Frontiers in Anti-Cancer Drug Discovery: Volume 8 E-Book
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- Herausgeber: Bentham Science Publishers
- Kategorie: Fachliteratur
- Serie: Frontiers in Anti-Cancer Drug Discovery
- Sprache: Englisch
Frontiers in Anti-Cancer Drug Discovery is a book series devoted to publishing the latest and the most important advances in anti-cancer drug design and discovery. Eminent scientists write contributions on all areas of rational drug design and drug discovery including medicinal chemistry, in-silico drug design, combinatorial chemistry, high-throughput screening, drug targets, recent important patents, and structure-activity relationships. The book series should prove to be of interest to all pharmaceutical scientists involved in research in anti-cancer drug design and discovery. Each volume is devoted to the major advances in anti-cancer drug design and discovery. The book series is essential reading to all scientists involved in drug design and discovery who wish to keep abreast of rapid and important developments in the field.
The eighth volume of the series features chapters covering the following topics:
- T cells in gastrointestinal cancers
- The pharmacology of adjudin – a male contraceptive with anti-cancer properties
- Manipulating the tumor microenvironment
- Treatment of hepatocellular carcinoma
- Gold-based compounds as potential anti-cancer drug candidates
- Oral nanostructure drug delivery for anti-cancer treatment
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Seitenzahl: 327
Veröffentlichungsjahr: 2017
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Frontiers in Anti-Cancer Drug Discovery
(Volume 8)
Edited by:
Atta-ur-Rahman, FRS
Kings College,University of Cambridge,Cambridge, UK
M. Iqbal Choudhary
H.E.J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences,University of Karachi,Karachi, Pakistan
BENTHAM SCIENCE PUBLISHERS LTD.
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Preface
Cancer is a grand health challenge of modern times, being the second leading cause of death. Despite tremendous investments in this field, the prognosis of cancer has not improved substantially. There have been some advances in cancer chemotherapy and radiation therapy, but other treatment options, such as surgery, burn, immunotherapy, etc remain primitive and far from being perfect. Chemotherapy, the “holy grail” of cancer treatment, is based on targeting certain biomolecular pathways in the complex cascade of cancer progression. However, the limited understanding of cancer biology often makes this a fishing expedition. As a result, many of the currently available anti-cancer drugs are non-specific and less effective. Heterogenicities in cancer pheno- and geno-types, often make the identification of genuine targets difficult. However recent advancements in genomics, metabolomics, transcriptomics, and molecular biology have fuelled major research projects in the fields of oncology and anti-cancer drug discovery and development. The scientific literature is now full of exciting discoveries against this disease of modern society, cancer. It is often difficult, even for a prolific reader, to keep pace with these developments. Thus, the need of a comprehensive book review series is greatly felt.
The last seven volumes of the ebook series “Frontiers in Anti-Cancer Drug Discovery” have attracted major interest, making this series a welcome addition to the global literature on this dynamic topic. The present 8th volume of this internationally recognized books series comprises six carefully selected topics focused on various aspects of cancer chemotherapy and cancer biology, contributed by leading experts in this field. Each chapter deals with anti-cancer drug discovery and development based on various innovative approaches, including identification of new molecular targets, manipulation of cancer microenvironment, and outcomes of pre-clinical and clinical studies on new drugs, and combination therapies.
Amedei et al. have reviewed the recent progress in the use various immunotherapies in cancer treatment in chapter 1. Their emphasis is on the treatment of gastrointestinal cancers by T-cell based immunotherapies. T-Cells, also called T-lymphocytes, are a subtype of white blood cells that play a central role in cell-mediated immunity. T-Cell based immunotherapies have attracted considerable scientific attention. However, T-cell based immunotherapy of cancers is not free of adverse side effects.
