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Thomas Flaig, MD


Can BCG Vaccination Induce Immune Responses Against COVID-19?

By: Lauren Velentzas
Posted: Tuesday, September 12, 2023

The boosted immune response of bacillus Calmette-Guérin (BCG) vaccination is known to be one of the most efficient adjuvant therapies for high-risk, non–muscle-invasive bladder cancer. This trained immunity may also boost immune responses to viral respiratory infections, suggesting it may ultimately induce a response against SARS–CoV-2 in patients with bladder cancer, a population more vulnerable to COVID-19. Renate Pichler, MD, PhD, FEBU, of the Medical University of Innsbruck, Austria, and colleagues evaluated the intravesical application of BCG triggers against SARS–CoV-2, using blood samples from unvaccinated SARS–CoV-2–naive patients with high-risk, non–muscle-invasive bladder cancer and looking for the presence of SARS–CoV-2 neutralizing antibodies. The investigators published their findings in Frontiers in Immunology.

“Although intravesical BCG did not induce adaptive immune responses, repetitive intravesical instillations of BCG induced circulating innate immune cells that produce TI cytokines also in response to SARS–CoV-2,” the investigators stated.

To control for preexisting immunity to SARS–CoV-2, the blood samples used were taken between 2014 and 2015, prior to the COVID-19 outbreak, from 11 patients with high-risk non–muscle-invasive bladder cancer. Blood samples were collected before each BCG bladder instillation. The treatment schedule was based on a standard regimen of a 6-week induction course followed by three weekly maintenance courses at 3, 6, 12, 18, 24, 30, and 36 months.

When analyzing the plasma antibodies against SARS–CoV-2 receptor binding domain, the researchers identified neither SARS–CoV-2–neutralizing antibodies nor SARS–CoV-2–reactive T cells. However, the expression of key cytokines of trained immunity such as interleukin-1 β (IL-1β), IL-6, and TNFα was noted to be higher in at least four of the samples, along with a “significant” increase in mRNA.

“The increased fitness of the innate immune system that is induced by repetitive BCG administrations may be important in the context of various therapeutic and preventive strategies,” the study authors concluded.

Disclosure: The study authors reported no conflicts of interest.

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