Regulation of hepatic fibrosis by carcinoembryonic antigen-related cell adhesion molecule 1

OBJECTIVE

NAFLD is a complex disease marked by cellular abnormalities leading to NASH. NAFLD patients manifest low hepatic levels of CEACAM1, a promoter of insulin clearance. Consistently, Cc1^-/- null mice displayed spontaneous hyperinsulinemia/insulin resistance and steatohepatitis. Liver-specific reconstitution of Ceacam1 reversed these metabolic anomalies in 8-month-old Cc1^-/-xliver+ mice fed a regular chow diet. The current study examined whether it would also reverse progressive hepatic fibrosis in mice fed a high-fat (HF) diet.

METHODS

3-Month-old mice were fed a high-fat diet for 3-5 months, and metabolic and histopathological analysis were conducted to evaluate their NASH phenotype.

RESULTS

Reconstituting CEACAM1 to Cc1^-/- livers curbed diet-induced liver dysfunction and NASH, including macrovesicular steatosis, lobular inflammation, apoptosis, oxidative stress, and chicken-wire bridging fibrosis. Persistence of hepatic fibrosis in HF-fed Cc1^-/- treated with nicotinic acid demonstrated a limited role for lipolysis and adipokine release in hepatic fibrosis caused by Ceacam1 deletion.

CONCLUSIONS

Restored metabolic and histopathological phenotype of HF-fed Cc1^{-/-xliver+xliver+} assigned a critical role for hepatic CEACAM1 in preventing NAFLD/NASH including progressive hepatic fibrosis.

Introduction to the CEA Family: Structure, Function and Secretion

Due to the phenomenal progress in the field of tumor immunology that took place during the last twenty years, we dispose today of highly specific and sensitive techniques and reagents like monoclonal antibodies (MAbs). In this context the discovery in human carcinomas of tumor-associated antigens, such as CEA, was of primary importance, especially since the latter was found to have clinical relevance as a tumor marker. Based on animal models, a new in vivo technology for the detection of tumors and metastases was developed in recent years, that uses anti-CEA MAbs, or fragments of them, coupled to radio-isotopes. This technique, called radioimmunodetection (RAID), also paved the way for immunotherapeutic procedures, where again CEA served as the target-antigen. This new technique holds great promise, provided the epitope-specificity of the MAbs is well-controlled: it has been shown that CEA belongs to a large gene-family of at least 22 members, which can be subdivided into two subgroups (i.e., the CEA- and the PSG-subgroup) and which in turn belongs to the immunoglobulin-supergene family. Great structural similarities render the distinction of the various cross-reactive molecules by immunological means rather difficult.

CEA and NCA Expressed by Colon Carcinoma Cells Affect their Interaction with and Lysability by Activated Lymphocytes

Heterogeneous lysability by interleukin-2 activated lymphocytes (LAK) and other immune effectors was observed in the human colon-carcinoma lines LoVo/Dx, LoVo/H and HT29. The tumor cells with high susceptibility to LAK (LoVo/Dx, HT29) expressed higher amounts of the adhesion molecules ICAMl, LFA3 and NCA/CEA than cells with low LAK sensitivity (LoVo/H). Monoclonal antibodies against these molecules caused a marked reduction of lysis by LAK of LoVo/Dx and HT29. A pool of these antibodies induced a nearly complete inhibition of the LAK lysis of both lines. Treatment of LoVo/Dx with differentiating agents (dimethylformamide and retinoic acid) led to a decreased expression of the adhesion molecules, including NCA, accompanied by increased resistance to LAK-mediated lysis. Moreover, the presence of CEA soluble antigen drastically inhibited the cytotoxic activity of LAK effectors against HT29 and LoVo/Dx cells, in a dose-dependent manner. These data indicate that sensitivity of colon-carcinoma cells to activated lymphocytes depends on the level of expression of adhesion molecules, including CEA and NCA. Given the role of CEA-related antigens in tumor/lymphocyte interaction, soluble CEA, frequently released by colon-carcinoma, may be involved in immunosuppressive effects induced in vivo by tumor cells.

The CEA Family: A System in Transitional Evolution?

The CEA family consists of two structurally and functionally distinct subgroups; the group including CEA, NCA and CGM-6 which are cell surface-bound by phosphatidylinositol (PI) linkages, and the group of BGP splice variants which have transmembrane and cytoplasmic domains. Although all CEA family members mediate intercellular adhesion in vitro, the PI-linked group show Ca++ and temperature independent adhesion whereas the BGP group show rapidly reversible Ca++ and temperature dependent adhesion. From the close alignment in cDNA nucleotide sequences between family members and between repeated domains in one family member, it is apparent that the CEA family is now rapidly evolving; in fact, analogs of only the transmembrane BGP group have been found so far in the mouse. The addition of a new group of potent adhesion molecules to complex species at some time after the rodent radiation has strong evolutional implications, which are discussed.

Whole liver CT texture analysis to predict the development of colorectal liver metastases-A multicentre study

OBJECTIVES

CT texture analysis has shown promise to differentiate colorectal cancer patients with/without hepatic metastases.

AIM

To investigate whether whole-liver CT texture analysis can also predict the development of colorectal liver metastases.

MATERIAL AND METHODS

Retrospective multicentre study (n=165). Three subgroups were assessed: patients [A] without metastases (n=57), [B] with synchronous metastases (n=54) and [C] who developed metastases within ≤24 months (n=54). Whole-liver texture analysis was performed on primary staging CT. Mean grey-level intensity, entropy and uniformity were derived with different filters (σ0.5-2.5). Univariable logistic regression (group A vs. B) identified potentially predictive parameters, which were tested in multivariable analyses to predict development of metastases (group A vs. C), including subgroup analyses for early (≤6 months), intermediate (7-12 months) and late (13-24 months) metastases.

RESULTS

Univariable analysis identified uniformity (σ0.5), sex, tumour site, nodal stage and carcinoembryonic antigen as potential predictors. Uniformity remained a significant predictor in multivariable analysis to predict early metastases (OR 0.56). None of the parameters could predict intermediate/late metastases.

CONCLUSIONS

Whole-liver CT-texture analysis has potential to predict patients at risk of developing early liver metastases ≤6 months, but is not robust enough to identify patients at risk of developing metastases at later stage.

[Predictive value of combination detection of tissue Pgp1 expression and preoperative serum CEA level for colorectal cancer]

OBJECTIVE

To explore the predictive value of combination detection of Pgp1 expression in cancer tissue and serum CEA level for the prognosis of colorectal cancer (CRC) patients.

METHODS

Clinicopathological data, complete 5-year follow-up data and CRC tissue samples of 153 CRC patients with stage I( to II( tumor undergoing radical operation in our department from January 2004 to August 2006 were retrospectively collected. Immunohistochemical staining was used to detect the expression level of Pgp1. The combined evaluation of staining intensity and positive cell percentage was performed to determine the expression level of Pgp1. Pgp1 staining (-) and (+) was defined as low expression; and staining (++) and (+++) as high expression. Electrochemiluminescence immunoassay was used to detect the level of serum CEA. CEA > 5 μg/L was defined as positive. χ² and Fisher's exact test were performed to analyze the association of Pgp1 expression with CEA level and clinicopathological variables. Moreover, Kaplan-Meier method was used to analyze the survival. Univariate and multivariate Cox proportional hazard regression models were used to evaluate the roles of Pgp1 expression combined with serum CEA level in prognosis prediction.

