Expression of transgenic carcinoembryonic antigen (CEA) in tumor-prone mice: an animal model for CEA-directed tumor immunotherapy

Papilloma-pseudovirus eradicates intestinal tumours and triples the lifespan of ApcMin/+ mice

Inducing tumour-specific adaptive immunity, such as cytotoxic T lymphocyte (CTL) response, can result in promising antitumour effect against several human malignancies, especially in combination with immune checkpoint blockade strategies. However, little is known whether activation of innate immunity can lead to direct tumoricidal effect. Here, we develop a papilloma pseudovirus-based oral immunotherapeutic approach that shows strong tumoricidal effects in the gut, resulting in an almost tripled lifespan of Apc^Min/+ mice (an animal model of human intestinal tumorigenesis). Mechanistically, these pseudoviruses activate the NLRP3 and AIM2 inflammasomes, leading to caspase-1-mediated tumour regression that is dependent on neither cytotoxic T lymphocytes nor humoral immune response. Blocking caspase-1 activation abrogated the therapeutic effects of the pseudoviruses. Thus, targeting innate immune sensors in tumours by the pseudoviruses might represent a strategy to treat intestinal tumours.

Efficient tumor regression by adoptively transferred CEA-specific CAR-T cells associated with symptoms of mild cytokine release syndrome

Carcinoembryonic antigen (CEA) is a cell surface antigen highly expressed in various cancer cell types and in healthy tissues. It has the potential to be a target for chimeric antigen receptor (CAR)-modified T-cell therapy; however, the safety of this approach in terms of on-target/off-tumor effects needs to be determined. To address this issue in a clinically relevant model, we used a mouse model in which the T cells expressing CEA-specific CAR were transferred into tumor-bearing CEA-transgenic (Tg) mice that physiologically expressed CEA as a self-antigen. The adoptive transfer in conjunction with lymphodepleting and myeloablative preconditioning mediated significant tumor regression but caused weight loss in CEA-Tg, but not in wild-type mice. The weight loss was not associated with overt inflammation in the CEA-expressing gastrointestinal tract but was associated with malnutrition, reflected in elevated systemic levels of cytokines linked to anorexia, which could be controlled by the administration of an anti-IL-6 receptor monoclonal antibody without compromising efficacy. The apparent relationship between lymphodepleting and myeloablative preconditioning, efficacy, and off-tumor toxicity of CAR-T cells would necessitate the development of CEA-specific CAR-T cells with improved signaling domains that require less stringent preconditioning for their efficacy. Taken together, these results suggest that CEA-specific CAR-based adoptive T-cell therapy may be effective for patients with CEA⁺ solid tumors. Distinguishing the fine line between therapeutic efficacy and off-tumor toxicity would involve further modifications of CAR-T cells and preconditioning regimens.

Carcinoembryonic antigen related cellular adhesion molecule 1 alleviates dextran sulfate sodium-induced ulcerative colitis in mice

AIMS

To investigate the effects of exogenous carcinoembryonic antigen related cellular adhesion molecule 1 (CEACAM1) on ulcerative colitis (UC) in a dextran sulfate sodium (DSS)-induced mouse model.

MAIN METHODS

UC mice model was induced by administration of DSS in drinking water for 7days. Treatment of CEACAM1 was performed by a transrectal injection of CEACAM1 gene packed adenovirus in the mice. The severity of UC was evaluated using disease activity index and colon length. Histological changes were observed after hematoxylin and eosin staining. ELISA was used to measure secretion of pro-inflammatory cytokines in the colon tissue. The expression of mRNA and protein were detected using real-time PCR and western blotting. The effect of CEACAM1 on epithelial cell restitution was evaluated using wound-healing test in Caco-2 cells.

KEY FINDINGS

CEACAM1 overexpression attenuated the symptoms of UC as evidenced by decreased DAI score, increased colon length and histopathologic score. In addition, exogenous CEACAM1 reduced the levels of inflammatory cytokines and downregulated COX-2 and iNOS expression levels. Moreover, CEACAM1 overexpression decreased colonic permeability by upregulating expression of tight junction proteins. In the in vitro study, exogenous CEACAM1 promoted proliferation and migration of Caco-2 cell.

