Mosunetuzumab-axgb (Lunsumio™)

Author: Marisa Healy, BSN, RN
Content Contributor: Mitchell Hughes, PharmD
Last Reviewed: December 30, 2022

Pronounce: moe-SUN-e-TOOZ-ue-mab axgb

Classification: Bispecific CD20-directed CD3 T-cell engager

About: Mosunetuzumab-axgb (Lunsumio™)

Mosunetuzumab-axgb is a monoclonal antibody. Monoclonal antibodies are created in a lab to attach to targets found on specific types of cancer cells. The antibody “calls” the immune system to attack the cell it is attached to, causing the immune system to kill the cell. These antibodies can work in different ways, including stimulating (revving up) the immune system to kill the cell, blocking cell growth or other functions needed for cell growth. This medication binds to two things (“bispecific”):

  • A protein called CD20, found on the surface of normal and cancerous B-cells, which are part of the immune system, and
  • The CD3 receptor on the surface of T-cells, which helps start an immune response in your body.

How to take Mosunetuzumab-axgb

Mosunetuzumab-axgb is given by intravenous (IV, into a vein) infusion. The first time you receive this medication, you will receive a smaller dosage for the first two visits (days 1 and 8). This is called “step-up dosing.” If you tolerate these doses, you will receive the full dose going forward.

You will be given “pre-medications” before each step-up dose of mosunetuzumab-axgb. These may include a steroid, a histamine-1 (H1) receptor antagonist (such as diphenhydramine/Benadryl), and an antipyretic (such as acetaminophen/Tylenol). Some patients will need these pre-medications with every dose depending on adverse reactions.

Possible Side Effects of Mosunetuzumab-axgb

There are a number of things you can do to manage the side effects of mosunetuzumab-axgb. Talk to your care team about these recommendations. They can help you decide what will work best for you. These are some of the most common or important side effects:

Cytokine Release Syndrome (CRS)

Cytokine release syndrome (CRS) can occur. T cells are activated by this medication, causing them to release many cytokines. The cytokines cause an inflammatory response in the body. This reaction, if left untreated, can be very dangerous. Signs and symptoms may be fever, having a hard time breathing, chills, low blood pressure, fast heart rate, headache, and higher levels of liver enzymes in your blood. Your care team will monitor you closely for CRS while you are on therapy with mosunetuzumab-axgb. You should call your provider right away if you have any signs or symptoms of CRS so that treatment can be started.

Infection and Low White Blood Cell Count

This medication can cause life threatening infections, with or without a decrease in white blood cell counts.
White blood cells (WBC) are important for fighting infection. While receiving treatment, your WBC count can drop, putting you at a higher risk of getting an infection. You should let your doctor or nurse know right away if you have a fever (temperature greater than 100.4°F or 38°C), sore throat or cold, shortness of breath, cough, burning with urination, or a sore that doesn't heal.
Tips to preventing infection:

  • Washing hands, both yours and your visitors, is the best way to prevent the spread of infection.
  • Avoid large crowds and people who are sick (i.e.: those who have a cold, fever or cough or live with someone with these symptoms).
  • When working in your yard, wear protective clothing including long pants and gloves.
  • Do not handle pet waste.
  • Keep all cuts or scratches clean.
  • Shower or bath daily and perform frequent mouth care.
  • Do not cut cuticles or ingrown nails. You may wear nail polish, but not fake nails.
  • Ask your oncology care team before scheduling dental appointments or procedures.
  • Ask your oncology care team before you, or someone you live with, has any vaccinations.

Electrolyte Abnormalities

This medication can affect the normal levels of electrolytes (potassium, magnesium, phosphate, etc.) in your body. Your levels will be monitored using blood tests. If your levels become too low, your care team may prescribe specific electrolytes to be given by IV or taken by mouth. Do not take any supplements without first consulting with your care team.

Low Red Blood Cell Count (Anemia)

Your red blood cells are responsible for carrying oxygen to the tissues in your body. When the red cell count is low, you may feel tired or weak. You should let your oncology care team know if you experience any shortness of breath, difficulty breathing or pain in your chest. If the count gets too low, you may receive a blood transfusion.

