Immunity to stemness genes in human cancer

Targeted immunotherapy to cancer stem cells: A novel strategy of anticancer immunotherapy

Cancer is a major disease that endangers human health. Cancer drug resistance and relapse are the two main causes contributing to cancer treatment failure. Cancer stem cells (CSCs) are a small fraction of tumor cells that are responsible for tumorigenesis, metastasis, relapse, and resistance to conventional anticancer therapies. Therefore, CSCs are considered to be the root of cancer recurrence, metastasis, and drug resistance. Novel anticancer strategies need to face this new challenge and explore their efficacy against CSCs. Recently, immunotherapy has made rapid advances in cancer treatment, and its potential against CSCs is also an interesting area of research. Meanwhile, immunotherapy strategies are novel therapeutic modalities with promising results in targeting CSCs. In this review, we summarize the targeting of CSCs by various immunotherapy strategies such as monoclonal antibodies(mAb), tumor vaccines, immune checkpoint inhibitors, and chimeric antigen receptor-T cells(CAR-T) in pre-clinical and clinical studies. This review provides new insights into the application of these immunotherapeutic approaches to potential anti-tumor therapies in the future.

Immunization with Embryonic Stem Cells/Induced Pluripotent Stem Cells Induces Effective Immunity against Ovarian Tumor-Initiating Cells in Mice

Cancer stem cells (CSCs) express pluripotent markers and share many features with normal pluripotent stem cells. It is possible that immunity induced by embryonic stem cells (ESCs) and induced pluripotent stem cells- (IPSCs-) based vaccines may selectively target CSCs. In our study, cells expressing the pluripotent marker CD133 in the murine ovarian cancer cell-line ID8 were isolated and identified as CSCs. We investigated the preventive efficacy of ESCs and IPSCs-based vaccines against the development of ovarian cancer in vivo and evaluated the humoral and cellular immunities targeting CSCs in vitro. Our study showed that preimmunization with both mouse-derived embryonic stem cells (mESCs) and mouse-induced pluripotent stem cells (mIPSCs) lysates, combined with an immunostimulatory adjuvant CpG, elicited strong humoral and cellular responses. These responses effectively suppressed the development of CSC-derived tumors. Immune sera collected from mESCs and mIPSCs-vaccinated mice contained antibodies that were capable of selectively targeting CSCs, resulting in the lysis of CSCs in the presence of complement. Cytotoxic T-lymphocytes generated from splenocytes of mESCs and mIPSCs-vaccinated hosts could secrete interferon- (IFN-) γ in response to CSCs and kill CSCs in vitro. These findings indicate that vaccines based on mESCs and mIPSCs can elicit effective antitumor immunities. These immunities are related to the conferring of humoral and cellular responses that directly target CSCs.

Pluripotent Stem Cells: Cancer Study, Therapy, and Vaccination

INTRODUCTION

Pluripotent stem cells (PSCs) are promising tools for modern regenerative medicine applications because of their stemness properties, which include unlimited self-renewal and the ability to differentiate into all cell types in the body. Evidence suggests that a rare population of cells within a tumor, termed cancer stem cells (CSCs), exhibit stemness and phenotypic plasticity properties that are primarily responsible for resistance to chemotherapy, radiotherapy, metastasis, cancer development, and tumor relapse. Different therapeutic approaches that target CSCs have been developed for tumor eradication.

RESULTS AND DISCUSSION

In this review, we first provide an overview of different viewpoints about the origin of CSCs. Particular attention has been paid to views believe that CSCs are probably appeared through dysregulation of very small embryonic-like stem cells (VSELs) which reside in various tissues as the main candidate for tissue-specific stem cells. The expression of pluripotency markers in these two types of cells can strengthen the validity of this theory. In this regard, we discuss the common properties of CSCs and PSCs, and highlight the potential of PSCs in cancer studies, therapeutic applications, as well as educating the immune system against CSCs.

CONCLUSION

In conclusion, the resemblance of CSCs to PSCs can provide an appropriate source of CSC-specific antigens through cultivation of PSCs which brings to light promising ideas for prophylactic and therapeutic cancer vaccine development.

