CEA-expressing Tumor Cells Research Articles

Abstract 2911: The CEA-targeted ISAC, BDC-2034, shows preclinical efficacy associated with innate immune activation, phagocytosis, and myeloid reprogramming

Abstract Introduction: Immune-stimulating antibody conjugates (ISACs) direct a TLR7/8 agonist into tumors through engagement of cell surface antigens to activate tumor-associated myeloid cells and initiate a broad innate and adaptive anti-tumor immune response. We are developing the ISAC BDC-2034 to target the tumor antigen, CEA (CEACAM5), which is expressed in many solid tumors. BDC-2034 comprises our proprietary antibody, CEA1, covalently conjugated to a potent TLR7/8 agonist via a non-cleavable linker. The strong pro-phagocytic capacity and slow internalization rate of CEA1 makes it an ideal antibody for the ISAC approach. Methods: The ability of BDC-2034 to induce the secretion of pro-inflammatory cytokines was evaluated in vitro using co-cultures of tumor cells and primary immune cells (including monocytes and dendritic cells). Anti-tumor efficacy was demonstrated in vivo with xenograft and syngeneic mouse tumor models. In parallel studies, the mechanism of BDC-2034 action was assessed by quantifying intratumoral immune infiltration, cytokine levels, and transcript profile. Results: In co-cultures of CEA-expressing tumor cells and immune cells, BDC-2034 induced the secretion of cytokines and chemokines that are essential for a broad anti-tumor immune response, including IL-12p70, CXCL10, and TNFα. These effects were accompanied by myeloid cell activation as demonstrated by elevation in costimulatory surface markers such as CD40. In vivo, BDC-2034 inhibited tumor growth in multiple xenograft and syngeneic mouse tumor models having CEA expression comparable to human cancers. Consistent with the proposed mechanism of action, BDC-2034 induced intratumoral immune cell infiltration, inflammatory cytokine secretion, and myeloid re-programming in a dose-dependent and CEA-dependent fashion. The constellation of BDC-2034 effects translated to durable therapeutic activity. Conclusions: These preclinical findings demonstrate the potential of BDC-2034 to generate anti-tumor activity in CEA-expressing cancers through direct innate immune activation and the induction of adaptive anti-tumor immunity. Citation Format: Lisa K. Blum, Cecelia I. Pearson, Laughing Bear Torrez Dulgeroff, Rishali Gadkari, Angela Luo, Andrew Luo, Jennifer E. Melrose, Jess L. Nolin, Hai Li, Arthur Lee, Matthew N. Zhou, Puneet Anand, Ganapathy Sarma, Karla A. Henning, Steven J. Chapin, Shelley E. Ackerman, Romas Kudirka, Yuyi Shen, Bruce Hug, Edith A. Perez, Marcin Kowanetz, Michael N. Alonso, Brian S. Safina, David Dornan, William G. Mallet. The CEA-targeted ISAC, BDC-2034, shows preclinical efficacy associated with innate immune activation, phagocytosis, and myeloid reprogramming [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2911.

A carcinoembryonic antigen-specific cell therapy selectively targets tumor cells with HLA loss of heterozygosity in vitro and in vivo.

The CEACAM5 gene product [carcinoembryonic antigen (CEA)] is an attractive target for colorectal cancer because of its high expression in virtually all colorectal tumors and limited expression in most healthy adult tissues. However, highly active CEA-directed investigational therapeutics have been reported to be toxic, causing severe colitis because CEA is expressed on normal gut epithelial cells. Here, we developed a strategy to address this toxicity problem: the Tmod dual-signal integrator. CEA Tmod cells use two receptors: a chimeric antigen receptor (CAR) activated by CEA and a leukocyte Ig-like receptor 1 (LIR-1)-based inhibitory receptor triggered by human leukocyte antigen (HLA)-A*02. CEA Tmod cells exploit instances of HLA heterozygous gene loss in tumors to protect the patient from on-target, off-tumor toxicity. CEA Tmod cells potently killed CEA-expressing tumor cells in vitro and in vivo. But in contrast to a traditional CEA-specific T cell receptor transgenic T cell, Tmod cells were highly selective for tumor cells even when mixed with HLA-A*02-expressing cells. These data support further development of the CEA Tmod construct as a therapeutic candidate for colorectal cancer.

Development of CAR-T Cell Persistence in Adoptive Immunotherapy of Solid Tumors.

