Broad cross-neutralizing activity in serum is associated with slow progression and low risk of transmission in primate lentivirus infections

HIV-2 and its role in conglutinated approach towards Acquired Immunodeficiency Syndrome (AIDS) Vaccine Development

Acquired Immunodeficiency Syndrome (AIDS) is one of the most critically acclaimed endemic diseases, caused by two lentiviruses HIV-1 and 2. HIV-2 displays intimate serological and antigenic resemblance to Simian Immunodeficiency Virus (SIV) along with less pathogenicity, lower infectivity and appreciable cross reactivity with HIV-1 antigens. The present era is confronted with the challenge to fabricate a vaccine effective against all clades of both the species of HIV. But vaccine development against HIV-1 has proven highly intricate, moreover the laborious and deficient conventional approaches has slackened the pace regarding the development of new vaccines. These concerns may be tackled with the development of HIV-2 vaccine as a natural control of HIV-1 that has been found in ancestors of HIV-2 i.e. African monkeys, mangabeys and macaques. Thereby, suggesting the notion of cross protection among HIV-2 and HIV-1. Assistance of bioinformatics along with vaccinomics strategy can bring about a quantum leap in this direction for surpassing the bottleneck in conventional approaches. These specifics together can add to our conception that HIV-2 vaccine design by in silico strategy will surely be a constructive approach for HIV-1 targeting.

Broad neutralization of human immunodeficiency virus type 1 (HIV-1) elicited from human rhinoviruses that display the HIV-1 gp41 ELDKWA epitope

In efforts to develop AIDS vaccine components, we generated combinatorial libraries of recombinant human rhinoviruses that display the well-conserved ELDKWA epitope of the membrane-proximal external region of human immunodeficiency virus type 1 (HIV-1) gp41. The broadly neutralizing human monoclonal antibody 2F5 was used to select for viruses whose ELDKWA conformations resemble those of HIV. Immunization of guinea pigs with different chimeras, some boosted with ELDKWA-based peptides, elicited antibodies capable of neutralizing HIV-1 pseudoviruses of diverse subtypes and coreceptor usages. These recombinant immunogens are the first reported that elicit broad, albeit modest, neutralization of HIV-1 using an ELDKWA-based epitope and are among the few reported that elicit broad neutralization directed against any recombinant HIV epitope, providing a critical advance in developing effective AIDS vaccine components.

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.

B cell immunopathology during HIV-1 infection: lessons to learn for HIV-1 vaccine design

Induction of broad HIV-1 neutralizing antibodies should be a major goal of an effective HIV-1 vaccine. However, B cells are severely damaged during HIV-1 infection with loss of memory B cells and decline of serological memory. The molecular events leading to B cell damage must be further characterized with the aim of selecting vaccine components allowing preservation of B cell functions. This review focuses on B cell damage and antibody responses in HIV-1-infected patients during vaccination studies with viral and bacterial antigens. In addition novel data indicate that B cell activation may be at the basis of impaired immune responses.

Dynamics of T-cell responses and memory T cells during primary simian immunodeficiency virus infection in cynomolgus macaques

Cellular immune responses make an important contribution to both the control of human immunodeficiency virus (HIV) replication and disease progression. We used a pathogenic model of SIVmac251 infection of cynomolgus macaques to longitudinally evaluate cellular immune responses in association with various rates of disease progression. We found an inverse relationship between plasma viral load and the simian immunodeficiency virus (SIV)-specific T cells responses in peripheral blood and lymph nodes. SIV-specific T-cell responses in peripheral blood were transient during primary infection, with the highest responses detected around 3 months after infection. There was also a transient increase of central memory CD8(+) T cells in peripheral blood during primary infection, and effector memory T-cell counts in peripheral lymph nodes were increased. This study emphasizes the importance of the early virus-specific immune responses in the outcome of HIV/SIV disease and provides details about the changes of virus-specific immune responses over time.

