Autophagy in Immune Response: Impact on Cancer Immunotherapy

Autophagy in Immune Response: Impact on Cancer Immunotherapy focuses on the status and future directions of autophagy with respect to different aspects of its interaction with the immune system and immunotherapy. The book takes scientific research in autophagy a step further by presenting reputable information on the topic and offering integrated content with advancements in autophagy, from cell biology and biochemical research, to clinical treatments. This book is a valuable source for cancer researchers, oncologists, graduate students and several members of biomedical field who are interested in learning more on the relationship between autophagy and immunotherapies.

• Presents updated knowledge on autophagy at the basic level and its potential use in cancer treatment
• Offers the first book to cover autophagy at the interface of cell biology, immunology and tumor biology
• Provides a wealth of information on the topic in a coherent and comprehensive collection of contributions by world renowned scientists and investigators

• Language: English
• Publisher: Academic Press
• Release date: May 11, 2020
• ISBN: 9780128227572

Book preview

Chapter 1

Dual effect of autophagy in the regulation of cell-mediated cytotoxicity

Salem Chouaiba,b; Jerome Thierya    a Integrative Tumor Immunology and Genetic Oncology, Gustave Roussy, Equipe Labellisée par La Ligue Contre Le Cancer, EPHE, Faculté de Médecine, Université Paris-Sud, Université Paris-Saclay, Villejuif, France

b Thumbay Research Institute for Precision Medicine, Gulf Medical University, Ajman, United Arab Emirates

Abstract

The immune system is a potent defense mechanism regulating tumor development and progression. The ultimate goal of cancer immunotherapy is to eradicate malignant cells through the cytotoxic machinery of immune cells such as cytotoxic T cells (CTLs) and Natural killer (NK) cells. However, the killing potential of these cells is often dampened by the tumor microenvironment (TME) known for its complexity and hostility. Blockers of checkpoint inhibitors have yielded impressive clinical results and have recently been approved for use in a wide variety of cancers. Although the advent of these new immunotherapy approaches has improved the survival of many patients with advanced malignancies, the high prevalence of non-responders, also provides a strong reminder that we possess only a partial understanding of the events underlying the immune resistance of tumors. Several factors within the tumor microenvironment are involved in sculpting, regulating stroma and tumor reactivity through the regulation of tumor resistance, immune suppression and tumor heterogeneity and plasticity.

In this chapter we will discuss how autophagy shapes the quality of adaptive and natural cell cytotoxic response and survival pathways and therefore may impact the clinical benefit of immune cell-based therapies. In addition, this review will critically assess whether autophagy confers cancer cell susceptibility to cell death. Thus, a better understanding for eliciting the dual effect of autophagy is needed to integrate its induction or targeting in the future immunotherapy approaches.

Keywords

Tumor cells; Cytotoxic T cells; Natural killer cells; Tumor microenvironment; Hypoxia; Autophagy; Immunotherapy

Abbreviations

CTL 

cytotoxic T lymphocytes

Cx43 

connexin43

NK 

natural killer

TME 

tumor microenvironment

Conflict of interest

No potential conflicts of interest were disclosed.

Killer cells in the center of anti-tumor immunity

Both adaptative and innate immunity are involved in the regulation of tumor development and progression. Resurrecting the patient's suppressed immune system to launch sustained attacks against tumor cells resulting in the eradication of cancer continues to attract a lot of interest in the field of cancer immunotherapy. It is well established that tumor-specific CD8+ T cells found in human solid tumors are often dysfunctional and that tumor rejection in patients does not always follow successful induction of tumor-specific immune responses [1]. Indeed, several reports have pointed to the existence of a paradoxical coexistence of tumor antigen-specific CD8+ T cells and tumor resistance and progression in patients that arises from multiple negative immunoregulatory pathways impeding T cell-mediated tumor destruction in the TME [2].

