Anti-idiotypic antibody and recombinant antigen vaccines in colorectal cancer patients

Review on the immunotherapy strategies against metastatic colorectal carcinoma

Colorectal cancer (CRC) is one of the most common malignancies throughout the world and the leading cause of cancer-related mortality in Western countries. Recent progress in CRC treatment options, such as surgery, chemotherapy, radiotherapy and target therapy, has improved the prognosis, but advanced disease with recurrence or distant metastasis is usually incurable and has an unfavorable prognosis. The introduction of immunotherapy-associated strategies, both active and passive, to the treatment of CRC aims to overcome the limits of classical treatments. We review the state of the art for CRC with respect to different immunotherapeutic approaches, such as the use of cancer vaccines and/or adoptive cellular therapy, their most current advances and limitations and perspectives for further improvements.

Idiotypes as immunogens: facing the challenge of inducing strong therapeutic immune responses against the variable region of immunoglobulins

Idiotype (Id)-based immunotherapy has been exploited as cancer treatment option. Conceived as therapy for malignancies bearing idiotypic antigens, it has been also extended to solid tumors because of the capacity of anti-idiotypic antibodies to mimic Id-unrelated antigens. In both these two settings, efforts are being made to overcome the poor immune responsiveness often experienced when using self immunoglobulins as immunogens. Despite bearing a unique gene combination, and thus particular epitopes, it is normally difficult to stimulate the immune response against antibody variable regions. Different strategies are currently used to strengthen Id immunogenicity, such as concomitant use of immune-stimulating molecules, design of Id-containing immunogenic recombinant proteins, specific targeting of relevant immune cells, and genetic immunization. This review focuses on the role of anti-Id vaccination in cancer management and on the current developments used to foster anti-idiotypic B and T cell responses.

Screening and Identification of Recombinant Anti-Idiotype Antibodies against Gastric Cancer and Colon Cancer Monoclonal Antibodies by a Phage-Displayed Single-Chain Variable Fragment Library

Several monoclonal antibodies (McAbs) have been developed that show high sensitivity and specificity to gastric cancer and colorectal cancer. However, few of the antigens recognized by these antibodies have been identified. The authors now report the selection of anti-idiotype (anti-id) antibodies of MGb1 McAb against gastric cancer and MC5 McAb against colorectal cancer using phage-displayed single-chain variable fragment (ScFv) libraries. After purification, the anti-id antibodies were approximately 30 kd and could be recognized by MGb1/MC5 McAb. Anti-id antibodies significantly blocked the binding of MGb1 and MC5 to gastric cancer/colorectal cancer cells, respectively, suggesting that the antibodies were specific to MGb1 and MC5. Antibodies against gastric and colorectal cancer could be detected in mice at 6 weeks after immunization with the anti-id antibodies. At week 8, antibody titers reached 1:400. The anti-id antibodies may be useful as novel reagents for developing vaccines against gastric cancer and colorectal cancer.

Harnessing the immune system for ovarian cancer therapy

The clinical course of ovarian cancer is often marked by periods of relapse and remission until chemo-resistance develops. Patients in remission with minimal disease burdens are ideally suited for the evaluation of immune-based strategies. Major obstacles to the development of successful immune strategies include the identification of tumor-restricted immunogenic targets, generation of a sufficient immune response to cause tumor rejection, and approaches to overcome evasion of immune attack. Many questions remain as optimal strategies are developed, which include: (i) What is the best antigen form (e.g. peptides, proteins or tumor lysates)? (ii) What are the appropriate adjuvants? (iii) Are mono-valent or multi-valent vaccines likely to be more effective? (iv) What is the optimal frequency and duration of vaccination? (v) How should antigen-specific responses be monitored? and (vi) How should the anti-cancer response be maintained? In this review, we explore representative examples of immune strategies under investigation for patients with ovarian carcinoma which illustrate many of these issues. Basic principles generic to all these immunotherapeutic approaches will also be discussed.

Antitumor effect of an antibody against gastrointestinal cancer-associated antigen CA19.9

Despite tremendous efforts in developing cancer vaccines and monoclonal antibodies (mAbs), only a few passive or active immunotherapeutic modalities have succeeded. The failure may be due to the existence of immunosuppressive factors, which caused anergy of patients' immune system. In this study, we discovered that CA19.9 is one such immunosuppressive factor, which could inhibit the proliferation of activated human lymphocytes. However, this inhibition could be reversed by a mAb, LC44, which was specifically generated against CA19.9. An in vitro cytotoxic experiment showed that mAb LC44 could form an immunocomplex with CA19.9, which subsequently induced the production of cytotoxic T-cells reacting to CA19.9-positive cancer cells. In addition, mAb LC44 could mediate the complement-dependent cytotoxicity to CA19.9-positive cancer cells. mAb LC44 showed an antitumor effect in immunodeficient mice with colon cancer burden in the presence or absence of CA19.9. Based on the observations from this study, we postulated that the mAb, LC44, could be a promising antitumor agent for gastrointestinal cancer and worthy of further investigation.

