Infection and immunity

PROFILE:A difficile discovery

Nigel Minton
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Funded by the MRC, Professor Nigel Minton at the University of Nottingham has made an important discovery about the hospital-acquired infection C. difficile.

Nigel is a Professor of Applied Molecular Microbiology and leads a team of researchers dedicated to studying a group of bacteria called Clostridia. He jokingly badges himself as a “Clostridia fanatic” and when he describes the wide range of potential uses for these bacteria, it’s easy to see why he is so enthusiastic.

“They’re a fantastic group of organisms and I always say that the antics of a few give the rest a bad name. Of the 100 or so Clostridia species only about 12 cause diseases. But there are all these other wonderful Clostridia that can do amazing things – we can use them to make biofuels, they can selectively destroy tumour tissue and treat cancer, and they can even be genetically modified to make aviation fuel. But at the same time, some Clostridia can cause serious health problems, and I am determined to do something about that by understanding more about how pathogenic Clostridia infect their hosts.”

One species, Clostridium difficile (C. difficile) is a major public health problem, causing healthcare-acquired infections. In 2008/09, C. difficile was responsible for over 4,000 deaths in UK hospitals, four times more than the number who died from MRSA infection.

“Most people don’t realise that it’s actually a bigger problem than MRSA,” says Nigel. ”C. difficile is principally a disease of the elderly. When older people go into hospital and are given antibiotics, the normal beneficial bacteria within the gut are disrupted, and if C. difficile is around it takes over the gut, and can cause severe, explosive diarrhoea and produces spores – dormant seeds – which spread around the hospital. It causes greatest devastation in the elderly and until recently the UK had the highest infection rates it the world, so there have been major strides in recent years by the NHS to reduce infection rates, and fortunately the incidence of C. difficile is now starting to come down.”

Nigel and his research team have developed genetic tools to study C. difficile to try and understand all the different components of the bug that contribute to how it infects people.

“For any disease, bacterial infection or otherwise, in order to understand the individual factors that contribute, you need to look at what happens when it isn’t there. That’s really how you find out what the products of different genes do and how they affect virulence. Until recently, it was practically impossible to genetically manipulate C. difficile, so that was the driving force behind setting up my research group and we’ve now developed some very efficient systems.”

Nigel explains that C. difficile causes severe diarrhoea by producing two powerful toxins, toxin A and toxin B, which cause damage to the lining of the gut. For a long time, scientists believed that toxin A was the more important factor in causing disease. This appeared to be confirmed definitively in 2009 with the publication of a high profile paper which showed that a version of C. difficile that had been genetically manipulated to produce only toxin B caused diarrhoea in hamster model, and that a version which could produce only toxin A did not.

But around the same time, Nigel’s group were doing similar experiments, and their results were very different:

“With our MRC funding we were making mutants with a more efficient technology which were more stable. In direct contrast to the findings of the other group, our bacterium which had only toxin A did cause diarrhoea.

“Our finding is really important because there are a lot of companies out there looking to develop drugs that protect against C. difficile by targeting the toxins. The study that preceded ours gave them the message that they possibly didn’t need to bother making drugs or diagnostic kits which targeted toxin A because it wasn’t important – but our finding showed that this wasn’t the case, and re-directed attention of companies back to toxin A.”

Nigel and his group are now trying to establish whether additional mutations in the genome of the bacterial strains used in the other study caused the differing results. They have also reproduced the results of their study using a particularly virulent strain of C. difficile which caused major outbreaks at Stoke Mandeville Hospital in Buckinghamshire in 2005 and 2006, causing 36 deaths.

When asked about his motivation for doing research, Nigel gives a straight-talking answer:

“I don’t believe in doing research for esoteric reasons – there has to be a reason for doing it, which is why I asked for my professorial title to include the word ‘applied’. The tax payer deserves value for money so there must be output. Perversely, I’ve never believed in focusing on getting the next paper published in a high profile journal, so it’s ironic that we ended up getting this research published in Nature!”

Achievements

A vaccine to target HIV’s weak spot

Thanks to the development of antiretroviral drug therapy, most people with HIV can now expect to enjoy good health and a near-normal life expectancy. However, there is still no cure for the infection.

Dr Lucy Dorrell and her colleague Dr Tomas Hanke at the MRC Human Immunology Unit in Oxford are exploring the possibility of combining antiretroviral therapy with a new vaccine to improve treatment of the disease. The aim is to increase the effectiveness of specialised white blood cells (called CD8+ T cells) which can destroy HIV-infected cells in the body.

