Rearrangement of T-cell receptor beta and gamma genes in thymoma.

To investigate the differentiation stage of tumor-infiltrating lymphocytes in thymoma tissue, we performed Southern blot analysis of T-cell receptor beta and gamma genes in thymomas resected from 19 patients. At the same time, we conducted flow cytometric analysis of T-cell surface markers and examined the clinicopathological features of the thymomas. We found that the incidence of T-cell receptor gamma gene rearrangement was significantly higher in Masaoka stage I thymomas (11 of 12 cases) than in stage II or III invasive thymomas (3 of 7 cases). Moreover, gamma gene rearrangement was observed in all 10 type AB and B1 thymoma specimens and in 4 of 6 type B2 thymoma specimens. The 2 specimens of type B3 thymomas, which were classified as stage III, showed neither gamma nor beta gene arrangement and were single-positive for CD4 or CD8. Six thymoma specimens that showed beta gene rearrangement expressed both CD4 and CD8. In conclusion, thymomas have the capability of T-lineage cell differentiation, except for a subset of invasive thymomas with malignant characteristics.