We previously reported to identify SOX5 as a glioma antigen by serological screening using a testis cDNA library. The present study was designed to analyze SOX5 expression, its immunoreactivity, and the correlation between SOX5 IgG responses and clinical features in glioma patients to evaluate the possibility of its use as a diagnostic marker. Quantitative RT-PCR and Western blot analysis revealed that SOX5 was expressed in glioma tissues, but not in normal adult tissues, except in the testis. An immunohistochemical analysis showed that SOX5 was expressed in glioma cells, but only a few SOX5-positive cells were detected in non-neoplastic tissues from the cerebral cortex. IgG antibodies against SOX5 were detected in sera from 8 of the 27 glioma patients (27.6%), 0 of the 14 patients with other brain diseases (0%), 1 of the 54 other cancer patients (1.9%) and 1 of the 37 healthy individuals (2.7%). Patients with glioblastoma (GBM) who showed IgG responses against SOX5 exhibited significantly better survival periods than GBM patients without SOX5 antibodies. In summary, SOX5 is aberrantly expressed in glioma and can be recognized as a glioma antigen using IgGs from the sera of glioma patients. Furthermore, there is a statistically significant correlation between the presence of SOX5 IgGs and survival in GBM patients, suggesting that the glioma antigen SOX5 may be useful not only as a diagnostic marker, but also as a prognositic marker in glioma patients. ' 2007 Wiley-Liss, Inc.Key words: glioma; tumor antigen; SOX5; SEREX; IgG response Gliomas are the most common neoplasms of the central nervous system, comprising more than 60% of primary brain tumors. Glioblastoma multiforme (GBM) is the most malignant of these tumors, with an average survival time of less than 16 months and a 5-year survival time of approximately 5%.1 Despite aggressive multimodal therapy, the prognosis for patients with malignant glioma is still poor. Thus, the development of new therapeutic strategies is required.The identification of human tumor antigens is important not only for the analysis of antitumor immune responses and the development of immunotherapy, but also for the development of diagnostic methods.2 Various methods for the identification of tumor antigens have recently been applied, including cDNA expression cloning using tumor-reactive T cells and IgG antibodies in patients' sera as well as a reverse immunology strategy that evaluates the induction of T cells against candidate molecules identified by various techniques, such as systematic gene expression analysis.As of yet, several immunologic markers for glioma patients have been reported.3,4 However, it is unclear how immune responses against these antigens could be induced in glioma patients or whether these immune responses are specific for glioma patients because these antigens were expressed not only in glioma tissue, but also in normal adult tissues. Previously, we reported SOX5 and SOX6 as glioma antigens detected by serological screening using a testis cDNA library and s...