Induction of Cross-Reactive and Protective Antibody Responses After DNA Vaccination With MHCII-Targeted Stem Domain From Influenza Hemagglutinin

Novel and more broadly protective vaccines against influenza are needed to efficiently meet antigenic drift and shift. Relevant to this end, the stem domain of hemagglutinin (HA) is highly conserved, and antibodies specific for epitopes located to the stem have been demonstrated to be able to confer broad protection against various influenza subtypes. However, a remaining challenge is to induce antibodies against the poorly immunogenic stem by vaccination strategies that can be scaled up for prophylactic vaccination of the general population. Here, we have developed DNA vaccines where the conserved stem domain of HA from influenza A/PR/8/34 (H1N1) and A/Shanghai/2/2013 (H7N9) was targeted toward MHC class II molecules on antigen-presenting cells (APC) for increased immunogenicity. Each of these vaccines induced antibodies that cross-reacted with other subtypes in the corresponding phylogenetic influenza groups. Importantly, when mixing the MHCII-targeted stem domains from H1N1 and H7N9 influenza viruses into one vaccine bolus, we observed broad protection against candidate stains from both phylogenetic groups 1 and 2.

Needle-free delivery of DNA: Targeting of hemagglutinin to MHC class II molecules protects rhesus macaques against H1N1 influenza

Conventional influenza vaccines are hampered by slow and limited production capabilities, whereas DNA vaccines can be rapidly produced for global coverage in the event of an emerging pandemic. However, a drawback of DNA vaccines is their generally low immunogenicity in non-human primates and humans. We have previously demonstrated that targeting of influenza hemagglutinin to human HLA class II molecules can increase antibody responses in larger animals such as ferrets and pigs. Here, we extend these observations by immunizing non-human primates (rhesus macaques) with a DNA vaccine encoding a bivalent fusion protein that targets influenza virus hemagglutinin (HA) to Mamu class II molecules. Such immunization induced neutralizing antibodies and antigen-specific T cells. The DNA was delivered by pain- and needle-free jet injections intradermally. No adverse effects were observed. Most importantly, the immunized rhesus macaques were protected against a challenge with influenza virus.