Clustered, regularly interspaced, short palindromic repeats (CRISPR)–Cas9 has been a promising tool for gene engineering, for example, in correcting disease-associated mutant alleles in somatic or stem cells [1]. Cas9 is a single endonuclease evolved in bacteria and archaea to function as a natural adaptive immune system [2,3]. Cas9 programmed with crRNA (CRISPR RNA) and tracrRNA (trans-activating crRNA) (Cas9–sgRNA ribonucleoprotein complex) has HNH and RuvC nuclease domains to cleave target DNA, generating two blunt ends of double-strand breaks (DSBs), usually 3 bp upstream of a protospacer adjacent motif (PAM, NGG for SpCas9 from Streptococcus pyogenes) sequence [3,4].

Acute myeloid leukemia (AML) is an aggressive malignancy of the blood system and the most common acute leukemia in adults [1,2]. Improvements in chemotherapy combined with a limited number of targeted approaches, thanks to better understanding of the disease mechanisms, have significantly extended survival in younger patients. Yet, the outcomes in advanced-age AML patients (≥65 years, constituting more than half of all cases) remain dismal. Although studies have reported survival benefit of induction chemotherapy dose intensification [3,4], most patients are unable to tolerate aggressive treatment because of comorbidities and frailty [2,5].

Patients with acute myeloid leukemia (AML) have a poor prognosis. The accumulation of genetic and nongenetic alterations in hematopoietic stem/progenitor cells (HSPCs) results in AML, and a growing body of evidence has provided ideas for leukemia prevention and interventions of preleukemic conditions [1–4]. Approximately 10% of healthy adults aged over 65 years have leukemia-related mutations in hematopoietic cells, a condition called clonal hematopoiesis (CH) [5–7]. The leukemic transformation from this “preleukemic” status occurs in some high-risk patients who harbor multiple mutations in specific genes (e.g., splicing factors, ASXL1) and higher variant allele frequency of mutated genes [8–10].

Bone marrow stromal cells (BMSCs) are essential cells of the bone marrow (BM) [1,2]. Particularly mesenchymal stromal cells (MSCs), also referred to as CXCL12-abundant reticular (CAR) cells, have been reported to play key roles in both the homeostatic and malignant BM niches [1]. Classically, MSCs are defined by in vitro characteristics including trilineage differentiation [1,2] and typical surface marker expression and, thus, are often termed progenitor stromal cells [3]. Cultured bone marrow-derived stromal cells (cBMSCs) are relatively easy to propagate and are used widely for in vitro assays.

Sickle cell disease (SCD) is an inherited blood disorder that affects millions of people worldwide [1,2] and is caused by a point mutation within the β-globin gene, resulting in a substitution of valine for glutamic acid at position 6 in the β-globin chain. The abnormal β-globin chain combines with α-globin resulting in the production of hemoglobin S (HbS). HbS polymerizes on deoxygenation resulting in red cell fragility, hemolysis, and anemia. In addition, those with SCD suffer from acute and chronic pain episodes, multisystem organ damage, and a shorter lifespan [3].