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The prognosis for patients with relapsed or refractory (R/R) B-cell non-Hodgkin lymphoma (B-NHL) remains poor, with a need for alternatives to current salvage therapies. Loncastuximab tesirine (ADCT-402) is an antibody-drug conjugate comprising a humanized anti-CD19 monoclonal antibody conjugated to a pyrrolobenzodiazepine dimer toxin. Presented here are final results of a Phase 1 dose-escalation and dose-expansion study in patients with R/R B-NHL. Objectives were to determine the maximum tolerated dose (MTD) and recommended dose(s) for expansion and to evaluate safety, clinical activity, pharmacokinetics, and immunogenicity of loncastuximab tesirine. Overall, 183 patients received loncastuximab tesirine, with 3+3 dose escalation at 15-200 µg/kg and dose expansion at 120 and 150 µg/kg. Dose-limiting toxicities (all hematologic) were reported in 4 patients. The MTD was not reached, although cumulative toxicity was higher at 200 µg/kg. Hematologic treatment-emergent adverse events were most common, followed by fatigue, nausea, edema, and liver enzyme abnormalities. Overall response rate (ORR) in evaluable patients was 45.6%, including 26.7% complete responses (CR). ORRs in patients with diffuse large B-cell lymphoma (DLBCL), mantle cell lymphoma, and follicular lymphoma were 42.3%, 46.7%, and 78.6%, respectively. Median duration of response in all patients was 5.4 months and not reached in patients with DLBCL (doses ≥120 µg/kg) who achieved CR. Loncastuximab tesirine had good stability in serum, notable anti-tumor activity, and an acceptable safety profile, warranting continued study in B-NHL. The recommended dose for Phase 2 was determined as 150 µg/kg every 3 weeks (Q3W) for 2 doses followed by 75 µg/kg Q3W. Study: NCT02669017.

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Purpose: ADCT-402 (loncastuximab tesirine) is an antibody-drug conjugate comprising a CD19-targeting antibody and pyrrolobenzodiazepine dimers. A first-in-human study evaluated the safety and preliminary clinical activity of loncastuximab tesirine in patients with B-cell non-Hodgkin lymphoma (NHL).Patients and Methods: A multicenter, phase I, doseescalation and dose-expansion study enrolled patients ages !18 years with relapsed/refractory (R/R) B-cell NHL. Patients received loncastuximab tesirine every 3 weeks at doses assigned by a 3þ3 dose-escalation design. Dose escalation was used to assess the safety and tolerability of loncastuximab tesirine to determine the dose for expansion. Secondary objectives evaluated clinical activity, characterized the pharmacokinetic profile, and evaluated antidrug antibodies.Results: During dose escalation, 88 patients with R/R B-cell NHL were treated with loncastuximab tesirine at doses 15 to 200 mg/kg. Treatment-emergent adverse events (TEAEs) were experienced by 87/88 (98.9%) patients. Most common TEAEs (!20% of patients) were hematologic abnormalities, fatigue, edema, liver test abnormalities, nausea, rash, and dyspnea. Grade !3 TEAEs (!5% of patients) included hematologic abnormalities, liver test abnormalities, fatigue, and dyspnea. Overall response rate at doses !120 mg/kg was 59.4% (41 of 69 patients; 40.6% complete response; 18.8% partial response). Median duration of response, progression-free survival, and overall survival (all doses) were 4.8, 5.5, and 11.6 months, respectively. Drug exposure increased with increasing dose, showing moderate accumulation with multiple doses !150 mg/kg. There was no evidence of immunogenicity.Conclusions: Loncastuximab tesirine had promising activity with acceptable safety in this dose-escalation study. A phase II study with initial dosing at 150 mg/kg has been initiated based on these results.