Envelope sequences of two new United States HIV-1 isolates

Genetic organization of a chimpanzee lentivirus related to HIV-1

Simian immunodeficiency viruses have been isolated from four species of monkey, the 'captive' macaque and mangabey and the 'feral' African green monkey and mandrill. While none of these viruses is a replica of HIV-1, the macaque and mangabey viruses represent correct genetic models for HIV-2, possessing exactly the same complement of genes. Recently a lentivirus has been identified in two wild chimpanzees (Pan troglodytes troglodytes) in Gabon, west equatorial Africa, and isolated from one of them. This virus is referred to as SIVCPZ. Sera from these animals cross reacted with all the HIV-1 proteins including the envelope glycoproteins. Here, we describe the molecular cloning and sequencing of an infectious proviral clone of SIVCPZ. The overall genetic organization was the same as that of HIV-1, but phylogenetic analysis revealed that the sequence was more divergent than any HIV-1 sequence reported so far. The vpu gene product, found only in the type 1 viruses, was particularly different (64% divergent to HIV-1BRU) suggesting that the SIVCPZ represents a distinct subtype. These findings indicate that there is a larger pool of simian lentiviruses than previously suspected and revives debate as to the origins of HIV-1.

Functional contribution of cysteine residues to the human immunodeficiency virus type 1 envelope

Although the envelope gene of human immunodeficiency virus type 1 shows considerable strain variability, cysteine residues of the envelope protein are strongly conserved, suggesting that they are important to the envelope structure. We constructed and analyzed mutants of a biologically active molecular clone of human immunodeficiency virus type 1 in which different cysteines were replaced by other amino acids in order to determine their functional importance. Substitution of cysteines 296 and 331, on either side of a region recognized by type-specific neutralizing antibodies, or on either side (residues 418 and 445) of a region important for CD4 binding, resulted in noninfectious mutants. These mutants were blocked early in the viral life cycle. Their gp160 envelope precursor polypeptides were poorly cleaved, and CD4 binding was also strongly impaired. Similar substitutions in the first variable region (residue 131) or between the first and second variable regions (residue 196) also gave noninfectious mutant virus, but here the block was late in the virus life cycle; these mutants were defective for syncytium formation. Substitution of cys386, between the neutralization and CD4 binding regions, resulted in a virus which retained infectivity but which spread much more slowly than the wild type. As with the cys131 and cys196 mutants, the cys386 mutant appeared to be defective in syncytium formation. These results show that all seven of the tested cysteines are vital for envelope function and suggest that this is likely true for all envelope cysteines. The results further show that regions important for CD4 binding, proteolytic cleavage recognition, and syncytium formation are all multiple and distributed over a relatively large part of the gp120 and therefore are likely dependent on protein tertiary structure.

Possible beneficial effects of neutralizing antibodies and antibody-dependent, cell-mediated cytotoxicity in human immunodeficiency virus infection

We studied the relationship between early human immunodeficiency virus type 1 (HIV-1) specific immune responses and pathogenesis of infection in participants enrolled in the multicenter AIDS cohort study (MACS). Sera collected at 6-month intervals for 2 years (visit 1-5) from 39 persons who seroconverted by enzyme-linked immunosorbent assay (ELISA) 6 months (visit 2) after enrollment were examined for isotype-specific Western blot reactivity, neutralizing antibodies (NA) against two divergent strains of HIV-1 (HIV-1IIIB and HIV-1RF), and for antibodies capable of participating in antibody-dependent, cell-mediated cytotoxicity (ADCC). These results were compared with changes in CD4+ cell number and episodes of lymphadenopathy. Twenty-five subjects had antibodies of at least one isotype reactive to at least one HIV-1 protein by Western blot at visit 1, before they became ELISA positive. NA reactive with HIV-1IIIB were detected before those reactive with HIV-1RF. NA were first observed in 11 sera at visit 2, in 22 sera at visit 3, and in 3 sera at visit 4; sera from three patients remained nonneutralizing through visit 5. In most cases, NA were detected after a decline in CD4+ cell numbers. The data are consistent with the interpretation that NA develop after about 16 to 18 months of declining CD4+ cell numbers, following which the rate of decline in CD4+ cell numbers slows. In contrast, HIV-1 envelope antigen-specific ADCC responses were first observed in 11 subjects at visit 1 when all 39 were NA and ELISA negative, in 12 subjects at visit 2, in 13 subjects at visit 3, and 1 subject at visit 4. Early ADCC responses were associated with high mean % CD4+ cell numbers and absence of lymphadenopathy throughout the 2-year observation period. Not all subjects who developed ADCC developed NA. In some subjects, ADCC and NA were detectable for the first time at the same visit, for others ADCC was detectable prior to NA, and for a few NA was detectable prior to ADCC. These findings suggest that ADCC and neutralization are mediated by different antibody populations, that they may partially inhibit the progress of HIV-1 infection, and that the late appearance of NA may relate to the failure of immunity to effect recovery from this infection.

