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Host antigen-presenting cells (APCs) have been shown to induce acute graft-versus-host disease (aGVHD) in experimental models. In this study, we investigated whether pretransplantation blood levels of host APCs, such as plasmacytoid and myeloid dendritic cells and monocytes, correlate with the development of aGVHD. A total of 89 consecutive patients undergoing allogeneic hematopoietic stem cell transplantation (HSCT) from HLA-matched related (n = 48) or unrelated (n = 41) donors were enrolled in the study. Blood samples were analyzed by flow cytometry before initiating the conditioning regimen. In related donor transplants, patient–donor sex mismatch and monocyte levels significantly correlated with aGVHD grade II–IV in both univariate and multivariate analyses. Similar results were not observed in recipients of matched unrelated transplants, possibly due to use of antithymocyte globulin (ATG) or differences in graft source in these patients. In conclusion, pretransplantation recipient monocyte levels are relevant to the development of GVHD in HSCT from related donors.

Human dendritic cells (DC) comprise 2 subsets-plasmacytoid CD123+ and myeloid CD11c+ DC-that may have distinct roles in the regulation of immunity after allogeneic hematopoietic stem cell transplantation. In this study, we analyzed the kinetics of CD123+ DC and CD11c+ DC reconstitution in 31 patients who underwent transplantation with allogeneic granulocyte colony-stimulating factor-mobilized peripheral blood (PB) stem cells from HLA-identical sibling donors after myeloablative conditioning. Lineage marker-negative HLA-DR+ CD11c+ CD11c+ DC and lineage marker-negative HLA-DR+ CD123+ CD123+ DC, as well as monocytes and lymphoid subsets, were enumerated in donor grafts and in the PB of patients at various time points after transplantation. Reconstitution of both CD11c+ DC and CD123+ DC to normal levels occurred within 6 to 12 months and was not affected by the diagnosis, preparatory regimen, or graft composition. However, PB CD11c+ DC and CD123+ DC counts were significantly reduced in patients with acute GVHD grade II to IV (at 1 and 3 months) and grade I (at 1 month). Patients with chronic GVHD instead showed reduced CD123+ DC counts only 6 months after transplantation. Moreover, treatment with steroids (>0.1 mg/kg) was significantly associated with reduced PB CD11c+ DC and CD123+ DC counts at all time points after transplantation. In multivariate analysis, only acute GVHD affected DC reconstitution early after transplantation. These results will prompt new studies addressing whether DC reconstitution correlates with immunity against infectious agents or with graft-versus-tumor reactions after PB stem cell allotransplantation. © 2004 American Society for Blood and Marrow Transplantation