CD19 and leukemia: To explore the comparative efficacy of the tandem-CAR constructs in vitro, especially in light of recent descriptions of leukemia escape mechanisms, we used the Raji cell line (which expresses CD19, CD20, and CD22) and the NALM-6 cell line (which expresses CD19, CD22, and low levels of CD20) to explore the ability of leukemia cell lines to escape the strong effector activity of CAR-T, Fig. 7a.