Barriers between circulation and the central nervous system (CNS) play a key role in the development and modulation of CNS immune responses. Structural variations in the vasculature traversing different anatomical regions within the CNS strongly influence where and how CNS immune responses first develop. Here, we provide an overview of cerebrovascular anatomy, focusing on the blood-CNS interface and how anatomical variations influence steady-state immunology in the compartment. We then discuss how CNS vasculature is affected by and influences the development of different pathophysiological states, such as CNS autoimmune disease, cerebrovascular injury, cerebral ischemia, and infection.Arterial blood enters the cranial cavity, primarily through two sets of blood vessels: the internal carotid arteries, which give rise to anterior brain circulation, and the vertebral arteries, which give rise to posterior circulation. These are interconnected through the circle of Willis located in subarachnoid cisterns at the base of the brain (11). The circle of Willis allows any one of these four vessels to take over brain perfusion and provides a protective mechanism against ischemia. The internal carotid arteries supply the cerebrum, whereas the vertebral arteries join to form the basilar artery that supplies the brainstem and cerebellum. Second-order branches form vessels that traverse the subarachnoid space and pia mater, giving rise to smaller arterioles ( Fig. 1) that enter the brain parenchyma ( Fig. 1A) (12). These penetrating vessels are surrounded by perivascular spaces that can vary in size. For example, in the cortex, a packed barrier of endothelial cells, basement membrane, and glia limitans surrounds penetrating arteries, leaving little to no fluid-filled space, whereas the lenticulostriate branches in the basal ganglia are surrounded by a larger perivascular space (13). Pia mater covers all arteries in the subarachnoid space, whereas coverage of veins is incomplete. In addition, the fluid in perivascular spaces can move directly into the subarachnoid space through fenestrations in the pia mater ( Fig. 1A) (14). This allows direct communication between perivascular, subpial, and subarachnoid spaces. The communication of the perivascular compartment with the subarachnoid space plays an important role in antigen presentation, which will be described in more detail below. Venous drainage in the CNS occurs through an interconnected system of valveless veins and dural sinuses. Postcapillary venules in the CNS parenchyma drain capillaries and are surrounded by fluidfilled perivascular spaces (Figs. 1, A and B, and 2) (15). They connect into a deep and superficial venous system. Deep venous drainage occurs through the subependymal veins, internal cerebral veins, basal vein, and the great vein of Galen, which connect into the straight sinus beneath the brain. Superficial drainage occurs through cortical veins in the pia mater that drain into the dural sinuses. The venous system ultimately drains into the jugular veins or pt...

Gene therapy has emerged as an alternative for the treatment of diseases refractory to conventional therapeutics. Synthetic nanoparticle-based gene delivery systems offer highly tunable platforms for the delivery of therapeutic genes. However, the inability to achieve sustained, high-level transgene expression in vivo presents a significant hurdle. The respiratory system, although readily accessible, remains a challenging target, as effective gene therapy mandates colloidal stability in physiological fluids and the ability to overcome biological barriers found in the lung. We formulated highly stable DNA nanoparticles based on state-of-theart biodegradable polymers, poly(β-amino esters) (PBAEs), possessing a dense corona of polyethylene glycol. We found that these nanoparticles efficiently penetrated the nanoporous and highly adhesive human mucus gel layer that constitutes a primary barrier to reaching the underlying epithelium. We also discovered that these PBAE-based mucus-penetrating DNA nanoparticles (PBAE-MPPs) provided uniform and high-level transgene expression throughout the mouse lungs, superior to several gold standard gene delivery systems. PBAE-MPPs achieved robust transgene expression over at least 4 mo following a single administration, and their transfection efficiency was not attenuated by repeated administrations, underscoring their clinical relevance. Importantly, PBAE-MPPs demonstrated a favorable safety profile with no signs of toxicity following intratracheal administration.lung gene therapy | mucus-penetrating particles | nanotechnology | biodegradable polymer | nonviral gene delivery

Gene delivery to the central nervous system (CNS) has potential as a means for treating numerous debilitating neurological diseases. Non-viral gene vector platforms are tailorable and can overcome key limitations intrinsic to virus-mediated delivery; however, lack of clinical efficacy with non-viral systems to date may be attributed to limited gene vector dispersion and transfection in vivo. We show that the brain extracellular matrix strongly limits penetration of polymer-based gene vector nanoparticles through the brain parenchyma, even when they are very small (<60 nm) and coated with a polyethylene glycol (PEG) corona of typical density. Following convection enhanced delivery (CED), these “conventional gene vectors” were confined to the injection site, presumably by adhesive interactions with the brain extracellular matrix, and did not provide gene expression beyond the point of administration. In contrast, we found that incorporating highly PEGylated polymers allowed production of compacted (~43 nm) and colloidally stable DNA nanoparticles that avoided adhesive trapping within the brain parenchyma. When administered by CED into the rat striatum, highly PEGylated DNA nanoparticles distributed throughout and provided broad transgene expression without vector-induced toxicity. The use of these “brain-penetrating gene vectors”, in conjunction with CED, offers an avenue to improve gene therapy for CNS diseases.