The mammalian organisms have all many tumors as their cells, which are incredibly complex little machines, reproduce themselves often incorrectly so there is the need of quality mechanisms to remove those many aberrant cells. The immune system is one of those quality system, the check points in the cell cycle are another. Even in DNA replication there are quality controls!
Human leukocyte antigens are molecules on the surface of cells that allow their identification by the immune system. They are the marker of the "self" as opposed to foreign materials. These proteins are generally 7-11 amino acids long and come from proteins expressed by the cell. Under normal conditions, cytotoxic T lymphocytes, which normally patrol the body in the blood, and "read" the peptide presented by the complex.
T cells bind to foreign peptides and a series of events is launched culminating in cell death via apoptosis. In this way, the human body eliminates cells that are expressing foreign proteins.
To take advantage of this mechanism, vaccine immunotherapy administrates ad hoc proteins that mimics proteins expressed by a specific cancer cell.
Those small proteins, called peptides, are synthesized by laboratories and then injected into the body as a vaccine to try to induce an immune response against the cancer cells.
Designing those peptides is not easy, they must be tailored to the patient. They must be effective, close enough to a protein produced by the cancerous cell to make the immune system to kill those cancer cells when it will encounter them.
Unfortunately those vaccines are useful only for a short time as the cancer cells evolve quickly. Another thing is that cancer cells can recruit the immune cells for their own purpose or make normal cells in the surrounding extracellular matrix to silence the immune system cells.
It might seems that cancer is a terrible, incredibly foreign thing, but actually it might simply be that it is merely the tissue's healing process that went rogue.
Another aspect that might ruin the effectiveness of the best vaccine, is the magnitude of side effects. Side effects should be expected as pathways are never specific, they are used in several purposes. Side effects might be so hard to endure that the patient might decide to leave the treatment, or might die from it.
We wrote a PoC of a peptide vaccine design web service. The code is available on Github at https://github.com/Hjertesvikt/peptide_PoC
And a demo can be played at: www.padiracinnovation.org