In chapter 2, Cheng et al. have contributed a comprehensive review on the anticancer activity of the newly discovered compound adjudin, a well-known male reversible contraceptive used in animals. Adjudin is a structural analogue of the anticancer drug lonidamine. Apart from its known potent anti-spermatogenic activities, adjudin is found to have many other biological properties. Notable among them is its activity against neuroinflammation, protection against gentamicin-induced ototoxicity, and prevention of cancer growth and development. The authors have critically reviewed the recent literature on new indications of this old contraceptive drug. The focus of the article is on recently discovered anticancer activities of adjudin, either alone or in combination with other anticancer drugs as well as with nanocarriers. Adjudin, similar to lonidamine, inhibit cancer growth by targeting mitochondria and blocking energy metabolism in certain kinds of tumor cells in mice, indicating that it is potential anticancer agent.
Tumor microenvironment (TME) plays an important role in the progression of tumor growth, and treatment outcome. This cellular environment includes surrounding blood vessels, immune cells, fibroblasts, bone marrow-derived inflammatory cells, lymphocytes, signalling molecules and the extracellular matrix (ECM). Recently TME has been identified as potential target for novel cancer chemotherapies. Mabtel and Pepper have contributed a comprehensive review in chapter 3 on the role of tumor microenvironment in tumor progression, angiogenesis, cellular invasion, metastatic dissemination, resistance against chemotherapy and its potential as drug target. Recently developed treatments which can modulate TME against tumor growth, along with their mechanisms of action, have also been discussed.
In chapter 4, Fatima et al. have focussed on the current and emerging therapies for the treatment of hepatocellular carcinoma (HCC) or malignant hepatoma. Hepatocellular carcinoma accounts for most liver cancers, and is a leading cause of cancer related deaths. HCC occurs more frequently in men than women and is usually diagnosed in people of age 50 or older. HCC’s prognosis is among the poorest of all cancer types. This review provides a detailed description of various treatment options for HCC, and their advantages and disadvantages. Future directions of development in this field are also reviewed.
Gold complexes are known for a variety of biological activities. In chapter 5 Sun et al. discuss the anti-cancer properties of gold-based compounds and their potential. After the serendipitous discovery of cisplatin, a platinum (II) based compound, as a potent anti-cancer agent, interest in metal complexes has increased exponentially. Sun et al. have critically reviewed the recent literature on the therapeutic potential of novel gold complexes (I and III), particularly against various cancers.
In the last chapter, Anreddy et al. have reviewed the application of nanostructures as oral drug delivery vehicles for the treatment of various cancers. One of the key issues in cancer chemotherapy is that the most potent anticancer therapies can only be administered through injection, as their oral drug delivery is associated with many limitations. This makes cancer chemotherapy quite challenging. Recently many new classes of nanoparticles (NPs), such as liposomes, polymeric NPs, polymeric conjugates, micelles, dendrimers, polymersomes, and metallic and inorganic NPs, have been developed as new drug delivery vehicles for oral administration in cancer chemotherapy. These nanoparticle-based anti-cancer drugs are often devoid of problems such as poor solubility, low intrinsic permeability, and metabolic changes. The potential of NPs in on-target and sustained administration of drugs is also discussed.
We wish to express our sincere gratitude to all the authors for their excellent scholarly contributions to this 8th volume of this book series. We also appreciate the efforts of the impressive production team of Bentham Science Publishers for the efficient processing the treatise. The efforts of Ms. Fariya Zulfiqar (Assistant Manager Publications) & Mr. Shehzad Naqvi (Senior Manager Publications) and excellent management of Mr. Mahmood Alam (Director Publications) are greatly appreciated. We also hope that like the previous volumes of this internationally recognized book series, the current volume will also receive wide readership and recognition.
