of forty-five highly exposed uninfected partners (EUs) of HIV-1 infected individuals in Central African Republic, in comparison with forty-four low-risk blood donors (UCs).

RESULTS

Analysis of T lymphocyte subsets and activation markers in whole blood showed that the absolute values and the percentage of HLA-DR+CD4 T cells and of CCR5+CD4 T cells were lower in the EUs than in the UCs (p = 0.0001). Mutations in the CCR5 coding region were not found in either group. Susceptibility to in vitro infection of unstimulated peripheral blood mononuclear cells, prior of PHA activation, was decreased in EUs compared to UCs, either using a CXCR4-tropic or a CCR5-tropic HIV-1 strain (p = 0.02 and p = 0.05, respectively). Levels of MIP-1beta, but not of MIP-1alpha or RANTES, in the supernatants of PHA-activated PBMC, were higher in the EUs than in the UCs (p = 0.007).

CONCLUSION

We found low levels of CD4 T cell activation and reduced PBMC susceptibility to HIV-1 infection in Central African EUs, indicating that both may contribute to the resistance to HIV-1 infection.

Induction of serum and mucosal FIV-specific immune responses by intranasal immunization with p24Gag

We examined the ability of FIV p24Gag to induce systemic and mucosal FIV-specific immune responses when delivered as a nasal immunogen alone, or with a mucosal adjuvant, Escherichia coli heat labile toxin LT(R192G). Nasal immunization with p24Gag alone induced FIV-specific immune responses but overall responses were weak, transient, and/or present only in a few animals. Co-administration of LT(R192G) resulted in strong FIV-specific serum IgG and enhanced salivary IgA responses. Moreover, FIV-specific IgA was detected in vaginal wash fluid from 6/6 cats co-immunized with LT(R192G) and p24Gag versus 1/6 immunized with p24Gag alone. This is the first report detailing induction of systemic or mucosal FIV-specific immune responses by nasal immunization alone. As such, this study demonstrates that nasal immunization of cats can be a relevant and effective route for the delivery of candidate vaccines. However, while nasal immunization of cats with p24Gag induces antigen-specific systemic immune responses, development of strong systemic and mucosal immune responses requires co-administration of a mucosal adjuvant, such as LT(R192G).

Global human genetics of HIV-1 infection and China

Genetic polymorphisms in human genes can influence the risk for HIV-1 infection and disease progression, although the reported effects of these alleles have been inconsistent. This review highlights the recent discoveries on global and Chinese genetic polymorphisms and their association with HIV-1 transmission and disease progression.

[Mechanisms of resistance to sexual transmission of HIV-1]

Sexual transmission is the most common pathway for HIV-1; nevertheless some individuals remain seronegative despite repeated high risk sexual exposure. These were grouped in cohorts of "highly exposed but persistently seronegative" individuals, mostly prostitutes and flailing couples. Three lines of defence were observed in these cohorts. The first one is the mucosal barrier, the determining factors of which are the type of epithelium (monolayer or multilayer), epithelial integrity, and the pre-existing microflora. The second one is linked to innate immunity directly related to the genetic and/or immune predispositions of the individual: mutations affecting the CCR5 chemokine receptor, secretion of protective soluble factors, and particular HLA alleles. The third one is acquired immunity via the mechanisms of humoral and/or specific cellular immunity. These studies suggest anti HIV-1 vaccinal strategies aiming at a local immunization combining the different types of responses observed in these individuals.

Enhanced potency of plasmid DNA microparticle human immunodeficiency virus vaccines in rhesus macaques by using a priming-boosting regimen with recombinant proteins

DNA vaccines have been used widely in experimental primate models of human immunodeficiency virus (HIV), but their effectiveness has been limited. In this study, we evaluated three technologies for increasing the potency of DNA vaccines in rhesus macaques. These included DNA encoding Sindbis virus RNA replicons (pSINCP), cationic poly(lactide-co-glycolide) (PLG) microparticles for DNA delivery, and recombinant protein boosting. The DNA-based pSINCP replicon vaccines encoding HIV Gag and Env were approximately equal in potency to human cytomegalovirus (CMV) promoter-driven conventional DNA vaccines (pCMV). The PLG microparticle DNA delivery system was particularly effective at enhancing antibody responses induced by both pCMV and pSINCP vaccines and had less effect on T cells. Recombinant Gag and Env protein boosting elicited rapid and strong recall responses, in some cases to levels exceeding those seen after DNA or DNA/PLG priming. Of note, Env protein boosting induced serum-neutralizing antibodies and increased frequencies of gamma interferon-producing CD4 T cells severalfold. Thus, PLG microparticles are an effective means of delivering DNA vaccines in nonhuman primates, as demonstrated for two different types of DNA vaccines encoding two different antigens, and are compatible for use with DNA prime-protein boost regimens.

Evidence of HIV exposure and transient seroreactivity in archived HIV-negative severe hemophiliac sera

Background

Approximately 25% of hemophiliacs that were frequently exposed to blood clotting factor concentrates (CFCs) contaminated with human immunodeficiency virus (HIV) are presently HIV seronegative. In this study, we sought to determine if some of these individuals were at any time transiently HIV seropositive. In the early to mid-1980s the majority of severe hemophilia patients were exposed to CFCs contaminated with HIV. Although many of these hemophiliacs became HIV-positive, a small percentage did not become infected. To determine if some of these individuals successfully resisted viral infection, we attempted to document the presence of transient HIV reactive antibodies in archived plasma samples (1980–1992) from currently HIV-negative severe hemophiliacs who had a high probability of repeated exposure to HIV contaminated CFC. Archived plasma samples were retrospectively tested using an FDA approved HIV-1Ab HIV-1/HIV-2 (rDNA) enzyme immunoassay (EIA) and a HIV-1 Western blot assay (Wb), neither of which were commercially available until the late 1980s, which was after many of these samples had been drawn.

Results

We found that during the high risk years of exposure to HIV contaminated CFC (1980–1987), low levels of plasma antibodies reactive with HIV proteins were detectable in 87% (13/15) of the haemophiliacs tested. None of these individuals are presently positive for HIV proviral DNA as assessed by polymerase chain reaction (PCR).

Conclusion

Our data suggest that some severe hemophiliacs with heavy exposure to infectious HIV contaminated CFC had only transient low-level humoral immune responses reactive with HIV antigens yet remained HIV-negative and apparently uninfected. Our data supports the possibility of HIV exposure without sustained infection and the existence of HIV-natural resistance in some individuals.