Intracellular antibodies as a new class of therapeutic molecules for gene therapy.

Intracellularly expressed antibodies, referred to as "intrabodies" can be designed to bind and inactivate target molecules inside cells. In our previous study, mammalian cells were transduced to produce an anti-gp120 single-chain intrabody sFv105 to inactivate human immunodeficiency virus type-1 (HIV-1) infection. Here, an inducible expression vector was constructed in which the sFv105 intrabody, which reacts with the CD4-binding site of HIV-1 gp120, is under the control of the HIV-1 long terminal repeat (LTR)/promoter. The sFv105 intrabody is inducibly expressed after HIV-1 infection or in the presence of Tat protein and is retained intracellularly. A human CD4+ lymphocyte line transformed with the expression vector exhibits resistance to the virus-mediated syncytium formation and a decreased ability to support HIV-1 production. Surface gp120 expression is markedly reduced and surface CD4 is restored to normal following HIV-1 infection in the transformed lymphocytes. Cell-surface phenotype, replication rate, morphology, and response to mitogenic stimulation of the transformed cells are also normal. Thus, intrabodies are a new class of active molecules that may be useful for the gene therapy of acquired immunodeficiency virus (AIDS) and other diseases.