Chimeric antigen receptor (CAR) T (CAR-T) cell transfer has made great success in hematological malignancies, but only shown a limited effect on solid tumors. One of the major hurdles is the poor persistence of infused cells derived from ex vivo activation/expansion and repeated antigen encounter after re-infusion. Bcl-xL has been demonstrated to play an important role on normal T cell survival and function as well as genetically engineered cells. In the current study, we developed a retroviral CAR construct containing a second-generation carcinoembryonic antigen (CEA)-targeting CAR with the Bcl-xL gene and tested the anti-CEA CAR-T cell immunotherapy for colorectal cancer. In vitro, the anti-CEA CAR-T cells destroyed CEA-expressing tumor cells and sustained survival. In vivo, adoptive cell transfer of anti-CEA CAR-T cells significantly enhanced the ability of the CAR-T cells to accumulate in tumor tissues, suppress tumor growth and increase the overall survival rate of tumor-bearing mice in a murine model of colorectal cancer. These results demonstrate a novel CAR-T platform that has the ability to increase the persistence of CAR-T cells in solid tumors through exogenous expression of persistent genes. The data provide a potentially novel approach to augment CAR-T immunotherapy for solid tumors.

Pharmacologically upregulated carcinoembryonic antigen-expression enhances the cytolytic activity of genetically-modified chimeric antigen receptor NK-92MI against colorectal cancer cells

BackgroundThe natural killer cell line, NK-92MI, is cytotoxic against various types of cancer. The aim of this study was to develop chimeric antigen receptor-modified (CAR) NK-92MI cells targeting carcinoembryonic antigen-expressing (CEA) tumours and increase killing efficacy by pharmacologically modifying CEA-expression.ResultWe generated anti-CEA-CAR NK-92MI cells by retroviral vector transduction. This genetically-modified cell line recognised and lysed high CEA-expressing tumour cell lines (LS174T) at 47.54 ± 12.60% and moderate CEA-expressing tumour cell lines (WiDr) at 31.14 ± 16.92% at a 5:1 effector: target (E/T) ratio. The cell line did not lyse low CEA-expressing tumour cells (HCT116) as they did their parental cells (NK-92MI cells). The histone deacetylase-inhibitor (HDAC) sodium butyrate (NaB) and the methylation-inhibitor 5-azacytidine (5-AZA), as epigenetic modifiers, induced CEA-expression in HCT116 and WiDr cells. Although the IC50 of 5 fluorouracil (5-FU) increased, both cell lines showed collateral sensitivity to anti-CEA-CAR NK-92MI cells. The cytolytic function of anti-CEA-CAR NK-92MI cells was increased from 22.99 ± 2.04% of lysis background to 69.20 ± 11.92% after NaB treatment, and 69.70 ± 9.93% after 5-AZA treatment, at a 10:1 E/T ratio in HCT116 cells. The WiDr cells showed similar trend, from 22.99 ± 4.01% of lysis background to 70.69 ± 10.19% after NaB treatment, and 59.44 ± 10.92% after 5-AZA treatment, at a 10:1 E/T ratio.ConclusionsThis data indicates that the effector-ability of anti-CEA-CAR NK-92MI increased in a CEA-dependent manner. The combination of epigenetic-modifiers like HDAC-inhibitors, methylation-inhibitors, and adoptive-transfer of ex vivo-expanded allogeneic-NK cells may be clinically applicable to patients with in 5-FU resistant condition.

A filamentous bacteriophage targeted to carcinoembryonic antigen induces tumor regression in mouse models of colorectal cancer.

Colorectal cancer is a deadly disease, which is frequently diagnosed at advanced stages, where conventional treatments are no longer effective. Cancer immunotherapy has emerged as a new form to treat different malignancies by turning-on the immune system against tumors. However, tumors are able to evade antitumor immune responses by promoting an immunosuppressive microenvironment. Single-stranded DNA containing M13 bacteriophages are highly immunogenic and can be specifically targeted to the surface of tumor cells to trigger inflammation and infiltration of activated innate immune cells, overcoming tumor-associated immunosuppression and promoting antitumor immunity. Carcinoembryonic antigen (CEA) is highly expressed in colorectal cancers and has been shown to promote several malignant features of colorectal cancer cells. In this work, we targeted M13 bacteriophage to CEA, a tumor-associated antigen over-expressed in a high proportion of colorectal cancers but largely absent in normal cells. The CEA-targeted M13 bacteriophage was shown to specifically bind to purified CEA and CEA-expressing tumor cells in vitro. Both intratumoral and systemic administration of CEA-specific bacteriophages significantly reduced tumor growth of mouse models of colorectal cancer, as compared to PBS and control bacteriophage administration. CEA-specific bacteriophages promoted tumor infiltration of neutrophils and macrophages, as well as maturation dendritic cells in tumor-draining lymph nodes, suggesting that antitumor T-cell responses were elicited. Finally, we demonstrated that tumor protection provided by CEA-specific bacteriophage particles is mediated by CD8+ T cells, as depletion of circulating CD8+ T cells completely abrogated antitumor protection. In summary, we demonstrated that CEA-specific M13 bacteriophages represent a potential immunotherapy against colorectal cancer.

