Integrating multiplexing into confineable gene drives effectively overrides resistance in Anopheles stephensi

Abstract

Anopheles stephensi is a major malaria vector mainly present in southern Asia and the Arabian Peninsula. Since 2012 it has invaded several countries of eastern Africa, stimulating urgent efforts to develop more efficient strategies for vector control such as CRISPR/Cas9-based homing gene drives. Target site resistance is a significant challenge to the deployment of these systems. When a double-stranded break is repaired by NHEJ, it can lead to mutations which destroy the target site, making that allele unrecognizable to the sgRNA and resistant to further cleavage. The use of multiple sgRNAs has the potential to solve this issue. We performed experimental crosses to assess the homing and cutting efficiency of two different multiplexing strategies targeting the cardinal locus, in the presence and absence of a resistance allele. We found pre-existing mutations at one sgRNA target site did not significantly reduce the homing efficiency for either strategy. Modelling indicates that while both strategies can overcome resistance allele formation, the fitness of the drive-carrying alleles is a critical factor in determining the overall performance and persistence of a split drive.