Systemic delivery of a high-capacity adenoviral vector expressing mouse CTLA4Ig improves skeletal muscle gene therapy

Adenoviral vectors (AdV) are promising vectors for gene transfer of skeletal muscle. To alleviate humoral and cellular immune responses that limit successful gene transfer, the present study determined the route of administration of AdmCTLA4Ig (an adenovirus that encodes a fusion protein of mouse cytotoxic T lymphocyte-associated protein 4 (CTLA4) and the Fc protion of immunoglobulin G (IgG), CTLA4Ig) that provided optimal AdV-mediated immunosuppression. AdmCTLA4Ig was administered either intramuscularly (i.m.), intravenously (i.v.), or in the footpad (f.p.) of mice that simultaneously received an i.m. injection of an AdV encoding enhanced green fluorescent protein (AdEGFP). EGFP expression in muscle and serum levels of CTLA4Ig were higher in the i.v. and f.p. groups than the i.m. group 30 days after treatment. The i.v. and f.p. groups showed lower levels of CD4(+) and CD8(+) T-cell infiltration and decreased interferon-gamma (IFN-gamma) and interleukin 2 (IL-2) production by splenocytes. The T helper cell (Th) 2 cytokine, interleukin 4 (IL-4), was increased 30 days after treatment in the i.v. group. Neutralizing antibodies to AdV were lower in the i.v. and f.p. groups, whereas total antibodies to AdV and EGFP were lower only in the f.p. group. Our results suggest that the optimal route of administration of AdmCTLA4Ig is i.v., providing at least 2 months of stable transgene expression in muscle. The inhibition of the cellular immune response, especially the Th1 response, appeared to play a critical role in prolonging transgene expression. These results suggest that AdV-mediated delivery of targeted immune suppression will be a useful adjunct to muscle gene delivery.