Malignant mesothelioma‐associated antigens recognized by tumor‐infiltrating B cells and the clinical significance of the antibody titers

Abstract

Malignant pleural mesothelioma (MPM) is difficult to diagnose at an early stage. The present study attempted to obtain a tumor-specific antibody against MPM derived from tumor-infiltrating B lymphocytes in MPM by using a xenotransplanted severe combined immunodeficiency (SCID) mouse model, and to identify the antigens recognized by the antibodies. Among the antigen-antibody relationships, the clinical usefulness of antibody titers in the sera was evaluated from the viewpoint of diagnosis of MPM and monitoring of therapeutic effects. Tumor tissue specimens from two patients with MPM were engrafted subcutaneously in SCID mice and blood samples were obtained and pooled every 2 weeks after xenotransplantation until 14 weeks when the mice were killed. A cDNA library was constructed from the mRNA of a MPM cell line (K921MSO). Immunoscreening of the libraries was carried out by serological identification of antigens by a recombinant expression cloning method (SEREX) and four antigens were identified as MPM-associated antigens. Among them, antibody titers against two antigens, Gene-X and thrombospondin-2 (THBS-2), were analyzed by phage plaque assay as the first step. ELISA systems correlated with the phage plaque assay to detect antibody titers against the two antigens were constructed using 20-mer peptides of the antigencoding genes. The cut-off value was decided by the average and standard deviation of normal healthy persons. Antibody against Gene-X was detected in 10 out of 18 (55.6%) mesothelioma patients and antibody against THBS-2 was detected in 16 out of 18 (88.9%) mesothelioma patients. No patients with lung cancer regardless of asbestos exposure exhibited positive antibody titer against the two antigens. Furthermore, the serum antibody titers decreased after surgical treatment of MPM and increased after recurrence of the disease. The titers of the antibodies against Gene-X and THBS-2 could be used as tumor markers for the diagnosis and follow up of patients with MPM. (Cancer Sci 2009; 100: 1326-1334) M alignant pleural mesothelioma (MPM) is an aggressive neoplasm arising from mesothelial cells and it is usually fatal. MPM is thought to be associated with previous exposure to asbestos fibers. Due to the widespread use of asbestos fibers in the latter half of the 20th century, the incidence of MPM is predicted to rise sharply in industrialized countries in the next few decades after 30 -40 years of a latent period.(1) The number of new cases in Europe is expected to double between 1998 and 2018.(2) Based on the prevalence in USA and Europe, Japan is also facing an epidemic of MPM belatedly. In Japan, 500 patients with MPM died in 1995 and the number of deaths increased to approximately 900 patients in 2003.(3) Not only occupational exposure, but also environmental exposure becomes a public health problem, because asbestos was used widely in buildings as a construction material and asbestos cement pipes. (4,5) Malignant pleural mesothelioma is difficult to diagnose radiographically at an early stage and often pr...

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Chronic inflammation in tumor stroma is an independent predictor of prolonged survival in epithelioid malignant pleural mesothelioma patients

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Overexpressed genes in malignant pleural mesothelioma: implications in clinical management

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