Vaccines by Dr.Jayshree Nellore

Prepared By:
Dr. JAYSHREE and Dr.Karthickraja
Professor
Sathyabama Institute of Science and Technology
MEDICAL BIOTECHNOLOGY
Vaccines

01. Vaccines by definition are biological agents that elicit an immune response to a specific
antigen derived from an infectious disease-causing pathogen. Edward Jenner developed
the first vaccine in 1796 using cowpox to inoculate against smallpox. His groundbreaking
work ultimately led to the global eradication of smallpox, officially declared in 1980. Since
then, vaccines have helped to suppress the spread of several infectious diseases
including polio, which has been eliminated from many countries, including all of those
located within North and South America and Europe.
02. With the continued use of vaccines, it is tempting to speculate that other infectious
diseases will soon follow suit. Unfortunately, we have taken a large step backward with
the vocalization of the anti-vaccine movement and the reduction in vaccine acceptance.
4.1 Vaccines

03. Although arguably one of man’s greatest discoveries, vaccines have always been met
with some hesitation, even in the late 18th and early 19th centuries. Yet recently,
vaccination has rapidly become a highly controversial issue, due in large part to an
erroneous link between vaccines and autism. It is important to shed light on the necessity
of immunization and the value it offers both personally and publicly.
04. Universal vaccine acceptance is essential to providing herd immunity, such that those
who are unable to be directly protected by vaccination are protected by communal
immunity. Vaccine education will be critical in maintaining the forward progress that has
been made in reducing or eliminating many infectious diseases. In an effort to ease some
of these concerns, Federman suggests improved vaccine education as a public
imperative in his perspective piece. He advocates that widely improving vaccine
understanding will improve public perception of immunization and promote vaccine
acceptance.

05. Lack of vaccine education and acceptance is one reason that many vaccines are under-
utilized. One such vaccine is the influenza vaccine, which is one of the most complex and
useful tools for preventing the spread of influenza. In this issue, both Lawrence and
Murphy examine the lack of influenza vaccine coverage in at-risk populations, namely
college students and pediatric asthma patients, respectively. Both suggest a lack of
understanding as a barrier to proper vaccine acceptance.
06. Similar to the influenza vaccine, the hepatitis B vaccine lacks coverage in at-risk
populations. Frew and colleagues examine the reasoning behind suboptimal
immunization rates among Vietnamese Americans, an at-risk group for hepatitis B.
Importantly, there is a vaccine available to combat this disease, which is not always true
for infectious diseases that often predominate in underprivileged populations. In his
perspective, Erfe elaborates on the need for vaccines in developing nations and
suggests a plan to mobilize pharmaceutical companies to research and produce vaccines
for diseases such as Ebola, which have very little threat to the First World, but are
ravaging sub-Saharan Africa and other vulnerable populations.

07. In addition to infectious disease-targeted vaccines, a recent endeavor has begun in the
pursuit of anti-cancer vaccines. Similar to the foundation of infectious disease vaccines,
anti-cancer vaccines stimulate an immune response to target cancer-specific antigens. In
a comprehensive review, Liu describes the initial progress made and the potential for
expanding the field by describing both therapeutic and preventive types of anti-cancer
vaccines. In an equally thorough review, Datta and colleagues discuss the role of
dendritic cells in cancer immunotherapy, not just in regard to the success of the FDA-
approved sipuleucel-T for prostate cancer, but also the potential advancements for
dendritic cell immunotherapy in other cancer treatment.

08. Conventional Vaccines:
8.1 Classification:
8.1.1 Conventional vaccines originate from viruses or bacteria and can be divided in
live attenuated vaccines and non-living vaccines. In addition, three vaccine
generations can be distinguished for non-living vaccines.
8.1.1.1 First generation vaccines consist of aninactivated suspension of the
pathogenic microorganism. Little or no purification is applied.
8.1.1.2 For second generation vaccines purification steps are applied, varying
from the purification of a pathogenic micro-organism (e.g., improved
non-living polio vaccine) to the complete purification of the protective
component (e.g., polysaccharide vaccines).
8.1.1.3 Third generation vac-cine are either a well-defined combination of
protective components (e.g., acellular pertussis vaccine) or the
protective component with the desired immunological properties (e.g.,
polysaccharides conjugated with carrier proteins).

