HIV-Regulated Diphtheria Toxin A Chain Gene Confers Long-Term Protection Against HIV Type 1 Infection in the Human Promonocytic Cell Line U937

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Abstract
Gene therapy approaches have recently been investigated for the treatment of acquired immunodeficiency syndrome (AIDS), both in preclinical and clinical studies, because more traditional antiviral agents have proven to be of limited effectiveness. We have previously shown that long-term protection against both laboratory and clinical isolates of human immunodeficiency virus type 1 (HIV-1) was conferred by HIV-regulated diphtheria toxin A (DT-A) chain in a human T cell line. Because the monocyte/macrophage cell is an important reservoir for HIV-1 in infected individuals, we sought here to determine whether HIV-regulated DT-A would also be effective in the promonocytic cell line U937. We report here that long-term protection, conferred by HIV-regulated DT-A, was observed in U937 cells, but that protection was dependent on the stock of HIV IIIB used for challenge. HIV production was measured by p24 assays, polymerase chain reaction (PCR) for HIV vif, gag, and reverse transcriptase (RT) sequences, and cocultivation with peripheral blood mononuclear cells (PBMCs). Complete protection was seen in DT-A-transduced cells with a stock of IIIB propagated on H9 cells and titered on peripheral blood mononuclear cells (PBMCs), while protection in these same cells with a second stock of IIIB, propagated and titered on H9 cells, was only partial and dose dependent. U937 cells transduced with an human immunodeficiency virus (HIV)-regulated diphtheria toxin A (DT-A) chain gene showed long-term protection against a stock of HIV IIIB prepared and titered on PBMCs. However, protection against a second stock of IIIB, prepared and titered on H9 cells, was only partial and dose dependent. This finding supports the idea that HIV-regulated DT-A can be very effective at inhibiting HIV production in a promonocytic cell type, but that further optimization of this approach is required to be effective against all potential HIV strains and target cell types.