Administration of embryonic stem cells generates effective antitumor immunity in mice with minor and heavy tumor load

Recent Findings on Therapeutic Cancer Vaccines: An Updated Review

Cancer remains one of the global leading causes of death and various vaccines have been developed over the years against it, including cell-based, nucleic acid-based, and viral-based cancer vaccines. Although many vaccines have been effective in in vivo and clinical studies and some have been FDA-approved, there are major limitations to overcome: (1) developing one universal vaccine for a specific cancer is difficult, as tumors with different antigens are different for different individuals, (2) the tumor antigens may be similar to the body's own antigens, and (3) there is the possibility of cancer recurrence. Therefore, developing personalized cancer vaccines with the ability to distinguish between the tumor and the body's antigens is indispensable. This paper provides a comprehensive review of different types of cancer vaccines and highlights important factors necessary for developing efficient cancer vaccines. Moreover, the application of other technologies in cancer therapy is discussed. Finally, several insights and conclusions are presented, such as the possibility of using cold plasma and cancer stem cells in developing future cancer vaccines, to tackle the major limitations in the cancer vaccine developmental process.

GPC3 and PEG10 peptides associated with placental gp96 elicit specific T cell immunity against hepatocellular carcinoma

The placenta and tumors can exhibit a shared expression profile of proto-oncogenes. The basis of placenta-derived heat shock protein gp96, which induces prophylactic and therapeutic T cell responses against cancer including hepatocellular carcinoma (HCC), remains unknown. Here, we identified the associated long peptides from human placental gp96 using matrix-assisted laser desorption/ionization-time-of-flight and mass spectrometry and analyzed the achieved proteins through disease enrichment analysis. We found that placental gp96 binds to numerous peptides derived from 73 proteins that could be enriched in multiple cancer types. Epitope-harboring peptides from glypican 3 (GPC3) and paternally expressed gene 10 (PEG10) were the major antigens mediating anti-HCC T cell immunity. Molecular docking analysis showed that the GPC3- and PEG10-derived peptides, mainly obtained from the cytotrophoblast layer of the mature placenta, bind to the lumenal channel and client-bound domain of the gp96 dimer. Immunization with bone marrow-derived dendritic cells pulsed with recombinant gp96-GPC3 or recombinant gp96-PEG10 peptide complex induced specific T cell responses, and T cell transfusion led to pronounced growth inhibition of HCC tumors in nude mice. We demonstrated that the chaperone gp96 can capture antigenic peptides as an efficient approach for defining tumor rejection oncoantigens in the placenta and provide a basis for developing GPC3 and PEG10 peptide-based vaccines against HCC. This study provides insight into the underlying mechanism of the antitumor response mediated by embryonic antigens from fetal tissues, and this will incite more studies to identify potential tumor rejection antigens from placenta.

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.

Human amniotic epithelial cells exert anti-cancer effects through secretion of immunomodulatory small extracellular vesicles (sEV)

We identified here mechanism by which hAECs exert their anti-cancer effects. We showed that vaccination with live hAEC conferred effective protection against murine colon cancer and melanoma but not against breast cancer in an orthotopic cancer cell inoculation model. hAEC induced strong cross-reactive antibody response to CT26 cells, but not against B16F10 and 4T1 cells. Neither heterotopic injection of tumor cells in AEC-vaccinated mice nor vaccination with hAEC lysate conferred protection against melanoma or colon cancer. Nano-sized AEC-derived small-extracellular vesicles (sEV) (AD-sEV) induced apoptosis in CT26 cells and inhibited their proliferation. Co-administration of AD-sEV with tumor cells substantially inhibited tumor development and increased CTL responses in vaccinated mice. AD-sEV triggered the Warburg’s effect leading to Arginine consumption and cancer cell apoptosis. Our results clearly showed that it is AD-sEV but not the cross-reactive immune responses against tumor cells that mediate inhibitory effects of hAEC on cancer development. Our results highlight the potential anti-cancer effects of extracellular vesicles derived from hAEC.

Anti-cancer effects of hAEC depend on cancer type.

Cross-reactive humoral responses do not mediate anti-cancer effects of hAEC.

Anti-cancer effects of hAECs are mainly mediated by small-extracellular vesicles (sEV).

hAEC-derived sEV (AD-sEV) trigger the Warburg’s effect leading to Arginine consumption and cancer cell apoptosis.

AD-sEV substantially inhibits tumor development and increases survival and CTL responses.