8.1 Classification:
8.1.2 An overview of the various groups of conventional vaccines and their
generations is given in Table

8.2 Live Attenuated Vaccines:
8.2.1 Before the introduction of recombinant-DNA (rDNA) technology, a first step to
improved live vaccines was the attenuation of virulent microorganisms by serial
passage and selection of mutant strains with reduced virulence or toxicity.
Examples are vaccine strains for oral polio vaccine, measles-rubella-mumps
(MMR) combination vaccine, and tuberculosis vaccine consisting of bacille
Calmette-Gue´rin (BCG). An alter-native approach is chemical mutagenesis. For
instance, by treating Salmonella typhi with nitrosoguanidine, a mutant strain
lacking some enzymes that are responsible for the virulence was isolated
(Germanier and Fuer, 1975).

8.2.2 Live attenuated organisms have a number of advantages as vaccines over non-
living vaccines. After administration, live vaccines may replicate in the host
similar to their pathogenic counterparts. This confronts the host with a larger and
more sustained dose of antigen, which means that few and low doses are
required. In general, the vaccines give long-lasting humoral and cell-mediated
immunity.
8.2.3 Live vaccines also have drawbacks. Live viral vaccines bear the risk that the
nucleic acid is incorporated into the host’s genome. Moreover, reversion to a
virulent form may occur, although this is unlikely when the attenuated seed
strain contains several mutations. Nevertheless, for diseases such as viral
hepatitis, AIDS and cancer, this drawback makes the use of conventional live
vaccines virtually unthinkable.

8.2.4 Furthermore, it is important to recognize that immunization of immunodeficient
children with live organisms can lead to serious complications. For instance, a
child with T-cell deficiency may become overwhelmed with BCG and die.

8.3 Non-Living Vaccines: Whole Organisms:
8.3.1 An early approach for preparing vaccines is the inactivation of whole bacteria or
viruses. A number of reagents (e.g., formaldehyde, glutaraldehyde) and heat are
commonly used for inactivation. Examples of this first generation approach are
pertussis, cholera, typhoid fever, and inactivated polio vaccines. These non-living
vaccines have the disadvantage that little or no CMI is induced. Moreover, they
more frequently cause adverse effects as compared to live attenuated vaccines
and second and third generation non-living vaccines.

8.4 Non-Living Vaccines: Subunit Vaccines:
8.4.1 Diphtheria and Tetanus Toxoids:
8.4.1.1 Some bacteria such as Corynebacterium diphtheriae and Clostridium
tetani form toxins. Antibody-mediated immunity to the toxins is the main
protection mechanism against infections with these bacteria. Both toxins
are proteins. Around the beginning of the twentieth century, a
combination of diphtheria toxin and antibodies to diphtheria toxin was
used as diphtheria vaccine.
8.4.1.2 This vaccine was far from ideal and was replaced in the 1920s with
formaldehyde-treated toxin. The chemically treated toxin is devoid of
toxic properties and is called toxoid. The immuno-genicity of this
preparation was relatively low and was improved after adsorption of the
toxoid to a suspension of aluminum salts.

8.4.1 Diphtheria and Tetanus Toxoids:
8.4.1.3 This combination of an antigen and an adjuvant is still used in existing
combination vaccines. Similarly, tetanus toxoid vaccines have been
developed. Diphtheria toxin has also been detoxified by chemical
mutagenesis of Corynebacterium diphtheriae with nitrosoguanidine.
These diphtheria toxoids are referred to as cross-reactive materials (e.g.,
CRM197).

8.4.2 Acellular Pertussis Vaccines:
8.4.2.1 The relatively frequent occurrence of side effects of whole-cell pertussis
vaccine was the main reason to develop subunit vaccines in the 1970s,
which are referred to as acellular pertussis vaccines. These vaccines
were prepared by either extraction of the bacterial suspension followed
by purification steps, or purification of the cell-free culture supernatant.
These second generation vaccines showed relatively large lot-to-lot
variations, as a result of their poorly controlled production processes.