Strategies for Cancer Immunotherapy Using Induced Pluripotency Stem Cells-Based Vaccines

Despite improvements in cancer therapy, metastatic solid tumors remain largely incurable. Immunotherapy has emerged as a pioneering and promising approach for cancer therapy and management, and in particular intended for advanced tumors unresponsive to current therapeutics. In cancer immunotherapy, components of the immune system are exploited to eliminate cancer cells and treat patients. The recent clinical successes of immune checkpoint blockade and chimeric antigen receptor T cell therapies represent a turning point in cancer treatment. Despite their potential success, current approaches depend on efficient tumor antigen presentation which are often inaccessible, and most tumors turn refractory to current immunotherapy. Patient-derived induced pluripotent stem cells (iPSCs) have been shown to share several characteristics with cancer (stem) cells (CSCs), eliciting a specific anti-tumoral response when injected in rodent cancer models. Indeed, artificial cellular reprogramming has been widely compared to the biogenesis of CSCs. Here, we will discuss the state-of-the-art on the potential implication of cellular reprogramming and iPSCs for the design of patient-specific immunotherapeutic strategies, debating the similarities between iPSCs and cancer cells and introducing potential strategies that could enhance the efficiency and therapeutic potential of iPSCs-based cancer vaccines.

Risk-associated alterations in marrow T cells in pediatric leukemia

Current management of childhood leukemia is tailored based on disease risk determined by clinical features at presentation. Whether properties of the host immune response impact disease risk and outcome is not known. Here, we combine mass cytometry, single cell genomics, and functional studies to characterize the BM immune environment in children with B cell acute lymphoblastic leukemia and acute myelogenous leukemia at presentation. T cells in leukemia marrow demonstrate evidence of chronic immune activation and exhaustion/dysfunction, with attrition of naive T cells and TCF1⁺ stem-like memory T cells and accumulation of terminally differentiated effector T cells. Marrow-infiltrating NK cells also exhibit evidence of dysfunction, particularly in myeloid leukemia. Properties of immune cells identified distinct immune phenotype–based clusters correlating with disease risk in acute lymphoblastic leukemia. High-risk immune signatures were associated with expression of stem-like genes on tumor cells. These data provide a comprehensive assessment of the immune landscape of childhood leukemias and identify targets potentially amenable to therapeutic intervention. These studies also suggest that properties of the host response with depletion of naive T cells and accumulation of terminal-effector T cells may contribute to the biologic basis of disease risk. Properties of immune microenvironment identified here may also impact optimal application of immune therapies, including T cell–redirection approaches in childhood leukemia.

In high risk pediatric leukemia, naive and stem-like memory T cells are depleted and terminally differentiated effector T cells accumulate.

Moving Immunoprevention Beyond Virally Mediated Malignancies: Do We Need to Link It to Early Detection?

Vaccines can successfully prevent viral infections and have emerged as an effective strategy for preventing some virally mediated malignancies. They also represent our major hope for cost-effective reduction of the cancer burden. The concept that the immune system mediates surveillance and editing roles against tumors is now well-established in murine models. However, harnessing the immune system to prevent human cancers that do not have a known viral etiology has not yet been realized. Most human cancers originate in a premalignant phase that is more common than the cancer itself. Many of the genetic changes that underlie carcinogenesis originate at this stage when the malignant phenotype is not manifest. Studies evaluating host response in human premalignancy have documented that these lesions are immunogenic, setting the stage for immune-based approaches for targeted prevention of human cancer. However, recent studies suggest that the hierarchy of T cell exhaustion and immune-suppressive factors have already begun to emerge in many preneoplastic states. These considerations underscore the need to link immune prevention to earlier detection of such lesions and to personalize such approaches based on the status of the pre-existing immune response.

