The Duffy antigen receptor for chemokines (DARC) belongs to a family of ‘silent’ heptahelical chemokine receptors that do not couple to G proteins and fail to transmit measurable intracellular signals. DARC binds most inflammatory chemokines and is prominently expressed on venular endothelial cells, where its function has remained contentious. Here we show that DARC, like other silent receptors, internalized chemokines but did not effectively scavenge them. Instead, DARC mediated chemokine transcytosis, which led to apical retention of intact chemokines and more leukocyte migration across monolayers expressing DARC. Mice overexpressing DARC on blood vessel endothelium had enhanced chemokine-induced leukocyte extravasation and contact-hypersensitivity reactions. Thus, interactions of chemokines with DARC support their activity on apposing leukocytes in vitro and in vivo.

Despite improved molecular characterization of malignancies and development of targeted therapies, acute leukemia is not curable and few patients survive more than 10 years after diagnosis. Recently, combinations of different therapeutic strategies (based on mechanisms of apoptosis, differentiation and cytotoxicity) have significantly increased survival. To further improve outcome, we studied the potential efficacy of boosting the patient's immune response using specific immunotherapy. In an animal model of acute promyelocytic leukemia, we developed a DNA-based vaccine by fusing the human promyelocytic leukemia-retinoic acid receptor-alpha (PML-RARA) oncogene to tetanus fragment C (FrC) sequences. We show for the first time that a DNA vaccine specifically targeted to an oncoprotein can have a pronounced effect on survival, both alone and when combined with all-trans retinoic acid (ATRA). The survival advantage is concomitant with time-dependent antibody production and an increase in interferon-gamma (IFN-gamma). We also show that ATRA therapy on its own triggers an immune response in this model. When DNA vaccination and conventional ATRA therapy are combined, they induce protective immune responses against leukemia progression in mice and may provide a new approach to improve clinical outcome in human leukemia.

In the version of this article initially published, the vessel label 'Afferent' beneath the lymph node in Figure 1c is incorrect. The correct label is 'Efferent' . The error has been corrected in the HTML and PDF versions of the article.c o r r i g e n d a a n d e r r ata