BASIC Ad BIOLOGY
Ads are non-enveloped viruses with an icosahedral protein capsid that harbors a double-stranded linear DNA genome with a size of 36-40 kbp. They were first isolated in 1953 from adenoid tissue (Rowe et al. 1953). The family of Adenoviridae comprises the five genera AtAd, AviAd, IchtAd, Siadenovirus, and MastAd with the latter including human Ads. Human Ads were divided into species A-G based on their ability to agglutinate erythrocytes (Rosen 1960). Based on sequence analysis at least 57 types can be distinguished. The most frequently used and best-characterized Ad gene transfer vectors are derived from types 5 and 2 of human species C. Importantly, during the past years other types and chimera have been characterized and generated (e.g., Mack et al. 1997; Wickham et al. 1997; Shayakhmetov et al. 2000; Mei et al. 2002; Lu et al. 2009). Also non-human Ads have been vectorized (see e.g., Roy et al. 2006, 2007, 2009; Peruzzi et al. 2009; Colloca et al. 2012; Capone et al. 2013), studied in vitro in animal models and in humans (Green et al. 2015; Kelly et al. 2015).