Comparison of human immunodeficiency virus (HIV)-specific T-cell responses in HIV-1- and HIV-2-infected individuals in Senegal

Effect of Human Immunodeficiency Virus Infection on Human Papillomavirus Clearance Among Women in Senegal, West Africa

BACKGROUND

Persistent infection with high-risk human papillomavirus (HPV) is associated with development of invasive cervical cancer.

METHODS

Longitudinal data was collected from 174 Senegalese women. We employed marginal Cox proportional hazards models to examine the effect of human immunodeficiency virus (HIV) status (HIV positive vs HIV negative) and HIV type (HIV-1 vs HIV-2 vs dual HIV-1/HIV-2) on clearance of type-specific HPV infection. Analyses were stratified by incident versus prevalent HPV infection.

RESULTS

Incident HPV infections in HIV-positive women were less likely to clear than those in HIV-negative women (adjusted hazard ratio [HR] = 0.60; 95% confidence interval [CI], .38-.94). Among HIV-positive women, HIV-2-infected women and HIV-1/2 dually infected women were more likely to clear HPV incident infections than HIV-1-infected women (HR = 1.66; 95% CI, .95-2.92 and HR = 2.17; 95% CI, 1.12-4.22, respectively). Incident HPV infections in HIV-positive women with CD4 cell count ≤500 cells/μL were less likely to clear than those in HIV-positive women with CD4 cell count >500 cells/μL (HR = 0.65; 95% CI, .42-1.01). No significant associations were observed for prevalent HPV infections.

CONCLUSIONS

HIV infection reduced the likelihood of clearance of incident HPV infection. Furthermore, among HIV-positive women, low CD4 cell count and dual HIV infection were each associated with reduced likelihood of clearance.

Chronic pain and infection: mechanisms, causes, conditions, treatments, and controversies

Throughout human history, infection has been the leading cause of morbidity and mortality, with pain being one of the cardinal warning signs. However, in a substantial percentage of cases, pain can persist after resolution of acute illness, manifesting as neuropathic, nociplastic (eg, fibromyalgia, irritable bowel syndrome), or nociceptive pain. Mechanisms by which acute infectious pain becomes chronic are variable and can include immunological phenomena (eg, bystander activation, molecular mimicry), direct microbe invasion, central sensitization from physical or psychological triggers, and complications from treatment. Microbes resulting in a high incidence of chronic pain include bacteria such as the Borrelia species and Mycobacterium leprae, as well as viruses such as HIV, SARS-CoV-2 and herpeses. Emerging evidence also supports an infectious cause in a subset of patients with discogenic low back pain and inflammatory bowel disease. Although antimicrobial treatment might have a role in treating chronic pain states that involve active infectious inflammatory processes, their use in chronic pain conditions resulting from autoimmune mechanisms, central sensitization and irrevocable tissue (eg, arthropathy, vasculitis) or nerve injury, are likely to cause more harm than benefit. This review focuses on the relation between infection and chronic pain, with an emphasis on common viral and bacterial causes.

Host Defence RNases as Antiviral Agents against Enveloped Single Stranded RNA Viruses

Owing to the recent outbreak of Coronavirus Disease of 2019 (COVID-19), it is urgent to develop effective and safe drugs to treat the present pandemic and prevent other viral infections that might come in the future. Proteins from our own innate immune system can serve as ideal sources of novel drug candidates thanks to their safety and immune regulation versatility. Some host defense RNases equipped with antiviral activity have been reported over time. Here, we try to summarize the currently available information on human RNases that can target viral pathogens, with special focus on enveloped single-stranded RNA (ssRNA) viruses. Overall, host RNases can fight viruses by a combined multifaceted strategy, including the enzymatic target of the viral genome, recognition of virus unique patterns, immune modulation, control of stress granule formation, and induction of autophagy/apoptosis pathways. The review also includes a detailed description of representative enveloped ssRNA viruses and their strategies to interact with the host and evade immune recognition. For comparative purposes, we also provide an exhaustive revision of the currently approved or experimental antiviral drugs. Finally, we sum up the current perspectives of drug development to achieve successful eradication of viral infections.

HIV-2 as a model to identify a functional HIV cure

Two HIV virus types exist: HIV-1 is pandemic and aggressive, whereas HIV-2 is confined mainly to West Africa and less pathogenic. Despite the fact that it has been almost 40 years since the discovery of AIDS, there is still no cure or vaccine against HIV. Consequently, the concepts of functional vaccines and cures that aim to limit HIV disease progression and spread by persistent control of viral replication without life-long treatment have been suggested as more feasible options to control the HIV pandemic. To identify virus-host mechanisms that could be targeted for functional cure development, researchers have focused on a small fraction of HIV-1 infected individuals that control their infection spontaneously, so-called elite controllers. However, these efforts have not been able to unravel the key mechanisms of the infection control. This is partly due to lack in statistical power since only 0.15% of HIV-1 infected individuals are natural elite controllers. The proportion of long-term viral control is larger in HIV-2 infection compared with HIV-1 infection. We therefore present the idea of using HIV-2 as a model for finding a functional cure against HIV. Understanding the key differences between HIV-1 and HIV-2 infections, and the cross-reactive effects in HIV-1/HIV-2 dual-infection could provide novel insights in developing functional HIV cures and vaccines.

T-cell and B-cell perturbations identify distinct differences in HIV-2 compared with HIV-1-induced immunodeficiency

BACKGROUND

For unknown reasons, HIV-2 is less pathogenic than HIV-1, and HIV-2-induced immunodeficiency may be different from that caused by HIV-1. Previous immunological studies have hinted at possible shifts in both T-cell and B-cell subsets, which we aimed to characterize further.

METHODS

From an HIV clinic in Guinea-Bissau, 63 HIV-2, 83 HIV-1, and 26 HIV-negative participants were included. All HIV-infected participants were ART-naive. The following cell subsets were analysed by flow cytometry; T cells (maturation and activation), regulatory T cells, and B cells (maturation and activation).

RESULTS

After standardizing for sex, age, and CD4 T-cell count HIV-2 had 0.938 log10 copies/ml lower HIV RNA levels than the HIV-1-infected patients. Whereas T-cell maturation and regulatory T-cell profiles were similar between patients, HIV-2-infected patients had higher proportions of CD8CD28 and lower proportions of CD8PD-1+ T cells than HIV-1-infected patients. This finding was independent of HIV RNA levels. HIV-2 was also associated with a more preserved proportion of naive B cells.

CONCLUSION

HIV-2 is characterized by lower viral load, and lower T-cell activation, which may account for the slower disease progression.

