There are immunotherapy treatments for cancer already. Infections and cancer use the immune system the correct way: "tag" the problem cell/virus part with an antibody, make a lot more antibody and flood your body with it to clear the problem cell/virus.

This is the process a vaccine uses. The old vaccine method is to take a bunch of dead bacteria or inactivated virus and put that in your body. Your body should identify it and begin making antibodies against it. If you do get exposed to the disease, your body is full of antibodies which can immediately clear it, rather than letting the infection/cancer work for a few days without much of an immune response.

An autoimmune disease, a body "tags" its own cells. Then the immune system invades the person's own tissue.

I have celiac disease. If I eat gluten, the enzymes I use to digest gluten become tagged. Unfortunately, humans make one gluten enzyme (TG2) that's found everywhere in the body. A third of celiacs will have their thyroid tissue affected if they consume gluten.

One particular antibody, IgE, is known for extreme reactions to antigens. These are the ones known for the immediate and life-threatening allergies (peanuts, shellfish, bees, wheat).

This new stuff appears to be a way to tag antibodies or antigens or memory T cells (they hold the "blueprints" to make antibodies really quickly after your natural antibodies go away) and have the immune system "re-evaluate" the antigen. I'm guessing from the post above and a little of the article. I haven't heard of this process in the body before.

Cancer itself is not autoimmune (autoimmune inflammation can make it more likely to happen, but tumors don't form directly through autoimmune mechanisms). So the first pathway used for normal vaccination is what's needed. The difficulty lies in knowing something in each specific cancer that would make a good antibody target. It is a person's own cells and DNA, so a lot of care has to be taken to find an appropriate antigen. Immunotherapy treatments that exist are really specific to certain types of cancer. They have much less severe side effects than radiotherapy and chemotherapy.