Liver staining. One-month-old mice received either control buffer (A) or GP64/CMV-βgal vector (B-C). Three weeks after injection, livers were X-gal stained and examined under stereomicroscopy (2 representative mice from 3 separate sets of experiments from 15 experimental and 8 control animals are shown). (D) Liver tissue section. Most of the nuclear-targeted β-gal–positive cells were hepatocytes. In some cases 2 neighboring cells had blue nuclei (arrowheads), suggesting clonal expansion. (E) Plasma SGOT (left) and SGPT (right) levels at 24 hours after injection with PBS or FIV vector (5 experimental and 3 control mice, mean ± SE).