A tumor cell vaccine is created by surgically removing tumor cells, inactivating them, and then reinjecting the cells to stimulate rejection of the tumor, much like someone can be vaccinated against chicken pox. Cancer cells that had migrated to the lung also were taken out by the combination therapy, indicating that the technique may help deal with metastases, that is, cancers that spread from the original site. Interestingly, the mice who survived subsequently were immunized against a second injection of melanoma cells, indicating that the treatment has a protective effect as well. Similarly, preliminary results suggest that blocking CTLA-4 may be effective in treating prostate tumors in mice. One, a receptor called CD28, triggers an attack while the other, CTLA-4, suppresses it.
Antigens are molecules sported by tumor cells that advertise they are abnormal.
Blocking the CTLA-4 receptor thus removes the brake on the T cell and allows it to attack the tumor. Because CTLA-4 blockade apparently unleashes an autoimmune attack against the tumor, the treatment sometimes may cause the immune system to attack normal tissue as well. In the mice they treated for melanoma, for example, Allison and his colleagues observed that the immune system sometimes attacked and eliminated melanin containing skin cells, turning the mice white. This condition, called depigmentation, occurs in many patients treated for melanoma, and correlates with an improvement in the patient's condition. That's the beauty of this - we are activating the immune system, basically trying to get T cells to go on the attack for a while and ambush the tumor, and then we let the immune system go back to normal.