Gene Drive Organisms: A new dimension of genetic engineering - Applications, risks and regulation
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Gene Drive Organisms: A new dimension of genetic engineering Applications, risks and regulation
CONTENT 04
Gene drive regulation 29
01 Regulation of gene drive organisms in Germany
Genetic Engineering Safety Ordinance: safety standards for gene drive research
Positioning of the German Bundesrat
30
30
31
Positioning of the German federal states 31
What are gene drive organisms? 03 Positioning of the German Federal Ministry for the Environment 31
‘Selfish’ reproduction 04 Process in the German Parliament 31
CRISPR/Cas9 makes it possible 05 Positioning of the German parties 32
Research project on risk assessment & monitoring of gene drive organisms on behalf of
the German Federal Agency for Nature Conservation (BfN) 32
Regulation of gene drive organisms at EU level 32
02 The European legislation on genetic engineering
Legal interpretation of the EU Directive 2001/18 with regard to gene drive organisms
Risk assessment by the European Food Safety Authority (EFSA)
33
33
34
Recommendation: Strengthen the precautionary principle in the risk assessment of
Potential applications of gene drive organisms 09 genetically modified organisms in the EU through exclusion criteria 35
Gene drives for the elimination of disease carriers 10 Regulation of gene drive organisms at the international level 37
Malaria 10 Discussions about gene drive organisms in the UN Convention on Biological Diversity (CBD) 37
Lyme disease 11 Provisions on gene drive organisms under the Cartagena Protocol 38
Using gene drives to combat invasive species 13 Provisions on gene drive organisms under the Nagoya-Kuala Lumpur Supplementary
The discussion on gene drives in the International Union for Conservation of Nature (IUCN) 13 Protocol on Liability and Redress to the Cartagena Protocol 39
Gene drives in agriculture 14 Regulations of the World Health Organization (WHO) 39
Patent applications for agricultural applications 14 Provisions of the UN Biological Weapons Convention (BWC) 39
Examples of gene drive applications in agriculture 17
Spotted wing drosophila 17
Psyllids 17
The New World screwworm fly
Open questions regarding applications in plants
Gene drive organisms as bioweapons
17
21
21
05
Policy recommendations 42
A global moratorium on the release of gene drive organisms 43
03 Requirements for retrievability and controllability of gene drive organisms
A global process for decision-making on the release of gene drive organisms
An integrated system of assessment, evaluation and management of risks from
44
44
gene drive organisms to the environment and health 44
Ecological risks 23 Concepts of international inclusive technology assessments for gene drive organisms 44
Uncontrollability 24 Binding and specific global rules for liability and redress for damage caused by
Irreversibility 26 gene drive organisms 45
Outcrossing across species boundaries 26 Mandatory global reporting of gene drive organism research in contained systems and
Unexpected effects of CRISPR/Cas9 27 uniform safety standards for gene drive research 45
Resistances 27 A ban on the development of gene drive organisms with potential for military use 45
Unpredictable impacts on ecosystems 27
List of abbreviations 46
List of references 47
Imprint 57Enabled by new genetic engineering techniques
such as CRISPR/Cas9, so-called gene drives have
been developed in recent years that enable humans
to spread new genes throughout the genome of wild
01 animal populations. Gene drives force the inheritance
of newly introduced genes to be inherited by all
What are gene offspring, even if this lowers the survival chances
of the affected species. In the most extreme case,
gene drive technology could drive an entire species
drive organisms? to extinction or replace wild populations with
genetically modified organisms. 4
‘Selfish’ reproduction
In nature, the process of evolution is slow: It takes these genetic elements: Some gave rise to important
many generations before inherited changes take hold. functional, usually regulatory, units. In many other
In sexual reproduction, genetic material recombines cases, mechanisms have been developed to silence
in each generation. New traits are in constant the ‘jumping genes’ in the genome (for more
competition with older ones. However, only one of information, see infobox).
the two is passed on to the offspring. Which one is
determined by chance. According to Mendel‘s rules, Gene drives are based on a similar principle. In 2003,
the probability that a new trait will be passed on to the British researcher Austin Burt formulated the idea that
offspring is 50 percent. As a rule, a higher inheritance genes can spread rapidly if they over-write competing
rate only occurs if the traits are associated with variants. The natural evolutionary process then no
advantages for the survival of the species. longer applies.1
However, not all natural genetic traits follow these
What are gene drive organisms?
Mendelian rules of inheritance. In plants, animals
and humans, there are genetic elements that copy
themselves into other parts of the genome with the With gene drives humans can
help of enzymes, spreading independently and thus
increasing the frequency of their inheritance. They are alter the genetic makeup of
often referred to as naturally occurring gene drives
and have been termed ‘selfish‘ genes because they wild organisms and spread
can spread throughout the genome without benefiting
the species. Examples are so-called ‘jumping genes’ new characteristics that
(transposons). In the course of evolution, plants,
animals and humans have found a way to deal with serve human purposes alone.CRISPR/Cas9 makes it possible Difference between ‘selfish‘ gene variants, The new dimension: The difference between Until now, all experiments with genetically engineered
‘natural‘ gene drives and engineered genetically modified organisms and genetically gene drives have taken place exclusively in the
The realization of Burt‘s idea of repurposing ‘selfish‘ gene drives modified gene drive organisms laboratory or in closed containers. But gene drives
genetic elements for human purposes failed for a are actually intended for use in the wild. They are
long time due to technical hurdles. That changed So-called ‘selfish‘ genetic elements are found in the genome of For several years, release experiments with genetically designed to introduce new genes into the genome of
in 2012, when Jennifer Doudna and Emanuelle almost all living beings. Their reproduction seems to be of no engineered insects have been taking place in the environment wild populations, even if these reduce the chances of
Charpentier, now both Nobel laureates, recogni- consequence in the short term. However, they play an important for research purposes. For example, since 2011, the company survival of the species concerned. 16
zed the potential of the CRISPR/Cas9 system for role within longer periods of evolution. They contribute to Oxitec in Brazil has repeatedly released genetically.
