III yr Botany Hons SKBU

1. Vaccination and ImmunityVaccination and Immunity
Sujit Ghosh
Dept of Botany

8. Passive ImmunizationPassive Immunization
 Passive immunization is the administration of preformed
antibodies either intravenously or intramuscularly.
 It is used to provide rapid protection in certain infections such
as diptheria or tetanus or in the event of accidental exposure to
certain pathogens such as hepatitis B.
 It is also used to provide protection in immune compromised
individuals.

9. Passive ImmunizationPassive Immunization
Infection Source of Antiserum Indications
Tetanus Immune human; horse Post exposure (plus vaccine)
Diptheria Horse Post-exposure
Gas gangrene Horse Post-exposure
Botulism Horse Post-exposure
Varicella-Zoster Immune human Post-exposure in immunodeficiency
Rabies Immune human Post exposure (plus vaccine)
Hepatitis B Immune human Post-exposure prophylaxis
Hepatitis A Pooled human Ig Prophylaxis
Measles Immune human Prophylaxis
Snakebite Horse Post-bite
Some autoimmune disease Pooled human ig Acute thrombocytopenia and
neutropenia

10. Principles of VaccinationPrinciples of Vaccination
 The primary goal in vaccination is to provide protective
immunity by inducing a memory response to an infectious
microorganism using a non-toxic antigen preparation. It is
important to produce immunity of the appropriate kind: antibody
/ or cellular immunity.
 Antibodies produced as a result of immunization are effective
primarily against extracellular organisms and their products e.g.,
toxins. Passively administered antibodies have the same effect as
induced antibodies.
 Cell-mediated immunity (T cells, macrophages) induced by
vaccination is important particulary in preventing intracellular
bacterial and viral infections and fungal infections.
 The ultimate goal of any immunization program is the eradication
of the disease.
 This requires that the infection is limited only to humans, with
no animal or environmental reservoir, and the absence of any
subclinical or carrier state in humans.

11. Principles of VaccinationPrinciples of Vaccination
 Achieving elimination requires a high level of herd immunity to
prevent person to person spread.
 This requires considerable infrastructure support to ensure that
all at-risk populations are targeted for immunization.
 This has been achieved for small pox, although we are close to
the elimination of polio.

12. Characteristics of Effective VaccinesCharacteristics of Effective Vaccines
 Safety
No disease must be caused by the vaccine itself.
 Protection
Protection must be at the population level and prevent disease when the
infectious agent is encountered.
 Long lasting effects
Protection must be long-lasting i.e. induce T and B cell memory.
 Cost
Inexpensive to produce and deliver.
 Administration
Easy to deliver with no side-effects.

13. Active ImmunizationActive Immunization
 Active immunization is the administration of vaccines containing
microbial products with or without adjuvants in order to obtain
long term immunological protection against the offending
microbe.
 At present the normal route of vaccination in most instances is
either intramuscularly or subcutaneously.
 Oral immunization is the method of choice for polio and
Salmonella typhi vaccines. However, there is an increasing
awareness that this route of immunization may be the best for
most immunizations since nearly all infectious agents gain
entrance through the mucosal surfaces.

14. Approaches to Vaccine DesignApproaches to Vaccine Design
 Intact pathogen
Heat-killed or chemically denatured.
Attenuated by growth conditions or genetic manipulation.
 Subunit vaccines
Recombinant proteins.
Synthetic peptides.
 Vaccine vehicles
Live vectors: viral (e.g. Adenovirus) and bacteria (Mycobacteria).
 Adjuvants
Conjugated to lipid or protein carrier molecules.
Microencapsulated in lipids.
 DNA immunisation
Injection of plasmid DNA.

15. Antigen PreparationsAntigen Preparations
 Protection against pathogenic microorganisms require the
generation of effective immune mechanisms.
 Thus, vaccines must be capable of targeting the immune system
appropriately i.e. cellular / or humoral mechanisms.
 Most vaccines consist of either attenuated organisms, killed
organisms, inactivated toxins, or subcellular fragments and more
recently genes for antigens in viral ‘vectors’, and DNA itself.

16. Antigen Preparations Used inVaccinesAntigen Preparations Used inVaccines
Type of antigen Examples
Viruses Bacteria
Normal heterologous organism Vaccinia (Cowpox)
Living attenuated organism Measles BCG
Mumps Typhoid (New)
Rubella
Polio (Sabin)
Yellow fever
Varicella-Zoster
Whole killed oranism Rabies Pertussis
Poli (Salk) Typhoid
Influenza Cholera
Subcellular fragment
Inactivated toxin (toxoid) Diphtheria
Tetanus
Cholera (New)
Capsular polysaccharide Meningococcus
Pneumococcus
Haemophilus
Typhoid (New)
Surface antigen Hepatitis B

17. AdjuvantsAdjuvants
 Nonliving vaccines, especially those consisting of small molecules
require the inclusion of agents to enhance their effectiveness.
 These adjuvants include microbial, synthetic and endogenous
preparations having adjuvant activity, but at present only
aluminium or calcium salts are generally used in humans.
 Adjuvants should enable antigens to be slowly released, preserve
antigen integrity, target antigen presenting cells and induce
cytotoxic lymphocytes.