RESULTS

Of 153 patients, 105 were males and 48 females with mean age of 59 (27 to 90) years; 41 cases were rectal cancer, and 112 cases colon cancer; 23 patients were TNM stage I( tumor, and 130 patients stage II( tumor; median follow-up time was 64 months; 30 cases were dead. Positive rate of Pgp1 expression in colorectal cancer tissues was 66.0%(101/153). The expression of Pgp1 was associated with gender, tumor location, and survival during the follow-up (all P<0.05). The preoperative positive rate of serum CEA was 28.1% (43/153). The preoperative serum CEA level was associated with tumor recurrence and survival (all P<0.05). Kaplan-Meier analysis showed the overall 5-year survival rate was 81.7%. The 5-year survival rate of patients with high expression of Pgp1 was 88.1%, which was significantly higher than 69.2% of those with low expression of Pgp1(P=0.003). The 5-year survival rate of patients with preoperative positive serum CEA was 72.1%, which was significantly lower than 86.1% of those with preoperative negative serum CEA(P=0.023). Furthermore, the 5-year survival rate of patients with negative Pgp1 plus positive CEA was 66.7%, which was significantly lower than 91.0% of those with positive Pgp1 plus negative CEA(P=0.002). Univariate analysis showed that gender, Pgp1 expression level, preoperative serum CEA level, and Pgp1 combined with CEA were significantly associated with the prognosis of patients(all P<0.05). Multivariate analysis showed that Pgp1 expression was an independent prognostic factor of CRC [HR(95%CI:1.261 to 64.224), P=0.028].

CONCLUSIONS

Low expression of Pgp1 in cancer tissue indicates poor prognosis in patients with stage I( and II( tumor. Combination detection of Pgp1 expression and serum CEA can be applied to predict the prognosis of patients with stage I( and II( colorectal cancer.

[TSST-1 regulated synergistically by 5HRE and CEAp activates lymphocytes to kill CEA-positive tumor cells specifically]

AIM

To evaluate the inhibitory effect of lymphocytes activated by the superantigen of toxic shock syndrome toxin-1 (TSST-1), which is regulated synergistically by 5 copies of hypoxia-responsive element (5HRE) and promoter of carcino-embryonic antigen (CEAp), against the carcino-embryonic antigen (CEA)-positive human colon carcinoma cell line LoVo under hypoxia condition in vitro.

METHODS

The eukaryotic expressive vector was constructed with the transmembrane superantigen gene of 5HRE-CEAp-regulated TSST-1-linker-CD80TM, and was transfected into CEA-positive human colon carcinoma cell line LoVo and CEA-negative human cervical carcinoma cell line HeLa by Lipofectamine 2000. Stably transfected cell lines were selected by G418. RT-PCR was employed to examine the expression of TC mRNA. Peripheral blood lymphocytes(PBL) of healthy people were extracted and then activated by the lysates of tumor cells stably transfected with TC. Concurrently, PBL were cultured together with stably transfected tumor cells in order to kill these cells. Then the proliferative effect of TSST-1 on PBL, and the killing effect of PBL against the stably transfected tumor cells were detected by MTT.

RESULTS

Monoclonal LoVo and HeLa cells stably transfected with TC were successfully obtained. Expression of TC mRNA in monoclonal LoVo cells under hypoxia condition was significantly higher than those under normoxia condition as confirmed by RT-PCR. Monoclonal HeLa cells did not express TC under either hypoxia condition or normoxia condition. As is shown by MTT assay, TSST-1 expressed by the monoclonal LoVo cells could effectively activate PBL to proliferate under hypoxia condition, resulting in dose-dependent inhibition on the proliferation of LoVo cells that expressed TSST (P<0.05). But HeLa cells and wild LoVo cells could not activate PBL to proliferate. PBL could not inhibit proliferation of HeLa cells and wild LoVo cells, either.

CONCLUSION

The superantigen of TSST-1 regulated dually by 5HRE and CEAp could activate human PBL to kill CEA-positive tumor cells specifically under hypoxia condition.

Heparan sulfate is a binding molecule but not a receptor for CEACAM1-independent infection of murine coronavirus

A highly neurovirulent mouse hepatitis virus (MHV) JHMV strain (wt) with receptor (MHVR)-independent infection activity and its low-virulent mutant srr7 without such activity were found to attach to MHVR-negative, non-permissive BHK cells. To identify the molecule that interacts with JHMV, we focused on heparan sulfate (HS) since it works as a receptor of a mutant MHV-rec1 that infects in an MHVR-independent fashion. The present study indicates that HS interacts with both wt JHMV and srr7 but it does not function as an entry receptor as it apparently does for MHV-rec1. Furthermore, HS failed to serve as an entry receptor in the MHVR-independent infection of wt JHMV, indicating that HS is not a host factor that wt JHMV utilizes in an MHVR-independent infection.

Carcinoembryonic antigen-stimulated THP-1 macrophages activate endothelial cells and increase cell–cell adhesion of colorectal cancer cells

The liver is the most common site for metastasis by colorectal cancer, and numerous studies have shown a relationship between serum carcinoembryonic antigen (CEA) levels and metastasis to this site. CEA activates hepatic macrophages or Kupffer cells via binding to the CEA receptor (CEA-R), which results in the production of cytokines and the up-regulation of endothelial adhesion molecules, both of which are implicated in hepatic metastasis. Since tissue macrophages implicated in the metastatic process can often be difficult to isolate, the aim of this study was to develop an in vitro model system to study the complex mechanisms of CEA-induced macrophage activation and metastasis. Undifferentiated, human monocytic THP-1 (U-THP) cells were differentiated (D-THP) to macrophages by exposure to 200 ng/ml phorbol myristate acetate (PMA) for 18 h. Immunohistochemistry showed two CEA-R isoforms present in both U- and D-THP cells. The receptors were localized primarily to the nucleus in U-THP cells, while a significant cell-surface presence was observed following PMA-differentiation. Incubation of D-THP-1 cells with CEA resulted in a significant increase in tumor necrosis factor-alpha (TNF-alpha) release over 24 h compared to untreated D-THP-1 or U-THP controls confirming the functionality of these cell surface receptors. U-THP cells were unresponsive to CEA. Attachment of HT-29 cells to human umbilical vein endothelial cells significantly increased at 1 h after incubation with both recombinant TNF-alpha and conditioned media from CEA stimulated D-THP cells by six and eightfold, respectively. This study establishes an in vitro system utilizing a human macrophage cell line expressing functional CEA-Rs to study activation and signaling mechanisms of CEA that facilitate tumor cell attachment to activated endothelial cells. Utilization of this in vitro system may lead to a more complete understanding of the expression and function of CEA-R and facilitate the design of anti-CEA-R therapeutic modalities that may significantly diminish the metastatic potential of CEA overexpressing colorectal tumors.

Evolution of a tumorigenic property conferred by glycophosphatidyl-inositol membrane anchors of carcinoembryonic antigen gene family members during the primate radiation

GPI membrane anchors of cell surface glycoproteins have been shown to confer functional properties that are different from their transmembrane (TM)-anchored counterparts. For the human carcinoembryonic antigen (CEA) family, a subfamily of the immunoglobulin superfamily, conversion of the mode of membrane linkage from TM to GPI confers radical changes in function: from tumor suppression or neutrality toward inhibition of differentiation and anoikis and distortion of tissue architecture, thereby contributing to tumorigenesis. We show here that GPI anchorage in the CEA family evolved twice independently in primates, very likely from more primitive TM anchors, by different packages of mutations. Both mutational packages, one package found in many primates, including humans, and a second, novel package found only in the Cebidae radiation of New World monkeys, give rise to efficiently processed GPI-linked proteins. Both types of GPI anchors mediate inhibition of cell differentiation. The estimated rate of nonsynonymous mutations (Ka) in the anchor-determining domain for conversion from TM to GPI anchorage in the CEA family that were fixed during evolution in these primates is 7 times higher than the average Ka in primates, indicating positive selection. These results suggest therefore that the functional changes mediated by CEA GPI anchors, including the inhibition of differentiation and anoikis, could be adaptive and advantageous.

