Figure 6: Hypothesis for the accumulation of somatic mutations.

Mature T cells undergo thymic selection, and during the expansion phase after antigen stimulation, mutation(s) occur (1st mutation). When the cell population continues to grow, additional mutations may arise in the same clone, thereby resulting in different VAFs in the same clonal population. In our patient cohort, CD4+ cells presented a more equally distributed T-cell repertoire than did CD8+ T cells (analysed with flow cytometry), and we did not find any somatic variants in CD4+ cells. APC, antigen-presenting cell; DN, double negative; DP, double positive; SP, single positive; MHC, major histocompatibility complex.