A new study reveals why people with asthma seem to be less likely to develop brain tumours than others.
Asthma causes T cell activation, and researchers discovered in a mouse study that asthma causes the T cells to behave in a way that induces lung inflammation but prevents the growth of brain tumours.
The findings, appearing in Nature Communications, suggest that reprogramming T cells in brain tumour patients to act more like T cells in asthma patients could be a new approach to treating brain tumours.
“Of course, we’re not going to start inducing asthma in anyone; asthma can be a lethal disease,” said senior author David H. Gutmann, MD, PhD, at Washington University School of Medicine. “But what if we could trick the T cells into thinking they’re asthma T cells when they enter the brain, so they no longer support brain tumor formation and growth? These findings open the door to new kinds of therapies targeting T cells and their interactions with cells in the brain.”
Based on epidemiologic observations, 15 years ago it was first proposed that people with inflammatory diseases, such as asthma or eczema, are less prone to developing brain tumours. However, there was no explanation for the link between the two very different kinds of diseases, and some scientists questioned whether the association was real.
Gutmann is an expert on neurofibromatosis (NF), a set of complex genetic disorders that cause tumours to grow on nerves in the brain and throughout the body. Children with NF type 1 (NF1) can develop an optic pathway glioma, where tumours grow within the optic nerves. Gutmann, director of the Washington University NF Center, noted an inverse association between asthma and brain tumours among his patients more than five years ago but didn’t know what to make of it. When more recent studies from his lab began to reveal the crucial role that immune cells play in the development of optic pathway gliomas, he began to wonder whether immune cells could account for the asthma–brain tumour link.
Jit Chatterjee, PhD, a postdoctoral researcher and the paper’s first author, took up the investigation. Working with co-author Professor Michael J. Holtzman, MD, Dr Chatterjee studied mice genetically modified to carry a mutation in their NF1 genes and form optic pathway gliomas by three months of age.
Dr Chatterjee exposed groups of mice to asthma-inducing irritants at age four weeks to six weeks, and treated a control group with saltwater. Then, he checked for optic pathway gliomas at three months and three months of age. The mice with asthma did not form these brain tumours.
Further experiments revealed that inducing asthma in tumour-prone mice changes the behaviour of their T cells. After the mice developed asthma, their T cells began secreting decorin, a protein that asthma researchers are well acquainted with.
Decorin is a problem in the airways, acting on lining tissues and exacerbating asthma symptoms. But the researchers found that in the brain, decorin is beneficial. There, the protein acts on microglia immune cells, blocking their activation by interfering with the NFkappaB activation pathway. Activated microglia promote brain tumour growth and development.
Treatment with either decorin or caffeic acid phenethyl ester (CAPE), a compound that inhibits the NFkappaB activation pathway, protected mice with NF1 mutations from developing optic pathway gliomas. The findings suggest that blocking microglial activation may be a potentially useful therapeutic approach for brain tumours.
“The most exciting part of this is that it shows that there is a normal communication between T cells in the body and the cells in the brain that support optic pathway glioma formation and growth,” said Prof Gutmann. “The next step for us is to see whether this is also true for other kinds of brain tumours. We’re also investigating the role of eczema and early-childhood infections, because they both involve T cells. As we understand this communication between T cells and the cells that promote brain tumours better, we’ll start finding more opportunities to develop clever therapeutics to intervene in the process.”
