PHENOTYPICALLY VIF(-) HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 IS PRODUCEDBY CHRONICALLY INFECTED RESTRICTIVE CELLS

The permissivity of CD4(+) transformed T cells for the replication of human immunodeficiency virus type 1 (HIV-1) vif mutants varies widely between different cell lines. Mutant vif-negative viruses propagate no rmally in permissive CD4(+) cell lines but are unable to establish a p roductive infection in restrictive cell lines such as H9. As a consequ ence, elucidation of the function of Vif has been considerably hampere d by the inherent difficulty in obtaining a stable source of authentic ally replication-defective vif-negative viral particles produced by re strictive cells. vif-negative, vpr-negative HIV-1 strain NDR stock, pr oduced by the permissive SupT1 cell line, was used to infect restricti ve H9 cells. By using a high multiplicity, infection of H9 cells was a chieved, leading to persistent production of viral particles displayin g a dramatically reduced infectious virus titer when measured in a sin gle-cycle infectivity assay. Although these viral particles were unabl e to further propagate in H9 cells, they could replicate normally in C EM and SupT1 cells. Comparison of unprocessed and processed Gag protei ns in the persistently produced vif-negative viral particles revealed no defect in the processing of polypeptide precursors, with no inversi on of the Pr55(gag)/p24 ratio. In addition, there was no defect in Env incorporation for the vif-negative viral particles. Despite their app arently normal protein content, these particles were morphologically a bnormal when examined by transmission electron microscopy, displaying a previously described abnormally condensed nucleoid. Chronically infe cted restrictive cell lines producing stable levels of phenotypically vif-negative HIV-1 particles could prove particularly useful in furthe r studies on the function of Vif in the virus life cycle.