Cd47 (Integrin-Associated Protein) Engagement of Dendritic Cell and Macrophage Counterreceptors Is Required to Prevent the Clearance of Donor Lymphohematopoietic Cells

Abstract

Integrin-associated protein (CD47) is a broadly expressed protein that costimulates T cells, facilitates leukocyte migration, and inhibits macrophage scavenger function. To determine the role of CD47 in regulating alloresponses, CD47+/+ or CD47−/− T cells were infused into irradiated or nonconditioned major histocompatibility complex disparate recipients. Graft-versus-host disease lethality was markedly reduced with CD47−/− T cells. Donor CD47−/− T cells failed to engraft in immunodeficient allogeneic recipients. CD47−/− marrow was unable to reconstitute heavily irradiated allogeneic or congenic immune–deficient CD47+/+ recipients. These data suggested that CD47−/− T cells and marrow cells were cleared by the innate immune system. To address this hypothesis, dye-labeled CD47−/− and CD47+/+ lymphocytes or marrow cells were infused in vivo and clearance was followed. Dye-labeled CD47−/− cells were engulfed by splenic dendritic cells and macrophages resulting in the clearance of virtually all CD47−/− lymphohematopoietic cells within 1 day after infusion. Host phagocyte-depleted CD47+/+ recipients partially accepted allogeneic CD47−/− T cells. Thus, dendritic cells and macrophages clear lymphohematopoietic cells that have downregulated CD47 density. CD47 expression may be a critical indicator for determining whether lymphohematopoietic cells will survive or be cleared.

Intravenous apoptotic spleen cell infusion induces a TGF-β-dependent regulatory T-cell expansion

“…Pretreatment of mice with clodronate-loaded liposomes reduced significantly both the number of splenic CD11b þ macrophages and apoptotic cell-induced donor BM engraftment ( Figure 1c). As described previously, 33 we observed that not all splenic DC subsets were depleted by clodronate-loaded liposome infusion due to their anatomic location (Supplementary Figure 1 online). To further explore the role of host DC in the graftfacilitating effect of apoptotic cells, a transgenic mouse model for in vivo DC ablation 34 was used.…”

“…To deplete resident host phagocytes, liposomes loaded with clodronate 32,33 were infused before BMT. Pretreatment of mice with clodronate-loaded liposomes reduced significantly both the number of splenic CD11b þ macrophages and apoptotic cell-induced donor BM engraftment ( Figure 1c).…”

“…infusion were performed as described. 32,33 Briefly, liposomes consisting of phosphatidyl choline and cholesterol (Sigma) in 6 : 1 molar ratio were resuspended in PBS and injected via the tail vein (final volume of 0.2 ml containing about 2 mg of clodronate-loaded liposomes). The day after, mice were irradiated and grafted as described above.…”

Anti-CD47 antibodies promote phagocytosis and inhibit the growth of human myeloma cells

“…The importance of macrophages for anti-CD47 antibody-mediated anti-tumor effects was reported in previous studies wherein immunocompromised mice lacking T cells, B cells and NK cells rapidly eliminated transplanted CD47-deficient hematopoietic cells or human AML cells, but this elimination was blocked following the depletion of macrophages. 12,33 The bone marrow microenvironment is critical for myeloma cell survival and proliferation. [34][35][36][37] In addition, the bone marrow microenvironment has been reported to protect myeloma cells from chemotherapy.…”

CD47 on experimentally senescent murine RBCs inhibits phagocytosis following Fcγ receptor–mediated but not scavenger receptor–mediated recognition by macrophages

“…[20][21][22][23] CD47 is highly expressed on RBCs, but ubiquitously expressed by most cells in the body, and can also negatively regulate phagocytosis of platelets and leukocytes. [24][25][26] The amount of CD47 on the cell surface regulates macrophage phagocytosis, since IgG-opsonized RBCs from CD47 ϩ/Ϫ mice (expressing about 50% of normal levels of CD47) are taken up faster than wild-type (WT) RBCs, but slower than CD47 Ϫ/Ϫ RBCs. 27 We have shown that the phagocytosis-inhibitory effect of CD47 does not come into play on apoptotic nucleated cells, where CD47 is clustered into patches on the apoptotic cell surface and segregated away from prophagocytic ligands such as PS or calreticulin.…”