Differences in proviral DNA load between HIV-1- and HIV-2-infected patients

The HIV-2 OGH double reporter virus shows that HIV-2 is less cytotoxic and less sensitive to reactivation from latency than HIV-1 in cell culture

A better understanding of HIV-1 latency is a research priority in HIV cure research. Conversely, little is known about the latency characteristics of HIV-2, the closely related human lentivirus. Though both viruses cause AIDS, HIV-2 infection progresses more slowly with significantly lower viral loads, even when corrected for CD4+ T cell counts. Hence a direct comparison of latency characteristics between HIV-1 and HIV-2 could provide important clues towards a functional cure. Transduction of SupT1 cells with single-round HIV-1 and HIV-2 viruses with an enhanced green fluorescent protein (eGFP) reporter showed higher levels of eGFP expression for HIV-2 than HIV-1, while HIV-1 expression appeared more cytotoxic. To compare HIV-1 and HIV-2 gene expression, latency and reactivation in more detail, we have generated HIV-2 OGH, a replication deficient, near full- length, double reporter virus that discriminates latently and productively infected cells in cell culture. This construct is based on HIV-1 OGH, and to our knowledge, first of its kind for HIV-2. Using this construct we have observed a higher eGFP expression for HIV-2, but higher losses of HIV-1 transduced cells in SupT1 and Jurkat cells and a reduced sensitivity of HIV-2 for reactivation with TNF-α. In addition, we have analysed HIV-2 integration sites and their epigenetic environment. HIV-1 and HIV-2 share a preference for actively transcribed genes in gene-dense regions and favor active chromatin marks while disfavoring methylation markers associated with heterochromatin. In conclusion the HIV-2 OGH construct provides an interesting tool for studying HIV-2 expression, latency and reactivation. As simian immunodeficiency virus (SIV) and HIV-2 have been proposed to model a functional HIV cure, a better understanding of the mechanisms governing HIV-2 and SIV latency will be important to move forward. Further research is needed to investigate if HIV-2 uses similar mechanisms as HIV-1 to achieve its integration site selectivity.

Intra-Patient Evolution of HIV-2 Molecular Properties

Limited data are available on the pathogenesis of HIV-2, and the evolution of Env molecular properties during disease progression is not fully elucidated. We investigated the intra-patient evolution of molecular properties of HIV-2 Env regions (V1-C3) during the asymptomatic, treatment-naïve phase of the infection in 16 study participants, stratified into faster or slower progressors. Most notably, the rate of change in the number of potential N-linked glycosylation sites (PNGS) within the Env (V1-C3) regions differed between progressor groups. With declining CD4⁺ T-cell levels, slower progressors showed, on average, a decrease in the number of PNGSs, while faster progressors showed no significant change. Furthermore, diversity increased significantly with time in faster progressors, whereas no such change was observed in slower progressors. No differences were identified between the progressor groups in the evolution of length or charge of the analyzed Env regions. Predicted virus CXCR4 use was rare and did not emerge as a dominating viral population during the studied disease course (median 7.9 years, interquartile range [IQR]: 5.2-14.0) in either progressor groups. Further work building on our observations may explain molecular hallmarks of HIV-2 disease progression and differences in pathogenesis between HIV-1 and HIV-2.

Molecular Biology and Diversification of Human Retroviruses

Studies of retroviruses have led to many extraordinary discoveries that have advanced our understanding of not only human diseases, but also molecular biology as a whole. The most recognizable human retrovirus, human immunodeficiency virus type 1 (HIV-1), is the causative agent of the global AIDS epidemic and has been extensively studied. Other human retroviruses, such as human immunodeficiency virus type 2 (HIV-2) and human T-cell leukemia virus type 1 (HTLV-1), have received less attention, and many of the assumptions about the replication and biology of these viruses are based on knowledge of HIV-1. Existing comparative studies on human retroviruses, however, have revealed that key differences between these viruses exist that affect evolution, diversification, and potentially pathogenicity. In this review, we examine current insights on disparities in the replication of pathogenic human retroviruses, with a particular focus on the determinants of structural and genetic diversity amongst HIVs and HTLV.

