The influence of culture conditions on the production of colony-stimulating activity by human placenta.

The growth of human granulopoietic progenitor cells (CFUc) in vitro is stimulated by supernatants of human placental tissue cultures. The placenta culture was the subject of systematic experiments with the aim of improving the concentration of colony-stimulating activity (CSA) in the crude material. Different culture parameters were varied and analyzed separately on the basis of dose-response studies. Maximum levels of CSA in human placental conditioned medium (HPCM) were obtained from 7-day cultures with a tissue-to-medium ratio of 1 to 20 and a depth of the culture fluid of 3 mm. Moreover, these modifications of the placenta culture resulted in a considerable reduction of inhibitors. HPCM stimulation of colony growth in agar unfailingly equaled feeder layer stimulation both in terms of colony number and size, each placenta producing enough material for maximum stimulation of 30,000 cultures.