Five years ago, David C. Fajgenbaum, MD, MBA, MSc, both a Penn Medicine researcher and patient, tried an experimental treatment based on his laboratory research findings in the hopes of saving his own life. He has been in remission ever since. Now his research is shedding new light on why it worked, paving the way for further testing of a new treatment approach in Castleman disease, a rare and deadly condition with limited options for patients.