DNA Vaccine Construct Incorporating Intercellular Trafficking and Intracellular Targeting Motifs Effectively Primes and Induces Memory B- and T-Cell Responses in Outbred Animals

We developed a vaccine construct in which a BVP22 domain and an invariant-chain major histocompatibility complex class II-targeting motif capable of enhancing dendritic cell antigen uptake and presentation were fused to a sequence encoding a B- and T-cell antigen from the Anaplasma marginale major surface protein 1a and tested whether this construct would prime and expand immune responses in outbred calves. A single inoculation with this construct effectively primed the immune responses, as demonstrated by a significant enhancement of CD4 T-cell proliferation compared to that in calves identically inoculated but inoculated with a DNA construct lacking the targeting domains and compared to that in calves inoculated with an empty vector. These proliferative responses were mirrored by priming and expansion of gamma interferon-positive CD4 T cells and immunoglobulin G responses against the linked B-cell epitope. Priming by the single immunization induced memory that underwent rapid recall following reexposure to the antigen. These results demonstrate that DNA vaccines targeting key intercellular and intracellular events significantly enhance priming and expansion and support the feasibility of single-dose DNA immunization in outbred populations. The ability to prime and expand immune responses with a single immunogen is critically important for humans, for whom vaccine coverage inversely correlates with the number of booster immunizations required, and for livestock, for which economic considerations drive vaccine delivery. Nucleic acidbased vaccination is a contemporary strategy for single-dose priming and expansion of antigen-specific B- and T-lymphocyte responses against infectious organisms in animals and humans (12, 28). Host cell transfection by a DNA vaccine