Vectors based on adeno-associated virus (AAV) serotype 9 are candidates for in vivo gene delivery to many organs, but the receptor(s) mediating these tropisms have yet to be defined. We evaluated AAV9 uptake by glycans with terminal sialic acids (SAs), a common mode of cellular entry for viruses. We found, however, that AAV9 binding increased when terminal SA was enzymatically removed, suggesting that galactose, which is the most commonly observed penultimate monosaccharide to SA, may mediate AAV9 transduction.

Here the authors discuss evidence in human and animal models supporting two opposing views regarding the pathogenesis of human immunodeficiency virus (HIV) in the central nervous system (CNS): (1) HIV infection in the CNS is a compartmentalized infection, with the virus-infected macrophages entering the CNS early, infecting resident microglia and astrocytes, and achieving a state of latency with evolution toward a fulminant CNS infection late in the course of disease; or alternatively, (2) events in the periphery lead to altered monocyte/macrophage (MΦ) homeostasis, with increased CNS invasion of infected and/or uninfected MΦs. Here the authors have reevaluated evidence presented in the favor of the latter model, with a discussion of phenotypic characteristics distinguishing normal resident microglia with those accumulating in HIV encephalitis (HIVE). CD163 is normally expressed by perivascular MΦs but not resident microglia in normal CNS of humans and rhesus macaques. In agreement with other studies, the authors demonstrate expression of CD163 by brain MΦs in HIVE and simian immunodeficiency virus encephalitis (SIVE). CNS tissues from HIV-sero positive individuals with HIVE or HIV-associated progressive multifocal leukoencephalopathy (PML) were also examined. In HIVE, the authors further demonstrate colocalization of CD163 and CD16 (FcγIII recptor) gene expression, the latter marker associated with HIV infection of monocyte in vivo and permissivity of infection. Indeed, CD163 + MΦs and microglia are often productively infected in HIVE CNS. In SIV infected rhesus macaques, CD163 + cells accumulate perivascularly, within nodular lesions and the parenchyma in animals with encephalitis. Likewise, parenchymal microglia and perivascular MΦs are CD163 + in HIVE. In contrast to HIVE, CD163 + perivascular and parenchymal MΦs in HIV-associated PML were only associated with areas of demyelinating lesions. Interestingly, SIV-infected rhesus macaques whose viral burden was predominantly at 1 × 10 6 copies/ml or greater developed encephalitis. To further investigate the relationship between CD163 + /CD16 + MΦs/microglia in the CNS and altered homeostasis in the periphery, the authors performed flow-cytometric analyses of peripheral blood

b Adeno-associated virus serotype 9 (AAV9) vectors show promise for gene therapy of a variety of diseases due to their ability to transduce multiple tissues, including heart, skeletal muscle, and the alveolar epithelium of the lung. In addition, AAV9 is unique compared to other AAV serotypes in that it is capable of surpassing the blood-brain barrier and transducing neurons in the brain and spinal cord. It has recently been shown that AAV9 uses galactose as a receptor to transduce many different cell types in vitro, as well as cells of the mouse airway in vivo. In this study, we sought to identify the specific amino acids of the AAV9 capsid necessary for binding to galactose. By site-directed mutagenesis and cell binding assays, plus computational ligand docking studies, we discovered five amino acids, including N470, D271, N272, Y446, and W503, which are required for galactose binding that form a pocket at the base of the protrusions around the icosahedral 3-fold axes of symmetry. The importance of these amino acids for tissue tropism was also confirmed by in vivo studies in the mouse lung. Identifying the interactions necessary for AAV9 binding to galactose may lead to advances in vector engineering.A deno-associated virus (AAV) vectors show great potential for use in gene therapy applications due to their ability to transduce many different types of tissues and provide stable, long-term gene expression (41). Numerous serotypes of AAV have been characterized, and more than 120 other variants have been isolated from both human and nonhuman primate tissues (13-15, 27, 35, 35a). Each of these variants has its own unique properties providing a large pool of potential vectors for gene therapy. Different AAV serotypes display distinctive tissue tropism and transduction efficiency. For example, AAV1 demonstrates efficient muscle transduction, AAV6 shows promise in targeting the conducting airway epithelium of the lung, and AAV8 provides impressive liver transduction (6,15,18,24,46).The three-dimensional structure of the capsid of many AAV serotypes has been determined by X-ray crystallography (7,16,22,28,29,47,48). The core of the virion consists of a highly conserved eight stranded ␤-barrel motif with large loops inserted between these ␤-strands that contain defined variable regions (VRs) (16,28,29). The VRs are present at the surface of the capsid structure and are therefore readily available for cellular interactions. The high diversity of the VRs between AAV serotypes likely defines their respective phenotypes in regard to tropism, transduction efficiency, and antigenicity. Most of the VRs are located at or near the icosahedral 3-fold axes of symmetry of the capsid, forming protrusions around these axes (16,28,29).Receptor binding is a proximal step necessary for AAV vector transduction. Interaction with cell surface receptors allows internalization of the virion and subsequent trafficking to the nucleus where gene expression occurs (8). Receptors for many AAV serotypes have been identified. AAV2 has been shown ...

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Our studies demonstrate the existence of a functional hierarchy of proinflammatory cytokines in the eye, and we show that IL-1β is the most pathogenic when it is continuously expressed in the eye.