Figure 2.

Four kinds of vaccine candidates against SARS-CoV-2

(A) Schematic illustration of a BC-PIV-based chimeric vaccine. The Spike (S) gene of SARS-CoV-2 is inserted at cloning site 1 of the BC-PIV (Ohtsuka et al., 2019) to enable the high expression of S relative to the downstream genes. S protein (S1M, S-2P, and S-2PM; see the panel (B) is incorporated in the viral particle as an envelope protein, resulting in the chimeric virus.

(B) A diagram of the transgene cassettes of four vaccine candidates. S, full-length wild-type S of SARS-CoV-2 for reference; NTD, N-terminal domain; RBD, receptor-binding domain; S1/S2, S1/S2 protease cleavage site, S2′, S2′ protease cleavage site; FP, fusion peptide; HR1, heptad repeat 1; CH, central helix; CD, connector domain; HR2, heptad repeat 2; TM, transmembrane domain; CT, cytoplasmic tail; PP, two proline mutations at amino acid positions K986 and V987 in the S2 region to stabilize S in the prefusion conformation; S1, entire region of S1; S1M, S1 fused with the transmembrane and cytoplasmic tail regions of hPIV2 F protein; S-2P, prefusion-stabilized full-length spike protein; S-2PM, ectodomain of S-2P fused with TM and CT regions of hPIV2F.

(C) A Western blot analysis of the packaging cells infected with each vaccine vector and probed with anti-SARS-CoV S1, anti-NP of hPIV2, and anti-glyceraldehyde 3-phosphate dehydrogenase (GAPDH) antibodies. S0, uncleaved S protein.

(D) A Western blot analysis of the viral particles of each vaccine vector probed with the anti-SARS-CoV S1 and anti-P of hPIV2 antibodies.

(E) A Western blot analysis of the viral particles of each vaccine vector probed with the anti-SARS-CoV S2 and anti-NP of hPIV2 antibodies.