Role of hematopoietic growth factors/flt3 ligand in expansion and regulation of dendritic cells.

Dendritic cells (DCs) are hematopoietic cells that initiate immune responses by presenting antigen to T cells. Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a primary growth factor for DCs in vitro, but recently it was recognized that other factors including flt3 ligand (FL) and G-CSF expand various DC subsets in vivo. DCs undergo a complex series of maturation and activation steps after they acquire antigen and before they can activate resting T cells. In addition, they must traffic to T-cell-rich areas of lymph nodes (LN) to achieve this. Each of these steps is tightly regulated, and in the last year progress has been made in identifying some of the key molecules involved in each of these steps. This progress will further the efforts underway to develop DCs as vaccine adjuvants.