Attenuation of human immunodeficiency virus type 1 cytopathic effects by replacing a 424-bp region of envelope from a noncytopathic biological clone

Enhancement of human immunodeficiency virus type 1 infectivity by replacing the region including Env derived from defective particles with an ability to form particle-mediated syncytia in CD4+T cells

The infection and subsequent replication rates of human immunodeficiency virus type 1 (HIV-1) affect the pathogenicity. The initial stage of HIV-1 infection is largely regulated by viral envelope sequence. We previously reported that the defective doughnut-shaped particles produced from a persistently infected cell clone, named L-2, obtained from human CD4+ T-cell line MT-4 that was persistently infected with HIV-1 LAI strain, efficiently form particle-mediated syncytia with uninfected human CD4+ T-cell line, MOLT-4. Here, we prepared a molecular clone (pL2) containing the L-2 provirus to characterize the viral genetic region contributing to this activity to form particle-mediated syncytia. Several recombinants were constructed with pNL4-3 by replacing the pL2-derived region including full-length env. Characterization of the particles obtained by transfection with these recombinant clones confirmed that pL2-derived env carried the particle-mediated syncytia formation activity. It is noteworthy that the pL2-derived env region could also contribute to enhancement of infectivity in CD4+ T-cell lines as well as primary peripheral blood mononuclear cells (PBMCs). Thus, the HIV-1 particle-mediated syncytium formation activity could also contribute to the enhancement of HIV-1 infectivity.

Evidence for a cytopathogenicity determinant in HIV-1 Vpr

HIV-1 is cytopathic for CD4(+) T lymphocytes in vitro and this property of HIV-1 is generally considered to account for some of its in vivo cytopathogenicity. Thus, the extent of lymphocyte depletion correlates with the level of viremia whereas low levels of viral replication are typically associated with stable lymphocyte levels and asymptomatic infection such as is observed in non-progressors. Here, we describe a non-progressor who did not fit this general pattern in that CD4(+) T lymphocyte homeostasis was maintained in the face of high-level viral replication. Biological viral isolates from this patient replicated in primary lymphocytes without inducing cytopathicity. Because this phenotype is reminiscent of Vpr-deleted viruses, we examined the contribution of the Vpr gene to the viral phenotype. Vpr alleles derived from this patient contained both premature stop codons and an unusual Q3R polymorphism. Insertion of patient-derived Vpr alleles or a Q3R substitution into a cytopathic HIV-1 clone resulted in a marked impairment of cytopathicity without affecting viral replication efficiency. The effect of Vpr on cytopathicity was unrelated to reported activities of Vpr including virion association, interaction with uracil DNA glycosylase, G(2) arrest, or enhancement of macrophage infection but correlated with the ability of Vpr to induce host cell apoptosis. This study suggests the presence of a determinant of in vivo cytopathogenicity within HIV-1 Vpr and further indicates that viral replication can be uncoupled from cytopathicity in vitro and in vivo.