Nitric oxide short-circuits interleukin-12-mediated tumor regression

IFN-γ: A cytokine at the right time, is in the right place

Interferon gamma has long been studied as a critical mediator of tumor immunity. In recent years, the complexity of cellular interactions that take place in the tumor microenvironment has become better appreciated in the context of immunotherapy. While checkpoint inhibitors have dramatically improved remission rates in cancer treatment, IFN-γ and related effectors continue to be identified as strong predictors of treatment success. In this review, we provide an overview of the multiple immunosuppressive barriers that IFN-γ has to overcome to eliminate tumors, and potential avenues for modulating the immune response in favor of tumor rejection.

The role of nitric oxide in melanoma

Nitric oxide (NO) is a small gaseous signaling molecule that mediates its effects in melanoma through free radical formation and enzymatic processes. Investigations have demonstrated multiple roles for NO in melanoma pathology via immune surveillance, apoptosis, angiogenesis, melanogenesis, and on the melanoma cell itself. In general, elevated levels of NO prognosticate a poor outcome for melanoma patients. However, there are processes where the relative concentration of NO in different environments may also serve to limit melanoma proliferation. This review serves to outline the roles of NO in melanoma development and proliferation. As demonstrated by multiple in vivo murine models and observations from human tissue, NO may promote melanoma formation and proliferation through its interaction via inhibitory immune cells, inhibition of apoptosis, stimulation of pro-tumorigenic cytokines, activation of tumor associated macrophages, alteration of angiogenic processes, and stimulation of melanoma formation itself.

Colonization of xenograft tumors by oncolytic vaccinia virus (VACV) results in enhanced tumor killing due to the involvement of myeloid cells

Background

The mechanisms by which vaccinia virus (VACV) interacts with the innate immune components are complex and involve different mechanisms. iNOS-mediated NO production by myeloid cells is one of the central antiviral mechanisms and this study aims to investigate specifically whether iNOS-mediated NO production by myeloid cells, is involved in tumor eradication following the virus treatment.

Methods

Human colon adenocarcinoma (HCT-116) xenograft tumors were infected by VACV. Infiltration of iNOS⁺ myeloid cell population into the tumor, and virus titer was monitored following the treatment. Single-cell suspensions were stained for qualitative and quantitative flow analysis. The effect of different myeloid cell subsets on tumor growth and colonization were investigated by depletion studies. Finally, in vitro culture experiments were carried out to study NO production and tumor cell killing. Student’s t test was used for comparison between groups in all of the experiments.

Results

Infection of human colon adenocarcinoma (HCT-116) xenograft tumors by VACV has led to recruitment of many CD11b⁺ ly6G⁺ myeloid-derived suppressor cells (MDSCs), with enhanced iNOS expression in the tumors, and to an increased intratumoral virus titer between days 7 and 10 post-VACV therapy. In parallel, both single and multiple rounds of iNOS-producing cell depletions caused very rapid tumor growth within the same period after virus injection, indicating that VACV-induced iNOS⁺ MDSCs could be an important antitumor effector component. A continuous blockade of iNOS by its specific inhibitor, L-NIL, showed similar tumor growth enhancement 7–10 days post-infection. Finally, spleen-derived iNOS⁺ MDSCs isolated from virus-injected tumor bearing mice produced higher amounts of NO and effectively killed HCT-116 cells in in vitro transwell experiments.

Conclusions

We initially hypothesized that NO could be one of the factors that limits active spreading of the virus in the cancerous tissue. In contrast to our initial hypothesis, we observed that PMN-MDSCs were the main producer of NO through iNOS and NO provided a beneficial antitumor effect, The results strongly support an important novel role for VACV infection in the tumor microenvironment. VACV convert tumor-promoting MDSCs into tumor-killing cells by inducing higher NO production.

