32. Towards a Phase I Clinical Trial for Cystinosis

Cystinosis is an autosomal recessive lysosomal storage disorder characterized by the accumulation of cystine in the lysosomes leading to cystine crystals formation. The gene involved, CTNS, encodes a lysosomal cystine transporter, cystinosin. Cystinosis leads to a renal Fanconi's syndrome before the age of one characterized by polyuria and nutrients loss, and to multi-organ degeneration especially the eyes and kidneys. The cysteamine treatment allows the exit of cystine out of the lysosomes but only delays the evolution of the disease. We showed that transplantation of wild-type Hematopoietic Stem and Progenitor Cells (HSPCs) in a lethally irradiated Ctns−/− mouse leads to cystine content decrease in every tissues tested and kidney, eye and thyroid function and structure improvement in treated mice compared to mock-treated mice. An autologous HSPCs gene therapy approach has then been developed with Ctns−/− HSPCs gene-modified ex vivo to express a functional CTNS cDNA using the lentiviral vector pCCL-CTNS. Tissue cystine decrease and kidney function rescue were observed with this strategy. The toxicology and pharmacology studies required by the FDA are in progress with a targeted Vector Copy Number (VCN) included between 1 and 3. The in vitro studies, Colony Forming Unit assay and In Vitro Immortalization assay, have been completed using peripheral blood CD34+ cells from five healthy donors and four cystinosis patients. The in vivo studies are in progress: Ctns−/− HSPCs are isolated and transduced with pCCL-CTNS and transplanted into primary Ctns−/− mice and 6-months later their bone marrow cells are transplanted into secondary Ctns−/− recipients. Primary and secondary mice are carefully monitored and comprehensive histological, biochemical, molecular and clinical analyses are performed at 6 months post-transplant. So far, seven primary and one secondary Ctns−/− mice transplanted with pCCL-CTNS-transduced Ctns−/− HSPCs have reached the 6 month post-transplantation time point. The primary mice had a mean VCN of 1.713 and the secondary 2.04. Clinical evaluations, histopathology and Vector Integration Site (VIS) analyses revealed no adverse event so far suggesting a good safety profile of our product. Moreover, cystine content was significantly decreased in all tissues tested. Analysis of the remaining primary and secondary recipient mice is in progress and these data will be included in an Investigational New Drug (IND) for a phase 1 clinical trial for autologous transplantation of pCCL-CTNS-modified CD34+ HSPCs in patients with nephropathic cystinosis, For the design and conduct of the future clinical trial, the Cystinosis Stem Cell and Gene Therapy Consortium was recently created and is composed of experts in cystinosis, bone marrow transplant and gene therapy. The clinical grade pCCL-CTNS virus preparation is about to be produced at the Gene Therapy Resources Program (GTRP), Clinical Grade Lentivirus Vector Core directed by Dr. Kenneth Cornetta who prepared the Good Manufactory Practice-comparable (GMPc) virus used for the pharmacology/toxicology studies. We are currently preparing the documents necessary for the IND such as the clinical protocol, the toxicology/pharmacology report, the Chemistry, Manufacturing and Controls (CMC) report, etc. This clinical trial will represent the first stem cell and gene therapy treatment strategy for cystinosis.