Summary

With a growing human population and rising living standards, demand for animal-derived food products increases even as the availability of arable land and water decreases. Among the approaches that can be applied to increase the efficiency and sustainability of food-animal production is genetic improvement. Science-based selective breeding of livestock for production of meat, milk, eggs, wool, or other products traces back to the late 18th century. The rise of molecular genetics and its application to selective breeding in the late 20th century led to the identification of genes with major effects upon the productivity of livestock. The application of biotechnological methods—gene transfer and genome editing—in combination with improved methods for assisted reproductive technologies and the consequent development of food animals with a heritable genetic modification (HGM) offers the potential for enhancing the productivity and sustainability of animal agriculture. However, there are concerns regarding animal welfare, the safety of HGM animal-derived food products to the consumer, and other possible risk endpoints. A National Academies of Sciences, Engineering, and Medicine study, which was conducted at the request of the National Institutes of Health Office of Science Policy, to address these concerns is especially timely as the first lines of HGM animals are becoming commercialized in the United States and other countries. In August 2023, NASEM appointed the Committee on Heritable Genetic Modification in Food Animals to conduct this study. The committee’s charge is presented in Box S-1.

To address its charge, the committee reviewed information from scientific literature, presentations of experts at National Academies-sponsored workshops, and previous National Academies’ reports. On the basis of this information and its deliberations, the committee developed conclusions and recommendations for the consideration of the National Institutes of Health Office of Science Policy and other parties involved in addressing animal welfare and the safety of HGM animal-derived food products to the consumer. This report does not contain policy recommendations¹ as this was not part of the committee’s charge. Selected conclusions and recommendations are highlighted in this summary; full conclusions and recommendations are detailed in the report chapters.

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¹ The Committee on Future Biotechnology Products and Opportunities to Enhance Capabilities of the Biotechnology Regulatory System (NASEM, 2017; described the possible products of biotechnology and provided insights for developing the capabilities needed within regulatory agencies moving forward.

HERITABLE GENETIC MODIFICATION OF FOOD ANIMALS

The development of genetically improved lines of food animals depends upon the existence of genetic variation for a trait of interest and the application of a selection method that exploits that variation. While genetic variability traditionally was derived only from naturally occurring random mutations, the tools of animal biotechnology (i.e., gene transfer and genome editing) can also contribute useful genetic variation. First applied to animals in the 1970s and accelerating in the 1980s, gene transfer (transgenesis) is a process that introduces a gene, which may or may not be from the same species, into a food-animal host. However, when using classical gene transfer techniques, there is little to no control over where the transgene becomes integrated into the host genome or over its structural integrity upon integration. Since the 2010s, most new lines of HGM animals have been produced through genome-editing methods. First applied to animals in the late 1980s and accelerating with the development of new techniques in the 2010s, gene or genome editing employs techniques that allow genetic material to be added, removed, or altered at a precise location within the host genome.

Gene transfer and genome-editing methods have been applied within each major animal production sector to generate founders of new lines of food-animal species (some examples are shown in Table S-1).

While many HGM animals are being developed to increase productivity and sustainability of animal agriculture, very few have been approved for consumption in the United States or other countries. Among the HGM food animals produced through classical transgenesis, the AquAdvantage growth hormone-transgenic Atlantic salmon is

TABLE S-1 New Lines of Food-Animal Species Generated Using Gene Transfer or Genome Editing

now in commercial production at U.S. and Canadian facilities operated by AquaBounty Technologies. Among HGM food animals developed using genome editing, the myostatin-knockout red sea bream and leptin receptor-knockout tiger puffer and olive flounder are in commercial production in facilities operated by the Regional Fish Institute in Japan. No HGM food animals are yet under widespread production by conventional farmers in the United States or the rest of the world, although SLICK cattle will reach the market soon. Non-regulatory impediments to commercialization of HGM food animals include long generation times including breeding after stabilization and validated incorporation of the HGM into the host genome, costs associated with regulatory review, and costs associated with resistance of the market to purchase HGM food products.

Conclusion 2-1: The potential contribution of animal biotechnology to genetic improvement of livestock is substantial, and both distinct from and complementary to the goals of conventional selective breeding. Like conventional selective breeding, techniques for genetic modification such as transgenesis and genome editing offer the prospect of producing animals with unique phenotypes that improve production, sustainability, efficiency, and profitability, including improvements to animal health and welfare. Moreover, the use of gene editing can expedite the introgression of a desired gene variant into a recipient line of animals without the need for the traditional approach of crossbreeding and repeated backcrossing.