biotechnology.2 In bacteria, it can serve as a kind of the emergence of new gene variants and may well facilitate modified mosquitoes of the species Aedes aegypti. Their The goal of their use in the wild may be to replace
immune system to provide protection against viru- adaptation to changing environmental conditions. Numerous genetic modification was intended to render the offspring the entire wild population with genetically modified
ses: The CRISPR sequence in the bacteria‘s genome protective mechanisms limit the uncontrolled multiplication of the mosquitoes unable to reproduce.13 The goal of these gene drive organisms or to greatly reduce it. In the
recognizes the invader and activates enzymes that of these elements in the genome and limit the damage to the releases was to significantly reduce the tropical disease- most extreme case, deployment could drive the entire
attack the virus and cut up its genome. living being. carrying mosquito population. Whether the goal was achieved species to extinction.
is debatable.14 In any case, none of the past releases involved
These two researchers were the first to realize that Transposons are among the most common ‘selfish‘ elements.7 insects that inherit gene drives.
the combination of CRISPR sequences and Cas9 They essentially consist of an enzyme that makes copies of
could be used to specifically alter the genome of the transposon and inserts them elsewhere in the genome. But what is the difference between genetically modified First field trials with gene drive
many living organisms and introduce new segments This is where the term ‘jumping genes‘ comes from. They were organisms (GMO) and genetically modified organisms that
into their DNA. It was the missing tool needed to originally discovered by Barbara McClintock, who was awarded inherit a gene drive, making them a gene drive organism (GDO)? mosquitoes could be carried out
turn Burt‘s idea into reality.3 In 2015, a functional the Nobel Prize in 1983.
5 CRISPR/Cas9 gene drive in fruit flies was published The new dimension of genetically modifying wild populations in Burkina Faso as early as 2024.17 6
for the first time.4 In the years that followed, trials In bacteria, a particular variant of ‘selfish‘ elements called with gene drives is in stark contrast to the previous goals,
in mosquitoes5 and mice6 were also successful. homing endonucleases has been discovered.8 They, too, consist strategies, and possibilities of genetic engineering. This would be an experiment
Researchers now suspect that almost any animal of only a single enzyme and can insert themselves precisely
species could be manipulated with a gene drive. into specific DNA sequences. Synthetic homing gene drives Until now, genetically modified organisms have not been without any safeguards:
based on CRISPR/Cas9 have been designed along these lines. expected to produce viable offspring, have not been
expected to survive in the wild for long, in the wild, or have mechanisms that effectively
Engineered gene drives, on the other hand, are artificial been prevented from mating with wild conspecifics. Thus, so
genetic elements that come with specific human-determined far, the spread of GMO should have remained limited in space control a gene drive in nature
purposes and functions. They have not evolved and adapted or time outside of their point of origin in the laboratory. Neither
through evolutionary processes. They are designed to serve these genetically modified organisms nor their modified genes only exist in theory.
human interests. Evolutionarily established mechanisms that were supposed to persist in nature.
control the spread of ‘jumping genes‘ are often ineffective
here. Engineered or synthetic gene drives thus set in motion The gene drive approach breaks radically with these
a ‘mutagenic chain reaction‘9, the consequences of which considerations. In contrast to conventional GMO, genetically According to the current state of science, the
cannot be controlled. modified organisms that inherit gene drives aim to spread outcome of the experiment would no longer be
genes synthesized in the laboratory into wild populations or to controllable by humans. All manipulations of this
Some publications refer to Wolbachia bacteria as ‘natural‘ gene eliminate natural genes. And they do so even if this harms the kind on animals, plants and entire ecosystems
drives. This is not quite correct: Wolbachia is a bacterial infection species or offers it no survival advantage, which is why these would be irreversible.
of insects that is heritable over generations.10 Wolbachia genes would not prevail on the basis of natural selection.
bacteria occur naturally in the cells of certain insects, such as
fruit flies. They reduce the reproductive capacity of infected Gene drives shift the locus of genetic modification from the
insects. Therefore, with the hope of combating dengue fever, genetic engineering laboratory to the wild: In the case
mosquitoes of the species Aedes aegypti were infected with of CRISPR/Cas9-based homing gene drives, the genetic
Wolbachia bacteria in the laboratory. It was found that certain engineering mechanism (CRISPR/Cas9) copies itself into the
What are gene drive organisms?
Wolbachia bacteria can block the transmission of dengue fever genome of wild offspring every time a GDO reproduces - over
to humans.11 Field trials with Wolbachia infected mosquitoes generations. The ‘forced‘ inheritance of even harmful genes
first took place in 2011 for testing purposes in Australia.12 Unlike triggered by the gene drive sets in motion a theoretically
synthetic gene drives, this approach does not use genetic unstoppable ”mutagenic chain reaction”15.
engineering. This means that the risks of genetic side effects
associated with genetic engineering through cross-breeding Thus, via gene drives, human-induced genetic modifications
and interaction with wild populations are not relevant in can spread faster through wild populations much faster than
Wolbachia interventions. conventional GMO, based on natural selection mechanisms,
could have done.16How does a homing gene drive with
CRISPR /Cas9 work?
Natural inheritance Forced inheritance How does a CRISPR/Cas based or
with gene drives homing gene drive work?
Normal Mouse with Mouse with Normal
mouse gene drive gene drive mouse So-called homing gene drives based on CRISPR/Cas9
are the most common variant of synthetic gene drives.
Such a gene drive consists of at least two components:
the Cas9 genetic ‘scissors’ and a messenger molecule.
In addition, a new or modified gene can be introduced.
50% chance to inherit The gene drive is first introduced into the genome of the
1. CRISPR identifies
the mutation target organism, e.g. a mouse, in the laboratory. This gene
the target sequence.
drive becomes active after fertilization of the egg cell
and identifies a target sequence in the non-manipulated
CRISPR chromosome with the help of the messenger molecule.
Cas9 There, Cas9 induces a double-strand break. Natural repair
Gene Drive mechanisms in the damaged cell then attempt to repair the
possibly break using a template. The gene drive on the genetically
additionally NEW
modified chromosome serves as a template: it is very likely
introduced to be copied completely and incorporated within the target
new gene sequence on the previously unmanipulated chromosome.
