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Cancer Therapy: Clinical |
Department of Immunology, University of Pittsburgh, School of Medicine, Pittsburgh, Pennsylvania
Requests for reprints: Olivera J. Finn, E1040 Biomedical Science Tower, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261. Phone: 412-648-9816; Fax: 412-383-8859; E-mail: ojfinn{at}pitt.edu.
| ABSTRACT |
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Experimental Design: Recombinant cyclin B1 protein from two different sources was purified and used as antigen in ELISA assays to test sera from patients with breast, pancreatic, colon, and lung cancer for the presence of anti-cyclin B1 antibody. We also analyzed patients with benign lung disease, premalignant disease, and a known history of heavy smoking.
Results and Conclusions: Cyclin B1 elicits helper T celldependent antibody responses in vivo. Tumors with higher level of cyclin B1 expression elicit higher anti-cyclin B1 antibody levels. Antibodies in patients with breast and colon cancer are primarily of the IgG isotype whereas patients with pancreatic and lung cancer have in addition anti-cyclin B1 IgA. Cyclin B1specific IgG was also detected in long-term smokers and in patients with preneoplastic lung disease. Immune responses to aberrantly expressed cyclin B1 in tumors and premalignant lesions should be further explored as diagnostic and prognostic markers, in addition to their immunotherapeutic potential.
Key Words: tumor antigen cancer vaccine cell cycle
| INTRODUCTION |
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In this paper, we extend our published observations on cyclin B1 as a tumor antigen recognized by human cytotoxic T cells by studying in more detail its ability to elicit T celldependent humoral immune responses in patients with various types of tumors. Two previously published studies have shown that antibody against cyclin B1 can be found in patients with various tumors and might be a useful diagnostic marker in combination with antibodies against several other tumor antigens (15, 16). Focusing more closely on lung cancer, we show that antibody is present at both early and late stages of cancer, as well as in sera of heavy smokers that in their lungs have preneoplastic changes that overexpress cyclin B1.
| MATERIALS AND METHODS |
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ELISA Assay. ELISAs for detecting anti-cyclin B1 antibody were done as previously described (17). Briefly, 50 µL of recombinant cyclin B1 protein (source and isolation procedure described below) at a concentration of 1 µg/mL in PBS were loaded into 96-well microtiter polystyrene base immunoassay plates (Dynex, Chantilly, VA), and incubated overnight at 4°C. Plates were washed with PBS and blocked with 2.5% bovine serum albumin in PBS for 1 hour. After washing, 50 µL of diluted serum were added and incubated for 1 hour at room temperature. Plates were washed with 0.1% Tween 20 in PBS, and the secondary antibody, ALP-labeled polyvalent goat anti-human IgM, IgG, and IgA (Sigma-Aldrich, St. Louis, MO) in 2.5% bovine serum albumin was added and plates incubated for 1 hour at room temperature. The plates were washed and filled with 100 µL per well of ALP substrate solution (Sigma-Aldrich). After 1 hour of incubation in the dark, the reaction was stopped with 50 µL of 0.5 mol/L NaOH and the absorbance at 405 nm was measured using the plate reader MRX Revelation (Thermo Labsystems, Chantilly, VA). The isotype of the anti-cyclin B1 antibody was determined using the same method described above except that isotype-specific ALP-labeled goat anti-human IgM, IgG, and IgA antibodies were used as secondary antibodies in the ELISA.
Recombinant cyclin B1 protein was obtained from two different sources. Insect cells infected with recombinant baculovirus expressing human cyclin B1 were purchased from BD PharMingen (San Diego, CA). The cell pellet was lysed with a lysis buffer consisting of 1% CHAPS (Sigma-Aldrich), 150 mmol/L NaCl, and 20 mmol/L Tris-Cl (pH 8.0) in the presence of protease inhibitors (Aprotinin, leupeptin, pepstatin phenylmethylsulfonyl fluoride, EDTA, and iodoacetamide). The lysate was centrifuged at 10,000 x g for 20 minutes and the supernatant was run over a column of protein G-Sepharose (Amersham Biosciences, Piscataway, NJ) before it was applied to an affinity column containing anti-cyclin B1 antibody (BD PharMingen) covalently coupled to protein G-Sepharose. Cyclin B1 was eluted from the column in 1 mL fractions using 0.1 mol/L triethylamine (pH 11.5) into a tube containing the same volume of 1 mol/L Tris (pH 6.7), to neutralize the pH. For further purification, ion exchange chromatography was done using a Rainin HPLC separation system (Varian, Woburn, MA). Either lysate or affinity column products were dialyzed into HEPES-buffered saline (10 mmol/L HEPES and 150 mmol/L NaCl) and applied to a Mono Q anion exchange column (Amersham Biosciences). Fractions were eluted with a 30-minute linear gradient of 150 to 500 mmol/L NaCl, at a flow rate of 1 mL/min. To identify column fractions that contained cyclin B1, samples were run on a 10% SDS gel and analyzed for purity by Coomassie blue staining and for specificity by Western blot. The preparation was highly pure as judged by the lack of detection of other protein bands on the gel. When purified recombinant protein became available through Santa Cruz Biotechnology, Inc. (Santa Cruz, CA), that was expressed in Escherichia coli, samples of positive and negative sera were retested and results confirmed with this new commercial preparation.
