Introduction Classification mRNA Vaccines Mechanism of action of mRNA-based vaccines Delivery systems mRNA vaccine Manufacturing Application Summary

1. Addis Ababa University
College of health science
School of Pharmacy
Department of Pharmaceutics and Social
pharmacy
Presented by : Zerlealem Tsegaye
Date: December, 2021
A Review on mRNA vaccines and
novel delivery approaches
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2. Presentation outline
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 Introduction
 Classification mRNA Vaccines
 Mechanism of action of mRNA-based
vaccines
 Delivery systems
 mRNA vaccine Manufacturing
 Application
 Summary

3. Introduction
 Vaccination with attenuated pathogens has
successfully decreased the burden of a number
of infectious diseases.
 Conventional vaccines comprised of attenuated
viruses take years to develop due to the time
required to collect and subsequently adapt
(attenuate) the virus in vitro.
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4. Introduction
 Traditionally, vaccine development is a complex
expensive, slow, laborious undertaking that
requires substantial investment
 Creating a new vaccine candidate using
established technologies is estimated to cost
>500 million USD, with additional expenses of 50
to 700 million USD required to retrofit
manufacturing facilities and equipment
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5. Introduction
 The average development of a conventional
vaccine from the preclinical phase requires >10
years and has a market entry probability of 6%.
 The long lead time and hundreds of potentially
complex steps required for manufacturing
highlight the urgent need for new approaches to
expedite vaccine development.
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6. Introduction
 Manufacturers desperately require new
technologies able to promote rapid vaccine
development and large scale production, reduce
the cost, shorten the time to licensure, and to
allow responding quickly to pandemic threats.
 Viral vector and nucleic acid-based vaccine
platforms created during the past few decades
promise to provide solutions to these vaccine
challenges.
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7. Classification mRNA Vaccines
 RNA vaccines can be divided into two types:
 conventional mRNA-based vaccines and
 self-amplifying mRNA vaccines (SAM),
 Both of which utilize the host cell translational
machinery to produce the antigen target and launch
an adaptive immune response.
 Conventional mRNA vaccines are conceptually similar
to host cell mRNA molecules and encode only the
antigen of interest.
 Self-amplifying mRNA vaccines are commonly based
on the engineered RNA genome of positive-sense
single-stranded RNA viruses, such as alphaviruses,
flaviviruses, and picornaviruses 3/3/2024
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8. Classification mRNA Vaccines
 The major advantages of the conventional mRNA
vaccine approach are the simplicity and relatively
small size of the RNA molecule.
 In the simplest form, the stability and activity of
the conventional mRNA in vivo is limited, because
of tendency of cells to limit duration of
expression.
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9. Mechanism of action of mRNA-
based vaccines
 The process of mRNA vaccine recognition by
cellular sensors and the mechanism of sensor
activation are still not clear.
 Intra-cellularly, two kinds of RNA sensors,
endosomal toll-like receptors (TLRs) and the
Retinoic acid-inducible gene I (RIG-I-like)
receptor family, have been identified.
 The former set is divided into TLR-3, TLR7, TLR8,
and TLR9, which are localized in the endosomal
compartment of professional immune surveillance
cells, such as DCs, macrophages and
monocytes. 3/3/2024
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10. Delivery systems
 To produce an antigen-specific immune response,
an mRNA vaccine must reach the cytosol of
recipient cells and express the antigen.
 Uptake and expression in vivo is in some cases
can be better than spontaneous uptake observed
in vitro and, often, comparable to cells transfected
in vitro under optimal conditions
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11. Delivery systems
 The bio-distribution and cellular uptake of mRNA
after administration are influenced by several
parameters
 Including the vascular system
 endothelial barriers
 molecule size
 Interactions between the molecule and host cell
receptors.
 RNA molecules are large, hydrophilic, and
negatively charged
 Diffusion across membranes is unfavorable
 Efficient delivery of RNA into the cytoplasm of
target cells requires a delivery system.
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12. Delivery systems
 The ideal vehicle should protect RNA from
ribonucleases present in the tissues, avoid entry
into off-target cells, and facilitate release into the
target cell cytoplasm.
 Several strategies have been evaluated for RNA
vaccine delivery, such as nanoparticles carriers.
 Particulate formulations have been shown to
protect mRNA from degradation leading to
enhanced cellular uptake, increase antigen
expression and vaccine potency
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13. Delivery systems
 Formulations can influence the quantity and
quality of local gene expression patterns, innate
immune stimulation, and can provide a synergistic
adjuvant effect.