Correlation Between Preoperative Serum Carcinoembryonic Antigen Levels and Expression on Pancreatic and Rectal Cancer Tissue.

Carcinoembryonic antigen (CEA)–targeted imaging and therapeutic agents are being tested in clinical trials. If CEA overexpression in malignant tissue corresponds with elevated serum CEA, serum CEA could assist in selecting patients who may benefit from CEA-targeted agents. This study aims to assess the relationship between serum CEA and CEA expression in pancreatic (n = 20) and rectal cancer tissues (n = 35) using histopathology. According to local laboratory standards, a serum CEA >3 ng/mL was considered elevated. In pancreatic cancer patients a significant correlation between serum CEA and percentage of CEA-expressing tumor cells was observed (P = .04, ρ = .47). All 6 patients with homogeneous CEA expression in the tumor had a serum CEA >3 ng/mL. Most rectal cancer tissues (32/35) showed homogeneous CEA expression, independent of serum CEA levels. This study suggests that selection of pancreatic cancer patients for CEA-targeted agents via serum CEA appears adequate. For selection of rectal cancer patients, serum CEA levels are not informative.

In VivoFluorescence Imaging of the Activity of CEA TCB, a Novel T-Cell Bispecific Antibody, Reveals Highly Specific Tumor Targeting and Fast Induction of T-Cell–Mediated Tumor Killing

CEA TCB (RG7802, RO6958688) is a novel T-cell bispecific antibody, engaging CD3ε upon binding to carcinoembryonic antigen (CEA) on tumor cells. Containing an engineered Fc region, conferring an extended blood half-life while preventing side effects due to activation of innate effector cells, CEA TCB potently induces tumor lysis in mouse tumors. Here we aimed to characterize the pharmacokinetic profile, the biodistribution, and the mode of action of CEA TCB by combining in vitro and in vivo fluorescence imaging readouts. CEA-expressing tumor cells (LS174T) and human peripheral blood mononuclear cells (PBMC) were cocultured in vitro or cografted into immunocompromised mice. Fluorescence reflectance imaging and intravital 2-photon (2P) microscopy were employed to analyze in vivo tumor targeting while in vitro confocal and intravital time-lapse imaging were used to assess the mode of action of CEA TCB. Fluorescence reflectance imaging revealed increased ratios of extravascular to vascular fluorescence signals in tumors after treatment with CEA TCB compared with control antibody, suggesting specific targeting, which was confirmed by intravital microscopy. Confocal and intravital 2P microscopy showed CEA TCB to accelerate T-cell-dependent tumor cell lysis by inducing a local increase of effector to tumor cell ratios and stable crosslinking of multiple T cells to individual tumor cells. Using optical imaging, we demonstrate specific tumor targeting and characterize the mode of CEA TCB-mediated target cell lysis in a mouse tumor model, which supports further clinical evaluation of CEA TCB. Clin Cancer Res; 22(17); 4417-27. ©2016 AACRSee related commentary by Teijeira et al., p. 4277.

Abstract 1494: Combination of CEA TCB, a novel T-cell bispecific antibody for the treatment of solid tumors, with PD-L1 checkpoint blockade

Abstract Recent results from clinical trials have shown that immune therapies, particularly immune checkpoint inhibitors, can extend the overall survival of cancer patients and lead to durable responses. Despite these promising results, current immune-based therapies are only effective in a proportion of patients and combination strategies are needed to improve therapeutic benefit. Programmed death-ligand 1(PD-L1) is found on the surface of immune and tumor cells and its expression is induced by interferon gamma (IFNg). It prevents the immune system from destroying cancer cells by interacting with the inhibitory programmed death-1 (PD-1) and B7.1 receptors on activated T cells, which results in a T-cell inhibitory signal. CEA TCB (RG7802, RO6958688) is a novel T cell bispecific antibody targeting the carcinoembryonic antigen (CEA) on tumor cells and CD3 on T cells, currently being investigated as single agent in a Phase I study in patients with advanced and/or metastatic CEA-expressing tumors. CEA TCB-mediated killing of tumor cells led to T cell activation, IFNg secretion and subsequent up-regulation of the PD-1/PD-L1 immune suppressive pathway in vitro and in vivo, similarly to what happens during tumor adaptive immune resistance mechanisms where upon recognition of tumor antigens, TILs produce IFNg, which drives PD-L1 expression in the tumor microenvironment and delivers a suppressive signal to T cells upon binding to PD-1. Incubation of the high-CEA expressing gastric carcinoma cell line (MKN45) with human PBMCs (E:T 10:1) and increasing concentrations of CEA TCB, led to a dose-dependent up-regulation of PD-1 receptor on both CD4+ or CD8+ T cell subsets as well as of PD-L1 on surviving tumor cells as early as 24 h following treatment. PD-1 expression was specific as it did not occur in the absence of CEA-expressing tumor cells or upon treatment with un-targeted control TCB. In vivo studies performed using MKN45 tumor xenografts (MKN45) in fully humanized NOG mice demonstrated that CEA TCB treatment led to increased frequency of intra-tumoral T cells expressing PD-1 and to a strong induction of PD-L1 expression in tumors. Combination of CEA TCB with a PD-L1 blocking antibody showed significant increase of anti-tumor activity as compared to the respective single agents. These preclinical data indicate that CEA TCB treatment leads to up-regulation of the PD-1/PD-L1 immune suppressive pathway and that the combination of CEA TCB with PD-L1 blocking agents results in enhanced anti-tumor activity. Phase Ib clinical trials investigating the combination of CEA TCB and atezolizumab are currently ongoing. Citation Format: Marina Bacac, Tanja Fauti, Sara Colombetti, Linda Fahrni, Valeria Nicolini, Christian Gerdes, Jose Saro, Vaios Karanikas, Christian Klein, Pablo Umana. Combination of CEA TCB, a novel T-cell bispecific antibody for the treatment of solid tumors, with PD-L1 checkpoint blockade. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1494.

