A SERUM-FREE CULTURE MODEL FOR STUDYING THE DIFFERENTIATION OF HUMAN DENDRITIC CELLS FROM ADULT CD34(+) PROGENITOR CELLS

The antigen-presenting capacity of dendritic cells (DCs) makes them at tractive potential cellular adjuvants for vaccination strategies. Curr ently, most in vitro culture systems for the production of these DCs i nclude serum. However, this is undesirable because serum contains grow th factors that vary between individuals and could affect DC developme nt. Unless the patient's own serum is used, foreign antigens and the r isk of infection will detract from the usefulness of these cells in cl inical strategies. In this study we investigated the production of DCs from CD34(+) progenitor cells of cancer patients or normal donors und er serum-free conditions. We have established a model system for the i nvestigation of DC development and maturation. Dendritic cells that de veloped from myeloid precursors accumulated after 2 weeks in an interm ediate CD1a(+++) CD80(-), CD83(-), CD86(-) stage. Intermediate DCs adh ered to plastic surfaces, expressed Birbeck granules, and were negativ e for CD2 and CD14. In the presence of granulocyte-macrophage colony-s timulating factor and tumor necrosis factor-alpha, interleukin-4 promo ted the development of these stages. Spontaneous maturation of interme diate DCs into fully activated DCs expressing CD83 and costimulatory m olecules occurred asynchronously over the ensuing 2 to 3 weeks. This m aturation involved increased expression of CD80, CD83, CD86, CMRF-44, HLA-A, -B, -C, and -DR as well as downregulation of CD1a and CD11b. Ac tivated DCs are characterized by the lack of adherence to plastic surf aces and the absence of Birbeck granules. By day 28, these cells were nonphagocytic, potent antigen-presenting cells with an irreversible ph enotype. This serum-free system offers advantages in that the process of differentiation and maturation of committed DCs is extended over a period of more than 28 days, allowing investigators to study the effec ts of individual cytokines or other supplements during distinct phases of DC development in a defined environment.