in vivo 24: 607-628 (2010) Review Colon Cancer Vaccines: An Update E. MERIKA1, M.W. SAIF2, A. KATZ2, C. SYRIGOS3 and M. MORSE4 1West London Renal and Transplant Centre, Hammersmith Hospital, London, U.K.; 2Section of Medical Oncology, Yale University School of Medicine, New Haven, CT, U.S.A.; 3Oncology Unit, Third Department of Medicine, Athens Medical School, Athens, Greece; 4Division of Medical Oncology, GI Oncology, Molecular Therapeutics Program, Duke University Medical Centre, Durham, NC, U.S.A. Abstract. Despite advances in research and treatment more than 1 million cases diagnosed each year worldwide. It modalities, colorectal cancer still accounts for around half represents more than half of all intestinal malignancies a million deaths yearly worldwide. Traditional and even (52.6%) and has a poor 5-year survival (64% for cancer of all newer pharmaceutical therapeutic regimens are limited in stages at diagnosis but only 11% for metastatic cancer) with terms of tolerance, efficacy and cross-resistance. Additional 50-60% metastatic rate, despite advances in treatment non-cross resistant therapies with non-overlapping toxicities modalities (1). Surgery is the only potentially curative are needed to improve the outcome for patients with treatment choice available, but is rarely sufficient in patients colorectal cancer. Cancer vaccines, designed to activate with regionally advanced or metastatic disease. Traditional immune effectors (T-cells and antibodies) to prevent pharmaceutical therapeutic regimens including chemo- recurrence or treat advanced cancers, have now demon- radiotherapy are limited in terms of toxicity and lack of strated clinical benefit in prostate cancer and lymphoma. tumour specificity and at best reduce the death rate for stage Because immune effector infiltration into colon tumours is III disease by 30-40% (2) and prolong survival modestly in associated with improved clinical outcome, vaccines intended metastatic disease. Alternative therapeutic strategies are clearly to activate immune responses against colon cancer have needed and data supportive of the concept that colorectal generated significant interest. This review discusses data tumours are immunoresponsive has led to the application of supportive of the immune responsiveness of colorectal immunotherapy in the management of colorectal cancer. cancer, as well as the current status of colon cancer vaccines under development including those based on whole tumour Colorectal Cancer Immunology cells or lysates, peptide or protein antigens, anti-idiotype and Immune Evasion antibodies, viral vectors, and dendritic cells. We also discuss challenges to colon cancer vaccine development, such as Before discussing the technologies developed to activate tumour associated mechanisms for immune evasion, and how immune responses against colon cancer, it is important to future strategies may address these challenges. describe the current understanding of colorectal cancer immunology and immune evasion. Colorectal cancer is the third most common cancer diagnosis and cause of cancer-related death in the US and accounts for Colorectal cancer activates immune responses. Colorectal tumours clearly harbour immunogenic proteins. At least ten tumour-associated antigens and thirty-five major Conflict of interest: The Authors have no potential conflicts of histocompatibility complex (MHC) restricted epitopes interest. derived from tumour antigens have been identified, potential targets for T-cell mediated adaptive immune response (3, 4). Correspondence to: Muhammad W. Saif, Section of Medical Antigenic stimulation leads to the generation of a small Oncology, Yale University School of Medicine, 333 Cedar Street, population of antigen-specific memory T-cells, which remain FMP:116, New Haven, CT 06520, U.S.A. Tel: +1 2037371569, Fax: +1 2037853788, e-mail: [email protected] in the tissue (5). Greater numbers of infiltrating memory T- cells have been linked to attenuation of metastatic potential Key Words: Colon cancer immunogenicity, dendritic cell vaccine, (6). Intra-tumour lymphocytic infiltration has been shown not autologous vaccine, anti-idiotype vaccine, review. only to inhibit tumour growth (7) but also to improve 0258-851X/2010 $2.00+.40 607 in vivo 24: 607-628 (2010) survival (8-10), which suggests that the immune system is (29-31). Low CD4+/CD8+ ratio has been associated with a capable of mounting an immune response to colorectal better clinical course and 5-year survival (8). cancer but is not always effective in sustaining it or The exact mechanism of shift in immune response from preventing tumour progression (11). Importantly, the patients Th1 to Th2 is still unclear and is likely to involve chronic with the best survival had tumours with greater