This targeted process is called homing. In addition to the
integration of the gene ‘scissors‘ at the target site, existing
gene sequences can be switched off and/or new one can
2. Cas9 creates a double be additionally inserted. This process ultimately results in all
strand break at the target offspring inheriting a copy of the gene drive. The gene drive
Inheritance with gene drive sequence. mechanism is re-activated with each reproduction - and in
all subsequent generations. It theoretically only comes to
NEW
a halt when the target sequence has disappeared from the
entire population.
Normal Mouse with
mouse gene drive
during
germ cell
development 3. With high likelihood the
cell‘s own repair mechanism
up to 100% forced copies the gene drive into the
inheritance site of fracture on the opposi-
NEW NEW
te chromosome.
4. Almost all germ cells carry
the gene drive (here e.g.
sperm cells).Gene drives could be applied in numerous fields.
Currently, research is focused on three areas: the
control of disease vectors, the removal of invasive
species from sensitive ecosystems, and the control
02 of so-called pests in agriculture.
Potential applications
of gene drive GENE DRIVES FOR THE
10
organisms
political will, a functioning health system, good training
of medical personnel, national programs for education
ELIMINATION OF DISEASE and prevention activities, medical surveillance
programs, rapid and correct diagnosis and treatment,
CARRIERS and rapid responses to outbreaks that do occur. 20
But there remain 87 countries where such measures
have not been adequately implemented. In 2017, more
Infectious diseases such as malaria, dengue fever than 200 million people contracted malaria, and more
and Lyme disease are transmitted to humans by than 400,000 people died from it. Sub-Saharan Africa
mosquitoes or ticks. Controlling these vectors has is the hardest hit, with mortality particularly high
long been part of disease prevention. Gene drives are among children under five.21 Gene Drives are intended
expected to take these efforts to a new level. to remedy this situation by massively reducing the
number of Anopheles mosquitoes in Africa and thus
also the transmission
of malaria.
Malaria
Target Malaria, an international research
The malaria pathogen is spread by several species of consortium, is playing a leading role in the
Anopheles mosquitoes. A concerted global program of development of such gene drives. The consortium
Potential applications of gene drive organisms
malaria control using mosquito nets, insecticides and has a budget of around 100 million U.S. dollars,
medicines has helped push back the disease in many most of which comes from the Bill & Melinda Gates
regions of the world, reducing deaths by about half Foundation and the Open Philanthropy Project.22 23
between 2000 and 2015.18 In 2016, the World Health
Organization (WHO) identified 21 countries with the Target Malaria‘s plans have already reached the stage
potential to reach the goal of zero indigenous malaria where the first model projects have been launched in
cases by 2020. Burkina Faso, Mali, Ghana and Uganda.
In the process, 39 countries have already been To control mosquito populations, Target Malaria is
certified as malaria-free, most recently Sri Lanka taking two different approaches:
(2016), Paraguay (2018), Algeria (2019) and El Salvador
(2021).19 China, Malaysia and Iran are also well on their One aims to create sterile female Anopheles
way to achieving the three-year malaria-free status mosquitoes by altering a gene called Doublesex. A
required for certification. Other factors for successful CRISPR/Cas9 gene drive will be used to spread this
control of the disease include, above all, strong genetic modification into the wild population. In2018, experiments in large cages showed that this Lyme disease
approach works in principle: The gene drive caused the
population to collapse after about ten generations.24 In temperate climates, the use of gene drives against How does a gene drive with X-Shredder work?
Lyme disease is being considered. In the U.S., Lyme
Target Malaria‘s second approach involves disease spread rapidly in 2018, affecting about Genetically modified mosquitoes that carry an X-shredder are supposed to only produce
manipulating the sex distribution of mosquitoes so 300,000 people annually.34 For Germany, according male offspring.
that only male mosquitoes are born. This approach to a projection from 2017, the number of new cases is
is being tested in a project in Burkina Faso in three estimated at about 100 000 per year.35 During the formation of the mosquito germ cells, an enzyme is produced that cuts the X
different phases, in which a gene drive will only be chromosomes and thus destroys them. Therefore, only male germ cells that pass on a Y
used in the third phase. The disease is triggered by Borrelia bacteria, which chromosome are produced. Up to 95 percent of the offspring are therefore male and can
often infect wild mice and are transmitted to humans spread the X-shredder in the population.37
In the first phase, male mosquitoes were rendered by ticks. If the infection is not detected in time, a
unable to reproduce using genetic engineering.25 Field chronic disease can develop that is difficult to treat. X-Shredder variant 1 - No gene drive – If the X-Shredder is inserted on a chromosome that
trials with these sterile mosquitoes were conducted does not determine the sex, it is inherited according to Mendelian rules and probably cannot be
in Burkina Faso in 2019.26 According to Target Malaria, On two islands in the northeastern United States, a found in the genetic material of the population after a few generations.
these preliminary trials are aimed at gaining field project was launched in 2016 that aims to interrupt the
experience and familiarizing the population in Burkina transmission of the disease with the help of genetic X-Shredder variant 2 - gene drive – The X-Shredder only becomes a gene drive when it is
Faso with such trials. Although Target Malaria claims engineering. The target of the genetic manipulation is inserted on the male Y chromosome. In theory, it could then spread through the population as
to have involved the local population in the decision- not the ticks as carriers, but the native white-footed aggressively as a CRISPR/Cas-based homing gene drive. However, the development of such a
making process, these experiments caused protests mice, which are the most important host for Borrelia variant currently face biological hurdles: epigenetic regulation of gene expression in mosquitoes
11 both in Burkina Faso and internationally.27 28 in these regions. An intervention in the immune prevents the X shredder from being activated on the Y chromosome.38
12
system is supposed to make the mice resistant and
In the second phase the mosquitoes are to be genetically interrupt the transmission chain of Borrelia. According X-Shredder variant 3 - gene drive – It is also possible to combine the X-Shredder (variant
modified so that they produce predominantly male to a citizen survey on the islands of Nantucket and 1) with a CRISPR/Cas-based gene drive. This is then called Sex Distorter Gene Drive (SDGD): If
offspring.29 The genetic modification introduced via a so- Martha‘s Vineyard in Massachusetts, USA, a majority females mate with males carrying the CRISPR/Cas gene drive with the coupled X-Shredder,
called X-shredder (see box) would be inherited according rejected the use of gene drives. Instrad, the release the gene drive is integrated into the gene Doublesex, which prevents the development of
to Mendelian rules. Thus it is not yet a gene drive at of genetically engineered mice is forseen. They are fertile females. The additionally integrated X-Shredder causes the X chromosome to be cut
this stage. In order to reduce the mosquito population supposed to mate with their wild counterparts and during the formation of the germ cells. The overall result is predominantly male offspring.39 In
with these releases, genetically modified mosquitoes crossbreed a resistance to Lyme disease into the the combination of CRISPR/Cas gene drive and X-Shredder, both systems mutually safeguard
produced in the laboratory would have to be released natural population. However, should trials on larger each other: Should one system fail, the other will function. According to model calculations,
repeatedly in high quantities. land masses be planned for the future, the use of gene the number of (biting) female mosquitoes could be reduced much faster with the Sex Distorter
drive mice would again be up for debate.36 Gene Drive than with an exclusive CRISPR/Cas gene drive.
