Intracompartmental delivery of CNTF as therapy for Huntington's disease and retinitis pigmentosa.

Ciliary neurotrophic factor (CNTF) is a cytokine with neurotrophic activity across a broad spectrum of peripheral and central nervous system (CNS) cells. While its therapeutic potential for CNS diseases has been clear for sometime, the blood brain barrier (BBB) hinders the systemic delivery of CNTF and direct bolus injections are not suitable due to the short half-life of CNTF. One means of overcoming the BBB while providing continuous delivery of CNTF is with immunoisolated cellular implants that produce and deliver CNTF directly to the region of interest. Cells can be protected from host rejection by encapsulating, or surrounding, them within an immunoisolatory, semipermeable membrane that admits oxygen and required nutrients and releases bioactive cell secretions, but restricts passage of larger cytotoxic agents from the host immune defense system. The selective membrane eliminates the need for chronic immunosuppression of the host and allows the implanted cells to be obtained from nonhuman sources. In this review we discuss cell immunoisolation for Huntington's disease and retinitis pigmentosa. These two indications are highlighted because of extensive pre-clinical data supporting the general concept and recent clinical data that both strengthens the theoretical role of CNTF for treating neurodegeneration and justifies additional clinical evaluation in these and other diseases.