Abstract

The U.S. Navy Marine Mammal Program recognizes the critical need for development of marine mammal vaccines. To address this need, we are investigating the use of DNA vaccine technology in cetaceans. A proof-of-concept experiment was designed and executed, which involved the use of reporter gene plasmid-based DNA vaccines. Specifically, two reporter gene plasmids were chosen, human influenza A nucleoprotein (NP) and B-galactosidase (B-gal). Vical, Inc. supplied both the NP and B-gal vaccines, which were constructed, purified, and previously tested at their facility. Two age-matched male dolphins were chosen for the study. Baseline hematology and immunology data were collected on both animals. One dolphin designated NIH received the B-gal plasmid, while the dolphin designated BUS received the NP plasmid. Each animal received three doses of plasmid vaccine (IM) on the following schedule: Day 0, 500 mg; Day 28, 1 mg; Day 70, 1.5 mg. Blood samples were taken every 14 days for 126 days, and both humoral and cellular responses to NP and B-gal were measured. To measure antibody titers to both B-gal and NP, ELISAs specific for these two proteins were modified for dolphins and utilized for this study. The cellular response was measured by the lymphocyte proliferation assay. Preliminary results strongly suggest that NIH mounted a cellular immune response but not a humoral response to the B-gal vaccine. Cellular responses to plasmid vaccines, with or without a weak humoral response, coincide with the findings from plasmid vaccine studies in other large animal species. BUS, the dolphin that received the NP plasmid, did not show a humoral or cellular response to the vaccine. The lack of a response in BUS could be due to individual variability in immune system response, inability of current laboratory methods to detect subtle immune changes, or decreased efficacy of the NP plasmid vaccine in the dolphin. Currently, we are optimizing methods of plasmid delivery to the dolphin, and working to develop more sensitive immunoassays. Future plans include testing a newly-constructed dolphin morbillivirus DNA vaccine in dolphins, as well as a canine distemper DNA vaccine in California sea lions.

Acknowledgments

This work was funded by SPAWARSYSCEN San Diego In-house Laboratory Independent Research Program and the Office of Naval Research (N0001402WR20141). The authors thank Drs. Eric Jensen, Sam Ridgway, George Miller, Roger Geertsema, and the VetLab staff for their support. In addition, we recognize Lisa Tanner, Brit Swenberg, Justine Zafran, Jenny Briar, Mark Beeler, and Mandy Keogh for their commitment to this project.