Gene targeting of X chromosome-linked chronic granulomatous disease locus in a human myeloid leukemia cell line and rescue by expression of recombinant gp91

The X chromosome-linked chronic granulomatous disease (X-CGD) locus, which encodes the gp91^phox subunit of the phagocyte respiratory-burst oxidase cytochrome b, was disrupted by homologous recombination in the PLB-985 human myeloid cell line to develop an in vitro model of X-CGD. Superoxide formation was absent in targeted cells after differentiation to granulocytes but was rescued by stable transfection and expression of wild-type gp91^phox cDNA. The targeted cell line should be useful in experiments aimed at defining functional regions within gp91^phox by expression of mutant gp91^phox cDNAs, complementing studies of naturally occurring mutations in X-CGD. In addition, the mutant line provides a model system in which to establish an experimental basis for the treatment of X-CGD patients with gene replacement therapy. Rescued clones containing even modest amounts of recombinant gp91^phox had respiratory-burst activity comparable to the wild-type PLB-985 line, suggesting that functional correction of X-CGD neutrophils may not require high-level expression of gp91^phox.