Cyclin B1 and Other Cyclins As Tumor Antigens in Immunosurveillance and Immunotherapy of Cancer

Review

Cyclin B1 and Other Cyclins as Tumor Antigens in Immunosurveillance and Immunotherapy of Cancer

Ann Marie Egloff, Laura A. Vella, and Olivera J. Finn

Department of Immunology, University of Pittsburgh School of Medicine and the University of Pittsburgh Cancer Institute, University of Pittsburgh, Pittsburgh, Pennsylvania

Abstract presented by cancer cells, where the peptides are constitutively Uncontrolled cell division is an indispensable event in tumor present at high levels, presumably reaching the threshold for progression, and numerous molecules involved in this process immune recognition. have been the focus of intense investigation in tumor biology. We and others have found that at least one member of the cyclin Cyclins, molecules that orchestrate normal cell cycle progres- family, cyclin B1, plays an important role as a tumor antigen. sion, are abnormally overexpressed in various human cancers. Cyclin B1 is recognized by the immune system early in cancer We review evidence that the immune system recognizes some development, and both antibodies and T cells are generated in abnormally expressed cyclins as tumor antigens, such as cyclin response to its aberrant expression. In this review, we use our B1, and we analyze the potential of cyclins D, E, and A to serve knowledge of cyclin B1 regulation and expression in cancer and its a similar function in cancer immunosurveillance. (Cancer Res documented tumor antigen potential as a template to assess 2006; 66(1): 6-9) the potential of other aberrantly expressed cyclins to be recognized by the immune system. Because cyclins are expected to be deregulated early in disease, we propose that monitoring immune Introduction responses against cyclins that are recognized as tumor antigens The immune system has evolved to protect individual organisms can be an important approach to early cancer detection (2). from external pathogens as well as from internal changes in the Furthermore, because cyclin deregulation is associated with normal function of cells and tissues that might threaten the increased tumor malignancy (3), we suggest that eliciting or integrity of the organism. One such threat is cancer, and immune boosting immunity to tumor cyclins through vaccines or other responses to the altered self employ both the innate and the immunotherapy approaches could lead to the elimination of the adaptive arms of the immune system. Examples of tumor-specific most malignant cancer cells and thus to a more favorable disease alterations include changes in protein sequence and/or protein outcome. quantity, as seen during activation of proto-oncogenes or overexpression of nonfunctional tumor suppressor genes (e.g., Her-2/ Cyclin B1, the Prototype Cyclin Tumor Antigen neu and p53, respectively). Such changes are found in virtually all In 1997, it was reported that patients with hepatocellular tumors and have been used increasingly by pathologists to assess carcinoma generate antibodies to cyclin B1, whereas such tissue biopsies for cancer diagnosis and prognosis. Immunologists antibodies were not found in the healthy control subjects (4). have also learned that many mutated or overexpressed proteins are Subsequently, in our efforts to identify new tumor antigens, we processed and presented to the immune system as tumor antigens found that a peptide fraction eluted from breast adenocarcinoma that can trigger both humoral and cellular immune responses (1). MHC class I molecules was able to stimulate tumor-specific This review is focused on the tumor-associated changes in the cytotoxic T cells from breast and head and neck cancer patients (5). expression of one family of cell cycle regulatory proteins, the Sequencing of the peptides in the immunostimulatory fraction cyclins, and the potential of some of these proteins to serve as identified the peptides as having been derived from cyclin B1 (5). stimulators of antitumor immunity and targets of immunotherapy. Antibody responses against cyclin B1 have since been reported by Unlike normal cells that turn on transient expression of minute us and others in patients with prostate, breast, colorectal, lung, and amounts of cyclin proteins at specific points in the cell cycle, hepatocellular cancers (6, 7). In recursive partitioning analyses many tumors have high constitutive levels of one or more cyclins. assessing antibody levels against a panel of tumor antigens as a In normal and tumor cells, cyclins are ubiquitinated for method to differentiate subjects with cancer from those without, immediate degradation by proteasomes into peptides. This same the presence of anti-cyclin B1 antibodies was an important degradation pathway is used for processing and presentation of discriminator for subjects with the aforementioned cancers (6). antigens to the immune system. It would thus be expected that Importantly for early cancer detection and intervention, we also immunosurveillance of cyclin peptides presented by normal cells, found that in lung cancer, early transformation events led to where they appear transiently and probably below the threshold aberrant expression of cyclin B1 in premalignant lung lesions, and of immune detection, would differ significantly from those this correlated with the presence of T cell–dependent antibody responses (7). Under normal conditions, cyclin B1 is expressed at very low levels and accumulates appreciably only at the G2-M cell cycle transition, concurrent with its scheduled translocation to Requests for reprints: Olivera J. Finn, University of Pittsburgh School of Medicine, the nucleus (8). In cancer cells, cyclin B1 is found overexpressed E1040 Biomedical Science Tower, Pittsburgh, PA 15261. Phone: 412-648-9816; Fax: 412- throughout the cell cycle and resides primarily in the cytoplasm. 648-7042; E-mail: [email protected]. I2006 American Association for Cancer Research. This alteration in the regulation of cyclin B1 expression was found doi:10.1158/0008-5472.CAN-05-3389 by us to be the result of inactivation of the tumor suppressor

