Earlier work has shown that pre-B cells can be converted into macrophages by the 
transcription factor CCAAT/enhancer binding protein α at very high frequencies. 
Using this system, we performed a systematic analysis of whether during 
transdifferentiation the cells transiently reactivate progenitor-restricted 
genes or even retrodifferentiate. A transcriptome analysis of 
transdifferentiating cells showed that most genes are up- or down-regulated 
continuously, acquiring a macrophage phenotype within 5 d. In addition, we 
observed the transient reactivation of a subset of immature myeloid markers, as 
well as low levels of the progenitor markers Kit and FMS-like tyrosine kinase 3 
and a few lineage-inappropriate genes. Importantly, however, we were unable to 
observe the reexpression of cell-surface marker combinations that characterize 
hematopoietic stem and progenitor cells, including c-Kit and FMS-like tyrosine 
kinase 3, even when CAAT/enhancer binding protein α was activated in pre-B cells 
under culture conditions that favor growth of hematopoietic stem and progenitor 
cells or when the transcription factor was activated in a time-limited fashion. 
Together, our findings are consistent with the notion that the conversion from 
pre-B cells to macrophages is mostly direct and does not involve overt 
retrodifferentiation.