SIGNIFICANCE

Exogenous CEACAM1 effectively rescues the symptoms of UC in DSS mice through preventing inflammatory responses, improving epithelial barrier and promoting epithelial cells restitution.

Carcinoembryonic antigen-related cell adhesion molecules (CEACAM) 1, 5 and 6 as biomarkers in pancreatic cancer

Background

Aim of this study was to assess the biological function in tumor progression and metastatic process carcinoembryonic antigen-related cell adhesion molecules (CEACAM) 1, 5 and 6 in pancreatic adenocarcinoma (PDAC).

Experimental Design

CEACAM knock down cells were established and assessed in vitro and in a subcutaneous and intraperitoneal mouse xenograft model. Tissue and serum expression of patients with PDAC were assessed by immunohistochemistry (IHC) and by enzyme linked immunosorbent assays.

Results

Presence of lymph node metastasis was correlated with CEACAM 5 and 6 expression (determined by IHC) and tumor recurrence exclusively with CEACAM 6. Patients with CEACAM 5 and 6 expression showed a significantly shortened OS in Kaplan-Meier survival analyses. Elevated CEACAM6 serum values showed a correlation with distant metastasis and. Survival analysis revealed a prolonged OS for patients with low serum CEACAM 1 values. In vitro proliferation and migration capacity was increased in CEACAM knock down PDAC cells, however, mice inoculated with CEACAM knock down cells showed a prolonged overall-survival (OS). The number of spontaneous pulmonary metastasis was increased in the CEACAM knock down group.

Conclusion

The effects mediated by CEACAM expression in PDAC are complex, though overexpression is correlated with loco-regional aggressive tumor growth. However, loss of CEACAM can be considered as a part of epithelial-mesenchymal transition and is therefore of rather importance in the process of distant metastasis.

Expression of a neuroendocrine gene signature in gastric tumor cells from CEA 424-SV40 large T antigen-transgenic mice depends on SV40 large T antigen

BACKGROUND

A large fraction of murine tumors induced by transgenic expression of SV40 large T antigen (SV40 TAg) exhibits a neuroendocrine phenotype. It is unclear whether SV40 TAg induces the neuroendocrine phenotype by preferential transformation of progenitor cells committed to the neuroendocrine lineage or by transcriptional activation of neuroendocrine genes.

METHODOLOGY/PRINCIPAL FINDINGS

To address this question we analyzed CEA424-SV40 TAg-transgenic mice that develop spontaneous tumors in the antral stomach region. Immunohistology revealed expression of the neuroendocrine marker chromogranin A in tumor cells. By ELISA an 18-fold higher level of serotonin could be detected in the blood of tumor-bearing mice in comparison to nontransgenic littermates. Transcriptome analyses of antral tumors combined with gene set enrichment analysis showed significant enrichment of genes considered relevant for human neuroendocrine tumor biology. This neuroendocrine gene signature was also expressed in 424GC, a cell line derived from a CEA424-SV40 TAg tumor, indicating that the tumor cells exhibit a similar neuroendocrine phenotype also in vitro. Treatment of 424GC cells with SV40 TAg-specific siRNA downregulated expression of the neuroendocrine gene signature.

CONCLUSIONS/SIGNIFICANCE

SV40 TAg thus appears to directly induce a neuroendocrine gene signature in gastric carcinomas of CEA424-SV40 TAg-transgenic mice. This might explain the high incidence of neuroendocrine tumors in other murine SV40 TAg tumor models. Since the oncogenic effect of SV40 TAg is caused by inactivation of the tumor suppressor proteins p53 and RB1 and loss of function of these proteins is commonly observed in human neuroendocrine tumors, a similar mechanism might cause neuroendocrine phenotypes in human tumors.