Cancer stem cells and immunoresistance: clinical implications and solutions

Tumor cells can be contained, but not eliminated, by traditional cancer therapies. A cell minor subpopulation is able to evade attack from therapies and may have cancer stem cell (CSC) characteristics, including self-renewal, multiple differentiation and tumor initiation (tumor initiating cells, or TICs). Thus, CSCs/TICs, aided by the microenvironment, produce more differentiated, metastatic cancer cells which the immune system detects and interacts with. There are three phases to this process: elimination, equilibrium and escape. In the elimination phase the immune system recognizes and destroys most of the tumor cells. Then the latency phase begins, consisting of equilibrium between immunological elimination and tumor cell growth. Finally, a minor attack-resistant subpopulation escapes and forms a clinically detectable tumor mass. Herein we review current knowledge of immunological characterization of CSCs/TICs. Due to the correlation between CTCs/TICs and drug resistance and metastasis, we also comment on the crucial role of key molecules involved in controlling CSCs/TICs properties; such molecules are essential to detect and destroy CSCs/TICs. Monoclonal antibodies, antibody constructs and vaccines have been designed to act against CSCs/TICs, with demonstrated efficacy in human cancer xenografts and some antitumor activity in human clinical studies. Therefore, therapeutic strategies that selectively target CSCs/TICs warrant further investigation. Better understanding of the interaction between CSCs and tumor immunology may help to identify strategies to eradicate the minor subpopulation that escapes conventional therapy attack, thus providing a solution to the problem of drug resistance and metastasis.

Prospective analysis of antigen-specific immunity, stem-cell antigens, and immune checkpoints in monoclonal gammopathy

Blockade of immune checkpoints (ICPs) has led to impressive responses in cancer patients. However, the impact of preexisting immunity and ICPs on the risk of malignant transformation in human preneoplasia has not been prospectively studied. We prospectively analyzed antigen-specific B/T-cell immunity, immune composition of the tumor microenvironment, and the expression of a panel of ICPs on tumor and tumor-infiltrating immune cells in 305 patients with asymptomatic monoclonal gammopathy enrolled in S0120 under the auspices of SWOG. T-cell immunity against stem-cell antigen SOX2 and preserved humoral responses at study entry independently correlated with reduced risk of progression to clinical myeloma. Among the ICPs analyzed, expression of programmed death-ligand 1 (PD-L1) on tumor and infiltrating T cells correlated with increased risk of clinical malignancy, and blockade of this pathway boosted anti-SOX2 immunity in culture. These data suggest that stem-cell antigens and PD-L1 may be targeted for immunoprevention of myeloma. This trial was registered at www.clinicaltrials.gov as #NCT00900263.

Restoring immunosurveillance by dendritic cell vaccines and manipulation of the tumor microenvironment

Cancer cells evolve from normal cells throughout life and are usually recognized by our immune system and destroyed, a process called immunosurveillance. Unfortunately, in some instances cancer cells paralyze our immune system, resulting in outgrowth and spreading of the tumor. Understanding the complexity of immunomodulation by tumors is important for the development of therapeutical strategies. Nowadays, various approaches have been developed to enhance anti-tumor immune responses and abrogate the immune dampening effect of the tumor and its surrounding environment, including dendritic cell-based vaccines, therapies to counteract myeloid derived suppressor cell function within the tumor and antagonists of inhibitory signaling pathways to overcome 'immune checkpoints'. The challenge is now to find the right combination of immune based therapies to fully restore immune function and provide a more efficacious and enduring anti-tumor response.

Myeloma stem cell concepts, heterogeneity and plasticity of multiple myeloma

Multiple myeloma (MM) is a haematological malignancy characterized by the accumulation of clonal plasma cells (PCs) in the bone marrow (BM). Although novel therapeutic strategies have prolonged survival of patients, the disease remains difficult to treat with a high risk of relapse. The failure of therapy is thought to be associated with a persistent population of the so-called MM stem cells or myeloma initiating cells (MIC) that exhibit tumour-initiating potential, self-renewal and resistance to chemotherapy. However, the population responsible for the origin and sustainability of tumour mass has not been clearly characterized so far. This review summarizes current myeloma stem cell concepts and suggests that high phenotypic and intra-clonal heterogeneity, together with plasticity potential of MM might be other contributing factors explaining discrepancies among particular concepts and contributing to the treatment failure.

