Kesimpta works by targeting and removing specific immune cells called B cells that contribute to the nerve damage in multiple sclerosis.

The Simple Version

Think of your immune system as a security team. In multiple sclerosis, part of that team — specifically, cells called B lymphocytes (B cells) — starts attacking your own body by mistake. They target the protective coating around your nerves (called myelin), causing the inflammation, nerve damage, and symptoms that define MS.

Kesimpta (Ofatumumab) is like a precision tool that identifies and removes those rogue B cells from your system. It does this by locking onto a specific marker on their surface called CD20, essentially flagging them for destruction.

What Happens in Your Body

Here's the step-by-step process, simplified:

1. You inject Kesimpta under your skin (subcutaneously). The medication enters your bloodstream and tissues.
2. Kesimpta finds B cells by binding to the CD20 protein on their surface. CD20 is like a name tag that B cells wear — it's present on most B cells but not on very early or very late-stage B cells, which means your immune system can rebuild over time.
3. B cells are destroyed through two mechanisms:
   • Complement-dependent cytotoxicity (CDC) — The drug activates a part of the immune system called the complement system, which punches holes in the B cell's membrane.
   • Antibody-dependent cell-mediated cytotoxicity (ADCC) — Other immune cells (like natural killer cells) are recruited to destroy the flagged B cells.
4. B cell levels drop significantly, reducing the immune attacks on your nervous system.
5. MS disease activity decreases — fewer relapses, less new inflammation visible on MRI, and slower disability progression.

The analogy: If your immune system is a building with a broken alarm that keeps triggering the sprinklers and flooding the place, Kesimpta disables the specific sensor that's malfunctioning — without tearing down the whole building.

How Long Does It Take to Work?

Kesimpta begins depleting B cells quickly. In clinical trials:

• Within 1 to 2 weeks of the first loading dose, B cell levels drop significantly.
• By Week 4 (when monthly dosing begins), most patients have very low B cell counts.
• Clinical benefits — reduced relapses, fewer new MRI lesions — become measurable over the first 3 to 6 months of treatment, though you may not "feel" different right away.

It's important to keep up with your monthly injections even if you feel fine. MS can be active on MRI even when you're not experiencing obvious symptoms.

How Long Does It Last?

Each Kesimpta injection suppresses B cells for approximately one month, which is why it's dosed monthly. If you stop treatment, B cells will gradually recover over a period of several months — the exact timeline varies by individual.

This recovery period is one reason your doctor may want to plan carefully around treatment changes, vaccinations, or pregnancy. For example, Novartis recommends waiting at least 6 months after the last dose before trying to conceive.

What Makes Kesimpta Different From Similar Medications?

Kesimpta isn't the only anti-CD20 therapy for MS. Here's how it stacks up against its closest relatives:

Kesimpta vs. Ocrevus (Ocrelizumab)

• Same target: Both target CD20 on B cells.
• Different delivery: Ocrevus is an IV infusion given every 6 months at an infusion center. Kesimpta is a monthly self-injection at home.
• Convenience: Kesimpta wins here — no infusion center visits, no IV line, no sitting in a chair for hours.
• Efficacy: Clinical trial data suggests comparable efficacy in reducing relapses and MRI lesions.
• Approved indications: Ocrevus is also approved for primary progressive MS (PPMS); Kesimpta is not.

Kesimpta vs. Rituximab

• Rituximab is an older anti-CD20 antibody used off-label for MS. It's given as an IV infusion, typically every 6 months.
• Rituximab is significantly cheaper (especially as a generic/biosimilar) but is not FDA-approved for MS.
• Some neurologists prescribe rituximab when cost is a major barrier.

Kesimpta vs. Tysabri (Natalizumab)

• Different mechanism: Tysabri blocks a protein called alpha-4 integrin to prevent immune cells from crossing into the brain and spinal cord.
• Tysabri is given as a monthly IV infusion. It carries a higher risk of PML (progressive multifocal leukoencephalopathy) compared to anti-CD20 therapies.
• Both are considered high-efficacy MS treatments.

Kesimpta vs. Oral MS Therapies

• Oral options like Aubagio (Teriflunomide) and Mavenclad (Cladribine) offer the convenience of pills but may have different efficacy and side effect profiles.
• Kesimpta is generally considered a higher-efficacy option, often chosen for patients with active disease or those switching from less effective therapies.

For a full comparison, see our guide to Kesimpta alternatives.

Final Thoughts

Kesimpta works by surgically removing the B cells that drive MS disease activity. It's a targeted, at-home treatment that has changed the landscape for people living with relapsing MS. Understanding how it works can help you have more productive conversations with your neurologist — and feel more confident in your treatment plan.

Want to learn more? Read our complete overview: What Is Kesimpta? Or if you need help finding it, Medfinder can help you locate Kesimpta in stock near you.