Novel assays to investigate the mechanisms of latent infection with HIV-2

Although there have been great advancements in the field of HIV treatment and prevention, there is no cure. There are two types of HIV: HIV-1 and HIV-2. In addition to genetic differences between the two types of HIV, HIV-2 infection causes a slower disease progression, and the rate of new HIV-2 infections has dramatically decreased since 2003. Like HIV-1, HIV-2 is capable of establishing latent infection in CD4+ T cells, thereby allowing the virus to evade viral cytopathic effects and detection by the immune system. The mechanisms underlying HIV latency are not fully understood, rendering this a significant barrier to development of a cure. Using RT-ddPCR, we previously demonstrated that latent infection with HIV-1 may be due to blocks to HIV transcriptional elongation, distal transcription/polyadenylation, and multiple splicing. In this study, we describe the development of seven highly-specific RT-ddPCR assays for HIV-2 that can be applied to the study of HIV-2 infections and latency. We designed and validated seven assays targeting different HIV-2 RNA regions along the genome that can be used to measure the degree of progression through different blocks to HIV-2 transcription and splicing. Given that HIV-2 is vastly understudied relative to HIV-1 and that it can be considered a model of a less virulent infection, application of these assays to studies of HIV-2 latency may inform new therapies for HIV-2, HIV-1, and other retroviruses.

Inverted CD8 T-Cell Exhaustion and Co-Stimulation Marker Balance Differentiate Aviremic HIV-2-Infected From Seronegative Individuals

HIV-2 is less pathogenic compared to HIV-1. Still, disease progression may develop in aviremic HIV-2 infection, but the driving forces and mechanisms behind such development are unclear. Here, we aimed to reveal the immunophenotypic pattern associated with CD8 T-cell pathology in HIV-2 infection, in relation to viremia and markers of disease progression. The relationships between pathological differences of the CD8 T-cell memory population and viremia were analyzed in blood samples obtained from an occupational cohort in Guinea-Bissau, including HIV-2 viremic and aviremic individuals. For comparison, samples from HIV-1- or dually HIV-1/2-infected and seronegative individuals were obtained from the same cohort. CD8 T-cell exhaustion was evaluated by the combined expression patterns of activation, stimulatory and inhibitory immune checkpoint markers analyzed using multicolor flow cytometry and advanced bioinformatics. Unsupervised multidimensional clustering analysis identified a cluster of late differentiated CD8 T-cells expressing activation (CD38+, HLA-DR^int/high), co-stimulatory (CD226+/-), and immune inhibitory (2B4+, PD-1^high, TIGIT^high) markers that distinguished aviremic from viremic HIV-2, and treated from untreated HIV-1-infected individuals. This CD8 T-cell population displayed close correlations to CD4%, viremia, and plasma levels of IP-10, sCD14 and beta-2 microglobulin in HIV-2 infection. Detailed analysis revealed that aviremic HIV-2-infected individuals had higher frequencies of exhausted TIGIT+ CD8 T-cell populations lacking CD226, while reduced percentage of stimulation-receptive TIGIT-CD226+ CD8 T-cells, compared to seronegative individuals. Our results suggest that HIV-2 infection, independent of viremia, skews CD8 T-cells towards exhaustion and reduced co-stimulation readiness. Further knowledge on CD8 T-cell phenotypes might provide help in therapy monitoring and identification of immunotherapy targets.

Genetic Variability of Long Terminal Repeat Region between HIV-2 Groups Impacts Transcriptional Activity

