Photomicroscopic images demonstrating oxidase correction (NBT-positive staining in gp91^phox–transduced X-CGD cells) and CFP transgene expression (fluorescence of CFP–transduced normal cells), panels A and B, respectively, in colonies derived from transduced CD34⁺ cells purified from chimeric mice. (A) NBT-positive colony from RD114-MFGSgp91^phox–transduced X-CGD CD34⁺ PBSCs, 14 days after immunobead selection of human CD34⁺ cells from mouse bone marrow. Original magnification, × 60. NBT-negative colonies do not form formazan precipitate but can be delineated by safranin counter staining (not shown). (B) CFP-positive colony from RD114-MFGS-CFP–transduced normal CD34⁺ PBSCs, 14 days after immunobead selection of human CD34⁺ cells from mouse bone marrow. Original magnification, × 100.