Balancing between antitumor efficacy and autoimmune pathology in T-cell-mediated targeting of carcinoembryonic antigen

Carcinoembryonic antigen (CEA) is intensively studied as a potential target for immunotherapy of colorectal cancers. Although overexpressed by tumors, CEA is also expressed in normal tissues, raising questions about the feasibility and safety of CEA-targeted immunotherapy. We investigated these issues in transgenic mice in which the expression of human CEA in normal tissues closely resembles that in man. Our data show that the T-cell response against CEA in these mice is blunted by both thymic and peripheral tolerance. Consequently, effective tumor targeting is only achieved by adoptive transfer of T cells from nontolerant donors in combination with interventions that eliminate peripheral immune regulatory mechanisms. However, such treatments can result in severe intestinal autoimmune pathology associated with weight loss and mortality. Interestingly, preconditioning of recipient mice by depletion of T-regulatory cells results in immune-mediated tumor control in the absence of toxicity. In this setting, CEA-specific T-cell responses are lower than those induced by toxic regimens and accompanied by additional T-cell responses against non-self antigen. These findings illustrate the importance of testing adoptive immunotherapies targeting self antigens such as CEA in preclinical in vivo models and show that the choice of immune intervention regimen critically determines the balance between therapeutic efficacy and toxicity.

Carcinoembryonic antigen transgenic mouse models for immunotherapy and development of cancer vaccines

The goal of cancer therapy remains as the long-term eradication of tumor cells without adverse effects on normal tissue. Conventional approaches utilizing chemotherapy and radiotherapy are limited by both their toxicity and lack of specificity. In recent years, investigators have carried out several studies designed to evaluate whether human tumor-associated antigens (TAAs) can be exploited as targets for immunotherapy, specifically for human cancer vaccine development. A major limitation in immunotherapy studies of human cancer is the general lack of appropriate preclinical models. Clinical studies can be difficult to implement, particularly when a clear understanding of the potential efficacy, limitation, and safety of an immunotherapeutic strategy is not available from relevant animal investigations. However, mice carrying a transgene for a human tumor self-antigen may provide a more acceptable experimental model in which knowledge about immunotherapeutic strategies aiming at the TAA of interest can be enhanced prior to initiating clinical trials. Since the different strategies in experimental immunotherapy of cancer have been directed to activate different immune system components, a variety of transgenic mouse models have been generated expressing either TAA, human leukocyte antigen (HLA), oncogene, or immune effector cell molecules. These models may serve as an excellent platform for the identification of novel targets for immunotherapy as well as to evaluate the efficacy of targeted therapies and will lead to the development of clinical trials for cancer patients. In this unit, a brief overview of the generation and study of different vaccine approaches in carcinoembryonic antigen (CEA) transgenic mouse models and the experimental findings in mouse models that spontaneously develop gastrointestinal tumors and express the CEA transgene is provided.

Colorectal hyperplasia and dysplasia due to human carcinoembryonic antigen (CEA) family member expression in transgenic mice

CEA and CEACAM6 are immunoglobulin family intercellular adhesion molecules that are up-regulated without structural mutations in approximately 70% of human cancers. Results in in vitro systems showing tumorigenic effects for these molecules suggest that this correlation could indicate an instrumental role in tumorigenesis. To test whether this applies in vivo, transgenic mice harboring 187 kb of the human genome containing four CEA family member genes including the CEA and CEACAM6 genes were created and their copy numbers increased by mating until colonocyte expression levels reached levels seen in human colorectal carcinomas. The colonocyte surface level of integrin alpha5 and the activation of AKT increased progressively with the expression levels of CEA/CEACAM6. Colonic crypts showed a progressive increase in colonocyte proliferation, an increase in crypt fission, and a strong inhibition of both differentiation and anoikis/apoptosis. All transgenic mice showed massively enlarged colons comprising a continuous mosaic of severe hyperplasia, dysplasia and serrated adenomatous morphology. These results suggest that up-regulated non-mutated adhesion molecules could have a significant instrumental role in human cancer.

Relevance, advantages and limitations of animal models used in the development of monoclonal antibodies for cancer treatment

Antibody humanisation through recombinant DNA technology was a key step in allowing monoclonal antibodies (mAbs) to reach the clinic, particularly for the treatment of cancer. As a consequence, they are less adapted to animal studies, although these studies continue to be important tools to study antibody distribution and action at the level of a whole organism. Moreover, preclinical studies in animals are mandatory before the approval of biologics license applications for mAbs by the U.S. Food and Drug Administration (FDA) or European Agency for the Evaluation of Medicinal Products (EMEA). Different parameters should be taken in consideration before starting animal experiments with recombinant mAbs, including antibody cross-reactivity, immunogenicity, pharmacokinetics, and possible interactions with the host immune system. The various interspecies differences are reviewed and discussed in light of the pharmacological properties expected in patients. In doing so, this article aims to provide a critical review of the animal models used in preclinical studies of mAbs for cancer treatment. In particular, their relevance, advantages and limitations will be discussed.