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Immunology ofImmunology of
VaccinesVaccines
It is important to
understand the immune
mechanism that delivers
protection
This understanding
guides the design of more
effective vaccines

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Overview of the ImmuneOverview of the Immune
ResponseResponse
When a microbe enters the body the
immune system responds in an attempt
to eliminate the infectious agent.
◦ Innate immune system relies on
immediate recognition of antigenic structures
common to many micro-organisms (pathogen
associated molecular patterns /PAMPS)
◦ Adaptive immune response made up of T
& B lymphocytes that have unique
receptors specific to microbial antigens, take
time to respond

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AdaptiveAdaptive
immuneimmune
responseresponse
- review- review

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Goal ofGoal of
VaccinationVaccination
 To generate and sustain the number of antigen specific B & T cells
against a particular pathogen / antigen sufficient to provide protection.
 Most of the successful vaccines are against small organisms (viruses &
bacteria)
 Microorganisms have evolved complex defense mechanisms that interfere
with the immune response. Some of these are
◦ Molecular mimicry
◦ Interference with antigen processing
◦ Prevention of apoptosis of infected cells

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PrimaryPrimary
response to aresponse to a
vaccinevaccine
most currentmost current
vaccinesvaccines
induceinduce
protectiveprotective
antibodiesantibodies

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SecondarySecondary
responseresponse
to anto an
infectioninfection
primed byprimed by
vaccinevaccine

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Primary & secondary antibodyPrimary & secondary antibody
responsesresponses
vaccination & infectionvaccination & infection

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1. Properties of an1. Properties of an ideal vaccineideal vaccine
(easy to define, difficult to achieve)(easy to define, difficult to achieve)
Give life-long
immunity (the vaccine
illustrated at left is required yearly)
Broadly protective
against all variants of
organism
Prevent disease
transmission
Rapidly induce
immunity
Effective in all

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2. Properties of an2. Properties of an ideal vaccineideal vaccine
(easy to define, difficult to achieve)(easy to define, difficult to achieve)
Transmit maternal
protection to the
foetus
Require few
immunisations to
induce protection
Not need to be
administered by
injection (oral,
intranasal,
transcutaneous)
Stable, cheap & safe

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Development ofDevelopment of
immunity inimmunity in
infantsinfants
 Infant’s immune system is relatively complete at birth.
 IgG antibodies received from mother are important for the protection of the
infant while the infant is developing its own repertoire of antibodies.
 Passive transient protection by IgA against many common illnesses is also
provided to the infant in breast milk.

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What happens in a natural infection to produce immunity?What happens in a natural infection to produce immunity?
 To develop a vaccine to we must first consider what happens in a natural
infection to produce protective immunity - these are called “the correlates
of protection”
 An effective vaccine against intracellular pathogens should only induce
effector mechanisms ultimately leading to the destruction of the parasites.
 The vaccine should not trigger components of the immune response
favoring the survival of the parasites.

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FourFour
types oftypes of
traditionaltraditional
vaccinesvaccines
 Killed microorganisms - these are previously virulent micro-organisms that have
been killed with chemicals or heat.
 Live, attenuated microorganisms - live micro-organisms that have been
cultivated under conditions that disable their virulent properties. They typically
provoke more durable immunological responses and are the preferred type for
healthy adults.
 Toxoids - inactivated toxic compounds from micro-organisms in cases where these
toxins (rather than the micro-organism itself) cause illness.
 Subunit - A fragment of a microorganism can create an immune response. Example
is the subunit vaccine against HBV that is composed of only the surface proteins of
the virus which are produced in yeast

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Understanding of theUnderstanding of the stages of thestages of the
immune responseimmune response will assist designwill assist design
of vaccinesof vaccines
 We will look at these stages
1. Initiation of immune response
2. Development of immunological memory
3. Deciding on appropriate immune response for
protective vaccine
 Current challenge is to achieve strong
immunogenicity without increasing the
incidence of adverse events to vaccines

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Initiation of immune response-Initiation of immune response-
danger signaldanger signal An antigen must be recognised as foreign i.e. a danger signal
◦ Binding through pattern recognition receptors (e.g. Tolls)
◦ Tissue damage
 Initial recognition is likely by dendritic cells & tissue resident
macrophages in non-lymphoid tissue
 Activation of dendritic cells is crucial in initiation of a primary immune
response
 Uptake of antigen initiates:
1. Antigen processing
2. Migration of cells to lymph nodes
3. Maturation of dendritic cells