The goal of Target Malaria in the third phase is to
produce mosquitoes that carry the X-shredder on There are several alternative strategies to prevent
the Y chromosome, which would make all offspring the transmission of Lyme disease to humans apart
male for generations and all carry the X-shredder. from gene drives and other genetic engineering
The genetic modification thus spreads like a gene methods. Infection can already be prevented by simple
Formation of the male The X chromosome is Only male germ cells with a Only male offspring is
drive throughout the population. 30 means: by wearing suitable clothing, applying anti-
germ cell ”shredded” (inactivated) Y chromosome are capable born. In variants 2 and
tick medication and regularly scanning the body. For of development 3, all males inherit the
While Target Malaria focuses on reducing the number a short time in the past, a vaccine by the American X shredder.
of mosquitoes, Gene drive developers at the University company GlaxoSmithKline (GSK) was readily available,
Potential applications of gene drive organisms
of California in San Diego are taking a different but it was taken off the market again due to lack of
approach. With a multi-million dollar grant from India‘s interest.
Tata Foundation31, they are looking for a way to create x
resistance in Anopheles mosquitoes that kills the malaria
pathogen and prevents the infection of humans.32
y
However, such gene drive organisms had proven to have
only limited viability in initial cage experiments.33 Offspring
Illustration adapted from: Galizi, R., Doyle, L.A., Menichelli, M., Bernardini, F., Deredec, A., Burt, A., Windbichler, N., Crisanti,
A., 2014. A synthetic sex ratio distortion system for the control of the human Malaria mosquito. Nat. Commun. 5, 3977.
https://doi.org/1038/ncomms4977USING GENE DRIVES stoats and the Australian fox cusu. With the Predator An analysis conducted by the research and advocacy GENE DRIVES IN
Free 2050 program, the New Zealand government organization ETC Group48 concluded that a majority
TO COMBAT INVASIVE pursued the goal of eradicating all invasive predators of the report‘s authors were known proponents AGRICULTURE
by 2050. The measures have already been successful of genetic engineering and should not have been
SPECIES on more than 100 smaller islands. To achieve success engaged by IUCN, in part because of their economic
on the main islands as well, the use of gene drives was self-interest in developing the technologies studied. In the long run, agriculture could become the most
considered. In a subsequent open letter signed by 231 civil society important field of application for gene drives - a fact
Humans have carried numerous animal species to organizations and several scientists, the report was that has hardly been discussed in public so far. Patents
foreign islands and continents, where they have In light of the consideration of using gene drives criticized as ”regrettably one-sided”, ”biased”, and on CRISPR/Cas-based gene drives list hundreds of
become a serious threat to native flora and fauna. for invasive species eradication in New Zealand, ”inappropriate for the intended policy discussion”. animals and plants whose containment or eradication
Major problems are caused, for example, by rats and two gene drive developers published an article in This report, they said, is not consistent with the could increase agricultural yields. However, a number
mice, which significantly reduce populations of smaller 2017 warning against hasty releases and the use precautionary considerations of the Hawaii resolution. of hurdles would still have to be overcome along the
animals and native birds. Conventional measures such of gene drive organisms in conservation.43 The undersigned organizations therefore called on way.
as hunting, trapping, or poison baiting have been able IUCN to commission another scientific report based on
to drive invasive species off small islands. On larger Since the change of government that same year, a precautionary analysis of the risks of the technology
land masses, these measures reach their limits. Gene there has been greater restraint in New Zealand in and to wait until such a counter-report is available
drives are intended to offer an alternative here. this regard. Before Predator Free returns to the topic, before taking a decision on the issue.49 In a similar Patent applications for
the many technical, social and ethical considerations vein was the request of an October 2019 letter from
The Genetic Biocontrol of Invasive Rodents (GBIRd) and regulatory hurdles first have to be explored and 23 IUCN members to the IUCN Council. According to agricultural applications
project, which is supported by seven universities, overcome.44 its signatories, more time is needed for a fundamental,
13 public authorities and non-governmental organizations comprehensive, balanced discussion based on the At least six patents on gene drives refer to 14
from the USA and Australia, is investigating this precautionary principle, with greater involvement of specific applications in agriculture. The focus
approach. IUCN members, prior to any IUCN decision-making.50 is on controlling pests and weeds and reversing
The discussion on gene drives herbicide resistance.
GBIRd aims to address the question of whether Confronted with this criticism, the IUCN Council
mice can be eradicated through gene drives and in the International Union for withdrew its plan to adopt a position at its Members‘ Two key applications come from leading developers
under what conditions this intervention would be Assembly, originally planned for June 2020. Instead, of the CRISPR/Cas-based Gene Drive, the research
acceptable. The bulk of the project is funded by the Conservation of Nature (IUCN) principles51 for the discussion on the topic were groups led by Kevin Esvelt52 and Ethan Bier53.