Tolerogenic Phenotype of IFN-γ-Induced IDO+ Dendritic Cells Is Maintained via an Autocrine IDO-Kynurenine/AhR-IDO Loop

Previous studies demonstrated that IL-12-driven antitumor activity is short-circuited by a rapid switch in dendritic cell (DC) function from immunogenic to tolerogenic activity. This process was dependent on IFN-γ and the tolerogenic phenotype was conferred by IDO. Extended monitoring of IDO(+) DC in the tumor-draining lymph nodes of IL-12 plus GM-CSF-treated tumor-bearing mice revealed that whereas IFN-γ induction was transient, IDO expression in DC was maintained long-term. An in vitro system modeling the IFN-γ-mediated change in DC function was developed to dissect the molecular basis of persistent IDO expression in post-IL-12 DC. Stimulation of DC with IFN-γ and CD40L resulted in rapid induction of IDO1 and IDO2 transcription and recapitulated the in vivo switch from immunogenic to tolerogenic activity. Long-term maintenance of IDO expression was found to be independent of exogenous and autocrine IFN-γ, or the secondary cytokines TGF-β, TNF-α, and IL-6. In contrast, both IDO enzymatic activity and IFN-γ-induced AhR expression were required for continued IDO transcription in vitro and in vivo. Addition of the tryptophan catabolite kynurenine to DC cultures in which IDO activity was blocked restored long-term IDO expression in wild-type DC but not in AhR-deficient DC, establishing the central role of the kynurenine-AhR pathway in maintaining IDO expression in tolerogenic DC. These findings shed further light on the cellular and molecular biology of the post-IL-12 regulatory rebound and provide insight into how feedback inhibitory mechanisms dominate in the long-term.

TRUCKs: the fourth generation of CARs

INTRODUCTION

Adoptive cell therapy of malignant diseases takes advantage of the cellular immune system to recognize and destroy cancer cells. This is impressively demonstrated by redirecting T cells with a chimeric antigen receptor (CAR) towards CD19, inducing complete and lasting remission of leukemia in more than two-thirds of patients in early phase trials.

AREAS COVERED

We outline how the CAR strategy is highly specific in redirecting T cells towards pre-defined target cells, however, reaches its limits when targeting solid tumors with a tremendous phenotypic heterogeneity. After initial tumor reduction by CAR T cells, antigen-negative cancer cells not recognized by CAR may give rise to tumor relapse. The situation may be overcome by CAR-mediated activation of T cells in the tumor, releasing inducible IL-12 which augments T-cell activation and attracts and activates innate immune cells to eliminate antigen-negative cancer cells in the targeted lesion.

EXPERT OPINION

CAR T cells with a transgenic 'payload', so-called TRUCK T cells or the 'fourth-generation' CAR T cells, are worthwhile to explore to shape the tumor environment by the inducible release of transgenic immune modifiers. Such TRUCK T cells are moreover envisioned to be applied in fields beyond cancer therapy including the therapy of virus infections, auto-immune diseases or metabolic disorders.

Inducible nitric oxide synthase response and associated cytokine gene expression in the spleen of mice infected with Clonorchis sinensis

Clonorchis sinensis is a food-borne parasite that induces a permanent increase of nitrosation in the body upon infection. The spleen is an important secondary lymphoid organ for the regulation of immune responses locally and in the whole body. However, the functions and mechanisms of the spleen in nitric oxide (NO) responses after C. sinensis infection remain unknown. In this study, BALB/c mice were infected with 20, 40, and 80 C. sinensis metacercariae to simulate mild, moderate, and severe infections, respectively. We examined the expression of inducible nitric oxide synthase (iNOS) in the spleen and the relevant cytokine transcription in splenocytes from the mice infected with different amounts of metacercariae. The iNOS of the mice infected with 80 metacercariae was expressed in the spleen as early as 10 days post-infection (dpi) and gradually increased until 90 dpi. The iNOS expression in the mice infected with 40 metacercariae was detected only at 45 and 90 dpi, but not in the mice infected with 20 metacercariae. The level of interferon (IFN)-γ messenger RNA (mRNA) transcription in splenocytes significantly increased at 10 and 20 dpi (P < 0.05) in response to mild/moderate infection but gradually decreased to normal levels after 45 dpi. The level of IL-12p35 mRNA transcription did not change at 10 and 20 dpi but significantly decreased after 45 dpi under moderate/severe infection (P < 0.05/0.01/0.001). The level of IL-18 mRNA transcription significantly increased at 10 dpi (P < 0.05/0.01) but significantly decreased after 20 dpi (P < 0.05/0.01/0.001). These results suggest that spleen is an important organ for iNOS/NO responses, which correspond to the severity of C. sinensis infection, but cannot be attributed to the expression of the Th1 cytokines.

