Primary immunodeficiencies in the costimulatory molecule CD27 and its ligand, CD70, predispose for pathologies of uncontrolled Epstein-Barr virus (EBV) infection in nearly all affected patients. We demonstrate that both depletion of CD27⁺ cells and antibody blocking of CD27 interaction with CD70 cause uncontrolled EBV infection in mice with reconstituted human immune system components. While overall CD8⁺ T-cell expansion and composition are unaltered after antibody blocking of CD27, only some EBV-specific CD8⁺ T-cell responses, exemplified by early lytic EBV antigen BMLF1-specific CD8⁺ T cells, are inhibited in their proliferation and killing of EBV-transformed B cells. This suggests that CD27 is not required for all CD8⁺ T-cell expansions and cytotoxicity but is required for a subset of CD8⁺ T-cell responses that protect us from EBV pathology.