Increased mucosal transmission but not enhanced pathogenicity of the CCR5-tropic, simian AIDS-inducing simian/human immunodeficiency virus SHIV(SF162P3) maps to envelope gp120

Replication competent HIV-guided CRISPR screen identifies antiviral factors including targets of the accessory protein Nef

Innate antiviral factors are essential for effective defense against viral pathogens. However, the identity of major restriction mechanisms remains elusive. Current approaches to discover antiviral factors usually focus on the initial steps of viral replication and are limited to a single round of infection. Here, we engineered libraries of >1500 replication-competent HIV-1 constructs each expressing a single gRNAs to target >500 cellular genes for virus-driven discovery of antiviral factors. Passaging in CD4+ T cells robustly enriched HIV-1 encoding sgRNAs against GRN, CIITA, EHMT2, CEACAM3, CC2D1B and RHOA by >50-fold. Using an HIV-1 library lacking the accessory nef gene, we identified IFI16 as a Nef target. Functional analyses in cell lines and primary CD4+ T cells support that the HIV-driven CRISPR screen identified restriction factors targeting virus entry, transcription, release and infectivity. Our HIV-guided CRISPR technique enables sensitive discovery of physiologically relevant cellular defense factors throughout the entire viral replication cycle.

Tandem bispecific antibody prevents pathogenic SHIVSF162P3CN infection and disease progression

Although progress has been made on constructing potent bi-specific broadly neutralizing antibody (bi-bNAb), few bi-bNAbs have been evaluated against HIV-1/AIDS in non-human primates (NHPs). Here, we report the efficacy of a tandem bi-bNAb, namely BiIA-SG, in Chinese-origin rhesus macaques (CRM) against the CRM-adapted R5-tropic pathogenic SHIV_SF162P3CN challenge. Pre-exposure BiIA-SG injection prevents productive viral infection in 6 of 6 CRMs with unmeasurable proviral load, T cell responses, and seroconversion. Single BiIA-SG injection, at day 1 or 3 post viral challenge, significantly reduces peak viremia, achieves undetectable setpoint viremia in 8 of 13 CRMs, and delays disease progression for years in treated CRMs. In contrast, 6 of 8 untreated CRMs develop simian AIDS within 2 years. BiIA-SG-induced long-term protection is associated with CD8⁺ T cells as determined by anti-CD8β antibody depletion experiments. Our findings provide a proof-of-concept that bi-bNAb treatment elicits T cell immunity in NHPs, which warrant the clinical development of BiIA-SG for HIV-1 prevention and immunotherapy.

Rational design and in vivo selection of SHIVs encoding transmitted/founder subtype C HIV-1 envelopes

Chimeric Simian-Human Immunodeficiency Viruses (SHIVs) are an important tool for evaluating anti-HIV Env interventions in nonhuman primate (NHP) models. However, most unadapted SHIVs do not replicate well in vivo limiting their utility. Furthermore, adaptation in vivo often negatively impacts fundamental properties of the Env, including neutralization profiles. Transmitted/founder (T/F) viruses are particularly important to study since they represent viruses that initiated primary HIV-1 infections and may have unique attributes. Here we combined in vivo competition and rational design to develop novel subtype C SHIVs containing T/F envelopes. We successfully generated 19 new, infectious subtype C SHIVs, which were tested in multiple combinatorial pools in Indian-origin rhesus macaques. Infected animals attained peak viremia within 5 weeks ranging from 10³ to 10⁷ vRNA copies/mL. Sequence analysis during primary infection revealed 7 different SHIVs replicating in 8 productively infected animals with certain clones prominent in each animal. We then generated 5 variants each of 6 SHIV clones (3 that predominated and 3 undetectable after pooled in vivo inoculations), converting a serine at Env375 to methionine, tyrosine, histidine, tryptophan or phenylalanine. Overall, most Env375 mutants replicated better in vitro and in vivo than wild type with both higher and earlier peak viremia. In 4 of these SHIV clones (with and without Env375 mutations) we also created mutations at position 281 to include serine, alanine, valine, or threonine. Some Env281 mutations imparted in vitro replication dynamics similar to mutations at 375; however, clones with both mutations did not exhibit incremental benefit. Therefore, we identified unique subtype C T/F SHIVs that replicate in rhesus macaques with improved acute phase replication kinetics without altering phenotype. In vivo competition and rational design can produce functional SHIVs with globally relevant HIV-1 Envs to add to the growing number of SHIV clones for HIV-1 research in NHPs.

Nonhuman primates provide useful models for studying HIV transmission, pathogenesis and cure strategies. Due to species-specific antiviral factors, however, HIV cannot replicate in Asian macaques directly. Some chimeric viruses incorporating HIV Envelope genes in simian immunodeficiency virus (SIV) backbone can replicate to sufficient levels in Asian macaques to permit evaluation of anti-HIV interventions. Here we describe the generation of new SHIV clones unique to the field in 4 important ways. First, these clones were generated from the globally relevant HIV-1 subtype C, which is the most prevalent form of HIV globally and is found predominately in sub-Saharan Africa where the pandemic is particularly devastating but is poorly represented among SHIVs studied to date. Second, we utilized Envelope genes from viruses that established primary infection, making these clones particularly useful in transmission studies. Third, these clones were not generated by animal passage, which may alter some of the unique properties of these Envelopes. Finally, we used direct within animal competition studies and two targeted mutations to select highly replicative clones. We provide here both the discovery of new SHIV clones, and also a process to generate additional clones in the future.

Genetic diversity in the env V1-V2 region of proviral quasispecies from long-term controller MHC-typed cynomolgus macaques infected with SHIVSF162P4cy

Intra-host evolution of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) has been shown by viral RNA analysis in subjects who naturally suppress plasma viremia to low levels, known as controllers. However, little is known about the variability of proviral DNA and the inter-relationships among contained systemic viremia, rate of reservoir reseeding and specific major histocompatibility complex (MHC) genotypes, in controllers. Here, we analysed the proviral DNA quasispecies of the env V1-V2 region, in PBMCs and in anatomical compartments of 13 long-term controller monkeys after 3.2 years of infection with simian/human immunodeficiency virus (SHIV)SF162P4cy. A considerable variation in the genetic diversity of proviral quasispecies was present among animals. Seven monkeys exhibited env V1-V2 proviral populations composed of both clusters of identical ancestral sequences and new variants, whereas the other six monkeys displayed relatively high env V1-V2 genetic diversity with a large proportion of diverse novel sequences. Our results demonstrate that in SHIVSF162P4cy-infected monkeys there exists a disparate pattern of intra-host viral diversity and that reseeding of the proviral reservoir occurs in some animals. Moreover, even though no particular association has been observed between MHC haplotypes and the long-term control of infection, a remarkably similar pattern of intra-host viral diversity and divergence was found within animals carrying the M3 haplotype. This suggests that in animals bearing the same MHC haplotype and infected with the same virus, viral diversity follows a similar pattern with similar outcomes and control of infection.

A Degraded Fragment of HIV-1 Gp120 in Rat Hepatocytes Forms Fibrils and Enhances HIV-1 Infection

Identification of the host or viral factors that enhance HIV infection is critical for preventing sexual transmission of HIV. Amyloid fibrils derived from human semen, including semen-derived enhancer of virus infection and semenogelins, enhance HIV-1 infection dramatically in vitro. In this study, we reported that a short-degraded peptide fragment 1 (DPF1) derived from native HIV-1 envelope protein gp120-loaded rat hepatocytes, formed fibrils by self-assembly and thus enhanced HIV-1 infection by promoting the binding of HIV-1 to target cells. Furthermore, DPF1-formed fibrils might be used as a crossing seed to accelerate the formation of semen-derived enhancer of virus infection and semenogelin fibrils. It will be helpful to clarify the viral factors that affect HIV-1 infection. DPF1 as an analog of gp120 containing the critical residues for CD4 binding might be useful for designing of HIV vaccines and developing HIV entry inhibitors.