N-[3-(aminomethyl)benzyl]acetamidine (1400 W) as a potential immunomodulatory agent

This study was designed to investigate the relationship between NO, IL-12, and TNF-α production by J774A.1 macrophages activated with LPS and IFN-γ in the presence of N-[3-(aminomethyl)benzyl]acetamidine (1400 W). 1400 W is a novel, highly selective inhibitor of inducible nitric oxide synthase (iNOS). We compared the obtained data with the effect of N^G-monomethyl-L-arginine (L-NMMA) (a nonselective NOS inhibitor) and L-N^G-(1-iminoethyl)lysine (L-NIL) (a relatively selective inhibitor of iNOS activity) on cells in this model. To investigate the involvement of an exogenous NO on IL-12 and TNF-α production we used NO donor—S-nitrosocaptopril (S-NO-Cap). The most potent inhibitor of NO generation was 1400 W. This compound also markedly increased IL-12 p40 secretion and decreased TNF-α release. L-NIL suppressed both NO and TNF-α production, but it did not change IL-12 p40 synthesis. The effect of L-NMMA on NO generation was weaker than other inhibitors. Moreover, it decreased TNF-α secretion slightly but not significantly. IL-12 p40 production by stimulated cells was inhibited by S-NO-Cap in a dose dependent manner, but no effect on TNF-α release was observed. The potency and selectivity of 1400 W as an inhibitor of iNOS and cytokine release modifier are encouraging for therapeutic use.

CAR T cells transform to trucks: chimeric antigen receptor-redirected T cells engineered to deliver inducible IL-12 modulate the tumour stroma to combat cancer

Adoptive T cell therapy recently achieved impressive efficacy in early-phase clinical trials; this significantly raises the profile of immunotherapy in the fight against cancer. A broad variety of tumour cells can specifically be targeted by patients' T cells, which are redirected in an antibody-defined, major histocompatibility complex-unrestricted fashion by endowing them with a chimeric antigen receptor (CAR). Despite promising results for some haematologic malignancies, the stroma of large, established tumours, the broad plethora of infiltrating repressor cells, and cancer cell variants that had lost the target antigen limit their therapeutic efficacy in the long term. This article reviews a newly described strategy for overcoming some of these shortcomings by engineering CAR T cells with inducible or constitutive release of IL-12. Once redirected, these T cells are activated, and released IL-12 accumulates in the tumour lesion where it promotes tumour destruction by at least two mechanisms: (1) induction of an innate immune cell response towards those cancer cells which are invisible to redirected T cells and (2) triggering programmatic changes in immune-suppressive cells. Given the enormous complexity of both tumour progression and immune attack, the upcoming strategies using CAR-redirected T cells for local delivery of immune-modulating payloads exhibited remarkable efficacy in pre-clinical models, suggesting their evaluation in clinical trials.

Characterization of iNOS(+) Neutrophil-like ring cell in tumor-bearing mice

Background

Myeloid-derived Suppressor Cells (MDSC) have been identified as tumor-induced immature myeloid cells (IMC) with potent immune suppressive activity in cancer. Whereas strict phenotypic classification of MDSC has been challenging due to the highly heterogeneous nature of cell surface marker expression, use of functional markers such as Arginase and inducible nitric oxide synthase (iNOS) may represent a better categorization strategy. In this study we investigated whether iNOS could be utilized as a specific marker for the identification of a more informative homogenous MDSC subset.