Immunohistochemical Staining of Cyclin B1 in Tissue Sections. Formalin-fixed, paraffin-embedded tissues were sectioned (3-5 µm), air-dried overnight at 37°C, deparaffinized and dehydrated, and stained with the mouse anti-human cyclin B1 antibody, GNS-1 (BD PharMingen). The avidin-biotin peroxidase method was applied according to the manufacturer's instructions supplied with the Vecstatin ABC Elite staining kit (DAKO Co., Carpinteria, CA).
Statistical Analysis. A Student's t test was used to detect significant differences in the ELISA assays between absorbance values in the cancer patients' sera and healthy age-matched controls. Differences with P < 0.05 were considered significant.
| RESULTS |
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1). Breast cancer patients were the best responders, 43% of the sera falling into the strong positive group, followed by colon cancer patients (22% strong positive) and pancreatic cancer patients (18% strong positive). The lowest level of antibody was found in lung cancer patients. We considered that this might be due to the stage of the disease at diagnosis, when the sera were collected. Among the lung cancer patients, we had 29 patients at stage I, 11 patients at stage II, 16 patients at stage III, and 4 patients at stage IV at the time of diagnosis. For nine patients, this information was not available. Figure 2A shows that there is no significant difference in antibody levels at different stages of disease. Antibody was found already at stage I, with a trend towards a slight increase with a more advanced stage II disease and then a slight decrease as the tumor progresses. In Fig. 2B, we show that both, nonsmall cell lung cancers as well as small cell lung cancers can elicit anti-cyclin B1 antibody responses.
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40 pack-years) or light or nonsmokers (n = 11; <40 pack-years; Fig. 6A). The antibody level in the sera from heavy smokers was higher (absorbance, 0.469 ± 0.17) than in light smokers or nonsmokers (absorbance, 0.308 ± 0.128), and that difference was significant (P < 0.01). Immunohistochemical staining of sections of lung tissue from two heavy smokers, one diagnosed with a displastic lesion (patient 1) and the other with a metaplastic lesion (patient 2), showed that cyclin B1 protein was already overexpressed in both premalignant lesions to levels equal or higher to those seen in fully transformed cancer cells (Fig. 6B).
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| DISCUSSION |
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Recently, we discovered that aberrantly expressed cyclin B1 is recognized by human T cells as a tumor-specific antigen and that patients with breast and head and neck cancer have circulating CD8+ T cells specific for various peptides derived from this molecule. In the current study, we sought to determine if there were also specific antibody responses in patients with tumors known to overexpress cyclin B1. We found that cyclin B1 elicits helper T celldependent antibodies as evidenced by high frequency of isotype switching, indirectly demonstrating that in addition to previously detected cyclin B1specific CTL, helper T cells can also be generated that are specific for this antigen and functional in providing help to B cells.
Whereas the differences in antibody levels and isotypes found in patients with different tumor types are not statistically significant, we nevertheless found them informative. For example, we find in general higher level of antibody in recurrent (metastatic) disease than in nonrecurrent disease. This may be related to our observation that metastatic cells express the highest levels of cyclin B11 and thus provide the highest level of antigen. Most of the sera we tested from breast, pancreatic and colon cancer patients were derived in the setting of recurrent disease. The sera from lung cancer patients were primarily derived at the time of diagnosis of the primary disease, the majority being stages I and II.
We also found less isotype switching and highest levels of IgM in patients with pancreatic and colon cancer. This may be a direct result of the profound T-cell suppression in these two tumor types that we and others have published on before (23, 24) . In the absence of optimally functioning helper T cells, isotype switching would be expected to proceed at a much slower rate. In pancreatic and lung cancer patients, we also found IgA antibody. Pancreatic, lung, and other cancers produce transforming growth factor-ß (24, 25) that is known to be the cytokine that induces isotype switching to IgA (26). Thus, whereas cyclin B1specific helper T cells promote the switch from cyclin B1 IgM to IgG, switching to IgA may be also due to tumor-produced transforming growth factor-ß.
Data presented here, showing that aberrantly expressed cyclin B1 can elicit T celldependent antibody responses, confirming and extending the previously published data by Koziol et al. (16), together with our previously published data on cyclin B1 specific human cytotoxic T-cell responses (13), validate the designation of this otherwise normal cell cycle regulatory protein as a tumor antigen.
Our finding that aberrant expression of cyclin B1 characterizes not only primary tumors but also metastatic tumors and premalignant lesions, suggests that it may be a good candidate antigen for cancer vaccines intended to prevent cancer recurrence or progression from premalignant disease to cancer. Detection of anti-cyclin B1 antibodies in long-term smokers and overexpression of this antigen in premalignant lesions, suggests that anti-cyclin B1 antibody may also serve as a serum marker for premalignant disease or for early detection of cancer.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Note: H. Suzuki is currently at Department of Surgery I, Fukushima Medical University, Fukushima, Japan.
Received 3/17/04; revised 11/ 9/04; accepted 11/11/04.
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