Retroviral vectors expressing soluble CD4: a potential gene therapy for AIDS

Retroviral vectors have been developed which produce a secreted form of the helper/inducer T-cell antigen, CD4. Amphotropically packaged vectors were used to transduce cells, and these cells were shown to express the secreted CD4 (sCD4) gene product. The sCD4 produced by the viral vectors is immunoprecipitated by monoclonal antibodies against CD4, which specifically block human immunodeficiency virus (HIV) infection of helper/inducer T cells. A direct physical interaction of vector-produced sCD4 and HIV-1 gp120 was demonstrated by coprecipitation of sCD4/gp120 with antiserum directed against HIV gp120. Furthermore, transduced cells producing sCD4 can protect HIV-susceptible cells from infection by HIV. These data suggest that gene therapy is a potential approach for the treatment of AIDS.

Sequence of a novel simian immunodeficiency virus from a wild-caught African mandrill

Since the isolation of an HIV-2-related virus from captive macaques (SIVMAC), the origin of human immunodeficiency viruses, a much debated subject, has been attributed to monkeys. The sequence of SIVAGM, which is derived from a naturally infected African green monkey, shows equal relatedness to HIV-1 and HIV-2, suggesting that the derivation of these viruses from SIVAGM is unlikely. Recent sequence analysis of SIV from a captive sooty mangabey (SIVMAC), however, shows its close relatedness to HIV-2 and SIVMAC, indicating a possible origin of HIV-2 and SIVMAC from SIVSM (refs 4, 7, 9). We report here the sequence of a novel simian lentivirus, SIVMND, isolated from a wild-caught mandrill in Africa. It is distinct from the three other main groups, HIV-1, HIV-2/SIVMAC/SIVSM and SIVAGM, and therefore represents a fourth main group of primate lentiviruses. Phylogenetic analysis indicates that these four main virus groups might have diverged from a common ancestor at about the same time, long before the spread of AIDS in humans.

Monoclonal antibodies to HTLV-III451 gp41: delineation of an immunoreactive conserved epitope in the transmembrane region of divergent isolates of HIV-1

We report on the development of monoclonal antibodies directed against the transmembrane portion of the envelope of HTLV-III451 gp41. One of these monoclonal antibodies, designated M71/2B4, was found to cross-react with transmembrane proteins from other independent isolates of HIV-1, namely IIIB, MN, and RF. Thus, this monoclonal antibody identifies an epitope located in a region of gp41 that is conserved among all these isolates. To identify this conserved region a series of E. coli recombinant proteins were screened in immunoblot with M71/2B4. From these results the epitope recognized by this antibody appears to map at the amino terminus of gp41, in the region indicated between the cleavage site with gp120 (aa 508) and the HindIII site (aa647).

Nucleotide sequences of gag and env genes of a Japanese isolate of HIV-1 and their expression in bacteria

A DNA clone of HIV-1, JH3, was isolated from a Japanese patient with hemophilia and the gag and env genes were sequenced. The nucleotide and deduced amino acid sequences were similar to those reported and showed high divergence in the env gene, particularly in the extracellular domain of the env. The genetic variation of JH3 isolated from a Mongolian was within the range of those of isolates from whites and blacks. The gag and env polypeptides were efficiently expressed in E. coli as fusion proteins with beta-galactosidase, and the products were shown to be useful as diagnostic reagents.