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% Cl, 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.