A new protein-based vaccine candidate combined with a potent adjuvant provided effective protection against SARS-CoV-2 when tested in animals, suggesting that the combination could add one more promising COVID-19 vaccine to the list of candidates for human use.
The protein antigen, based on the receptor binding domain (RBD) of SARS-CoV-2, was expressed in yeast instead of mammalian cells – which the authors say could enable a scalable, temperature-stable, low-cost production process well suited for deployment in the developing world.
In a study by Maria Pino and colleagues, the adjuvant – a TLR7/TLR8 agonist named 3M-052, formulated with alum – substantially improved performance of the vaccine compared with vaccine adjuvanted with alum alone, inducing stronger antibody and T cell responses in vaccinated rhesus macaques.
The vaccine and adjuvant combination also significantly reduced the quantity of virus in the respiratory tracts of macaques challenged by infection with SARS-CoV-2, and reduced lung inflammation as well.
Pino et al. vaccinated 5 macaques with the RBD protein and the 3M-052/alum adjuvant and another 5 with the RBD protein and alum alone, each at 0, 4, and 9 weeks; they also included 5 unvaccinated macaques as controls. The vaccine and adjuvant combination induced more neutralizing antibodies with higher binding affinity for the virus RBD and also enhanced CD4+ and CD8+ T cell responses compared with the alum-only formulation.
About one month after the third round of vaccinations, the researchers then infected the macaques with SARS-CoV-2, and noted the macaques vaccinated with the novel adjuvant formulation showed a reduced viral load in their nasal mucus and lung fluid, as well as fewer inflammatory cytokines in their plasma.
Featured image: The RBD+3M-052-alum vaccine induces robust humoral immunity in RMs. © Authors
Reference: Maria Pino, Talha Abid, Susan Pereira Ribeiro, Venkata Viswanadh Edara, Katharine Floyd, Justin C. Smith, Muhammad Bilal Latif, Gabriela Pacheco-Sanchez, Debashis Dutta, Shelly Wang, Sanjeev Gumber, Shannon Kirejczyk, Joyce Cohen, Rachelle L. Stammen, Sherrie M. Jean, Jennifer S. Wood, Fawn Connor-Stroud, Jeroen Pollet, Wen-Hsiang Chen, Junfei Wei, Bin Zhan, Jungsoon Lee, Zhuyun Liu, Ulrich Strych, Neeta Shenvi, Kirk Easley, Daniela Weiskopf, Alessandro Sette, Justin Pollara, Dieter Mielke, Hongmei Gao, Nathan Eisel, Celia C. LaBranche, Xiaoying Shen, Guido Ferrari, Georgia D. Tomaras, David C. Montefiori, Rafick P. Sekaly, Thomas H. Vanderford, Mark A. Tomai, Christopher B. Fox, Mehul S. Suthar, Pamela A. Kozlowski, Peter J. Hotez, Mirko Paiardini, Maria Elena Bottazzi, Sudhir Pai Kasturi, “A yeast expressed RBD-based SARS-CoV-2 vaccine formulated with 3M-052-alum adjuvant promotes protective efficacy in non-human primates”, Science Immunology 15 Jul 2021: Vol. 6, Issue 61, eabh3634 DOI: https://doi.org/10.1126/sciimmunol.abh3634
Provided by AAAS