Envelope glycoproteins from human immunodeficiency virus types 1 and 2 and simian immunodeficiency virus can use human CCR5 as a coreceptor for viral entry and make direct CD4-dependent interactions with this chemokine receptor

Slow Receptor Binding of the Noncytopathic HIV-2UC1 Envs Is Balanced by Long-Lived Activation State and Efficient Fusion Activity

Many HIV strains downregulate the levels of CD4 receptor on the surface of infected cells to prevent superinfection. In contrast, the rare HIV-2_UC1 strain is noncytopathic and has no effect on CD4 expression in infected cells but still replicates as efficiently as more cytopathic strains in peripheral blood mononuclear cells (PBMCs). Here, we show that HIV-2_UC1 Env interactions with the CD4 receptor exhibit slow association kinetics, whereas the dissociation kinetics is within the range of cytopathic strains. Despite the resulting 10- to 100-fold decrease in binding affinity, HIV-2_UC1 Envs exhibit long-lived activation state and efficient fusion activity. These observations suggest that HIV-2_UC1 Envs evolved to balance low affinity with an improved and readily triggerable molecular machinery to mediate entry. Resistance to cold exposure, similar to many primary HIV-1 isolates, and to sCD4 neutralization suggests that HIV-2_UC1 Envs preferentially sample a closed Env conformation. Our data provide insights into the mechanism of HIV entry.

Comparison of the integrin α4β7 expression pattern of memory T cell subsets in HIV infection and ulcerative colitis

Anti-α4β7 therapy with vedolizumab (VDZ) has been suggested as possible immune intervention in HIV. Relatively little is known about the α4β7-integrin (α4β7) expression of different T-cell subsets in different anatomical compartments of healthy individuals, patients with HIV or inflammatory bowel disease (IBD). Surface expression of α4β7 as well as the frequency of activation, homing and exhaustion markers of T cells were assessed by multicolour flow cytometry in healthy volunteers (n = 15) compared to HIV infected patients (n = 52) or patients diagnosed with ulcerative colitis (UC) (n = 14), 6 of whom treated with vedolizumab. In addition, lymph nodal cells (n = 6), gut-derived cells of healthy volunteers (n = 5) and patients with UC (n = 6) were analysed. Additionally, we studied longitudinal PBMC samples of an HIV patient who was treated with vedolizumab for concomitant UC. Overall, only minor variations of the frequency of α4β7 on total CD4⁺ T cells were detectable regardless of the disease status or (VDZ) treatment status in peripheral blood and the studied tissues. Peripheral α4β7⁺ CD4⁺ T cells of healthy individuals and patients with UC showed a higher activation status and were more frequently CCR5⁺ than their α4β7^- counterparts. Also, the frequency of α4β7⁺ cells was significantly lower in peripheral blood CD4⁺ effector memory T cells of HIV-infected compared to healthy individuals and this reduced frequency did not recover in HIV patients on ART. Conversely, the frequency of peripheral blood naïve α4β7⁺ CD4⁺ T cells was significantly reduced under VDZ treatment. The results of the current study will contribute to the understanding of the dynamics of α4β7 expression pattern on T cells in HIV and UC and will be useful for future studies investigating VDZ as possible HIV cure strategy.

Antibody Fab-Fc properties outperform titer in predictive models of SIV vaccine-induced protection

Characterizing the antigen-binding and innate immune-recruiting properties of the humoral response offers the chance to obtain deeper insights into mechanisms of protection than revealed by measuring only overall antibody titer. Here, a high-throughput, multiplexed Fab-Fc Array was employed to profile rhesus macaques vaccinated with a gp120-CD4 fusion protein in combination with different genetically encoded adjuvants, and subsequently subjected to multiple heterologous simian immunodeficiency virus (SIV) challenges. Systems analyses modeling protection and adjuvant differences using Fab-Fc Array measurements revealed a set of correlates yielding strong and robust predictive performance, while models based on measurements of response magnitude alone exhibited significantly inferior performance. At the same time, rendering Fab-Fc measurements mathematically independent of titer had relatively little impact on predictive performance. Similar analyses for a distinct SIV vaccine study also showed that Fab-Fc measurements performed significantly better than titer. These results suggest that predictive modeling with measurements of antibody properties can provide detailed correlates with robust predictive power, suggest directions for vaccine improvement, and potentially enable discovery of mechanistic associations.

Chandipura virus changes cellular miRNome in human microglial cells

Chandipura virus (CHPV) is a neurotropic virus, known to cause encephalitis in humans. The microRNAs (miRNA/miR) play an important role in the pathogenesis of viral infection. The present study is focused on the role of miRNAs during CHPV (strain 1653514) infection in human microglial cells. The deep sequencing of CHPV-infected human microglial cells identified a total of 12 differentially expressed miRNA (DEMs). To elucidate the role of DEMs, the target gene prediction, Gene Ontology term (GO Term), pathway enrichment analysis, and miRNA-messenger RNA (mRNA) interaction network analysis was performed. The GO terms and pathway enrichment analysis provided 146 enriched genes; which were involved in interferon response, cytokine and chemokine signaling. Further, the WGCNA (weighted gene coexpression network analysis) of the enriched genes were discretely categorized into three modules (blue, brown, and turquoise). The hub genes in the blue module may correlate to CHPV induced neuroinflammation. Altogether, the miRNA-mRNA interaction network and WGCNA study revealed the following pairs, hsa-miR-542-3p and FAF1, hsa-miR-92a-1-5p and MYD88, and hsa-miR-3187-3p and TNFRSF21, which may contribute to neuroinflammation during CHPV infection in human microglial cells.

Modified Newcastle Disease virus as an improved vaccine vector against Simian Immunodeficiency virus

SIV infection in macaques is a relevant animal model for HIV pathogenesis and vaccine study in humans. To design a safe and effective vaccine against HIV, we evaluated the suitability of naturally-occurring avirulent Newcastle disease virus (NDV) strains and several modified versions of NDV as vectors for the expression and immunogenicity of SIV envelope protein gp160. All the NDV vectors expressed gp160 protein in infected cells. The gp160 expressed by these vectors formed oligomers and was incorporated into the NDV envelope. All the NDV vectors expressing gp160 were attenuated in chickens. Intranasal immunization of guinea pigs with modified NDV vectors such as rNDV-APMV-2CS/gp160 and rNDV-APMV-8CS/gp160 (NDV strain LaSota containing the cleavage site sequences of F protein of avian paramyxovirus (APMV) serotype 2 and 8, respectively), and rNDV-BC-F-HN/gp160 (NDV strain BC containing LaSota F cleavage site and LaSota F and HN genes) elicited improved SIV-specific humoral and mucosal immune responses compared to other NDV vectors. These modified vectors were also efficient in inducing neutralizing antibody responses to tier 1 A SIVmac251.6 and tier 1B SIVmac251/M766 strains. This study suggests that our novel modified NDV vectors are safe and immunogenic and can be used as vaccine vector to control HIV.

Comparison of the editing patterns and editing efficiencies of TALEN and CRISPR-Cas9 when targeting the human CCR5 gene

The human C-C chemokine receptor type-5 (CCR5) is the major transmembrane co-receptor that mediates HIV-1 entry into target CD4+ cells. Gene therapy to knock-out the CCR5 gene has shown encouraging results in providing a functional cure for HIV-1 infection. In gene therapy strategies, the initial region of the CCR5 gene is a hotspot for producing functional gene knock-out. Such target gene editing can be done using programmable endonucleases such as transcription activator-like effector nucleases (TALEN) or clustered regularly interspaced short palindromic repeats (CRISPR-Cas9). These two gene editing approaches are the most modern and effective tools for precise gene modification. However, little is known of potential differences in the efficiencies of TALEN and CRISPR-Cas9 for editing the beginning of the CCR5 gene. To examine which of these two methods is best for gene therapy, we compared the patterns and amount of editing at the beginning of the CCR5 gene using TALEN and CRISPR-Cas9 followed by DNA sequencing. This comparison revealed that CRISPR-Cas9 mediated the sorting of cells that contained 4.8 times more gene editing than TALEN+ transfected cells.