List of Contributors
T Cells in Gastrointestinal Cancers: Role and Therapeutic Strategies
Carolina V. De Almeida1,Ramon Kaneno2,Amedeo Amedei1,*Abstract
Conventional treatments of gastrointestinal cancers based on surgical resection and chemotherapy are not enough to eradicate potentially relapsing tumor cells and can also impair the immune system functions. Immunotherapies aim to help the body to eradicate cancer and other diseases, by modulating the immune system. They can be performed by active approaches, usually orchestrated by dendritic cell vaccines that present a specific tumor associated antigen to T cells, or passive approaches, which have the T cells as protagonist, and are based on antitumor antibodies, or adoptive cell transfer. T lymphocyte subsets can exhibit different role face to a tumor scenario, varying from an effective cellular antitumor response to a regulatory participation. Although a lot of protocols to combat cancer progression have been proposed, T cell-based immunotherapies in gastrointestinal cancers are still not approved for clinical applications mainly because of their side effects. Nowadays, promising protocols combining two or more approaches, aiming to create an efficient therapy without or with fewer side effects. In this chapter, we made a review about the role of T cells on cancer, especially focusing on gastrointestinal cancer immunoth-erapeutic methods.
INTRODUCTION
Gastrointestinal (GI) cancers, including colorectal (CRC), gastric, pancreatic, liver and bile duct cancers, are complex diseases that figure among the ten most frequent types of cancers annually diagnosed worldwide [1], which incidences have a variable geographic distribution [2]. Most of these tumors occur in a sporadic way, and the distribution variability is closely associated with diet
culture and lifestyle [3-6]. The development of GI cancers could also be associated with microbial infections, which seems to play an important role on both, initiation and progression. For instance, Streptococcus bovis is an important inducer of CRC development [7], while Helicobacter pylori is highly associated with gastric cancer [8], and the Hepatitis C virus induces liver cancer [9]. The association of these pathogens with previously stabilized chronic inflammatory microenvironment can induce DNA damage in proliferating cells through the action of reactive oxygen species (ROS) and inflammatory cytokines that can culminate in gene mutations and/or epigenetic changes [10].
Conventional treatment of patients with localized GI cancers consists in surgical resection of tumor tissue. However, post-surgery relapsing disease frequently develops within 2 years in approximately 40% of patients. Therefore, adjuvant therapy is required to improve anti-cancer responsiveness in high-risk patients, and then, surgery is usually followed by adjuvant chemotherapy or adjuvant che-mo-radiotherapy. Frequently, patients are submitted to perioperative chemot-herapy [11, 12] (also called neoadjuvant therapy administrated before surgery), in order to reduce the tumor mass and facilitate surgical intervention. Despite these combinations, metastasis and relapsing diseases are until the main causes of death in GI patients. Moreover, in vitro and in vivo studies have shown that cytotoxic chemotherapy, as well as the surgery stress itself, can impair the immu-nological steady state and also the ability to develop an antitumor immune res-ponse [13].
The immune system plays an important role in the battle against cancer devel-opment. The capacity to promote an effective immunological reaction against tumor antigens was firstly described by Macfarlane Burnet and Lewis Thomas and called immunosurveillance [14]. Immunosurveillance occurs when some antigens, encoded by mutated genes and expressed by tumor cells, became a functional target and are quickly recognized and destroyed by innate effector cells such as natural killer cells. This concept of surveillance can be extended to recognition, processing, and presentation of tumor antigens by professional antigen-presenting cells (APCs) to naïve lymphocytes (Ly) [15, 16]. In this scenario, autologous CD4+ and CD8+ T lymphocytes recognize these antigens, and attack transformed cells inducing their lysis [17]. In fact, the presence of strong lymphocyte infiltration in tumor site such as in melanoma, CRC and ovarian cancers is associated with a good clinical outcome, since they have the function to inhibit the tumor growth [18].
Lymphocytes originate from a common lymphoid precursor cell in bone marrow. During fetal development, some of these lymphoid precursors move to thymic epithelium to develop this organ where all T lymphocytes will evolve (Fig. 1). T cells have surface receptors (TCRs) that recognize antigen peptide linked to molecules of the Major Histocompatibility Complex (MHC), especially expressed on the surface of the APCs such as macrophage and dendritic cells (DC), or also on the target cells, such as allogeneic cells and virus or intracellular bacterial - infected cells.
