HPC-derived T cells respond to CD3 signaling. T cells were isolated from the splenocytes of chimeric Rag2^−/−γ_c^−/− mice (n = 3) and WT 129/SvJ control mice (n = 2). The T cells were subsequently cultured in the absence (▭) or presence (▬) of plate-bound antibodies against CD3 and CD28 for 24 to 36 hours. The supernatant of cultures were then collected and assessed for IL-2 (A) and IFN-γ (B) production by ELISA. Error bars represent SD.