Yoshinori Narita

Liposome-encapsulated CpG oligodeoxynucleotides as a potent adjuvant for inducing type 1 innate immunity.

Unmethylated cytosine-phosphorothioate-guanine oligodeoxynucleotides (CpG-ODNs) exhibit potent immunostimulating activity by binding with Toll-like receptor 9 (TLR9) expressed on antigen-presenting cells. Here, we show that CpG-ODN encapsulated in cationic liposomes (CpG-liposomes) improves its incorporation into CD11c+ dendritic cells (DCs) and induces enhanced serum interleukin (IL)-12 levels compared with unmodified CpG-ODN. CpG-liposome potently activated natural killer (NK) cells (84.3%) and NKT cells (48.3%) to produce interferon-γ (IFN-γ), whereas the same dose of unmodified CpG-ODN induced only low numbers of IFN-γ–producing NK cells (12.7%) and NKT cells (1.6%) to produce IFN-γ. In contrast with the NKT cell agonist α-galactosylceramide, which induces both IFN-γ and IL-4 production by NKT cells, CpG-liposome only induced IFN-γ production by NKT cells. Such potent adjuvant activities of CpG-liposome were absent in TLR9-deficient mice, indicating that CpG-liposome was as effective as CpG-ODN in stimulating type 1 innate immunity through TLR9. In addition to TLR9, at least two other factors, IL-12 production by DCs and direct contact between DCs and NK or NKT cells, were essential for inducing type 1 innate immunity by CpG-liposome. Furthermore, ligation of TLR9 by CpG-liposome coencapsulated with ovalbumin (OVA) caused the induction of OVA-specific CTLs, which exhibited potent cytotoxicity against OVA-expressing tumor cells. These results indicate that CpG-liposome alone or combined with tumor antigen protein provides a promising approach for the prevention or therapy of tumors.

Anti-IL-6 receptor mAb eliminates myeloid-derived suppressor cells and inhibits tumor growth by enhancing T-cell responses

CD11b+Gr‐1+ immature myeloid cells (ImCs), which are abnormally increased in tumor‐bearing mice, were classified into three different subsets according to their phenotypic and morphological characteristics: Gr‐1low F4/80+ macrophages (MΦ‐ImCs), Gr‐1mid stab neutrophils (Neutstab‐ImCs), and Gr‐1high segmented neutrophils (Neutseg‐ImCs). In the spleen, only MΦ‐ImCs but not Neutstab‐ImCs and Neutseg‐ImCs exhibited a significant immunosuppressive activity in MLR. In contrast, tumor‐infiltrating leukocytes (TILs) contained only two ImC subsets, MΦ‐ImCs and Neutseg‐ImC, both of which exhibited stronger inhibitory activity against T cells compared with spleen‐MΦ‐ImCs. Thus, we concluded that tumor‐infiltrating MΦ‐ImCs and Neutseg‐ImCs were fully differentiated myeloid‐derived suppressor cells (MDSCs) with stronger T‐cell inhibitory activity. Indeed, spleen MΦ‐ImCs were converted into stronger MΦ‐MDSCs by tumor‐derived factor (TDF). Moreover, both spleen Neutstab‐ImCs and Neutseg‐ImCs differentiated into Neutseg‐MDSCs with suppressive activity after culture with TDF. We first demonstrated that administration of anti‐IL‐6R mAb could downregulate the accumulation of MΦ‐MDSCs and Neutseg‐MDSCs in tumor‐bearing mice. The elimination of those MDSCs caused subsequent enhancement of antitumor T‐cell responses, including IFN‐γ‐production. The therapeutic effect of anti‐IL‐6R mAb was further enhanced by combination with gemcitabine (GEM). Thus, we propose that anti‐IL‐6R mAb could become a novel tool for the downmodulation of MDSCs to enhance antitumor T‐cell responses in tumor‐bearing hosts.

An Essential Role of Antigen-Presenting Cell/T-Helper Type 1 Cell-Cell Interactions in Draining Lymph Node during Complete Eradication of Class II–Negative Tumor Tissue by T-Helper Type 1 Cell Therapy

Prior studies have shown that transfer of ovalbumin (OVA)-specific T helper type 1 (Th1) cells into mice bearing MHC class II+ OVA-expressing tumor cells (A20-OVA) causes complete tumor rejection. Here we show that, although Th1 cell therapy alone was not effective against MHC class II- OVA-expressing tumor cells (EG-7), treatment of mice bearing established EG-7 tumors by i.v. transfer of Th1 cells combined with i.t. injection of the model tumor antigen OVA induced complete tumor rejection. Transferred Th1 cells enhanced the migration of tumor-infiltrating antigen-presenting cells (APC) that had processed OVA into the draining lymph node (DLN). Although transferred Th1 cells were randomly distributed in DLN, distal LN, spleen, and tumor tissue, active proliferation of Th1 cells always initiated in DLN, where Th1 cells efficiently interacted with APC that presented OVA. In parallel, OVA-tetramer+ CTLs, showing EG-7-specific cytotoxicity, were highly induced in DLN and the local tumor site. The OVA-tetramer+ CTL functioned systemically because two bilateral tumor masses were both completely rejected on treatment of one tumor. Furthermore, either active proliferation of transferred Th1 cells or generation of tetramer+ CTL was not induced in MHC class II-deficient mice and LN-deficient Aly/Aly mice. These results indicate that DLN is an indispensable organ for initiating active APC/Th1 cell interactions, which is critical for inducing complete eradication of tumor mass by tumor-specific CTL.

