A living enzymatic adenosine switch couples metabolic rescue to IL-12-driven antitumor immunity

Cancer is not just a mass of rogue cells; it is an ecosystem that actively reshapes its surroundings to survive. One of the most effective ways a tumor defends itself is by flooding its immediate neighborhood with a specific chemical called adenosine. In a healthy body, adenosine acts as a signal to calm inflammation and protect tissues from damage. However, tumors hijack this natural mechanism, using high levels of adenosine to put the immune system to sleep. When immune cells like T cells and natural killer cells encounter this chemical soup, they become exhausted, their metabolism slows down, and they lose the ability to hunt and destroy the cancer. For years, scientists have tried to block the receptors that sense this chemical or stop the enzymes that create it, but these approaches have often failed because the adenosine itself remains in the environment, still capable of causing harm.

A new study from researchers at Dana-Farber Cancer Institute and Harvard Medical School proposes a different strategy: instead of just blocking the signal, they aim to change the chemical itself. They engineered a harmless, non-pathogenic bacterium to act as a living factory right inside the tumor. These bacteria are designed to grab the adenosine and instantly convert it into a different molecule called inosine. Unlike adenosine, which suppresses the immune system, inosine can actually fuel the immune cells, giving them the energy they need to function. To make this even more powerful, the researchers attached a second tool to the bacteria: a protein called interleukin-12, which acts as a loud alarm bell to wake up the immune system. By combining a metabolic switch that removes the suppressive chemical with a direct signal to activate the immune response, the team created a dual-action therapy that has shown remarkable promise in laboratory models of leukemia and solid tumors.

The researchers began by building this living tool using a common, safe strain of bacteria known as E. coli K-12. They genetically modified these bacteria to display a specific enzyme on their outer surface. This enzyme, called adenosine deaminase, acts like a molecular scissors that cuts adenosine and transforms it into inosine. In laboratory tests, the team confirmed that these bacteria could rapidly deplete adenosine from their surroundings and replace it with inosine. When they exposed human immune cells to high levels of adenosine, the cells became sluggish and their energy production dropped. However, when the researchers added the engineered bacteria, the adenosine levels fell, and the immune cells regained their metabolic strength. They began to breathe more efficiently, produce more energy, and start dividing again. The bacteria essentially turned a toxic environment back into a supportive one, restoring the cells to a healthy state.

While restoring the energy of the immune cells was a major step, the researchers noticed that simply fixing the metabolism did not make the cells attack the cancer any harder than they would have in a normal, healthy environment. The cells were back to their baseline, but they were not supercharged. To solve this, the team added a second component to the bacteria: interleukin-12. This protein is a powerful stimulant for the immune system, known for boosting the killing power of T cells and natural killer cells. The challenge was that interleukin-12 can be dangerous if it circulates through the whole body, causing severe inflammation. By attaching it directly to the bacteria, the researchers ensured that this potent signal was released only where the bacteria gathered: inside the tumor.

The results of combining these two functions were striking. In test tubes, immune cells treated with the dual-function bacteria not only recovered their energy but also became significantly more aggressive against cancer cells. They released more of the chemicals that kill tumors and showed higher levels of activation markers on their surfaces. The bacteria effectively broke through the "ceiling" that adenosine had placed on the immune system. In a mouse model of melanoma, a type of skin cancer, the researchers injected these bacteria directly into the tumors. The treatment slowed tumor growth dramatically, and in many cases, the tumors disappeared completely. Perhaps most importantly, the mice that survived the initial treatment developed a long-lasting memory of the cancer. When the researchers injected the same cancer cells into these survivors weeks later, the mice's immune systems recognized and destroyed the new tumors immediately, preventing the disease from returning.

The team then tested whether this approach could work for blood cancers, which are harder to treat with localized therapies because the cancer cells float freely in the bloodstream. They looked at patients with acute myeloid leukemia and found that their bone marrow contained high levels of adenosine, which correlated with the amount of cancer cells present. This confirmed that the adenosine problem exists in blood cancers too. When they treated mice with this leukemia using the bacteria injected into their veins, the bacteria traveled to the liver and spleen, where the cancer cells had gathered. There, the bacteria converted the adenosine and released the immune-stimulating protein. The treatment significantly reduced the number of cancer cells in the blood and bone marrow and extended the survival of the mice. Crucially, the treatment did not cause the severe systemic inflammation that often limits the use of immune-stimulating drugs, suggesting it was safe and well-tolerated even when given repeatedly.

To see if this method could help with solid tumors that are difficult to reach, the researchers combined their bacteria with a type of advanced therapy called CAR-NK cells. These are immune cells that have been genetically engineered to hunt down specific cancer markers, but they often struggle to survive and work inside the dense, suppressive environment of a solid tumor. In a model of pancreatic cancer, the researchers gave the mice the engineered bacteria along with the CAR-NK cells. The bacteria created a local environment where the CAR-NK cells could thrive. Instead of being blocked by adenosine, the CAR-NK cells were able to infiltrate the tumor in greater numbers and kill the cancer cells more effectively. The mice treated with this combination lived significantly longer than those treated with the CAR-NK cells alone or with the bacteria alone.

Finally, the researchers wanted to know if their living bacterial platform offered an advantage over simply injecting the two proteins (the enzyme and the immune stimulant) as separate drugs. They treated mice with breast cancer using either the bacteria or a mixture of the soluble proteins. The bacteria performed better. The tumors shrank more, and the mice lived longer. This suggests that the bacteria do more than just deliver the drugs; their presence and the way they hold the proteins together on their surface create a sustained, localized effect that free-floating proteins cannot match. The bacteria seem to act as a stable platform that keeps the therapeutic agents right where they are needed, protecting them from breaking down and ensuring they work together in the same spot.

The study concludes that this living, enzymatic switch offers a new way to fight cancer by rewiring the tumor's metabolic environment. Instead of just trying to block the immune system's brakes, this approach replaces the suppressive chemical with a fuel source and simultaneously presses the gas pedal with a localized immune signal. While the research is currently in preclinical stages and has only been tested in animals and human cells in a lab, the results suggest a powerful new direction for cancer therapy. The ability to use a harmless bacterium to perform complex chemical transformations and deliver immune signals directly to a tumor site opens the door to treating cancers that have previously been resistant to immunotherapy. The researchers emphasize that this is a modular platform, meaning the specific enzymes and signals could be swapped out to target different types of cancer or different metabolic barriers, offering a versatile tool for future medical breakthroughs.