Roles Of Tumor Recruited Myeloid Cells In Immune Evasion In Cancer

Tumor-associated immune cells, in particular myeloid cells, have opposing roles during cancer development by facilitating antitumor immune responses and driving cancer-promoting inflammation. Defective antitumor immunity is prevalent in cancers, and it is now clear that overcoming the myeloid cell-mediated immunosuppressive microenvironment poses tremendous interest for future cancer therapies. JAK/STAT signaling has come to the forefront as a crucial pathway to induce immunosuppression and procancer inflammation. Specifically, STAT3 activation is critical for the phenotype of myeloid cells by regulating immunosuppressive and prometastatic factors, thereby providing myeloid cells with a multitude of tumor-promoting functions. Genetic ablation of STAT3 in the myeloid compartment induces potent innate and adaptive antitumor immunity along with an inhibition of tumor growth and metastasis. Recently, therapeutic targeting of JAK/STAT3 has shown great promise in blocking immunosuppression in preclinical models. One such example is the use of novel siRNA to selectively target STAT3 in myeloid cells, through conjugation to CpG oligonucleotides that agonize Toll receptor TLR9 on myeloid cells. Along with other novel therapeutic strategies to inhibit JAK/STAT signaling, it seems likely that future efforts to target this pathway will be made in single and combination approaches for effective anticancer immunotherapy.

Tumor-Induced Immune Suppression - Prospects and Progress in Mechanisms and Therapeutic Reversal presents a comprehensive overview of large number of different mechanisms of immune dysfunction in cancer and therapeutic approaches to their correction. This includes the number of novel mechanisms that has never before been discussed in previous monographs. The last decades were characterized by substantial progress in the understanding of the role of the immune system in tumor progression. Researchers have learned how to manipulate the immune system to generate tumor specific immune response, which raises high expectations for immunotherapy to provide breakthroughs in cancer treatment. It is increasingly clear that tumor-induced abnormalities in the immune system not only hampers natural tumor immune surveillance, but also limits the effect of cancer immunotherapy. Therefore, it is critically important to understand the mechanisms of tumor-induced immune suppression to make any progress in the field and this monograph provides these important insights.

The book starts with an introduction to and history of myeloid-derived suppressor cells (MDSCs), followed by a description of their differentiation, their role in the tumour microenvironment and their therapeutic targeting. It closes with an outlook on future developments. In cancer patients, myelopoiesis is perturbed and instead of generating immunogenic myeloid cells (such as dendritic cells, inflammatory macrophages and granulocytes), there is an increase in highly immature MDSCs. These cells are distributed systemically, resulting in general immunosuppression. They also infiltrate tumours, promoting their progression and metastasis by inhibiting the natural anti-tumour immune response. As these cells also interact with classical anti-neoplastic treatments, they have become major therapeutic targets in the pharmaceutical industry and in oncology research.

This monograph, for the first time, presents a comprehensive overview of different mechanisms of immune dysfunction in cancer as well as therapeutic approaches to their correction. It discusses a number of new mechanisms that have never been discussed in a monograph before: T-cell inhibitory molecules, regulatory tolerogenic DCs, and signaling pathways in antigen-presenting cells involved in T-cell tolerance. There is now a pressing need to discuss the already described and newly emerging mechanisms to see how they can be put together in a more or less cohesive structure and how they can help to improve immune response to tumors.

Now, it its second edition, this book summarizes the role of immune cells in tumor suppression and progression. It describes in detail why tumor cells can survive and spread in spite of the antitumor response of immune cells. Since immunotherapy is an attractive approach to cancer therapy, this book also provides information on the two main strategies: monoclonal antibodies and adaptive T cell immunotherapy, with a focus on recent human clinical trials. A newly added chapter also focuses on the role of Natural Killer cells in tumor progression. The book provides a state-of-the-art, comprehensive overview of immune cells in cancer and is an indispensable resource for researchers and practitioners working or lecturing in the field of cancer research and immunology.

Myeloid Derived Suppressor Cells (MDSCs) are a heterogeneous population of immature myeloid cells that can suppress the function of multiple immune cells and in particular, T cells, through various mechanisms. MDSCs can be divided into two major subtypes based on their cell surface phenotype and morphology: polymorphonuclear MDSC (PMN-MDSC or G-MDSC) and monocytic MDSC (M-MDSC). Additional subtypes have been proposed, such as the early MDSC (e-MDSC) that lack both macrophage and granulocyte markers. There is still considerable ambiguity about the phenotype of these cells that corresponds to their immunosuppressive function and there are on-going challenges on how to identify, purify and/or potentially generate and expand these cells in vitro. MDSCs were first discovered in cancer patients where they have been most extensively studied as components of the immunosuppressive tumor microenvironment. In the last several years, however, the importance of their immunomodulatory role in many other disease and clinical settings has emerged. Acknowledgments We acknowledge the initiation and support of this Research Topic by the International Union of Immunological Societies (IUIS). We hereby state publicly that the IUIS has had no editorial input in articles included in this Research Topic, thus ensuring that all aspects of this Research Topic are evaluated objectively, unbiased by any specific policy or opinion of the IUIS.