Eric Ehrke‐Schulz

Background Adenoviral vectors are among the most frequently used vectors for gene therapy and cancer treatment. Most vectors are derived from human adenovirus (Ad) serotype 5 despite limited applicability caused by pre‐existing immunity and unfavorable liver tropism, whereas the other more than 100 known human serotypes remain largely unused. Here, we screened a library of human Ad types and identified Ad4 as a promising candidate vector. Methods Reporter‐gene‐expressing viruses representative of the natural human Ad diversity were used to transduce an array of muscle cell lines and two‐ or three‐dimensional tumor cultures. The time‐course of transgene expression was monitored by fluorescence or luminescence measurements. To generate replication‐deficient Ad4 vector genomes, successive homologous recombination was applied. Results Ad4, 17 and 50 transduced human cardiomyocytes more efficiently than Ad5, whereas Ad37 was found to be superior in rhabdomyocytes. Despite its moderate transduction efficiency, Ad4 showed efficient and long‐lasting gene expression in papillomavirus (HPV) positive tumor organoids. Therefore, we aimed to harness the potential of Ad4 for improved muscle transduction or oncolytic virotherapy of HPV‐positive tumors. We deleted the E1 and E3 transcription units to produce first generation Ad vectors for gene therapy. The E1‐ and E1/E3‐deleted vectors were replication‐competent in HEK293 cells stably expressing E1 but not in the other cell lines tested. Furthermore, we show that the Ad5 E1 transcription unit can complement the replication of E1‐deleted Ad4 vectors. Conclusions Our Ad4‐based gene therapy vector platform contributes to the development of improved Ad vectors based on non‐canonical serotypes for a broad range of applications.