Expansion of such B2 cell clones could have been driven by antigen, e.g., with cross-reactive micro-organisms in patients without thymoma (109) or be driven by acetylcholine receptor specific autoreactive helper CD4+ T cells in thymoma-associated myasthenia gravis where such autoreactive T cells have escaped tolerance mechanisms (110, 111). This evidence concerns the gene CD4 and thymoma.