The HIV-2 long terminal repeat (LTR) region contains several transcription factor (TF) binding sites. Efficient LTR transactivation by cellular TF and viral proteins is crucial for HIV-2 reactivation and viral production. Proviral LTRs from 66 antiretroviral-naive HIV-2-infected patients included in the French ANRS HIV-2 CO5 Cohort were sequenced. High genetic variability within the HIV-2 LTR was observed, notably in the U3 subregion, the subregion encompassing most known TF binding sites. Genetic variability was significantly higher in HIV-2 group B than in group A viruses. Notably, all group B viruses lacked the peri-ETS binding site, and 4 group B sequences (11%) also presented a complete deletion of the first Sp1 binding site. The lack of a peri-ETS binding site was responsible for lower transcriptional activity in activated T lymphocytes, while deletion of the first Sp1 binding site lowered basal or Tat-mediated transcriptional activities, depending on the cell line. Interestingly, the HIV-2 cellular reservoir was less frequently quantifiable in patients infected by group B viruses and, when quantifiable, the reservoirs were significantly smaller than in patients infected by group A viruses. Our findings suggest that mutations observed in vivo in HIV-2 LTR sequences are associated with differences in transcriptional activity and may explain the small cellular reservoirs in patients infected by HIV-2 group B, providing new insight into the reduced pathogenicity of HIV-2 infection.IMPORTANCE Over 1 million patients are infected with HIV-2, which is often described as an attenuated retroviral infection. Patients frequently have undetectable viremia and evolve at more slowly toward AIDS than HIV-1-infected patients. Several studies have reported a smaller viral reservoir in peripheral blood mononuclear cells in HIV-2-infected patients than in HIV-1-infected patients, while others have found similar sizes of reservoirs but a reduced amount of cell-associated RNA, suggesting a block in HIV-2 transcription. Recent studies have found associations between mutations within the HIV-1 LTR and reduced transcriptional activities. Until now, mutations within the HIV-2 LTR region have scarcely been studied. We conducted this research to discover if such mutations exist in the HIV-2 LTR and their potential association with the viral reservoir and transcriptional activity. Our study indicates that transcription of HIV-2 group B proviruses may be impaired, which might explain the small viral reservoir observed in patients.

Quantification of HIV-2 DNA in Whole Blood

Time to AIDS infection is longer with HIV-2, compared to HIV-1, but without antiretroviral therapy both infections will cause AIDS-related mortality. In HIV-2 infection, monitoring of antiretroviral treatment (ART) efficacy is challenging since a large proportion of HIV-2-infected individuals displays low or undetectable plasma RNA levels. Hence, quantification of cellular DNA load may constitute an alternative method for monitoring ART efficacy. Moreover, sensitive HIV-2 DNA quantification protocols are also important for the characterization of the HIV-2 reservoirs, and ultimately for the development of HIV-2 cure strategies. We have developed a sensitive and robust HIV-2 DNA quantification protocol based on whole blood as DNA source, including normalization of leukocyte cell numbers using parallel quantification of the single copy porphobilinogen deaminase gene. The specificity and sensitivity of the assay was 100%. The limit of detection was 1 copy and limit of quantification was 5 copies. When applying this protocol to HIV-2 infected, it was found that HIV-2 viral DNA was detectable in individuals in whom viral RNA was undetectable or under quantification level. Thus, this method provides a sensitive approach to HIV-2 DNA viral quantification from whole blood of HIV-2 infected patients.

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.

Performance of Bio-Rad HIV-1/2 Confirmatory Assay in HIV-1, HIV-2 and HIV-1/2 dually reactive patients - comparison with INNO-LIA and immunocomb discriminatory assays

BACKGROUND

Being able to discriminate between HIV-1, HIV-2 and HIV-1/2 dual infection is imperative for the appropriate selection of antiretroviral therapy (ART) in regions with high HIV-2 endemicity.

OBJECTIVES

To evaluate Bio-Rad Geenius HIV-1/2 Confirmatory Assay against INNO-LIA HIV 1/2 Score and ImmunoComb HIV 1/2 BiSpot with an emphasis towards ability to discriminate between HIV-1, HIV-2 and HIV-1/2 dual infection.

MATERIAL AND METHODS

131 samples from ART naïve HIV infected patients in Guinea-Bissau were selected retrospectively and tested with Geenius, INNO-LIA and Immunocomb. HIV-1/2 RNA were measured in all samples and HIV-1/2 DNA in 59 samples.

RESULTS

The Geenius reader typed 62 samples as HIV-1 reactive, 37 samples as HIV-2 reactive and 32 samples as HIV-1/2 dually reactive. Geenius manual reading classified 10% more samples as HIV-1/2 dually reactive (n = 35). INNO-LIA typed 63 samples as HIV-1 reactive, 36 samples as HIV-2 reactive and 32 samples as HIV-1/2 dually reactive while Immunocomb classified a large proportion of samples as HIV-1/2 dually reactive (n = 45). The measurement of agreement of the Geenius reader compared with INNO-LIA and Immunocomb was 92.4% and 84.0% respectively while the measurement of agreement of Geenius manual reading compared with INNO-LIA and Immuncomb was 93.1% and 89.3% respectively.

CONCLUSIONS

Geenius has similar performance characteristics as INNO-LIA, and performs considerably better than Immunocomb, for differentiating between HIV types. This is especially true when using the Geenius reader while manual reading of the Geenius assay seemed to overestimate the numbers of HIV-1/2 dually reactive samples.

