[CANCERRESEARCH36, 4657-4662,December1976] SUMMARY The myalogenous leukemia call line K-562 with a Ph'+ chromosome, derived from a patient with chronic myalo ganous leukemia in terminal blashic crisis, is not a bone marrow-derived lymphoblastic call line, because the cells

The myalogenous leukemia call line K-562 with a Ph'+ chromosome, derived from a patient with chronic myalo ganous leukemia in terminal blashic crisis, is not a bone marrow-derived lymphoblastic call line, because the cells neither produce immunoglobulins nor possess complement receptors. Since it has been suspected that blasts found in some patients with chronic myelogenous leukemia in bIas tic crisis might be lhymus-denived calls, we have studied several parameters to demonstrate that K-562 cells are not thymus-denivad lymphoblasts. The results of this study show: (a) no cross-reactivity of antisera to K-562 cells with normal human thymocylas; (b) lack of cytoloxicily of a specific horse anti-human thymocyhe globulin for K-562 cells; (c) failure of the treatment of K-562 calls with bovine Ihymosin to induce anhigenic determinant and erylhrocyhe rosette receptors on K-562 cells; (d) presence of receptors forthe Fc portionof immunoglobulinG; (a)absence of terminal deoxynucleotidyl transferase; and (f) cytotoxicity of monkey antiserum to K-562 cells for malignant thymus derived cells (Moll-4). However, absorption with Molt-4 cells abolished the cross-reactivity with Molt-4 cells, whereas 60% of the antibody to K-562 cells remained in the immune serum. Studies of DNA polymenase activities revealed that K-562 cells have levels of polymerase a and /3, like other proliferating calls, and an RNA-depandanl DNA polymenase activity, presumably representing polymarase †̃y.