Exhausted T cells hijacking the cancer-immunity cycle: Assets and liabilities.

T cell exhaustion is an alternative differentiation path of T cells, sometimes described as a dysfunction. During the last decade, insights of T cell exhaustion acting as a bottle neck in the field of cancer immunotherapy have undoubtedly provoked attention. One of the main drivers of T cell exhaustion is prolonged antigen presentation, a prerequisite in the cancer-immunity cycle. The umbrella term "T cell exhaustion" comprises various stages of T cell functionalities, describing the dynamic, one-way exhaustion process. Together these qualities of T cells at the exhaustion continuum can enable tumor clearance, but if the exhaustion acquired timeframe is exceeded, tumor cells have increased possibilities of escaping immune system surveillance. This could be considered a tipping point where exhausted T cells switch from an asset to a liability. In this review, the contrary role of exhausted T cells is discussed.

An Antibody Targeting ICOS Increases Intratumoral Cytotoxic to Regulatory T-cell Ratio and Induces Tumor Regression.

The immunosuppressive tumor microenvironment constitutes a significant hurdle to immune checkpoint inhibitor responses. Both soluble factors and specialized immune cells, such as regulatory T cells (Treg), are key components of active intratumoral immunosuppression. Inducible costimulatory receptor (ICOS) can be highly expressed in the tumor microenvironment, especially on immunosuppressive Treg, suggesting that it represents a relevant target for preferential depletion of these cells. Here, we performed immune profiling of samples from tumor-bearing mice and patients with cancer to demonstrate differential expression of ICOS in immune T-cell subsets in different tissues. ICOS expression was higher on intratumoral Treg than on effector CD8 T cells. In addition, by immunizing an Icos knockout transgenic mouse line expressing antibodies with human variable domains, we selected a fully human IgG1 antibody called KY1044 that bound ICOS from different species. We showed that KY1044 induced sustained depletion of ICOShigh T cells but was also associated with increased secretion of proinflammatory cytokines from ICOSlow effector T cells (Teff). In syngeneic mouse tumor models, KY1044 depleted ICOShigh Treg and increased the intratumoral TEff:Treg ratio, resulting in increased secretion of IFNγ and TNFα by TEff cells. KY1044 demonstrated monotherapy antitumor efficacy and improved anti-PD-L1 efficacy. In summary, we demonstrated that using KY1044, one can exploit the differential expression of ICOS on T-cell subtypes to improve the intratumoral immune contexture and restore an antitumor immune response.

GADD45ß Loss Ablates Innate Immunosuppression in Cancer.

T-cell exclusion from the tumor microenvironment (TME) is a major barrier to overcoming immune escape. Here, we identify a myeloid-intrinsic mechanism governed by the NF-κB effector molecule GADD45ß that restricts tumor-associated inflammation and T-cell trafficking into tumors. In various models of solid cancers refractory to immunotherapies, including hepatocellular carcinoma and ovarian adenocarcinoma, Gadd45b inhibition in myeloid cells restored activation of proinflammatory tumor-associated macrophages (TAM) and intratumoral immune infiltration, thereby diminishing oncogenesis. Our results provide a basis to interpret clinical evidence that elevated expression of GADD45B confers poor clinical outcomes in most human cancers. Furthermore, they suggest a therapeutic target in GADD45ß for reprogramming TAM to overcome immunosuppression and T-cell exclusion from the TME.Significance: These findings define a myeloid-based immune checkpoint that restricts T-cell trafficking into tumors, with potentially important therapeutic implications to generally improve the efficacy of cancer immunotherapy. Cancer Res; 78(5); 1275-92. ©2017 AACR.

Cancer-selective targeting of the NF-κB survival pathway with GADD45ß/MKK7 inhibitors.

Constitutive NF-κB signaling promotes survival in multiple myeloma (MM) and other cancers; however, current NF-κB-targeting strategies lack cancer cell specificity. Here, we identify the interaction between the NF-κB-regulated antiapoptotic factor GADD45ß and the JNK kinase MKK7 as a therapeutic target in MM. Using a drug-discovery strategy, we developed DTP3, a D-tripeptide, which disrupts the GADD45ß/MKK7 complex, kills MM cells effectively, and, importantly, lacks toxicity to normal cells. DTP3 has similar anticancer potency to the clinical standard, bortezomib, but more than 100-fold higher cancer cell specificity in vitro. Notably, DTP3 ablates myeloma xenografts in mice with no apparent side effects at the effective doses. Hence, cancer-selective targeting of the NF-κB pathway is possible and, at least for myeloma patients, promises a profound benefit.

The nuclear factor kappa B signaling pathway: integrating metabolism with inflammation.

Nuclear factor kappa B (NF-κB) transcription factors are evolutionarily conserved, coordinating regulators of immune and inflammatory responses. They also play a pivotal role in oncogenesis and metabolic disorders. Several studies during the past two decades have highlighted the key role of the IKK/NF-κB pathway in the induction and maintenance of the state of inflammation that underlies metabolic diseases such as obesity and type 2 diabetes. Recent reports, however, reveal an even more intimate connection between NF-κB and metabolism. These studies demonstrate that NF-κB regulates energy homeostasis via direct engagement of the cellular networks governing glycolysis and respiration, with profound implications beyond metabolic diseases, including cancer, ageing and anticancer therapy. In this review, we discuss these emerging bioenergetic functions of NF-κB and their significance to oncogenesis.

Cancer: NF-κB regulates energy metabolism.

NF-κB transcription factors are evolutionarily conserved, central coordinators of immune and inflammatory responses. They also play a pivotal role in oncogenesis. NF-κB exerts these functions by regulating the transcription of genes encoding many immunoregulators, inflammatory mediators and inhibitors of apoptosis. Several studies during the past few years have also underscored the key role of the IKK/NF-κB pathway in the induction and maintenance of the state of inflammation that underlies metabolic pathologies such as obesity, insulin resistance and type-2 diabetes, reflecting the co-evolution and integration of nutrient- and pathogen-sensing systems. Recent reports, however, are revealing an even more intimate, direct connection between NF-κB and metabolism. These studies demonstrate that NF-κB regulates energy homeostasis via direct engagement of the cellular networks governing glycolysis and respiration, with profound implications that extend beyond metabolic pathologies, to cellular physiology, cancer, and anti-cancer therapy. In this review article, we discuss these emerging metabolic functions of NF-κB and their significance to oncogenesis and cancer treatment.

NF-κB controls energy homeostasis and metabolic adaptation by upregulating mitochondrial respiration.

Cell proliferation is a metabolically demanding process. It requires active reprogramming of cellular bioenergetic pathways towards glucose metabolism to support anabolic growth. NF-κB/Rel transcription factors coordinate many of the signals that drive proliferation during immunity, inflammation and oncogenesis, but whether NF-κB regulates the metabolic reprogramming required for cell division during these processes is unknown. Here, we report that NF-κB organizes energy metabolism networks by controlling the balance between the utilization of glycolysis and mitochondrial respiration. NF-κB inhibition causes cellular reprogramming to aerobic glycolysis under basal conditions and induces necrosis on glucose starvation. The metabolic reorganization that results from NF-κB inhibition overcomes the requirement for tumour suppressor mutation in oncogenic transformation and impairs metabolic adaptation in cancer in vivo. This NF-κB-dependent metabolic pathway involves stimulation of oxidative phosphorylation through upregulation of mitochondrial synthesis of cytochrome c oxidase 2 (SCO2; ref. ). Our findings identify NF-κB as a physiological regulator of mitochondrial respiration and establish a role for NF-κB in metabolic adaptation in normal cells and cancer.