Low Postseroconversion CD4+ T-cell Level Is Associated with Faster Disease Progression and Higher Viral Evolutionary Rate in HIV-2 Infection

The relationship between HIV evolution and disease progression is fundamental to our understanding of HIV immune control and vaccine design. There are no clear definitions for faster and slower HIV-2 disease progression and for the relationship of the rate of progression with HIV-2 evolution. To address the hypothesis that viral evolution is correlated with disease progression in HIV-2 infection, we determined faster and slower disease progression based on follow-up data from a prospective cohort of police officers in Guinea-Bissau. The analysis showed that although the CD4⁺ T-cell level and the decline in the level were independently associated with progression to AIDS, only the CD4⁺ T-cell level or a combined CD4⁺ T-cell level/decline stratification was associated with the rate of HIV-2 evolution. The HIV-2 evolutionary rate was almost twice as high among the faster progressors as among the slower progressors. Importantly, this report defines previously unknown characteristics linking HIV-2 disease progression with virus evolution.

A positive correlation between virus evolutionary rate and disease progression has been shown for human immunodeficiency virus type 1 (HIV-1) infection. Much less is known about HIV-2, the second causative agent of AIDS. We analyzed 528 HIV-2 env V1-C3 sequences generated from longitudinal plasma samples that were collected from 16 study participants during a median observation time of 7.9 years (interquartile range [IQR], 5.2 to 14.0 years). Study participants were classified as faster or slower disease progressors based on longitudinal CD4⁺ T-cell data. The HIV-2 evolutionary rate was significantly associated with CD4⁺ T-cell levels and was almost twice as high among the faster progressors as among the slower progressors. Higher evolutionary rates were accounted for by both synonymous and nonsynonymous nucleotide substitutions. Moreover, slow disease progression was associated with stronger positive selection on HIV-2/SIVsm (simian immunodeficiency virus infecting sooty mangabey) surface-exposed conserved residues. This study demonstrated a number of previously unknown characteristics linking HIV-2 disease progression with virus evolution. Some of these findings distinguish HIV-2 from HIV-1 and may contribute to the understanding of differences in pathogenesis.

The challenge of discriminating between HIV-1, HIV-2 and HIV-1/2 dual infections

OBJECTIVES

Discrimination between HIV-1 and HIV-2 is important to ensure appropriate antiretroviral treatment (ART) and epidemiological surveillance. However, serological tests have shown frequent mistyping when applied in the field. We evaluated two confirmatory tests, INNO-LIA HIV I/II Score and ImmunoComb HIV 1/2 BiSpot, for HIV type discriminatory capacity.

METHODS

Samples from 239 ART-naïve HIV-infected patients from the Bissau HIV Cohort in Guinea-Bissau were selected retrospectively based on the initial HIV typing performed in Bissau, ensuring a broad representation of HIV types. INNO-LIA results were interpreted by the newest software algorithm, and three independent observers read the ImmunoComb results. HIV-1/HIV-2 RNA and DNA were measured for confirmation.

RESULTS

INNO-LIA results showed 123 HIV-1 positive samples, 69 HIV-2 positive and 47 HIV-1/2 dually reactive. There was agreement between INNO-LIA and HIV-1/HIV-2 RNA and DNA detection, although not all HIV-1/2 dually reactive samples could be confirmed by the nucleic acid results. Overall, the observers found that the ImmunoComb results differed from the INNO-LIA results, with agreements of 90.4, 91.2 and 92.5%, respectively, for HIV-1, HIV-2 and HIV-1/2. The combined kappa-score for agreement between the three observers was 0.955 (z-score 35.1; P < 0.01). Of the HIV-2 mono-reactive samples (INNO-LIA), the three observers interpreted 24.6-31.9% as HIV-1/2 dually infected by ImmunoComb. None of these samples had detectable HIV-1 RNA or DNA.

CONCLUSIONS

There was accordance between INNO-LIA calls and nucleic acid results, whereas ImmunoComb overestimated the number of HIV-1/2 dually infected patients. Confirmatory typing is needed for patients diagnosed with HIV-1/2 dual infection by ImmunoComb.