A single gp120 residue can affect HIV-1 tropism in macaques

Species-dependent variation in proteins that aid or limit virus replication determines the ability of lentiviruses to jump between host species. Identifying and overcoming these differences facilitates the development of animal models for HIV-1, including models based on chimeric SIVs that express HIV-1 envelope (Env) glycoproteins, (SHIVs) and simian-tropic HIV-1 (stHIV) strains. Here, we demonstrate that the inherently poor ability of most HIV-1 Env proteins to use macaque CD4 as a receptor is improved during adaptation by virus passage in macaques. We identify a single amino acid, A281, in HIV-1 Env that consistently changes during adaptation in macaques and affects the ability of HIV-1 Env to use macaque CD4. Importantly, mutations at A281 do not markedly affect HIV-1 Env neutralization properties. Our findings should facilitate the design of HIV-1 Env proteins for use in non-human primate models and thus expedite the development of clinically relevant reagents for testing interventions against HIV-1.

Promise and problems associated with the use of recombinant AAV for the delivery of anti-HIV antibodies

Attempts to elicit antibodies with potent neutralizing activity against a broad range of human immunodeficiency virus (HIV) isolates have so far proven unsuccessful. Long-term delivery of monoclonal antibodies (mAbs) with such activity is a creative alternative that circumvents the need for an immune response and has the potential for creating a long-lasting sterilizing barrier against HIV. This approach is made possible by an incredible array of potent broadly neutralizing antibodies (bnAbs) that have been identified over the last several years. Recombinant adeno-associated virus (rAAV) vectors are ideally suited for long-term delivery for a variety of reasons. The only products made from rAAV are derived from the transgenes that are put into it; as long as those products are not viewed as foreign, expression from muscle tissue may continue for decades. Thus, use of rAAV to achieve long-term delivery of anti-HIV mAbs with potent neutralizing activity against a broad range of HIV-1 isolates is emerging as a promising concept for the prevention or treatment of HIV-1 infection in humans. Experiments in mice and monkeys that have demonstrated protective efficacy against AIDS virus infection have raised hopes for the promise of this approach. However, all published experiments in monkeys have encountered unwanted immune responses to the AAV-delivered antibody, and these immune responses appear to limit the levels of delivered antibody that can be achieved. In this review, we highlight the promise of rAAV-mediated antibody delivery for the prevention or treatment of HIV infection in humans, but we also discuss the obstacles that will need to be understood and solved in order for the promise of this approach to be realized.

Repertoire comparison of the B-cell receptor-encoding loci in humans and rhesus macaques by next-generation sequencing

Rhesus macaques (RMs) are a widely used model system for the study of vaccines, infectious diseases and microbial pathogenesis. Their value as a model lies in their close evolutionary relationship to humans, which, in theory, allows them to serve as a close approximation of the human immune system. However, despite their prominence as a human surrogate model system, many aspects of the RM immune system remain ill characterized. In particular, B cell-mediated immunity in macaques has not been sufficiently characterized, and the B-cell receptor-encoding loci have not been thoroughly annotated. To address these gaps, we analyzed the circulating heavy- and light-chain repertoires in humans and RMs by next-generation sequencing. By comparing V gene segment usage, J-segment usage and CDR3 lengths between the two species, we identified several important similarities and differences. These differences were especially notable in the IgM(+) B-cell repertoire. However, the class-switched, antigen-educated B-cell populations converged on a set of similar characteristics, implying similarities in how each species responds to antigen. Our study provides the first comprehensive overview of the circulating repertoires of the heavy- and light-chain sequences in RMs, and provides insight into how they may perform as a model system for B cell-mediated immunity in humans.

Generation of a neutralization-resistant CCR5 tropic simian/human immunodeficiency virus (SHIV-MK38) molecular clone, a derivative of SHIV-89.6

Previously, we reported that a new genetically diverse CCR5 (R5) tropic simian/human immunodeficiency virus (SHIV-MK38) adapted to rhesus monkeys became more neutralization resistant to SHIV-infected plasma than did the parental SHIV-KS661 clone. Here, to clarify the significance of the neutralization-resistant phenotype of SHIV in a macaque model, we initially investigated the precise neutralization phenotype of the SHIVs, including SHIV-MK38 molecular clones, using SHIV-MK38-infected plasma, a pooled plasma of human immunodeficiency virus (HIV)-infected individuals, soluble CD4 and anti-HIV-1 neutralizing mAbs, the epitopes of which were known. The results show that SHIV-KS661 had tier 1 neutralization sensitivity, but monkey-adapted R5 tropic SHIV-MK38 acquired neutralization resistance similar to that of tier 2 or 3 as a clone virus. Sequence analysis of the env gene suggested that the neutralization-resistant phenotype of SHIV-MK38 was acquired by conformational changes in Env associated with the net charge and potential N-linked glycosylation sites. To examine the relationship between neutralization phenotype and stably persistent infection in monkeys, we performed in vivo rectal inoculation experiments using a SHIV-MK38 molecular clone. The results showed that one of three rhesus monkeys exhibited durable infection with a plasma viral load of 105 copies ml- 1 despite the high antibody responses that occurred in the host. Whilst further improvements are required in the development of a challenge virus, it will be useful to generate a neutralization-resistant R5 tropic molecular clone of the SHIV-89.6 lineage commonly used for vaccine development - a result that can be used to explore the foundation of AIDS pathogenesis.

Development of SHIVs with circulating, transmitted HIV-1 variants

SHIV/macaque model is critical for pre-clinical HIV-1 research. The ability of this model to predict efficacious intervention(s) in humans depends on how faithfully the model recapitulates key features of HIV-1 transmission and pathogenesis. Here, we provide insights for rationally designing SHIVs with transmitted HIV-1 variants for vaccine and prevention research.

Mutations in HIV-1 envelope that enhance entry with the macaque CD4 receptor alter antibody recognition by disrupting quaternary interactions within the trimer

Chimeric simian immunodeficiency virus (SIV)/human immunodeficiency virus (HIV) (SHIV) infection of macaques is commonly used to model HIV type 1 (HIV-1) transmission and pathogenesis in humans. Despite the fact that SHIVs encode SIV antagonists of the known macaque host restriction factors, these viruses require additional adaptation for replication in macaques to establish a persistent infection. Additional adaptation may be required in part because macaque CD4 (mCD4) is a suboptimal receptor for most HIV-1 envelope glycoprotein (Env) variants. This requirement raises the possibility that adaptation of HIV-1 Env to the macaque host leads to selection of variants that lack important biological and antigenic properties of the viruses responsible for the HIV-1 pandemic in humans. Here, we investigated whether this adaptation process leads to changes in the antigenicity and structure of HIV-1 Env. For this purpose, we examined how two independent mutations that enhance mCD4-mediated entry, A204E and G312V, impact antibody recognition in the context of seven different parental HIV-1 Env proteins from diverse subtypes. We also examined HIV-1 Env variants from three SHIVs that had been adapted for increased replication in macaques. Our results indicate that these different macaque-adapted variants had features in common, including resistance to antibodies directed to quaternary epitopes and sensitivity to antibodies directed to epitopes in the variable domains (V2 and V3) that are buried in the parental, unadapted Env proteins. Collectively, these findings suggest that adaptation to mCD4 results in conformational changes that expose epitopes in the variable domains and disrupt quaternary epitopes in the native Env trimer.

IMPORTANCE

These findings indicate the antigenic consequences of adapting HIV-1 Env to mCD4. They also suggest that to best mimic HIV-1 infection in humans when using the SHIV/macaque model, HIV-1 Env proteins should be identified that use mCD4 as a functional receptor and preserve quaternary epitopes characteristic of HIV-1 Env.

Associated changes in the transcription levels of IL-17A and tight junction-associated genes in the duodenal mucosa of rhesus macaques repeatedly exposed to simian/human immunodeficiency virus

BACKGROUND

Mucosal barrier dysfunction might play a key role in HIV/AIDS, yet the early effects of HIV-1 on intestinal mucosal barrier, especially tight junctions (TJ) have not been well addressed.

AIMS

To investigate the effects of acute HIV-1 infection on the expression of intestinal IL-17A and TJ-associated genes using an NHP-AIDS model.

METHODS

TaqMan probe real-time RT-PCR methods were established and claudin-1, claudin-3, occludin and zonula occluden-1 (ZO-1) mRNA levels in the duodenal biopsies of rhesus macaques collected before and after rectal exposures to SHIV-SF162P4 were examined and compared with that of IL-17A, IL-6, TGF-β, RORγt, T-bet, Foxp-3 and GATA-3.

