Hemagglutinin influenza (HA), which is identified from avian strains of H7N9 influenza, causes inadequate immunological response. This low immunogenicity can be caused by the H7N9 isolate A/Anhui/1/2013 (Anh/13) stimulation of a HA regulatory T cell (Trego) epitope. In this paper, the wild-type H7 HA amino acid sequence of this Treg stimulating sequence is eliminated, replaced with a conserved CD4+T cell, which stimulates human seasonal H3N2 strains and develops OPT1 H7 HA. The efficacy of this improved H7 HA protein was tested by a humanised mouse (HLA-DR3) which expresses the human DR3 allele leucocyte (HLA). 

HLA-DR3 mice were pre immunized with either WT H7 HA from Anh/13 or OPT1 H7 HA antigen without adjuvant by H3N2 influenza virus A/Hong Kong/4108/ 2014 and then vaccinated intramuscularly. The vaccination group OPT1 H7 HA has produced greater H7 HA-specific IgG titers which result in lower death rate, weight loss, and lung virus titer as compared with the WT-vaccinated mice after a lethal H7N9 Anh/13 influenza challenge. Overall, T-cell epitope vaccinations can boost H7 HA immunogenicity, resulting in increased survival and decreased morbidity to the challenge of H7N9.

Reference: https://www.tandfonline.com/doi/full/10.1080/21645515.2020.1793711