Since publication of the above paper, the authors have identified two errors.

Firstly, the RT2 and T9 cell lines used in the manuscripts were originally obtained by Dr Martin R Graf (Department of Anatomy, Virginia Commonwealth University, Richmond, VA, USA) from Dr Yancey Gillespie (Department of Neurobiology, University of Alabama at Birmingham, AL, USA) and Dr Gale Granger (Department of Molecular Biology, University of California, Irvine, CA, USA) and not the American Tissue Type Culture Collection (ATTCC) as stated in the Methods section.

Secondly, in the Acknowledgments section, the authors neglected to acknowledge Dr Graf, the investigator who kindly supplied the unpublished information showing that T9 cells were less tumorigenic in vivo than RT2 cells. The authors would like to apologise to Dr Graf for this omission.