Capability of Human Dendritic Cells Pulsed with Autologous Induced Pluripotent Stem Cell Lysate to Induce Cytotoxic T Lymphocytes against HLA-A33-Matched Cancer Cells

Irradiated murine induced-pluripotent stem cells (iPSCs) elicit the antitumor response in vivo. However, it is unclear whether human iPSCs would elicit antitumor effects. In the present study, we investigated the capability of human iPSC lysate (iPSL)-pulsed dendritic cells (DCs) (iPSL/DCs) to induce cancer-responsive cytotoxic T lymphocytes (CTLs) in vitro. iPSCs and DCs were induced from peripheral blood mononuclear cells isolated from a human leukocyte antigen (HLA)-A33 homozygous donor. The iPSL was pulsed with immature DCs, which were then stimulated to allow full maturation. The activated DCs were co-cultured with autologous CTLs and their responses to SW48 colorectal carcinoma cells (HLA-A32/A33), T47D breast cancer cells (HLA-A33/A33), and T98G glioblastoma cells (HLA-A02/A02) were tested with enzyme-linked immunospot (ELISPOT) assays. Comprehensive gene expression analysis revealed that the established iPSCs shared numerous tumor-associated antigens with the SW48 and T47D cells. Immunofluorescent analysis demonstrated that the fluorescent-labeled iPSL was captured by the immature DCs within 2 h. iPSL/DCs induced sufficient CTL numbers in 3 weeks for ELISPOT assays, which revealed that the induced CTLs responded to SW48 and T47D cells. Human iPSL/DCs induced cancer-responsive CTLs on HLA-A33-matched cancer cells in vitro and could be a promising universal cancer vaccine for treating and preventing cancer.

Development of the T-ALLiPSC-based therapeutic cancer vaccines for T-cell acute lymphoblastic leukemia

The T-cell acute lymphoblastic leukemia (T-ALL) is a kind of hematological malignancy in children. Despite the significant improvement in the cure rate of T-ALL upon treatment with chemotherapy regimens, steroids, and allotransplantation there are relapses. This study focuses on the tumor-specific therapeutic vaccines derived from the induced pluripotent stem cells (iPSC) to address the issue of T-ALL recurrence. Patient-derived tumor cells and healthy donor cells were reprogrammed into the iPSCs and the RNA-seq data of the T-ALL-iPSCs and H-iPSCs were analyzed. In vitro, the whole-cell lysate antigens of iPSCs were prepared to induce the dendritic cells (DC) maturation, which in turn stimulated the tumor-specific T cells to kill the T-ALL tumor cells (Jurkat, CCRF-CEM, MOLT-4). The cytotoxic T lymphocyte stimulated by the DC-loaded T-ALL-iPSC-derived antigens showed specific cytotoxicity against the T-ALL cells in vitro. In conclusion, the T-ALL-iPSC-based therapeutic cancer vaccine can elicit a specific anti-tumor effect on T-ALL.

Recent advances in regenerative medicine strategies for cancer treatment

Cancer stands as one of the most leading causes of death worldwide, while one of the most significant challenges in treating it is revealing novel alternatives to predict, diagnose, and eradicate tumor cell growth. Although various methods, such as surgery, chemotherapy, and radiation therapy, are used today to treat cancer, its mortality rate is still high due to the numerous shortcomings of each approach. Regenerative medicine field, including tissue engineering, cell therapy, gene therapy, participate in cancer treatment and development of cancer models to improve the understanding of cancer biology. The final intention is to convey fundamental and laboratory research to effective clinical treatments, from the bench to the bedside. Proper interpretation of research attempts helps to lessen the burden of treatment and illness for patients. The purpose of this review is to investigate the role of regenerative medicine in accelerating and improving cancer treatment. This study examines the capabilities of regenerative medicine in providing novel cancer treatments and the effectiveness of these treatments to clarify this path as much as possible and promote advanced future research in this field.

Cancer Vaccines: Promising Therapeutics or an Unattainable Dream

The advent of cancer immunotherapy has revolutionized the field of cancer treatment and offers cancer patients new hope. Although this therapy has proved highly successful for some patients, its efficacy is not all encompassing and several cancer types do not respond. Cancer vaccines offer an alternate approach to promote anti-tumor immunity that differ in their mode of action from antibody-based therapies. Cancer vaccines serve to balance the equilibrium of the crosstalk between the tumor cells and the host immune system. Recent advances in understanding the nature of tumor-mediated tolerogenicity and antigen presentation has aided in the identification of tumor antigens that have the potential to enhance anti-tumor immunity. Cancer vaccines can either be prophylactic (preventative) or therapeutic (curative). An exciting option for therapeutic vaccines is the emergence of personalized vaccines, which are tailor-made and specific for tumor type and individual patient. This review summarizes the current standing of the most promising vaccine strategies with respect to their development and clinical efficacy. We also discuss prospects for future development of stem cell-based prophylactic vaccines.

Antitumor effects of iPSC-based cancer vaccine in pancreatic cancer

Induced pluripotent stem cells (iPSCs) and cancer cells share cellular similarities and transcriptomic profiles. Here, we show that an iPSC-based cancer vaccine, comprised of autologous iPSCs and CpG, stimulated cytotoxic antitumor CD8⁺ T cell effector and memory responses, induced cancer-specific humoral immune responses, reduced immunosuppressive CD4⁺ T regulatory cells, and prevented tumor formation in 75% of pancreatic ductal adenocarcinoma (PDAC) mice. We demonstrate that shared gene expression profiles of “iPSC-cancer signature genes” and others are overexpressed in mouse and human iPSC lines, PDAC cells, and multiple human solid tumor types compared with normal tissues. These results support further studies of iPSC vaccination in PDAC in preclinical and clinical models and in other cancer types that have low mutational burdens.

