a, c, Flow cytometric analysis of D42 cells matured on 3T3-CD19 (a) or 3T3-CD19–41BBL (c). Gated on live CD45+CD7+ cells. b, Flow cytometric analysis of D35 and D42 phenotypes of stimulated DP TRAC-1XX-iT cells. D35 TRAC-1XX-iT cells were sorted for a CD4+CD8αβ+ DP phenotype, stimulated on 3T3-CD19–41BBL and expanded for seven days. Gated on live CD45+CD7+ cells. d, Fold Expansion and T cell phenotype marker expression of TRAC-1XX-iT cells matured on 3T3-CD19–41BBL (3T3) or recombinant CD19-Fc. e, 4 h cytotoxicity assay of 3T3-CD19–41BBL stimulated TRAC-1XX-iT cells in response to NALM6-CD19+ an NALM6-CD19−/− target cells (n = 3 technical replicates, data are means ± s.d.) f CD19 expression on primary CLL cells.