Lessons learned from humoral responses of HIV patients

PURPOSE OF REVIEW

Since 2009 many broadly neutralizing antibodies against HIV have been identified, yet there is still no vaccine capable of inducing such antibodies in humans. This review considers the early observations of HIV sera neutralization in light of more recent studies and highlights areas for future research.

RECENT FINDINGS

Large clinical cohort studies using standardized neutralization assays and pseudoviruses derived from primary isolates have shown that 10-30% of HIV infections result in some level of serum neutralization breadth. However, less than 10% of individuals develop a greater breadth of neutralization and are termed elite neutralizers.

SUMMARY

During HIV infection, many individuals develop strain-specific neutralization against their viral quasispecies, and similar immunogen-matched activity can now be induced in animal models. However, only in a minority of infections do broadly neutralizing antibodies develop. Therefore, understanding how the viral diversity, host immune environment, and antibody repertoires intersect to support the generation of neutralization breadth in elite neutralizers could provide guidelines as to how to improve immunization responses.

Insight into HIV-2 latency may disclose strategies for a cure for HIV-1 infection

HIV-1 and HIV-2 originate from two distinct zoonotic transmissions of simian immunodeficiency viruses from primate to human. Although both share similar modes of transmission and can result in the development of AIDS with similar clinical manifestations, HIV-2 infection is generally milder and less likely to progress to AIDS. HIV is currently incurable due to the presence of HIV provirus integrated into the host DNA of long-lived memory cells of the immune system without active replication. As such, the latent virus is immunologically inert and remains insensitive to the administered antiviral drugs targeting active viral replication steps. Recent evidence suggests that persistent HIV replication may occur in anatomical sanctuaries such as the lymphoid tissue due to low drug penetration. At present, different strategies are being evaluated either to completely eradicate the virus from the patient (sterilising cure) or to allow treatment interruption without viral rebound (functional cure). Because HIV-2 is naturally less pathogenic and displays a more latent phenotype than HIV-1, it may represent a valuable model that provides elementary information to cure HIV-1 infection. Insight into the viral and cellular determinants of HIV-2 replication may therefore pave the way for alternative strategies to eradicate HIV-1 or promote viral remission.

Increased T cell breadth and antibody response elicited in prime-boost regimen by viral vector encoded homologous SIV Gag/Env in outbred CD1 mice

BACKGROUND

A major obstacle for the development of HIV vaccines is the virus' worldwide sequence diversity. Nevertheless, the presence of T cell epitopes within conserved regions of the virus' structural Gag protein and conserved structures in the envelope (env) sequence raises the possibility that cross-reactive responses may be induced by vaccination. In this study, the aim was to investigate the importance of antigenic match on immunodominance and breadth of obtainable T cell responses.

METHODS

Outbred CD1 mice were immunized with either heterologous (SIVmac239 and HIV-1 clade B consensus) or homologous (SIVmac239) gag sequences using adenovirus (Ad5) and MVA vectors. Env (SIVmac239) was co-encoded in the vectors to study the induction of antibodies, which is a primary target of current HIV vaccine designs. All three vaccines were designed as virus-encoded virus-like particle vaccines. Antibody responses were analysed by ELISA, avidity ELISA, and neutralization assay. T cell responses were determined by intracellular cytokine staining of splenocytes.

RESULTS

The homologous Env/Gag prime-boost regimen induced higher Env binding antibodies, and induced stronger and broader Gag specific CD8+ T cell responses than the homologous Env/heterologous Gag prime-boost regimen. Homologous Env/heterologous Gag immunization resulted in selective boosting of Env specific CD8+ T cell responses and consequently a paradoxical decreased recognition of variant sequences including conserved elements of p24 Gag.

CONCLUSIONS

These results contrast with related studies using Env or Gag as the sole antigen and suggest that prime-boost immunizations based on homologous SIVmac239 Gag inserts is an efficient component of genetic VLP vaccines-both for induction of potent antibody responses and cross-reactive CD8+ T cell responses.

Impact of Depression and Inflammation on the Progression of HIV Disease

The human immunodeficiency virus type 1 (HIV-1) epidemic has negatively affected over 40 million people worldwide. Antiretroviral therapy (ART) has improved life expectancy and changed the outcome of HIV-1 infection, making it a chronic and manageable disease. However, AIDS and non-AIDS comorbid illnesses persist during the course of infection despite the use of ART. In addition, the development of neuropsychiatric comorbidities (including depression) by HIV-infected subjects significantly affects quality of life, medication adherence, and disease prognosis. The factors associated with depression during HIV-1 infection include altered immune response, the release of pro-inflammatory cytokines, and monoamine imbalance. Elevated plasma pro-inflammatory cytokine levels contribute to the development of depression and depressive-like behaviors in HIV⁺ subjects. In addition, comorbid depression influences the decline rates of CD4⁺ cell counts and increases plasma viral load. Depression can manifest in some subjects despite their adherence to ART. In addition, psychosocial factors related to stigma (negative attitudes, moral issues, and abuse of HIV⁺ subjects) are also associated with depression. Both neurobiological and psychosocial factors are important considerations for the effective clinical management of HIV and the prevention of HIV disease progression.

Structure/Function Studies Involving the V3 Region of the HIV-1 Envelope Delineate Multiple Factors That Affect Neutralization Sensitivity

Antibodies (Abs) specific for the V3 loop of the HIV-1 gp120 envelope neutralize most tier 1 and many tier 2 viruses and are present in essentially all HIV-infected individuals as well as immunized humans and animals. Vaccine-induced V3 Abs are associated with reduced HIV infection rates in humans and affect the nature of transmitted viruses in infected vaccinees, despite the fact that V3 is often occluded in the envelope trimer. Here, we link structural and experimental data showing how conformational alterations of the envelope trimer render viruses exceptionally sensitive to V3 Abs. The experiments interrogated the neutralization sensitivity of pseudoviruses with single amino acid mutations in various regions of gp120 that were predicted to alter packing of the V3 loop in the Env trimer. The results indicate that the V3 loop is metastable in the envelope trimer on the virion surface, flickering between states in which V3 is either occluded or available for binding to chemokine receptors (leading to infection) and to V3 Abs (leading to virus neutralization). The spring-loaded V3 in the envelope trimer is easily released by disruption of the stability of the V3 pocket in the unliganded trimer or disruption of favorable V3/pocket interactions. Formation of the V3 pocket requires appropriate positioning of the V1V2 domain, which is, in turn, dependent on the conformation of the bridging sheet and on the stability of the V1V2 B-C strand-connecting loop.

IMPORTANCE The levels of antibodies to the third variable region (V3) of the HIV envelope protein correlate with reduced HIV infection rates. Previous studies showed that V3 is often occluded, as it sits in a pocket of the envelope trimer on the surface of virions; however, the trimer is flexible, allowing occluded portions of the envelope (like V3) to flicker into an exposed position that binds antibodies. Here we provide a systematic interrogation of mechanisms by which single amino acid changes in various regions of gp120 (i) render viruses sensitive to neutralization by V3 antibodies, (ii) result in altered packing of the V3 loop, and (iii) activate an open conformation that exposes V3 to the effects of V3 Abs. Taken together, these and previous studies explain how V3 antibodies can protect against HIV-1 infection and why they should be one of the targets of vaccine-induced antibodies.

Envelope gene evolution and HIV-1 neuropathogenesis

In the era of combined antiretroviral therapy (cART), HIV-associated neurocognitive disorders (HAND) account for 40 to 56% of all HIV⁺ cases. During the acute stage of HIV-1 infection (<6 months), the virus invades and replicates within the central nervous system (CNS). Compared to peripheral tissues, the local CNS cell population expresses distinct levels of chemokine receptors, which levels exert selective pressure on the invading virus. HIV-1 envelope (env) sequences recovered from the brains and cerebrospinal fluid (CSF) of neurocognitively impaired HIV⁺ subjects often display higher nucleotide variability as compared to non-impaired HIV⁺ subjects. Specifically, env evolution provides HIV-1 with the strategies to evade host immune response, to reduce chemokine receptor dependence, to increase co-receptor binding efficiency, and to potentiate neurotoxicity. The evolution of env within the CNS leads to changes that may result in the emergence of novel isolates with neurotoxic and neurovirulent features. However, whether specific factors of HIV-1 evolution lead to the emergence of neurovirulent and neurotropic isolates remains ill-defined. HIV-1 env evolution is an ongoing phenomenon that occurs independently of neurological and neurocognitive disease severity; thus HIV env evolution may play a pivotal and reciprocal role in the etiology of HAND. Despite the use of cART, the reactivation of latent viral reservoirs represents a clinical challenge because of the replenishment of the viral pool that may subsequently lead to persistent infection. Therefore, gaining a more complete understanding of how HIV-1 env evolves over the course of the disease should be considered for the development of future therapies aimed at controlling CNS burden, diminishing persistent viremia, and eradicating viral reservoirs. Here we review the current literature on the role of HIV-1 env evolution in the setting of HAND disease progression and on the impact of cART on the dynamics of viral evolution.

