CD27 plays an important role in T-cell co-stimulation and is also expressed on lymphomas. In the present study, we generated novel depleting and non-depleting monoclonal antibodies (mAbs) against mouse CD27 and characterized their co-stimulatory activity in vitro and anti-tumor effects in immune-competent mice bearing syngeneic T-cell lymphoma (EG7) expressing or lacking CD27. A profound anti-tumor effect was observed with a non-depleting mAb (RM27-3E5), but not with a depleting mAb (RM27-3C1), against either EG7/CD27(+) or EG7/CD27(-) tumors, which was associated with the induction of EG7-specific cytotoxic T lymphocytes (CTLs). Consistently, the anti-tumor effect of RM27-3E5 was abolished in T cell-deficient nude mice. These results indicate that a non-depleting agonistic mAb against CD27 is promising for cancer therapy by co-stimulating tumor-specific CTL induction. (C) 2010 Elsevier Inc. All rights reserved.