WT1 specific T cells are selected in the thymus. (A) FACS analysis of thymocytes isolated from A2Kb mice transplanted with lin⁻ A2Kb BM stem cells transduced with the lentiviral WT1-TCR vector. Thymocytes were stained with antimurine CD3, CD4, and CD8 antibodies together with anti–human Vβ2.1 to detect the WT1-TCR β chain. SP indicates single positive; DP, double positive; and DN, double negative. Representative plots from a total of 8 mice are shown. (B) Percentage of murine thymocytes expressing the WT1-TCR as detected by anti–human Vβ2.1 antibody at each stage of thymic selection was determined by FACS analysis after gating on DN, DP, or SP populations. A total of 8 transplanted A2Kb → A2Kb mice were analyzed.