POTENTIAL HAZARDS TO ANIMALS AND CONSUMERS

HGM of food animals can help increase productivity and sustainability, including through enhanced disease resistance, improved quality of animal products for consumers, and dissemination of improved genetics to the animal production industry; however, there is concern about hazards to the health of food animals and to human consumers of products derived from HGM animals (those that are developed through human intervention, not arising from natural mutations) and other risk endpoints. Hazards may result from unintended alterations at the genomic target site, or from unintended alterations elsewhere in the genome. There may also be unanticipated

consequences of the intended genome alteration, including effects due to the modification of genes with multiple functions or from random insertion of transgenes into the genome.

Regulatory authorities in the United States and other countries have expressed interest in the composition of food products derived from HGM animals; however, there have been relatively few case studies on changes in the composition of foods derived from HGM animals. An important food-safety issue is allergenicity. Animal food allergens usually originate from organs or tissues that are not present in the human body (such as chicken eggs), that are secreted (such as cow milk), or that are from non-mammalian animals (such as fish and shellfish) that are evolutionarily distinct from humans and thus have many proteins that are distinct from those of humans. Another concern is toxicity, such as from toxins that plants produce to protect themselves from herbivory; traditional food animals do not produce and express toxins, and genes for toxins would not be purposefully transferred into a food-animal host. Because antibiotic-resistance genes are often included in the DNA constructs (often plasmids) utilized in classical gene transfer, there is also concern that subsequent expression of resistance to the antibiotic in the host would lead to heightened frequency of resistance in pathogenic microbes that could be shed into the environment, potentially resulting in the antibiotic becoming ineffective for treatment of human or animal disease. While development of disease-resistant or -resilient animals could help reduce the loss of livestock to disease, it may also pose the risk that these animals present selective pressure for the pathogen to evolve and potentially spill over into other animal and human populations. Such risk is difficult to assess with current knowledge, and understanding this risk will require research into the evolution of pathogens in food-animal populations.

Conclusion 3-1: While HGM of livestock poses benefits of increased productivity and food system resiliency, there are also concerns regarding hazards to the health of livestock and to the human consumer of foods derived from HGM animals. Potential hazards are those things that might occur during the development of HGM animals, such as unanticipated molecular alterations, allergen risks, toxins, and disease spillover, etc., but because there are mechanisms in place to recognize these hazards (or most of them) prior to commercialization, they are unlikely to pose an actual risk to human health or the welfare of HGM animals raised commercially.

LIKELIHOOD OF HERITABLE GENETIC MODIFICATION PRESENTING HARMS TO FOOD ANIMALS OR HUMANS

Because of their long history of use, traditional animal-derived foods are generally recognized as safe. In contrast, foods derived from HGM animals are subject to risk assessment to identify hazards, the probability of exposure to the hazards, and the probability of harm being realized given exposure to the hazards. The absolute likelihood of harm being realized to an animal with a heritable genetic modification or to the consumer of a food derived from an HGM animal cannot be directly estimated. However, the likelihood of harm being realized relative to an appropriate comparator can be estimated to assess animal safety or the safety of foods derived from HGM animals. With current knowledge, in many contexts, risk likelihoods can only be estimated qualitatively, for example, characterized as zero, near-zero, low, moderate, or high.

The committee believes that having unanticipated effects on the phenotype of the founder generation of an HGM line has moderate likelihood of occurrence. This is because experimental rigor during HGM line development requires that genotypic alterations that give rise to phenotypic changes are fully characterized in the prototype founders. Once the genotypic alteration has been determined to be heritable through the germline of founders, the focus then shifts to assessing the durability of the phenotype in subsequent generations and in production-relevant settings, and thereafter continued assessment of genotype becomes less important. Any unintended genetic modifications would be recognized during the process of HGM line development and any HGMs negatively affecting phenotype would be culled or removed from lines that are candidates for eventual commercialization.

To the consumer, any risk of harm being realized given exposure to a food derived from an HGM animal would follow from the estimation of the concentrations of biologically active substances or nutrients. The risk of harm from exposure to bioactive compounds in an HGM animal-derived product can be minimized by cooking

prior to consumption of the product. In addition, because humans eat varied diets, any change in the composition of a particular HGM animal-derived product would likely prove inconsequential to the nutrition of the consumer.

