DNA vaccination with the Aleutian mink disease virus NS1 gene confers partial protection against disease

Aleutian disease virus (ADV) causes severe losses in mink. This happens in nature as well as in farms. In spite of several attempts to provide an efficient protective protein based vaccine, experiments have failed so far. Only partial protection has been obtained. The aim of this work was to construct and test a protective DNA vaccine based on the gene encoding for the ADV non-structural protein 1 (NS1) and to test this construct as a potential vaccine candidate against ADV infection or disease. First, the vaccine construct was tested by in vitro transfection studies. NS1 protein expression was found by immunofluorescent studies and the expected size of translated protein confirmed by Western blot. Then, 18 female mink were divided into three groups: a control group, a DNA vaccinated group, and a group which received DNA vaccine plus a boost with recombinant NS1 protein in the last immunization. After virus challenge, the two DNA vaccinated groups induced higher antibody levels in the first 23 weeks of the 32 week observation period. One month after virus challenge, the most interesting finding was, that the "DNA+protein" group exhibited a significantly higher percentage of CD8+ cells, when compared to the levels in the two other groups. This, we believe, indicate a memory CTL response created by the vaccination. Most CD8+ cells were found to contain interferon gamma as measured by FACS intracellular staining. Severity of Aleutian disease was judged by quantification of plasma gammaglobulin levels and mink death statistics. The findings let us to conclude, that the two DNA vaccinated groups of mink did show milder disease characteristics, but that the vaccine effect also in this trial could only be characterized as partial.