The first thing you should know is that truly allergen-free cats are a myth. We’re sorry.
This is because all cats – long hair, short hair, no hair – secrete a harmful little protein called Fel d 1, which is found in saliva and sebum glands and is what causes most cat allergies. Some cats lose 80 times more of it than others of the same breed; nobody knows why. Some lose more one month and less the next. While certain races can make less Fel d 1 on average, the evidence is sparse. In the 2000s, a much-touted start-up that claimed to have bred hypoallergenic cats collapsed into disgrace, leaving some customers with pets who still made them gasp and others who spent thousands of dollars upfront without a cat had. That said, the demand for allergen-free cats is great. Only nobody has managed to breed one yet.
However, where old-fashioned breeding failed, scientists are now turning to biotechnology. In recent years, a number of science fiction-like strategies have been targeted at Fel d 1: a kibble coated with an egg yolk derivative that neutralizes the allergen, a vaccine that uses cucumber mosaic virus to fool the cat’s immune system, and a gene therapy that uses CRISPR editing technology to remove the Fel d 1 gene from cat DNA. This kibble is indeed available on the shelves as Purinas Pro Plan LiveClear cat food. The vaccine has been tested on more than 100 cats. And although useful gene therapy is much further away, scientists have succeeded in removing Fel d 1 from cat cells in a Petri dish.
Neither of these strategies will completely eliminate Fel d 1 in a cat, but they could reduce allergen levels enough to stave off itchy eyes and sneezes. (Incidentally, hypoallergenic is often used colloquially for “allergen-free”, but technically it just means “reduce allergies”.) This reduction can be enough to let allergy sufferers keep their beloved cats. “When I was growing up, I used to say, ‘Oh, you really need to get rid of your cat,'” says William Nish, an allergist in Georgia. “That made me very unpopular.” Allergists like him are now suggesting that cat owners try allergy pills or allergy injections for themselves – vacuuming with a HEPA filter, bathing their cat regularly and keeping them out of the bedroom.
While these strategies are largely aimed at humans, newer biotech ideas all aim at customizing the cat to what humans want. And that may not be so new. These ideas incorporate newfangled technology, but they may just be the next logical step in our millennia-long relationship with cats that turned a savage killer into Fluffy, who meows after nibbles and snuggles into bed at 8 p.m.
A century ago, domestic cats spent most of their time outdoors. The exclusive indoor cat is a fairly modern development – made possible by the invention of bedding. And it wasn’t until the cats got closer to us physically that all of the little bits of Fel d 1 that they spilled became a problem.
Ebenezer Satyaraj, the director of molecular nutrition at Purina’s parent company Nestlé, began thinking about how to use cat food against Fel d 1 more than a decade ago. One important finding, he told me, was simply that cats spend a lot of time grooming themselves. Usually, this behavior spreads the Fel d 1 with its saliva all over its fur, which in turn ends up on your couch, sweater, bed, etc., etc., etc. But what if you could interrupt this process by feeding the cats something that neutralized the field 1 in the mouth?
Satyaraj and his team came up with the idea of using anti-Fel d 1 proteins purified from egg yolk, which are made by injecting Fel d 1 into a hen. Your immune system treats this field 1 like a piece of a foreign pathogen and raises antibodies that bind and neutralize it. These antibodies get into the egg yolk to pass on protection to the chicks. But it is noteworthy that they can also function as a kind of immunity transfer between the species: There is, for example, a pig feed additive that is made with the egg yolk antibodies, which are supposed to protect against E. coli. In this case, Satyaraj wanted the egg yolk antibodies to neutralize Fel d 1 in cats and ultimately activate a chicken’s immune system to protect allergic people.
It worked. The egg yolk coating on Purina’s cat food reduces the amount of allergens by an average of 47 percent. The goal here, says Satyaraj, is to bring Fel d 1 levels below a threshold to minimize allergy symptoms – it might not be enough for all, but it should be enough for some. A study in allergic people found that using Purina’s cat food helped reduce congestion and itchy eyes. How well the kibble works depends on how much Fel d 1 a cat starts with and how sensitive the owner is to even the smallest amounts of the allergen. And any effect only lasts as long as you feed them Purina’s food.
