In vitro methods for vaccine evaluation

This paper reviews aspects related to the establishment of in vitro assays for fish vaccine evaluation and presents mainly assays for potency testing where specific immune responses are monitored. Aspects related to the evaluation of currently available bacterial vaccines are focused on, and results are mainly presented where both immune responses and protection are assessed in the same trial. Although there is no agreement on which antigens are protective in such vaccines, results show that there are candidate antigens from the various pathogens that are strongly immunogenic in fish, and a correlation between the immune responses they elicit and protection is striking. For some antigens, a clear relationship between immunizing dose, antibody response and protection is evident, which is an important basis for a potency test. Results presented on the evaluation of live vaccines show that assays to measure specific T-cell responses are required. These assays, like lymphocyte proliferation and detection of macrophage activation factor, are considered to be less specific than antibody assays and are hampered by greater variations between individual responses. However, when reagents become available for the assessment of cytokine release in an ELISA based assay, this will allow easier assessment of cellular immune responses in fish and could form the basis for potency testing of vaccines where protection is correlated with cellular immunity.