Enrichment of enzymatically corrected cells in vitro and in vivo in mixed-cell culture experiments evidenced by the increase in enzymatic activity. LB44 (□), LB44-LUDSN (▧), and a mixture of LB44 (80%) and LB44-LUDSN (20%) (▨) was cultured in vitro for 5 and 10 days or injected into immunodeficient mice and analyzed after 30 to 45 days. LB cells or B-cell tumors were resected and UROD activity was measured. * P < .05, **P < .01 v the LB44/LB44-LUDSN11 cells at day 0.