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).