Vaccine-induced Human Antibodies Specific for the Third Variable Region of HIV-1 gp120 Impose Immune Pressure on Infecting Viruses

To evaluate the role of V3-specific IgG antibodies (Abs) in the RV144 clinical HIV vaccine trial, which reduced HIV-1 infection by 31.2%, the anti-V3 Ab response was assessed. Vaccinees' V3 Abs were highly cross-reactive with cyclic V3 peptides (cV3s) from diverse virus subtypes. Sieve analysis of CRF01_AE breakthrough viruses from 43 vaccine- and 66 placebo-recipients demonstrated an estimated vaccine efficacy of 85% against viruses with amino acids mismatching the vaccine at V3 site 317 (p = 0.004) and 52% against viruses matching the vaccine at V3 site 307 (p = 0.004). This analysis was supported by data showing that vaccinees' plasma Abs were less reactive with I³⁰⁷ when replaced with residues found more often in vaccinees' breakthrough viruses. Simultaneously, viruses with mutations at F³¹⁷ were less infectious, possibly due to the contribution of F³¹⁷ to optimal formation of the V3 hydrophobic core. These data suggest that RV144-induced V3-specific Abs imposed immune pressure on infecting viruses and inform efforts to design an HIV vaccine.

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The RV144 vaccine reduced infection by viruses with isoleucine in V3 position 307.

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Many vaccine-induced antibodies are cross-reactive and target an epitope including I³⁰⁷.

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There was selection for breakthrough viruses carrying F³¹⁷ in V3 (p = 0.004).

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F³¹⁷ is needed to maintain optimal infectivity.

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F³¹⁷ is a poor or non-contact residue for vaccine induced V3 antibodies.

Toll-like receptor 3 signaling inhibits simian immunodeficiency virus replication in macrophages from rhesus macaques

Toll-like receptor 3 (TLR3) recognizes double-stranded RNA and induces multiple intracellular events responsible for innate antiviral immunity against viral infections. Here we demonstrate that TLR3 signaling of monocyte-derived macrophages (MDM) from rhesus monkeys by poly I:C inhibited simian immunodeficiency virus (SIV) infection and replication. Investigation of the mechanisms showed that TLR3 activation resulted in the induction of type I and type III interferons (IFNs) and IFN-inducible antiviral factors, including APOBEC3G (A3G), tetherin and SAMHD1. In addition, poly I:C-treated macaque macrophages expressed increased levels of CC chemokines including CCL3, CCL4 and CCL5, the ligands for HIV or SIV coreceptor CCR5. Furthermore, TLR3 signaling of macaque macrophages induced the expression of cellular microRNAs (miR-29a, -29b, -146a and -9), the newly identified intracellular SIV restriction factors. TLR3 activation-mediated anti-SIV effect could be compromised by the knockdown of IRF3 and IRF7. These findings indicate that TLR3-mediated induction of multiple viral restriction factors contribute to the inhibition of SIV infection in macaque macrophages, which support future preclinical studies using rhesus macaques to determine whether in vivo TLR3 activation is safe and beneficial for treating people infected with HIV.

CCR5 as a treatment target in pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PH), whether idiopathic or related to underlying diseases such as HIV infection, results from complex vessel remodeling involving both pulmonary artery smooth muscle cell (PA-SMC) proliferation and inflammation. CCR5, a coreceptor for cellular HIV-1 entry expressed on macrophages and vascular cells, may be involved in the pathogenesis of PH. Maraviroc is a new CCR5 antagonist designed to block HIV entry.

METHODS AND RESULTS

Marked CCR5 expression was found in lungs from patients with idiopathic PH, in mice with hypoxia-induced PH, and in Simian immunodeficiency virus-infected macaques, in which it was localized chiefly in the PA-SMCs. To assess the role for CCR5 in experimental PH, we used both gene disruption and pharmacological CCR5 inactivation in mice. Because maraviroc does not bind to murine CCR5, we used human-CCR5ki mice for pharmacological and immunohistochemical studies. Compared with wild-type mice, CCR5-/- mice or human-CCR5ki mice treated with maraviroc exhibited decreased PA-SMC proliferation and recruitment of perivascular and alveolar macrophages during hypoxia exposure. CCR5-/- mice reconstituted with wild-type bone marrow cells and wild-type mice reconstituted with CCR5-/- bone marrow cells were protected against PH, suggesting CCR5-mediated effects on PA-SMCs and macrophage involvement. The CCR5 ligands CCL5 and the HIV-1 gp120 protein increased intracellular calcium and induced growth of human and human-CCR5ki mouse PA-SMCs; maraviroc inhibited both effects. Maraviroc also reduced the growth-promoting effects of conditioned media from CCL5-activated macrophages derived from human-CCR5ki mice on PA-SMCs from wild-type mice.

CONCLUSION

The CCL5-CCR5 pathway represents a new therapeutic target in PH associated with HIV or with other conditions.

Use of G-protein-coupled and -uncoupled CCR5 receptors by CCR5 inhibitor-resistant and -sensitive human immunodeficiency virus type 1 variants

Small-molecule CCR5 inhibitors such as vicriviroc (VVC) and maraviroc (MVC) are allosteric modulators that impair HIV-1 entry by stabilizing a CCR5 conformation that the virus recognizes inefficiently. Viruses resistant to these compounds are able to bind the inhibitor-CCR5 complex while also interacting with the free coreceptor. CCR5 also interacts intracellularly with G proteins, as part of its signal transduction functions, and this process alters its conformation. Here we investigated whether the action of VVC against inhibitor-sensitive and -resistant viruses is affected by whether or not CCR5 is coupled to G proteins such as Gαi. Treating CD4(+) T cells with pertussis toxin to uncouple the Gαi subunit from CCR5 increased the potency of VVC against the sensitive viruses and revealed that VVC-resistant viruses use the inhibitor-bound form of Gαi-coupled CCR5 more efficiently than they use uncoupled CCR5. Supportive evidence was obtained by expressing a signaling-deficient CCR5 mutant with an impaired ability to bind to G proteins, as well as two constitutively active mutants that activate G proteins in the absence of external stimuli. The implication of these various studies is that the association of intracellular domains of CCR5 with the signaling machinery affects the conformation of the external and transmembrane domains and how they interact with small-molecule inhibitors of HIV-1 entry.

Analysis of V2 antibody responses induced in vaccinees in the ALVAC/AIDSVAX HIV-1 vaccine efficacy trial

The RV144 clinical trial of a prime/boost immunizing regimen using recombinant canary pox (ALVAC-HIV) and two gp120 proteins (AIDSVAX B and E) was previously shown to have a 31.2% efficacy rate. Plasma specimens from vaccine and placebo recipients were used in an extensive set of assays to identify correlates of HIV-1 infection risk. Of six primary variables that were studied, only one displayed a significant inverse correlation with risk of infection: the antibody (Ab) response to a fusion protein containing the V1 and V2 regions of gp120 (gp70-V1V2). This finding prompted a thorough examination of the results generated with the complete panel of 13 assays measuring various V2 Abs in the stored plasma used in the initial pilot studies and those used in the subsequent case-control study. The studies revealed that the ALVAC-HIV/AIDSVAX vaccine induced V2-specific Abs that cross-react with multiple HIV-1 subgroups and recognize both conformational and linear epitopes. The conformational epitope was present on gp70-V1V2, while the predominant linear V2 epitope mapped to residues 165–178, immediately N-terminal to the putative α4β7 binding motif in the mid-loop region of V2. Odds ratios (ORs) were calculated to compare the risk of infection with data from 12 V2 assays, and in 11 of these, the ORs were ≤1, reaching statistical significance for two of the variables: Ab responses to gp70-V1V2 and to overlapping V2 linear peptides. It remains to be determined whether anti-V2 Ab responses were directly responsible for the reduced infection rate in RV144 and whether anti-V2 Abs will prove to be important with other candidate HIV vaccines that show efficacy, however, the results support continued dissection of Ab responses to the V2 region which may illuminate mechanisms of protection from HIV-1 infection and may facilitate the development of an effective HIV-1 vaccine.

