Hematopoietic Stem Cell Gene Therapy for the Multisystemic Lysosomal Storage Disorder Cystinosis

Cystinosis is an autosomal recessive metabolic disease that belongs to the family of lysosomal storage disorders (LSDs). The defective gene is CTNS encoding the lysosomal cystine transporter, cystinosin. Cystine accumulates in all tissues and leads to organ damage including end-stage renal disease. Using the Ctns^−/− murine model for cystinosis, we tested the use of hematopoietic stem and progenitor cells (HSPC) genetically modified to express a functional CTNS transgene using a self-inactivating-lentiviral vector (SIN-LV). We showed that transduced cells were capable of decreasing cystine content in all tissues and improved kidney function. Transduced HSPC retained their differentiative capabilities, populating all tissue compartments examined and allowing long-term expression of the transgene. Direct correlation between the levels of lentiviral DNA present in the peripheral blood and the levels present in tissues were demonstrated, which could be useful to follow future patients. Using a new model of cystinosis, the DsRed Ctns^−/− mice, and a LV driving the expression of the fusion protein cystinosin-enhanced green fluorescent protein (eGFP), we showed that cystinosin was transferred from CTNS-expressing cells to Ctns-deficient adjacent cells in vitro and in vivo. This transfer led to cystine decreases in Ctns-deficient cells in vitro. These data suggest that the mechanism of cross-correction is possible in cystinosis.