Effect of scaffold attachment region on transgene expression in retrovirusvector-transduced primary T cells and macrophages

The scaffold attachment region of the human interferon beta gene (IFN-SAR) inserted into a retroviral vector improved transgene expression in human pr imary CD4(+) and CD8(+) T cells, and in primary monocyte-macrophages. In T cells, expression of the Maloney murine leukemia virus (Mo-MuLV)-based retr oviral vectors was high in activated cells but low in resting cells. Additi on of the IFN-SAR sequence enhanced vector expression 2- to 10-fold, and th e effect was particularly pronounced in resting T cells. In CD33(+)CD14(+)C D4(+) monocyte-macrophages derived from transduced hematopoietic stem/proge nitor cells (HSPCs) in vitro, the IFN-SAR enhanced vector expression three- to sixfold. We have used the IFN-SAR-containing vectors to express the Rev M10 gene, a trans-dominant mutant of the human immunodeficiency virus type 1 (HIV-1) rev gene. Compared with a standard retroviral vector, the IFN-SAR -containing vector was significantly (p < 0.01) more potent at inhibiting H IV-1 replication in infected CD4+ peripheral blood lymphocytes. In monocyte s, however, addition of the IFN-SAR did not significantly improve antiviral efficacy. To understand better the reason for the strong effect of the SAR on antiviral efficacy in T cells we have studied the expression of HIV, Mo -MuLV, and Mo-MuLV + SAR vectors in resting and activated cells. While the expression of all three vectors was lower in resting compared with activate d cells, the kinetics of the decrease in expression were fastest for the Mo -MuLV vector, followed by the HIV vector and then the Mo-MuLV + SAR vector. Thus, higher level expression of the Mo-MuLV + SAR vector relative to wild -type HIV at all stages of T cell activation is the most likely explanation for the strong antiviral efficacy. Overall, this study demonstrates the ut ility of the IFN-SAR sequence for achieving high-level retroviral vector ex pression in lymphoid and myeloid hematopoietic cells.