Simian immunodeficiency virus from African green monkeys

Infection of rhesus macaques with a pool of simian immunodeficiency virus with the envelope genes from acute HIV-1 infections

Background

New simian–human immunodeficiency chimeric viruses with an HIV-1 env (SHIVenv) are critical for studies on HIV pathogenesis, vaccine development, and microbicide testing. Macaques are typically exposed to single CCR5-using SHIVenv which in most instances does not reflect the conditions during acute/early HIV infection (AHI) in humans. Instead of individual and serial testing new SHIV constructs, a pool of SHIVenv_B derived from 16 acute HIV-1 infections were constructed using a novel yeast-based SHIV cloning approach and then used to infect macaques.

Results

Even though none of the 16 SHIVenvs contained the recently reported mutations in env genes that could significantly enhance their binding affinity to RhCD4, one SHIVenv (i.e. SHIVenv_B3-PRB926) established infection in macaques exposed to this pool. AHI SHIVenv_B viruses as well as their HIVenv_B counterparts were analyzed for viral protein content, function, and fitness to identify possible difference between SHIVenv_B3-PRB926 and the other 15 SHIVenvs in the pool. All of the constructs produced SHIV or HIV chimeric with wild type levels of capsid (p27 and p24) content, reverse transcriptase (RT) activity, and expressed envelope glycoproteins that could bind to cell receptors CD4/CCR5 and mediate virus entry. HIV-1env_B chimeric viruses were propagated in susceptible cell lines but the 16 SHIVenv_B variants showed only limited replication in macaque peripheral blood mononuclear cells (PBMCs) and 174×CEM.CCR5 cell line. AHI chimeric viruses including HIVenv_B3 showed only minor variations in cell entry efficiency and kinetics as well as replicative fitness in human PBMCs. Reduced number of N-link glycosylation sites and slightly greater CCR5 affinity/avidity was the only distinguishing feature of env_B3 versus other AHI env’s in the pool, a feature also observed in the HIV establishing new infections in humans.

Conclusion

Despite the inability to propagate in primary cells and cell lines, a pool of 16 SHIVenv viruses could establish infection but only one virus, SHIVenv_B3 was isolated in the macaque and then shown to repeatedly infected macaques. This SHIVenv_B3 virus did not show any distinct phenotypic property from the other 15 SHIVenv viruses but did have the fewest N-linked glycosylation sites.

Electronic supplementary material

The online version of this article (doi:10.1186/s12981-016-0125-8) contains supplementary material, which is available to authorized users.

HIV latency. Proliferation of cells with HIV integrated into cancer genes contributes to persistent infection

Antiretroviral treatment (ART) of HIV infection suppresses viral replication. Yet if ART is stopped, virus reemerges because of the persistence of infected cells. We evaluated the contribution of infected-cell proliferation and sites of proviral integration to HIV persistence. A total of 534 HIV integration sites (IS) and 63 adjacent HIV env sequences were derived from three study participants over 11.3 to 12.7 years of ART. Each participant had identical viral sequences integrated at the same position in multiple cells, demonstrating infected-cell proliferation. Integrations were overrepresented in genes associated with cancer and favored in 12 genes across multiple participants. Over time on ART, a greater proportion of persisting proviruses were in proliferating cells. HIV integration into specific genes may promote proliferation of HIV-infected cells, slowing viral decay during ART.

Interactions with DCAF1 and DDB1 in the CRL4 E3 ubiquitin ligase are required for Vpr-mediated G2 arrest

Background

HIV-1 Vpr-mediated G₂ cell cycle arrest is dependent on the interaction of Vpr with an E3 ubiquitin ligase that contains damage-specific DNA binding protein 1 (DDB1), Cullin 4A (Cul4A), DDB1 and Cul4-associated factor 1 (DCAF1), and Rbx1. Vpr is thought to associate directly with DCAF1 in the E3 ubiquitin ligase complex although the exact interaction pattern of the proteins in the complex is not completely defined. The Vpr of SIV_agm induces G₂ arrest of cognate African Green Monkey (AGM) cells but not human cells. The molecular mechanism by which SIV_agm Vpr exhibits its species-specific function remained unknown.

Methods

Physical interaction of proteins in the E3 ubiquitin ligase complex was assessed by co-immunoprecipitation followed by western blotting. In addition, co-localization of the proteins in cells was investigated by confocal microscopy. The cell cycle was analyzed by propidium iodide staining and flow cytometry. DNA damage response elicited by Vpr was evaluated by detecting phosphorylation of H2AX, a marker for DNA damage response.

Results

We show that RNAi knock-down of DCAF1 prevented the co-immunoprecipitation of DDB1 with HIV-1 Vpr while DDB1 knock-down did not influence the binding of Vpr to DCAF1. HIV-1 Vpr mutants with a L64P or a R90K mutation maintained the ability to associate with DCAF1 but did not appear to be in a complex with DDB1. SIV_agm Vpr associated with AGM DCAF1 and DDB1 while, in human cells, it binds to human DCAF1 but hardly binds to human DDB1, resulting in the reduced activation of H2AX.

Conclusions

The identification of Vpr mutants which associate with DCAF1 but only poorly with DDB1 suggests that DCAF1 is necessary but the simple binding of Vpr to DCAF1 is not sufficient for the Vpr association with DDB1-containing E3 ligase complex. Vpr may interact both with DCAF1 and DDB1 in the E3 ligase complex. Alternatively, the interaction of Vpr and DCAF1 may induce a conformational change in DCAF1 or Vpr that promotes the interaction with DDB1. The ability of SIV_agm Vpr to associate with DDB1, but not DCAF1, can explain the species-specificity of SIV_agm Vpr-mediated G₂ arrest.

The D-amino acid peptide D3 reduces amyloid fibril boosted HIV-1 infectivity

Background

Amyloid fibrils such as Semen-Derived Enhancer of Viral Infection (SEVI) or amyloid-β-peptide (Aβ) enhance HIV-1 attachment and entry. Inhibitors destroying or converting those fibrils into non-amyloidogenic aggregates effectively reduce viral infectivity. Thus, they seem to be suitable as therapeutic drugs expanding the current HIV-intervening repertoire of antiretroviral compounds.

Findings

In this study, we demonstrate that the small D-amino acid peptide D3, which was investigated for therapeutic studies on Alzheimer’s disease (AD), significantly reduces both SEVI and Aβ fibril boosted infectivity of HIV-1.

Conclusions

Since amyloids could play an important role in the progression of AIDS dementia complex (ADC), the treatment of HIV-1 infected individuals with D3, that inhibits Aβ fibril formation and converts preformed Aβ fibrils into non-amyloidogenic and non-fibrillar aggregates, may reduce the vulnerability of the central nervous system of HIV patients for HIV associated neurological disorders.

Full-length genome characterization of a novel simian immunodeficiency virus lineage (SIVolc) from olive Colobus (Procolobus verus) and new SIVwrcPbb strains from Western Red Colobus (Piliocolobus badius badius) from the Tai Forest in Ivory Coast

Simian immunodeficiency viruses (SIVs) are found in an extensive number of African primates and humans continue to be exposed to these viruses by hunting and handling of primate bushmeat. Full-length genome sequences were obtained from SIVs derived from two Colobinae species inhabiting the Taï forest, Ivory Coast, each belonging to a different genus: SIVwrc from western red colobus (Piliocolobus badius badius) (SIVwrcPbb-98CI04 and SIVwrcPbb-97CI14) and SIVolc (SIVolc-97CI12) from olive colobus (Procolobus verus). Phylogenetic analysis showed that western red colobus are the natural hosts of SIVwrc, and SIVolc is also a distinct species-specific lineage, although distantly related to the SIVwrc lineage across the entire length of its genome. Overall, both SIVwrc and SIVolc, are also distantly related to the SIVlho/sun lineage across the whole genome. Similar to the group of SIVs (SIVsyk, SIVdeb, SIVden, SIVgsn, SIVmus, and SIVmon) infecting members of the Cercopithecus genus, SIVs derived from western red and olive colobus, L'Hoest and suntailed monkeys, and SIVmnd-1 from mandrills form a second group of viruses that cluster consistently together in phylogenetic trees. Interestingly, the divergent SIVcol lineage, from mantled guerezas (Colobus guereza) in Cameroon, is also closely related to SIVwrc, SIVolc, and the SIVlho/sun lineage in the 5' part of Pol. Overall, these results suggest an ancestral link between these different lentiviruses and highlight once more the complexity of the natural history and evolution of primate lentiviruses.

