High proliferation of early hemopoietic progenitors in tumor-bearing mice.

During the progression of Lewis lung carcinoma (LLC) in C57Bl/6 mice, a neutrophilia with granulocytosis develops. This heightened myeloid response is further reflected in a progressively increasing concentration of precursors CFU-GM (colony-forming unit, granulocyte-macrophage) in the marrow. However, during the final days of tumor growth (day 19) the cycling fraction of CFU-GM declines in LLC mice, although their concentration remains high. It was of interest to explore in the present study whether this decline in proliferation of committed myeloid progenitors was due to exhaustion of the pool of early and late pluripotential stem cells CFU-S (colony-forming unit, spleen). The results indicate that early stem cells experience an initial proliferative burst (day 14) during tumor growth, but fail to replenish their own pool by day 19, suggesting that their self-replicative ability may become exhausted during growth of this cancer. The implications of these findings to conditions of chronic hemopoietic stress are discussed.