Ciliary neurotrophic factor (CNTF) is a member of the interleukin-6 family of cytokines. CNTF is a differentiating cytokine that drives cells toward a predominantly astrocytic fate. In HD, CNTF is the most widely studied neurotrophic factor. CNTF is the first and currently the only trophic factor to enter clinical trails in HD. CNTF has trophic effects on striatal neurons as seen in both in vitro and in vivo studies. Some of the earliest studies administered CNTF to the brain by direct infusion of the protein using pumps. An infusion cannula was implanted directly into the striatum and recombinant CNTF was continuously infused using an osmotic pump. This method of CNTF administration was efficient at significantly reducing cell death within the QA-lesioned striatum. A major pitfall of this method of administration is the need to constantly infuse CNTF into striatum. Additionally, large amounts of CNTF may be needed at one time to establish adequate diffusion throughout the striatum.