8.4.2 Acellular Pertussis Vaccines:
8.4.2.2 The development of third generation acellular pertussis vaccines in the
1980s exemplifies how a better insight into factors that are important for
pathogenesis and immunogenicity can lead to an improved vaccine. It
was conceived that a subunit vaccine consisting of a limited number of
purified immunogenic components and devoid of (toxic)
lipopolysaccharide would significantly reduce unde-sired effects. Four
protein antigens important for protection have been identified. However,
as yet there exists no consensus about the optimal composition ofan
acellular pertussis vaccine. Current vaccines con-tain different amounts
of two to four of these proteins.

8.4.3 Polysaccharide Vaccines:
8.4.3.1 Bacterial capsular polysaccharides consist of pathogen-specific multiple
repeating carbohydrate epitopes, which are isolated from cultures of the
pathogenic species. Plain capsular polysaccharides (second generation
vaccines) are thymus-independent antigens that are poorly immunogenic
in infants and show poor immunological memory when applied in older
children and adults. The immunogenicity of polysaccharides is highly
increased when they are chemically coupled to carrier proteins
containing Th-epitopes.

8.4.3.2 This coupling makes them T-cell dependent, which is due to the
participation of Th-cells that are activated during the response to the
carrier. Examples of such third generation polysaccharide conjugate
vaccines include meningococcal type C, pneumococcal and
Haemophilus influenzae type b (Hib) polysaccharide vaccines that have
recently been introduced in many national immunization programs. Four
different conjugated Hib polysaccharide structures are presently
available, i.e., chemically linked to either tetanus toxoid, diphtheria
toxoid, CRM197 (mutagenically detoxified diphtheria toxin, see above)
or meningococcal outer membrane complexes.

8.4.3.3 Apart from the carrier, the four structures vary in the size of the
polysaccharide moiety, the nature of the spacer group, the
polysaccharide-to-protein ratio, and the molecular size and aggregation
state of the conjugates. As a result, they induce different immunological
responses. This illustrates that not only the antigen, but also its
presentation form determines the immunogenicity of a vaccine.
Therefore, the determination of optimal conjugation procedures, the
standardization of conjugation, as well as the separation of conjugates
from free proteins and polysaccharides are of utmost importance.

09. Recombinant Vaccines:
9.1 Several genes from different etiologic agents have been cloned, expressed and
purified to be tested as vaccines. There are a variety of expression systems for
antigenic protein components, such as bacteria, yeast, mammalian cells and insect
cells, in which the DNA encoding the antigenic determinant can be inserted and
expressed. However, several factors must be taken into account before selecting the
system for antigen expression.
9.2 The level of expression obtained using each specific expression vector and promoter,
the selection marker of choice, the presence or absence of post-translational
modification by the recombinant vector, among others, are essential features that
interfere in the efficacy of production of recombinant antigens as vaccines. Bacterial
expression systems are the most used due to the ease of handling and to their
capacity for high level expression. However, for antigens in which post-translational
modifications (e.g., glycosylation) are necessary, the use of mammalian or insect
cells should be considered

9.3 Recombinant protein vaccines:
9.3.1 Most of the vaccines under investigation today are based on highly purified
recombinant proteins or subunits of pathogens. The classical example of
recombinant protein vaccines currently in use in humans is the vaccine against
hepatitis B (Table 1). Hepatitis B virus (HBV) infection is a chronic liver disease
occurring worldwide.

aLicensed by national regulatory agencies such as ANVISA in Brazil or FDA in the USA.
OPV = oral polio vaccine; IPV = inactivated polio vaccine; BCG = bacillus Calmette-Guérin.
Table 1.
Licenseda viral and bacterial vaccines for use in humans.

9.3.2 HBV presents a marked tropism for human liver cells, partially due to a specific
receptor that is expressed on the surface of infected cells. The current vaccines
are produced by expressing the hepatitis B surface antigen (HBsAg) in yeast
cells. The HBsAg assembles into virus-like particles (VLPs), which are
extremely immunogenic, making the HBV vaccine a very efficacious vaccine.
The yeast expression system may secrete the antigen into the culture
supernatant that can facilitate its purification.
9.3.3 Furthermore, yeast cells offer some of the eukaryotic cellular machinery
responsible for the post-translational modification of proteins, being capable of
rendering proteins glycosylated. The technology of production of the HBV
vaccine has been transferred to several manufacturers and the prices have
decreased due to competition, which has rendered this vaccine affordable to
most developing countries.

