Gene Drives on the Horizon Advancing Science, Navigating Uncertainty, and Aligning Research with Public Values (2016) / Chapter Skim
Currently Skimming:
5 Phased Testing and Scientific Approaches to Reducing Potential Harms of Gene Drives
5 Phased Testing and Scientific Approaches to Reducing Potential Harms of Gene Drives
Pages 86-111
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 86... ...
Thus, effective strategies to carry out laboratory and field research are needed to study each type of gene-drive modified organism, its potential benefits and harms, and approaches to reduce or mitigate the potential harms. The preceding chapters of this report describe what is known about gene drives, key population ecology and ecosystem considerations for gene drive research, and human values that may influence whether and how gene-drive modified organisms are used.
|
From page 87... ...
In addition, gene n e-drive modified organism may potentia be able to interbreed with related, wild species. For th ms ally h hese reasons, confinement and containmen are critical considerations throughout the phased testing pathway.
|
From page 88... ...
Identify risk assessment needs Phase 1: Laboratory-Based Research Acquire required laboratory regulatory approvals Develop containment and confinement strategies Detect and measure off-target effects Optimize design of guide RNAs (when using CRISPR/Cas9-based gene drives) Utilize an optimized endonuclease with high cutting efficiency and accuracy Optimize for the use of homology-directed repair versus non-homologous end joining in order to maximize precision of editing Evaluate effects on organismal fitness in the presence of the gene drive Evaluate gene drive stability over multiple generations Mark gene-drive modified organisms Use quantitative and computational methods Set baseline population-level effects Phase 2: Field-Based Research Acquire site-specific regulatory approvals Validate efficacy Validate population-level effects Estimate impact on selected non-targets Phase 3: Staged Environmental Release Acquire site-specific regulatory approvals Conduct monitoring and surveillance for efficacy Conduct monitoring and surveillance for harms Phase 4: Post-Release Surveillance Acquire regulatory approvals Conduct monitoring and surveillance Measure impact
|
From page 89... ...
for a Gene-Drive Modified Organism Specification Minimum Threshold Gene drive construct uptake >95% uptake in target species Off-target effects Organism survivorship >98% in target species Mating competitiveness at least 5% greater than unmodified male Hybridization with sympatric species <1% over 10 generations Interaction with existing applications No change in efficacy of existing application Impact >60% reduction of target population Time to impact No greater than 1 year after release Throughput Two releases per day in target area by one technician Deliverability Delivered using existing health system Training Can be deployed by community volunteer Cost at full scale deployment No greater than current standard technology Manufacturing Meets demand
|
From page 90... ...
The set of reasonable potential locations may expand or shrink as more information is gathered. Where research infrastructure is lacking, for example, opportunities for capacity-building as a direct result of research funding could be considered, such as occurred with the TARGET MALARIA Project.1 Phase 1: Laboratory-Based Research Phase 1 research on gene-drive modified organisms will be performed in the laboratory and physically contained settings under highly controlled conditions.
|
From page 91... ...
. Also, ph hase 1 includes laboratory exxperiments designed to evalu the stability of the gene uate y drive constru (that is, wh uct hether the gene drive constru behaves in a predictable way across e uct n e generations)
|
From page 92... ...
. Other examples of research that could be considered in phase 2 are small-scale ecologically or biologically confined field testing of gene-drive modified organisms.
|
From page 93... ...
Phase 3 studies will therefore help refine parameter thresholds, that once reached, that will allow the gene drive to spread throughout the wild-type population. To that end, characterization of the population structure of wild-type organisms of the same species as gene-drive modified organisms in the setting where testing will occur will be important to guide study design related to release rates (e.g., density and timing)
|
From page 94... ...
Two important dimensions of research carried out through the phased testing pathway are: 1. Containment and confinement to reduce the potential for unintended release or persis tence of gene-drive modified organisms, respectively; and 2.
|
From page 95... ...
Carefully discussing containment and confinement measures during phase 0 is crucial since organisms containing a gene drive will, by essence, spread the gene drive if released in an environment that promotes their survival and reproduction. In order to prevent lab-based gene drives from escaping into wild populations, many researchers have offered suggestions for developing methods to contain gene-drive modified organisms (Esvelt et al., 2014; Oye et al., 2014)
|
From page 96... ...
