Common features of parvovirus capsids are open pores at the fivefold symmetry axes that traverse the virion shell. Upon limited heat treatment in vitro, the pores can function as portals to externalize VP1/VP2 protein N-terminal sequences which harbor infection-relevant functional domains, such as a phospholipase A 2 catalytic domain. Here we show that adeno-associated virus type 2 (AAV2) also exposes its VP1/VP2 N termini in vivo during infection, presumably in the endosomal compartment. This conformational change is influenced by treatment with lysosomotropic reagents. While incubation of cells with bafilomycin A1 reduced exposure of VP1/VP2 N termini, incubation with chloroquine stimulated externalization transiently. N-terminally located basic amino acid clusters with nuclear localization activity also become exposed in this process and are accessible on the virus capsid when it enters the cytoplasm. This is an obligatory step in AAV2 infection. However, a direct role of these sequences in nuclear translocation of viral capsids could not be determined by microinjection of wild-type or mutant viruses. This suggests that further modifications of the capsid have to take place in a precytoplasmic entry step that prepares the virus for nuclear entry. Microinjection of several capsid-specific antibodies into the cell nucleus blocked AAV2 infection completely, supporting the conclusion that AAV2 capsids bring the infectious genome into the nucleus.Viruses which replicate in the nucleus have evolved different mechanisms to cross the two main cellular barriers, the plasma membrane and the nuclear membrane (43,58,59). Cell entry is commonly achieved by binding to cell surface receptors and either direct penetration into the cytoplasm by membrane fusion or uptake into cellular vesicles followed by release into the cytoplasm. Delivery of genetic material into the cell nucleus occurs through nuclear pore complexes in association with viral proteins which have nuclear targeting activity. This requires in most cases partial disassembly of the viral coat before or after interaction with the nuclear pore complexes (22). Because of their small size, intact parvoviruses have the potential to cross the nuclear pore and to deliver their genome within the intact capsid directly into the nucleus. However, there is no evidence so far that the capsid delivers the infectious genome into the nucleus.Infection of cultured cells by adeno-associated virus type 2 (AAV2) is initiated by binding to heparan sulfate proteoglycan as an attachment receptor followed by interaction with either human fibroblast growth factor receptor 1, integrin ␣ V ␤5, or hepatocyte growth factor receptor (35,50,62,63). After receptor binding, AAV2 enters the host cell via clathrin-coated vesicles in a dynamin-dependent process (2, 15) and is transported to a perinuclear vesicle compartment (1,2,16,27,31,55,73). Acidification of the endosomal compartment appears to be important for AAV2 infection, since treatment of cells with bafilomycin A1 significantly, albeit...

Oncolytic virotherapy may be a means of improving the dismal prognosis of malignant brain tumors. The rat H-1 parvovirus (H-1PV) suppresses tumors in preclinical glioma models, through both direct oncolysis and stimulation of anticancer immune responses. This was the basis of ParvOryx01, the first phase I/IIa clinical trial of an oncolytic parvovirus in recurrent glioblastoma patients. H-1PV (escalating dose) was administered via intratumoral or intravenous injection. Tumors were resected 9 days after treatment, and virus was re-administered around the resection cavity. Primary endpoints were safety and tolerability, virus distribution, and maximum tolerated dose (MTD). Progression-free and overall survival and levels of viral and immunological markers in the tumor and peripheral blood were also investigated. H-1PV treatment was safe and well tolerated, and no MTD was reached. The virus could cross the blood-brain/tumor barrier and spread widely through the tumor. It showed favorable pharmacokinetics, induced antibody formation in a dose-dependent manner, and triggered specific T cell responses. Markers of virus replication, microglia/macrophage activation, and cytotoxic T cell infiltration were detected in infected tumors, suggesting that H-1PV may trigger an immunogenic stimulus. Median survival was extended in comparison with recent meta-analyses. Altogether, ParvOryx01 results provide an impetus for further H-1PV clinical development.

As a prerequisite to clinical application, we determined the long-term therapeutic effectiveness and safety of adeno-associated viral (AAV) S100A1 gene therapy in a preclinical, large animal model of heart failure. S100A1, a positive inotropic regulator of myocardial contractility, becomes depleted in failing cardiomyocytes in humans and various animal models, and myocardial-targeted S100A1 gene transfer rescues cardiac contractile function by restoring sarcoplasmic reticulum calcium Ca2+ handling in acutely and chronically failing hearts in small animal models. We induced heart failure in domestic pigs by balloon-occlusion of the left circumflex coronary artery, resulting in myocardial infarction. After 2 weeks, when the pigs displayed significant left ventricular contractile dysfunction, we administered through retrograde coronary venous delivery, AAV9-S100A1 to the left ventricular non-infarcted myocardium. AAV9-luciferase and saline treatment served as control. At 14 weeks, both control groups showed significantly decreased myocardial S100A1 protein expression along with progressive deterioration of cardiac performance and left ventricular remodeling. AAV9-S100A1 treatment prevented and reversed this phenotype by restoring cardiac S100A1 protein levels. S100A1 treatment normalized cardiomyocyte Ca2+ cycling, sarcoplasmic reticulum calcium handling and energy homeostasis. Transgene expression was restricted to cardiac tissue and extra-cardiac organ function was uncompromised indicating a favorable safety profile. This translational study shows the pre-clinical feasibility, long-term therapeutic effectiveness and a favorable safety profile of cardiac AAV9-S100A1 gene therapy in a preclinical model of heart failure. Our study presents a strong rational for a clinical trial of S100A1 gene therapy for human heart failure that could potentially complement current strategies to treat end-stage heart failure.