The ultimate goal of most reported immunotherapy strategies is to induce a strong cytotoxic T lymphocyte (CTL) response. However, if a strong and sustained cytotoxic response is induced, complex issues such as tumor evasion and selection of immune-resistant tumor cell variants remain [3]. The selection of invasive cancer cells and their ability to evade the host immune system in particular killer cells involving T and NK (Natural killer) cells remain open fundamental questions in tumor immunology. It has become clear that the induction of a good T cell response is not necessarily efficient to control tumor progression and that simply avoiding immune suppression does not necessarily result in the induction of an effective and efficient antitumor immune response. In fact, tumor cells have evolved multiple escape strategies to circumvent the body's immune defenses such as the attack by NK CTLs cells and currently, the mechanisms of innate and adaptive resistance are attracting a lot of interest.

Place the killer cells in the context of tumor microenvironment: The role of hypoxic stress and relationship with autophagy

Cancer cells evolve in the TME, which is now well established as an integral part of the tumor and a determinant player in cancer cell adaptation and resistance to anti-cancer therapies. Despite the remarkable and fairly rapid progress over the past two decades regarding our understanding of the role of the TME in cancer development, its precise contribution to cancer resistance to cell-mediated cytotoxicity is still fragmented. The microenvironment is nevertheless considered a part of the tumor that constantly changes in parallel with cancer progression, as a result of bidirectional interactions between tumor cells and cellular and molecular components of their niche [4, 5]. It is well established that Immunotherapy effectiveness may be dependent on the qualitative and/or quantitative features of the killer cells and the complexity of the genomic aberrations harbored by cancer cells, but is also regulated by the dynamic properties of the tumor microenvironment. TME controls all the steps of the anti-tumor immune cycle from the release of cancer antigens and their presentation and the priming and activation of T cells, to their trafficking infiltration, recognition of tumor cells by the cells and finally their killing. Collectively, the immunosuppressive signals in the TME shape the dysfunctional state of intra-tumoral T cells by influencing the expression of inhibitory receptors, changing metabolic pathways, modifying the epigenetic state, and altering their transcription factor profiles [6].

TME is a complex system playing an important role in tumor development and progression [7] involving not only soluble factors and metabolic changes but also several metabolic changes such as, hypoxia [8]. Emerging data indicate that several factors, such as hypoxic stress, activate a plethora of resistance mechanisms, including autophagy, in tumor cells. Hypoxia-induced autophagy in the tumor microenvironment also activates several tumor escape mechanisms, which effectively counteract anti-tumor immune responses mediated by natural killer and cytotoxic T lymphocytes. We and others provided evidence indicating that hypoxia-induced autophagy is an important regulator of the innate and adaptive tumor immunity mediated by NK cells and CTL, respectively. In fact, in the context of TME, tumors impose several limitations to dampen T cell immunity as T cells, experiencing the metabolic framework of growing tumors, fail to activate distinct pathways to accomplish their functional requirements. In this respect, hypoxic stress is a relevant example demonstrating how the tumor microenvironment can paralyze and neutralize T cell functions. Recently, Verginis et al. have demonstrated that tumor-infiltrating autophagy-deficient monocytic MDSCs displayed impaired suppressive activity in vitro and in vivo, whereas transcriptome analysis revealed substantial differences in genes related to lysosomal function [9].

Since intra-tumoral hypoxia has long been considered as a driving in remodeling the tumor stroma and favoring the emergence of tolerance, immune suppression and tumor resistance and plasticity, efforts to incorporate components of the hypoxic microenvironment are attracting at present a particular attention to guide the successful design of future cancer immunotherapeutic approaches.

Autophagy as a protective mechanism toward adaptative and innate cell-mediated cytotoxicity

Several studies have shown that autophagy constitutes a potential target for cancer therapy and that the induction of autophagy in response to therapeutics can be viewed as having a pro-death or a pro-survival role [10]. The role of autophagy as a cell protective mechanism in response to oxidative stress is well established [11]. In this regard, we showed that hypoxia leads to autophagy induction in tumor cells in response to hypoxic stress and provided evidence indicating that hypoxia-induced autophagy impairs CTL-mediated tumor cell lysis by regulating phospho-STAT3 in target cell [12]. Additionally, boosting the CTL response, using a TRP-2-peptide vaccination strategy, and targeting autophagy in hypoxic tumors, improves the efficacy of this cancer vaccine and promotes in vivo tumor regression [13]. While the molecular mechanisms by which autophagy impairs tumor susceptibility to NK and CTL are different, experimental evidence demonstrated that blocking autophagy may improve tumor immunity [14].