Evidence of proviral clearance following postpartum transmission of an ovine lentivirus

Lentiviral transmission by transfer of infected colostrum and/or milk is considered to be highly efficient. In this study, postpartum transmission of ovine progressive pneumonia virus (OPPV) from 10 naturally infected ewes to their 23 lambs was followed from the perinatal period throughout a four-year period. The lambs were allowed to suckle from their dam from birth through 32 weeks of age. Virus was tracked by virus isolation, quantitative PCR (qPCR), and anti-OPPV antibody responses as measured by cELISA. Cell-associated OPPV was isolated from colostrum/milk cells in 7 out of 10 ewes and provirus envelope (env) loads ranged 8 to 10(5) copies/mug DNA in colostrum/milk cells from the 10 ewes using qPCR. Provirus env loads were also detected in the peripheral circulation of 21 lambs at 8 weeks and two lambs at 22 weeks. The qPCR product at 8 weeks was confirmed as the transmembrane (tm) gene of OPPV by cloning and sequencing. Both cELISA titers ranging from 325 to 3125 and cross-neutralizing antibody titers ranging from 6 to 162 to seven different OPPV strains were found in the colostrum of the 10 ewes. Furthermore, cELISA titers in serum from lambs remained detectable through 32 weeks following the clearance of provirus at 24 weeks. After 32 weeks, both provirus and anti-OPPV antibody responses have subsequently remained undetectable through 4 years of age. These data suggest the clearance of cell-associated lentiviruses from lamb circulation after passive transfer of antibody via colostrum.

Comparison of heterologous neutralizing antibody responses of human immunodeficiency virus type 1 (HIV-1)- and HIV-2-infected Senegalese patients: distinct patterns of breadth and magnitude distinguish HIV-1 and HIV-2 infections

Neutralizing antibody responses against heterologous isolates in human immunodeficiency virus type 1 (HIV-1) and HIV-2 infections were compared, and their relationships with established clinical markers of progression were examined. Neutralizing responses against 7 heterologous primary isolates and 1 laboratory strain were compared between 32 untreated HIV-1-infected subjects and 35 untreated HIV-2-infected subjects using a pseudotyped reporter virus assay. The breadth of the neutralizing response, defined as the proportion of panel viruses positively neutralized by patient plasma, was significantly greater among HIV-2-infected subjects than among HIV-1-infected subjects. Notably, for fully one-third of HIV-2 subjects, all viruses were effectively neutralized in our panel. Magnitudes of responses, defined as reciprocal 50% inhibitory concentration (IC(50)) titers for positive reactions, were significantly greater among HIV-1-infected subjects than among HIV-2-infected subjects. When plasma samples from HIV-1 patients were tested for cross-neutralization of HIV-2 and vice versa, we found that these intertype responses are very rare and their prevalences comparable in both HIV-1 and HIV-2 infection. The significantly higher magnitude of heterologous responses for HIV-1 compared to HIV-2 prompted us to examine associations with viremia, which is known to be significantly higher in HIV-1 infection. Importantly, there was a significant positive correlation between the IC(50) titer and viral load within both the HIV-1 and HIV-2 groups, suggesting heterologous antibodies may be driven by viral replication. We conclude that HIV-2 infection is characterized by a broad, low-magnitude intratype neutralization response, while HIV-1 is characterized by a narrower but higher-magnitude intratype response and that a significant positive association between the IC(50) titer and viremia is common to both HIV-1 and HIV-2 infections.