A Novel Carcinoembryonic Antigen T-Cell Bispecific Antibody (CEA TCB) for the Treatment of Solid Tumors.

CEA TCB is a novel IgG-based T-cell bispecific (TCB) antibody for the treatment of CEA-expressing solid tumors currently in phase I clinical trials (NCT02324257). Its format incorporates bivalent binding to CEA, a head-to-tail fusion of CEA- and CD3e-binding Fab domains and an engineered Fc region with completely abolished binding to FcγRs and C1q. The study provides novel mechanistic insights into the activity and mode of action of CEA TCB. CEA TCB activity was characterized on 110 cell lines in vitro and in xenograft tumor models in vivo using NOG mice engrafted with human peripheral blood mononuclear cells. Simultaneous binding of CEA TCB to tumor and T cells leads to formation of immunologic synapses, T-cell activation, secretion of cytotoxic granules, and tumor cell lysis. CEA TCB activity strongly correlates with CEA expression, with higher potency observed in highly CEA-expressing tumor cells and a threshold of approximately 10,000 CEA-binding sites/cell, which allows distinguishing between high- and low-CEA-expressing tumor and primary epithelial cells, respectively. Genetic factors do not affect CEA TCB activity confirming that CEA expression level is the strongest predictor of CEA TCB activity. In vivo, CEA TCB induces regression of CEA-expressing xenograft tumors with variable amounts of immune cell infiltrate, leads to increased frequency of activated T cells, and converts PD-L1 negative into PD-L1-positive tumors. CEA TCB is a novel generation TCB displaying potent antitumor activity; it is efficacious in poorly infiltrated tumors where it increases T-cell infiltration and generates a highly inflamed tumor microenvironment. Clin Cancer Res; 22(13); 3286-97. ©2016 AACR.

A novel CEA-based cancer vaccine that blocks tumor implantation and tumor foci formation in vivo (P4459)

Abstract Metastatic forms of cancer account for most cancer-related deaths. Essentially all patients with advanced metastatic cancer are given palliative care in the absence of any useful curative strategies. Since tumour foci formation and expansion are directly linked to cell-cell adhesion events, we have developed a human carcinoembryonic antigen (CEA)-based subunit vaccine using only an altered-self form of its IgV like N domain responsible for the homotypic adhesion of CEA-expressing cancer cells. We now report that simply vaccinating CEA-expressing transgenic mice intramuscularly with this subunit and MF59 (squalene) engenders anti-adhesive as well as cytocidal (CDC and ADCC) antibodies in these transgenic animals that effectively block the subsequent lodging and formation of tumour foci at sites such as the peritoneal cavity and kill CEA-expressing murine tumour cells. This vaccine formulation may represent a simple, safe, preventive strategy against the long-term establishment of metastases in patients diagnosed with CEA-expressing colon, lungs, ovarian and breast cancer.

Abstract LB-264: Development of 3D microtissue models to study the activity of novel tumor-targeted immunotherapeutics.

