Characterization of a neutralization-escape variant of SHIVKU-1, a virus that causes acquired immune deficiency syndrome in pig-tailed macaques

Novel Compound Inhibitors of HIV-1NL4-3 Vpu

HIV-1 Vpu targets the host cell proteins CD4 and BST-2/Tetherin for degradation, ultimately resulting in enhanced virus spread and host immune evasion. The discovery and characterization of small molecules that antagonize Vpu would further elucidate the contribution of Vpu to pathogenesis and lay the foundation for the study of a new class of novel HIV-1 therapeutics. To identify novel compounds that block Vpu activity, we have developed a cell-based ‘gain of function’ assay that produces a positive signal in response to Vpu inhibition. To develop this assay, we took advantage of the viral glycoprotein, GaLV Env. In the presence of Vpu, GaLV Env is not incorporated into viral particles, resulting in non-infectious virions. Vpu inhibition restores infectious particle production. Using this assay, a high throughput screen of >650,000 compounds was performed to identify inhibitors that block the biological activity of Vpu. From this screen, we identified several positive hits but focused on two compounds from one structural family, SRI-41897 and SRI-42371. We developed independent counter-screens for off target interactions of the compounds and found no off target interactions. Additionally, these compounds block Vpu-mediated modulation of CD4, BST-2/Tetherin and antibody dependent cell-mediated toxicity (ADCC). Unfortunately, both SRI-41897 and SRI-42371 were shown to be specific to the N-terminal region of NL4-3 Vpu and did not function against other, more clinically relevant, strains of Vpu; however, this assay may be slightly modified to include more significant Vpu strains in the future.

A simian-human immunodeficiency virus carrying the rt gene from Chinese CRF01_AE strain of HIV is sensitive to nucleoside reverse transcriptase inhibitors and has a highly genetic stability in vivo

Human immunodeficiency virus (HIV)-1 subtype CRF01_AE is one of the major HIV-1 subtypes that dominate the global epidemic. However, its drug resistance, associated mutations, and viral fitness have not been systemically studied, because available chimeric simian-HIVs (SHIVs) usually express the HIV-1 reverse transcriptase (rt) gene of subtype B HIV-1, which is different from subtype CRF01_AE HIV-1. In this study, a recombinant plasmid, pRT-SHIV/AE, was constructed to generate a chimeric RT-SHIV/AE by replacing the rt gene of simian immunodeficiency virus (SIVmac239) with the counterpart of Chinese HIV-1 subtype CRF01_AE. The infectivity, replication capacity, co-receptor tropism, drug sensitivity, and genetic stability of RT-SHIV/AE were characterized. The new chimeric RT-SHIV/AE effectively infected and replicated in human T cell line and rhesus peripheral blood mononuclear cells (rhPBMC). The rt gene of RT-SHIV/AE lacked the common mutation (T215I) associated with drug resistance. RT-SHIV-AE retained infectivity and immunogenicity, similar to that of its counterpart RT-SHIV/TC virus following intravenous inoculation in Chinese rhesus macaque. RT-SHIV-AE was more sensitive to nucleoside reverse transcriptase inhibitors (NRTIs) than the RT-SHIV/TC. RT-SHIV/AE was genetically stable in Chinese rhesus macaque. The new chimeric RT-SHIV/AE may be a valuable tool for evaluating the efficacy of the rt-based antiviral drugs against the subtype CRF01_AE HIV-1.

Protection against SHIV-KB9 infection by combining rDNA and rFPV vaccines based on HIV multiepitope and p24 protein in Chinese rhesus macaques

Developing an effective vaccine against HIV infection remains an urgent goal. We used a DNA prime/fowlpox virus boost regimen to immunize Chinese rhesus macaques. The animals were challenged intramuscularly with pathogenic molecularly cloned SHIV-KB9. Immunogenicity and protective efficacy of vaccines were investigated by measuring IFN-γ levels, monitoring HIV-specific binding antibodies, examining viral load, and analyzing CD4/CD8 ratio. Results show that, upon challenge, the vaccine group can induce a strong immune response in the body, represented by increased expression of IFN-γ, slow and steady elevated antibody production, reduced peak value of acute viral load, and increase in the average CD4/CD8 ratio. The current research suggests that rapid reaction speed, appropriate response strength, and long-lasting immune response time may be key protection factors for AIDS vaccine. The present study contributes significantly to AIDS vaccine and preclinical research.

Heavily glycosylated, highly fit SIVMne variants continue to diversify and undergo selection after transmission to a new host and they elicit early antibody dependent cellular responses but delayed neutralizing antibody responses

BACKGROUND

Lentiviruses such as human and simian immunodeficiency viruses (HIV and SIV) undergo continual evolution in the host. Previous studies showed that the late-stage variants of SIV that evolve in one host replicate to significantly higher levels when transmitted to a new host. However, it is unknown whether HIVs or SIVs that have higher replication fitness are more genetically stable upon transmission to a new host. To begin to address this, we analyzed the envelope sequence variation of viruses that evolved in animals infected with variants of SIVMne that had been cloned from an index animal at different stages of infection.

