New City Osaki Clinic homepage > Frequently asked questions > Question 10
Cancer vaccine therapy is a method in which a part of the cancer antigen in cancer cells is artificially created (cancer peptide vaccine) or the immune system is stimulated by injecting dendritic cells that were allowed to take in the cancer antigen (dendritic cell vaccine), thereby ultimately inducing cancer-attacking T cells based on the cancer information from the cancer antigen. It is characterized by the fact that cancer information is memorized and remains for a long time, and is a good therapy following the immunological theory. There are, however, a few problems.
1) Vaccine therapy requires several steps in the body to induce cancer-attacking T cells and assumes that these steps go as smoothly as in healthy people. In fact, however, immunity is weakened in cancer patients and important steps often stagnate. For example, dendritic cells cannot easily respond to the cancer antigen, or cancer information cannot be transferred from dendritic cells to T cells. Vaccination may not result in immune response or production of cancer-attacking T cells (see the figure below).
2) Cancer-attacking T cells cannot attack unless MHC class I molecules are present on the surface of the cancer cells. One of the reasons that T cells cannot attack cancer cells in cancer patients is thought to be the alteration of the shape or disappearance of these molecules caused by cancer cells. Even when dendritic cells are stimulated and activated by a vaccine, it is often the case that cancer cells became in a condition that T cells cannot attack in reality.
3) One type of peptide vaccine corresponds to one type of cancer antigen. However, more than 100 types of cancer antigen have been reported. Even if the cancer cells that correspond to a particular peptide disappear, the cancer cells corresponding to other types of cancer antigen can proliferate. In such cases, the therapy is not effective.
In highly active NK (natural killer) cell therapy, the step for educating T cells as described in 1) is not necessary. As for the problem explained in 2), the NK cell is known to characteristically attack the cancer cells that do not present MHC class I molecules even better. Moreover, NK cells attack cancer cells by targeting the antigen unique to cancer, such as NKG2D and TRAIL, as is the case with cancer-attacking T cells. In particular, NKG2D activate NK cells to attack cancer cells regardless of the inhibitory signal of NK cells. The unique culture method at our clinic allows the molecules that detect such marks indicating cancer to appear in a large number.