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Initiation of immune response-Initiation of immune response-
danger signaldanger signal

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Initiation ofInitiation of
immuneimmune
response-response-
antigenantigen
processingprocessing Antigens entering cells by endocytosis (such as bacteria) are broken down in
lysosomal vesicles
 Peptides are loaded into MHC II molecules for transport to the cell surface
 Antigens synthesised in the cell (such as viruses) are broken down to peptides
by proteasomes and transported to rough endoplasmic reticulum for loading
into MHC I molecules and transport to cell surface
 Thus surface expression of MHC molecules increases

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Initiation ofInitiation of
immune responseimmune response
migration &migration &
maturation ofmaturation of
DCsDCs
Antigen presenting dendritic cells migrate from
the tissues to the draining lymph nodes.
◦ The migration is controlled by chemokines &
receptors
Dendritic cells mature to display more of the
surface molecules needed for interaction with T
cells

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Example of DC maturation inExample of DC maturation in
measles infectionmeasles infection

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Two aspectsTwo aspects
important forimportant for vaccinevaccine
designdesign
1. Need for the “danger signal” to initiate
immune response
◦ Whole micro-organism may deliver the right signals but sub-unit vaccines may
be poorly immunogenic
◦ Adjuvants may be needed to increase “danger signal”
1. The nature of the “danger signal” has an
important impact on the type of immune
response generated
◦ Adjuvants tend to drive a strong antibody response
◦ Need to better understand the signals that drive DCs
◦ Need to design for appropriate immune response

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Development of immunologicalDevelopment of immunological
memorymemory
Almost all vaccines have the
objective of long-lasting
protective immunity (not
certain how to achieve this)
◦ Memory populations of cells
have encountered antigen and
changed phenotype as a result
of stimulation
◦ Phenotypically defined memory
cells are shown to divide more
rapidly than naïve cells

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Constraints onConstraints on
immunological memoryimmunological memory
T lymphocyte clones can only undergo a limited
number of cell divisions, then they become
senescent
◦ Absence of re-exposure to antigen may limit duration of immunological memory
◦ There is constraint of space in the space in the memory pool. Every time a new
antigen is encountered, expansion occurs and other cells must die to provide
space in the memory pool.
If initial stimulation is large - memory persists
longer
If antigen persists - memory cells may also
persist

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Strategies for future vaccinesStrategies for future vaccines
based on understanding thebased on understanding the
immune responseimmune response
 Most of the present generation of vaccines depend principally on
generating high titres of antibody (Th2 bias)
 Natural protection against many organisms is Th1(cell mediated), especially
for intracellular parasites
 Cellular vaccines are being designed to induce Th1 and cytotoxic
responses.
◦ These require MHC I stimulation via intracellular antigen.
◦ One effective way of doing this is through the use of live vectors vaccines that infect cells
and introduce antigen to the cytoplasm.
◦ DNA vaccines also can generate antigen inside cells

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DNA vaccinesDNA vaccines
generate antigengenerate antigen
inside the cellinside the cell
DNA plasmid vector vaccines carry theDNA plasmid vector vaccines carry the
genetic information encoding angenetic information encoding an
antigenantigen,,
The DNA vaccine-derived protein antigen isThe DNA vaccine-derived protein antigen is
degraded by proteosomes into intracellulardegraded by proteosomes into intracellular
peptidespeptides
These vaccine derived-peptides binds MHCThese vaccine derived-peptides binds MHC
class I moleculesclass I molecules
Peptide antigen/MHC I complexes arePeptide antigen/MHC I complexes are
presented on the cell surface bindingpresented on the cell surface binding
cytotoxic CD 8+ lymphocytes, and inducing acytotoxic CD 8+ lymphocytes, and inducing a
cell-mediated immunecell-mediated immune response.response.

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FactorsFactors
DeterminingDetermining
Vaccine EfficacyVaccine Efficacy
Successful immunization requires
◦ Activation
◦ Replication
◦ Differentiation
◦ of T and B lymphocytes leading to the generation of
memory cells.
Many vaccines require multiple immunisations to
maintain effective immunity
Live infection induces a greater frequency of

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Vaccination strategiesVaccination strategies
The best way to confer immune
resistance to a pathogen is to mimic the
pathogens without causing disease or to
devise formulations which mimic its
characteristics

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1. Properties of an1. Properties of an ideal vaccineideal vaccine
(review)(review)
1. Give life-long immunity
2. Broadly protective against all variants of
organism
3. Prevent disease transmission
4. Rapidly induce immunity
5. Effective in all subjects (the old & very

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2. Properties of an2. Properties of an ideal vaccineideal vaccine
(review)(review)6. Transmit maternal protection to the
foetus
7. Require few immunisations to induce
protection
8. Not need to be administered by injection
(oral, intranasal, transcutaneous)
9. Stable, cheap & safe