Bacille Calmette-Guérin, widely known as BCG, is a vaccine derived from a weakened strain of Mycobacterium bovis, a bacterium found in cattle. This attenuated form does not cause disease in humans but stimulates the immune system. Developed by French bacteriologists Albert Calmette and Camille Guérin, BCG was first administered to humans in 1921. It functions as an immunotherapeutic agent, modulating the body’s immune response.
Primary Role in Tuberculosis Prevention
BCG’s primary application is its use as a vaccine against tuberculosis (TB), a serious infectious disease caused by Mycobacterium tuberculosis. It is the only vaccine available for TB and is one of the most widely administered vaccines globally. Countries with a high incidence of TB often include BCG in their routine newborn immunization schedules, recommending a single dose soon after birth.
The vaccine is administered via an intradermal injection, typically into the skin. BCG offers substantial protection against severe forms of TB in young children, such as tuberculous meningitis and disseminated TB, with protection rates against these forms estimated to be around 64% to 78%. Its efficacy against pulmonary TB in adults is quite variable. In regions with a low prevalence of TB, routine BCG vaccination is generally not recommended due to this variable efficacy against adult pulmonary forms of the disease.
Beyond Tuberculosis: Bladder Cancer Treatment
Beyond its role in TB prevention, BCG is also used as an immunotherapy for non-muscle-invasive bladder cancer (NMIBC). This type of cancer is confined to the innermost lining of the bladder and has not yet spread into the muscle layer. BCG is an effective treatment for preventing the recurrence and progression of NMIBC.
For bladder cancer treatment, BCG is administered directly into the bladder through a catheter in a procedure called intravesical instillation. This localized delivery allows the weakened bacteria to interact directly with the bladder lining. Intravesical BCG therapy significantly reduces the risk of tumor recurrence compared to surgical removal alone or other intravesical chemotherapy treatments. Some studies report 5-year recurrence-free survival rates of around 83% with BCG, demonstrating its effectiveness in managing this specific cancer type.
How Bacille Calmette-Guérin Works
BCG stimulates the body’s immune system to recognize and eliminate threats. As a vaccine against TB, BCG primes the immune system to respond to Mycobacterium tuberculosis. It activates immune cells, including macrophages and T cells, which produce pro-inflammatory cytokines and recruit other immune cells. This prepares the body to mount a more effective defense if it encounters the actual TB bacteria.
For bladder cancer treatment, BCG triggers a localized immune response within the bladder lining. The weakened Mycobacterium bovis bacteria are taken up by bladder cancer cells, stimulating immune cells, particularly T cells, to attack the cancer cells. This leads to an inflammatory response that targets and destroys malignant cells. Activated immune cells can continue to monitor the bladder lining, potentially preventing cancer recurrence.
Important Considerations and Side Effects
BCG administration, both as a vaccine and a cancer treatment, can lead to side effects. Common reactions at the vaccine injection site include redness, swelling, tenderness, and the formation of a small ulcer that typically heals within 2 to 5 months, leaving a superficial scar. Flu-like symptoms such as fever, chills, muscle aches, and fatigue are also common and usually resolve within 2 to 3 days after vaccination.
When used for bladder cancer, patients commonly experience bladder irritation, including frequent and painful urination, and sometimes blood in the urine. These bladder-related symptoms often appear 4 to 6 hours after instillation and can last for 24 to 72 hours, potentially increasing in severity with subsequent treatments. Flu-like symptoms are also reported after bladder instillations.
BCG is a live vaccine and is contraindicated in individuals with weakened immune systems due to conditions like HIV infection, congenital immunodeficiency, malignancy, or those receiving immunosuppressive drugs. Pregnant and lactating women are advised against receiving the BCG vaccine due to insufficient safety evidence. Patients should seek medical attention if they experience a high fever (103°F or higher), prolonged inflammation, or any severe or unusual reactions.