Globin vector regulatory elements are active in early hematopoietic progenitor cells

Preclinical efficacy of a modified gamma-globin lentivirus gene therapy in Berkeley sickle cell anemia mice and human xenograft models

We previously showed correction of sickle cell anemia (SCA) in mice utilizing a lentiviral vector (LV) expressing human γ-globin. Herein, we made a G16D mutation in the γ-globin gene to generate the G16D mutation (GbGM) LV to increase fetal hemoglobin formation. We also generated an insulated version of this LV, GbGMI, inserting a 36-bp insulator from the Foamy virus in the long terminal repeats of the LV. Preclinical batches of GbGM and GbGMI LV showed both were highly efficacious in correcting SCA in mice, with sustained gene transfer in primary transplanted SCA mice and high hematopoietic stem cell (HSC) transduction in colony-forming unit-spleen in secondary transplanted mice. CRISPR-mediated targeting of the proviruses into the LMO2 proto-oncogene showed remarkably reduced LMO2 activation by both insulated and uninsulated LV, compared to the SFFV γ-RV vector targeted to the same locus. We therefore used the GbGM LV to perform preclinical human CD34+ gene transfer. We assessed gene transfer and engraftment of human HSCs in two immunocompromised mouse models: persistent stable GbGM-transduced cell engraftment was comparable to that of untransduced cells with no detrimental effects on hematopoiesis up to 20 weeks post transplant. These robust preclinical studies in mouse and human HSCs allowed its translation into a clinical trial.

Large-scale discovery of potent, compact and erythroid specific enhancers for gene therapy vectors

Gene expression during cell development and differentiation is orchestrated by distal regulatory elements that precisely modulate cell selective gene activity. Gene therapy vectors leverage these elements for precise spatiotemporal transgene expression. Here, we develop a one-shot approach to screen candidate regulatory sequences from large-scale epigenomics data for programmable transgene expression within gene therapy viral vectors. We assess a library of 15,000 short sequences derived from developmentally active elements during erythropoiesis using a clinically relevant reporter vector. These elements display a gradient of transcriptional enhancer activity in erythroid cells, with high cell type restriction and developmental stage specificity. Finally, replacing the canonical β-globin μLCR with a compact enhancer in a β-thalassemia lentiviral vector successfully corrects the thalassemic phenotype in patient-derived hematopoietic and stem and progenitor cells (HSPCs), while increasing viral titers and cell transducibility. Our approach provides further insights into enhancer biology with wider implications for human gene therapy.

Gene therapy for sickle cell disease: recent advances, clinical trials and future directions

Sickle cell disease (SCD) is the most common inherited blood disorder worldwide, impacting millions and imposing severe healthcare challenges, particularly in resource-limited regions. Current treatments have variable efficacy and require lifelong adherence. Allogeneic Hematopoietic Stem Cell Transplantation can be curative but comes with significant side effects and limited donor availability limits its widespread applicability. Gene therapy, by addressing the root genetic causes, offers a revolutionary alternative. This article discusses the molecular mechanisms of SCD and β-thalassemia and highlights advancements in gene therapy, such as gene addition via lentiviral vectors and gene editing with CRISPR/Cas9 technology. Clinical trials have brought about significant progress but challenges remain, including leukemogenesis, delivery efficiency and cost. Future efforts must focus on enhancing efficiency, reducing costs, developing nongenotoxic conditioning regimens and methods for in vivo application.

The Optimized γ-Globin Lentiviral Vector GGHI-mB-3D Leads to Nearly Therapeutic HbF Levels In Vitro in CD34+ Cells from Sickle Cell Disease Patients

We have previously demonstrated that both the original γ-globin lentiviral vector (LV) GGHI and the optimized GGHI-mB-3D LV, carrying the novel regulatory elements of the 3D HPFH-1 enhancer and the 3' β-globin UTR, can significantly increase HbF production in thalassemic CD34⁺ cells and ameliorate the disease phenotype in vitro. In the present study, we investigated whether the GGHI-mB-3D vector can also exhibit an equally therapeutic effect, following the transduction of sickle cell disease (SCD) CD34⁺ cells at MOI 100, leading to HbF increase coupled with HbS decrease, and thus, to phenotype improvement in vitro. We show that GGHI-mB-3D LV can lead to high and potentially therapeutic HbF levels, reaching a mean 2-fold increase to a mean value of VCN/cell of 1.0 and a mean transduction efficiency of 55%. Furthermore, this increase was accompanied by a significant 1.6-fold HbS decrease, a beneficial therapeutic feature for SCD. In summary, our data demonstrate the efficacy of the optimized γ-globin lentiviral vector to improve the SCD phenotype in vitro, and highlights its potential use in future clinical SCD trials.