Doye I, Toure M, Sy MP, Kiviat NB, Sow PS, Gottlieb GS, Hawes SE. Increasing prevalence of hypertension among HIV-positive and negative adults in Senegal, West Africa, 1994-2015

BACKGROUND

Non-communicable diseases, including hypertension (HTN), are increasingly recognized as important causes of morbidity and mortality among people living with HIV (PLHIV) in resource-limited settings. The goals of this study were to determine the prevalence of HTN among PLHIV in Senegal over time and to identify predictors of HTN among HIV-positive versus HIV-negative adults.

METHODS

We conducted a retrospective study using data from individuals enrolled in previous studies in Senegal from 1994-2015. Blood pressure (BP) measurements taken during study visits were used for analysis. HTN was defined as systolic BP≥140 or diastolic BP≥90. We used logistic regression to identify predictors of HTN.

RESULTS

We analyzed data from 2848 adults (1687 HIV-positive, 1161 HIV-negative). Among PLHIV, the prevalence of HTN increased from 11% during 1994-1999 to 22% during 2010-2015. Among HIV-negative individuals, the prevalence of HTN increased from 16% to 32%. Among both groups, the odds of HTN more than doubled from 1994-1999 to 2010-2015 (HIV-positive OR 2·4, 95% CI 1·1-5·0; HIV-negative OR 2·6, 95% CI 1·5-4·6). One quarter of all individuals with HTN had stage 2 HTN. The strongest risk factor for HTN was obesity (HIV-positive OR 3·2, 95% CI 1·7-5·8; p<0·01; HIV-negative OR 7·8, 95% CI 4·5-13·6; p<0·01). Male sex and age ≥50 were also predictive of HTN among both groups. Among HIV-positive subjects, WHO stage 1 or 2 disease was predictive of HTN and among HIV-negative subjects, having no formal education was predictive.

CONCLUSION

Over the past 20 years, the prevalence of HTN has doubled among both HIV-positive and HIV-negative adults in Senegal. Our study indicates that there is an increasing need for the integration of chronic disease management into HIV programs in Senegal. Furthermore, our findings highlight the need for enhanced prevention, recognition, and management of non-communicable diseases, including hypertension and obesity, among both HIV-positive and HIV-negative individuals in Senegal.

HIV and the dual burden of malnutrition in Senegal, 1994-2012

The aims of this study were to determine the nutritional status of HIV-positive versus HIV-negative adults in Senegal and to identify predictors of nutritional status among people living with HIV (PLHIV). We conducted a retrospective study using data from individuals enrolled in previous studies in Senegal. Undernutrition was defined as body mass index (BMI) <18.5 and overnutrition was defined as BMI ≥25.0. Subcategories of overnutrition were overweight (defined as BMI 25.0-29.9) and obesity (BMI ≥30.0). Predictors of nutritional status were identified using multinomial logistic regression. Data from 2448 adults were included; 1471 (60%) were HIV positive. Among HIV-negative individuals, the prevalence of undernutrition decreased from 23% in 1994-1999 to 5% in 2006-2012, while the prevalence of overnutrition increased from 19 to 55%. Among PLHIV, undernutrition decreased from 52 to 37% and overnutrition increased from 10 to 15%. Women had greater odds of obesity (odds ratio [OR] 11.4; p < 0.01). Among HIV-positive women, undernutrition was associated with WHO stage 3 or 4 and CD4 cell count <200; antiretroviral therapy (ART) and education were protective. Obesity was associated with age > 35 years, commercial sex work, and alcohol use. Among HIV-positive men, WHO stage 3 or 4 and CD4 cell count <200 were predictive of undernutrition; ART was protective. Our study highlights the need for the integration of nutrition interventions into HIV programs in Senegal and suggests that for nutrition programs to be most effective, strategies may need to differ when targeting men versus women. Furthermore, improving access to education and focusing on women for nutrition interventions could be of particularly high impact at the household level.

A Comparison of the Natural History of HPV Infection and Cervical Abnormalities among HIV-Positive and HIV-Negative Women in Senegal, Africa

Background: There is evidence of an interaction between HIV and human papillomavirus (HPV) resulting in increased HPV-associated morbidity and cancer mortality among HIV-positive women. This study aims to determine how the natural history of cervical HPV infection differs by HIV status.Methods: A total of 1,320 women (47% were positive for HIV-1 and/or HIV-2) were followed for an average of two years in Senegal, West Africa between 1994 and 2010. Cytology (with a sub-sample of histology) and HPV DNA testing were performed at approximately 4-month intervals yielding data from over 7,900 clinic visits. Competing risk modeling was used to estimate rates for transitioning between three clinically relevant natural history stages: Normal, HPV, and HSIL (high-grade squamous intraepithelial lesions). Among HIV-positive women, exploratory univariate analyses were conducted examining the impact of HPV type, infection with multiple HPV types, HIV type, CD4⁺ count, and age.Results: HIV-positive women had higher rates of progression and lower rates of regression compared with HIV-negative women (i.e., adverse transitions). HIV-positive women had a 2.55 [95% confidence interval (CI), 1.69-3.86; P < 0.0001] times higher rate of progression from HPV to HSIL than HIV-negative women (with 24-month absolute risks of 0.18 and 0.07, respectively). Among HIV-positive women, HPV-16/18 infection and CD4⁺ count <200/mm³ were associated with adverse transitions.Conclusions: Adverse HIV effects persist throughout HPV natural history stages.Impact: In the limited-resource setting of sub-Saharan Africa where cervical cancer screening is not widely available, the high-risk population of HIV-positive women may be ideal for targeted screening. Cancer Epidemiol Biomarkers Prev; 26(6); 886-94. ©2017 AACR.

Multiple Approaches for Increasing the Immunogenicity of an Epitope-Based Anti-HIV Vaccine

The development of a highly effective vaccine against the human immunodeficiency virus (HIV) will likely be based on rational vaccine design, since traditional vaccine approaches have failed so far. In recent years, an understanding of what type of immune response is protective against infection and/or disease facilitated vaccine design. T cell-based vaccines against HIV have the goal of limiting both transmission and disease progression by inducing broad and functionally relevant T cell responses. In this context, CD4(+) T cells play a direct cytotoxic role and are also important for the generation and maintenance of functional CD8(+) T and B cell responses. The use of MHC-binding algorithms has allowed the identification of novel CD4(+) T cell epitopes that could be used in vaccine design, the so-called epitope-driven vaccine design. Epitope-based vaccines have the ability to focus the immune response on highly antigenic, conserved epitopes that are fully recognized by the target population. We have recently mapped a set of conserved multiple HLA-DR-binding HIV-1 CD4 epitopes and observed interferon (IFN)-γ-producing CD4(+) T cells when we tested these peptides in peripheral blood mononuclear cells (PBMCs) from HIV-infected individuals. We then designed multiepitopic DNA vaccines that induced broad and polyfunctional T cell responses in immunized mice. In this review we will focus on alternative strategies to increase the immunogenicity of an epitope-based vaccine against HIV infection.

