The identification of human tumour antigens: Current status and future developments

Natural humoral immune response to ribosomal P0 protein in colorectal cancer patients

Background

Tumor associated antigens are useful in colorectal cancer (CRC) management. The ribosomal P proteins (P0, P1, P2) play an important role in protein synthesis and tumor formation. The immunogenicity of the ribosomal P0 protein in head and neck, in breast and prostate cancer patients and the overexpression of the carboxyl-terminal P0 epitope (C-22 P0) in some tumors were reported.

Methods

Sera from 72 colorectal tumor patients (67 malignant and 5 benign tumors) were compared with 73 healthy donor sera for the presence of antibodies to CEA, EGFR, ErbB2 and ribosomal P proteins by western blotting or ELISA. Expression of the C-22 P0 epitope on tissues and colon cancer cells was determined by immunoperoxidase staining and indirect immunofluorescence/western blotting, respectively, employing MAb 2B2. Biological effects of MAb 2B2 on colon cancer cells were assessed by the Sulforhodamine B cell proliferation assay, trypan blue exclusion test and cleaved caspase-3 detection. Fisher’s exact test was used to compare the number of auto-antibodies positive patients with healthy donors. Variation in the C-22 P0 expression, and in the number of apoptotic cells was evaluated by Student’s t-test. Variation in cell survival and cell death was evaluated by Newman-Keuls test.

Results

No significant humoral response was observed to CEA, EGFR and ErbB2 in CRC patients. Conversely, 7 out of 67 CRC patient sera reacted to ribosomal P proteins. The prevalence of P proteins auto-antibodies in CRC patients was significant. Five patients showed restricted P0 immunoreactivity, while two patients reacted simultaneously to all P proteins. The C-22 P0 epitope was homogenously expressed both in malignant tumors and the adjacent mucosa, but the intensity of expression was higher in the tumor. Starved colon cancer cells showed a higher C-22 P0 epitope plasma membrane expression compared to control cells. MAb 2B2 inhibited colon cancer cell growth and induced cell death in a dose dependent manner.

Conclusions

Our study shows a spontaneous humoral immune response to ribosomal P0 protein in CRC patients and the inhibition of in vitro cancer cell growth after C-22 P0 epitope targeting. The ribosomal P0 protein might be a useful immunological target in CRC patients.

Expression of the tumour antigen T21 is up-regulated in prostate cancer and is associated with tumour stage

OBJECTIVES

• To define the expression pattern of the tumour antigen T21 at the protein level in prostate tissues, prostate cell lines and a panel of normal tissues. • To correlate the expression pattern of T21 in prostate cancer with clinical parameters.

PATIENTS AND METHODS

• Tissue samples were collected from 79 patients presenting at clinic with either prostate cancer (63 patients) or benign prostatic hyperplasia (BPH, 16 patients). • A tissue microarray (TMA) was constructed from 44 of the prostate cancer tissues and areas of benign disease (43 patients) from these tissues were also included on the TMA. The remaining tissues (prostate cancer 19 patients and BPH 16 patients) were mounted fresh frozen onto cork boards and sectioned. • Full ethical approval was granted for all aspects of the study and informed patient consent was taken before tissue collection. • Immunohistochemistry was used on the prostate tumour TMA, the normal tissue TMA and the fresh-frozen prostate tissues. Fluorescent microscopy and flow cytometry was performed on prostate cell lines.

RESULTS

• Expression of T21 was highly restricted within normal tissues with only the stomach, ovary, breast and prostate having detectable T21 expression. • T21 was significantly over-expressed in prostate cancer glands compared with benign tissue and was present in >80% of the malignant specimens analysed. • Increased expression was positively correlated to pathological stage of prostate tumours. • Additionally, T21 was associated with Gleason grade and prostate-specific antigen recurrence, although statistical significance was not reached in this restricted cohort of patients.

CONCLUSION

• Taken together these results show that T21 is a potential new biomarker for advanced disease and that elevated levels of T21 appear relevant to prostate cancer development.

