Visualization of transfer of a fluorescently-labeled membrane raft protein to T cells using lentivirus.

Lentivirus vector systems have been developed for the safe delivery of foreign genes to target tissues. However, the use of these systems for delivering specific proteins to target cells has been largely unexplored. To test this concept, the lentivirus expression plasmid pLenti was utilized to overexpress in producer cells a YFP-fusion protein that is specifically targeted to glycolipid-enriched membrane rafts, which is the site of virus assembly. Our data show that virus generated in producer cells that expressed the YFP fusion protein were able to effectively label target cells by a 2-3 hr incubation with the virus. Labeling of the target cells was specific to the lentivirus, as it was blocked by pre-incubating the virus with antibody to the surface protein, and it was not affected by pre-treating the target cells with cyclohexamide. T cells that were labeled using the lentivirus underwent a robust stimulation following crosslinking the T cell receptor, thus showing that T cells labeled using lentivirus remained responsive to extracellular cues. Altogether, these results show that overexpression of foreign proteins in lentivirus producer cells can yield protein-loaded viruses, which can then function to deliver the protein to target cells. Thus, our findings suggest an avenue for targeting specific proteins to cells where foreign gene expression is not feasible.