Posttranscriptional regulatory elements enhance antigen expression and DNA vaccine efficacy

In higher eukaryotes, introns are usually required for efficient pre-mRNA processing. However, some viruses have alternative approaches involving posttranscriptional regulatory elements (PREs) to enhance intronless heterologous gene expression through enabling stability and 3' end formation, and to facilitate the nucleocytoplasmic export of unspliced mRNAs. In the current study, we compared the human cytomegalovirus (hCMV) immediate/early (IE) intronA, as well as virus-derived PREs-the PRE of Hepatitis B virus (HPRE) and Woodchuck Hepatitis virus (WPRE) on their ability to enhance antigen gene expression in vitro and immune responses induced by DNA vaccination in animal. Among all the constructs, the plasmids carrying the HPRE element showed the highest gene expression level in both in vivo and in vitro models. During immunization of mice with low doses (10 microg) of HIV-1 DNA vaccine, only -intronA/+HPRE and +intronA/+HPRE vaccine constructs induced anti-Gag antibodies, although the -intronA/+WPRE construct also elicited antigen-specific cellular immune responses. In addition, pInHGag (+intronA/+HPRE) at a 10 mug dose could induce higher anti-Gag antibody level than that induced by pGag (-intronA/-HPRE) or pInGag (+intronA/-HPRE) at 40 microg dose (p < 0.05). Our data are useful for the optimization of heterologous expression and immunogenicity of DNA vaccines.