Experimental design. (A) To create mice with MHCI− or MHCII− parenchyma but with MHC+ hematopoietic cells (including APCs), B6 β2M−/− or IAbβ−/− mice (both CD45.2) were irradiated and reconstituted with TCD wt B6 CD45.1 BM. (B) After 3 months to allow for engraftment of the wt B6 hematopoietic system, these chimeras were used as recipients in a second, GVHD-inducing alloBMT.