Immunization with a DNA vaccine expressing a truncated form of varicella zoster virus glycoprotein E.
The gE glycoprotein of varicella zoster virus (VZV) is involved with cell entry and it is the most abundant glycoprotein produced in VZV-infected cells. It is also the first glycoprotein to be recognized by the immune system and induces neutralizing antibodies and cellular immunity. We have shown previously that immunization with a DNA vaccine encoding full length gE induces high antibody titres in BALB/c mice. In this study, we engineered a truncated form of gE to facilitate secretion of the glycoprotein, which is thought to increase the quantity of antigen available for B cells to mount an immune response. This hypothesis was tested by using inverse PCR mutagenesis (IPCRM) to engineer a mutated form of gE that was secreted from the cell. This construct was then evaluated as a potential DNA vaccine. Following immunization studies, the magnitude of the immune response induced with the mutant form of gE was found to be similar to that induced by membrane bound protein. This finding suggests that, in the case of VZV, a DNA vaccine expressing a secreted protein has no advantage over one expressing a membrane bound protein. However, mice immunized with the truncated form of gE (gED) displayed responses favouring IgG1 (Th2) in comparison with mice immunized with the full length gE construct, which generated an IgG2a (Th1) response. This observation indicates that immunization with a truncated form of a gene may induce immune modulation, a phenomenon that should be taken into account for the design of vaccines.