Grafting of encapsulated BDNF-producing fibroblasts into the injured spinal cord without immune suppression in adult rats

Grafting of genetically modified cells that express therapeutic products is a promising strategy in spinal cord repair. We have previously grafted BDN F-producing fibroblasts (FB/BDNF) into injured spinal cord of adult rats, b ut survival of these cells requires a strict protocol of immune suppression with cyclosporin A (CsA). To develop a transplantation strategy without th e detrimental effects of CsA, we studied the properties of FB/BDNF that wer e encapsulated in alginate-poly-L-ornithine, which possesses a semipermeabl e membrane that allows production and diffusion of a therapeutic product wh ile protecting the cells from the host immune system. Our results show that encapsulated FB/BDNF, placed in culture, can survive, secrete bioactive BD NF and continue to grow for at least one month. Furthermore, encapsulated c ells that have been stored in liquid nitrogen retain the ability to grow an d express the transgene. Encapsulated FB/BDNF survive for at least one mont h after grafting into an adult rat cervical spinal cord injury site in the absence of immune suppression. Transgene expression decreased within two we eks after grafting but resumed when the cells were harvested and re-culture d, suggesting that soluble factors originating from the host immune respons e may contribute to the downregulation. In the presence of capsules that co ntained FB/BDNF, but not cell-free control capsules, there were many axons and dendrites at the grafting site. We conclude that alginate encapsulation of genetically modified cells may be an effective strategy for delivery of therapeutic products to the injured spinal cord and may provide a permissi ve environment for host axon growth in the absence of immune suppression.