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Neoplastic cells from BALB/c mice with transplanted myelo-monocytic leukemia (WEHI-3) proliferated in vitro in semisolid agar cultures to form hematopoietic colonies. These colonies resembled normal in vitro hematopoietic colonies in gross morphology, growth patterns, and cell content. Chromosome analysis of colony cells and transplantation of individual colonies to BALB/c recipients confirmed that colonies were composed of tumor cells. Unlike colony formation by normal hematopoietic cells, colony growth by tumor cells was not dependent on the presence of the “colony-stimulating factor” (CSF), but colony numbers and growth rates were increased by the addition of the CSF. Serum levels of CSF were elevated in BALB/c mice carrying transplanted myelomonocytic leukemic cells. The myelomonocytic leukemic cells appear to be in a conditioned state with respect to the CSF and offer an ideal system for comparative studies on normal and neoplastic hematopoietic proliferation and differentiation in vitro. In mixed cultures, myelomonocytic leukemic cells stimulated granulocytic colony formation in vitro by normal bone marrow cells; this property was not seen in lymphoid leukemic, erythroleukemic, or plasma cell tumor cells in similar mixed cultures.
Metcalf et al. (Wed,) studied this question.