CD19 and acute lymphoblastic leukemia: Importantly, in recent years, the treatment paradigm for primary refractory and relapsed Philadelphia (Ph) negative ALL has been revolutionised with the introduction of blinatumomab, a first-in-class bispecific T-cell engager anti-CD19 monoclonal antibody (mAb) and the drug conjugate, inotuzumab ozogamicin, an anti-CD22-calicheamicin mAb.