Ocrevus (ocrelizumab) is technically an immunosuppressant, but not in the broad, blanket way that older drugs like methotrexate or cyclophosphamide suppress the immune system. It’s formally classified as an anti-CD20 monoclonal antibody, and experts categorize it as a “selective immunosuppressant” because it targets one specific part of your immune system rather than weakening the whole thing.
What “Selective Immunosuppressant” Means
Immunosuppressants exist on a spectrum. On one end, you have systemic immunosuppressants like long-term corticosteroids and chemotherapy drugs. These reduce the activity of your entire immune system through broad cytotoxic effects. On the other end, you have selective immunosuppressants like Ocrevus, which zero in on a specific immune cell type.
Ocrevus locks onto a protein called CD20, found on the surface of B cells. B cells are a type of white blood cell that plays a role in the immune attacks on nerve tissue that drive multiple sclerosis. After Ocrevus binds to CD20, it depletes those B cells through several mechanisms: triggering the cells to self-destruct, flagging them for destruction by other immune cells, and activating the body’s complement system to break them down. The result is a sharp reduction in circulating B cells while leaving much of the rest of your immune system intact. T cells, for example, are not directly targeted.
This selectivity is why neurologists often distinguish Ocrevus from older, broader immunosuppressants. It suppresses a specific arm of immunity rather than the whole system. That said, B cells do play a legitimate role in fighting infections and producing antibodies, so depleting them still carries real immune consequences.
How It Affects Your Ability to Fight Infections
Because Ocrevus removes a significant portion of your B cells, your body’s ability to mount certain immune responses is reduced. In a pooled analysis of over 6,100 patients across 13 clinical trials, 6.8% experienced serious infections (excluding COVID-19) over a median treatment period of 3.7 years. Upper respiratory infections are among the most common side effects reported.
A longer-term concern is a condition called hypogammaglobulinemia, where your levels of immunoglobulins (the antibodies your body uses to fight pathogens) drop below normal. In real-world data, about 9.8% of patients on Ocrevus or similar anti-CD20 therapies developed this condition. The risk increases with age over 50 and with treatment duration beyond three years. This is why doctors typically monitor your immunoglobulin levels with periodic blood tests during long-term treatment.
Screening Before You Start
Because Ocrevus suppresses part of your immune system, several safety checks are required before your first infusion. The FDA’s prescribing information mandates hepatitis B screening for all patients. Ocrevus is contraindicated if you have active hepatitis B, because reactivating a dormant or active hepatitis B infection in the context of B-cell depletion can be dangerous. Patients who test positive for certain hepatitis B antibodies but don’t have active disease may still be candidates, but their doctors will typically involve a liver specialist.
Before every infusion, not just the first, your care team will assess whether you have any active infection. If you do, the infusion gets postponed until it clears.
Vaccines Need to Happen Early
Vaccine timing is one of the most practical things to plan around if you’re starting Ocrevus. Live or live-attenuated vaccines (such as the shingles vaccine Zostavax or the MMR vaccine) need to be given at least four weeks before your first dose. Non-live vaccines, like the flu shot, should ideally be given at least two weeks before starting treatment.
Once you’re on Ocrevus, live vaccines are generally avoided because your depleted B-cell population may not be able to handle even a weakened virus safely. Non-live vaccines can still be given during treatment, but your immune response to them will likely be blunted, meaning they may not work as well. If you know you’re heading toward Ocrevus, getting your vaccinations up to date beforehand gives you the strongest protection.
How It Compares to Other MS Therapies
MS treatments fall into three broad categories. Immunomodulators like interferon beta and glatiramer acetate tweak the immune system’s behavior without outright suppressing it. Systemic immunosuppressants like mitoxantrone and cyclophosphamide broadly dampen immune function. Selective immunosuppressants, the category Ocrevus falls into alongside drugs like natalizumab and fingolimod, target specific molecules or pathways.
In practice, this means Ocrevus is more potent than immunomodulators but more targeted than old-school immunosuppressants. It’s FDA-approved for both relapsing MS and primary progressive MS, making it one of the few therapies available for the progressive form of the disease. The trade-off for that potency is the infection risk and the need for ongoing immune monitoring, which is less of a concern with milder immunomodulators.
So if you’ve been told Ocrevus “isn’t really an immunosuppressant,” that’s an oversimplification. It is one. It just works with a scalpel rather than a sledgehammer, selectively depleting B cells instead of broadly suppressing everything. That precision reduces some risks but doesn’t eliminate them, which is why the screening, vaccine timing, and long-term blood work all matter.