•

The iPSC-based cancer vaccine prevents tumor growth in pancreatic cancer

•

The iPSC-based cancer vaccine induces cytotoxic antitumor T cell and B cell responses

•

The iPSC-based cancer vaccine reduces immune-suppressive Treg cells

•

iPSC-cancer signature genes are upregulated in mouse PDAC and human tumors

LncRNA APCDD1L-AS1 induces icotinib resistance by inhibition of EGFR autophagic degradation via the miR-1322/miR-1972/miR-324-3p-SIRT5 axis in lung adenocarcinoma

BACKGROUND

Epidermal growth factor receptor-tyrosinase kinase inhibitor (EGFR-TKI) resistance is the major obstacle in the treatment of lung adenocarcinoma (LUAD) patients harboring EGFR-sensitive mutations. However, the long non-coding RNAs (lncRNAs) related to EGFR-TKIs resistance and their functional mechanisms are still largely unknown. This study aimed to investigate the role and regulatory mechanism of lncRNA APCDD1L-AS1 in icotinib resistance of lung cancer.

METHODS

Molecular approaches including qRT-PCR, MTT assay, colony formation, RNA interference and cell transfection, RNA immunoprecipitation (RIP), dual luciferase reporter assay, RNA fluorescence in situ hybridization, TUNEL assay, flow cytometry, immunoblotting, xenograft model and transcriptome sequencing were used to investigate the mechanism of APCDD1L-AS1 in icotinib resistance.

RESULTS

A novel lncRNA, APCDD1L-AS1 was identified as the most significantly upregulated lncRNA in icotinib-resistant LUAD cells by the transcriptome sequencing and differential lncRNA expression analysis. We found that APCDD1L-AS1 not only promoted icotinib resistance, but also upregulated the protein expression level of EGFR. Mechanistically, APCDD1L-AS1 promoted icotinib resistance and EGFR upregulation by sponging with miR-1322/miR-1972/miR-324-3p to remove the transcription inhibition of SIRT5. Furthermore, SIRT5 elevated EGFR expression and activation by inhibiting the autophagic degradation of EGFR, finally promoting icotinib resistance. Consistently, the autophagy initiator rapamycin could decrease EGFR levels and increase the sensitivity of icotinib-resistant LUAD cells to icotinib.

CONCLUSION

APCDD1L-AS1 could promote icotinib resistance by inhibiting autophagic degradation of EGFR via the miR-1322/miR-1972/miR-324-3p-SIRT5 axis. The combination of autophagy initiator and EGFR-TKIs might serve as a potential new strategy for overcoming EGFR-TKIs resistance in LUAD patients.

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.

Tumorigenic and Immunogenic Properties of Induced Pluripotent Stem Cells: a Promising Cancer Vaccine

Induced pluripotent stem cells (iPSCs) are mainly characterized by their unlimited proliferation abilities and potential to develop into almost any cell type. The creation of this technology has been of great interest to many scientific fields, especially regenerative biology. However, concerns about the safety of iPSC application in transplantation have arisen due to the tumorigenic and immunogenic properties of iPSCs. This review will briefly introduce the developing history of somatic reprogramming and applications of iPSC technology in regenerative medicine. In addition, the review will highlight two challenges to the efficient usage of iPSCs and the underlying mechanisms of these challenges. Finally, the review will discuss the expanding application of iPSC technology in cancer immunotherapy as a potential cancer vaccine and its advantages in auxiliary treatment compared with oncofetal antigen-based and embryonic stem cell (ESC)-based vaccines.

Recent Progress of Stem Cell Therapy in Cancer Treatment: Molecular Mechanisms and Potential Applications

The insufficient and unspecific target of traditional therapeutic approaches in cancer treatment often leads to therapy resistance and cancer recurrence. Over the past decades, accumulating discoveries about stem cell biology have provided new potential approaches to cure cancer patients. Stem cells possess unique biological actions, including self-renewal, directional migration, differentiation, and modulatory effects on other cells, which can be utilized as regenerative medicine, therapeutic carriers, drug targeting, and generation of immune cells. In this review, we emphasize the mechanisms underlying the use of various types of stem cells in cancer treatment. In addition, we summarize recent progress in the clinical applications of stem cells, as well as common risks of this therapy. We finally give general directions for future studies, aiming to improve overall outcomes in the fight against cancer.