9.3.4 A more recently developed example of recombinant vaccine is the vaccine
against human papillomaviruses (HPVs) (Table 1). HPV is one of the most
common sexually transmitted diseases and this infection is associated with
many types of mucocutaneous diseases in humans, including cervical, vulva,
and vaginal cancers, and genital warts. There are two vaccines in use against
HPV, which have both been developed based on VLPs derived from HPV-6, -
11, -16, and/or -18 subtypes.
9.3.5 These vaccines utilize the L1 recombinant proteins of each subtype, produced
either in yeast or in an insect-cell system. The L1 is the major capsid protein
and its expression in vitro results in the assembly of VLPs.

9.3.6 The vaccines are given in a three-dose regimen, using aluminum potassium
sulfate as adjuvant, which induces high titers of virus-neutralizing serum
antibodies. These vaccines are proprietary and extremely expensive, and
therefore will have limited accessibility for low-income countries for some time.
9.3.7 Even though vaccines based on recombinant proteins offer several advantages
when compared with traditional vaccines, such as safety and production cost,
most of them present weak or poor immunogenicity when given alone, and
thereby require the use of adjuvants to elicit a protective and long-lasting
immune response. The successful use of recombinant proteins as vaccines,
including hepatitis B and, more recently, HPV, was possible due to the use of
aluminium salt as adjuvant. Therefore, the investigation of new adjuvants is an
extremely important field in vaccinology.

Recombinant Adjuvants Protein Vaccines
Vaccine Adjuvants
Review | InvivoGen

9.3.8 The main difficulties for the development of new adjuvants involve understanding
their molecular complexity and the mechanisms by which they operate to
stimulate or induce the immune response. For example, the mechanism of action
of the aluminum salts, which are the most commonly used adjuvants in human
and animal vaccines worldwide, remains unknown. However, Richard Flavell's
group recently suggested that they would activate an intracellular innate immune
response system called Nalp3 inflammosome. An alternative path for antigen
presentation has been the use of live vectors, such as bacteria and viruses, in
which their natural adjuvant properties are explored. Formulation and safety,
among other concerns, are also important aspects to be considered

Activation of the NALP3 inflammasome by microbes, toxins, and danger signals. (Journal of
Leukocyte Biology Volume 82, August 2007 )

9.4 Live recombinant vaccines using bacterial or viral vectors:
9.4.1 As a result of advances in the fields of molecular biology and genetic
engineering it is now possible to create live recombinant vectors capable of
delivering heterologous antigens by the introduction of antigen-encoding genes.
The idea behind this approach is to use the capacity of infection and the
immunological properties of the live vector to elicit an immune response against
its own proteins, as well as towards the heterologous protein being presented.
9.4.2 A number of bacteria [such as Salmonella typhi and bacille Calmette-Guérin
(BCG)] and viruses [such as vaccinia (smallpox) and adenovirus] have been
investigated as live recombinant vector vaccines. In general, these approaches
have advantages that are intrinsic to the pathogen itself, such as mimicry of a
natural infection, their capacity of stimulating both CD4+ and CD8+ T-cell
subsets, and, in some cases, the possibility to be administered orally.

Mycobacterium bovis BCG vaccine

9.4.3 The use of live-attenuated bacterial vaccines is not novel. However, their
utilization as carriers or delivery vehicles for heterologous antigen expression
represents a technology with broad applicability that may have a significant
impact on vaccine development. Significant advances in molecular biology have
enabled precise deletions of genes encoding important virulence factors, as
well as the introduction of recombinant DNA into avirulent yet immunogenic
vaccine strains.
9.4.4 Bacterial vectors have many advantages that make them attractive systems for
heterologous antigen presentation. They can elicit humoral and/or cellular
immune responses and can be administered orally, thereby eliciting mucosal
immunity. Most are antibiotic-sensitive strains, which allow antibiotic treatment if
any adverse reaction occurs. In general, they display very favorable cost-
effectiveness.

