Interleukin-6 modulates graft-versus-host responses after experimental allogeneic bone marrow transplantation

Purpose: The graft-versus-tumor (GVT) effect is a potent form of immunotherapy against many hematologic malignancies and some solid tumors. The beneficial GVT effect after allogeneic bone marrow transplantation (BMT) is tightly linked to its most significant complication, graft-versus-host disease (GVHD). The role of interleukin-6 (IL-6) after allogeneic BMT is not well understood. This study used a series of complementary knockout and antibody blockade strategies to analyze the impact of IL-6 in multiple clinically relevant murine models of GVHD and GVT

Histone deacetylase inhibition modulates indoleamine 2,3-dioxygenase–dependent DC functions and regulates experimental graft-versus-host disease in mice

Histone deacetylase (HDAC) inhibitors are antitumor agents that also have antiinflammatory properties. However, the mechanisms of their immunomodulatory functions are not known. We investigated the mechanisms of action of 2 HDAC inhibitors, suberoylanilide hydroxamic acid (SAHA) and ITF 2357, on mouse DC responses. Pretreatment of DCs with HDAC inhibitors significantly reduced TLR-induced secretion of proinflammatory cytokines, suppressed the expression of CD40 and CD80, and reduced the in vitro and in vivo allostimulatory responses induced by the DCs. In addition, injection of DCs treated ex vivo with HDAC inhibitors reduced experimental graft-versus-host disease (GVHD) in a murine allogeneic BM transplantation model. Exposure of DCs to HDAC inhibitors increased expression of indoleamine 2,3-dioxygenase (IDO), a suppressor of DC function. Blockade of IDO in WT DCs with siRNA and with DCs from IDO-deficient animals caused substantial reversal of HDAC inhibition–induced in vitro suppression of DC-stimulated responses. Direct injection of HDAC inhibitors early after allogeneic BM transplantation to chimeric animals whose BM-derived cells lacked IDO failed to protect from GVHD, demonstrating an in vivo functional role for IDO. Together, these data show that HDAC inhibitors regulate multiple DC functions through the induction of IDO and suggest that they may represent a novel class of agents to treat immune-mediated diseases

Immunization with host-type CD8α+ dendritic cells reduces experimental acute GVHD in an IL-10–dependent manner

Little is known about the role of active immunization in suppressing undesirable immune responses. Because CD8α+ dendritic cells (DCs) suppress certain immune responses, we tested the hypothesis that immunization of donors with host-derived CD8α+ DCs will reduce host-specific donor T-cell responses. BALB/c T cells from the animals that were immunized with B6 CD8α+ DCs demonstrated, in vitro and in vivo, significantly reduced proliferation and secretion of inflammatory cytokines but showed enhanced secretion of interleukin-10 (IL-10). The responses against third-party and model antigens were preserved demonstrating antigen specificity. The in vivo relevance was further demonstrated by the reduction on graft-versus-host disease (GVHD) in both a major histocompatibility complex–mismatched clinically relevant BALB/c → B6 model and major histocompatibility complex–matched, minor-mismatched C3H.SW → B6 model of GVHD. Immunization of the donors that were deficient in IL-10 (IL-10−/−) or with CD8α+ DCs from B6 class II (class II−/−) failed to reduce T-cell responses, demonstrating (1) a critical role for secretion of IL-10 by donor T cells and (2) a direct contact between the T cells and the CD8α+ DCs. Together, these data may represent a novel strategy for reducing GVHD and suggest a broad counterintuitive role for vaccination strategies in mitigating undesirable immune responses in an antigen-specific manner

Targeting of microRNA-142-3p in dendritic cells regulates endotoxin-induced mortality

While miRNAs are increasingly linked to various immune responses, whether they can be targeted for regulating in vivo inflammatory processes such as endotoxin-induced Gram-negative sepsis is not known. Production of cytokines by the dendritic cells (DCs) plays a critical role in response to endotoxin, lipopolysaccharide (LPS). We profiled the miRNA and mRNA of CD11c+ DCs in an unbiased manner and found that at baseline, miR-142-3p was among the most highly expressed endogenous miRs while IL-6 was among the most highly expressed mRNA after LPS stimulation. Multiple computational algorithms predicted the IL-6 3′ untranslated region (UTR) to be a target of miR-142-3p. Studies using luciferase reporters carrying wild-type (WT) and mutant IL-6 3′UTR confirmed IL-6 as a target for miR-142-3p. In vitro knockdown and overexpression studies demonstrated a critical and specific role for miR142-3p in regulating IL-6 production by the DCs after LPS stimulation. Importantly, treatment of only WT but not the IL-6–deficient (IL-6−/−) mice with locked nucleic acid (LNA)–modified phosphorothioate oligonucleotide complementary to miR 142-3p reduced endotoxin-induced mortality. These results demonstrate a critical role for miR-142-3p in regulating DC responses to LPS and provide proof of concept for targeting miRs as a novel strategy for treatment of endotoxin-induced mortality