Murine PGK Promoter in a Lentiviral Vector in Canine Leukocyte Adhesion Deficiency and in Human Lad-1 Cd34⁺cells in NSG Mice

The safety of lentiviral (LV) vectors for gene therapy of genetic hematopoietic diseases would be considerably enhanced by the identification of a non-viral promoter capable of driving therapeutic levels of transgene expression in the target cell. Here, we tested the efficacy of the murine phosphoglycerate kinase (mPgk) promoter in a self-inactivating (SIN) LV vector to express canine CD18 in animals with canine leukocyte adhesion deficiency (CLAD) and in human LAD-1 CD34+ cells in NSG mice. Despite high transduction levels and high levels of CD18 expression per cell in CLAD CD34+ cells in vitro using the mPgk vector to drive canine CD18 expression, only two of five CLAD animals treated with ex vivo gene therapy achieved therapeutic levels of CD18+ neutrophils in vivo. Similarly, despite high transduction efficiency and high levels of CD18 expression in human LAD-1 CD34+ cells in vitro, the mPgk-hCD18 promoter resulted in a low percentage of CD45+/CD18+ cells and low levels of CD18 expression per neutrophil, when the transduced cells were transplanted into NSG mice. In contrast, human LAD-1 CD34+ cells transduced with a LV vector containing the viral MND promoter (MND-hCD18) and injected into NSG mice displayed a high percentage of CD45+/CD18+ cells and high levels of CD18 expression per neutrophil. These studies demonstrated that the mPgk promoter does not direct sufficient CD18 expression in neutrophils to replace a viral promoter for gene therapy of children with LAD-1.