(15b) Lentiviral Delivery From Multiple Channel Bridges for Spinal Cord Regeneration

Spinal cord injury results in loss of sensory and motor function below the level of injury for which there are currently limited therapies. Recovery of function is rare due to the limited capacity of neurons to regenerate in the hostile microenvironment of the injury, which includes an insufficient supply of growth promoting factors and the glial scar that contains an abundant supply of inhibitory factors. Toward creating a permissive microenvironment for regeneration, we have developed a multiple channel bridge to support neurite growth through the injury, and are developing the ability to locally deliver lentivirus in order to promote neurite growth. These bridges stabilize the injury and provide physical guidance for neurite growth. Following implantation of bridges into a lateral hemisection, neurite growth was observed within the channels and crossed the bridge. Levels of NFs were evaluated from 1 to 12 weeks at three areas within the bridge (rostral, center, and caudal) by four blinded observers. The rostral section of the bridge had the highest level of NF staining at all time points, with maximal values obtained at 2 weeks and remained consistent thereafter. At the caudal section, NF levels increased at a slower rate relative to the rostral end, and reached the same staining level as the rostral area by week 4. At week 12, NF levels at all three sections had similar staining.

We subsequently investigated the delivery of lentivirus from the multiple channel bridge that can be employed to supply neurotrophic factors to increase the number of axons or to reduce inhibitory factors, which can encourage axonal re-entry into the host tissue. The polymer was modified with phosphatidylserine, which is normally present in the plasma membrane and is known to bind lentivirus. Bridges with immobilized lentivirus were implanted into the lateral hemisection. Substantial transgene expression was observed within the spinal cord, with greatest levels at the implant site (T-10) after 1 week. Expression was observed in adjacent segments of the spinal cord, with levels decreasing as distance from the implant site increased. These multiple channel bridges provide a structure that stabilizes the injury and facilitates neurite growth into and through the bridge, and localized lentivirus delivery provides the potential to promote axonal regrowth and reentry into the host tissue.