Evolution of human immunodeficiency virus type 2 coreceptor usage, autologous neutralization, envelope sequence and glycosylation

To investigate why human immunodeficiency virus type 2 (HIV-2) is less virulent than HIV-1, the evolution of coreceptor usage, autologous neutralization, envelope sequence and glycosylation was studied in sequentially obtained virus isolates and sera from four HIV-2-infected individuals. Neutralization of primary HIV-2 isolates was tested by a cell line-based assay and IgG purified from patients' sera. Significant autologous neutralization was observed for the majority (39 of 54) of the HIV-2 serum-virus combinations tested, indicating that neutralization escape is rare in HIV-2 infection. Furthermore, sera from 18 HIV-2 patients displayed extensive heterologous cross-neutralization when tested against a panel of six primary HIV-2 isolates. This indicates that HIV-2 is intrinsically more sensitive to antibody neutralization than HIV-1. In line with earlier reports, HIV-2 isolates could use several alternative receptors in addition to the major coreceptors CCR5 and CXCR4. Intrapatient evolution from CCR5 use to CXCR4 use was documented for the first time. Furthermore, CXCR4 use was linked to the immunological status of the patients. Thus, all CXCR4-using isolates, except one, were obtained from patients with CD4 counts below 200 cells microl(-1). Sequence analysis revealed an association between coreceptor usage and charge of the V3 loop of the HIV-2 envelope, as well as an association between the rate of disease progression and the glycosylation pattern of the envelope protein. Furthermore, HIV-2 isolates had fewer glycosylation sites in the V3 domain than HIV-1 (two to three versus four to five). It is proposed here that HIV-2 has a more open and accessible V3 domain than HIV-1, due to differences in glycan packing, and that this may explain its broader coreceptor usage and greater sensitivity to neutralizing antibodies.

CD4-dependent and CD4-independent HIV-2: consequences for neutralization

BACKGROUND

HIV-2 is less pathogenic than HIV-1. In contrast to HIV-1, many isolates of HIV-2, including primary isolates, can infect cells independently of CD4.

OBJECTIVE

To compare the sensitivity of CD4-dependent and CD4-independent isolates of HIV-2 to antibody-mediated neutralization.

METHODS

The neutralization sensitivity of CD4-dependent and CD4-independent molecular clones of HIV-2 to a panel of HIV-2-positive serum samples was tested. Monoclonal antibodies to various epitopes across the viral envelope were used to determine whether a specific epitope conferred neutralization sensitivity. Neutralization sensitivity of primary isolates of HIV-2 able to infect in the absence of cellular CD4 was also investigated. Antibody binding to sensitive and resistant envelopes was analysed using enzyme-linked immunosorbent assay and flow cytometry.

RESULTS

CD4-independent ROD B was highly sensitive to neutralization by HIV-2-positive sera compared with the CD4-dependent isolate ROD A. Induction of ROD A to infect CD4-negative cells by soluble CD4 rendered it equally sensitive to antibody neutralization. Similarly, primary X4, R5 or dual-tropic isolates of HIV-2 were significantly more susceptible to neutralization when utilizing a CD4-independent route of infection. Neutralization sensitivity was not epitope specific but several conformation-dependent antibodies accentuated this phenotype. Antibody binding to monomeric or oligomeric envelope did not correlate with neutralization sensitivity.

CONCLUSIONS

HIV-2 isolates utilizing a CD4-independent route of infection are more sensitive to antibody-mediated neutralization. Cellular CD4 may protect HIV-2 from neutralization. This sensitivity to neutralization may, in part, explain the lower virus load and slower progression to disease in HIV-2-infected individuals.

Therapeutic dendritic-cell vaccine for simian AIDS

An effective immune response against human immunodeficiency virus or simian immunodeficiency virus (SIV) is critical in achieving control of viral replication. Here, we show in SIV-infected rhesus monkeys that an effective and durable SIV-specific cellular and humoral immunity is elicited by a vaccination with chemically inactivated SIV-pulsed dendritic cells. After three immunizations made at two-week intervals, the animals exhibited a 50-fold decrease of SIV DNA and a 1,000-fold decrease of SIV RNA in peripheral blood. Such reduced viral load levels were maintained over the remaining 34 weeks of the study. Molecular and cellular analyses of axillary and inguinal node lymphocytes of vaccinated monkeys revealed a correlation between decreased SIV DNA and RNA levels and increased SIV-specific T-cell responses. Neutralizing antibody responses were augmented and remained elevated. Inactivated whole virus-pulsed dendritic cell vaccines are promising means to control diseases caused by immuno- deficiency viruses.

