Sartor and colleagues report results of their investigations into the relationship between the severity of acute GVHD and the expression of the chemokine receptors CCR5 and CCR7 on dendritic cells, which are critical molecules for mediating DC trafficking into tissues. They evaluated serial peripheral blood samples from 32 patients after allogeneic SCT and 11 developed grade II-IV GVHD. The percentage of DC expressing either CCR5 or CCR7 was calculated and correlated with the development of acute GVHD. CCR7 expression showed no association with GVHD. In contrast, higher CCR5 expression was detected on DC in patients developing grade II-IV GVHD compared to DC in patients with grade 0-I GVHD (P < 0.0001). All 11 patients with grade II-IV GVHD expressed CCR5 in over 35% of their DCs while only 2 of 21 patients with grade 0-1 GVHD expressed CCR5 at this high a percentage. Most importantly, the expression of CCR5 on DC preceded the development of moderate to severe GVHD by a median of 19 days (range 2-47 days; samples drawn twice weekly). This is an exciting study which identifies a biologic marker which predicts for the development of GVHD; if verified, this could result in preventative modulation of immunosuppressive therapy for certain patients found to be at higher and lower risk for GVHD. In addition this study highlights a specific potential target for GVHD intervention (the CCR5 receptor), which has gained notoriety as the site of entry for HIV into lymphocytes. Other studies have suggested that CCR5 is important for development of GVHD [8, 9] . For this reason CCR5 antagonists such as maraviroc may be potential mediators of GVHD and should be studied in clinical trials.