contributed little protective immunity to infants and young children [56]. Moreover, investigators have used conjugates of capsular
polysaccharides and proteins to enhance immunogenicity. Conjugate polysaccharide vaccines have been developed against the diseases caused by encapsulated bacteria such as Haemophilus
influenzae, Neisseria meningitidis, and Streptococcus pneumoniae.
These vaccines have reduced global childhood morbidity and mortality, with their efficacy to induce long-lasting immunity in a range
of age groups [52, 57–60].
Adjuvants are used in conjunction with vaccines to induce a
fast, effective, and prolonged humoral or cellular immune response
against the antigen. The significance of adjuvants is increasing
because highly purified subunit and synthetic vaccines are more
specific, costly, but less immunogenic. So a potent adjuvant should
cause the use of fewer antigens to induce the desired immune
response. The some examples of adjuvants are biodegradable polymeric microspheres, liposomes, oil adjuvants, lipopolysaccharide,
and aluminum salts [61–63]. Some of the vaccine components are
mentioned in Fig. 1 that can be significantly used in the process of
developing vaccines.
Subunits are another category of vaccines developed by using
part of the antigen of the causative microorganism. Subunit vaccines use only part of antigen from a target pathogen to induce an
immune response. Thus, a specific antigen is isolated from a pathogen and presented as an antigen of its own [41]. Purified antigens
may be surface molecules, subcellular fragments, and toxoids which
require different carriers to be transported. Immune responses
raised by subunit vaccine are based on the type of antigen
[38]. The high levels of purity of subunit vaccines contribute to
enhancement in the specificity of a vaccine and a significant reduction in adverse effects. Such vaccines may be a capsular polysaccharide (Streptococcus pneumoniae, Haemophilus influenzae),
inactivated protein toxins (diphtheria, pertussis, and tetanus), and
viral coat proteins (hepatitis B vaccines). Sometimes capsular polysaccharide vaccines are chemically conjugating with protein components and used as an antigen for the development of vaccines
[64–66]. Conjugated vaccines are also considered as a subclass of a
subunit vaccine, which contains a polysaccharide-based antigen
[67]. Such types of vaccines have been reported for influenza
virus using viral hemagglutinin (HA) protein, rabies vaccine using
rabies glycoprotein, a vaccine against Salmonella, and meningitis
and acellular pertussis vaccines using one to five proteins from the
pertussis bacillus [17, 18, 68–72].
Researchers have used the genetic engineering approach to
enhance the efficacy and increased the production of vaccines in
different hosts [73]. Investigators also have discussed the role of
gene editing tools for cost-effective production of antibodies and
therapeutic proteins [74, 75]. In this approach, the genes of
254
Punit Kumar et al.
polysaccharides and proteins to enhance immunogenicity. Conjugate polysaccharide vaccines have been developed against the diseases caused by encapsulated bacteria such as Haemophilus
influenzae, Neisseria meningitidis, and Streptococcus pneumoniae.
These vaccines have reduced global childhood morbidity and mortality, with their efficacy to induce long-lasting immunity in a range
of age groups [52, 57–60].
Adjuvants are used in conjunction with vaccines to induce a
fast, effective, and prolonged humoral or cellular immune response
against the antigen. The significance of adjuvants is increasing
because highly purified subunit and synthetic vaccines are more
specific, costly, but less immunogenic. So a potent adjuvant should
cause the use of fewer antigens to induce the desired immune
response. The some examples of adjuvants are biodegradable polymeric microspheres, liposomes, oil adjuvants, lipopolysaccharide,
and aluminum salts [61–63]. Some of the vaccine components are
mentioned in Fig. 1 that can be significantly used in the process of
developing vaccines.
Subunits are another category of vaccines developed by using
part of the antigen of the causative microorganism. Subunit vaccines use only part of antigen from a target pathogen to induce an
immune response. Thus, a specific antigen is isolated from a pathogen and presented as an antigen of its own [41]. Purified antigens
may be surface molecules, subcellular fragments, and toxoids which
require different carriers to be transported. Immune responses
raised by subunit vaccine are based on the type of antigen
[38]. The high levels of purity of subunit vaccines contribute to
enhancement in the specificity of a vaccine and a significant reduction in adverse effects. Such vaccines may be a capsular polysaccharide (Streptococcus pneumoniae, Haemophilus influenzae),
inactivated protein toxins (diphtheria, pertussis, and tetanus), and
viral coat proteins (hepatitis B vaccines). Sometimes capsular polysaccharide vaccines are chemically conjugating with protein components and used as an antigen for the development of vaccines
[64–66]. Conjugated vaccines are also considered as a subclass of a
subunit vaccine, which contains a polysaccharide-based antigen
[67]. Such types of vaccines have been reported for influenza
virus using viral hemagglutinin (HA) protein, rabies vaccine using
rabies glycoprotein, a vaccine against Salmonella, and meningitis
and acellular pertussis vaccines using one to five proteins from the
pertussis bacillus [17, 18, 68–72].
Researchers have used the genetic engineering approach to
enhance the efficacy and increased the production of vaccines in
different hosts [73]. Investigators also have discussed the role of
gene editing tools for cost-effective production of antibodies and
therapeutic proteins [74, 75]. In this approach, the genes of
254
Punit Kumar et al.