Bone marrow stromal cells as a genetic platformfor systemic delivery of therapeutic proteins in vivo : human factor IX model

Abstract

Background Hemophilia B is an X-linked bleeding disorder that results from a deficiency in functional coagulation factor IX (hFIX). In patients lacking FIX, the intrinsic coagulation pathway is disrupted leading to a lifelong, debilitating and sometimes fatal disease. Methods We have developed an ex vivo gene therapy system using genetically modified bone marrow stromal cells (BMSCs) as a platform for sustained delivery of therapeutic proteins into the general circulation. This model exploits the ability of BMSCs to form localized ectopic ossicles when transplanted in vivo . BMSCs were transduced with MFG-hFIX, a retroviral construct directing the expression of hFIX. The biological activity of hFIX expressed by these cells was assessed in vitro and in vivo . Results Transduced cells produced biologically active hFIX in vitro with a specific activity of 90% and expressed hFIX at levels of ∼497 ng/10 6 cells/24 h and 322 ng/10 6 cells/24 h for human and porcine cells, respectively. The secretion of hFIX was confirmed by Western blot analysis of the conditioned medium using a hFIX-specific antibody. Transduced BMSCs (8 × 10 6 cells per animal) were transplanted within scaffolds into subcutaneous sites in immunocompromised mice. At 1 week post-implantation, serum samples contained hFIX at levels greater than 25 ng/ml. Circulating levels of hFIX gradually decreased to 11.5 ng/ml at 1 month post-implantation and declined to a stable level at 6.1 ng/ml at 4 months. Conclusions These findings demonstrate that genetically modified BMSCs can continuously secrete biologically active hFIX from self-contained ectopic ossicles in vivo , and thus represent a novel delivery system for releasing therapeutic proteins into the circulation. Copyright © 2002 John Wiley & Sons, Ltd.