Modulation of Moloney leukemia virus long terminal repeat transcriptional activity by the murine CD4 silencer in retroviral vectors

We investigated whether CD4 gene regulatory sequences might be useful for d eveloping transcriptionally targeted Moloney murine leukemia Virus (Mo-M LV )-based retroviral vectors for gene expression specifically in CD4(+) cells . We could modulate Mo-MLV long terminal repeat (LTR) activity by inserting a 438-bp-long fragment containing the murine CD4 silencer in the LTR of th e vector; both beta -galactosidase and green fluorescent protein reporter g ene activities were strongly down-regulated in both murine and human CD8(+) cells, but not in CD4(+) lymphoid cell lines and freshly isolated lymphocy tes transduced with this vector, compared with the findings using a control vector carrying wild-type LTRs. Titration experiments on NIH-3T3 cells rev ealed that inclusion of the CD4 silencer in the LTRs did not reduce the tit er of the vectors. These findings indicate that a cellular silencer can be successfully included in retroviral vectors, where it maintains its transcr iption-regulatory function, thus suggesting a novel approach to transcripti onal targeting. (C) 2000 Academic Press.