RETROVIRAL VECTOR TARGETING HUMAN-CELLS VIA C-KIT STEM-CELL FACTOR INTERACTION

Targeted gene transfer into hematopoietic stem cells by retroviral vec tors would greatly facilitate the development of in vivo strategies fo r stem cell gene therapy. We engineered a recombinant retroviral vecto r that can target human cells expressing a c-Kit receptor via a ligand -receptor interaction. The ecotropic (Moloney murine leukemia virus) e nvelope protein was modified by insertion of a sequence encoding the N -terminal 161 amino acids of murine stem cell factor (mSCF), the ligan d for murine c-Kit, The chimeric envelope protein was correctly proces sed and incorporated into viral particles as efficiently as the mild-t ype envelope protein. Virions pseudotyped with the chimeric envelope p roteins bound to 293 cells expressing murine c-Kit (293KIT) preferenti ally; however, they could not transduce any c-Kit-positive cells under conventional conditions. They could transduce 293KIT cells in the pre sence of chloroquine, and HEL cells expressing human c-Kit on a fibron ectin 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-Ki t interaction for the initial step of transduction in either case. The vector may prove useful for targeting cells expressing c-Kit on their surface.