RESULTS

The mRNA levels of TJ-associated genes were statistically significantly reduced soon after viral exposures and the mRNA levels of claudin-1, occludin and ZO-1 in viral positive tissues (from Group I) were lower than that in viral negative tissues (from Group II) after viral exposure. IL-17A mRNA levels were also decreased and positively correlated with the mRNA levels of the TJ-associated genes after viral exposure or infection, although the levels of IL-6, TGF-β and RORγt mRNA showed no statistical difference. The levels of GATA-3 mRNA in tissues collected before viral exposure were statistically different between Group I and Group II animals. The balance between T-bet and GATA-3 mRNA levels in Group II was markedly altered and statistically significantly different from that in Group I.

CONCLUSIONS

Acute SHIV, and by extension HIV infection could affect the expression of TJ-associated genes, probably through IL-17A and other immune alterations.

Structural insights on the role of antibodies in HIV-1 vaccine and therapy

Despite 30 years of effort, there is no effective vaccine for HIV-1. However, antibodies can prevent HIV-1 infection in humanized mice and macaques when passively transferred. New single-cell-based methods have uncovered many broad and potent donor-derived antibodies, and structural studies have revealed the molecular bases for their activities. The new data suggest why such antibodies are difficult to elicit and inform HIV-1 vaccine development efforts. In addition to protecting against infection, the newly identified antibodies can suppress active infections in mice and macaques, suggesting they could be valuable additions to anti-HIV-1 therapies and to strategies to eradicate HIV-1 infection.

3-hydroxyphthalic anhydride-modified human serum albumin as a microbicide candidate against HIV type 1 entry by targeting both viral envelope glycoprotein gp120 and cellular receptor CD4

We previously reported that 3-hydroxyphthalic anhydride-modified human serum albumin (HP-HSA) as an anti-HIV microbicide could potently inhibit infection by a broad spectrum of HIV-1 strains; however, its mechanism of action is still elusive. Here, we aimed to identify the target(s) of HP-HSA. HIV-1 envelope glycoprotein (Env)-mediated cell-cell fusion assays were conducted using noninfectious CHO-WT cells or infectious HIV-1IIIB-infected H9 cells as effector cells and MT-2 as target cells. The cell-to-cell transmission and single-round HIV-1 infection assays were performed by measuring luciferase activity. Binding of HP-HSA to CD4 or gp120 was determined by enzyme-linked immunosorbent assay (ELISA) and flow cytometry, while binding of HP-HSA to the coreceptor CXCR4 or CCR5 was detected by cell-based ELISA. HP-HSA strongly inhibited HIV-1 Env-mediated cell-cell fusion and blocked infection by HIV-1 pseudoviruses bearing Env of HIV-1HXB2 (X4 strain) or HIV-1SF162 (R5 strain). HP-HSA was also effective in blocking HIV-1BaL transmission from infected to uninfected cells. HP-HSA could strongly bind to HIV-1 Env gp120 and cellular receptor CD4. These results suggest that HP-HSA inhibits HIV-1 entry into the target cell by interacting with viral Env gp120 and/or the cellular CD4 receptor, making it a promising microbicide candidate for preventing HIV-1 sexual transmission.

In vitro neutralization of low dose inocula at physiological concentrations of a monoclonal antibody which protects macaques against SHIV challenge

BACKGROUND

Passive transfer of antibodies can be protective in the simian human immunodeficiency virus (SHIV)--rhesus macaque challenge model. The human monoclonal antibody IgG1 b12 neutralizes human immunodeficiency type 1 (HIV-1) in vitro and protects against challenge by SHIV. Our hypothesis is that neutralizing antibodies can only completely inactivate a relatively small number of infectious virus.

METHODS AND FINDINGS

We have used GHOST cell assays to quantify individual infectious events with HIV-1SF162 and its SHIV derivatives: the relatively neutralization sensitive SHIV(SF162P4) isolate and the more resistant SHIV(SF162P3). A plot of the number of fluorescent GHOST cells with increasing HIV-1SF162 dose is not linear. It is likely that with high-dose inocula, infection with multiple virus produces additive fluorescence in individual cells. In studies of the neutralization kinetics of IgG1 b12 against these isolates, events during the absorption phase of the assay, as well as the incubation phase, determine the level of neutralization. It is possible that complete inactivation of a virus is limited to the time it is exposed on the cell surface. Assays can be modified so that neutralization of these very low doses of virus can be quantified. A higher concentration of antibody is required to neutralize the same dose of resistant SHIV(SF162P3) than the sensitive SHIV(SF162P4). In the absence of selection during passage, the density of the CCR5 co-receptor on the GHOST cell surface is reduced. Changes in the CD4 : CCR5 density ratio influence neutralization.

CONCLUSIONS

Low concentrations of IgG1 b12 completely inactivate small doses of the neutralization resistant SHIV(SF162P3). Assays need to be modified to quantify this effect. Results from modified assays may predict protection following repeated low-dose shiv challenges in rhesus macaques. It should be possible to induce this level of antibody by vaccination so that modified assays could predict the outcome of human trials.

Comparison of systemic and mucosal immunization with helper-dependent adenoviruses for vaccination against mucosal challenge with SHIV

Most HIV-1 infections are thought to occur at mucosal surfaces during sexual contact. It has been hypothesized that vaccines delivered at mucosal surfaces may mediate better protection against HIV-1 than vaccines that are delivered systemically. To test this, rhesus macaques were vaccinated by intramuscular (i.m.) or intravaginal (ivag.) routes with helper-dependent adenoviral (HD-Ad) vectors expressing HIV-1 envelope. Macaques were first immunized intranasally with species C Ad serotype 5 (Ad5) prior to serotype-switching with species C HD-Ad6, Ad1, Ad5, and Ad2 vectors expressing env followed by rectal challenge with CCR5-tropic SHIV-SF162P3. Vaccination by the systemic route generated stronger systemic CD8 T cell responses in PBMC, but weaker mucosal responses. Conversely, mucosal immunization generated stronger CD4 T cell central memory (Tcm) responses in the colon. Intramuscular immunization generated higher levels of env-binding antibodies, but neither produced neutralizing or cytotoxic antibodies. After mucosal SHIV challenge, both groups controlled SHIV better than control animals. However, more animals in the ivag. group had lower viral set points than in in the i.m. group. These data suggest mucosal vaccination may have improve protection against sexually-transmitted HIV. These data also demonstrate that helper-dependent Ad vaccines can mediate robust vaccine responses in the face of prior immunity to Ad5 and during four rounds of adenovirus vaccination.

Phenotypic properties of transmitted founder HIV-1

Defining the virus-host interactions responsible for HIV-1 transmission, including the phenotypic requirements of viruses capable of establishing de novo infections, could be important for AIDS vaccine development. Previous analyses have failed to identify phenotypic properties other than chemokine receptor 5 (CCR5) and CD4+ T-cell tropism that are preferentially associated with viral transmission. However, most of these studies were limited to examining envelope (Env) function in the context of pseudoviruses. Here, we generated infectious molecular clones of transmitted founder (TF; n = 27) and chronic control (CC; n = 14) viruses of subtypes B (n = 18) and C (n = 23) and compared their phenotypic properties in assays specifically designed to probe the earliest stages of HIV-1 infection. We found that TF virions were 1.7-fold more infectious (P = 0.049) and contained 1.9-fold more Env per particle (P = 0.048) compared with CC viruses. TF viruses were also captured by monocyte-derived dendritic cells 1.7-fold more efficiently (P = 0.035) and more readily transferred to CD4+ T cells (P = 0.025). In primary CD4+ T cells, TF and CC viruses replicated with comparable kinetics; however, when propagated in the presence of IFN-α, TF viruses replicated to higher titers than CC viruses. This difference was significant for subtype B (P = 0.000013) but not subtype C (P = 0.53) viruses, possibly reflecting demographic differences of the respective patient cohorts. Together, these data indicate that TF viruses are enriched for higher Env content, enhanced cell-free infectivity, improved dendritic cell interaction, and relative IFN-α resistance. These viral properties, which likely act in concert, should be considered in the development and testing of AIDS vaccines.

3-Hydroxyphthalic anhydride-modified human serum albumin as a microbicide candidate inhibits HIV infection by blocking viral entry

OBJECTIVES

We recently demonstrated that both 3-hydroxyphthalic anhydride (HP)- and maleic anhydride-modified chicken ovalbumin (OVA) could effectively inhibit HIV-1 infection. But because OVA may cause allergy in some human subjects, here we replaced OVA with human serum albumin (HSA) in designing a new anti-HIV-1 agent, HP-HSA, and then tested its anti-HIV-1 activity and cytotoxicity.