New Highly Sensitive Real-Time PCR Assay for HIV-2 Group A and Group B DNA Quantification

HIV-2 infection is characterized by a very low replication rate in most cases and low progression. This necessitates an approach to patient monitoring that differs from that for HIV-1 infection. Here, a new highly specific and sensitive method for HIV-2 DNA quantification was developed. The new test is based on quantitative real-time PCR targeting the long terminal repeat (LTR) and gag regions and using an internal control. Analytical performance was determined in three laboratories, and clinical performance was determined on blood samples from 63 patients infected with HIV-2 group A (n = 35) or group B (n = 28). The specificity was 100%. The 95% limit of detection was three copies/PCR and the limit of quantification was six copies/PCR. The within-run coefficients of variation were between 1.03% at 3.78 log₁₀ copies/PCR and 27.02% at 0.78 log₁₀ copies/PCR. The between-run coefficient of variation was 5.10%. Both manual and automated nucleic acid extraction methods were validated. HIV-2 DNA loads were detectable in blood cells from all 63 patients. When HIV-2 DNA was quantifiable, median loads were significantly higher in antiretroviral-treated than in naive patients and were similar for groups A and B. HIV-2 DNA load was correlated with HIV-2 RNA load (r = 0.68; 95% confidence interval [CI], 0.4 to 0.8; P < 0.0001). Our data show that this new assay is highly sensitive and quantifies the two main HIV-2 groups, making it useful for the diagnosis of HIV-2 infection and for pathogenesis studies on HIV-2 reservoirs.

H11/HSPB8 Restricts HIV-2 Vpx to Restore the Anti-Viral Activity of SAMHD1

Virus-host interactions play vital roles in viral replication and virus-induced pathogenesis. Viruses rely entirely upon host cells to reproduce progeny viruses; however, host factors positively or negatively regulate virus replication by interacting with viral proteins. The elucidation of virus-host protein interaction not only provides a better understanding of the molecular mechanisms by which host cells combat viral infections, but also facilitates the development of new anti-viral therapeutics. Identification of relevant host factors requires techniques that enable comprehensive characterization of virus-host protein interactions. In this study, we developed a proteomic approach to systematically identify human protein kinases that interact potently with viral proteins. For this purpose, we synthesized 412 full-length human protein kinases using the wheat germ cell-free protein synthesis system, and screened them for their association with a virus protein using the amplified luminescent proximity homogenous assay (AlphaScreen). Using this system, we attempted to discover a robust anti-viral host restriction mechanism targeting virus protein X (Vpx) of HIV-2. The screen identified H11/HSPB8 as a Vpx-binding protein that negatively regulates the stability and function of Vpx. Indeed, overexpression of H11/HSPB8 promoted the degradation of Vpx via the ubiquitin-proteasome pathway and inhibited its interaction with SAMHD1, a host restriction factor responsible for blocking replication of HIV. Conversely, targeted knockdown of H11/HSPB8 in human trophoblast cells, which ordinarily express high levels of this protein, restored the expression and function of Vpx, making the cells highly susceptible to viral replication. These results demonstrate that our proteomic approach represents a powerful tool for revealing virus-host interaction not yet identified by conventional methods. Furthermore, we showed that H11/HSPB8 could be a potential host regulatory factor that may prevent placental infection of HIV-2 during pregnancy.

HIV-2 infects resting CD4+ T cells but not monocyte-derived dendritic cells

Background

Human Immunodeficiency Virus-type 2 (HIV-2) encodes Vpx that degrades SAMHD1, a cellular restriction factor active in non-dividing cells. HIV-2 replicates in lymphocytes but the susceptibility of monocyte-derived dendritic cells (MDDCs) to in vitro infection remains partly characterized.

Results

Here, we investigated HIV-2 replication in primary CD4+ T lymphocytes, both activated and non-activated, as well as in MDDCs. We focused on the requirement of Vpx for productive HIV-2 infection, using the reference HIV-2 ROD strain, the proviral clone GL-AN, as well as two primary HIV-2 isolates. All HIV-2 strains tested replicated in activated CD4+ T cells. Unstimulated CD4+ T cells were not productively infected by HIV-2, but viral replication was triggered upon lymphocyte activation in a Vpx-dependent manner. In contrast, MDDCs were poorly infected when exposed to HIV-2. HIV-2 particles did not potently fuse with MDDCs and did not lead to efficient viral DNA synthesis, even in the presence of Vpx. Moreover, the HIV-2 strains tested were not efficiently sensed by MDDCs, as evidenced by a lack of MxA induction upon viral exposure. Virion pseudotyping with VSV-G rescued fusion, productive infection and HIV-2 sensing by MDDCs.