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Downloaded from cancerres.aacrjournals.org on September 24, 2021. © 2006 American Association for Cancer Research. Immunosurveillance of Cyclin Tumor Antigens protein p53 function (9). Our finding that cyclin B1–derived frequently with poor clinical outcome. Like cyclin B1, these cyclins peptides can be eluted from MHC class I molecules on tumor undergo ubiquitin-mediated proteolysis and could, therefore, cells shows that this constitutively overexpressed protein is be available as whole proteins as well as processed peptides for naturally processed into peptides that bind MHC class I molecules presentation to the immune system. However, whether or not and stimulate cytotoxic T cells. Furthermore, the finding of T these other peptides can effectively stimulate the immune response helper cell–dependent anti-cyclin B1 antibodies (IgG and IgA) in will depend on the precise molecular mechanisms that underlie cancer patients shows that the overexpressed protein can activate the aberrant expression of each of the individual cyclins and on B cells and can also be taken up by antigen-presenting cells and the extent of quantitative and qualitative differences in their processed and presented to helper T cells (see Fig. 1). expression between normal and cancer cells. Thus, some cyclins may be anticipated to be more immunogenic or better immunotherapy targets than others. Using the criteria we and others have Other Cyclins as Tumor Antigens determined to be important for cyclin B1 immunogenicity and In the ongoing effort to discover tumor antigens, the immuno- tumor specificity, it is possible to examine alterations in the genicity of overexpressed and aberrantly localized normal cellular expression and localization of cyclins D, E, and A in cancer as a way components is emerging as a common theme. Some notable to evaluate their potential to alter antigen loading at the cancer cell examples of overexpressed normal cellular proteins are the tumor surface or provide increased levels of protein for cross-presentation antigens MUC1 (10), HER-2/neu (11), and p53 (12). by antigen presenting cells. A, D, and E type cyclins all have been shown to be overexpressed D type cyclins. Cyclin D1 is the most commonly reported in many cancers, where their overexpression has been associated overexpressed cyclin in cancer and the best characterized of the

Figure 1. Establishment of an immune response to cyclin B1. Top, the priming phase. At the tumor site, overexpressed cyclin B1 is released by cancer cells, endocytosed by immature dendritic cells (DC) and transported to the tumor draining lymph node. In the lymph node, the mature dendritic cell process and cross-present cyclin B1–derived peptides to naive T cells. This leads to the activation and expansion of helper (CD4+) and cytotoxic (CD8+) cyclin B1–specific T cells. Soluble cyclin B1 protein is also drained to the lymph node, where it stimulates naive B cells and primes them to receive help from cyclin B1–specific T cells in the production of anti-cyclin B1 antibody. Bottom, the effector phase. The lytic function of cyclin B1–specific cytotoxic (CD8+) T cells is restricted to cancer cells overexpressing cyclin B1. Activated cyclin B1–specific CD8+ T cells migrate from the lymph node to the tumor site, where they recognize and kill the cancer cells that present a high density of CB1 peptides. Normal cells that express transient, low levels of cyclin B1 do not provide sufficient peptide density to trigger the T-cell function. www.aacrjournals.org 7 Cancer Res 2006; 66: (1). January 1, 2006

