. >> pelley: 60-year old donna clegg was a social worker from idaho.t her in 2014, puffy from the steroids used to reduce the swelling in her brain. >> donna clegg: i want to be able to live. so that's kind of how i feel, that this is going to be my opportunity to have a full life. >> pelley: donna's polio infusion was three times more potent than the one that had worked for stephanie. but in her case, this higher dose set off an immune response that was much too powerful. donna battled the inflammation for nine months, before she died in march 2015. donna clegg suffered quite a lot. and i wonder how that weighs on your mind? >> friedman: every patient who has an outcome that is not positive weighs on my mind. i think that when you're doing a phase one study, you know that these things can happen. but she is a patient who really did not derive benefit and yet taught us something important. >> pelley: you discovered that putting in too much poliovirus created too large an immune response? >> friedman: absolutely. >> pelley: after that hard lesson, docto