Stimulation of differentiation and proliferation of haemopoietic cells in vitro

Abstract A liquid culture system, for haemopoietic cells, has been developed using bone marrow cells alone, or co‐cultures of thymus and bone marrow cells, inoculated into four ounce medical bottles. After several days growth, such cultures consisted of an attaching population of cells, forming discrete colonies, and a non‐attaching population. In the (co‐cultures) there was a 2 X enhancement of monolayer colony development compared with the combined total present in the (marrow alone) plus (thymus alone) cultures. Also, better maintenance of non‐attaching cells was seen in the (co‐cultures). Normal CFU S and CFU C were present in both the (marrow alone) and the (co‐cultures) for at least 14 days. In the (marrow alone) cultures, granulocytes in all stages of development were present for the first week, but by 12 days the culture consisted mainly of mono‐nuclear cells. In the (co‐cultures), however, at 12 days more than 60% of the cells were granulocytes, in all stages of differentiation. (Co‐cultures) established using lethally irradiated thymus cells were not able to support this prolonged myeloid differentiation. By feeding the (co‐cultures) it was possible to maintain production of (granulocytic) cells for at least ten weeks, although no fully mature granulocytes were observed. After the second feeding, no CFU S were detectable, but variable numbers of agar colony forming cells (not classical CFU C ) were present at least for ten weeks.