Fig. (1)) T lymphocytes’ differentiation: from the common progenitor to the different subpopulations CD8, CD4 and Natural killer T lymphocytes (NKT). When a naïve lymphocyte recognizes an antigen, which was presented by a major histocompatibility complex class I (MHC-I) is induced to differentiate to a CD8+ profile. However, the recognition of antigen presented by MHC-II in turn, guides the lymphocytes’ differentiation for a CD4+ subpopulation, which after activation may enter several different pathways depending on antigen-presenting cell (APC) co-stimulatory factors and cytokine setting. The presence of Interleukin (IL)-12, for example, directs the CD4+ to Th (T helper) -1 profile, while IL-4 to Th2, IL-6 and TGF-β to Th17, IL-4 and TGF-β to Th9, IL-6 and IL-21 to T follicular helper (TFh) cells and finally, the presence of IL-2 conducts the CD4+ T lymphocytes to differentiate in T regulatory (Treg) cells. The differentiation of NKT cells in the other hand occurs when naïve T lymphocytes recognize CD1d in the presence of IL-12 and IL-15.TCR are heterodimers composed of two polypeptide chains, usually α and β, that show a constant (C) and a variable (V) regions. The V region presents three hype-rvariable regions called Complementary Determining Regions (CDR), which are responsible for the recognition of the peptide-MHC complex. Those T lymp-hocytes CD4+ can recognize peptides linked to class II MHC molecules, while those CD8+ link the peptides which are complexed with MHC class I molecules. After the peptide recognition, CD4 and CD8 molecules link to a non-polymorphic region of MHC molecules to stabilize the TCR-MHC association and then signalize for the T cell activation. Lymphocytes also express accessory molecules that take part in antigen-induced cell activation, such as CD2, CD11a, CD28, CD40 ligand [19]. Besides the regular αβ polypeptide receptors, there is a low percentage of T cells with TCR formed by γ and δ chains (Tγδ), whose features will be discussed further.
The CD4+, also called T helpers (Th), have the role of helping the others cells of the immune system in their function, such as B lymphocytes, macrophage, NK cells and other T Ly, producing cytokines responsible for their activation (Fig. 2A). The T helper lymphocytes are classified as Th1, Th2, Th17, Th9 and Tfh according to their functions and with the secreted cytokines (Fig. 1). The Th1 lymphocytes, for example, produce high levels of IFN-γ and drive immune system towards to a cellular response. This reactivity is characterized by activation of macrophages and cytotoxic T cells that evolve to an effective response against intracellular bacteria and virus. This responsiveness is also essential for the acute rejection of allografts [20], and is the most important for resistance to tumor cell [21]. Moreover, the development of CD8+ T lymphocytes depends on the Th1 profile immune response activation [22].
The Th2 cell subset is responsible to produce IL-4, IL-5, IL-10 and IL-13, and its immune response toward polarization results in high levels of IgE, improving the immunity against extracellular parasites as well as, can determinate type I hyper-sensitivity. Interleukins produced by Th2 lymphocytes have a strong negative regulatory role of Th1 cells, therefore the prevalence of Th2 responsiveness is associated with effectiveness delays of antitumor defenses [23].
Secreted by Th17 lymphocytes, the IL-17, IL-21 and IL-22 cytokines lead to an immune response towards to inflammatory reactions. Then, although inflam-mation is an innate reaction of the body against aggressors, it can also be triggered as a consequence of a specific immune response. This defense reaction is particularly relevant in fungal and extracellular bacterial infections responses [24], however, it is strongly associated with auto-inflammatory diseases, such as autoimmune arthritis [25], and Crohn´s disease [26]. The negative influence of Th17 on tumor development deserves special attention in CRC, since inflamma-tion is one of the main predisposing factors of this cancer type development. In fact, while administration of non-steroidal anti-inflammatory drugs helps to control the cancer growth [27], the recruitment of Th17 lymphocytes is associated with enhancement of the CRC development [28].
Follicular helper T cells (Tfh), which help B lymphocytes at lymphoid follicles, produce IL-21 and seem to be derived from Th2 lymphocytes [29, 30]. In fact, some human Tfh cells express the Th2 marker CRTH2 and can also produce IL-4 [31]. Another subset that seems to result from the Th2 plasticity is referred as Th9 cells, a population that switches the production of IL-4 to IL-9 upon stimulation with TGF-β [32]. Similarly to Th2, Th9 also takes part in anti-helm-intic response and allergic reaction [33, 34].
