Submitted September 22, 2008
Accepted February 26, 2009
Ectopic HOXB4 overcomes the inhibitory effect of tumor necrosis factor-
on Fanconi anemia hematopoietic stem and progenitor cells
Michael D. Milsom, Bernhard Schiedlmeier, Jeff Bailey, Mi-Ok Kim, Dandan Li, Michael Jansen, Abdullah Mahmood Ali, Michelle Kirby, Christopher Baum, Leslie J. Fairbairn, and David A Williams*
Division of Experimental Hematology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, United States
Department of Experimental Hematology, Hannover Medical School, Hannover, Germany
Center for Epidemiology and Biostatistics, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, United States
Gene Therapy Group, Cancer Research UK Paterson Institute for Cancer Research, Manchester, United Kingdom
* Corresponding author; email: dawilliams{at}childrens.harvard.edu.
Ectopic delivery of HOXB4 elicits the expansion of engrafting hematopoietic stem cells (HSC). We hypothesized that inhibition of TNF
signaling may be central to the self-renewal signature of HOXB4. Since HSC derived from Fanconi anemia (FA) knockout mice are hypersensitive to TNF, we studied Fancc-/- HSC to determine the physiologic effects of HOXB4 on TNF sensitivity and the relationship of these effects to the engraftment defect of FA HSC. Overexpression of HOXB4 reversed the in vitro hypersensitivity to TNF of Fancc-/- HSC and progenitors (P) and partially rescued the engraftment defect of these cells. Co-expression of HOXB4 and the correcting FA-C protein resulted in full correction compared with wild type (WT) HSC. Ectopic expression of HOXB4 resulted in a reduction in both apoptosis and reactive oxygen species in Fancc-/- but not WT HSC/P. HOXB4 overexpression was also associated with a significant reduction in surface expression of TNF receptors on Fancc-/- HSC/P. Finally, enhanced engraftment was seen even when HOXB4 was expressed in a time-limited fashion during in vivo reconstitution. Thus the HOXB4 engraftment signature may be related to its effects on TNF signaling and this pathway may be a molecular target for timed pharmacologic manipulation of HSC during reconstitution.
