Table 2. Semisynthetic glycoconjugate vaccine candidates of selected Gram-positive bacteria.

Bacterium and serotype (ST)	Type of glycan	Saccharide (identified as most promising)	Approach	Carrier protein	Preclinical evaluation	Ref.
S. pneumoniae pentavalent semisynthetic glycoconjugate vaccine ST2, ST3, ST5, ST8, ST14	CPS	oligosaccharides depending on the STs	Semi-synthetic	CRM197	rabbits	[35]
S. pneumoniae ST1		trisaccharide		CRM197	rabbits	[36]
S. pneumoniae ST2		hexasaccharide		CRM197	mice	[26]
S. pneumoniae ST3		tetrasaccharide		CRM197	mice	[27]
		tetrasaccharide		BSA	mice & rabbits	[37]
		hexasacchride		TT	mice	[40]
					rabbit	[41]
S. pneumoniae ST3 and ST14		tetrasaccharides		bacteriophage Qβ	mice	[48]
S. pneumoniae ST4		tetrasaccharide		CRM197	mice	[28]
S. pneumoniae ST5		oligosaccharides		CRM197	rabbits	[34]
S. pneumoniae ST8		tetrasaccharide		CRM197	rabbits	[30]
S. pneumoniae ST14		hexasaccharide		BSA	mice	[42]
		hexasaccharide		BSA	mice	[38,39]
		tetrasaccharide		pneumococcal surface adhesin A	mice	[45]
		repeating unit connected with aliphatic spacer		CRM197	mice	[47]
S. pneumoniae ST19A and ST19F		chimeric antigen comprised of a repeating unit of ST19A and ST19F CPS each		CRM197	rabbits	[44]
GAS various serotypes	cell-wall polysaccharide	branched oligosaccharides containing one, two and three repeating units of CPS		inactive mutant of group A streptococcal C5a peptidase (ScpA), ScpA193	mice	[50,51]
GAS various serotypes		oligorhamnoside fragments		gold nanoparticles	competitive ELISA	[52]
GBS type Ia	CPS	a dimer composed of two pentasaccharides and its corresponding monomer		CRM197	mice	[53]
GBS type III		hexasaccharide		CRM197	competitive ELISA & mice	[54–56]