In vivo selection for Neisseria gonorrhoeae opacity protein expression in the absence of human carcinoembryonic antigen cell adhesion molecules

The neisserial opacity (Opa) proteins are phase-variable, antigenically distinct outer membrane proteins that mediate adherence to and invasion of human cells. We previously reported that Neisseria gonorrhoeae Opa protein expression appeared to be selected for or induced during experimental murine genital tract infection. Here we further defined the kinetics of recovery of Opa variants from the lower genital tracts of female mice and investigated the basis for this initial observation. We found that the recovery of different Opa phenotypes from mice appears cyclical. Three phases of infection were defined. Following intravaginal inoculation with primarily Opa- gonococci, the majority of isolates recovered were Opa+ (early phase). A subsequent decline in the percentage of Opa+ isolates occurred in a majority of mice (middle phase) and was followed by a reemergence of Opa+ variants in mice that were infected for longer than 8 days (late phase). We showed the early phase was due to selection for preexisting Opa+ variants in the inoculum by constructing a chloramphenicol-resistant (Cm(r)) strain and following Cm(r) Opa+ populations mixed with a higher percentage of Opa- variants of the wild-type (Cm(s)) strain. Reciprocal experiments (Opa- Cm(r) gonococci spiked with Opa+ Cm(s) bacteria) were consistent with selection of Opa+ variants. Based on the absence in mice of human carcinoembryonic antigen cell adhesion molecules, the major class of Opa protein adherence receptors, we conclude the observed selection for Opa+ variants early in infection is not likely due to a specific adherence advantage and may be due to Opa-mediated evasion of innate defenses.

Redirecting coronavirus to a nonnative receptor through a virus-encoded targeting adapter

Murine hepatitis coronavirus (MHV)-A59 infection depends on the interaction of its spike (S) protein with the cellular receptor mCEACAM1a present on murine cells. Human cells lack this receptor and are therefore not susceptible to MHV. Specific alleviation of the tropism barrier by redirecting MHV to a tumor-specific receptor could lead to a virus with appealing properties for tumor therapy. To demonstrate that MHV can be retargeted to a nonnative receptor on human cells, we produced bispecific adapter proteins composed of the N-terminal D1 domain of mCEACAM1a linked to a short targeting peptide, the six-amino-acid His tag. Preincubation of MHV with the adapter proteins and subsequent inoculation of human cells expressing an artificial His receptor resulted in infection of these otherwise nonsusceptible cells and led to subsequent production of progeny virus. To generate a self-targeted virus able to establish multiround infection of the target cells, we subsequently incorporated the gene encoding the bispecific adapter protein as an additional expression cassette into the MHV genome through targeted RNA recombination. When inoculated onto murine LR7 cells, the resulting recombinant virus indeed expressed the adapter protein. Furthermore, inoculation of human target cells with the virus resulted in a His receptor-specific infection that was multiround. Extensive cell-cell fusion and rapid cell killing of infected target cells was observed. Our results show that MHV can be genetically redirected via adapters composed of the S protein binding part of mCEACAM1a and a targeting peptide recognizing a nonnative receptor expressed on human cells, consequently leading to rapid cell death. The results provide interesting leads for further investigations of the use of coronaviruses as antitumor agents.

GPI-anchored CEA family glycoproteins CEA and CEACAM6 mediate their biological effects through enhanced integrin α5β1-fibronectin interaction

Carcinoembryonic antigen (CEA) and CEA family member CEACAM6 are glycophosphatidyl inositol (GPI)-anchored, intercellular adhesion molecules that are up-regulated in a wide variety of human cancers, including colon, breast, and lung. When over-expressed in a number of cellular systems, these molecules are capable of inhibiting cellular differentiation and anoikis, as well as disrupting cell polarization and tissue architecture, thus increasing tumorigenicity. The present study shows that perturbation of the major fibronectin receptor, integrin alpha5beta1, underlies some of these biological effects. Using confocal microscopy and specific antibodies, CEA and CEACAM6 were demonstrated to co-cluster with integrin alpha5beta1 on the cell surface. The presence of CEA and CEACAM6 was shown to lead to an increase in the binding of the integrin alpha5beta1 receptor to its ligand fibronectin, without changing its cell surface levels, resulting in increased adhesion of CEA/CEACAM6-expressing cells to fibronectin. More tenacious binding of free fibronectin to cells led to enhanced fibronectin matrix assembly and the formation of a polymerized fibronectin "cocoon" around the cells. Disruption of this process with specific monoclonal antibodies against either fibronectin or integrin alpha5beta1 led to the restoration of cellular differentiation and anoikis in CEA/CEACAM6 producing cells.

[The carcinoembryonic antigen: apropos of an old friend]

The carcinoembryonic antigen (CEA) is glycoprotein localized in the apical surface of mature enterocytes. The members of the CEA gene family are clustered on chromosome 19q13.2. It is formed by 29 genes, of which 18 are expressed. Many functions of CEA have been known in healthy indiuiduals, however its role as cell adhesion molecule is the most studied. Besides the colon, CEA is expressed in the stomach, tongue, oesophagus, cervix, and prostate. The most important clinical function is in colorectal, gastric and ovary cancer. It is used as prognosis marker, staging system, recurrence, treatment response and liver metastases. There are many non-neoplasic diseases that enhance CEA value. Actually, CEA is being studying as target of immunotherapy.

Carcinoembryonic antigen (CEA) inhibits NK killing via interaction with CEA-related cell adhesion molecule 1

The NK killing activity is regulated by activating and inhibitory NK receptors. All of the activating ligands identified so far are either viral or stress-induced proteins. The class I MHC proteins are the ligands for most of the inhibitory NK receptors. However, in the past few years, several receptors have been identified that are able to inhibit NK killing independently of class I MHC recognition. We have previously demonstrated the existence of a novel inhibitory mechanism of NK cell cytotoxicity mediated by the homophilic carcinoembryonic Ag (CEA)-related cell adhesion molecule 1 (CEACAM1) interactions. In this study, we demonstrate that CEACAM1 also interacts heterophilically with the CEA protein. Importantly, we show that these heterophilic interactions of CEA and CEACAM1 inhibit the killing by NK cells. Because CEA is expressed on a wide range of carcinomas and commonly used as tumor marker, these results represent a novel role for the CEA protein enabling the escape of tumor cells from NK-mediated killing. We further characterize, for the first time, the CEACAM1-CEA interactions. Using functional and binding assays, we demonstrate that the N domains of CEACAM1 and CEA are crucial but not sufficient for both the CEACAM1-CEACAM1 homophilic and CEACAM1-CEA heterophilic interactions. Finally, we suggest that the involvement of additional domains beside the N domain in the heterophilic and homophilic interactions is important for regulating the balance between cis and trans interactions.

Induction of an antigen cascade by diversified subcutaneous/intratumoral vaccination is associated with antitumor responses

PURPOSE

Cancer vaccines targeting tumor-associated antigens are being investigated for the therapy of tumors. Numerous strategies, including the direct intratumoral (i.t.) vaccination route, have been examined. For tumors expressing carcinoembryonic antigen (CEA) as a model tumor-associated antigen, we previously designed poxviral vectors that contain the transgenes for CEA and a triad of T-cell costimulatory molecules, B7-1, intercellular adhesion molecule-1, (ICAM-1), and leukocyte function associated antigen-3 (LFA-3) (CEA/TRICOM). Two types of poxvirus vectors were developed: replication-competent recombinant vaccinia and replication-defective recombinant fowlpox. We have shown previously that a vaccine regimen composed of priming mice s.c. with recombinant vaccinia-CEA/TRICOM and boosting i.t. with recombinant fowlpox-CEA/TRICOM was superior to priming and boosting vaccinations using the conventional s.c. route in inducing T-cell responses specific for CEA. These studies also showed that CEA was needed to be present both in the vaccine and in the tumor for therapeutic effects.

EXPERIMENTAL DESIGN

To determine specific immune responses associated with vaccination-mediated tumor regression, CEA-transgenic mice bearing CEA(+) tumors were vaccinated with the CEA/TRICOM s.c./i.t. regimen, and T-cell immune responses were assessed.

