CLL cells can be infected with an adenovirus encoding GFP. CLL cells were infected with AdGFP, containing the GFP gene under the control of a CMV promoter (Quantum Biotechnologies). Three days later, cells were assayed for green fluorescence by flow cytometry using a cytometer equipped with an argon laser at 488 nm. The heavy line represents the fluorescence of infected cells. The light line represents the fluorescence of uninfected cells.