Caribou Biosciences has developed a gene-editing system that uses CRISPR hybrid RNA-DNA (chRDNA) guides to improve on traditional CRISPR Cas9 gene editing. The system allows multiple gene edits to, for example, remove PD-1 from the surface of T-cells used in CAR-T cell therapies. The aim is to remove the “brakes” from the cell therapy product to maintain high tumor activity and improve clinical benefits.