Lentiviral Insertion Site Analysis of Corrected Mouse Model of β Thalassemia Following Lentiviral Transduction of Embryonic Stem Cells.

The delivery of therapeutic transgenes via lentiviral transduction of stem cells holds great promise for future cell based therapies for inherited genetic disorders. The regulation of any transgene integrated into patient derived embryonic stem (ES) cells (generated via nuclear transfer or reprogramming) needs to be studied in great detail prior to their differentiation and transplantation back into the patient. Because genetically manipulated ES cells can be clonally isolated, expanded to great numbers in an undifferentiated state, and differentiated to specific cell types, they can be carefully tested in vitro prior to their reintroduction back into patients. ES cells derived from a mouse model of β thalassemia were transduced with a recombinant, self inactivating (SIN) lentiviral vector containing a 2.3 kb human β-globin gene and a 3.2 kb Locus Control Region composed of regulatory elements; HS2, HS3, and HS4. Clonal populations of transfected β thalassemic ES cells were isolated, archived, and utilized to produce genetically identical offspring by injection into tetraploid blastocysts or eight-cell embryos. Real-Time QPCR expression analyses demonstrated high levels of human β-globin gene expression in the peripheral blood of five of the six lines produced. The average expression level per transgene copy number ranged from 13% to 62% of endogenous mouse α-globin levels. Peripheral blood hemolysates analyzed by HPLC confirmed the high level production of human β-globin chains. Measurement of the red blood indices in these five lines showed that the anemia was corrected. In order to examine the influence of chromosomal position effects on individual transgene expression, the lentiviral insertion sites were mapped by linear amplification (LAM) PCR. Cloned mice from the six lines were bred in order to segregate each of their individual lentiviral transgenes. Offspring containing single insertion sites were analyzed for human β-globin transgene expression and synthesis by Real-Time QPCR of blood RNA and by HPLC of hemolysates, respectively. These analyses demonstrate that there is a preference for provirus integration in ES cells; all transgene insertions are not expressed equally; lentiviral transduction of a human β-globin gene into ES cells can cure a severe hemoglobinopathy; and that the delivery of therapeutic transgenes via lentiviral transduction of ES cells did not harm the developmental potential of the cells to produce an entire mouse.