Transduction of clonogenic human progenitors recovered from long-term engrafted bnx/hu mice. Human-specific CFU were plated ± G418 from the marrow of each mouse. CFU were plucked from the plates and subjected to PCR for the neo gene to confirm the presence of integrated vector. The percentages of transduction were calculated as (#G418-resistant CFU/# total CFU) × 100 = % G418-resistance.