Conclusion

Vpx allows the non-productive infection of resting CD4+ T cells, but does not confer HIV-2 with the ability to efficiently infect MDDCs. In these cells, an entry defect prevents viral fusion and reverse transcription independently of SAMHD1. We propose that HIV-2, like HIV-1, does not productively infect MDDCs, possibly to avoid triggering an immune response mediated by these cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12977-014-0131-7) contains supplementary material, which is available to authorized users.

Antiretroviral therapy and drug resistance in human immunodeficiency virus type 2 infection

One to two million people worldwide are infected with the human immunodeficiency virus type 2 (HIV-2), with highest prevalences in West African countries, but also present in Western Europe, Asia and North America. Compared to HIV-1, HIV-2 infection undergoes a longer asymptomatic phase and progresses to AIDS more slowly. In addition, HIV-2 shows lower transmission rates, probably due to its lower viremia in infected individuals. There is limited experience in the treatment of HIV-2 infection and several antiretroviral drugs used to fight HIV-1 are not effective against HIV-2. Effective drugs against HIV-2 include nucleoside analogue reverse transcriptase (RT) inhibitors (e.g. zidovudine, tenofovir, lamivudine, emtricitabine, abacavir, stavudine and didanosine), protease inhibitors (saquinavir, lopinavir and darunavir), and integrase inhibitors (raltegravir, elvitegravir and dolutegravir). Maraviroc, a CCR5 antagonist blocking coreceptor binding during HIV entry, is active in vitro against CCR5-tropic HIV-2 but more studies are needed to validate its use in therapeutic treatments against HIV-2 infection. HIV-2 strains are naturally resistant to a few antiretroviral drugs developed to suppress HIV-1 propagation such as nonnucleoside RT inhibitors, several protease inhibitors and the fusion inhibitor enfuvirtide. Resistance selection in HIV-2 appears to be faster than in HIV-1. In this scenario, the development of novel drugs specific for HIV-2 is an important priority. In this review, we discuss current anti-HIV-2 therapies and mutational pathways leading to drug resistance.

Frequent intratype neutralization by plasma immunoglobulin a identified in HIV type 2 infection

Human immunodeficiency virus type 2 (HIV-2) is less transmissible and less pathogenic compared to HIV-1 and, when matched for CD4(+) T cell count, the plasma viral load in HIV-2-infected individuals is approximately one log lower than in HIV-1-infected individuals. The explanation for these observations is elusive, but differences in virus controlling immunity generated in the two infections may be contributing factors. In the present study, we investigated neutralization by immunoglobulin A (IgA), in parallel with IgG, purified from plasma of HIV-1, HIV-2, and HIV-1/HIV-2 dually (HIV-D) infected individuals. Neutralization was analyzed against HIV-1 and HIV-2 isolates using a plaque reduction assay. In HIV-2 infection, intratype-specific neutralization by IgA was frequently detected, although at a lesser magnitude then the corresponding IgG neutralizing titers. In contrast, neutralization by IgA could rarely be demonstrated in HIV-1 infection despite similar plasma IgA levels in both infections. In addition, IgA and IgG of HIV-D plasma neutralized the HIV-2 isolate more potently than the HIV-1 isolate, suggesting that the difference between neutralizing activity of plasma IgA and IgG depends on the virus itself. Taken together, these findings suggest that both IgA and IgG add to the potent intratype neutralizing activity detected in HIV-2 plasma, which may contribute to virus control in HIV-2 infection.

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.

An improved PCR method for detection of HIV-1 proviral DNA of a wide range of subtypes and recombinant forms circulating globally

Proviral DNAs are being measured increasingly as a marker of the efficacy of highly active anti-retroviral therapy (HAART) and is accepted for the early diagnosis of perinatal HIV-1 infections. This requires a standardized test which enables the detection of a wide range of subtypes worldwide including O, N and circulating recombinant forms (CRFs). Based on a previous publication, a PCR - Test for HIV-1 provirus detection in peripheral blood mononuclear cells (PBMCs) was developed. Blood samples from 80 individuals infected with HIV-1 and 20 persons negative for HIV-1&2 from Africa and Germany were tested for the presence of HIV-1 provirus DNA. The primer system used enables the detection of proviral DNA despite the high concentrations of human DNA. The limit of detection was determined to be 5 copies per 10(5) cells. All 20 samples from persons negative for HIV were negative for HIV-1 proviral DNA while provirus DNA was amplified from 76 of the 80 (95%) samples from persons infected with HIV. The amplified products were detected by gel-electrophoresis, flow cytometry and real-time PCR. All three detection systems provided the same results.

