Table 1 |.

Prefusion-stabilized spike trimer variants and characteristics

Variant	Stabilizing mutations	Rationale	Yield	Cell line	Ref
S-2P	K986P, V987P, furina	Proline	0.5 mg/L	FreeStyle 293-F	Wrapp et al.19
HexaPro	K986P, V987P, F817P, A892P, A899P, A942P, furina	Proline	10.5 mg/L (FreeStyle 293-F) 32.5 mg/L (ExpiCHO)	FreeStyle 293-F ExpiCHO	Hsieh et al.36
rS2d	K986P, V987P, S383C, D985C, furina	Disulfide	Not reported	FreeStyle 293-F	Henderson et al.21
u1S2q	A570L T572I F855Y N856I (u1S2q) K986P, V987P, A570L, T572I, F855Y, N856I, furina	Cavity filling	Not reported	FreeStyle 293-F	Henderson et al.21
S-R/PP/x1	K986P, V987P, S383C, D985C, furinb	Disulfide	~0.4 mg/L	Expi293F	Xiong et al.57
S-R/x2	K986P, G413C, V987C, furinb	Disulfide	~0.4 mg/L	Expi293F	Xiong et al.57
S-closed +Fd	K986P, V987P, D614N, A892P, A942P, V987P, furina	Cavity filling/proline	Sixfold increased relative to S-2P	Expi293F	Juraszek et al.53
2P DS S	K986P, V987P, S383C/D985C, furinc	Disulfide	Tenfold reduced relative to S-2P	FreeStyle 293-F	McCallum et al.56
N234A	K986P, V987P, N234A	Glycan deletion	2.0 mg/L	FreeStyle 293-F	Henderson et al.58
VFLIP	F817P, A892P, A899P, A942P, K986P, Y707C, T883C, K986, furind	Proline, disulfide, linker	7.1 mg/L (HEK293F) 157 mg/L (ExpiCHO)	HEK293F ExpiCHO	Olmedillas et al.73

^aS1/S2 furin cleavage site (₆₈₂RRAR₆₈₅) mutated to ₆₈₂GSAS₆₈₅

^bS1/S2 furin cleavage site mutated to ₆₈₁PRRAR₆₈₅.

^cS1/S2 furin cleavage site mutated to ₆₈₂SGAG₆₈₅.

^dS1/S2 furin cleavage site mutated to ₆₇₅GGSGGGS₆₉₁.