Induced Pluripotent Stem Cell-Based Cancer Vaccines

Over a century ago, it was reported that immunization with embryonic/fetal tissue could lead to the rejection of transplanted tumors in animals. Subsequent studies demonstrated that vaccination of embryonic materials in animals induced cellular and humoral immunity against transplantable tumors and carcinogen-induced tumors. Therefore, it has been hypothesized that the shared antigens between tumors and embryonic/fetal tissues (oncofetal antigens) are the key to anti-tumor immune responses in these studies. However, early oncofetal antigen-based cancer vaccines usually utilize xenogeneic or allogeneic embryonic stem cells or tissues, making it difficult to tease apart the anti-tumor immunity elicited by the oncofetal antigens vs. graft-vs.-host responses. Recently, one oncofetal antigen-based cancer vaccine using autologous induced pluripotent stem cells (iPSCs) demonstrated marked prophylactic and therapeutic potential, suggesting critical roles of oncofetal antigens in inducing anti-tumor immunity. In this review, we present an overview of recent studies in the field of oncofetal antigen-based cancer vaccines, including single peptide-based cancer vaccines, embryonic stem cell (ESC)- and iPSC-based whole-cell vaccines, and provide insights on future directions.

Sending Cancer into the Fetal Position

Malignant cells gain the ability to self-renew and reacquire expression of proteins associated with embryonic development. In this issue of Cell Stem Cell, Kooreman et al. (2018) demonstrate that vaccination of mice with syngeneic inactivated iPSCs generates T cell immunity against embryonic antigens and provides resistance to several different types of cancers.

Dendritic cells pulsed with placental gp96 promote tumor-reactive immune responses

Defining and loading of immunogenic and safe cancer antigens remain a major challenge for designing dendritic cell (DC)-based cancer vaccines. In this study, we defined a prototype strategy of using DC-based vaccines pulsed with placenta-derived heat shock protein gp96 to induces anti-tumor T cell responses. Placental gp96 was efficiently taken up by CD11c+ bone marrow-derived DCs (BMDCs) and resulted in moderate BMDC maturation. Splenocytes and cytotoxic T cells (CTLs) generated with mouse BMDCs pulsed with placental gp96 specifically lysed B16 melanoma and LLC lung carcinoma cells. In both transplantable melanoma and lung carcinoma mice models, immunization with placental gp96-stimulated BMDCs led to a significant decrease in tumor growth and mouse mortality with respect to mice treated with liver gp96-pulsed BMDCs or placental gp96 alone. This vaccine induced strong cross-reactive tumor-specific T cell responses. Our results revealed that DCs pulsed with placenta-derived gp96 represent an effective immunotherapy to induce tumor-reactive immune responses, possibly via loading DCs with its associated carcinoembryonic antigens.

Exosomes from GM-CSF expressing embryonic stem cells are an effective prophylactic vaccine for cancer prevention

The antigenic similarity between embryos and tumors has raised the idea of using embryonic material as a preventative vaccine against neoplastic disease. Indeed, we have previously reported that a vaccine comprises allogeneic murine embryonic stem cells (ESCs) and murine fibroblasts expressing GM-CSF (to amplify immune responses) successfully blocks the outgrowth of an implantable cancer (Lewis lung carcinoma; LLC) and lung tumors generated in mice using a combination of a mutagen followed by chronic pulmonary inflammation. However, such a vaccine is obviously impractical for application to humans. The use of fibroblasts to generate GM-CSF is needlessly complicated, and intact whole ESCs carry the hazard of generating embryomas/teratomas. Here, we report the successful application of an alternative prophylactic vaccine comprises exosomes derived from murine ESCs engineered to produce GM-CSF. Vaccination of mice with these exosomes significantly slowed or blocked the outgrowth of implanted LLC while control exosomes lacking GM-CSF were ineffective. Examination of tumor-infiltrating immune cells from mice vaccinated with the GM-CSF-expressing exosomes showed robust tumor-reactive CD8⁺ T effector responses, Th1 cytokine responses, and higher CD8⁺ T effector/CD4⁺CD25⁺Foxp3⁺ T regulatory cell ratio in the tumors. We conclude that a similar vaccine derived from GM-CSF- expressing human ESCs can be employed as a preventative vaccine for humans with an increased risk of developing cancer.

Cancer stem cell surface markers on normal stem cells

The cancer stem cell (CSC) hypothesis has captured the attention of many scientists. It is believed that elimination of CSCs could possibly eradicate the whole cancer. CSC surface markers provide molecular targeted therapies for various cancers, using therapeutic antibodies specific for the CSC surface markers. Various CSC surface markers have been identified and published. Interestingly, most of the markers used to identify CSCs are derived from surface markers present on human embryonic stem cells (hESCs) or adult stem cells. In this review, we classify the currently known 40 CSC surface markers into 3 different categories, in terms of their expression in hESCs, adult stem cells, and normal tissue cells. Approximately 73% of current CSC surface markers appear to be present on embryonic or adult stem cells, and they are rarely expressed on normal tissue cells. The remaining CSC surface markers are considerably expressed even in normal tissue cells, and some of them have been extensively validated as CSC surface markers by various research groups. We discuss the significance of the categorized CSC surface markers, and provide insight into why surface markers on hESCs are an attractive source to find novel surface markers on CSCs.