Abstract IL-2 therapy can result in durable responses in a proportion of cancer patients, but the treatment is associated with significant toxicity. To improve the liabilities associated with IL-2 therapy, we recently developed a novel monomeric tumor-targeted immunocytokine (CEA-IL2v), which completely lacks binding to CD25 (IL-2Rα) but retains binding to IL-2Rβγ. When tested in classical 2D tumor/lymphocyte co-culture systems, CEA-IL2v induces concentration-dependent proliferation and activation of NK, CD4 and CD8 T cells, but differently from IL-2, does not lead to preferential activation of Tregs and induces lower levels Fas-induced apoptosis. To further explore the properties of CEA-IL2v, including the assessment of antibody targeting and stimulation of immune-cell activation and infiltration, we developed a novel 3D heterotypic microtissues model consisting of tumor cells, fibroblasts and lymphocytes. To address the penetration and targeting, heterotypic 3D microtissues consisting of CEA-expressing human tumor cells and fibroblasts were incubated with tumor-targeted IL-2v (CEA-IL2v), stroma-targeted IL-2v (FAP-IL2v), and the corresponding untargeted control (DP47-IL2v). CEA-IL2v successfully penetrated into microtissues and specifically bound to CEA-positive tumor cells, FAP-IL2v was specifically retained by FAP-expressing fibroblasts whereas the DP47-IL2v was not detected in any of the components. The activity of the immunocytokines was further evaluated by addition of human lymphocytes to 3D microtissues. CEA-IL2v and DP47-IL2v activated different lymphocyte subsets, stimulated their infiltration and selectively promoted the elimination of tumor cells as shown by (a) reduction of microtissue size, (b) increase of LDH release, (c) elimination of CEA-positive tumor cells, (d) increase of lymphocytes infiltrating into the microtissues and (e) increase of cytokine and chemokine levels secreted in the supernatants, including MIP-1β, IL-6 and IFN-γ. Taken together, the heterotypic tumor/fibroblast/lymphocyte 3D microtissue model presented here offers the possibility to monitor antibody penetration and targeting to tumor and stroma components, to study the interaction of tumor cells with immune cells in a system that more closely resembles the in vivo tumor microenvironment and thus provides an in vitro platform for optimal immunotherapy development. The study also points out that the tumor-targeted CEA-IL2v immunocytokine is an elegant tool for expansion and activation of immune effector cells, which may successfully be applied for cancer immunotherapy. Citation Format: Inja Waldhauer, Laura Morra, Steffi Lehmann, Irina Agarkova, Philine Zumstein, Jens M. Kelm, Pablo Umana, Christian Klein, Marina Bacac. Development of 3D microtissue models to study the activity of novel tumor-targeted immunotherapeutics. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-264. doi:10.1158/1538-7445.AM2013-LB-264

Blocking the attachment of cancer cells in vivo with DNA aptamers displaying anti-adhesive properties against the carcinoembryonic antigen

The formation of metastatic foci occurs through a series of cellular events, initiated by the attachment and aggregation of cancer cells leading to the establishment of micrometastases. We report the derivation of synthetic DNA aptamers bearing anti-adhesive properties directed at cancer cells expressing the carcinoembryonic antigen (CEA). Two DNA aptamers targeting the homotypic and heterotypic IgV-like binding domain of CEA were shown to block the cell adhesion properties of CEA, while not recognizing other IgV-like domains of CEACAM family members that share strong sequence and structural homologies. More importantly, the pre-treatment of CEA-expressing tumour cells with these aptamers prior to their intraperitoneal implantation resulted in the prevention of peritoneal tumour foci formation. Taken together, these results highlight the effectiveness of targeting the cell adhesion properties of cancer cells with aptamers in preventing tumour implantation.

Liver sinusoidal endothelial cells contribute to CD8 T cell tolerance toward circulating carcinoembryonic antigen in mice

Immunity against cancer is impeded by local mechanisms promoting development of tumor-specific T cell tolerance, such as regulatory T cells, myeloid-derived suppressor cells, or immunosuppressive factors in the tumor microenvironment. The release of soluble antigens, such as carcinoembryonic antigen (CEA) from colorectal carcinoma (CRC) cells, has been investigated for diagnostic purposes, but not for its immunological consequences. Here, we address the question of whether soluble CEA influences tumor-specific immunity. Mice were injected with soluble CEA protein, and CEA-specific CD8 T cells were analyzed for their phenotype and functionality by means of restimulation ex vivo or antitumor efficacy in vivo. We furthermore characterized the CD8 T cell population in peripheral blood mononuclear cell (PBMCs) from healthy donors and colorectal carcinoma patients. In mice, circulating CEA was preferentially taken up in a mannose receptor-dependent manner and cross-presented by liver sinusoidal endothelial cells, but not dendritic cells, to CD8 T cells. Such systemically circulating CEA promoted tolerization of CEA-specific CD8 T cells in the endogenous T cell repertoire through the coinhibitory molecule B7H1. These CD8 T cells were not deleted but were rendered nonresponsive to antigen-specific stimulation and failed to control growth of CEA-expressing tumor cells. These nonresponsive CD8 T cells were phenotypically similar to central memory T cells being CD44(high) CD62L(high) CD25(neg) . We found T cells with a similar phenotype in PBMCs of healthy donors and at increased frequency also in patients with colorectal carcinoma. Our results provide evidence for the existence of an unrecognized tumor immune escape involving cross-presentation of systemically circulating tumor antigens that may influence immunotherapy of cancer.