HIV is able to change its genetic make-up rapidly, so designing a vaccine against it is difficult. But the virus does have vulnerable regions in its genome, known as highly conserved regions, where genetic mutations rarely develop.

Dr Dorrell explained: “We have developed a vaccine which consists of a synthetic gene that is based on the highly conserved regions of HIV. The aim is to divert CD8+ T cell responses away from variable regions within viral proteins, as the virus can easily evade these responses, and to target CD8+ T cells towards conserved regions in which mutations could weaken the virus.”

The vaccine, called MVA.HIVconsv, is currently being trialled in HIV-infected adults; so far they have tolerated the vaccine well.

Dr Dorrell adds: “Laboratory tests on the immune response are ongoing but there are some early indications that the vaccine is boosting responses to the highly conserved regions in HIV. We expect full results to be available in 2012.”

Penetrating flu’s disguise

With funding from the MRC and Wellcome Trust, Dr Sarah Gilbert and her team at the Jenner Institute, University of Oxford, have developed a new vaccine that could transform the way we vaccinate against seasonal flu and also offer immunity to a bird flu pandemic.

Current flu vaccines work by causing the production of protective antibodies directed against proteins on the outer surface of the influenza virus. These external proteins differ between flu strains and change over time, so each vaccine works only against a specific strain.

Dr Gilbert explains: “This new vaccine works by targeting internal proteins essential to the flu virus that alter very little over time or between strains. It induces T cells, part of the body’s immune system, to kill any cells infected by the flu virus, so controlling the infection.

“The body maintains a low-level T cell response to flu from previous flu infections which the vaccine should boost to levels high enough to protect against subsequent infection. So by targeting these proteins, we should be able to develop a universal flu jab.”

In the first clinical trial in healthy volunteers, the vaccine caused an increase in influenza-specific T cells in all participants. A second version will soon be tested that uses a different viral vector to deliver the influenza antigens. The two vaccines will be assessed to see which is most suitable for further development.

Breakthrough opens up new line of attack on viruses

A landmark discovery that antibodies can fight viruses from within infected cells has transforming previous scientific understanding of our immunity to viral diseases like the common cold, the ‘winter vomiting bug’ and gastroenteritis.

Viruses are mankind’s biggest killer. For many years, scientists have believed that antibodies could reduce infection only by attacking viruses outside cells and also by blocking their entry into cells. But the new MRC-funded research shows that antibodies remain attached when viruses enter healthy cells. Once inside, the antibodies trigger a response, led by a protein called TRIM21, which pulls the virus into a disposal system used by the cell to get rid of unwanted material. This process happens quickly and the scientists have shown that increasing the amount of TRIM21 protein in cells makes destruction of viruses even more effective, suggesting new ways of making better antiviral drugs.

Dr Leo James from Cambridge’s MRC Laboratory of Molecular Biology, who led the research, said: “Although we don’t expect all viruses to be cleared by this mechanism, we are excited that our discoveries may open multiple avenues for developing new antiviral drugs.” Dr James is now working with MRC Technology to investigate the next steps in the development of potential new drugs.

Trial reveals better drug to beat malaria

Results from the largest-ever clinical trial in patients hospitalised with severe malaria have shown that the drug artesunate should now be the preferred treatment for malaria worldwide. By treating patients with artesunate, rather than the more traditional drug quinine, the number of deaths from severe malaria could be reduced by 22.5 per cent.

The trial, run by an international consortium of researchers including MRC Principal Investigator Dr Kalifa Bojang at MRC The Gambia Unit, was carried out over a five-year period in hospitals across nine African countries and involved 5,425 children with severe malaria. The results showed that with artesunate treatment 8.5 per cent of the patients died, compared to 10.9 per cent of those treated with quinine. In addition, children treated with artesunate were less likely to slip into a deeper coma or have seizures after the treatment was started.

Dr Bojang, who led the Gambian arm of the research at the Royal Victoria Teaching Hospital in Banjul, explained: “Taking part in this trial has been a long and sometimes difficult journey, but it has all been worthwhile, as our findings have the potential to save many thousand more lives across the developing world.”

Predicting kidney transplant success

An MRC-supported study has found a set of immunological markers in the blood which could help predict the long-term success of a person’s kidney transplant.

Kidney transplant patients have to take drugs for the rest of their lives to prevent their immune systems from rejecting the donor organ. But these drugs, immunosuppressants, can cause serious health complications. This research could point the way to more personalised care for these patients, by helping doctors single out those who may not need immunosuppressants.

