Will the Making of Plasmacytoid Dendritic Cells in Vitro Help Unravel Their Mysteries?

In this issue, two papers describe the in vitro generation of an intriguing subset of human dendritic cells (DCs), the plasmacytoid DCs (pDCs [1, 2]). For nearly 20 years after their discovery 3, DCs had to be painstakingly isolated from tissues 4. Progress was rather slow, as DCs represent a minor cell population in all tissues, and relatively few investigators appreciated their importance in antigen presentation and the control of immunity. In 1992, in vitro culture systems were identified to generate large numbers of mouse 5 and human DCs 6. These culture systems considerably accelerated the study of DCs, with many groups joining the search to unravel their mysteries 7,8,9. Currently, DCs are being developed in vitro from (a) bone marrow progenitors cultured in GM-CSF, with TNF being...