Species barrier of HIV-1 and its jumping by virus engineering

Monkey infection models are absolutely necessary for studies of human immunodeficiency virus type 1 (HIV-1) pathogenesis and of developing drugs/vaccines against HIV-1. In addition, currently unknown roles of its accessory proteins for in vivo replication await elucidation by experimental approaches. Due to the fact that HIV-1 is tropic only for chimpanzees and humans, studies of this line have been impeded for a long time, although various investigations have been carried out utilising genetically related SIV and SIV/HIV chimeric virus (SHIV) as pathogens. Recent findings of anti-HIV-1 innate factors such as tripartite motif protein 5alpha (TRIM5alpha) and APOBEC3G/F prompted us to re-initiate an old and vital research project which would, as a result, confer the capability to overcome the species barrier on the HIV-1. We currently have obtained, by virus engineering through genetic manipulation and adaptation, some new and promising HIV-1 clones for in vivo studies in macaque monkeys as mentioned above. In this review, we summarise the past, present and future of HIV-1/SIV chimeric viruses with special reference to relevant basic HIV-1/SIV studies.

Going wild: lessons from naturally occurring T-lymphotropic lentiviruses

Over 40 nonhuman primate (NHP) species harbor species-specific simian immunodeficiency viruses (SIVs). Similarly, more than 20 species of nondomestic felids and African hyenids demonstrate seroreactivity against feline immunodeficiency virus (FIV) antigens. While it has been challenging to study the biological implications of nonfatal infections in natural populations, epidemiologic and clinical studies performed thus far have only rarely detected increased morbidity or impaired fecundity/survival of naturally infected SIV- or FIV-seropositive versus -seronegative animals. Cross-species transmissions of these agents are rare in nature but have been used to develop experimental systems to evaluate mechanisms of pathogenicity and to develop animal models of HIV/AIDS. Given that felids and primates are substantially evolutionarily removed yet demonstrate the same pattern of apparently nonpathogenic lentiviral infections, comparison of the biological behaviors of these viruses can yield important implications for host-lentiviral adaptation which are relevant to human HIV/AIDS infection. This review therefore evaluates similarities in epidemiology, lentiviral genotyping, pathogenicity, host immune responses, and cross-species transmission of FIVs and factors associated with the establishment of lentiviral infections in new species. This comparison of consistent patterns in lentivirus biology will expose new directions for scientific inquiry for understanding the basis for virulence versus avirulence.

Inhibition of CCR5-mediated infection by diverse R5 and R5X4 HIV and SIV isolates using novel small molecule inhibitors of CCR5: effects of viral diversity, target cell and receptor density

Highly active anti-retroviral therapy (HAART) has been very effective in reducing viral loads in human immunodeficiency virus (HIV)-1 patients. However, current therapies carry detrimental side effects, require complex drug regimes and are threatened by the emergence of drug-resistant variants. There is an urgent need for new anti-HIV drugs that target different stages of the replication cycle. Several synthetic small organic molecules that inhibit HIV infection by binding to the CCR5 coreceptor without causing cell activation have already been reported. Here, we have exploited a series of CCR5 antagonists to investigate their effects on diverse HIV and the simian counterpart (SIV) isolates for infection of a variety of cell types via different concentrations of cell surface CCR5. These inhibitors show no cross-reactivity against alternative HIV coreceptors including CCR3, CCR8, GPR1, APJ, CXCR4 and CXCR6. They are able to inhibit a diverse range of R5 and R5X4 HIV-1 isolates as well as HIV-2 and SIV strains. Inhibition was observed in cell lines as well as primary PBMCs and macrophages. The extent of inhibition was dependent on cell type and on cell surface CCR5 concentration. Our results underscore the potential of CCR5 inhibitors for clinical development.

Simultaneous detection of multiple cytokines and chemokines from nonhuman primates using luminex technology

Cytokines and chemokines are soluble mediators of the immune system that play a crucial role in intercellular signaling, and in the recruitment of cells to inflammation sites. Identification of these molecules in nonhuman primates (NHP) is crucial for the understanding of complex physiological and pathological mechanisms that occur in these species, and to demonstrate whether these mechanisms function similarly in humans. The Luminex100 system is a bench-top flow cytometer that allows the user to perform up to 100 tests simultaneously in a single tube. Recently, a significant number of commercial vendors have developed kits for the simultaneous detection of multiple cytokines and chemokines of human origin with the Luminex system. These kits were tested for their capacity to recognize chemokines and cytokines of nonhuman primate origin. ELISA and ELISPOT assays were also adapted to the Luminex format, and novel assays based on new combinations of antibodies were developed. PBMC were isolated from blood from chimpanzees, rhesus macaques, baboons, cynomolgus macaques, pig-tailed macaques, and African green monkeys; these cells were stimulated in vitro and culture supernatants were used for the determination of cytokines and chemokines. Crossreactivity tables were prepared based on the ability of the reagents to detect cytokines and chemokines in NHP samples with similar intensity to the ones observed in human samples. By mixing commercially available reagents and newly developed ones, a combination has been created that allows for the detection of 20 NHP chemokines and cytokines in a single sample, including G-CSF, GM-CSF, IFN-gamma, IL-1beta, IL-1Ra, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12 (p40), IL-17, IL-18, MCP-1, MIP-1alpha, MIP-1beta, RANTES, TNF-alpha, and TNF-beta. These reagents may become a very useful resource for scientists working with these NHP species, which are relevant pre-clinical models for human diseases and transplantation because they approximate humans in physiology and genetics more closely than any other animal.

Down-regulation of SHP1 and up-regulation of negative regulators of JAK/STAT signaling in HTLV-1 transformed cell lines and freshly transformed human peripheral blood CD4+ T-cells

Adult T-cell leukemia (ATL) is an aggressive malignancy that is associated with human T-cell lymphotropic virus I (HTLV-I) infection. HTLV-I transformed T-cell lines and fresh ATL cells are characterized by constitutive activation of the interleukin-2 receptor (IL-2R) signaling pathway however, the mechanism(s) responsible for constitutive IL-2R activation are unknown. To further examine the cause of this signaling pathway deregulation, we measured mRNA and protein expression levels by real-time PCR and Western blots, respectively, of four negative regulators of the IL-2R signaling pathway including src homology 2 (SH2)-containing phosphatase (SHP1), cytokine-inducible (CIS) SH2-containing protein, suppressor of cytokine signaling-1 (SOCS1) and protein inhibitor of activated signal transducer and activator of transcription 3 (STAT3) (PIAS3) in six HTLV-1 negative and seven HTLV-1 positive T-cell leukemia lines. The activation status of the JAK/STAT pathway was also examined. SHP1 mRNA and protein expression levels were selectively down regulated in all HTLV-1-infected transformed cell lines, while CIS, SOCS1, and PIAS3 protein expression were markedly but variably upregulated and the cells showed evidence of constitutive STAT3 activation. In acutely HTLV-1 infected primary CD4+ T-cells there was a gradual loss of SHP1 expression over 10 weeks in culture which correlated with progression from immortalization to transformation and loss of IL-2 dependence for growth. Two transformed cell lines that were established following HTLV-1 infection showed loss of SHP1 expression and overexpression of CIS, SOCS1, PIAS3. However, this overexpression was not adequate to block constitutive activation of the JAK/STAT pathway. Thus, multiple levels of IL-2 receptor signal deregulation are found in HTLV-1 transformed cells, which may be a result of early loss of SHP1 expression.

Specific nature of cellular immune responses elicited by chimpanzees against HIV-1

Recent epidemiologic and phylogenetic analyses suggest that in the human population human immunodeficiency virus (HIV-1) is a relatively new pathogen that arose by zoonotic transmission from chimpanzees. In humans the morbidity and mortality figures due to HIV infection are extremely high. In a very small percentage of the human population, however, individuals have been identified who were infected for more than 20 years and have no evidence of disease progression. In contrast to most infected humans, almost all chimpanzees appear to be resistant to the pathologic effects caused by lentiviruses such as HIV-1. Here we review the characteristics of the HIV-1-specific cell-mediated immune responses mounted by chimpanzees, and we postulate the mechanisms that have evolved that facilitate their resistance to acquired immunodeficiency syndrome.