A novel strategy for efficient production of anti-V3 human scFvs against HIV-1 clade C

Background

Production of human monoclonal antibodies that exhibit broadly neutralizing activity is needed for preventing HIV-1 infection, however only a few such antibodies have been generated till date. Isolation of antibodies by the hybridoma technology is a cumbersome process with fewer yields. Further, the loss of unstable or slowly growing clones which may have unique binding specificities often occurs during cloning and propagation and the strongly positive clones are often lost. This has been avoided by the process described in this paper, wherein, by combining the strategy of EBV transformation and recombinant DNA technology, we constructed human single chain variable fragments (scFvs) against the third variable region (V3) of the clade C HIV-1 envelope.

Results

An antigen specific phage library of 7000 clones was constructed from the enriched V3- positive antibody secreting EBV transformed cells. By ligation of the digested scFv DNA into phagemid vector and bio panning against the HIV-1 consensus C and B V3 peptides followed by random selection of 40 clones, we identified 15 clones that showed V3 reactivity in phage ELISA. DNA fingerprinting analysis and sequencing showed that 13 out of the 15 clones were distinct. Expression of the positive clones was tested by SDS-PAGE and Western blot. All the 13 anti-V3 scFvs showed cross-reactivity against both the clade C and B V3 peptides and did not show any reactivity against other unrelated peptides in ELISA. Preliminary neutralization assays indicated varying degrees of neutralization of clade C and B viruses. EBV transformation, followed by antigen selection of lines to identify specific binders, enabled the selection of phage from un-cloned lines for scFv generation, thus avoiding the problems of hybridoma technology. Moreover, as the clones were pretested for antigen binding, a comparatively small library sufficed for the selection of a considerable number of unique antigen binding phage. After selection, the phage clones were propagated in a clonal manner.

Conclusions

This strategy can be efficiently used and is cost effective for the generation of diverse recombinant antibodies. This is the first study to generate anti-V3 scFvs against HIV-1 Clade C.

The trinity of the cortical actin in the initiation of HIV-1 infection

For an infecting viral pathogen, the actin cortex inside the host cell is the first line of intracellular components that it encounters. Viruses devise various strategies to actively engage or circumvent the actin structure. In this regard, the human immunodeficiency virus-1 (HIV-1) exemplifies command of cellular processes to take control of actin dynamics for the initiation of infection. It has becomes increasingly evident that cortical actin presents itself both as a barrier to viral intracellular migration and as a necessary cofactor that the virus must actively engage, particularly, in the infection of resting CD4 blood T cells, the primary targets of HIV-1. The coercion of this most fundamental cellular component permits infection by facilitating entry, reverse transcription, and nuclear migration, three essential processes for the establishment of viral infection and latency in blood T cells. It is the purpose of this review to examine, in detail, the manifestation of viral dependence on the actin cytoskeleton, and present a model of how HIV utilizes actin dynamics to initiate infection.

V3 determinants of HIV-1 escape from the CCR5 inhibitors Maraviroc and Vicriviroc

HIV-1 develops resistance to CCR5 antagonists such as Maraviroc (MVC) and Vicriviroc (VVC) both in vitro and in vivo, with most changes arising in the gp120 V3 region. Both compounds bind to the same hydrophobic cavity in CCR5 in subtly different ways. Here, we investigated which V3 sequence changes are most associated with MVC and VVC resistance and how they affect the interaction between gp120 and the CCR5 NT. We found that VVC- and MVC-selected amino acid changes map to different V3 locations and involve residues that interact with the CCR5 NT in different ways. Changes in VVC-selected, but not MVC-selected, variants often involve charged residues. Although the overall V3 charge tends not to change, the introduction or removal of charged residues at specific positions affects the local electrostatic potential and could have structural and functional implications. In summary, VVC and MVC trigger the evolution of distinct HIV-1 resistance patterns in V3.

Can natural antibodies to VIP or VIP-like HIV-1 glycoprotein facilitate prevention and supportive treatment of breast cancer?

OBJECTIVES

The incidence of non-AIDS-defining cancer is remarkably higher in HIV-infected than in the general population. In contrast, breast cancer risk is significantly reduced in the HIV-infected population. The molecular mechanisms underlying the phenomenon of suppression of breast cancer in the HIV-infected population may serve as a basis for development of a new platform for prevention and treatment of breast cancer.

HYPOTHESIS

Various evidences indicate that vasoactive intestinal peptide (VIP) plays an important role in growth, and differentiation of breast cancer. We previously showed (i) that natural antibodies recognizing VIP and the gp120-derived peptide NTM significantly contribute to the control of HIV disease progression by suppression of VIP-like activity of HIV-1 gp120 and (ii) that physical exercise stimulates production of these natural antibodies. These findings suggest that natural anti-VIP/NTM antibodies could contribute to a decrease of breast cancer in the HIV-infected population by suppression of VIP, which may play a pro/oncogenic function. Aerobic exercise which stimulates production of anti-VIP/NTM antibodies could be used as prevention and supportive treatment of breast cancer.

IMPACT

Immunotherapy based on natural anti-VIP/NTM antibodies could serve as an effective adjunct therapy for the treatment of breast cancer. Similarly, aerobic exercise, which stimulates production of these antibodies, should be considered as an inexpensive and safe preventive and supportive breast cancer therapy. Natural anti-VIP/NTM antibodies also represent promising prognostic marker for breast cancer.

Structure-guided design and immunological characterization of immunogens presenting the HIV-1 gp120 V3 loop on a CTB scaffold

V3 loop is a major neutralizing determinant of the HIV-1 gp120. Using 3D structures of cholera toxin B subunit (CTB), complete V3 in the gp120 context, and V3 bound to a monoclonal antibody (mAb), we designed two V3-scaffold immunogen constructs (V3-CTB). The full-length V3-CTB presenting the complete V3 in a structural context mimicking gp120 was recognized by the large majority of our panel of 24 mAbs. The short V3-CTB presenting a V3 fragment in the conformation observed in the complex with the 447-52D Fab, exhibited high-affinity binding to this mAb. The immunogens were evaluated in rabbits using DNA-prime/protein-boost protocol. Boosting with the full-length V3-CTB induced high anti-V3 titers in sera that potently neutralize multiple HIV virus strains. The short V3-CTB was ineffective. The results suggest that very narrow antigenic profile of an immunogen is associated with poor Ab response. An immunogen with broader antigenic activity elicits robust Ab response.

Structure-function relationships of HIV-1 envelope sequence-variable regions refocus vaccine design. Nat Rev Immunol. 2010;10:527-535. [PMID: 20577269 DOI: 10.1038/nri2801]

One of the main challenges of developing an HIV-1 vaccine lies in eliciting immune responses that can overcome the antigenic variability exhibited by HIV. Most HIV-1 vaccine development has focused on inducing immunity to conserved regions of the HIV-1 envelope. However, new studies of the sequence-variable regions of the HIV-1 gp120 envelope glycoprotein have shown that there are conserved immunological and structural features in these regions. Recombinant immunogens that include these features may provide the means to address the antigenic diversity of HIV-1 and induce protective antibodies that can prevent infection with HIV-1.