U.S. military‘s Defense Advanced Research Projects defined in a consultation open to members. These Numerous claims are also filed in a patent by Bruce
Agency (DARPA) to the tune of $6.4 million.40 In view of the possibility of using gene drives to are to be voted on at the IUCN World Conservation Hay‘s group.54 Most of the claims are general, but one
remove introduced invasive species from sensitive Congress in 2021 and will serve as the basis for a for patent already contains detailed goals and methods
Among the most active members of GBIRd is the small ecosystems, the International Union for Conservation discussions until a position will be voted on at the that enable commercial use.
conservation organization Island Conservation. It has of Nature (IUCN), also known as the World Conservation following Members‘ Assembly.
been dedicated to the protection of seabirds for 25 Union, has also been discussing this technology since However, the commercialization of gene drives faces
years and says it has already rid 63 islands of rodents. late 2015. a fundamental problem: their spread cannot yet be
So far, this has been done using conventional methods, contained, either spatially or temporally. Individual
but Island Conservation believes that further progress At its General Assembly in Hawaii in September 2016, releases could result in the transboundary spread of
will require the use of gene drives.41 IUCN adopted a resolution45 that, among other things, GDO into neighboring ecosystems for decades. The
mandated IUCN to prepare a scientific report on the classic business model of agribusinesses, which is
The first steps in this direction were taken at the implications of synthetic biology and gene drives for based on continuous sales of the products, would be
University of California in San Diego, USA, when gene biodiversity conservation. Based on this scientific difficult to apply under these conditions.
Potential applications of gene drive organisms
drives for mice were developed there for the first time report, IUCN originally intended to take a position on the
in 2019.42 However, the developers encountered an role of gene drive technology for nature conservation at In theory, its use appears commercially interesting in
unexpected phenomenon: CRISPR/Cas9 was able its subsequent General Assembly in 2020. two scenarios: A gene drive could eliminate natural
to cut the DNA strand in all test animals, but only resistances that wild plants have developed to
in females did the repair mechanism kick in, which In part through public protest and at the urging of common herbicides. An agribusiness could then profit
activley spreads the new DNA segments in the global conservation luminaries46 , IUCN committed from increased sales of the herbicide because they
genome. The gene drive was therefore only successful in its 2016 resolution to refrain from any support or would become usable again. Another scenario would
in one of the two sexes, and even there it only achieved endorsement of research, field trials, or use of gene be for large agricultural associations to fund
an efficiency of about 70 percent. The gene drive in this drive technology until this report would be available. the development of a gene drive that would benefit
form is probably not suitable for manipulating wild- all association members.
living mammal population. The report, entitled ‘Genetic Frontiers for
Conservation47, was published in May 2019 and
New Zealand‘s former government also showed was met with harsh criticism from IUCN member
interest in using gene drives. The country‘s unique flora organizations as well as conservation and
and fauna suffer great damage from introduced rats, development organizations around the world.Number of patent claims on possible
agricultural gene drive applications
WO 2015/105928 A1 WO 2017/049266 A2
Titel: RNA-Guided Gene Drives Title: Methods for Autocatalytic Genome Editing and Neutralizing Autocatalytic
Assignee: President and fellows of Harvard College Genome Editing and Compositions Thereof
Inventors: Kevin Esvelt, Andrea Smidler Assignee: The Regents of the Univeristy of California
International publication date: July 16, 2015 Inventors: Ethan Bier, Valentino Gantz, Stephen Hedrick
International publication date: March 23, 2017
12 corn pests 9 cotton pests 13 small grain pests 301 agricultural 20 agricultural 96 agricultural
insect pests pest mites pest nematodes
10 soybean pests 11 grape vine pests 13 palm tree pests 68 plant 48 insect 27 ornamental
mentioned ”within the pathogenic vectors of plant insect pests
scope of the present nematodes pathogens
disclosure”
16 pests of nightshade 14 stone fruit 8 cyst nematode 6 mollusc 18 grape 6 strawberry
crops, including peppers, pests species pests pests pests
tomatoes, eggplants,
tobacco, petunias,
potatoes
24 bark beetle 11 pests of 186 8 honey bee 34 mentioned weeds
species mollusc pests name brand pests resistant to pesticides or
herbicides herbicides
11 pests of 27 agribusinesses
moth species named
112 noxious weed 52 ”additional weeds 46 pesticide
varieties (19 aquatic within the scope of the species, e.g.,
weed species, 5 present disclosure” (e.g., atrazine, glyphosate,
parasitic weed species, ragweed, poison ivy, napthalene, copper
88 terrestrial weed goldenrod) hydroxide
species)
Infographic adapted from: ETC Group, Heinrich Böll Foundation (2018). Forcing the Farm. How Gene Drive Organisms Infographic adapted from: ETC Group, Heinrich Böll Foundation (2018). Forcing the Farm. How Gene Drive Organisms
Could Entrench Industrial Agriculture and Threaten Food Sovereignty. Could Entrench Industrial Agriculture and Threaten Food Sovereignty.Examples of gene drive Asian citrus psyllids (Diaphorina citri), which ingest
the bacteria while sucking plant sap and can then
applications in agriculture infect other trees. Within three years, the disease,
called Huanglongbing, spread across most of
The use of gene drives would be conceivable for almost Florida‘s cultivation regions, with citrus production
every field crop and for numerous farm animals or plummeting by 70 percent.60 Europe has so far been
so-called pests. In three cases, there are already spared from the disease, but spread cannot be ruled
concrete plans. out.61
Citrus growers in California are considering the
Spotted wing drosophila use of gene drives to protect their plantations.62
One option would be to release gene drive psyllids
Originally native to Southeast Asia, the spotted wing that cannot transmit the bacteria. A research How does a Medea Drive work?
