Host antigen-presenting cells (APC) persist after high-dose chemotherapy and hematopoietic stem cell transplantation (HSCT) and initiate graft-versus-host disease (GvHD) in mouse models of HSCT. The role for donor APC on transplant outcomes is less clear. In clinical allogeneic HSCT from HLA-matched siblings, larger numbers of donor plasmacytoid dendritic cell (DC) precursors were associated with more relapse, and worse survival. Depletion of CD11b+ cells from bone marrow (containing CD11b+ DC) modestly augmented graft-versus-leukemia (GvL) activity in murine allogeneic HSCT. In this study, using allogeneic MHC mis-matched HSCT (C57BL/6→B10.BR) of mice bearing a lymphoblastic leukemia (LBRM), recipients of FACS–purified CD11b donor DC plus FACS–purified HSC and T-cells had dramatically improved long-term survival (45% alive at >100 days) compared to d 5% survival among recipients of HSC and T-cells, or HSC, T-cells and CD11b+ DC (p<0.001). Both donor CD11b and CD11b+ DC homed to lymphoid organs, and physically contacted donor T-cells, but only the CD11b DC subset led to higher levels of interferon-γ (IFN- γ) in serum and higher levels of donor spleen-derived T-cells that synthesized IFN-γ in vivo in the first 10 days post-transplant. In contrast, recipients of CD11b+ DC had higher level of sera of IL–10. In CD11b DC recipients, donor effector-memory CD8+ T-cells proliferated more rapidly and expanded in recipients, but did not cause debilitating GvHD in mice transplanted without leukemia. Donor-spleen-derived T-cells among recipients of CD11b DC were predominately CD8+ (CD4:CD8 ratio 0.7:1), while donor spleen-derived T-cells were predominately CD4+ (p<0.02; CD4:CD8 ratio 1.3:1) among recipients of CD11b+ DC. In vitro co-culture of purified DC with homologous T-cells responding to allo-antigen demonstrated the same pattern of cytokine production as found in vivo, supporting the ability of CD11b DC to generate Th1 immune responses that are associated with enhanced GvL effects and improved immune reconstitution. In vitro stimulation of DC subsets by CD40L (1μg/mL) and LPS (1μg/mL) showed that CD11b+ DC had higher level of PD–L1 expression compared to CD11b DC. In vitro exposure of LBRM to IFN-γ, at doses of 10–300 pg/ml, similar to those observed in vivo, had no direct cytotoxic effect, and had no long-term growth-inhibitory effect on proliferation during 5 days of culture. CD11b+ DC expressed higher levels of PD–L1 and led to higher T-cell synthesis of IL–10 in vivo and in vitro. Transplantation of CD11b DC resulted in higher levels of donor T-cell production of IFN-γ, and enhanced the GvL effect of donor T-cells without producing debilitating GvHD. These data indicated that purified donor DC can regulate post-transplant immunity via indirect antigen presentation to donor T-cells. CD11b+ DC expressed higher level of PD–L1 and led to higher level of IL–10 that resulted in more relapse and light GvHD. CD11b DC led to higher level of donor IFN-γ that resulted in a stronger GvL effect while no debilitating GvHD. Engineering the DC content of an allograft may augment immune reconstitution and GvL activity without significantly increasing GvHD in allogeneic HSCT.

Author notes

Disclosure:Research Funding: National Institute of Health grant R01- CA-74364-03 and Amy Strelzer Manasevit fellowsship sponsored by National Marrow Donor Program and the Supergen Corporation.