Anti-CCR9 CAR has potent anti-leukemic activity in PDX models of T-ALL with low CCR9 antigen density. (A) Flow diagram of low-density PDX models. (B-E) PDX models 3 to 7. CCR9 antigen density in PDX blasts before injection, molecules per cell (left), leukemic burden in peripheral blood in PDX models (center), and survival curves of animals in PDX models (right). n = 5 per group in all models.