“Glow in the dark cats may be vital in AIDS research,” the Daily Mirror has today reported. Several other newspapers have also featured the fluorescent felines, which scientists have created through genetic modification.
In a study published today, scientists explain how they have used a new technique to inject cat egg cells with genes for fluorescence and for resistance to feline immunodeficiency virus (FIV), a cat equivalent of the human immunodeficiency virus (HIV). Cats that have successfully received the genes will glow under UV light, indicating that they have both the fluorescence and FIV-resistance genes. While scientists have performed modifications of this type in other species, this is the first time the method has been used successfully in a carnivore.
Although the cats were successfully given a gene that has been found to fight FIV in a lab, the primary goal of this research was to explore a method of producing genetically modified cats that could be used in the future for biomedical research, and not directly to further AIDS research.
While this future research in cats might eventually help us to develop treatments for HIV and AIDS, at present this study does not indicate a way to perform human gene therapy to prevent or cure HIV. There have already been very limited trials of gene therapy in a few patients with HIV, which provide directly relevant evidence on the matter.
Where did the story come from?
The study was carried out by researchers from the Mayo Clinic, USA and Yamaguchi University, Japan. It was funded by the US National Institutes of Health and published in the peer-reviewed scientific journal Nature.
Understandably, the media focused on the cats’ modification that made them glow in the dark. This property was actually just a means for assessing whether the cats had been successfully modified to carry a virus-resistance gene. The coverage in some papers also overstated the potential benefits for HIV research. Although the results have some relevance, they do not seem to present any direct applications for the study of HIV.
What kind of research was this?
The researchers say that research on domestic cats has a “distinctive potential” for advancing both human and feline health, with more than 250 hereditary conditions common to both cats and humans and more than 90% of identified cat genes having a human equivalent. Given the parallels between species, the researchers say cats could be of value in medical and neurobiological experiments, especially in conditions where mice and rats are not useful. In particular, they say, the virus that causes feline AIDS (FIV) is similar genetically and in several other ways to HIV.
The researchers therefore argue the need for a practical method of producing genetically modified cats to realise this potential, as the methods currently used for generating transgenic mice are not feasible in cats. Mouse modification methods are achieved through injecting DNA into fertilised eggs or into embryonic stem cells, but this laboratory research was intended to explore an alternative method of transferring genetic material into cats by directly injecting genetic material into eggs at an unfertilised stage.
What did the research involve?
The researchers obtained the unfertilised eggs and sperm from the ovaries and testes of cats being neutered. They used a type of virus called a lentivirus (related to the viruses that cause HIV and FIV) to carry genetic material that would be introduced into the unfertilised cat eggs. The virus was carrying a gene from macaque monkeys that contains the instructions to produce a protein that may be able to stop lentiviruses such as FIV from reproducing themselves. The researchers hoped that the addition of this gene might make the cats resistant to FIV.
The virus also carried a jellyfish gene containing instructions for making a green fluorescent protein that would glow under UV light. This enabled researchers to track how successful the modification of the cats had been by looking for fluorescent cells. A successfully modified cat should glow green, indicating it carried both the fluorescence gene and the gene for virus resistance.
The modified lentivirus was directly injected into either unfertilised eggs or eggs that had just been fertilised by IVF. Injecting the unfertilised eggs before carrying out IVF seemed to produce more uniform results, so this approach was used subsequently.
The eggs were then fertilised in the laboratory and successful embryos implanted into healthy adult female cats, which were monitored for any resulting pregnancies and births. White blood cells from the resulting offspring were tested for resistance to the FIV.
What were the basic results?
The researchers transferred multiple fertilised embryos into 22 female cats, and five such transfers resulted in pregnancies. These pregnancies resulted in five births and three live, healthy kittens. In all five births, the kittens were found to be transgenic. This means the fluorescent protein gene and the viral resistance gene were active. Two of the kittens died shortly after birth, and one of the male kittens that lived had some health problems, such as undescended testicles and a skin condition.
The researchers looked for the presence of the green protein in cells from various sites of the body, including blood, semen and cells from the mouth obtained by scraping the inside of the cheek. Between 15 and 80% of sample cells from these locations contained an active green fluorescent protein gene. The proportion of cells containing an active green fluorescent protein gene increased as the cats got older.
The white blood cells from these animals were shown to be resistant to FIV replication in the laboratory.
Sperm cells from two of the male transgenic cats appeared to be healthy and were able to produce offspring that also carried the transgenes. Eight of the nine offspring from the transgenic males were alive and healthy.
How did the researchers interpret the results?
The researchers say that the experiment shows that transgenic cats may be used as experimental animals for biomedical research. They say they achieved “uniformly transgenic outcomes, which reduce screening and time”.
They add that, being able to manipulate the genes of a species that is susceptible to the type of viruses that cause AIDS in humans could help in testing the potential of HIV gene therapy as well as building models of other diseases.
The researchers have shown that this particular method of creating genetically modified cats is successful and more efficient than previously attempted methods in cats. In the future it is possible that this technology could be used to study FIV and look at whether gene therapy could be used to protect cats from this disease. This subsequent research may also be useful in suggesting ways to protect humans from HIV, a related virus.
However, it is important to draw a clear distinction between producing genetically modified cats born carrying a virus-resistance gene and using techniques such as gene therapy to help cure or block infections in living cats or humans. There have already been some experimental trials attempting to use gene therapy to stop the effects of HIV in humans. This is a very different technical and ethical premise from modifying people’s genes to make them resistant to HIV. As such, rather than telling us how to prevent or treat FIV in existing cat populations or, importantly, HIV in humans, the research should be seen as an exploration of how cats could be used in experimental research.
Overall, although this type of research may be valuable for the study of HIV and AIDS, far more research is required before the role of transgenic cats in this area is known.
Professor Helen Sang and Professor Bruce Whitelaw, from the Roslin Institute, University of Edinburgh have considered the implications of this research. They say: “Cats are susceptible to feline immunodeficiency virus (FIV), a close relative of HIV, the cause of AIDS. The application of this new technology suggested in this paper is to develop the use of genetically-modified cats for the study of FIV, providing valuable information for the study of AIDS. This is potentially a valuable application but the uses of genetically modified cats as models for human diseases are likely to be limited and only justified if other models, for example in more commonly used laboratory animals, like mice and rats, are not suitable.”
- Wongsrikeao P, Saenz D, Rinkoski T et al. Antiviral restriction factor transgenesis in the domestic cat. Nature Methods, Published online 11 September 2011.