CEACAMs: their role in physiology and pathophysiology

Carcinoembryonic antigen-related cell adhesion molecules (CEACAMs) belong to a group of mammalian immunoglobulin-related glycoproteins. They are involved in cell–cell recognition and modulate cellular processes that range from the shaping of tissue architecture and neovascularization to the regulation of insulin homeostasis and T-cell proliferation. CEACAMs have also been identified as receptors for host-specific viruses and bacteria in mice and humans, respectively, making these proteins an interesting example of pathogen–host co-evolution. Forward and reverse genetics in the mouse now provide powerful novel models to elucidate the action of CEACAM family members in vivo.

Induction of mucosal and systemic immune responses against human carcinoembryonic antigen by an oral vaccine

Carcinoembryonic antigen (CEA) is a tumor-associated antigen targeted for the development of colorectal tumor vaccines. In this study, we developed papillomavirus pseudoviruses encoding the truncated CEA without NH2-terminal signal peptide (PV-CEA) as an oral vaccine to induce CEA-specific CTL responses. In CEA transgenic (CEA-Tg) mice orally immunized with PV-CEA, the immunologic tolerance to CEA as a "self-antigen" was overcome and both mucosal and systemic CEA-specific cytolytic activities were detected by in vitro 51Cr release assays. In a tumor prevention model, the growth rate of CEA+ tumors was significantly delayed in CEA-Tg mice orally immunized with PV-CEA when compared with the control vaccine. Further, the IFN-gamma enzyme-linked ImmunoSPOT and in vitro 51Cr release assay results showed that HLA-A2-restricted, CEA-specific CTL responses were induced in both mucosal and systemic lymphoid tissues in A2 transgenic mice after oral immunization with PV-CEA. Finally, we showed that coadministration of papillomavirus pseudoviruses encoding interleukin-2 with PV-CEA enhanced the generation of A2-restricted, CEA-specific CTLs in aged CEA/A2 double transgenic mice, which were more clinically relevant. Our data suggest that PV-CEA pseudovirus vaccine is a promising oral CEA vaccine for humans to induce CEA-specific CTLs at the site of colorectal tumors (i.e., intestinal mucosa), which might efficiently eliminate CEA+ colorectal tumor cells in the mucosa.

Mouse models expressing human carcinoembryonic antigen (CEA) as a transgene: evaluation of CEA-based cancer vaccines

In recent years, investigators have carried out several studies designed to evaluate whether human tumor-associated antigens might be exploited as targets for active specific immunotherapy, specifically human cancer vaccines. Not too long ago such an approach would have been met with considerable skepticism because the immune system was believed to be a rigid discriminator between self and non-self which, in turn, protected the host from a variety of pathogens. That viewpoint has been challenged in recent years by a series of studies indicating that antigenic determinants of self have not induced absolute host immune tolerance. Moreover, under specific conditions that evoke danger signals, peptides from self-antigen can be processed by the antigen-presenting cellular machinery, loaded onto the major histocompatibility antigen groove to serve as targets for immune intervention. Those findings provide the rationale to investigate a wide range of tumor-associated antigens, including differentiation antigens, oncogenes, and tumor suppressor genes as possible immune-based targets. One of those tumor-associated antigens is the carcinoembryonic antigen (CEA). Described almost 40 years ago, CEA is a M(r) 180-200,000 oncofetal antigen that is one of the more widely studied human tumor-associated antigens. This review will provide: (i) a brief overview of the CEA gene family, (ii) a summary of early preclinical findings on overcoming immune tolerance to CEA, and (iii) the rationale to develop mouse models which spontaneously develop gastrointestinal tumors and express the CEA transgene. Those models have been used extensively in the study of overcoming host immune tolerance to CEA, a self, tumor-associated antigen, and the experimental findings have served as the rationale for the design of early clinical trials to evaluate CEA-based cancer vaccines.

