The document discusses transdermal delivery of vaccines as a needle-free method of immunization. It describes the skin as a barrier to vaccine delivery and various approaches to overcome these barriers, including needle-free injection devices, powder-based delivery, topical adjuvants, colloidal carriers, and energy-based methods. It provides examples of research demonstrating the ability of these approaches to enhance immune responses to various vaccines compared to traditional needle injection.

1. TRANSDERMAL DELIVERY
OF VACCINES
Dr. A. SUMATHI
Professor, Department of Pharmaceutics
NANDHA COLLEGE OF PHARMACY, ERODE

3. TRANSDERMAL DELIVERY OF VACCINES
• The World Health Organisation estimates that
32% of Hepatitis B Virus infections
40% of Hepatitis C Virus infections
5% of Human Immunodeficiency Virus infections
in developing countries are attributable to unsafe injection practices
• The development of needle free immunization methods has thus become an
important goal in global health care
15-Feb-23 Dr. A. SUMATHI 3

4. TRANSDERMAL DELIVERY OF VACCINES
• Dermal vaccination or transcutaneous immunisation is a needle free method of
vaccine delivery which has the potential
To reduce the risk of needle-borne diseases
To improve access to vaccination by simplifying procedures
Trained personnel and use of sterile equipment not required
To assist in the implementation of multiple boosting and multivalent vaccine
regimes
15-Feb-23 Dr. A. SUMATHI 4

5. Skin as a site for vaccine delivery
• The skin has multiple barrier
properties
To minimize water loss from
the body
To prevent the permeation of
environmental contaminants
into the body
15-Feb-23 Dr. A. SUMATHI 5

6. Barriers
• Skin barriers can be considered as
Physical barrier
Enzymatic barrier
Immunological barrier
15-Feb-23 Dr. A. SUMATHI 6

7. Physical Barrier
• The epidermis is in a constant state of renewal
• Formation of a new cell layer of keratinocytes at
the stratum basale
• Loss of their nucleus and other organelles
• Forms desiccated, proteinaceous corneocytes on
their journey towards desquamation
• Desquamation occurs from the skin surface at
the same rate as formation, in normal skin
15-Feb-23 Dr. A. SUMATHI 7

8. Physical Barrier
• The outermost layer - Stratum corneum
• It consists of a brick wall like structure of
corneocytes in a matrix of intercellular lipids,
with desmosomes acting as molecular rivets
between the corneocytes
• The stratum corneum presents an effective
physical barrier to the permeation of large
molecules such as vaccines
• This is the first barrier property that must be
overcome to provide effective transdermal
vaccine delivery
15-Feb-23 Dr. A. SUMATHI 8

9. Enzymatic Barrier
• The skin possesses many enzymes capable of hydrolyzing peptides and proteins
• These are involved in
Keratinocyte maturation and desquamation process
Formation of natural moisturizing factor
General homeostasis
• Their potential to degrade topically applied vaccine antigens should be
considered
15-Feb-23 Dr. A. SUMATHI 9

10. Immunological Barrier
• When the skin is damaged, environmental contaminants can access the
epidermis to initiate an immunological response. This includes
i. Epithelial defence produced by keratinocytes
ii. Innate-inflammatory immunity, involving expression of pro-inflammatory
cytokines and interferons
iii. Adaptive immunity based on APCs, such as epidermal Langerhans and
dendritic cells, mediating T-cell responses
• Thus transdermal delivery targets the vaccine to the skin, thereby promoting its
contact with Langerhans cells and potentially reducing the required dose of
vaccine
15-Feb-23 Dr. A. SUMATHI 10

11. Approaches to Overcome Barriers
• Many approaches have been investigated to overcome the skins barrier
properties in order to deliver antigens via the skin
• They range from formulation approaches such as liposomes, microneedles
• All methods aim to overcome the stratum corneum barrier and target vaccine to
immune-responsive cells such as Langerhans cells
Liquid-jet injection - Needle-free injection devices
Epidermal powder immunization
Topical application - Topical adjuvants & Colloidal carriers
15-Feb-23 Dr. A. SUMATHI 11

