373. Expression of Human Iduronidase from Sleeping Beauty Engineered Human B Lymphocytes as a Cellular Therapy for Mucopolysaccharidosis Type I

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive lysosomal storage disorder cause by absence of the glycosidase alpha-L-idurondase (IDUA), resulting in the systemic accumulation of glycosaminoglycan storage materials heparan sulfate and dermatan sulfate. Affected individuals exhibit a range of manifestations including hepatosplenomegaly, skeletal dysplasias, and cardiopulmonary obstruction. The severe form of the disease (Hurler syndrome) is associated with progressive neurologic dysfunction and death by age 10. Current treatments for MPS I include enzyme replacement (ERT), and hematopoietic stem cell transplantation (HSCT). However, these treatments are expensive, insufficiently effective, and allogeneic HSCT is associated with considerable morbidity and mortality.As an alternate approach to MPS I, Immusoft Corporation is developing as a cellular therapeutic primary B cells that have been genetically engineered for long-term expression and secretion of IDUA. At the core of the technology is the generation of genetically engineered autologous human B cells, which are isolated and expanded from patient blood. Mature B cells (specifically long-lived plasma cells) are the ideal cell type to produce protein since they live for long periods of time, occupy diverse tissues throughout the body and are capable of secreting very high levels of protein. In collaboration with Discovery Genomics, Inc., the University of Minnesota and the Fred Hutchinson Cancer Research Center, Immusoft has developed a treatment for Mucopolysaccharidosis type I (MPS I). In initial tests, Sleeping Beauty (SB) transposons expressing the human iduronidase gene were introduced into cultured B lymphoblastoid cells with and without a source of SB transposase, demonstrating long-term, high level expression of IDUA activity in vitro. SB transposons expressing both IDUA and a methotrexate-resistant human dihydrofolate reductase allowed for a >10-fold expansion of IDUA-expressing cells in the presence of methotrexate, as determined by intracellular staining for human IDUA and flow cytometry. Overall IDUA expression was also increased >10-fold in the methotrexate-selected cell population. IDUA encoding SB transposons were also nucleofected along with a source of SB transposase into primary human memory B cells, demonstrating expression of IDUA at levels more than 100 times greater than that observed in cultures of untreated primary B cells. These data support the development of a clinical trial to test SB-engineered B cells in the treatment of MPS I, with implications for improved treatment of other lysosomal storage disorders as well.