At the end of April, Mammoth Biosciences came out of stealth mode and announced a new CRISPR system for use in highly sensitive diagnostics for infectious disease and cancer. Around the same time, the demonstration of CRISPR diagnostics in detecting dengue and Zika viruses opened up new possibilities for the detection and surveillance of outbreaks in low-resource field settings. But whether the focus is diagnostics, research reagents or therapeutic interventions, new discoveries around CRISPR endonucleases, such as Cas13 and Cas12a, are giving rise to a clutch of new companies including Mammoth, Arbor Biotechnologies and most recently Beam Therapeutics, launched in May. As gene editing research continues at a breathless pace the commercial sector is scrambling to keep up.
CRISPR-based diagnostics focus on two different formats; one leverages the capacity of Cas12a, the other of Cas13. Researchers led by Mammoth co-founder Jennifer Doudna of the University of California, Berkeley, describe a system based on Cas12a (also known as Cpf1) to detect human papilloma virus (HPV) in a Science paper (360, 436, 2018). The DETECTR (DNA-endonuclease-targeted CRISPR trans reporter) diagnostic is so-called because it capitalizes on the induction of non-specific 'collateral' (trans) cleavage of single-stranded DNA (ssDNA) sequences after Cas12a binds to the double-stranded DNA (dsDNA) sequence of its target (e.g., cDNA derived from the RNA genomes of dengue or Zika). To exploit this mechanism in a diagnostic, the researchers supply short ssDNA fluorescent reporters that glow only when quencher molecules are removed from the reporter ends via Cas12a collateral cleavage. The authors demonstrate the system can detect, with attomolar sensitivity, HPV types 16 and 18 from clinical specimens (in which levels of HPV dsDNA are boosted by recombinase polymerase amplification).
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