Specifically, Mandel et al. [20] observed TJ proteins of the claudin (CLN) family—notably CLN-1 (CLN-1+) and CLN-5 (CLN-5+)—in peripheral blood leukocytes (PBLs) from both healthy individuals and those affected with the neuroinflammatory condition multiple sclerosis (MS). Here, PPT1 is linked to myeloid sarcoma.