Identification of a subset of human immunodeficiency virus type 1 (HIV-1), HIV-2, and simian immunodeficiency virus strains able to exploit an alternative coreceptor on untransformed human brain and lymphoid cells

The chemokine receptors CCR5 and CXCR4 are the major coreceptors for human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV). At least 12 other chemokine receptors or close relatives support infection by particular HIV and SIV strains on CD4(+) transformed indicator cell lines in vitro. However, the role of these alternative coreceptors in vivo is presently thought to be insignificant. Infection of cell lines expressing high levels of recombinant CD4 and coreceptors thus does not provide a true indication of coreceptor use in vivo. We therefore tested primary untransformed cell cultures that lack CCR5 and CXCR4, including astrocytes and brain microvascular endothelial cells (BMVECs), for naturally expressed alternative coreceptors functional for HIV and SIV infection. An adenovirus vector (Ad-CD4) was used to express CD4 in CD4(-) astrocytes and thus confer efficient infection if a functional coreceptor is present. Using a large panel of viruses with well-defined coreceptor usage, we identified a subset of HIV and SIV strains able to infect two astrocyte cultures derived from adult brain tissue. Astrocyte infection was partially inhibited by several chemokines, indicating a role for the chemokine receptor family in the observed infection. BMVECs were weakly positive for CD4 but negative for CCR5 and CXCR4 and were susceptible to infection by the same subset of isolates that infected astrocytes. BMVEC infection was efficiently inhibited by the chemokine vMIP-I, implicating one of its receptors as an alternative coreceptor for HIV and SIV infection. Furthermore, we tested whether the HIV type 1 and type 2 strains identified were able to infect peripheral blood mononuclear cells (PBMCs) via an alternative coreceptor. Several strains replicated in Delta32/Delta32 CCR5 PBMCs with CXCR4 blocked by AMD3100. This AMD3100-resistant replication was also sensitive to vMIP-I inhibition. The nature and potential role of this alternative coreceptor(s) in HIV infection in vivo is discussed.

Characterization and comparison of recombinant simian immunodeficiency virus from drill (Mandrillus leucophaeus) and mandrill (Mandrillus sphinx) isolates

Since simian immunodeficiency virus (SIV) was found to be the source of the human AIDS pandemic, a major goal has been to characterize the diversity of SIV strains in the wild and to assess their potential for crossover into humans. In the present study, SIV was isolated from a seropositive drill (Mandrillus leucophaeus) and three seropositive mandrills (Mandrillus sphinx) by using macaque peripheral blood mononuclear cells (PBMC). Full-length sequences were obtained from a drill and mandrill and designated SIVdrl1FAO and SIVmnd5440, respectively. A 182-bp fragment of the pol genes of the two remaining mandrill SIV isolates was also analyzed. Phylogenetic analyses demonstrated that SIVdrl1FAO formed a monophyletic clade with SIVmnd5440 and SIVmndM14, recently designated SIVmnd type 2. Both the SIVdrl and SIVmnd type 2 genomes carried a vpx gene and appeared to share a common ancestor with SIVrcm in the 5' region of the genome and with SIVmndGB1 (type 1) in the 3' region of the genome. A statistically significant recombination breakpoint was detected at the beginning of envelope, suggesting that the viruses were descendents of the same recombinant. Phylogenetic analysis of vpx and vpr genes demonstrated that the vpx genes formed a monophyletic cluster that grouped with vpr from SIVagm. In addition, both SIVdrl1FAO and SIVmnd5440 replicated in human PBMC and therefore could pose a risk of transmission to the human population.

Characterization of novel simian immunodeficiency viruses from red-capped mangabeys from Nigeria (SIVrcmNG409 and -NG411)

Two novel simian immunodeficiency virus (SIV) strains from wild-caught red-capped mangabeys (Cercocebus torquatus torquatus) from Nigeria were characterized. Sequence analysis of the fully sequenced SIV strain rcmNG411 (SIVrcmNG411) and gag and pol sequence of SIVrcmNG409 revealed that they were genetically most closely related to the recently characterized SIVrcm from Gabon (SIVrcmGB1). Thus, red-capped mangabeys from distant geographic locations harbor a common lineage of SIV. SIVrcmNG411 carried a vpx gene in addition to vpr, suggesting a common evolutionary ancestor with SIVsm (from sooty mangabeys). However, SIVrcm was only marginally closer to SIVsm in that region than to any of the other lentiviruses. SIVrcm showed the highest similarity in pol with SIVdrl, isolated from a drill, a primate that is phylogenetically distinct from mangabey monkeys, and clustered with other primate lentiviruses (primarily SIVcpz [from chimpanzees] and SIVagmSab [from African green monkeys]) discordantly in different regions of the genome, suggesting a history of recombination. Despite the genetic relationship to SIVcpz in the pol gene, SIVrcmNG411 did not replicate in chimpanzee peripheral blood mononuclear cells (PBMC), although two other viruses unrelated to SIVcpz, SIVmndGB1 (from mandrills) and SIVlhoest (from L'Hoest monkeys), were able to grow in chimpanzee PBMC. The CCR5 24-bp deletion previously described in red-capped mangabeys from Gabon was also observed in Nigerian red-capped mangabeys, and SIVrcmNG411, like SIVrcmGB1, used CCR2B and STRL33 as coreceptors for virus entry. SIVrcm, SIVsm, SIVmndGB1, and all four SIVlhoest isolates but not SIVsun (from sun-tailed monkeys) replicated efficiently in human PBMC, suggesting that the ability to infect the human host can vary within one lineage.

Mutations within the putative membrane-spanning domain of the simian immunodeficiency virus transmembrane glycoprotein define the minimal requirements for fusion, incorporation, and infectivity

The membrane-spanning domain (MSD) of a number of retroviral transmembrane (TM) glycoproteins, including those from the human and simian immunodeficiency viruses (HIV and SIV), have been predicted to contain a charged arginine residue. The wild-type SIV TM glycoprotein is 354 amino acids long. The entire putative cytoplasmic domain of SIV (amino acids 193 to 354) is dispensable for virus replication in vitro, and such truncation-containing viruses are capable of reaching wild-type titers after a short delay. We show here that further truncation of eight additional amino acids to TM185 results in a protein that lacks fusogenicity but is, nevertheless, efficiently incorporated into budding virions. By analyzing a series of nonsense mutations between amino acids 193 and 185 in Env expression vectors and in the SIVmac239 proviral clone, a region of the SIV TM that contains the minimum requirement for glycoprotein-mediated cell-to-cell fusion and that for virus replication was identified. Virus entry and infectivity were evident in truncations to a minimum of 189 amino acids, whereas cell-cell fusion was observed for a protein of only 187 amino acids. Glycoprotein was efficiently incorporated into budding virions in truncations up to 185 amino acids, indicating that such proteins are membrane anchored and are transported to the cell surface. However, truncation of the TM to 180 amino acids resulted in a protein that displays a transport defect and may be retained in the endoplasmic reticulum. Based on our analyses of these mutants, an alternative model for the MSD of SIV is proposed. Our model suggests that membrane-imbedded charged residues can be neutralized by side-chain interactions with lipid polar head groups. As a consequence, the membrane-spanning region can be reduced by more than a helical turn. This new model accounts for the ability of truncations within the predicted MSD to remain membrane anchored and maintain biological activity.

Frequent substitution polymorphisms in African green monkey CCR5 cluster at critical sites for infections by simian immunodeficiency virus SIVagm, implying ancient virus-host coevolution

In contrast to humans, several primate species are believed to have harbored simian immunodeficiency viruses (SIVs) since ancient times. In particular, the geographically dispersed species of African green monkeys (AGMs) are all infected with highly diversified SIVagm viruses at high prevalences (greater than 50% of sexually mature individuals) without evident diseases, implying that the progenitor monkeys were infected prior to their dispersal. If this is correct, AGMs would be expected to have accumulated frequent resistance-conferring polymorphisms in host genes that are important for SIV replication. Accordingly, we analyzed the coding sequences of the CCR5 coreceptors from 26 AGMs (52 alleles) in distinct populations of the four species. These samples contained 29 nonsynonymous coding changes and only 15 synonymous nucleotide substitutions, implying intense functional selection. Moreover, 24 of the resulting amino acid substitutions were tightly clustered in the CCR5 amino terminus (D13N in the vervets and Y14N in the tantalus species) or in the first extracellular loop (Q93R and Q93K in all species). The Y14N substitution was extremely frequent in the 12 wild-born African tantalus, with 7 monkeys being homozygous for this substitution and 4 being heterozygous. Although two of these heterozygotes and the only wild-type homozygote were naturally infected with SIVagm, none of the Y14N homozygotes were naturally infected. A focal infectivity assay for SIVagm indicated that all five tested SIVagms efficiently use CCR5 as a coreceptor and that they also use CXCR6 (STRL33/Bonzo) and GPR15 (BOB) with lower efficiencies but not CXCR4. Interestingly, the D13N, Y14N, Q93R, and Q93K substitutions in AGM CCR5 all strongly inhibited infections by the SIVagm isolates in vitro. The Y14N substitution eliminates a tyrosine sulfation site that is important for infections and results in partial N-linked glycosylation (i.e., 60% efficiency) at this position. Nevertheless, the CCR5(Y14N) component that lacks an N-linked oligosaccharide binds the chemokine MIP-lbeta with a normal affinity and is fully active in signal transduction. Similarly, D13N and Q93R substitutions did not interfere with signal transduction. Thus, the common substitution polymorphisms in AGM CCR5 strongly inhibit SIVagm infections while substantially preserving chemokine signaling. In contrast, polymorphisms of human CCR5 are relatively infrequent, and the amino acid substitutions are randomly situated and generally without effects on coreceptor function. These results support an ancient coevolution of AGMs and SIVagm viruses and establish AGMs as a highly informative model for learning about host proteins that play critical roles in immunodeficiency virus infections.

