A novel programmed death 1 isoform-based fusion DNA vaccine enhances functional antigen-specific CD8+ T cell immunity

Abstract

Inducing an effective CD8+ T cell immunity is important in the protection and elimination of infectious pathogens. Programmed death-1 (PD1) up-regulation in in chronic infections (e.g. HIV-1 and TB) results in 'exhausted' function of CD8+ T cells, but is restored by blockade of the PD1/PD-L pathway with antibodies or a soluble form of (s)PD1. Apart from sPD1, the other three spliced variants previously identified currently have no known function. In this study, we identified a new isoform of human PD1 that contains a 42-nucleotide in-frame deletion located at exon 2 near its IgV domain found expressed in PBMCs, named {Delta}42PD1. We found that {Delta}42PD1 is distinct from PD1 as it does not engage PD-L1 or PD-L2 and capable of inducing the production of pro-inflammatory cytokines (TNF-α, IL-6, IL-1β). Next, we used {Delta}42PD1 as an intramolecular adjuvant to construct a DNA fusion vaccine with HIV-1 Gag p24 antigen. Following immunization in Balb/c mice, a significantly enhanced level of anti-p24 antibody titer and p24-specific CD8+ T cell responses were elicited that persisted for at least 7.5 months. Furthermore, vaccinated mice were protected against pathogenic vaccinia-Gag virus challenge, likely due to the improved proliferative and cytotoxic functions of the elicited CD8+ T cells. Therefore, our study demonstrates that a novel {Delta}42PD1 variant that amplifies the generation of antigen-specific CD8+ T cell immunity when used in a DNA vaccine.