HIV-1 and HIV-2 differentially mature plasmacytoid dendritic cells into IFN-producing cells or APCs

HIV-1 causes a progressive impairment of immune function. HIV-2 is a naturally attenuated form of HIV, and HIV-2 patients display a slow-progressing disease. The leading hypothesis for the difference in disease phenotype between HIV-1 and HIV-2 is that more efficient T cell-mediated immunity allows for immune-mediated control of HIV-2 infection, similar to that observed in the minority of HIV-1-infected long-term nonprogressors. Understanding how HIV-1 and HIV-2 differentially influence the immune function may highlight critical mechanisms determining disease outcome. We investigated the effects of exposing primary human peripheral blood cells to HIV-1 or HIV-2 in vitro. HIV-2 induced a gene expression profile distinct from HIV-1, characterized by reduced type I IFN, despite similar upregulation of IFN-stimulated genes and viral restriction factors. HIV-2 favored plasmacytoid dendritic cell (pDC) differentiation into cells with an APC phenotype rather than IFN-α-producing cells. HIV-2, but not HIV-1, inhibited IFN-α production in response to CpG-A. The balance between pDC maturation into IFN-α-producing cells or development of an APC phenotype differentiates the early response against HIV-1 and HIV-2. We propose that divergent paths of pDC differentiation driven by HIV-1 and HIV-2 cause the observed differences in pathogenicity between the two viruses.

Human papillomavirus type 16 viral load in relation to HIV infection, cervical neoplasia and cancer in Senegal

BACKGROUND

The importance of human papillomavirus (HPV) viral load in the pathogenesis of cervical cancer among HIV-infected and HIV-uninfected women has not yet been established.

METHODS

In this cross-sectional study, HPV-16 viral loads were measured using previously-collected and frozen cervical swab samples from 498 HPV-16 positive Senegalese women (368 HIV-seronegative, 126 HIV-1 and/or HIV-2 seropositive). The real-time polymerase chain reaction assay was used to quantify HPV-16 E7 copy number normalized by human cellular DNA (β-actin), and viral loads were log10 transformed. Associations between HPV-16 viral load, degree of cervical abnormality, and HIV status were assessed using multinomial and linear regression methods.

RESULTS

Compared to women with normal cytology, the likelihood of CIN1 (ORa: 1.21, 95% CI 0.93-1.57), CIN2-3 (ORa: 2.38, 95% CI 1.72-3.29) and cancer (ORa: 2.12, 95% CI 1.52-2.96) was found to increase for each 1-unit log10 increase in HPV-16 viral load. Compared to HIV-negative women, HIV-positive women had higher average HPV-16 viral load values (βa: 0.39, 95% CI 0.03-0.75), even after accounting for degree of cervical abnormality.

CONCLUSION

In our study of women including those with cancer, HPV-16 viral load was associated with a higher likelihood of cervical abnormalities. However, substantial overlaps across categories of disease severity existed. Higher viral load among HIV-infected individuals may indicate that HIV infection influences HPV viral replication factors.

Influence of HIV-1 and/or HIV-2 infection and CD4 count on cervical HPV DNA detection in women from Senegal, West Africa

BACKGROUND

HIV infection is associated with greater risk of precancerous lesions and cervical cancer in women. However, several factors remain unclarified regarding the association between HIV infection and HPV detection, especially among those with HIV type 2 versus type 1 infection and severely immunocompromised persons.

OBJECTIVES

To evaluate HPV overall and type-specific detection among HIV-infected and uninfected women in Senegal.

STUDY DESIGN

Detection of HPV DNA for 38 genotypes in cervical swabs using PCR-based methods was evaluated in HIV-positive (n=467) and HIV-negative (n=2139) women participating in studies in Senegal. Among HIV-1 and/or HIV-2 positive women, CD4 counts were assessed. Adjusted multivariable prevalence ratios (PR) were calculated.

RESULTS

The prevalence of any HPV DNA and multiple HPV types was greater among HIV-infected individuals (78.2% and 62.3%, respectively) compared with HIV-negative women (27.1% and 11.6%). This trend was also seen for HPV types 16 and 18 (13.1% and 10.9%) compared to HIV-negative women (2.2% and 1.7%). HIV-infected women with CD4 cell counts less than 200 cells/μl had a higher likelihood of any HPV detection (PRa 1.30; 95% CI 1.07-1.59), multiple HPV types (PRa 1.52; 95% CI 1.14-2.01), and HPV-16 (PRa 9.00; 95% CI 1.66-48.67), but not HPV-18 (PRa 1.20, 95% CI 0.45-3.24) compared to those with CD4 counts 500 cells/μl or above.

CONCLUSION

HIV-infected women, especially those most severely immunocompromised, are more likely to harbor HPV. Measures to prevent initial HPV infection and subsequent development of cervical cancer through focused screening efforts should be implemented in these high risk populations.

Comparing HIV-1 and HIV-2 infection: Lessons for viral immunopathogenesis

HIV-1 and HIV-2 share many similarities including their basic gene arrangement, modes of transmission, intracellular replication pathways and clinical consequences: both result in AIDS. However, HIV-2 is characterised by lower transmissibility and reduced likelihood of progression to AIDS. The underlying mechanistic differences between these two infections illuminate broader issues of retroviral pathogenesis, which remain incompletely understood. Comparisons between these two infections from epidemiological, clinical, virologic and immunologic viewpoints provide a basis for hypothesis generation and testing in this 'natural experiment' in viral pathogenesis. In terms of epidemiology, HIV-2 remains largely confined to West Africa, whereas HIV-1 extends worldwide. Clinically, HIV-2 infected individuals seem to dichotomise, most remaining long-term non-progressors, whereas most HIV-1 infected individuals progress. When clinical progression occurs, both diseases demonstrate very similar pathological processes, although progression in HIV-2 occurs at higher CD4 counts. Plasma viral loads are consistently lower in HIV-2, as are average levels of immune activation. Significant differences exist between the two infections in all components of the immune system. For example, cellular responses to HIV-2 tend to be more polyfunctional and produce more IL-2; humoral responses appear broader with lower magnitude intratype neutralisation responses; innate responses appear more robust, possibly through differential effects of tripartite motif protein isoform 5 alpha. Overall, the immune response to HIV-2 appears more protective against disease progression suggesting that pivotal immune factors limit viral pathology. If such immune responses could be replicated or induced in HIV-1 infected patients, they might extend survival and reduce requirements for antiretroviral therapy.

