CD4 and primary central nervous system lymphoma: In six patients diagnosed with primary CNS lymphoma, EBV-specific CD4+ T cell IFN-γ responses were measured in PBMC obtained 0.5–4.7 y before lymphoma diagnosis, and these responses were compared to the same T cell responses in PBMC obtained from 16 matched controls (i.e., participants who were HIV positive but did not develop PCNS lymphoma).