1. ¹Molecular Hematopoiesis Section, Hematology Branch, National Heart, Lung, Blood Institute, National Institute of Health, Bethesda,Maryland,USA
2. ²Genome Technology Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland, USA
3. ³HIV Drug Resistance Program, National Cancer Institute at Frederick, Frederick, Maryland, USA
4. ⁴Department of Medicine, Division of Hematology, University of Washington, Seattle, Washington, USA

Correspondence: Cynthia E. Dunbar, Hematology Branch, National Heart, Lung, Blood Institute, National Institute of Health, Building 10-CRC, Room 4-5132, 10 Center Drive, Bethesda, Maryland, USA. E-mail: dunbarc@nhlbi.nih.gov

Received 21 February 2008; Accepted 21 May 2008; Published online 24 June 2008.

Abstract

Insertional mutagenesis continues to be a major concern in hematopoietic stem-cell gene therapy. Nonconventional gene transfer vectors with more favorable integration features in comparison with conventional retrovirus and lentivirus vectors are being developed and optimized. In this study, we report for the first time a systematic analysis of 198 avian sarcoma leukosis virus (ASLV) insertion sites identified in rhesus long-term repopulating cells, and a comparison of ASLV insertion patterns to Moloney murine leukemia virus (MLV) (n = 396) and simian immunodeficiency virus (SIV) (n = 289) using the newly released rhesus genome databank. Despite a weak preference toward gene-coding regions, ASLV integration is nonclustered, does not favor gene-rich regions, transcription start sites, or CpG islands. There was no propensity for ASLV insertions within or near proto-oncogenes, and most importantly, no insertions close to or within the Mds1-Evi1 locus, which is in contrast to the significant over-representation of this insertion site for MLV vectors in the same transplantation model. Furthermore, ASLV long terminal repeats (LTRs) do not have detectable promoter and enhancer activity in a quantitative luciferase assay to measure neighboring gene activation. The combination of these features is unique for ASLV and suggests that optimized vectors based on this virus could be useful and safe for gene transfer to hematopoietic stem cells and progenitor cells.