Comparison of the transduction efficiencies using amphotropic versus ecotropic retroviral vectors. (A) and (C) depict the Lin⁻/FSC^low/c-Kit⁺ stem cell–enriched population, whereas (B) and (D) depict the Lin⁻/FSC^high/c-Kit⁺ progenitor cell–enriched population. The shaded areas represent nontransduced ASMKO cells, whereas the open areas depict transduced cells. Note that FL-1 measures B12SPM. The experiment was repeated three times, and the representative data from one experiment are shown.