12. Liquid-jet injection - Needle-free injection devices
• Liquid jet injectors use a high-velocity jet (typically 100 to 200 m/s) to deliver
molecules through the skin into the subcutaneous or intramuscular region
• Depending on the number of injections carried out with a single device, Jet
injectors can be broadly classified into
Multi-use nozzle jet injectors (MUNJIs)
Disposable cartridge jet injectors (DCJIs)
15-Feb-23 Dr. A. SUMATHI 12

13. Liquid-jet injection - Needle-free injection devices
• Commercially available liquid jet injectors consists of
Power source (compressed gas or spring)
Piston
Drug or vaccine-loaded compartment
Application nozzle, with typical orifice size in the range of 150 to 300 μm
15-Feb-23 Dr. A. SUMATHI 13

14. 15-Feb-23 Dr. A. SUMATHI 14
Needle-free injection devices

15. Needle-free injection devices
• Upon actuation the power source pushes the piston rapidly increases the
pressure within the drug-loaded compartment, thereby forcing the drug solution
through the orifice as a high velocity liquid jet
• When the jet impacts on the skin it creates a hole through allowing the liquid to
enter the skin
• The process of hole formation and liquid jet deposition occurs within
microseconds
• The deposited liquid can then disperse within the tissues to illicit an immune
response
15-Feb-23 Dr. A. SUMATHI 15

16. 15-Feb-23 Dr. A. SUMATHI 16
Schematic Models Showing
the working of
Needle-free injection devices

17. • Applications of liquid-jet injectors have been focused on delivery of
macromolecules that do not passively permeate the skin
• Commercially available devices include
Antares Vision® and Choice® (Antares, Minneapolis) that deliver a variable
dose of insulin
V-Go Mini-Ject system for insulin (Valeritas, Parsippany, NJ)
Biojector 2000 (Bioject, Tualatin, OR)
PenJet (PenJet Corp., Santa Monica, CA) for smallpox vaccination
Injex (HNS International, Anaheim, CA) for administration of insulin and
human growth hormone
Zeneo (Crossject, Paris, France)
15-Feb-23 Dr. A. SUMATHI 17

18. 15-Feb-23 Dr. A. SUMATHI 18

19. • Needle-free injection has been shown to increase immune responses to both
conventional and DNA-based vaccines.
• For example, seroconversion rates and antibody titres elicited in humans, by a
hepatitis A vaccine or a trivalent influenza vaccine, were found to be increased by
at least 10% when using needle-free injections compared to needle and syringe
administration (Williams et al., 2000)
• Clinical studies have shown that the number of responders and the mean
antibody response were comparable to or better as compared to needle
injection, possibly due to better tissue distribution of the vaccine
15-Feb-23 Dr. A. SUMATHI 19

20. • Recently, the Centers for Disease Control and Prevention (CDC) presented positive
clinical data for the Biojector® 2000 administration of influenza vaccination
• They reported that intradermal vaccination by jet injection, permitted reduced
"dose-sparing" amounts of vaccine, increasing the speed and avoiding the risks
and discomfort of the traditional "Mantoux" needle method commonly used for
tuberculosis skin testing. Vet Jet® is a transdermal jet-injector for administration
of Purevax® (Merial, Duluth, GA), a non-adjuvanted leukemia vaccination for cats
• Despite the potential advantages of jet injectors, the uptake of the technology
has been limited due to variable reactions, including pain and bruising, at the site
of administration
15-Feb-23 Dr. A. SUMATHI 20

21. • Some studies reported higher levels of pain associated with jet injectors as
compared to standard injections whereas others have found no difference
between the two methods (Jackson et al., 2001, Sarno et al., 2000)
• Arora et al recently reported a novel pulsed micro-jet system designed to reduce
the adverse effects at the site of administration (Arora et al., 2007)
• In this case a piezoelectric transducer is used to control the delivery volumes (2–
15 nL), jet diameters (50–100 μm) and injection velocity (>100 m/s) thus
minimizing pain and tissue damage
• In order to see future vaccine applications of the jet-injector approach, further
technology development will be required to provide effective pain-free delivery
at reasonable cost
15-Feb-23 Dr. A. SUMATHI 21

