BCG vaccine destroys bladder cancer cells, scientists find

A team of scientists from the Champalimaud Foundation reveals in an article published this Thursday how a tuberculosis vaccine used to treat bladder cancer destroys tumor cells, based on an experiment carried out with zebrafish.

The tuberculosis vaccine, known by its initials BCG, is used as immunotherapy for early-stage bladder cancer after tumor removal.

The BCG solution, inserted into the bladder through a catheter, contains live, weakened bacteria that stimulate the immune system to kill cancer cells in the bladder.

“How the BCG vaccine acts as an immunomodulator to eliminate bladder tumors is not fully understood,” the Champalimaud Foundation said in a statement.

In a paper published Thursday in the open-access medical journal Models and Mechanisms of Disease, the Champalimaud Foundation team describes how zebrafish macrophages (immune cells) “literally induce cancer cells to commit suicide and then rapidly devour these dead cells.”

“Macrophages are actively recruited to the tumor site after BCG injection, directly killing bladder cancer cells through a process of cell suicide (apoptosis) dependent on a substance called tumor necrosis factor (TNF) secreted by macrophages, which acts as a potent signaling molecule for the immune system,” the statement said.

In this work, the researchers used microscopy techniques to observe macrophages interacting with tumor cells previously taken from a patient with bladder cancer and then injected into zebrafish embryos where the tumors were growing.

When macrophages were removed from zebrafish containing human bladder cancer cells, “the antitumor effects of the BCG vaccine were completely blocked, demonstrating that macrophages are in fact critical for the initial antitumor response induced by the vaccine,” he said in a statement.

This experiment was developed in the Laboratory of Cancer Development and Innate Immunity, coordinated by biologist Rita Fiore.