Methods

Single-cell suspensions from tumors and other organs were prepared essentially by enzymatic digestion. Flow cytometric analysis was performed on a four-color flow cytometer. Morphology, intracellular structure and localization of iNOS⁺ ring cells in the tumor were determined by cytospin analysis, immunofluorescence microscopy and immunohistochemistry, respectively. For functional analysis, iNOS⁺ ring subset were sorted and tested in vitro cell culture experiments. Pharmacologic inhibition of iNOS was performed both in vivo and in vitro.

Results

The results showed that intracellular iNOS staining distinguished a granular iNOS⁺ SSC^hi CD11b⁺ Gr-1^dim F4/80⁺ subset with ring-shaped nuclei (ring cells) among the CD11b⁺ Gr-1⁺ cell populations found in tumors. The intensity of the ring cell infiltrate correlated with tumor size and these cells constituted the second major tumor-infiltrating leukocyte subset found in established tumors. Although phenotypic analysis demonstrated that ring cells shared characteristics with tumor-associated macrophages (TAM), morphological analysis revealed a neutrophil-like appearance as detected by cytospin and immunofluorescence microscopy analysis. The presence of distinct iNOS filled granule-like structures located next to the cell membrane suggested that iNOS was stored in pre-formed vesicles and available for rapid release upon activation. Tumor biopsies showed large areas with infiltrating ring cells primarily surrounding necrotic areas. Importantly, these cells significantly impaired CD8⁺ T-cell proliferation and induced apoptotic death. The intratumoral accumulation and suppressive activity of ring cells could be blocked through pharmacologic inhibition of iNOS, demonstrating the critical role of this enzyme in mediating both the differentiation and the activity of these cells.

Conclusions

In this study, iNOS expression was linked to a homogeneous subset; ring cells with a particular phenotype and immune suppressive function, in a common and well-established murine tumor model; 4T-1. Since the absence of a Gr-1 homolog in humans has made the identification of MDSC much more challenging, use of iNOS as a functional marker of MDSC may also have clinical importance.

Agaricus subrufescens: A review

Medicinal mushrooms have currently become a hot issue due to their various therapeutic properties. Of these, Agaricus subrufescens, also known as the "almond mushroom", has long been valued by many societies (i.e., Brazil, China, France, and USA). Since its discovery in 1893, this mushroom has been cultivated throughout the world, especially in Brazil where several strains of A. subrufescens have been developed and used as health food and alternative medicine. This article presents up-to-date information on this mushroom including its taxonomy and health promoting benefits. Medicinal properties of A. subrufescens are emphasized in several studies which are reviewed here. In addition, safety issues concerning the use of this fungus will be discussed.

Tumor-associated myeloid cells can be activated in vitro and in vivo to mediate antitumor effects

Tumor growth is often accompanied by the accumulation of myeloid cells in the tumors and lymphoid organs. These cells can suppress T cell immunity, thereby posing an obstacle to T cell-targeted cancer immunotherapy. In this study, we tested the possibility of activating tumor-associated myeloid cells to mediate antitumor effects. Using the peritoneal model of B16 melanoma, we show that peritoneal cells (PEC) in tumor-bearing mice (TBM) had reduced ability to secrete nitric oxide (NO) following in vitro stimulation with interferon gamma and lipopolysaccharide, as compared to PEC from control mice. This reduced function of PEC was accompanied by the influx of CD11b(+) Gr-1(+) myeloid cells to the peritoneal cavity. Nonadherent PEC were responsible for most of the NO production in TBM, whereas in naïve mice NO was mainly secreted by adherent CD11b(+) F4/80(+) macrophages. Sorted CD11b(+) Gr-1(-) monocytic and CD11b(+) Gr-1(+) granulocytic PEC from TBM had a reduced ability to secrete NO following in vitro stimulation (compared to naïve PEC), but effectively suppressed proliferation of tumor cells in vitro. In vivo, treatment of mice bearing established peritoneal B16 tumors with anti-CD40 and CpG resulted in activation of tumor-associated PEC, reduction in local tumor burden and prolongation of mouse survival. Inhibition of NO did not abrogate the antitumor effects of stimulated myeloid cells. Taken together, the results indicate that in tumor-bearing hosts, tumor-associated myeloid cells can be activated to mediate antitumor effects.