β2M^−/− and IA^bβ^−/− mCP-CML are resistant to CD8- and CD4-mediated GVL. (A) B6 mice were irradiated and reconstituted with TCD C3H.SW BM, wt B6 or β2M^−/− mCP-CML, with or without C3H.SW donor CD8⁺ T cells. (B) B6 mice were irradiated and reconstituted with TCD 129 BM, wt B6 or IA^bβ^−/− mCP-CML, with or without purified 129 CD4⁺ T cells. (C) To determine whether the GVL resistance of IA^bβ^−/− mCP-CML is in the effector phase, irradiated B6 mice were reconstituted with TCD C3H.SW BM, wt mCP-CML, or IA^bβ^−/− mCP-CML or a mix of both wt and IA^bβ^−/− mCP-CML, with or without purified C3H.SW CD4⁺ T cells. Note that the only survivors were recipients of wt mCP-CML cells and donor C3H.SW CD4 cells, indicating that IA^bβ^−/− mCP-CML is GVL-resistant because of a defect in the effector phase. (D) Experimental design for panel C.