Anti-idiotype antibodies in cancer treatment

As a cancer immunotherapy tool, idiotypes (Ids) have been used in different ways over the last three decades, depending on the actual human tumor cell target. It all started with passive, monoclonal, anti-Id antibody treatment of B-cell lymphoma, a setting in which results were tantalizing, but logistics unsustainable. It then moved toward the development of anti-Id vaccines for the treatment of the same tumors, a setting in which we have recently provided the first formal proof of principle of clinical benefit associated with the use of a human cancer vaccine. Meanwhile, it also expanded in the direction of exploiting the antigenic mimicry of some Ids with Id-unrelated, tumor-associated antigens for the immunotherapy of a number of solid tumors, a setting in which clinical results are still far from being consolidated. All in all, over the years Id-based immunotherapy has paved the way for a number of seminal therapeutic improvements for cancer patients, including the development of most if not all Id-unrelated monoclonal antibodies that have recently revolutionized the field.

Immunologic approaches to ovarian cancer treatment

The clinical course of ovarian cancer is often marked by periods of relapse and remission until chemotherapy resistance develops. Patients in remission with minimal disease burdens are ideally suited for the evaluation of immune-based strategies. The role of immune surveillance in improving outcome has been supported by the correlation of increased survival with the presence or absence of tumor-infiltrating lymphocytes in a given patient. Major obstacles to the development of successful immune strategies include the identification of tumor-restricted immunogenic targets, generation of a sufficient immune response to cause tumor rejection, and approaches to overcome evasion of immune attack. As optimal strategies are being developed, many questions remain. Some of the questions are as follows: What is the best antigen form (eg, peptides, proteins, or tumor lysates)? What are the appropriate adjuvants? Are monovalent or multivalent vaccines likely to be more effective? What is the optimal frequency and duration of vaccination? How should antigen-specific responses be monitored? How should the anticancer response be maintained? In this review, we will explore representative examples of immune strategies under investigation for patients with ovarian carcinoma that illustrate many of these issues. We will review ongoing phase III studies for patients in first clinical remission. Basic principles generic to all these immunotherapeutic approaches will be discussed in the hopes of yielding the most promising results as the field continues to evolve.

The anti-idiotypic antibody abagovomab in patients with recurrent ovarian cancer. A phase I trial of the AGO-OVAR

BACKGROUND

Abagovomab is a murine anti-idiotypic antibody against the antigen CA-125 which has been shown to elicit humoral and cellular immune responses against ovarian cancer (oc).

PATIENTS AND METHODS

This phase I trial included 36 patients with recurrent oc comparing two subcutaneous (s.c.) vaccination schedules: nine (group L) versus six injections (group S), 18 patients in each group. Four injections of 2.0 mg abagovomab were administered every 2 weeks and then two or five additional doses monthly. Primary endpoint was drop-out rate due to toxicity, and the secondary endpoint was analysis of immunological response.

RESULTS

Treatment was completed in eight (44%) and 16 (89%) patients in groups L and S, respectively. Premature termination occurred due to patient withdrawal or disease progression. No treatment-limiting toxicities occurred in either group. The most common toxicity related to the vaccine was grade 1/2 local injection site reaction. Induction of Ab3 was observed in all evaluable patients. There were no differences between the groups with regard to induction of human anti-mouse antibody (P = 0.1006). IFNgamma-expressing CA125-specific CD8+ T-cells were significantly more frequent in group L, while there was no significant difference between CD4+ T-cells in the two groups.

CONCLUSIONS

Abagovomab s.c. vaccination is safe and well tolerated. The long vaccination schedule tended to be more effective with regard to AB3-induction and cellular cytotoxicity.

Targeted therapy for epithelial ovarian cancer

Ovarian cancer is the leading cause of death in women with gynecological malignancies and overall survival for patients with advanced epithelial ovarian cancer (EOC) remains poor. The majority of patients recur after initial treatment. A strategy for improving outcome is to minimise recurrence via targeted therapy in patients after front-line therapy, or more appropriately as consolidation therapy. EOC represents an attractive target because of the biology of the disease and that the bulk of disease occurs in the peritoneal cavity. To initiate targeted therapy, a candidate target must be identified. Innovative approaches via targeted therapy to control metastatic residual EOC are currently under investigation. The targets are molecules and pathways, on which cancer cells depend to proliferate, invade, metastasise and prevent apoptosis. Potential targeted therapies include: proapoptototic therapy, suicide gene therapy, signal transduction, antiangiogenesis, immunotherapy and cytokine therapy. The utilisation of these targets in the clinic demands carefully conducted, well-coordinated but discovery-oriented translational research in the form of clinical trials that can quickly assess alternative strategies or combination of strategies that could result in clinical benefit. Therefore, targeted therapy for epithelial ovarian cancer, especially after complete response to standard regimens, represents a paradigm whose time has come to be nurtured.

