Frontiers in Cancer Immunology

Cancer is not one simple disease but a group of heterogeneous diseases sharing a common feature of uncontrolled cell growth. Cancer is a leading health issue in modern society and patients succumb to the disease every day. Among many different treatment approaches, harnessing the immune system to treat cancer has gained prominence in recent years. While some of the cancer cells can evade the host immune surveillance as well as spread distally, the majority of cancer cells are removed from the host immune system in premalignant stages of the disease. Accumulating evidence indicates that the host immune system is highly involved in the elimination of cancer cells, but ultimately, cancer cells have developed their own mechanisms to subvert the immune system. A comprehensive understanding of the immune system and its interaction with cancer is crucial to develop immune-based treatments. The currently available cancer immunotherapies are developed from a systemic understanding of the human immune system. This opening chapter will serve as an introductory remark to briefly summarize the human immune system, cancer and both positive and negative interactions between the immune system and cancer.

From its humble beginning in the 19th century, immunotherapy for cancer has emerged as a prospective curative approach in the last decade. Currently, different immunotherapies are being used in the clinic including monoclonal antibodies (MAbs), adoptively transferred T cells and cancer vaccines. Of these immunotherapies, MAbs are the most widely used, however their efficacy is restricted by their limited biodistribution, and reliance on antibody-dependent cell cytotoxicity and/or complement-mediated cell death, which can be impaired in cancer patients. In contrast, adoptively transferred T cells have the capacity to effectively traffic to tumor sites, recruit multiple cellular and humoral effector mechanisms, and persist for many years. In this chapter, we review T cell based immunotherapy for cancer, describe its current clinical impact, and discuss approaches that aim to combine T cells with other cancertargeted therapies.

The debate has been raging for many years about the immune system’s ability to identify and destroy emerging tumor cells, and to thereby act as a barrier to cancer development. Investigators have now used both murine models and human studies to offer convincing evidence in support of this concept. Accumulating information about the particular effector molecules and immune cell types involved in this process has formed the basis for rational design of immunotherapies. Both T lymphocytes and Natural killer (NK) cells participate in cancer immune surveillance. Intricate effector mechanisms are involved in providing protection against both malignant and virally infected cells. Our vision of NK cells as therapeutic agents has evolved from the seminal discovery of inhibitory and activating NK receptors. NK cells can recognize tumor cells while preserving normal self, and the understanding of the mechanisms allowing for this preferential recognition pattern has greatly impacted the success of stem cell therapy and immunotherapy. Two main strategies are used by NK cells to recognize tumor targets. A number of tumor cells down-regulate major histocompatibility complex (MHC) class I molecules, protecting against T-cell recognition but releasing the inhibitory breaks in NK cells. The balance of activating and inhibitory NK receptor signals determines whether nascent tumor cells will be recognized and destroyed. In this chapter, the concepts of immune surveillance, immunoediting and NK immunotherapy are discussed. Effective NK immunotherapy may become a reality for many types of cancers in the near future.

Dendritic cell-based vaccines are considered the most advanced examples of active specific immunotherapy against cancer. Dendritic cells, being pivotal for the induction of immunity or tolerance, are not a single cell-type but comprise a large group of cells with differing phenotypes, all with crucial implications for the resulting immune response. To date, cancer vaccines are even being developed for cancers that have traditionally not been regarded as immunogenic, like brain cancer, which might even display underexplored opportunities rather than only hurdles. The major actual challenge is the full integration of the vaccines into the complex interface of the patient as host of the tumor, the tumor micro-environment and the conventional and other therapies applied.

During the past decades, a large body of evidence has revealed that cytokinebased immunotherapy can potently stimulate anti-tumor immune responses and are beneficial for cancer patients. IL-12 is recognized as a prototype cytokine that can induce type 1 (Th1/Tc1) anti-tumor immune responses. However, clinical trials using IL-12 as a single regime, or as a vaccine substance, have demonstrated limited effectiveness in the majority of cases. Recent evidence suggests that IL-12 induces T cell terminal differentiation/exhaustion and thus T cell responses could not be sustained to resulting in tumor rejection. Thus, evaluation of other novel cytokines such as IL-27 that has potent anti-tumor activity yet induces sustained immune responses is highly desired. In this book chapter, we will discuss the Yin and Yang aspects of IL-12 family of cytokines (i.e., IL-12, IL-23, IL-27 and IL-35) in cancer pathogenesis and immunotherapy.

