Use of cis- and trans-acting viral regulatory sequences to improve expression of human immunodeficiency virus vectors in human lymphocytes

We compared the efficiency of human immunodeficiency virus (HIV-I) vectors that express a marker gene (chloramphenicol acetyltransferase, CAT) using different promoter elements. In one vector, CAT was expressed under the control of an internal murine leukemia virus (MuLV) long terminal repeat (LTR). In other vectors, CAT production was regulated by the HIV-1 LTR; these vectors also contained the HIV-I tat gene and pol sequences reported to exert cis-acting positive effects on reverse transcription or gene expression. Vectors employing the Tat-driven HIV-I LTR exhibited up to 500-foId greater CAT expression in Jurkat lymphocytes or human peripheral blood mononuclear cells compared with vectors using the internal MuLV LTR element as a promoter. This difference was not due to improved packaging of the vector RNA into virions, but to an improved level of gene expression in the target cells. Target cell CAT expression was two- to threefold higher for the vector containing the pol sequences and was only slightly less than that seen for a trans-complemented env-deleted provirus. These results indicate that defective HIV-I vectors with efficiencies of gene transfer and expression comparable with that of HIV-1 itself are feasible.