Add I understand it, it's not about actively ignoring something. Rather, the immune system somehow learned to react more strongly to specific antigens, and undo

Add I understand it, it's not about actively ignoring something. Rather, the immune system somehow learned to react more strongly to specific antigens, and undoing that. The natural immune reaction should still happen when encountering diseases, and not when encountering normal body tissues. It's possible to use such tricks to actively shut down the immune system, but you either have to incorporate it into the disease (which actually happens in nature) or take that medicine continuously.