CD44 and infection: Moreover, infecting these knockout clones with the IN− NL-GFPΔEnv virus at a multiplicity of infection (MOI) of ~0.3 revealed a similar level of GFP+ cells (from 29% to 43% positive, Fig. 1b) to that seen in WT CEM-SS cells infected with an IN+ form of NL-GFPΔEnv (32% positive, Fig. 1c), although the IN+ virus induced a higher mean fluorescence intensity.