In contrast, a large number of tdT+ (CD34+) cells accumulated in the adventitia and co‐expressed common fibroblast markers (PDGFRa, DDR2, Vimentin) (Figure S5B–D, Supporting Information) and myofibroblast markers (Periostin) (Figure 2G) upon Ang II or CaCl2 stimulation, demonstrating that CD34+ cells were activated to transdifferentiate into myofibroblasts during AAA progression. Here, DDR2 is linked to triple-A syndrome.