The scientists studied 11 kidney transplant patients from across Europe who appeared to have developed a natural tolerance to their donor organ, alongside stable transplant patients on immunosuppressants, others who were showing signs of rejecting their donor organ, and healthy volunteers. They carried out a range of lab tests to try to identify any characteristics in the blood specific to those who had become tolerant of their transplanted organ.

They were able to show that these individuals shared a ‘tolerance fingerprint’, or a particular set of immunological markers in the blood including more of a certain type of white blood cell, and different ratios of gene expression. This ‘fingerprint’ has since been duplicated in two other sets of patients.

Senior study author Dr Maria Hernandez-Fuentes from the MRC Centre for Transplantation at King’s College London was excited with the results: “In future we may be able to screen patients for these markers, and perhaps identify small numbers who can safely withdraw or reduce their use of immunosuppressants.”

Using bugs to deliver drugs

Inflammatory bowel disease (IBD) affects one in 400 people in the UK, causing symptoms such as weight loss, diarrhoea and bleeding. It can be treated with immune-system-suppressing drugs, but these can cause unpleasant side effects.

Proteins called growth factors show promise for treating IBD without suppressing the immune system, but it is hard to get them to the gut because they are unstable and get broken down in the body before they reach their intended target.

To get around this problem, scientists have come up with an ingenious new way to deliver growth factors directly to the gut. They have genetically engineered a bacterium, Bacteroides ovatus, which is able to make a type of growth factor called KGF-2 from inside the gut, but only when it comes into contact with a dietary sugar called xylan, which is found in plants. In mice with damage to the bowel lining, the bacteria successfully made KGF-2, speeding up healing of the bowel and reducing weight loss, inflammation and rectal bleeding.

The research was led by MRC Clinical Fellow Dr Zaed Hamady of the University of Leeds, who explained: “If we can reproduce these results in people, this could work as a targeted treatment for IBD. The patient would be able activate the bacteria themselves whenever they needed it, simply by eating xylan. This approach might also have potential for treating bowel cancer, perhaps lengthening survival and improving quality of life for these patients.”

Reducing infection after bone marrow transplants

Cytomegalovirus (CMV) is one of the most serious viral infections to affect patients who have recently had a transplant. Half of all adults in the UK have previously been exposed to CMV and, while it is usually harmless for healthy adults, it can be life-threatening for those with compromised immune systems such as newborns, people with HIV or transplant patients.

Dr Emma Morris at University College London Medical School has received MRC funding to put together an early-stage clinical trial to assess a potential new treatment which could prevent these deadly infections. The trial will determine whether a single infusion of immune cells from a bone marrow donor, which have been genetically altered in the laboratory to make them able to recognise and kill CMV, can be used safely in patients with leukaemia and lymphoma who have received a bone marrow transplant. If successful, it could dramatically improve the success of bone marrow transplants.

Dr Morris says: “Current treatments to combat CMV infection in transplant patients can often carry huge side-effects, require long-term recurrent admissions and at times risk damaging the new bone marrow itself.

“We hope through our clinical trial we are able to prove that cells of a bone marrow donor’s immune system can be engineered in the laboratory to recognise viruses they have not previously encountered, and therefore stem the tide of infection in transplant patients before it can take hold.”

Dr Morris and her team have also been awarded an MRC Development Pathway Funding Scheme grant to carry out work towards testing a similar approach in a type of cancer called nasopharyngeal carcinoma.

Turning white blood cells against arthritis

Rheumatoid arthritis affects around 400,000 people in the UK. It occurs when the body’s immune system attacks the joints, causing painful inflammation.

Dr Catharien Hilkens from Newcastle University is working on a potential new treatment for the disease based on manipulating the behaviour of a certain kind of white blood cell called the dendritic cell. This is because dendritic cells are able to stop other types of white blood cells, T-cells, from attacking the joint tissue and causing disease.

Dr Hilkens, who is co-funded by the MRC and Arthritis Research UK, says: “My team has developed a cellular therapy for rheumatoid arthritis, made by treating dendritic cells with a combination of chemicals. Injection of these modified dendritic cells into arthritic mice has been shown to effectively reduce swelling and inflammation of the diseased joints.”

The next challenge for Dr Hilkens is to trial this new cellular therapy in rheumatoid arthritis patients. She added: “We are currently preparing for a first human trial with our dendritic cell therapy in patients with rheumatoid arthritis. Our success with arthritic mice is a fantastic start, and from working with these mice we have learned how the therapy may work in patients with established disease. We hope that this treatment will ultimately provide real benefit for patients.”