Adenovirus Vector Vaccines Against COVID-19: Production and Mechanism of Action
Johnson & Johnson
Adenovirus type 26 (Ad26), a mild human adenovirus, is isolated
Previous exposure to Ad5 or Ad26 may have sensitized immune system to the adenovirus vector1
Potential for human adenovirus vaccine to fail due to previous exposureàimmunity not built against spike protein
CanSino
Adenovirus type 5 (Ad5), a mild human adenovirus, is isolated
Oxford/AstraZeneca
Chimpanzee adenovirus AZD1222 (ChAdOx1), previously shown to be safe & to elicit an immune response in humans2, is isolated
Vaccine Production
SARS-CoV-2 (virus causing COVID-19) synthetic DNA library sequenced from viral RNA using reverse transcriptase polymerase chain reaction and whole genome sequencing technology
Spike protein DNA sequence isolated from SARS-CoV-2 genome
A promoter sequence is added to the spike protein DNA sequence, allowing human RNA polymerase to recognize and transcribe the spike protein DNA when introduced into human cells
Recombinant genetic technology inserts the modified spike protein DNA into a plasmid: a circular piece of DNA that acts as a shuttle allowing for the insertion of new genes (such as the spike protein gene) into host genomes (like the adenovirus vector DNA genome)
Adenoviral DNA isolated using various lytic & washing reagents (chemicals that break open cell membranes and remove non- nucleic acid cellular materials)
Adenoviral DNA sequenced using whole genome sequencing, then modified as follows:
Chimpanzee virus negates possibility of previous immunity to the viral vector1
Chimpanzee viral vector more likely to successfully
generate immune response to the spike protein
E1 region of adenoviral genome E3 region of adenoviral genome deleted to create deleted to block viral replication3 room for insertion of SARS-CoV-2 spike protein DNA3
Adenovirus used in the final vaccine cannot replicate
within human cells and cannot cause human disease
References
1. ACS Nano 2020, 14, 10, 12522–12537, Publication Date: October 9, 2020, https://doi.org/10.1021/acsnano.0c07197
Modified adenoviral DNA genome is reinserted into The viral vector & the spike protein plasmid are mixed together, and DNA recombination
the adenovirus particle, creating the “viral vector”
technology inserts the spike protein gene from the plasmid into the adenovirus DNA2
Adenovirus containing transcribable SARS-CoV-2 spike protein DNA is introduced into a special cellular culture, allowing the virus to replicate despite its modified DNA2, 3
Authors: Ryan Brenneis, Yan Yu* Reviewers: Davis MacLean, Hannah Yaphe Stephen Vaughan* * MD at time of publication
2. Nature 2020, 586, 578–582, Publication Date: October 20, 2020, https://doi.org/10.1038/s41586- 020-2608-y
3. Frontiers in Immunology 2018, 9, 1963, Publication Date: September 19, 2018, doi: 10.3389/fimmu.2018.01963
4. NPJ Vaccines 2020, 5, 69, Publication Date: July 27, 2020, doi: 10.1038/s41541-020-00221-3
5. The Lancet 2020, Publication Date: Dec. 8, 2020, https://doi.org/10.1016/S0140-6736(20)32623-4
6. BMJ 2000, 321, 7271, 1237-1238, Publication Date: November 18, 2000,
DOI: 10.1136.bmj.321.7271.1237
7. NEJM 2021, Publication Date: Jan. 13, 2021, DOI: 10.1056/NEJMoa2034201
Adenovirus containing transcribable SARS-CoV-2 spike protein DNA is isolated and concentrated to a high enough level for administration as a vaccine
Adenoviruses have an outer protein layer (called a capsid) to protect its DNA
DNA is more stable than mRNA due to deoxyribose sugar backbone and intermolecular bonds between strands
Enhanced stability compared to mRNA lipid nanoparticle vaccines
Can be stored at 2-8°C for up to 3-6 months
Muscles are preferred injection sites as they have greater blood supply than other body tissues
Immune cells arrive faster to The viral vector vaccine is injected intramuscularly into a healthy person process foreign antigens6
Foreign substance can cause local tissue inflammation
