Base editing and prime editing for sickle cell disease

St. Jude Children'S Research Hospital, Memphis TN

Investigators

Linked publications, trials & patents

Abstract

PROJECT SUMMARY Despite advances in the medical care of sickle cell disease (SCD), most patients still experience poor quality of life, progressive organ damage, and premature death. Allogeneic hematopoietic stem cell (HSC) transplantation can cure SCD but is associated with immune toxicities and only 20% of patients have optimal donors. In December 2023, two new SCD therapies based on genetic modification of autologous HSCs with Cas9 or lentiviral vector were FDA-approved. While these treatments are promising, ongoing concerns include their long- term efficacy and safety, including Cas9- or lentiviral vector-associated genotoxicities and the requirement for toxic myeloablative bone marrow (BM) conditioning to facilitate engraftment of modified HSCs. This renewal application summarizes our ongoing efforts to treat SCD using two “next-generation” genome engineering tools with potentially superior safety and efficacy than the currently approved approaches and to develop reduced toxicity BM conditioning. Aim 1 employs base editing to induce the expression of red blood cell fetal hemoglobin (HbF, 22), a potent anti-sickling agent. Aim 2 utilizes prime editing to revert the mutant SCD mutation to normal, which represents the most physiological genetic intervention and has been difficult to achieve with other technologies. Compared to Cas9, base editing and prime editing install more precise, predictable genetic changes with low levels of double strand DNA breaks that can cause structural chromosomal abnormalities, cell death, or malignant transformation. During the first four years of this grant, we optimized base editor-mediated induction of HbF and prime editor correction of the SCD mutation in BM repopulating HSCs from heathy donors and SCD patients to greater levels than achieved with Cas9-based approaches, and acceptable safety profiles. Now we will perform advanced process optimization, scale-up, and more extensive safety studies to support FDA investigational new drug applications for each strategy. Developing both strategies simultaneously will allow us to compare their outcomes directly in future clinical studies and ultimately to determine the best therapeutic approach. Long-term, we aim to couple our editing approaches with reduced toxicity methods for BM conditioning. Thus, Aim 3 explores the use of anti-CD117 (Kit) monoclonal antibody ± enhancing approaches, including low-dose total body irradiation, CD47 inhibition and antibody-drug conjugates for BM conditioning in a humanized SCD mouse model. Preliminary studies indicate that the efficacy of anti-CD117-based approaches is disease-specific and influenced by HSC gene modification. Therefore, it is essential to study these approaches specifically in gene-modified SCD HSCs and the abnormal SCD BM microenvironment. Overall, our planned studies have the potential to expand and improve curative strategies for SCD, and more generally, to create new paradigms for treating other monogenic blood disorders via precise genetic manipulation of HSCs.