April 17, 2026 —
A major limitation in advancing in vivo CRISPR therapies has not been the editing chemistry itself, but the physical size of genome-editing enzymes. Widely used nucleases such as Cas9 and Cas12a are too large to efficiently fit داخل adeno-associated virus (AAV) vectors, the leading delivery system for gene therapy. This size constraint has pushed much of the field toward ex vivo editing approaches, leaving many tissues inaccessible for direct in vivo treatment.
A new study published in Nature Structural & Molecular Biology by researchers at the University of Texas at Austin reports a promising solution: a compact CRISPR enzyme from the Cas12f family that demonstrates robust editing efficiency in human cells. The enzyme, identified as Al3Cas12f, is significantly smaller—approximately one-third the size of Cas9—yet achieved unexpectedly strong genome editing performance across multiple genomic targets.
In initial experiments, Al3Cas12f demonstrated editing efficiencies exceeding 50% at numerous loci and reaching over 90% at select sites. These results mark a notable advance for Cas12f systems, which historically have shown limited activity in mammalian cells. Structural analysis using cryo-electron microscopy revealed that the enzyme forms a stable dimer with an optimized guide RNA architecture, enabling efficient DNA targeting and cleavage through enhanced R-loop formation.
Building on these insights, the researchers engineered an improved variant, Al3Cas12f RKK, which significantly boosted editing efficiency, achieving over 80% editing at many genomic sites in human cells. The system was validated in leukemia-derived human cell lines and applied to genes associated with diseases such as cancer, atherosclerosis, and amyotrophic lateral sclerosis.
Comparative structural analysis with other Cas12f orthologs further highlighted unique features of Al3Cas12f, including enhanced dimerization and streamlined RNA-protein interactions that contribute to its high activity. These findings suggest that structural optimization may be key to unlocking the full potential of compact CRISPR systems.
The next critical step will be to evaluate whether Al3Cas12f retains its efficiency when packaged into AAV vectors. If successful, this platform could overcome one of the most significant bottlenecks in gene therapy delivery, enabling scalable, in vivo genome editing across a broader range of tissues and diseases.