Vaccination with human amniotic epithelial cells confer effective protection in a murine model of Colon adenocarcinoma

As a prophylactic cancer vaccine, human amniotic membrane epithelial cells (hAECs) conferred effective protection in a murine model of colon cancer. The immunized mice mounted strong cross-protective CTL and antibody responses. Tumor burden was significantly reduced in tumor-bearing mice after immunization with hAECs. Placental cancer immunotherapy could be a promising approach for primary prevention of cancer. In spite of being the star of therapeutic strategies for cancer treatment, the results of immunotherapeutic approaches are still far from expectations. In this regard, primary prevention of cancer using prophylactic cancer vaccines has gained considerable attention. The immunologic similarities between cancer development and placentation have helped researchers to unravel molecular mechanisms responsible for carcinogenesis and to take advantage of stem cells from reproductive organs to elicit robust anti-cancer immune responses. Here, we showed that vaccination of mice with human amniotic membrane epithelial cells (hAECs) conferred effective protection against colon cancer and led to expansion of systemic and splenic cytotoxic T cell population and induction of cross-protective cytotoxic responses against tumor cells. Vaccinated mice mounted tumor-specific Th1 responses and produced cross-reactive antibodies against cell surface markers of cancer cells. Tumor burden was also significantly reduced in tumor-bearing mice immunized with hAECs. Our findings pave the way for potential future application of hAECs as an effective prophylactic cancer vaccine.

Vaccination efficacy with marrow mesenchymal stem cell against cancer was enhanced under simulated microgravity

Stem cell vaccination can induce consistent and strong anti-tumor immunity against cancer in mice model. The antigenic similarity between tumors and embryos has been appreciated for many years and reflects the expression of embryonic gene products by cancer cells and/or cancer-initiating stem cells. Taking advantage of this similarity, we have tested a prophylactic lung cancer vaccine composed of allogeneic murine MSCs. Based on this conception, we first compared their tumor vaccines intervention effects of adult MSCs and MSCs under simulated microgravity (MSC/SMG). In this study, BALB/c mice were vaccinated with MSCs or MSC/SMG, compared with mice vaccinated with phosphate buffered saline (PBS) as negative controls. We then subcutaneously implanted the A549 human lung cancer cell line into vaccinated mice and monitored tumor growth potential in vivo. The smaller tumor size and less tumor weight were observed in mice vaccinated with MSCs or MSC/SMG, compared with that of the Control group. Particularly, it was much more significant in the group of MSC/SMG than that group of the MSCs. Vaccination with SMG treated MSCs inhibited proliferation and promoted apoptosis of tumor tissue. SMG/MSC vaccination induced bothTh1-mediated cytokine response; CD8-dependent cytotoxic response which reduced the proportion of Treg cells. Furthermore, SMG/MSC vaccination significantly increased MHC1 and HSPs proteins expression. In conclusion, we demonstrated the SMG could improve tumor-suppressive activity of MSC. The enhanced anti-tumor immune response of MSCs/SMG was strongly associated with the higher expression of MHC class I molecule on DCs, and the abundance of HSPs in the SMG treated MSCs may make antigens in the MSC more cross-presentable to the host DCs for generating protective antitumor activity. This study gains an insight into the mechanism of MSCs anti-tumor efficacy and gives a new strategy for cancer therapies in the future.

A hepatic stem cell vaccine is superior to an embryonic stem cell vaccine in the prophylaxis and treatment of murine hepatocarcinoma

Stem cells and cancer cells express a common subset of antigens called oncofetal antigens. Theoretically, vaccination with stem cells is effective at boosting the preexisting anticancer immune response. Herein we describe the efficacy of two stem cell-based vaccines in the prophylaxis and treatment of subcutaneous hepatic tumors transplanted into mice. C57BL/6j mice were vaccinated weekly with either hepatic stem cells (HSCs) or embryonic stem cells (ESCs) for three weeks, followed by a subcutaneous challenge with Hepa 1-6 cells at one week (group 1) or four weeks (group 2) after vaccination. No tumor formation was observed in HSC-vaccinated mice when challenged within one week after vaccination (group 1), but tumors formed in 10% of mice in the ESC-vaccinated group and in 60% of mice in the unvaccinated group. When the long-term memory response was examined (group 2), only 10% of HSC-vaccinated mice and 20% of ESC-vaccinated mice developed macroscopic hepatocarcinomas compared to 60% of the unvaccinated mice. Besides their function as prophylactic vaccines, administration of either HSC or ESC could be a potential treatment for cancer. In mice with subcutaneous hepatocarcinomas, complete clearance of tumor burden was observed in 80% of mice receiving HSC vaccination, but 40% of ESC-vaccinated mice presented with tumors that did not increase in size over time. These data support that HSC is a superior vaccine candidate for durable antitumor protection in this hepatocarcinoma model.