Expression of a natural tumor antigen by thymic epithelial cells impairs the tumor-protective CD4+ T-cell repertoire

A variety of antigens that display a highly tissue-specific expression pattern have recently found to be also expressed in medullary thymic epithelial cells (mTEC). This unique feature of mTEC plays an important role in preventing hazardous autoimmune responses through thymic tolerization of T-cell subsets directed against autoantigens but could also limit the possibility of exploiting tumor-associated antigens for immune-mediated targeting of cancers. Our present study shows that expression of carcinoembryonic antigen (CEA) in thymic epithelial cells of CEA-transgenic mice results in tolerization of a major fraction of the CD4+ T-cell repertoire against this antigen, thereby markedly limiting the effect of CEA-specific immunization against CEA-overexpressing tumors. The expression of CEA in mTEC of CEA-transgenic mice is mirrored by its expression in human mTEC, arguing that promiscuous gene expression in these thymic stromal cells needs to be considered as a potential hurdle for immunotherapies of cancer that target tissue-specific autoantigens.

Pathogenesis of Afa/Dr diffusely adhering Escherichia coli

Over the last few years, dramatic increases in our knowledge about diffusely adhering Escherichia coli (DAEC) pathogenesis have taken place. The typical class of DAEC includes E. coli strains harboring AfaE-I, AfaE-II, AfaE-III, AfaE-V, Dr, Dr-II, F1845, and NFA-I adhesins (Afa/Dr DAEC); these strains (i) have an identical genetic organization and (ii) allow binding to human decay-accelerating factor (DAF) (Afa/Dr(DAF) subclass) or carcinoembryonic antigen (CEA) (Afa/Dr(CEA) subclass). The atypical class of DAEC includes two subclasses of strains; the atypical subclass 1 includes E. coli strains that express AfaE-VII, AfaE-VIII, AAF-I, AAF-II, and AAF-III adhesins, which (i) have an identical genetic organization and (ii) do not bind to human DAF, and the atypical subclass 2 includes E. coli strains that harbor Afa/Dr adhesins or others adhesins promoting diffuse adhesion, together with pathogenicity islands such as the LEE pathogenicity island (DA-EPEC). In this review, the focus is on Afa/Dr DAEC strains that have been found to be associated with urinary tract infections and with enteric infection. The review aims to provide a broad overview and update of the virulence aspects of these intriguing pathogens. Epidemiological studies, diagnostic techniques, characteristic molecular features of Afa/Dr operons, and the respective role of Afa/Dr adhesins and invasins in pathogenesis are described. Following the recognition of membrane-bound receptors, including type IV collagen, DAF, CEACAM1, CEA, and CEACAM6, by Afa/Dr adhesins, activation of signal transduction pathways leads to structural and functional injuries at brush border and junctional domains and to proinflammatory responses in polarized intestinal cells. In addition, uropathogenic Afa/Dr DAEC strains, following recognition of beta(1) integrin as a receptor, enter epithelial cells by a zipper-like, raft- and microtubule-dependent mechanism. Finally, the presence of other, unknown virulence factors and the way that an Afa/Dr DAEC strain emerges from the human intestinal microbiota as a "silent pathogen" are discussed.

A novel transgenic mouse model for immunological evaluation of carcinoembryonic antigen-based DNA minigene vaccines

A lack of relevant animal models has hampered preclinical screening and critical evaluation of the efficacy of human vaccines in vivo. Carcinoembryonic antigen-A2Kb (CEA-A2Kb) double transgenic mice provide a biologically relevant model for preclinical screening and critical evaluation of human CEA vaccine efficacy in vivo, particularly because such animals are peripherally tolerant of CEA. We established the utility of this model by demonstrating that an oral DNA minigene vaccine induces effective HLA-A2-restricted, CEA-specific antitumor CTL responses. This finding is supported by three lines of evidence: (a). an effective HLA-A2-restricted, CEA(691)-specific CTL response; (b). specific in vitro killing of CEA-A2Kb transduced MC-38 colon carcinoma cells; and (c). protective immunity induced in vaccinated mice against challenges of these tumor cells. Importantly, peripheral T cell tolerance against CEA in CEA-A2Kb double transgenic mice was broken by the CEA(691) (IMIGVLVGV) minigene vaccine. In conclusion, CEA-A2Kb double transgenic mice were demonstrated to be good candidates for in vivo testing of human CEA-based vaccines. This result suggests a potential for these vaccines in future human vaccine development. The feasibility of using nonmutated self-antigens as targets for therapeutic vaccinations was indicated, provided that such antigens are presented in an immunogenic context; that is, as a DNA minigene in a bacterial carrier system.