22. Epidermal powder immunization
• Powder injectors were first used for DNA and RNA transfection into plants
• The technique has subsequently been investigated for transdermal protein
delivery, gene therapy and vaccination
• The device design principles are similar to liquid injectors, with
Powder compartment
Compressed carrier gas, such as helium
• Upon actuation, the particles are carried by the gas, to impact the skin surface at
high velocity, puncturing micron-sized holes in the epidermis to facilitate skin
deposition
15-Feb-23 Dr. A. SUMATHI 22

23. Epidermal powder immunization
• Humoral and cell mediated immune response following vaccination with jet
propelled particles (including influenza, hepatitis B, rabies) has been
demonstrated in animal studies by Fuller et al., 2006
• Clinical studies have also been undertaken, with immune responses generated
against
• Influenza (Drape et al., 2006)
• Malaria (McConkey et al., 2003)
15-Feb-23 Dr. A. SUMATHI 23

24. Epidermal powder immunization
• A commercial example is the Particle Mediated Epidermal Delivery (PMED®)
technology, initially developed at Oxford University, U.K. and currently owned by
Pfizer
• PMED delivers DNA vaccines into the skin in a dry powder formulation of
microscopic gold particles and is currently in development for a range of vaccines
• Powder injectors offer advantages over liquids in terms of formulation and
stability issues
• Initial safety studies suggest that the powder injectors are reasonably well
tolerated, and the particle bombardment offers advantages with regard to
Langerhans cell targeting and immune system activation
15-Feb-23 Dr. A. SUMATHI 24

25. TOPICAL APPLICATIONS
• In addition to the systems that bombard the skin with liquid or solid vaccines, a
number of other methods have been investigated that can be applied to the skin,
to reduce the stratum corneum barrier, and/or carry vaccine into the skin
• Topical applications range from
Non-invasive formulation based approaches - Colloidal carriers
Energy based approaches - Ultrasound or sonophoresis, and electroporation
Stratum corneum ablation
Minimally invasive approaches - Microneedles
15-Feb-23 Dr. A. SUMATHI 25

26. TOPICAL ADJUVANTS
• Topical administration of the vaccine with adjuvants, such as cholera toxin, has
been shown to induce strong systemic and mucosal immune responses
• The adjuvant activates the Langerhans cells in the skin thus priming the immune
response to the co-administered vaccine
• A number of animal studies have provided positive immune responses for
vaccines including
HIV (Belyakov et al., 2004)
Japanese encephalitis(Cheng et al., 2009)
Helicobacter pylori (Hickey et al., 2009b)
Chlamydia infections(Hickey et al., 2009a)
15-Feb-23 Dr. A. SUMATHI 26

27. TOPICAL ADJUVANTS
• Another example – a study conducted in human volunteers
• They were administered with patches containing recombinant Escherichia coli
colonization factor CS6, either with heat-labile enterotoxin adjuvant or patches
containing CS6 alone
• There were no responses to the CS6 alone patch, whilst strong IgG and IgA
immune responses were found in volunteers who received the adjuvant
combination patch
15-Feb-23 Dr. A. SUMATHI 27

28. TOPICAL ADJUVANTS
• Another example
• In this case, an adjuvant patch containing heat labile Escherichia coli enterotoxin
was placed at the site of an intramuscular H5N1 vaccine injection and compared
to vaccine injection alone
• The adjuvant patch significantly enhanced the immune response to the H5N1
vaccine, with a 73% seroprotection rate
15-Feb-23 Dr. A. SUMATHI 28

29. 1) COLLOIDAL CARRIERS
• The rationale for the use of colloidal carriers is that compounds with
unfavourable permeation characteristics can be packaged within carriers that will
permeate the skin
• Whilst there has been considerable research in the application of liposomes and
lipid particle carriers, there is no conclusive evidence that these carriers can
permeate the skin intact
Nanoparticles & Nanocarriers
Liposomes & Elastic vehicles
15-Feb-23 Dr. A. SUMATHI 29

30. Nanoparticles & Nanocarriers
• These are polymeric particles
• Nanoparticles – nanometer size range
• Microparticles – micrometer size range
• Compounds can be incorporated into the particles in form of a solid dispersion or
a solid solution, or bound to the particle surface by physical adsorption and
chemical binding, thus allowing the particles to act as carriers or as adjuvants for
the vaccine
15-Feb-23 Dr. A. SUMATHI 30

