genome editing

1. HUMAN GENOME EDITING
DR Murali L Vydya
ASSOCIATE PROFESSOR
DEPARTMENT OF COMMUNITY MEDICINE
KAKATIYA MEDICAL COLLEGE, HANAMKONDA.
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2. Contents
• What is HGE?
• Genome editing methods
• CRISPR Cas 9
• Research in animals
• Gene therapy in humans
• Ethical concern
• Limitations
• Current status
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3. What is Genome editing?
• Genome editing is a method that
lets scientists change the DNA of
many organisms.
• Editing DNA can lead to changes in
• physical traits
• eye color
• Athletic ability
• disease risk.
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4. Why HGE?
• Alteration of DNA started even in
1970s.
• To treat human genetic diseases
like
• Cancer
• Sickle cell anaemia
• Cystic fibrosis
• Blindness
• Deafness etc.,.
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5. What is happening?
• Scientists use different technologies to
do this.
• These technologies act like scissors,
cutting the DNA at a specific spot.
• Then scientists can remove, add, or
replace the DNA where it was cut.
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6. Genome Editing Methods
Four different types of genome editing methods are
1. Homologous recombination technology
2. Zinc finger nucleases
3. TALEN
4. CRISPR
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7. Homologous recombination technology
• Discovered in 1970s.
• It is the exchange of genetic information between two similar
(homologous) strands of DNA.
• Generate and isolate DNA fragments with sequences similar to the
portion of the genome that is to be edited.
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8. • These fragments can be injected into individual cells.
• Once inside a cell, these DNA fragments can then recombine with the
cell's DNA to replace the targeted portion of the genome.
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9. HRT
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10. Disadvantages of HRT
• It is extremely inefficient in most cell types.
• As low as a one-in-a-million probability of successful editing.
• It is inaccurate.
• It has a high rate of error when the injected DNA fragments insert
into an unintended part of the genome, causing what are known as
off-target edits.
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11. Zinc finger nucleases - 1990
• To improve the specificity of genome editing and reduce off-target
edits.
• The structures of ZFNs are engineered from naturally
occurring proteins that were discovered in eukaryotic organisms.
• Scientists can engineer these proteins.
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12. • Introduced into the targets.
• The ZFNs cut the genome, allowing scientists to either delete the
target DNA sequence or replace it with a new DNA sequence via
homologous recombination.
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13. Advantages and disadvantages
• The success rate of genome editing to about 10 percent.
• But it is
• Difficult
• Time-consuming to design, construct, and produce successful zinc finger
proteins
• A new ZFN must be engineered for each new target DNA sequence.
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14. TALENs
• Discovered in 2009.
• A new class of proteins called Transcription Activator-Like Effector
Nucleases (TALENs) arrived to the genome editing scene.
• Everything is similar to ZFN.
• It bear the advantage of greater simplicity.
• It is much easier to engineer TALENs than it is to synthesize ZFNs.
• Both are expensive and difficult to synthesize to proteins.
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15. CRISPR
• Clustered Regularly Interspaced Palindromic Repeats.
• Unique technology that enables researchers to edit parts of
the genome by removing, adding or altering sections of
the DNA sequence.
• Now gene editing is cheaper and inexpensive because of this.
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16. • It is a family of DNA sequences found in the prokaryotic organisms
such as bacteria.
• The CRISPR – Cas 9 system consists of two key molecules. They are
• Cas 9 associated protein
• Guide RNA
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17. Cas 9
• Cas9 also known as "CRISPR-associated protein 9”.
• It is an enzyme that uses guide RNA to recognize and cleave specific strands
of DNA that are complementary to the CRISPR sequence.
• Cas9 with CRISPR form the basis of a technology known as CRISPR-
Cas9 that can be used to edit genes within organisms.
• Nobel Prize in Chemistry in 2020 which was awarded to Emmanuelle
Charpentier and Jennifer Doudna.
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18. 18

19. CRISPR
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20. Limitations of CRISPR cas9
• CRISPR sometimes mis-recognizes a DNA sequence that is similar to
the one it’s looking for and cuts in the wrong place, causing “off-
target mutations.”
• Other times it might cut in the right place, but cause mistakes where
DNA is incorrectly inserted or deleted.
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21. Research in animals
• Scientists edit the genome of
animals like
• Mice
• Zebra fish
• They can observe how these
changes affect the animals health
and predict how similar changes
can be seen in humans.
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22. Burgess lab - NHGRI
• Scientist at the National Human
Genome Research Institute are doing
the research in Zebrafish genomes.
• Deleting different genes in zebrafish
to see how the deletion impacts the
fish.
• These genes are similar to human
deafness genes.
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23. Gene therapies
• Scientists are developing gene therapies - treatments involving
genome editing - to prevent and treat diseases in humans.
• HGE tools have been used to treat diseases with genomic basis.
• There are two categories for gene therapies.
