Tumor-involved lymph nodes from lymphoma patients express high levels of CD137 mRNA and are infiltrated by CD137⁺ T cells. (A) Publicly available microarray gene expression data^16,18  from bulk tumor specimens of 184 patients were analyzed for the expression of CD137 across histopathological groups. DLBCL and FL specimens significantly overexpressed CD137 compared with nonlymphoma specimens (P < .001 for each comparison). Aside from FL (n = 11) and DLBCL (n = 11), no other histopathological group significantly overexpressed CD137 compared with other tumor types. CA indicates carcinoma; NSCLC, non–small cell lung adenocarcinoma; CRC, colorectal adenocarcinoma; TCC, transitional cell carcinoma; AML, acute myeloid leukemia; and ALL, acute lymphoblastic leukemia. (B-C) Tumor-involved lymph nodes from untreated lymphoma patients (FL, MCL, and DLBCL) and PBMCs from healthy donors were analyzed by flow cytometry for CD137 expression on B and T cells. (B) CD137 expression on tumor B cells, and CD4 and CD8 T cells for 1 representative lymphoma sample (DLBCL). (C) The percentage of CD137⁺ cells among CD8 T cells in healthy PBMCs and lymphoma samples from different histologies.