Dacetuzumab, a CD40-targeted, humanized antibody, mediates antitumor activity through effector cell functions and direct apoptotic signal transduction. Preclinical studies demonstrated synergistic activity between dacetuzumab, gemcitabine and rituximab against non-Hodgkin lymphoma in vivo. A phase 1b safety/efficacy study of dacetuzumab in combination with rituximab and gemcitabine was conducted in relapsed/refractory diffuse large B-cell lymphoma (DLBCL). Patients received dacetuzumab at doses of 8 or 12 mg/kg IV weekly with rituximab (375 mg/m(2) IV weekly in cycle 1, then every 28 days) and gemcitabine (1000 mg/m(2) IV, days 1, 8 and 15, or days 1 and 15). Thirty-three patients with a median age of 67 years were enrolled. Common adverse events (≥ 15%) were grade 1/2 cytokine release syndrome, nausea, fatigue, thrombocytopenia, headache, decreased appetite, dyspnea, neutropenia, pyrexia, anemia, diarrhea, edema, constipation and cough. Dacetuzumab-related grade 3/4 adverse events occurred infrequently. Six of 30 evaluable patients achieved a complete response (CR) and eight a partial response (PR) per investigator assessment for an overall response rate (ORR) of 47%.