Trends of HIV-1, HIV-2 and dual infection in women attending outpatient clinics in Senegal, 1990-2009

We assessed trends in the relative prevalences of HIV-1, HIV-2 and dual HIV-1/HIV-2 infection in 10,321 women attending outpatient clinics in Senegal between 1990 and 2009. The relative prevalence of HIV-1 (defined as the proportion of seropositive subjects having HIV-1) rose sharply from 38% in 1990 until 1993 (P < 0.001), whereupon it continued to rise, but at a slower rate, reaching 72% of HIV infections in 2009. As compared with HIV-1, the relative prevalence of HIV-2 decreased sharply from 54% in 1990 until 1993 (P < 0.001) and continued to decrease at a slower rate through 2009. The relative prevalence of dual infection, as compared with HIV-1, was stable from 1990 to 1993, but decreased slightly thereafter (P < 0.001). These study findings indicate that during the early 1990s, the relative prevalence of HIV-1 increased markedly, while the relative prevalence of HIV-2 decreased and the relative prevalence of dual infection remained stable in Senegal. From 1993 to 2009, the relative prevalence of HIV-1 increased at a slower rate, while the relative prevalences of HIV-2 and dual infection decreased. These results confirm trends in HIV prevalence observed in other West African populations and provide a critical update on HIV transmission risk among women in Senegal.

Validation for clinical use of a novel HIV-2 plasma RNA viral load assay using the Abbott m2000 platform

BACKGROUND

Optimal care of persons infected with human immunodeficiency virus type 2 (HIV-2) requires an accurate assessment of HIV-2 plasma viral load (VL), but no clinically approved quantitative HIV-2 RNA VL assay exists.

OBJECTIVES

To validate a novel quantitative HIV-2 RNA assay for clinical and research use.

STUDY DESIGN

The Abbott m2000sp/rt platform was adapted for quantification of HIV-2 RNA in plasma. Amplification targeted a region of the long terminal repeat conserved in Group A and B HIV-2. Electron microscopy-counted-HIV-2 standards, the WHO/NIBSC HIV-2 International Standard and clinical specimens (N=162) were used to determine the precision, sensitivity, specificity, linear range, accuracy, and clinical performance of the assay.

RESULTS

The quantitative linear range of the HIV-2 RNA assay was 10-1,000,000 copies/mL (R(2)>0.99), with a limit of detection of 8 copies/mL (95% CI, 5-18 copies/mL). The assay did not cross-react with HIV-1, and quantification of HIV-2 RNA was not affected by the presence of >5 log(10)HIV-1 RNA copies/mL. The total standard deviation (SD) and intra- and inter-run SD were 0.095, 0.093 and 0.162, respectively, at nominal inputs of 3.7, 1.7 and 1.0 log(10)HIV-2 RNA copies/mL. The HIV-2 WHO/NIBSC International Standard (1000 IU) was shown to contain 152 RNA copies/mL (95% CI 141-163). Overall, HIV-2 RNA was quantified at ≥10 copies/mL from 86 (53%) clinical specimens (median, 2.24 log(10) copies/mL; range 10-16,870), and nine specimens (6%) had HIV-2 RNA detected at <10 copies/mL.

CONCLUSIONS

We developed and validated a highly sensitive HIV-2 VL assay that is suitable for clinical and research use.

Inhibition of HIV-1 disease progression by contemporaneous HIV-2 infection

BACKGROUND

Progressive immune dysfunction and the acquired immunodeficiency syndrome (AIDS) develop in most persons with untreated infection with human immunodeficiency virus type 1 (HIV-1) but in only approximately 20 to 30% of persons infected with HIV type 2 (HIV-2); among persons infected with both types, the natural history of disease progression is poorly understood.

METHODS

We analyzed data from 223 participants who were infected with HIV-1 after enrollment (with either HIV-1 infection alone or HIV-1 and HIV-2 infection) in a cohort with a long follow-up duration (approximately 20 years), according to whether HIV-2 infection occurred first, the time to the development of AIDS (time to AIDS), CD4+ and CD8+ T-cell counts, and measures of viral evolution.

RESULTS

The median time to AIDS was 104 months (95% confidence interval [CI], 75 to 133) in participants with dual infection and 68 months (95% CI, 60 to 76) in participants infected with HIV-1 only (P=0.003). CD4+ T-cell levels were higher and CD8+ T-cell levels increased at a lower rate among participants with dual infection, reflecting slower disease progression. Participants with dual infection with HIV-2 infection preceding HIV-1 infection had the longest time to AIDS and highest levels of CD4+ T-cell counts. HIV-1 genetic diversity was significantly lower in participants with dual infections than in those with HIV-1 infection alone at similar time points after infection.

CONCLUSIONS

Our results suggest that HIV-1 disease progression is inhibited by concomitant HIV-2 infection and that dual infection is associated with slower disease progression. The slower rate of disease progression was most evident in participants with dual infection in whom HIV-2 infection preceded HIV-1 infection. These findings could have implications for the development of HIV-1 vaccines and therapeutics. (Funded by the Swedish International Development Cooperation Agency-Swedish Agency for Research Cooperation with Developing Countries and others.).

Association between peripheral γδ T-cell profile and disease progression in individuals infected with HIV-1 or HIV-2 in West Africa

BACKGROUND

Human gammadelta (γδ) T cells play an important role in protective immunity in HIV-1 and simian immunodeficiency virus infection; their role in HIV-2 infection is unknown.

OBJECTIVE

To determine the role of γδ T cells in control of plasma viral load and CD4 T-cell count in HIV-1 and HIV-2 infections in West Africa.

METHODS

Thirty HIV-1 and 25 HIV-2 treatment-naive chronically infected individuals, and 20 HIV-seronegative individuals from Senegal were studied using multiparametric flow cytometry to investigate the frequencies and phenotypes of peripheral γδ T cells. γδ T-cell parameters and correlates of HIV disease progression were assessed.

RESULTS

: We observed an expansion of Vδ1 T-cell populations in both HIV-1 and HIV-2 infection. However, unlike HIV-1 infection, no significant contraction of the frequency of total Vδ2 T cells was observed in HIV-2 infection. Significantly lower frequencies of CD4Vδ2 T cells were observed in HIV-2-infected individuals. Furthermore, frequencies of CD28CD45RO and CD27CD28CD45RO Vδ2 T cell were low in HIV-1-infected individuals. Vδ2 T-cell activation levels were elevated in both HIV-1-infected and HIV-2-infected individuals. The frequency of HLA-DRCD38-activated Vδ1 and Vδ2 T cells was associated with a decline in CD4 T-cell counts and increased viral load in both HIV-1 and HIV-2 infection.

CONCLUSIONS

Although maintaining the normal frequency of total Vδ2 T cells, HIV-2 infection reduces the frequency of CD4Vδ2 T cells and alters the frequencies of subsets of Vδ1 T cells. Both HIV-1 and HIV-2 infection induce γδ T-cell activation, and this activation is associated with the disease progression.

