There is speculation as to how the polyhistidine tag at the N-terminal end of the monomers may affect the selfassembly process, the final nanoparticle structure, or the immunogenicity of the vaccine, but attempts at producing his-tag free versions of the nanoparticle constructs either did not reliably provide pure protein or never adequately self-assembled. Similarly, we attempted to include CD4 T cell epitopes to increase the immune response, but this also interfered with nanoparticle formation.