A DNA immunization model study with constructs expressing the tick-borne encephalitis virus envelope protein E in different physical forms

We have conducted a DNA immunization study to evaluate how the immune respo nse Is influenced by the physical structure and secretion of the expressed Ag, For this purpose, we used a series of plasmid constructs encoding diffe rent forms of the envelope glycoprotein E of the flavivirus tick-borne ence phalitis virus. These Included a secreted recombinant subviral particle, a secreted carboxyl-terminally truncated soluble homodimer, a nonsecreted ful l-length form, and an inefficiently secreted truncated form. Mice were immu nized using both i.m. injection and Gene Gun-mediated application of plasmi ds, The functional immune response was evaluated by determining specific ne utralizing and hemagglutination-inhibiting Ab activities and by challenging the mice with a lethal dose of the virus. As a measure for the induction o f a Th1 and/or Th2 response, we determined specific IgG subclasses and exam ined IFN-gamma, IL-4, and IL-5 induction. The plasmid construct encoding a secreted subviral particle, which carries multiple copies of the protective Ag on its surface, was superior to the other constructs in terms of extent and functionality of the Ab response as well as protection against virus c hallenge. As expected, the type of Th response was largely dependent on the mode of application (i.m. vs Gene Gun), but our data show that it was also strongly influenced by the properties of the Ag, Most significantly, the p lasmid encoding the particulate form was able to partially overcome the Th2 bias imposed by the Gene Gun, resulting in a balanced Th1/Th2 response.