9.4.5 Several bacteria have been used as vectors, such as Mycobacterium
bovis BCG, Listeria monocytogenes, Salmonellae spp and Shigellae spp, all of
which have been shown to be capable of eliciting immune responses against
important viral, bacterial, protozoan, and metazoan pathogens in animal
models.
9.4.6 Although such bacterial vectors present similar features, they have distinct
characteristics that should be considered before making a choice for any one of
them. For instance, while Listeria elicits strong antigen-specific T helper (Th)1-
driven CD8+ T cells, BCG and Salmonella induce immune responses with
mixed Th1/Th2 patterns

•Mycobacterium bovis BCG vaccine (November 2014 Clinical and vaccine Immunology: CVI 22(1)

Listeria monocytogenes vaccine (Vaccines 2018, 6(3),
48; https://doi.org/10.3390/vaccines6030048)

9.4.7 Among these bacterial vectors, M. bovis BCG and S. typhi are the most
representative of the current status of this approach, as it can be seen by the
numerous and assorted papers that have been published using both vectors.
BCG offers several features that render it an attractive vaccine vector. It is safe
and has been administered to over 3 billion individuals with minimum side
effects, it can be administrated soon after birth, it is a potent adjuvant, and it
provides the possibility of generating T cell-mediated immunity against the
cloned heterologous antigen. This last feature is considered to be an essential
element of a successful vaccine against intracellular pathogens.

9.4.8 Several examples of recombinant BCG (rBCG) expressing foreign antigens from
diverse pathogens have been described, such as malaria, tuberculosis (TB),
HIV, leishmania, pertussis, and others. These were demonstrated to induce both
humoral and cellular immune responses and, in some cases, protection against
challenge with the infective microorganism.
9.4.9 Much work has been done on rBCG expressing HIV antigens, in which different
antigens have been found to elicit specific antibodies, production of interferon
(IFN)-γ, as well as to induce T helper cells and cytotoxic T lymphocytes (CTLs),
thus demonstrating the ability of different strains of rBCG-HIV to produce both
humoral and cellular immune responses against HIV antigens

9.4.10 Recently, many studies have focused on the use of rBCG as a means of
increasing the protection against TB. Recombinant BCG expressing
important M. tuberculosis antigens, such as Ag85A, have been shown to
induce better immune responses than those elicited by standard BCG in
animal models and, as a consequence, these strains are under evaluation in
clinical trials. In fact, rBCG-Ag85A was the first rBCG vaccine to be used in a
clinical trial against TB. The idea was to improve the BCG vaccine by over-
expressing an immunodominant antigen that had been demonstrated to be
protective.

9.4.11 Numerous viral vectors are available for vaccine development, such as
vaccinia, modified vaccinia virus Ankara (MVA), adenovirus (Ad), adeno-
associated virus (AAV), retrovirus/lentivirus, alphavirus, herpes virus, and
many others. There are many differences between the viral vectors available.
They can be classified according to the virion type (DNA or RNA), particle size,
transgene capacity, and cell tropism
9.4.12 Viral vectors can be replicating or non-replicating viruses; the replication-
defective viruses being the most tested in clinical trials, partly due to their
higher safety. However, some groups are focusing on the use of replicating
vectors in clinical trials as they are more likely to elicit stronger cellular and
mucosal immune responses, as well as antibodies against the expressed
proteins, depending on their cell tropism and sites of replication.

9.4.13 Several studies have demonstrated that recombinant viral vectors encoding
genes from important pathogens, (such as malaria, HIV and TB) are able to
induce both humoral and cell-mediated immune responses against their
expressed antigens in immunized animals and, in some cases, may even
protect the animals from lethal challenge. Co-expression of
immunomodulating cytokines in viral vectors has also been used in order to
enhance their immunogenicity, also with the above-cited restrictions.
9.4.14 This strategy has been used extensively in the development of vaccines
against HIV. Similar to other viral vaccines or viral vector-based vaccines
developed, a vaccine against HIV infection could be devised based on its
attenuation.