Immunobiology and signaling pathways of cancer stem cells: implication for cancer therapy

Cancer stem cells (CSCs) need to survive cancer treatments with a specific end goal to provide new, more differentiated, metastatic-prone cancerous cells. This happens through diverse signals delivered within the tumor microenvironment where ample evidence indicates that altered developmental signaling pathways play an essential role in maintaining CSCs and accordingly the survival and the progression of the tumor itself. This review summarizes findings on the immunobiological properties of CSCs as compared with cancerous non-stem cells involving the expression of immunological molecules, cytokines and tumor antigens as well as the roles of the Notch, Wnt and Hedgehog pathways in the brain, breast and colon CSCs. We concluded that if CSCs are the main driving force behind tumor support and growth then understanding the molecular mechanisms and the immunological properties directing these cells for immune tolerance is of great clinical significance. Such knowledge will contribute to designing better targeted therapies that could prevent tumor recurrence and accordingly significantly improve cancer treatments and patient survival.

Immunotargeting of cancer stem cells

Cancer stem cells (CSCs) represent a distinctive population of tumour cells that control tumour initiation, progression, and maintenance. Their influence is great enough to risk the statement that successful therapeutic strategy must target CSCs in order to eradicate the disease. Because cancer stem cells are highly resistant to chemo- and radiotherapy, new tools to fight against cancer have to be developed. Expression of antigens such as ALDH, CD44, EpCAM, or CD133, which distinguish CSCs from normal cells, together with CSC immunogenicity and relatively low toxicity of immunotherapies, makes immune targeting of CSCs a promising approach for cancer treatment. This review will present immunotherapeutic approaches using dendritic cells, T cells, pluripotent stem cells, and monoclonal antibodies to target and eliminate CSCs.

Cancer vaccines: Looking to the future

These are exciting times for the field of cancer immunotherapy. Although the clinical efficacy of monoclonal antibodies has been demonstrated since the early 1990s, the therapeutic profile of other immunotherapeutic approaches-especially vaccines-has not yet been formally clarified. However, the recent success of several immunotherapeutic regimens in cancer patients has boosted the development of this treatment modality. These achievements stemmed from recent scientific advances demonstrating the tolerogenic nature of cancer and the fundamental role of the tumor immune microenvironment in the suppression of antitumor immunity. New immunotherapeutic strategies against cancer attempt to promote protective antitumor immunity while disrupting the immunoregulatory circuits that contribute to tumor tolerance. Cancer vaccines differ from other anticancer immunotherapeutics in that they initiate the dynamic process of activating the immune system so as to successfully re-establish a state of equilibrium between tumor cells and the host. This article reviews recent clinical trials involving several different cancer vaccines and describes some of the most promising immunotherapeutic approaches that harness antitumor T-cell responses. In addition, we describe strategies whereby cancer vaccines can be exploited in combination with other therapeutic approach to overcome-in a synergistic fashion-tumor immunoevasion. Finally, we discuss prospects for the future development of broad spectrum prophylactic anticancer vaccines.

Placenta-derived gp96 as a multivalent prophylactic cancer vaccine

A major challenge for designing prophylactic cancer vaccines is to define immunogenic and safe cancer antigens. Given the striking similarity of antigen expression patterns between cancer and embryonic tissues, we defined a prototype strategy of using placenta-derived heat shock protein gp96, which induces prophylactic anti-tumor T cell responses. Immunization with placental gp96 provided partial protection and long-term (at least 3 months) anti-tumor immunity against growth of transplantable melanoma or breast tumors in mice, elicited total protection against 7, 12-dimethylbenz(a)-anthracene (DMBA)-induced mammary tumors in rats, and significantly reduced the occurrence and growth of autochthonous breast tumors in HER2 transgenic mice. Placental gp96 activated HER2- and MUC1-specific T cell responses through binding to tumor-associated antigens. Our results reveal the novel immunogenicity of placental gp96 and its potential use as a multivalent cancer vaccine.

Human embryonic stem cells--a potential vaccine for ovarian cancer

OBJECTIVE

To investigate the therapeutic potential of human embryonic stem cells (hESCs) as a vaccine to induce an immune response and provide antitumor protection in a rat model.

METHODS

Cross-reactivity of antigens between hESCs and tumour cells was screened by immunohistochemistry. Fischer 344 rats were divided into 7 groups, with 6 rats in each, immunized with: Group 1, hESC; Group 2, pre-inactivated mitotic NuTu-19; Group 3 PBS; Group 4, hESC; Group 5, pre-inactivated mitotic NuTu-19; Group 6, PBS; Group 7, hESC only. At 1 (Groups 1-3) or 4 weeks (Groups 4-6) after the last vaccination, each rat was challenged intraperitoneally with NuTu-19. Tumor growth and animal survival were closely monitored. Rats immunized with H9 and NuTu- 19 were tested by Western blot analysis of rat orbital venous blood for cytokines produced by Th1 and Th2 cells.

