Model for gene therapy of the cystic fibrosis airway: human bronchial 
xenograft reconstituted with cells from a CF patient following retro- 
viral infection with the ^-galactosidase reporter gene. Darkfield photo- 
micrograph shows blue cells following a histochemical stain for 
0-galactosidase. 
Research and photograph by fohn Engelhardt in the laboratory of 
fames Wilson. 
