We previously reported that PD-1 expression on circulating monocytes in patients with ruptured cerebral aneurysms correlated with cerebral vasospasm, while systemic sPD-L1 administration prevented vasospasm after subarachnoid hemorrhage in an ICA perforation model by inhibiting ingress of PD-1+, Ly6Chi, CCR2hi inflammatory monocytes into the brain (Jackson et al., 2021). Here, PDCD1 is linked to subarachnoid hemorrhage.