Live attenuated influenza vaccine viral vector induces functional cytotoxic T-cell immune response against foreign CD8+ T-cell epitopes inserted into NA and NS1 genes using the 2A self-cleavage site

Abstract

The development of viral vector vaccines against various pathogens for which conventional vaccination approaches are not applicable has been a priority for a number of years. One promising approach is the insertion of immunodominant conservative cytotoxic T-cell (CTL) epitopes into the genome of a viral vector, which then delivers these epitopes to target cells, inducing immunity. Many different viruses have been assessed as viral vectors for CTL-based vaccines, but only a few of them are clinically relevant, mainly because of safety issues and limited knowledge about their performance in humans. In this regard, the use of licensed cold-adapted live attenuated influenza vaccine (LAIV) viruses as a vector delivery system has clear advantages for CTL-based vector vaccines against other respiratory pathogens: LAIV is known to induce all arms of the adaptive immune system and is administered via nasal spray, and its production process is relatively easy and inexpensive. Here we present the first results of the use of an LAIV backbone for designing a CTL epitope-based vaccine against respiratory syncytial virus (RSV). The chimeric LAIV-RSV vaccine candidates were attenuated in mice and induced strong, fully functional CTL immunity in this animal model.

Keywords: Live attenuated influenza vaccine (LAIV); cytotoxic T cells; epitope-based vaccine; respiratory syncytial virus (RSV); viral vector system.

Figure 1.

The LAIV-RSV constructs. (a). Distribution of major histocompatibility complex (MHC) class I (green) and class II (blue) restricted epitopes over M2-1 protein. The epitopes dataset was queried from the Immune Epitope DataBase in April 2017 (host organism: BALB/c mouse; antigen: matrix M2-1; positive assays only). The yellow lengths denote the RSV cassette fragments. (b). Scheme for generating chimeric influenza NA gene carrying RSV cassette. (c). Scheme for generating chimeric influenza NS1 gene carrying RSV cassette. (d). Genome composition of LAIV viruses.P2A: porcine teschovirus-1 P2A self-cleavage site (GSGATNFSLLKQAGDVEENPG↓P).

Figure 2.

CD8+ T-cell response in mice after LAIV immunization measured by IFN-gamma ICS assay. (a). Stimulation of cells by M2-1_82–90 peptide. (b). Stimulation with M2-1_126–145 peptide. (c). Stimulation with LAIV vector whole virus. (d). Stimulation with DMSO. Bars denote median and interquartile range. P values for Mann-Whitney U test are indicated. ns: not significant (P ≥ 0.05). Red asterisks denote significant differences in levels of IFN-gamma+ CD8+ T cell between PBS and LAIV vaccine groups.

Figure 3.

Comparison of in vivo CTL activity against RSV peptide-loaded targets in immunized mice. (a). M2-1_82–90-peptide. (b). M2-1_126–145 peptide.Bars denote median and interquartile range. Multiplicity adjusted P values are indicated. ns: not significant (P ≥ 0.05).