Vaccination with Ep-CAM protein or anti-idiotypic antibody induces Th1-biased response against MHC class I- and II-restricted Ep-CAM epitopes in colorectal carcinoma patients

PURPOSE

The tumor-associated antigen Ep-CAM (epithelial cell adhesion molecule) is overexpressed in colorectal carcinoma (CRC). The aim of the present study was to evaluate and compare the safety and immunogenicity of a recombinant Ep-CAM protein and a human anti-idiotypic antibody (anti-Id) mimicking Ep-CAM.

EXPERIMENTAL DESIGN

Patients with resected American Joint Committee on Cancer stages II-IV CRC without remaining macroscopic disease received intradermal/subcutaneous injections of Ep-CAM (400 microg/dose; n = 7) or anti-Id (500 microg/dose; n = 6) at weeks 0, 2, and 6 in combination with granulocyte macrophage colony-stimulating factor (75 microg/day, for 4 consecutive days).

RESULTS

Adverse reactions were mild (grade I-II). All patients immunized with the Ep-CAM protein produced Ep-CAM-specific IgG antibodies, predominantly IgG1 and IgG3 subclasses, whereas no humoral response was induced by the anti-Id vaccine. All patients, with one exception in each group, mounted an Ep-CAM-specific proliferative T-cell response. The immune response was more rapid, potent, and protracted after Ep-CAM in comparison with anti-Id vaccination. Interferon-gamma-secreting cells (ELISPOT) were detected in both immunization groups against the Ep-CAM protein as well as various Ep-CAM-derived MHC class I- and II-restricted peptides. Flow cytometry analysis showed that Ep-CAM-specific interferon-gamma- and perforin-producing cells predominantly resided within CD8(+)CD56- and CD8(dim)CD56+ T cells.

CONCLUSIONS

Ep-CAM protein in combination with granulocyte macrophage colony-stimulating factor induced a long-lasting, Th1-biased humoral and cellular immune response compared with anti-Id. Ep-CAM-specific T cells and natural killer-like T cells responding in a MHC class I- and II-restricted manner were also induced. Vaccination with Ep-CAM protein may warrant further investigation as a novel therapeutic approach to CRC.

Quality of Recombinant Protein Determines the Amount of Autoreactivity Detected against the Tumor-Associated Epithelial Cell Adhesion Molecule Antigen: Low Frequency of Antibodies against the Natural Protein

The human epithelial cell adhesion molecule (EpCAM) is expressed on normal epithelial cells and is overexpressed in most carcinomas. EpCAM-targeted immunotherapy has been tried in several clinical studies. High titers of autoantibodies against EpCAM have been reported by different authors. We have generated large amounts of purified protein in S2 Drosophila cells (S2-EpCAM) with a purity of >96%. In contrast, the protein produced in baculovirus-dependent systems (baculo-EpCAM) that has been used in previous studies shows a purity of 79%. (1)H nuclear magnetic resonance spectrum of S2-EpCAM is typical of folded protein, whereas the baculo-EpCAM sample shows a spectrum corresponding to a partially unfolded protein. Using S2-EpCAM, denatured S2-EpCAM, and baculo-EpCAM, we measured EpCAM Abs of different isotypes in the serum of healthy controls and cancer patients. We found Ab titers against EpCAM in a much lower percentage of sera as published previously, and support the hypothesis that Ab reactivity in some published studies might be due to reactivity against denatured protein, to contaminating proteins in the baculovirus preparations, and to reactivity with BSA. Tetanus toxoid-reactive IgG Abs are present in 1000-fold higher titers compared with EpCAM-reactive Abs. Only IgA Abs were found in higher proportions and in higher concentrations than tetanus toxoid-specific Abs. Our study shows that EpCAM only rarely induces autoantibodies against native protein and emphasizes the importance of using extremely purified Ag preparations when evaluating Abs against tumor-associated Ags.

