Expression of Avian Influenza Virus (H5N1) Hemagglutinin and Matrix Protein 1 in Pichia pastoris and Evaluation of their Immunogenicity in Mice

The conventional avian influenza vaccines rely on development of neutralizing antibodies against the HA and NA antigens. However, these antigens are highly variable, and hence there is a need for better vaccine candidates which would offer broader protection in animals. The M1 of avian influenza is another major structural protein that has conserved epitopes that are reported to induce CD8+ T cells and can contribute to protection against morbidity and mortality from influenza. Hence in an effort to study the immune response of rM1 either alone or in combination with rHA, the hemagglutinin (HA) and matrix protein (M1) of A/Hatay/2004/H5N1 strain of avian influenza were expressed in Pichia pastoris as his-tagged proteins and purified through Ni-NTA chromatography. The His-tag was removed using TEV protease cleavage site and the immunogenicity of purified rHA and rM1 either alone or in combination was determined in mice. One group of mice was immunized with 5 μg of purified rHA, the other group was immunized with rM1, and a third group of mice were immunized with 5 μg of rHA and rM1. All the animals were boosted twice, once on 28 days postimmunization (dpi) and the second on 42 dpi. The immune response was evaluated by enzyme-linked immunosorbent assay (ELISA) and hemagglutination inhibition (HI) assay. The group of mice immunized with rHA and rM1 together showed significantly higher immune response against rHA and rM1 than mice immunized with either HA or M1 antigens. The addition of rM1 with rHA resulted in increased HI titer in animals immunized with both the antigens. These results suggest that the HA and M1 expressed in P. pastoris can be utilized in combination for the development of faster and cost-effective vaccines for circulating and newer strains of avian influenza and would aid in combating the disease in a pandemic situation, in which production time matters greatly.