The functions of these T helper cell subsets are regulated by immunosuppressive cells named regulatory T cells (Treg), which comprise heterogeneous subpopula-tions with phenotypical and functional particularities, but sharing common features such as the expression of CD4 and the α chain receptor for IL-2 (CD25) [35, 36]. Transcription factor Forkhead Box P3 (FoxP3) is also used to identify Treg, although subsets called Tr1 and Th3 do not have this factor (FoxP3- subsets) [37].
The CD8+ T cells usually evolve to effector cytolytic T lymphocytes (CTL) (Fig. 2B). These cells have cytoplasmic granules full of perforin monomers, granzyme and granulysin that are released at the intercellular pouch formed between effector and target cell membranes after the target recognition by the CTL [38]. Perforin monomers polymerize on target cell membranes, forming transmembrane pores on this surface, allowing the cytoplasmic content leaking, the influx of hypotonic extracellular liquid, and consequently the osmotic lysis [39]. In addition, these perforin-formed pores permit the release of granzyme into the target cells triggering the cell apoptosis [40], that is induced by the DNA break, which can be caused by diverse pathways such as the induction of caspase activation, mito-chondrial impairment, and nuclear disruption [41, 42].
Therefore, CD8+ CTL are classically considered the main antitumor effector cells, since they recognize tumor antigens in a HLA ABC-restricted manner, show clonal expansion, and their effectiveness could be improved including immuno-logical memory [43]. However, their activation and evolution into cytolytic antitumor cells improve the antitumor status [44].
Other immune cells that are involved in the immune response against cancer are the natural killer (NK) and the natural killer T cells (NKT). NK cells are circulating lymphocytes able to extravasate and infiltrate different tissues containing malignant cells [45, 46]. Most natural killer activity is attributed to a population of cells morphologically defined as large granular lymphocytes (LGL), found in peripheral blood and lymphoid organs [47-49]. These cells are larger than typical small lymphocytes, with higher cytoplasm: nucleus ratio and large azurophilic cytoplasm granules [50].
Fig. (2)) CD4+ and CD8+ T cells’ activation by tumor cells. A) Tumor associated antigens (TAA) are presented by an antigen-presenting cell (APC) through the major histocompatibility complex class II (MHC-II) to a naïve lymphocyte. After recognizing this antigen, the naïve T lymphocyte becomes a mature CD4+ or also named as T helper lymphocyte (Th), and start to produce cytokines that will help other cells of the immune system, such as macrophages, CD8+, Natural killer T lymphocytes (NKT) and lymphocyte B, to execute their functions. B) In a second way, antigens derived from endogenous peptides are presented to the naïve T lymphocyte by the APC through MHC-I, managing it differentiation to a cytotoxic T lymphocyte (CTL-CD8+) profile, which will produce cytotoxic granulates such as granzymes, perforin, and granulysin able to induce tumor cell apoptosis.NK cells comprise 10-15% of all circulating lymphocytes, but can also be found in peripheral tissues such as liver, peritoneal cavity, lung and placenta. They are usually present in a standby state in the peripheral blood, but after their activation by specific cytokines, they become capable of extravasation and infiltration into most infected tissues or the tumor site [51]. These cells are potent effectors of the innate immune system, since they have a critical role in early host defense against invading intracellular pathogens [52], and for their ability to kill virus-infected and cancer cells [53], are suitable candidates for immunotherapy of both hemato-logic and solid tumors [54].
As previously reviewed by Kaneno R, since NK do not express CD3, TCR or any other TCR chains (α, β, γ or δ), nor even B lymphocyte markers CD19 and surface Ig, these cells are classified as non-T, non-B lymphocytes. Although these cells share the CD16 expression with macrophages and neutrophils, they are non-adherent leukocytes and do not show phagocytic activity [46].
