Donor DC Subsets Polarize Donor T-Cell Immune Responses in Allogeneic BMT.

Introduction: Impaired or inappropriate immune reconstitution after allogeneic bone marrow transplantation (BMT) can lead to infection, graft-versus-host disease (GvHD) and leukemia relapse. We have previously reported that BM contains two populations of dendritic cell (DC) subsets, CD11b⁺ DC and CD11b⁻ DC, and that CD11b depleted donor BM promoted increased donor T-cell chimerism and increased graft-versus-leukemia (GvL) activity in C57BL/6 → B10BR transplants [BBMT, 2004, 10: 540]. To explore the mechanism by which CD11b-depletion improved allo-reactivity, we performed allogeneic hematopoietic cell transplants using defined populations of donor stem cells, DCs, and T-cells in a MHC mis-matched BMT model. Methods: We transplanted FACS purified populations of 50,000 GFP⁺ CD11b^- DC or CD11b⁺ DC in combination with 5,000 FACS purified Lin^- Sca-1⁺ c-kit⁺ hematopoietic stem cells (HSC) and 300,000 or 1,000,000 congenic spleen T-cells from C57BL/6 donors into C57BL/6[H-2K^b], B10BR[H-2K^k] and PL/J[H-2K^u] recipients. Proliferation of CFSE stained donor T-cells was measured at 72 hours post-transplant. FACS cytometric bead array and intracellular cytokine staining measured serum and intracellular cytokines in donor T-cells. Results: The initial proliferation and Ki-67 expression of CFSE labeled donor T-cells in allogeneic recipients were much higher than in syngeneic recipients (homeostatic proliferation). Confocal microscopy showed co-localization of donor DC subsets with donor T-cells in the recipient spleens at 3 and 10 days post-transplant. In the allogeneic transplant settings, donor T-cells co-transplanted with CD11b^- DC showed increased IFN-γ synthesis at 3 and 10 days post-transplant compared to donor T-cells co-transplanted with HSC plus CD11b⁺ DC or HSC alone. Increased proliferation of donor T-cells led to increased donor T-cell chimerism at day 10, 30, 60, and day105 post-transplant among recipients of CD11b^- DC compared to recipients of HSC alone or HSC plus CD11b⁺ DC (Figure 1). Transplantation of spleen T-cells and CD11b^- DC did not increase GvHD, but was associated with full donor chimerism. In contrast, transplantation of allogeneic CD11b⁺ DC led to persistence and expansion of residual host T-cells (Figure 2), increased numbers of donor CD4⁺CD25⁺⁺Foxp3⁺ T-cells, and higher serum level of IL-10 supporting early post-transplant expansion of donor T regulatory cells (Treg). Conclusions: Donor CD11b^- DC promoted immune reconstitution by polarizing donor T-cells to Th1 immune responses associated with increased IFN-γ synthesis and donor T-cell proliferation, while donor CD11b⁺ DC suppressed immune reconstitution by inhibiting donor T-cell allogeneic immune responses. These data support a novel paradigm for the regulation of post-transplant immunity and suggest clinical methods to test the hypothesis that manipulation of the DC content of a hematopoietic cell allograft regulates post transplant immunity in the clinical setting.

Figure 1.

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Donor Spleen Derived T-cells in Peripheral Blood [* p<0.05, v.s. recipients of HSC plus CD11b(+)DC and spleen T-cells]

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Donor Spleen Derived T-cells in Peripheral Blood [* p<0.05, v.s. recipients of HSC plus CD11b(+)DC and spleen T-cells]

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Figure 2.

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Host Derived T-cells in Peripheral Blood [* p<0.05, v.s. recipients of HSC plus CD11b(-)DC and spleen T-cells]

Figure 2.

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Host Derived T-cells in Peripheral Blood [* p<0.05, v.s. recipients of HSC plus CD11b(-)DC and spleen T-cells]

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