This has a precondition: the existence of targets unique to the cancer cell. That's not necessarily true. In theory you can have cancerous cells that are (at least in the epitope-space) indistinguishable from normal cells. I'm not a doctor, and I guess (and hope) this is an usual case, but finding a truly unique and dissimilar mutation sounds pretty hard, training the immune system to detect it correctly without generalizing sounds even harder. Potential, sure, and I hope this proceeds and yields some therapies that are safer than chemotherapy, but we need to be realistic with what we'll probably get.