CD19 and acute lymphoblastic leukemia: Indeed, acute CD19 depletion using CD19-targeting shRNAs led to apoptosis in REH and SEM cells (Figure 4A and S4A), suggesting that competent CD19 signaling was indispensable for the survival of these B-ALL cells, and CD19 depletion caused by CD19-AARC cells may lead to target cell death.