Shin Foong Ngiow

Classifying Cancers Based on T-cell Infiltration and PD-L1

Cancer immunotherapy may become a major treatment backbone in many cancers over the next decade. There are numerous immune cell types found in cancers and many components of an immune reaction to cancer. Thus, the tumor has many strategies to evade an immune response. It has been proposed that four different types of tumor microenvironment exist based on the presence or absence of tumor-infiltrating lymphocytes and programmed death-ligand 1 (PD-L1) expression. We review this stratification and the latest in a series of results that shed light on new approaches for rationally designing ideal combination cancer therapies based on tumor immunology.

Anti–ErbB-2 mAb therapy requires type I and II interferons and synergizes with anti–PD-1 or anti-CD137 mAb therapy

Trastuzumab, a monoclonal antibody targeting human epidermal growth factor receptor-2 (HER2/ErbB-2), has become the mainstay of treatment for HER2-positive breast cancer. Nevertheless, its exact mechanism of action has not been fully elucidated. Although several studies suggest that Fc receptor-expressing immune cells are involved in trastuzumab therapy, the relative contribution of lymphocyte-mediated cellular cytotoxicity and antitumor cytokines remains unknown. We report here that anti–ErbB-2 mAb therapy is dependent on the release of type I and type II IFNs but is independent of perforin or FasL. Our study thus challenges the notion that classical antibody-dependent, lymphocyte-mediated cellular cytotoxicity is important for trastuzumab. We demonstrate that anti–ErbB-2 mAb therapy of experimental tumors derived from MMTV-ErbB-2 transgenic mice triggers MyD88-dependent signaling and primes IFN-γ–producing CD8+ T cells. Adoptive cell transfer of purified T cell subsets confirmed the essential role of IFN-γ–producing CD8+ T cells. Notably, anti–ErbB-2 mAb therapy was independent of IL-1R or IL-17Ra signaling. Finally, we investigated whether immunostimulatory approaches with antibodies against programmed death-1 (PD-1) or 41BB (CD137) could be used to capitalize on the immune-mediated effects of trastuzumab. We demonstrate that anti–PD-1 or anti-CD137 mAb can significantly improve the therapeutic activity of anti–ErbB-2 mAb in immunocompetent mice.

Anti-TIM3 Antibody Promotes T Cell IFN-γ–Mediated Antitumor Immunity and Suppresses Established Tumors

Strategies to activate and rescue exhausted tumor-specific T cells, including the use of monoclonal antibodies (mAb) that block the negative costimulatory receptors CTLA-4 and PD-1 are proving very effective, but TIM3 has been relatively neglected as a target. Here we report an extensive characterization of the therapeutic activity and mechanism of action of an anti-mouse TIM3 mAb against experimental and carcinogen-induced tumors. For the first time we specifically define the mechanism of antitumor action of anti-TIM3 requiring IFN-γ producing CD8(+) T cells and CD4(+) T cells, and a higher ratio of tumor infiltrating CD8(+):CD4(+) T cells correlating with therapeutic success. Interestingly, in some models, anti-TIM3 appeared to be effective sometime before the appearance and accumulation of significant TIM3(+)PD-1(+) T cell populations in tumor bearing mice. Anti-TIM3 displayed modest prophylactic and therapeutic activity against a small fraction of carcinogen-induced sarcomas, but comparative and combination studies of anti-TIM3 with anti-CTLA-4 and anti-PD-1 against experimental and carcinogen-induced tumors suggested that these agents might be well-tolerated and very effective in combination.

