Topic Highlight
Copyright ©The Author(s) 2016. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. May 7, 2016; 22(17): 4275-4286
Published online May 7, 2016. doi: 10.3748/wjg.v22.i17.4275
Dendritic cell-based cancer immunotherapy for colorectal cancer
Mikio Kajihara, Kazuki Takakura, Tomoya Kanai, Zensho Ito, Keisuke Saito, Shinichiro Takami, Shigetaka Shimodaira, Masato Okamoto, Toshifumi Ohkusa, Shigeo Koido
Mikio Kajihara, Kazuki Takakura, Tomoya Kanai, Zensho Ito, Keisuke Saito, Shinichiro Takami, Toshifumi Ohkusa, Shigeo Koido, Division of Gastroenterology and Hepatology, Department of Internal Medicine, The Jikei University School of Medicine (Kashiwa Hospital), Kashiwa, Chiba 277-8567, Japan
Shigetaka Shimodaira, Cell Processing Center, Shinshu University Hospital, Nagano 390-8621, Japan
Masato Okamoto, Department of Advanced Immunotherapeutics, Kitasato University School of Pharmacy, Tokyo 108-8641, Japan
Toshifumi Ohkusa, Shigeo Koido, Institute of Clinical Medicine and Research, the Jikei University School of Medicine, Chiba 277-8567, Japan
Author contributions: Kajihara M, Takakura K, Kanai T, Ito Z, Saito K, Takami S, Shimodaira S, Okamoto M, Ohkusa T and Koido S designed the study; Koido S wrote the paper; Kajihara M, Takakura K and Koido S contributed equally to this manuscript.
Supported by Grants in Aid for Scientific Research (C) from the Japanese Ministry of Education, Culture, Sports, Science, and Technology.
Conflict-of-interest statement: No potential conflicts of interest were disclosed by any of the authors.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Correspondence to: Shigeo Koido, MD, Division of Gastroenterology and Hepatology, Department of Internal Medicine, The Jikei University School of Medicine (Kashiwa Hospital), 163-1 Kashiwashita, Kashiwa, Chiba 277-8567, Japan. shigeo_koido@jikei.ac.jp
Telephone: +81-4-71641111 Fax: +81-4-71633488
Received: February 11, 2016
Peer-review started: February 11, 2016
First decision: March 7, 2016
Revised: March 15, 2016
Accepted: April 7, 2016
Article in press: April 7, 2016
Published online: May 7, 2016

Abstract

Colorectal cancer (CRC) is one of the most common cancers and a leading cause of cancer-related mortality worldwide. Although systemic therapy is the standard care for patients with recurrent or metastatic CRC, the prognosis is extremely poor. The optimal sequence of therapy remains unknown. Therefore, alternative strategies, such as immunotherapy, are needed for patients with advanced CRC. This review summarizes evidence from dendritic cell-based cancer immunotherapy strategies that are currently in clinical trials. In addition, we discuss the possibility of antitumor immune responses through immunoinhibitory PD-1/PD-L1 pathway blockade in CRC patients.

Key Words: Colorectal cancer, Dendritic cell, Cancer immunotherapy, Cytotoxic T lymphocyte, Immune-checkpoint inhibitors

Core tip: Dendritic cell (DC) is potent antigen-presenting cells that play a pivotal role in the induction of antitumor immune responses. Strategies for delivering antigens to DCs have been developed and used in clinical trials in cancer patients, including colorectal cancer (CRC). Numerous reports indicate that the use of DC-based immunotherapy for CRC patients is promising to induce antigen-specific CTL responses. However, the immune suppression induced through CRC and the tumor microenvironment continues to be a major hurdle. Thus, the combination of DC-based immunotherapy with immune-modulating agents may be necessary to maximize antitumor immunity. These combinatorial therapies may have the potential for clinical benefit.



INTRODUCTION

Colorectal cancer (CRC) is a common cancer and remains one of the leading causes of cancer-related deaths worldwide. Although surgery is the only curative treatment available for localized disease, more than 20% of CRC patients are not eligible for surgery due to liver metastases at the time of diagnosis[1]. To date, surgery, neoadjuvant radiotherapy and adjuvant chemotherapy have improved the outcome of CRC patients; however, 50% of patients still die from recurrent or metastatic disease[1,2]. Indeed, the treatment of CRC patients with distant metastases or recurrence through surgery or chemotherapy currently remains limited. Therefore, alternative strategies, including immunotherapy, for treating advanced CRC have been considered[3].

Recent studies have suggested that CRC is a good candidate for immunotherapy. As potential targets for cancer immunotherapy, human CRC cells express numerous numbers of tumor-associated antigens (TAAs), such as carcinoembryonic antigen (CEA)[4-6], Wilms’ tumor gene 1 (WT1)[7,8], mucin 1 (MUC1)[4,9], melanoma-associated antigen gene (MAGE)[10-12], or p53[13]. Moreover, CRC is a heterogeneous disease with genetic and epigenetic characterizations, such as the mutation of oncogenes, microsatellite instability (MSI) phenotype, chromosomal instability (CIN) pathway, CpG island methylator phenotype (CIMP), and DNA hypomethylation[14]. For example, the MSI phenotype reflects various deficiencies in the DNA mismatch-repair system, leading to an increased mutation rate of oncogenes[15]. The CIN pathway in cancers reveals aneuploidy and chromosomal rearrangements[15]. Cancers with the CpG island methylator phenotype (CIMP) exhibit DNA methylation associated with the transcriptional inactivation of tumor-suppressor genes[15]. These genetic and epigenetic characterizations lead to multiple mutations of oncogenes, resulting in immunogenic CRC. Therefore, some patients with CRC may be effective candidates for immunotherapy. Moreover, immunotherapy mediates a potent antitumor effect when combined with chemotherapy and/or radiotherapy[16-18]. Indeed, cancer immunotherapy targeting these TAAs can be combined with surgery, radiotherapy, and conventional chemotherapy for treating patients with CRC. Interestingly, given the success of immune-checkpoint inhibitors in several tumors, we believe that cancer immunotherapy may also be combined with immune checkpoint blockade agents to induce efficient antitumor immunity in CRC patients.

ANTITUMOR IMMUNITY

T cells with the αβ T cell receptor (TCR) generally express CD4+ or CD8+ lineage markers and have primarily been classified as helper or cytotoxic subsets, respectively[19]. Major histocompatibility complex (MHC) class I molecules on cancer cells bound to antigenic peptide derived from tumor-associated antigens (TAAs) are recognized by the TCR of CD8+ T cells. However, CD4+ T cells recognize peptides in association with MHC class II molecules on antigen-presenting cells (APCs)[3,19]. The goal of cancer immunotherapy is to induce efficient antigen-specific cytotoxic CD8+T cells (CTLs). The induction of efficient CD8+ CTLs requires helper functions mediated through CD4+ T cells via the production of cytokines, such as interleukin (IL)-2 and interferon (IFN)-γ, resulting in the maintenance of antigen-specific CD8+ CTLs[20,21]. Therefore, the simultaneous interaction of the TCR of T cells with antigenic peptides/MHC class I and class II complexes on APCs is essential for the induction of CD4+ and CD8+ T cell-mediated antitumor immune responses. Moreover, antigen-specific CD8+ CTLs respond to antigenic peptides presented by MHC class I molecules on cancer cells and identify and kill TAA-expressing cancer cells.

Dendritic cells (DCs) are potent APCs that play a pivotal role in the initiation, programming, and regulation of antitumor immune responses[20]. DCs capture antigens, resulting in a mature phenotype and the release of IL-12 from DCs. The exogenous antigens are processed by DCs, and antigenic peptides are presented on MHC class I molecules, a process known as antigen cross-presentation[20]. In addition, DCs also process endogenously synthesized antigens into antigenic peptides, presented to MHC class I molecules. However, exogenous antigens are also processed to antigenic peptides and complexed with MHC class II molecules[20,21]. Antigen presentation primarily occurs in the draining lymph node, where antigenic peptides are presented by DCs, resulting in the simultaneous activation of CD4+ and CD8+ T cells. Moreover, interactions between DCs and innate and innate-like immune cells, such as natural killer (NK), invariant natural killer T (iNKT), and γδ T cells, can bypass the T helper arm in CTL induction[22,23]. NK, iNKT, and γδ T cells also have the ability to attack tumor cells directly[23]. Therefore, efficient induction of antitumor immunity via DC-based cancer vaccines may require interaction between DCs and innate and innate-like immune cells with central roles in DC-based cancer immunotherapy[23,24].

