Chimeric Rag2^−/−γ_c^−/− mice generate peptide-specific T cells after LCMV infection, and HPC-derived APCs are capable of presenting viral-specific peptide to T cells. (A) Splenocytes of viral-infected mice were short-term incubated in the presence or absence of LCMV peptide NP396-404. CD8-positive T-cell responses were determined by intracellular IFN-γ staining, and IFN-γ–secreting cells were detected in WT and chimeric mice but not in control nonchimeric Rag2^−/−γ_c^−/− mice. IFN-γ–positive CD8-positive T cells were nearly undetectable in all controls. Representative flow cytometric plots are shown for each group of mice (n = 3). (B) The IFN-γ–positive cells in the chimeric Rag2^−/−γ_c^−/− mice were also GFP positive, suggesting they were derived from HPCs. The numbers represent percentages of cells in each quadrant. Numbers in plots are percentages of total cells in that quadrant. (C) HPC-derived APCs pulsed with the LCMV NP396-404 peptide, control OVA257-264 peptide, and nonpulsed cells were coincubated with WT T cells isolated from LCMV-infected WT mice for 6 hours, respectively. T-cell responses were determined by intracellular staining of IFN-γ and analyzed by FACS. The HPC-derived APCs significantly presented viral specific peptide but not control peptide to primed T cells (n = 3). Error bars represent SD.