Rather than spaying and neutering feral animals, giving them a single shot might be enough to help control the pet population one day. Researchers have developed a DNA injection that causes muscle cells to produce antibodies that stop the production of sperm and eggs. And so far it works with mice. The findings were published in Current Biology this week.
Vaccines that trigger an immune response against reproductive hormones already exist. But so-called immunocontraception, like many other immunizations, relies on an immune response that may diminish over time. "In recent years, a number of labs have shown that you can express high levels of antibodies in small and larger animals to prevent disease,” Caltech’s Bruce Hay said in a statement. “We thought: why not try it to manipulate physiology as well?"
To find a non-surgical method of long-term (or even permanent) contraception, Hay and colleagues turned to an antibody that can neutralize gonadotropin-releasing hormone (GnRH) in mice. Made in the brain, GnRH helps promote the secretion of hormones in males and females that stimulate sperm and egg development. They packed a gene for the anti-GnRH antibody inside the shell of a virus that infects mammals but doesn’t cause symptoms.
Rather than use the immune system, they delivered the packaged DNA into muscle, and once there, muscle cells used the DNA to produce the antibodies. Unlike immune cells, muscle cells rarely turn over, so they can likely produce the antibodies for the recipient’s lifetime. The shots appeared to have no side effects, and after about two months, all of the mice who received it become infertile. “That two-month delay is because of how long it takes the muscle to start producing enough antibody,” Hay tells Science.
Additionally, the team also managed to make female mice infertile by using an antibody that binds the zona pellucida, the protein layer surrounding the egg cells. This method prevents sperm from fertilizing the egg without interfering with hormone levels.
"Spaying and neutering wild animals is not a trivial process – it takes money and time to anesthetize them, do the surgery, and let them recover," Hay added. "This is a much more benign way of managing populations." The team is currently conducting a pilot study on female cats.
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