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 hematopoi etic progenitor cells via retroviral vectors while adherent to this fr agment (J Clin Invest 93:1451, 1994). Here we report that (1) transduc tion of reconstituting murine HSC assayed 12 months after infection wi th retrovirus supernatant on FN 30/35 is as effective as cocultivation directly on producer cells; (2) recombinant retrovirus particles dire ctly 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 pr otein phosphorylation typically induced by integrin-fibronectin intera ctions. Therefore, we speculate that supernatant infection of HSC on F N 30/35 leads to colocalization of retrovirus particles and target cel ls on FN 30/35 molecule with a large increase in local virus titer pre sented to the cell. These findings have direct and important implicati ons for the modification of current human gene therapy protocols. (C) 1996 by The American Society of Hematology.