Monoclonal antibodies and how they work
Plasma cells, the most mature B-cells in the body, are white blood cells that specialize in making antibodies. Each plasma cell is responsible for one antibody, otherwise known as a monoclonal antibody (MAb). Each MAb acts specifically against a particular antigen, which is sort of like a beacon that attracts antibodies and immune cells (such as lymphocytes). Using new technologies, scientists can now produce large amounts of antibodies that can be directed to a single antigen on the cell's surface. A MAb is similar to a guided missile that homes in on a lymphoma cell and destroys it.
A number of strategies involving the use of MAbs to treat cancer are being studied, including: (a) MAbs that react with specific types of cancer cells, thereby enhancing a patient's immune response to the cancer, (b) MAbs that are combined with other anticancer drugs, toxins, or radioisotopes, allowing the delivery of these drugs directly to the tumor and bypassing toxicity to most normal cells, and (c) MAbs that are used to help purge and destroy cancer cells before a patient’s stem cells are re-infused in autologous bone marrow transplant.
Rituximab (Rituxan®)
Rituximab was the first monoclonal antibody approved for the treatment of relapsed or refractory, low-grade or follicular, CD-20 positive, B-cell NHL. Rituxan targets the CD-20 antigen found on almost all B-cells, killing both cancerous and normal B-cells. All other cells and tissues are spared by Rituxan. Researchers believe that this therapy works in part via the body's immune system response triggered by the MAb's attachment to cancer cells. Because the youngest B-cells in the body (precursor cells that will become B-cells) do not yet have the CD-20 antigen, they are not affected. Thus, after treatment the body can replenish its B-cell supply from these young cells.
Rituxan is commonly administered in four weekly infusions on an outpatient basis over a 22-day period. Rituxan side effects are generally confined to the time when the medication is being given. Flu-like symptoms (for example, chills, fever, and sweating) occur in many patients during the first infusion, but generally decrease with subsequent infusions. Side effects that occur less frequently include nausea, vomiting, rashes, fatigue, headache, wheezing, infection, and a sensation of tongue or throat swelling. Severe but rare side effects have been reported. These effects have generally occurred in patients who have a high level of circulating lymphoma cells or a history of heart or lung problems. Patients should tell their doctors if they have these conditions. Overall, the infusion is well tolerated with few long-term side effects.
There is some evidence that Rituxan may be useful as maintenance therapy, in which the medication is given after a patient has achieved a response. Clinical trials are under way to answer this important question.
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