Neutralization of IFN-γ with MoAb R4-6A2 in leukemic allogeneic BMT recipients treated with IL-12 results in diffuse invasion of leukemic cells and severe GVHD-associated mononuclear cell infiltration of the liver. (Top) Liver was obtained from an IL-12–protected leukemic recipient of allogeneic BMT that died on day 51. (Bottom) Liver was obtained from an IL-12–treated leukemic recipient of allogeneic BMT plus neutralizing anti–IFN-γ MoAb R4-6A2 that died on day 42. 160× and 400× photomicrographs of hematoxylin and eosin stains are shown in left and right panels, respectively.