Synthetic peptide strategy for the detection of and discrimination among highly divergent primate lentiviruses

We developed a simple, rapid, inexpensive, and highly sensitive and specific strategy for the detection and lineage differentiation of primate lentiviruses (PIV-ELISA). It is based on the use of two indirect ELISA methods using synthetic peptides mapping the gp41/36 region (detection component) and the V3 region (differentiation component) of four lentivirus lineages, namely SIVcpz/HIV-1 (groups M, O, N, and SIVcpz-gab), SIVmnd, SIVagm, and SIVsm/SIVmac/HIV-2. This strategy was evaluated with panels of sera originating from both humans and nonhuman primates. The human reference panel consisted of 144 HIV Western blot (WB)-positive sera in which the corresponding virus had been genotyped (HIV-1: 72 group M, 28 group O, and 6 group N; HIV-2: 21 subtype A and 10 subtype B; and 7 HIV-1+2) and 105 HIV WB-negative samples. The nonhuman primate reference panel consisted of 24 sera from monkeys infected by viruses belonging to the four lineages included in the PIV-ELISA strategy (5 chimpanzees, 5 macaques, 8 mandrills, and 6 vervets) and 42 samples from seronegative animals. Additional field evaluation panels consisted of 815 human sera from Gabon, Cameroon, and France and 537 samples from 25 nonhuman primate species. All the samples from the two reference panels were correctly detected and discriminated by PIV-ELISA. In the human field evaluation panel, the gp41/36 component correctly identified all the test samples, with 98% specificity. The V3 component discriminated 206 HIV-1 group M, 98 group O, 12 group M+O, and 128 HIV-2 sera. In the primate field evaluation panel, both gp41/36 and V3 detected and discriminated all the WB-positive samples originating from monkeys infected with SIVcpz, SIVagm-ver, SIVmnd-1, SIVmnd-2, SIVdrl, or SIVsun. These results were confirmed by genotyping in every case. Four SIV-infected red-capped mangabeys (confirmed by PCR) were correctly identified by gp41/36, but only two reacted with the V3 peptides in the absence of a specific SIVrcm V3 peptide. Addition of a V3 SIVrcm peptide discriminated all the SIVrcm-positive samples. Fourteen Papio papio samples were positive for SIVsm gp 36 and by WB, but negative by PCR, whereas three Papio cynocephalus samples were positive by gp41/36 but indeterminate by WB and negative by PCR. This combined ELISA system is thus highly sensitive and specific for antibodies directed against HIV and SIV. In addition, the V3-based serotyping results always agreed with genotyping results. This method should prove useful for studies of lentivirus prevalence and diversity in human and nonhuman primates, and may also have the potential to detect previously undescribed SIVs.

Differential incorporation of CD45, CD80 (B7-1), CD86 (B7-2), and major histocompatibility complex class I and II molecules into human immunodeficiency virus type 1 virions and microvesicles: implications for viral pathogenesis and immune regulation

Human immunodeficiency virus (HIV) infection results in a functional impairment of CD4(+) T cells long before a quantitative decline in circulating CD4(+) T cells is evident. The mechanism(s) responsible for this functional unresponsiveness and eventual depletion of CD4(+) T cells remains unclear. Both direct effects of cytopathic infection of CD4(+) cells and indirect effects in which uninfected "bystander" cells are functionally compromised or killed have been implicated as contributing to the immunopathogenesis of HIV infection. Because T-cell receptor engagement of major histocompatibility complex (MHC) molecules in the absence of costimulation mediated via CD28 binding to CD80 (B7-1) or CD86 (B7-2) can lead to anergy or apoptosis, we determined whether HIV type 1 (HIV-1) virions incorporated MHC class I (MHC-I), MHC-II, CD80, or CD86. Microvesicles produced from matched uninfected cells were also evaluated. HIV infection increased MHC-II expression on T- and B-cell lines, macrophages, and peripheral blood mononclear cells (PBMC) but did not significantly alter the expression of CD80 or CD86. HIV virions derived from all MHC-II-positive cell types incorporated high levels of MHC-II, and both virions and microvesicles preferentially incorporated CD86 compared to CD80. CD45, expressed at high levels on cells, was identified as a protein present at high levels on microvesicles but was not detected on HIV-1 virions. Virion-associated, host cell-derived molecules impacted the ability of noninfectious HIV virions to trigger death in freshly isolated PBMC. These results demonstrate the preferential incorporation or exclusion of host cell proteins by budding HIV-1 virions and suggest that host cell proteins present on HIV-1 virions may contribute to the overall pathogenesis of HIV-1 infection.

Simian immunodeficiency virus replicates to high levels in naturally infected African green monkeys without inducing immunologic or neurologic disease

African green monkeys can maintain long-term persistent infection with simian immunodeficiency viruses (SIVagm) without developing AIDS and thus provide an important model for understanding mechanisms of natural host resistance to disease. This study assessed the levels and anatomic distribution of SIVagm in healthy, naturally infected monkeys. Quantitative competitive reverse transcriptase PCR assays developed to measure SIVagm from two African green monkey subspecies demonstrated high levels of SIV RNA in plasma (>6 x 10(6) RNA copies/ml) in sabaeus and vervet monkeys. Infectious virus was readily recovered from plasma and peripheral blood mononuclear cells and shown to be highly cytopathic in human cell lines and macrophages. SIVagm DNA levels were highest in the gastrointestinal tract, suggesting that the gut is a major site for SIVagm replication in vivo. Appreciable levels of virus were also found within the brain parenchyma and the cerebrospinal fluid (CSF), with lower levels detected in peripheral blood cells and lymph nodes. Virus isolates from the CSF and brain parenchyma readily infected macrophages in culture, whereas lymph node isolates were more restricted to growth in human T-cell lines. Comparison of env V2-C4 sequences showed extensive amino acid diversity between SIVagm recovered from the central nervous system and that recovered from lymphoid tissues. Homology between brain and CSF viruses, macrophage tropism, and active replication suggest compartmentalization in the central nervous system without associated neuropathology in naturally infected monkeys. These studies provide evidence that the nonpathogenic nature of SIVagm in the natural host can be attributed neither to more effective host control over viral replication nor to differences in the tissue and cell tropism from those for human immunodeficiency virus type 1-infected humans or SIV-infected macaques.

Anti-HIV-1 activity in vitro of ceftazidime degradation products

Cephalosporins in aqueous solutions generate degradation products that inhibit in vitro HIV-1 replication in cell lines, as well as in primary cells (lymphocytes and macrophages). This effect is observed at concentrations that do not interfere with the normal functions of these cells. Upon chromatographic fractionation of an aqueous solution of hydrolysed ceftazidime, a high molecular weight fraction (MW 8000) with antiviral activity was isolated. The exact chemical nature of the active component responsible for the anti-HIV activity in vitro appears to be complex and is currently unknown. Inhibition of HIV-1 reverse transcriptase and RNase H activity was observed, however, higher concentrations than those needed to inhibit HIV replication were required. The inhibitory action of the hydrolysed ceftazidime was manifested during the early phase of the HIV-1 life-cycle. Despite a lack of a direct effect of the CD4/gp120 interaction, HIV-1 mediated cell fusion was inhibited by the hydrolysed ceftazidime, suggesting that the active principle acts in a very early stage of the viral life-cycle.