Analysis of a primary isolate-like virus from simian and human immunodeficiency virus-infected macaque having broad neutralizing activity

To investigate the changes of neutralizing antibodies and viruses during simian and human immunodeficiency virus (SHIV) infection, we examined the cross-neutralizing ability of sequential sera from three macaques infected with SHIV, NM-3rN, and analyzed the sensitivity of the reisolate to neutralizing antibodies. Neutralizing activities of macaques' sera against the parental HIV-1 showed a persistent increase. Neutralizing activities were highly strain specific, but the spectrum of the neutralizing activity expanded against various clades of primary HIV-1s at 3 years after infection in one of the three macaques. The reisolate from an NM3-rN-infected macaque at 56 wpi, designated as R4356, was neutralized by sera from this macaque at a much lower titer than NM-3rN, even by the sera collected 2 years after the reisolation. Sera from macaques that were newly infected with R4356 also did not neutralize R4356 despite neutralizing NM-3rN strongly. These results suggested that long-term persistent infection with SHIV induced neutralizing antibodies with a broad spectrum. However, a virus resistant to the neutralizing antibodies emerged in the persistently infected macaque.

Genetic variability of the V1 and V2 env domains of SIVcpz-ant and neutralization pattern of plasma viruses in a chimpanzee infected naturally

Specific neutralizing epitope changes have been observed in a chimpanzee infected naturally with SIVcpz, which differ from HIV-1 infecting humans. To characterize further these changes, a longitudinal study of env genomic sequence variation of SIVcpz-ant isolates was undertaken in this animal. The V1 and V2 regions of the env were determined to arise from specific recombination events. To determine whether recombination of the V1 and V2 domains was possibly associated with the emergence of neutralization escape viruses, envelope sequences and gene length polymorphisms from PBMC and plasma viral variants were studied over a 7-year period. PBMCs and plasma-associated infectious virus titers as well as plasma RNA viral loads were monitored longitudinally. The first 5 viruses isolated from the plasma were found to be neutralization escape variants. Sequence analysis of their V1 and the V2 regions indicated that a 20 amino acid stretch of the V1 region had undergone recombination and was also associated with the emergence of isolates eliciting strong neutralization responses. These findings support the hypothesis that recombination of the V1 and V2 regions of the envelope play a role in neutralization escape of SIVcpz in chimpanzees infected naturally. Furthermore, the data confirm that the neutralizing antibody response plays an important role in the decline of plasma infectious virus titers in HIV-1 related SIVcpz nonpathogenic infection.

Up-regulation of CCR5 expression in the placenta is associated with human immunodeficiency virus-1 vertical transmission

The role of placenta in vertical transmission is not yet fully understood. A protective role of the placenta during gestation is suggested by the finding that caesarian sections reduce the risk of transmission of human immunodeficiency virus (HIV)-1 from mother to child three- to fourfold. Here we investigated whether the immunological milieu of the placenta might be important in HIV-1 transmission. In situ imaging of immunohistochemically stained placenta sections and reverse transcriptase-polymerase chain reaction demonstrated a fourfold increase in CCR5:CXCR4 expression ratio in placentae from transmitting women compared to placentae from nontransmitting women. This chemokine receptor repertoire was consistent with an up-regulation of interleukin-4 and interleukin-10 expression in placentae from nontransmitting placentae compared to transmitting placentae. In situ imaging demonstrated that CCR5 and CXCR4 were expressed on placental macrophages and lymphocytes but not in trophoblasts. Simultaneous immunofluorescence/ultrasensitive in situ hybridization for HIV-1 gag-pol mRNA revealed that HIV-1 infects primarily CXCR4-expressing cells in placentae from nontransmitting women whereas predominantly CCR5-expressing cells were infected in placentae from transmitting women. These data are consistent with transmission of a homogeneous population of nonsyncytium-inducing HIV-1 isolates that use CCR5 as co-receptor.

