6.3 Recombinant Subunit Vaccines
Subunit vaccines are superior to other types of vaccines since they are highly safe and possess fewer adverse effects via eliciting the immune system without drawing into any infectious viruses (Graham et al., 2013). It has also been reported that the enhancement of T cell responses and generation of high titer neutralizing Abs were observedin vivo during the vaccine development researches (Okba et al., 2017). Clover Biopharmaceuticals was pre-clinically testing a recombinant subunit vaccine in the light of the S-Trimer of the SARS-CoV-2 (Clover Biopharmaceuticals, 2020). The researchers detected the antigen-specific neutralizing Abs in the sera of fully recovered patients (Clover Biopharmaceuticals, 2020). Besides, GlaxoSmithKline (GSK) disclosed a vaccine which can elicit a protective immune response against SARS. The vaccine contains an S protein immunogen, which was combined with the emulsion adjuvant, GSK2, yielding elevated level of anti-SARS-CoV IgG2a/IgG2b Ab responses. Recently, GSK and Clover Biopharmaceuticals announced a partnership to enhance immune response via introducing GSK’s adjuvant system to S-Trimer (GSK, 2020). In addition, the team of the University of Queensland is also designing subunit vaccines via the transformative technology, known as “molecular clamp” (University of Queensland, 2020). Molecular clamps are peptides that stabilize surface proteins, improve the recognition of the correct antigens, and lead to a more robust immune response. This vaccine platform can be easily applied to a variety of enveloped viruses and can rapidly manufacture their products (University of Queensland, 2020).
Further, patent application US20060002947 disclosed the fabrication of hybrid peptides comprised of three elements: (a) an invariant chain (Ii) essential peptide; (b) a chemical structure linking the Ii to the antigenic epitope; (c) an antigen epitope binding MHC II molecule. This theory was harnessed to produce Ii-Key/MHC II SARS hybrids. In this respect, Generex reported that they will employ its Ii-Key immune system activation biotechnology to generate a COVID-19 viral peptide vaccine for human clinical practice (Generex, 2020).