Adenovirus vectors can transfer recombinant genes efficiently into a wide variety of cells in vivo, but have serious limitations: gene expression is transient and secondary gene transfer is inefficient or impossible because of cellular and humoral immune responses against adenovirus-transduced cells. To solve these limitations, we have constructed an adenovirus vector, Adex1CACTLA4IgG, that expresses CTLA4IgG molecules. After in vivo administration of Adex1CACTLA4IgG (9.0 x 109 PFU), the peak level of serum CTLA4IgG was 29.8 mg/ml on day 4. The serum CTLA4IgG concentration gradually fell but was still 5.7 mg/ml on day 90, However, the serum concentration of CTLA4IgG was elevated after a second administration of Adex1CACTLA4IgG. The production of antibody against adenovirus was completely prevented after treatment with Adex1CACTLA4IgG. In addition, coadministration of Adex1CALacZ with Adex1CACTLA4IgC induced persistent hepatic expression of β-Gal molecules, while administration of Adex1CALacZ alone induced transient expression of β-Gal molecules. More importantly, on day 160 a secondary challenge with Adex1CALacZ was possible in mice treated with Adex1CALacZ plus Adex1CACTLA4IgG. Thus, we have demonstrated that (1) gene expression of a recombinant adenovirus, Adex1CACTLA4IgG, is persistent in liver and secondary administration of this adenovirus is possible, (2) coadministration of Adex1CACTLA4IgG virus with another adenovirus, AdexCALacZ, prolongs AdexCALacZ-mediated gene expression, and (3) Adex1CACTLA4IgG is useful for secondary challenge with Adex1CALacZ.
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