In 8 out of 14 mice affected by xenogeneic GVHD-like condition, microscopic changes at site of transplantation were characterized by dense plasma cell-rich lymphoid infiltrates of human origin with severe effacement of melanoma xenografts as demonstrated by the identification of scattered groups of Melan A, HMB45 and/or Tyrosinase-positive tumor cells interspersed among the reactive infiltrates (Fig 3). The gene discussed is MLANA; the disease is melanoma.