Deregulated expression of the human tumor marker CEA and CEA family member CEACAM6 disrupts tissue architecture and blocks colonocyte differentiation

Human carcinoembryonic antigen (CEA) and the CEA family member CEACAM6 (formerly nonspecific cross-reacting antigen [NCA]) function in vitro, at least, as homotypic intercellular adhesion molecules and, in model systems, can block the terminal differentiation and anoikis of several different cell types. We have recently demonstrated that the increased cell surface levels of CEA and CEACAM6 in purified human colonocytes from freshly excised, well to poorly differentiated colon carcinomas are inversely correlated with the degree of cellular differentiation. Thus, deregulated expression of CEA/CEACAM6 could directly contribute to colon tumorigenesis by the inhibition of terminal differentiation and anoikis. Evidence against this view includes the common observation of increased CEA/CEACAM6 expression as normal colonocytes differentiate in their migration up colonic crypt walls. We report here the direct effects of deregulated overexpression of CEA/CEACAM6, at levels observed in colorectal carcinomas, on the differentiation of two human colonic cell lines, SW-1222 and Caco-2. Stable transfectants of both of these cell lines that constitutively express 10- to 30-fold higher cell surface levels of CEA/CEACAM6 than endogenous levels failed to polarize and differentiate into glandular structures in monolayer or 3D culture or to form colonic crypts in a tissue architecture assay in nude mice. In addition, these transfectants were found to exhibit increased tumorigenicity in nude mice. These results thus support the contention that deregulated overexpression of CEA and CEACAM6 could provide a tumorigenic contribution to colon carcinogenesis.

Deregulated expression of the human tumor marker CEA and CEA family member CEACAM6 disrupts tissue architecture and blocks colonocyte differentiation

Human carcinoembryonic antigen (CEA) and the CEA family member CEACAM6 (formerly nonspecific cross-reacting antigen [NCA]) function in vitro, at least, as homotypic intercellular adhesion molecules and, in model systems, can block the terminal differentiation and anoikis of several different cell types. We have recently demonstrated that the increased cell surface levels of CEA and CEACAM6 in purified human colonocytes from freshly excised, well to poorly differentiated colon carcinomas are inversely correlated with the degree of cellular differentiation. Thus, deregulated expression of CEA/CEACAM6 could directly contribute to colon tumorigenesis by the inhibition of terminal differentiation and anoikis. Evidence against this view includes the common observation of increased CEA/CEACAM6 expression as normal colonocytes differentiate in their migration up colonic crypt walls. We report here the direct effects of deregulated overexpression of CEA/CEACAM6, at levels observed in colorectal carcinomas, on the differentiation of two human colonic cell lines, SW-1222 and Caco-2. Stable transfectants of both of these cell lines that constitutively express 10- to 30-fold higher cell surface levels of CEA/CEACAM6 than endogenous levels failed to polarize and differentiate into glandular structures in monolayer or 3D culture or to form colonic crypts in a tissue architecture assay in nude mice. In addition, these transfectants were found to exhibit increased tumorigenicity in nude mice. These results thus support the contention that deregulated overexpression of CEA and CEACAM6 could provide a tumorigenic contribution to colon carcinogenesis.