Combination cancer immunotherapies tailored to the tumour microenvironment

Evidence suggests that cancer immunotherapy will be a major part of the combination treatment plan for many patients with many cancer types in the near future. There are many types of immune processes involving different antitumour and tumour-promoting leucocytes, and tumour cells use many strategies to evade the immune response. The tumour microenvironment can help determine which immune suppressive pathways become activated to restrain antitumour immunity. This includes immune checkpoint receptors on effector T-cells and myeloid cells, and release of inhibitory cytokines and metabolites. Therapeutic approaches that target these pathways, particularly immune-checkpoint receptors, can induce durable antitumour responses in patients with advanced-stage cancers, including melanoma. Nevertheless, many patients do not have a good response to monotherapy approaches and alternative strategies are required to achieve optimal therapeutic benefit. These strategies include eliminating the bulk of tumour cells to provoke tumour-antigen release and antigen-presenting cell (APC) function, using adjuvants to enhance APC function, and using agents that enhance effector-cell activity. In this Review, we discuss the stratification of the tumour microenvironment according to tumour-infiltrating lymphocytes and PD-L1 expression in the tumour, and how this stratification enables the design of optimal combination cancer therapies tailored to target different tumour microenvironments.

Selective depletion of Foxp3+ regulatory T cells improves effective therapeutic vaccination against established melanoma.

Tumor-bearing individuals have been reported to harbor increased numbers of Foxp3(+) regulatory T cells (Treg), which prevent the development of efficient antitumor immune responses. Thus, Treg depletion has already been tested as a promising therapeutic approach in various animal models and entered clinical trials. However, the use of nonspecific Treg targeting agents such as CD25 depleting antibodies, which in addition to CD25(+) Tregs also deplete recently activated CD25(+) effector T cells, potentially masked the tremendous potential of this therapeutic strategy. To avoid such nonspecific effects, we used transgenic DEREG (depletion of regulatory T cells) mice, which express a diphtheria toxin receptor under control of the Foxp3 locus, allowing selective depletion of Foxp3(+) Tregs even during ongoing immune responses. We showed that Foxp3(+) Treg depletion induced partial regression of established ovalbumin (OVA)-expressing B16 melanoma, which was associated with an increased intratumoral accumulation of activated CD8(+) cytotoxic T cells. The antitumor effect could be significantly enhanced when Treg depletion was combined with vaccination against OVA. To further assess whether this therapeutic approach would break self-tolerance, we crossed DEREG mice with RipOVA(low) mice, expressing OVA as neo-self-antigen under control of the rat insulin promoter. In these mice, combined Treg depletion and vaccination also induced tumor regression without the onset of diabetes. Together, our data suggest that selective Treg targeting strategies combined with vaccinations against tumor-associated (self) antigens have the potential to evoke efficient antitumor responses without inducing overt autoimmunity. These findings might have implications for future therapeutic interventions in cancer patients.

Conditional regulatory T-cell depletion releases adaptive immunity preventing carcinogenesis and suppressing established tumor growth.

Foxp3 is a central control element in the development and function of regulatory T cells (Treg), and mice expressing a diphtheria toxin (DT) receptor-enhanced green fluorescent protein fusion protein under the control of the foxp3 gene locus (DEREG mice) allow conditional and efficient depletion of Foxp3(+) Treg by DT injection. Herein, we use DEREG mice and a mouse model of carcinogenesis to show that conditional and effective Treg depletion can both protect mice from carcinogenesis by innate control, yet permanently eradicate a proportion of de novo-established tumors in mice in a largely CD8(+) T-cell- and IFN-γ-dependent manner. Tumors displayed a heterogeneous response to Treg depletion, and suppression of established tumors was accompanied by an increase in the tumor-infiltrating CD8(+) T-cell/B-cell ratio. Tumor rejection occurred in the absence of overt autoimmunity, suggesting that effective transient Treg depletion strategies may be therapeutic in at least a proportion of spontaneous tumors developing in the host.

TIGIT predominantly regulates the immune response via regulatory T cells.

