532. Foamy Viral Vector Integration Sites in SCID-Repopulating Cells After MGMTP140K-Mediated In Vivo Selection

Foamy virus (FV) vectors are promising for hematopoietic stem cell (HSC) gene therapy but preclinical data on the clonal composition of FV vector transduced human repopulating cells is needed. Human CD34+ human cord blood cells were transduced with an FV vector encoding a methylguanine methyltransferase (MGMT) P140K transgene, transplanted into immunodeficient NOD/SCID IL2Rgnull (NSG) mice, and selected in vivo for gene-modified cells. The retroviral insertion site (RIS) profile of repopulating clones was examined using modified genomic sequencing PCR (MGS-PCR). We observed polyclonal repopulation with no evidence of clonal dominance even with the use of a strong internal spleen focus forming virus (SFFV) promoter known to be genotoxic. However we did observe that highly captured sites were found more often near proto-oncogenes than less frequently captured sites (Figure 1Figure 1). Our data supports the use of FV vectors with MGMTP140K for HSC gene therapy, but also suggests additional safety features should be developed and evaluated.Figure 1(a) Proximity of RIS to TSS of proto-oncogenes in Network of Cancer Genes 4.0 (NCG 4.0) cancer gene list (n = 2048). (b) Proportion of RIS within NCG 4.0 proto-oncogene transcripts or within 50 kb of a proto-oncogene TSS. In vivo low and in vivo high represent the lowest and highest thirds of RIS ranked by recovery frequency. Abbreviations: ns, not significant; RIS, retroviral insertion site; TSS, transcription start site.View Large Image | Download PowerPoint Slide