The invention provides a method of identifying an antigen from a pathogen or a disease antigen comprising the use of an adenoviral vector array comprising two or more different adenoviral vectors, wherein each adenoviral vector comprises a nucleic acid sequence encoding a different antigen of a pathogen. The adenoviral vectors are administered to antigen presenting cells (APCs) in vitro or to an animal in vivo. The immunogenicity of the antigen is measured by screening for an immune response from effector T lymphocytes in vitro and by screening for the absence of pathogen-induced disease onset in vivo.