Finally, we provided evidence for the existence of a link between hypoxia, autophagy, glucose metabolism and clinical outcome. Our studies pointed to a role of elevated glycogenic flux that correlates with a poor clinical response in melanoma treated with checkpoint inhibitor anti-PD1 [15]. These studies further suggest that channeling of glucose through glycogen may promote the survival of melanoma cells under hypoxia. Through elevated glycogenic flux and induction of autophagy, hypoxia appears to be a potential critical molecular program that could be considered as a prognostic factor for melanoma. We have also obtained data indicating that NANOG is a driver of autophagy through the induction of BNIP3L [16], Nanog in linking two resistant mechanisms stemness and autophagy.

With respect to the influence of autophagy on the regulation of NK-mediated cell lysis, several studies pointed on its role involving several different mechanisms. Baginska et al. have first reported that under hypoxic conditions, the granzyme B (GzmB)-containing endosomes (called gigantosomes) [17] fuse with autophagosomes to form an amphisome and to facilitate GzmB degradation by the lysosome [18]. This team also showed that targeting Beclin1 was associated with a significant decrease in tumor growth as a consequence of potentiation of tumor cell killing by NK cells. They have elegantly shown a massive infiltration of NK cells into Beclin1-defective compared with control B16-F10 tumors. The infiltration of NK cells was related to the ability of Beclin1-defective tumor cells to overexpress CCL5 chemokine responsible for the trafficking of NK cells to the tumor [14].

In cancer biology, autophagy appears to play dual roles in tumor promotion and suppression and contributes to cancer-cell development and proliferation. Whether autophagy is a promising potential therapeutic target in cancer treatment remains to be fully understood and remains the subject of a big debate. More importantly, Tittarelli et al. demonstrated that Cx43 degradation is caused by autophagy during hypoxia. In fact, autophagy may interfere with cell-to-cell communication and interaction as activation of autophagy in hypoxic melanoma cells selectively degrades gap-junctional Cx43, leading to the destabilization of the immune synapse and the impairment of NK cell-mediated killing [19]. The authors demonstrated that inhibition of autophagy by genetic or pharmacological approaches as well as expression of the non-degradable form of Cx43 significantly restore its accumulation at the immune synapse and improves NK cell-mediated lysis of hypoxic melanoma cells. This strongly suggests that the hypoxic microenvironment negatively affects the immune surveillance of tumors by NK cells through the modulation of Cx43-mediated intercellular communications.

Positive regulation of the cytotoxic antitumor immune response by autophagy

Even if numerous reports have implicated autophagy as a protective mechanism during cellular stress, autophagy can also participate to cell death induction or regulation [20]. In other words, in certain circumstances, autophagy can help to induce apoptosis and both processes can cross-talk through interconnecting signaling pathways [21, 22]. For example, mammalian Beclin-1, an activator of cellular autophagy, cross-regulates autophagy and apoptosis through direct interaction with anti-apoptosis family members, including Bcl-2 and Bcl-XL[23]. Another example is the tumor suppressor p53, which promotes apoptosis thought the regulation of mitochondrial outer membrane permeabilization (MOMP) in response to different cell death inducers but can also positively and negatively regulates autophagy [24]. Indeed, several p53-dependent mechanisms involved in autophagy induction have been described [25] especially sestrin-1 and -2 [26, 27] or unc-51-like kinase 1 (ULK1) [28] transactivation. Sestrin-1 and -2 facilitate the AMP-activated protein kinase (AMPK) phosphorylation, which in turn phosphorylates and activates the TSC1-TSC2 complex, thereby inhibiting the signaling of mammalian target of rapamycin (mTOR), a major autophagy inhibitor [26]. The serine/threonine protein kinase ULK-1, together with ULK-2, autophagy-related gene (ATG)-101, ATG13 and focal adhesion kinase family interacting protein of 200 kDa (FIP200) form the ULK complex which drives the phagophore formation, the initial autophagosomal precursor membrane structure [29]. On the opposite, several studies also demonstrated that p53 can stimulate anti-autophagic responses. For example, wild type (wt) p53 proteins localized in the cytosol have an inhibitory effect on autophagy [30, 31], as gain-of-function mutant p53 proteins [32,