Because the immune system already knows how to kill tumors. It just needs to know where to look.
There is a moment every cancer scientist knows. You spend years on a new technology, a new vaccine, a new cell therapy, or a new ADC. The data looks beautiful on paper. Then the tumor reminds you it has been outsmarting us for thirty years. The antigen is lousy. The immune system is exhausted. And the patient you were trying to save runs out of time.
For one of us, that patient was a father. There was nothing modern medicine could offer to change the outcome, so he became a PhD in immunology and spent the next twenty-five years trying to build the thing that might have helped.