Since 1979, when p53 was discovered as a tumor-associated antigen, it has attracted an enormous number of scientists in several fields. p53 has since been revealed to be a multifaceted protein functioning as a transcriptional transactivator or repressor, as a key molecule in DNA repair, apoptosis, growth suppression, differentiation, senescence, control of angiogen-esis and mitotic spindle function [1-4]. p53 seems to have a singular position among the class of growth suppressor genes because it is inactivated with a high frequency in most types of human cancers [5], p53 seems to prevent cells from developing into cancerous cells and, therefore, it was regarded as the "guardian of the genome" [6]. Beside the inactivation of p53 in somatic cells, individuals with germline mutations were also found who were of high risk to develop cancer [7]. A steadily increasing number of papers revealed that in many cases alterations in the p53 gene or protein were found to be predictive factors for tumor formation and an unfavorable prognosis. Unusual forms of p53 are associated with aggressive tumors, early metastasis and low 5-years survival rates. Therefore, changes in the p53 gene, protein expression or protein modification as well as different subcellular localizations of the p53 protein were used in clinical oncology for early diagnosis, for prognostic evaluation, to trail treatment of individual patients and to assess the response to therapy [8]. The analysis of p53 gene alterations or p53 protein modifications requires tumor material and a variety of skilful techniques and, therefore, these types of analysis are inadequate for the individual patient or for medical-care people. In 1982, p53 autoantibod ies were discovered in sera of breast cancer patients [9]. The following articles then described detectable levels of p53 autoantibodies in sera from a variety of other cancer patients [10, 11]. Analyzing a great number of sera it was shown that p53 autoantibodies are very rare in healthy donors (<0.5%). These early findings suggested that the serological search for antibodies against the p53 protein may help to improve the diagnosis of malignant neoplasia, without invasive treatment of patients.


So far, it is unclear what triggers an immune response to p53. The most frequent alterations in human tumors are point mutations in the p53 gene, although also wild-type p53 was found in a number of tumor cells. However, mutant and wild-type p53 in tumor cells in general exhibit a prolonged half-life accounting for the accumulation of the protein in tumor cells. Most patients with p53 autoantibodies exhibit an accumulation of the p53 protein in the tumor material suggesting that elevated levels of the p53 protein may account for the generation of an immune response against p53. However, there are also observations that patients may develop antibodies against p53 without an overexpression of the protein in the corresponding tumor material [12, 13]. It has been suggested that the site of mutation within the p53 gene may be a determinant for the p53 autoantibody response [1416]. However, such a correlation was not found in other studies [15, 17]. The site of mutation is not expected to influence the antibody response against p53 because the immunogenic sites of the p53 molecule reside in the amino-terminal and more weakly in the carboxy-terminal part of the p53 polypeptide chain [18, 19]. These two regions are unaffected by mutations in human tumors [18,20], Furthermore, human sera react equally with mutant and wild-type p53 and with conformational and denaturation resistant antigenic epitopes [10, 14, 21]. Another study connects the immunogenicity of p53 to its ability to form complexes with the heat shock protein HSP70 [16], because co-immunoprecipitation experiments showed that tumor tissue from patients with circulating antibodies contained hsp70/p53 complexes, whereas, no such complexes were found in tissue from patients without p53 autoantibodies [22-24],

Typing of p53 autoantibodies revealed that they correspond mainly to IgGl and IgG2 subclasses, but some patients exhibit a predominant IgA response. In addition, primary cytotoxic T-lymphocyte responses to wild-type and mutant peptides of p53 in vitro and in a mouse model were described.


A variety of different methods were applied to detect p53 autoantibodies. Early studies on p53 autoantibodies used radioactively labeled p53 from cell extracts which was immunoprecipitated with sera from patients, run on a gel under denaturing conditions and positive sera were detected by autoradiography [9,16], Alternatively, monoclonal antibodies against p53 were used to precipitate p53 from tumor cell extracts, run on a gel under denaturing conditions and the patients' sera were used in a Western Blot analysis [11], In the last 6 years, ELISAs were developed which allow a rapid and highly sensitive screening of large numbers of sera. The ELISAs differ in as much as bacteri-ally expressed, p53 synthetic peptides consisting of 15 amino acids, p53 from insect cells infected with recombinant baculoviruses or p53 from human tumor cells were used. Comparing some of these different methods within the same study it turned out that most but not all sera were positive with at least three different methods [25, 26]. However, some sera were negative in one type of ELISA and positive in another, and either negative or positive in Western Blot analysis. The conclusion of one of these studies was that using different assay systems and taking multiple blood samples from the same patient helps to optimize the detection of p53 autoantibodies [26].


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