Effect of Administration Route on the Biodistribution and Shedding of Replication-Deficient HAdV-5: A Qualitative Modelling Approach

Gene therapy is a rapidly developing field in which recombinant nucleic acid sequences are introduced to individuals. Its therapeutic, prophylactic or diagnostic effect relates directly to the sequence it contains or to the product of genetic expression of this sequence. Recombinant adenoviral vectors (in particular HAdV-5 vectors) are frequently used in gene therapy. Knowledge on biodistribution and shedding is crucial in the risk assessment for the patient and the patient's environment. This review presents a critical overview on biodistribution and shedding data of non-replicating viral vector HAdV-5, related to the used administration route. Based on these data, a qualitative model for the biodistribution and shedding of HAdV-5-based viral vectors is presented. Biodistribution and shedding depend on the route of administration. Some routes lead to local biodistribution and no shedding or one shedding route only. Other routes lead to systemic biodistribution and to shedding via several excreta. Shedding via semen and transport across the blood-brain barrier is not expected for HAdV-5. The presented qualitative model can help researchers and risk assessors to determine the possible distribution in the body and the risk of shedding via the different excretion routes. Furthermore, it can help regulators to predict the different shedding routes after a certain administration route and thus in deciding which studies are warranted or which safety precautions are needed after administration to patients.