RESULTS

In CEA(+) tumor-bearing mice vaccinated with the CEA/TRICOM s.c./i.t. regimen, T-cell responses could be detected not only to CEA encoded in vaccine vectors but also to other antigens expressed on the tumor itself: wild-type p53 and an endogenous retroviral epitope of gp70. Moreover, the magnitude of CD8(+) T-cell immune responses to gp70 was far greater than that induced to CEA or p53. Finally, the predominant T-cell population infiltrating the regressing CEA(+) tumor after therapy was specific for gp70.

CONCLUSION

These studies show that the breadth and magnitude of antitumor immune cascades to multiple antigens could be critical in the therapy of established tumors.

Ceacam1a-/- mice are completely resistant to infection by murine coronavirus mouse hepatitis virus A59

CEACAM1a glycoproteins are members of the immunoglobulin (Ig) superfamily and the carcinoembryonic antigen family. Isoforms expressing either two or four alternatively spliced Ig-like domains in mice have been found in a number of epithelial, endothelial, or hematopoietic tissues. CEACAM1a functions as an intercellular adhesion molecule, an angiogenic factor, and a tumor cell growth inhibitor. Moreover, the mouse and human CEACAM1a proteins are targets of viral or bacterial pathogens, respectively, including the murine coronavirus mouse hepatitis virus (MHV), Haemophilus influenzae, Neisseria gonorrhoeae, and Neisseria meningitidis, as well as Moraxella catarrhalis in humans. We have shown that targeted disruption of the Ceacam1a (MHVR) gene resulting in a partial ablation of the protein in mice (p/p mice) led to reduced susceptibility to MHV-A59 infection of the modified mice in the BALB/c background. We have now engineered and produced a Ceacam1a-/- mouse that exhibits complete ablation of the CEACAM1a protein in every tissue where it is normally expressed. We report that 3-week-old Ceacam1a-/- mice in the C57BL/6 genetic background are fully resistant to MHV-A59 infection by both intranasal and intracerebral routes. Whereas virus-inoculated wild-type +/+ C57BL/6 mice showed profound liver damage and spinal cord demyelination under these conditions, Ceacam1a-/- mice displayed normal livers and spinal cords. Virus was recovered from liver and spinal cord tissues of +/+ mice but not of -/- mice. These results indicate that CEACAM1a is the sole receptor for MHV-A59 in both liver and brain and that its deletion from the mouse renders the mouse completely resistant to infection by this virus.

Granulocyte CEACAM3 is a phagocytic receptor of the innate immune system that mediates recognition and elimination of human-specific pathogens

Carcinoembryonic antigen-related cell adhesion molecules (CEACAMs) are used by several human pathogens to anchor themselves to or invade host cells. Interestingly, human granulocytes express a specific isoform, CEACAM3, that participates together with CEACAM1 and CEACAM6 in the recognition of CEACAM-binding microorganisms. Here we show that CEACAM3 can direct efficient, opsonin-independent phagocytosis of CEACAM-binding Neisseria, Moraxella, and Haemophilus species. CEACAM3- but not CEACAM6-mediated uptake is blocked by dominant-negative versions of the small GTPase Rac. Moreover, CEACAM3 engagement triggers membrane recruitment and increased GTP loading of Rac that are not observed upon bacterial binding to CEACAM6. Internalization and Rac stimulation are also inhibited by compromising the integrity of an immunoreceptor tyrosine-based activation motif (ITAM)–like sequence in the cytoplasmic tail of CEACAM3 or by interference with Src family protein tyrosine kinases that phosphorylate CEACAM3. In contrast to interfering with CEACAM6, blockage of CEACAM3-mediated events reduces the ability of primary human granulocytes to internalize and eliminate CEACAM-binding bacteria, indicating an important role of CEACAM3 in the control of human-specific pathogens by the innate immune system.

Engulfment of Neisseria gonorrhoeae: revealing distinct processes of bacterial entry by individual carcinoembryonic antigen-related cellular adhesion molecule family receptors

Individual Neisseria gonorrhoeae colony opacity-associated (Opa) protein variants can bind up to four different carcinoembryonic antigen-related cellular adhesion molecule (CEACAM) receptors. Most human cells encountered by gonococci express a combination of CEACAM receptors, thereby complicating the elucidation of intracellular signaling pathways triggered by individual receptors. Here, we compare the process of bacterial engulfment by a panel of stably transfected HeLa epithelial cell lines expressing each CEACAM receptor in isolation. CEACAM1 and CEACAM3 each contain proteinaceous transmembrane and cytoplasmic domains; however, the processes of neisserial uptake mediated by these receptors differ with respect to their susceptibilities to both tyrosine kinase inhibitors and the actin microfilament-disrupting agent cytochalasin D. Neisserial uptake mediated by glycosylphosphatidylinositol (GPI)-anchored CEACAM5 and CEACAM6 was not significantly affected by any of a broad spectrum of inhibitors tested. However, cleavage of the GPI anchor by phosphatidylinositol-specific phospholipase C reduced bacterial uptake by HeLa cells expressing CEACAM5, consistent with a single zipper-like mechanism of uptake mediated by this receptor. Regardless of the CEACAM receptor expressed, internalized gonococci were effectively killed by a microtubule-dependent process that required acidification of the bacterium-containing phagosome. Given the phase-variable nature of neisserial Opa proteins, these results indicate that the mechanism of bacterial engulfment and the cellular response to gonococcal infection depend on both the receptor specificities of the neisserial Opa protein variants expressed and the spectrum of CEACAM receptors present on target cells, each of which determines the combination of receptors ultimately engaged.

[CEACAM1--a less well-known member of the family of carcinoembryonic antigens]

CEACAM1 (carcinoembryonic antigen-related cell adhesion molecule 1) is a transmembrane glycoprotein belonging to the carcinoembryonic antigen (CEA) family and immunoglobulin superfamily. It is localized mainly in the apical domains of polarized epithelia, leukocytes and endothelia. With respect to this wide tissue distribution the research is focused on the study of its biological functions. Structural and functional analyses show that the extracellular domain of CEACAM1 participates in homotypic and heterotypic adhesion, whereas the cytoplasmic domain takes part in cell growth inhibition and signal transduction. Whereas CEA is highly expressed in adenocarcinomas, CEACAM1 expression is down regulated in many tumors and its tumor-supressive function was confirmed. CEACAM1 also takes part in insulin metabolism, acts as a promotor of cholesterol crystallization and serves as a binding receptor for certain bacterial strains in humans as well as hepatitis virus in mice.

Activation of CEA-CAM-1-mediated cell adhesion via CD98: involvement of PKCδ

CD98 is a multifunctional protein involved in amino acid transport and regulation of integrin-mediated cell adhesion. Herein, we demonstrated that CD98 stimulation by anti-CD98 antibodies induced CEA-CAM-1-mediated cell adhesion in BaF3 cells expressing CEA-CAM-1, and suggest that this might be responsible for compact clumping of F9 embryonic carcinoma cells by CD98 stimulation. CEA-CAM-1 was co-immunoprecipitated by anti-CD98 antibody. CD98 stimulation induced the translocation of cytoplasmic protein kinase Cdelta (PKCdelta) to the cell adhesion sites, and rottlerin that inhibited the PKCdelta translocation abolished the cell aggregation without affecting integrin activation. The results suggested that CD98 stimulation could activate CEA-CAM-1-mediated cell adhesion independently of integrins.

