Keratinocyte growth factor stimulates transduction of the respiratory epithelium by retroviral vectors

Cell proliferation is required for transduction by standard retrovirus vect ors derived from viruses in the murine leukemia virus (MuLV) group. Since p roliferation rates are low in the mature pulmonary epithelium, me tested th e hypothesis that the efficiency of retrovirus-mediated transduction of res piratory epithelial cells can be enhanced by stimulation of cell proliferat ion with recombinant human keratinocyte growth factor (rhKGF). A marked inc rease in proliferation of bronchiolar and alveolar epithelial cells was obs erved after intratracheal administration of rhKGF (30 mg/kg) to adult FVB/N mice. Two days after rhKGF or saline treatment, 10(7) AP(+) FFU of LAPSN, a recombinant amphotropic retrovirus that expresses human placental alkalin e phosphatase (AP), was instilled intratracheally into the mice. Transducti on efficiency, measured 2 days after infection, was increased approximately 70-fold by rhKGF pretreatment. However, even after KGF treatment the total numbers of AP-expressing cells were few. Transduction efficiency was simil ar using either LAPSN packaged by amphotropic host range packaging cells or LAPSN pseudotyped with 10A1 MuLV envelope protein (0.091 +/- 0.006 versus 0.094 +/- 0.028 transduction events/mm(2), respectively). Amphotropic vecto rs use Pit-2 for cell entry, while 10A1 MuLV vectors can use Pit-1 or Pit-2 for cell entry. By in situ hybridization the retroviral receptor Pit-2 (Ra m-l) mRNA was expressed only in the pulmonary vasculature, and Pit-1 (Glvr- 1) mRNA was expressed at low levels throughout the lung. In vitro studies d emonstrated that retrovirus was inactivated by pulmonary surfactant. Stimul ating proliferation of the respiratory epithelium increased retroviral tran sduction in vivo, but the paucity of retroviral receptors and inactivation by surfactant are additional barriers to high-level retroviral gene transfe r in the lung.