Bioinformatic and literature assessment of toxicity and allergenicity of a CRISPR-Cas9 engineered gene drive to control the human malaria mosquito vector Anopheles gambiae

Abstract

AbstractBackground Population suppression gene drive is currently being evaluated, including via environmental risk assessment (ERA), for malaria vector control. One such gene drive involves thedsxFCRISPRhtransgene encoding (i) hCas9 endonuclease, (i) T1 guide RNA (gRNA) targeting thedoublesexlocus, and (iii) DsRed fluorescent marker protein, in genetically modified mosquitoes (GMMs). Problem formulation, the first stage of ERA, for environmental releases ofdsxFCRISPRhpreviously identified nine potential harms to the environment or health that could occur, should expressed products of the transgene cause allergenicity or toxicity. Methods Amino acid sequences of hCas9 and DsRed were interrogated against those of toxins or allergens from NCBI, UniProt, COMPARE and AllergenOnline bioinformatic databases and the gRNA was compared with microRNAs from the miRBase database for potential impacts on gene expression associated with toxicity or allergenicity. PubMed was also searched for any evidence of toxicity or allergenicity of Cas9 or DsRed, or of the donor organisms from which these products were originally derived. Results While Cas9 nuclease activity can be toxic to some cell typesin vitroand hCas9 was found to share homology with the prokaryotic toxin VapC, there was no evidence of a risk of toxicity to humans and other animals from hCas9. Although hCas9 did contain an 8-mer epitope found in the latex allergen Hev b 9, the full amino acid sequence of hCas9 was not homologous to any known allergens. Combined with a lack of evidence in the literature of Cas9 allergenicity, this indicated negligible risk to humans of allergenicity from hCas9. No matches were found between the gRNA and microRNAs from eitherAnophelesor humans. Moreover, potential exposure todsxFCRISPRhtransgenic proteins from environmental releases was assessed as negligible. Conclusions Bioinformatic and literature assessments found no convincing evidence to suggest that transgenic products expressed fromdsxFCRISPRhwere allergens or toxins, indicating that environmental releases of this population suppression gene drive for malaria vector control should not result in any increased allergenicity or toxicity in humans or animals. These results should also inform evaluations of other GMMs being developed for vector control andin vivoclinical applications of CRISPR-Cas9.