1.1.5 Colloidal Carriers
Colloidal carriers facilitate the encapsulation of vaccines for topical
delivery. Studies have reported the use of colloidal carriers for
topical delivery of vaccines, all in animals. Topical application of
Tetanus Toxoid (TT) encapsulated in lipid vesicles, after booster
immunization, has been shown to elicit a specific immune response
(IgG) comparable to that produced by the conventional intramuscular injections of alum adsorbed TT [31]. DNA vaccines have also
been delivered using a lipid-based system in animals. Topical application of this DNA–lipid vaccine can result in generating both
humoral and cell-mediated immune responses. Several other combinations like cationic nanoparticles coated with DNA and microemulsion systems have been used for DNA immunization in
animals [32]. The precise mechanisms by which colloidal carriers
penetrate the stratum corneum and the feasibility of translating this
concept to human use remains a topic of research.
1.1.6 Physical Methods
Microneedles, tape stripping, ultrasound, microporation or electroporation, and shock waves are the physical methods that have been
used to deliver vaccines across the skin [1]. Most of these techniques have recently emerged as successful immunization techniques.
Microporation involves focused deposition of thermal energy into
the skin through an electrically heated element to remove small
areas of the stratum corneum [33]. This leads to exposing the
immunocompetent epidermis. Application of an adenoviral vector
to microporated skin with hair removed resulted in 10- to 100-fold
greater cellular and humoral immune responses as compared to
unshaved skin. Microneedles are solid and hollow arrays of
micrometer-scale silicon projections. They have also been used to
carry out topical immunization with various vaccines [34]. Microprojection arrays have been demonstrated to deliver naked plasmid
DNA, inducing stronger and less variable immune responses as
compared to needle-based injections. Full seroconversion, which
is the time required for eliciting a maximum response against an
antigen, can be rapidly achieved with a smaller number of immunizations with these methods [35]. In another study, shock waves
have been employed to deliver vaccines to the epidermis. Shock
waves accelerate the vaccine/drug to form a high velocity liquid jet
[2, 13]. This jet gets deposited into the skin making it accessible to
the Langerhans cells for further immune processing (Fig. 1). Several of the protocols reported in the open literature have been
described in the following section. Protocols have been written in
a generalized manner for further adaptation by the reader.
440
Akshay Datey et al.
Colloidal carriers facilitate the encapsulation of vaccines for topical
delivery. Studies have reported the use of colloidal carriers for
topical delivery of vaccines, all in animals. Topical application of
Tetanus Toxoid (TT) encapsulated in lipid vesicles, after booster
immunization, has been shown to elicit a specific immune response
(IgG) comparable to that produced by the conventional intramuscular injections of alum adsorbed TT [31]. DNA vaccines have also
been delivered using a lipid-based system in animals. Topical application of this DNA–lipid vaccine can result in generating both
humoral and cell-mediated immune responses. Several other combinations like cationic nanoparticles coated with DNA and microemulsion systems have been used for DNA immunization in
animals [32]. The precise mechanisms by which colloidal carriers
penetrate the stratum corneum and the feasibility of translating this
concept to human use remains a topic of research.
1.1.6 Physical Methods
Microneedles, tape stripping, ultrasound, microporation or electroporation, and shock waves are the physical methods that have been
used to deliver vaccines across the skin [1]. Most of these techniques have recently emerged as successful immunization techniques.
Microporation involves focused deposition of thermal energy into
the skin through an electrically heated element to remove small
areas of the stratum corneum [33]. This leads to exposing the
immunocompetent epidermis. Application of an adenoviral vector
to microporated skin with hair removed resulted in 10- to 100-fold
greater cellular and humoral immune responses as compared to
unshaved skin. Microneedles are solid and hollow arrays of
micrometer-scale silicon projections. They have also been used to
carry out topical immunization with various vaccines [34]. Microprojection arrays have been demonstrated to deliver naked plasmid
DNA, inducing stronger and less variable immune responses as
compared to needle-based injections. Full seroconversion, which
is the time required for eliciting a maximum response against an
antigen, can be rapidly achieved with a smaller number of immunizations with these methods [35]. In another study, shock waves
have been employed to deliver vaccines to the epidermis. Shock
waves accelerate the vaccine/drug to form a high velocity liquid jet
[2, 13]. This jet gets deposited into the skin making it accessible to
the Langerhans cells for further immune processing (Fig. 1). Several of the protocols reported in the open literature have been
described in the following section. Protocols have been written in
a generalized manner for further adaptation by the reader.
440
Akshay Datey et al.