Strategies to improve the efficiency of homing gene drives with multiplexed gRNAs

CRISPR homing gene drive holds great potential for pest control, but its success is challenged by the generation of resistance alleles through end-joining repair. Using multiple gRNAs to target adjacent sites within a conserved gene can prevent functional resistance by allowing repeated cleavage events, but poor homology during DNA repair may compromise efficiency.

We first assessed the efficiency of single gRNA drives with truncated homology arms in Drosophila melanogaster mimicking a multiplexed system in which only one site is cleaved. Integrating results into a detailed gRNA multiplexing model, we found that efficiency loss was greater than expected. To mitigate this, we evaluated two new strategies: (1) extended homology arms to span all target sites (with mutations in the PAMs to prevent self-cleavage) and (2) a population-level gRNA multiplexing system involving two or more drives, each carrying two gRNAs. Extended homology arms did not result in notable improvement in conversion efficiency, and the extended region could be lost during drive conversion. The population-level multiplexing gRNAs strategy was more promising, though the intentionally mutated PAM also could not be consistently inherited. Simulations of homing suppression drives applying population-level multiplexed gRNAs increased the success rate of population elimination and reduced the time required for suppression.

Future drive designs requiring a larger number of gRNAs could potentially be improved. The design relying on extended homology arms may not represent an optimal strategy. However, population-level multiplexing gRNAs could serve as a promising alternative, enhancing efficiency while maintaining tolerance to functional resistance.