Functional OCT4-specific CD4+ and CD8+ T cells in healthy controls and ovarian cancer patients

The identification of growth and differentiation pathways that are responsible for the proliferation and survival of cancer stem cells (CSCs) has opened avenues for the discovery of novel therapeutic targets. In the initial phase of an anticancer immune response, T cells specific for tumor-associated antigens develop in patients and, at least under selected circumstances, are able to eliminate malignant cells. However, it remains unknown whether CSC-specific T cells are also operational. We found naturally occurring multifunctional CD4⁺ and CD8⁺ T cells specific for the stem cell marker OCT4 among the peripheral blood mononuclear cells (PBMCs) of both healthy individuals and ovarian cancer patients. Moreover, lymphocytes isolated from the ascites of patients affected by ovarian malignancies also contained OCT4-specific T cells. OCT4-reactive CD4⁺ T cells did not produce interferon γ (IFNγ) and IFNγ-inducible protein 10 (IP-10) but were capable of proliferation upon stimulation with dendritic cells (DCs) loaded with an OCT4-derived peptide or OCT4 mRNA. OCT4-reactive CD8⁺ cells did not proliferate in response to a similar challenge, yet produced IP-10 as well as sufficient amounts of IFNγ to induce IP-10 . Furthermore, CD8⁺ cytotoxic T cells were able to release their lysosomal components, as indicated by the mobilization of CD107a. These results demonstrate the existence of anti-CSC specific T cells in ovarian cancer patients.

Brain cancer immunoediting: novel examples provided by immunotherapy of malignant gliomas

A number of studies in murine models have suggested that the immune system may edit different tumors by forcing their expression profiles so that they escape immune reactions and proliferate. Glioblastoma (GB), the most frequent and aggressive primary brain tumor, provides a good example of this, thanks to the production of numerous immunosuppressive molecules (with TGF-β being of paramount importance), downregulation of the MHC complex and deregulation of the potential for antigen presentation by the surrounding microglia. Given that surgery, radiotherapy and chemotherapy with available protocols have limited effects on the survival of GB patients, different immunotherapy strategies have been developed, based on the use of dendritic cells, antibodies and peptide vaccination. Presently, bevacizumab, a humanized anti-VEGF antibody, provides the most successful example for immune-based treatment of GB, however, its action is limited in time, as the often tumor relapses due to still undefined immunoediting mechanisms. Altered function of EGF receptor-driven pathways is common in GB and is most frequently due to the presence of a deleted form named EGFRvIII, providing a unique cancer epitope that has been targeted by immunotherapy. A recent trial of GB immunotherapy based on vaccination with the EGFRvIII peptide has shown clinical benefit: interestingly most GBs at relapse were negative for EGFRvIII expression, a relevant, direct example of cancer immunoediting. Investigations on the mechanisms of GB immunoediting will lead to an increased understanding of the biology of this malignancy and hopefully provide novel therapeutic targets.

Concise review: transmissible animal tumors as models of the cancer stem-cell process

Tasmanian devil facial tumor disease (DFTD) and canine transmissible venereal tumor (CTVT) are highly unusual cancers capable of being transmitted between animals as an allograft. The concept that these tumors represent a cancer stem-cell process has never been formally evaluated. For each, evidence of self-renewal is found in the natural history of these tumors in the wild, tumor initiation in recipient animals, and serial transplantation studies. Additional data for stem-cell-specific genes and markers in DFTD also exist. Although both tumor types manifest as undifferentiated cancers, immunocytohistochemistry supports a histiocytic phenotype for CTVT and a neural crest origin, possibly a Schwann-cell phenotype, for DFTD. In these data, differential expression of lineage markers is seen which may suggest some capacity for differentiation toward a heterogeneous variety of cell types. It is proposed that DFTD and CTVT may represent and may serve as models of the cancer stem-cell process, but formal investigation is required to clarify this. Appreciation of any such role may act as a stimulus to ongoing research in the pathology of DFTD and CTVT, including further characterization of their origin and phenotype and possible therapeutic approaches. Additionally, they may provide valuable models for future studies of their analogous human cancers, including any putative CSC component.

Ten years of progress in vaccination against cancer: the need to counteract cancer evasion by dual targeting in future therapies

Although cancer immunology has made vigorous progress over the last decade, its future remains uncertain. Tumors have clearly proved subject to immune surveillance, leading to antigenic editing, and means of activating both T and B arms of the immune system have been devised. Therapeutic vaccination and monoclonal antibody therapy have so far proved disappointing, because tumors prove adept at evasion from immune control. Dual targeting could well counteract evasion, provided that the two targets are independent and are attacked simultaneously. This stage has nearly but not quite been reached in several forms of immunotherapy, particularly of B-cell cancers, although such treatment also carries hazards.

