The gene targeting techniques used to modify chromosomes in mouse embryonic stem cells have had limited success with many other cell types, especially normal primary cells with restricted growth capacity outside the organism. This is due in large part to the technical problems and/or inefficiency of conventional DNA transfer methods, as well as the low rates of homologous recombination obtained in unselected cell populations. We recently described an alternative approach in which adeno-associated virus (AAV) vectors were used to modify homologous chromosomal sequences, and targeting rates close to 1% were observed at the single copy hypoxanthine phosphoribosyl transferase (HPRT) locus in normal human cells (D, W, Russell and R, K, Hirata, Nat, Genet, 18:325-330, 1998), Here we report experiments in which we used a retroviral shuttle vector system to introduce and characterize target loci in human chromosomes, and demonstrate that AAV vectors can correct several types of mutations with high fidelity, independent of chromosomal position, The gene targeting rates varied depending on the type of mutation being corrected, implicating cellular mismatch recognition functions in the reaction, Since AAV vectors can efficiently deliver DNA to many cell types both in vivo and ex vivo, our results suggest that AAV-mediated gene targeting will have wide applicability, including therapeutic gene correction.