RESULTS

We found that there was more evolution of envelope sequences from animals infected with the late-stage, highly replicating variants than in animals infected with the early-stage, lower replicating variant, despite the fact that the late virus had already diversified considerably from the early virus in the first host, prior to transmission. Many of the changes led to the addition or shift in potential-glycosylation sites-, and surprisingly, these changes emerged in some cases prior to the detection of neutralizing antibody responses, suggesting that other selection mechanisms may be important in driving virus evolution. Interestingly, these changes occurred after the development of antibody whose anti-viral function is dependent on Fc-Fcgamma receptor interactions.

CONCLUSION

SIV variants that had achieved high replication fitness and escape from neutralizing antibodies in one host continued to evolve upon transmission to a new host. Selection for viral variants with glycosylation and other envelope changes may have been driven by both neutralizing and Fcgamma receptor-mediated antibody activities.

Human immunodeficiency virus type 1 Vpu protein interacts with CD74 and modulates major histocompatibility complex class II presentation

The human immunodeficiency virus type 1 (HIV-1) Vpu accessory protein is a transmembrane protein that down regulates CD4 expression and promotes the release of new virions. We screened a human leukocyte-specific yeast two-hybrid expression library to discover novel Vpu-interacting cellular proteins. The major histocompatibility complex class II (MHC II) invariant chain, also called Ii or CD74, was found to be one such protein. We show direct binding of Vpu and CD74 by using a yeast two-hybrid assay and coimmunoprecipitation from HIV-1-infected cells. The cytoplasmic region of Vpu was found to interact with the 30-amino-acid cytoplasmic tail of CD74. Human monocytic U937 cells infected with wild-type or Vpu-defective HIV-1 and transfected cells showed that Vpu down modulated the surface expression of mature MHC II molecules. The reduction in cell surface mature MHC II molecules correlated with decreased antigen presentation to T cells in culture. Thus, the Vpu protein also contributes to viral persistence by attenuating immune responses during HIV infection. This report further exemplifies the rich diversity and redundancy shown by HIV in immune evasion.

Virus-like particles: designing an effective AIDS vaccine

Viruses that infect eukaryotic organisms have the unique characteristic of self-assembling into particles. The mammalian immune system is highly attuned to recognizing and attacking these viral particles following infection. The use of particle-based immunogens, often delivered as live-attenuated viruses, has been an effective vaccination strategy for a variety of viruses. The development of an effective vaccine against the human immunodeficiency virus (HIV) has proven to be a challenge, since HIV infects cells of the immune system causing severe immunodeficiency resulting in the syndrome known as AIDS. In addition, the ability of the virus to adapt to immune pressure and reside in an integrated form in host cells presents hurdles for vaccinologists to overcome. A particle-based vaccine strategy has promise for eliciting high titer, long-lived, immune responses to a diverse number of viral epitopes against different HIV antigens. Live-attenuated viruses are effective at generating both cellular and humoral immune responses. However, while these vaccines stimulate immunity, challenged animals rarely clear the viral infection and the degree of attenuation directly correlates with protection from disease. Further, a live-attenuated vaccine has the potential to revert to a pathogenic form. Alternatively, virus-like particles (VLPs) mimic the viral particle without causing an immunodeficiency disease. VLPs are self-assembling, non-replicating, non-pathogenic particles that are similar in size and conformation to intact virions. A variety of VLPs for lentiviruses are currently in preclinical and clinical trials. This review focuses on our current status of VLP-based AIDS vaccines, regarding issues of purification and immune design for animal and clinical trials.

Anti-V3 humanized antibody KD-247 effectively suppresses ex vivo generation of human immunodeficiency virus type 1 and affords sterile protection of monkeys against a heterologous simian/human immunodeficiency virus infection

In an accompanying report (Y. Eda, M. Takizawa, T. Murakami, H. Maeda, K. Kimachi, H. Yonemura, S. Koyanagi, K. Shiosaki, H. Higuchi, K. Makizumi, T. Nakashima, K. Osatomi, S. Tokiyoshi, S. Matsushita, N. Yamamoto, and M. Honda, J. Virol. 80:5552-5562, 2006), we discuss our production of a high-affinity humanized monoclonal antibody, KD-247, by sequential immunization with V3 peptides derived from human immunodeficiency virus type 1 (HIV-1) clade B primary isolates. Epitope mapping revealed that KD-247 recognized the Pro-Gly-Arg V3 tip sequence conserved in HIV-1 clade B isolates. In this study, we further demonstrate that in vitro, KD-247 efficiently neutralizes CXCR4- and CCR5-tropic primary HIV-1 clade B and clade B' with matching neutralization sequence motifs but does not neutralize sequence-mismatched clade B and clade E isolates. Monkeys were provided sterile protection against heterologous simian/human immunodeficiency virus challenge by the passive transfer of a single high dose (45 mg per kg of body weight) of KD-247 and afforded partial protection by lower antibody doses (30 and 15 mg per kg). Protective neutralization endpoint titers in plasma at the time of virus challenge were 1:160 in animals passively transferred with a high dose of the antibody. The antiviral efficacy of the antibody was further confirmed by its suppression of the ex vivo generation of primary HIV-1 quasispecies in peripheral blood mononuclear cell cultures from HIV-infected individuals. Therefore, KD-247 promises to be a valuable tool not only as a passive immunization antibody for the prevention of HIV infection but also as an immunotherapy for the suppression of HIV in phenotype-matched HIV-infected individuals.

