377. Intravascular Delivery of Adenovirus Vectors Rapidly Targets Platelets to the Reticuloendothelial System

Abstract

Top of pageAbstract Following intravenous (iv) delivery of an adenovirus (Ad) vector a severely adverse event was seen in a phase I clinical trial. Systemic inflammatory response syndrome (SIRS) and biochemically detectable disseminated intravascular coagulation (DIC) were among complications that ultimately resulted in multiple organ system failure 98 hours after iv delivery of a dose of 6 x 1011 viral particles/kg. DIC is a complex clinical syndrome characterized by a systemic activation of coagulation leading to the intravascular deposition of fibrin in the (micro) vasculature and the simultaneous consumption of coagulation factors and platelets. Since platelet consumption is a symptom of DIC and Ad vectors are known to induce thrombocytopenia after iv delivery we decided to investigate Ad- platelet interactions as part of a safety and toxicity study. We investigated the interactions of an Ad5 vector, chimeric Ad5 vectors possessing the CD46 interacting Ad11 or Ad35 fibers (Ad5/F11 or Ad5/F35), and an Ad11 vector, early after iv delivery to mice. Transgenic mice that express human CD46 were injected in the tail vein with a total of 1011 viral particles of each vector. Within 10 minutes of iv delivery we found Ad particles associated with circulating platelets, with the highest levels seen with Ad11 vectors. Subsequently, different organs where monitored by immunohistochemistry and transmission electron microscopy (TEM) for evidence of in vivo Ad-platelet interactions. Within 5 minutes of administration degranulated platelets containing Ad5, Ad5/F11, Ad5/F35 or Ad11 vector particles could be seen directly interacting with endothelial cells within the liver sinusoids by TEM. Ad particles could also be seen within platelet aggregates and inside Kupffer cells. Triple label immunohistochemistry revealed widespread co-labeling of platelets (CD41), Kupffer cells (F4/80) and Ad (hexon) throughout the liver. In the spleen immunohistochemistry showed Ad particles in macrophage and platelet-rich areas of the marginal zone within 5 minutes. In the lung Ad genomes were found within 5 minutes with higher numbers of Ad11 genomes present. Widespread platelet accumulation was seen after delivery of all Ad vectors, with platelet-endothelial interaction and platelet aggregates visible throughout the pulmonary vasculature by immunohistochemistry and TEM. Polymorphonuclear cells and leukocytes within the pulmonary vasculature were also seen interacting with platelet aggregates. These data suggest that Ad and platelets interact rapidly after iv Ad delivery and that this interaction causes rapid targeting of platelets to the reticuloendothelial system. We are currently investigating the mechanisms of Ad-platelet interaction and subsequent platelet reticuloendothelial targeting.