MATURE CD4 SINGLE POSITIVE THYMOCYTES IN HUMAN THYMOMA - T-CELLS MAY DIFFERENTIATE IN THE THYMIC EPITHELIAL-CELL TUMOR

Human thymoma, which is occasionally associated with autoimmune diseas e, is a thymic epithelial cell tumor and often contains a large number of lymphocytes, In a previous study, we have shown that a proportion of CD4 single positive T cells in human thymomas lack CD3, suggesting immaturity. In this study, we focused on the rest of the CD4 single po sitive T cells in thymomas that expressed CD3/TcR alpha beta and inves tigated the maturity of single positive a cells by analyzing lymphocyt e surface antigens and the cells' proliferative response to a mitogen, CD4 single positive cells that expressed CT)3 or TcR alpha beta also expressed CD69 and had probably undergone positive selection in the tu mor. Further, isolated CD4 or CD8 single positive cells from the thymo mas responsed to a mitogen although at lower levels than the correspon ding single positive cells in the peripheral blood, These results indi cate that thymomas contain single positive T cells which have mature p henotype and proliferative ability, and suggest that T cells may diffe rentiate in thymoma.