Cancer immunotherapy, including peptide vaccines, whole tumor cell vaccines, viral vector vaccines, and adopted cell transfer therapy, have been developed to treat CRC patients[3]. In particular, peptide vaccines have been widely tested in clinical trials, reflecting the simple, safe, stable, and economical features of these vaccine types. However, there are several drawbacks to the peptide vaccines, including: (1) limitations due to the MHC type; (2) limited numbers of identified epitopes; and (3) impaired DC function in cancer patients[3,25]. Therefore, DCs have been loaded with multiple antigenic peptides[26-28], whole tumor cell-mRNA[29], whole tumor cell lysates[30], and whole tumor-derived apoptotic bodies[31] or fused with whole tumor cells to form hybrid cells (DCs-tumor fusions)[32]. DC-tumor fusion cells process a broad array of TAAs, including both known and unidentified, and present these molecules by MHC class I and class II pathways in the context of co-stimulatory molecules[32,33]. In our laboratory, patient-derived DCs are generated through adherent mononuclear cells from a single leukapheresis collection after culture in the presence of granulocyte macrophage colony-stimulating factor (GM-CSF) and IL-4. Immature DCs are matured with penicillin-killed and lyophilized preparations of a low-virulence strain (Su) of Streptococcus pyogenes (OK-432) and with prostaglandin E2 (PGE2). Subsequently, a large number of DCs can be cryopreserved in ready-for-use aliquots for immunotherapy[27].

IMMUNOSUPPRESSION MECHANISMS

Although antigen-specific CTLs are induced in cancer patients, cancer cells often escape immune surveillance through several mechanisms, including (1) the down-regulation of certain antigens, TAP-1/2, MHC class I, or peptide-processing machinery in tumor cells[34,35]; (2) the induction of regulatory T cells (Tregs) producing proinflammatory and immunosuppressive cytokines, such as IL-10 and TGF-β[36]; (3) the presence of immunosuppressive cells (e.g., cancer-associated fibroblasts (CAFs), M2 macrophages, myeloid-derived suppressor cells (MDSCs), immunosuppressive tumor-associated macrophages (TAMs), tolerogenic DCs, and Tregs) in the tumor microenvironment[36]; (4) the production of multiple immune suppressive factors from tumor cells[37]; and (5) the expression of immune checkpoint blockade between tumor cells and activated T cells[38,39]. Although, activated CD8+ T cells associated with clinical prognosis often infiltrate in CRC[40], this benefit is controlled through immune suppressive cell populations in the tumor microenvironment, promoting tumor escape from immune surveillance[14,41,42]. The direct production of immune suppressive factors, such as IL-6, IL-10, TGF-β, vascular endothelial growth factor (VEGF), soluble Fas ligand (Fas-L), and indolamine-2,3-dioxygenase (IDO), by tumor cells also promotes the accumulation of heterogeneous populations of CAFs, M2 macrophages, TAMs, MDSCs, tolerogenic DCs, and Tregs[37]. These immunosuppressive cells in the tumor microenvironment inhibit antitumor immunity through various mechanisms, including the elaboration of arginase (Arg), nitrogen oxide (NO), and reactive oxygen species (ROS) from immunosuppressive cells[37]. Indeed, the tumor microenvironment is extremely complex and suppresses antitumor immunity, thus explaining why cancer immunotherapy is occasionally unsuccessful[41]. Therefore, the functional inhibition of Arg, NO, or ROS in immunosuppressive cells may augment antitumor immunity.

Programmed death 1 (PD-1) is expressed on the surface of activated T cells and inhibits T cell activation upon binding to the associated ligands PD-L1/PD-L2[3]. Moreover, cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) is another mechanism that inhibits T cell activation upon binding CD80/CD86 on DCs. CTLA-4 is expressed on naive or memory T cells. PD-1 is highly expressed in antigen-specific CTLs and activated DCs. PD-L1 is not constitutively expressed in some tumors but is induced in response to inflammatory signals, such as IFN-γ, produced by antigen-specific CTLs. In contrast, the CTLA-4-mediated immune checkpoint is induced in T cells during the initial response to antigen. Therefore, antibodies can be used to block inhibitory ligand-receptor interactions by acting on tumor cells and DCs (e.g., anti-PD-L1) or T cells (e.g., anti-CTLA-4 or anti-PD1). Indeed, CRC cells express PD-L1 associated with CTL inactivation and Treg development in the tumor microenvironment, resulting in worse survival[43-45]. Combining the blockade of multiple immune inhibitory pathways may synergistically activate antitumor immunity.

DC-BASED PASSIVE IMMUNOTHERAPY

DC-based cancer immunotherapy has been developed to induce TAA (e.g., CEA, WT1, MAGE, or MUC1)-specific CTLs in patients with CRC. To date, various strategies for delivering TAAs to DCs have been developed and tested in clinical trials in cancer patients, including CRC (Table 1). In particular, as most CRC cells express CEA, CEA-targeted DC-based CRC immunotherapy has been reported.

