Immunohistochemical pictures of frozen tissue sections showing donor-cell infiltration in the GVL (A and C) or GVH (B and D) system in liver (A and B) and spleen (C and D) 8 days after immune cell transfer. Donor cells were stained with anti-β₂M^b immunecomplexes using a one-step immunolabeling method (original magnification × 160).