Cell-based therapeutics, once very popular, were relegated to background mode because of the seemingly complex and highly technical nature of producing the cells at specialized facilities. However, they once again are emerging as promising biomedicines with the potential to substantially impact cancer. The resurgence in adoptive immunotherapy comes with renewed interest in our ability to endow cells with novel attributes by genetic modification. We now have techniques at our disposal to enable the creation of designer therapeutics since the T cells now are handled beyond simple manipulation with growth factors. For cellular immunotherapies, T cells can be expanded and manipulated ex vivo prior to adoptive transfer into the host to achieve a novel immune function and with signaling capability. Also, genetic engineering of T cells has been successfully implemented to redirect the specificity of cytotoxic T lymphocytes towards tumor-associated antigens without MHC restriction. Over 70 Investigative New Drug applications are listed on the Food and Drug Administration maintained website www.clinicaltrials.gov that involve genetically engineered T lymphocytes or T cells endowed with chimeric antigen receptors. While the majority of these trials focus on treatment of hematopoietic diseases generally involving B cells, here, we focus on the description of clinical trials currently testing these modified T cells in patients with solid tumors and even more specifically, for those involving treatment of primary malignant brain tumors.

For the past three decades monoclonal and recombinant antibodies have emerged as major therapeutic agents in the field of targeted therapy mainly in cancer and immunological disorders. To date, the United States Food and Drug Administration (FDA) as well as the European Medicines Agency (EMA) have approved more than 30 antibodies or antibody-based drugs for clinical applications. Many more are being developed for various therapeutic applications. This huge interest in antibody therapy is due to their specificity and affinity that allows for targeted therapy, as well as increased understanding of antibody sequence, structure and mechanism of action. With the development of hybridoma technology and the advancement of recombinant DNA technology and antibody engineering methods, novel antibody derived molecules have gained momentum due to their improved pharmacokinetics, increased selectivity and enhanced efficacy. Furthermore, modular antibody design permits careful engineering and development of the new generation therapeutics suitable for the personalized medicine. Many challenges still remain, to improve antibody recognition properties, to engineer their serum half-life, to improve their stability and to better control their immunogenicity and side effects.

In this chapter general principles of therapeutic antibody engineering will be addressed with the view to present the latest molecular engineering strategies for the production of next generation antibody-based therapeutics.

Colorectal cancers are the third leading cause of cancer-associated deaths in the United States. Carcinoembryonic antigen (CEA) is a glycoprotein which is overexpressed in all adenocarcinomas of the colon and rectum and is extensively used as a serologic marker of colon cancer. Its presence in the normal fetal colon, as well as in gut crypts and healing intestinal mucosa of adults makes it a challenging immunologic target, as cytotoxic T lymphocytes (CTL) must overcome tolerance and be directed towards CEA-expressing cancer cells while sparing normal CEA-expressing cells. CAP1-6D, a unique 9-mer peptide of the CEA protein with a single amino acid mutation has been identified as a tumor specific antigen that can induce a stronger immune response than the wild type CEA peptide. Costimulatory signals, such as B7.1 are also critically important in the generation of an effective T cell response to any antigen. The cytokine GM-CSF is a useful vaccine adjuvant for its ability to increase antigen-presenting cells and enhance the antigen-specific anti-tumor response. Additionally, interferon-alpha as an adjuvant can enhance the expression of tumor antigens, such as CEA. This chapter describes the rationale for a clinical trial in which two virus-based CEA vaccines encoding the CAP1-6D peptide as well as costimulatory molecules (B7.1, ICAM-1, and LFA-3) were administered along with the vaccine adjuvants interferon-alpha and GM-CSF.

T lymphocytes can be modified by gene transfer to enhance their anti-tumor activities for the cancer treatment. Yet to further improve this therapeutic approach, current efforts are being made to define and generate better T cells, manipulate the tumor microenvironment, and develop broad-spectrum tumor-reactive T cells. As a key element in T cell activation, differentiation, survival, and effector activity, costimulation signals have been widely incorporated in T cell modification, chimeric antigen receptor (CAR) design and T cell manufacture to directly boost the antitumor activities of T cell, or to counteract tumor suppressive microenvironment. Tumors are able progress in immunocompetent hosts for the reason they could handle to avoid from the immune system, for which they have used multiple mechanisms. Nearly all components of the immune system and all stages of immune response can be interfered by cancers. Selectively providing costimulation signals and cytokines during T cell stimulation and expansion process can dramatically influence the phenotype and T cells function in vitro/in vivo, which have strong impacts on the therapeutic antitumor efficacy. Therefore, the inclusion of costimulatory signals in the design of CAR would elicit enhanced anti-tumor activities compared with signaling via CD3-ζ alone. Direct introducing of costimulatory molecular ligands into the T cells delivers costimulatory signals and so offsets the costimulatory deficit of tumor antigen reactive CD4+ or CD8+ T cells. Also, manipulating other molecule, such as Cbl-b, that regulates T cell costimulation function is a promising strategy in designing cancer immunotherapy.

