Blocking NF-κB nuclear translocation inhibits human CD34⁺ bone marrow cell colony formation. Human CD34⁺ bone marrow was purified (>96% pure) and cultured in methyl cellulose medium containing various cytokines and (1) 200 μg/mL NF-κB NLS peptide, (2) 200 μg/mL control peptide, and (3) no peptides. Error bars indicate 1 standard error of mean (SEM) for 5 cultures and are omitted when smaller than the data symbol. *Significant decrease compared with cultures containing the control peptide (P ≤ .05).