Table 1 Clinical trials of dendritic cell-based cancer immunotherapy in patients with colorectal cancer.
TargetsImmunotherapyPhasePatientsResultsRef.Year
CEADCs loaded with CEA peptide (HLA-A2 restricted)I21 advanced CEA-expressing malignancies including 11 CRCSkin punch biopsy at DC injection sites demonstrated pleomorphic, perivascular infiltration of cells consistent with a DTH responseMorse et al[46]1999
DCs loaded with CEA mRNAI13 patients with resected hepatic metastases of CRC9 of the 13 CRC patients relapsed at a median of 122 dMorse et al[47]2003
DCs modified with a recombinant fowlpox vector encoding CEA and a triad of costimulatory molecules [rF-CEA(6D)-TRICOM]I14 patients with HLA-A2 (11 CRC and 3 non-small cell lung cancer)CEA-specific T cells responses were detected in 10 patients; 5 patients were stable through at least 1 cycle of immunization (3 mo)Morse et al[48]2005
Fowlpox vector encoding CEAI14 patients (5 CRC, 3 lung cancer, and 1 urachal adenocarcinoma)Of the 9 patients analyzed, all with stable disease (n = 5) displayed increased NK activityOsada et al[49]2006
Mature DCs induced by activation with a combination of OK-432, low-dose prostanoid, and IFN-α and loaded with CEA peptide10 CRC patientsCRC patients with stable disease (n = 8) exhibited increased levels of NK cell frequency and CEA-specific CTL activity with a central memory phenotype. Lack of CTL activity was found in 2 CRC patients with progressive disease, but NK cell proliferation was detectedSakakibara et al[51]2011
DCs loaded with altered CEA peptide (HLA-A2 restricted) with Flt3 ligandI12 patients with HLA-A2+ malignancies (10 CRC and 2 non-small cell lung cancer)CEA-specific CD8+ CTLs were detected in 7 patients; 1 patient with progressive metastatic CRC had a complete resolution of pulmonary metastasis and malignant pleural effusion at 4 mo after vaccination, and 1 patient with CRC developed a mixed response after vaccination, with regression of some but not all liver metastasesFong et al[52]2001
DCs loaded with CEA peptide (HLA-A24 restricted)I10 advanced CEA-expressing malignancies including 7 CRC2 patients (CRC and lung cancer) exhibited positive DTH reactions against CEA and remained stable for 6 and 9 mo, respectivelyItoh et al[53]2002
DCs loaded with CEA peptides (HLA-A2- or HLA-A24-restricted)I10 CRC patients (6 HLA-A24 and 4 HLA-A2) who had failed standard chemotherapyCEA-specific CTLs were detected in 7 patients; 2 patients exhibited stable disease for at least 12 wkLiu et al[54]2004
DCs loading with CEA peptide (HLA-A24 restricted)I8 patients with advanced CEA-expressing gastrointestinal malignancies (7 CRC and 1 gall bladder cancer)4 patients developed CEA-specific CTL responses; a DTH reaction was observed in 1 patient, with skin biopsy at the injection site showing lymphocyte infiltration, and 3 patients, including 2 CRC, exhibited stable disease after vaccinationMatsuda et al[55]2004
DCs loaded with CEA peptide (HLA-24 restricted)I8 patients with CEA-expressing metastatic gastrointestinal or lung adenocarcinomaLong-term stable disease or marked decreases in the serum CEA level was observed in some patients. CEA-specific immune responses were demonstrated in most of the patients in whom treatment was clinically effectiveUeda et al[56]2004
DCs loaded with CEA peptide (HLA-2 restricted)I10 CRC patients with resection of liver metastasesCEA-specific CTLs were demonstrated in 7 patients; CEA-specific CTLs were detected in a resected lymph node in 1 patientLesterhuis et al[57]2006
DCs loaded with CEA altered peptideI9 patients with CEA-expressing malignancies (7 CRC and 2 lung cancer)5 patients exhibited CEA altered peptide-specific CTL responses, and 3 patients exhibited CEA-specific CTL responsesBabatz et al[58]2006
WT1DCs loaded with WT1 peptide (MHC class I and class II restricted)I3 advanced CRCWT1-specific CTLs were detected and persisted for 2 yr with prolonged disease-free and overall survivalShimodaira et al[8]2015
MAGEDCs loaded with MAGE-3 peptide (HLA-A2 or A24 restricted)I12 patients with advanced gastrointestinal carcinoma (6 stomach, 3 esophagus, and 3 CRC)MAGE-3-specific CTL responses were observed in 4 patients. Tumor markers were decreased in 7 patients, and evidence of minor tumor regression was detected in 3 patientsSadanaga et al[65]2001
DCs loaded with MAGE-3 or MAGE-1 peptides (HLA-A2 0r A24 restricted)I28 patients with advanced gastrointestinal carcinoma, including 7 CRCPeptide-specific CTL responses, tumor marker decreases, and minor tumor regressions were observed in some patients after vaccinationTanaka et al[66]2008
CEA and MUC1DCs modified with CEA/MUC1 (PANVAC)II74 patients, disease free after CRC metastasectomy and perioperative chemotherapyCEA-specific CTLs were detectedMorse et al[67]2013
CEA, MAGE, and HER2DCs loaded with CEA/MAGE/HER2/neu/pan-DR peptides (HLA-A2 restricted) and keyhole limpet hemocyanin (KLH) proteinI13 advanced CRCAll patients exhibited progressive disease. CEA-specific CTLs were detected in 3 of 11 evaluated patients. Multiple TAAs-specific CTLs were inducedKavanagh et al[70]2007
Autologous whole tumor mRNADCs transfected with whole-tumor mRNAI15 advanced CRC received the immunotherapy and KLH intravenously11 of the 13 CRC patients evaluated developed a positive KLH skin test, and 7 CRC patients exhibited CEA-specific responsesRains et al[75]2001
Autologous whole tumor cellsDCs-autologous whole-tumor fusion cells and IL-12I5 gastrointestinal tumors, including CRCAmong the 3 patients evaluated, 1 exhibited stable disease, and 2 exhibited progressive disease. No DTH-positive patients were detected in this trial. Good therapeutic responses in some patients with brain tumors were detectedHomma et al[78]2005
Allogeneic whole tumor cell lysateDCs loaded with allogeneic tumor cell lysateI6 advanced CRC (HLA-A2)Antitumor immune responses in some patients and transient stabilization or even reduction of CEA levels were detectedTamir et al[82]2007
DCs loaded with allogeneic melanoma cell lysate expressing at least one of six MAGE-A antigensII20 advanced CRC1 patient experienced a partial response, 7 patients achieved stable disease, and 5 patients exhibited prolonged progression-free survivalToh et al[83]2009
CEA

CEA is a so-called onco-fetal antigen abundantly present in a majority of CRC cases. Importantly, the elevated expression of CEA is associated with adenocarcinoma, particularly CRC. Therefore, CEA-targeted cancer immunotherapy has been developed. Morse et al[46] first conducted a phase I study using DCs loaded with an HLA-A2-restricted CEA peptide for the treatment of patients with 21 advanced CEA-expressing malignancies, including 11 CRC cases. One patient with ovarian cancer had a minor response, and one patient with breast cancer exhibited stable disease. Skin punch biopsy at DC injection sites demonstrated the pleomorphic, perivascular infiltration of cells consistent with a delayed-type hypersensitivity (DTH) response. This group also reported a phase II study of 13 patients with resected hepatic metastases of CRC, who received DCs loaded with CEA mRNA (DC/CEA mRNA). The administration of DC/CEA mRNA to CRC patients was feasible and safe. Nine of the 13 patients relapsed at a median of 122 days[47]. Furthermore, DCs modified with a recombinant fowlpox vector encoding CEA and a triad of costimulatory molecules [rF-CEA(6D)-TRICOM] was developed from the same group[48]. In this trial, 14 patients with HLA-A2 (11 with CRC and 3 with non-small cell lung cancer) were enrolled. CEA-specific T cells responses were detected in 10 patients. Five patients were stable through at least one cycle of immunization (3 mo)[48]. As recent reports indicate that DC-NK cell interaction plays a critical role in the induction of antitumor immunity[23,24], the same group conducted a phase I clinical trial of a vaccine consisting of autologous DCs loaded with a fowlpox vector encoding CEA[49]. Fourteen patients (5 CRC, 3 lung cancer, and 1 urachal adenocarcinoma) were enrolled in the trial; of the 9 patients analyzed, all with stable disease (n = 5) exhibited increased NK activity. Therefore, NK responses following DC vaccination may correlate with clinical benefit, and evaluation of NK responses should accordingly be included as a biomarker for DC-based cancer vaccines in clinical trials[49,50]. Another recent clinical trial also supports the importance of NK activity in CEA peptide-loaded DC-based cancer vaccines. In this trial, mature DCs activated by a combination of OK-432, low-dose prostanoid, and IFN-α were used[51], loaded with the CEA peptide and administrated to 10 CRC patients. Interestingly, the CRC patients with stable disease (n = 8) exhibited increased levels of NK cell frequency and CEA-specific CTL activity with a central memory phenotype. Conversely, a lack of CTL activity was observed in those with progressive disease, even though NK cell proliferation was detected. To induce efficient CEA-specific CTL responses, another study developed altered CEA peptides restricted with HLA-A2-loaded DCs, which were administered along with Flt3 ligand, a hematopoietic growth factor, to 12 patients with CRC (n = 10) or non-small cell lung cancer (n = 2)[52]. After vaccination, the expansion of CEA-specific CD8+ CTLs was detected in 7 out of 12 patients. Interestingly, 2 out of 12 CRC patients experienced dramatic tumor regression. One patient with progressive metastatic CRC had a complete resolution of pulmonary metastasis and malignant pleural effusion at 4 mo after vaccination, and one patient with CRC developed a mixed response after vaccination, with the regression of some but not all liver metastases. Clinical trials of DCs loaded with HLA-A24 restricted CEA peptides have also been reported. The vaccines were injected with adjuvant cytokines, such as natural human interferon alpha (IFN-α) and natural human tumor necrosis factor alpha (TNF-α), in patients with 10 advanced CEA-expressing metastatic malignancies, including 7 CRC cases[53]. Two patients (CRC and lung cancer) exhibited positive DTH reactions against CEA remained stable for 6 mo and 9 mo, respectively. Therefore, HLA-A24 and A2-restricted CEA peptide might be useful for inducing CEA-specific immune responses. Liu et al[54] immunized 10 metastatic CRC patients (6 patients with HLA-A24 and 4 with HLA-A2) who failed standard chemotherapy with DCs loaded with HLA-A2- or HLA-A24-restricted CEA peptides. In this clinical trial, the DC vaccine was injected into one inguinal lymph node under sonographic guidance. After vaccination, CEA-specific T cells were detected in 7 out of 10 patients. Two patients exhibited stable disease for at least 12 wk. Matsuda et al[55] also conducted a pilot study of DCs loaded with HLA-A24-restricted CEA peptide for 8 patients with advanced CEA-expressing gastrointestinal malignancies (7 CRCs and 1 gall bladder cancer). Four out of 7 patients developed CEA-specific CTL responses after vaccination. A DTH reaction was observed in 1 patient. Skin biopsy at the injected site showed the infiltration of lymphocytes. Three patients, including 2 CRCs, exhibited stable disease after vaccination. Reports from clinical trials using DCs loaded with HLA-restricted CEA peptide vaccines have also been reported in Japan, as 60% of the Japanese population and some Caucasians express HLA-A24. Ueda et al[56] injected the vaccines into 8 patients with CEA-expressing metastatic gastrointestinal or lung adenocarcinomas positive for HLA-A24. In this trial, no definite tumor shrinkage was observed; however, long-term stable disease or marked decreases in the serum CEA level was observed in some patients after therapy. CEA-specific immune responses have also been demonstrated in most of the patients in whom treatment was clinically effective. Another study examining the vaccination of patients with resectable liver metastases from CRC using mature DCs loaded with HLA-A2-restricted CEA-peptide has been reported in the Netherlands[57]. A total of 10 CRC patients with resection of liver metastases were treated, and the induction of CEA-specific T cells was demonstrated in 7 out of 10 patients. Interestingly, CEA-specific CTL responses were detected in a resected lymph node in one patient. CEA altered peptide (CEAalt) was also administered with DCs to induce antitumor immunity in patients with CEA-positive CRC (n = 7) or lung cancer (n = 2)[58]. In this trial, 5 out of 9 patients exhibited CEAalt-specific CTL responses, and 3 of 9 patients exhibited CEA-specific CTL responses[58]. As CEA is typically produced in gastrointestinal tissue during fetal development, the immune system exhibits some degree of tolerance. Therefore, a break in tolerance is required to induce efficient CEA-specific immunity.

