The rate of spontaneous mutations in human myeloid cells

The mutation rate (mu) is likely to be a key parameter in leukemogenesis, but historically, it has been difficult to measure in humans. The PIG-A gene has some advantages for the detection of spontaneous mutations because it is X-linked, and therefore only one mutation is required to disrupt its function. Furthermore, the PIG-A-null phenotype is readily detected by flow cytometry. Using PIG-A, we have now provided the first in vitro measurement of mu in myeloid cells, using cultures of CD34+ cells that are transduced with either the AML-ETO or the MLL-AF9 fusion genes and expanded with cytokines. For the AML-ETO cultures, the median mu value was similar to 9.4 x 10(-7) (range similar to 3.6-23 x 10(-7)) per cell division. In contrast, few spontaneous mutations were observed in the MLL-AF9 cultures. Knockdown of p53 or introduction of mutant NRAS or FLT3 alleles did not have much of an effect on mu. Based on these data, we provide a model to predict whether hypermutability must occur in the process of leukemogenesis. (C) 2013 Elsevier B.V. All rights reserved.