Pilot and Feasibility Study of Hematopoietic Stem Cell Gene Transfer for the Wiskott-Aldrich Syndrome

Wiskott-Aldrich syndrome (WAS) (OMIM 301000) is a rare X-linked immunodeficiency caused by mutations in a single gene, WAS, mapping to Xp11.22-Xp11.3 and coding for the Wiskott-Aldrich Syndrome Protein (WASP) 1. WASP is a critical regulator of actin signaling with expression limited to hematopoietic cells, and thus is required for multiple functions including T cell activation, dendritic cell migration and podosome formation, and B cell terminal development and function. WAS is characterized by microthrombocytopenia, recurrent infections, eczema and associated with a high incidence of auto-immunity and of lymphoid malignancies. Classic or severe WAS, is generally observed in patients with nonsense mutations or insertions/deletions resulting in frameshift or splice-site mutations or missense mutations and resulting in unstable protein 2. With few exceptions, WASP-negative patients have classical disease. Affected patients have a severely reduced life expectancy.

Currently, the only curative option for WAS patients is hematopoietic stem cell transplantation (HSCT). This treatment is most successful when an HLA-identical sibling or matched unrelated donor is available and results in correction of microthrombocytopenia and immune dysfunction, even when stable mixed chimerism occurs. However, even patients undergoing matched HSCT can suffer from considerable morbidity and mortality due to graft versus host disease (GVHD) and many patients lack an HLA-identical donor. The outcome of mismatched related HSCT is consistently poor with survival of approximately 50%. Gene transfer is an attractive alternative treatment for WAS. Successful gene transfer using autologous gene-corrected HSC would overcome clinical complications linked to GVHD and its treatment. Furthermore, in contrast to allogeneic HSCT, gene transfer would not be limited by the availability of compatible donors. Several lines of evidence indicate that partial reconstitution with gene corrected cells may be sufficient to ameliorate the disease.

We propose here a Pilot and Feasibility study of ex vivo gene transfer using a lentiviral vector (LV) to transduce autologous bone marrow derived CD34+ HSC. Cells will be infused into patients conditioned with cytoreductive chemotherapy. Our collaborating investigators in Europe have developed a LV encoding the human WAS cDNA under control of the WAS promoter and pseudotyped with the Vesicular Stomatitis Virus glycoprotein (VSVg) envelope. This w1.6_hWASP_WPRE (VSVg) LV (abbreviated as w1.6W) has been shown to be efficacious in both in vitro and in vivo preclinical models. Safety including cellular toxicity, insertional mutagenesis and tumor formation has been studied by a number of methods including: 1) a sensitive in vitro transformation assay, 2) toxicity studies in transduced human CD34+ cells, 3) examination of the insertional pattern in transduced murine cells, and 4) long-term observation and secondary transplant studies in mice. In the United States, we plan to enroll 5 boys with classic WAS who lack a matched related or unrelated donor. Parallel studies (not under our Investigational New Drug application) using the same LV produced in the same facility, Genethon, will be conducted in London, UK (5 subjects) and Paris, France (5 subjects). The primary objective will be to demonstrate feasibility and safety. The secondary objective will be to assess therapeutic efficacy.