NEW YORK ( TheStreet) -- Pfizer ( PFE - Get Report) announced late Monday the failure of its experimental Alzheimer's disease drug bapineuzumab in a late-stage clinical trial. Bapineuzumab is being co-developed by Johnson & Johnson ( JNJ - Get Report) with certain economic rights held by Irish drug maker Elan ( ELN. Investors widely expected bapineuzumab clinical trials to fail based on similarly poor results from mid-stage studies presented in July 2008. The study announced Monday enrolled patients with mild to moderate Alzheimer's who also carried a gene known as ApoE4 that confers a higher risk of developing the disease. Patients treated with bapineuzumab showed no cognitive or functional improvement compared to patients treated with a placebo, Pfizer said. Three other phase III studies of bapineuzumab, enrolling both Apoe4 carriers and non carriers, are still underway with results expected later this year. Elan shares are down 16% to $11.26 in Monday after-hours trading. --Written by Adam Feuerstein in Boston. >To contact the writer of this article, click here: Adam Feuerstein. >To follow the writer on Twitter, go to http://twitter.com/adamfeuerstein. >To submit a news tip, send an email to: firstname.lastname@example.org. Follow TheStreet on Twitter and become a fan on Facebook.