Promoter Attenuation in Gene Therapy: Interferon-γand Tumor Necrosis Factor-αInhibit Transgene Expression

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Abstract
One of the major limitations to current gene therapy is the low-level and transient vector gene expression due to poorly defined mechanisms, possibly including promoter attenuation or extinction. Because the application of gene therapy vectors in vivo induces cytokine production through specific or nonspecific immune responses, we hypothesized that cytokine-mediated signals may alter vector gene expression. Our data indicate that the cytokines interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) inhibit transgene expression from certain widely used viral promoters/enhancers (cytomegalovirus, Rous sarcoma virus, simian virus 40, Moloney murine leukemia virus long terminal repeat) delivered by adenoviral, retroviral or plasmid vectors in vitro. A constitutive cellular promoter (β-actin) is less sensitive to these cytokine effects. Inhibition is at the mRNA level and cytokines do not cause vector DNA degradation, inhibit total cellular protein synthesis, or kill infected/transfected cells. Administration of neutralizing anti-IFN-γ monoclonal antibody results in enhanced transgene expression in vivo. Thus, standard gene therapy vectors in current use may be improved by altering cytokine-responsive regulatory elements. Determination of the mechanisms involved in cytokine-regulated vector gene expression may improve the understanding of the cellular disposition of vectors for gene transfer and gene therapy. Transgene expression can be eliminated even in the presence of substantial amounts of vector DNA in the transduced cells, which suggests that mechanisms other than the antigen-specific immune response may mediate non-cytodestructive events that determine the presence of transgene expression. Our data indicate that the cytokines interferon-γ) (IFN-γ) and tumor necrosis factor-α (TNF-α) inhibit transgene expression from certain widely used viral promoters/enhancers (human cytomegalovirus immediate early, Rous sarcoma virus long terminal repeat, simian virus 40, Moloney murine leukemia virus long terminal repeat) delivered by adenoviral, retroviral, or plasmid vectors in vivo. Inhibition is at the mRNA level and cytokines do not cause vector DNA degradation, inhibit total cellular protein synthesis, or kill infected/transfected cells. Thus, cytokine-regulated promoter function rather than specific immune destruction could limit transgene expression. These results have significant implications for the construction of transfer vectors for human gene therapy because gene transfer vectors could be exposed to a cytokine-rich environment when they are administered in vivo.