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B-cell therapy (also called B-cell depletion therapy) is a treatment for people with multiple sclerosis (MS). It targets certain cells -- called B cells -- that can damage nerve fibers in your brain and spinal cord.

Each of the treatments available has potential side effects that you should know about.

Ocrelizumab (Ocrevus)

Ocrelizumab is one of three B-cell therapies approved by the FDA to treat MS. This medicine sticks to B cells and keeps them from causing damage. It has the approval to treat:

  • Clinically isolated syndrome
  • Relapsing-remitting MS
  • Secondary progressive MS
  • Primary progressive MS

Side effects of ocrelizumab include:

Reactions during or after the medication is injected into your vein, like swelling and itching. Some people may have more serious reactions, like shortness of breath or a fast heartbeat. Your doctor may give you a corticosteroid, an antihistamine, or other medications before your treatment to prevent and ease any negative reactions. They’ll also watch you for at least an hour after you get your treatment.

A higher chance of infections, including respiratory infections, skin infections, and herpes. That’s because ocrelizumab temporarily weakens your immune system. Your doctor will watch you for signs of infection after you get the medicine. They'll also ask you to let them know if you notice issues like:

  • Eye pain
  • A fever or chills
  • A headache that doesn’t go away

PML (progressive multifocal leukoencephalopathy), a rare but serious brain infection. There haven't been any reported cases of PML with ocrelizumab. But since the risk is there, your doctor will watch you for signs of PML, like:

  • Weakness on one side of your body
  • Vision problems
  • Confusion or memory problems  

A higher chance of cancer. Ocrelizumab could bring a slightly higher risk of cancer, though researchers aren’t sure of the connection. You should keep following general guidelines for cancer screening and talk to your doctor about your chance of cancer and whether ocrelizumab is the best choice for you.

Ofatumumab (Kesimpta)

Ofatumumab is the other B-cell therapy approved by the FDA to treat MS. It's a human-made protein that attaches itself to B cells and weakens them so they can’t cause damage. 

It’s used for:

  • Clinically isolated syndrome
  • Relapsing remitting MS
  • Secondary progressive MS

Side effects of ofatumumab include:

Infections, including upper respiratory infections. This may be because ofatumumab lowers the number of B cells that you have. In addition to their role in MS, B cells are a type of white blood cell that fights infection. When your number of B cells goes down, your immune system gets weaker.

Your doctor will check your B-cell levels before and after your treatment. They’ll also monitor you closely after you take it. If you get a serious infection, they'll recommend that you stop using it.

Headache. Your doctor may recommend acetaminophen (Tylenol) to ease pain. 

Reactions after the injection, like fever and chills. Your doctor may give you corticosteroids (steroids that ease inflammation), antihistamines, or acetaminophen before you get the injection. That can help manage potential reactions.

Swelling, itching, or pain are possible where you get your infusion. Your doctor may use corticosteroids, antihistamines, or acetaminophen to manage these.  

PML (progressive multifocal leukoencephalopathy). Just as with ocrelizumab, there haven't been any cases of PML with ofatumumab, but your doctor will watch you for signs of this rare brain disorder during and after your treatment.

Rituximab (Rituxan)

Rituximab is the third type of B cell therapy used to treat MS. Unlike the other two, the FDA hasn’t approved it for MS. But some doctors may use it “off label” to treat MS.  

Rituximab is an antibody that targets an inflammation-causing protein on the surface of certain B cells.  

A 2018 study showed that it was safe and effective as a treatment for neurological diseases, including MS. But another study done in the same year found that five out of 30 people in a study on rituximab for relapsing-remitting MS had to stop using it because of issues like pneumonia and septic arthritis.

Other possible side effects include:   

Infection. This is the most common side effect for people who take rituximab for MS. Your doctor will watch you for signs of infection after you get the medication and will ask you to let them know if you notice new health problems.

Reactions after your injection, like fever and chills. Your doctor will ask you to let them know if you have any of these issues after you receive treatment.

A higher chance of cancer. Studies show that people who take rituximab for MS may be more likely to get cancer than those who don't, though researchers aren’t sure of the connection.

PML (progressive multifocal leukoencephalopathy), just as with the other treatments, your doctor will watch you during and after treatment for signs of this rare brain disorder.

Ublituximab-xiiy (Briumvi)

Ublituximab-xiiy was approved in late 2022 and is the second anti-CD20 monoclonal antibody approved for individuals with relapsing forms of MS. Its use includes clinically isolated syndrome, relapsing-remitting disease, and active secondary progressive disease.

It’s administered as a 4-hour intravenous infusion after the starting dose, followed by a second dose 2 weeks later, after that, the drug is administered every 24 weeks with the other infusions lasting one hour each.

Side Effects: The most common adverse reactions reported include reactions, such as fever, chills, flu-like symptoms, and upper respiratory tract infections. There can also be reactions at the site of the infusion.

Again, your doctor will watch you during and after treatment for signs of the rare brain disorder.PML (progressive multifocal leukoencephalopathy). 

Show Sources

Photo Credit: Ridofranz / Getty Images


MS Society (UK): “Targeting B cells to treat progressive MS.”

Mayo Clinic: “Multiple Sclerosis.”

National Multiple Sclerosis Society: “FDA Approves Kesimpta® (ofatumumab), Similar to Ocrevus®, for Relapsing MS,” “Non-approved treatments used for MS disease modification,” “Ocrevus.”

Novartis: “Kesimpta: Full Prescribing Information.”

Genenetch: “Medication Guide: Ocrevus.”

Annals of Neurology: “B Cell Therapy for Multiple Sclerosis: Entering an Era.”

PLOS ONE: “Long-term safety of rituximab induced peripheral B-cell depletion in autoimmune neurological diseases.”

Multiple Sclerosis Journal: “Adverse event profile differences between rituximab and ocrelizumab: Findings from the FDA Adverse Event Reporting Database.”

Neurology: “Rituximab in multiple sclerosis: A retrospective observational study on safety and efficacy.”

2018 Consortium of Multiple Sclerosis Centers: “Potential Infectious Complications of B-Cell Depleting Therapies-a Focus on Rituximab in Multiple Sclerosis.”