Generation of dendritic cells: A critical comparison of different methodological approaches

Dendritic cells (DCs) represent the most important antigen presenting cells (APCs). In vivo they originate from bone marrow myeloid and lymphoid precursors. In a first stage, the so-called immature DCs stay into nonlymphoid tissues and show high capacity of antigen capture and processing, but low T cell stimulatory capacity. After the internalization of the antigen, in the presence of inflammatory mediators, DCs mature and migrate out of nonlymphoid tissues into the blood or lymph, reaching secondary lymphoid organs. In this second stage the mature DCs lose the ability to capture antigens and increase the capacity to stimulate T cells, controlling the immune responses. Indeed, DCs are a family of heterogeneous cells and each subset exerts control over a different area of immunity, activating innate and acquired systems or maintaining the tolerance to antigens. For in vitro studies, dendritic cells can be isolated directly from peripheral blood through blood dendritic cell antibodies (BDCA), but they have been difficult to obtain due to their low concentration. So a wide variety of methods to have DCs has been performed, including the generation from circling CD14+ monocytes or from CD34+ progenitors. A multitude of systems have been carried out also to obtain these precursor cells. The method employed could affect morphological and functional features of the resultant DCs. For example, Ratta M and co-workers affirm that peripheral blood CD34+ cells generate a significantly higher number of fully functional DCs, capable of processing and presenting soluble antigens to autologous T cells. Elkord E and coworkers state that DCs generated from a positive immunoselected monocytes drastically reduce their ability to secrete cytokines as interleukin (IL)-12, IL-10, TNF-α, if compared to those generated from plastic adherence-isolated monocytes. Our own results indicate that monocytes selected by a positive selection method originate partially-mature DCs also without a maturational stimulus, characterized by low capacity of internalizing antigens and of inducing T cell proliferation also after lipopolysaccharide addition. Accordingly, in this commentary we review the recent progress in understanding the correlation between the approach used to obtain dendritic cells and their related properties, in order to indicate a correct application of DCs for research or clinical studies.