Despite decades of research, Crohn’s remains one of medicine’s most stubborn mysteries. What triggers the immune system to attack the gut? And why do only certain people, often the young, develop this life-long inflammatory illness?

Could a bacterium be the problem?

With the support of some dedicated donors, King’s researchers hit upon a possible answer: a bacterium called mycobacterium avium subspecies paratuberculosis (MAP).

MAP causes Johne’s disease in cows, a gut illness strikingly similar to Crohn’s, and it can enter the food chain through infected milk and meat. This led scientists to ask: could MAP also be the cause of Crohn’s disease in humans? And if MAP plays a role in Crohn’s, then could we develop a targeted vaccine to fight it?

The first step was to prove the link between MAP and Crohn’s disease.

This breakthrough was achieved by King’s Professor John Hermon-Taylor (pictured above), who died in 2021. He and his team developed a cutting-edge diagnostic test to detect the presence of MAP. When they tested this on a sample of Crohn’s disease patients, MAP could be detected in the gut of 100 per cent of them. This provided the strongest evidence yet that MAP could be a key player in the disease.

Professor Hermon-Taylor’s discovery laid the groundwork for something extraordinary: the design of a modern vaccine aimed at training the immune system to recognise and destroy MAP, a potential game-changer for Crohn’s treatment.

Could a MAP vaccine help tame Crohn’s disease?

Crohn’s disease has traditionally been treated by calming the immune system with drugs, but these don’t cure the disease and often come with side effects. Bland diets are also recommended. These can reduce Crohn’s symptoms by removing some of the irritants which trigger inflammation.

But with the discovery that MAP is present in Crohn’s, King’s researchers argued that if MAP is part of the problem, then simply suppressing the immune system is like turning off a fire alarm without putting out the fire. To see real results, you need to target the cause, not just the symptoms.

With this in mind, the team set out to develop a MAP vaccine. Working with hospital partners and global collaborators, researchers at King’s – now led by Dr Jeremy Sanderson – designed a cutting-edge viral-vector vaccine. This modern approach trains T cells (blood cells that help to protect you from infection and disease) to recognise and destroy MAP bacteria.

The project quickly became a rallying point for Crohn’s families worldwide. Much of the funding came from generous donors who shared the vision of a future where Crohn’s disease could be treated at its root – and not just managed.

Trial success

In early 2025, King’s unveiled results from a small but significant trial of 28 Crohn’s patients who received an experimental MAP vaccine. The trial’s goal was to determine whether the vaccine was safe and to measure immune responses. The results were quietly impressive.

The vaccine successfully activated MAP-targeting T cells, supercharging them to hunt down bacteria hiding in gut tissue. This was combined with very mild side effects, just sore arms and brief fatigue. And although the trial wasn’t built to measure symptom relief, something remarkable happened: patients on higher doses saw their symptoms ease and gut health improve, with early signs of tissue healing.

Although small, this trial’s implications are enormous. Backed by visionary philanthropy, King’s researchers have not only strengthened the case for MAP as a culprit but also opened the door to a treatment that targets the root cause of Crohn’s disease.

Larger trials are still needed to see if these vaccines truly improve symptoms and prevent flare-ups. But the ramifications are huge. For decades, Crohn’s care has meant a lifetime of managing symptoms. This research signals something far more ambitious: tackling the disease at its source.

What’s next?

The next few years will be decisive. If the MAP vaccine moves successfully into large-scale trials and if the diagnostic test continues to confirm MAP’s presence, the entire Crohn’s treatment landscape could shift. Instead of managing flare-ups with heavy medication, patients might one day receive a simple vaccine.

And the potential doesn’t stop there. If proven effective, the vaccine could be used both therapeutically (to treat Crohn’s) and preventively (for people at high risk), or even in livestock, to reduce MAP exposure in the food chain.

This isn’t just a new treatment. It’s a new way of thinking about Crohn’s disease and it could rewrite the future for millions.

It’s a bold vision. But then again, bold visions are exactly what have driven this research at King’s from the beginning.

If you’re interested in supporting the next stage of this research, contact giving@kcl.ac.uk.