P1-01-09: A Focused Immune Response Targeting the Homotypic Binding Domain of the Carcinoembryonic Antigen Blocks the Establishment of Tumor Foci In Vivo.

Abstract Background: The carcinoembryonic antigen (CEA) is over-expressed in ∼56% of breast cancer biopsies but is absent on normal breast tissues. Clinically, high preoperative serum concentrations of CEA in breast cancer patients correlate with metastasis, treatment failure and poor overall prognosis. More importantly, the homotypic cell adhesion functions of CEA have been associated with cancer progression and tumor metastasis. One approach to prevent the establishment of CEA-dependent metastatic foci in breast cancer patients would thus be to interfere with the cell adhesion functions of this cell surface antigen. We hypothesize that vaccinating CEA-expressing transgenic (CEA. Tg) mice with a recombinant, altered-self form of the Ig V-like N domain of CEA, involved in homotypic interactions, should result in a focused immune response able to block the CEA-mediated adhesion of murine carcinoma cells expressing CEA (MC38.CEA) and the establishment of metastatic foci in this transgenic mouse model. Material and Methods: A recombinant form of the CEA N domain was expressed in E.coli, purified and shown in cell-based assays to bind to the A3 domain of human CEA and to block cell adhesion in CEA-expressing tumor cell lines. CEA-expressing transgenic mice were vaccinated i.p. with the recombinant CEA N domain protein and poly I:C. Resulting serum Ig [IgG1 and IgG2a] as well as cytokine expression levels [IFN-g, IL-4 and IL10 responses] were measured by ELISA and ELISPOT assays. The CEA-expressing MC38 murine tumor cells were implanted s.c. into CEA.Tg mice [hind leg; primary site model; tumor growth within 7 days] or administered i.v. to generate lung tumor metastases within 60 days or injected i.p. to generate peritoneal tumor nodules within 35 days in unvaccinated animals. Results: The recombinant folded, deglycosylated N domain of human CEA is perceived as an altered self-antigen by CEA.Tg mice when administered i.p. with poly I:C acting as an adjuvant. The vaccinated mice develop strong IgG1 and IgG2a responses able to kill CEA-expressing human breast cancer cell lines [MCF-7 and MDA-MB231] in vitro by both Antibody-Dependent Cellular Cytotoxicity (ADCC) and Complement-Dependent Cytotoxicity (CDC) mechanisms. The sera of such animals also inhibited cell-cell aggregation mediated by CEA expression. Vaccination of CEA.tg mice following the establishment of CEA-expressing MC38 murine hind leg tumor mass resulted in a significant delay in tumor growth. More importantly, animals pre-vaccinated with the recombinant CEA N domain did not display lung or peritoneal tumor foci following the i.v. or i.p. injection of CEA-expressing murine tumor cells. Discussion: A simple vaccination protocol using a recombinant form of the N domain of CEA as an immunogen is sufficient to engender an immune response that can block the development of CEA-expressing tumor foci in the lungs and peritoneal cavity of CEA.tg mice and destroys human breast cancer cells expressing CEA. These results suggest that mounting a focused antibody response to the N domain of CEA may represent a simple therapeutic strategy to control the establishment of metastatic foci in breast cancer patients expression high levels of the antigen CEA. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P1-01-09.

A dendritic cell-based vaccine effects on T-cell responses compared with a viral vector vaccine when administered to patients following resection of colorectal metastases in a randomized phase II study.

2533 Background: CD8+ T cell responses to colorectal cancer are associated with longer survival. This has led to the hypothesis that cancer vaccines, capable of activating T cell responses, may improve clinical outcome. Vaccines based on antigen-presenting cells/dendritic cells (DC) and viral vectors, potent stimulators of adaptive immunity, have been associated with enhanced survival in prostate cancer patients. We compared rates of tumor antigen-specific T cell and antibody responses between a DC and a poxvector vaccine. The clinical outcome data is reported elsewhere. Methods: 74 patients with no evidence of disease after colorectal cancer metastasectomy and completion of peri-operative chemotherapy were randomized 1:1 to receive injections of one of either: DC mixed with PANVAC-VF (poxvectors encoding CEA, MUC1, CD54, CD58, CD80) or PANVAC-VF along with local injections of GM-CSF. Peripheral blood was drawn before and after completing the immunizations for analysis of CEA and MUC-1 immune (T cell and antibody) responses by ELISPOT and ELISA. Results: T cell responses against CEA were significantly more frequent in the DC arm (69 versus 41%, p=0.02) although the magnitude of the T cell response among responders was similar. There was a trend for improved relapse-free survival among patients with CEA-specific T cell responses (log rank p = 0.10). The antibody response to CEA was more frequent with the PANVAC alone (100% versus 67%, (p= 0.018)) and the antibodies in serum from vaccinated patients could bind to CEA-expressing tumor cells and mediated ADCC. No antibody response was induced against MUC-1. The antibody response against CEA did not correlate with clinical benefit. Few deaths were observed limiting comparison of survival by immune response. Conclusions: A dendritic cell vaccine leads to a greater frequency of CEA-specific T cell responses which is associated with enhanced RFS. Ongoing studies are evaluating the role of additional immunostimulatory cytokines and modulation of regulatory cell populations and molecules in enhancing the adaptive immune response to the DC-based vaccine.

