Current influenza vaccines induce potent antibody responses against the Influenza A Virus (IAV) surface proteins hemagglutinin (HA) and neuraminidase (NA). Nevertheless, the effectiveness of current vaccines is limited and subjected to strong variation, due to continuous antigenic change of these surface proteins. This antigenic change is mainly dependent on two mechanisms: The highly prevalent point mutations in these proteins due to the viral RNA polymerase lacking a proofreading function (antigenic shift) and the unique ability of IAV to reassort its genome upon co-infection with other IAV strains (antigenic drift). In addition to the potential mismatch between current vaccines and seasonal or pandemic IAV strains, yearly reformulation of vaccines causes a high financial burden. Therefore, a universal influenza vaccine that provides a heterosubtypic protection against all IAV strains is highly desirable.
Contrasting the IAV HA and NA surface proteins, internal viral proteins like the matrix protein 1 (M1) or the viral polymerase (PA) are highly conserved between different strains of IAV. Therefore, we have developed a T-cell vaccination approach targeting MHC-I epitopes of these conserved proteins to potentially achieve a heterosubtypic protection. We encapsulated the HLA-0201 restricted peptides M158-66 and PA46-54 together with the TLR3/RIG-I Ligand Riboxxim into Poly(lactic-co-glycolic-acid) (PLGA) microspheres (MS). PLGA-MS exhibit excellent properties as a vaccine platform, owing to their high bioavailability, biodegradability, and antigen depot effect. Using Tetramer staining, ELISpot and intracellular cytokine staining we observed a potent induction of CD8+ T-cells in PLGA-MS vaccinated HLA-A transgenic AAD mice. Furthermore, we could show that the cytotoxic T-cell response induced by vaccination with PLGA-MS reduced IAV titer in the lungs of infected mice and led to reduced mortality after infection with a lethal dose of IAV. In future experiments, the protection against several antigenically distinct IAV strains will be investigated, to confirm a heterosubtypic protection by this vaccine.