Effect of transfected PA317 cell supernatants on murine marrow cultures propagated in vitro. (A) Media from PA317 cells transfected with vector alone or transfected with (B) vector with HIV-1 Vpr expression cassette or (C) vector with HIV-1 Tat expression cassette. E, free erythrocyte; M, erythrocyte-coated mononuclear phagocyte. The results shown are typical of at least three independent experiments.