The V1, V2, and V3 regions of the human immunodeficiency virus type 1 envelope differentially affect the viral phenotype in an isolate-dependent manner

It is well documented that removal of the V1V2 region or of the V2 loop alone from the envelope glycoprotein of human immunodeficiency virus type 1 (HIV-1) or simian immunodeficiency virus (SIV) increases the susceptibility of these viruses to neutralization by antibodies. The specific role of the V1 loop in defining the neutralization susceptibility of HIV is, however, not well documented. Our current studies indicate that although the V1V2 region is a global modulator of the HIV-1 neutralization susceptibility, the individual roles the V1 and V2 loops have in defining the neutralization susceptibility profile of HIV-1 differ and in some cases are opposite. While deletion of the V2 loop renders the virus more susceptible to neutralization by antibodies that recognize diverse epitopes, in particular certain ones located in the CD4 binding site and the V3 loop, deletion of the V1 loop renders the virus refractory to neutralization, especially by antibodies that recognize CD4-induced epitopes and certain CD4-site binding antibodies. Our current studies also indicate that the relative involvement of the V2 loop of the HIV-1 envelope during virus-cell entry appears to be envelope background dependent. As a result, although deletion of the V2 loop from the clade B, R5-tropic SF162 HIV-1 virus resulted in a virus that was replication competent, the same modification introduced on the background of two other R5-tropic isolates, SF128A (clade B) or SF170 (clade A), abrogated the ability of these envelopes to mediate virus-cell entry.

Live attenuated HIV vaccines: pitfalls and prospects

PURPOSE OF REVIEW

When simian immunodeficiency virus (SIV) deleted in the nef gene caused no disease in macaques and provided protection against wild-type SIV challenge, hopes were high that the removal of nef would convert a pathogenic immunodeficiency virus into a live attenuated vaccine. We seek to highlight recent studies focused on several major issues regarding live attenuated AIDS viruses as vaccine candidates: (1). safety, (2). efficacy, (3). the correlates of immune protection, and (4) the molecular determinants for lentiviral virulence or attenuation.

RECENT FINDINGS

Nef-deletion mutants have retained virulence; compared with wild-type SIV, disease progression was slowed but not abrogated. After long-term observation, all adult macaques given SIVmac239delta3 exhibited immune dysfunction; over 50% had T-cell depletion, and 18% developed AIDS. Vaccine efficacy has been disappointing, with limited or no cross-protection and no protection against homologous virus challenge years after initial vaccination. To date, the correlates of protective immunity have defied precise definition; no dominant mechanism has yet emerged. Data from passive serum transfer and CD8+ T-cell depletion studies have raised the possibility that alternate mechanism of protection may be operative. Due to relentless viral replication and continuous selective pressure, initially benign viruses can generate virulent progeny with unpredictable genotypes.

SUMMARY

Neither safety nor efficacy of the current live attenuated primate immunodeficiency virus vaccines has withstood the test of time. However, such viruses are invaluable tools to address two key questions: (1). what are the correlates of protection, and (2). what are the molecular determinants of viral immunopathogenesis?

N-linked glycosylation of the V3 loop and the immunologically silent face of gp120 protects human immunodeficiency virus type 1 SF162 from neutralization by anti-gp120 and anti-gp41 antibodies

We examined how asparagine-linked glycans within and adjacent to the V3 loop (C2 and C3 regions) and within the immunologically silent face (V4, C4, and V5 regions) of the human immunodeficiency virus (HIV) SF612 envelope affect the viral phenotype. Five of seven potential glycosylation sites are utilized when the virus is grown in human peripheral blood mononuclear cells, with the nonutilized sites lying within the V4 loop. Elimination of glycans within and adjacent to the V3 loop renders SF162 more susceptible to neutralization by polyclonal HIV(+)-positive and simian/human immunodeficiency virus-positive sera and by monoclonal antibodies (MAbs) recognizing the V3 loop, the CD4- and CCR5-binding sites, and the extracellular region of gp41. Importantly, our studies also indicate that glycans located within the immunologically silent face of gp120, specifically the C4 and V5 regions, also conferred on SF162 resistance to neutralization by anti-V3 loop, anti-CD4 binding site, and anti-gp41 MAbs but not by antibodies targeting the coreceptor binding site. We also observed that the amino acid composition of the V4 region contributes to the neutralization phenotype of SF162 by anti-V3 loop and anti-CD4 binding site MAbs. Collectively, our data support the proposal that the glycosylation and structure of the immunologically silent face of the HIV envelope plays an important role in defining the neutralization phenotype of HIV type 1.

