Recent advances in gene editing technologies have literally opened a new revolutionary avenue in precision medicine. Alongside zinc fingers nucleases and TALENs (Transcription activator-like effector nucleases), CRISPR-cas9 technology is gaining a dominant role in the new era of personalized and molecular medicine with up to 51 ongoing clinical trials on ClinicalTrials.gov. Broadly applicable technologies like TALENs maintain their role in specific settings (e.g. the targeting of noncycling cells and heterochromatin) even if they have been developed years ago. CRISPR is an acronym for Clustered Regularly Interspaced Short Palindromic Repeats referring to short DNA sequences of viral origin intercalated into the genome of prokaryotic organisms such as bacteria and archaea. Cas9 (CRISPR associated nuclease 9) is an enzyme able to create DSB (double-strand breaks) into DNA and together with CRISPR sequences is part of an ancient RNA-mediated bacterial adaptive immune system machinery, which has been firstly uncovered in a seminal article [1] by Charpentier and colleagues. The functioning of this defensive mechanisms in bacteria (i.e. S. pyogenes) is based on the generation of guide RNAs (themselves composed of a crRNA, complementary to the viral sequence and a tracrRNA, serving as a scaffold) from CRISPR genomic regions which target complementary viral DNA in case of a new infection and recruit the Cas9 nuclease inducing the destruction of bacteriophage DNA. Specifically, the Cas9 recognizes PAM (protospacer adjacent motif) regions in viral DNA and through the gRNA binding viral DNA is cleaved, with the consequent death of an infectious agent without DNA repair machinery (Figure 1).

Transporting this concept into eukaryotic cells with the purpose of gene editing has been and still is a complex task for several reasons including off-target insertions and deletions occurring after a DSB. Indeed, in eukaryotic cells DSBs serve as the sites for DNA repair mechanisms, with non-homologous end joining (NHEJ) and homology directed domain (HDR) [2]. A compelling body of evidence showed that HDR is a more precise tool while NHEJ is prone to errors [3], thus configuring HDR as the preferred DNA repair mechanism for inserting new genetic sequences into the genome reactivating specific genes and NHEJ for disrupting existing genes. Furthermore, other nucleases apart from Cas9 such as Cas13 [4] are being studied.

Despite recent advances, acute myeloid leukemia (AML) global outcome is still unsatisfactory and new strategies are eagerly awaited. While gene editing has already been used in cellular therapies such as CAR-T cells product using retroviral, lentiviral vectors, transposons [5] and plasmids, CRISPR-based technology offers intriguing options for new AML therapies.