Glia maturation factor-β is produced by thymoma and may promote intratumoral T-cell differentiation

Aims : To investigate whether Glia maturation factor‐β (GMFB) is expressed in thymomas and is associated with T‐cell development. Methods and results : We investigated the expression of GMFB by immunohistochemistry in 86 cases of thymoma classified into five type A, 35 type AB, 11 type B1, 26 type B2, and nine type B3 thymomas according to the World Health Organization classification system. Immunoblotting and in situ hybridization (ISH) studies were also performed in selected cases. The results of the immunoblot analysis were in accordance with those of immunohistochemical scoring. The ISH study ascertained the tumour cells producing the protein. Immunohistochemically, GMFB expression was observed in one (20%) of type A, 32 (80%) of type AB, all (100%) of type B1 and B2, and eight (89%) of type B3 thymoma with statistically significant differences between type A and type AB, type B1, or type B2 thymoma, and between type B3 and type AB or type B2 thymoma. There was a significant correlation between GMFB expression and the amount of accompanying non‐neoplastic T cells. GMFB promoted T‐cell differentiation into CD4–/CD8+ cells when analysed by two‐colour flow cytometry. Conclusions : The present study suggests that T‐cell development in thymoma may be maintained partly by GMFB produced by the tumour cells.