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Human spleen-conditioned medium can induce the formation in vitro of large granulocyte colonies from normal human bone marrow cells. The granulocyte colonies contained cells in various stages of differentiation, from myeloblasts to mature neutrophile granulocytes. Human spleen-conditioned medium also induced colony formation with rodent bone-marrow cells, whereas rodent spleen-conditioned medium induced colony formation with rodent bone marrow but not with human cells. This in vitro system has been used to determine the potentialities for cell differentiation in bone-marrow and peripheral blood cells from patients with a block in granulocyte differentiation in vivo. The cloning efficiency, colony size, and number of mature granulocytes in bone-marrow colonies from patients with congential neutropenia, whose bone marrow contained only 1% mature granulocytes, were not less than in people whose bone marrow had the normal level of about 40% mature granulocytes. The cloning efficiency of peripheral blood cells from patients with acute myeloid leukemia was 350 times higher, with 10 times larger colonies, than the cloning efficiency of peripheral blood cells from normal people. The cytochemical properties and number of mature granulocytes in colonies from the leukemic patients were the same as in colonies from non-leukemic people. The results indicate that a block in cell differentiation in vivo, in these cases with neutropenia and acute myeloid leukemia, was overcome in vitro, in the presence of an inducer in the conditioned medium. In patients with chronic myeloid leukemia, colony formation was induced only in some of the cases. This indicates that there are blast cells with different potentialities for the development of colonies in different patients.
Paran et al. (Sun,) studied this question.