WT1

The WT1 gene possesses oncogenic functions and is highly expressed in various types of malignancies, including CRC[59]. Moreover, WT1 expression in CRC is significantly associated with tumor progression, lymph node metastasis, distant metastasis and clinical stage[60]. Therefore, the WT1 protein may be one of the most promising cancer antigens. Indeed, the National Cancer Institute (NCI) has ranked WT1 as the number 1 target for cancer immunotherapy based on several factors[61]. Moreover, WT1 expression may be essential for maintaining the transformed characteristics of cancer cells. Tumor escape from immune surveillance, reflecting the downmodulation of WT1, is unlikely to occur[62,63]. Therefore, WT1-specific immune responses for the elimination of tumors may be induced in many types of cancers. Shimodaira et al[8] conducted a phase I study to investigate the safety and immunogenicity of DCs loaded with WT1 peptides restricted by MHC class I and class II (DC/WT1-I/II) for advanced CRC patients. Standard treatment comprising surgical resection and chemotherapy was followed by 1 course of 7 biweekly administrations of DC/WT1-I/II with OK-432 in 3 CRC patients. Importantly, WT1-specific CTLs were detected after the first vaccination and persisted for two years with prolonged disease-free and overall survival (OS)[8]. The maintenance of long-term WT1-specific memory CD8+ T cells through DC/WT1-I/II may be associated with clinical benefits in cancer patients[64].

MAGE

MAGE is a cancer-testis antigen aberrantly expressed in various types of human malignancies, including CRC. MAGE is not expressed in normal tissues except the testis. Thus, MAGE has been developed as a cancer immunotherapy target[10-12]. Sadanaga et al[65] initially examined DCs loaded with MAGE-3 peptide in patients with gastrointestinal carcinomas, depending on the HLA haplotype (HLA-A2 or A24). Twelve patients with advanced gastrointestinal carcinoma (six stomach, three esophagus, and three colon) were enrolled. After vaccination, MAGE-3-specific CTL responses were observed in 4 out of 8 patients. Tumor markers were decreased in 7 patients, and importantly, evidence of minor tumor regression was detected in 3 patients. This group also conducted clinical trials for CRC patients using MAGE-3 or MAGE-1 peptide[66]. Twenty-eight patients with advanced gastrointestinal carcinoma, including 7 CRCs, were administered mature DCs loaded with MAGE-3 or MAGE-1 peptide, depending on the HLA haplotype (HLA-A2 or A24). Peptide-specific CTL responses, tumor marker decreases and minor tumor regressions were observed in some patients after vaccination.

CEA and MUC1

A recent report from a randomized phase II clinical trial also indicated the clinical benefits of TAA-targeted DC-based cancer immunotherapy for CRC patients[67]. The aim of this trial was to determine whether 1 of 2 vaccines based on DCs and poxvectors encoding CEA and MUC1 (PANVAC)[68] would lengthen the survival of patients with resected CRC metastases. A total 74 patients, disease-free after CRC metastasectomy and perioperative chemotherapy, were randomized to injections of DCs modified with MUC1 PANVAC (DC/PANVAC) or PANVAC with per injection GM-CSF. The results indicated no differences in the clinical outcomes [progression-free survival (PFS) or OS] between the 2 vaccine strategies. Although CEA-specific T cell responders after DC/PANVAC were more frequently detected compared with PANC, the clinical benefits were not significant[67].

CEA, MAGE, and HER2

HER2/neu is a proto-oncogene product overexpressed in CRC cells[69]. Therefore, Kavanagh et al[70] conducted a phase I/II clinical trial administering a DC-based cancer immunotherapy targeting multiple TAAs, including CEA, MAGE, and HER2/neu, to patients with advanced CRC. The DCs were loaded with HLA-A2-restricted peptides derived from CEA, MAGE, and HER2/neu, pan-DR non-natural peptide optimized for both HLA-DR binding and TCR stimulation, and keyhole limpet hemocyanin (KLH) protein[71]. In this trial, 13 HLA-A2+ advanced CRC patients received the immunotherapy. Although, all patients exhibited progressive disease, CEA-specific T cell responses were detected in 3 out of 11 evaluated patients. Moreover, this pilot study demonstrated the induction of immune responses to multiple TAAs in patients with advanced CRC.

DCs loaded with whole tumor cell-derived antigens

DCs can present TAA-derived epitopes in various manners. Unlike antigenic peptide-loaded DCs, other strategies, such as DCs loaded with whole tumor cells (DC/whole tumor) through whole tumor lysates, apoptotic whole tumor cells, DNA, mRNA, or fusion with whole tumor cells, have been developed[72]. DC/whole tumor cells simultaneously induce numerous TAA-specific CD4+ and CD8+ T cell responses that are at least theoretically more effective than antigenic peptide-loaded DCs[72]. Moreover, for DC/whole tumor-based immunotherapy, allogeneic tumor cell lines can also be used instead of autologous tumor cells to induce autologous tumor specific antitumor immunity. However, unlike defined antigenic peptides, whole tumor cell-based therapy is applicable to all patients, regardless of HLA type.

DCs transfected with mRNA

We have previously reported that murine DCs transfected with MUC1 mRNA exhibited MUC1 expression on DCs in the context of co-stimulatory molecules, resulting in the induction of MUC1-specific CTL responses against CRC cells in vivo and in vitro[73]. Comparative studies have suggested that mRNA-transfected DCs are superior to other antigen-loaded DCs in inducing CTL responses[29,74]. In a clinical trial, DCs were transfected with whole tumor mRNA to induce antitumor immunity in CRC patients[74]. Fifteen patients with advanced CRC received the immunotherapy and KLH intravenously[75]. As a result, 11 out of the 13 CRC patients evaluated developed a positive KLH skin test, and 7 CRC patients exhibited CEA-specific responses.

Fusion of DCs with whole tumor cells

The fusion of DCs with whole tumor cells generates a heterokaryon expressing DC-derived co-stimulatory molecules and a broad array of TAAs, including both known and unidentified molecules. Thus, this method offers several advantages for presenting antigenic peptides and subsequently inducing polyclonal antigen-specific CD4+ cells and CD8+ T cell-mediated antitumor immune responses, resulting in long-term antitumor immunity activation without inducing tolerance[76]. Moreover, this strategy circumvents the daunting task of identifying TAAs for individualized immunotherapy. Interestingly, DC-tumor fusion cells are potent immune stimulators compared with DCs loaded with either apoptotic tumor-cell fragments or tumor lysates in mice studies[77]. In DC-tumor fusion cells, TAAs access the endogenous antigen-processing pathway, whereas DCs loaded with apoptotic tumor-cell fragments or tumor lysates rely on the cross-presentation of the antigen, which is typically not efficient[33]. In a phase I study, DC-tumor fusion cell vaccines were also administered with IL-12 in 5 gastrointestinal tumors, including CRC[78]. Among the 3 patients evaluated, 1 patient exhibited stable disease, and 2 patients exhibited progressive disease. Moreover, no DTH-positive patients were detected in this trial. Immunotherapy through DC-tumor fusion cells with IL-12 induced no serious adverse events and provided good therapeutic responses in some patients with brain tumors. In addition, patients with elevated serum levels of anti-nuclear antibody (ANA) had significantly longer treatment periods than those without treatment in these trials[79].

