Lentiviral gene therapy corrects the metabolic and immune abnormalities in purine nucleoside phosphorylase-deficient mice.

Purine nucleoside phosphorylase (PNP) deficiency impairs purine metabolism leading to severe T cell defects, which can be corrected by allogeneic hematopoietic stem cell (HSC) transplant, however the associated complications are significant. Therefore, autologous gene therapy is an attractive alternative treatment option. Here, we present a third-generation self-inactivating lentiviral vector expressing the human PNP gene under the control of the elongation factor-1 alpha short promoter (LVV-EFS-PNP), which was delivered ex vivo to HSCs and was tested for its ability to correct the abnormalities in PNP-deficient (Pnp-/-) mice. The LVV-EFS-PNP vector demonstrated effective gene transfer, without jeopardizing hematopoietic colony formation in vitro. In vivo, Pnp-/- mice transplanted with Pnp-/- lineage-negative cells transduced with LVV-EFS-PNP achieved sustained correction of the immune and metabolic abnormalities, including restoration of thymocyte development, T cell proliferation, and T cell-dependent and independent antibody responses. Importantly, genotoxicity assessments demonstrated that LVV-EFS-PNP had a low transformation potential and did not significantly dysregulate gene expression signature linked to vector-induced transformation, similar to other clinically used lentiviruses. These results demonstrate the safety and efficacy of gene therapy using LVV-EFS-PNP in a pre-clinical model of PNP deficiency, providing evidence for a promising new treatment strategy.