Reversal of hypopigmentation in phenylketonuria mice by adenovirus-mediated gene transfer

Phenylketonuria (PKU) is caused by deficiency of phenylalanine hydroxylase (PAH) in the liver. Patients with PKU show increased L-phenylalanine in blo od, which leads to mental retardation and hypopigmentation of skin and hair . As a step toward gene therapy for PKU, we constructed a replication-defec tive, E1/E3-deleted recombinant adenovirus harboring human PAH cDNA under t he control of a potent CAG promoter. When a solution containing 1.2 X 10(9) plaque-forming units of the recombinant adenovirus was infused into tail v eins of PKU model mice (Pah(enu2)), predominant expression of PAH activity was observed in the liver. The gene transfer normalized the serum phenylala nine level within 24 h. However, it also provoked a profound host immune re sponse against the recombinant virus; as a consequence, the biochemical cha nges lasted for only 10 d and rechallenge with the virus failed to reduce t he serum phenylalanine concentration. Administration of an immunosuppressan t, FK506, to mice successfully blocked the host immune response, prolonged the duration of gene expression to more than 35 d, and allowed repeated gen e delivery. We noted a change in coat pigmentation from grayish to black af ter gene delivery. The current study is the first to demonstrate the revers al of hypopigmentation, one of the major clinical phenotypes of PKU in mice as well as in humans, by adenovirus-mediated gene transfer, suggesting the feasibility of gene therapy for PKU.