Impact of plasmacytoid dendritic cells on outcome after reduced-intensity conditioning allogeneic stem cell transplantation.

The reconstitution of the plasmacytoid dendritic cells (PDCs) compartment might influence outcome after allogeneic stem cell transplantation (allo-SCT). Thus, we investigated the impact of blood PDCs measured at the third month after reduced-intensity conditioning (RIC) in 54 patients who received an HLA-identical sibling allo-SCT. The absence of grade II-IV acute graft-versus-host-disease (GVHD) was associated with an improved PDC count at 3 months after RIC-allo-SCT (P=0.003; OR=6.4; 95% CI, 1.9-22). The CD34+ stem cell dose and other lymphoid subsets infused with the allograft did not affect PDC recovery. Although PDC count could not predict death from progression or relapse, patients with a "high" PDC recovery profile had an improved overall survival (OS; P=0.03), in contrast to patients with a "low" PDC recovery profile who had an increased incidence of nonrelapse mortality (GVHD, infections) (P=0.03). The overall incidence of late infections (viral, fungal and bacterial) was significantly higher in the "low" PDC recovery group as compared to the "high" PDC recovery group (59 vs 19%; P=0.002). In a multivariate analysis, only a "high" PDC count was significantly predictive of a decreased risk of death (P=0.04; RR=0.34; 95% CI, 0.12-0.96). Monitoring of PDCs at 3 months after RIC-allo-SCT may be a useful indicator predictor of long-term outcome.