One of the unexpected problems of modern gene therapy is size. A molecular tool may work perfectly in the laboratory, but turn out to be too bulky to be efficiently delivered inside a living organism.
This problem is especially acute for CRISPR-based gene activation systems. Many of them use large dCas9 proteins along with additional activating components. Packaging all of this into a single adeno-associated virus — AAV, widely used for delivering genetic constructs — is difficult.
Researchers at Stanford Medicine have created an alternative — TIGRa, an ultracompact programmable gene activator. It is based on the TIGR-Tas system, discovered by researchers at the Broad Institute, MIT, and Harvard and described in Science in 2025.
TIGRa acts as a molecular switch: a guide RNA brings the system to a selected region of the genome, after which it enhances the activity of the desired gene. The DNA sequence itself does not necessarily change.
The main advantage is size. TIGRa is less than half the size of comparable dSpCas9-based activators while maintaining high efficiency. This allows the entire system, together with guide RNAs, to fit into a single AAV vector.
But even more interesting turned out to be TIGRa's ability to work with several genes at once. In cell experiments, researchers managed to simultaneously activate up to 12 endogenous genes from a single compact construct. In another experiment, TIGRa switched on seven genes at once and reprogrammed adult human fibroblasts into induced pluripotent stem cells.
When compared with CRISPR activators, TIGRa also showed high efficiency. The scientists tested nine therapeutically interesting genes, and for six of them TIGRa provided stronger activation.
Testing in a living organism
The next step was the mouse retina.
The researchers packaged TIGRa into AAV and tuned the system to activate two neuroprotective genes — CaMKIIa and CaMKIIb — in retinal ganglion cells.
Two weeks later, the animals were subjected to retinal damage using NMDA. In mice that received TIGRa, the survival of ganglion cells increased approximately twofold, and about a third of visual function was preserved after the damage. In untreated animals, vision was almost completely lost.
Moreover, the protective effect persisted after four months.
This is important, but so far it is precisely a proof of concept in mice, not a ready-made therapy for glaucoma or other neurodegenerative diseases.
The authors suggest that the ability to simultaneously control multiple genes may prove especially valuable precisely in complex diseases where a single molecular switch is insufficient.
Potential areas of application are significantly broader than the eye: heart and liver diseases, skin conditions, neurodegeneration, stroke, and some areas of oncology. However, all this is still prospects that have yet to be tested experimentally. The researchers have filed a preliminary patent application for the technology.
The work was published on 10 August 2026 in the journal Cell Stem Cell.
TIGRa represents an interesting shift in the development of gene therapy. The question is no longer only how precisely we can target the genome. Equally important is how compact a molecular tool must be to actually be delivered where it is needed.
And here, small size becomes not a compromise but an advantage: a single compact molecular switch can control an entire program of genes at once.
