Background: Inflammatory responses play a critical role in left ventricular remodeling after myocardial infarction (MI). Tolerogenic dendritic cells (tDCs) can modulate immune responses, inducing regulatory T cells in a number of inflammatory diseases. Methods: We generated tDCs by treating bone marrow–derived dendritic cells with tumor necrosis factor-α and cardiac lysate from MI mice. We injected MI mice, induced by a ligation of the left anterior descending coronary artery in C57BL/6 mice, twice with tDCs within 24 hours and at 7 days after the ligation. Results: In vivo cardiac magnetic resonance imaging and ex vivo histology confirmed the beneficial effect on postinfarct left ventricular remodeling in MI mice treated with tDCs. Subcutaneously administered infarct lysate–primed tDCs near the inguinal lymph node migrated to the regional lymph node and induced infarct tissue–specific regulatory T-cell populations in the inguinal and mediastinal lymph nodes, spleen, and infarcted myocardium, indicating that a local injection of tDCs induces a systemic activation of MI-specific regulatory T cells. These events elicited an inflammatory-to-reparative macrophage shift. The altered immune environment in the infarcted heart resulted in a better wound remodeling, preserved left ventricular systolic function after myocardial tissue damage, and improved survival. Conclusions: This study showed that tDC therapy in a preclinical model of MI was potentially translatable into an antiremodeling therapy for ischemic tissue repair.

Dendritic cells (DCs) are the most potent professional antigen presenting cells and inducers of T cell-mediated immunity. However, few specific markers of mature DCs (mDC) have been reported. A previous microarray analysis revealed expression of mDC-specific genes and identified Rsad2 (radical S-adenosyl methionine domain containing 2) as a candidate specific marker for DC maturation. Mouse bone marrow-derived DCs were transfected with Rsad2 siRNA and examined by flow cytometry, ELISA, western, and confocal microscopy. C57BL/6 mice received intravenously B16F10 cells to establish a pulmonary metastasis model. Tumor-bearing mice then received subcutaneously two injections of mDCs or Rsad2 knockdown DCs. The cytotoxic T lymphocyte (CTL) population was examined from splenocytes of DC-vaccinated mice by flow cytometry. Rsad2 was induced at high levels in LPS-stimulated mDCs and mDC function was markedly attenuated under conditions of Rsad2 knockdown. Moreover, Rsad2 was necessary for mDC maturation via the IRF7-mediated signaling pathway. The importance of Rsad2 was confirmed in an Rsad2 knockdown lung metastasis mouse model in which mDCs lost their antitumor efficacy. Data on the CTL population further supported the results as above. Taken together, Rsad2 was an obvious and specific marker necessary for DC maturation and these findings will be clearly helpful for further understanding of DC biology.

Immature dendritic cells (imDCs) are increasingly viewed as mediators of T-cell tolerance. We investigated factors enabling induction of regulatory T (Treg) cells through syngeneic imDC/mesenchymal stem cell (MSC) co-cultures in vitro and immunosuppressive effects of MSC-mediated imDCs (MSCs were excluded after 72 h co-culture) in vivo. In these experiments, we found that Foxp3(+) Treg cell population remarkably increased after the T cell priming phase when splenocytes were co-cultured with both imDCs and MSCs, presumably inducing naïve T cells into Treg cells by MSCs and imDCs. In parallel, TGF-β secretion was markedly induced from the imDC+MSC+splenocyte culture supernatant to a significant level at 72-h co-culture, compared to the MSC or imDC+splenocyte co-culture. Based on these results, using a murine melanoma tumor model, we confirmed that the subcutaneous injection of B16 cells induced a perfect tumor incidence in allogeneic recipients when MSC-mediated DCs were coinjected. Consequently, these results suggested that immune tolerance with MSC-mediated DCs leads to immunosuppression induced by at least Foxp3-specific Treg cells. This tool may be useful in clinical trials due to the yet unknown side effects of stem cell therapy.

Chimeric antigen receptor (CAR)-T cells are effective in the treatment of hematologic malignancies but have shown limited efficacy against solid tumors. Here, we demonstrated an approach to inhibit recurrence of B cell lymphoma by co-expressing both a human anti-CD19-specific single-chain variable fragment (scFv) CAR (CD19 CAR) and a TGF-β/IL-7 chimeric switch receptor (tTRII-I7R) in T cells (CD19 CAR-tTRII-I7R-T cells). The tTRII-I7R was designed to convert immunosuppressive TGF-β signaling into immune-activating IL-7 signaling. The effect of TGF-β on CD19 CAR-tTRII-I7R-T cells was assessed by western blotting. Target-specific killing by CD19 CAR-tTRII-I7R-T cells was evaluated by Eu-TDA assay. Daudi tumor-bearing NSG (NOD/SCID/IL2Rγ^-/-) mice were treated with CD19 CAR-tTRII-I7R-T cells to analyze the in vivo anti-tumor effect. In vitro, CD19 CAR-tTRII-I7R-T cells had a lower level of phosphorylated SMAD2 and a higher level of target-specific cytotoxicity than controls in the presence of rhTGF-β1. In the animal model, the overall survival and recurrence-free survival of mice that received CD19 CAR-tTRII-I7R-T cells were significantly longer than in control mice. These findings strongly suggest that CD19 CAR-tTRII-I7R-T cell therapy provides a new strategy for long-lasting, TGF-β-resistant anti-tumor effects against B cell lymphoma, which may lead ultimately to increased clinical efficacy.

Autoimmunity plays an important role in the pathogenesis of viral myocarditis and giant cell myocarditis. Experimental autoimmune myocarditis (EAM) is a mouse model of myocarditis that is induced by cardiac myosin. Tolerogenic dendritic cells (tDCs) are used as anti-inflammatory and immunosuppressive targets in a number of autoimmune disease models, but their effect on EAM has not been addressed. The aim of this study was to investigate whether tDC therapy in an EAM mouse model can suppress inflammatory myocarditis, a potential precursor of dilated cardiomyopathy. tDCs were generated by treating immature DCs (imDCs) with TNF-α and cardiac myosin. Mice with EAM were injected twice with tDCs (with a 1-week interval) at three doses (2 × 10⁵, 1 × 10⁶, or 2 × 10⁶). The severity of myocarditis was histopathologically assessed. The phenotypes of the DC and regulatory T (Treg) cell populations were determined by flow cytometry and the effect of tDCs on autoimmunity-inducing cytokines was examined by ELISA. Myosin-pulsed tDCs displayed lower levels of DC-related surface markers and expressed higher levels of indoleamine 2, 3-dioxygenase (IDO) than mature DCs (mDCs). Histopathological examination revealed that hearts from tDC-treated mice showed markedly reduced myocardial inflammation compared with those of untreated EAM mice. These therapeutic effects by tDCs were mediated at least by enhanced myosin-specific Treg cell induction and anti-inflammatory cytokine secretion. Taken together, these results show for the first time that myosin-pulsed tDCs ameliorate EAM, and that this occurs most likely via the induction of antigen-specific Treg cells.

Dendritic cells (DCs) have a critical effect on the outcome of adaptive immune responses against growing tumors. Recent studies on the metabolism on DCs provide new insights on the functioning of these critical controllers of innate and adaptive immunity. DCs within the tumor microenvironment (TME) often exist in an inactive state, which is thought to limit the adaptive immune response elicited by the growing tumor. Tumor-derived factors in the TME are known to suppress DC activation and result in functional alterations in DC phenotype. We are now beginning to appreciate that many of these factors can also induce changes in immune cell metabolism. In this review, we discuss the functional alternation of DC phenotype by tumor metabolites.