CD19 and leukemia: Several CD19-specific therapies indeed evidenced cases of relapse resulting from CD19 antigen loss in leukaemia cells post-CD19-specific CAR T cell therapy.7–10 Furthermore, these therapies are also associated with significant levels of toxicity,11 12 including cytokine release syndrome (CRS), neurotoxicity and on-target off-tumour toxicity against normal cells (eg, CD19-specific CAR T cells also target normal B cells expressing CD19, causing prolonged B cell aplasia and hypogammaglobulinaemia13 14).