Haemopoietic progenitor cells measured by limiting dilution in microwell culture

Microwell culture assays, termed the "negative" well technique and the "positive" well technique have been used to measure the concentration of murine haemopoietic progenitor cells (HPC) by limiting dilution. Using morphologic examination and 3H-TdR uptake, the number of HPC of Balb/c mice per 10(5) bone marrow cells was 33 and 31 respectively. the linear relation between the number of harvested cells and input cells seen on the 4th and 7th days of culture reflected the growth of HPC in microwells. Besides measuring the concentration of HPC, this culture system may facilitate the analysis of effects on proliferation and differentiation of HPC of culture conditions, haemopoietic factors as well as cytotoxic agents.