CD19 and leukemia: To overcome these resistance mechanisms, OXS-1550 (DT2219ARL), a CD19 × CD22 BsAb conjugated to a modified form of diphtheria toxin was developed and is currently being evaluated in Phase I study in patients with relapsed/refractory B cell lymphoma or leukemia (Bachanova et al. 2015; Schmohl et al. 2018).