Improved lentiviral vectors for Wiskott-Aldrich syndrome gene therapy mimic endogenous expression profiles throughout haematopoiesis

Wiskott-Aldrich syndrome (WAS) gene therapy requires highly efficient and well-controlled vectors. Here we studied the performance of a lentiviral vector (LV) harbouring a 500-bp fragment of the WAS proximal promoter (WW), which we previously characterized as haematopoietic-specific and capable of restoring WAS phenotype in patients' T cells. We used an LV (WE) expressing eGFP to evaluate whether this promoter was following the expression pattern of endogenous WASp. Transgene expression was analysed in WE-transduced hCD34(+) population and its progeny after in vitro and in vivo differentiation in the Rag(2)(/), gamma c (/) humanized mouse. We revealed very poor expression from the WE internal promoter in macrophages and erythroid cells. Therefore, we designed a novel LV including a fragment of the alternative WAS promoter in WE vector (AWE). This new vector sustained high transgene levels along the whole lymphoid lineage in vivo. Most importantly, the performance of AWE vector was highly superior to WE vector since AWE clearly improved transgene levels in in vitro and in vivo hCD34(+)-derived macrophages, erythroid cells, megakaryocytes and B cells while supporting a high expression in human T cells. This emphasizes that it is a suitable LV backbone for gene therapy of haematopoietic diseases such as WAS.