Combined analysis of transcriptome and proteome data as a tool for the identification of candidate biomarkers in renal cell carcinoma

Results obtained from expression profilings of renal cell carcinoma using different "ome"-based approaches and comprehensive data analysis demonstrated that proteome-based technologies and cDNA microarray analyses complement each other during the discovery phase for disease-related candidate biomarkers. The integration of the respective data revealed the uniqueness and complementarities of the different technologies. While comparative cDNA microarray analyses though restricted to up-regulated targets largely revealed genes involved in controlling gene/protein expression (19%) and signal transduction processes (13%), proteomics/PROTEOMEX-defined candidate biomarkers include enzymes of the cellular metabolism (36%), transport proteins (12%), and cell motility/structural molecules (10%). Candidate biomarkers defined by proteomics and PROTEOMEX are frequently shared, whereas the sharing rate between cDNA microarray and proteome-based profilings is limited. Putative candidate biomarkers provide insights into their cellular (dys)function and their diagnostic/prognostic value but still warrant further validation in larger patient numbers. Based on the fact that merely three candidate biomarkers were shared by all applied technologies, namely annexin A4, tubulin alpha-1A chain, and ubiquitin carboxyl-terminal hydrolase L1, the analysis at a single hierarchical level of biological regulation seems to provide only limited results thus emphasizing the importance and benefit of performing rather combinatorial screenings which can complement the standard clinical predictors.

Current research status of immunology in the genomic era

This review updates the current status of immunology research under the influence of genomics, both conceptually and technologically. It particularly highlights the advantages of employing the high-throughput and large-scale technology, the large genomic database, and bioinformatic power in the immunology research. The fast development in the fields of basic immunology, clinical immunology (tumor and infectious immunology) and vaccine designing is illustrated with respect to the successful usage of genomic strategy. We also speculate the future research directions of immunology in the era of genomics and post-genomics.

HAGE, a cancer/testis antigen with potential for melanoma immunotherapy: identification of several MHC class I/II HAGE-derived immunogenic peptides

There remains a need to identify novel epitopes of potential tumour target antigens for use in immunotherapy of cancer. Here, several melanoma tissues and cell lines but not normal tissues were found to overexpress the cancer-testis antigen HAGE at the mRNA and protein level. We identified a HAGE-derived 15-mer peptide containing a shorter predicted MHC class I-binding sequence within a class II-binding sequence. However, only the longer peptide was found to be both endogenously processed and immunogenic for T cells in transgenic mice in vivo, as well as for human T cells in vitro. A different class I-binding peptide, not contained within a longer class II sequence, was subsequently found to be both immunogenic and endogenously processed in transgenic mice, as was a second class II epitope. These novel HAGE-derived epitopes may contribute to the range of immunotherapeutic targets for use in cancer vaccination programs.

Proteome informatics for cancer research: from molecules to clinic

Proteomics offers the most direct approach to understand disease and its molecular biomarkers. Biomarkers denote the biological states of tissues, cells, or body fluids that are useful for disease detection and classification. Clinical proteomics is used for early disease detection, molecular diagnosis of disease, identification and formulation of therapies, and disease monitoring and prognostics. Bioinformatics tools are essential for converting raw proteomics data into knowledge and subsequently into useful applications. These tools are used for the collection, processing, analysis, and interpretation of the vast amounts of proteomics data. Management, analysis, and interpretation of large quantities of raw and processed data require a combination of various informatics technologies such as databases, sequence comparison, predictive models, and statistical tools. We have demonstrated the utility of bioinformatics in clinical proteomics through the analysis of the cancer antigen survivin and its suitability as a target for cancer immunotherapy.

Challenges for cancer vaccine development

The first generation of human cancer vaccines has been tested in phase III clinical trials, but only a few of these have demonstrated sufficient efficacy to be licensed for clinical use. This article reviews some of the mechanisms that could contribute to these limited clinical responses, and highlights the challenges faced for development of future vaccines.

Tumor-associated antigen arrays for the serological diagnosis of cancer

The recognition that human tumors stimulate the production of autoantibodies against autologous cellular proteins called tumor-associated antigens (TAAs) has opened the door to the possibility that autoantibodies could be exploited as serological tools for the early diagnosis and management of cancer. Cancer-associated autoantibodies are often driven by intracellular proteins that are mutated, modified, or aberrantly expressed in tumor cells and hence are regarded as immunological reporters that could help uncover molecular events underlying tumorigenesis. Emerging evidence suggests that each type of cancer might trigger unique autoantibody signatures that reflect the nature of the malignant process in the affected organ. The advent of novel genomic, proteomic, and high throughput approaches has accelerated interest in the serum autoantibody repertoire in human cancers for the discovery of candidate TAAs. The use of individual anti-TAA autoantibodies as diagnostic or prognostic tools has been tempered by their low frequency and heterogeneity in most human cancers. However, TAA arrays comprising several antigens significantly increase this frequency and hold great promise for the early detection of cancer, monitoring cancer progression, guiding individualized therapeutic interventions, and identification of novel therapeutic targets. Our recent studies suggest that the implementation of TAA arrays in screening programs for the diagnosis of prostate cancer and other cancers should be preceded by the optimization of their sensitivity and specificity through the careful selection of the most favorable combinations of TAAs.