Episomal Vectors Based On S/Mar And The Beta-Globin Replicator, Encoding A Synthetic Transcriptional Activator, Mediate Efficient Gamma-Globin Activation In Haematopoietic Cells

We report the development of episomal vectors for the specific gamma-globin transcription activation in its native position by activator Zif-VP64, based on the Scaffold/Matrix Attachment Region (S/MAR) for episomal retention and the beta-globin Replicator, the DNA replication-Initiation Region from the beta-globin locus. Vector Zif-VP64-Ep1 containing transcription cassettes CMV-Zif-VP64 and CMV-eGFP-S/MAR transfected a)K562 cells; b)murine beta-YAC bone marrow cells (BMC); c)human haematopoietic progenitor CD34(+) cells, with transfection efficiencies of 46.3 +/- 5.2%, 23.0 +/- 2.1% and 24.2 +/- 2.4% respectively. K562 transfections generated stable cell lines running for 28 weeks with and without selection, with increased levels of gamma-globin mRNA by 3.3 +/- 0.13, of gamma-globin protein by 6.75 +/- 3.25 and HbF protein by 2 +/- 0.2 fold, while the vector remained episomal and non integrated. In murine beta-YAC BMCs the vector mediated the activation of the silent human gamma-globin gene and in CD34+ cells, increased gamma-globin mRNA, albeit only transiently. A second vector Zif-VP64-Ep2, with both transcription cassettes carrying promoter SFFV instead of CMV and the addition of beta-globin Replicator, transferred into CD34+ cells, produced CD34(+) eGFP(+) cells, that generated colonies in colony forming cell cultures. Importantly, these were 100% fluorescent, with 2.11 +/- 0.13 fold increased gamma-globin mRNA, compared to non-transfected cells. We consider these episomal vectors valid, safer alternatives to viral vectors.