METHODS

The in vitro anti-HIV-1 activities of HP-HSA were detected by measuring p24 production and luciferase activity. The cytotoxicities of HP-HSA on target cells and human vaginal and cervical epithelial cells and the effect of HP-HSA on human peripheral blood mononuclear cell (PBMC) proliferation were evaluated by XTT assay. The effect of HP-HSA on interferon-γ secretion by PBMCs was detected by enzyme-linked immunospot (ELISPOT) assay.

RESULTS

We found that HP-HSA exhibited broad and potent antiviral activity against infection by the HIV-1 strains tested, including drug-resistant strains. HP-HSA displayed no or low cytotoxicity on human vaginal and cervical epithelial cells and the cells used for testing HIV-1 infectivity. In addition, HP-HSA had no significant effect on proliferation or interferon-γ secretion by normal or phytohaemagglutinin-stimulated human PBMCs. A time-of-addition assay indicated that HP-HSA was an HIV-1 entry inhibitor.

CONCLUSIONS

Because of its broad and potent anti-HIV-1 activity, low cytotoxicity and low immunogenicity to humans, HP-HSA has great potential for further development as a microbicide to prevent the sexual transmission of HIV.

A species-specific amino acid difference in the macaque CD4 receptor restricts replication by global circulating HIV-1 variants representing viruses from recent infection

HIV-1 replicates poorly in macaque cells, and this had hindered the advancement of relevant nonhuman primate model systems for HIV-1 infection and pathogenesis. Several host restriction factors have been identified that contribute to this species-specific restriction to HIV-1 replication, but these do not fully explain the poor replication of most strains of HIV-1 in macaque cells. Only select HIV-1 envelope variants, typically those derived from viruses that have been adapted in cell culture, result in infectious chimeric SIVs encoding HIV-1 envelope (SHIVs). Here we demonstrate that most circulating HIV-1 variants obtained directly from infected individuals soon after virus acquisition do not efficiently mediate entry using the macaque CD4 receptor. The infectivity of these viruses is ca. 20- to 50-fold lower with the rhesus and pig-tailed macaque versus the human CD4 receptor. In contrast, culture-derived HIV-1 envelope variants that facilitate efficient replication in macaques showed similar infectivity with macaque and human CD4 receptors (within ∼2-fold). The ability of an envelope to mediate entry using macaque CD4 correlated with its ability to mediate entry of cells expressing low levels of the human CD4 receptor and with soluble CD4 sensitivity. Species-specific differences in the functional capacity of the CD4 receptor to mediate entry mapped to a single amino acid difference at position 39 that is under strong positive selection, suggesting that the evolution of CD4 may have been influenced by its function as a viral receptor. These results also suggest that N39 in human CD4 may be a critical residue for interaction of transmitted HIV-1 variants. These studies provide important insights into virus-host cell interactions that have hindered the development of relevant nonhuman primate models for HIV-1 infection and provide possible markers, such as sCD4 sensitivity, to identify potential HIV-1 variants that could be exploited for development of better SHIV/macaque model systems.

Pathogenicity and mucosal transmissibility of the R5-tropic simian/human immunodeficiency virus SHIV(AD8) in rhesus macaques: implications for use in vaccine studies

There is an urgent need to develop new pathogenic R5 simian/human immunodeficiency viruses (SHIVs) for the evaluation of candidate anti-HIV vaccines in nonhuman primates. Here, we characterize swarm SHIV(AD8) stocks, prepared from three infected rhesus macaques with documented immunodeficiency at the time of euthanasia, for their capacity to establish durable infections in macaques following inoculation by the intravenous (i.v.) or intrarectal (i.r.) route. All three viral stocks (SHIV(AD8-CE8J), SHIV(AD8-CK15), and SHIV(AD8-CL98)) exhibited robust replication in vivo and caused marked depletion of CD4(+) T cells affecting both memory and naïve CD4(+) T lymphocyte subsets following administration by either route. Eleven of 22 macaques inoculated with the new SHIV(AD8) stocks were euthanized with clinical symptoms of immunodeficiency and evidence of opportunistic infections (Pneumocystis, Candida, and Mycobacterium). A single but unique founder virus, also present in the SHIV(AD8-CE8J) swarm stock, was transmitted to two animals following a single i.r. inoculation of approximately 3 50% animal infectious doses, which is close to the threshold required to establish infection in all exposed animals. Because the three new SHIV(AD8) viruses are mucosally transmissible, exhibited tier 2 sensitivity to anti-HIV-1 neutralizing antibodies, deplete CD4(+) T lymphocytes in vivo, and induce AIDS in macaques, they are eminently suitable as challenge viruses in vaccine experiments.

Peptides derived from a distinct region of GB virus C glycoprotein E2 mediate strain-specific HIV-1 entry inhibition

The nonpathogenic human GB virus C (GBV-C), a member of the Flaviviridae, is highly prevalent in individuals with HIV-1 infections or with parenteral and sexual risk factors. Long-term GBV-C viremia has been associated with better survival or improved diagnosis in several epidemiological studies. In a previous study we reported that the E2 glycoprotein of GBV-C interferes with HIV-1 entry in vitro. To address the question what region of the E2 protein is involved in suppression of HIV-1 replication, we performed an E2-derived peptide scanning and determined the HIV-inhibitory activity of each peptide in HIV replication assays. We demonstrate here that peptides representing the N-terminal part of the E2 protein from amino acids (aa) 29 to 72 are able to inhibit efficiently HIV-1 replication in vitro. In particular, the peptides P6-2 (representing the E2-region from aa 45 to 64) and P4762 (aa 37 to 64) showed the highest potency in HIV replication assays performed on TZM-bl cells with 50% inhibitory concentrations between 0.1 and 2 μM. However, primary HIV-1 isolates representing clades A to H showed a high variability in their sensitivity to E2 peptides. Pseudovirus inhibition assays revealed that the sensitivity is determined by the gp120/gp41 envelope proteins. Using HIV-1 BlaM-Vpr-based fusion assays, we demonstrate that the E2-derived peptides prevent HIV-1 binding or fusion, presumably via interaction with the HIV-1 particle. Together, these findings reveal a new mechanism of viral interference, suggesting that the envelope protein E2 of GBV-C target directly HIV-1 particles to avoid entry of these virions.

Adaptation of subtype a human immunodeficiency virus type 1 envelope to pig-tailed macaque cells

The relevance of simian/human immunodeficiency virus (SHIV) infection of macaques to HIV-1 infection in humans depends on how closely SHIVs mimic HIV-1 transmission, pathogenesis, and diversity. Circulating HIV-1 strains are predominantly subtypes C and A and overwhelmingly require CCR5 for entry, yet most SHIVs incorporate CXCR4-using subtype B envelopes (Envs). While pathogenic subtype C-based SHIVs have been constructed, the subtype A-based SHIVs (SHIV-As) constructed to date have been unable to replicate in macaque cells. To understand the barriers to SHIV-A replication in macaque cells, HIVA(Q23)/SIV(vif) was constructed by engineering a CCR5-tropic subtype A provirus to express SIV vif, which counters the macaque APOBEC3G restriction. HIVA(Q23)/SIV(vif) replicated poorly in pig-tailed macaque (Ptm) lymphocytes, but viruses were adapted to Ptm lymphocytes. Two independent mutations in gp120, G312V (V3 loop) and A204E (C2 region), were identified that increased peak virus levels by >100-fold. Introduction of G312V and A204E to multiple subtype A Envs and substitution of G312 and A204 with other residues increased entry into Ptm cells by 10- to 100-fold. G312V and A204E Env variants continued to require CCR5 for entry but were up to 50- and 200-fold more sensitive to neutralization by IgG1b12 and soluble CD4 and had a 5- to 50-fold increase in their ability to utilize Ptm CD4 compared to their wild-type counterparts. These findings identify the inefficient use of Ptm CD4 as an unappreciated restriction to subtype A HIV-1 replication in Ptm cells and reveal amino acid changes to gp120 that can overcome this barrier.