Structural conservation predominates over sequence variability in the crown of HIV type 1's V3 loop

The diversity of HIV-1 is a confounding problem for vaccine design, as the human immune response appears to favor poor or strain-specific responses to any given HIV-1 virus strain. A significant portion of this diversity is manifested as sequence variability in the loops of HIV-1's surface envelope glycoprotein. Here we show that the most variable sequence positions in the third variable (V3) loop crown cluster to a small zone on the surface of one face of the V3 loop ss-hairpin conformation. These results provide a novel visualization of the gp120 V3 loop, specifically demonstrating a surprising preponderance of conserved three-dimensional structure in a highly sequence-variable region. From a structural point of view, there appears to be less diversity in this region of the HIV-1 "principle neutralizing domain" than previously appreciated.

HIV-1 Entry, Inhibitors, and Resistance

Entry inhibitors represent a new class of antiretroviral agents for the treatment of infection with HIV-1. While resistance to other HIV drug classes has been well described, resistance to this new class is still ill defined despite considerable clinical use. Several potential mechanisms have been proposed: tropism switching (utilization of CXCR4 instead of CCR5 for entry), increased affinity for the coreceptor, increased rate of virus entry into host cells, and utilization of inhibitor-bound receptor for entry. In this review we will address the development of attachment, fusion, and coreceptor entry inhibitors and explore recent studies describing potential mechanisms of resistance.

Anti-V3 monoclonal antibodies display broad neutralizing activities against multiple HIV-1 subtypes

Background

The V3 loop of the HIV-1 envelope (Env) glycoprotein gp120 was identified as the “principal neutralizing domain” of HIV-1, but has been considered too variable to serve as a neutralizing antibody (Ab) target. Structural and immunochemical data suggest, however, that V3 contains conserved elements which explain its role in binding to virus co-receptors despite its sequence variability. Despite this evidence of V3 conservation, the ability of anti-V3 Abs to neutralize a significant proportion of HIV-1 isolates from different subtypes (clades) has remained controversial.

Methods

HIV-1 neutralization experiments were conducted in two independent laboratories to test human anti-V3 monoclonal Abs (mAbs) against pseudoviruses (psVs) expressing Envs of diverse HIV-1 subtypes from subjects with acute and chronic infections. Neutralization was defined by 50% inhibitory concentrations (IC₅₀), and was statistically assessed based on the area under the neutralization titration curves (AUC).

Results

Using AUC analyses, statistically significant neutralization was observed by ≥1 anti-V3 mAbs against 56/98 (57%) psVs expressing Envs of diverse subtypes, including subtypes A, AG, B, C and D. Even when the 10 Tier 1 psVs tested were excluded from the analysis, significant neutralization was detected by ≥1 anti-V3 mAbs against 46/88 (52%) psVs from diverse HIV-1 subtypes. Furthermore, 9/24 (37.5%) Tier 2 viruses from the clade B and C standard reference panels were neutralized by ≥1 anti-V3 mAbs. Each anti-V3 mAb tested was able to neutralize 28–42% of the psVs tested. By IC₅₀ criteria, 40/98 (41%) psVs were neutralized by ≥1 anti-V3 mAbs.

Conclusions

Using standard and new statistical methods of data analysis, 6/7 anti-V3 human mAbs displayed cross-clade neutralizing activity and revealed that a significant proportion of viruses can be neutralized by anti-V3 Abs. The new statistical method for analysis of neutralization data provides many advantages to previously used analyses.

Persistence of CCR5 usage among primary human immunodeficiency virus isolates of individuals receiving intermittent interleukin-2

OBJECTIVE

To investigate the impact of intermittent interleukin-2 (IL-2) plus combination antiretroviral therapy (cART) on HIV-1 entry co-receptor use.

METHODS

Primary HIV-1 isolates were obtained from 54 HIV-1-positive individuals at baseline and after 12 months using co-cultivation of peripheral blood mononuclear cells (PBMC) with activated PBMC of HIV-negative healthy donors. HIV-1 co-receptor use was determined on U87-CD4 cells.

RESULTS

Fourteen out of the 21 (67%) IL-2-treated individuals harbouring a primary CCR5-dependent (R5) HIV-1 isolate at baseline confirmed an R5 virus isolation after 12 months in contrast to 3 out of 7 (43%) of those receiving cART only. After 12 months, only 1 R5X4 HIV-1 isolate was obtained from 21 cART+IL-2-treated individuals infected with an R5 virus at entry (5%) vs. 2/7 (29%) patients receiving cART alone, as confirmed by a 5-year follow-up on some individuals.

CONCLUSIONS

Intermittent IL-2 administration plus cART may prevent evolution towards CXCR4 usage in individuals infected with R5 HIV-1.

Cross-clade neutralizing antibodies against HIV-1 induced in rabbits by focusing the immune response on a neutralizing epitope

Studies were performed to induce cross-clade neutralizing antibodies (Abs) by testing various combinations of prime and boost constructs that focus the immune response on structurally-conserved epitopes in the V3 loop of HIV-1 gp120. Rabbits were immunized with gp120 DNA containing a V3 loop characterized by the GPGR motif at its tip, and/or with gp120 DNA with a V3 loop carrying the GPGQ motif. Priming was followed by boosts with V3-fusion proteins (V3-FPs) carrying the V3 sequence from a subtype B virus (GPGR motif), and/or with V3 sequences from subtypes A and C (GPGQ motif). The broadest and most consistent neutralizing responses were generated when using a clade C gp120 DNA prime and with the V3(B)-FP boost. Immune sera displayed neutralizing activity in three assays against pseudoviruses and primary isolates from subtypes A, AG, B, C, and D. Polyclonal Abs in the immune rabbit sera neutralized viruses that were not neutralized by pools of human anti-V3 monoclonal Abs. Greater than 80% of the neutralizing Abs were specific for V3, showing that the immune response could be focused on a neutralizing epitope and that vaccine-induced anti-V3 Abs have cross-clade neutralizing activity.

Transitions to and from the CD4-bound conformation are modulated by a single-residue change in the human immunodeficiency virus type 1 gp120 inner domain

Binding to the primary receptor CD4 induces conformational changes in the human immunodeficiency virus type 1 (HIV-1) gp120 envelope glycoprotein that allow binding to the coreceptor (CCR5 or CXCR4) and ultimately trigger viral membrane-cell membrane fusion mediated by the gp41 transmembrane envelope glycoprotein. Here we report the derivation of an HIV-1 gp120 variant, H66N, that confers envelope glycoprotein resistance to temperature extremes. The H66N change decreases the spontaneous sampling of the CD4-bound conformation by the HIV-1 envelope glycoproteins, thus diminishing CD4-independent infection. The H66N change also stabilizes the HIV-1 envelope glycoprotein complex once the CD4-bound state is achieved, decreasing the probability of CD4-induced inactivation and revealing the enhancing effects of soluble CD4 binding on HIV-1 infection. In the CD4-bound conformation, the highly conserved histidine 66 is located between the receptor-binding and gp41-interactive surfaces of gp120. Thus, a single amino acid change in this strategically positioned gp120 inner domain residue influences the propensity of the HIV-1 envelope glycoproteins to negotiate conformational transitions to and from the CD4-bound state.

Initiation of antiretroviral therapy 48 hours after infection with simian immunodeficiency virus potently suppresses acute-phase viremia and blocks the massive loss of memory CD4+ T cells but fails to prevent disease

We investigated whether a 28-day course of potent antiretroviral therapy, initiated at a time point (48 h postinoculation) following simian immunodeficiency virus (SIV) inoculation when the acquisition of a viral infection was virtually assured, would sufficiently sensitize the immune system and result in controlled virus replication when treatment was stopped. The administration of tenofovir 48 h after SIV inoculation to six Mamu-A*01-negative rhesus macaques did, in fact, potently suppress virus replication in all of the treated rhesus macaques, but plasma viral RNA rapidly became detectable in all six animals following its cessation. Unexpectedly, the viral set points in the treated monkeys became established at two distinct levels. Three controller macaques had chronic phase virus loads in the range of 1 x 10(3) RNA copies/ml, whereas three noncontroller animals had set points of 2 x 10(5) to 8 x 10(5) RNA copies/ml. All of the noncontroller monkeys died with symptoms of immunodeficiency by week 60 postinfection, whereas two of the three controller animals were alive at week 80. Interestingly, the three controller macaques each carried major histocompatibility complex class I alleles that previously were reported to confer protection against SIV, and two of these animals generated cytotoxic T-lymphocyte escape viral variants during the course of their infections.

