Abstract 192: Persistence of First Generation Adenovirus in the Myocardium: Refuting Old Dogma

Abstract

Introduction: Adenovirus (Ad) vectors do not integrate into host genomes and thus offer clinical benefits as non-mutagenic, acute-term gene delivery vehicles. One limitation to Ad vector use is the transient duration of transgene expression, supposedly resulting from immune-mediated cytolysis of Ad-infected cells. Our recent observation of Ad-induced transdifferentiation of infected cardiac fibroblasts into induced cardiomyocytes over 28 days in vivo called this premise into question. Therefore, we hypothesized that Ad remains in the myocardium for over 28 days and, to our knowledge, are the first to suggest alternate mechanisms for this persistence. Methods and Results: Ad encoding green fluorescent protein (AdGFP) or mock was administered via intramyocardial injection into Sprague-Dawley rats, and Ad genome and GFP expression were analyzed 3 or 28 days later (n=6 per group, 3 euthanized at each time point). Polymerase chain reaction typing and amplicon sequencing confirmed the presence of Ad DNA in all 6 treated animals. Quantitative real time polymerase chain reaction assays further demonstrated more than a three-fold increase in Ad DNA levels at both days 3 and 28 compared to untreated control animals (3.41±1.40 and 3.37±1.23, respectively). Thus, at 28 days Ad DNA persisted at a high level comparable to that which was present at 3 days. Next, AdGFP expression and host immune response were characterized by fluorescence microscopy and histology. We found that GFP-expressing cells decreased five-fold by 28 days (49±9 v. 3±0 cells). In addition, hematoxylin and eosin staining showed minimal infiltrating mononuclear inflammatory cells in AdGFP and mock-treated animals at both time points. Conclusions: Ad DNA and infected host cell persistence suggests that host-mediated cytolysis may not be responsible for the downregulation of transgene expression, indicating that Ad vectors may consequently be useful for therapies like cellular reprogramming wherein host cell persistence is required.