CD11b+ Gr-1 + immature myeloid cells (

ABSTRACT

Agonistic antibodies targeting CD137 have been clinically unsuccessful due to systemic toxicity. Since conferring tumor selectivity through tumor-associated antigen limits its clinical use to cancers that highly express such antigen, we exploited extracellular adenosine triphosphate (exATP), which is a hallmark of the tumor microenvironment and highly elevated in solid tumors, as a broadly tumor selective switch. We generated a novel anti-CD137 switch antibody, STA551, which exerts agonistic activity only in the presence of exATP. STA551 demonstrated potent and broad anti-tumor efficacy against all mouse and human tumors tested and a wide therapeutic window without systemic immune activation in mice. STA551 was well tolerated even at 150 mg/kg/week in cynomolgus monkeys. These results provide a strong rationale for the clinical testing of STA551 against a broad variety of cancers regardless of antigen expression, and for the further application of this novel platform to other targets in cancer therapy.

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.

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.

No abstract

We have evaluated the capacity of a novel, nanoparticle-based tumor vaccine to eradicate established tumors in mice. C57BL/6 mice were intradermally (i.d.) inoculated with ovalbumin (OVA)-expressing EG-7 tumor cells. When the tumor size reached 7-8 mm, the tumor-bearing mice were i.d. injected near the tumor-draining lymph node (DLN) with liposomes encapsulated with unmethylated cytosine-phosphorothioate-guanine containing oligodeoxynucleotides (CpG-ODN) (CpG-liposomes) co-encapsulated with OVA. This vaccination protocol markedly prevented the growth of the established tumor mass and approximately 50% of tumor-bearing mice became completely cured. Tumor eradication correlated with the generation of OVA/H-2K(b)-tetramer(+) CTLs in the tumor DLN and at the tumor site with specific cytotoxicity toward EG-7 cells. Interestingly, tetramer(+) CTLs failed to be induced in lymph node-deficient Aly/Aly mice. Thus, tetramer(+) CTLs appeared to be generated in the tumor DLN and subsequently migrated into the tumor site. In vivo antibody blocking experiments revealed that CD8(+) T cells, but not CD4(+) T, NK or NKT cells, were the major effector cells mediating tumor eradication. CTL induction was also inhibited when vaccinated tumor-bearing mice were treated with both anti-IFN-alpha and anti-IFN-beta mAbs but not with anti-IFN-alpha or anti-IFN-beta mAb alone. Neither IFN-gamma(-/-) nor IL-12(-/-) mice showed impaired induction of tetramer(+) CTLs. Thus, these findings revealed that CpG-ODN-induced IFN-alpha/beta, but not IL-12 or IFN-gamma, is critical for the generation of tumor-specific CTLs in response to vaccination. These results highlight the potential utility of CpG-liposomes co-encapsulated with protein tumor antigens as therapeutic vaccines in cancer patients.

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.