CD4 and infection: Regarding DCs as virus-donor cells, two types of cell-to-cell viral transfer and infection of T-cell targets have been proposed: in cis-infection, DCs are productively infected and can then transfer viruses to CD4+ T cells, whereas in trans-infection, DCs are able to capture HIV-1 independently of CD4 and then transfer viruses to CD4+ T cells through the formation of the so-called “infectious synapse” (39, 83–85) (Figure 1E).