While toxicity of HGM animal products might stem from mycotoxins or bacterial contamination or from toxic materials in feeds, toxins would not be expressed by the animals themselves and are not any more at issue for HGM animals than for other animals. This indicates that the risk of an unintended introduction of a toxin into an HGM animal is negligible.

The potential for novel expression or increase or decrease of allergenic compounds in an HGM animal product is relevant to risk assessment. Screening of products using a range of assays in a weight-of-evidence approach should prove sufficient to assess the allergenicity potential of HGM animal-derived products. In the committee’s opinion, the risk likelihood posed by allergenicity is low to moderate, although the effect in sensitive individuals could be large. Risk is minimized by adherence to U.S. Food and Drug Administration requirements for manufacturing and labeling of foods bearing defined allergens.

Harm to a consumer might conceivably result from a change in the composition of a food product. However, any risk associated with a change in the composition of an HGM animal-derived food may prove difficult to quantify, as the composition of any animal-derived food is also influenced by animal production practices as well as the animal’s genetic background, stage of development, reproductive status, and other factors. Therefore, to assess food safety, it is important to compare the levels of key nutritional components of HGM animal-derived food products to the range of variation of those levels in corresponding non-HGM animal-derived food products that are sold commercially. Research is needed to develop a compendium of data on important nutrient parameters in key animal species. Other needs include an analysis of data gaps, generation of critical “missing” data, and sustained public access to these data. Addressing this gap is considered necessary since the comparison of HGM animal-derived food products to conventional food products is the foundational principle for food safety assessment.

The health status and phenotype of the HGM animal is the most reliable indicator of the safety of foods derived from that HGM animal, which can be used in combination with the results of ante- and postmortem inspections to determine that food from those animals is safe to eat. Because risk mitigation measures are included in the process of HGM line development and testing, the likelihood of unintended, biologically significant changes in the composition of food products from fully developed HGM animal lines is low.

Conclusion 4-1: Risk assessment is the process of identifying potential harms to the HGM animal or to the consumer from consumption of a food product derived from an HGM animal. Risk assessment involves identifying hazards, assessing the probability of exposure to the hazards, and the probability of harm being realized given exposure to the hazards. All risks and hazards associated with HGM animals with the exception of allergens are minimized when the food product is cooked prior to its consumption. Concerns with composition of meat from HGM animals will not have any effect on the final consumer of the animal product and therefore will not have an influence on consuming decision.

Recommendation 4-1: The assessment of the food safety of an HGM animal-derived product should continue to be considered on a case-by-case basis, and to the degree possible, based upon the testing of defined food safety hypotheses.

Recommendation 4-2: Research needs to be directed to better understand how disease-resistant or disease-resilient HGM animals could drive the evolution of pathogen transmission and virulence.

EXPERIMENTAL STRATEGIES FOR ADDRESSING RISK ISSUES

Existing experimental approaches may be employed to assess the risk posed by changes to the genome of HGM food animals, subsequent food safety concerns for food products derived from these animals, and potential risks associated with the development of disease-resistant or disease-resilient food animals. In addition to phenotypic assessment carried out at every generation prior to regulatory approval, characterization of inherited changes to DNA sequence is important in evaluating the F1-F3 generations of an HGM animal line. DNA alterations can arise

from the genome-editing process or from naturally occurring random mutations, but currently it is not possible to differentiate between alterations due to natural mutation (which are considered to pose no risk) and alterations resulting from the use of animal biotechnology methods (which require risk assessment). To date, the most rigorous approach for identifying changes to the genome is the comparison and analysis of genome sequences among sire, dam, and edited offspring (also referred to as “trio sequencing”). This approach, however, is not applicable to all genome-editing approaches for food animals because the reference genomes that have been developed for most food-animal species do not capture variation across breeds.

Graph-based “pangenomes” and complete telomere-to-telomere genomes are needed to identify structural DNA variants and account for breed-specific variation. Improved gene annotation (i.e., attribution of gene function) and understanding of the function of gene regulatory regions will contribute to determining the effects of HGMs and assessing potential phenotypic effects. These issues constitute a gap in current knowledge that should be addressed to support risk assessment for HGM food animals.

