TKT and coinfection: In order to generate the triple pIX-modified Ad carrying poly-lysine (pK), HSV-1 thymidine kinase mutant (HSV-1 sr39tk), and monomeric red fluorescent protein (mRFP1) by co-infection, three parental viruses were generated first: Ad-IX-Flag-pK, Ad-IX-H6-TK, and Ad-IX-myc-mRFP1.