Calling all cat people! There’s been a breakthrough in gene therapy that’s going to change TNR forever 😺

Imagine a world where TNR rescues are just cat colony caretakers. Imagine a quick course in administering injections, and being ready to tackle every cat colony in your area with nothing but love, food, and some sterile jabs in your arsenal. Imagine low-income families being able to schedule a sterilization appointment with their pet’s routine vaccinations and not having to think twice! Sounds too good to be true, right? Well that’s the world that The Michelson Found Animals Foundation imagined when they launched a grant-funded study back in 2009 offering a $25 million prize to develop a nonsurgical sterilization method for cats and dogs. After this most recent study, it seems we are finally making monumental leaps in accomplishing that world!

To claim the prize, the treatment must be permanent in a single, non-surgical dose, and be both safe and effective for male and female cats and dogs. Phew! That’s quite the stipulation, no wonder it’s taking so long! But Michelson Found wanted to light the fire under scientists to find this solution because you don’t need to be an expert in the field to know that every year, shelter animals are dying at an alarming rate.

The Shelter Animals Count (SAC) Q2 Analysis Report for 2023 has predicted that this year we’ll see 9% more cats entering shelters than leaving, which is so disheartening considering the final count for 2021 was just 1%. It’s no surprise that the added stress on resources – space, hands, food, medicine – has only seen an increase in non-live outcomes. 25% more in just two years! And that’s without factoring in what might happen now that student loan payments are restarting, or the fact that spay/neuter surgeries are getting harder and harder to schedule leading to even MORE animals to take care of.

So what could save our healthy, homeless fur-friends from needless euthanasia? For the first time in 14 years, a pair of scientists, David Pépin and William Swanson, have given us hope that non-surgical sterilization will be possible! 6 cats were treated almost 4 years ago, and through periodic ultrasounds every 3 months and blood work every 6, they’ve found no sign of pregnancy in any of them!!!

What’s the Science?

Gene therapy is most often used in the treatment of diseases by injecting new genetic material into existing cells. To do this, the genetic material (the treatment) has to be “packaged” in a form that the body can absorb. Cell membranes have a negative charge, so they naturally repel each other. In order for the treatment to have a chance at survival, it has to be packaged into a vector (most often a virus) that can penetrate a cell wall to deliver said treatment.

For this study, the scientists used Adeno-Associated Vectors (AAV). These viral vectors have been praised for their safety and efficacy as they can infect both dividing and non-dividing cells without actually integrating into the genome of the host cell. Meaning they’ll use the cell to help produce and reproduce the therapy, without altering the original genes. Specifically, the AAV9 serotype has been favorable in administering gene therapy in cats due to the low antibody reaction.

The therapy itself was to focus on the Anti-Müllerian Hormone (AMH). Naturally occurring AMH in cats is produced in the follicles of a sexually mature ovary, but by increasing the amount of AMH to supraphysiological levels (more than naturally occurring), Pépin and Swanson found it actually suppressed folliculogenesis (the process by which the female germ cell develops in the ovary and matures into a fertilizable egg). Gives new meaning to everything in moderation, right?

The Test!

6 cats were injected with a vector carrying the AMH treatment (AAV9-fcMISv2) – 3 with a high dose, 3 with a low dose – and 3 cats were injected with a blank vector for the control group. This way, the researchers could be sure that any effects they were witnessing was purely because of the treatment and not the virus they were using to administer it.

Each cat went through a physical exam and bloodwork two weeks prior to the first treatment and again on Day 0 right before treatment. This would establish a baseline for that cat so they could monitor any significant changes or declines in the cats’ health as the study progressed. After treatment, the cats went through the same physical and bloodwork every 3 months through the first year, and every 6 months after that. Consistently, every cat showed normal results from testing and no clinically relevant increases of markers of renal, liver, or skeletal muscle damage.

Interestingly, the AMH levels gradually decreased through the first year before reaching a plateau by year 2. This plateau was still above the target concentration that would allow for the suppression of folliculogenesis.

The Result…

It worked. It kept working. It’s still working!

Each cat went through two 4-month long mating trials, the first at 8 months post-treatment, and the second at 20 months. One proven-breeder male was housed with the 9 females for 8 hours a day, 5 days a week and monitored through video for any breeding interactions. In BOTH trials, all 3 control kitties were pregnant on the first breeding bout and gave birth to 2-4 healthy babies in each litter. More importantly, in BOTH trials, NOT ONE treated female became pregnant.

Notably, the treatment didn’t completely eliminate breeding behavior or activity, one of the low-dose cats (Dolly) allowed 6 breeding bouts and a high-dose cat (Barbara) allowed 1. This suggests that while increasing AMH in cats can efficiently prevent a viable ovulation (again, none of the treated females became pregnant), it doesn’t prevent the cycle altogether which makes it a less than ideal solution for domestic pets. No one wants a cat in heat running through their house!

The 6 treated kitties received their injections about 4 years ago. They’ve continued to have physical exams every 3 months, and bloodwork every 6, and there has still been no evidence of pregnancy. In short, this study has demonstrated that gene therapy can prevent pregnancy for multiple years with no apparent health effects in treated female cats – still a far cry from winning the Michelson prize, but if this doesn’t excite you, you’ve not yet stopped to consider the implications.

The Takeaway

David Pépin and William Swanson have made historic progress towards finding an alternative to surgical sterilization. When you factor in the cost of vet school to be able to perform a surgery, the cost of equipment and anesthesia, the risk of anesthesia, the time consumed in both surgery and recovery, and the sheer number of feral cats in a post-pandemic world, it’s easy to be overwhelmed. It’s easy to lose yourself in the feeling of futility and that animal rescuers will just have to handle what they can until they inevitably burn out. But look at what this study has achieved!

One, easily-administered injection, and these cats were able to go about their lives and their normal behaviors – just without the babies. Could this breakthrough help us catch up for the lost year of TNR? Would volunteers even be willing to administer these injections if they become readily available? While this particular study couldn’t provide a solution for domestic cats, imagine freeing up your low-cost spay/neuter clinics from the backlog of feral kitties for helping more low-income families or families in crisis! The potential is there for helping both animals and humans, pet owners and rescuers!