Fibronectin improves transduction of reconstituting hematopoietic stem cells by retroviral vectors: Evidence of direct viral binding to chymotryptic carboxy-terminal fragments

Efficient transduction of reconstituting hematopoietic stem cells (HSC) is currently only possible by cocultivation of target cells directly on producer cell lines, a method not applicable to human gene therapy protocols. Our laboratory has previously shown adhesion of primitive hematopoietic stem and progenitor cells to the carboxy-terminal 30/35-kD fragment of the extracellular matrix molecule fibronectin (FN 30/35) (Nature 352:438, 1991) and increased transduction of human hematopoietic progenitor cells via retroviral vectors while adherent to this fragment (J Clin Invest 93:1451, 1994). Here we report that (1) transduction of reconstituting murine HSC assayed 12 months after infection with retrovirus supernatant on FN 30/35 is as effective as cocultivation directly on producer cells; (2) recombinant retrovirus particles directly adhere to FN 30/35 in a quantitative and dose-dependent fashion; and (3) increased transduction efficiency on FN 30/35 does not appear to be associated with increased cell proliferation or activation of protein phosphorylation typically induced by integrin-fibronectin interactions. Therefore, we speculate that supernatant infection of HSC on FN 30/35 leads to colocalization of retrovirus particles and target cells on FN 30/35 molecule with a large increase in local virus titer presented to the cell. These findings have direct and important implications for the modification of current human gene therapy protocols. (C) 1996 by The American Society of Hematology.