In vitro correlates of HIV-2-mediated HIV-1 protection

A prospective study of high-risk commercial sex workers in Senegal has shown that HIV-2 infection may reduce the risk of subsequent HIV-1 infection; these findings have been confirmed and extended, now with 13 years of observation. While exploring the biological mechanisms behind this natural protection, we found that a significant proportion of peripheral blood mononuclear cells obtained from HIV-2-infected subjects resisted in vitro challenge with CCR5-dependent HIV-1 viruses but not CXCR4-dependent viruses. High levels of beta-chemokines, the natural ligands of the CCR5 coreceptor, were correlated with low levels of viral replication, and resistance was abrogated by antibodies to beta-chemokines. Our results suggest that beta-chemokine-mediated resistance may be an important correlate of HIV protection against HIV-1 infection and relevant to HIV vaccine design.

Role of maternal humoral immunity in vertical transmission of HIV-1 subtype E in Thailand

The significance of the maternal humoral immune response in relation to vertical transmission of HIV-1 was investigated in 123 mothers infected with subtype E from Thailand. Antibody binding titers to HIV-1 env domains (monomeric gp120, the CD4/gp120 binding site [BS], V3 loop, and gp41) and antibody-mediated neutralization of primary and T-cell line-adapted (TCLA) subtypes B and E HIV-1 isolates were investigated. No correlation between maternal anti HIV-1 antibodies at delivery and vertical transmission of HIV-1 subtype E was found. However, a trend to higher titer antibody-mediated cross-neutralization of a heterologous subtype B TCLA isolate, HIV-1MN, was observed in nontransmitting mothers postpartum. The HIV-1-specific antibody titers in these infected mothers increased significantly from delivery to 6 months postpartum (p < .05), but this was only partially attributable to hemodilution and an additional factor or factors appear to affect humoral immunity to HIV-1 during late pregnancy.

Immunological responses to envelope glycoprotein 120 from subtypes of human immunodeficiency virus type 1

The outer envelope glycoprotein (gp120) from subtypes A-E of HIV-1 was purified using a specific high mannose-binding lectin, Galanthus nivalis agglutinin. All isolates were grown in peripheral blood lymphocyte cells in order to avoid selection in cell lines. A comparison of the reactivities of the envelope proteins was made using sera from patients infected with the different subtypes. In this study, the B and C subtype envelope glycoproteins showed the strongest immunological reactivity, when reacted with sera from patients infected with the same subtype of virus. On the other hand, sera of patients infected with subtype A or C virus had the strongest and broadest reactivities, to envelope glycoproteins of many subtypes. The purified gp120 proteins from all five subtypes stimulated mononuclear cells from HIV-1 (subtype B)-infected patients, indicating conserved T cell-activating epitopes. The immunological reactivities indicate that strong antigenicity does not always predict the broadest immunogenicity of an envelope glycoprotein. Glycoprotein 120 from foreign subtypes may serve to induce strong cross-reactive immune responses.

Dynamics of cytotoxic T-lymphocyte exhaustion

We examine simple mathematical models to investigate the circumstances under which the dynamics of cytotoxic T-lymphocyte (CTL) activation and differentiation may result in the loss of virus specific CD8+ cells, a process known as CTL exhaustion. We distinguish between two general classes of viruses: (i) viruses infecting cells that are not involved in the immune response; and (ii) viruses infecting antigen presenting cells (APCs) and helper cells. The models specify host and viral properties that lead to CTL exhaustion and indicate that this phenomenon is only likely to be observed with viruses infecting APCs and helper cells. Moreover, it is found that for such viruses, a high rate of replication and a low degree of cytopathogenicity promote the exhaustion of the CTL response. In addition, a high initial virus load and a low CD4+ cell count promote the occurrence of CTL exhaustion. These conclusions are discussed with reference to empirical data on lymphocytic choriomeningitis virus and on human immunodeficiency virus.