A universal and orthogonal safety valve for CRISPR/Cas12a without chemical modification or external stimulation.

CRISPR/Cas-based gene editing technologies have achieved remarkable progress over the past decade, yet their broad practical applications remain limited by safety concerns. Although regulatory strategies applied before or during CRISPR/Cas activation have substantially improved sequence, temporal, and spatial specificity, persistent activity of already activated Cas nucleases may still increase the risk of uncontrolled editing. Therefore, an effective post-activation control strategy is urgently needed. Here, we report a modification- and stimulation-free RNA inhibitor (iRNA) that functions as a post-activation safety valve for CRISPR/Cas12a. By exploiting Cas12a's allosteric sensitivity and the thermodynamic and kinetic programmability of nucleic acid strand displacement, iRNA drives already activated Cas12a ribonucleoproteins back to an inactive state, enabling universal, sequence-programmable, and orthogonal post-activation inhibition within the validated Cas12a framework. Experiments and simulations elucidate the mechanistic basis of iRNA-mediated strand displacement and demonstrate its high inhibitory efficiency, reversible cyclic control, compatibility, expandability, orthogonality, and universality. Importantly, iRNA also acts as a programmable, autonomously operating safety valve in cells, suppressing uncontrolled editing while preserving PCSK9 gene knockout. With its simple design, excellent biocompatibility, and autonomous intracellular expression, iRNA provides a foundation for next-generation controllable CRISPR systems and holds broad potential for precision therapeutics, cell therapy, and molecular diagnostics.