Synthesis of human globin polypeptides mediated by recombinant adeno-associated virus Vectors

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Adeno-associated virus, serotype 2 (AAV2)-based chimeric plasmids that harbored a near-full-length human α- or α- or β-globin cDNA were constructed. The cDNAs were spliced into an AAV plasmid, pAAVΔK, downstream from the viral P40 promoter, substituting the capsid gene region. The correctness of the insertion with regard to the transcriptional polarity was ascertained by both restriction enzyme analysis and DNA sequencing. One of the constructs, pAAVcHBBLCR, contained the enythroid-specific enhancer elements, the locus control region, HS1 and HS2, to ensure an efficient and tissue-specific gene expression. Use of a defective complementing helper, pAVXB (Dixit, M.; et al. Gene 1991, 104, 253-257.) and adenovirus 2 made it possible to prepare recombinant AAVs (rAAVs). Infection of human 293 cells (embryonal kidney cell line) with the resultant rAAV (AAVcHBB) and cotransfection of mouse erythroleukemia (MEL) cells with the β-globin construct (pAAVcHBBLCR) and an α-globin construct (pAAVcHAB) triggered efficient synthesis of human globin polypeptides in the cells, as analyzed by biochemical and immunohistochemical means. The LCR made the construct respond to an inducer, N,N-hexamethylenebisacetamide, the amount of expressed human β-globin reaching a similar level as the endogenous mouse β-globin in MEL cells. Electrotransfection of mouse bone marrow hematopoietic stem/progenitor cells with the constructs dramatically increased the number of benzidine-positive cells in liquid suspension culture, indicating expression and synthesis of a human hemoglobin in these cells. Thus, the rAAV constructs may be useful for gene therapy of hemoglobinopathies.

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