Fig. 4. Principle of adenovirus vector vaccines.

a Schematic of replication-incompetent adenoviral vector particle and its DNA. E1 and E3: Early adenovirus genes 1 and 3, respectively. b Formation of vaccine particles in production cell line complementing E1 from chromosomally integrated E1 gene. Release of newly produced vector particles through cell lysis. c Expression of spike in cells of vaccinated individuals. More or less shedding of S1 and conversion of S2 into its post-fusion structure (S2*) may occur in the absence of stabilizing mutations.