Because immune tolerance is the opposite of immune protection, when it comes to the adaptive immune system, whose business is deciding what to do the next time

Because immune tolerance is the opposite of immune protection, when it comes to the adaptive immune system, whose business is deciding what to do the next time it encounters an antigen (it's a memory response either way). But really what they found here should maybe be called an inverse vaccine adjuvant (the part of the vaccine which tells your immune system that the associated antigen is dangerous, and a protective response should be mounted to it)