Expanded HIV-1 cellular tropism by phenotypic mixing with murine endogenous retroviruses

In view of the current interest in in vivo murine models for acquired immunodeficiency syndrome (AIDS), the interaction between human immunodeficiency virus type 1 (HIV-1) and endogenous murine leukemia virus (MuLV)-related retroviruses was investigated with a human leukemic T cell line (PF-382x) that acquired xenotropic MuLV (X-MuLV) after in vivo passage in immunosuppressed mice. Despite similar levels of membrane CD4 expression and HIV-1 125I-labeled gp 120 binding, a dramatic acceleration in the time course of HIV-1 infection was observed in PF-382x compared to its X-MuLV-negative counterpart (PF-382). Moreover, PF-382 cells coinfected by X-MuLV and HIV-1 generated a progeny of phenotypically mixed viral particles, enabling HIV-1 to productively infect a panel of CD4- human cells, including B lymphoid cells and purified normal peripheral blood CD4-/CD8+ T lymphocytes. Mixed viral phenotypes were also produced by human CD4+ T cells coinfected with an amphotropic MuLV-related retrovirus (A-MuLV) and HIV-1. These data show that endogenous MuLV acquired by human cells transplanted into mice can significantly interact with HIV-1, thereby inducing important alterations of HIV-1 biological properties.