Allogeneic whole tumor cell lysate-loaded DCs

The use of autologous whole tumor cell lysates as a potential source of TAAs for DC loading has several potential advantages compared with defined antigenic peptides. DC-loaded whole tumor cell lysates and DC-tumor fusion cells express both known and unidentified TAAs, circumventing the daunting task of identifying TAAs. Moreover, DC-loaded whole tumor cell lysates also induce the simultaneous activation of polyclonal CD8+ and CD4+ T cells[80,81]. The activation of CD4+ and CD8+ T cells can provide robust assistance for the induction and maintenance of CD8+ CTLs. However, autologous whole tumor cell-based immunotherapy is often limited by the availability of sufficient numbers of autologous tumor cells, which may not be obtained when surgery is not a component of the treatment. Therefore, an alternative approach involves a use of allogeneic tumor cell lines instead of autologous tumor cells. This approach is based on the fact that some TAAs, such as CEA, WT1 and MUC1, are shared among most tumors. We demonstrated that allogeneic CRC cell-loaded autologous DCs induce antigen-specific CTL responses in CRC patients in vitro[4].

In clinical settings, autologous tumor lysate-loaded DC vaccines were used in advanced patients with CEA-positive CRC cells[82]. Six HLA-A2+ CRC patients received the immunotherapy and tetanus toxoid antigen, hepatitis B, and influenza matrix peptides. The results revealed antitumor immune responses in some patients, and the transient stabilization or even reduction of CEA levels were also detected. Moreover, DCs loaded with allogeneic melanoma cell lysate expressing at least one of six MAGE-A antigens were examined in this phase II study[83]. Twenty patients with advanced CRC received a total of 161 vaccinations. One patient experienced a partial response. Seven patients achieved stable disease. Five patients exhibited prolonged PFS.

IMMUNE CHECKPOINT THERAPY

DNA mismatch repair (MMR) is a group of genes encoding four proteins that play a key role in repairing mistakes and maintaining genomic stability[84]. Deficiencies in MM lead to MSI; thus, CRCs with MSI contain 10- to 100-fold more somatic mutations than metastatic CRC without MSI[85-87]. MSI reflects defective MMR in 15% to 20% of CRC patients[88]. Accumulating evidence indicates that the neoantigens produced from mutated proteins in tumors with MSI are recognized by the immune system, inducing CTL infiltration in tumors[87]. In addition, CD8+ CTL infiltration in CRC has a well-supported prognostic value[42]. However, the tumor microenvironment comprises not only CD8+ CTLs but also immune regulatory cell populations. Recent evidence indicates that CD8+ CRLs infiltration in tumors is associated with the therapeutic effects of immune checkpoint strategies[42]. Le et al[89] conducted a phase II trial to evaluate the clinical benefit of an anti-PD-1 immune checkpoint inhibitor, pembrolizumab, in 41 patients (11 MMR-deficient CRC, 21 MMR-proficient CRC, and 9 MMR-deficient non-CRC) (Table 2). Most patients (40 of 41) had previously received treatment of two or more lines of therapy; all patients then received pembrolizumab until either disease progression or unacceptable toxicity occurred. Pembrolizumab was well tolerated, and the immune-related objective response rates for MMR-deficient CRC and MMR-proficient CRC were 40% (4 of 10 patients) and 0% (0 of 18 patients), respectively. Moreover, the 20-wk immune-related progression-free survival rates were 78% (7 of 9 patients) and 11% (2 of 18 patients) for MMR-deficient CRC and MMR-proficient CRC, respectively. Additionally, patients with MMR-deficient non-CRC displayed responses similar to those of patients with MMR-deficient CRC[89]. Importantly, PD-1 blockade in patients with tumors with MSI has exhibited dramatic and durable responses, even in patients with colon cancer[89,90].

Table 2 Clinical trials of immune checkpoint therapy in patients with colorectal cancer.
TargetImmunotherapyPhasePatientsResultsRefYear
PD-1Pembrolizumab, anti-PD-1 immune checkpoint inhibitorII11 MMR-deficient CRC, 21 MMR-proficient CRC, and 9 MMR-deficient non-CRCThe immune-related objective response rate and immune-related progression-free survival rate were 40% (4 of 10 patients) and 78% (7 of 9 patients), respectively, for MMR-deficient CRC and 0% (0 of 18 patients) and 11% (2 of 18 patients) for MMR-proficient CRCLe et al[89]2015
CONCLUSION

The goal of CRC immunotherapy is to induce efficient antigen-specific polyclonal CD4+ and cytotoxic CD8+ CTLs in patients. DCs are potent APCs that play a pivotal role in the induction of antitumor immune responses. Therefore, the use of DC-based immunotherapy for CRC patients is promising. However, the immune suppression synergistically generated from CRC and the tumor microenvironment continues to be a major hurdle. Here, we described the ability of DC-based therapeutic immunotherapies to activate antitumor immune responses in CRC patients. However, these strategies may require combination with immune-modulating agents to maximize antitumor immunity. The induction of antigen-specific polyclonal T cell activation may be associated with the success of immune checkpoint therapeutic strategies. The combination of DC-based immunotherapy and simultaneous blockade of multiple immune checkpoints may have the potential for clinical benefit and should be evaluated[91].

Footnotes

P- Reviewer: Essani K, Ozhan G, Lee CH S- Editor: Qi Y L- Editor: A E- Editor: Wang CH