Purification, characterization, and immunogenicity of a soluble trimeric envelope protein containing a partial deletion of the V2 loop derived from SF162, an R5-tropic human immunodeficiency virus type 1 isolate

The envelope (Env) glycoprotein of human immunodeficiency virus type 1 (HIV-1) is the major target of neutralizing antibody responses and is likely to be a critical component of an effective vaccine against AIDS. Although monomeric HIV envelope subunit vaccines (gp120) have induced high-titer antibody responses and neutralizing antibodies against laboratory-adapted HIV-1 strains, they have failed to induce neutralizing antibodies against diverse heterologous primary HIV isolates. Most probably, the reason for this failure is that the antigenic structure(s) of these previously used immunogens does not mimic that of the functional HIV envelope, which is a trimer, and thus these immunogens do not elicit high titers of relevant functional antibodies. We recently reported that an Env glycoprotein immunogen (o-gp140SF162DeltaV2) containing a partial deletion in the second variable loop (V2) derived from the R5-tropic HIV-1 isolate SF162, when used in a DNA priming-protein boosting vaccine regimen in rhesus macaques, induced neutralizing antibodies against heterologous subtype B primary isolates as well as protection to the vaccinated animals upon challenge with pathogenic SHIV(SF162P4) virus. Here we describe the purification of this protein to homogeneity, its characterization as trimer, and its ability to induce primary isolate-neutralizing responses in rhesus macaques. Optimal mutations in the primary and secondary protease cleavage sites of the env gene were identified that resulted in the stable secretion of a trimeric Env glycoprotein in mammalian cell cultures. We determined the molecular mass and hydrodynamic radius (R(h)) using a triple detector analysis (TDA) system. The molecular mass of the oligomer was found to be 324 kDa, close to the expected M(w) of a HIV envelope trimer protein (330 kDa), and the hydrodynamic radius was 7.27 nm. Negative staining electron microscopy of o-gp140SF162DeltaV2 showed that it is a trimer with considerable structural flexibility and supported the data obtained by TDA. The structural integrity of the purified trimeric protein was also confirmed by determinations of its ability to bind the HIV receptor, CD4, and its ability to bind a panel of well-characterized neutralizing monoclonal antibodies. No deleterious effect of V2 loop deletion was observed on the structure and conformation of the protein, and several critical neutralization epitopes were preserved and well exposed on the purified o-gp140SF162DeltaV2 protein. In an intranasal priming and intramuscular boosting regimen, this protein induced high titers of functional antibodies, which neutralized the vaccine strain, i.e., SF162. These results highlight a potential role for the trimeric o-gp140SF162DeltaV2 Env immunogen in a successful HIV vaccine.

The presence of the casein kinase II phosphorylation sites of Vpu enhances the CD4(+) T cell loss caused by the simian-human immunodeficiency virus SHIV(KU-lbMC33) in pig-tailed macaques

The simian-human immunodeficiency virus (SHIV)/ macaque model for human immunodeficiency virus type 1 has become a useful tool to assess the role of Vpu in lentivirus pathogenesis. In this report, we have mutated the two phosphorylated serine residues of the HIV-1 Vpu to glycine residues and have reconstructed a SHIV expressing this nonphosphorylated Vpu (SHIV(S52,56G)). Expression studies revealed that this protein was localized to the same intracellular compartment as wild-type Vpu. To determine if this virus was pathogenic, four pig-tailed macaques were inoculated with SHIV(S52,56G) and virus burdens and circulating CD4(+) T cells monitored up to 1 year. Our results indicate that SHIV(S52,56G) caused rapid loss in the circulating CD4(+) T cells within 3 weeks of inoculation in one macaque (CC8X), while the other three macaques developed no or gradual numbers of CD4(+) T cells and a wasting syndrome. Histological examination of tissues revealed that macaque CC8X had lesions in lymphoid tissues (spleen, lymph nodes, and thymus) that were typical for macaques inoculated with pathogenic parental SHIV(KU-1bMC33) and had no lesions within the CNS. To rule out that macaque CC8X had selected for a virus in which there was reversion of the glycine residues at positions 52 and 56 to serine residues and/or compensating mutations occurred in other genes associated with CD4 down-regulation, sequence analysis was performed on amplified vpu sequences isolated from PBMC and from several lymphoid tissues at necropsy. Sequence analysis revealed a reversion of the glycine residues back to serine residues in this macaque. The other macaques maintained low virus burdens, with one macaque (P003) developing a wasting syndrome between months 9 and 11. Histological examination of tissues from this macaque revealed a thymus with severe atrophy that was similar to that of a previously reported macaque inoculated with a SHIV lacking vpu (Virology 293, 2002, 252). Sequence analysis revealed no reversion of the glycine residues in the vpu sequences isolated from this macaque. These results contrast with those from four macaques inoculated with the parental pathogenic SHIV(KU-1bMC33), all of which developed severe CD4(+) T cell loss within 1 month after inoculation. Taken together, these results indicate that casein kinase II phosphorylation sites of Vpu contributes to the pathogenicity of the SHIV(KU-1bMC33) and suggest that the SHIV(KU-1bMC33)/pig-tailed macaque model will be useful in analyzing amino acids/domains of Vpu that contribute to the pathogenesis of HIV-1.

