Researchers at the Harvard Medical School have developed a universal gene therapy for Diamond-Blackfan Anemia (DBA), a rare genetic disorder characterized by impaired erythropoiesis caused by ribosomal protein mutations. According to a Cell Stem Cell research article, the approach entails controlling the expression of GATA1, a crucial transcription factor in erythropoiesis, only in developing erythroid cells using an erythroid-specific enhancer called hG1E. These discoveries lay the groundwork for a first-in-human universal gene therapy clinical trial and create a novel approach to treating hematopoietic disorders by focusing on downstream pathways instead of directly fixing or swapping out damaged genes.
DBA mutations affect GATA1 translation
DBA is a condition characterized by impaired red blood cell (RBC) production that is usually treated with chronic transfusions, corticosteroids, or hematopoietic stem cell (HSC) transplantation. Up to 37 distinct genes can have mutations that cause DBA, with RPS19 mutations accounting for around 25% of cases. Although lentiviral delivery of the RPS19 gene has shown preclinical success, it does not apply to more than 75% of DBA patients who do not have RPS19 mutations.
DBA mutations converge to diminish ribosome levels, preferentially affecting the translation of specific mRNAs, particularly the hematopoietic master regulator GATA1. Furthermore, loss-of-function GATA1 mutations can bring on DBA.
Researchers from Vijay Sankaran’s lab previously demonstrated that increasing GATA1 expression in bone marrow samples from patients with DBA is sufficient to overcome erythroid differentiation defects in vitro, implying that restoring sufficient GATA1 protein levels could be a therapeutic avenue for DBA patients regardless of genotype. Long-term HSC (LT-HSC) maintenance is hampered by unchecked GATA1 expression in HSCs, necessitating a lineage-based approach to boost GATA1 expression exclusively in RBCs.
Fine-tuned GATA1 gene therapy
Building on their earlier findings, Sankaran’s team replicated the temporal pattern of endogenous GATA1 expression by identifying human regulatory enhancers upstream of the GATA1 gene that drive erythroid-restricted expression. Specifically, lead author Richard A. Voit, MD, PhD, and colleagues identified three DNA regions that are only accessible during erythroid maturation and bound by erythroid transcription factors. These lineage-restricted enhancers were concatenated to form the human GATA1 enhancer (hG1E) element, which was then delivered with a clinical-grade lentiviral vector to maximize GATA1 protein synthesis in erythroid progenitors.
Applying the hG1E-GATA1 vector to human hematopoietic stem/progenitor cells (HSPCs) in culture and xenotransplantation promoted normal maturation and accelerated early erythroid differentiation without compromising HSC function. Additionally, the method effectively increased erythroid production in several in vitro and in vivo DBA models, including primary patient samples from DBA patients with various mutations (e.g., RPL5, RPS19). The treatment overcame the usual erythropoiesis block by stimulating erythroid differentiation in most DBA patient samples. Additionally, the gene therapy was well-tolerated, with no negative impact on non-erythroid differentiation.
Crucially, examination of the hG1E-GATA1 vector’s integration sites in human cells revealed no preferential integration close to genes linked to cancer, indicating a safe profile for clinical application. Moreover, there were no indications of clonal expansion associated with oncogenic risks in the dynamics of clones in mouse models.
While the observed results are promising—showing up to a 21-fold increase in erythroid production—there are limitations. The study does not yet confirm whether these preclinical results will translate into clinical benefits for DBA patients, particularly regarding anemia alleviation. However, hG1E-GATA1 therapy may provide a more significant improvement in erythropoiesis when compared to other treatments, such as corticosteroid therapy and RPS19 gene addition. Ultimately, clinical trials must validate this approach’s safety and therapeutic potential.