References
1.  Brenner H, Kloor M, Pox CP. Colorectal cancer. Lancet. 2014;383:1490-1502.  [PubMed]  [DOI]
2.  Kerr D. Clinical development of gene therapy for colorectal cancer. Nat Rev Cancer. 2003;3:615-622.  [PubMed]  [DOI]
3.  Koido S, Ohkusa T, Homma S, Namiki Y, Takakura K, Saito K, Ito Z, Kobayashi H, Kajihara M, Uchiyama K. Immunotherapy for colorectal cancer. World J Gastroenterol. 2013;19:8531-8542.  [PubMed]  [DOI]
4.  Koido S, Hara E, Homma S, Torii A, Toyama Y, Kawahara H, Watanabe M, Yanaga K, Fujise K, Tajiri H. Dendritic cells fused with allogeneic colorectal cancer cell line present multiple colorectal cancer-specific antigens and induce antitumor immunity against autologous tumor cells. Clin Cancer Res. 2005;11:7891-7900.  [PubMed]  [DOI]
5.  Zhu MZ, Marshall J, Cole D, Schlom J, Tsang KY. Specific cytolytic T-cell responses to human CEA from patients immunized with recombinant avipox-CEA vaccine. Clin Cancer Res. 2000;6:24-33.  [PubMed]  [DOI]
6.  Berinstein NL. Carcinoembryonic antigen as a target for therapeutic anticancer vaccines: a review. J Clin Oncol. 2002;20:2197-2207.  [PubMed]  [DOI]
7.  Oji Y, Ogawa H, Tamaki H, Oka Y, Tsuboi A, Kim EH, Soma T, Tatekawa T, Kawakami M, Asada M. Expression of the Wilms’ tumor gene WT1 in solid tumors and its involvement in tumor cell growth. Jpn J Cancer Res. 1999;90:194-204.  [PubMed]  [DOI]
8.  Shimodaira S, Sano K, Hirabayashi K, Koya T, Higuchi Y, Mizuno Y, Yamaoka N, Yuzawa M, Kobayashi T, Ito K. Dendritic Cell-Based Adjuvant Vaccination Targeting Wilms’ Tumor 1 in Patients with Advanced Colorectal Cancer. Vaccines (Basel). 2015;3:1004-1018.  [PubMed]  [DOI]
9.  Ajioka Y, Allison LJ, Jass JR. Significance of MUC1 and MUC2 mucin expression in colorectal cancer. J Clin Pathol. 1996;49:560-564.  [PubMed]  [DOI]
10.  Mashino K, Sadanaga N, Tanaka F, Yamaguchi H, Nagashima H, Inoue H, Sugimachi K, Mori M. Expression of multiple cancer-testis antigen genes in gastrointestinal and breast carcinomas. Br J Cancer. 2001;85:713-720.  [PubMed]  [DOI]
11.  Li M, Yuan YH, Han Y, Liu YX, Yan L, Wang Y, Gu J. Expression profile of cancer-testis genes in 121 human colorectal cancer tissue and adjacent normal tissue. Clin Cancer Res. 2005;11:1809-1814.  [PubMed]  [DOI]
12.  Sang M, Lian Y, Zhou X, Shan B. MAGE-A family: attractive targets for cancer immunotherapy. Vaccine. 2011;29:8496-8500.  [PubMed]  [DOI]
13.  Speetjens FM, Kuppen PJ, Welters MJ, Essahsah F, Voet van den Brink AM, Lantrua MG, Valentijn AR, Oostendorp J, Fathers LM, Nijman HW. Induction of p53-specific immunity by a p53 synthetic long peptide vaccine in patients treated for metastatic colorectal cancer. Clin Cancer Res. 2009;15:1086-1095.  [PubMed]  [DOI]
14.  Grizzi F, Bianchi P, Malesci A, Laghi L. Prognostic value of innate and adaptive immunity in colorectal cancer. World J Gastroenterol. 2013;19:174-184.  [PubMed]  [DOI]
15.  Ahmed D, Eide PW, Eilertsen IA, Danielsen SA, Eknæs M, Hektoen M, Lind GE, Lothe RA. Epigenetic and genetic features of 24 colon cancer cell lines. Oncogenesis. 2013;2:e71.  [PubMed]  [DOI]
16.  Takahara A, Koido S, Ito M, Nagasaki E, Sagawa Y, Iwamoto T, Komita H, Ochi T, Fujiwara H, Yasukawa M. Gemcitabine enhances Wilms’ tumor gene WT1 expression and sensitizes human pancreatic cancer cells with WT1-specific T-cell-mediated antitumor immune response. Cancer Immunol Immunother. 2011;60:1289-1297.  [PubMed]  [DOI]
17.  Koido S, Homma S, Takahara A, Namiki Y, Komita H, Uchiyama K, Ito M, Gong J, Ohkusa T, Tajiri H. Immunotherapy synergizes with chemotherapy targeting pancreatic cancer. Immunotherapy. 2012;4:5-7.  [PubMed]  [DOI]
18.  Al-Ejeh F, Darby JM, Brown MP. Chemotherapy synergizes with radioimmunotherapy targeting La autoantigen in tumors. PLoS One. 2009;4:e4630.  [PubMed]  [DOI]
19.  Boon T, Coulie PG, Van den Eynde B. Tumor antigens recognized by T cells. Immunol Today. 1997;18:267-268.  [PubMed]  [DOI]
20.  Steinman RM, Swanson J. The endocytic activity of dendritic cells. J Exp Med. 1995;182:283-288.  [PubMed]  [DOI]
21.  Tanaka Y, Koido S, Ohana M, Liu C, Gong J. Induction of impaired antitumor immunity by fusion of MHC class II-deficient dendritic cells with tumor cells. J Immunol. 2005;174:1274-1280.  [PubMed]  [DOI]
22.  Adam C, King S, Allgeier T, Braumüller H, Lüking C, Mysliwietz J, Kriegeskorte A, Busch DH, Röcken M, Mocikat R. DC-NK cell cross talk as a novel CD4+ T-cell-independent pathway for antitumor CTL induction. Blood. 2005;106:338-344.  [PubMed]  [DOI]
23.  van Beek JJ, Wimmers F, Hato SV, de Vries IJ, Sköld AE. Dendritic cell cross talk with innate and innate-like effector cells in antitumor immunity: implications for DC vaccination. Crit Rev Immunol. 2014;34:517-536.  [PubMed]  [DOI]
24.  Wehner R, Dietze K, Bachmann M, Schmitz M. The bidirectional crosstalk between human dendritic cells and natural killer cells. J Innate Immun. 2011;3:258-263.  [PubMed]  [DOI]
25.  Steinman RM, Banchereau J. Taking dendritic cells into medicine. Nature. 2007;449:419-426.  [PubMed]  [DOI]
26.  Nestle FO, Alijagic S, Gilliet M, Sun Y, Grabbe S, Dummer R, Burg G, Schadendorf D. Vaccination of melanoma patients with peptide- or tumor lysate-pulsed dendritic cells. Nat Med. 1998;4:328-332.  [PubMed]  [DOI]
27.  Koido S, Homma S, Okamoto M, Takakura K, Mori M, Yoshizaki S, Tsukinaga S, Odahara S, Koyama S, Imazu H. Treatment with chemotherapy and dendritic cells pulsed with multiple Wilms’ tumor 1 (WT1)-specific MHC class I/II-restricted epitopes for pancreatic cancer. Clin Cancer Res. 2014;20:4228-4239.  [PubMed]  [DOI]
28.  Kimura Y, Tsukada J, Tomoda T, Takahashi H, Imai K, Shimamura K, Sunamura M, Yonemitsu Y, Shimodaira S, Koido S. Clinical and immunologic evaluation of dendritic cell-based immunotherapy in combination with gemcitabine and/or S-1 in patients with advanced pancreatic carcinoma. Pancreas. 2012;41:195-205.  [PubMed]  [DOI]
29.  Gilboa E, Vieweg J. Cancer immunotherapy with mRNA-transfected dendritic cells. Immunol Rev. 2004;199:251-263.  [PubMed]  [DOI]
30.  Mackensen A, Herbst B, Chen JL, Köhler G, Noppen C, Herr W, Spagnoli GC, Cerundolo V, Lindemann A. Phase I study in melanoma patients of a vaccine with peptide-pulsed dendritic cells generated in vitro from CD34(+) hematopoietic progenitor cells. Int J Cancer. 2000;86:385-392.  [PubMed]  [DOI]
31.  Palucka K, Ueno H, Banchereau J. Recent developments in cancer vaccines. J Immunol. 2011;186:1325-1331.  [PubMed]  [DOI]
32.  Gong J, Chen D, Kashiwaba M, Kufe D. Induction of antitumor activity by immunization with fusions of dendritic and carcinoma cells. Nat Med. 1997;3:558-561.  [PubMed]  [DOI]
33.  Gong J, Koido S, Calderwood SK. Cell fusion: from hybridoma to dendritic cell-based vaccine. Expert Rev Vaccines. 2008;7:1055-1068.  [PubMed]  [DOI]
34.  Cavallo F, Curcio C, Forni G. Immunotherapy and immunoprevention of cancer: where do we stand? Expert Opin Biol Ther. 2005;5:717-726.  [PubMed]  [DOI]
35.  Giorda E, Sibilio L, Martayan A, Moretti S, Venturo I, Mottolese M, Ferrara GB, Cappellacci S, Eibenschutz L, Catricalà C. The antigen processing machinery of class I human leukocyte antigens: linked patterns of gene expression in neoplastic cells. Cancer Res. 2003;63:4119-4127.  [PubMed]  [DOI]