• Germ line therapy
• Somatic therapy
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24. Two types of gene therapies
• Germline therapies - Change DNA in reproductive cells like sperm and eggs.
• Changes to the DNA of reproductive cells are passed down from generation
to generation.
• Somatic therapies - Target non-reproductive cells.
• Changes made in these cells affect only the person who receives the gene
therapy.
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25. HGE in humans
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26. Study in Layla.
• Somatic gene therapy done in 2015 in UK for a one year old kid
named Layla to fight against acute lymphoblastic leukaemia.
• Here cancerous stem cells releases vast number of immature immune
cells into the blood.
• Usual treatment for this is chemotherapy and bone marrow
transplant.
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27. • But both failed in case of Layla.
• The basic idea is
• Remove immune cells from a patient’s body,
• Genetically engineer them to attack cancerous cells
• Place them back in the body.
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28. • Adding a gene for a receptor called CAR19, which sits on the outside
of the T-cells.
• This programs the T-cells to seek out and kill any cells with a protein
called CD19 on their surface – which is found on the cells that cause
ALL.
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29. • She didn’t have enough T cells left out.
• In a process of donating T cells from a healthy donor to Layla.
• Chance of donor recipient reaction.
• Gene editing done to disable a gene in the donor T cells.
• Editing a T cell receptor that recognizes other cells as foreign.
• T cells are made invisible.
• UCART 19 T cells were introduced into Layla.
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30. • Three months later again second bone marrow transplant have been done.
• These healthy immune cells recognised the UCART19 cells as foreign and
destroyed them.
• Layla no longer has any genetically modified cells in her body.
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31. Healthy as of now..
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32. Lulu and Nana
• In 2018, Hi Jiankui from China
announced the birth of twin girls
(first gene edited babies) named
Lulu and Nana.
• It was achieved using the sperm of
a man known as Mark who is an
HIV carrier.
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33. • The purpose is medical alteration and resistance to disease, namely,
the HIV/AIDS virus.
• He had edited the DNA of two embryos and used them to start a
pregnancy.
• The babies were born prematurely and their current health status
is unknown.
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34. Ethical Concerns
• Is it okay to use gene therapy on an embryo when it is impossible to
get permission from the embryo for treatment?
• Is getting permission from the parents enough?
• What if gene therapies are too expensive and only wealthy people
can access and afford them?
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35. • That could worsen existing health inequalities between the rich and
poor.
• Will some people use genome editing for traits not important for
health, such as athletic ability or height? Is that okay?
• Should scientists ever be able to edit germline cells?
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36. • Edits in the germline would be passed down through generations.
• Nearly 40 countries and organizations have strict regulations to
prevent germline editing for this reason.
• The NIH, for example, does not fund research to edit human embryos.
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37. Limitations
• The risk of off-target edits, or unintended edits, and their effects are
still unknown.
• Mosaicism may be present.
• That there is still much to learn about which genes are involved in
which diseases.
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38. • What changes in these genes are happening in getting a disease?.
• Many genes have more than one function, and in some cases editing
a gene to "cure" one disease could create another.
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39. What is happening in HGE right now?
• The National Academies of Sciences, Engineering, and Medicine
(NASEM) launched an initiative in Dec 2015 to facilitate decision
making for the responsible use of human gene-editing research.
• This initiative examined the clinical, ethical, legal and social
implications of human gene editing.
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40. • Their efforts included an international summit, and public
meetings to hear from different groups including patients,
community leaders and policy makers.
• The summit lasted three days.
• On February 14, 2017, the committee published a report of their
study findings, Human Genome Editing: Science, Ethics, and
Governance.
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41. • The report concluded that while current regulations are sufficient to
the use of genome editing in somatic therapy trials, there are still
safety, technical, and ethical issues barring the wide application of
this technology in germline therapy trials.
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42. Who decides?
• Human germline editing is not just a scientific or technical issue.
• It affects what kind of future we want to build.
• It has implications for society as a whole, not just individuals.
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43. • Decisions about whether to permit germline modification should not
be made by small groups of scientists or bioethicists, by
biotechnology companies, or by wealthy elites.
• Human germline editing we need public discussions of it that are
open to all.
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44. Summary
• Genome editing is a method that lets the scientists change the DNA
of any organism.
• Can be used to treat human genetic diseases.
• CRISPR Cas 9 technique was used for HGE.
• Research are still going on all over world regarding HGE.
• Ethical issues are more, not accepted in many countries.
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45. References
• Gene therapy: https://www.newscientist.com/article/dn28454-gene-
editing-saves-life-of-girl-dying-from-leukaemia-in-world-
first/#ixzz7UFIKGXV1
• https://en.wikipedia.org/wiki/CRISPR
• CRISPR cas https://www.yourgenome.org/facts/what-is-crispr-
cas9#:~:text=CRISPR-
Cas9%20is%20a%20genome%20editing%20tool%20that%20is,wide%
20range%20of%20potential%20applications.%20What%20is%20CRIS
PR-Cas9%3F
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