CXCL12 is the signature cytokine secreted by CAR cells and this chemokine is known to be important, not only in hematopoiesis but also as a marker for the severity of osteoporosis in postmenopausal women.(34, 35) Indeed, analysis of BM plasma and blood serum revealed increased protein levels of CXCL12 in female Ccl19‐Cre ERαfl/fl mice compared with controls (Fig. 7F, G). The gene discussed is CCL19; the disease is osteoporosis.