If you’ve recently been diagnosed with leukemia, your doctor may have told you to be careful when it comes to infections. This is because leukemia harms your immune system, making it harder to fight off invading viruses and bacteria. Your immune system is complex, but we’re here to help you understand how leukemia affects it.

This article will look at how leukemia interacts with different parts of the immune system. We’ll also cover how leukemia treatments impact your immunity. If you have other questions about your specific leukemia case or treatments, talk to your oncologist (cancer specialist).

How Do Blood Cells Develop?

To better understand how leukemia develops, it helps to understand how your body makes new blood cells. It’s always producing healthy new ones to replace old ones. Blood cells form in the bone marrow — the soft, spongy tissue inside your bones.

You have several types of blood cells, each with a unique function:

• Red blood cells (RBCs) carry oxygen throughout your bloodstream.
• White blood cells (WBCs) are immune cells that fight infections.
• Platelets are sticky cell fragments that help create blood clots.

Your bone marrow contains hematopoietic stem cells that make all of your blood cells. These stem cells make cells on two different pathways — lymphoid or myeloid. As your blood cells mature, they become more specialized for a specific function.

Lymphoid cells eventually become natural killer (NK) cells or lymphocytes. These are WBCs that help fight infections. Lymphocytes are divided into T lymphocytes (T cells) and B lymphocytes (B cells).

Myeloid cells go on to become RBCs, platelets, and some WBCS, such as:

• Basophils
• Neutrophils
• Eosinophils
• Monocytes and macrophages

How Does Leukemia Develop?

Leukemia is a type of cancer that develops in your bone marrow. Specifically, it begins in immature blood cells. These cells haven’t fully matured yet, and they’re still growing and thus cannot function properly. Changes in the leukemia cells’ DNA let them grow out of control. Eventually, the leukemia cells crowd your bone marrow and prevent the formation of other healthy blood cells.

There are many types of leukemia. The four most common are divided according to the types of WBCs affected and how mature they are. They include:

• Acute myeloid leukemia (AML), also called “acute myelogenous leukemia”
• Chronic myeloid leukemia (CML), also called “chronic myelogenous leukemia”
• Acute lymphoblastic leukemia (ALL), also called “acute lymphocytic leukemia”
• Chronic lymphocytic leukemia (CLL)

Each type of leukemia affects the immune system differently. Acute leukemias occur when blood cells stop maturing early in their development. This means that they never become fully mature blood cells, and they can’t function properly at all. People with AML and ALL have more severe symptoms than those with chronic leukemia.

Among chronic leukemias, CLL occurs in blood cells that have already matured. In CML, blood cells are present in both mature and immature forms — referred to as a “bimodal distribution of cells.” Blood cells in people with CLL and CML can still function to a degree, but not as well as they used to. CML and CLL grow more slowly and tend to have a better prognosis (outlook).

How Do Different Types of Leukemia Affect the Immune System?

Leukemia develops in immature blood cells that form either lymphocytic or myeloid cells. The type of leukemia you have will affect the immune system differently. Most leukemias affect blood cells that would have matured into B cells.

For example, around 75 percent of people with ALL have cancer that affects immature B cells. The other 25 percent have leukemia that affects immature T cells. B cells and T cells each have unique roles in the immune system.

B cells are responsible for making antibodies — specialized immune proteins made during infections. T cells work by activating different parts of the immune system to fight illnesses. They also activate B cells to make antibodies.

AML and CML affect myeloid cells, which become different types of innate immune cells. These cells, especially neutrophils, are the first to react during an infection. Studies have found that people with myeloid leukemias are more likely to develop fungal infections. This is because neutrophils and macrophages play an important part in fighting and destroying fungi.

Does Leukemia Depress the Immune System?

Leukemia stops your bone marrow from making healthy immune cells that fight infections. This depresses your immune system and puts you at risk of infections — a state known as immunodeficiency. You may get infections from viruses, bacteria, or fungi.

People with leukemia and other blood cancers tend to get sick more easily than people without leukemia. Their illnesses may be more severe or last longer than in people with a fully functioning immune system. In severe cases, an infection may even lead to blood poisoning or death. This is why it’s important to protect yourself from infections while living with leukemia.

Leukemia and Your Lymphatic System

Your lymphatic system is a key part of your immune system that protects you from infections. You can think of this system as similar to your blood vessels that carry blood cells throughout the body. But instead of blood, your lymphatic system carries a clear liquid known as lymph fluid.

This fluid contains immune cells that travel to your lymph nodes. These glands are found all throughout your body. Lymph nodes help filter cancer cells, bacteria, and viruses from the blood. Immune cells then attack these foreign substances and clear them from your body.

You may have felt swollen lymph nodes in your neck when you’re sick. Swollen lymph nodes are a sign your immune system is working hard to fight an infection. People living with leukemia can also develop swollen lymph nodes as a sign of their disease. This is because too many abnormal leukemia cells are collecting in the lymph nodes, and they can’t be filtered out.

While swollen lymph nodes are a sign your immune system is working, they can cause problems. If lymph fluid can’t properly flow throughout your body, your immune cells can’t travel where they’re needed. This means you’ll have trouble fighting infections, especially while living with leukemia.

How Do Leukemia Treatments Affect the Immune System?

If you’ve been diagnosed with leukemia, your oncologist will go over your treatment options. Many medications for leukemia focus on altering your immune system to destroy cancer cells.

Chemotherapy and Bone Marrow Transplant

Chemotherapy uses toxic chemicals to kill rapidly dividing cells throughout the body. Certain chemotherapy drugs can destroy blood stem cells in the bone marrow. This gets rid of any leukemia cells and makes room for new blood cells.

Your doctor can then take healthy bone marrow cells from a donor and infuse them into your bloodstream. The healthy cells travel to your bone marrow and make new tissue. You’ll then be able to make new, healthy blood cells.

Immunotherapy

Immunotherapy is a cancer treatment that activates your immune system to fight cancer. There are several types of immunotherapy used to treat leukemia.

Chimeric antigen receptor (CAR) T-cell therapy engineers your immune cells to fight your leukemia. A doctor removes your T cells and alters them in a lab. The cells are then injected back into your bloodstream. They travel around your body looking for leukemia cells to target and destroy.

Monoclonal antibodies are lab-made immune system protein drugs used to treat cancer. They specifically target markers on the outside of leukemia cells. Rituximab (Rituxan) is a monoclonal antibody that treats CLL. It specifically binds to proteins on certain leukemia cells and tells the immune system to attack them.

Since immunotherapies work on your immune system, they can also raise your risk of infections. Talk to your doctor about ways you can protect yourself while undergoing leukemia treatment.

Find Your Team

MyLeukemiaTeam is the social network for people with leukemia and their loved ones. On MyLeukemiaTeam, more than 18,000 members who understand life with leukemia come together to share support, advice, and stories from their daily lives.

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