When the body is invaded by bacteria, a virus or parasites, an immune alarm goes off, setting off a chain reaction of cellular activity in the immune system. Macrophages or other innate immune cells, such as basophils, dendritic cells or neutrophils, may be deployed to help attack the invading pathogen. Those cells often do the job, and the invader is destroyed. But sometimes, when the body needs a more sophisticated attack, it turns to its T-cells and B-cells. These cells are the special ops of the immune system—a line of defense that uses past behaviors and interactions to learn to recognize specific foreign threats and attack them when they reappear.
They may also play a critical role in the development and treatment of cancer. T-cells, especially, are the focal point for two emerging immunotherapy treatments: checkpoint inhibitors, which have been federally approved to treat multiple cancers, and CAR T-cell therapy, which is being studied in clinical trials as a potential treatment for cancers of the bloodstream, such as leukemia and lymphoma.
The immune system is made up of two armies of cells: innate and acquired. Innate immune cells are the body's first line of defense. They quickly respond to foreign cells to fight infection, battle a virus or defend the body against bacteria. Our acquired immunity—also called adaptive immunity—uses T-cells and B-cells when invading organisms slip through that first line. These cells take longer to develop, because their behaviors evolve from learned experiences, but they tend to live longer than innate cells. Adaptive immune cells remember foreign invaders after their first encounter and fight them off the next time they enter the body. This is the fundamental premise for how vaccines work—using a small, harmless amount of protein from a disease to allow the immune system to recognize that protein if the pathogen were to invade the body.
B-cells and T-cells are also called lymphocytes. Like all blood cells, they are made in the bone marrow. While B-cells mature in the bone marrow, T-cells travel through the bloodstream to the thymus gland—a small organ between the lungs and behind the sternum—and mature there.
B-cells fight bacteria and viruses by making Y-shaped proteins called antibodies, which are specific to each pathogen and are able to lock onto the surface of an invading cell and mark it for destruction by other immune cells. B-lymphocytes and cancer have what may be described as a love-hate relationship. For example, B-cells sometimes inhibit tumor development by producing antibodies that may attack cancer cells or oncogenic viruses, such as human papillomavirus (HPV), which is responsible for most cervical, anal, penile and other reproductive cancers. Other times, regulatory B-cells may release immune-suppressive cytokines that stifle an anti-tumor response. Also, B-cells are far more likely than T-cells to mutate into a liquid cancer such as chronic lymphocytic leukemia (CLL) or B-cell lymphoma.
There are two main types of T-cells: helper T-cells and killer T-cells. Helper T-cells stimulate B-cells to make antibodies and help killer cells develop. Killer T-cells directly kill cells that have already been infected by a foreign invader. T-cells also use cytokines as messenger molecules to send chemical instructions to the rest of the immune system to ramp up its response. Activating T-cells against cancer cells is the basis behind checkpoint inhibitors, a relatively new class of immunotherapy drugs that have recently been federally approved to treat lung cancer, melanoma and other difficult cancers. Cancer cells often evade patrolling T-cells by sending signals that make them seem harmless. Checkpoint inhibitors disrupt those signals and prompt the T-cells to attack the cancer cells.
Researchers are also developing a technology called CART therapy, in which T-cells are engineered to attack specific cancer cells. In this potential treatment, which is still in clinical trials, a patient’s T-cells are collected and genetically engineered to produce chimeric antigen receptors (CAR). This is designed to allow the T-cells to recognize a specific protein on the tumor cells. These engineered CAR T-cells are grown by the billions in the laboratory and then infused into a patient’s body, where the cells are designed to multiply and recognize the cancer cells that express the specific protein. This technology, also called adoptive cell transfer, is generating excitement among researchers as a potential next-generation immunotherapy treatment.
While both are critical to the body's defense against disease and infection, T-cells and B-cells play very different roles. CART therapy and checkpoint inhibitors are examples of how researchers are using what they’ve learned about T-cells specifically in developing new cancer treatments. But as their differences and similarities show, both types of immune cells employ important natural defenses in helping the body fight cancer.
The language of cancer can be a confusing mix of unpronounceable words, sound-alike terms and scientific jargon. But some of the nuances in cancer types, terms and titles may indicate deep differences in the diseases, diagnoses and treatments. This blog is an installment in an occasional series called “What's the difference?” designed to help clear up some of the confusion in cancer vocabulary and help increase our cancer IQ.
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