Mechanisms of receptor/coreceptor-mediated entry of enveloped viruses

Enveloped viruses enter host cells either through endocytosis, or by direct fusion of the viral envelope and the membrane of the host cell. However, some viruses, such as HIV-1, HSV-1, and Epstein-Barr can enter a cell through either mechanism, with the choice of pathway often a function of the ambient physical chemical conditions, such as temperature and pH. We develop a stochastic model that describes the entry process at the level of binding of viral glycoprotein spikes to cell membrane receptors and coreceptors. In our model, receptors attach the cell membrane to the viral membrane, while subsequent binding of coreceptors enables fusion. The model quantifies the competition between fusion and endocytotic entry pathways. Relative probabilities for each pathway are computed numerically, as well as analytically in the high viral spike density limit. We delineate parameter regimes in which fusion or endocytosis is dominant. These parameters are related to measurable and potentially controllable quantities such as membrane bending rigidity and receptor, coreceptor, and viral spike densities. Experimental implications of our mechanistic hypotheses are proposed and discussed.

Multiple roles for chemokines in the pathogenesis of SIV infection

Chemokines are small chemoattractant cytokines involved in homeostatic and inflammatory immune cell migration. These small proteins have multiple functional properties that extend beyond their most recognized role in controlling cellular migration. The complex immunobiology of chemokines, coupled with the use of subsets of chemokine receptors as HIV-1 and SIV entry co-receptors, suggests that these immunomodulators could play important roles in the pathogenesis associated with infection by HIV-1 or SIV. This review provides an overview of the effects of pathogenic infection on chemokine expression in the SIV/macaque model system, and outlines potential mechanisms by which changes in these expression profiles could contribute to development of disease. Key challenges faced in studying chemokine function in vivo and new opportunities for further study and development of therapeutic interventions are discussed. Continued growth in our understanding of the effects of pathogenic SIV infection on chemokine expression and function and the continuing development of chemokine receptor targeted therapeutics will provide the tools and the systems necessary for future studies of the roles of chemokines in HIV-1 pathogenesis.

High-affinity binding of southern African HIV type 1 subtype C envelope protein, gp120, to the CCR5 coreceptor

HIV-1 subtype C is the fastest spreading subtype worldwide and predominantly uses the CCR5 coreceptor, showing minimal transition to the X4 phenotype. This raises the possibility that envelope proteins of HIV-1 subtype C have structural features that favor interaction with CCR5. Preference for CCR5 could arise from enhanced affinity of HIV-1 subtype C for CCR5. To test this, we have characterized the interaction of gp120 envelope proteins from HIV-1 subtype C clones with CD4 and CCR5. Recombinant gp120 proteins from isolates of HIV-1 subtypes B and C were expressed, purified, and assessed in a CD4 binding assay and a CCR5 chemokine competition binding assay. All gp120 proteins bound to CD4-expressing cells, except one, 97ZA347ts, which had Arg substituted for the Cys239 in the conserved C2 loop. Reconstitution of Cys239, using site-directed mutagenesis, restored CD4 binding, while introducing Arg or Ser into position 239 of the functional Du151 gp120 protein abrogated CD4 binding. This shows that the Cys228-Cys239 disulfide bond of gp120 is required for high-affinity binding to CD4. Recombinant gp120 proteins from two HIV-1 subtype B clones bound CCR5 in the presence of CD4, while gp120 from the X4-tropic, HxB2, clone did not bind CCR5. gp120 from two functional HIV-1 subtype C clones, Du151 and MOLE1, bound CCR5 with high affinity in the presence of CD4 and Du151 showed significant CCR5 binding in the absence of CD4. A gp120 from a nonfunctional subtype C clone had lower affinity for CCR5. These results indicate that HIV-1 subtype C proteins have high affinity for CCR5 with variable dependence on CD4.

Early Therapy in HIV-1-Infected Children: Effect on HIV-1 Dynamics and HIV-1-Specific Immune Response

Background

Perinatal HIV-1 infection is acquired in the milieu of a developing immune system, leading to high levels of uncontrolled viral replication. Few data have been reported that address the viral dynamics and immunological response in infants who initiated aggressive antiretroviral therapy (ART) shortly after birth.

Methods

Six HIV-1-infected infants who started ART within 3 months of age were studied. The median follow-up was 61 months. Plasma HIV-1 RNA, cell-associated HIV-1 DNA, unspliced and multiply spliced HIV-1 mRNAs, HIV-1 antibodies, and CD4+ and CD8+ T-cell subsets were assessed in sequential peripheral blood samples. HIV-1 cellular immune response was measured by EliSpot assay.

Results

All children showed a decline in plasma viraemia to undetectable levels. HIV-1 DNA persisted in four children, but only two of these had detectable HIV-1 mRNA. All viral parameters remained persistently negative in two children. Only two children produced HIV-1 antibodies, while the others, after having lost maternal antibodies, remained seronegative. No HIV-1 cellular immune response was observed in any child. Therapy interruption was performed in two children: one HIV-1-seropositive and one HIV-1-seronegative with persistently undetectable levels of all viral parameters. Rebound of HIV-1 plasma viraemia in the seronegative child was more rapid and higher than that observed in the seropositive child.

Conclusions

Early ART treatment in infants modifies the natural course of infection by controlling HIV-1 replication and reducing viral load to below the threshold levels required for onset of HIV-1 immune response, but does not prevent the establishment of a reservoir of latently infected cells that precludes virus eradication.

Towards Covalent Vaccination

Rare monoclonal antibodies (Abs) can form irreversible complexes with antigens by enzyme-like covalent nucleophile-electrophile pairing. To determine the feasibility of applying irreversible antigen inactivation by Abs as the basis of vaccination against microbes, we studied the polyclonal nucleophilic Ab response induced by the electrophilic analog of a synthetic peptide corresponding to the principal neutralizing determinant (PND) of human immunodeficiency virus type-1 (HIV) gp120 located in the V3 domain. Abs from mice immunized with the PND analog containing electrophilic phosphonates (E-PND) neutralized a homologous HIV strain (MN) approximately 50-fold more potently than control Abs from mice immunized with PND. The IgG fractions displayed binding to intact HIV particles. HIV complexes formed by anti-E-PND IgG dissociated noticeably more slowly than the complexes formed by anti-PND IgG. The slower dissociation kinetics are predicted to maintain long-lasting blockade of host cell receptor recognition by gp120. Pretreatment of the anti-PND IgG with a haptenic electrophilic phosphonate compound resulted in more rapid dissociation of the HIV-IgG complexes, consistent with the hypothesis that enhanced Ab nucleophilic reactivity induced by electrophilic immunization imparts irreversible character to the complexes. These results suggest that electrophilic immunization induces a sufficiently robust nucleophilic Ab response to enhance the anti-microbial efficacy of candidate polypeptide vaccines.

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.

HIV-1 gp120 compromises blood-brain barrier integrity and enhances monocyte migration across blood-brain barrier: implication for viral neuropathogenesis

Human immunodeficiency virus-1 (HIV-1) encephalitis is characterized by brain infiltration of virus-infected monocytes and macrophages. Cellular products and viral proteins secreted by infected cells likely play an important role in blood-brain barrier (BBB) impairment and the development of HIV-1-associated dementia (HAD). We previously demonstrated that HIV-1 envelope glycoprotein gp120 induces toxicity and alters expression of tight junction proteins in human brain microvascular endothelial cells (HBMECs). Here, we delineate the mechanisms of gp120-induced BBB dysfunction. Human brain microvascular endothelial cells expressed HIV-1 co-receptors (CCR5 and CXCR4). Exposure of HBMECs to gp120 derived from macrophage (CCR5) or lymphocyte (CXCR4)-tropic viruses decreased BBB tightness, increased permeability, and enhanced monocyte migration across in vitro BBB models. Blood-brain barrier integrity was restored after gp120 removal. CCR5 antibodies and inhibitors of myosin light chain kinase or protein kinase C (PKC) blocked gp120-enhanced monocyte migration and permeability of BBB in vitro. Exposure of HBMECs to gp120 induced release of intracellular calcium ([Ca(2+)](i)) that was prevented by CCR5 antibody and partially blocked by CXCR4 antagonist. Human immunodeficiency virus-1 gp120 activated three PKC isoforms in HBMECs [PKC-alpha/betaII, PKC(pan)-betaII and PKC-zeta/lambda]. Furthermore, specific PKC inhibitors (acting at the ATP-binding and calcium release site) blocked gp120-induced PKC activation and prevented increase in BBB permeability, supporting the biologic significance of these results. Thus, gp120 can cause dysfunction of BBB via PKC pathways and receptor mediated [Ca(2+)](i) release leading to cytoskeletal alterations and increased monocyte migration.