The adhesion and differentiation-inhibitory activities of the immunoglobulin superfamily member, carcinoembryonic antigen, can be independently blocked

The external domains of Ig superfamily members are involved in multiple binding interactions, both homophilic and heterophilic, that initiate molecular events leading to the execution of diverse cell functions. Human carcinoembryonic antigen (CEA), an Ig superfamily cell surface glycoprotein used widely as a clinical tumor marker, undergoes homophilic interactions that mediate intercellular adhesion. Recent evidence supports the view that deregulated overexpression of CEA has an instrumental role in tumorigenesis through the inhibition of cell differentiation and the disruption of tissue architecture. The CEA-mediated block of the myogenic differentiation of rat L6 myoblasts depends on homophilic binding of its external domains. We show here that L6 transfectant cells expressing CEA can "trans-block" the myogenesis of juxtaposed differentiation-competent L6 transfectant cells expressing a deletion mutant of CEA (DeltaNCEA). This result implies the efficacy of antiparallel CEA-CEA interactions between cells in the differentiation block. In addition, DeltaNCEA can acquire differentiation blocking activity by cross-linking with specific anti-CEA antibodies, thus implying the efficacy of parallel CEA-CEA interactions on the same cell surface. The myogenic differentiation blocking activity of CEA was demonstrated by site-directed mutations to involve three subdomains of the amino-terminal domain, shown previously to be critical for its intercellular adhesion function. Monovalent Fab fragments of monoclonal antibodies binding to the region bridging subdomains 1 and 2 could both inhibit intercellular adhesion and release the myogenic differentiation block. Amino acid substitutions Q80A, Q80R, and D82N in subdomain 3, QNDTG, however, were found to completely ablate the differentiation blocking activity of CEA but had no effect on intercellular adhesion activity. A cyclized peptide representing this subdomain was the most effective at releasing the differentiation block.

CEA-based vaccines

Carcinoembryonic antigen (CEA), the first tumor-associated antigen to be described, was cloned in 1987 and is expressed on nearly 50% of all human tumors. The identification of T-cell specific epitopes within the coding region of the CEA protein has led to the development of various vaccine strategies that target CEA and CEA-expressing tumors. These vaccines have shown evidence of therapeutic effectiveness in animal models and are being evaluated in early phase clinical trials. Although trials are not designed to elucidate clinical responses, they have provided important information about the ability of individual vaccines to induce CEA-specific immune responses through the use of newer in vitro monitoring assays. Continued clinical testing in patients with less advanced disease and the administration of vaccines in combination with other standard therapy will help define the role of CEA-based vaccines in the treatment and prevention of human cancer.

Inhibition of endogenous carcinoembryonic antigen (CEA) increases the apoptotic rate of colon cancer cells and inhibits metastatic tumor growth

It has been suggested that carcinoembryonic antigen (CEA) enhances metastatic seeding of colon cancer cells due to its homo- and heterophilic binding properties. Our recent finding that endogenous CEA protects colon cancer cells against apoptosis suggests a more complex role of CEA in cancer progression. In this study we compared the in vitro effects of endogenous CEA on tumor cell aggregation and cell cycle regulation of human HT29 colon cancer cells with the corresponding in vivo effects, i.e. tumor cell seeding and formation of metastatic lesions. Stable expression of CEA targeted ribozymes (Rz) under control of a tet-off promoter system allowed regulation of CEA levels on the mRNA and protein level by 50%. Downregulation of CEA levels inhibited tumor cell aggregation by 70%. In accordance with previous studies, reduction of CEA levels increased in vitro the apoptotic rate and reduced colony formation by 30% to 50%. To determine the in vivo effect of CEA-dependent aggregate formation and its growth regulating role under apoptotic stress, HT29 cells with high and low CEA levels, respectively, were injected into nude mice. Immunostaining of lung microsections revealed similar numbers of tumor cells one hour after injection. 24 h later virtually all cells were removed from the lung in both groups. However, after 6 weeks all doxycycline treated mice (Rz off = CEA high) showed 14.5 +/- 4.6 metastatic lung lesions/mouse while 0.2 +/- 0.2 lesions/mouse appeared in the untreated group (Rz on = CEA low) (P < 0.001). Our study demonstrates a multifunctional role of CEA and indicates a prometastatic role of CEA independent of its adhesive function possibly due to its anti-apoptotic function.

Carcinoembryonic antigen-related cell adhesion molecule 1 expression and signaling in human, mouse, and rat leukocytes: evidence for replacement of the short cytoplasmic domain isoform by glycosylphosphatidylinositol-linked proteins in human leukocytes

Carcinoembryonic Ag-related cell adhesion molecule 1 (CEACAM1), the primordial carcinoembryonic Ag gene family member, is a transmembrane cell adhesion molecule expressed in leukocytes, epithelia, and blood vessel endothelia in humans and rodents. As a result of differential splicing, CEACAM1 occurs as several isoforms, the two major ones being CEACAM1-L and CEACAM1-S, that have long (L) or short (S) cytoplasmic domains, respectively. The L:S expression ratios vary in different cells and tissues. In addition to CEACAM1, human but not rodent cells express GPI-linked CEACAM members (CEACAM5-CEACAM8). We compared the expression patterns of CEACAM1-L, CEACAM1-S, CEACAM6, and CEACAM8 in purified populations of neutrophilic granulocytes, B lymphocytes, and T lymphocytes from rats, mice, and humans. Human granulocytes expressed CEACAM1, CEACAM6, and CEACAM8, whereas human B lymphocytes and T lymphocytes expressed only CEACAM1 and CEACAM6. Whereas granulocytes, B cells, and T cells from mice and rats expressed both CEACAM1-L and CEACAM1-S in ratios of 2.2-2.9:1, CEACAM1-S expression was totally lacking in human granulocytes, B cells, and T cells. Human leukocytes only expressed the L isoforms of CEACAM1. This suggests that the GPI-linked CEACAM members have functionally replaced CEACAM1-S in human leukocytes. Support for the replacement hypothesis was obtained from experiments in which the extracellular signal-regulated kinases (Erk)1/2 were activated by anti-CEACAM Abs. Thus, Abs against CEACAM1 activated Erk1/2 in rat granulocytes, but not in human granulocytes. Erk1/2 in human granulocytes could, however, be activated by Abs against CEACAM8. We demonstrated that CEACAM1 and CEACAM8 are physically associated in human granulocytes. The CEACAM1/CEACAM8 complex in human cells might accordingly play a similar role as CEACAM1-L/CEACAM1-S dimers known to occur in rat cells.

Clustering-induced signaling of CEACAM1 in PC12 cells

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1), an Ig-like transmembrane protein, functions in cell adhesion, angiogenesis and epithelial cell morphogenesis, and has been identified as a tumor suppressor. For all of these functions, CEACAM1 requires signaling capabilities. However, the mechanisms of CEACAM1-mediated signaling are only poorly understood. Here we characterized for the first time CEACAM1 expression and signaling in the neuroendocrine rat pheochromocytoma PC12 cell line. Stimulation of CEACAM1 by ligation on the cell surface with antibodies induced formation of large CEACAM1 clusters and a rapid and transient CEACAM1 tyrosine dephosphorylation. Functionally, this dephosphorylation correlated with a reduced association between CEACAM1 and the tyrosine phosphatase SHP2. Clustering also stimulated binding of CEACAM1 to the actin cytoskeleton, measured by a partial translocation of CEACAM1 into the insoluble fraction after detergent extraction. Both tyrosine dephosphorylation and interaction with the cytoskeleton were sensitive to neuronal differentiation of PC12 cells. The first detected downstream activation of the mitogen-activated protein kinases ERK1 and ERK2, but not of JNK or p38, describes a novel target of CEACAM1-mediated signaling and contributes to the understanding of how CEACAM1 regulates cellular function.

