Priming by DNA immunization augments T-cell responses induced by modified live bovine herpesvirus vaccine

DNA vaccines have several advantages over conventional vaccines. One of the most important characteristics is the presentation of antigen via both MHC class I and class II receptors. Although this generally results in strong T-cell responses, antibody production and protection achieved by DNA immuni zation are unfortunately not always adequate. In contrast, modified live vi rus (MLV) vaccines usually induce adequate antibody and moderate cellular r esponses, whereas killed vaccines tend to elicit weak immune responses in g eneral. A DNA prime-MLV boost regimen should result in enhanced cellular im munity and possibly improved antibody production. To test this hypothesis, plasm ids encoding bovine herpesvirus-1 (BHV-1) glycoproteins Band D were d elivered by gene gun to the genital mucosa of cattle prior to immunization with modified live BHV-1 vaccine. The immune responses induced were compare d to those of an MLV-vaccinated group and a negative control group. Althoug h significantly enhanced T-cell responses were induced by priming with the DNA vaccine, there was no increase in antibody titres. Similar levels of pr otection were induced by the MLV vaccine alone and the DNA prime and MLV bo ost regimen, which suggests that there is no correlation between the induct ion of T-cell responses and protection from BHV-1 challenge.