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This eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contact

Immune checkpoint --- Lymphoma --- PD-1 --- target therapy --- microenvironment

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This eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contact

lymphocyte --- inhibitory receptor --- inhibitory signaling --- checkpoint blockade --- immunotherapy --- autoimmunity --- cancer

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For the faultless function of the immune system, tight regulation of immune cell activation, immuno-suppression and the strength and efficiency of the immune response is essential. Immune checkpoint (ICP) molecules can amplify or dampen signals that lead to the modulation of specific immune activities. Under physiological conditions, immune checkpoints are essential to prevent autoimmune manifestations and to preserve self-tolerance. They help modulate immune responses by either promoting or inhibiting T-cell activation. However, in the context of cancer, malignant cells can dysregulate the expression of immune checkpoint proteins on immune cells in order to suppress anti-tumor immune responses and to gain immune resistance. Moreover, tumor cells themselves can also express some checkpoints proteins, thereby enabling these cells to externally orchestrate immune regulatory mechanisms. Several recent studies have confirmed that the expression of immune checkpoints could be an important prognostic parameter for cancer development and for patient outcome. Therefore, cancer immunotherapy based on the modulation of immune checkpoint molecules alone, or in combination with conventional tumor therapy (chemo- or/and radiotherapy), is now in focus as a means of developing new therapeutic strategies for different types of cancer. The two well-known molecules – CTLA4 and PD-1 - serve as important examples of such checkpoint proteins of important therapeutic potential. Thus far, inhibitors of CTLA4 and PD-1 have been approved to treat only a limited number of malignancies (e.g. malignant Melanoma, Non-Small Cell Lung Cancer). Many others are currently under investigation and the list of immune checkpoint molecules for potential therapeutic targeting is still growing. However, the clinical response to inhibitors of checkpoint molecules is not sufficient in all cases. Therefore, further studies are needed to improve our knowledge of such immunomodulatory proteins and their associated signaling pathways. Several key signaling pathways which are involved in the regulation of expression of checkpoint molecules in immune cells and in cancer cells have already been identified including MAPK, PI3K, NF-kB, JAKs and STATs. These (and future discovered) signaling pathways could give rise to the development of new strategies for modulating the expression of ICPs and thereby, improving anti-cancer immune responses. The main aim of the Research Topic is to collect novel findings from scientists involved in basic research on immune checkpoints as well as in translational studies investigating the use of checkpoint inhibtors in immunotherapy in experimental settings. We welcome the submission of Review, Mini-Review and Original Research articles that cover the following topics: 1. Molecular mechanisms underlying regulation of ICP expression in immune and/or cancer cells. 2. Characterization of signaling pathways downstream ICP molecules. 3. Cellular responses to ICP blockade. 4. Identification of new compounds interfering with ICP expression and/or signaling. 5. ICP-mediated interactions between cancer cells and immune cells. 6. Functional links between ICP and cytokines/chemokines. 7. Molecular mechanisms of ICP inhibition in the context of experimental cancer immunotherapy.

CTLA-4 (CD152) --- checkpoint blockade --- Immunosuppression --- cancer immunotherapy --- PD-1 (CD279) --- Tumor Microenvironment --- Metabolic checkpoints --- immune checkpoint molecules --- cytotoxic T lymphocytes --- PDL1

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For this eBook, and the associated Research Topic in Frontiers in Genetics, entitled: ‘Cancer-associated defects in the DNA damage response: drivers for malignant transformation and potential therapeutic targets’ we have selected 10 papers that each discusses important, yet distinct aspects of the response to DNA damage in normal cells and cancer cells. Using an evolutionary conserved signaling network called the ‘DNA damage response (DDR)’ cells maintain the integrity of their genome, and thus safeguard cellular functioning and the ability to create viably progeny. Initially, the DDR appeared to consist of few linear kinase-driven pathways. However, research over the past decades in model organisms, as well as in the human system has revealed that the DDR is a complex signaling network, wired by multiple parallel pathways and displaying extensive crosstalk. Besides phosphorylation, multiple other post-translational modifications, including ubiquitination and sumoylation, are involved to achieve chromatin remodeling and initiation of DNA repair. Also, rather than being a cell-intrinsic phenomenon, we increasingly appreciate that cell-cell communication is involved. The recognition and repair of DNA damage is essential to maintain normal physiology. Multiple pathological conditions have been attributed to defective DNA repair, most notably accelerated aging, neurodegeneration and cancer. In the context of cancer, through repair of DNA damage or elimination of irreparably damaged cells, the DDR clearly has a tumor-suppressive role. Indeed, many tumor cells show partially inactivated DDR signaling, which allows proliferation in the context of DNA damage-inducing oncogenes. Simultaneously, loss of specific DDR signaling nodes creates a specific dependence of tumor cells on their remaining DDR components, and thus creates therapeutic opportunities. Especially in the context of cancer treatment, numerous targeted agents are under investigation, either to potentiate the cytotoxic effects of chemo-radiotherapy, or to induce synthetic lethality with cancer-specific alterations, with the treatment of BRCA1/2 mutant cancers with PARP1 inhibitors as a prototype example. We have selected four review articles that provide insight into the key components and the wiring of the DDR and DNA repair. Torgovnick and Schumacher review the involvement of DNA repair in the initiation and treatment of cancer, Brinkmann et al., describe the involvement of ubiquitination in DNA damage signaling and Jaiswal and Lindqvist discuss how cell-extrinsic signaling participates in communication of DNA damage to neighboring cells. In addition, Shatneyeva and colleagues review the connection between the cellular response to DNA damage and escape from immune surveillance. Concerning the therapeutic application of targeting the DDR and DNA repair, three articles were included. Krajewska and van Vugt review the wiring of homologous recombination and how this offers therapeutic opportunities. Additionally, Knittel and colleagues describe how genetic loss of the central DDR component ATM in chronic lymphocytic leukemia can be exploited therapeutically by targeting certain parallel DNA repair pathways. Syljuasen and colleagues report on how targeting of the DDR can be used as a therapeutic strategy in lung cancer. Finally, three chapters describe newly identified regulators of the cellular response to DNA damage. Von Morgen et al. describe the R2TP complex, Lezzi and Fanciluuli review the involvement of Che-1/AATF in the DDR, and Ohms and co-authors describe how retrotransposons are at the basis of increased genomic instability. Altogether, these articles describe how defective responses to DNA damage underlie disease - and especially in the context of cancer -can be exploited to better treat disease.

checkpoint --- Ubiquitin --- cancer therapy --- Cell Cycle --- DNA Repair --- DNA Damage --- Cancer

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This eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contact

dendritic cell vaccination --- dendritic cell tolerization --- anticancer immunotherapeutic combination --- immune checkpoint inhibitor --- immunogenic cell death