A recent study of immune cells derived from human stem cells shows that experimental antibodies for Parkinsons and Alzheimers can trigger harmful brain inflammation, offering one possible explanation for clinical trials dismal failure rates. In the 1990s, drug makers began developing antibodies for treating Alzheimers and Parkinsons therapies designed to clear aggregates of proteins found in the brains of people with the diseases. But after decades of research, clinical trials of these investigational antibodies showed that the drugs have largely failed to slow patients cognitive and functional decline , despite showing initial promise in mice studies.