Pain, redness, swelling at injection site (Transient)
Note: The Johnson and Johnson vaccine may be 90% effective after a single dose7
Foreign vaccine material drains away fasterà minimizing local reactions6
2nd dose after 28 days recommended to strengthen the immune response (to a level exceeding the immune response in patients recovered from Covid-19), boosting vaccine efficacy especially in older individuals5
Vaccine Action
Cell-mediated Immunity
Spike protein degraded by intracellular enzymes into fragments
Adenovirus surface antigens interact with human cellular receptors, allowing viral entry into human cell via endocytosis3 Adenovirus vector travels to cell nucleus, merges with nuclear envelope and injects its DNA (including the spike protein DNA) into the nucleus
RNA polymerases in the nucleus transcribe the viral DNA, making messenger RNA (mRNA) for SARS-CoV-2 spike protein
mRNA is transported back into the cytosol & translated by ribosomes naturally found there, producing full length SARS-CoV-2 spike protein
Humoral Immunity
Natural cellular processes release spike protein components from the cell into the bloodstream
Spike protein components are engulfed by antigen presenting cells (dendritic cells, B cells, macrophages), fragmented, & bound to unique MHC Class II proteins
MHC Class II proteins bring spike protein fragments to the antigen presenting cell’s surface, to present them to circulating naïve CD4+ (helper) T cells
Some naïve helper T cells are able to successfully bind to the spike protein-MHC Class II protein complexes
Binding activates these spike-protein specific helper T cells
Spike protein fragments are bound by MHC Class I proteins
MHC Class I proteins bring spike protein fragments to the human cell surface MHC Class I proteins present spike protein fragments to naïve CD8+ T cell
Naïve CD8+ T cells that able to bind to the spike protein-MHC Class I protein complex become activated, and travel to the lymphatic system to mature3
MHC = Major Histocompatability Complex; cell surface proteins key to immune function
CD = Cluster of Differentiation; glycoproteins on T cell surfaces that are co-receptors and facilitate T cell binding to antigens/MHC complexes. They also distinguish the types of T cells.
Some of these T cells mature into cytotoxic T cells that now recognize the SARS-CoV-2 spike spike protein
Cytotoxic T cells bind to human cells expressing spike protein or spike protein fragments (e.g. future COVID-19 infection)
Cytotoxic T cells release enzymes perforating infected human cells, causing cell death to occur
Immune system can now more quickly identify & destroy human cells showing signs of COVID-19 infection
Some T cell’s can mature into memory T cells (stimulated by cytokines released by helper T cells)
Memory T cells travel to lymphatic tissue, awaiting activation from exposure to spike protein in the future
More rapid cell-mediated immune response to
future SARS-CoV-2 infection (immunity)
Activated helper T cells specific to the viral spike protein secrete cytokines to stimulate immune activity
Systemic cytokine releaseàsystemic reactions like fever, chills, fatigue, myalgias (Transient)
Note: Duration of cellular/ humoral immunity is unknown
Some B cells mature into plasma cells that produce IgG antibodies against the viral spike protein
Antibodies to spike protein mark SARS-CoV-2, allowing immune system to destroy virus
Eradication of SARS-CoV-2 in extracellular compartments
Activated helper T cell interacts with naïve B cells in lymphatic tissue
Some B cells mature into memory B cells specific to SARS-CoV- 2 spike protein
Future exposure to spike protein re-activates memory B cell in lymphatic tissue & creates plasma cells, producing antibodies more rapidly
Rapid humoral immune response to future SARS-CoV-2 infection (immunity)3
Legend:
Pathophysiology
Mechanism
Sign/Symptom/Clinical Finding
End result
Published February 11, 2021 on www.thecalgaryguide.com