numbers of inflammatory changes (32) but overexpression of cyclo- infiltrating CD8 and granzyme B-expressing T-cells. oxygenase 2 (COX-2) (33-36), histamine (37-40) and IL10 (17, 41-11) have all been implicated as affecting How colorectal cancer inhibits immune responses. Similar to angiogenesis, cell apoptosis, modulation of immune response other types of cancer, colorectal cancer arises through and hence tumourigenesis. evasion of the host’s immuno-surveillance, as a result of Endogenous tumour synthesis and up-regulation of weak immunogenicity or immunosuppressive effects of histamine and histidine decarboxylase causes immuno- tumour cells (12-15). Restoration of antitumour immuno- suppression, again inhibiting Th1 cytokines (38) and cell- logical function after tumour resection has been observed in mediated immunity (45) and correlating with tumour stage several studies (16, 17) suggesting that colorectal cancer has (46). COX-2 has also been implicated in colorectal cancer a direct immunosuppressive effect at a molecular and cellular carcinogenesis by inhibiting apoptosis, increasing level with suppression of cell mediated immunity [Th1 CD4+ angiogenesis and invasiveness, converting pro-carcinogens to T lymphocytes producing cytokines, interleukin 2 (IL2), carcinogens and modulating inflammation and immuno- interferon (IFN) gamma and tumour necrosis factor (TNF)- suppression as well as production of Th2 cytokines which alpha]. The mechanism of colorectal cancer immune evasion inhibit synthesis of Th1 cytokines (35). IL10 is is multifactorial and in summary involves shift from Th1- overexpressed in colorectal cancer (30) and may inhibit Th1 Th2 immune responses, loss/down-regulation of human cytokine production as well as antigen presentation to Th1 leucocyte antigen (HLA) class I antigen processing and cells (41). The level of IL10 serves as a negative prognostic presentation, defective dendritic cell function, T-cell loss of factor for treatment response as well as survival (47). Further signalling molecules, escaping death receptors, HLA G research has highlighted the importance of p53-specific Th1 expression, transforming growth factor (TGF) beta, vascular cells for improved tumour infiltration. The tumour antigen endothelial growth factor (VEGF), impaired natural killer p53 is commonly mutated and overexpressed in colorectal (NK) activity, regulatory T-cells, and complement decay cancer and p53-specific T-helper cells have been identified accelerating factor CD55 (18). as lacking cytokines such as IFN-gamma, TNF-alpha, IL4, White blood cell composition seems to vary in colorectal IL5, or IL10 (48). In contrast, tumours in patients with p53- cancer patients, with elevated percentages of CD8 T-cells in specific IFN-gamma-producing Th cell immunity were the initial stages, but reduced numbers of total lymphocyte associated with better leukocyte infiltration. count, monocyte and NK cells, IL4 and IL6 production in The Th1 hypothesis was also supported in a recent study advance tumour stage as well as reduced levels of IFN by Burgdorf et al. in which increasing levels of pro- gamma, TNF-alpha seen in vascular invasion. This shift in inflammatory cytokines such as plasma GM-CSF, TNF- cytokine balance has been observed by many others (16, 20- alpha, IFN-gamma, IL2 and IL5 were detected in patients 21). TGF-beta regulates cell proliferation, differentiation, with stable disease after dendritic cell vaccination (49). This adhesion, apoptosis and angiogenesis (22) and levels suggests that vaccine induced Th1 responses will be correlate with Duke’s staging (23). Notably TGF-beta important for efficacy of colorectal cancer vaccines. inhibits immunotherapeutic agents including vaccines (24). Research into Th1 associated genes has shown that patients IFN-gamma, TNF-alpha and IL2 are key components of with up-regulation of Th1-related genes had a better cell-mediated immunity and released by Th1 CD4+ T-cells. prognosis possibly because intra-tumoural T-cells can modify In contrast IL4, IL6 and IL10 play a major role in humoural cancer cells and attenuate their metastatic potential. mediated immunity (25), through Th2 CD4+ lymphocytes. HLA I antigens also play a key role in tumour Th1 activation and in turn cytotoxic T-cell, NK, macrophage immunology as they present tumour associated antigen- and monocyte activation may result in tumour rejection, peptides to cytotoxic T lymphocytes (50). While it has been whereas Th2 activation causes the opposite effect (26). In reported that some colorectal tumours lack the HLA-ABC colorectal cancer helper T-cell responses are impaired; antigens, Diederichsen et al. showed that some tumours were reduced concentrations of Th1 CD4+ and related cytokines in fact weakly positive for HLA-ABC