CD34 and acute myeloid leukemia: The absolute LSC content within the CD34+CD38− fraction, quantified using limiting dilution xenograft assays, established that the LSC frequency was high (1/286; range: 1/102–1/804) (Table 2) when compared to the spectrum of LSC frequencies from fractions obtained from primary AML samples [9, 34] (Supplementary Fig. S2A).