Displaying epidermal growth factor on spleen necrosis virus-derived targeting vectors

Targeted gene transfer into human cells has previously been achieved with spleen necrosis virus (SNV)-derived vector particles harboring envelope (Env) proteins which carry single chain Fv (scFv) domains derived from antibodies. Such cell targeting vectors have been found to directly transduce human cells expressing the cell surface molecules recognized by the respective scFv. In an attempt to achieve targeted gene transfer into epidermal growth factor receptor (EGFR)-positive human cells, SNV vector particles carrying a surface (SU) envelope protein N-terminally modified with the EGF domain and the wildtype transmembrane protein were generated. However, direct transduction of EGFR-positive cells was not detected. Canine D17 cells, which can be infected by wildtype SNV, were also not transduced. Infectivity of D17 cells was restored by removal of the EGF modification via cleavage of a factor Xa site located between the EGF domain and the SU protein or by blocking the EGFRs on the cell surface by EGF treatment. The properties of SNV-EGF vector particles as described here are similar to those of murine leukemia virus-derived vector particles harboring envelope proteins modified with a growth factor-derived domain. It seems therefore that, although scFv-modified SNV allows direct cell targeting, EGF-modified SNV allows only indirect cell targeting.