CpG DNA-based, needle-free, vaccination methods against bovine viral diarrhoea virus in newborn calves
Bovine viral diarrhea virus (BVDV) is one of the most important respiratory pathogens in cattle. The newborn animal is one of the target groups for vaccination against BVDV. Since newborn animals tend to respond less effectively to infection or vaccination, novel vaccines and/or formulations are needed to induce robust immune responses. Our overall goal is to develop a CpG DNA-based vaccination strategy as a method to vaccinate newborn calves against BVDV type 1 and type 2. The E2 protein is the major protective antigen of BVDV. Calves were vaccinated with a DNA vaccine encoding type 1 and type 2 E2, using three different delivery methods, intramuscular (IM) delivery, intramuscular delivery followed by electroporation (EP), and intradermal (ID) delivery with a Biojector. IM delivery resulted in enhanced numbers of IFN-γ secreting cells in the blood, whereas ID delivery lead to increased serum antibody titers and lymphoproliferation in comparison to placebo. The group vaccinated by IM delivery followed by electroporation developed the strongest immune responses, based on elevated antibody titers, stronger lymphocyte proliferation and higher numbers of IFN-γ secreting cells when compared with the placebo group. Since activated T cells were observed in this group after one vaccination, this shows the newborn calves to be capable of developing a T cell response at one month of age. Despite differences in immune responses to vaccination, there appeared to be no difference between the vaccinated groups in the level of protection from BVDV-2 challenge. Regardless of the method of delivery, all groups immunized with the E2.1+E2.2 DNA vaccine were protected from clinical disease after BVDV-2 challenge, in contrast to the placebo-vaccinated group, which had significantly enhanced temperatures and weight loss during the post-challenge period.
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