They constitute a phenotypically heterogeneous population with a variety of surface markers involved in antigen recognition, lytic activity triggering and cell regulation [55-57]. Among them, NKG2D is the main activation C-type lectin-like receptor that binds to DAP-10 adaptor molecule that triggers tumor cell lysis [58]. NKG2D interacts with MIC A and MIC B, homologous to class I structures that conserve the domains α1, α2 and α3 of class I MHC molecules, but fail to express both β2-microglobulin and peptides bound to the α chain [59]. MIC A and MIC B are uncommon on normal cells while epithelial tumor cells express them in a high density, being important targets for NK [57, 60, 61]. After the interaction between effector and target cells, immunological synapses are formed between the cell surfaces and NK cells release the contents of cytoplasmic gran-ules, as previously described for CTL.
Although experimental data have shown that NK activity can be important to inhibit the occurrence of colon cancer metastasis, their efficiency in the immuno-surveillance of this cancer type in humans cannot be very easily demonstrable. Although CRC shows a low number of infiltrating NK cells [62, 63], their pres-ence is associated with a better prognosis for patients not only with CRC [64], but also with gastric carcinoma [65].
The NK cells of CRC patients show the same level of lytic activity from normal donors, however, the cells isolated from tumor tissue have a reduced lytic activity when compared with NK cells of peripheral blood or mucosa-associated lymphoid tissue of the same patient [66]. This is in agreement with the local suppressive environment, induced by suppressive factors produced by the tumor cells thems-elves, associated with a strong Treg activity in gastrointestinal tissue.
Tissues obtained from metastasis also show reduced frequency or even absence of NK cells, whereas patients submitted to treatment with cytokines show a marked increase in these effector cells (CD56+/CD3-), in the adjacent tumor [67]. Consi-dering that NK activity results from the balance between stimulatory and inhibitory signals, it must be remembered that, similar to other regulatory syste-ms, inhibitory signals are more potent than the simulated ones. So, in some cond-itions NK cells require additional stimulation by cytokines, whose in vivo prod-uction can improve the defensive role of these cells [68].
NKT cells recognize, and share phenotypic and functional properties common to both conventional NK cells and T cells [69]. They are able to induce tumor cell death by producing cell-death-inducing effectors molecules such as perforins, FasL, TRAIL, IFN-γ and IL-4 [70, 71]. NKT cells are a group of lymphocytes that express both, TCR and NK markers, and recognize lipid antigens (mainly glycolipids and glycerols) presented by the class Ib molecule, CD1d, differently from conventional T cells that recognize protein (peptide) antigens presented by MHC molecules. They are an important immunoregulatory cell subset activated during the immune differentiation towards Th1 or Th2, and are key tags in several studies, including transplantation, tumors, autoimmunity and allergy [72, 73].
Mucous, enterocytes, and the bowel wall work as physical innate barriers of gastrointestinal system to pathogens. When they fail, gut can be infiltrated by phagocytic cells, such as neutrophils and macrophages, followed by activation of inflammatory and complement pathways [74]. Inflammatory process aims to destroy pathogens and abnormal tissues, and is responsible for promoting tissue reconstruction. However, in the cancer scenario, this inflammatory process is rather associated with the carcinogenesis promotion, especially for the secretion of several cytokines and growth factors with carcinogenic activity as TNF [75], IL-8 [76], VEGF [77]. Thus, increased density of microvessel density, as well as maintenance of the inflammatory response is associated with poor survival and enhancement of cancer growth. An example of inflammation pro-carcinogenic role in CRC includes the strong association with chronic inflammatory diseases such as Crohn’s disease and ulcerative colitis [78-81].
These dual effects of the immune system on developing tumors required the reformulation of the immunosurveillance hypothesis, and at 2002 the new term ‘cancer immunoediting’ was suggested by Dunn et al [14]. According to them, the immune response to cancer development occurs in three phases collectively denoted as the ‘three Es’ of cancer immunoediting: elimination (cancer immunos-urveillance), equilibrium (tumor cell variant that has survived the elimination phase are contained, but not fully extinguish), and escape (tumor cell variants selected in the equilibrium phase now can grow in an immunologically integral environment) [82].