RESULTS

hESCs presented tumour antigens, markers, and genes related to tumour growth, metastasis, and signal pathway interactions. The vaccine administered to rats in Group 1 led to significant antitumor responses and enhanced tumor rejection in rats with intraperitoneal inoculation of NuTu-19 cells compared to control groups. In contrast, rats in Group 4 did not display any elevation of antitumour responses. Western blot analysis found cross-reactivity among antibodies generated between H9 and NuTu-19. However, the cytokines did not show significant differences, and no side effects were detected.

CONCLUSION

hESC-based vaccination is a promising modality for immunotherapy of ovarian cancer.

Antitumor effect of embryonic stem cells in a non-small cell lung cancer model: antitumor factors and immune responses

Research in recent years has revealed that embryonic stem cells (ESCs) could generate obvious antitumor effects in both vitro and vivo. In vitro, ESCs could secrete soluble factors that are capable of blocking cancer cells proliferation, moreover, embryonic microenvironments could effectively inhibit tumorigenesis and metastasis; while in vivo, administration of ESCs in tumor-bearing mice could generate significant antitumor effects by indirectly activating the antitumor immune system. In this study, non-small cell lung cancer cells (Lewis Lung Carcinoma cells, LLCs) and ESCs were co-injected together into mice, after that subcutaneous tumor growth was monitored, cellular and humoral immune responses were detected, and different control groups were set to compare the results in different conditions. Our results suggested that compared to be injected alone, ESCs co-injected with cancer cells could inhibit cancer cell growth more efficiently in vivo, with more CD8+ lymphocytes generated in both peripheral circulation and spleen, and with higher serum anticancer cytokine level (interleukin (IL)-2 and interferon (IFN)-γ). We conclude that the boosted antitumor effects induced by ESCs and cancer cells co-injection may be both the effects of antitumor factors secreted by ESCs and immune responses induced by ESCs in vivo.

Immunogenicity of in vitro maintained and matured populations: potential barriers to engraftment of human pluripotent stem cell derivatives

The potential to develop into any cell type makes human pluripotent stem cells (hPSCs) one of the most promising sources for regenerative treatments. Hurdles to their clinical applications include (1) formation of heterogeneously differentiated cultures, (2) the risk of teratoma formation from residual undifferentiated cells, and (3) immune rejection of engrafted cells. The recent production of human isogenic (genetically identical) induced PSCs (hiPSCs) has been proposed as a "solution" to the histocompatibility barrier. In theory, differentiated cells derived from patient-specific hiPSC lines should be histocompatible to their donor/recipient. However, propagation, maintenance, and non-physiologic differentiation of hPSCs in vitro may produce other, likely less powerful, immune responses. In light of recent progress towards the clinical application of hPSCs, this review focuses on two antigen presentation phenomena that may lead to rejection of isogenic hPSC derivates: namely, the expression of aberrant antigens as a result of long-term in vitro maintenance conditions or incomplete somatic cell reprogramming, and the unbalanced presentation of receptors and ligands involved in immune recognition due to accelerated differentiation. Finally, we discuss immunosuppressive approaches that could potentially address these immunological concerns.

Vaccination with embryonic stem cells generates effective antitumor immunity against ovarian cancer

To date, only a few studies have suggested that human embryonic stem cells (hESCs) might effectively immunize against colon and lung cancer. The purpose of this study was to investigate the therapeutic potential of hESCs as a vaccine to induce widespread antitumor effects in different animal models and various types of cancer. C57BL/6 mice with ID8 ovarian cancer cell and Fischer 344 rats with NuTu-19 ovarian cancer cell models were used. Fifty-four mice were divided into six groups with nine mice in each group. Each mouse was immunized with pre-inactivated hESCs (H9) or mouse embryonic stem cells (mESCs; IVP-ES1) or ID8 or phosphate-buffered saline (PBS). Twenty-four rats were divided into four groups with six rats in each group, each rat immunized with pre-inactivated hESCs (H9) or NuTu-19 or PBS. After the vaccination, each mouse was challenged with live ID8 cells subcutaneously, and each rat was challenged with live NuTu-19 cells intraperitoneally. We discovered that vaccination of mice with the hESC line H9 and the mESC line IVP-ES1 generated consistent cellular and humoral immune responses against ID8 ovarian cancer. H9 and IVP-ES1 vaccinated mice obtained antitumor immune protection, and H9 vaccinated rats had the longest survival time and least distant metastases. No evidence of side-effects was observed. We also compared the immunogenicity against ovarian cancer between the hESC line, H9, and the mESC line, IVP-ES1, that derived from the inner cell mass in different species. We found that there were no significant differences between them. Furthermore, immunohistochemical staining revealed that several oncogenes and tumor suppressor genes, such as HER-2, C-myc, p53, and nm23, were expressed in H9, many of which were also shared by ovarian cancer. hESC vaccines can induce antitumor effects in two animal models and in ovarian cancer, indicating that the activity of the vaccine is universal, and, more importantly, it is safe.

Vaccination with embryonic stem cells protects against lung cancer: is a broad-spectrum prophylactic vaccine against cancer possible?

