Figure 1.

Strategies to overcome potential barriers in delivering oncolytic adenoviruses (OAs) into tumor sites. For systemic administration (a) such as intravenous injection, the complement, neutralizing antibodies, platelets and erythrocytes present in blood circulation bind to OAs (b) and block the migration of OAs into tumor sites. Cell carriers and extracellular-vesicles-delivered OAs escape the above-mentioned barriers to some extent before the OAs reach the tumor site (c). Local infusion represents an alternative strategy to avoid the interaction with blood components (d).