MKI67 and neoplasm: To confirm that limitation of the post-therapy CD8+ T cell response by ATRi QDx9 is not restricted to the CT26 tumor model or to the BALB/c mouse strain, we examined proliferating (Ki67+) CD8+ T cells in the DLN and TILs of B16 tumor–bearing C57BL/6 mice treated with two 4 Gy fractions of tumor-targeted radiation (RT 4 Gy x 2), ATRi QDx3 plus RT, ATRi QDx9 plus RT, or vehicle.