In order to test the hypothesis that embryonal carcinoma cells are multipotential stem cells of a teratocarcinoma, an in vivo cloning technic was designed. Small embryoid bodies containing mostly embryonal carcinoma were obtained from ascitic conversion of a murine teratocarcinoma and were dissociated with trypsin to form a suspension of single cells; the single cells were picked up in small capillary tubes and transplanted directly into mice.

From over 1700 single cell grafts, 44 clonal lines were obtained; 43 of these lines were teratocarcinomas composed of as many as fourteen well differentiated somatic tissues in addition to embryonal carcinoma. These 43 lines varied in their degree of differentiation, capacity to produce embryoid bodies, and in growth rate. The remaining clonal line showed limited potential for differentiation, producing only yolk sac, trophoblast, and embryonal carcinoma.

The results demonstrated the multipotentiality of single embryonal carcinoma cells, as well as the heterogeneity of the embryonal carcinoma of a teratocarcinoma. The capacity of single embryonal carcinoma cells to differentiate into benign tissues supports neither the dogma of the irreversibility of the malignant transformation nor the somatic cell mutation theory of cancer. These findings were interpreted as giving strong support to the stem cell theory of cancer.

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This work was supported in part by an Institutional Grant from the American Cancer Society, Inc., and grants E-105 from the American Cancer Society, Inc., and CA 6113 from the United States Public Health Service.

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