Cytolysis by CCR5-using human immunodeficiency virus type 1 envelope glycoproteins is dependent on membrane fusion and can be inhibited by high levels of CD4 expression

T-tropic (X4) and dualtropic (R5X4) human immunodeficiency virus type 1 (HIV-1) envelope glycoproteins kill primary and immortalized CD4(+) CXCR4(+) T cells by mechanisms involving membrane fusion. However, because much of HIV-1 infection in vivo is mediated by M-tropic (R5) viruses whose envelope glycoproteins use CCR5 as a coreceptor, we tested a panel of R5 and R5X4 envelope glycoproteins for their ability to lyse CCR5(+) target cells. As is the case for CXCR4(+) target cells, HIV-1 envelope glycoproteins expressed by single-round HIV-1 vectors killed transduced CD4(+) CCR5(+) cells in a membrane fusion-dependent manner. Furthermore, a CD4-independent R5 HIV-1 envelope glycoprotein was able to kill CD4-negative target cells expressing CCR5, demonstrating that CD4 is not intrinsically required for the induction of death. Interestingly, high levels of CD4 expression protected cells from lysis and syncytium formation mediated by the HIV-1 envelope glycoproteins. Immunoprecipitation experiments showed that high levels of CD4 coexpression inhibited proteolytic processing of the HIV-1 envelope glycoprotein precursor gp160. This inhibition could be overcome by decreasing the CD4 binding ability of gp120. Studies were also undertaken to investigate the ability of virion-bound HIV-1 envelope glycoproteins to kill primary CD4(+) T cells. However, neither X4 nor R5X4 envelope glycoproteins on noninfectious virions caused death in primary CD4(+) T cells. These results demonstrate that the interaction of CCR5 with R5 HIV-1 envelope glycoproteins capable of inducing membrane fusion leads to cell lysis; overexpression of CD4 can inhibit cell killing by limiting envelope glycoprotein processing.

Changes in the immunogenic properties of soluble gp140 human immunodeficiency virus envelope constructs upon partial deletion of the second hypervariable region

Immunization of macaques with the soluble oligomeric gp140 form of the SF162 envelope (SF162gp140) or with an SF162gp140-derived construct lacking the central region of the V2 loop (DeltaV2gp140) results in the generation of high titers of antibodies capable of neutralizing the homologous human immunodeficiency virus type 1 (HIV-1), SF162 virus (Barnett et al. J. Virol. 75:5526-5540, 2001). However, the DeltaV2gp140 immunogen is more effective than the SF162gp140 immunogen in eliciting the generation of antibodies capable of neutralizing heterologous HIV-1 isolates. This indicates that deletion of the V2 loop alters the immunogenicity of the SF162gp140 protein. The present studies were aimed at identifying the envelope regions whose immunogenicity is altered following V2 loop deletion. We report that the antibodies elicited by the SF162gp140 immunogen recognize elements of the V1, V2, and V3 loops, the CD4-binding site, and the C1 and C2 regions on the homologous SF162 gp120. With the exception of the V1 and V2 loops, the same regions are recognized on heterologous gp120 proteins. Surprisingly, although a minority of the SF162gp140-elicited antibodies target the V3 loop on the homologous gp120, the majority of the antibodies elicited by this immunogen that are capable of binding to the heterologous gp120s tested recognize their V3 loops. Deletion of the V2 loop has two effects. First, it alters the immunogenicity of the V3 and V1 loops, and second, it renders the C5 region immunogenic. Although deletion of the V2 loop does not result in an increase in the immunogenicity of the CD4-binding site per se, the relative ratio of anti-CD4-binding site to anti-V3 loop antibodies that bind to the heterologous gp120s tested is higher in sera collected from the DeltaV2gp140-immunized animals than in the SF162gp140-immunized animals. Overall, our studies indicate that it is possible to alter the immunogenic structure of the HIV envelope by introducing specific modifications.

Live attenuated, nef-deleted SIV is pathogenic in most adult macaques after prolonged observation

OBJECTIVE

A live attenuated SIV vaccine strain, termed SIVmac239Delta3 and containing large deletions in, and the negative regulatory element, was previously shown to cause AIDS mostly in monkeys vaccinated as infants. In the present study, we demonstrate that SIVmac239Delta3 is pathogenic in most vaccinated adult monkeys, given enough time.

METHODS

Eleven rhesus macaques vaccinated as adults with SIVmac239Delta3 were followed for extended periods (up to 6.8 years).

RESULTS

We found signs of immune dysregulation in all 11 adult vaccinees. All animals developed persistently inverted CD4 : CD8 T-cell ratios, seven (64%) had persistent recurrent viremia, and six (55%) had decreased CD4 T-cell counts (< 500 x 10 cells/l). Further signs included low CD4CD29 lymphocyte subsets, loss of anti-Gag antibodies, anemia, thrombocytopenia, wasting, and opportunistic infections. Two adult vaccinees (18%) subsequently developed AIDS. Development of chronic, recurrent viremia with plasma viral RNA loads > or = 10 copies/ml and cytoviremia was a poor prognostic sign.

