“…2,3 Several clinical trials utilizing AAV for the treatment of cystic fibrosis, hemophilia, prostate cancer and muscular dystrophy are underway, with early evidence of human clotting factor IX production in hemophilia B patients. [4][5][6] In spite of its acknowledged safety, AAV has recently produced surprises in the field of gene therapy. Traces of AAV have been observed in treated patient's semen, and liver tumors of uncertain cause have been found in diseased mice treated with AAV vectors.…”