Viral packaging of introduced proteins - Is it possible?

[Jonathan Rosen]

I am curious as to whether anyone has ever packaged a "protein 
of interest" into viral particles. Even better would be if it was 
possible without also packaging the viral genome, but maintaining the 
coat proteins and fusion ability of the particles. Any references of this 
kind would be of interest, and especially those relating to  
HIV/lentiviruses.

Thanks,

Jon