Activation-induced expression of carcinoembryonic antigen-cell adhesion molecule 1 regulates mouse T lymphocyte function

Carcinoembryonic Ag cell adhesion molecule 1 (CEACAM1) consists of highly related homologs in humans and rodents that are characterized by significant alternate splicing generating isoforms capable of negative intracellular signaling by virtue of two immunoreceptor tyrosine-based inhibition motifs in its cytoplasmic (cyt) tail. Although human T cells have been recently observed to express CEACAM1, the expression and function of CEACAM1 in mouse T cells have not been defined. Although resting mouse spleen T cells exhibited no evidence of CEACAM1 on the cell surface, CEACAM1 was rapidly up-regulated on CD4+ and CD8+ T cells after activation with either Con A or anti-CD3 without a requirement for either de novo transcription or translation due to the fact that CEACAM1 was present intracellularly before activation. Using a GST-CEACAM1-cytoplasmic tail fusion protein, it was shown that the cytoplasmic tail of CEACAM1 bound the src homology domain-containing phosphatase 1 and adaptor protein 1 complex in its phosphorylated and nonphosphorylated states, respectively. CEACAM1 ligation with an anti-CEACAM1 mAb resulted in inhibition of an allogeneic MLR and anti-CD3 plus anti-CD28 Ab-induced proliferation of spleen T cells in vitro and inhibition of a delayed-type hypersensitivity response to oxazolone in vivo. Inhibition of the delayed-type hypersensitivity response required that the anti-CEACAM1-specific mAb be present at the time of T cell sensitization. These studies support a role for CEACAM1 as a novel class of immunoreceptor tyrosine-based inhibition motif-bearing regulatory molecules on T cells that are active during early phases of the immune response in mice.

Biliary glycoprotein (BGPa, CD66a, CEACAM1) mediates inhibitory signals

Biliary glycoprotein (BGP, CD66a, CEACAM1) is a member of the carcinoembryonic antigen family (CEA, CD66), a group of transmembrane proteins belonging to the immunoglobulin superfamily. The structural features surrounding the tyrosine residues in the cytoplasmic domain of BGP share similarity with the consensus sequence of the immunoreceptor tyrosine-based inhibition motif (ITIM), the docking site for SHIP, SHP-1, and SHP-2 molecules. Using the well-characterized inhibitory receptor, FcgammaRIIB, we constructed a FcgammaRIIB-BGPa chimeric molecule that contained the extracellular and transmembrane domain of FcgammaRIIB and the cytoplasmic tail of BGPa and expressed it in DT40 B cells. Our results showed that FcgammaRIIB-BGPa, just like the unmodified FcgammaRIIB molecule, inhibited calcium influx in activated DT40 B cells. Substitution of tyrosine with phenylalanine (Y459F) in FcgammaRIIB-BGPa completely abrogated its ability to inhibit calcium influx, indicating that the motif surrounding Y459 is ITIM. The presence of ITIM was also supported by showing that the FcgammaRIIB-BGPa-mediated inhibitory effect was reduced in SHP-1and SHP-2 mutant DT40 B cells and further diminished in a SHP-1/-2 double-deficient mutant line. The results suggest that SHP-1 and SHP-2 are required for the FcgammaRIIB-BGPa-mediated inhibitory signals.

Carcinoembryonic Antigen-Related Cell Adhesion Molecule 1 on Murine Dendritic Cells Is a Potent Regulator of T Cell Stimulation

Dendritic cells (DC) are important APCs that play a key role in the induction of an immune response. The signaling molecules that govern early events in DC activation are not well understood. We therefore investigated whether DC express carcinoembryonic Ag-related cell adhesion molecule 1 (CEACAM1, also known as BGP or CD66a), a well-characterized signal-regulating cell-cell adhesion molecule that is expressed on granulocytes, monocytes, and activated T cells and B cells. We found that murine DC express in vitro as well as in vivo both major isoforms of CEACAM1, CEACAM1-L (having a long cytoplasmic domain with immunoreceptor tyrosine-based inhibitory motifs) and CEACAM1-S (having a short cytoplasmic domain lacking phosphorylatable tyrosine residues). Ligation of surface-expressed CEACAM1 on DC with the specific mAb AgB10 triggered release of the chemokines macrophage inflammatory protein 1alpha, macrophage inflammatory protein 2, and monocyte chemoattractant protein 1 and induced migration of granulocytes, monocytes, T cells, and immature DC. Furthermore, the surface expression of the costimulatory molecules CD40, CD54, CD80, and CD86 was increased, indicating that CEACAM1-induced signaling regulates early maturation and activation of dendritic cells. In addition, signaling via CEACAM1 induced release of the cytokines IL-6, IL-12 p40, and IL-12 p70 and facilitated priming of naive MHC II-restricted CD4(+) T cells with a Th1-like effector phenotype. Hence, our results show that CEACAM1 is a signal-transducing receptor that can regulate early maturation and activation of DC, thereby facilitating priming and polarization of T cell responses.

The CGM1a (CEACAM3/CD66d)-mediated phagocytic pathway of Neisseria gonorrhoeae expressing opacity proteins is also the pathway to cell death

Phagocytosis of Opa+ Neisseria gonorrhoeae (gonococcus, GC) by neutrophils is in part dependent on the interaction of Opa proteins with CGM1a (CEACAM3/CD66d) antigens, a neutrophil-specific receptor. However, the signaling pathways leading to phagocytosis have not been characterized. Here we show that interaction of OpaI bacteria with neutrophils or CGM1a-transfected DT40 cells induces calcium flux, which correlates with phagocytosis of bacteria. We identified an immunoreceptor tyrosine-based activation motif (ITAM) in CGM1a, and showed that the ability of CGM1a to transduce signals and mediate phagocytosis was abolished by mutation of the ITAM tyrosines. We also demonstrated that CGM1a-ITAM-mediated bacterial phagocytosis is dependent on Syk and phospholipase C activity in DT40 cells. Unexpectedly, the activation of the CGM1a-ITAM phagocytic pathway by Opa+ GC results in induction of cell death.

Carcinoembryonic antigen as a marker for colorectal cancer: is it clinically useful?

BACKGROUND

Carcinoembryonic antigen (CEA) is one of the most widely used tumor markers worldwide. Its main application is mostly in gastrointestinal cancers, especially in colorectal malignancy. Although in use for almost 30 years, the clinical value of CEA in colorectal cancer is still not clear.

METHODS

The literature relevant to the clinical value of CEA in colorectal cancer was reviewed. Particular attention was paid to studies involving metaanalyses and guidelines issued by Expert Panels.

RESULTS

Although of little use in detecting early colorectal cancer, high preoperative concentrations of CEA correlate with adverse prognosis. Serial CEA measurements can detect recurrent colorectal cancer with a sensitivity of approximately 80%, a specificity of approximately 70%, and can provide a lead time of approximately 5 months. CEA is the most frequent indicator of recurrence in asymptomatic patients and currently is the most cost-effective test for the preclinical detection of resectable disease. CEA is most useful for the early detection of liver metastasis in patients with diagnosed colorectal cancer. Overall, however, little evidence is available that monitoring of all patients with diagnosed colorectal cancer leads to enhanced patient outcome or quality of life.

CONCLUSIONS

Currently, the most useful application of CEA is in the detection of liver metastasis from colorectal cancers. Because of the relative success of surgery in resecting hepatic metastases, serial determinations of the marker are recommended for detecting cancer spread to the liver. In the future, preoperative concentrations of CEA may be included with the standard staging procedures for assessing prognosis.

Role of carcinoembryonic antigen in the progression of colon cancer cells that express carbohydrate antigen

Carcinoembryonic antigen (CEA) has been reported to promote the metastatic potential in some experimental tumors. Adhesion molecules are known to play an important role in the process of metastasis. Cytokines, including interleukin 1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha), which are produced by Kupffer cells, induce endothelial cells to express adhesion molecules. As a result, the present study was designed to investigate whether the interaction between CEA and Kupffer cells accelerated the metastatic potential of tumors in the liver. Kupffer cells isolated from the liver of male BALB/c mice were cultured with CEA, either with or without the addition of a cytokine inhibitor. The levels of IL-1beta and TNF-alpha were examined in a culture medium. An adhesion assay of colon cancer cell lines to human umbilical vein endothelial cells was also performed. When CEA was added to the Kupffer cell culture medium, cytokines were produced. Elevated levels of cytokines appeared to lead to increased rates of adhesion of cancer cells to endothelial cells. However, these phenomena were blocked by the addition of cytokine inhibitors. CEA stimulated Kupffer cells to produce cytokines. An elevated number of cytokines have been proven to promote the expression of adhesion molecules in endothelial cells. These processes are therefore considered to contribute to the metastasis of malignant cells to the liver. These results suggest that cytokine inhibitors may therefore play an important role in the inhibition of hepatic metastasis.

