Targeted gene transfer into hematopoietic stem cells by retroviral vectors would greatly facilitate the development of in vivo strategies for stem cell gene therapy. We engineered a recombinant retroviral vector that can target human cells expressing a c-Kit receptor via a ligand–receptor interaction. The ecotropic (Moloney murine leukemia virus) envelope protein was modified by insertion of a sequence encoding the N-terminal 161 amino acids of murine stem cell factor (mSCF), the ligand for murine c-Kit. The chimeric envelope protein was correctly processed and incorporated into viral particles as efficiently as the wild-type envelope protein. Virions pseudotyped with the chimeric envelope proteins bound to 293 cells expressing murine c-Kit (293KIT) preferentially; however, they could not transduce any c-Kit-positive cells under conventional conditions. They could transduce 293KIT cells in the presence of chloroquine, and HEL cells expressing human c-Kit on a fibronectin fragment (CH296)-coated dish. The fact that recombinant mSCF in the medium at the time of transduction greatly reduced the efficiency of both gene deliveries implies that the vector utilized the mSCF–c-Kit interaction for the initial step of transduction in either case. The vector may prove useful for targeting cells expressing c-Kit on their surface.
Overview summary
The development of retroviral-targeted gene delivery would be beneficial to in vivo gene therapy. To redirect the viral host range, we modified Moloney murine leukemia virus envelope proteins to display murine stem cell factor as an N-terminal fusion. A recombinant retroviral vector pseudotyped with the chimeric protein could target cells expressing c-Kit via the specific ligand–receptor interaction under experimental conditions either with chloroquine or on a recombinant fibronectin fragment-coated dish at the time of transduction, whereas it could not under conventional conditions. Although some improvements seem to be required for future clinical trials, this type of vector would be of great value for targeted gene transfer to cells expressing c-Kit, such as hematopoietic stem cells.
