Primary AML cells are specifically targeted by CD123 specific T cells. (A) Pair-matched CD19 or CD123-specific T cells were cocultured for 4 hours with 51Cr labeled CD34+ primary AML samples at an E:T of 25:1. Pre-B ALL 802 is a primary patient sample double positive for CD19 and CD123. Data represents mean values of triplicate wells + SD (B) Specific lysis of AML blasts from the 3 primary AML patient samples in panel A. Data represent mean values ± SEM. *P < .05 and **P < .0005 using the unpaired Student t test comparing 26292 and 32716 to CD19R. (C-D) CD34-enriched primary AML or CB cells were cocultured with CAR T cells or left untreated for 4 hours prior to flow cytometric analysis. Percentages in each quadrant are indicated. For CD123 histograms (second and third rows), the y-ordinate scale was adjusted according to the number of events captured and the relative fluorescence (RFI) index is indicated. The RFI is the ratio of the median of the anti-CD123 antibody (clone 9F5)-stained signal to isotype-matched control stain. Gates were placed according to fluorescence-minus-one controls.
