Activation of the human immunodeficiency virus type 1 long terminal repeat by vaccinia virus

A variety of DNA viruses are known to activate gene expression directed by the long terminal repeat (LTR) of human immunodeficiency virus type 1 (HIV-1). In light of the proposed use of recombinant vaccinia virus for HIV-1 vaccines, evaluation of the role of vaccinia virus in HIV-1 activation is warranted. To investigate whether vaccinia virus induces HIV LTR-directed gene expression, transient expression assays in Jurkat cells persistently infected with vaccinia virus (J_vac) using plasmid DNA containing the LTR linked to the bacterial chloramphenicol acetyltransferase (CAT) gene were performed. CAT activity in J_vac cells was always recorded, although the level appears to fluctuate independently of virus titers. Dual intracytoplasmic staining and fluorescence-activated cell sorter analysis showed that CAT activity was expressed in the infected cells. CAT expression was not due to plasmid replication, since plasmid DNA extracted from J_vac cells 48 h after transfection was restricted only by enzymes which recognize methylated sequences, indicating a prokaryotic source for the DNA. These findings suggest that a factor(s) present in vaccinia virus-infected cells is capable of activating the LTR of HIV-1.