THE BIOLOGY AND CLINICAL-APPLICATIONS OF DENDRITIC CELLS

Dendritic cells (DC) have an essential role in the induction of immune responses to antigen by naive T cells. As 'professional' antigen-pres enting cells they are specialized to take up, process and present solu ble antigens in complexes with either class I or class II MHC molecule s. They are present in only trace numbers in most tissues and in a rel atively immature state but, in the presence of inflammatory signals, t hey rapidly take up foreign antigens and undergo maturation into poten t antigen-presenting cells that migrate to secondary lymphoid tissue w here they initiate an immune response. It is now possible to expand po pulations of DC in vitro both from primitive haemopoietic progenitors as well as from more mature peripheral blood mononuclear cells. This h as shed light on many developmental aspects of DC biology and furthere d our knowledge of the mechanisms of antigen processing and presentati on. It is clear that there is more than one pathway of DC differentiat ion and that some DC may actually induce immunological unresponsivenes s - a possible mechanism for tolerance to self-antigens. For clinician s the most exciting prospect is of their use as cellular adjuvants to generate beneficial responses to antigens of low immunogenicity such a s tumour antigens. This review outlines aspects of human DC developmen t and the way in which a greater understanding of their biology may le ad to promising clinical applications.