Bovine monocyte derived dendritic cell based assay for measuring vaccine immunogenicity in vitro

During both human and animal vaccine development phases, animal testing is necessary to demonstrate vaccine efficacy. Since the number of antigen candidates for testing is usually large when developing a potential vaccine, it is too costly, time consuming and would involve higher risks to carry out selection using in vivo models. The currently available in vitro assays that measure immunogenicity do not adequately reproduce the in vivo state and this is especially true for vaccine research in livestock species. With this in mind, we have developed a bovine monocyte derived dendritic cell (MODC)s based assay to prime CD4 and CD8 lymphocytes in order to investigate vaccine immunogenicity in vitro. MODCs were generated, pulsed with diphtheria toxoid (DT) and co-cultured with lymphocytes for priming. Immunogenicity was measured through antigen recall when antigen pulsed MODC were re-introduced to the co-culture and proliferation of CD4 and CD8 positive lymphocytes were quantified using expressed Ki-67. Having developed the protocol for the assay, we then employed two licenced vaccines against blue tongue virus and rabies virus to validate the assay. Our results show the ability of the assay to satisfactorily measure immunogenicity in cattle. The assay could be used to identify antigens that induce CD4 and CD8 T cell responses prior to embarking on in vivo experiments and can also be used for the quality control of established vaccines in vaccine production facilities as a supplement for in vivo experiments.