Proliferation of dendritic cell progenitors in long term culture is not dependent on granulocyte macrophage-colony stimulating factor

A unique long term culture (LTC) system has been developed which supports t he production of dendritic cells (DC), Cell production is dependent on a st romal cell layer derived from murine spleen. This LTC system produces a hig h turnover of non-adherent cells that express DC morphology, cell-surface m arkers, and antigen-presenting capacity. Objective. The long term production of these cells suggests that the LTC sy stem supports hemopoiesis, It was of interest to examine the number and nat ure of hemopoietic progenitors present in LTC. Materials and Methods. A combination of approaches, including FAGS analysis , spleen colony-forming unit assays, and in vitro colony assays were undert aken. Results. Pluripotent haemopoietic stem cells are not detectable among the n on-adherent cell population produced in LTC. Instead, LTC support a replica ting c-kit(+) progenitor population, which generates only dendritic-like co lonies in in vitro colony assays. In addition, this population does not res pond to combinations of growth factors thought to stimulate DC proliferatio n, including granulocyte macrophage-colony stimulating factor (GM-CSF) and Flt3L, Production of DC occurs only in the presence of LTC-derived culture supernatant or a confluent stromal cell layer. Conclusions. These results suggest that LTC contain a dendritic progenitor that is dependent upon the stromal cell network for proliferation and diffe rentiation. The development of only DC within LTC allows easy collection of cells for experimentation. This, in combination with the fact that DC deve lopment occurs in the absence of exogenous growth factors, makes the LTC sy stem a practical model for the study of DC function and development. (C) 20 00 International Society for Experimental Hematology, Published by Elsevier Science Inc.