Subcutaneous Administration of a Replication-Competent Adenovirus Expressing HSV-tk to Cotton Rats: Dissemination, Persistence, Shedding, and Pathogenicity

Abstract

Since human adenoviruses replicate only in human cells, toxicology studies with adenoviral vectors are hampered by the lack of a permissive nonhuman host. Before a replication-competent adenoviral vector expressing HSV-tk (Ad.OW34) can be used in clinical studies for intratumoral injections in patients with cutaneous lesions of head and neck cancer or intralesional injection for in situ vaccination strategy in advanced metastatic melanoma patients, risks have to be estimated in animal studies. In an attempt to assess potential toxicology, dissemination, persistence and shedding, we injected Ad.OW34 subcutaneously into cotton rats. (Sigmodon hispidus), which are considered a semipermissive host for human adenoviruses. The animals underwent one or two subcutaneous injection cycles with 2.3 × 10¹² viral particles/kg each or a single course with 6.9 × 10¹³ viral particles/kg and were analyzed at defined time points for histopathological changes in the brain, heart, lungs, spleen, liver, kidneys, ovaries, and skin. Additionally, these tissues as well as urine, feces, mouth, and skin swabs were analyzed at multiple time points by real-time quantitative polymerase chain reaction for the presence of vector sequences. The only significant treatment-related histopathologic finding was dermatitis with mild acanthosis at the site of vector injection. All other tissues evaluated were within normal limits or showed changes that were most likely incidental or spontaneous in nature. Vector sequences were detected in the skin at the injection site and to a lesser extent in the liver, spleen, and lungs. In addition, small amounts of vector DNA were detected in the ovaries. The vector sequences were rapidly cleared and the absence of viral sequences in the excreta and swabs of the majority of animals suggest that there was no significant replication of the vector in this host. The administration of Ad.OW34 was also associated with mild hyperamylasemia, lymphocytosis, and granulocytosis; however, we did not observe any clinical signs of illness or death in the experimental animals over the course of the study.