drosophila (Drosophila suzukii) is a fruit fly that has project on this was completed in 2017 and
spread worldwide and causes significant crop losses in identified a number of genes that could prevent The goal of a Medea Drive can be to replace or decimate a wild insect population. The Medea Drive consists of two
numerous fruit varieties. It lays its eggs in nearly ripe, transmission.63 However, a gene drive has not genetic components that act according to the principle of poison and antidote. A new gene variant can be inserted
undamaged fruit with thin skins. In 2008, the spotted yet been developed from this. as the third component, which is inherited by all surviving offspring. Both males and females can inherit the Medea
wing drsophila reached California and caused more Drive. But the toxin is produced only by the mother and is deposited all eggs. The antidote, on the other hand, is
than $38 million in damage to cherry orchards the not deposited in the eggs but is formed in the fertilized embryos. For embryos to develop in the poisoned eggs,
very next year. According to calculations, these losses The New World screwworm fly the genetic information for producing for the antidote must also be anchored in their genome. The offspring are
17 can rise to over $500 million annually in the western therefore only viable if they carry the Medea Drive in their genome, which also produces the antidote. Since the
18
United States.55 Since 2011, it has also appeared in The New World screwworm fly (Cochliomyia female fly carries only one copy of the Medea Drive, only half of her offspring inherit a Medea Drive. Thus, only half
Germany, jeopardizing the harvest of cherries, grapes, hominivorax) is found primarily in the Americas and of the offspring can produce the antidote. The Medea Drive is available with and without CRISPR/Cas based homing
raspberries, blackberries and strawberries.56 lays its eggs near body cavities or open wounds of gene drive.67 The gene drive version without CRISPR/Cas probably spreads less invasively.68
mammals and birds. The hatching larvae burrow
In 2013 the California Cherry Board, an association deeply into the tissues of infested animals, causing
of California cherry growers, began funding severe inflammation. The New World screwworm
research on a gene drive with $100,000 annually.57 fly also infests livestock such as cows, sheep, and
A group of researchers at the University of San goats, which can die from the inflammation without
Diego, USA, developed a so-called Medea Drive. veterinary treatment.64 The screwworm fly was
Medea Drive: Poison and antidote
eradicated from the continental United States and
The flies‘ offspring are not viable. This can affect one or Central America in the 1960s by releasing sterile
both sexes (for more information, see infobox). male flies. To prevent new introductions from The Medea Drive is a genetic
South America, a protected zone was established element that spreads genes for
a ”poison” and an ”antidote”.
In initial laboratory experiments, a high number in Panama, but it is very costly to maintain.
of modified flies was necessary to establish the Scientists at the University of North Carolina, USA,
Medea Drive in the population. In addition, many fly therefore proposed the use of gene drives.65 It
populations in the wild have natural resistances that could also be used to eradicate the screwworm fly Female flies, which inherit a copy
of the Medea Drive, deposit the
would probably strongly hinder the spread of the in South America. In 2019, an international group of
”poison” in all of its eggs.
Medea Drive. The researchers therefore suspect that researchers was able to apply CRISPR/Cas9 in the
a very large number of modified spotted wing fruit screwworm fly for the first time, altering a gene in
Potential applications of gene drive organisms
flies would have to be released to keep the Medea the fly that is crucial for the development of the fly‘s
Drive in the population for several years. No field tests sex. This resulted in females that had male sexual One half of the decendents inherits
have been planned yet.58 The patent applied for in characteristics and were presumably sterile.66 only the natural genes and dies.
2017 on this Medea Drive also covers other species of This intervention is a first step toward developing
tropical fruit flies as well as mosquitoes of the genera a CRISPR/Cas-based gene drive that would aim to
Anopheles and Aedes, which transmit malaria and completely eradicate the screwworm fly.
numerous viral diseases.59 The other half of the decendents
inherits the ”antidote” and survives.
Psyllids
Other potential target organisms for a gene drive Quelle: Volker Henn. https://www.wissensschau.de/synthetische_biologie/gene_drive_medea_daisy_x-shredder.php
are psyllids. In 2005, bacteria that infect citrus trees
and render their fruit inedible were detected for
the first time in the USA. It is spread by introducedThe Gene Driven Farm Gene drives to eradicate, for
example, rats, mice, flour
beetles and moths that
infest grain silos.
This picture illustrates the areas in
which gene drive organisms are
being developed or considered for Gene drives to eradicate, for
example, the screwworm fly,
agricultural use.
which lays its eggs in the wounds
of cattle.
Gene drives to eradicate, for example, Gene drives to eradicate the Gene drives to eradicate Gene drives to
psyllids that spread Citrus greening spotted wing drosophila, a fruit nematodes that cause decimate
disease (Huanglongbing in Chinese) fly which lays its eggs in ripe plant diseases. cabbage moths.
in citrus fruit. fruit, such as cherries.
Illustration adapted from ”The Gene Driven Farm” in ETC Group, Heinrich Böll Foundation (2018).
Forcing the Farm. How Gene Drive Organisms Could Entrench Industrial Agriculture and Threaten Food Sovereignty.Open questions regarding applications in plants Gene drive organisms as While the effect of a gene drive Conflict from the use of gene drive technology
in the environment could also be triggered by a
Theoretically, gene drives could also be used in plants. bioweapons organism might be considered lack of public (or international) consensus on a
The U.S. National Academies of Science identified release of gene drive organisms in one‘s own or
as one of the possible targets the foxtail plant A release of gene drive organisms could, in theory, positive in a particular region, neighboring countries. Resulting damages, such as
Amaranthus palmeri69, which has become a resistant have large-scale and long-lasting negative effects on crop loss, biodiversity loss, or unintended health,
superweed in the United States since the 1990s due ecosystems and societies. The release of gene drive its consequences might be social, or economic effects, can lead to conflict if
to the overuse of herbicides such as glyphosate.70 organisms for civilian purposes could therefore cause there is no adequate compensation for them. Even
Amaranthus palmeri is a dioecious plant that produces conflict or lead to misuse. The targeted development considered undesirable or the unintended presence of a GDO in a country
either male or female flowers. Researchers have of gene drive organisms for hostile purposes is also that has not consented to a release can lead to
identified a gene that controls the formation of female conceivable.75 negative in other affected interstate conflict or diplomatic crises.79 For these
flowers.71 If it were possible to switch off this gene reasons, experts at the UN Biological Weapons
by means of a gene drive, only male plants could be One way that gene drive organisms could be used regions, leading to insurgency Convention have been monitoring and discussing
formed, making natural reproduction impossible. as bioweapons would be to use them to eradicate the issue for years.80
important beneficial insects for agriculture in a or conflict.
