CD11b− Donor Dendritic Cells Enhance Donor T-Cells’ Th1 Polarization and Graft Versus Leukemia Activity in Allogeneic Hematopoietic Stem Cell Transplantation

Background: Based on a clinical association of donor plasmacytoid dendritic cell (DC) content with leukemia relapses after allogeneic BMT (Waller, Blood 2001), we have previously reported that CD11b − donor DC added to a graft containing FACS-purified hematopoietic stem cells (HSC) and T-cells enhanced interferon-γ (IFN-γ) production and GvL activity in MHC-mismatched allogeneic transplant mouse models (Li, Blood 2007). Objective: In this study, we studied the mechanisms whereby donor DC in the graft modulate donor T-cell activity and the graft-versus-leukemia (GvL) effect in MiHA (C3H.SW → C57BL/6J)- and MHC (C57BL/6J → B10.BR)- mismatched models of allogeneic hematopoietic stem cell transplantation (HSCT). Methods: Mice irradiated to 11 Gy received 5 × 10 4 log-phase viable MMB3.19 myeloid lymphoma cells via intraperitoneal injection or intravenous injection of 1 x 10 5 LBRM T-cell lymphoma cells one day before transplant. Allografts consisted of 5 × 10 4 FACS-purified donor BM CD11b − DC or CD11b + DC plus 3 × 10 3 FACS-purified c-kit + sca-1 + lineage − hematopoietic stem cells (HSC) in combination with either 3 × 10 5 T-cells, 3 × 10 5 CD8 + T-cells or no additional T-cells transplanted via tail vein. Graft-versus-host disease (GvHD) clinical scores (based on body weight loss, posture, skin, fur texture, activity) were recorded twice weekly in non-tumor bearing recipients. In vitro proliferation and cytotoxic activity of donor-derived T-cells against tumor targets was assessed by CFSE staining and a caspase flow cytometry assay (CyToxiLux PLUS) using donor T-cells harvested from recipients on day 34 and day 82 post transplant. Serum and intracellular Th1 cytokines (IFN-γ, IL-2, and TNF-α) and Th2 cytokines (IL-4, IL-5, and IL-10) from recipients’ peripheral blood and spleens day 3 and day 10 post-transplant was measured by ELISA and flow cytometry. IFN-γ direct killing of leukemia cells was tested by in vitro IFN-γ exposure. Results: In non-tumor bearing mice, recipients of all combinations of donor DC subsets, with and without donor T-cells had equivalent survival (75% – 85%) at 3 months post transplant without significant clinical signs of GvHD. Transplantation of tumor cells to recipients of HSC alone, HSC plus donor T-cells, or HSC plus T-cells and CD11b + DC in the MiHA- and the MHC-mismatched transplant models led to 0% or 5% 3 month survival, respectively. Strikingly, tumor-bearing mice transplanted with CD11b − DC had significantly enhanced 3 month survival (35% in the MiHA-mismatched model and 45% in the MHCmismatched model) without increased GvHD (p − DC and a mixture of CD4 + and CD8 + donor T-cells versus mice that received HSC plus CD11b − DC and only CD8 + donor T-cells. Donor T-cells harvested from recipients of CD11b − DC 34 days after transplant in the MiHA-mismatched model as well as 82 days after transplant in the MHC-mismatched model displayed increased cell proliferation following co-culture with irradiated hosttype splenocytes as a source of alloantigen compared with donor T-cells harvested from recipients of CD11b + DC or recipients of HSC plus T-cells without donor DC. Leukemia cell killing was greater following incubation of purified donor T-cells recovered from recipients of CD11b − DC with tumor targets compared to T-cells recovered from other treatment groups. Recipients of CD11b − DC had higher serum levels of Th1 cytokines IFN-γ and IL-2 and higher number of Th1 positive donor T-cells compared with recipients of other treatment groups. In contrast, recipients of CD11b + DC had higher serum levels of Th2 cytokines IL-4, IL-5, and IL-10 and higher number of Th2 positive donor T-cells. IFN-γ added to in vitro cultures with MMB3.19, and LBRM, had no direct cell killing effect. Conclusion: CD11b − donor DC enhanced Th1 polarization of donor T-cells and GvL without increasing GvHD. Donor CD8 + T-cells mediated tumor killing effect. CD11b + donor DC enhanced Th2 polarization of donor CD4 + T-cells and led to limited GvHD and GvL.