Regulatory consideration should be given as to whether the intended phenotypic change that occurs in an HGM animal is likely to alter the composition of derived food products, as well as to whether the HGM could have been achieved from conventional breeding or whether it relied on expression of novel, exogenous DNA. Unless the HGM was intended to alter compositional characteristics, the HGM animal-derived foods are expected to be within the range of natural variation of nutritional composition for that product already in commerce and should not introduce allergenic potential. However, food composition will vary considerably depending upon the breed, management practices in raising animals, specific food product, and how it is prepared. A knowledge gap that needs to be addressed is the lack of sufficient fundamental information that captures the range of variation necessary to define “normal” food composition, which complicates the assessment of whether the composition of an HGM animal-derived product differs from that of a non-HGM animal-derived equivalent.

In the future, there may be HGMs that are intentionally designed to incorporate novel, desirable biochemical, compositional, or physiological changes. If a novel gene product is expressed in HGM animals and is likely to be in food derived from these animals, then toxicity and allergenicity would be evaluated as part of an assessment to ensure that the animal-derived food is safe for consumption. Hence, to ensure food safety, current approaches for determining allergenicity would need to be updated to incorporate new approaches and advances in the understanding of allergens. Methods for assessing the long-term impact of food intolerance and for determining the impact of food intolerance would also be useful and need to be developed.

Practices for identifying and managing food-animal health and welfare already exist in food-animal production systems, and practices to ensure safe food are well established across multiple stages of food production. The committee regards existing welfare laws as applying equally well to HGM and non-HGM animals and therefore recommends that welfare-assessment protocols be applied to HGM animals.

Lessons learned from the generation of disease- and insect-resistant crops and from studies of pathogen virulence and evolution indicate that multiple genes or biochemical pathways might be targeted simultaneously to avoid the evolution of pathogens to overcome a single barrier to pathogenicity. However, fundamental research is needed to identify additional HGMs that could contribute to resistance to key diseases of HGM animals. Because pathogens themselves are evolving, disease-resistant animals should be periodically tested against newly identified field isolates (using in vitro or in vivo testing) to ensure continued efficacy in combination with best-practice biosecurity measures. A crucial part of any approach for management of disease risk is surveillance. The need for surveillance of disease is not particular to HGM animals per se, but rather is part of a more general concern regarding diseases of production animals and wildlife.

Conclusion 5-1: The current experimental strategies used in conventional breeding can be used to assess HGM animals. When assessing phenotype, it is important to determine if the effect of the HGM is biologically relevant or statistically significant and to determine if the HGM could be achieved using conventional breeding. Allergenicity testing should be advanced to better understand allergens and how they function. Most importantly, animal welfare laws must incorporate HGM animals similarly to non-HGM animals including biosecurity measures, surveillance, testing, etc., to ensure safe foods and healthy animals.

SCIENTIFIC QUESTIONS TO BE ADDRESSED

Methods for producing HGM livestock are continually under refinement, and there are gaps in knowledge that need to be resolved regarding the effects of HGM techniques upon animals and upon consumers of HGM animal-derived foods. Addressing such knowledge gaps will require research that might be undertaken or supported by the U.S. Department of Health and Human Services (e.g., National Institutes of Health, U.S. Food and Drug Administration), the U.S. Department of Agriculture (USDA) (e.g., National Institute of Food and Agriculture, Agricultural Research Service), other federal government agencies, and non-governmental entities over the next 3-10 years. Recommendations related to addressing scientific questions are presented in Box S-2.

The advent of genome editors, in particular the clustered regularly interspersed short palindromic repeats (CRISPR)-Cas9 system, poses advances in the efficiency and specificity of HGM methods. However, research is needed to assess technical issues and to apply new, more precise and efficient genome-editing tools to livestock systems. Improved genome editors merit further development and evaluation in targeted research. The committee recommends the allocation of resources to investigate how various genome-editing techniques influence the frequency, consistency, and predictability of both intended and unintended alterations to genotype and phenotype. Detection of the effects of both intended and unintended modifications is of interest for assessing animal health and food safety. The committee recommends the development of best-practice workflows to assess the outcomes of HGM applications. The committee also recommends additional research supporting use of in silico tools that simulate in vivo or in vitro conditions to facilitate rapid and accurate prediction of unintended edits. Addressing these gaps in the knowledge is considered useful but not critical.

The committee recommends that, where no viable alternative is available and viral-based delivery methods, such as adeno-associated virus, are used for HGM of food animals, owing to concerns about viral integration into the host genome, an HGM candidate founder animal be screened to demonstrate absence of integration of the viral vector. Careful screening should be conducted to be sure that lines to be commercialized do not have unidentified or uncharacterized viral integration events.