A second idea of making cats hypoallergenic is to harness the power of the cat’s immune system, with the effects potentially lasting longer. In 2013, scientists from the University of Zurich founded a company, now called Saiba Animal Health, to manufacture a vaccine for cats that reduces the excretion of Fel d 1 in the shell of a cucumber mosaic virus, which in turn is embedded with a little tetanus toxin. This simulates the cat’s immune system that Fel d 1 is part of a virus, says Gary Jennings, Saiba’s chief operating officer. After immunization, the cat begins to produce antibodies that neutralize Fel d 1. Her allergen levels actually dropped over several weeks, and Saiba found that the allergic cat owners were able to spend more time petting their vaccinated cats. The company has since licensed the technology to a large animal health company, whose name Jennings claims cannot reveal in order to collect the data required for regulatory approval.
Both the human doctors and the veterinarians I spoke to thought such a vaccine would exist on an interesting frontier: Was a vaccine given to cats to treat humans considered an animal vaccine or a human vaccine? Who would regulate it anyway? Jennings told me that based on discussions with the FDA and the European Medicines Agency, both would oversee it as an animal vaccine – but a little differently. The FDA needs to make sure that the vaccine does not harm cats and works in humans, but the EMA wants to weigh the harm and benefit to the cat itself.
How do we balance the risks of treating a pet against the convenience and pleasure of its owner? This question felt very new for a second, until I realized that only the novelty of a cat allergy vaccine made the question seem that way. We used to declaw cats to protect our furniture. (No longer acceptable.) We still remove their testicles or ovaries to curb sexual behavior that would bother them as pets in the house. (Completely acceptable, very encouraged.) Could you even say that surgery or a vaccine will benefit the cat itself when a pet that has been modified into a more suitable indoor pet makes its owner happier and more fond of it?
Also, to assess the potential harm in fighting Fel d 1, we need a better understanding of the protein and its precise effects in cats. Unfortunately, “nobody really knows the answer,” says Drew Weigner, an Atlanta veterinarian who specializes in cats. Scientists have hypothesized that Fel d 1 could act like a pheromone for social signals. That could mean it is less important for house cats, especially those that live alone. Male cats also tend to produce more Fel d 1, and neutering them even decreases their levels by three to five times – meaning we are already routinely changing the cat’s Fel d 1 production. The high variability in allergen concentrations from cat to cat suggests that a reduction should not have massive consequences. Indeed, the studies of cats fed anti-Fel d 1 nibbles and those given the vaccine did not find any significant side effects associated with a decrease in protein levels.
But what if you went further and deleted the very gene that codes for Fel d 1 from a cat’s DNA? Nicole Brackett, researcher at Indoor Biotechnologies, used the powerful new gene editing technology CRISPR to remove the gene from cat cells. And as part of that work, she investigated the role of Fel d 1 in all domesticated and wild cats. She discovered that the Fel d 1 gene sequence varies enormously from species to species – let’s say panther to lion – but also from cat to cat. The fact that it is not preserved through evolution, Brackett says, suggests that “it may not be functionally important to the cat”.
Indoor Biotechnologies’ goal is not to genetically engineer a new cat without Fel d 1, as the company is not interested in getting into the cat breeding business. Rather, Brackett and her colleagues hope to lay the foundation for gene therapy in the form of an injection that will remove Fel d 1 from enough cells to lower the cat’s overall production. In the laboratory, Brackett Fel d 1 was able to switch off up to 55 percent of the cat cells in a Petri dish. That reduction could be enough to make a cat hypoallergenic, she says, if a pet went to the vet for a new injection of gene therapy every few months or once a year. However, there are still many challenges ahead. Brackett tested CRISPR in a type of cell commonly used in laboratories because it grows well – but they come from cat’s kidneys and do not produce natural field 1. So she still has to make sure that CRISPR works in cells in the saliva and sebum, and then figure out how to smuggle the CRISPR machinery into those cells in a living animal – which is still a key problem for human CRISPR therapies.
But scientists have come a long way too. Martin Chapman, President and CEO of Indoor Biotechnologies, was part of the original team that first isolated the gene for Fel d 1 in the 1990s. Even then, he says, he remembered thinking, wouldn’t it be great if we could delete these genes? But that was not possible with the technology at the time. All of these new ideas for dealing with cat allergies are based on breakthroughs in other areas: CRISPR of course, but also the development of egg yolk antibodies and the invention of new strategies for making human vaccines. In the 21st century, biotechnology is silently touching so many aspects of our lives that it comes as no surprise to our pets either.
The indoor cat is already a distinctly different creature than the first feral cat to roam human settlements in search of rodents. We have adapted cats to our lifestyle and will continue to do so for as long as ordinary pets are. At some point we might even have a really allergen-free cat.