31. Nanoparticles & Nanocarriers
• Whilst there have been sporadic reports of
nanoparticle based skin delivery, the general
consensus is that nanoparticles administered to
the skin do not permeate the intact stratum
corneum, but may accumulate in hair follicles
• Consequently their potential utility for passive
transdermal vaccine delivery is limited
15-Feb-23 Dr. A. SUMATHI 31

32. Liposomes & Elastic Vesicles
15-Feb-23 Dr. A. SUMATHI 32
• Liposomes consist of multiple bilayers of phospholipids capable of solubilising
both lipophilic and hydrophilic compounds within their structure
• They could act as skin permeation carriers
• But no evidence of their permeation across the stratum corneum intact
• Alteration of the composition including incorporation of surfactants, provides
elastic or deformable liposomes, claimed to be capable of deforming in shape so
as to “squeeze through” narrow pores in the stratum corneum

33. 15-Feb-23 Dr. A. SUMATHI 33

34. 15-Feb-23 Dr. A. SUMATHI 34

35. Liposomes & Elastic Vesicles
• Gupta et al. evaluated the potential of elastic vesicle transfersomes, non-ionic
surfactant vesicles (niosomes) and liposomes in non-invasive delivery of tetanus
toxoid (TT)
• Topically administered TT containing transfersomes, elicited an immune response
(anti-TT-IgG) equivalent to intramuscularly alum-adsorbed TT-based
immunization
15-Feb-23 Dr. A. SUMATHI 35

36. Liposomes & Elastic Vesicles
• Strong cellular and humoral immune responses were reported following
transcutaneous immunization with
HBsAg DNA-cationic deformable liposome complex (Wang et al., 2007) and
Hepatitis B surface antigen-loaded ethosomes (Mishra et al., 2008)
• Whilst this is an active research area for the permeation enhancement of small
molecules, vaccine development is more limited, and there are significant
formulation and stability considerations with these systems
15-Feb-23 Dr. A. SUMATHI 36

37. 2) Energy Based Approaches
• Exposure of the skin to energy in the
form of electrical pulses or ultrasonic
waves can disrupt the stratum corneum
barrier to increase permeability
• This approach has been extensively
investigated for drugs and
macromolecules, and to a lesser extent
for vaccine delivery
15-Feb-23 Dr. A. SUMATHI 37

38. Electroporation
• Electroporation involves the administration of electrical pulses to create transient
pores in the skin and thus increase the skin permeability to drugs and
macromolecules
• Inovio Biomedical Corporation (Blue Bell, PA) has developed a series of hand-
held, cordless electroporation devices that have been used in vaccine delivery
studies
15-Feb-23 Dr. A. SUMATHI 38

39. Electroporation
• Delivery of DNA vaccines into muscle or skin tissue with electroporation systems
generated robust immune responses in a number of disease models including
Influenza (H5N1 and H1N1)
Human papillomavirus
HIV
• Recently, the electroporation technique itself, independent of DNA delivery, was
shown to recruit and trigger cells involved in antigen presentation and immune
response
• This adjuvant-like property is likely to enhance the continued development and
success of electroporation based DNA vaccines and immunotherapeutics
15-Feb-23 Dr. A. SUMATHI 39

40. Ultrasound or Sonophoresis
• Low frequency sonophoresis involves application of ultrasound waves at
frequencies between 20 to 100 kHz to the skin surface to reduce the stratum
corneum barrier and thereby increase skin permeability
• Treatments protocols have involved concurrent ultrasound administration and
pretreatment prior to the application of a drug solution or patch
• Low frequency ultrasound (20 kHz) was used to deliver a tetanus toxoid, illiciting
a robust immune response in mice
• IgG antibody titres generated were similar for 1.3 g of toxoid delivered by
ultrasound to the skin and 10 g administered by subcutaneous injection
15-Feb-23 Dr. A. SUMATHI 40

41. 3) Thermal Ablation or Microporation
• Thermal ablation generates micron-size holes in the stratum corneum by
selectively heating small areas of the skin surface to hundreds of degrees
• The heat is applied for micro- to milliseconds so that heat transfer to the viable
tissues is avoided, thus minimising pain and damage
• Using this technique, a 100-fold increase in reported gene expression was
obtained following application to mice of an adenovirus vaccine carrying a
melanoma antigen, when compared to application to intact skin
15-Feb-23 Dr. A. SUMATHI 41

