To test if FRC targeting in this CD8+ T cell–dependent model required cognate interaction with MHC class I–expressing target cells, we established BM chimeras where radioresistant stromal cells either did or did not express MHC class I (i.e., [B6 male→B6 male] versus [B6 male→B2m–/– male] BM chimeras, respectively) and then, induced GVHD following a second BMT. This evidence concerns the gene CD8A and graft versus host disease.