Generation of a dual RT Env SHIV that is infectious in rhesus macaques

BACKGROUND

The best current animal model for HIV infection and evaluation of antiviral compounds is the Simian-human immunodeficiency virus (SHIV)/macaque system. There are multiple recombinant SHIVs available, but these viruses have limitations in evaluating combination drug strategies for prevention. Drug combinations that target reverse transcriptase (RT, either nRTI or nnRTI) and envelope (entry or fusion inhibitors) have to be tested separately, which does not permit the assessment of additive, synergistic, or antagonistic effects of ARV combinations. We describe construction of a dual SHIV containing both HIV RT and a CCR5-specific HIV envelope gene in a simian immunodeficiency virus backbone.

METHODS

The RT Env SHIV molecular clone was constructed using RT SHIV and SHIV162p3 sequences as templates to generate RT Env SHIV. RT Env SHIV was expanded in vitro in CD8-depleted macaque peripheral blood mononuclear cells (PBMC). Recombinant virus was used to infect a rhesus macaque (4.3 x 10(4) tissue culture infectious dose [TCID(50)], intravenously [IV]). A second passage in a macaque by IV transfer of 10 ml of blood obtained from the first infection was also done. The in vivo adapted virus stock from these macaques was used to produce high titer stocks in vitro and used to rectally infect an additional macaque.

RESULTS

Peak viral load reached 6 x 10(5) vRNA copies/ml in plasma in both IV-exposed macaques and remained detectable in the one animal for 16 weeks after infection. A viral stock (1.68 x 10(4) TCID(50)) derived from the second macaque passage has been produced in CD8-depleted rhesus PBMC and was successfully used to demonstrate mucosal transmission. The resulting RT Env SHIV retained the sensitivity to HIV RT and entry inhibitors of its parental viruses.

CONCLUSIONS

The objective of this study was to develop and characterize a SHIV recombinant virus for evaluating the efficacy of ART and microbicide products that target both HIV RT and/or Env-mediated entry. RT Env SHIV can productively infect macaques by both the IV and mucosal route, making it a valuable tool for transmission studies.

Immunization with wild-type or CD4-binding-defective HIV-1 Env trimers reduces viremia equivalently following heterologous challenge with simian-human immunodeficiency virus

We recently reported that rhesus macaques inoculated with CD4-binding-competent and CD4-binding-defective soluble YU2-derived HIV-1 envelope glycoprotein (Env) trimers in adjuvant generate comparable levels of Env-specific binding antibodies (Abs) and T cell responses. We also showed that Abs directed against the Env coreceptor binding site (CoRbs) were elicited only in animals immunized with CD4-binding-competent trimers and not in animals immunized with CD4-binding-defective trimers, indicating that a direct interaction between Env and CD4 occurs in vivo. To investigate both the overall consequences of in vivo Env-CD4 interactions and the elicitation of CoRbs-directed Abs for protection against heterologous simian-human immunodeficiency virus (SHIV) challenge, we exposed rhesus macaques immunized with CD4-binding-competent and CD4-binding-defective trimers to the CCR5-tropic SHIV-SF162P4 challenge virus. Compared to unvaccinated controls, all vaccinated animals displayed improved control of plasma viremia, independent of the presence or absence of CoRbs-directed Abs prior to challenge. Immunization resulted in plasma responses that neutralized the heterologous SHIV challenge stock in vitro, with similar neutralizing Ab titers elicited by the CD4-binding-competent and CD4-binding-defective trimers. The neutralizing responses against both the SHIV-SF162P4 stock and a recombinant virus pseudotyped with a cloned SHIV-SF162P4-derived Env were significantly boosted by the SHIV challenge. Collectively, these results suggest that the capacity of soluble Env trimers to interact with primate CD4 in vivo and to stimulate the production of moderate titers of CoRbs-directed Abs did not influence the magnitude of the neutralizing Ab recall response after viral challenge or the subsequent control of viremia in this heterologous SHIV challenge model.

Incorporation of podoplanin into HIV released from HEK-293T cells, but not PBMC, is required for efficient binding to the attachment factor CLEC-2

BACKGROUND

Platelets are associated with HIV in the blood of infected individuals and might modulate viral dissemination, particularly if the virus is directly transmitted into the bloodstream. The C-type lectin DC-SIGN and the novel HIV attachment factor CLEC-2 are expressed by platelets and facilitate HIV transmission from platelets to T-cells. Here, we studied the molecular mechanisms behind CLEC-2-mediated HIV-1 transmission.

RESULTS

Binding studies with soluble proteins indicated that CLEC-2, in contrast to DC-SIGN, does not recognize the viral envelope protein, but a cellular factor expressed on kidney-derived 293T cells. Subsequent analyses revealed that the cellular mucin-like membranous glycoprotein podoplanin, a CLEC-2 ligand, was expressed on 293T cells and incorporated into virions released from these cells. Knock-down of podoplanin in 293T cells by shRNA showed that virion incorporation of podoplanin was required for efficient CLEC-2-dependent HIV-1 interactions with cell lines and platelets. Flow cytometry revealed no evidence for podoplanin expression on viable T-cells and peripheral blood mononuclear cells (PBMC). Podoplanin was also not detected on HIV-1 infected T-cells. However, apoptotic bystander cells in HIV-1 infected cultures reacted with anti-podoplanin antibodies, and similar results were obtained upon induction of apoptosis in a cell line and in PBMCs suggesting an unexpected link between apoptosis and podoplanin expression. Despite the absence of detectable podoplanin expression, HIV-1 produced in PBMC was transmitted to T-cells in a CLEC-2-dependent manner, indicating that T-cells might express an as yet unidentified CLEC-2 ligand.

CONCLUSIONS

Virion incorporation of podoplanin mediates CLEC-2 interactions of HIV-1 derived from 293T cells, while incorporation of a different cellular factor seems to be responsible for CLEC-2-dependent capture of PBMC-derived viruses. Furthermore, evidence was obtained that podoplanin expression is connected to apoptosis, a finding that deserves further investigation.

[Application studies of animal models in evaluating safety and efficacy of HIV-1 microbicides]

As the HIV/AIDS pandemic continues unabated, novel prophylactic strategy for the spread of HIV are urgently needed. Topical microbicides are designed to prevent transmission of HIV when applied vaginally or rectally. Although there are many microbicide candidates in the pipeline, animal models for evaluating their safety and efficacy are urgently needed. On the basis of comparing the non-primate small animal models and the non-human primate animal models in evaluating safety and efficacy of HIV microbicides, this review summarizes the major advantages and disadvantages of the relevant animal models. The suggested direction of research that would benefit the development of microbicides is also reviewed.

Maleic anhydride-modified chicken ovalbumin as an effective and inexpensive anti-HIV microbicide candidate for prevention of HIV sexual transmission

Background

Previous studies have shown that 3-hydroxyphthalic anhydride (HP)-modified bovine milk protein, β-lactoglobulin (β-LG), is a promising microbicide candidate. However, concerns regarding the potential risk of prion contamination in bovine products and carcinogenic potential of phthalate derivatives were raised. Here we sought to replace bovine protein with an animal protein of non-bovine origin and substitute HP with another anhydride for the development of anti-HIV microbicide for preventing HIV sexual transmission.

Results

Maleic anhydride (ML), succinic anhydride (SU) and HP at different conditions and variable pH values were used for modification of proteins. All the anhydrate-modified globulin-like proteins showed potent anti-HIV activity, which is correlated with the percentage of modified lysine and arginine residues in the modified protein. We selected maleic anhydride-modified ovalbumin (ML-OVA) for further study because OVA is easier to obtain than β-LG, and ML is safer than HP. Furthermore, ML-OVA exhibited broad antiviral activities against HIV-1, HIV-2, SHIV and SIV. This modified protein has no or low in vitro cytotoxicity to human T cells and vaginal epithelial cells. It is resistant to trypsin hydrolysis, possibly because the lysine and arginine residues in OVA are modified by ML. Mechanism studies suggest that ML-OVA inhibits HIV-1 entry by targeting gp120 on HIV-1 virions and also the CD4 receptor on the host cells.

Conclusion

ML-OVA is a potent HIV fusion/entry inhibitor with the potential to be developed as an effective, safe and inexpensive anti-HIV microbicide.