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.

Induction of immunity to human immunodeficiency virus type-1 by vaccination

Recent findings have brought optimism that development of a successful human immunodeficiency virus type-1 (HIV-1) vaccine lies within reach. Studies of early events in HIV-1 infection have revealed when and where HIV-1 is potentially vulnerable to vaccine-targeted immune responses. With technical advances in human antibody production, clues about how antibodies recognize HIV-1 envelope proteins have uncovered new targets for immunogen design. A recent vaccine regimen has shown modest efficacy against HIV-1 acquisition. However, inducing long-term T and B cell memory and coping with HIV-1 diversity remain high priorities. Mediators of innate immunity may play pivotal roles in blocking infection and shaping immunity; vaccine strategies to capture these activities are under investigation. Challenges remain in integrating basic, preclinical and clinical research to improve predictions of types of immunity associated with vaccine efficacy, to apply these insights to immunogen design, and to accelerate evaluation of vaccine efficacy in persons at-risk for infection.

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.

Major depletion of plasmacytoid dendritic cells in HIV-2 infection, an attenuated form of HIV disease

Plasmacytoid dendritic cells (pDC) provide an important link between innate and acquired immunity, mediating their action mainly through IFN-α production. pDC suppress HIV-1 replication, but there is increasing evidence suggesting they may also contribute to the increased levels of cell apoptosis and pan-immune activation associated with disease progression. Although having the same clinical spectrum, HIV-2 infection is characterized by a strikingly lower viremia and a much slower rate of CD4 decline and AIDS progression than HIV-1, irrespective of disease stage. We report here a similar marked reduction in circulating pDC levels in untreated HIV-1 and HIV-2 infections in association with CD4 depletion and T cell activation, in spite of the undetectable viremia found in the majority of HIV-2 patients. Moreover, the same overexpression of CD86 and PD-L1 on circulating pDC was found in both infections irrespective of disease stage or viremia status. Our observation that pDC depletion occurs in HIV-2 infected patients with undetectable viremia indicates that mechanisms other than direct viral infection determine the pDC depletion during persistent infections. However, viremia was associated with an impairment of IFN-α production on a per pDC basis upon TLR9 stimulation. These data support the possibility that diminished function in vitro may relate to prior activation by HIV virions in vivo, in agreement with our finding of higher expression levels of the IFN-α inducible gene, MxA, in HIV-1 than in HIV-2 individuals. Importantly, serum IFN-α levels were not elevated in HIV-2 infected individuals. In conclusion, our data in this unique natural model of “attenuated” HIV immunodeficiency contribute to the understanding of pDC biology in HIV/AIDS pathogenesis, showing that in the absence of detectable viremia a major depletion of circulating pDC in association with a relatively preserved IFN-α production does occur.

Infection by HIV-2, the second AIDS-associated virus, is considered a unique natural model of attenuated HIV disease. HIV-2 infected individuals exhibit much lower levels of circulating virus (viremia) and progress to AIDS at slower rates than HIV-1 infected patients. In this study, we characterized for the first time blood plasmacytoid dendritic cells (pDC), important mediators between innate and acquired immunity, in HIV-2 infection. We observed a profound reduction in circulating pDC levels in HIV-2 infected patients, even in those with undetectable viremia, to levels similar to those found in HIV-1 infection. Moreover, we documented a more differentiated pDC phenotype in both infected cohorts relative to healthy individuals. Despite these similarities between HIV-1 and HIV-2 infections, pDC from HIV-2 patients with undetectable viremia exhibited, upon in vitro stimulation, a better-preserved ability to produce interferon-α (IFN-α), an important anti-viral cytokine with potential to stimulate other immune cells. Overall, our data suggest that the presence of virus in circulation, although not critical for the reduction in pDC number, appears to be central for the impairment of their function. This study of pDC in HIV-2 infection fills a gap in the understanding of their potential role in HIV/AIDS pathogenesis.

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.

HIV-2: the forgotten AIDS virus

HIV type 2 (HIV-2), a closely related retrovirus discovered a few years after HIV type 1, causes AIDS in only a minority of infected individuals. Determining why HIV-2 causes asymptomatic infection in most patients could further our understanding of HIV immunopathogenesis. Studies to date have suggested that both enhanced immune responses and lower viral replication could play a role. We summarize the important findings to date and highlight areas that warrant further exploration.

Gag-specific CD4+ T-cell frequency is inversely correlated with proviral load and directly correlated with immune activation in infection with human immunodeficiency virus type 2 (HIV-2) but not HIV-1

Human immunodeficiency virus type 2 (HIV-2) infection, unlike HIV-1 infection, is normally characterized by low rates of CD4 depletion and low-to-undetectable viremia. We found that the frequency of Gag-specific CD4(+) T cells featured positive correlations with the expression of markers of CD4 activation and a negative correlation with peripheral blood mononuclear cell-associated proviral load in infection with HIV-2, in contrast with HIV-1. Moreover, HIV-2-infected individuals exhibited a greater ability to respond to HIV-1 Gag peptides (heterologous responses). Our data suggest a potential link between HIV-2-specific CD4 responses, immune activation, and viral control, which may in turn relate to the better prognosis associated with HIV-2 infection.

Higher homologous and lower cross-reactive Gag-specific T-cell responses in human immunodeficiency virus type 2 (HIV-2) than in HIV-1 infection

Human immunodeficiency virus type 2 (HIV-2) infection results in slower CD4(+) T-cell decline, lower plasma viral load levels, and hence slower progression of the disease than does HIV-1 infection. Although the reasons for this are not clear, it is possible that HIV-2 replication is more effectively controlled by host responses. We used aligned pools of overlapping HIV-1 and HIV-2 Gag peptides in an enhanced gamma interferon enzyme-linked immunospot assay to compare the levels of homologous and cross-reactive Gag-specific T-cell responses between HIV-1- and HIV-2-infected patients. HIV-2-infected patients showed broader and stronger homologous Gag-specific T-cell responses than HIV-1-infected patients. In contrast, the cross-reactive T-cell responses in HIV-2-infected patients were both narrower and weaker than those in HIV-1-infected patients, in line with overall weaker correlations between homologous and heterologous T-cell responses among HIV-2-infected patients than among HIV-1-infected patients. Cross-reactive responses in HIV-2-infected patients tended to correlate directly with HIV-1/HIV-2 Gag sequence similarities; this was not found in HIV-1-infected patients. The CD4(+) T-cell counts of HIV-2-infected patients correlated directly with homologous responses and inversely with cross-reactive responses; this was not found in HIV-1-infected patients. Our data support a model whereby high-level HIV-2-specific T-cell responses control the replication of HIV-2, thus limiting viral diversification and priming of HIV-1 cross-reactive T-cell responses over time. However, we cannot exclude the possibility that HIV-2 replication is controlled by other host factors and that HIV-2-specific T-cell responses are better maintained in the context of slow viral divergence and a less damaged immune system. Understanding the nature of immune control of HIV-2 infection could be crucial for HIV vaccine design.

