The β-globin Replicator greatly enhances the potential of S/MAR based episomal vectors for gene transfer into human haematopoietic progenitor cells

• DOI: 10.1038/srep40673
• Publication Date: 2017-01-20T11:42:36Z
• Authors: Eleana F. Stavrou; Vassileios M. Laz...; Aristeidis Gianna...; Eirini Papapetrou; Alexandros Spyrid...; Nikolas C. Zoumbos; Antonis Gkountis; Aglaia Athanassiadou
• Keywords: 0301 basic medicine; Genetic Vectors; Gene Dosage; Gene Transfer Techniques; Gene Expression; beta-Globins; Hematopoietic Stem Cells; Transfection; Article; Mice; 03 medical and health sciences; Genes, Reporter; Gene Order; Animals; Humans; Transgenes; K562 Cells; Plasmids

AbstractSpecific human chromosomal elements enhance the performance of episomal gene-transfer vectors. S/MAR-based episomal vector pEPI-eGFP transfects CD34+ haematopoietic cells, but only transiently. To address this issue we reinforced (1) transgene transcription by replacing the CMV promoter driving eGFP with the EF1/HTLV or SFFV promoters to produce vectors pEPI-EF1/HTLV and pEPI-SFFV, respectively; and (2) plasmid replication by inserting the replication-Initiation Region (IR) from the β-globin locus into vector pEPI-SFFV to produce vector pEP-IR. All vectors supported stable transfections in K562 cells. Transfections of CD34+ cells from peripheral blood of healthy donors reached 30% efficiency. Upon evaluation of CD34+/eGFP+ cells in colony-forming cell (CFC) assays, vector pEP-IR showed superior performance after 14 days, by fluorescent microscopy: 100% eGFP+-colonies against 0% for pEPI-eGFP, 56.9% for pEPI-SFFV and 49.8% for pEPI-EF1/HTLV; 50% more plasmid copies per cell and 3-fold eGFP expression compared to the latter two constructs, by quantitative (q)PCR and RT-qPCR, respectively. Importantly, the establishment rate in CFC assays was 15% for pEP-IR against 5.5% for pEPI-SFFV and 5% for pEPI-EF1/HTLV. Vector pEP-IR shows extremely low delivery rate but supports eGFP expression in thalassaemic mouse haematopoietic progenitor cells. The IR is a novel human control element for improved episomal gene transfer into progenitor cells.