COMPARISON OF VARIOUS EXPRESSION PLASMIDS FOR THE INDUCTION OF IMMUNE-RESPONSE BY DNA IMMUNIZATION

Intramuscular injection of plasmid DNA is an efficient method to intro duce a foreign gene into a Live animal. We investigated several factor s affecting the gene transfer efficiency and the following immune resp onse by intramuscular injection of plasmid DNA. When the strength of s everal highly efficient viral promoters was compared in muscle by usin g the chloramphenicol acetyltransferase (CAT) gene as an indicator, cy tomegalovirus (CMV) immediate early promoter was found to be stronger than any other viral promoters including Rous sarcoma virus (RSV), mur ine leukemia virus (SL3-3) and simian virus 40 (SV40) early promoters. Inclusion of adenovirus tripartite leader (TPL) sequences and a synth etic intron in the 5' untranslated region of mRNA moderately stimulate d the CAT expression. On the other hand, the expression of encephalomy ocarditis virus (EMCV) VP1 gene was greatly enhanced by the TPL sequen ces and an intron. The level of humoral immune response by intramuscul ar injection of various VP1 expression plasmids was compared. The sero conversion rate was highly dependent on the strength of the expression vector. However, the ratio of IgG1 and IgG2a immune response was not significantly variable depending on the strength of the expression vec tor. Also, the efficiency of the sindbis virus-based DNA vector was ex amined for the gene expression and immune response. Although a high le vel of CAT expression was obtained in muscle by using this system, VP1 was not produced as much as the conventional expression vectors. Furt hermore, little humoral immune response was elicited by intramuscular injection of VP1-expressing sindbis vector, suggesting that this syste m was not superior to the conventional vector for DNA immunization.