Grafts of Alginate-Encapsulated BDNF-Producing Fibroblasts for Treatment of Spinal Cord Injury

Nikhil O. Dhoot, Chris A. Tobias, Marion Murray, Itzhak Fischer and Margaret A. Wheatley
Drexel University, MCP/Hahnemann University
3141 Chestnut Street
Philadelphia, PA 19104
nikhil@drexel.edu
(215) 895 5831

Ex vivo gene therapy is a strategy in which therapeutic genes are delivered to the host by a graft of genetically modified cells.  Previously, it has been shown that when primary fibroblasts are modified to produce BDNF and grafted into the injured spinal cord (SC) of adult rats, these cells survive, rescue axotomized neurons, promote regeneration and contribute to recovery of function (Liu et al., J. Neurosci. 1999 19:4370-4387). However, these grafted cells only survive in the injured rat SC under strict immunosuppression protocols with Cyclosporin A. The disadvantage of immunosuppression is the vulnerability of the recipient to infections, potential development of tumors by the transplanted cells, and possible adverse effects on regeneration and recovery.  To address these problems, genetically modified cells can be encapsulated in a biocompatible microcapsule with a semipermeable membrane that facilitates cell survival and allows production and diffusion of the therapeutic product while protecting the cells from the host immune system.  We examined (1) the important factors for encapsulation of BDNF producing fibroblasts (BDNF/FB) with the biocompatible polysaccharide alginate, (2) the ability of the encapsulated cells to grow in vitro, and (3) the properties of the encapsulated cells following SC grafting.  We found that the encapsulated BDNF/FB proliferated and continued to express the transgene for at least 14 days in culture.  In addition, when transplanted into a partial hemisected cervical adult rat SC, without immune suppression, the encapsulated cells survived and appeared to provide a permissive environment for sprouting of neurons as indicated by staining for CGRP, neurofilament, and MAP-2 after 4 weeks.  Immunocytochemical stains showed that the transplant induced a non-specific immune response. We conclude that alginate encapsulation may provide an effective strategy for delivery of therapeutic products to the injured SC in the absence of immune suppression. 
 

Supported by NIH grants NS24707, NS10090 and HD07467, and by EPVA, APA, ISRT and the Research Service of the Veterans Administration.