, all personnel will need to see examples of the modified organisms to avoid confusion with other organisms without the gene drive and provided with appropriate materials, such as vials or cages, for collecting test organisms found outside of their normal area. Physical marking of adults, such as the use of fluorescent proteins, can allow for easy visualization of the research organism being studied (Hagler and Jackson, 2001)
|
From page 97... ...
Another approach is to design gene drives to be "self-limiting", for example, by carrying both a gene that encodes for a toxin and another gene that confers immunity to the toxin. Such gene drives could self-destruct either over time or upon addition of a chemical (Gould et al., 2008; Marshal and Hay, 2012)
|
From page 98... ...
Non-target effects may also be hard to control, and redressing potential undesirable ecological and evolutionary consequences of the gene drive, even when accounting for changes over time, may be difficult. These issues are discussed in detail in Chapter 2.
|
From page 99... ...
Depending on the application, gene drives may require the introduction of specific genes into the target chromosome and thus would require HDR. This could be one of the biggest challenges facing gene drives, because the mechanism of repair will depend on species, cell cycle stage, cell type, and stage of development (Esvelt et al., 2014)
|
From page 100... ...
These same types of assays will also need to be conducted for an organism in which the genetic alteration has been made using a different editing method, is found naturally in the population, or is created through genome-wide mutagenesis for all comparison purposes. Although it is often assumed that genome alterations, including gene drives, will tend to negatively impact individual fitness relative to that observed in the unaltered wild-type organism (e.g., due to the addition of foreign DNA that slows replication, and/or interferes with native transcription and translation)
|
From page 101... ...
The ability to quantify these effects on organism fitness, if not masked by compensatory pathways that are up-regulated by the organism as observed previously (Rossi et al., 2015) , will lead to questions regarding whether gene drives provide the best technology for editing a specific gene, and whether fitness effects are consistent with intended applications.
|
From page 102... ...
For example, if a limited number of non-driving genetically modified organisms are released into the wild, this fundamentally differs from the release of gene-drive modified organisms because only the latter case involves sustained modification of individuals across multiple generations in the target population. Therefore, it would be naïve to assume that intensive quantitative modeling and other prior efforts would suffice to predict the accuracy of gene drive manipulations and determine how these altered genotypes would affect natural communities.
|
From page 103... ...
LEARNING FROM FIELD RESEARCH AND BIOCONTROL EFFORTS WITH OTHER TYPES OF MODIFIED ORGANISMS Due to the expectation that organisms will disperse in the open environment during phases 3 and 4, causing the gene drive to spread and potentially impact broader human and environmental communities, mitigation in these phases offers additional challenges to those described for laboratory (phase 1) and contained releases (phase 2)
|
From page 104... ...
. The approval to deploy transgenic Aedes aegypti using RIDL technology in Brazil for dengue control demonstrates that assessment of benefits and harms based on data gathered on the biology, ecology and planned mitigation strategies can support a favorable decision (see Case Study 2)
|
From page 105... ...
. CONCLUSIONS AND RECOMMENDATIONS Although the potential for gene drives to address and solve problems associated with vector-borne diseases, invasive pests, and agriculture is truly exciting, before field testing or en 10 www.mosquitoage.org/en/HOME.aspx.
|
From page 106... ...
Recommendation 5-1: Scientists conducting research on gene drives should follow a phased testing pathway, a step-by-step framework that begins with developing a research plan and continues through, if applicable, monitoring gene-drive modified organisms in the environ ment. Each phase in such a pathway should include pre-defined "go/no-go" decisions for de termining whether to transition to the next phase based on evidence regarding harms and benefits, efficacy, and safety.
|
From page 107... ...
2015b. Gene Drives in Mosquitoes: Disease Vector Control.Webinar, October 15, 2015.
|
From page 108... ...
2015. Safeguarding CRISPR-Cas9 gene drives in yeast.
|
From page 109... ...
2012. Impacts of Wolbachia infection on predator prey relationships: evaluating survival and horizontal transfer between wMel Pop infected Aedes aegypti and its predators.
|
From page 110... ...
2015. Systematic evaluation of Drosophila CRISPR tools reveals safe and robust alternatives to autonomous gene drives in basic research.
|
From page 111... ...
2014. The Guidance Framework for Testing Genetically Modified Mosquitoes.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.