Cancer Stem Cells and Pediatric Solid Tumors

Recently, a subpopulation of cells, termed tumor-initiating cells or tumor stem cells (TSC), has been identified in many different types of solid tumors. These TSC, which are typically more resistant to chemotherapy and radiation compared to other tumor cells, have properties similar to normal stem cells including multipotency and the ability to self-renew, proliferate, and maintain the neoplastic clone. Much of the research on TSC has focused on adult cancers. With considerable differences in tumor biology between adult and pediatric cancers, there may be significant differences in the presence, function and behavior of TSC in pediatric malignancies. We discuss what is currently known about pediatric solid TSC with specific focus on TSC markers, tumor microenvironment, signaling pathways, therapeutic resistance and potential future therapies to target pediatric TSC.

T cell-tumor interaction directs the development of immunotherapies in head and neck cancer

The competent immune system controls disease effectively due to induction, function, and regulation of effector lymphocytes. Immunosurveillance is exerted mostly by cytotoxic T-lymphocytes (CTLs) while specific immune suppression is associated with tumor malignancy and progression. In squamous cell carcinoma of the head and neck, the presence, activity, but also suppression of tumor-specific CTL have been demonstrated. Functional CTL may exert a selection pressure on the tumor cells that consecutively escape by a combination of molecular and cellular evasion mechanisms. Certain of these mechanisms target antitumor effector cells directly or indirectly by affecting cells that regulate CTL function. This results in the dysfunction or apoptosis of lymphocytes and dysregulated lymphocyte homeostasis. Another important tumor-escape mechanism is to avoid recognition by dysregulation of antigen processing and presentation. Thus, both induction of functional CTL and susceptibility of the tumor and its microenvironment to become T cell targets should be considered in CTL-based immunotherapy.

Astaxanthin improves stem cell potency via an increase in the proliferation of neural progenitor cells

The present study was designed to investigate the question of whether or not astaxanthin improves stem cell potency via an increase in proliferation of neural progenitor cells (NPCs). Treatment with astaxanthin significantly increased proliferation and colony formation of NPCs. For identification of possible activated signaling molecules involved in active cell proliferation occurring after astaxanthin treatment, total protein levels of several proliferation-related proteins, and expression levels of proliferation-related transcription factors, were assessed in NPCs. In Western blot analysis, astaxanthin induced significant activation of phosphatidylinositol 3-kinase (PI3K) and its downstream mediators in a time-dependent manner. Results of RT-PCR analysis showed upregulation of proliferation-related transcription factors and stemness genes. To estimate the relevance of PI3K and mitogen-activated protein, or extracellular signal-regulated kinase kinase (MEK) signaling pathways in cell growth of astaxanthin-treated NPCs, inhibition assays were performed with LY294002, a specific inhibitor of PI3K, and PD98059, a specific inhibitor of MEK, respectively. These results clearly showed that astaxanthin induces proliferation of NPCs via activation of the PI3K and MEK signaling pathways and improves stem cell potency via stemness acting signals.

T-cell immunotherapy for malignant glioma: toward a combined approach

PURPOSE OF REVIEW

Immunotherapies using T lymphocytes are now considered as promising approaches for treating malignant glioma patients. This review discusses how basic understanding of antitumor T-cell responses in the brain are now leading to the rational planning of such novel therapeutic modalities.

RECENT FINDINGS

Clinical trials show that therapeutic vaccination with defined glioma antigens or dendritic cells pulsed with glioma lysates is feasible and generally well tolerated, but clinical efficacy has yet to be demonstrated in randomized trials. Preclinical data have established that effector T cells can be engineered to more efficiently recognize tumor cells via high-affinity T-cell receptors or chimeric antibody-like receptors. Animal studies have demonstrated that glioma immunotherapy is enhanced if immunosuppressive molecules (including transforming growth factor-beta) and glioma infiltrating regulatory T cells are inactivated. Clinical trials are under way assessing transforming growth factor-beta2 antisense oligonucleotides and regulatory T cell depletion. Combination of any of the above approaches with chemotherapy or radiotherapy is strongly supported by animal and clinical observations.

