A live, biologically-contained vaccine against severe acute respiratory syndrome coronavirus 2 (SARS CoV-2)

In the last months of 2019, several cases of pneumonia caused by a novel coronavirus emerged in Wuhan, China. The virus was initially linked to animal-to-human transmission in local wet markets. Shortly after, however, the virus started to be transmitted human-to-human, resulting in its spread across China and at least 20 other nations. In February 2020, the World Health Organization named the virus SARS-CoV-2, while the syndrome was named coronavirus disease 2019 (COVID-19). The symptoms develop as a severe respiratory illness with significant mortality among the population at risk, as individuals over the age of 60 or those with pre-existing conditions such as diabetes, cardiovascular illness, or hypertension. SARS-CoV-2 is highly transmissible, even from asymptomatic infected individuals. The ability of SARS-CoV-2 to cause a pandemic disease within a short time, suggests that the development of a vaccine is of utmost importance for the control of this viral infection. Due to this urgency, several laboratories around the world started to work in vaccine development against SARS-CoV-2, with over 120 vaccines in the pipeline so far. These vaccines can be generally classified in four groups: i) virus vaccines (weakened or inactivated); ii) nucleic-acid vaccines (DNA or RNA); iii) viral-vector vaccines (replicating or non-replicating) and iv) protein-based vaccines (protein subunits or virus-like particles). In this proposal, we will design a vaccine platform to create immunity against SARS CoV-2 based on a novel technology recently published by our group. This technology differs fundamentally from the aforementioned four vacine groups that are currently under development elsewhere: we will use live recombinant spores of Bacillus subtilis, applied via the oral route, for the delivery of SARS-CoV-2 antigens. Once orally applied, the spores bypass the stomach barrier reaching the small intestine to germinate in the gut and develop into functional biofilms that express the antigens of interest as a fusion-protein with the abundant biofilm matrix protein TasA. Using this technology we have already successfully vaccinated dogs and mice, eliciting both humoral and cellular immune responses against the fluorescent protein mCherry, and also to paramyosin and tropomyosin from Echinococcus granulosus. Using this principle, we will work on two parallel strategies to develop a vaccine that will induce an immune response against SARS-CoV-2:1)We will use two different domains of the spike protein from SARS-CoV-2 as antigens, one encompassing the Receptor Binding Domain (RBD) from the S1 fragment and a second encompassing the highly conserved heptad repeat HR1 motif from the S2 fragment of the protein. The viral S-protein has been described as essential for cell entry via the receptor ACE2.2)We will also use the N-terminus domain of the SARS-CoV-2 Protein E as antigen. Protein E is a viroporin with ion channel activity, and has been implicated in multiple aspects of the viral replication cycle: from assembly and induction of membrane curvature to scission or budding and release to apoptosis, inflammation and even autophagy.B. subtilis is a safe, non-pathogenic bacterial vector, with an excellent record of human and animal use as both probiotic and food additive. The genetic manipulation of B. subtilis is straightforward, and the spores have remarkable resistance to heat and chemicals. Since our platform is based on live B. subtilis, in this proposal we will address an aspect that was not addressed in our previous research: the biological containment in a markerless strain (no genes providing antibiotic resistance). Biological containment is an important issue to crack in order to satisfy Swiss and European regulations and thus expediting the market introduction. The vaccine will be tested in a transgenic mouse model expressing a human ACE2 receptor. The technology to be developed in this proposal will solve several problems of the current enteric vaccination strategies: i) substantial reduction of operational cost since B. subtilis spores are exceptionally resistant to harsh conditions, with no need of a cold chain for storage or delivery; ii) production of vaccine doses does not require expensive equipment or complex media, making scaling-up simple and inexpensive for broader use, and importantly iii) the vaccine will be biologically contained. Once completed, we will benefit from a platform that can be easily adapted to rapidly create a vaccine against emerging viral pathogens, contributing to our preparedness for future pandemics