Tenets of protection from progression to AIDS: lessons from the immune responses to HIV-2 infection

In the past 25 years, life survival curves of many countries have been remodeled owing to HIV infection. Both HIV-1 and HIV-2 can cause AIDS, yet patients infected with HIV-2 fare much better clinically and most will never experience detrimental effects of the infection. Despite over two decades of comprehensive research into vaccine development, a prophylactic vaccine is not yet realized. An essential missing link in the innovation of a successful vaccine strategy is the description of a favorable immune response that abolishes virus replication. Lessons learned from studying the role of the immune system in the long-term nonprogression characteristic of HIV-2 infection will offer insight into how a balanced immune response can protect from the destruction of the immune system associated with chronic HIV-1 infection.

Polyfunctional T cell responses are a hallmark of HIV-2 infection

HIV-2 is distinguished clinically and immunologically from HIV-1 infection by delayed disease progression and maintenance of HIV-specific CD4(+) T cell help in most infected subjects. Thus, HIV-2 provides a unique natural human model in which to investigate correlates of immune protection against HIV disease progression. Here, we report a detailed assessment of the HIV-2-specific CD4(+) and CD8(+) T cell response compared to HIV-1, using polychromatic flow cytometry to assess the quality of the HIV-specific T cell response by measuring IFN-gamma, IL-2, TNF-alpha, MIP-1beta, and CD107a mobilization (degranulation) simultaneously following Gag peptide stimulation. We find that HIV-2-specific CD4(+) and CD8(+) T cells are more polyfunctional that those specific for HIV-1 and that polyfunctional HIV-2-specific T cells produce more IFN-gamma and TNF-alpha on a per-cell basis than monofunctional T cells. Polyfunctional HIV-2-specific CD4(+) T cells were generally more differentiated and expressed CD57, while there was no association between function and phenotype in the CD8(+) T cell fraction. Polyfunctional HIV-specific T cell responses are a hallmark of non-progressive HIV-2 infection and may be related to good clinical outcome in this setting.

CCR5-restricted HIV type 2 variants from long-term aviremic individuals are less sensitive to inhibition by beta-chemokines than low pathogenic HIV type 1 variants

Many HIV-2-infected individuals maintain low, often undetectable, viral loads for prolonged periods. Virus and/or host factors that contribute to this high level of virus control are largely unknown. Previously we demonstrated that HIV-2 variants from long-term aviremic individuals have relatively low replication kinetics in vitro in comparison to HIV-1 variants. We hypothesized that the relatively low replication rates of HIV-2 in vitro as well as the high level of virus control in vivo might be explained by HIV-2 replication being more sensitive to inhibitory host factors like beta-chemokines or other CD8+ T cell-derived factors than HIV-1 replication. To test this we determined the effect of exogenously added beta-chemokines and healthy donor CD8+ T cells on the in vitro virus production of HIV-2 and HIV-1 variants from long-term nonprogressors (LTNPs). Contrary to expectations, HIV-2 replication was inhibited less efficiently by RANTES and MIP-1alpha than HIV-1 replication. CD8+ T cells from 8 of 12 healthy donors reduced HIV replication minimally 2-fold. Interestingly, cells from five of these donors inhibited HIV-1 but hardly affected HIV-2 replication, while the reverse was observed for cells from one donor. For HIV-1, but not HIV-2, the magnitude of the antiviral effect of CD8+ T cells correlated with their effect on RANTES levels in culture supernatants. Our findings indicate that RANTES is a more important factor of CD8+ T cell-associated anti-HIV-1 activity than it is of HIV-2 activity and that the benign clinical course of HIV-2 infection is not due to enhanced beta-chemokine sensitivity of HIV-2 variants.

Comparison of viro-immunological marker changes between HIV-1 and HIV-2-infected patients in France

BACKGROUND

HIV-2 is known to be less pathogenic than HIV-1, although the underlying mechanisms are still debated. We compared the changes over time in viro-immunological markers in HIV-1 and HIV-2-infected patients living in France during natural history and after initiation of the first combination antiretroviral therapy (CART).

METHOD

Patients were included in the ANRS CO3 HIV-1 cohort (N = 6707) or the ANRS CO5 HIV-2 cohort (N = 572). HIV-1-infected patients were matched to HIV-2 patients according to sex, age, HIV transmission group and period of treatment initiation. Changes in markers were estimated using linear mixed models.

RESULTS

Analyses were performed for three groups of patients: those with estimated date of contamination (98 HIV-1 and 49 HIV-2-seroincident patients); untreated seroprevalent patients (320 HIV-1 and 160 HIV-2); and those initiating a first CART (59 HIV-1 and 63 HIV-2). In group 1, CD4 T-cell counts decreased less rapidly in HIV-2 than HIV-1 patients (-9 versus -49 cells/microl per year, P < 10(-4)). Results were similar in group 2. Baseline CD4 cell count at CART initiation was not different according to the type of infection. During the first 2 months of treatment, the CD4 cell count increased by +59 cells/microl per month (CI 34; 84) for HIV-1 and +24 (CI 6; 42) for HIV-2. The plasma viral load drop was threefold more important in HIV-1 patients: -1.56 log10/ml per month versus -0.62 among HIV-2 patients (P < 10(-4)).

CONCLUSION

Differences between the two infections during natural history are similar to those previously described in Africa. Once treatment is started, response is poorer in HIV-2 than in HIV-1 patients.

Robust Gag-specific T cell responses characterize viremia control in HIV-2 infection

HIV-2 infection in the majority of infected subjects follows an attenuated disease course that distinguishes it from infection with HIV-1. Antigen-specific T cells are pivotal in the management of chronic viral infections but are not sufficient to control viral replication in HIV-1-positive subjects, and their function in HIV-2 infection is not fully established. In a community-based cohort of HIV-2 long-term nonprogressors in rural Guinea-Bissau, we performed what we believe is the first comprehensive analysis of HIV-2-specific immune responses. We demonstrate that Gag is the most immunogenic protein. The magnitude of the IFN-gamma immune response to the HIV-2 proteome was inversely correlated with HIV-2 viremia, and this relationship was specifically due to the targeting of Gag. Furthermore, patients with undetectable viremia had greater Gag-specific responses compared with patients with high viral replication. The most frequently recognized peptides clustered within a defined region of Gag, and responses to a single peptide in this region were associated with low viral burden. The consistent relationship between Gag-specific immune responses and viremia control suggests that T cell responses are vital in determining the superior outcome of HIV-2 infection. A better understanding of how HIV-2 infection is controlled may identify correlates of effective protective immunity essential for the design of HIV vaccines.