Another theoretical possibility would be to reverse particular region.
resistance to common pesticides that dozens of plant
species have developed and that pose major problems However, until gene drive organisms and their
for industrial agriculture. These resistances caused by harmful effects can be limited both spatially or
genetic changes that are often well researched and temporally, there are few convincing scenarios for
21 could theoretically be reversed by a gene drive.72 government gene drive weapons programs.76 22
Despite these challenges, the U.S. military‘s Defense
Advanced Research Projects Agency (DARPA) is
Several technical hurdles one of the largest funders of gene drive research
and is financially involved in almost every gene
must be overcome before drive research project. 77
gene drives can be applied The DARPA research program, titled Safe Genes,
sets out to control, limit, or recover GDO from the
in plants. environment. There are numerous gray areas in the
spectrum between unexpected negative effects of
gene drive organisms in nature, their misuse, and
Double strand breaks caused by CRISPR/Cas9 in the deliberate development of gene drives for hostile
the genome of plants are often repaired using error- purposes.
prone mechanisms.73 This prevents the gene drive
from taking hold in plants. To inherit the gene drive
to all offspring, another type of repair mechanism
would have to repair the double-strand break using a
template. In addition, many plants have significantly
longer generation times than insects. The effect
Potential applications of gene drive organisms
of a gene drive would only take effect after many
years. And ultimately, the seeds of some plants can
persist in the soil for years, significantly delaying the
breakthrough of the Gene Drive.74
The implementation of a gene drive in plants is not
yet possible with the current state of knowledge.Gene drives are at an early stage of development. The
discussion about possible consequences and risks is
therefore still largely speculative. However, numerous
critical points are already emerging that must be taken
03 into account before considering a release.
Ecological
risks 24
Uncontrollability
The vast diversity of natural habitats and ecosystems
affected will make the prediction and control of
potential risks much more difficult.
In 2016, the U.S. Academy of Sciences recommended
that gene drive organisms first be tested on small
and remote islands.81 However, calculations using
Once released into nature, a
models show that this would not provide sufficient
containment individual GDO can reach other regions
gene drive organism actively
through water, wind or unintentional transport and
spread the gene drive further.82 Moreover, GDO could
spreads in wild populations
be spread deliberately.
and can spread rapidly over
A group of researchers led by gene drive developer
Kevin Esvelt at the Massachusetts Institute of
large distances.
Ecological risks
Technology (MIT) in Boston, USA, is working on a gene
drive variant that can be limited in its spatial spread.
They call this gene drive the Daisy Chain Drive.83 So far,
however, this gene drive variant exists only in theory
(for more information, see infobox).Irreversibility Outcrossing across
What is a Daisy Chain Drive?
A gene drive causes a permanent genetic modification species boundaries
The Daisy Chain Drive is a variant of gene drive based on CRISPR/Cas9 that has not yet been of the genetic material, which is passed on to
implemented. In theory, the CRISPR/Cas-based gene drive would consist of individual elements all subsequent generations. Even if a gene drive Gene drives are tailored to the genome of a single
located on different chromosomes.84 Element C consists of the gene ‘scissors’ and a guidepost encounters resistance and no longer spreads on species, but in many cases outcrossing across
for B. Element B is the gene ‘scissors’ Cas9 plus guidepost for C. C is the target site of the gene its own accord, these changes can continue to be species boundaries could be inevitable. For
drive, an essential gene that is knocked out by the DNA double-strand break and replaced by inherited according to Mendelian rules and persist example, the malaria-carrying mosquito Anopheles
a new gene if necessary. Component C is inherited according to Mendelian rules. Therefore, for a long time in the genome of the population. Only gambiae belongs to a complex of seven different
the process should stop on its own at a certain point, which could limit its spatial and temporal if the deactivated gene drive severely impairs the subspecies that are genetically very similar and can
distribution. survivability of the individuals do the mechanisms of produce fertile offspring with each other.87 A gene
natural selection take effect, eliminating the change in drive by Target Malaria targets disruption of the
the natural populations. Doublesex gene, which has undergone little change
during the evolution of the mosquito species. This
Standard Gene Drive: A leads to the As early as 2014, a discussion started about the need approach could drive all seven related mosquito
inheritance of A
for a so-called Reversal Drive, which would be intended species to the brink of extinction, although at least
A A
to reverse the changes caused by a gene drive in the one species does not transmit malaria.88
manipulated populations. In principle, this is a modified
version of the original gene drive that overwrites A similar risk exists in fruit flies of the genus
the previous genetic manipulations and prevents Drosophila, which have played a central role in the
25 their further spread. However, even such a Reversal development and application of gene drives. It has 26
Drive can not restore the original genetic state of been known for over 90 years that different species
the population, but only introduce further genetic of Drosophila can interbreed and produce fertile
modifications into the genome of these populations. offspring.89 Thousands of other animal and plant
species form natural hybrids, so the spread of gene
cuts repairs In a study on fruit flies, genetic elements were drives would not be limited to one species but could
W A A A A
presented that were designed to switch off or also extend to its closer relatives.
completely remove CRISPR/Cas-based gene drives
from the genome. Specific signposts of the CRISPR/
Cas9 ‘gene scissors‘ are used to terminate the chain
reaction of a CRISPR/Cas-based gene drive. The result:
Daisy Chain Drive: C leads to B leads to the the ‘gene scissors‘ paralyze themselves. Results from
inheritance of B inheritance of C
cage experiments show that these elements can
C B A prevail for 10 generations. However, synthetic genetic
elements remain in the genome and are inherited
according to Mendelian rules. In addition, unintended
changes to the genome occur. It is difficult to estimate
how these remaining genetic changes will behave in
the wild populations in the long term and whether they
will be influenced by external factors.85
According to current knowledge, any release of
cuts / a gene drive carries the risk of irreversibly and
W C W B W A repairs W C B B A A uncontrollably altering the genetic material of a
natural population.86
Illustration adapted from: Noble C, Min J, Olejarz J, Buchthal J, Chavez A, Smidler AL, DeBenedictis EA, Church GM, Nowak MA,
Esvelt KM (2019). Daisy-chain gene drives for the alteration of local populations. Proc Natl Acad Sci USA 116:8275.
