Clonal Analysis of the Action of GM-CSF on the Proliferation and Differentiation of Myelomonocytic Leukemic Cells

With 214 subclones of the BALB/c myelomonocytic leukemia WEHI-3B, the granulocyte-macrophage colony-stimulating factor (GM-CSF) in impure or purified form, consistently increased the proportion of colonies exhibiting partial or complete differentiation in agar cultures. GM-CSF also increased colony size and content of daughter colony-forming cells. Serial recloning of WEHI-3B colonies in the presence of GM-CSF showed that when colonies differentiated completely, self-replication of the colony-forming cell was suppressed (clonal extinction). However, WEHI-3B cells exhibited clonal instability and even in the continuous presence of GM-CSF many colony-forming cells still generated cells able to form undifferentiated colonies. It appears unlikely that GM-CSF can completely suppress the progressive proliferation of a myeloid leukemic population of the WEHI-3B type.