When Tysabri first came on the market after clinical trials, there were 3 deaths from PML and it was pulled from the market. All 3 patients had been on
one of the first line DMDs while they were also taking
Tysabri. The thought at the time was that if patients took Tysabri alone, PML would not be an issue. Tysabri was re-released to the market, but with strict conditions and monitoring requirements, known as the TOUCH program.
Unfortunately, that has not proven to be true.