The antigenic similarity between tumors and embryos has been appreciated for many years and reflects the expression of embryonic gene products by cancer cells and/or cancer-initiating stem cells. Taking advantage of this similarity, we have tested a prophylactic lung cancer vaccine composed of allogeneic murine embryonic stem cells (ESC). Naïve C57BL/6 mice were vaccinated with ESC along with a source of granulocyte macrophage-colony stimulating factor (GM-CSF) in order to provide immunostimulatory adjuvant activity. Vaccinated mice were protected against subsequent challenge with implantable Lewis lung carcinoma (LLC). ESC-induced anti-tumor immunity was not due to a non-specific “allo-response” as vaccination with allogeneic murine embryonic fibroblasts did not protect against tumor outgrowth. Vaccine efficacy was associated with robust tumor-reactive primary and memory CD8⁺ T effector responses, Th1 cytokine response, higher intratumoral CD8⁺ T effector/CD4⁺CD25⁺Foxp3⁺ T regulatory cell ratio, and reduced myeloid derived suppressor cells in the spleen. Prevention of tumorigenesis was found to require a CD8-mediated cytotoxic T lymphocyte (CTL) response because in vivo depletion of CD8⁺ T lymphocytes completely abrogated the protective effect of vaccination. Importantly, this vaccination strategy also suppressed the development of lung cancer induced by the combination of carcinogen administration and chronic pulmonary inflammation. Further refinement of this novel vaccine strategy and identification of shared ESC/tumor antigens may lead to immunotherapeutic options for lung cancer patients and, perhaps more importantly, could represent a first step toward the development of prophylactic cancer vaccines.

Vaccines targeting cancer stem cells: are they within reach?

Increased appreciation of intraclonal heterogeneity of tumors in the past decade has led to the resurgence of the cancer stem cell hypothesis. This hypothesis also has potential implications for immunologic approaches targeting cancer, and it has been suggested that vaccines targeting cancer stem cells may be essential for durable antitumor immunity. Recent studies have provided novel insights into the nature of antigenic targets expressed on putative cancer stem cells and the capacity of both the innate and the adaptive immune system to target these cells, as well as the associated challenges. While the phenotypic properties of cancer stem cells may be plastic, their stemness and capacity for self-renewal may depend on a limited set of genes. Several of these genes overlap with those regulating stemness in embryonal stem cells and are also emerging as potential oncogenes in some cancers. Immunologic approaches targeting stemness-associated pathways in cancer may provide an important strategy for the prevention of diverse cancers, including those occurring in the context of regenerative therapies.

Effective colon cancer prophylaxis in mice using embryonic stem cells and carbon nanotubes

Introduction

In recent years, a new concept of an anticancer vaccine has been proposed to prevent and control the proliferation and expansion of cancer cells by eliciting an immune boost in biological systems. The recent literature supports the role of embryonic stem cells (ESC) as cellular agents that stimulate the biological systems to destroy cancer cells. However, at present, a true anticancer vaccine remains elusive. There are several lines of evidence showing that carbon nanotubes may be used to initiate and maintain immune responses.

Objective

The authors proposed to test the therapeutic potential of multiwalled carbon nanotubes (MWCNTs) combined with ESC as agents to induce an immune boost and provide subsequent anticancer protection in mice.

Methods

C57 BL/6 mice were immunized with ESC and MWCNTs.

Results

The proposed vaccine led to significant antitumor responses and enhanced tumor rejection in mice with subcutaneous inoculation of MC38 colon malign cells compared with groups only administered ESC, only MWCNTs, and controls.

Conclusion

The application and potential of ESC combined with MWCNTs as anticancer immunization agents may represent the beginning of a new chapter in the treatment of colon cancer.

Potential barriers to therapeutics utilizing pluripotent cell derivatives: intrinsic immunogenicity of in vitro maintained and matured populations

The potential to develop into any tissue makes pluripotent stem cells (PSCs) one of the most promising sources for cellular therapeutics. However, numerous hurdles exist to their clinical applications, three of the most concerning include the inability to separate therapeutic population from heterogeneously differentiated cultures, the risk of teratoma formation from residual pluripotent cells, and immunologic rejection of engrafted cells. The recent development of induced PSCs has been proposed as a solution to the histocompatibility barrier. Theoretically, creation of patient-specific induced PSC lines would exhibit a complete histocompatibility antigen match. However, regardless of the PSC source, in vitro propagation and nonphysiologic differentiation may result in other, likely less powerful, mechanisms of immune rejection. In light of recent progress towards clinical application, this review focuses on two such potential immunologic mechanisms applicable to isogenic PSC derivates: namely, the immunogenicity of aberrant antigens resulting from long-term in vitro maintenance and alterations in immunologic properties due to rapid in vitro differentiation. These issues will be considered with attention to their relation to effector cells in the adult immune system. In addition, we highlight immunosuppressive approaches that could potentially address the immunogenicity of these proposed mechanisms.