Stimulation of CD19- and MP1-bispecific T cells through introduced and endogenous immunoreceptor results in augmented activation. (A) To measure proliferation, 10⁶ HLA A2⁺ MP1-tetramer⁺CD19R⁺CD8⁺ T cells were cultured for 96 hours at a 1:1 ratio with irradiated HLA A2⁺ aAPCs. For the last 18 hours, the cells were pulsed with ³H-thymidine, and the incorporated thymidine was determined using a scintillation counter. Data are presented as mean ± SD. (B) To measure IFN-γ cytokine production, bispecific MP1×CD19 CTLs were cocultured with the aAPCs, and the conditioned tissue-culture supernatant was collected after 48 hours and analyzed using a CBA. The U251T aAPCs were genetically modified to durably express tCD19, HyMP1, tCD19 and HyMP1, or Hy genes.