Background: In normal human tissue, expression of cluster of differentiation 19 (CD19) is limited to the developmental stages of the B cell and is lost in terminally differentiated plasma cells. Expression of CD19 is maintained in hematologic B-cell malignancies, including B-NHL. ADCT-402 is an antibody drug conjugate (ADC) composed of a humanized monoclonal antibody (RB4v1.2), directed against human CD19, conjugated to SG3199, a pyrrolobenzodiazepine (PBD) dimer cytotoxin, through a protease-cleavable valine-alanine linker. The PBD dimer cytotoxin (SG3199) attached to the linker is designated as SG3249. Methods: This is a Phase 1, open-label, dose escalation (Part 1) and expansion (Part 2) study of the safety and tolerability of ADCT-402, used as monotherapy, in patients with relapsed or refractory B-NHL. The study will determine the maximum tolerated dose, as well as evaluate the preliminary activity, PK, pharmacodynamics (PD), and other exploratory assessments of ADCT-402. Patients will be assigned to treatment according to a modified continual reassessment method (mCRM) with oversight by a Dose Escalation Steering Committee (DESC). In Part 2, all patients will be assigned to the dose level of ADCT-402 identified in Part 1. Clinical trial information: NCT02669017