The Key Role of IL-6–Arginase Cascade for Inducing Dendritic Cell–Dependent CD4+ T Cell Dysfunction in Tumor-Bearing Mice

Evaluation of immune dysfunction during the tumor-bearing state is a critical issue in combating cancer. In this study, we initially found that IL-6, one of the cachectic factors, suppressed CD4+ T cell–mediated immunity through downregulation of MHC class II by enhanced arginase activity of dendritic cells (DC) in tumor-bearing mice. We demonstrated that administration of Ab against IL-6R (anti–IL-6R mAb) greatly enhanced T cell responses and inhibited the growth of tumor in vivo. We also found that IL-6 upregulated the expression of arginase-1 and arginase activity of DC in vitro. Tumor-infiltrating CD11c+ DC exhibited upregulated mRNA expression of arginase-1 but reduced expression of MHC class II in parallel with the increase in serum IL-6 levels at the late stage in tumor-bearing hosts. However, the administration of anti–IL-6R mAb into tumor-bearing mice inhibited both the downmodulation of MHC class II and the upregulation of arginase-1 mRNA levels in DC. Furthermore, we noted that Nω-hydroxy-L-arginine or L-arginine, an arginase-1 inhibitor, blocked the reduction in MHC class II levels on CD11c+ DC during the tumor-bearing state. Finally, we demonstrated that the administration of Nω-hydroxy-L-arginine at the peritumor site significantly enhanced CD4+ T cell responses and inhibited tumor growth. Thus, IL-6–mediated arginase activation and the subsequent reduction in MHC class II expression on DC appeared to be critical mechanisms for inducing dysfunction of the immune system in the tumor-bearing state. Blockade of the IL-6–arginase cascade is a promising tool to overcome the dysfunction of antitumor immunity in tumor-bearing hosts.

IFN-γ-dependent type 1 immunity is crucial for immunosurveillance against squamous cell carcinoma in a novel mouse carcinogenesis model

3-Methylcholanthrene (MCA)-induced sarcomas have been used as conventional tools for investigating immunosurveillance against tumor development. However, MCA-induced sarcoma is not always an ideal model for the study of the human cancer system because carcinomas and not sarcomas are the dominant types of human cancers. To resolve this problem, we established a novel and simple method to induce mouse squamous cell carcinomas (SCCs). As well known, the subcutaneous injection of MCA caused the formation of sarcomas at 100% incidence. However, we here first succeeded at inducing SCC at 60% of incidence within 2 months by a single intra-dermal injection of MCA. Using this primary SCC model, we demonstrated the critical role of interferon (IFN)-gamma-dependent type 1 immunity in immunosurveillance against SCC from the following results: (i) The incidence of SCC was accelerated in IFN-gamma-deficient mice compared with that in wild-type mice; (ii) In vivo injection of CpG-oligodeoxynucleotides (CpG-ODN) caused a marked reduction in the incidence of SCC in parallel with the activation of type 1-dependent antitumor immunity and (iii) The antitumor activity of CpG-ODN was significantly decreased in IFN-gamma-deficient mice. Thus, our established MCA-induced mouse SCC model could be a powerful tool for evaluating immunosurveillance mechanisms during the development of SCC and might result in a novel strategy to address immunosurveillance mechanisms of human cancer.

CSF-1–Dependent Red Pulp Macrophages Regulate CD4 T Cell Responses

The balance between immune activation and suppression must be regulated to maintain immune homeostasis. Tissue macrophages (MΦs) constitute the major cellular subsets of APCs within the body; however, how and what types of resident MΦs are involved in the regulation of immune homeostasis in the peripheral lymphoid tissues are poorly understood. Splenic red pulp MΦ (RPMs) remove self-Ags, such as blood-borne particulates and aged erythrocytes, from the blood. Although many scattered T cells exist in the red pulp of the spleen, little attention has been given to how RPMs prevent harmful T cell immune responses against self-Ags. In this study, we found that murine splenic F4/80hiMac-1low MΦs residing in the red pulp showed different expression patterns of surface markers compared with F4/80+Mac-1hi monocytes/MΦs. Studies with purified cell populations demonstrated that F4/80hiMac-1low MΦs regulated CD4+ T cell responses by producing soluble suppressive factors, including TGF-β and IL-10. Moreover, F4/80hiMac-1low MΦs induced the differentiation of naive CD4+ T cells into functional Foxp3+ regulatory T cells. Additionally, we found that the differentiation of F4/80hiMac-1low MΦs was critically regulated by CSF-1, and in vitro-generated bone marrow-derived MΦs induced by CSF-1 suppressed CD4+ T cell responses and induced the generation of Foxp3+ regulatory T cells in vivo. These results suggested that splenic CSF-1–dependent F4/80hiMac-1low MΦs are a subpopulation of RPMs and regulate peripheral immune homeostasis.

Sialyl lewisx antigen-expressing human CD4+ T and CD8+ T cells as initial immune responders in memory phenotype subsets

Cytokine production by memory T cells in secondary immune responses has a critical role in host defenses. Previously, we had demonstrated that a unique antigen composed of sialyl lewisx (sLex) was expressed on CD45RO+ memory‐phenotype subsets of human T cells. Here, we found that the sLex antigen was up‐regulated on CD45RA+ naïve human CD4+ T and CD8+ T cells by TCR stimulation. In addition, sLex antigen‐expressing CD4+ T and CD8+ T cells in human PBMCs were activated immediately by cytokine stimulations composed of IL‐2 plus IL‐12 or IL‐15 in an antigen‐independent manner. Moreover, the sLex‐positive human CD8+ T cells significantly enhanced reverse antibody‐dependent cellular cytotoxicity compared with a sLex‐negative population. These findings clearly indicate that sLex antigen‐expressing memory phenotype CD4+ T and CD8+ T cells contribute to early‐stage immunity by providing a source of IFN‐γ and cytotoxicity, suggesting that they would be a key immunomodulator in host defenses.