Cancer arises when normal cells undergo changes, leading to uncontrolled growth and division. The body’s immune system, a complex network of cells and organs, acts as a natural defense against foreign invaders and abnormal cells, including cancerous ones. Understanding which specific cells within this system fight cancer helps clarify how the body protects itself.
The Body’s Natural Immune Cells
The immune system’s innate components provide an immediate, non-specific response. Natural Killer (NK) cells are part of this rapid defense, acting as “first responders” that identify and eliminate cancer or virus-infected cells without prior exposure. They recognize abnormal cells by detecting a lack of “self” markers, such as MHC Class I molecules, or by sensing stress signals on the cell surface.
Macrophages are another innate immune cell, playing a role in the initial response. These large white blood cells function as phagocytes, engulfing and digesting cellular debris, pathogens, and abnormal cells. They also contribute to the immune response by presenting antigens, markers that alert other immune cells to a threat. Their direct killing of cancer cells is often through engulfment rather than targeted destruction.
Targeted Immune Responses
Beyond the immediate innate response, the immune system employs adaptive immune cells that offer a highly specific, memory-based defense. Cytotoxic T Lymphocytes (CTLs), often called Killer T-cells, directly destroy cancer cells. They are highly specialized, recognizing specific cancer-related markers (antigens) displayed on tumor cell surfaces through a “lock and key” mechanism.
Helper T-cells do not directly kill cancer cells but coordinate the immune response. They activate other immune cells, including CTLs and B-cells, by releasing signaling molecules.
B-cells contribute to the adaptive immune response by producing antibodies, proteins that specifically bind to cancer cells. These antibodies can mark cancer cells for destruction by other immune cells or directly neutralize substances promoting cancer growth. Their direct cytotoxic impact on solid tumors is less pronounced compared to CTLs.
How Cancer Evades Immune Detection
Despite the immune system’s capabilities, cancer often develops strategies to avoid detection and destruction. Cancer cells can hide by reducing the display of identifying markers like antigens or MHC molecules on their surface. This makes them less visible to T-cells, allowing escape from immune surveillance.
Cancer cells can also create an immunosuppressive environment within and around a tumor, known as the tumor microenvironment. They do this by secreting substances that suppress immune cell activity or by recruiting other immune-suppressing cells, such as regulatory T cells and tumor-associated macrophages. This hostile environment shields the tumor from immune attack.
Cancer cells can exploit natural “checkpoint” pathways that normally prevent the immune system from attacking healthy cells. Proteins like PD-L1 on cancer cells can bind to PD-1 on T-cells, effectively braking immune activity and allowing evasion. Chronic cancer stimulation can also lead to immune cell exhaustion, particularly in T-cells, rendering them less effective at clearing the tumor.
Harnessing Immune Cells for Treatment
Medical science is learning from these natural processes to develop treatments that boost the immune system’s ability to fight cancer. Immunotherapy is a broad approach that aims to stimulate or restore the immune system’s anti-cancer capabilities.
One prominent immunotherapy type involves checkpoint inhibitors. These drugs block “brakes” like PD-1 or PD-L1 proteins that cancer cells use to turn off immune cells. Blocking this interaction unleashes T-cells, allowing them to attack the tumor more effectively.
CAR T-cell therapy is another advanced, personalized treatment. A patient’s T-cells are collected and genetically engineered in a laboratory. These modified T-cells receive a chimeric antigen receptor (CAR) enabling them to better recognize and kill specific cancer cells. Engineered CAR T-cells are then multiplied and infused back into the patient to target the cancer.
Cancer vaccines also stimulate a patient’s immune response against specific cancer antigens. These vaccines train the immune system to recognize and attack cancer cells, sometimes preventing recurrence after other treatments.