Extracellular N-domain alone can mediate specific heterophilic adhesion between members of the carcinoembryonic antigen family, CEACAM6 and CEACAM8

The domain(s) responsible for the specific heterophilic adhesion between two members of the carcinoembryonic antigen (CEA) family, CEACAM6 and CEACAM8, both of which with three extracellular domains, were investigated using Chinese hamster ovary (CHO) transfectants expressing chimeric antigens. Using a chimeric antigen in which the N-domain, a sole extracellular domain, of CEACAM3 was substituted with that of CEACAM6, it was shown that the N-domain of CEACAM6 alone was able to mediate specific adhesion to CEACAM8. Furthermore, the chimeric antigen was shown to bind significantly to chimeric CEA whose N-domain was substituted with that of CEACAM8, but not to unsubstituted CEA. These results demonstrate that the N-domain alone is sufficient and other domains of CEACAM6 or CEACAM8 are not required for this specific binding. We therefore propose a model of heterophilic interaction between the N-domains, which is distinct from that of CEA-CEA homophilic binding.

Transcriptional control: an essential component of cancer gene therapy strategies?

The therapeutic index of cancer gene therapy approaches will, at least in part, be dictated by the spatial and temporal control of expression of the therapeutic transgenes. Strategies which allow precise control of gene transcription are likely to play a crucial role in the future pre-clinical and clinical development of gene therapy. In this review, we discuss these issues as they relate to tissue and tumor specific promoters. In addition, the exciting opportunities offered by the development of regulated gene expression systems using small molecules, radiation and heat are reviewed. It is realistic to expect that the future offers the prospect of amalgamating elements of a number of these different systems in a co-ordinated gene delivery approach with the potential to increase the efficacy and reduce the toxicity of treatment.

[Standards, Options and Recommendations (SOR) for tumor markers in breast cancer. SOR Working Group]

CONTEXT

The "Standards, Options and Recommendations" (SOR) project, started in 1993, is a collaboration between the Federation of the French Cancer Centres (FNCLCC), the 20 French Cancer Centres and specialists from French Public Universities, General Hospitals and Private Clinics. The main objective is the development of clinical practice guidelines to improve the quality of health care and outcome for cancer patients. The methodology is based on literature review and critical appraisal by a multidisciplinary group of experts, with feedback from specialists in cancer care delivery.

OBJECTIVES

To define, according to the definitions of the Standards, Options and Recommendations project, the characteristics of various tumour markers in breast cancer and the potential role of these markers in the management of patients with this malignancy.

METHODS

Data were identified by searching Medline and the personal reference lists of members of the expert groups. Once the guidelines were defined, the document was submitted for review to 43 independent reviewers, and to the medical committees of the 20 French Cancer Centres.

RESULTS

The main recommendations are: 1) CA 15.3 and CEA are the serum tumour markers most often used in breast cancer (standard). 2) If the CA 15.3 is raised at presentation, there is no place for the measurement of other tumour markers (standard, expert agreement). 3) All analyses for each patient must be performed in the same laboratory, using the same technique (standard, expert agreement). 4) CA 15.3 should not be used for screening or diagnosis. 5) The level of CA 15.3 before treatment is a recognised prognostic factor, the independent value of which has not been proven (standard, level of evidence C). 6) If the initial value of CA 15.3 is greater than 50 kU.L(-1), disseminated disease should be actively sought before any treatment decisions are made (standard, expert agreement). 7) An initial elevation of CA 15.3 that does not return to normal, reflects a lack of response to treatment and is a strong adverse prognostic factor (standard, level of evidence C). 8) The accuracy of tumours markers (especially CA 15.3) as early indicators of metastatic disease is well recognised (standard) but the clinical benefit has not been established. 9) There is a correlation between tumour markers and clinical response in the treatment of metastatic disease (level of evidence C). The level of CA 15.3 in metastatic disease does not predict response to treatment.

Induction of cytotoxic T cells and their antitumor activity in mice transgenic for carcinoembryonic antigen

In order to develop immunotherapy strategies that are based on eliciting immune responsiveness to the self-antigen, human carcinoembryonic antigen (CEA), we examined whether cytotoxic T lymphocyte (CTL) activity against CEA could be elicited in CEA-transgenic and nontransgenic mice. CEA-transgenic [C57BL/ 6-TGN(CEAGe)18FJP] and nontransgenic mice were primed with CEA-transfected syngeneic fibroblasts in combination with Corynebacterium parvum. Spleen cells from immunized mice were cultured with irradiated syngeneic MC-38 colon carcinoma cells transfected with CEA (MC-38.CEA) as stimulators prior to the measurement of CTL activity. Primed nontransgenic spleen cells showed augmented CTL activity against MC-38.CEA cells as compared with control parental MC-38 cells, nontransfected or transfected with vector only. Moreover, primed CEA transgenic spleen cells showed augmented CTL activity against MC-38.CEA cells that was similar to that observed in nontransgenic mice. All CTL clones derived from either transgenic or nontransgenic mice showed cross-reactivity with MC-38 cells expressing the CEA-related antigen, nonspecific cross-reacting antigen, but not biliary glycoprotein. CEA-specific CTL clones were not identified. Adoptive transfer of cloned CTL resulted in inhibition of MC-38.CEA but not MC-38.BGP tumor growth. Tumor cures were elicited in mice treated with a combination of cloned CTL and cyclophosphamide. Histopathological examination of CEA-expressing colons from either immunized mice or recipients of cloned CTL did not reveal any autoimmune reactions. These studies demonstrate that CTL recognizing cross-reactive class I epitopes on the CEA molecule can be induced in transgenic mice. The expression of these epitopes on tumor cells creates effective targets for CTL in vivo without inducing adverse reactions in CEA-expressing normal tissues. Since anti-CEA CTL have been generated in humans, CEA-transgenic mice may be a useful model to study vaccines that are based on CTL effector mechanisms.

Human carcinoembryonic antigen functions as a general inhibitor of anoikis

Human carcinoembryonic antigen (CEA), a widely used tumor marker, and CEACAM6 [formerly nonspecific cross-reacting antigen (NCA)] are up-regulated in many types of human cancers, whereas family member CEACAM1 [formerly biliary glycoprotein (BGP)] is usually down-regulated. Deregulated overexpression of CEA/CEACAM6 but not CEACAM1 can inhibit the differentiation and disrupt the polarization and tissue architecture of many different types of cells. In this report, we show that CEA and CEACAM6, but not CEACAM1, markedly inhibit the apoptosis of cells when deprived of their anchorage to the extracellular matrix, a process known as anoikis. By blocking this tissue architecture surveillance mechanism, the architectural perturbation initiated by CEA/CEACAM6 can thus be maintained.

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.

Carcinoembryonic antigen: cell adhesion molecule and useful diagnostic marker

Carcinoembryonic antigen (CEA) was first identified over 30 years ago as a marker of malignant colonic cells, but has since been shown to be expressed by a range of normal epithelial cells. Moreover, CEA is one member of a larger gene family and shares structural homology with other family molecules. Despite this confused picture, CEA is now known to function in several biological roles, including cell-cell adhesion. Its use in the diagnostic setting has also changed over the years, where in routine immunohistochemistry, monoclonal antibodies to CEA are useful in aiding diagnosis when used as part of a panel. Here, recent advances in understanding the biological role(s) that CEA and CEA-related antigens may play in cell adhesion are highlighted, together with results from molecular studies that illustrate how structure can influence the choice of CEA antibodies for use in both the research and diagnostic laboratory.