Ecological risksUnexpected effects of Unpredictable impacts
CRISPR/Cas9 on ecosystems Food web of mosquitoe larva and mosquitoe
Many engineered gene drives use CRISPR/Cas9 to Every living creature, even if it appears dangerous or
create a double-strand break at defined locations harmful to humans, performs important tasks in its
in the genome. However, this tool does not work habitat. The extinction or even manipulation of one
flawlessly.90 species will therefore have consequences for the
entire ecosystem.
CRISPR/Cas9 can change the activity of the target
gene in unpredictable ways, increase the mutation This can be well illustrated by the example of 01
rate in the genome, lead to unexpected mutations,
or be disrupted in its function by emerging
mosquitoes. In the course of their life cycle, they
form important food sources for various animals. For
10 02 Mosquito larva
resistances. For example, there are increasing example, mosquito larvae living in water are a food
reports of so-called off-target effects, unintended
changes to non-target sequences that can occur
source for water bugs, beetles, flies, spiders, flatworms,
tadpoles, fish and crustaceans. It is assumed that 95
09 03 1. spiders
2. flatworms
3. tadpoles
when the CRISPR/Cas system is applied.91 percent of the larvae of the African malaria mosquito 4. fish
Anopheles gambiae are being eaten before becoming 5. crustaceans
6. decaying detritus
Moreover, the genetic modifications not only affect
the target area, but often also other areas in the
adults.94 Adult mosquitoes are also an important food
source and are consumed by dragonflies, spiders, bats
08 04 7. aquatic micro-organisms
27 genome.92 One of the reasons for this is that in wild and birds, among others. In the Camargue, a nature
8. beetles
9. water bugs 28
10. flies
populations there are more sequences in the genome
to which CRISPR/Cas9 can dock than the computer
reserve in southern France, reduction of mosquito
populations with a biological control agent has also led 07 05
programs used for this purpose were able to determine to a reduction in the number and diversity of birds and
06
in the laboratory. Gene drives can therefore lead to dragonflies.95 A role in plant pollination also cannot be
the development of organisms with unpredictable ruled out, as adult mosquitoes feed on nectar, among
characteristics.93 other things.96 The role of mosquitoes in their tightly
interwoven ecosystem has hardly been studied so far,
so the consequences of a possible extinction are not
foreseeable.
Resistances
These consequences can also affect humans: If one
CRISPR/Cas-based gene drives search for a clearly mosquito species is displaced, other species, which
defined DNA sequence at which they are to cut may transmit even more dangerous diseases, can
the genetic material. Even single mutations to spread more widely. Such risk scenarios are known
this sequence can therefore render the target with regard to the control of the dengue fever- 01
unrecognizable to them. The organism thus becomes transmitting yellow fever mosquito (Aedes aegypti) in
resistant to the gene drive. Such resistance can arise North America and Brazil, which competes with the
if the DNA double-strand break generated by CRISPR/ invasive Asian tiger mosquito (Aedes albopictus).97 06 02 Mosquito
Cas9 is incorrectly repaired by the cell and alters If the yellow fever mosquito disappears, this could
the target sequence. However, resistance could also further promote the spread of the tiger mosquito, 1. spiders
2. birds
occur naturally, especially in populations with high which is no less dangerous and also transmits dengue 3. bats
genetic diversity. fever.98 4. blood (only female mosquitoes)
5. dragonflies
6. nectar
If a gene drive encounters resistance, it will break off
at this point and only change part of the population.
But even if a species is not wiped out, gene drives
harbor considerable risks: If the characteristics of
05 03
Whether it disappears again completely, however, the organisms change unintentionally, they can,
depends on the number of individuals already changed
and the disadvantages that the gene drive brings
for example, change their behavior, transmit more
diseases, or even disturb or destroy the habitat of
04
for their survival. It is therefore entirely possible for other species. Because the respective species are
the gene drive to persist for a long time in an animal closely linked to their ecosystems, the effects of
Ecological risks
species despite resistance. uncontrolled spread cannot be predicted reliably.99The political debate on the regulation of gene drive
technology is still in its infancy, both in Germany
and Europe, as well as internatonally. There is no
specific and binding regulation for handling this
04 new technology.
Gene drive
regulation REGULATION OF GENE
30
DRIVE ORGANISMS IN
GERMANY
In Germany, the political discussion and regulation of According to the Genetic Engineering Act (GenTG), the
gene drives is still in its infancy. An official position approval of a research project with GMO, its classification
of the German government on the evaluation by safety level and monitoring of safety requirements is
and regulation of gene drive organisms is not yet the responsibility of regional authorities. According to
available. §10 paragraph 7 of GenTG, these authorities are obliged
to obtain an opinion from the Central Commission
for Biological Safety (Zentrale Kommission für die
Genetic Engineering Safety Biologische Sicherheit, ZKBS) in this process.
Ordinance: safety standards In 2016, in the absence of a uniform regulation by
the Genetic Engineering Safety Ordinance, the ZKBS
for gene drive research had defined safety level 2 as sufficient for the work
with gene drive systems in the laboratory.100 This was
In the March 2021, gene drive organisms have been changed when the new version of the GenTSV came
included in federal genetic engineering legislation into force on 01.03.2021.
for the first time. The Genetic Engineering Safety
Ordinance (GenTSV) sets safety standards for In the revised Genetic Engineering Safety Ordinance,
handling GMO in research laboratories. laboratory work with genetically engineered
organisms containing gene drives is assigned to
In this context, laboratory work with genetically safety level 3 as a precautionary measure101. This
Gene drive regulation
modified organisms is assigned to one of four safety ensures that every research project involving gene
levels depending on its hazard potential for humans, drives is reported to a supervisory authority and that
animals and the environment. Safety level 1 applies a case-by-case risk assessment is carried out by the
to work with no hazard potential, while safety level ZKBS before experiments begin. In order to reliably
4 applies to work with a high hazard potential. prevent the escape and spread of GDO into wild
Depending on the safety level, different safety populations, Article 1, §11, Paragraph 6 stipulates the
measures must be upheld during experiments. ZKBS has to recommend specific safty measures toYou can also read