Partial activation and induction of apoptosis in CD4(+) and CD8(+) T lymphocytes by conformationally authentic noninfectious human immunodeficiency virus type 1

Increased levels of apoptosis are seen in human immunodeficiency virus (HIV) infection, and this has been proposed as an important mechanism contributing to HIV pathogenesis. However, interpretation of in vitro studies aimed at understanding HIV-related apoptosis has been complicated by the use of high concentrations of recombinant proteins or by direct cytopathic effects of replicating virus. We have developed an inactivation procedure that destroys retroviral infectivity while preserving the structural and functional integrity of the HIV surface proteins. These noninfectious virions interact authentically with target cells, providing a powerful tool to dissect mechanisms of HIV pathogenesis that do or do not require viral replication. Noninfectious CXCR4-tropic HIV-1 virions, but not microvesicles, partially activated freshly isolated CD4(+) and CD8(+) peripheral blood mononuclear cell T lymphocytes to express FasL and Fas, but not CD69 or CD25 (interleukin-2 receptor alpha) and eventually die via apoptosis starting 4 to 6 days postexposure. These effects required conformationally intact virions, as heat-denatured virions or equivalent amounts of recombinant gp120 did not induce apoptosis. The maximal apoptotic effect was dependent on major histocompatibility complex (MHC) class II proteins being present on the virion, but was not MHC restricted. The results suggest that the immunopathogenesis of HIV infection may not depend solely on direct cytopathic effects of HIV replication, but that effects due to noninfectious HIV-1 virions may also contribute importantly.

Characterization of a novel simian immunodeficiency virus from guereza colobus monkeys (Colobus guereza) in Cameroon: a new lineage in the nonhuman primate lentivirus family

Exploration of the diversity among primate lentiviruses is necessary to elucidate the origins and evolution of immunodeficiency viruses. During a serological survey in Cameroon, we screened 25 wild-born guereza colobus monkeys (Colobus guereza) and identified 7 with HIV/SIV cross-reactive antibodies. In this study, we describe a novel lentivirus, named SIVcol, prevalent in guereza colobus monkeys. Genetic analysis revealed that SIVcol was very distinct from all other known SIV/HIV isolates, with average amino acid identities of 40% for Gag, 50% for Pol, 28% for Env, and around 25% for proteins encoded by five other genes. Phylogenetic analyses confirmed that SIVcol is genetically distinct from other previously characterized primate lentiviruses and clusters independently, forming a novel lineage, the sixth in the current classification. Cercopithecidae monkeys (Old World monkeys) are subdivided into two subfamilies, the Colobinae and the Cercopithecinae, and, so far, all Cercopithecidae monkeys from which lentiviruses have been isolated belong to the Cercopithecinae subfamily. Therefore, SIVcol from guereza colobus monkeys (C. guereza) is the first primate lentivirus identified in the Colobinae subfamily and the divergence of SIVcol may reflect divergence of the host lineage.

Patterns of genomic sequence diversity among their simian immunodeficiency viruses suggest that L'Hoest monkeys (Cercopithecus lhoesti) are a natural lentivirus reservoir

Recently, we described a novel simian immunodeficiency virus (SIVlhoest) from a wild-caught L'Hoest monkey (Cercopithecus lhoesti) from a North American zoo. To investigate whether L'Hoest monkeys are the natural host for these viruses, we have screened blood samples from 14 wild animals from the Democratic Republic of Congo. Eight (57%) were found to be seropositive for SIV. Nearly full-length genome sequences were obtained for SIV isolates from three of these monkeys and compared to the original isolate and to other SIVs. The four samples of SIVlhoest formed a distinct cluster in phylogenetic trees. Two of these isolates differed on average at only about 5% of nucleotides, suggesting that they were epidemiologically linked; otherwise, the SIVlhoest isolates differed on average by 18%. Both the level of diversity and the pattern of its variation along the genome were very similar to those seen among isolates of SIVagm from vervet monkeys, pointing to similarities in the nature of, and constraints on, SIV evolution in these two species. Discordant phylogenetic relationships among the SIVlhoest isolates for different genomic regions indicated that mosaic viruses have been generated by recombination, implying that individual monkeys have been coinfected by more than one strain of SIV. Taken together, these observations provide strong evidence that L'Hoest monkeys constitute a natural reservoir for SIV.

Simian immunodeficiency virus (SIV) from sun-tailed monkeys (Cercopithecus solatus): evidence for host-dependent evolution of SIV within the C. lhoesti superspecies

Recently we reported the characterization of simian immunodeficiency virus (SIVlhoest) from a central African l'hoest monkey (Cercopithecus lhoesti lhoesti) that revealed a distant relationship to SIV isolated from a mandrill (SIVmnd). The present report describes a novel SIV (SIVsun) isolated from a healthy, wild-caught sun-tailed monkey (Cercopithecus lhoesti solatus), another member of the l'hoest superspecies. SIVsun replicated in a variety of human T-cell lines and in peripheral blood mononuclear cells of macaques (Macaca spp.) and patas monkeys (Erythrocebus patas). A full-length infectious clone of SIVsun was derived, and genetic analysis revealed that SIVsun was most closely related to SIVlhoest, with an amino acid identity of 71% in Gag, 73% in Pol, and 67% in Env. This degree of similarity is reminiscent of that observed between SIVagm isolates from vervet, grivet, and tantalus species of African green monkeys. The close relationship between SIVsun and SIVlhoest, despite their geographically distinct habitats, is consistent with evolution from a common ancestor, providing further evidence for the ancient nature of the primate lentivirus family. In addition, this observation leads us to suggest that the SIVmnd lineage should be designated the SIVlhoest lineage.

Isolation and partial characterization of a lentivirus from talapoin monkeys (Myopithecus talapoin)

We have identified a novel lentivirus prevalent in talapoin monkeys (Myopithecus talapoin), extending previous observations of human immunodeficiency virus-1 cross-reactive antibodies in the serum of these monkeys. We obtained a virus isolate from one of three seropositive monkeys initially available to us. The virus was tentatively named simian immunodeficiency virus from talapoin monkeys (SIVtal). Despite the difficulty of isolating this virus, it was readily passed between monkeys in captivity through unknown routes of transmission. The virus could be propagated for short terms in peripheral blood mononuclear cells of talapoin monkeys but not in human peripheral blood mononuclear cells or human T cell lines. The propagated virus was used to infect a naive talapoin monkey, four rhesus macaques (M. mulatta), and two cynomolgus macaques (M. fascicularis). All animals seroconverted and virus could be reisolated during a short period after experimental infection. A survey of SIVtal-infected captive talapoin monkeys revealed a relative decrease in CD4(+) cell numbers in chronically (>2 years) infected animals. No other signs of immunodeficiency were observed in any of the infected animals. PCR amplification followed by DNA sequencing of two fragments of the polymerase gene revealed that SIVtal is different from the presently known lentiviruses and perhaps most related to the SIV from Sykes monkeys.

Neutralizing antibody responses in Africa green monkeys naturally infected with simian immunodeficiency virus (SIVagm)

This study assessed the magnitude and cross-reactivity of the neutralizing antibody response generated by natural SIV infection in wild-caught African green monkeys. Neutralizing antibodies of variable potency, sometimes exceeding a titer of 1:1,000, were detected in 20 of 20 SIV-seropositive African green monkeys in Kenya. Detection of those neutralizing antibodies was dependent on the strain of virus and the cells used for assay, where the most sensitive detection was made with SIVagm1532 in Sup T1 cells. Potent neutralization of SIVagm1532 was seen with contemporaneous autologous serum. Potent neutralization was also detected with laboratory-passaged SIVmac251 and SIVsmB670, but not with SIVsmE660 and two additional strains of SIVagm. Serum samples from rhesus macaques (Macaca mulatta) experimentally infected with either SIVmac251 or SIVsmE660 were capable of low-level neutralization of SIVagm. These results indicate that natural infection with SIV can generate strain-specific neutralizing antibodies in African green monkeys. They also indicate that some neutralization determinants of SIVagm are partially shared with SIV strains that arose in sooty mangabys and were subsequently transmitted to rhesus macaques.

