Gene therapy of a mouse model of protoporphyria with a self-inactivating erythroid-specific lentiviral vector without preselection

Successful treatment of blood disorders by gene therapy has several complic ations, one of which is the frequent lack of selective advantage of genetic ally corrected cells. Erythropoietic protoporphyria (EPP), caused by a ferr ochelatase deficiency, is a good model of hematological genetic disorders w ith a lack of spontaneous in vivo selection. This disease is characterized by accumulation of protoporphyrin in red blood cells, bone marrow, and othe r organs, resulting in severe skin photosensitivity. Here we develop a self -inactivating lentiviral vector containing human ferrochelatase cDNA driven by the human ankyrin-1/alpha -globin HS-40 chimeric erythroid promoter/enh ancer. We collected bone marrow cells from EPP male donor mice for lentivir al transduction and injected them into lethally irradiated female EPP recip ient mice. We observed a high transduction efficiency of hematopoietic stem cells resulting in effective gene therapy of primary and secondary recipie nt EPP mice without any selectable system. Skin photosensitivity was correc ted for all secondary engrafted mice and was associated with specific ferro chelatase expression in the erythroid lineage. An erythroid-specific expres sion was sufficient to reverse most of the clinical and biological manifest ations of the disease. This improvement in the efficiency of gene transfer with lentiviruses may contribute to the development of successful clinical protocols for erythropoietic diseases.