title: Preselection of retrovirally transduced bone marrow avoids subsequent stem cell gene silencing and age-dependent extinction of expression of human beta-globin in engrafted mice.
abstract: Transcriptional silencing of genes transferred into hematopoietic stem cells poses one of the most significant challenges to the success of gene therapy. If the transferred gene is not completely silenced, a progressive decline in gene expression as the mice age often is encountered. These phenomena were observed to various degrees in mouse transplant experiments using retroviral vectors containing a human beta-globin gene, even when cis-linked to locus control region derivatives. Here, we have investigated whether ex vivo preselection of retrovirally transduced stem cells on the basis of expression of the green fluorescent protein driven by the CpG island phosphoglycerate kinase promoter can ensure subsequent long-term expression of a cis-linked beta-globin gene in the erythroid lineage of transplanted mice. We observed that 100% of mice (n = 7) engrafted with preselected cells concurrently expressed human beta-globin and the green fluorescent protein in 20-95% of their RBC for up to 9.5 mo posttransplantation, the longest time point assessed. This expression pattern was successfully transferred to secondary transplant recipients. In the presence of beta-locus control region hypersensitive site 2 alone, human beta-globin mRNA expression levels ranged from 0.15% to 20% with human beta-globin chains detected by HPLC. Neither the proportion of positive blood cells nor the average expression levels declined with time in transplanted recipients. Although suboptimal expression levels and heterocellular position effects persisted, in vivo stem cell gene silencing and age-dependent extinction of expression were avoided. These findings support the further investigation of this type of vector for the gene therapy of human hemoglobinopathies.
authors.affiliation: The Terry Fox Laboratory, British Columbia Cancer Agency, Vancouver, BC, Canada Y5Z 1L3.
authors.forename: C P
authors.initials: CP
authors.lastname: Kalberer
authors.forename: R
authors.initials: R
authors.lastname: Pawliuk
authors.forename: S
authors.initials: S
authors.lastname: Imren
authors.forename: T
authors.initials: T
authors.lastname: Bachelot
authors.forename: K J
authors.initials: KJ
authors.lastname: Takekoshi
authors.forename: M
authors.initials: M
authors.lastname: Fabry
authors.forename: C J
authors.initials: CJ
authors.lastname: Eaves
authors.forename: I M
authors.initials: IM
authors.lastname: London
authors.forename: R K
authors.initials: RK
authors.lastname: Humphries
authors.forename: P
authors.initials: P
authors.lastname: Leboulch
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology; D004912:Erythrocytes / Q000378:metabolism*; D020868:Gene Silencing; D005822:Genetic Vectors; D005914:Globins / Q000032:analysis / Q000235:genetics*; D049452:Green Fluorescent Proteins; D018380:Hematopoietic Stem Cell Transplantation; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000502:physiology*; D006801:Humans; D019901:Locus Control Region; D008164:Luminescent Proteins / Q000235:genetics; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D010735:Phosphoglycerate Kinase / Q000235:genetics; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012190:Retroviridae; D013997:Time Factors; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: D008164:Luminescent Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D005914:Globins; D010735:Phosphoglycerate Kinase