Low Platelet Count (Thrombocytopenia)

Platelets help your blood clot, so when the count is low you are at a higher risk of bleeding. Let your oncology care team know if you have any excess bruising or bleeding, including nose bleeds, bleeding gums or blood in your urine or stool. If the platelet count becomes too low, you may receive a transfusion of platelets.

  • Do not use a razor (an electric razor is fine).
  • Avoid contact sports and activities that can result in injury or bleeding.
  • Do not take aspirin (salicylic acid), non-steroidal, anti-inflammatory medications (NSAIDs) such as Motrin/Advil (ibuprofen), Aleve (naproxen), Celebrex (celecoxib) etc. as these can all increase the risk of bleeding. Please consult with your healthcare team regarding use of these agents and all over the counter medications/supplements while on therapy.
  • Do not floss or use toothpicks and use a soft-bristle toothbrush to brush your teeth.


Fatigue is very common during cancer treatment and is an overwhelming feeling of exhaustion that is not usually relieved by rest. While on cancer treatment, and for a period after, you may need to adjust your schedule to manage fatigue. Plan times to rest during the day and conserve energy for more important activities. Exercise can help combat fatigue; a simple daily walk with a friend can help. Talk to your healthcare team for helpful tips on dealing with this side effect.

High Blood Sugar

This medication can cause elevated blood sugar levels in patients with and without diabetes. Your oncology care team will monitor your blood sugar. If you develop increased thirst, urination or hunger, blurry vision, headaches, or your breath smells like fruit, notify your healthcare team. Diabetics should monitor their blood sugar closely and report elevations to the healthcare team.


Some patients may develop a rash, scaly skin, or red itchy bumps. Use an alcohol free moisturizer on your skin and lips; avoid moisturizers with perfumes or scents. Your oncology care team can recommend a topical medication if itching is bothersome. If your skin does crack or bleed, be sure to keep the area clean to avoid infection. Be sure to notify your oncology care team of any rash that develops, as this can be a reaction. They can give you more tips on caring for your skin.

Liver Toxicity

This medication can cause liver toxicity, which your oncology care team may monitor for using blood tests called liver function tests. Notify your healthcare provider if you notice yellowing of the skin or eyes, your urine appears dark or brown, or you have pain in your abdomen, as these can be signs of liver toxicity.

Muscle or Joint Pain/Aches and Headache

Your healthcare provider can recommend medications and other strategies to help relieve pain.


This medication may cause a new or worsening cough. Tell you care provider if you have this symptom.

High Uric Acid Levels

Mosunetuzumab-axgb can cause higher than normal levels of uric acid in your body. Your care team will monitor for this and other things with blood work.

Peripheral Neuropathy (Numbness or Tingling in the Hands and/or Feet)

Peripheral neuropathy is a toxicity that affects the nerves. It causes numbness or a tingling feeling in the hands and/or feet, often in the pattern of a stocking or glove. This can get progressively worse with additional doses of the medication. In some people, the symptoms slowly resolve after the medication is stopped, but for some it never goes away completely. You should let oncology care team know if you experience numbness or tingling in the hands and/or feet, as they may need to adjust the doses of your medication.

Less common, but important side effects can include:

  • Neurologic Toxicity including ICANS: Neurological (brain) toxicities, such as headache, insomnia (unable to fall or stay asleep), and dizziness can happen. If you have aphasia (being unable to understand speech or speak normally), a change in mental status, or seizures during or after you receive this medication, let your care team know right away. Your care team will be monitoring you very closely for any changes in your mental status.
  • Tumor Flare: While taking this medication, you can experience a "tumor flare" which can result in symptoms of the cancer getting temporarily worse. Notify your care team if you develop any swollen lymph nodes, fever, or pain.

Reproductive Concerns

Exposure of an unborn child to this medication could cause birth defects, so you should not become pregnant or father a child while on this medication. For women, effective birth control is necessary during treatment and for at least 3 months after treatment. Even if your menstrual cycle stops or you believe you are not producing sperm, you could still be fertile and conceive. You should not breastfeed during treatment or for at least 3 months after your last dose.


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