Immunotargeting with CD154 (CD40 Ligand) Enhances DNA Vaccine Responses in Ducks

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Abstract
Engagement of CD154 on activated T cells with CD40 on antigen-presenting cells (APCs) potentiates adaptive immune responses in mammals. Soluble multimeric forms of CD154 have been used as an adjuvant or in immunotargeting strategies to enhance vaccine responses. The objective of our study was to examine the ability of duck CD154 (DuCD154) to enhance DNA vaccine responses in the duck hepatitis B model. Constructs were generated to express the functional domain of DuCD154 (tCD154), truncated duck hepatitis B virus (DHBV) core antigen (tcore) and chimera of tcore fused to tCD154 (tcore-tCD154). Expression in LMH cells demonstrated that all proteins were secreted and that tCD154 and tcore-tCD154 formed multimers. Ducks immunized with the plasmid ptcore-tCD154 developed accelerated and enhanced core-specific antibody responses compared to ducks immunized with ptcore or ptcore plus ptCD154. Antibody responses were better sustained in both ptcore-tCD154- and ptcore plus ptCD154-immunized ducks. Core-specific proliferative responses of duck peripheral blood mononuclear cells were enhanced in ducks immunized with ptcore-tCD154 or ptcore alone. This study suggests that the role of CD154 in the regulation of adaptive immune responses had already evolved before the divergence of birds and mammals. Thus, targeting of antigens to APCs with CD154 is an effective strategy to enhance DNA vaccine responses not only in mammalian species but also in avian species.