Expression and characterization of HIV type 1 envelope protein associated with a broadly reactive neutralizing antibody response

We have studied envelope protein from a donor with nonprogressive HIV-1 infection whose serum contains broadly cross-reactive, primary virus NA. DNA was extracted from lymphocytes, which had been collected approximately 6 and 12 months prior to the time of collection of the cross-reactive serum, and env genes were synthesized, cloned, expressed on pseudoviruses, and phenotyped in NA assays. Two clones from each time point had identical V3 region nucleotide sequences, utilized CCR5 but not CXCR4 for cell entry, and had similar reactivities with reference sera. Analysis of the full nucleotide sequence of one clone (R2) demonstrated it to be subtype B and have normal predicted glycosylation. R2 pseudovirus was compared with others expressing env genes of various clades for neutralization by sera from U.S. donors (presumed or known subtype B infections), and from individuals infected with subtypes A, C, D, E, and F viruses. Neutralization by the U.S. sera of R2 and other clade B pseudoviruses was low to moderate, although R2 was uniquely neutralized by all. R2 was neutralized by 3/3, 3/3, 2/5, 5/8, and 3/4 clade A, C, D, E, and F sera, respectively. R2 and a clade E pseudovirus were neutralized by largely complementary groups of sera, potentially defining two antigenic subgroups of HIV-1. The results suggest that the epitope(s) that induced the cross-clade reactive NA in donor 2 may be expressed on the R2 envelope.

Characterization of a novel simian immunodeficiency virus (SIV) from L'Hoest monkeys (Cercopithecus l'hoesti): implications for the origins of SIVmnd and other primate lentiviruses

The human immunodeficiency virus types 1 and 2 (HIV-1 and HIV-2) appear to have originated by cross-species transmission of simian immunodeficiency virus (SIV) from asymptomatically infected African primates. Few of the SIVs characterized to date efficiently infect human primary lymphocytes. Interesting, two of the three identified to infect such cultures (SIVsm and SIVcpz) have appeared in human populations as genetically related HIVs. In the present study, we characterized a novel SIV isolate from an East African monkey of the Cercopithecus genus, the l'hoest monkey (C. l'hoesti), which we designated SIVlhoest. This SIV isolate efficiently infected both human and macaque lymphocytes and resulted in a persistent infection of macaques, characterized by high primary virus load and a progressive decline in circulating CD4 lymphocytes, consistent with progression to AIDS. Phylogenetic analyses showed that SIVlhoest is genetically distinct from other previously characterized primate lentiviruses but clusters in the same major lineage as SIV from mandrills (SIVmnd), a West African primate species. Given the geographic distance between the ranges of l'hoest monkeys and mandrills, this may indicate that SIVmnd arose through cross-species transmission from close relatives of l'hoest monkeys that are sympatric with mandrills. These observations lend support to the hypothesis that the primate lentiviruses originated and coevolved within monkeys of the Cercopithecus genus. Regarded in this light, lentivirus infections of primates not belonging to the Cercopithecus genus may have resulted from cross-species transmission in the not-too-distant past.

Evolution of neutralizing antibody response against HIV type 1 virions and pseudovirions in multicenter AIDS cohort study participants

Changes in neutralizing antibody (NA) titers in stored sera collected over 5 years from 10 participants in the Multicenter AIDS Cohort Study (MACS) were evaluated. The participants were HIV-1 infected on enrollment in the MACS, and remained AIDS free during the 5-year study interval. Seven viruses derived from molecular clones were used in NA assays; five of the viruses were T tropic (NL4-3, ALA1, NY5, SF2, and Z2Z6) and two were M tropic [AD8 and NL(SF162)]. In addition, pseudoviruses (PVs) were constructed that expressed envelope genes from NL4-3, ALA1, AD8, and SF162 and from primary viruses from two MACS participants (PV-9 and PV-10). There was significant correlation between NA titers obtained in four of five virus/PV comparisons, while the SF162 PV was more sensitive to NA than the corresponding virus. Comparable changes in NA titers were detected using viruses and PVs. Fourfold or greater increases in NA titers were noted in each of the participants, involving recognition of one to five of the nine strains tested. In some patients these NA titer changes appeared as discrete episodes of immune responses, while in others there may have been either multiple episodes or continuous evolution of the NA responses. The data indicate that changes in NA specificity occur during HIV-1 infection, which may result from the occurrence of neutralization escape mutation. The use of PVs for the study of phenotypic characteristics of envelope glycoproteins should facilitate the study of neutralization escape mutation in HIV-1 infection.

Simian immunodeficiency virus of African green monkeys is apathogenic in the newborn natural host

Several studies have demonstrated that newborn animals are more susceptible to disease development following infection with retroviruses than adults. Adult African green monkeys (AGMs) infected with SIVagm do not develop AIDS-like disease and the objective of the study was to determine whether experimental infection of newborn AGMs with SIVagm would result in pathogenesis. Neonatal AGMs were found to have a higher percentage of circulating CD4+ lymphocytes than adults (62% versus 14%) and therefore a higher potential pool of target cells for SIVagm infection. However, no differences in the in vitro replication kinetics of SIVagm in peripheral blood mononuclear cells of adult or neonatal AGMs could be observed. In vivo, the neonatal AGMs became viremic at the earliest two months after inoculation whereas the adult AGMs had evidence of virus replication already 2 to 6 weeks after infection. None of the animals developed AIDS-like symptoms upon infection. In the heterologous cynomolgus macaque host, a newborn infected with SIVagm developed early high virus loads and died two months after birth with AIDS-like histopathologic features. It would therefore appear that in contrast to the situation with many other retroviruses, newborn AGMs are no more permissive to SIVagm infection than are adults.

Phylogenetic analysis of SIV and STLV type I in mandrills (Mandrillus sphinx): indications that intracolony transmissions are predominantly the result of male-to-male aggressive contacts

Natural SIVmnd and STLVmnd infections of mandrills in a colony at the Centre International de Recherches Médicales de Franceville (CIRMF) in Gabon were investigated by genetic analysis to determine the extent of intracolony transmission. SIVmnd pol sequence analysis indicates that the six strains present in the colony belong to the SIVmnd lentivirus subgroup previously defined according to the only available prototype sequence (SIVmndGB1), which originated from the same colony. The intraanimal nucleotide diversity (1.1-3.1%) was similar in range to that reported in individuals infected by other HIV/SIVs. The interanimal diversity (0.5-4.3%) was not significantly different from that observed in each individual mandrill, indicating an epidemiological link among the SIVmnd isolates of distinct animals within the colony. Phylogenetic analysis of these isolates, together with seroepidemiological and behavior surveillance within the colony, indicates a predominant male-to-male transmission of SIVmnd that probably occurred during bouts of interanimal aggression. Moreover, our results suggest one case of vertical transmission of SIVmnd from a naturally infected founder female to one of her six offspring. The first genetic analysis of STLV isolates from mandrills is also reported here. Partial tax/rex sequences were used to evaluate the diversity between seven STLVmnd isolates and their phylogenetic relationships with other known strains of human and nonhuman primate T cell leukemia virus, types I and II (PTLV-I/II). They all belong to the PTLV-I subtype, but two genetically distinct STLVmnd groups were evidenced within the mandrill colony. The phylogenetic analyses of the STLVmnd isolates, together with seroepidemiological and behavior surveillance of the mandrills, indicate that intracolony transmissions of STLVmnd are also predominantly the result of male-to-male aggressive contacts.

Early regeneration of thymic progenitors in rhesus macaques infected with simian immunodeficiency virus

The thymus plays a critical role in the maturation and production of T lymphocytes and is a target of infection by human immunodeficiency virus (HIV) and the related simian immunodeficiency virus (SIV). Using the SIV/macaque model of AIDS, we examined the early effects of SIV on the thymus. We found that thymic infection by SIV resulted in increased apoptosis 7-14 d after infection, followed by depletion of thymocyte progenitors by day 21. A marked rebound in thymocyte progenitors occurred by day 50 and was accompanied by increased levels of cell proliferation in the thymus. Our results demonstrate a marked increase in thymic progenitor activity very early in the course of SIV infection, long before marked declines in peripheral CD4(+) T cell counts.

Induction of vigorous cytotoxic T-lymphocyte responses by live attenuated simian immunodeficiency virus

Although live attenuated vaccine strains of simian immunodeficiency virus (SIV) have proven highly effective in protecting macaques against challenge with pathogenic SIV strains, little is known about the mechanisms of protective immunity induced by these vaccines. We examined cytotoxic T-lymphocyte (CTL) responses against SIV in animals infected with SIVmac239delta nef (deficient in nef) or SIVmac239delta 3 (deficient in nef, vpr, and upstream sequences in U3). To enhance detection of SIV-specific CTL activity, we stimulated peripheral blood mononuclear cells with autologous B-lymphoblastoid cell lines which had been infected with recombinant vaccinia viruses expressing SIV proteins and subsequently inactivated with psoralen and UV light. Animals chronically infected with SIV239delta nef or SIV239delta 3 mounted vigorous CTL responses against the SIV Gag and Env proteins. This CTL activity was major histocompatibility class restricted and mediated by CD8+ T lymphocytes. CTL responses persisted at relatively high levels for more than 6 years after infection. Limiting dilution precursor frequency assays demonstrated that the frequency of SIV-specific CTLs was as high as 234 CTL precursors per 100,000 cells. Animals acutely infected with SIV239delta nef developed CTL activity by day 14 after infection, coincident with decreases in viral load. Animals acutely infected with SIV239delta 3 developed CTL responses within 4 weeks of infection. Thus, vaccination of juvenile or adult animals with SIV239delta nef or SIV239delta 3 results in the induction of a vigorous CTL response which arises early in the course of infection and persists for years after a single inoculation of virus.

