Alternative routes of EBV infection of B cells in immunocompetent and immunocompromised individuals. In healthy individuals, EBV-infected naïve B cells are driven to differentiate into memory cells within the germinal center. By contrast, HSCT recipients have poor germinal center responses for several months after transplant. Therefore, it is proposed that EBV either infects memory B cells present in the graft or newly emerging mature B cells that have recently differentiated from donor stem cells. In this latter scenario, it is unclear whether EBV infects naïve B cells and then drives them to differentiate into memory or directly infects rare memory B cells.