Nef alleles from human immunodeficiency virus type 1-infected long-term-nonprogressor hemophiliacs with or without late disease progression are defective in enhancing virus replication and CD4 down-regulation

Infection with human immunodeficiency virus (HIV)-encoding defective nef variants may contribute to a relatively benign course of disease in a minority of long-term nonprogressors (LTNP). We have examined the functions of nef alleles from six individuals belonging to the same cohort of hemophiliacs infected with HIV-1 prior to 1985 and classified as LTNP in 1995. Three out of six individuals have progressed to HIV disease (late progressors [LP]), whereas the three remainders have maintained their LTNP status at least up to 2003. The nef alleles were obtained from both plasma virus and peripheral blood mononuclear cells of all six individuals in 1995 and 1998. The proportion of sequences containing mutations not yielding Nef expression significantly diminished in 1998 versus that in 1995. Several previously defined functional regions of intact nef alleles were highly conserved. However, the major variant obtained in 1998 from plasma RNA of five out of six individuals significantly reduced HIV infectivity/replication and impaired Nef-mediated CD4 but not major histocompatibility complex class I antigen down-modulation from the cell surface. Thus, functional alterations of the nef gene are present in both LP and LTNP, suggesting that Nef defectiveness in vitro is not necessarily associated with the long-term maintenance of LTNP status. Of interest is the fact that isolates from three out of three LP showed a dual CCR5/CXCR4 coreceptor use (R5X4), in contrast to those from LTNP, which were exclusively R5. Thus, in vivo evolution of gp120 Env to CXCR4 use appears to be associated with HIV disease progression in individuals infected with nef-defective viruses.

Characterization of the human chemerin receptor--ChemR23/CMKLR1--as co-receptor for human and simian immunodeficiency virus infection, and identification of virus-binding receptor domains

Studies were conducted to elucidate co-receptor spectrum and function of the inflammatory receptor, CMKLR1/ChemR23, which was recently identified as the receptor for the cystatin-like chemoattractant, TIG2, also named chemerin. An infection model was applied based on stably transfected NP-2.CD4 host cells expressing various co-receptor constructs and exposed to panels of HIV-1, HIV-2 and SIV primary isolates. In a panel of 27 HIV-1 isolates tested, 12 isolates could use CMKLR1/ChemR23. As expected from a relatively high sequence homology with the extracellular domains of CCR3, HIV-1 isolates showing R3 tropism were particularly efficient in using CMKLR1/ChemR23. In addition, 5 out of 7 HIV-2 isolates and 13 out of 15 SIV (SMM-3 origin) used CMKLR1/ChemR23, in accordance with the previously documented ability of these isolates to use several co-receptors. In order to define important extracellular epitopes for the viral interaction, a hybrid receptor model was applied. This was based on the fact that the rat receptor, although structurally very similar to the human orthologue, was inefficient as viral co-receptor. When the rat receptor was "humanized" to include regions unique to the human receptor (N-terminus or second extracellular loop), exposure to HIV-1, HIV-2 and SIV isolates resulted in infection. The relative importance of the two critical receptor regions differed between HIV-1/HIV-2 on the one hand and SIV on the other. The results strongly support that the chemerin receptor, in the presence of CD4, functions as a "minor co-receptor" promoting infection by these classes of viruses.

Infection of CD4+ primary T cells and cell lines, generation of chronically infected cell lines, and induction of HIV expression

Acute infection of most primary cells and cell lines with HIV depends upon the sequential engagement of CD4 (primary receptor) and a chemokine coreceptor (usually CCR5 or CXCR4) by gp120 Env. Chronically infected cell lines and clones are currently used as sources of virus for infecting other cell types, as "factories" for large-scale production of virions or viral components, and as model systems for studies of regulation of virus expression. This unit provides detailed protocols for acute in vitro HIV infection of primary T cell blasts, interleukin-2-stimulated PBMC, and resting PBMC. The unit also contains information on how to determine the chemokine coreceptor usage of the virus for experimental infections. The use of cell lines as targets of acute infection is also described. Finally, protocols for generating and studying chronically HIV-infected cell lines are provided.

HIV-1 gp120 proteins alter tight junction protein expression and brain endothelial cell permeability: implications for the pathogenesis of HIV-associated dementia

Breakdown of the blood-brain barrier (BBB) is commonly seen in patients with HIV-associated dementia (HAD) despite the lack of productive infection of the brain endothelium. It is likely that secreted viral products play a major role in BBB damage and the development of HAD. The objective of this study is to determine the effects of gp120 proteins on brain endothelial cell permeability and junctional protein expression. Our results showed that treatment of cultured human brain endothelial cells with gp120 for 24 hours results in increased permeability of the endothelial monolayer. Also, gp120 proteins caused disruption and downregulation of the tight junction proteins ZO-1, ZO-2, and occludin in these cells. Other junctional proteins such as claudin-1 and claudin-5 were unaffected by gp120 treatment. These data demonstrate that HIV gp120 proteins alter both the functional and molecular properties of the BBB, which could increase trafficking of HIV, infected cells, and toxic humoral factors into the central nervous system and contribute to the pathogenesis of HAD.

Human immunodeficiency virus type 1 stimulates the expression and production of secretory leukocyte protease inhibitor (SLPI) in oral epithelial cells: a role for SLPI in innate mucosal immunity

The innate immune response is a key barrier against pathogenic microorganisms such as human immunodeficiency virus type 1 (HIV-1). Because HIV-1 is rarely transmitted orally, we hypothesized that oral epithelial cells participate in the innate immune defense against this virus. We further hypothesized that secretory leukocyte protease inhibitor (SLPI), a 12-kDa mucosal antiviral protein, is a component of the host immune response to this virus. Here we demonstrated constitutive expression and production of SLPI in immortalized human oral keratinocytes. Brief exposure of cells to HIV-1 BaL and HXB2 significantly increased SLPI mRNA and protein production compared to that in mock-exposed cells (P < 0.01), as evaluated by real-time quantitative reverse transcription-PCR and enzyme-linked immunosorbent assay. HIV-1-mediated stimulation of SLPI occurred at the transcriptional level, was dose and time dependent, was elicited by heat-inactivated and infectious viruses, and did not depend on cellular infection. Experiments with purified retroviral proteins showed that the stimulatory effect was induced specifically by external envelope glycoproteins from HIV-1 and simian immunodeficiency virus. SLPI responsiveness to HIV-1 was also observed in an unrelated oral epithelial cell line and in normal (nonimmortalized) human oral epithelial cells isolated from healthy uninfected gingival tissues. In this first report of SLPI regulation by HIV-1, we show that the expression and production of the antimicrobial and anti-inflammatory protein can be stimulated in oral epithelial cells by the virus through interactions with gp120 in the absence of direct infection. These findings indicate that SLPI is a component of the oral mucosal response to HIV-1.

