How Does Rituximab Work? — The CD20 Target Explained

CD20 was identified as a useful target for several reasons. It sits reliably on the surface of most mature B-cells and most B-cell cancers. It does not shed into the bloodstream, which would neutralise a circulating antibody before it ever reached a cancer cell. And — critically — it is absent on the stem cells that replenish the blood supply and on plasma cells, the B-cells responsible for maintaining existing antibody levels. Destroying CD20-positive cells therefore clears the cancer without permanently disabling the immune system's ability to recover.

They are the same molecule. MabThera is a brand name; rituximab is the international non-proprietary name, and you may see other brand names depending on where it was manufactured. Biosimilar versions of rituximab are also in use; these share the same mechanism of action and the same target, and are subject to the same regulatory standards as the original. If your team has moved between a branded version and a biosimilar, the clinical intent is unchanged and the treatment you are receiving is equivalent.

Response is assessed by imaging and blood tests after a set number of cycles, not after a single infusion. You will not see or feel the drug working on the day it is given. For lymphomas, a response assessment scan is typically done at defined points in your treatment plan — NCCN guidance specifies when interim imaging should take place. The absence of immediate visible change does not mean the treatment is not working. Your oncologist will explain what the imaging results mean for your specific situation once they are available.

B-cell counts typically fall during and for some months after treatment, then recover. Your immunoglobulin levels — the antibodies your B-cells produce — may also remain lower for a year or more in some people. For most patients this is manageable with monitoring and prompt treatment of any infections that arise. Recovery time varies from person to person and depends on how many cycles were given and whether other treatments were used alongside. Your team will monitor your blood counts throughout and tell you which symptoms to report between appointments.

Some vaccinations are worth completing before rituximab begins, because the drug depletes the very cells that generate responses to new vaccines. Live vaccines cannot be given safely once treatment starts. Your team will review your vaccination history at the outset and may advise you to catch up on specific vaccines beforehand. Influenza and pneumococcal vaccination are particularly relevant while your B-cell immunity is reduced. Raise this at your first appointment if your team has not already mentioned it.

Rituximab is a monoclonal antibody and is sometimes grouped under the broad heading of immunotherapy because it works by engaging the immune system. However, it is a distinct category from the checkpoint inhibitors — such as pembrolizumab or nivolumab — that are most commonly discussed when people say immunotherapy today. Checkpoint inhibitors broadly remove the brakes on the immune system; rituximab is a precisely targeted antibody that binds to one specific protein on one specific cell type. The two categories work by different mechanisms and are used for different cancers.