Nude mice as models for human leukemia studies.

Human leukemic promyelocytes of the HL-60 line were grown as tumors in nude mice and studied. A single nonmetastatic granulocytic sarcoma developed after subcutaneous inoculation with HL-60 cells. Some exceeded 5 cm in size. Almost all mice developed tumors after initial priming with cyclophosphamide. Older sarcomas showed viable tumor islands in necrotic and fibrotic tissue. Some tumors appeared greenish. Histologic and electron-microscopic analysis demonstrated large, vaguely outlined cells in poorly vascularized sheets. The cells displayed high nucleocytoplasmic ratios, basophilic granular cytoplasms lacking Auer rods, and enzymes characteristic of cultured HL-60 promyelocytes. Some tumor cells also demonstrated monocyte/macrophage enzymes, such as butyrate esterase. Induced HL-60 tumors also corresponded morphologically to a human subcutaneous promyelocytic tumor specimen. Comparative cytologic studies of induced HL-60 tumors in nude mice and cultured HL-60 cells revealed virtual identity, suggesting the nude mouse tumor as a useful model for in vivo studies of human leukemic cells.