3-hydroxyphthalic anhydride-modified chicken ovalbumin exhibits potent and broad anti-HIV-1 activity: a potential microbicide for preventing sexual transmission of HIV-1

Heterosexual transmission is the primary route by which women acquire human immunodeficiency virus (HIV)/AIDS. Thus, development of woman-controlled topical microbicides for prevention of sexual transmission of HIV is urgently needed. Here we report that 3-hydroxyphthalic anhydride-modified chicken ovalbumin (HP-OVA) exhibits potent antiviral activity against a broad spectrum of human immunodeficiency virus type 1 (HIV-1) isolates with different genotypes and biotypes. Its antiviral activity is correlated with the percentages of the chemically modified and unmodified lysines and arginines in OVA. HP-OVA inhibits HIV-1 fusion and entry through multiple mechanisms of action, including (i) blocking gp120 binding to CD4 and (ii) interfering with gp41 six-helix bundle formation. Because of the widespread availability and established safety profile of OVA, HP-OVA has good potential to be developed as an effective, safe, and affordable microbicide for prevention of HIV sexual transmission.

Generation of the pathogenic R5-tropic simian/human immunodeficiency virus SHIVAD8 by serial passaging in rhesus macaques

A new pathogenic R5-tropic simian/human immunodeficiency virus (SHIV) was generated following serial passaging in rhesus macaques. All 13 animals inoculated with SHIV(AD8) passaged lineages experienced marked depletions of CD4(+) T cells. Ten of these infected monkeys became normal progressors (NPs) and had gradual losses of both memory and naïve CD4(+) T lymphocytes, generated antiviral CD4(+) and CD8(+) T cell responses, and sustained chronic immune activation while maintaining variable levels of plasma viremia (10(2) to 10(5) RNA copies/ml for up to 3 years postinfection [p.i.]). To date, five NPs developed AIDS associated with opportunistic infections caused by Pneumocystis carinii, Mycobacterium avium, and Campylobacter coli that required euthanasia between weeks 100 and 199 p.i. Three other NPs have experienced marked depletions of circulating CD4(+) T lymphocytes (92 to 154 cells/microl) following 1 to 2 years of infection. When tested for coreceptor usage, the viruses isolated from four NPs at the time of their euthanasia remained R5 tropic. Three of the 13 SHIV(AD8)-inoculated macaques experienced a rapid-progressor syndrome characterized by sustained plasma viremia of >1 x 10(7) RNA copies/ml and rapid irreversible loss of memory CD4(+) T cells that required euthanasia between weeks 19 and 23 postinfection. The sustained viremia, associated depletion of CD4(+) T lymphocytes, and induction of AIDS make the SHIV(AD8) lineage of viruses a potentially valuable reagent for vaccine studies.

Protection against Mucosal SHIV Challenge by Peptide and Helper-Dependent Adenovirus Vaccines

Groups of rhesus macaques that had previously been immunized with HIV-1 envelope (env) peptides and first generation adenovirus serotype 5 (FG-Ad5) vaccines expressing the same peptides were immunized intramuscularly three times with helper-dependent adenovirus (HD-Ad) vaccines expressing only the HIV-1 envelope from JRFL. No gag, pol, or other SHIV genes were used for vaccination. One group of the FG-Ad5-immune animals was immunized three times with HD-Ad5 expressing env. One group was immunized by serotype-switching with HD-Ad6, HD-Ad1, and HD-Ad2 expressing env. Previous work demonstrated that serum antibody levels against env were significantly higher in the serotype-switched group than in the HD-Ad5 group. In this study, neutralizing antibody and T cell responses were compared between the groups before and after rectal challenge with CCR5-tropic SHIV-SF162P3. When serum samples were assayed for neutralizing antibodies, only weak activity was observed. T cell responses against env epitopes were higher in the serotype-switched group. When these animals were challenged rectally with SHIV-SF162P3, both the Ad5 and serotype-switch groups significantly reduced peak viral loads 2 to 10-fold 2 weeks after infection. Peak viral loads were significantly lower for the serotype-switched group as compared to the HD-Ad5-immunized group. Viral loads declined over 18 weeks after infection with some animals viremia reducing nearly 4 logs from the peak. These data demonstrate significant mucosal vaccine effects after immunization with only env antigens. These data also demonstrate HD-Ad vectors are a robust platform for vaccination.

Control of viremia and maintenance of intestinal CD4(+) memory T cells in SHIV(162P3) infected macaques after pathogenic SIV(MAC251) challenge

Recent HIV vaccine failures have prompted calls for more preclinical vaccine testing in non-human primates. However, similar to HIV infection of humans, developing a vaccine that protects macaques from infection following pathogenic SIV(MAC251) challenge has proven difficult, and current vaccine candidates at best, only reduce viral loads after infection. Here we demonstrate that prior infection with a chimeric simian-human immunodeficiency virus (SHIV) containing an HIV envelope gene confers protection against intravenous infection with the heterologous, highly pathogenic SIV(MAC251) in rhesus macaques. Although definitive immune correlates of protection were not identified, preservation and/or restoration of intestinal CD4(+) memory T cells were associated with protection from challenge and control of viremia. These results suggest that protection against pathogenic lentiviral infection or disease progression is indeed possible, and may correlate with preservation of mucosal CD4(+) T cells.

Selection of a simian-human immunodeficiency virus strain resistant to a vaginal microbicide in macaques

PSC-RANTES binds to CCR5, inhibits human immunodeficiency virus type 1 (HIV-1) entry, and has been shown as a vaginal microbicide to protect rhesus macaques from a simian-human immunodeficiency virus chimera (SHIV(SF162-p3)) infection in a dose-dependent manner. In this study, env gene sequences from SHIV(SF162-p3)-infected rhesus macaques treated with PSC-RANTES were analyzed for possible drug escape variants. Two specific mutations located in the V3 region of gp120 (K315R) and C-helical domain of gp41 (N640D) were identified in a macaque (m584) pretreated with a 100 microM dose of PSC-RANTES. These two env mutations were found throughout infection (through week 77) but were found at only low frequencies in the inoculating SHIV(SF162-p3) stock and in the other SHIV(SF162-p3)-infected macaques. HIV-1 env genes from macaque m584 (env(m584)) and from inoculating SHIV(SF162-p3) (env(p3)) were cloned into an HIV-1 backbone. Increases in 50% inhibitory concentrations to PSC-RANTES with env(m584) were modest (sevenfold) and most pronounced in cells expressing rhesus macaque CCR5 as compared to human CCR5. Nonetheless, virus harboring env(m584), unlike inoculating virus env(p3), could replicate even at the highest tissue culture PSC-RANTES concentrations (100 nM). Dual-virus competitions revealed a dramatic increase in fitness of chimeric virus containing env(m584) (K315R/N640D) over that containing env(p3), but again, only in rhesus CCR5-expressing cells. This study is the first to describe the immediate selection and infection of a drug-resistant SHIV variant in the face of a protective vaginal microbicide, PSC-RANTES. This rhesus CCR5-specific/PSC- RANTES resistance selection is particularly alarming given the relative homogeneity of the SHIV(SF162-p3) stock compared to the potential exposure to a heterogeneous HIV-1 population in human transmission.

Cellular gene expression profiles in rhesus macaques challenged mucosally with a pathogenic R5 tropic simian human immunodeficiency virus isolate

Insights into the host factors that contribute to an effective antiviral immune response may be obtained by examining global gene expression in simian human immunodeficiency virus (SHIV)-infected nonhuman primates that exhibit different virological outcomes. Immune responses and gene expression profiles in peripheral blood mononuclear cells (PBMCs) were compared between animals that controlled or did not control viremia after infection. Rectal inoculation of eight rhesus macaques with R5-tropic SHIV(SF162P3) resulted in a high level of plasma viremia during the acute phase of infection. The viremia was controlled to below levels of detection in six of these animals at the set point (controllers), whereas two animals had persistent viremia throughout the 140 wk that the animals were monitored (non-controllers). CD4(+) T-cell counts declined slightly in both controllers and non-controllers in the acute phase of infection, but CD4(+) T-cell counts continued to decline only in the non-controllers. Neutralizing antibodies to the challenge virus were variable and could not account for the control of viremia. However, analysis of the cellular gene expression profiles in the PBMCs from both groups of animals revealed distinctive gene expression patterns between controllers and non-controllers. Using the paired LPE test, 59 genes with p values <0.01 were identified and specific differences in the gene expression profiles in PBMCs from controllers versus non-controllers were detected.

