TOWARDS DEVELOPING HIV-2 LENTIVIRUS-BASED RETROVIRAL VECTORS FOR GENE-THERAPY - DUAL GENE-EXPRESSION IN THE CONTEXT OF HIV-2 LTR AND TAT

Because of the distinct ability of retroviruses to integrate into the target cell genome and thus achieve long-term expression, retrovirus v ectors hold great promise for stable gene transfer. Such vectors deriv ed from human immunodeficiency retroviruses (HIVs) and other lentiviru ses are envisioned to possess several advantages, especially for in vi vo gene therapy of HIV infection and acquired immunodeficiency syndrom e (AIDS) where targeting CD4+ T cells/macrophages and pluripotent non- dividing stem cells would be required. Among these is the ability of H IVs to transduce nondividing cells in contrast to the murine retroviru ses which require target cell mitosis. The advantages of the lentiviru s vectors will be further enhanced by the development of multigenic ve ctors carrying more than one gene in a dependent or independent transc riptional unit. Separate from the issue of transduction efficiency, in formation is needed about the impact of the configuration of the genes in a multigenic vector on their expression. Towards this end, we inve stigated the expression of genes specifically directed by the HIV-2 LT R and Tat in a prototypic minimal transfer vector. We found that the e xpression of a gene in a dual gene configuration depended upon its pos ition in the transcriptional unit and that the insertion of an interna l translational initiation mechanism improved the expression of the do wnstream gene. Apparently not sufficiently appreciated previously, the se effects were promoter and cell-type dependent. Our data also sugges t that the commonly used cellular or viral promoters may be orders of magnitude less effective than HIV-2 LTR in the presence of Tat, and th us may not be useful as internal promoters in the context of the HIV-2 LTR:Tat regulatory loop. (C) 1998 Wiley-Liss, Inc.dagger.