In cancer patients, a certain number of cytotoxic T lymphocytes (CTLs) specific for cancer antigen are formed; however, most of these CTLs remain inactive due to various suppressive mechanisms such as improper DC activation (anergy induction) or suppression by regulatory T cells. The conventional strategies have been directed to expand the remaining CTLs in vitro or in vivo, to diverge the anergic T cells to an activated status, or to inhibit regulatory T cells. Although the resulting activated CTLs exhibit certain activity in killing tumor cells, in most cases the activity of CTLs is not sufficient enough to result in cure of the patient. One of the major limiting factors in this type of approach is the short life span of activated CTLs. Currently we are trying to overcome this problem by utilizing the iPSC (induced pluripotent stem cell) technology. The concept of our strategy is that it is possible to obtain de novo generated tumor antigen specific CTLs almost unlimitedly when one firstly produces iPSCs from tumor antigen specific CTLs and subsequently regenerate CTLs from such iPSCs. In line with this concept, we have succeeded in establishing iPSCs from mature CTLs specific for the melanoma antigen MART-1, and in regenerating MART-1 specific T cells from such iPSCs. This approach may provide a breakthrough in the future in the tumor immunotherapy.

The maintenance of peripheral tolerance against self and environmental antigens needs regulatory T cells (Treg) that deploy a variety of suppressive mechanisms to control potentially harmful inflammatory and autoimmune reactions. These mechanisms include production of suppressive cytokines and small molecules, expression of inhibitory receptors as well as direct cytolysis and intracellular transfer of second messengers. However, the tumors may hijack Treg immunosuppressive function to escape the anti-cancer immune responses. Expression of self- or altered-self antigens on tumor cells may drive Treg expansion and enhance their suppressive activity. Therefore, Treg-mediated immunosuppression represents one of the main hurdles to the anti-tumor immunity accounting for the failure of anti-tumor therapies including the vaccination and adoptive cell transfer. It has been shown that inhibition of Treg development, survival, and function can alleviate tumor-induced immunosuppression and improve the efficacy of anticancer immunotherapy. Here we discuss current strategies of targeting Treg development and function, including Treg depletion, inhibition of extracellular adenosine production and modulation of signaling pathways in Treg through cell surface receptors.

This chapter will review the current status and future perspectives in the field of cancer vaccine development, and also introduce the glypican-3 (GPC3) peptide-based vaccine for hepatocellular carcinoma (HCC).

Cancer vaccine is administered to promote the induction of immune cells that respond to such antigens. Tumor-associated antigens (TAAs) are the principal targets of cancer vaccine therapy, which include peptide or protein vaccines, dendritic cell (DC) vaccines, tumor lysate vaccines, and genetic vaccines. TAA-specific immunotherapy is considered as an advantageous treatment, because it is likely that adverse effects could be reduced due to the high specificity. Several phase II/III clinical trials of vaccinebased immunotherapy to augment antitumor immunity in a number of cancer patients have been conducted and it is shown that immunotherapy could decrease the possibility of recurrence after therapeutic treatment in adjuvant settings. In 2010, for the first time, the US FDA approved a curative cancer vaccine, Provenge (sipuleucel-T), which is used for prostate cancer patients. However, vaccines as sole therapy do not substantially impact on patients with advanced solid tumors.

Therefore, a thorough understanding of tumor immunity would facilitate an improved application of potential vaccine-based therapy. The future perspectives of cancer vaccine application will likely focus on the combinatorial therapies, such as with vaccines and other immunomodulators.

Recently, we showed that a GPC3-derived peptide vaccination is considerably tolerated, and anti-tumor immunity are significant in a phase I trial in HCC patients. Based on these observations, we anticipate that the outcome of the current work will provide insights into a greater randomized clinical trial of the GPC3 peptide-based vaccine.

In this book series, the basis and proceeding of modern cancer immunotherapy have been extensively discussed; however, it is challenging to put all information in one book. It turns out in recent times that combining immunotherapy and targeted therapies are likely to hold the future of cancer treatment. To gain a comprehensive understanding of cancer immunotherapy, readers are encouraged to find other relevant materials. This chapter serves as a summary of this book as well as provided an outlook for the future development of cancer immunotherapy.