CAR-T cells retain cytotoxic potential after tumor re-challenge. A. Schematic of repetitive tumor-challenge assay. Effector cells were co-cultured with primary T-ALL cells (5,000 T cells; 25,000 primary T-ALL cells; E:T=1:5) and re-challenged with 5000 T-ALL cells every other day. B. Statistical analysis of CD7 antigen on primary T-ALL cells at different re-challenge points. C. CAR+ retains similar levels in T cells after several rounds of co-incubation with primary T-ALL cells. D. Frequency of naïve-like (Tscm/naive), effector memory RA+ (TemRA+), effector memory (Tem) and central memory (Tcm) T cells after re-challenge with primary T-ALL cells, ****P<0.0001. E. T-ALL cells were nearly all undergoing apoptosis after tumor re-challenge (n=3 replicates per data point).