D type cyclins (D1, D2, and D3). Cyclin D1 overexpression has from cancer patients, none of the patients tested had anti-cyclin often been found to correlate with worse disease prognosis (13). As E antibodies (4). in the case of cyclin B1, cytoplasmic localization of aberrantly A type cyclins. Cyclins A1 and A2 activate cyclin-dependent expressed cyclin D1 protein has been noted in non–small cell lung kinase 2 (cdk2) and cdk1 and function to promote transit through cancer. However, in the majority of tumors, overexpressed cyclin S phase and into mitosis. Cyclin A1, the expression of which is D1 protein resides primarily in the nucleus (13). Processing and confined mainly to hematopoietic progenitor cells and male germ presentation of antigens overexpressed in the nucleus have not cells, has been found to be highly overexpressed in acute myeloid been studied extensively; thus, the effect of cyclin D1 nuclear over- leukemia (AML) and testicular cancer (15). AML patients whose expression on peptide loading into MHC class I and consequent tumors had high levels of cyclin A1 have significantly lower increase in its tumor antigen potential will have to be specifically survival than those with low levels of cyclin A1 (19). In normal determined. Studies to date exploring the potential of cyclin hematopoietic cells, cyclin A1 is predominantly nuclear; however, D1 to stimulate immune responses include one report that 16% of in leukemic cell lines and tumor cells from AML patients, cyclin A1 patients with high-grade prostate cancer make T cell–dependent is predominantly cytoplasmic (20). Overexpression of cyclin A2, anti-cyclin D1 antibodies (14). Given the frequently documented which is expressed in all dividing somatic cells, has also been cyclin D1 overexpression in cancer, additional studies of the associated with poor prognosis in several cancers (15). Thus far, immune response in cancer patients to this potential new tumor nothing much is known about immune responses to A type cyclins antigen are warranted. in patients with AML or other tumors of hematopoietic origin. E type cyclins. Along with cyclin D1, the cyclins E1 and E2 However, two recent reports describe antibodies to cyclin A2 in direct and amplify the transition of cells from G1 phase into S sera of patients with solid tumors (4, 14). Although there is phase of the cell cycle. Cyclin E1 has been more extensively relatively limited information on cyclin A, its alteration in cancers studied and has been frequently found to be deregulated in tumor similar to cyclin B1 should prompt further attention concerning cells. As in the case of cyclins B1 and D1, deregulation of cyclin cyclin A as a potentially important tumor antigen. E1 has been reported to be associated with worse prognosis in lung and breast cancers (reviewed in ref. 15). Multiple mechanisms underlying increased expression of cyclin E1 are possible, Summary including gene amplification, disruption of Rb transcription The importance of altered cyclin function in malignant regulatory pathways, and errors in ubiquitination and degradation transformation has long been appreciated. More recently, the processes (16). Furthermore, there are low molecular weight consequences of aberrantly expressed cyclins on tumor behavior forms of cyclin E that are produced at high levels only in cancers are beginning to be understood and tumor cyclin status is and can serve as a source of antigenic peptides (17). Cyclin E increasingly recognized as an important cancer prognostic appearance is normally tightly restricted to mid-G phase to S 1 indicator. Immune responses that target specific tumor antigens phase of the cell cycle. In contrast, in several bladder cancer cell can also be important determinants of cancer and premalignant lines, cyclin E has been found to be present throughout the disease course. We have summarized evidence to date regarding cell cycle (18). This transition to unscheduled expression suggests cyclin B1 as a tumor antigen and reviewed what is known about the possibility of higher levels of cell surface presentation of aberrant expression of cyclins D, E, and A that might affect their cyclin E–derived peptides due to increased accessibility to antigen abilities to stimulate the immune system. We conclude that in processing machinery. However, aberrantly expressed cyclin E is addition to cyclin B1, which is increasingly being recognized as constitutively localized to the nucleoli rather than the cytoplasm; thus, it is postulated to be retained and not degraded (18). If an important player in the immune control of tumor growth, the major mechanism for this aberrant expression is a lack of cyclins A and D have the potential to be targets of immune degradation, then cyclin E is unlikely to be seen by the immune surveillance and hold promise as candidate targets for cancer system as a tumor antigen. The accumulated protein can still be immunotherapy. released by tumor cells and taken up by antigen-presenting cells and B cells to stimulate helper T cells and production of anti- cyclin E antibodies. However, in the only published study to date, Acknowledgments that has evaluated the presence of antibodies to cyclin E in sera Received 9/20/2005; revised 10/24/2005; accepted 11/4/2005.

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Downloaded from cancerres.aacrjournals.org on September 24, 2021. © 2006 American Association for Cancer Research. Cyclin B1 and Other Cyclins as Tumor Antigens in Immunosurveillance and Immunotherapy of Cancer

Ann Marie Egloff, Laura A. Vella and Olivera J. Finn

Cancer Res 2006;66:6-9.

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