 Approaches to nonviral delivery of mRNA have
included injection of naked mRNA, formulation
with liposomes, lipoplexes, polyplexes, particulate
carrier-mediated, electroporation, and gene gun.
 Cationic formulations effectively condense RNA
and can facilitate uptake by cells and delivery
across cellular membranes of cellular
compartments.
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14. Delivery vehicles for mRNA vaccines
 mRNA is large (104–106 Da) and negatively
charged,
 It cannot pass through the anionic lipid bilayer of
cell membranes.
 Inside the body, it is engulfed by cells of the
innate immune system and degraded by
nucleases.
 Various techniques, including electroporation,
gene guns and ex vivo transfection can
intracellularly deliver mRNA.
 In vivo application, however, requires the use of
mRNA delivery vehicles that transfect immune
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15. Lipid- based nanoparticles
 Lipid- based nanoparticles are the most clinically
advanced of the mRNA delivery vehicles.
 All SARSCoV-2 mRNA vaccines in development or
approved for clinical use as of June 2021 employ lipid
nanoparticles (LNPs)
 LNPs offer numerous benefits for mRNA delivery,
including ease of formulation, modularity,
biocompatibility and large mRNA payload capacity.
 LNPs typically include four components: an ionizable
lipid, cholesterol, a helper phospholipid and a
PEGylated lipid, which together encapsulate and
protect the fragile mRNA core.
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16. Polyplexes and polymeric
nanoparticles
 Although less clinically advanced than LNPs,
polymers offer similar advantages to lipids and
effectively deliver mRNA
 Cationic polymers condense nucleic acids into
complexes called polyplexes that have various
shapes and sizes and can be taken up into cells
by endocytosis.
 The mechanisms by which polyplexes escape
from endosomes are uncertain;
 one possible mechanism is that proton buffering by
the polymer leads to osmotic swelling and rupture of
the endosomes — the proton sponge hypothesis
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17. Polyplexes and polymeric
nanoparticles
 Polyethylenimine is the most widely studied polymer
for nucleic acid delivery.
 Although its efficacy is excellent, its application is limited
by its toxicity owing to its high charge density.
 Use of a low molecular weight form, incorporation of
PEG into the formulation, conjugation to cyclodextrin
and disulfide linkage can mitigate the toxicity of
polyethylenimine.
 Additionally, several alternative biodegradable
polymers have been developed that are less toxic.
 Poly(β- amino ester)s, for example, excel at mRNA
delivery, especially to the lung.
 Similar to poly(β- amino ester)s, poly(amidoamine)s
are biodegradable polymers.
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18. mRNA vaccine Manufacturing
 These can be grouped into the
 Upstream processing, which comprises the
enzymatic generation of mRNA.
 The downstream processing, which includes the
unit operations required to purify the mRNA product.
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19. mRNA vaccine Manufacturing
 The in vitro transcription (IVT) enzymatic reaction
used to generate mRNA relies on T7, SP6 or T3
RNA polymerases to catalyse the synthesis of the
target mRNA from the corresponding DNA
template.
 This template must be produced in advance,
usually by linearisation of a purified plasmid or by
amplification of the region of interest using PCR.
 Apart from the linear DNA template, the IVT
components must then include anRNA
polymerase, nucleotide triphosphates (NTPs)
substrates, the polymerase cofactor MgCl2, a pH
buffer containing polyamine and antioxidants.
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20. mRNA vaccine Manufacturing
 The reaction only takes a few hours incontrast
with the time-consuming processes used to
manufacture conventional vaccines.
 Furthermore, this reduced time lowers the
probability for contamination to occur.
 Milligrams of mRNA per milliliter of reaction can
be obtained
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21. mRNA vaccine Manufacturing
 Once the mRNA is generated by IVT, it must be
isolated and purified from the reaction mixture
using multiple purification steps to achieve clinical
purity standards.
 The reaction mixture contains not only the
desired product, but also a number of impurities,
which includes enzymes, residual NTPs and DNA
template, and aberrant mRNAs formed during the
IVT.
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22. mRNA vaccine Manufacturing
 Chromatography is a mainstream purification process
widely accepted in the pharmaceutical industry.
 Its high popularity is derived from several attributes such
as selectively, versatility, scalability and cost-effectiveness.
 The first published protocol for large scale purification of
synthetically produced RNA oligo nucleotides used size
exclusion chromatography.