36.  Koido S, Homma S, Takahara A, Namiki Y, Tsukinaga S, Mitobe J, Odahara S, Yukawa T, Matsudaira H, Nagatsuma K. Current immunotherapeutic approaches in pancreatic cancer. Clin Dev Immunol. 2011;2011:267539.  [PubMed]  [DOI]
37.  Koido S, Homma S, Hara E, Namiki Y, Takahara A, Komita H, Nagasaki E, Ito M, Ohkusa T, Gong J. Regulation of tumor immunity by tumor/dendritic cell fusions. Clin Dev Immunol. 2010;2010:516768.  [PubMed]  [DOI]
38.  Adachi K, Tamada K. Immune checkpoint blockade opens an avenue of cancer immunotherapy with a potent clinical efficacy. Cancer Sci. 2015;106:945-950.  [PubMed]  [DOI]
39.  Droeser RA, Hirt C, Viehl CT, Frey DM, Nebiker C, Huber X, Zlobec I, Eppenberger-Castori S, Tzankov A, Rosso R. Clinical impact of programmed cell death ligand 1 expression in colorectal cancer. Eur J Cancer. 2013;49:2233-2242.  [PubMed]  [DOI]
40.  Anitei MG, Zeitoun G, Mlecnik B, Marliot F, Haicheur N, Todosi AM, Kirilovsky A, Lagorce C, Bindea G, Ferariu D. Prognostic and predictive values of the immunoscore in patients with rectal cancer. Clin Cancer Res. 2014;20:1891-1899.  [PubMed]  [DOI]
41.  Merika E, Saif MW, Katz A, Syrigos K, Morse M. Review. Colon cancer vaccines: an update. In Vivo. 2010;24:607-628.  [PubMed]  [DOI]
42.  Quigley DA, Kristensen V. Predicting prognosis and therapeutic response from interactions between lymphocytes and tumor cells. Mol Oncol. 2015;9:2054-2062.  [PubMed]  [DOI]
43.  Shi SJ, Wang LJ, Wang GD, Guo ZY, Wei M, Meng YL, Yang AG, Wen WH. B7-H1 expression is associated with poor prognosis in colorectal carcinoma and regulates the proliferation and invasion of HCT116 colorectal cancer cells. PLoS One. 2013;8:e76012.  [PubMed]  [DOI]
44.  Wu P, Wu D, Li L, Chai Y, Huang J. PD-L1 and Survival in Solid Tumors: A Meta-Analysis. PLoS One. 2015;10:e0131403.  [PubMed]  [DOI]
45.  Zhao LW, Li C, Zhang RL, Xue HG, Zhang FX, Zhang F, Gai XD. B7-H1 and B7-H4 expression in colorectal carcinoma: correlation with tumor FOXP3(+) regulatory T-cell infiltration. Acta Histochem. 2014;116:1163-1168.  [PubMed]  [DOI]
46.  Morse MA, Deng Y, Coleman D, Hull S, Kitrell-Fisher E, Nair S, Schlom J, Ryback ME, Lyerly HK. A Phase I study of active immunotherapy with carcinoembryonic antigen peptide (CAP-1)-pulsed, autologous human cultured dendritic cells in patients with metastatic malignancies expressing carcinoembryonic antigen. Clin Cancer Res. 1999;5:1331-1338.  [PubMed]  [DOI]
47.  Morse MA, Nair SK, Mosca PJ, Hobeika AC, Clay TM, Deng Y, Boczkowski D, Proia A, Neidzwiecki D, Clavien PA. Immunotherapy with autologous, human dendritic cells transfected with carcinoembryonic antigen mRNA. Cancer Invest. 2003;21:341-349.  [PubMed]  [DOI]
48.  Morse MA, Clay TM, Hobeika AC, Osada T, Khan S, Chui S, Niedzwiecki D, Panicali D, Schlom J, Lyerly HK. Phase I study of immunization with dendritic cells modified with fowlpox encoding carcinoembryonic antigen and costimulatory molecules. Clin Cancer Res. 2005;11:3017-3024.  [PubMed]  [DOI]
49.  Osada T, Clay T, Hobeika A, Lyerly HK, Morse MA. NK cell activation by dendritic cell vaccine: a mechanism of action for clinical activity. Cancer Immunol Immunother. 2006;55:1122-1131.  [PubMed]  [DOI]
50.  Lion E, Smits EL, Berneman ZN, Van Tendeloo VF. NK cells: key to success of DC-based cancer vaccines? Oncologist. 2012;17:1256-1270.  [PubMed]  [DOI]
51.  Sakakibara M, Kanto T, Hayakawa M, Kuroda S, Miyatake H, Itose I, Miyazaki M, Kakita N, Higashitani K, Matsubara T. Comprehensive immunological analyses of colorectal cancer patients in the phase I/II study of quickly matured dendritic cell vaccine pulsed with carcinoembryonic antigen peptide. Cancer Immunol Immunother. 2011;60:1565-1575.  [PubMed]  [DOI]
52.  Fong L, Hou Y, Rivas A, Benike C, Yuen A, Fisher GA, Davis MM, Engleman EG. Altered peptide ligand vaccination with Flt3 ligand expanded dendritic cells for tumor immunotherapy. Proc Natl Acad Sci USA. 2001;98:8809-8814.  [PubMed]  [DOI]
53.  Itoh T, Ueda Y, Kawashima I, Nukaya I, Fujiwara H, Fuji N, Yamashita T, Yoshimura T, Okugawa K, Iwasaki T. Immunotherapy of solid cancer using dendritic cells pulsed with the HLA-A24-restricted peptide of carcinoembryonic antigen. Cancer Immunol Immunother. 2002;51:99-106.  [PubMed]  [DOI]
54.  Liu KJ, Wang CC, Chen LT, Cheng AL, Lin DT, Wu YC, Yu WL, Hung YM, Yang HY, Juang SH. Generation of carcinoembryonic antigen (CEA)-specific T-cell responses in HLA-A*0201 and HLA-A*2402 late-stage colorectal cancer patients after vaccination with dendritic cells loaded with CEA peptides. Clin Cancer Res. 2004;10:2645-2651.  [PubMed]  [DOI]
55.  Matsuda K, Tsunoda T, Tanaka H, Umano Y, Tanimura H, Nukaya I, Takesako K, Yamaue H. Enhancement of cytotoxic T-lymphocyte responses in patients with gastrointestinal malignancies following vaccination with CEA peptide-pulsed dendritic cells. Cancer Immunol Immunother. 2004;53:609-616.  [PubMed]  [DOI]
56.  Ueda Y, Itoh T, Nukaya I, Kawashima I, Okugawa K, Yano Y, Yamamoto Y, Naitoh K, Shimizu K, Imura K. Dendritic cell-based immunotherapy of cancer with carcinoembryonic antigen-derived, HLA-A24-restricted CTL epitope: Clinical outcomes of 18 patients with metastatic gastrointestinal or lung adenocarcinomas. Int J Oncol. 2004;24:909-917.  [PubMed]  [DOI]
57.  Lesterhuis WJ, de Vries IJ, Schuurhuis DH, Boullart AC, Jacobs JF, de Boer AJ, Scharenborg NM, Brouwer HM, van de Rakt MW, Figdor CG. Vaccination of colorectal cancer patients with CEA-loaded dendritic cells: antigen-specific T cell responses in DTH skin tests. Ann Oncol. 2006;17:974-980.  [PubMed]  [DOI]
58.  Babatz J, Röllig C, Löbel B, Folprecht G, Haack M, Günther H, Köhne CH, Ehninger G, Schmitz M, Bornhäuser M. Induction of cellular immune responses against carcinoembryonic antigen in patients with metastatic tumors after vaccination with altered peptide ligand-loaded dendritic cells. Cancer Immunol Immunother. 2006;55:268-276.  [PubMed]  [DOI]
59.  Oji Y, Yamamoto H, Nomura M, Nakano Y, Ikeba A, Nakatsuka S, Abeno S, Kiyotoh E, Jomgeow T, Sekimoto M. Overexpression of the Wilms’ tumor gene WT1 in colorectal adenocarcinoma. Cancer Sci. 2003;94:712-717.  [PubMed]  [DOI]
60.  Miyata Y, Kumagai K, Nagaoka T, Kitaura K, Kaneda G, Kanazawa H, Suzuki S, Hamada Y, Suzuki R. Clinicopathological significance and prognostic value of Wilms’ tumor gene expression in colorectal cancer. Cancer Biomark. 2015;15:789-797.  [PubMed]  [DOI]
61.  Cheever MA, Allison JP, Ferris AS, Finn OJ, Hastings BM, Hecht TT, Mellman I, Prindiville SA, Viner JL, Weiner LM. The prioritization of cancer antigens: a national cancer institute pilot project for the acceleration of translational research. Clin Cancer Res. 2009;15:5323-5337.  [PubMed]  [DOI]
62.  Oka Y, Sugiyama H. WT1 peptide vaccine, one of the most promising cancer vaccines: its present status and the future prospects. Immunotherapy. 2010;2:591-594.  [PubMed]  [DOI]
63.  Sugiyama H. WT1 (Wilms’ tumor gene 1): biology and cancer immunotherapy. Jpn J Clin Oncol. 2010;40:377-387.  [PubMed]  [DOI]
