Rituximab-coated, autologous lymphoma cells induce CD137 up-regulation on NK cells from human patients with B-cell malignancies. (A-B) Peripheral blood from patients with B-cell malignancies and CTCs were analyzed for CD137 expression on CD3⁻CD56⁺ NK cells after 24-hour culture with medium alone, trastuzumab, or rituximab. (A) CD16 and CD137 expression on CD3⁻CD56⁺ NK cells for a patient with marginal zone lymphoma (MZL) with 70% CTCs. (B) Percentage of CD137⁺ cells among CD3⁻CD56⁺ NK cells in a cohort of 25 patients with follicular lymphoma (FL), chronic lymphocytic leukemia (CLL), MZL, mantle cell lymphoma (MCL), diffuse large B-cell lymphoma (DLBCL), or CD20⁺ acute lymphoblastic leukemia (ALL). (C) Correlation (r² = 0.87, P < .001) between the percentage of peripheral blood CTCs and CD137 surface expression on CD3⁻CD56⁺ NK cells after 24-hour culture with rituximab from patient samples with FL (◐ ), CLL (●), MZL (◒), DLBCL (◑), or CD20⁺ ALL (◓).