CD4 and infection: Strikingly, HIV-1 with its own Env replicated poorly without Nef in cell-free infection tests (Figure 2C and Figure 3D), however, its infectivity was not affected by Nef in cocultures of 293T/CD4/X4 cells (Figure 2B) and was less dependent on Nef in Jurkat-Raji/CD4 cocultures than in cell-free test (compare Figure 3B,D).