Immobilized glycosylated mAbs stimulate CD137 expression on human NK cells. IL-2–stimulated NK cells were cultured for 24 hours in the presence of immobilized or soluble chimeric mAbs as indicated. CD137 expression was measured by flow cytometry. Gates were set around CD56⁺ (NK) cells and numbers in the dot plots indicate percentage of CD56⁺ (NK) cells expressing CD137. Immobilized mAb culture conditions and soluble mAb culture conditions are indicated with i- and s-, respectively. The data shown are representative of 1 of 6 individual experiments. Statistical analysis is based on 6 experiments; CD137 expression levels are significantly increased in NK-cell cultures with i-huIgG1 or i-GG (P = .023 and P = .007, respectively) compared with i-GA cultures. HuIgG1 indicates polyclonal human IgG1; GA, aglycosylated chimeric anti-CD137 mAb; GG, glycosylated chimeric anti-CD137 mAb; and CTM, cetuximab.