Multiple advantages of alpha-fetoprotein as a marker for in vivo gene transfer

The development of improved gene transfer vectors has been hampered by the lack of a nonimmunogenic reporter gene that can be serially quantified in t he serum or from other sites. In response to the need to develop a new repo rter protein, we have evaluated alpha -fetoprotein (AFP) as a potential can didate. A first-generation E1/E3-deleted adenoviral vector expressing human AFP (hAFP) was generated as a preliminary tool to evaluate AFP as a report er. Using both mouse and baboon models, hAFP expression was evaluated in se rum after intravenous delivery and in serum and bronchioalveolar lavage (BA L) fluid after delivery to the lung. In immunocompetent animals, intravenou s delivery of the hAFP adenoviral vector resulted in hAFP expression in the serum early after injection, which declined rapidly over time. Disappearan ce of hAFP from the serum was complete by 3-4 weeks after administration an d was accompanied by robust antibody responses to hAFP and loss of infected cells. After lung delivery, hAFP could be detected in both serum and BAL. This allowed the analysis of the kinetics of gene expression in the lung wi thout sacrificing the animals. In both liver and lung, immunohistochemical analysis correlated well with hAFP levels as detected in serum or BAL, indi cating that serum levels were a reliable marker of tissue expression. Preli minary results with a mouse AFP expressed in a helper-dependent adenoviral vector indicate that use of a species-specific version of AFP will eliminat e the complication of antibody development. These initial evaluations sugge st that AFP is useful as a reporter gene to evaluate gene expression of the rapeutic cassettes in multiple tissues, and it should be considered for use in human subjects.