These results suggest that these three antigens induced a humoral immune response in patient G603. == Antibodies against SEREXdefined antigens in lung cancer patients and healthy donors == The existence of antibodies against the three antigens was investigated in sera from 34 patients with NSCLC (other than patient G603) and 10 healthy individuals (Table3). was revealed to be Carbenoxolone Sodium MAGEB2 whereas the others were novel antigens. In the immunomonitoring of the patient’s sera, high antibody titer against MAGEB2 was observed before operation and the titer decreased after resection of the primary tumor. It was elevated again at the time of adrenal metastasis, but then decreased after resection. The change in antibody titer against the second antigen was similar to MAGEB2, and the antibody titer against the third antigen was low before the primary operation but increased at the time of recurrence. Our results suggest that TIB recognized tumor antigens and the Carbenoxolone Sodium antibody titers against these antigens were changed along with the patient’s clinical course. Therefore, these antibodies could be used as tumor markers for the patient. (Cancer Sci2005; 96: 882888) == Abbreviations: == cytotoxic T lymphocyte EpsteinBarr virustransformed B cell enzymelinked immunosorbent assay nonsmall cell lung cancer polymerase chain reaction plaqueforming unit reverse transcriptionpolymerase chain reaction severe combined immunodeficient mouse small cell lung cancer serological analysis of recombinantly expressed cDNA clones tumorinfiltrating B lymphocyte. Lung cancer is the leading cause of death for men and women in the USA, with 90 363 men and 65 606 women dying from lung cancer in 2001.(1)Among all of the malignant neoplasms, lung cancer is also one of the highest causes of death in Japan, accounting for 22.0% of all cancer deaths for men and 12.7% for women.(2)The incidence and mortality of lung cancer continues to increase worldwide. Lung cancer is classified into two groups: NSCLC and SCLC. For NSCLC patients, a complete surgical resection is the standard way to obtain a cure. However, the recurrence rate after a complete resection remains high even for early stage cases of NSCLC.(3,4,5)Chemotherapy and radiotherapy are fundamental modalities for advanced and recurrent lung cancer after surgery; however, their effectiveness remains unsatisfactory.(6,7,8,9)In addition to these conventional treatments, alternative therapies have also been developed, including immunotherapy, molecular targeting therapy and gene therapy. To improve the effectiveness of immunotherapy, the identification of highly immunogenic tumor antigens is very important. The cDNA expression cloning method has been used to identify genes coding for tumor antigens using CTL.(10,11,12)Another method to detect tumor antigens is serological analysis of recombinantly expressed cDNA clones, named SEREX. A number of tumor antigens have been identified by the SEREX method using patients sera. SEREX analysis has shown that vigorous humoral immune responses have been elicited in cancer patients due to a variety of cellular antigens, including differentiation antigens, mutational antigens, PGC1A cancertestis Carbenoxolone Sodium antigens and overexpressed tumor antigens.(13,14,15,16,17,18,19,20,21,22)However, these antigens identified from patients sera by the SEREX method included not only tumorassociated antigens but also autoreactive antigens from normal components. To overcome this problem, we used IgG produced by TIB to a SEREX analysis as a screening probe and thus found 37 tumor antigens in a large cell carcinoma of the lung.(23) Tumorinfiltrating B lymphocytes are one of the major components of mononuclear cells, which infiltrate solid tumors. To investigate the function of TIB, we engrafted fresh tumor tissue specimens onto SCID mice. We found that human IgG was produced by TIB in the serum of SCID mice, and western blot analysis revealed that such human IgG could react with the proteins from tumor lysates.(24)Williamset al.also reported that the serum from tumorengrafted SCID mice could react with the high and low molecular weight proteins derived from both the membrane and cytosolic fractions of tumor cell lysates.(25)In the present study, we identified the tumor antigens in the pleomorphic carcinoma of the lung by using IgG produced by TIB, and we also demonstrated serial changes in the humoral immune response against them in relation to the clinical course of the patient. == Materials and Methods == The study protocol was approved by the Human and Animal Ethics Review Committee of the University of Occupational and Environmental Health, Fukuoka, Japan, and written informed consent was obtained from each patient regarding the usage of surgical specimens. == Patient G603 == Patient G603, a 73yearold man, was diagnosed as having a pleomorphic carcinoma of the lung in June 2002, as previously described.(26)The primary tumor, which was located in the right upper lobe of the lung, was resected in June 2002. The lung cancer cell line, G603L, was thus established from the primary tumor. Seven months after the first operation for the primary lesion, a metastatic tumor was detected in the right adrenal gland, and a right adrenalectomy was carried out in January 2003. The tumor.