SARS-CoV-2 variant full length ectodomain spike with pre-fusion stabilizing mutations and receptor binding domain (RBD) proteins were purchased from Sino Biologicals (Wayne, PA, USA): Wuhan (40589-V08B1, S1+S2 ECD, 134.36 kDa, recombinant baculovirus), Delta (40589-V08B16, S1+S2 ECD, 134.20 kDa, recombinant baculovirus); Omicron BA.1 (40589-V08H26, S1+S2 ECD, 136.67 kDa, HEK293 Cells); Omicron BA.2 (S1+S2) (40589-V08H34); Omicron BA.4/5 (S1+S2) (40589-V08H32); Omicron XBB.1.5 (S1+S2) (40589-V08H45); Omicron RBD (40592-V08H121); human angiotensin-converting enzyme 2 (hACE2) protein (aa 1–740) fused to Fc tag (10108-H02H). Full-length ectodomain spike recombinant proteins (Wuhan, Delta, Omicron BA.1) displayed high levels of hACE2 receptor binding activity, with the Wuhan spike protein showing higher activity than Delta and Omicron BA.1 spike proteins, suggesting the integrity of the spike protein folding (Supplementary Figure S1). Wuhan RBD (NR-52366) was obtained from BEI (Biodefense and Emerging Infections Research Resources Repository). Monophosphoryl lipid A (MPL) and saponin QS-21 adjuvants were obtained from Sigma-Aldrich and Desert King (San Diego, CA, USA), respectively.
Liu R., Natekar J.P., Kim K.H., Pathak H., Bhatnagar N., Raha J.R., Park B.R., Guglani A., Shin C.H., Kumar M, & Kang S.M. (2024). Multivalent and Sequential Heterologous Spike Protein Vaccinations Effectively Induce Protective Humoral Immunity against SARS-CoV-2 Variants. Vaccines, 12(4), 362.
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