 The purpose of this study is to evaluate the potential benefits of CERE-110 in the treatment of Alzheimers disease. CERE-110 is an experimental drug that is designed to help nerve cells in the brain function better. CERE-110 uses a virus to transfer a gene that makes Nerve Growth Factor NGF, a protein that may make nerve cells in the brain healthier and protect them from dying. The virus used in CERE-110 does not cause disease in people. CERE-110 has been carefully studied in laboratory animals and is in the early stages of being tested in people. 