Balb/c EGFP mice are tolerant against immunization utilizing recombinant adenoviral-based vectors encoding EGFP: a novel model for the study of tolerance mechanisms and vaccine efficacy

Enhanced green fluorescent protein (EGFP) is a marker gene product which is readily detectable using the techniques of fluorescence microscopy, flow cytometry, or macroscopic imaging. Previous studies have demonstrated the immunogenicity of EGFP in Balb/c mice, identifying an immunodominant H2-K(d) restricted CTL epitope. To model immunological tolerance and vaccine efficiency against self-antigens, we generated a stable transgenic BALB/c mouse expressing EGFP (Balb/c EGFP) through back-crossing C57Bl/6-TG(ACTbEGFP)10sb more than ten times with Balb/c wildtype (wt) mice. High level EGFP expression was detected in the skin and heart, whereas low level expression was observed in the kidney, liver, gut, lung, and spleen. To characterize the immune reactivity to self-antigen, we immunized Balb/c EGFP and Balb/c wt mice with recombinant adenoviral-based vectors encoding EGFP (Ad-EGFP) or beta-galactosidase (Ad-betagal) as a control. Immunization utilizing the Ad-betagal vector expressing 'foreign' antigen induced robust humoral and cellular transgene-specific immunity, whereas Balb/c EGFP mice presented no reactivity following Ad-EGFP immunization against the 'self-antigen' EGFP. These findings describe the creation of a transgenic mouse line tolerant against the common Protein Marker EGFP, providing a novel system for the evaluation of methods of tolerance disruption and vaccine efficacy.