Identification of HLA-B27-restricted cytotoxic T lymphocyte epitope from carcinoembryonic antigen

Characterization of epitopes recognized by cytotoxic T lymphocytes (CTLs) in the sequence of tumor antigens is an important step in the development of tumor therapies. Because carcinoembryonic antigen (CEA) is a protein expressed in a high number of epithelial tumors, it is an interesting target to study. We screened for the presence of HLA-B27-restricted CTL epitopes from CEA by studying the binding to HLA-B27 of 31 synthetic peptides predicted to bind to this molecule. This afforded 16 peptides with moderate or high binding affinity. Immunization of HLA-B27 transgenic mice with the best binder peptides yielded 4 immunogenic peptides: CEA(9-17), CEA(9-18), CEA(138-146) and CEA(360-369). However, splenocytes from mice immunized with a vaccinia virus-expressing CEA recognized only CEA(9-18). These CTLs were of the CD8(+) phenotype, which upon stimulation with peptide specifically produced IFN-gamma. Moreover, they did not cross-react against peptides of region 9-18 from proteins of the CEA family. Our results show that CEA(9-18) may induce specific CTL responses against CEA.

Cancer immunotherapy: insights from transgenic animal models

A wide range of strategies in cancer immunotherapy has been developed in the last decade, some of which are currently being used in clinical settings. The development of these immunotherapeutical strategies has been facilitated by the generation of relevant transgenic animal models. Since the different strategies in experimental immunotherapy of cancer each aim to activate different immune system components, a variety of transgenic animals have been generated either expressing tumor associated, HLA, oncogenic or immune effector cell molecule proteins. This review aims to discuss the existing transgenic mouse models generated to study and develop cancer immunotherapy strategies and the variable results obtained. The potential of the various transgenic animal models regarding the development of anti-cancer immunotherapeutical strategies is evaluated.

Antibody targeting studies in a transgenic murine model of spontaneous colorectal tumors

Monoclonal antibodies (mAbs) have been used to treat malignancies in humans with varying degrees of success. Progress has been hindered by the lack of suitable animal models, which would ideally consist of immunocompetent animals that are tolerant to tumor-associated antigens. Suitable models would allow the study and optimization of anti-tumor immunotherapy. We describe a murine model for the study of immunotherapy in colorectal cancers. Carcinoembryonic antigen (CEA) is a cell-surface glycoprotein that is expressed on normal human intestinal epithelium and that is overexpressed in intestinal tumors. Mice that are transgenic for the human CEA gene (CEA.Tg) were crossed with multiple intestinal neoplasia (MIN) mice. MIN mice carry a germline APC mutation and are prone to the development of intestinal adenomas. The offspring from the MIN x CEA.Tg cross developed intestinal adenomas that were shown by immunohistochemistry to overexpress CEA. Pharmacokinetic studies by using (125)I-labeled anti-CEA mAb PR1A3 showed rapid localization of antibody to tissues expressing CEA, especially the gastrointestinal tract. Macroscopic and microscopic radioautographic analysis of the gastrointestinal tracts from MIN/CEA.Tg mice indicated that PR1A3 targeted and was retained in tumors at levels higher than in areas of normal gut. These results demonstrate the utility of the MIN/CEA.Tg mouse as a model for the study of anti-CEA immunotherapy and, furthermore, demonstrate the efficiency of tumor localization by PR1A3.

Tailoring cancer vaccines to the elderly: the importance of suitable mouse models

The incidence of cancer has increased over the last decade, mainly due to an increase in the elderly population. Vaccine therapy for cancer is potentially less toxic than chemotherapy or radiation and could, therefore, be especially effective in older, more frail cancer patients. However, it has been shown that older individuals do not respond to vaccine therapy as well as younger adults. This has been attributed to T cell unresponsiveness, a phenomenon also observed in cancer patients per se. Activation of tumor-specific T cells by cancer vaccines might be an approach, especially suitable for elderly patients, to eradicate or to prevent recurrence of tumors after primary treatment. To tailor pre-clinical testing of vaccine therapies to the elderly, it is important to have mouse models in which tumors develop at equivalent time points in their life span, as in humans. Such models are currently not available. This progress report first summarizes the current knowledge of tumor-immunological parameters potentially involved in T cell unresponsiveness in relation to aging in mice and humans. Secondly, it reviews those cancer vaccines that are known for their potential to induce tumor-specific T cell responses. Thirdly, it discusses the usefulness of currently available mouse models for pre-clinical testing of cancer vaccines applicable to the elderly population. Finally, experimental approaches are proposed, as to how to develop mouse models that allow the induction of specific tumors at will at different ages, expressing tumor-specific antigens in an 'immune competent' environment. These mouse models may teach us how to overcome immune deficits in the elderly, thereby facilitating the development of effective and safe cancer vaccines.