CANCER IMMUNOTHERAPY
Immunotherapy is defined as a form of biological therapy that can either activate or inhibit the immune system, assisting the body to eradicate cancer and other disease [83]. In cancer, specifically, the aim of the immunotherapy is to help the body to recognize the cancer cells, activate the immune cells, and break its immune tolerance. The immunotherapy can be classified as active, which aims to activate the adaptive immune system of the patients to destroy tumors and prevent their recurrence; or as adoptive that consists in transferred tumor reactive T cells to the patient and enhances pre-existing immune response [84]. They can also be categorized as nonspecific, which stimulate the host immunity with definite cytokines, DC-based vaccines, NK or NKT cells, or specific mechanisms that use antibodies, γδ T cells, or adoptive αβ T cell therapies [85].
The first adoptive immunotherapy against cancer was tested in 1956 by Dr E Donnall Thomas, who applied a lethal radiation dose in a leukaemia patient followed by bone marrow transplantation (BMT) from the patient's identical twin. The result was the complete disease regression of the disease, stating the prin-ciples of the BMT using non-related donor. These principles are still being pra-cticed today as the only curative option for several types of leukaemia.
In 2002, tumor infiltrating lymphocytes (TIL), isolated from a tumor excision, were clinically tested for the first time in a patient with a metastatic melanoma [86]. Four years later, a group had performed a clinical trial using peripheral blood T cells transfected with MART-1 TCR alpha and beta chain gene as TAA. They demonstrated that T cells, which were transduced ex vivo with anti-TAA–TCR genes and re-infused in cancer patients, can persist and express the transgene for a prolonged time in vivo and mediate the durable regression of large established tumors, becoming a potential method to use in patients for whom TILs are not available [87].
In GI cancers, immunotherapy seems to be a forward step in the path of treatment, and all the diverse strategies are vastly being explored such as 1) stimulation of immunity with inflammatory cytokines, or blocking inhibitory specific check points (e.g. CTLA-4 and PD-1) with monoclonal antibodies; 2) vaccines that use tumor antigens, irradiated autologous tumor cells or autologous DCs; 3) adoptive cell therapy with isolated tumor infiltrating lymphocytes [13].
Although preclinical models had demonstrated important results on immuno-therapy strategies mainly when associated with other targeted therapeutics, there is a lot of limitations in currently available immunotherapy for GI malignancies, especially the complex interplay between the tumor, the supporting tumor microenvironment, and the immune system (local and systemic). Moreover, it can cause some harmful autoimmune side effects, coming from the damage of peripheral tolerance to antigens expressed by normal tissues. Besides that, GI cancer studies focused on immunotherapy have shown that it can take more than 3 months to observe a radiographic effect in some patients [88].
The success of this approach depends not only on the ability to optimally select cells or genetically modify the same with targeted antigen, but also to induce these cells to proliferate, preserving their effector function and engraftment and homing abilities, and finally does not culminate in collateral effects to the patient. That is probably the reason, despite more than 60 years of research, only in 2010 FDA-approved the first adoptive T-cell therapy protocols for cancer [89].
THERAPY WITH CYTOTOXIC T LYMPHOCYTES
One of the first described adoptive immunotherapy was the infusion of in vitro cultured CTL in a melanoma patient [90, 91]. Despite the notable ability of CTL to in vitro kill tumor cells, establishment of successful CTL-based therapies is full of obstacles. For instance, some tumor cell variants can less or drastically decr-ease antigen expression, rising as resistant targets, or the levels of MHC-I molecules can be downregulated on tumor cell surface allowing the escape of MHC-restricted recognition [92]. Although previous results demonstrated that the CTL transfer in cancer patients might have a vaccine-like effect by generating new clones with high anti-tumor response [93], other studies concluded that it is a controversial approach since some of the transferred CTL cells could emerge from an antigen escape variant [94].
