Prime-Boost with Alternating DNA Vaccines Designed to Engage Different Antigen Presentation Pathways Generates High Frequencies of Peptide-Specific CD8+ T Cells

Abstract

The route for presentation of Ag to CD8+ or CD4+ T cells following DNA vaccination is critical for determining outcome, but the pathways involved are unclear. In this study, we compare two different DNA vaccine designs aimed to elicit CD8+ T cell responses against a specific peptide-epitope either by direct- or cross-presentation. Each carries sequences from tetanus toxin (TT) to provide essential CD4+ T cell help. In the first already proven design, the peptide-epitope is fused to the N-terminal domain of fragment C from TT. This appears to act mainly by cross-presentation. In the second design, the peptide-epitope is encoded by a minigene, with induction of Th responses mediated by coexpression of a hybrid invariant chain molecule, incorporating a single determinant from TT (p30) in exchange for class II-associated invariant chain peptide. This design appears to act mainly via direct presentation from transfected APCs. Both vaccines mediated Th-dependent priming of CD8+ T cells in mice, but the kinetics and level of the responses differed markedly, consistent with engagement of distinct pathways of Ag presentation. Importantly, the vaccines could be combined in an alternating prime-boost regime, in either order, generating substantially expanded memory CD8+ T cells, with potent effector function. Taken together, these results demonstrate that vaccination protocols involving different modes of Ag presentation at prime and boost can significantly improve the effectiveness of immunization.

Fusion of HBsAg and prime/boosting augment Th1 and CTL responses to HCV polytope DNA vaccine

“…Accordingly, the pcHPOL-primed/CE 4 E 6 N peptide-boosted group promoted both the highest epitope-specific (CD8 + ) and Th1-type responses evidenced by IFN--ELISpot and cytokine secretion assays. Consistently, kinetic studies have also indicated the induction of higher CD8 + T cell responses by priming and boosting that utilize alternate antigen presentation pathways [15].…”

Prolonged Antigen Expression following DNA Vaccination Impairs Effector CD8+ T Cell Function and Memory Development

“…We had observed previously that immunization with the crosspriming vector elicited a CD8 ϩ T cell response, which, in comparison to that induced by the direct-priming vaccine, was faster in onset but less sustained, resulting in a net lower peak burst size (14). In the current study, we have further investigated the quality of the CD8 ϩ T cell response.…”

“…1). In the first design, the CD8 ϩ T cell epitope is expressed as a minimal peptide specifically targeted to the endoplasmic reticulum by an N-terminal leader sequence (14). To provide critical "help" for the minigene product, a separate expression cassette is incorporated within the plasmid backbone encoding a hybrid invariant chain molecule, with the CLIP sequence replaced by a Th determinant from tetanus toxin (p30, Ref.…”

“…15). By separating the minimal epitope from a "protective polypeptide," this vaccine fails to cross-present Ag because of the short half-life of minigene products (16) and induces Th-dependent CD8 ϩ T cell responses via directly transfected APC (14). In the second design, the CD8 ϩ T cell epitope is fused immediately 3Ј of the N-terminal domain of fragment C from tetanus toxin (p30, Ref.…”

“…15). For this vaccine, effective CD8 ϩ T cell responses are highly dependent on CD4 ϩ T cell help generated following uptake of exogenous Ag; therefore, the design operates only via cross-presentation (14).…”