Systemic delivery of phagocytosis-shielded retroviral vectors enables in vivo HSC gene therapy for sickle cell disease.

Ex vivo hematopoietic stem cell (HSC) gene therapy is effective for non-malignant blood disorders including sickle cell disease (SCD), but requires hospitalization, ex vivo cell manipulation, and conditioning. Direct in vivo gene delivery could remove these barriers and widen access. Here, we explore phagocytosis-shielded lentiviral and alpha-retroviral vectors pseudotyped with the baboon endogenous retrovirus glycoprotein variant BaEVRLess for in vivo HSC gene transfer. Vector injection into mobilized humanized mice yielded up to 8.8% gene marking in hCD45+ cells, which chemoselection enriched to 70% of hCD45+ cells and 54% of HSCs. Barcode analysis showed polyclonal reconstitution in over 90% of mice, which remained stable in secondary recipients. For SCD, we targeted BCL11A and ZNF410 selectively in erythroid cells using miRNA-embedded shRNAs to derepress gamma-globin, reaching therapeutically relevant levels of 61.5% of beta-like globins. In summary, BaEVRLess-pseudotyped lentiviral vectors enable clinically relevant in vivo gene transfer and fetal globin induction for SCD.