Bispecific Adapter-Mediated Retargeting of a Receptor-Restricted HSV-1 Vector to CEA-Bearing Tumor Cells

The safety and efficacy of viral therapies for solid tumors can be enhanced by redirecting the virus infection to tumor-specific cell-surface markers. Successful retargeting of herpes simplex virus type 1 (HSV-1) has been achieved using vectors that carry a modified envelope glycoprotein D (gD) engineered to interact directly with novel receptors. In addition, soluble bridging molecules (adapters) have been used to link gD indirectly to cell-specific receptors. Here, we describe the development of an adapter connecting gD to the common tumor antigen carcinoembryonic antigen (CEA). The adapter consisted of a CEA-specific single-chain antibody fused to the gD-binding region of the gD receptor, herpes virus entry mediator (HVEM). We used this adapter in combination with a vector that is detargeted for recognition of the widely expressed gD receptor nectin-1, but retains an intact binding region for the less common HVEM. We show that the adapter enabled infection of HSV-resistant Chinese hamster ovary (CHO) cells expressing ectopic CEA and nectin-1/CEA-bearing human gastric carcinoma cells that are resistant to the vector alone. We observed cell-to-cell spread following adapter-mediated infection in vitro and reduced tumor growth in vivo, indicating that this method of vector retargeting may provide a novel strategy for tumor-specific delivery of tumoricidal HSV.

Abstract 5625: In vitro and in vivo pharmacology of MEDI-565 (MT111), a novel CEA/CD3-bispecific single-chain BiTE antibody in development for the treatment of gastrointestinal adenocarcinomas

Abstract MEDI-565 (MT111) is a novel bispecific single-chain antibody of the BiTE (Bispecific T cell engager) class that transiently links carcinoembryonic antigen (CEA) on cancer cells with human CD3 on T cells. MEDI-565 specifically binds to human CEA with an affinity of 8.5 nM but not to any other member of the CEACAM family. In targeted expression studies on cryopreserved and formalin-fixed paraffin-embedded sections, MEDI-565 demonstrated membrane-localized binding specifically to epithelial cells in human cancerous tissues. The highest prevalence of MEDI-565 binding (∼90%) was in adenocarcinomas of gastrointestinal origin. In in vitro killing assays, MEDI-565 recruited T cells via the CD3 antigen (affinity of 310 nM) in a process that required concomitant binding to CEA positive tumor cells for T cell activation. As a consequence, T cells expanded, increased cell surface expression of the activation markers CD69 and CD25, and released perforin and granzymes. The release of cytotoxic granule content led to a Ca2+-dependent activation of pro-caspases and subsequent apoptosis of CEA-expressing tumor cells. Efficient target cell lysis by MEDI-565 was predominantly mediated by CD8+ T cells and occurred within a wide range of effector-to-target ratios (80:1 to 5:1) for T cells derived from various human donors. BiTE mediated killing was not affected by the presence of soluble CEA (≤5 µg/mL). The in vivo activity of MEDI-565 was investigated in subcutaneous xenograft models using immunocompromised SCID mice inoculated with mixtures of human T cells and human cancer cell lines. The antibody was eliminated from the serum with a half-life of a few hours following a single intravenous (IV) or subcutaneous (SC) injection. Despite a relatively short serum half-life, daily IV or SC bolus treatments over 5 days provided sufficient levels of exposure to inhibit the growth of CEA-positive tumors in a dose-dependent manner. Inhibition of growth was observed for tumors of different tissue origins and was dependent on the presence of human T cells and CEA expression by tumor cells. There were no MEDI-565-related in-life observations following treatment. These studies demonstrated that MEDI-565 has potent and selective anti-cancer activity in vitro and in vivo and provides evidence that MEDI-565 may be an effective monotherapy to treat CEA-expressing malignancies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5625.

