Table 1.

The characteristic features of recombinant adenoviruses.

Type of Recombinant Adenovirus	Modification of Adenovirus	Advantage	Disadvantage	Applicable Diseases and Therapies	References
Replication-defective adenoviral vector	E1A deletion	Robust but transient transgene expression and high immunogenicity applicable to cancer gene therapy and vaccines	No indication for genetic diseases because of short-term effect and safety concerns	Gene medicine for solid tumor Vaccination to prevent infectious diseases	[28,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52]
Conditionally replicating adenovirus (CRA; oncolytic adenovirus)	A deletion in CR2 of the E1A gene and in the E1B55K gene within E1B Replacement of the native E1A promoter with a cancer-specific promoter	Predominantly replicating in and killing cancer cells Armed transgene enhancing therapeutic effects	Insufficient cancer-specific viral replication resulting in insufficient therapeutic effect of virotherapy alone	Virotherapy and immunotherapy for solid tumor	[21,25,53,54,55,56,57,58,59,60,61,62,63,64,65,66]
CRA that can specifically target tumors with multiple factors (m-CRA)	Simultaneously regulated by up to four independent factors of the E1 region Feasible to add a therapeutic gene with a suitable promoter and to modify adenoviral backbone in the step of viral constructions	Strictly cancer-specific and effective viral replication producing more potent anticancer effects and higher safety than the conventional CRAs More potently and safely enhancing therapeutic effects by a therapeutic gene with a suitable promoter and to alter infectivity		More potent and safer virotherapy and immunotherapy for solid tumor A new strategy to prevent stem cell-derived tumorigenesis in regenerative medicine	[67,68,69,70,71,72]