moDC Maturation Research Articles

Human monocyte-derived dendritic cells are deficient in prostaglandin E2 production

Monocyte-derived dendritic cells (moDCs) are increasingly used in clinical settings to stimulate tumor immunity. Prostaglandin E2 (PGE2), which is a member of the eicosanoid family of oxygenated arachidonic acid derivatives generated through the action of cyclooxygenases (COXs), is frequently used to enhance the tumor necrosis factor-α-induced terminal maturation of moDCs. We show here that one effect of interleukin (IL)-4, which is used together with GM-CSF to generate moDCs, is the suppression of endogenous PGE2 production in moDCs. IL-4 inhibits the cytoplasmic form of phospholipase A2, the enzyme that specifically liberates arachidonic acid from membrane phospholipids. Although moDCs failed to mobilize endogenous arachidonic acid, they converted exogenous arachidonic acid into PGE2 in a COX-1- and COX-2-dependent fashion. IL-4-mediated suppression of PGE2 biosynthesis in human moDCs explains the previously reported maturation-enhancing effect of exogenous PGE2. The general suppression of eicosanoid biosynthesis may, however, limit the immunological efficacy of moDCs generated with IL-4.

Rapamycin induces apoptosis in monocyte- and CD34-derived dendritic cells but not in monocytes and macrophages

AbstractRapamycin (Rapa), a recently introduced immunosuppressive drug, seems to be effective in preventing acute allograft rejection. Although its antiproliferative effect on T lymphocytes has been investigated extensively, its effect on the initiators of the immune response, the dendritic cells (DCs), is not known. Therefore, the effect of Rapa on monocyte- (mo-DCs) and CD34+-derived DCs in vitro but also on other myeloid cell types, including monocytes and macrophages, was examined. The present study shows that Rapa does not affect phenotypic differentiation and CD40L-induced maturation of mo-DCs. However, Rapa dramatically reduced cell recovery (40%-50%). Relatively low concentrations of Rapa (10−9 M) induced apoptosis in both mo-DCs and CD34+-derived DCs, as visualized by phosphatidylserine exposure, nuclear condensation and fragmentation, and DNA degradation. In contrast, Rapa did not affect freshly isolated monocytes, macrophages, or myeloid cell lines. The sensitivity to Rapa-induced apoptosis was acquired from day 2 onward of mo-DC differentiation. Rapa exerts its apoptotic effect via a reversible binding to the cytosolic receptor protein FKBP-12, as demonstrated in competition experiments with FK506, which is structurally related to Rapa. Partial inhibition of Rapa-induced apoptosis was obtained by addition of ZVAD-fmk, which implies caspase-dependent and caspase-independent processes. The fact that Rapa exerts a specific effect on DCs but not on monocytes and macrophages might contribute to the unique actions of Rapa in the prevention of allograft rejection and other immune responses.

A clinically approved oral vaccine against pneumotropic bacteria induces the terminal maturation of CD83 + immunostimulatory dendritic cells

Dendritic cells (DCs) are important antigen-presenting cells of the immune system that have attracted interest as cellular adjuvants to induce immunity in clinical settings. We have investigated the effects of Broncho-Vaxom®, an oral vaccine composed of lysates from eight pneumotropic bacteria, on human monocyte-derived dendritic cells (moDCs). Broncho-Vaxom® induced the terminal maturation of CD83 + moDCs. MoDCs stimulated with Broncho-Vaxom® displayed a phenotype of activated DCs with high levels of major histocompatibility complex (MHC) molecules and increased levels of adhesion and co-stimulatory molecules. In addition, moDCs activated with Broncho-Vaxom® exhibited enhanced T cell-stimulatory capacity in the allogeneic mixed leukocyte reaction. Broncho-Vaxom® at 100 μg/ml was as potent as TNF-α at 1000 U/ml in activating human moDCs. Neither LPS-like activity nor bacterial DNA was found to be responsible for the maturation-inducing activity of Broncho-Vaxom®, suggesting that Broncho-Vaxom® contains other bacterial factors that are capable of inducing the terminal maturation of moDCs. In DC-based immunotherapy, Broncho-Vaxom® could be used as a stimulus of DC maturation, which meets the standards of good manufacturing practice (GMP). In addition, vaccination with Broncho-Vaxom®-loaded moDCs may be an attractive treatment option in preventing recurrent airway infection in predisposed individuals.