Nature hides astonishing medical breakthroughs.

Take CRISPR, the transformative gene editing tool. It was inspired by a lowly bacterial immune defense system and co-opted to edit our genes to treat inherited diseases, bolster cancer treatments, or even extend lifespan. Now, Dr. Feng Zhang, one of the pioneers of CRISPR, is back with another creation that could unleash the next generation of gene therapy and RNA vaccines. Only this time, his team looked deep inside our own bodies.

Powerful as they are, DNA and RNA therapeutics need to hitch a ride into our cells to work. Scientists usually call on viral vectors—delivery vehicles made from safe viruses—or lipid nanoparticles, little blobs of protective fat, to encapsulate new genetic material and tunnel into cells.

The problem? Our bodies aren’t big fans of foreign substances—particularly ones that trigger an undesirable immune response. What’s more, these delivery systems aren’t great with biological zip codes, often swarming the entire body instead of focusing on the treatment area. These “delivery problems” are half the battle for effective genetic medicine with few side effects.

“The biomedical community has been developing powerful molecular therapeutics, but delivering them to cells in a precise and efficient way is challenging,” said Zhang at the Broad Institute, the McGovern Institute, and MIT.

Enter SEND. The new delivery platform, described in Science, dazzles with its sheer ingenuity. Rather than relying on foreign carriers, SEND (selective endogenous encapsidation for cellular delivery) commandeers human proteins to make delivery vehicles that shuttle in new genetic elements. In a series of tests, the team embedded RNA cargo and CRISPR components inside cultured cells in a dish. The cells, acting as packing factories, used human proteins to encapsulate the genetic material, forming tiny balloon-like vessels that can be collected as a treatment.

Even weirder, the source of these proteins relies on viral genes domesticated eons ago by our own genome through evolution. Because the proteins are essentially human, they’re unlikely to trigger our immune system.

Although the authors only tried one packaging system, far more are hidden in our genomes. “That’s what’s so exciting,” said study author Dr. Michael Segel, adding that the system they used isn’t unique; “There are probably other RNA transfer systems in the human body that can also be harnessed for therapeutic purposes.”

The Body’s Shipping Infrastructure

Our cells are massive chatterboxes. And they’ve got multiple phone lines.

Electricity is a popular one. It’s partly what keeps neurons hooked up into networks and heart cells in sync. Hormones are another, linking up cells from halfway around the body through chemicals in the bloodstream.

But the strangest comes from an age-old truce between human and virus. Scouring the human genome today, it’s clear we have viral DNA and other genetic elements embedded inside our own double helices. Most of these viral additions have lost their original functions. Some, however, have been recruited to build our bodies and minds.

Take Arc, a protein made from a gene otherwise known as gag—a core viral gene that’s common in our genomes. Arc is a memory grandmaster: as we learn, the protein forms tiny capsules that transfer biological material, which in turn helps to cement new memories into our neural network repertoire. Another protein similar to gag, dubbed PEG10, can grab onto RNA and also form bubbly spaceships to help develop the placenta and aid reproduction.

If PEG10 makes the cardboard packaging for genetic material, then the mail stamp comes from another viral gene family, fusogens. The gene creates a zip code of sorts, allowing each spaceship, carrying the cargo, to dock onto targeted cells.

Although originally viral in nature, these genes have immigrated into our genomes and adapted into an amazingly specific transportation system that allows cells to share information...