A combinatorial CRISPR-Cas12a attack on HIV DNA.

CRISPR-Cas12a is an alternative class 2 gene editing tool that may cause less off-target effects than the original Cas9 system. We have previously demonstrated that Cas12a attack with a single CRISPR RNA (crRNA) can neutralize all infectious HIV in an infected T cell line in cell culture. However, we demonstrated that HIV escapes from most crRNAs by acquisition of a mutation in the crRNA target sequence, thus providing resistance against Cas12a attack. Here, we tested the antiviral activity of seven dual crRNA combinations and analyzed the HIV proviral genomes for mutations at the target sites. We demonstrated that dual crRNA combinations exhibit more robust antiviral activity than a single crRNA attack and, more important, that the dual-crRNA therapy can prevent virus escape in long-term cultures. We confirmed the absence of any replication-competent virus in these apparently cured cultures. Surprisingly, we did not detect excision of the HIV sequences located between two Cas12a cleavage sites. Instead, we observed almost exclusively HIV inactivation by "hypermutation," that is, the introduction of indel mutations at both target sites due to the error-prone cellular DNA repair machinery.