 Further studies applying SEC with fast performance liquid
chromatography were performed.
 These techniques allowed a preparative scale purification
process, achieving high purity and high yields.
 However, SEC presents limitations, as it is not able to
remove similar size impurities, such as dsDNA.
 The use of ion pair reverse-phase chromatography (IPC)
proved to be an excellent method for mRNA purification
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23. Applications
mRNA Vaccines Targeting Allergies and Autoimmune Diseases
 The results of recent animal studies demonstrate
the potential use of RNA vaccines to prevent or
treat allergies and autoimmune diseases.
 Allergen-specific immunotherapy is an effective
treatment for type I hypersensitivity reactions.
 Prophylactic intervention in young children to
induce an immunological bias that prevents Th2
sensitization has been proposed to stop the
increase in patient numbers
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24. Application
mRNA Vaccines Targeting Cancer
 The majority of early work with mRNA vaccines
has focused on cancer.
 Clearly, conventional vaccine approaches are not
applicable to such non-infectious diseases.
 Cancer vaccines are therapeutic, rather than
prophylactic,
 Designed to target tumor-associated antigens
expressed preferentially by cancerous cells
 And, as a result, to stimulate cell-mediated
immune responses capable of reducing the tumor
burden.
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25. Application
mRNA Vaccines Targeting HIV Infection
 Several preclinical studies have delivered mRNA vaccines
encoding HIV proteins using multiple delivery vehicles,
including cationic nano-emulsions, DOTAP/DOPE
liposomes , polymers and ionizable LNPs , but they have
had varied success.
• 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE)
• 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP)
 A novel vaccination strategy against HIV is to isolate
broadly neutralizing mAbs from infected individuals who
neutralize several HIV strains.
 the broadly neutralizing mAbs, VRC01, have ability to
neutralize 98% of HIV strains and prevent transmission of
antibody- sensitive strains with 75.4% efficacy.
 In one study, a single 0.7 mg kg−1 intravenous injection of
a LNP- encapsulated, nucleoside- modified mRNA
expressing VRC01, produced similar antibody
concentrations to those typically achieved by injecting a
10–20 mg kg−1 dose of mAb protein. 3/3/2024
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26. Application
mRNA Vaccines Targeting SARS-CoV-2 infection
 As of December 29, 2020, there were 172vaccine
candidates under pre-clinical trials, and another
60vaccines were at least in phase I clinical trials
or above.
 Of the previous vaccines, a total of 7 (12%) that
are under clinical trials, and 22 (12.8%) from pre-
clinical trial settings are based on the RNA
platform technology.
 An LNP-formulated nucleoside-modified
conventional mRNA vaccine targeting Zika virus
has been recently moved into clinical
evaluation(ClinicalTrials.gov: NCT03014089).
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27. Application
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 mRNA Vaccines Targeting Zika Virus Infection
 mRNA Vaccines Targeting Rabies Virus Infection
 mRNA Vaccines Targeting Ebola virus
 mRNA Vaccines Targeting Bacterial and
Parasitical Infections

28. Summary
 RNA vaccines can be divided into two types: conventional mRNA-based vaccines
and self-amplifying mRNA vaccines,
 Both of which utilize the host cell translational machinery to produce the antigen
target and launch an adaptive immune response.
 mRNA vaccines produced in a simplified manufacturing process.
 It is produced by in vitro synthesis through an enzymatic process
 This contrasts with classical in vivo protein expression where time-consuming
cloning and amplification steps are needed.
 Because an in vitro synthesis process is used, there is no need to remove cells
or host cell proteins.
 Diffusion across membranes is thermodynamically unfavorable and efficient
delivery of RNA into the cytoplasm of target cells requires a delivery system.
 The ideal vehicle should protect RNA from ribonucleases present in the
tissues, avoid entry into off-target cells, and facilitate release into the target
cell cytoplasm.
 mRNA-based vaccines are a promising novel platform with the potential to
be highly potent and scalable. Importantly, mRNA-based vaccines may fill
the gap between emerging pandemic infectious diseases and a rapid,
abundant supply of effective vaccines.
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29. Acknowledgments
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 I would like to express my gratitude to my advisor
Dr. Anteneh Belete and Dr. Gebremariam
Birhanu for providing invaluable guidance,
comments and suggestions.
 I also thank and the department for giving an
opportunity to learn and present the seminar.

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Thank You