The direct passage of animal viruses between cells

The paradigm that viruses can move directly, and in some cases covertly, between contacting target cells is now well established for several virus families. The underlying mechanisms of cell-to-cell spread, however, remain to be fully elucidated and may differ substantially depending on the viral exit/entry route and the cellular tropism. Here, two divergent cell-to-cell spread mechanisms are exemplified: firstly by human retroviruses, which rely upon transient adhesive structures that form between polarized immune cells termed virological synapses, and secondly by herpesviruses that depend predominantly on pre-existing stable cellular contacts, but may also form virological synapses. Plant viruses can also spread directly between contacting cells, but are obliged by the rigid host cell wall to move across pore structures termed plasmodesmata. This review will focus primarily on recent advances in our understanding of animal virus cell-to-cell spread using examples from these two virus families, and will conclude by comparing and contrasting the cell-to-cell spread of animal and plant viruses.

► Animal viruses can move via release of cell-free virus or directly between contacting cells.
► Cell-to-cell spread requires virus–receptor interactions and viral membrane fusion.
► Retroviruses and HSV induce transient intercellular contacts called virological synapses.
► Cell-to-cell spread increases rate and multiplicity of infection and may reduce drug impact.
► Plant and animal viruses differ in mechanisms of intercellular spread, but share features of intracellular transport.