CONCLUSION

Our data demonstrate that with time, a live attenuated, multiply deleted SIV vaccine can cause immune dysregulation in most vaccine recipients, even in initially immune competent, healthy adults. Immune dysfunction can progress to full AIDS. However, pathogenic effects became evident only several years after vaccination. Thus, mass vaccination of humans with similarly constructed live attenuated HIV vaccines, recently suggested for countries with high HIV-1 transmission rates, seems contraindicated.

Equine infectious anemia virus envelope evolution in vivo during persistent infection progressively increases resistance to in vitro serum antibody neutralization as a dominant phenotype

Equine infectious anemia virus (EIAV) infection of horses is characterized by well-defined waves of viremia associated with the sequential evolution of distinct viral populations displaying extensive envelope gp90 variation; however, a correlation of in vivo envelope evolution with in vitro serum neutralization phenotype remains undefined. Therefore, the goal of the present study was to utilize a previously defined panel of natural variant EIAV envelope isolates from sequential febrile episodes to characterize the effects of envelope variation during persistent infection on viral neutralization phenotypes and to define the determinants of EIAV envelope neutralization specificity. To assess the neutralization phenotypes of the sequential EIAV envelope variants, we determined the sensitivity of five variant envelopes to neutralization by a longitudinal panel of immune serum from the source infected pony. The results indicated that the evolution of the EIAV envelope sequences observed during sequential febrile episodes produced an increasingly neutralization-resistant phenotype. To further define the envelope determinants of EIAV neutralization specificity, we examined the neutralization properties of a panel of chimeric envelope constructs derived from reciprocal envelope domain exchanges between selected neutralization-sensitive and neutralization-resistant envelope variants. These results indicated that the EIAV gp90 V3 and V4 domains individually conferred serum neutralization resistance while other envelope segments in addition to V3 and V4 were evidently required for conferring total serum neutralization sensitivity. These data clearly demonstrate for the first time the influence of sequential gp90 variation during persistent infection in increasing envelope neutralization resistance, identify the gp90 V3 and V4 domains as the principal determinants of antibody neutralization resistance, and indicate distinct complex cooperative envelope domain interactions in defining sensitivity to serum antibody neutralization.

Molecular evolution of human immunodeficiency virus env in humans and monkeys: similar patterns occur during natural disease progression or rapid virus passage

Neonatal rhesus macaque 95-3 was inoculated with nonpassaged simian-human immunodeficiency virus strain SHIV-vpu(+), which encodes env of the laboratory-adapted human immunodeficiency virus (HIV) strain IIIB and is considered nonpathogenic. CD4(+) T-cell counts dropped to <200 cells/microl within 4.6 years, and monkey 95-3 died with opportunistic infections 5.9 years postinoculation. Transfer of blood from 95-3 to two naive adult macaques resulted in high peak viral loads and rapid, persistent T-cell depletion. Progeny virus evolved in 95-3 despite high SHIV-vpu(+) neutralizing antibody titers and still used CXCR4 but, in contrast to parental SHIV-vpu(+), productively infected macrophages and resisted neutralization. Sequence analysis revealed three new potential glycosylation sites in gp120; another two were lost. Strikingly similar mutations were detected in a laboratory worker who progressed to AIDS after accidental HIV-IIIB infection (T. Beaumont et al., J. Virol. 75:2246-2252, 2001), thus supporting the SHIV-vpu(+)/rhesus macaque system as a relevant model. Similar mutations were also described after rapid passage of chimeric viruses encoding IIIB env in rhesus and pig-tailed macaques (M. Cayabyab et al., J. Virol. 73:976-984, 1999; Z. Q. Liu et al., Virology 260:295-307, 1999; S. V. Narayan et al., Virology 256:54-63, 1999; R. Raghavan et al., Brain Pathol. 7:851-861, 1997; E. B. Stephens et al., Virology 231:313-321, 1997). Thus, HIV-IIIB env evolved similarly in three different species; this selection occurred in chronically infected individuals during disease progression as well as after rapid virus passage. We postulate that evolutionary pressure led to the outgrowth of more aggressive viral variants in all three species.