Abstract A32: Pretargeted immunoPET of CEA-expressing in intraperitoneal human colonic tumor xenografts in nude mice

Abstract Objective: Radiolabeled antibodies were being developed commercially for the detection of several cancer types. However, imaging with radiolabeled antibodies require a relatively long interval between injection and imaging acquisition for adequate contrast to develop. The pretargeting method is a 2-step method: a unlabeled bsMAb with affinity for the tumor and a small radiolabeled molecule is injected, followed by the a radiolabeled compound. This aims to optimize the imaging system by specific tumor accumulation and fast blood clearance of the radiopharmacon, which allows imaging within one hour. Short-lived positron emitting radionuclides, e.g. 68Ga (half life: 68 min) match the pharmacokinetics of the small molecule. In this study, pretargeted immunoPET with a bispecific monoclonal anti-carcinoembryonic antigen (CEA) x anti-histamine-succinyl-glycine (HSG) antibody, TF2, and a radiolabeled peptide, IMP288, was compared to 18F-FDG in detecting CEA-expressing tumors in nude mice. Methods: Groups of five BALB/c nude mice were inoculated with CEA-expressing human colonic tumor cells intraperitoneally. One group received 5 MBq 18F-FDG intravenously (i.v.). Another group received TF2 and 5 MBq 68Ga-IMP288 i.v. 16 h later. After one hour PET/CT images were acquired. One day later this was repeated vice versa. Uptake of 68Ga-IMP288 or 18F-FDG in the tumors and other dissected tissues was determined. Results: High, specific tumor uptake of 68Ga-IMP288 (23.4 ± 7.2% ID/g) was observed, with very low accretion in the normal tissues (intestines: 0.50 ± 0.19 % ID/g; liver: 1.83 ± 0.45 % ID/g). This resulted in high tumor-to-background ratios (e.g. tumor-to-intestines 57.5 ± 22.4) and in the clear visualization of the small intra-abdominal tumor lesions (1.5–5 mm), as soon as one hour after the injection of 68Ga-IMP288. 18F-FDG localized efficiently in the tumors (8.7 ± 3.1 % ID/g), but with physiological uptake in various normal tissues (intestines: 2.15 ± 0.61 % ID/g; liver: 2.78 ± 0.52 % ID/g). The low tumor-to-background ratio (e.g. tumor-to-intestines 4.0 ± 0.9) complicated the detection of the tumors. Conclusions: This study indicated that pretargeted immunoPET with TF2 and 68Ga-IMP288 is a specific and sensitive method for detecting colon cancer. Citation Information: Clin Cancer Res 2010;16(7 Suppl):A32

Nanoparticles functionalised with recombinant single chain Fv antibody fragments (scFv) for the magnetic resonance imaging of cancer cells

Superparamagnetic iron oxide nanoparticles (SPIONs) can substantially improve the sensitivity of magnetic resonance imaging (MRI). We propose that SPIONs could be used to target and image cancer cells if functionalised with recombinant single chain Fv antibody fragments (scFv). We tested our hypothesis by generating antibody-functionalised (ab f) SPIONs using a scFv specific for carcinoembryonic antigen (CEA), an oncofoetal cell surface protein. SPIONs of different hydrodynamic diameter and surface chemistry were investigated and targeting was confirmed by ELISA, cellular iron uptake, confocal laser scanning microscopy (CLSM) and MRI. Results demonstrated that ab f-SPIONs bound specifically to CEA-expressing human tumour cells, generating selective image contrast on MRI. In addition, we observed that the cellular interaction of the ab f-SPIONs was influenced by hydrodynamic size and surface coating. The results indicate that ab f-SPIONs have potential for cancer-specific MRI.

Viral vector-induced expression of bone morphogenetic protein 2 produces inhibition of tumor growth and bone differentiation of stem cells

A number of hormonal factors have been shown to be instrumental in the calcification process. This study represents an attempt at using one of these factors to specifically induce calcification of tumors to arrest tumor growth. The gene encoding bone morphogenetic protein 2 (BMP-2) was placed under transcriptional control of the promoter for carcinoembryonic antigen (CEA). This gene cassette was cloned into a herpes simplex virus (HSV) amplicon vector (HSV-CEA-BMP2). This vector was used to induce local BMP-2 production in CEA-expressing tumor cells to retard cell growth. Lysates of tumor cells treated with HSV-CEA-BMP2 were applied to stem cells to determine if BMP-2 expression promotes differentiation to bone lineage. pHSV-CEA-BMP2 efficiently transduced both CEA-expressing and non-expressing cells. BMP-2 was only expressed in CEA-positive cells. BMP-2 expression led to an inhibition of tumor cell growth. BMP-2 released by these CEA-expressing tumors also drove the differentiation of mesenchymal stem cells to bone lineage. This proof-of-concept study demonstrates that tumor cells can be specifically engineered to produce BMP-2, which leads to growth retardation and to the differentiation of non-committed stem cells to bone. This 'Medusa' effect can theoretically be exploited to retard tumor growth.