CD34 and triple-A syndrome: Furthermore, by combining Cd34‐CreERT2;Rosa26‐tdTomato;(Apoe−/−) lineage tracing, bone marrow transplantation, and single‐cell sequencing, it is found that during AAA development, non‐bone marrow CD34+ cells are activated to transdifferentiate into Periostin+ myofibroblasts, thereby contributing to the formation of fibrotic collars.