A cell-line derived from a patient with chronic myelogenous leukemia (CML) is described. The new cell-line, which has over 175 serial passanges in a 3 1/2-yr period, has the following characteristics: (1) CML cells started to proliferate actively since they were first incubated in culture media. A threefold increase in the total number of cells was observed during the first seven passages; the cell population increased by a factor of 10 to 20 every 7 days from passage 8 through 85; from 20 to 40 times from passage 86 through 150, and more than 40 times after 150 passages. (2) The majority of the nononucleated cells are undifferentiated blasts. (3) The karyotype of all the cells examined show the Philadelphia (Ph1) chromosome and a long acrocentric marker plus aneuploidy. The Giemsa-banding studies identified the Ph1 chromosome as a terminal deletion of the long arm of chromosome 22:del(22)(q12) and the long acrocentric marker as an unbalanced reciprocal translocation of one chromosome 17 and the long arm of one chromosome 15. (4) The CML cells do not produce immunoglobulins, are free of mycoplasma, Epstein-Barr virus, and herpes-like virus particles. (5) CML cells have no alkaline phosphatase and myeloperoxidase activities and did not engulf inert particles. (6) Cultured CML cells provide a constant source of a specific antigen. This CML cell-line represents a unique source of CML cells with meaningful indicators of malignancy for clinical and experimental studies.

The K-562 leukemia cell line, originally established in our laboratory, has been Characterized as an early precursor of the granulocytic series with a block for differentiation. Since K-562 blasts did not differentiate when cultured for 7-8 days in liquid media or 14-16 days in agar-gel an attempt was made to stimulate their potential for spontaneous differentiation by prolonging the time in culture. Inducers of differentiation were not added to the cultures and the cells were studied when they reached the steady state rather than during exponential growth. The cultivation of K-562 cells for 10 to 1 1 days in media gradually depleted of the essential nutrients needed for cell division induced their differentiation into early precursors of the monocytic, granulocytic, and erythrocytic series. Thus, the peroxidase reaction for hemoglobin demonstrates benzidine-positive material limited to the region of the Golgi apparatus. Analysis of the hemoglobin by isoelectric focusing indicated major bands in the region of embryonic hemoglobin. Most cells (80-90s) give a strong reaction for a-naphthyl acetate esterase typical of monocytes and as many as 30 to 40% of the cells have abundant red cytoplasmic granules of naphthol AS-D chloroacetate esterase characteristic of granulocytic precursors. Myeloperoxidase activity was found in 5 to 10% of the cells. Polyploid cells (5 -8%) and early myelomonocytic precursors have PAS-positive material, were stained with Sudan black, and possessed abundant acid phosphatase. The data support the conclusion that K-562 is, indeed, a multipotential leukemia cell line of human origin.

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