INVERSE TARGETING OF RETROVIRAL VECTORS - SELECTIVE GENE-TRANSFER IN A MIXED POPULATION OF HEMATOPOIETIC AND NONHEMATOPOIETIC CELLS

We previously reported that retroviral vectors displaying epidermal gr owth factor (EGF) as part of a chimeric envelope glycoprotein are sequ estered upon binding to EGF receptor (EGFR)-positive target cells, lea ding to loss of infectivity. In the current study, we have displayed s tem cell factor (SCF) on beta-galactosidase-transducing ecotropic and amphotropic retroviral vector particles as a factor Xa protease-cleava ble N terminal extension of the envelope glycoprotein. Viral incorpora tion of the SCF chimeric envelopes was demonstrated by immunoblotting of pelleted virions and their specific attachment to Kit receptors was demonstrated by flow cytometry. Gene transfer studies showed that whe n SCF was displayed on an amphotropic envelope, the infectivity of the SCF displaying vectors was selectively inhibited on Kit-expressing ce lls, but could be restored by adding soluble SCF to block the Kit rece ptors or by cleaving the displayed SCF domain from the vector particle s with factor Xa protease. The host range properties of EGF-displaying and SCF-displaying vectors were then compared in cell mixing experime nts. When EGFR-positive cancer cells and Kit-positive hematopoietic ce lls were mixed and exposed to the different engineered vector particle s, the cancer cells were selectively transduced by the SCF displaying vector and the hematopoietic cells were selectively transduced by the EGF displaying vector. Retroviral display of polypeptide growth factor s can therefore provide the basis for a novel inverse targeting strate gy with potential use for selective transduction of hematopoietic or n onhematopoietic cells (eg, cancer cells) in a mixed cell population. ( C) 1998 by The American Society of Hematology.