Pathogenic and nef-interrupted simian-human immunodeficiency viruses traffic to the macaque CNS and cause astrocytosis early after inoculation

Several studies have shown that deletion of the nef gene of simian immunodeficiency virus (SIV) and simian-human immunodeficiency virus (SHIV) results in attenuated viruses. However, studies have not critically examined trafficking of attenuated viruses to the central nervous system (CNS) at early stages after inoculation. In this study, we investigated the colocalization of pathogenic and vpu-negative, nef-interrupted SHIVs at early stages following inoculation. The first virus, designated SHIV(50OLNV), was isolated from the lymph node of a pig-tailed macaque which developed severe CD4+ T cell loss and neurological disease. The second virus was a molecularly cloned virus in which the vpu gene was deleted and the gene for the enhanced green fluorescent protein from the jellyfish Aequoria victora had been inserted in-frame within the nef gene of the pathogenic SHIV(KU-1bMC33) (designated SHIV(KU-1bEGFP)). Three pig-tailed macaques were inoculated intravenously with equivalent amounts of two viruses, two macaques were inoculated with SHIV(KU-1bEGFP), and two macaques were inoculated with SHIV(50OLNV). The peripheral blood mononuclear cells (PBMCs) were isolated from bleeds obtained 3, 7, 10, and 14 days postinoculation and monitored for syncytia-inducing virus and for fluorescent cells. Virus was detected in the PBMCs as early as 3 days postinoculation and was present throughout the course of this short-term study. At 14 days postinoculation, the macaques were sacrificed and examined for virus in lymphoid tissues and different regions of the CNS following necropsy. Our results revealed the presence of both viruses in lymphoid and CNS tissues, although SHIV(50OLNV) was present to a much greater extent. Histological examination revealed that one macaque displayed signs of meningitis and all three macaques developed massive cortical astrocyte activation as demonstrated by immunostaining for glial fibrillary acidic protein, but only limited microglial activation. In the two macaques inoculated with SHIV(50OLNV), astrocyte activation similar to that in the macaques inoculated with both viruses was observed while no astrocyte activation was observed in macaques inoculated with SHIV(KU-1bEGFP). Thus, this study demonstrates that SHIVs with an intact nef(SHIV(50OLNV)) as well as those lacking a vpu gene and with a nonfunctional nef gene (SHIV(KU-1bEGFP)) are capable of invading the CNS and that pathogenic SHIVs are capable of causing reactive astrocytosis early after inoculation.

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

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

Deletion of the vpu sequences prior to the env in a simian-human immunodeficiency virus results in enhanced Env precursor synthesis but is less pathogenic for pig-tailed macaques

The Vpu protein of human immunodeficiency virus type 1 (HIV-1) has been reported to enhance virion release from infected cells and to down-regulate the expression of CD4 on infected cells. Previous studies have shown that Vpu and the envelope glycoprotein precursor (gp160) are translated from different reading frames of the same bicistronic messenger RNA (mRNA). In order to assess the effect of the Vpu sequences 5' to the Env open reading frame on Env biosynthesis and pathogenesis, we have constructed a deletion mutant of a molecularly cloned chimeric simian--human immunodeficiency virus (SHIV(KU-1bMC33)) in which the entire coding region of vpu upstream of env had been deleted (novpuSHIV(KU-1bMC33)). While both SHIV(KU-1bMC33) and novpuSHIV(KU-1bMC33) synthesized comparable amounts of env mRNA in infected cells, the novpuSHIV(KU-1bMC33)-infected cells synthesized more Env precursor when standardized against the p57 Gag precursor protein. While more Env was synthesized than Gag in novpuSHIV(KU-1bMC33)-infected cells, pulse--chase analysis revealed that p27 Gag protein was released from infected cells with delayed kinetics, a reflection of the lack of a Vpu protein. Inoculation of novpuSHIV(KU-1bMC33) into two pig-tailed macaques resulted in no loss of circulating CD4(+) T cells. However, replicating virus could be detected in the lymphoid tissues (lymph nodes, spleen, thymus) 1 year after inoculation and the thymus of one of the macaques exhibited severe atrophy. The results of these studies indicate that the Vpu coding sequences upstream of Env may attenuate the level of Env precursor biosynthesis but significantly contribute to the pathogenesis of this SHIV in pig-tailed macaques.

A simian human immunodeficiency virus with a nonfunctional Vpu (deltavpuSHIV(KU-1bMC33)) isolated from a macaque with neuroAIDS has selected for mutations in env and nef that contributed to its pathogenic phenotype

Previous studies have shown that passage of nonpathogenic SHIV-4 through a series of macaques results in the selection of variants of the virus that are capable of causing rapid subtotal loss of CD4(+) T cells and AIDS within 6-8 months following inoculation into pig-tailed macaques. Using a pathogenic variant of SHIV-4 known as SHIV(KU-1bMC33), we reported that a mutant of this virus with the majority of the vpu deleted was still capable of causing profound CD4(+) T cell loss and neuroAIDS in pig-tailed macaques (McCormick-Davis et al., 2000, Virology 272, 112-116). In this study, we have analyzed the tissue-specific changes in the env and nef in one macaque that developed neuroAIDS (macaque 50 O) and in three macaques that developed only a moderate or no significant loss of CD4(+) T cells and no neurological disease (macaques 50 Y, 20220, 20228) following inoculation with DeltavpuSHIV(KU-1bMC33). Sequence analysis of the gp120 region of env isolated from lymphoid tissues (lymph node and spleen) of macaques 50 Y, 20220, and 20228 revealed no consensus amino acid substitutions. In contrast, analysis of the gp120 sequences isolated from lymphoid and CNS tissues (parietal cortex, basal ganglia, and pons) of macaque 50 O revealed numerous amino acid substitutions. The significance of the amino acid substitutions in gp120 was supported by neutralization assays which showed that the virus isolated from the lymph node of macaque 50 O was neutralization resistant compared to the parental SHIV(KU-1bMC33). Analysis of changes in the nef gene from macaque 50 O revealed in-frame deletions in Nef that ranged from 4 to 13 amino acids in length, whereas the nef genes isolated from the other three macaques revealed no deletions or consensus amino acid substitutions. Inoculation of the virus isolated from the lymph node of the macaque which developed neuroAIDS, SHIV(50OLNV), into four pig-tailed macaques resulted in a severe loss of the circulating CD4(+) T cells within 2 weeks postinoculation, which was maintained for up to 20 weeks postinoculation, confirming that this virus had indeed become more pathogenic in pig-tailed macaques. Taken together, these observations suggest that DeltavpuSHIV(KU-1bMC33) has a low pathogenic phenotype in macaques but that individual pig-tailed macaques can select for additional mutations within the Env and Nef which can compensate for the lack of an intact Vpu and ultimately increase its pathogenicity.