64.  Chemoimmunotherapy targeting Wilms’ tumor 1 (WT1)-specific cytotoxic T lymphocyte and helper T cell responses for patients with pancreatic cancer Oncoimmunology. 2014;3:e958950.  [PubMed]  [DOI]
65.  Sadanaga N, Nagashima H, Mashino K, Tahara K, Yamaguchi H, Ohta M, Fujie T, Tanaka F, Inoue H, Takesako K. Dendritic cell vaccination with MAGE peptide is a novel therapeutic approach for gastrointestinal carcinomas. Clin Cancer Res. 2001;7:2277-2284.  [PubMed]  [DOI]
66.  Tanaka F, Haraguchi N, Isikawa K, Inoue H, Mori M. Potential role of dendritic cell vaccination with MAGE peptides in gastrointestinal carcinomas. Oncol Rep. 2008;20:1111-1116.  [PubMed]  [DOI]
67.  Morse MA, Niedzwiecki D, Marshall JL, Garrett C, Chang DZ, Aklilu M, Crocenzi TS, Cole DJ, Dessureault S, Hobeika AC. A randomized phase II study of immunization with dendritic cells modified with poxvectors encoding CEA and MUC1 compared with the same poxvectors plus GM-CSF for resected metastatic colorectal cancer. Ann Surg. 2013;258:879-886.  [PubMed]  [DOI]
68.  Mohebtash M, Tsang KY, Madan RA, Huen NY, Poole DJ, Jochems C, Jones J, Ferrara T, Heery CR, Arlen PM. A pilot study of MUC-1/CEA/TRICOM poxviral-based vaccine in patients with metastatic breast and ovarian cancer. Clin Cancer Res. 2011;17:7164-7173.  [PubMed]  [DOI]
69.  Brossart P, Stuhler G, Flad T, Stevanovic S, Rammensee HG, Kanz L, Brugger W. Her-2/neu-derived peptides are tumor-associated antigens expressed by human renal cell and colon carcinoma lines and are recognized by in vitro induced specific cytotoxic T lymphocytes. Cancer Res. 1998;58:732-736.  [PubMed]  [DOI]
70.  Kavanagh B, Ko A, Venook A, Margolin K, Zeh H, Lotze M, Schillinger B, Liu W, Lu Y, Mitsky P. Vaccination of metastatic colorectal cancer patients with matured dendritic cells loaded with multiple major histocompatibility complex class I peptides. J Immunother. 2007;30:762-772.  [PubMed]  [DOI]
71.  Brossart P, Heinrich KS, Stuhler G, Behnke L, Reichardt VL, Stevanovic S, Muhm A, Rammensee HG, Kanz L, Brugger W. Identification of HLA-A2-restricted T-cell epitopes derived from the MUC1 tumor antigen for broadly applicable vaccine therapies. Blood. 1999;93:4309-4317.  [PubMed]  [DOI]
72.  de Gruijl TD, van den Eertwegh AJ, Pinedo HM, Scheper RJ. Whole-cell cancer vaccination: from autologous to allogeneic tumor- and dendritic cell-based vaccines. Cancer Immunol Immunother. 2008;57:1569-1577.  [PubMed]  [DOI]
73.  Koido S, Kashiwaba M, Chen D, Gendler S, Kufe D, Gong J. Induction of antitumor immunity by vaccination of dendritic cells transfected with MUC1 RNA. J Immunol. 2000;165:5713-5719.  [PubMed]  [DOI]
74.  Nair SK, Hull S, Coleman D, Gilboa E, Lyerly HK, Morse MA. Induction of carcinoembryonic antigen (CEA)-specific cytotoxic T-lymphocyte responses in vitro using autologous dendritic cells loaded with CEA peptide or CEA RNA in patients with metastatic malignancies expressing CEA. Int J Cancer. 1999;82:121-124.  [PubMed]  [DOI]
75.  Rains N, Cannan RJ, Chen W, Stubbs RS. Development of a dendritic cell (DC)-based vaccine for patients with advanced colorectal cancer. Hepatogastroenterology. 2001;48:347-351.  [PubMed]  [DOI]
76.  Kajihara M, Takakura K, Ohkusa T, Koido S. The impact of dendritic cell-tumor fusion cells on cancer vaccines - past progress and future strategies. Immunotherapy. 2015;7:1111-1122.  [PubMed]  [DOI]
77.  Galea-Lauri J, Darling D, Mufti G, Harrison P, Farzaneh F. Eliciting cytotoxic T lymphocytes against acute myeloid leukemia-derived antigens: evaluation of dendritic cell-leukemia cell hybrids and other antigen-loading strategies for dendritic cell-based vaccination. Cancer Immunol Immunother. 2002;51:299-310.  [PubMed]  [DOI]
78.  Homma S, Kikuchi T, Ishiji N, Ochiai K, Takeyama H, Saotome H, Sagawa Y, Hara E, Kufe D, Ryan JL. Cancer immunotherapy by fusions of dendritic and tumour cells and rh-IL-12. Eur J Clin Invest. 2005;35:279-286.  [PubMed]  [DOI]
79.  Homma S, Sagawa Y, Ito M, Ohno T, Toda G. Cancer immunotherapy using dendritic/tumour-fusion vaccine induces elevation of serum anti-nuclear antibody with better clinical responses. Clin Exp Immunol. 2006;144:41-47.  [PubMed]  [DOI]
80.  Fields RC, Shimizu K, Mulé JJ. Murine dendritic cells pulsed with whole tumor lysates mediate potent antitumor immune responses in vitro and in vivo. Proc Natl Acad Sci USA. 1998;95:9482-9487.  [PubMed]  [DOI]
81.  Koido S, Homma S, Okamoto M, Namiki Y, Takakura K, Uchiyama K, Kajihara M, Arihiro S, Imazu H, Arakawa H. Fusions between dendritic cells and whole tumor cells as anticancer vaccines. Oncoimmunology. 2013;2:e24437.  [PubMed]  [DOI]
82.  Tamir A, Basagila E, Kagahzian A, Jiao L, Jensen S, Nicholls J, Tate P, Stamp G, Farzaneh F, Harrison P. Induction of tumor-specific T-cell responses by vaccination with tumor lysate-loaded dendritic cells in colorectal cancer patients with carcinoembryonic-antigen positive tumors. Cancer Immunol Immunother. 2007;56:2003-2016.  [PubMed]  [DOI]
83.  Toh HC, Wang WW, Chia WK, Kvistborg P, Sun L, Teo K, Phoon YP, Soe Y, Tan SH, Hee SW. Clinical Benefit of Allogeneic Melanoma Cell Lysate-Pulsed Autologous Dendritic Cell Vaccine in MAGE-Positive Colorectal Cancer Patients. Clin Cancer Res. 2009;15:7726-7736.  [PubMed]  [DOI]
84.  Parsons R, Li GM, Longley MJ, Fang WH, Papadopoulos N, Jen J, de la Chapelle A, Kinzler KW, Vogelstein B, Modrich P. Hypermutability and mismatch repair deficiency in RER+ tumor cells. Cell. 1993;75:1227-1236.  [PubMed]  [DOI]
85.  Timmermann B, Kerick M, Roehr C, Fischer A, Isau M, Boerno ST, Wunderlich A, Barmeyer C, Seemann P, Koenig J. Somatic mutation profiles of MSI and MSS colorectal cancer identified by whole exome next generation sequencing and bioinformatics analysis. PLoS One. 2010;5:e15661.  [PubMed]  [DOI]
86.  Aguiar PN, Tadokoro H, Forones NM, de Mello RA. MMR deficiency may lead to a high immunogenicity and then an improvement in anti-PD-1 efficacy for metastatic colorectal cancer. Immunotherapy. 2015;7:1133-1134.  [PubMed]  [DOI]
87.  Aaltonen LA, Peltomäki P, Leach FS, Sistonen P, Pylkkänen L, Mecklin JP, Järvinen H, Powell SM, Jen J, Hamilton SR. Clues to the pathogenesis of familial colorectal cancer. Science. 1993;260:812-816.  [PubMed]  [DOI]
88.  Hampel H, Frankel WL, Martin E, Arnold M, Khanduja K, Kuebler P, Nakagawa H, Sotamaa K, Prior TW, Westman J. Screening for the Lynch syndrome (hereditary nonpolyposis colorectal cancer). N Engl J Med. 2005;352:1851-1860.  [PubMed]  [DOI]
89.  Le DT, Uram JN, Wang H, Bartlett BR, Kemberling H, Eyring AD, Skora AD, Luber BS, Azad NS, Laheru D. PD-1 Blockade in Tumors with Mismatch-Repair Deficiency. N Engl J Med. 2015;372:2509-2520.  [PubMed]  [DOI]
90.  Lee V, Le DT. Efficacy of PD-1 blockade in tumors with MMR deficiency. Immunotherapy. 2016;8:1-3.  [PubMed]  [DOI]
91.  Yu P, Steel JC, Zhang M, Morris JC, Waldmann TA. Simultaneous blockade of multiple immune system inhibitory checkpoints enhances antitumor activity mediated by interleukin-15 in a murine metastatic colon carcinoma model. Clin Cancer Res. 2010;16:6019-6028.  [PubMed]  [DOI]