42. 3) Thermal Ablation or Microporation
• Commercially available examples are
PassPort® system by Altea Therapeutics Corp (Altanta, GA)
ViaDerm® device by TransPharma Ltd (Israel)
• Both devices have been tested with a range of small and macromolecules
• The PassPort system was utilized in the vaccine study described above and the
company has a development focus in the vaccine area
15-Feb-23 Dr. A. SUMATHI 42

43. 4) Microneedles
• Microneedles consist of pointed micro-sized projections, fabricated into arrays
with up to a hundred needles, that penetrate through the stratum corneum to
create microscopic holes, thus providing delivery pathways for vaccines and drugs
• A number of different microneedle systems have been investigated including:
Solid microneedles that pierce the skin to increase permeability allowing the vaccine solution
to then be applied via the skin surface;
Solid microneedles coated with dry powder vaccine for dissolution in the skin;
Microneedles composed of polymer with encapsulated vaccine for rapid or controlled release
in the skin, and
Hollow microneedles through which the vaccine solution can be infused into the skin
15-Feb-23 Dr. A. SUMATHI 43

44. 4) Microneedles
• Solid or insoluble microneedles are generally composed of metal such as titanium
or silicone
• The microneedles permeabilize the skin by forming micron-sized holes though
the stratum corneum. The microneedle array is then removed and a drug/vaccine
containing patch is applied. This approach is termed “poke & patch”
• Coated microneedles have an insoluble core coated with drug that dissolves off
within the skin; the so called “coat & poke” approach
15-Feb-23 Dr. A. SUMATHI 44

45. 4) Microneedles
• Polymer microneedles contain the drug or vaccine in a solid solution of needle
that dissolves, swells or degrades on skin insertion, then releasing the drug or
vaccine
• Insoluble hollow microneedles create holes through which the drug solution can
pass into the skin: the “poke & flow” approach
• Of these, the development of insoluble solid and hollow microneedles is most
advanced for vaccine delivery
15-Feb-23 Dr. A. SUMATHI 45

46. Microneedles
• Microneedles are seen as an attractive option for vaccine delivery although to
date, most data is based on animal studies
• A number of animals based studies have demonstrated immune responses
achieved by microneedle administration in excess of that achieved by
conventional injections
• This includes administration of
Influenza vaccine tested in mice
ChimeriVaxTM-JE for yellow fever tested in primates
Plasmid DNA encoding hepatitis B surface antigen
Recombinant protective antigen of Bacillus anthracis for anthrax tested in rabbits
15-Feb-23 Dr. A. SUMATHI 46

47. Microneedles
• In addition, the combination of microneedles and electroporation has been
investigated
• Smallpox DNA vaccine comprised of four vaccinia virus genes (4pox)
• 4pox DNA vaccine was administered by skin electroporation using plasmid DNA-
coated microneedle arrays
• Mice vaccinated with the 4pox DNA vaccine mounted robust antibody responses
against the four immunogens including neutralizing antibody titers that were
greater than those elicited by the traditional live virus vaccine administered by
scarification
• This was the first vaccine study in which microneedle-mediated electroporation
has been used to immunize animals
15-Feb-23 Dr. A. SUMATHI 47

48. Microneedles
• Clinical studies report no significant adverse effects from microneedles, including
minimal erythema and pain, because the projections are not long enough to
reach nerve endings in the deeper tissue
• A number of small and large pharmaceutical companies are actively developing
microneedle technologies.
• 3M (St Paul, MN)
• Becton Dickinson (Franklin Lakes, NJ)
• Zosano Pharma (Fremont, CA)
• Corium (Menlo Park, CA)
• Valeritas (Bridgewater, NJ)
• Nanopass Technologies Ltd (Nes Ziona, Israel)
15-Feb-23 Dr. A. SUMATHI 48

49. THANK YOU FOR YOUR PATIENCE
& PRECIOUS TIME
Dr. A. SUMATHI
Professor, Department of Pharmaceutics
NANDHA COLLEGE OF PHARMACY, ERODE