In vivo studies of gene expression via transient transgenesis using lipid-DNA delivery

As the sequencing of the human genome proceeds, the need for a new screen f or in vivo function is becoming apparent. Many investigators are turning to various transgenic models as a means of studying function. However, these approaches are very time consuming, with a transgene-expressing mouse model often taking months to establish. We have developed an efficient system fo r delivering genes in vivo, which allows the gene product to be studied as early as 24 h after introduction into the mouse model. The delivery system employs a novel cationic lipid, 1-[2-(9-(Z) -octadecenoyloxy)ethyl]-2-(8-(Z )-heptadecenyl)-3-(hydroxyethyl)imidazolinium chloride (DOTIM), and a neutr al lipid, cholesterol, complexed with an expression vector containing the r eporter gene chloramphenicol acetyl transferase (CAT), After a single intra venous injection of these complexes, several tissues were seen to express t he transgene, High, persistent expression in the vascular endothelial cells in the mouse lung was obtained. Delivery of DNA in vivo has been evaluated by quantitative polymerase chain reaction and protein expression by CAT ac tivity assays, In vivo studies showed reproducible expression in more than 500 mice injected via the tail vein. An early peak of expression was follow ed by lower, but sustained, expression for > 50 days. Transgene expression of CAT could also be identified by immunohistochemistry staining in mouse l ung and appeared to be located within the capillaries. The pattern of in vi vo expression could be modulated and targeted to specific organs by alterin g the lipid-DNA formulation. New expression vectors with altered introns an d polyadenylation sites further improved expression. The expression reporte d here may be sufficient in magnitude, duration, and flexibility to be an a ttractive alternative, in some cases, to establishing transgenic animals by stable gene transfer.