Loncastuximab tesirine (ADCT-402, RB4v1.2-SG-3249) is an antibody-drug conjugate (ADC) composed of an anti-CD19 (B lymphocyte surface antigen B4, Leu-12) chimeric monoclonal antibody , conjugated to Pyrrolobenzodiazepine (PDB) dimer SCX, via a cleavable (valine-alanine dipeptide as cathepsine B cleavage site) maleimide type linker containing a spacer PEG.