A transgenic mouse line that develops early-onset invasive gastric carcinoma provides a model for carcinoembryonic antigen-targeted tumor therapy

In an attempt to obtain suitable in vivo models for optimizing new tumor therapy strategies for intestinal adenocarcinomas, carcinoembryonic antigen (CEA) promoter/SV40 T antigen gene constructs have been used to generate transgenic mice. One transgenic line (L5496), which contains a 424-bp CEA promoter/SV40 T antigen transgene, exclusively developed multi-focal carcinomas in the pyloric region of the stomach in 100% of the offspring. Tumors were already observable in 37-day-old animals as dysplastic cell foci within the mucosal layer. In 50-day-old mice, the tumor mass was mainly restricted to the mucosa with invasive growth into the submucosal tissue. The animals became moribund at 100-130 days of age due to blockage of the pylorus. At this time, the tumor had penetrated into the duodenum and had invaded all tissue layers within the stomach. In contrast to most other stomach tumor models, this one perfectly matches the development of the most common stomach cancers found in humans. Furthermore, after crossing these mice with mice that are transgenic for the human CEA gene, the double transgenic offspring revealed expression of CEA in the resulting tumors. Thus, as well as being a model for studying gastric carcinoma development and prevention, this system should provide a useful preclinical model for CEA-targeted gastric tumor therapy.

A transgenic mouse line that develops early-onset invasive gastric carcinoma provides a model for carcinoembryonic antigen-targeted tumor therapy

In an attempt to obtain suitable in vivo models for optimizing new tumor therapy strategies for intestinal adenocarcinomas, carcinoembryonic antigen (CEA) promoter/SV40 T antigen gene constructs have been used to generate transgenic mice. One transgenic line (L5496), which contains a 424-bp CEA promoter/SV40 T antigen transgene, exclusively developed multi-focal carcinomas in the pyloric region of the stomach in 100% of the offspring. Tumors were already observable in 37-day-old animals as dysplastic cell foci within the mucosal layer. In 50-day-old mice, the tumor mass was mainly restricted to the mucosa with invasive growth into the submucosal tissue. The animals became moribund at 100-130 days of age due to blockage of the pylorus. At this time, the tumor had penetrated into the duodenum and had invaded all tissue layers within the stomach. In contrast to most other stomach tumor models, this one perfectly matches the development of the most common stomach cancers found in humans. Furthermore, after crossing these mice with mice that are transgenic for the human CEA gene, the double transgenic offspring revealed expression of CEA in the resulting tumors. Thus, as well as being a model for studying gastric carcinoma development and prevention, this system should provide a useful preclinical model for CEA-targeted gastric tumor therapy.

Animal models for tumor localization

Many factors influence the uptake of radiolabeled monoclonal antibodies (mAbs) in tumors. Some are dependent on the antibody, such as affinity, intact immunoglobulin or fragment, route of administration, choice of radio isotope, or method of labeling. Others depend on properties of the tumor, such as site, size, vasculature, and antigen density on the tumor cell surface. Animal models for studying these parameters are usually based on mice or rats bearing transplanted tumors. In this chapter, various tumor model systems will be described with some discussion of what data can be obtained using them.

The role of the epidermal growth factor receptor family in mammary tumorigenesis and metastasis

A number of receptor systems have been implicated to play an important role in the development and progression of many human cancers. The epidermal growth factor (EGF) receptor tyrosine kinase family has been found to consistently play a leading role in tumor progression. Indeed, in human breast cancer cases the prognosis of a patient is inversely correlated with the overexpression and/or amplification of this receptor family. Furthermore, downstream signaling components such as the Src kinases, PI3'K, and the Ras pathway display evidence of deregulation that can accelerate tumor progression. The transgenic mouse system has been ideal in elucidating the biological significance of this receptor family in mammary tumorigenesis. Molecular events involved in mammary tumorigenesis such as ligand binding, receptor dimerization, and the activation of downstream pathways have been addressed using this system. Although there are many molecular steps that appear to drive each stage of tumor development, the EGF receptor family appears to play a causal role in the progression to a transformed phenotype.