Characterization of immune escape viruses from a macaque immunized with live-virus vaccine and challenged with pathogenic SHIVKU-1

We characterized two immune escape viruses (SHIV(KU-1/105w52) and SHIV(KU-1/105w98)) from a macaque immunized with DeltavpuDeltanef SHIV-4 and challenged with pathogenic SHIV(KU-1). This macaque developed neutralizing antibodies as well as virus-specific CTLs against the challenge virus. However, the two new viruses could not be neutralized by anti-SHIV(KU-1)-specific neutralizing antibodies and were poorly recognized by challenge virus-specific CTLs. Sequence analysis of the gene encoding gp120 revealed several mutations in the protein that might have contributed to the development of the immune-escape viruses.

V2 loop glycosylation of the human immunodeficiency virus type 1 SF162 envelope facilitates interaction of this protein with CD4 and CCR5 receptors and protects the virus from neutralization by anti-V3 loop and anti-CD4 binding site antibodies

We examined the role of asparagine-linked glycosylation of the V2 loop of the human immunodeficiency virus (HIV) SF162 envelope on viral replication potential and neutralization susceptibility. We report that the asparagines located at the amino- and carboxy-terminal sites (at positions 154 and 195, respectively), as well as within the V2 loop of the SF162 envelope (at position 186), are glycosylated during in vitro replication of this virus in human peripheral blood mononuclear cells. Our studies indicate that glycosylation of the V2 loop, in particular at its base, facilitates the interaction of the HIV envelope with the CD4 and CCR5 receptor molecules present on the surface of target cells and affects viral replication kinetics in a cell type-dependent manner. In cells expressing high numbers of receptor molecules on their surfaces, the SF162-derived V2 loop-deglycosylated mutant viruses replicate as efficiently as the parental SF162 virus, while in cells expressing small numbers of receptor molecules, the mutant viruses replicate with markedly reduced efficiency. In addition to expanding the viral tropism, V2 loop glycosylation at the three sites examined prevents neutralization by anti-CD4 binding site antibodies. In contrast, glycosylation at the amino- and carboxy-terminal sites of the V2 loop but not within the loop itself offers protection against anti-V3 loop antibodies. Thus, the epitopes masked by the sugar molecules present on the three glycosylation sites examined are not identical but overlap.

A molecular clone of simian-human immunodeficiency virus (DeltavpuSHIV(KU-1bMC33)) with a truncated, non-membrane-bound vpu results in rapid CD4(+) T cell loss and neuro-AIDS in pig-tailed macaques

We report on the role of vpu in the pathogenesis of a molecularly cloned simian-human immunodeficiency virus (SHIV(KU-1bMC33)), in which the tat, rev, vpu, env, and nef genes derived from the uncloned SHIV(KU-1b) virus were inserted into the genetic background of parental nonpathogenic SHIV-4. A mutant was constructed (DeltavpuSHIV(KU-1bMC33)) in which 42 of 82 amino acids of Vpu were deleted. Phase partitioning studies revealed that the truncated Vpu was not an integral membrane protein, and pulse-chase culture studies revealed that cells inoculated with DeltavpuSHIV(KU-1bMC33) released viral p27 into the culture medium with slightly reduced kinetics compared with cultures inoculated with SHIV(KU-1bMC33). Inoculation of DeltavpuSHIV(KU-1bMC33) into two pig-tailed macaques resulted in a severe decline of CD4(+) T cells and neurological disease in one macaque and a more moderate decline of CD4(+) T cells in the other macaque. These results indicate that a membrane-bound Vpu is not required for the CD4(+) T cell loss and neurological disease in SHIV-inoculated pig-tailed macaques. Furthermore, because the amino acid substitutions in the Tat and Rev were identical to those previously reported for the nonpathogenic SHIV(PPc), our results indicate that amino acid substitutions in the Env and/or Nef were responsible for the observed CD4(+) T cell loss and neurological disease after inoculation with this molecular clone.