Peripheral blood stem cell harvests from G-CSF–stimulated donors contain a skewed Th2 CD4 phenotype and a predominance of type 2 dendritic cells

Objective To assess the numbers and function of dendritic cell (DC) subsets and T helper cells in bone marrow (BM) and peripheral blood stem cell (PBSC) harvests. Patients and Methods DC subsets in stem cell grafts were analyzed using three-color flow cytometry. Intracellular cytokine staining and the staining of IL-12Rβ2 were used for determining the proportion of Th1-, Th2-, and IL-12–producing DC in the grafts. The ability of DC1 and DC2 to induce T-cell proliferation and cytokine secretion were studied using thymidine incorporation and ELISA techniques. Results PBSC recipients received a significantly higher number of DC2 than BM recipients and a lower proportion of IL-12–producing DC. Purified DC1 from both BM and PBSC grafts were capable of inducing proliferation of allogeneic T cells and also induced a predominant Th1 response when cultured with CD4+/CD45RA+ cells. In contrast, DC2 induced a predominant Th2 cytokine response. PBSC grafts contained a higher number of both Th1 and Th2 cells compared to BM grafts; however, as a consequence of the increased number of Th2 cells the ratio of Th1:Th2 cells in PBSC grafts was 1.1:1 compared to 9.8:1 in BM. Furthermore, following in vitro activation of T cells, PBSC grafts contained a lower proportion of IL-12Rβ2+ T cells. Conclusion G-CSF does not have a direct effect on DC function but acts to increase the numbers of DC2 in the blood of PBSC donors. This is associated with a higher proportion of Th2 cells present in PBSC grafts and T cells in PBSC grafts were less likely to develop a Th1 response following in vitro activation.