Stanford Scientists Develop TIGRa, a Compact Gene Activation Tool Poised to Outperform CRISPR

For years, the promise of gene therapy has run up against a stubborn physical problem: the tools that can precisely control which genes turn on and off inside human cells are simply too large to fit inside the delivery vehicles that would carry them through the body. CRISPR, the most widely known of these tools, works powerfully in the laboratory, but when researchers try to package its genetic instructions into a virus small enough to slip into cells, there often isn't room. For diseases that might require adjusting multiple genes at once, the logistics become even more forbidding—multiple separate deliveries, each one a gamble.

Stanford Medicine researchers have now developed a tool that sidesteps this constraint entirely. Called TIGRa, it performs the same essential function as CRISPR-based gene activators but occupies less than half the physical space. The system is compact enough that its DNA instructions fit comfortably inside viral vectors with room remaining, opening the possibility of delivering multiple genetic adjustments in a single treatment.

TIGRa is built on a molecular system called TIGR-Tas, discovered only last year by researchers at the Broad Institute. Like CRISPR, which bacteria evolved as an immune defense against viruses, TIGR-Tas emerged in parasitic bacteria and viruses, though its original biological purpose remains unclear. Both systems work by using a guide RNA—essentially a molecular mug shot—to locate a specific stretch of DNA and then act on it. Scientists can reprogram these guides to target different genes, making the systems flexible tools for different therapeutic goals.

When Zhiquan Liu, a postdoctoral scholar in ophthalmology at Stanford, set out to engineer a smaller gene activation tool, he tested more than a dozen molecular prototypes. The results surprised him. TIGRa, one of the smallest candidates, emerged as the most efficient at actually turning genes on. "Usually when the size is smaller, the efficiency will be lower," Liu said, "but TIGRa had very high activation efficiency compared with the others, even though it's also very, very small." The team then refined the design further, creating variants including TIGRa-Pro and TIGRa-Ultra, which are slightly smaller and more powerful, and TIGRa-Mini, a stripped-down version retaining about 70 percent of the original's effectiveness.

In laboratory tests, TIGRa demonstrated the ability to activate up to twelve different genes simultaneously. In one striking demonstration, researchers used it to reprogram adult skin cells into an embryonic state—a feat requiring seven genes to be switched on in concert. When tested against nine genes of therapeutic interest, TIGRa outperformed CRISPR gene activators in six of them, including genes that could counter retinal degeneration, muscular dystrophy, and obesity.

The most compelling evidence came from animal studies. Researchers packed TIGRa into viral vectors and injected them directly into the eyes of mice, programming the tool to activate two protective genes known to shield retinal ganglion cells—the nerve cells damaged in glaucoma and other degenerative eye conditions. Two weeks later, when the mice were subjected to a retinal injury that typically causes blindness, those that had received the TIGRa treatment retained roughly one-third of their vision. Untreated mice became nearly blind. The survival rate of retinal ganglion cells doubled in treated animals, and the protective effect persisted four months later.

Yang Sun, the study's senior author and a professor of ophthalmology, chose the eye as a testing ground deliberately. "It's easier to measure whether the eye is able to see than whether the liver is working," he said. "In the visual system, you can tell right away." The work, published in Cell Stem Cell in August 2026, represents a proof of concept—but Sun and Liu acknowledge that human applications remain years away. Retinal degeneration and glaucoma are complex diseases, and the two genes activated in the mouse study, while protective, are insufficient on their own. Future treatments will likely need to regulate multiple genes in different combinations.

Stanford has filed a patent for TIGRa. Sun sees potential far beyond the eye. "Because it's very small and versatile, it could be used for many different diseases throughout the body, including heart conditions, liver conditions, skin conditions, cancer, neurodegeneration, stroke and any number of things," he said. The compact size that makes TIGRa fit into viral vectors also makes it theoretically suitable for treating conditions across multiple organ systems—a flexibility that CRISPR's bulk has constrained. If the right genes are targeted in the right diseases, Sun believes human trials could move faster than other gene therapies have managed.