9.4.15 However, due to the possible risk of reversion or recombinant events, which
can lead to a pathogenic HIV phenotype, vaccines based on HIV virus
attenuation have been avoided. Therefore, live recombinant viral vectors such
as Ad and MVA have been proposed as safer and less concern raising
approaches. Ad and MVA are among the most promising live viral vector
systems and, besides having been tested as vaccines against HIV, are
currently being used in clinical trials against other important infectious
diseases such as TB and malaria.

9.4.16 Adenoviruses are non-enveloped icosahedral viruses containing a linear
double-stranded DNA in their genome, which can infect and replicate in
different locations in the body, such as the respiratory tract and the urinary
bladder. There are over 50 subtypes of human Ad, with Ad serotype 5 (Ad5)
being the best characterized and most used in several vaccination trials.
9.4.17 Ad5 is a stable, non-replicating virus, characteristics that contribute to its safe
application. This virus allows the insertion of large segments of foreign DNA
(∼8 kb) into its genome and, in addition, it can be obtained in high titers and
easily purified. Replication-competent adenovirus vectors are also under
development as vaccine carriers for HIV.

9.4.18 The advantages of this type of adenoviruses vector are the lower doses
necessary for inducing immune responses and longer persistence in the host,
which may be associated with a more prolonged immune response. However,
contrary to the non-replicating type, replication-competent adenovirus vectors
present lower cloning capacity, limited to ∼3-4 kb. Noteworthy, both systems
elicit a potent and long-lasting immune response carrying the same gene
inserts

•Adenovirus Serotype 5 vaccine (July 2014 Expert Opinion on Drug Delivery 11(11):1-19

10. DNA Vaccines:
10.1 DNA vaccination is a technique for protecting an organism against disease by
injecting it with genetically engineered DNA to produce an immunological response.
Nucleic acid vaccines are still experimental, and have been applied to a number of
viral, bacterial and parasitic models of disease, as well as to several tumour models.
DNA vaccines have a number of advantages over conventional vaccines, including
the ability to induce a wider range of immune response types.
10.2 Vaccines are among the greatest achievements of modern medicine – in industrial
nations, they have eliminated naturally-occurring cases of smallpox, and nearly
eliminated polio, while other diseases, such as typhus, rotavirus, hepatitis A and B
and others are well controlled. Conventional vaccines, however, only cover a small
number of diseases, and infections that lack effective vaccines kill millions of people
every year, with AIDS, hepatitis C and malaria being particularly common.

10. DNA Vaccines:
10.3 The vaccine DNA is injected into the cells of the body, where the "inner machinery" of
the host cells "reads" the DNA and converts it into pathogenic proteins. Because
these proteins are recognised as foreign, they are processed by the host cells and
displayed on their surface, to alert the immune system, which then triggers a range
of immune responses. These DNA vaccines developed from “failed” gene therapy
experiments.
10.4 A DNA vaccine (or genetic vaccine as it is also called) consists of a plasmid
containing:
10.4.1 One origin of replication of Escherichia coli, for the amplification of the
plasmid
10.4.2 A strong promoter, generally from cytomegalovirus
10.4.3 Multiple Cloning Sites, in which one can insert the gene to be expressed
10.4.4 An antibiotic as selection marker

•Proposed mechanism of DNA vaccines (October 2009 Journal of Immune Based Therapies
and Vaccines 7(1):3

•Components of DNA Vaccines (October 2009 Journal of Immune Based Therapies and
Vaccines 7(1):3

10. DNA Vaccines:
10.5 The first demonstration of a plasmid-induced immune response was when mice
inoculated with a plasmid expressing human growth hormone elicited antibodies
instead of altering growth. Thus far, few experimental trials have evoked a response
sufficiently strong enough to protect against disease, and the usefulness of the
technique, while tantalizing, remains to be conclusively proven in human trials.
However, in June 2006 positive results were announced for a bird flu DNA vaccine
and a veterinary DNA vaccine to protect horses from West Nile virus has been
approved In August 2007, a preliminary study in DNA vaccination against multiple
sclerosis was reported as being effective.