Time course of total HIV-1 DNA and 2-long-terminal repeat circles in patients with controlled plasma viremia switching to a raltegravir-containing regimen

BACKGROUND

Early integration of HIV proviral DNA into the host cell genome prevents viral eradication, despite suppressive HAART. In vitro, integrase inhibitors reduce proviral DNA levels and rapidly increase 2-long-terminal repeat (LTR) circle levels. We examined the effect of raltegravir on the time course of HIV-1 DNA forms in patients with controlled viremia.

PATIENTS AND METHODS

The EASIER-ANRS 138 randomized trial demonstrated that switching from enfuvirtide to raltegravir maintained virological suppression in treatment-experienced patients with viral load below 400 copies/ml. We analyzed total HIV-1 DNA and 2-LTR circle levels measured at weeks (W)0 and 24 in the first 30 patients enrolled in each arm, and at W48 in the raltegravir arm.

RESULTS

At W0 the total DNA level was 3.6 log(10)/10(6) peripheral blood mononuclear cell (PBMC) in both groups, and 2-LTR circles were detected in six patients (median 89 copies/10(6) PBMC). At W24 the total DNA level was 3.6 log(10)/10(6) PBMC in both groups, and 2-LTR circles were detected in three new patients. At W48 the total HIV DNA level in the raltegravir group was 3.5 log(10)/10(6) PBMC, and 2-LTR circles were undetectable. No significant change in total HIV DNA occurred between W0 and W24 in either arm (P = 0.71) and no significant change was observed in the raltegravir arm at W48.

DISCUSSION

In most patients on effective HAART, including regimens containing an integrase inhibitor, the viral reservoir, reflected by the HIV-1 DNA load, is stable and nondynamic during the 48 weeks of follow-up.

A neutralization assay for HIV-2 based on measurement of provirus integration by duplex real-time PCR

Specific, effective and rapid neutralization assays are crucial for the development of an HIV vaccine based on the stimulation of neutralizing antibodies and the development of such an assay for the human immunodeficiency virus-2 (HIV-2) is described. Virus neutralization was measured as the reduction of provirus integration using a duplex real-time PCR with high efficiency (99.4%). This PCR uses primers and a probe specific for the proviral LTR. Amplification and quantitative analysis of the cellular GAPDH gene was carried out in parallel to control for toxic or growth-inhibitory components in the sera. The neutralization assay was used to screen sera from 23 HIV-2 infected patients. 21 sera were able to neutralize HIV-2(60415K), 20 sera neutralized HIV-2(7312A) and 7 sera cross-neutralized HIV-1 IIIB. In contrast, when 14 of these sera were tested in parallel with a conventional neutralization assay based on a p27Gag capture ELISA, only one was found to neutralize HIV-2(60415K) and 11 to neutralize HIV-2(7312A) compared with 12 and 13 sera respectively using the PCR-based assay.

In-house HIV-1 RNA real-time RT-PCR assays: principle, available tests and usefulness in developing countries

The principle of currently available licensed HIV-1 RNA assays is based on real-time technologies that continuously monitor the fluorescence emitted by the amplification products. Besides these assays, in-house quantitative (q) real-time reverse transcription (RT)-PCR (RT-qPCR) tests have been developed and evaluated particularly in developing countries, for two main reasons. First, affordable and generalized access to HIV-1 RNA viral load is urgently needed in the context of expected universal access to prevention and antiretroviral treatment programs in these settings. Second, since many non-B subtypes, circulating recombinant forms and unique recombinant forms circulate in these areas, in-house HIV-1 RNA RT-qPCR assays are ideal academic tools to thoroughly evaluate the impact of HIV-1 genetic diversity on the accuracy of HIV-1 RNA quantification, as compared with licensed techniques. To date, at least 15 distinct in-house assays have been designed. They differ by their chemistry and the HIV-1 target sequence (located in gag, Pol-IN or LTR gene). Analytical performances of the tests that have been extensively evaluated appear at least as good as (or even better than) those of approved assays, with regard to HIV-1 strain diversity. Their clinical usefulness has been clearly demonstrated for early diagnosis of pediatric HIV-1 infection and monitoring of highly active antiretroviral therapy efficacy. The LTR-based HIV-1 RNA RT-qPCR assay has been evaluated by several groups under the auspices of the Agence Nationale de Recherches sur le SIDA et les hépatites virales B et C. It exists now as a complete standardized commercial test.

