CD4 and post-transplant lymphoproliferative disease: EBNA1-specific CD4+ T lymphocytes seem to have an important protective role in vivo, as inferred by their reduction or absence in PTLD patients (164), in some pediatric forms of BL (165), in EBV-related Hodgkin lymphoma (166), in NHL that develop in HIV patients (167), and in central nervous system lymphomas (168).