Inactivation of HIV-1 chemokine co-receptor CXCR-4 by a novel intrakine strategy

CXC-chemokine receptor (CXCR)-4/fusin, a newly discovered co-receptor for T-cell line (T)-tropic HIV-1 virus, plays a critical role in T-tropic virus fusion and entry into permissive cells. The occurrence of T-tropic HIV viruses is associated with CD4-positive cell decline and progression to AIDS, suggesting that the T-tropic HIV-1 contributes to AIDS pathogenesis. In this study, we used a novel strategy to inactivate CXCR-4 by targeting a modified CXC-chemokine to the endoplasmic reticulum (ER) to block the surface expression of newly synthesized CXCR-4. The genetically modified lymphocytes expressing this intracellular chemokine, termed "intrakine", are immune to T-tropic virus infection and appear to retain normal biological features. Thus, this genetic intrakine strategy is uniquely targeted at the conserved cellular receptor for the prevention of HIV-1 entry and may be developed into an effective treatment for HIV-1 infection and AIDS.

Maintenance of an unusual polypurine tract in HIV-2: stability to passage in culture

A stretch of purine residues, the polypurine tract (PPT), is found in all retroviruses and is used to initiate plus-strand DNA synthesis. While the PPT of most lentiviruses is a homogeneous sequence of purine residues, the PPT of some isolates of the human and simian immunodeficiency viruses is interrupted with a single pyrimidine residue. The ROD strain of human immunodeficiency virus type 2 (HIV-2) has such a pyrimidine-containing variant PPT. Virus generated from an infectious molecular clone, pROD10, was used to infect two CD4-positive T-cell lines, H9 and CEM. The sequence of the PPT was determined after two passages. From both cell lines, the variant PPT was retained, demonstrating that the presence of a pyrimidine in the PPT was fully functional and that there was no strong selection for an all-purine PPT.

The African polio vaccine-acquired immune deficiency syndrome connection

Seroepidemiological, clinical and molecular findings suggest that the acquired immune deficiency syndrome virus human immunodeficiency virus-1 was introduced into the human species at the time (late 1950s) and in the geographic area (Zaire) in which millions of Africans were vaccinated with attenuated poliomyelitis virus strains that were produced in kidney tissue obtained from monkeys. Since monkeys not only harbor viruses that are remarkably similar to and genetically related to human immunodeficiency virus-1, but also served as tissue donors for the African polio vaccine, it is reasonable to suspect that a then non-detectable monkey virus with human-1-like properties was unknowingly co-cultured with the attenuated poliovirus virus and subsequently administered to the vaccinees. The possibility of such a polio vaccine-acquired immune deficiency syndrome connection is a reminder of the unpredictable danger of artifically crossing natural species-barriers in biomedical laboratories.

Genetic diversity of simian immunodeficiency viruses from West African green monkeys: evidence of multiple genotypes within populations from the same geographical locale

High simian immunodeficiency virus (SIV) seroprevalence rates have been reported in the different African green monkey (AGM) subspecies. Genetic diversity of these viruses far exceeds the diversity observed in the other lentivirus-infected human and nonhuman primates and is thought to reflect ancient introduction of SIV in the AGM population. We investigate here genetic diversity of SIVagm in wild-living AGM populations from the same geographical locale (i.e., sympatric population) in Senegal. For 11 new strains, we PCR amplified and sequenced two regions of the genome spanning the first tat exon and part of the transmembrane glycoprotein. Phylogenetic analysis of these sequences shows that viruses found in sympatric populations cluster into distinct lineages, with at least two distinct genotypes in each troop. These data strongly suggest an ancient introduction of these divergent viruses in the AGM population.

Constitutive cytokine release by simian T-cell lymphotrophic virus type I (STLV-I) and human T-cell lymphotrophic virus types I/II (HTLV-I/II) transformed cell lines

Simian T-cell lymphotrophic virus type I (STLV-I) and human T-cell lymphotrophic virus types I/II (HTLV-I/II) contain the tax gene which can transactivate the transcription of viral and cellular genes including several cytokines. These investigations used two STLV-I and four different HTLV-I/II transformed cell lines to quantitate constitutive cytokine release, p24 antigen production, and to correlate gag p24 antigen and cytokine release. These investigations are the first to report 1) quantitative comparison of constitutive release of multiple cytokines by several STLV-I and HTLV-I/II transformed cell lines and to determine the cytokines constitutively released by STLV-I transformed cell lines as IL-6, b-FGF, and GM-CSF (and TNF-beta, and PDGF in a higher viral producing line); 2) statistically significant differences in levels of cytokines produced by STLV-I and HTLV-I/II transformed cell lines, dependent on the method of results quantification; and 3) a correlation between levels of STLV-I and HTLV-I/II and gag p24 antigen production and cytokine production.

The nef gene from a long-term HIV type 1 nonprogressor

We examined the nef gene of HIV-1 in a long-term nonprogressor to look for evidence suggesting an attenuated virus. The nef gene was previously shown to be required for induction of AIDS. Simian immunodeficiency virus (SIV) deleted in nef, while infectious, fails to sustain the high viral loads necessary for the induction of AIDS in infected adult rhesus monkeys. The human subject of this report was found to harbor virus (HIV-1 Sur25) encoding open-nef reading frames. However, the nef genes of this subject bore a signature point mutation: a cysteine at amino acid 138. The sequence at this position was identical in all clones examined over a 3-year period. When this sequence was compared to the sequence database for AIDS and human retroviruses at Los Alamos, New Mexico, several isolates from other asymptomatic individuals were also found to encode nef genes with a cysteine at position 138. Furthermore, Cys-138 was found in chimpanzee immunodeficiency virus (CIV), a lentivirus that is similar to HIV but does not cause AIDS in chimpanzees. Multiple cysteines are also found in the nef gene of African green monkey virus, SVIagm, including cysteine at the position analogous to Cys-138. While seroprevalence of SIVagm is high in the wild, there is no known disease associated with this virus. The pathogenic virus isolated from Asian macaques, SIVmac, encodes a Nef protein that has few cysteines. Although the virus HIVSur25 encodes a completely open-nef gene, the virus from this individual is similar to attenuated SIVmac (SIVmac239/nef-deletion) as well as HIV deleted in nef in its growth properties in H9 cells. Nef containing a cysteine at position 138 was shown to be responsible for determining the ability to grow in H9.

Human monoclonal antibody 2G12 defines a distinctive neutralization epitope on the gp120 glycoprotein of human immunodeficiency virus type 1

We have isolated and characterized human monoclonal antibody 2G12 to the gp120 surface glycoprotein of human immunodeficiency virus type 1 (HIV-1). This antibody potently and broadly neutralizes primary and T-cell line-adapted clade B strains of HIV-1 in a peripheral blood mononuclear cell-based assay and inhibits syncytium formation in the AA-2 cell line. Furthermore, 2G12 possesses neutralizing activity against strains from clade A but not from clade E. Complement- and antibody-dependent cellular cytotoxicity-activating functions of 2G12 were also defined. The gp120 epitope recognized by 2G12 was found to be distinctive; binding of 2G12 to LAI recombinant gp120 was abolished by amino acid substitutions removing N-linked carbohydrates in the C2, C3, V4, and C4 regions of gp120. This gp120 mutant recognition pattern has not previously been observed, indicating that the 2G12 epitope is unusual. consistent with this, antibodies able to block 2G12 binding to recombinant gp120 were not detected in significant quantities in 16 HIV-positive human serum samples.

