THE HEMATOPOIETIC DEVELOPMENT OF DENDRITIC CELLS - A DISTINCT PATHWAYFOR MYELOID DIFFERENTIATION

Dendritic cells (DC) are leukocytes that are specialized to capture an tigens and initiate T cell-mediated immune responses, Because DC can p rime animals in the absence of any other adjuvant, they have been term ed 'nature's adjuvant', DC express high levels of antigen presenting m ajor histocompatibility complex (MHC) products (HLA-DP, DQ, DR; HLA-A, B, C) as well as several accessory molecules (e.g., B7-1, B7-2, LFA-3 , ICAM-1, ICAM-3, CD40) that mediate T cell binding and costimulation. This review outlines some of the ways in which DC are distinguished f rom two other myeloid lineages, macrophages and granulocytes, Recent d ata regarding DC development from class II MHC-negative precursors in the mouse, as well as unselected and selected CD34(+) progenitors in h uman bone marrow and peripheral and cord blood, are reviewed. Addition al pathways via post-colony-forming units, intermediate cell types hav e also become evident in suspension cultures where the cytokine milieu can alter terminal differentiation. The availability of larger number s of DC is opening new avenues for immune therapy that use this physio logic adjuvant.