CD19 and B-cell chronic lymphocytic leukemia: The efficacy in both the CD3ζ and CD28-CD3ζ CAR-redirected cytolysis does not furthermore increase with the level of CD19 expression on B-CLL cells (Figure 1(e)) implying that the CD19 levels on B-CLL cells are high enough to cross-link the anti-CD19 CAR for synapse formation and signalling.