Characterization of Hemagglutinin Antigens on Influenza Virus and within Vaccines Using Electron Microscopy

Abstract

Influenza viruses affect millions of people worldwide on an annual basis. Although vaccines are available, influenza still causes significant human mortality and morbidity. Vaccines target the major influenza surface glycoprotein hemagglutinin (HA). However, circulating HA subtypes undergo continual variation in their dominant epitopes, requiring vaccines to be updated annually. A goal of next-generation influenza vaccine research is to produce broader protective immunity against the different types, subtypes, and strains of influenza viruses. One emerging strategy is to focus the immune response away from variable epitopes, and instead target the conserved stem region of HA. To increase the display and immunogenicity of the HA stem, nanoparticles are being developed to display epitopes in a controlled spatial arrangement to improve immunogenicity and elicit protective immune responses. Engineering of these nanoparticles requires structure-guided design to optimize the fidelity and valency of antigen presentation. Here, we review electron microscopy applied to study the 3D structures of influenza viruses and different vaccine antigens. Structure-guided information from electron microscopy should be integrated into pipelines for the development of both more efficacious seasonal and universal influenza vaccine antigens. The lessons learned from influenza vaccine electron microscopic research could aid in the development of novel vaccines for other pathogens.

Characterization of Inactivated Influenza Vaccines Used in the Russian National Immunization Program

“…In the TEM images of all vaccine samples ( Figure 6), we were able to detect the abundance of structures identical to HA spikes present on the surface of native influenza virions. In the vast majority of cases, visible HA spikes were organized into morphologically diverse HA rosettes that were similar to the molecular aggregates detected on the electron microscopy images of recombinant HA [40,41]. Additional images of representative HA rosettes can be found in Figure S21.…”

“…We used negative-stain transmission electron microscopy (TEM) and dynamic light scattering (DLS) to evaluate the microstructure of IIVs. In interpreting the TEM images obtained, we used the results of previous electron microscopy studies of the influenza virus [37,38], whole inactivated virus vaccines [39], and purified recombinant HA [40,41], as well as TEM images of influenza virions we derived from the virus-containing allantoic fluid ( Figure S21).…”

Viral surface geometry shapes influenza and coronavirus spike evolution through antibody pressure

“…The first input to our model was an atomistic description of the geometry of our immunogens, which we generated from available structural information and pdb files (Gallagher et al, 2018;. For HA and S, solvent-accessible residues were identified using pymol script "findSurfaceResidues" (https://pymolwiki.org/index.php/FindSurfaceResidues), which identifies atoms with a solvent accessible area greater than or equal to 20 Ang 2 (HA) and 15 Ang 2 (S).…”

Immunoelectron Microscopy of Viral Antigens

“…Often samples prepared for immunoelectron microscopy are ultrathin sections of tissue treated for microscopy applications, but valuable information can also be obtained from immunogold labeling of liquid samples of viral suspensions. Not only can these techniques be applied to studying live viruses, but they are also useful for characterizing viral components in vaccines, viral‐like particles, proteins purified from viruses, and other specimen relevant in modern virology applications (Gallagher et al., ; Lynch, Meyers, Williamson, & Rybicki, ). Immunoelectron microscopy has also been applied to study many other molecular biology and nanotechnology specimens (Bruckman, Randolph, Gulati, Stewart, & Steinmetz, ; Geuze et al., ; Zuber, Spiro, Guhl, Spiro, & Roth, ).…”