Conserved positive selection signals in gp41 across multiple subtypes and difference in selection signals detectable in gp41 sequences sampled during acute and chronic HIV-1 subtype C infection

BACKGROUND

The high diversity of HIV variants driving the global AIDS epidemic has caused many to doubt whether an effective vaccine against the virus is possible. However, by identifying the selective forces that are driving the ongoing diversification of HIV and characterising their genetic consequences, it may be possible to design vaccines that pre-empt some of the virus' more common evasion tactics. One component of such vaccines might be the envelope protein, gp41. Besides being targeted by both the humoral and cellular arms of the immune system this protein mediates fusion between viral and target cell membranes and is likely to be a primary determinant of HIV transmissibility.

RESULTS

Using recombination aware analysis tools we compared site specific signals of selection in gp41 sequences from different HIV-1 M subtypes and circulating recombinant forms and identified twelve sites evolving under positive selection across multiple major HIV-1 lineages. To identify evidence of selection operating during transmission our analysis included two matched datasets sampled from patients with acute or chronic subtype C infections. We identified six gp41 sites apparently evolving under different selection pressures during acute and chronic HIV-1 infections. These sites mostly fell within functional gp41 domains, with one site located within the epitope recognised by the broadly neutralizing antibody, 4E10.

CONCLUSION

Whereas these six sites are potentially determinants of fitness and are therefore good candidate targets for subtype-C specific vaccines, the twelve sites evolving under diversifying selection across multiple subtypes might make good candidate targets for broadly protective vaccines.

HIV-1 Transmission, Replication Fitness and Disease Progression

Upon transmission, human immunodeficiency virus type 1 (HIV-1) establishes infection of the lymphatic reservoir, leading to profound depletion of the memory CD4(+) T cell population, despite the induction of the adaptive immune response. The rapid evolution and association of viral variants having distinct characteristics with different stages of infection, the level of viral burden, and rate of disease progression suggest a role for viral variants in this process. Here, we review the literature on HIV-1 variants and disease and discuss the importance of viral fitness for transmission and disease.

HIV-1 Transmission, Replication Fitness and Disease Progression

Upon transmission, human immunodeficiency virus type 1 (HIV-1) establishes infection of the lymphatic reservoir, leading to profound depletion of the memory CD4+ T cell population despite the induction of the adaptive immune response. The rapid evolution and association of viral variants having distinct characteristics during different stages of infection, the level of viral burden, and rate of disease progression suggest a role for viral variants in this process. Here, we review the literature on HIV-1 variants and disease and discuss the importance of viral fitness for transmission and disease.

Interactions of LSECtin and DC-SIGN/DC-SIGNR with viral ligands: Differential pH dependence, internalization and virion binding

The calcium-dependent lectins DC-SIGN and DC-SIGNR (collectively termed DC-SIGN/R) bind to high-mannose carbohydrates on a variety of viruses. In contrast, the related lectin LSECtin does not recognize mannose-rich glycans and interacts with a more restricted spectrum of viruses. Here, we analyzed whether these lectins differ in their mode of ligand engagement. LSECtin and DC-SIGNR, which we found to be co-expressed by liver, lymph node and bone marrow sinusoidal endothelial cells, bound to soluble Ebola virus glycoprotein (EBOV-GP) with comparable affinities. Similarly, LSECtin, DC-SIGN and the Langerhans cell-specific lectin Langerin readily bound to soluble human immunodeficiency virus type-1 (HIV-1) GP. However, only DC-SIGN captured HIV-1 particles, indicating that binding to soluble GP is not necessarily predictive of binding to virion-associated GP. Capture of EBOV-GP by LSECtin triggered ligand internalization, suggesting that LSECtin like DC-SIGN might function as an antigen uptake receptor. However, the intracellular fate of lectin-ligand complexes might differ. Thus, exposure to low-pH medium, which mimics the acidic luminal environment in endosomes/lysosomes, released ligand bound to DC-SIGN/R but had no effect on LSECtin interactions with ligand. Our results reveal important differences between pathogen capture by DC-SIGN/R and LSECtin and hint towards different biological functions of these lectins.

Semen-derived amyloid fibrils drastically enhance HIV infection

Sexual intercourse is the major route of HIV transmission. To identify endogenous factors that affect the efficiency of sexual viral transmission, we screened a complex peptide/protein library derived from human semen. We show that naturally occurring fragments of the abundant semen marker prostatic acidic phosphatase (PAP) form amyloid fibrils. These fibrils, termed Semen-derived Enhancer of Virus Infection (SEVI), capture HIV virions and promote their attachment to target cells, thereby enhancing the infectious virus titer by several orders of magnitude. Physiological concentrations of SEVI amplified HIV infection of T cells, macrophages, ex vivo human tonsillar tissues, and transgenic rats in vivo, as well as trans-HIV infection of T cells by dendritic or epithelial cells. Amyloidogenic PAP fragments are abundant in seminal fluid and boost semen-mediated enhancement of HIV infection. Thus, they may play an important role in sexual transmission of HIV and could represent new targets for its prevention.

Antibodies to CD4-induced sites in HIV gp120 correlate with the control of SHIV challenge in macaques vaccinated with subunit immunogens

Epitopes located in and around the coreceptor binding site of HIV-1 envelope glycoprotein (gp120) exhibit enhanced exposure after attachment to the CD4 receptor and comprise some of the most conserved and functionally important residues on the viral envelope. Therefore, antibody responses to these epitopes [designated as CD4-induced (CD4i)] should be highly cross-reactive and potentially useful for HIV vaccine development. To address this question, rhesus macaques were vaccinated with subunit immunogens designed to raise humoral responses against CD4i epitopes and challenged rectally with SHIV(162P3), which encodes a heterologous envelope versus the immunogen. We found that animals vaccinated with a rhesus full-length single-chain (rhFLSC) complex exhibited significantly accelerated clearance of plasma viremia and an absence of long-term tissue viremia compared with unvaccinated control animals. Such control of infection correlated with stronger responses to CD4i epitopes in the rhFLSC-vaccinated animals, compared with macaques immunized with gp120, cross-linked gp120-CD4 complexes, or soluble CD4 alone. These responses were strongly boosted in the rhFLSC-vaccinated animals by SHIV(162P3) infection. The control of infection was not associated with anti-CD4 responses, overall anti-gp120-binding titers, or neutralizing activity measured in conventional assays. Vaccine-naive animals also developed anti-CD4i epitope responses after simian/ human immunodeficiency virus (SHIV) challenge, which appeared later than the overall anti-gp120 responses and in concert with the decline of viremia to a low set point. Collectively, these data suggest that antibodies to CD4i epitopes may play a role in controlling SHIV infection and provide insights for HIV vaccine development.

A decline in CCL3-5 chemokine gene expression during primary simian-human immunodeficiency virus infection

BACKGROUND

The CC-chemokines CCL3, CCL4 and CCL5 have been found to block the entry of CCR5-tropic HIV into host cells and to suppress the viral replication in vitro, but the in vivo role of endogenous CC-chemokines in HIV-1 infection is still incompletely understood.

METHODOLOGY/PRINCIPLE FINDINGS

In this study, the primate host CCL3, CCL4 and CCL5 gene expression was evaluated in response to simian-human immunodeficiency virus (SHIV) infection in rhesus macaque model. Five rhesus macaques were inoculated with CCR5-tropic SHIV(SF162P4). The mRNA levels of CCL3, CCL4 and CCL5 were measured by real-time PCR at post inoculation day (PID) 0, 7, 14, 21, 35, 56 and 180 in peripheral blood. In addition, a selected subset of samples from CXCR4-tropic SHIV(Ku1)-infected macaques was included with objective to compare the differences in CC-chemokine down-regulation caused by the two SHIVs. Gut-associated lymphoid tissues (GALT) collected from SHIV(SF162P4)-infected animals were also tested by flow cytometry and confocal microscopy to corroborate the gene expression results. Predictably, higher viral loads and CD4+ T cell losses were observed at PID 14 in macaques infected with SHIV(Ku1) than with SHIV(SF162P4). A decline in CC-chemokine gene expression was also found during primary (PID 7-21), but not chronic (PID 180) stage of infection.

CONCLUSIONS

It was determined that A) SHIV(SF162P4) down-regulated the CC-chemokine gene expression during acute stage of infection to a greater extent (p<0.05) than SHIV(Ku1), and B) such down-regulation was not paralleled with the CD4+ T cell depletion. Evaluation of CC-chemokine enhancing immunomodulators such as synthetic CpG-oligonucleotides could be explored in future HIV vaccine studies.

