No abstract

Disruption of the vif gene of human immunodeficiency virus (HIV) type 1 affects virus infectivity to various degrees, depending on the T-cell line used.We have concentrated our studies on true phenotypic Vif ؊ mutant particles produced from CEMx174 or H9 cells. In a single round of infection, Vif ؊ virus is approximately 25 (from CEMx174 cells) to 100 (from H9 cells) times less infectious than wild-type virus produced from these cells or than the Vif ؊ mutant produced from HeLa cells. Vif ؊ virions recovered from restrictive cells, but not from permissive cells, are abnormal both in terms of morphology and viral protein content. Notably, they contain much reduced quantities of envelope proteins and altered quantities of Gag and Pol proteins. Although wild-type and Vif ؊ virions from restrictive cells contain similar quantities of viral RNA, no viral DNA synthesis was detectable after acute infection of target cells with phenotypically Vif ؊ virions. To examine the possible role of Vif in viral entry, attempts were made to rescue the Vif ؊ defect in H9 cells by pseudotyping Vif ؉ and Vif ؊ HIV particles with amphotropic murine leukemia virus envelope. Vif ؊ particles produced in the presence of HIV envelope could not be propagated when pseudotyped. In contrast, when only the murine leukemia virus envelope was present, significant propagation of Vif ؊ HIV particles could be detected. These results demonstrate that Vif is required for proper assembly of the viral particle and for efficient HIV Env-mediated infection of target cells.

Despite repeated exposure to HIV-1, certain individuals remain persistently uninfected. Such exposed uninfected (EU) people show evidence of HIV-1–specific T cell immunity and, in rare cases, selective resistance to infection by macrophage-tropic strains of HIV-1. The latter has been associated with a 32–base pair deletion in the C–C chemokine receptor gene CCR-5, the major coreceptor of macrophage-tropic strains of HIV-1. We have undertaken an analysis of the HIV-specific T cell responses in 12 EU individuals who were either homozygous for the wild-type CCR-5 allele or heterozygous for the deletion allele (CCR-5Δ32). We have found evidence of an oligoclonal T cell response mediated by helper T cells specific for a conserved region of the HIV-1 envelope. These cells produce very high levels of C–C chemokines when stimulated by the specific antigen and suppress selectively the replication of macrophage-tropic, but not T cell–tropic, strains of HIV-1. These chemokine-producing helper cells may be part of a protective immune response that could be potentially exploited for vaccine development.

Human immunodeficiency type 1 particle maturation is dependent upon proteolytic cleavage of the gag and gag-pol precursors by the pol-encoded viral protease. We have investigated the importance of domains of pol other than the protease for particle maturation and gag proteolytic processing. Truncations of the gag-pol polyprotein precursor of HIV-1 were created by deleting segments of the reverse transcriptase coding region or by introducing stop codons in the integrase region of an HIV-1 infectious molecular clone. In these mutants, the protease coding sequence was left intact. Particles produced by all of the mutants displayed abnormal morphologies and impaired proteolytic processing of gag. The severity of particle morphology abnormalities and of gag polyprotein processing impairment appeared to be affected both by the size and by the position of the deletions in pol, suggesting that the integrity of several pol domains within the gag-pol precursor is required for optimal protease activation and particle maturation. Additionally, cotransfection of a deletion mutant with wild-type provirus led to a marked reduction in the titer of infectious virus, suggesting that truncated gag-pol precursors can interfere with wild-type virus assembly and maturation.