Simian immunodeficiency virus variants: threat of new lentiviruses

Infection in humans with the lentivirus HIV-1 typically results in the development of a chronic disease state characterized by the slow decline of CD4+ lymphocytes, the development of immunosuppression, and the development of opportunistic infections, ultimately leading to death. Although the average course of disease runs approximately 10 years, shorter and longer progression times have been noted. These alterations are presumed to be, at least partially, a factor of viral variation. The simian immunodeficiency viruses (SIVs) are the nonhuman primate counterparts to HIV. Several of these isolates, including SIV from sooty mangabey monkeys, induce a remarkably similar disease in Asian macaques. Recently, variants of SIV from sooty mangabey monkeys and SIV from African green monkeys have been described, which are increasingly more pathogenic. As in HIV-1 infections, this is probably due to genetic variation. On the basis of these findings, atypical viruses with tremendous pathogenic potential can arise from apathogenic or moderately pathogenic viruses.

Regulatory genes of simian immunodeficiency viruses from west African green monkeys (Cercopithecus aethiops sabaeus)

The high seroprevalence of simian immunodeficiency viruses (SIVs) in African green monkeys (AGMs) without immunological defects in their natural hosts has prompted consideration of SIV-infected AGMs as a model of apathogenic SIV infection. Study of the molecular mechanisms of SIVagm asymptomatic infection could thus provide clues for understanding the pathogenesis of human immunodeficiency viruses. Regulatory genes could be candidates for genetic control of SIVagm apathogenicity. We have characterized Vpr, Tat, Rev, and Nef genes of two SIVagm strains isolated from naturally infected sabaeus monkeys captured in Senegal. The results provide further evidence that SIVagm from West African green monkeys is the most divergent class of AGM viruses, with structural features in long terminal repeat sequences and Vpr and Tat genes that distinguish them from viruses isolated from other AGM species (vervet, grivet, and tantalus monkeys).

T-helper reactivity to simian immunodeficiency virus gag synthetic peptides in human immunodeficiency virus type 2 infected individuals

West African populations are infected with divergent strains of human immunodeficiency virus type 2 (HIV2), some of which are closely related to simian immunodeficiency virus (SIV) and it has been postulated that the HIV2 epidemic might have arisen by cross-species spread of SIV into the human population in West Africa. To gain some insight into the possible basis for cross protection between these two closely related viruses, the T-helper responses to 15 synthetic peptides from SIV gag synthetic peptides were investigated in seven HIV2-infected subjects and in seven healthy controls. Significant reactivity to at least one of the synthetic peptides tested was found in all patients and a statistically significant correlation between CD4+ lymphocyte absolute numbers and the number of reacting peptides was observed. A marginal lymphocyte reactivity was found in two of the healthy controls studied. In conclusion, this preliminary evidence that HIV2-infected patients exhibit T-cell responses to SIV gag peptides suggests that both viruses share t-helper epitopes in the gag viral region and raises the possibility of cross protection between SIV and HIV2 which may be relevant for HIV2 vaccine research based on closely related retroviruses.

Kinetics of HIV infection of human placental syncytiotrophoblast cultures: an ultrastructural and immunocytochemical study

We previously demonstrated that syncytiotrophoblast (ST) cells from term human placentas could be infected when cocultured with HIV-infected lymphocytic cells. Here, we have used fluorescence microscopy and transmission electron microscopy to examine the kinetics of this infection process. Molt-4 clone 8 cells infected with HIV-1Lai or filtered supernatant from these cultures were incubated with ST cells for different times. In cell-associated infection, immunofluorescence microscopy revealed that some ST colonies were positive for HIV core proteins (p24,p55) after 1 hr. The number of positive colonies and the intensity of the ST-associated fluorescence increased with time. Transmission electron microscopy showed viral particles with HIV morphology associated with the ST cell surface at 1 hr. Immature virions with budding morphology were observed at 2 hr. In cell-free infection, positive p24,p55 staining was first detected in a few ST colonies at 4 hr. The number of positive colonies increased with time. At 24 hr, the fluorescence pattern and intensity resembled that seen with cell-mediated infection at 4 hr. Transmission electron microscopy revealed an increasing number of viral particles associated with the ST cell plasma membrane with respect to time, and budding virions first appeared at 8 hr. These results demonstrate that HIV infection of placental ST cells proceeds very rapidly in culture and that, furthermore, cell-associated infection of ST is much more efficient than the infection with cell-free virus.

Induction of AIDS by simian immunodeficiency virus from an African green monkey: species-specific variation in pathogenicity correlates with the extent of in vivo replication

Previous studies suggested that simian immunodeficiency viruses isolated from African green monkeys (SIVagm) are relatively nonpathogenic. The report describes the isolation and biologic and molecular characterization of a pathogenic SIVagm strain derived from a naturally infected African green monkey. This virus induced an AIDS-like syndrome characterized by early viremia, frequent thrombocytopenia, severe lymphoid depletion, opportunistic infections, meningoencephalitis, and death of five of eight macaques within 1 year after infection. An infectious clone derived from this isolate reproduced the immunodeficiency disease in pig-tailed (PT) macaques, providing definitive proof of the etiology of this syndrome. Although the virus was highly pathogenic in PT macaques, no disease was observed in experimentally infected rhesus macaques and African green monkeys despite reproducible infection of the last two species. Whereas infection of PT macaques was associated with a high viral load in plasma, peripheral blood mononuclear cells, and tissues, low-level viremia and infrequent expression in lymph nodes of rhesus macaques and African green monkeys suggest that differences in pathogenicity are associated with the extent of in vivo replication. The availability of a pathogenic molecular clone will provide a useful model for the study of viral and host factors that influence pathogenicity.

Complementation of human immunodeficiency virus type 1 vif mutants in some CD4+ T-cell lines

The viral infectivity factor gene, vif of human immunodeficiency virus type 1 (HIV-1), is required for full infectivity in most T-cell lines. The replication kinetics exhibited by these mutants has been shown to be cell type-dependent. In H9 cells as well as primary lymphocytes, vif mutants are incapable of establishing infection. This has led to classification of these cell types as non-permissive for vif mutant replication. The T-cell lines Sup T1 and C8166 are able to replicate the vif mutant virus, leading to their classification as permissive for vif mutant replication. In this study, four cell lines (Sup T1, C8166, Molt 4 Clone 8, and A3.01) were tested for their ability to replicate vif mutant virus derived from two different strains of HIV-1 (HXB2 and NL4-3) that had been passaged on various cell lines. Although the kinetics of initial infection was delayed in all cells, by the second passage of vif mutant virus on Sup T1 or Molt 4 cells the kinetics of replication were identical to wild type virus. In contrast, mutant virus displayed delayed replication kinetics in C8166 and A3.01 cells in both initial and subsequent passages. In addition, the levels of viral DNA in infected Sup T1 cells were similar for delta vif and wild type virus, but in C8166 cells delta vif virus DNA levels were reduced compared to wild type virus. These results argue that in Sup T1 and Molt 4 cells there is a factor present that is able to complement the defect in vif mutant viruses which is absent or inefficient in its activity in C8166 and A3.01 cells.

CD8+ T lymphocytes of African green monkeys secrete an immunodeficiency virus-suppressing lymphokine

Following natural and experimental infection by simian immunodeficiency virus SIVagm of African green monkeys (AGMs), the natural host, there is no evidence for the development of an immunodeficiency. Within the framework of our studies on human immunodeficiency virus (HIV)/SIV pathogenesis, we investigated the influence of CD8 T lymphocytes on SIVagm replication in AGM CD4 T lymphocytes in vitro. The following observations were made: (i) Peripheral blood mononuclear cells from both seronegative and seropositive AGMs contained only a low proportion (i.e., 10%) of CD4+ lymphocytes, whereas a high proportion (80%) of CD8+ cells was detected. Even after persistent SIVagm infection, CD4 T lymphocytes do not decrease in number. (ii) The target of in vitro infection of peripheral blood cells is the CD4+ mononuclear cell (T lymphocytes, monocytes) and SIVagm infects by binding to the CD4 molecule. (iii) In both naturally and experimentally SIVagm-infected AGMs the CD4+ T cells and monocytes, but not the CD8+ T cells, harbor DNA provirus. (iv) Virus reisolation and virus replication of SIVagm in CD4 T lymphocytes from seropositive AGMs is suppressed in the presence of autologous CD8 T lymphocytes or a soluble factor produced by these cells. Taken together, one possible reason for the apathogenicity of the SIVagm infection in AGMs may be the suppression of virus replication by a soluble, yet unidentified factor secreted by CD8 lymphocytes quantitatively dominating among peripheral blood cell populations. We have tentatively termed this factor "immunodeficiency virus-suppressing lymphokine." In addition, we show that immunodeficiency virus-suppressing lymphokine from AGMs is able to suppress HIV-1 replication in human CD4+ T cells.