Role of human immunodeficiency virus (HIV)-specific T-cell immunity in control of dual HIV-1 and HIV-2 infection

Progressive immune dysfunction and AIDS develop in most cases of human immunodeficiency virus type 1 (HIV-1) infection but in only 25 to 30% of persons with HIV-2 infection. However, the natural history and immunologic responses of individuals with dual HIV-1 and HIV-2 infection are largely undefined. Based on our previous findings, we hypothesized that among patients with dual infection the control of HIV-1 is associated with the ability to respond to HIV-2 Gag epitopes and to maintain HIV-specific CD4(+) T-cell responses. To test this, we compared the HIV-specific ex vivo IFN-gamma enzyme-linked immunospot (ELISPOT) assay responses of 19 dually infected individuals to those of persons infected with HIV-1 or HIV-2 only. Further, we assessed the functional profile of HIV Gag-specific CD4(+) and CD8(+) T cells from nine HIV dually infected patients by using a multicolor intracellular cytokine staining assay. As determined by ELISPOT assay, the magnitude and frequency of IFN-gamma-secreting T-cell responses to gene products of HIV-1 were higher than those to gene products of HIV-2 (2.64 versus 1.53 log(10) IFN-gamma spot-forming cells/10(6) cells [90% versus 63%, respectively].) Further, HIV-1 Env-, Gag-, and Nef- and HIV-2 Gag-specific responses were common; HIV-2 Nef-specific responses were rare. HIV-specific CD4(+) T helper responses were detected in nine of nine dually infected subjects, with the majority of these T cells producing gamma interferon (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) and, to a lesser extent, interleukin-2. The HIV-1 plasma viral load was inversely correlated with HIV-2 Gag-specific IFN-gamma-/TNF-alpha-secreting CD4(+) and HIV-2 Gag-specific IFN-gamma-secreting CD8(+) T cells. In conclusion, the T-cell memory responses associated with containment of single HIV-1 and HIV-2 infection play a similar significant role in the immune control of dual HIV-1 and HIV-2 infection.

Functional T cell subsets contribute differentially to HIV peptide-specific responses within infected individuals: correlation of these functional T cell subsets with markers of disease progression

Using a dual color ELISPOT assay able to detect HIV-specific IFN-gamma, IL-2 and dual IFN-gamma/IL-2 secreting lymphocytes we screened for HIV peptide-specific responses directed against the entire HIV proteome in two groups of untreated HIV-infected individuals, slow progressors (SP) and progressors. We found that the three functional lymphocyte subsets contributed differentially to individual HIV peptide-specific responses within a study subject. Among the identified stimulatory peptides, a higher proportion induced dual IFN-gamma/IL-2 secretion in SP than progressors. While the magnitude of single IFN-gamma secreting lymphocytes is similar between groups, the magnitude of peptide-specific dual IFN-gamma/IL-2 secreting lymphocytes is significantly more intense in SP. Neither single nor total IFN-gamma secreting cell magnitude and breadth measurements correlated with CD4 cell count or viral load whereas both parameters of dual IFN-gamma/IL-2 secreting responses correlated positively with CD4 counts and negatively with viremia.

Out of Africa: what can we learn from HIV-2 about protective immunity to HIV-1?

Most people infected with human immunodeficiency virus 2 (HIV-2) do not progress to disease, even though the minority who do cannot be distinguished clinically from HIV-1-infected patients. Here we review what is known about the basis of viral control in HIV-2 infection.

Protective immunity against HIV infection: lessons from HIV-2 infection

Despite two decades of intensive research, the correlates of protective immunity to HIV-1 infection remain elusive. Much less attention has been paid to the related human virus strain, HIV-2, which can cause AIDS, but does not usually do so in the majority of infected people. What can be learned from HIV-2 infection about how the human host can peacefully coexist with a pathogenic retrovirus?

An adaptation of recombinant vaccinia-based ELISPOT and intracellular cytokine staining for a comparative measurement of cellular immune responses in HIV-1 and HIV-2 infections in West Africa

An efficient and quantitative tool for rapid assessment of human immunodeficiency virus (HIV)-induced cellular immune responses is important for resource-limited settings, such as in sub-Saharan Africa. Modifications are required to previously reported methods for evaluating ex-vivo antigen-specific cellular responses based on direct recombinant vaccinia virus (rVV) stimulation of peripheral blood mononuclear cells (PBMCs) by enzyme linked immunosorbent assay (ELISPOT) and by flow cytometry intracellular cytokine assay (ICA). We made such modifications in order to detect specific responses and compared quantitative cellular immune responses in HIV-1 and HIV-2 infected Gambians. The sensitivity of the rVV-based ELISPOT assay was on average 1.25 interferon (IFN)-gamma spot forming cells (SFC) per 50 000 PBMCs specific for either infection, and 5 IFN-gamma-secreting CD8+ T cells/50 000 in the ICA. The level of IFN-gamma SFC detected by ELISPOT and by ICA were correlated (P < 0.02). ICA detected pol-specific responses in 88% and 67% of HIV-1 and HIV-2 subjects, respectively, and gag-specific responses in more than 80% of both infections. Lower proportions of responders were obtained with ELISPOT, for which pol responses were present in 60% of HIV-1 and 46% of HIV-2 infected patients, and gag responses in 55% and 69%, respectively. The assays did not show any significant difference in cellular immune responses between HIV-1 and HIV-2 infected subjects with CD4% >or= 20%. These outcomes are comparable with results obtained using standard techniques and thus this method is a suitable, rapid and less expensive assessment of cellular immunity.

Maintenance of HIV-specific CD4+ T cell help distinguishes HIV-2 from HIV-1 infection

Unlike HIV-1-infected people, most HIV-2-infected subjects maintain a healthy CD4+ T cell count and a strong HIV-specific CD4+ T cell response. To define the cellular immunological correlates of good prognosis in HIV-2 infection, we conducted a cross-sectional study of HIV Gag-specific T cell function in HIV-1- and HIV-2-infected Gambians. Using cytokine flow cytometry and lymphoproliferation assays, we show that HIV-specific CD4+ T cells from HIV-2-infected individuals maintained proliferative capacity, were not terminally differentiated (CD57-), and more frequently produced IFN-gamma or IL-2 than CD4+ T cells from HIV-1-infected donors. Polyfunctional (IFN-gamma+/IL-2+) HIV-specific CD4+ T cells were found exclusively in HIV-2+ donors. The disparity in CD4+ T cell responses between asymptomatic HIV-1- and HIV-2-infected subjects was not associated with differences in the proliferative capacity of HIV-specific CD8+ T cells. This study demonstrates that HIV-2-infected donors have a well-preserved and functionally heterogeneous HIV-specific memory CD4+ T cell response that is associated with delayed disease progression in the majority of infected people.

