Several clinical studies of gene-modified T cells have shown limited in vivo function of the cells, immunogenicity of the transgene, and lack of a selective advantage for genemodified T cells. To address these problems, we developed a lentiviral vector (LV) that provides a selectable, proliferative advantage and potentially decreases immunogenicity for transduced T cells. The bicistronic vector expressed two genes linked with an internal ribosomal entry site. One gene is a variant of the inosine monophosphate dehydrogenase 2, inosine monophosphate dehydrogenase (IMPDHIY), conferring resistance to the immunosuppressive drug mycophenolate mofetil (MMF). The other is a suicide gene, herpes simplex virus thymidine kinase (HSV-TK), rendering proliferating cells sensitive to ablation with ganciclovir, fused to the selectable transmembrane marker DCD34 (DCD34/TK). Cells transduced with V-DCD34/TK.IMPDHIY were efficiently enriched by immunomagnetic selection for CD34, proliferated in 0.5-5 μM MMF, and were killed by 0.5 25 μg ml1 ganciclovir. We demonstrate efficient selection and killing of gene-modified cells and suggest LV-ΔCD34/TK.IMPDHIY- transduced T cells could be used to facilitate allogeneic hematopoietic cell engraftment. The expression of IMPDHIY would allow in vivo selection with MMF, and DCD34/TK expression would allow rapid and safe elimination of transduced T cells if raft-versus-host disease developed.
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