Modulation of HIV and SIV neutralization sensitivity by DC-SIGN and mannose-binding lectin

The C-type lectin DC-SIGN binds to oligosaccharides on the human and simian immunodeficiency virus (HIV, SIV) envelope glycoproteins and promotes infection of susceptible cells. Here, we show that DC-SIGN recognizes glycans involved in SIV sensitivity to neutralizing antibodies and that binding to DC-SIGN confers neutralization resistance to an otherwise sensitive SIV variant. Moreover, we provide evidence that mannose-binding lectin (MBL) can interfere with HIV-1 neutralization by the carbohydrate-specific antibody 2G12.

Macaques infected with a CCR5-tropic simian/human immunodeficiency virus (SHIV) develop broadly reactive anti-HIV neutralizing antibodies

The development of anti-human immunodeficiency virus (anti-HIV) neutralizing antibodies and the evolution of the viral envelope glycoprotein were monitored in rhesus macaques infected with a CCR5-tropic simian/human immunodeficiency virus (SHIV), SHIVSF162P4. Homologous neutralizing antibodies developed within the first month of infection in the majority of animals, and their titers were independent of the extent and duration of viral replication during chronic infection. The appearance of homologous neutralizing antibody responses was preceded by the appearance of amino acid changes in specific variable and conserved regions of gp120. Amino acid changes first appeared in the V1, V2, C2, and V3 regions and subsequently in the C3, V4, and V5 regions. Heterologous neutralizing antibody responses developed over time only in animals with sustained plasma viremia. Within 2 years postinfection the breadth of these responses was as broad as that observed in certain patients infected with HIV type 1 (HIV-1) for over a decade. Despite the development of broad anti-HIV-1 neutralizing antibody responses, viral replication persisted in these animals due to viral escape. Our studies indicate that cross-reactive neutralizing antibodies are elicited in a subset of SHIVSF162P4 infected macaques and that their development requires continuous viral replication for extended periods of time. More importantly, their late appearance does not prevent progression to disease. The availability of an animal model where cross-reactive anti-HIV neutralizing antibodies are developed may facilitate the identification of virologic and immunologic factors conducive to the development of such antibodies.

Local and systemic effects of intranodally injected CpG-C immunostimulatory-oligodeoxyribonucleotides in macaques

Immunostimulatory CpG-C oligodeoxyribonucleotides (ISS-ODNs) represent a promising strategy to enhance vaccine efficacy. We have shown that the CpG-C ISS-ODN C274 stimulates macaque blood dendritic cells (DCs) and B cells and augments SIV-specific IFN-gamma responses in vitro. To further explore the potential of C274 for future vaccine studies, we assessed the in vivo effects of locally administered C274 (in naive and healthy infected macaques). Costimulatory molecules were marginally increased on DCs and B cells within cells isolated from C274-injected lymph nodes (LNs). However, cells from C274-injected LNs exhibited heightened responsiveness to in vitro culture. This was particularly apparent at the level of CD80 (less so CD86) expression by CD123(+) plasmacytoid DCs and was further boosted in the presence of additional C274 in vitro. Notably, cells from C274-injected LNs secreted significantly elevated levels of several cytokines and chemokines upon in vitro culture. This was more pronounced when cells were exposed to additional stimuli in vitro, producing IFN-alpha, IL-3, IL-6, IL-12, TNF-alpha, CCL2, CCL3, CCL5, and CXCL8. Following C274 administration in the absence of additional SIV Ag, endogenous IFN-gamma secretion was elevated in LN cells of infected animals, but SIV-specific responses were unchanged. Endogenous and SIV-specific responses decreased in blood, before the SIV-specific responses rebounded by 2 wk after C274 treatment. Elevated IFN-alpha, CCL2, and CCL5 were also detected in the plasma after C274 injection. Thus, locally administered C274 has local and systemic activities, supporting the potential for CpG-C ISS-ODNs to boost immune function to enhance anti-HIV vaccine immunogenicity.

DC-SIGN and CLEC-2 mediate human immunodeficiency virus type 1 capture by platelets

Platelets can engulf human immunodeficiency virus type 1 (HIV-1), and a significant amount of HIV-1 in the blood of infected individuals is associated with these cells. However, it is unclear how platelets capture HIV-1 and whether platelet-associated virus remains infectious. DC-SIGN and other lectins contribute to capture of HIV-1 by dendritic cells (DCs) and facilitate HIV-1 spread in DC/T-cell cocultures. Here, we show that platelets express both the C-type lectin-like receptor 2 (CLEC-2) and low levels of DC-SIGN. CLEC-2 bound to HIV-1, irrespective of the presence of the viral envelope protein, and facilitated HIV-1 capture by platelets. However, a substantial fraction of the HIV-1 binding activity of platelets was dependent on DC-SIGN. A combination of DC-SIGN and CLEC-2 inhibitors strongly reduced HIV-1 association with platelets, indicating that these lectins are required for efficient HIV-1 binding to platelets. Captured HIV-1 was maintained in an infectious state over several days, suggesting that HIV-1 can escape degradation by platelets and might use these cells to promote its spread. Our results identify CLEC-2 as a novel HIV-1 attachment factor and provide evidence that platelets capture and transfer infectious HIV-1 via DC-SIGN and CLEC-2, thereby possibly facilitating HIV-1 dissemination in infected patients.

Repetitive exposures with simian/human immunodeficiency viruses: strategy to study HIV pre-clinical interventions in non-human primates

BACKGROUND

Non-human primate models for human immunodeficiency virus (HIV) infection represent a valuable pre-clinical tool to evaluate interventions (e.g., topical microbicides, vaccines, and chemoprophylaxis) designed to prevent transmission or slow disease progression after infection. Standard transmission models use a single-dose exposure with high, non-physiologic levels of virus to approach 100% infection rates of control animals. These single-exposure models do not represent the circumstances of mucosal HIV transmission in humans and may result in misleading data with regard to intervention efficacy. Therefore, we have developed a repetitive mucosal exposure model using doses of virus that better reflects human exposures.

METHODS

The virus used for these evaluations was simian-human immunodeficiency virus [SHIVSF162P3 (R5-using, subtype B HIV-1 envelope)] and the virus dose used (approximately 10(5)-10(6) viral particle equivalents or approximately 10 tissue culture infectious doses per exposure) approximates viral loads observed in the semen during acute HIV-1 infection. Using the repeated mucosal exposure approach, we have evaluated a candidate vaginal microbicide (cellulose acetate phthalate, CAP) given 15 minutes prior to each weekly virus exposure. Pig-tailed macaques were exposed weekly by vaginal inoculations with and without microbicide until systemic viral RNA was detected.

RESULTS

Groups of naïve control monkeys were infected after an average of three to four exposures for the vaginal route of inoculation. Data from the first application of this monkey model to evaluate the topical microbicide CAP suggested that protection from SHIV infection was possible with three of four CAP-treated monkeys remaining uninfected after 12 exposures (P = 0.015). CAP efficacy was markedly improved from 66% in a previous single-dose virus exposure study to 92% in this repeated exposure system.

CONCLUSIONS

Our experience with using repetitive virus exposures to study topical microbicides and the findings to date from this study provides a basis to refine monkey models to more closely resemble human exposure during HIV transmission. This model may be highly relevant to pre-clinical evaluation for a variety of therapeutic interventions which is discussed here.

Identification of a d-amino acid decapeptide HIV-1 entry inhibitor

Entry of human immunodeficiency virus type 1 (HIV-1) virion into host cells involves three major steps, each being a potential target for the development of entry inhibitors: gp120 binding to CD4, gp120-CD4 complex interacting with a coreceptor, and gp41 refolding to form a six-helix bundle. Using a D-amino acid decapeptide combinatorial library, we identified peptide dC13 as having potent HIV-1 fusion inhibitory activity, and effectively inhibiting infection by several laboratory-adapted and primary HIV-1 strains. While dC13 did not block binding of gp120 to CD4, nor disrupt the gp41 six-helix bundle formation, it effectively blocked the binding of an anti-CXCR4 monoclonal antibody and chemokine SDF-1alpha to CXCR4-expressing cells. However, because R5-using primary viruses were also neutralized, the antiviral activity of dC13 implies additional mode(s) of action. These results suggest that dC13 is a useful HIV-1 coreceptor antagonist for CXCR4 and, due to its biostability and simplicity, may be of value for developing a new class of HIV-1 entry inhibitors.