Immunotherapy of malignant diseases. Challenges and strategies

In recent years, there has been growing interest in the application of immunotherapy as an alternative to chemotherapy and radiotherapy for the treatment of malignant diseases. This interest is due to a variety of factors, including revival of the immunosurveillance theory, availability of well-defined and structurally characterized human tumor-associated antigens (TAAs), progress in our understanding of the molecular pathways required for induction and maintenance of an immune response, and advances in methodologies to generate TAA-specific cytotoxic T lymphocytes (CTLs) and monoclonal antibodies (mAbs) as immunological probes. However, contrary to the positive results obtained with TAA-specific immunotherapy in animal model systems, the clinical response in patients has been disappointing. Frequently, the immune responses do not correlate with the clinical responses. Analysis of the underlying mechanisms of this dichotomy have identified the low immunogenicity of TAAs, the lack of immunological markers to predict clinical outcomes, and the ability of tumors to escape immune recognition and destruction as challenges to the development and application of immunotherapy. In this paper, we have reviewed the mechanisms underlying immune unresponsiveness to TAAs and strategies to overcome this unresponsiveness in the humoral and cellular immune responses, highlighting findings from different antigenic systems to prove the validity of these strategies. Additionally, we have addressed limitations to TAA-targeting immunotherapy as a result of the genetic instability of tumor cells, and have discussed strategies to overcome this limitation by targeting immunotherapy to molecules implicated in tumor-associated angiogenesis. Lastly, we have concluded by indicating the need to refine the implementation of clinical trials of immunotherapy, and to emphasize combination therapies to counteract the multiple tumor escape mechanisms.

Immunization with a plant-produced colorectal cancer antigen

Cancer vaccination has become an important focus of oncology in recent years. Active immunization with tumor-associated antigens such as colorectal cancer antigen GA733-2 is thought to potentially overcome the reoccurrence of metastasis. As recombinant protein production in bioreactors is costly and subject to growing safety concerns, we tested plants as an alternative for the expression of a potential colorectal cancer vaccine. Comparing colorectal cancer antigen GA733-2 produced in tobacco plants with the same antigen produced in insect cell culture, we found a similar humoral immune response to injection of either of the two antigen preparations into mice. Some minor differences were observed in the cellular response that might be due to impurities. Our studies compare for the first time, immunization with the same antigen expressed in either plants or insect cell culture. This will provide important data for use of plants as production systems of therapeutics.

Immunology and immunotherapy of colorectal cancer

This review critically discusses data on immunology of colorectal cancer, starting from pathology and molecular biology, and then considering the molecular characterisation of colon cancer antigens and the clinical trials of immunotherapy. A careful evaluation of histopathological studies on intra-epithelial infiltration by T cells in primary tumours, together with the analysis of HLA expression by colorectal cancer cells, suggest that anti-tumour T cell immune responses may take place in vivo in those patients, influencing prognosis and shaping the tumour immunological profile. Moreover, the molecular characterisation of tumour antigens expressed by colorectal carcinomas, together with improved understanding of mechanisms of the immune response and more sensitive methods for the in vivo detection of T cell responses, are now allowing researchers to design new and more effective vaccination protocols, with encouraging preliminary results. By drawing together the experimental evidence from different research fields, this review provides support for the concept that colorectal carcinoma is immunogenic and may reasonably be considered as a target for immunotherapy, and attempts to address critical issues and envisage future developments in this challenging research field.

GP letter writing in colorectal cancer: a qualitative study

BACKGROUND

The usual mode of communication with the specialist in the UK is a referral letter. Letters now primarily document the GPs' concerns for the patient and are no longer required to persuade the specialist to offer an appointment. The content of referral letters from GPs has failed to satisfy specialists responding to a series of surveys. Evidence suggests that GPs who improve their letters to specialists also refer more cases with significant pathology.

AIMS

The aims of this research are to explore the factors that may influence GPs in writing the referral letter when consulting patients presenting with lower bowel symptoms.

METHODS

A convenience sample of twelve GPs was interviewed in Nottinghamshire and inner city Sheffield practices. A framework approach was utilised in the analysis of data. Data from the interviews followed the prescribed steps, including: familiarisation, identifying a thematic framework, indexing, charting and mapping, and interpretation.

RESULTS

The thematic framework reflected four major themes. These were: (1) the nature and content of referral letters, (2) knowledge about colorectal cancer, (3) issues relating to the quality of referral letters in colorectal cases and (4) factors that effect the use of guidelines for referral.

CONCLUSIONS

GPs only have very short consultations in which to address many and complex issues. Pre-referral assessment in colorectal cases includes intimate examination of the patient. Therefore the writing of the letter of referral is often postponed until long after the patient has left the GP's office. Some GPs do not believe the consultant reads the letter of referral. However, GPs are keen to provide best care and welcome feedback about the quality of their letters. They acknowledge the responsibility to communicate with colleagues effectively and have differing ideas about what constitutes an adequate referral letter.