Development of an enhanced B-specific lentiviral vector expressing BTK: a tool for gene therapy of XLA.

ABSTRACT

Further development of haematopoietic stem cell (HSC) gene therapy will depend on enhancement of gene transfer safety ad hoc improvement of vector design relating to each particular disease is thus a crucial issue for HSC gene therapy. We modified a previously described lentiviral vector by adding the Emumar B-specific enhancer to a human CD19 promoter-derived sequence (Mol Ther 2004;1045-56). We thus significantly improved the level of expression of the green fluorescent protein (GFP) reporter gene while retaining the specificity of expression in B-cell progeny of transduced human CD34+ progenitor cells obtained from cord blood or adult bone marrow. Indeed, GFP was strongly expressed from early medullary pro-B cells to splenic mature B cells whereas transgene expression remained low in transduced immature progenitors as in myeloid and T-lymphoid progeny retrieved from xenografted NOD/SCID/gammac(null) mice. Using this lentiviral vector, we further demonstrated the possibility to express a functional human BTK protein in long-term human CD34+ cell B-lymphoid progeny. This newly designed lentiviral vector fulfils one of the pre-requisites for the development of efficient and safe gene therapy for X-linked agammaglobulinaemia, the most common primary humoral immunodeficiency disorder.