PDCD1 and myeloid sarcoma: Fransen et al. found an increased number of T cells clustering in the perivascular space and, in MS lesions with active and inactive features, identified a specific tissue-resident memory phenotype of CD8+ T cells that lack S1P1 and express CD69, CD103, CD44, CD49a, PD-1, in parallel with upregulated markers for homing (CXCR6), reactivation (Ki-67), and cytotoxicity (GPR56) [73].