In-cell infection: bringing uninvited guests.

Cell-in-cell structures resulting from live cell engulfment were identified more than 100 years ago, but their physiological significance has remained largely obscure. Now Ni et al. identify a new role for cell-in-cell structure formation, called "in-cell infection" that spreads Epstein-Barr virus from infected B cells to epithelial cells, an activity that may predispose to cancer.