Induction of antigen-specific CD4+T-cell anergy and deletion by in vivo viral gene transfer

Immune responses to the therapeutic gene product are a potentially serious complication in treatment of genetic disease by gene therapy. Induction and maintenance of immunologic hypo-responsiveness to the therapeutic antigen is therefore critical to the success of gene-based treatment of inherited protein deficiency. Here, we demonstrate induction of antigen-specific CD4(+) T-cell tolerance to a secreted transgene product (ovalbumin, ova) in ova-specific T-cell receptor (TCR) transgenic mice by hepatic adeno-associated virus (AAV)-mediated gene transfer. Transduced mice maintained stable circulating ova levels without evidence of an immune response. Lymph node cells and splenocytes were hyporesponsive to ova as early as day 10 after gene transfer. Numbers of TCR(+)CD4(+) cells were reduced in secondary lymphoid organs and in the thymus by 1 to 2 months after vector administration. The remaining TCR+CD4+ cell population was anergic to ova antigen in vitro and enriched for CD25(+) cells. These data provide direct evidence that transgene expression following in vivo viral gene transfer can induce CD4(+) T-cell tolerance to the transgene product, involving anergy and deletion mechanisms. (C) 2004 by The American Society of Hematology.