Carcino-embryonic antigen may function as a chemo-attractant in colorectal-carcinoma cell lines

Locomotion of colorectal-carcinoma cells was tested in order to establish whether it might be affected by carcino-embryonic antigen (CEA). CEA production, cell growth and DNA ploidy were measured in 22 colorectal-carcinoma cell lines. A cell-invasion assay was adapted using a transfilter chamber, the lower surface of which was coated with various substrates in the amount of 5 microgram/filter (CEA, type-IV collagen, laminin). Cells infiltrated into the lower surface of the filter were counted over 9-microscope fields (x400). All cell lines produced CEA, 9 producing more than 100 ng/ml medium. Of the total, 8 cell lines were diploid and 14 were aneuploid. Invasiveness, measured by the number of infiltrated cells, was highest in CEA-coated filters, and next highest in type-IV-collagen- and laminin-coated filters, in descending order (p < 0.001-0.05). Invasiveness of each cell line was closely correlated with 2 substrates. Poorly differentiated or advanced-stage tumors were more invasive than well-differentiated or early-stage tumors (p < 0.001-0. 05). However, invasiveness was not associated with DNA ploidy or CEA production. CEA may function as a chemo-attractant as well as an adhesion molecule in colorectal-carcinoma cell lines. In addition, adhesion to CEA appears to be related to type-IV collagen and laminin.

Lewis blood group and CEA related antigens; coexpressed cell-cell adhesion molecules with roles in the biological progression and dissemination of tumours

The Lewis blood group and carcinoembryonic antigen (CEA) related antigens have adhesive functions in human tissues, with roles in embryonic sorting and migration of cells (organogenesis), differentiation and protection of normal mucosal tissues, migration of neutrophils, bacterial binding, and tumour differentiation and dissemination. In the key areas of mucosal protection, neutrophil binding, and tumour metastasis, they are often coexpressed on the outer cell membrane, with Lewis blood group antigens forming the terminal carbohydrate chains on a CEA related glycoprotein backbone. The central role of these antigens in the mechanism of neutrophil binding to endothelium in inflammation highlights a fascinating paradigm for tumour cell dissemination and metastasis, and expression is linked to disease prognosis. This review outlines the structure, function, and comparative roles of these antigens in human tissues.

Involvement of circulating CEA in liver metastases from colorectal cancers re-examined in a new experimental model

Both experimental and clinical data show evidence of a correlation between elevated blood levels of carcinoembryonic antigen (CEA) and the development of liver metastases from colorectal carcinomas. However, a cause-effect relationship between these two observations has not been demonstrated. For this reason, we developed a new experimental model to evaluate the possible role of circulating CEA in the facilitation of liver metastases. A CEA-negative subclone from the human colon carcinoma cell line CO115 was transfected either with CEA-cDNA truncated at its 3' end by the deletion of 78 base pairs leading to the synthesis of a secreted form of CEA or with a full-length CEA-cDNA leading to the synthesis of the entire CEA molecule linked to the cell surface by a GPI anchor. Transfectants were selected either for their high CEA secretion (clone CO115-2C2 secreting up to 13 microg CEA per 10(6) cells within 72 h) or for their high CEA membrane expression (clone CO115-5F12 expressing up to 1 x 10(6) CEA molecules per cell). When grafted subcutaneously, CO115-2C2 cells gave rise to circulating CEA levels that were directly related to the tumour volume (from 100 to 1000 ng ml(-1) for tumours ranging from 100 to 1000 mm3), whereas no circulating CEA was detectable in CO115 and CO115-5F12 tumour-bearing mice. Three series of nude mice bearing a subcutaneous xenograft from either clone CO115-2C2 or the CO115-5F12 transfectant, or an untransfected CO115 xenograft, were further challenged for induction of experimental liver metastases by intrasplenic injection of three different CEA-expressing human colorectal carcinoma cell lines (LoVo, LS174T or CO112). The number and size of the liver metastases were shown to be independent of the circulating CEA levels induced by the subcutaneous CEA secreting clone (CO115-2C2), but they were directly related to the metastatic properties of the intrasplenically injected tumour cells.

Carcinoembryonic antigen as an adhesion molecule

Carcinoembryonic antigen (CEA), one of the most widely studied tumor markers, shows homotypic (CEA-CEA) intercellular adhesion and heterotypic adhesion to other members of CEA family, receptors on Kupffer cells, macrophages, microorganisms, and lectins. This review is focused on those adhesive properties of CEA which may pertain to the role of CEA in tumor progression.

Optimization of the sequence of antigen loading and CD40-ligand-induced maturation of dendritic cells

Dendritic cells (DCs), matured by CD40-ligand (CD40L), undergo marked changes in their ability to process and present antigen, resulting in augmented lymphocyte stimulatory activity. We demonstrate that the form of the tumor antigen (peptide or genetic material) used to load the DCs dictates the required sequence of antigen loading and maturation for antitumor immunotherapy. Optimal stimulation of carcinoembryonic antigen (CEA)-specific CTLs by peptide-loaded DCs occurs when DCs from cancer patients are matured with CD40L before exposure to CEA peptide, whereas optimal stimulation by RNA-transfected DCs occurs when the DCs are loaded with CEA RNA before maturation with CD40L.

Expression in cytotoxic T lymphocytes of a single-chain anti-carcinoembryonic antigen antibody. Redirected Fas ligand-mediated lysis of colon carcinoma

In the MD45 mouse cytotoxic T lymphocyte (CTL) hybridoma cell line, we have expressed a chimeric receptor, consisting of the single-chain variable domains (scFv) of anti-carcinoma embryonic antigen (CEA) mAb linked to Fcgamma receptor (FcgammaR) chain via a CD8 hinge. Transfected MD45 subclones lysed CEA-positive human colon carcinoma cell lines in an antigen-specific and FasL-dependent manner. The degree of lysis correlated with the level of chimeric receptor expressed on transduced MD45 subclones. The requirement for an intact Y65TGL motif in the signaling gamma chain suggested that interaction of the chimeric receptor with target cell CEA induced the cytotoxicity of MD45-scFv subclones. However, MD45 expressing a Y65F mutant chimera still displayed minor levels of lysis following PMA stimulation, suggesting that PMA could bypass gamma chain induction of functional FasL. Pretreatment of Fas-resistant CEA-positive colon carcinoma target cells with IFN-gamma increased their sensitivity of MD45-scFv subclones and FasL-mediated lysis. This study has demonstrated the successful activation of FasL function via a chimeric receptor introduced into lymphocytes and the susceptibility of human colon carcinoma to combined cytokine and CTL treatment.

Homotypic adhesion through carcinoembryonic antigen plays a role in hepatic metastasis development

We established a cell line with high metastatic potential to the liver (LS-LM4) after four successive repetitions of splenic injection of liver-metastatic cells in SCID mice. This cell line strongly expressed CEA and showed increased homotypic adhesion as compared with the parent cell line (LS174T). To examine the role of CEA in the increased homotypic adhesion, LS-LM4 cells were treated with anti-CEA antibody and subjected to an in vitro adhesion and aggregation assay. Further, to study the role of CEA in the hepatic metastasis of cells with high metastatic potential, LS-LM4 cells were treated with anti-CEA antibody, and the inhibition of hepatic metastasis after splenic injection in vivo was examined. There was a 62% decrease in the homotypic adhesion of anti-CEA antibody-treated (100 microg/ml) LS-LM4 cells under a Ca2+-free condition as compared with the control (P<0.01). Anti-CEA antibody (100 microg/ml) inhibited cell aggregation under a Ca2+-free condition (P<0.05). Treatment with anti-E-cadherin antibody (60 microg/ml) plus anti-CEA antibody (100 microg/ml) inhibited cell aggregation more potently than anti-E-cadherin antibody treatment alone in the presence of Ca2+. In vivo, there was a 75% decrease in the number of hepatic metastatic nodules in the G125 anti-CEA antibody-treated group as compared with the control group (P<0.01). Similarly, there was a 40% decrease in the diameter of metastatic nodules and there was a 90% decrease in total tumor volume of hepatic metastasis in the G125 anti-CEA antibody-treated group as compared with the control (P<0.01). These results suggest that increased metastatic potential to the liver is at least partly due to increased homotypic binding mediated by CEA.