HIV-1 and HIV-2 produce different amounts of 2-long terminal repeat circular DNA in vitro

We assessed HIV-1 and HIV-2 2-long terminal repeat (LTR) circular DNA production in peripheral blood mononuclear cells, MT4-CXCR4 cells and HeLa-CXCR4-CCR5 cells in vitro, relative to the respective total amounts of HIV DNA. Whatever the cell type, HIV-2 produced a smaller total amount of DNA than HIV-1 between 6 and 96 h; HIV-2 2-LTR DNA appeared later than HIV-1 2-LTR DNA, but rapidly became more abundant. This accumulation of HIV-2 2-LTR DNA points to less efficient host cell integration relative to HIV-1.

Envelope-specific antibody response in HIV-2 infection: C2V3C3-specific IgG response is associated with disease progression

OBJECTIVE

To examine the unspecific and envelope-specific IgA and IgG responses in acute and chronic HIV-2 infection.

METHODS

Twenty-eight chronically infected adults and two children with perinatal infection were studied. Total plasma concentrations of IgA and IgG were determined by nephelometry. IgA and IgG reactivity against the immunodominant region in gp36 and the C2V3C3 region in gp125 was tested with the enzyme-linked immunosorbent assay (ELISA)-HIV-2 assay. Clonal sequences of the C2V3C3 env region were obtained for most patients.

RESULTS

Total plasma IgG concentration, but not IgA, was significantly higher than normal in HIV-2 patients and correlated inversely with CD4 T-cell counts. Seroconversion to gp36 occurred during the first year of life in both infants. The infant with rapid disease progression did not elicit C2V3C3-specific antibodies. Most chronically infected patients produced plasma IgG1, IgG3 and IgA antibodies against gp36 and C2V3C3. Lack of C2V3C3-specific IgG response in two patients was associated with a major antigenic change in the V3 region. In longitudinal analysis, there was a significant inverse association between the C2V3C3-specific IgG antibody response and the number of CD4 T cells.

CONCLUSION

HIV-2 promotes an early, strong and broad gp36 and C2V3C3-specific IgG and IgA response. Increase in the IgG response against the envelope C2V3C3 region is associated with increased loss of CD4 T cells in chronically infected patients. These results provide further support for the immune protective role of the C2V3C3 envelope region during HIV-2 infection and have direct implications for HIV-2 diagnosis, clinical management and pathogenesis.

A universal real-time PCR assay for the quantification of group-M HIV-1 proviral load

Quantification of human immunodeficiency virus type-1 (HIV-1) proviral DNA is increasingly used to measure the HIV-1 cellular reservoirs, a helpful marker to evaluate the efficacy of antiretroviral therapeutic regimens in HIV-1-infected individuals. Furthermore, the proviral DNA load represents a specific marker for the early diagnosis of perinatal HIV-1 infection and might be predictive of HIV-1 disease progression independently of plasma HIV-1 RNA levels and CD4(+) T-cell counts. The high degree of genetic variability of HIV-1 poses a serious challenge for the design of a universal quantitative assay capable of detecting all the genetic subtypes within the main (M) HIV-1 group with similar efficiency. Here, we describe a highly sensitive real-time PCR protocol that allows for the correct quantification of virtually all group-M HIV-1 strains with a higher degree of accuracy compared with other methods. The protocol involves three stages, namely DNA extraction/lysis, cellular DNA quantification and HIV-1 proviral load assessment. Owing to the robustness of the PCR design, this assay can be performed on crude cellular extracts, and therefore it may be suitable for the routine analysis of clinical samples even in developing countries. An accurate quantification of the HIV-1 proviral load can be achieved within 1 d from blood withdrawal.

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.