10. DNA Vaccines:
10.6 Advantages and disadvantages of DNA vaccines:

10. DNA Vaccines:
10.7 DNA vaccines have been introduced into animal tissues by a number of different
methods. The two most popular approaches are injection of DNA in saline, using a
standard hypodermic needle, and gene gun delivery. A schematic outline of the
construction of a DNA vaccine plasmid and its subsequent delivery by these two
methods into a host is illustrated at Scientific American.

Construction of DNA Vaccines-DNA vaccine - Wikipedia

10. DNA Vaccines:
10.8 Injection in saline is normally conducted intramuscularly (IM) in skeletal muscle, or
intradermally (ID), with DNA being delivered to the extracellular spaces. This can be
assisted by electroporation by temporarily damaging muscle fibres with myotoxins
such as bupivacaine; or by using hypertonic solutions of saline or sucrose Immune
responses to this method of delivery can be affected by many factors, including
needle type, eedle alignment, speed of injection, volume of injection, muscle type,
and age, sex and physiological condition of the animal being injected.
10.9 Gene gun delivery, the other commonly used method of delivery, ballistically
accelerates plasmid DNA (pDNA) that has been adsorbed onto gold or tungsten
microparticles into the target cells, using compressed helium as an accelerant.

11. Vaccinia Vector Vaccines:
11.1 The most widely used virus for smallpox inoculation has been vaccinia, which
belongs to the genus Orthopoxvirus along with variola virus. Other species
of Orthopoxvirus include cowpox (the virus used by Jenner), monkeypox, and
camelpox, among others. Vaccinia is a double-stranded DNA virus with a wide host
range. Its origin is uncertain, and there are many strains of vaccinia with different
biological properties.
11.2 Vaccinia induces both cellular and humoral immunity to variola virus. The current
U.S. licensed smallpox vaccine (Dryvax, Wyeth Laboratories, Inc.) was prepared
from calf lymph using the New York City Board of Health (NYCBOH) strain of
vaccinia. Production of this vaccine was discontinued in 1982. The National
Pharmaceutical Stockpile also includes the Aventis Pasteur vaccine, which was also
manufactured from calf lymph. Multiple other strains of vaccinia have been used in
other regions the world.

•Vaccinia Virus-September 2004 Proceedings of the National Academy of Sciences 101(31):1117
92

Orthopox Virus (Poxviridae (stanford.edu)

11.3 Long-term research is underway using recombinant DNA technology to develop a
safer vaccine that will provide an effective immune response without replication of
vaccinia virus. Two companies are currently funded by the United States
government to develop and test a vaccine based on the modified Ankara strain of
vaccinia, which is nonreplicating in mammalian cells (Washington Post, February 26,
2003). In the short term, two new, unlicensed smallpox vaccines have been
developed by Acambis/Baxter Pharmaceuticals. Both use the NYCBOH strain of
vaccinia virus, but one is cultured from human embryonic lung cell culture and the
other uses African green monkey (vero) cells.
11.4 At this time it is not known if these vaccines will be more or less reactogenic than the
current calf-lymph derived vaccine. Clinical trials are underway. Until a new vaccine
is licensed by the U.S. Food and Drug Administration, existing doses of Dryvax can
be diluted 1:10 and still generate an adequate immune response if the number of
required vaccinations exceeds the number of doses in the national stockpile.

11.5 Effective smallpox vaccines have a vaccinia titer of approximately 108 pock-forming
units per mL, and more than 95% of individuals develop a ‘take’ with neutralizing
antibodies after primary vaccination. The efficacy of the vaccine has not been
evaluated in controlled studies, but epidemiologic data suggest that a high level of
protection persists for up to 5 years after vaccination, with partial immunity persisting
for 10 years or more. The vaccine will prevent infection or reduce the severity of
illness if given within a few days following exposure to smallpox.
11.6 There is typically an indurated area surrounding the central lesion. This is followed by
scab formation with development of a residual scar. The process of vesiculation and
pustule formation defines a ‘take’ of the vaccine. The take is considered equivocal if
a pustule, ulcer, or scab, does not develop at the vaccine site; revaccination is
recommended in this situation. Skin reactions following revaccination tend to be
milder and have an accelerated course.

Vaccines by Dr.Jayshree Nellore

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