Characterization of gp120 and its single-chain derivatives, gp120-CD4D12 and gp120-M9: implications for targeting the CD4i epitope in human immunodeficiency virus vaccine design

Single-chain derivatives of JRFL gp120 linked to the first two domains of human CD4 (gp120-CD4D12) or to the CD4 miniprotein analog CD4M9 (gp120-M9), have been constructed. Biacore studies revealed that gp120-CD4D12 and gp120-M9 bound to antibody 17b with dissociation constants of 0.8 and 25 nM, respectively, at pH 7.0, while gp120 alone did not bind. The binding of gp120-CD4D12 to 17b is not affected by the addition of excess soluble CD4D12, while the binding of gp120-M9 is enhanced. This finding indicates that the M9 component of the single chain interacts relatively weakly with gp120 and can be displaced by soluble CD4D12. Immunogenicity studies of gp120, gp120-CD4D12, and gp120-M9 were carried out with guinea pigs. All three molecules were highly immunogenic. The resulting antisera were examined for neutralizing activities against various human immunodeficiency virus type 1 isolates. Broadly neutralizing activity was observed only with sera generated against gp120-CD4D12. These antisera were depleted of anti-CD4D12 antibodies by being passed over a column containing immobilized CD4D12. The depleted sera showed a loss of broadly neutralizing activity. Sera that were affinity purified over a column containing immobilized gp120-M9 also lacked such neutralizing activity. This finding suggests that the broadly neutralizing response observed is exclusively due to anti-CD4 antibodies. Competition experiments showed that only antisera generated against gp120-CD4D12 competed with the CD4i antibody 17b and that this activity was not affected by depletion of anti-CD4 antibodies. The data indicate that although antibodies targeting the CD4i epitope were generated by the gp120-CD4D12 immunogen, these antibodies were nonneutralizing.

Innate immunity in experimental SIV infection and vaccination

Innate immunity represents the first line of defence to pathogens besides the physical barrier and seems to play a role in protection against HIV/SIV infection and disease progression. High production of beta-chemokines and CD8+ T cell anti-viral factors in naive as well as in vaccinated macaques has been associated with complete or partial protection against SIV infection indicating that genetic or environmental factors may influence their production. This innate immunity may help in generating HIV/SIV-specific responses upon the first exposure to HIV/SIV. SIV subunit vaccines given by the targeted iliac lymph node route have been shown to induce an increased production of CD8+ T cell suppressor factors and beta-chemokines. Only a few vaccine studies have focused on enhancing the innate immune response against HIV/SIV. The use of unmethylated CpG motifs, HSP and GM-CSF as adjuvants in SIV vaccines has been shown to induce production of HIV/SIV-inhibiting cytokines and beta-chemokines, which seem to be important in modulating and steering the adaptive immune responses. HSP has also been shown to induce gammadelta+ T cells, which contribute to the innate immunity. More knowledge about the interplay between the innate and adaptive immune responses is important to develop new HIV/SIV vaccine strategies.

Comprehensive cross-clade neutralization analysis of a panel of anti-human immunodeficiency virus type 1 monoclonal antibodies

Broadly neutralizing monoclonal antibodies (MAbs) are potentially important tools in human immunodeficiency virus type 1 (HIV-1) vaccine design. A few rare MAbs have been intensively studied, but we still have a limited appreciation of their neutralization breadth. Using a pseudovirus assay, we evaluated MAbs from clade B-infected donors and a clade B HIV(+) plasma against 93 viruses from diverse backgrounds. Anti-gp120 MAbs exhibited greater activity against clade B than non-B viruses, whereas anti-gp41 MAbs exhibited broad interclade activity. Unexpectedly, MAb 4E10 (directed against the C terminus of the gp41 ectodomain) neutralized all 90 viruses with moderate potency. MAb 2F5 (directed against an epitope adjacent to that of 4E10) neutralized 67% of isolates, but none from clade C. Anti-gp120 MAb b12 (directed against an epitope overlapping the CD4 binding site) neutralized 50% of viruses, including some from almost every clade. 2G12 (directed against a high-mannose epitope on gp120) neutralized 41% of the viruses, but none from clades C or E. MAbs to the gp120 V3 loop, including 447-52D, neutralized a subset of clade B viruses (up to 45%) but infrequently neutralized other clades ( Collapse

Key Words Collapse

MESH Headings

• AIDS Vaccines/immunology
• Antibodies, Monoclonal/immunology
• HIV Antibodies/immunology
• HIV Envelope Protein gp120/immunology
• HIV Envelope Protein gp41/immunology
• HIV-1/immunology
• Humans
• Neutralization Tests
• Protein Conformation

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Grants

• R01 HL059725 NHLBI NIH HHS
• R37 AI033292 NIAID NIH HHS
• R01 AI033292 NIAID NIH HHS
• HL 59725 NHLBI NIH HHS
• P30 AI027742 NIAID NIH HHS
• AI 27742 NIAID NIH HHS
• AI33292 NIAID NIH HHS
• R01 AI093278 NIAID NIH HHS

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Affiliation(s)

James M Binley IMM2, Department of Immunology, The Scripps Research Institute, 10550 N. Torrey Pines Rd., La Jolla, CA 92037, USA
Terri Wrin
Bette Korber
Michael B Zwick
Meng Wang
Colombe Chappey
Gabriela Stiegler
Renate Kunert
Susan Zolla-Pazner
Hermann Katinger
Christos J Petropoulos
Dennis R Burton

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Genotype and phenotype patterns of human immunodeficiency virus type 1 resistance to enfuvirtide during long-term treatment

The human immunodeficiency virus type 1 (HIV-1) fusion inhibitor enfuvirtide has recently been introduced into clinical practice and has exhibited efficient anti-HIV-1 activity in combination with other antiretroviral agents. In the present study, we addressed the effect of long-term treatment with enfuvirtide on the intrahost evolution of HIV-1. The genotype and phenotype patterns and the relative replication capacity (rRC) of enfuvirtide-resistant HIV-1 mutants were evaluated in samples from 11 subjects (7 virological nonresponders and 4 responders) who received the compound for more than 1 year in combination with different regimens. Selection of one or more mutations clustering in a sequence (amino acids 36 to 45) of the gp41 N-terminal heptad repeat was observed in samples from the seven virological nonresponders but not in those from responders. In two subjects who discontinued enfuvirtide, reversion of the resistant genotype was detected within 3 months. Recombinant clones bearing mutated gp41 sequences displayed reduced susceptibilities to enfuvirtide, with the 50% inhibitory concentrations (IC(50)s) ranging from 0.6 to 12.8 microg/ml, whereas the IC(50) for isolates with baseline sequences was 0.013 +/- 0.010 microg/ml. Interestingly, long-term monitoring of resistant variants provided evidence that ongoing adaptation to the drug is paralleled by phenotypic changes. A limited drop in the rRC in the absence of drug was observed for clones from four of the seven nonresponders bearing mutations associated with resistance. Overall, the data indicate that the different genotype patterns associated with a detectable degree of HIV-1 resistance to enfuvirtide generated during long-term treatments are characterized by a substantially low genetic barrier, possible ongoing adaptation with increased degrees of resistance, and limited influence on the viral rRC.

Inhibition of human immunodeficiency virus type 1 replication by Z-100, an immunomodulator extracted from human-type tubercle bacilli, in macrophages

Z-100 is an arabinomannan extracted from Mycobacterium tuberculosis that has various immunomodulatory activities, such as the induction of interleukin 12, interferon gamma (IFN-gamma) and beta-chemokines. The effects of Z-100 on human immunodeficiency virus type 1 (HIV-1) replication in human monocyte-derived macrophages (MDMs) are investigated in this paper. In MDMs, Z-100 markedly suppressed the replication of not only macrophage-tropic (M-tropic) HIV-1 strain (HIV-1JR-CSF), but also HIV-1 pseudotypes that possessed amphotropic Moloney murine leukemia virus or vesicular stomatitis virus G envelopes. Z-100 was found to inhibit HIV-1 expression, even when added 24 h after infection. In addition, it substantially inhibited the expression of the pNL43lucDeltaenv vector (in which the env gene is defective and the nef gene is replaced with the firefly luciferase gene) when this vector was transfected directly into MDMs. These findings suggest that Z-100 inhibits virus replication, mainly at HIV-1 transcription. However, Z-100 also downregulated expression of the cell surface receptors CD4 and CCR5 in MDMs, suggesting some inhibitory effect on HIV-1 entry. Further experiments revealed that Z-100 induced IFN-beta production in these cells, resulting in induction of the 16-kDa CCAAT/enhancer binding protein (C/EBP) beta transcription factor that represses HIV-1 long terminal repeat transcription. These effects were alleviated by SB 203580, a specific inhibitor of p38 mitogen-activated protein kinases (MAPK), indicating that the p38 MAPK signalling pathway was involved in Z-100-induced repression of HIV-1 replication in MDMs. These findings suggest that Z-100 might be a useful immunomodulator for control of HIV-1 infection.