CRISPR-Cas9n-mediated ELANE promoter editing for gene therapy of severe congenital neutropenia.

Severe congenital neutropenia (CN) is an inherited pre-leukemia bone marrow failure syndrome commonly caused by autosomal-dominant ELANE mutations (ELANE-CN). ELANE-CN patients are treated with daily injections of recombinant human granulocyte colony-stimulating factor (rhG-CSF). However, some patients do not respond to rhG-CSF, and approximately 15% of ELANE-CN patients develop myelodysplasia or acute myeloid leukemia. Here, we report the development of a curative therapy for ELANE-CN through inhibition of ELANE mRNA expression by introducing two single-strand DNA breaks at the opposing DNA strands of the ELANE promoter TATA box using CRISPR-Cas9D10A nickases-termed MILESTONE. This editing effectively restored defective neutrophil differentiation of ELANE-CN CD34+ hematopoietic stem and progenitor cells (HSPCs) in vitro and in vivo, without affecting the functions of the edited neutrophils. CRISPResso analysis of the edited ELANE-CN CD34+ HSPCs revealed on-target efficiencies of over 90%. Simultaneously, GUIDE-seq, CAST-Seq, and rhAmpSeq indicated a safe off-target profile with no off-target sites or chromosomal translocations. Taken together, ex vivo gene editing of ELANE-CN HSPCs using MILESTONE in the setting of autologous stem cell transplantation could be a universal, safe, and efficient gene therapy approach for ELANE-CN patients.

Paediatric autoimmune diseases with ELANE mutations associated with neutropenia.

OBJECTIVE: To explore the clinical characteristics of autoimmune diseases in children with ELANE mutations. METHODS: Three cases of children with ELANE mutations manifesting as autoimmune diseases, who were under treatment from April 2020 to May 2021, were retrospectively analysed. RESULTS: Among the three children, two were boys aged 15 years and 22 months (cases 1 and 3) respectively, and the other one was a 22-month-old girl (case 2). All the cases had recurrent infections. Case 1 presented with cyclic neutropenia and systemic lupus erythematosus (SLE). Case 2 presented with severe neutropenia and autoimmune haemolytic anaemia (AHIA). Case 3 presented with severe neutropenia and anti-neutrophil cytoplasm antibodies (ANCA)-associated small vasculitis. Genetic tests showed that they all had heterozygous mutations in the ELANE gene. Case 1 was treated with methylprednisolone and hydroxychloroquine sulphate for 2 years, making neutrophil level return to normal. Case 2 received allogeneic hematopoietic stem cell transplantation and has stopped taking antibiotics, steroids and all the immunosuppressors. Case 3 received subcutaneous injections of granulocyte colony-stimulating factor, oral prednisone and cyclophosphamide. The boy in case 3 has been followed up for one year, and his absolute neutrophil count has increased to 1.56 × 109/L. CONCLUSION: Patients with ELANE mutations, combined with autoimmune diseases, may have recurrent infections. Disease-modifying antirheumatic drugs (DMARDs) are effective for autoimmune diseases. Autoimmune diseases with ELANE mutations associated with neutropenia can be cured through allogeneic hematopoietic stem cell transplantation.

Neutrophil Elastase Defects in Congenital Neutropenia.

Severe congenital neutropenia (SCN) is a rare hematological condition with heterogenous genetic background. Neutrophil elastase (NE) encoded by ELANE gene is mutated in over half of the SCN cases. The role of NE defects in myelocytes maturation arrest in bone marrow is widely investigated; however, the mechanism underlying this phenomenon has still remained unclear. In this review, we sum up the studies exploring mechanisms of neutrophil deficiency, biological role of NE in neutrophil and the effects of ELANE mutation and neutropenia pathogenesis. We also explain the hypotheses presented so far and summarize options of neutropenia therapy.

New insights into the pathomechanism of cyclic neutropenia.

Cyclic neutropenia (CyN) is a hematologic disorder in which peripheral blood absolute neutrophil counts (ANCs) show cycles of approximately 21-day intervals. The majority of CyN patients harbor ELANE mutations, but the mechanism of ANC cycling is unclear. We performed analysis of bone marrow (BM) subpopulations in CyN patients at the peak and the nadir of the ANC cycle and detected high proportions of BM hematopoietic stem cells (HSCs) and hematopoietic stem and progenitor cells (HSPCs) at the nadir of the ANC cycle, as compared with the peak. BM HSPCs produced fewer granulocyte colony-forming unit colonies at the ANC peak. To investigate the mechanism of cycling, we found that mRNA expression levels of ELANE and unfolded protein response (UPR)-related genes (ATF6, BiP (HSPA5), CHOP (DDIT3), and PERK (EIF2AK3)) were elevated, but antiapoptotic genes (Bcl-2 (BCL2) and bcl-xL (BCL2L1)) were reduced in CD34+ cells tested at the ANC nadir. Moreover, HSPCs revealed increased levels of reactive oxygen species and gH2AX at the ANC nadir. We suggest that in CyN patients, some HSPCs escape the UPR-induced endoplasmic reticulum (ER) stress and proliferate in response to granulocyte colony-stimulating factor (G-CSF) to a certain threshold at which UPR again affects the majority of HSPCs. There is a cyclic balance between ER stress-induced apoptosis of HSPCs and compensatory G-CSF-stimulated HSPC proliferation followed by granulocytic differentiation.