The direct editing of germline stem cells combined with a surrogate sire breeding strategy could provide an efficient means for introgressing desired gene edits into breeding populations that have already been developed for specific traits. In addition, gene editing of germline stem cells in vitro could provide a means for characterization of intended and unintended DNA sequence alterations prior to the generation of cells capable of transmitting HGMs that could be used to generate whole animals. Hence, the committee recommends investment in research to improve the in vitro culture of germline stem cells from food-animal species.

There may be instances for early generations (F1-F3) of HGM animals where well-defined hypotheses can be formulated and genomic, proteomic, and metabolomic methods can be applied to gain insight into mechanisms contributing to the expression of phenotype. The committee recommends that conclusions about the importance of changes to the genome be considered in the context of any phenotypic effects in the animal, and that this assessment focus upon the phenotype of the pre-commercial generation rather than the initial HGM line progenitor.

The committee recommends that funding be allocated to develop gapless genomes and pangenomes for all food-animal species. Providing these genomic tools is considered useful but not critical. This will enhance the ability to identify structural DNA variants and make more informed choices regarding outcomes of genome editing, while also facilitating the evaluation of unintended genomic alterations.

The committee recommends more research and discussions with stakeholders to determine clear, reproducible, and quantitative assessments of food-animal welfare, particularly with respect to what constitutes a healthy mental state. This effort should encompass all vertebrate food animals, including poultry and fishes. The committee recommends discussion to define best practices for assessing and maintaining animal welfare during the development and production of HGM animal lines. The committee recommends further discussion and clarification by the animal welfare community and stakeholders regarding what types of HGMs would be considered “beneficial” or at least not render the animal “worse off.” These efforts are considered necessary and crucial to ensuring that public concerns regarding HGM food animals are being addressed. The committee notes that animal welfare laws and programs should clearly apply to the welfare of all food animals, irrespective of whether they are derived from conventional breeding programs or as a result of HGM procedures.

A leading issue for regulatory agencies and the consumer is the impact of HGM on the composition of animal-derived foods. A key threshold question is the normal composition of particular animal-derived food products, in particular, the range of variation in composition of that food product within a breed and species as the baseline for comparison to that of a corresponding product from HGM animals. The committee recommends significant investment in: (1) research that enables generation of nutrient profiles of animal-derived foods that reflect the range of nutrient variation that exists due to natural genetic variation across breeds and lines of animals, production environments, animal production and management practices, and processing and cooking methods; (2) cooperation with and expansion of USDA’s FoodData Central database for appropriate submission of profiles, capture of and associated metadata, and community standards for deposition of research data; and (3) sustained support

for FoodData Central’s Foundation Foods and Experimental Foods databases and personnel to ensure appropriate and long-term curation of these data. Sustained support for expansion and for public access to these resources will facilitate informed risk assessment of foods derived from HGM animals, as well as the effects of genotype variations on animal phenotypes.

The committee recommends hypothesis-driven compositional analysis based upon a focused approach considering the gene introduced or edited and the consequent composition changes expected for assessing the safety of HGM foods. The committee recommends that the effect of the HGM on the animal’s phenotype be considered, and that for novel products expressed in HGM animals, toxicity and allergenicity assays be performed on the resulting novel food products as appropriate. The committee recommends that allergenicity detection methods be validated and standardized to ensure utility and consistency in application before being considered for possible inclusion in evaluation by regulatory authorities.

Approval of a product for marketing within the United States or any country suggests that the product will likely enter not only domestic production, but also international trade. International trade in the products of animal biotechnology would be promoted by adoption of similar food safety assessment methods and reporting requirements across countries and supranational groupings. Scientists, developers, and regulators have met in several virtual and in-person international workshops supported by the USDA Foreign Agricultural Service that have promoted understanding of HGM technologies and adoption of science-based, risk-proportionate regulatory processes. The committee recommends that the USDA Foreign Agricultural Service and/or other agencies continue to support these international oversight harmonization activities.

Ultimately, the level of production of HGM animals and their utilization for food and products will be determined by the marketplace. Hence, public acceptance of foods derived from HGM animals is at issue. The committee recommends that a study group be established by the National Academies of Sciences, Engineering, and Medicine to gauge public understanding of and current attitudes toward animal biotechnology in agriculture and to address the need for public engagement activities related to HGM technologies, especially as applied to food animals. This study group should develop a set of best practices for engagement based on scientific assessments of past efforts at public engagement regarding emerging technologies. Such a committee should include both natural and social scientists.

REFERENCE

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