In vitro replication capacity of HIV-2 variants from long-term aviremic individuals

To establish whether efficient suppression of virus replication in HIV-2-infected individuals is associated with low replicative capacity of HIV-2, replication kinetics of HIV-2 variants from long-term aviremic individuals was analyzed and compared with that of the relatively slow-replicating HIV-1 variants from asymptomatics and long-term nonprogressors (AS/LTNP). On average, HIV-2 from aviremic individuals had lower replication rates than HIV-1 variants from AS/LTNP in cells of 8 donors (0.45 log10 [range 0.14-0.77] vs. 0.58 log10 [range 0.32-0.99] pg RT/ml/day, P = 0.036). The relatively low replication rate of HIV-2 compared to HIV-1 variants was not related to different sensitivities to inhibition by CD8+ T cells or different degrees of infectivity. HIV-2 replication rates increased with progressive infection and with switch from CCR5 to CXCR4 usage. The relatively low replicative capacity of HIV-2 variants from aviremic individuals likely contributes to the low viral load and benign course of infection in these individuals.

Inter-operator variation in ELISPOT analysis of measles virus-specific IFN-gamma-secreting T cells

The ELISPOT assay is a highly sensitive technique used for the detection of individual cytokine releasing cells. We have developed an IFN-gamma ELISPOT assay utilizing unfractionated frozen peripheral blood mononuclear cells (PBMC) to quantify the frequency of measles virus (MV)-specific IFN-gamma-secreting T cells in 117 healthy children who had been previously immunized with two doses of the measles-mumps-rubella vaccine. We have also estimated the variability associated with the quantification of ELISPOT plates and compared the number of MV-specific IFN-gamma-secreting T cells for each subject as determined by two different operators of an ELISPOT reader. The median frequency of MV-specific IFN-gamma-producing memory T cells detected by this assay was 0.005 % and 0.01 % as determined by an in-house and commercial operator, respectively. Although we found a significant correlation (r = 0.83, p<0.0001) between the number of spots counted by the commercial and in-house operators of an ELISPOT reader, the median number of spots counted by the commercial operator was twice the number of spots counted by an in-house operator (p<0.001). This demonstrates the importance of using a common ELISPOT reader and operator, among other parameters, to quantify the number of spots when a large volume of plates are being scanned and analyzed.

Natural killer cell function is well preserved in asymptomatic human immunodeficiency virus type 2 (HIV-2) infection but similar to that of HIV-1 infection when CD4 T-cell counts fall

Natural killer (NK) cells are potent effectors of natural immunity and their activity prevents human immunodeficiency virus type 1 (HIV-1) viral entry and viral replication. We sought to determine whether NK immune responses are associated with different clinical course of HIV-1 and HIV-2 infections. A cross-sectional analysis of NK cell responses was undertaken in 30 HIV-1 and 30 HIV-2 subjects in each of three categories of CD4(+)-T-cell counts (>500, 200 to 500, and <200 cells/microl) and in 50 HIV-uninfected control subjects. Lytic activity and gamma interferon (IFN-gamma) secretion were measured by chromium release and enzyme-linked immunospot assays, respectively. Flow cytometry was used to assess intracellular cytokines and chemokines. Levels of NK cytotoxicity were significantly higher in HIV-2 than in HIV-1 infections in subjects with high CD4(+)-T-cell counts and were similar to that of the healthy controls. In these HIV-2 subjects, cytolytic activity was positively correlated to NK cell count and inversely related to plasma viremia. Levels of intracellular MIP-1beta, RANTES, tumor necrosis factor alpha, and IFN-gamma produced by NK CD56(bright) cells were significantly higher in HIV-2- than HIV-1-infected subjects with high CD4(+)-T-cell counts but fell to similar levels as CD4 counts dropped. The data suggest efficient cytolytic and chemokine-suppressive activity of NK cells early in HIV-2 infection, which is associated with high CD4(+) T-cell counts. Enhancement of these functions may be important in immune-based therapy to control HIV disease.

Distinct profile of T cell activation in HIV type 2 compared to HIV type 1 infection: differential mechanism for immunoprotection

The mechanism for the lower rate of disease progression in HIV-2 infection remains undefined. We evaluated T cell activation in a cohort of HIV-infected commercial sex workers in Dakar, Senegal. CD8+ T cell activation was significantly lower in HIV-2- compared to HIV-1-infected volunteers and both groups displayed higher activation levels compared to seronegative individuals. In contrast, CD4+ T cell activation was similar between the HIV-1 and HIV-2 groups and significantly higher compared to the seronegative group. Interestingly, HIV-2-positive volunteers with evidence of Gag-specific CD8+ T cell responses displayed lower CD4+ T cell activation. Our data suggest that the distinct T cell activation profile in HIV-2-positive individuals may reflect on the presence of effective host immune responses in HIV-2 infection.

CD8+ T cell responses to human immunodeficiency viruses type 2 (HIV-2) and type 1 (HIV-1) gag proteins are distinguishable by magnitude and breadth but not cellular phenotype

The mechanisms underlying the relatively slow progression of human immunodeficiency virus type 2 (HIV-2) compared with HIV-1 infection are undefined and could be a result of more effective immune responses. We used HIV-2 and HIV-1 IFN-gamma enzyme-linked immunospot assays to evaluate CD8(+) T cell responses in antiretroviral-naive HIV-2- ('HIV-2(+)') and HIV-1-infected ('HIV-1(+)') individuals. Gag-specific responses were detected in the majority of HIV-2(+) and HIV-1(+) subjects. Overlapping gag peptide analysis indicated a significantly greater magnitude and breadth of responses in the HIV-1(+) cohort, and this difference was attributable to low responses in HIV-2(+) subjects with undetectable viral load (medians 2107 and 512 spot-forming units per 10(6) PBMC, respectively, p=0.007). We investigated the phenotype of viral epitope-specific CD8(+) T cells identified with HLA-B53- and HLA-B58-peptide tetramers (8 HIV-2(+), 11 HIV-1(+) subjects). HIV-2-specific CD8(+) T cells were predominantly CD27(+) CD45RA(-), and only a minority expressed perforin. The limited breadth and low frequency of CD8(+) T cell responses to HIV-2 gag in aviremic HIV-2(+) subjects suggests that these responses reflect antigen load in plasma, as is the case in HIV-1 infection. Immune control of HIV-2 does not appear to be related to the frequency of perforin-expressing virus-specific CD8(+) T cells.