The salmonella bacterium might not be all that bad. That is, when it comes to cancerous tumors.

A study published Wednesday in Science Translational Medicine reported that in mice, treating tumors with salmonella can induce an immune response that kills cancer cells.

Researchers out of Italy studied the effects the bacteria had on tumors in mice, noting that the promising results could help scientists create an injection containing tumor-killing immune cells or even a vaccine against cancer. The researchers chose to test the effects of salmonella -- the strain used to fight Salmonellosis -- because the bacterium had previously shown it had a natural ability to colonize tumors when injected, and it can be easily genetically manipulated, explained researcher Maria Rescigno in an e-mail to DOTmed News.
Immune cells that patrol the body can recognize early cancer cells and destroy them. The process responsible for this relies on a protein called connexin 43, which forms small communication channels or gap junctions between different types of cells. Bits of the tumor called peptides escape through the channels and enter immune cells that exhibit the peptides on their surfaces. The immune cells, seeing these peptides as red flags, trigger an attack against them. But as the cancer cells progress, they can become invisible to the immune cells.

But the researchers discovered that injecting salmonella into tumors can make the cells visible again, by reactivating the connexin 43. As a result, the report said, new gap junctions formed, allowing small molecules dyed fluorescent yellow to pass between tumor cells or from tumor cells into immune cells.

"We found that when we injected salmonella in tumors, it induced the recruitment of immune cells and had an effect both on the growth of the treated tumor as well as of an untreated tumor," Rescigno said. "This suggested that salmonella had an anti-tumor effect also at distance."

When tested in mice, the researchers found that the salmonella-infected cancer cells passed through the gap junctions into the immune cells. The newly activated immune cells were able to recognize and kill the tumor cells. This approach also protected against cancer spreading to other parts of the body, something the researchers called a vaccination-style preventive strategy.

"The transfer of these peptides allows the dendritic cells [guardian cells of the immune system] to initiate an immune response to that fingerprint [antigenic peptide] that will allow the recognition and killing of tumor cells," Rescigno explained.

The findings demonstrate that it's possible to exploit this process outside of the mice to generate immunotherapy protocols effective in controlling the growth of established tumors or vaccinating against tumors, she said. Moving forward, the results can help generate patient-tailored therapies, said Rescigno.

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