Coinhibitory receptors are critical for the maintenance of immune homeostasis. Upregulation of these receptors on effector T cells terminates T cell responses, while their expression on Tregs promotes their suppressor function. Understanding the function of coinhibitory receptors in effector T cells and Tregs is crucial, as therapies that target coinhibitory receptors are currently at the forefront of treatment strategies for cancer and other chronic diseases. T cell Ig and ITIM domain (TIGIT) is a recently identified coinhibitory receptor that is found on the surface of a variety of lymphoid cells, and its role in immune regulation is just beginning to be elucidated. We examined TIGIT-mediated immune regulation in different murine cancer models and determined that TIGIT marks the most dysfunctional subset of CD8+ T cells in tumor tissue as well as tumor-tissue Tregs with a highly active and suppressive phenotype. We demonstrated that TIGIT signaling in Tregs directs their phenotype and that TIGIT primarily suppresses antitumor immunity via Tregs and not CD8+ T cells. Moreover, TIGIT+ Tregs upregulated expression of the coinhibitory receptor TIM-3 in tumor tissue, and TIM-3 and TIGIT synergized to suppress antitumor immune responses. Our findings provide mechanistic insight into how TIGIT regulates immune responses in chronic disease settings.

Prospects for TIM3-Targeted Antitumor Immunotherapy

New insights into the control of T-cell activation and proliferation have led to the identification of checkpoint proteins that either up- or downmodulate T-cell reactivity. Monoclonal antibody immunotherapies that are reactive with cytotoxic T lymphocyte antigen 4 or programmed death receptor 1 have shown promising therapeutic outcomes in mice and humans with established cancer, highlighting the fact that cancer immunotherapy using T-cell checkpoint inhibitors is one of the most promising new therapeutic approaches. T-cell immunoglobulin and mucin domain 3 (TIM3) is one of many similar inhibitory molecules that are gaining attention as targets, but it remains relatively poorly studied in oncology. This review discusses our recent probing of the mechanism of action of anti-TIM3 antibody against established spontaneous and experimental tumors in mice, in the context of the exciting possibility of rationally combining agents that promote tumor-specific T-cell activation, proliferation, effector function, and survival.

IL-23 suppresses innate immune response independently of IL-17A during carcinogenesis and metastasis

IL-23 is an important molecular driver of Th17 cells and has strong tumor-promoting proinflammatory activity postulated to occur via adaptive immunity. Conversely, more recently it has been reported that IL-17A elicits a protective inflammation that promotes the activation of tumor-specific CD8+ T cells. Here we show the much broader impact of IL-23 in antagonizing antitumor immune responses primarily mediated by innate immunity. Furthermore, the majority of this impact was independent of IL-17A, which did not appear critical for many host responses to tumor initiation or metastases. IL-23–deficient mice were resistant to experimental tumor metastases in three models where host NK cells controlled disease. Immunotherapy with IL-2 was more effective in mice lacking IL-23, and again the protection afforded was NK cell mediated and independent of IL-17A. Further investigation revealed that loss of IL-23 promoted perforin and IFN-γ antitumor effector function in both metastasis models examined. IL-23-deficiency also strikingly protected mice from tumor formation in two distinct mouse models of carcinogenesis where the dependence on host IL-12p40 and IL-17A was quite different. Notably, in the 3′-methylcholanthrene (MCA) induction of fibrosarcoma model, this protection was completely lost in the absence of NK cells. Overall, these data indicate the general role that IL-23 plays in suppressing natural or cytokine-induced innate immunity, promoting tumor development and metastases independently of IL-17A.

A balance of interleukin-12 and -23 in cancer

Interleukin (IL)-12 and IL-23 share the IL-12p40 molecule. IL-12 promotes T helper (Th)1 immunity and IL-23 promotes Th17 immunity, and it has recently become apparent that the balance between IL-12 and IL-23 is important in carcinogenesis. A series of studies demonstrated that, where tumor initiation, growth, and metastasis are concerned, IL-12 may act independently of interferon (IFN)-γ, and IL-23 independently of IL-17A. This review explores the activity of IL-23 in carcinogenesis. In the context of the tumor-inhibitory effects of IL-12, and tumor-promoting effects of IL-23, we discuss the use of anti-IL-12p/23 monoclonal antibodies (mAbs) in autoimmune inflammatory disorders and the alternative specific neutralization of IL-23.