SUMMARY

Future T-cell immunotherapies will combine different strategies to deliver potent T cells to the glioma bed. The synergy of immunotherapies with radiotherapy and chemotherapy requires optimization, but it is now clear that these modalities are partners and not enemies.

Spontaneous and therapy-induced immunity to pluripotency genes in humans: clinical implications, opportunities and challenges

Recent studies have suggested that the core pathways regulating pluripotency in embryonal stem cells bear considerable overlap with oncogenesis. Here, we discuss recent insights into the capacity of the human immune system to target some of the key pluripotency-associated genes. Immunity to these genes is also induced in humans in the context of chemotherapy-induced cell death in patients with germ cell tumors. Immunologic targeting of pathways associated with stemness has implications for both immune regulation of tumor growth as well as emerging regenerative therapies with embryonal stem cells.

Dueling models in head and neck tumor formation

The two leading models that have been used to explain tumor progression in head and neck squamous cell carcinoma (HNSCC) are the stochastic clonal evolution model, in which many tumor cells are individually capable of recapitulating the entire tumor mass, and the cancer stem hierarchy model, in which only rare totipotential tumor stem cells can recapitulate the tumor. In this issue, Cameron et al use cell surface marker and clonal cell analyses in combination with a xenotransplant approach to provide data that support the stochastic clonal evolution model in HNSCC. This interpretation is subject, however, to limitations inherent in the experimental approach employed. Understanding the basis of tumor progression in HNSCC as well as other cancers should be further explored because of important implications for effective treatments.

Natural immunity to pluripotency antigen OCT4 in humans

OCT4 is a transcription factor critical for the pluripotency of human embryonal stem (ES) and induced pluipotency stem (IPS) cells. OCT4 is commonly expressed in germ-cell tumors as well as putative cancer stem cells in several tumors, and is a key determinant of oncogenic fate in germ-cell tumors. The capacity of the human immune system to recognize this critical stem-cell gene is not known, but has implications for preventing tumors with ES/IPS-based therapies and targeting stem-cell pathways in cancer. Here we show that OCT4-specific T cells can be readily detected in freshly isolated T cells from most (>80%) healthy donors. The reactivity to OCT4-derived peptides resides primarily in the CD45RO(+) memory T-cell compartment and consists predominantly of CD4(+) T cells. T cells reactive against OCT4-derived peptides can be readily expanded in culture using peptide-loaded dendritic cells. In contrast to healthy donors, immunity to OCT4 was detected in only 35% of patients with newly diagnosed germ-cell tumors. However, chemotherapy of germ-cell tumors led to the induction of anti-OCT4 immunity in vivo in patients lacking such responses at baseline. These data demonstrate the surprising lack of immune tolerance to this critical pluripotency antigen in humans. Harnessing natural immunity to this antigen may allow immune-based targeting of pluripotency-related pathways for prevention of cancers, including those in the setting of ES/IPS-based therapies.

Dendritic cell subsets as vectors and targets for improved cancer therapy

Current active immunotherapy trials have shown durable tumor regressions in a fraction of patients. However, the clinical efficacy of current vaccines is limited, possibly because tumors skew the immune system by means of myeloid-derived suppressor cells, inflammatory Type 2 T cells and regulatory T cells (Tregs), all of which prevent the generation of effector cells. To improve the clinical efficacy of cancer vaccines in patients with metastatic disease, we need to design novel and improved strategies that can boost adaptive immunity to cancer, help overcome Tregs and allow the breakdown of the immunosuppressive tumor microenvironment. This can be achieved by exploiting the fast increasing knowledge about the dendritic cell (DC) system, including the existence of distinct DC subsets. Critical to the design of better vaccines is the concept of distinct DC subsets and distinct DC activation pathways, all contributing to the generation of unique adaptive immune responses. Such novel DC vaccines will be used as monotherapy in patients with resected disease and in combination with antibodies and/or drugs targeting suppressor pathways and modulation of the tumor environment in patients with metastatic disease.