Epstein-Barr Virus and IL27 signaling
Genetic deficiency for IL27 receptor predisposes to EBV infection but protects from EBV-associated cancer
Happy weekend! I was reading about Epstein-Barr virus (EBV) this week, inspired by a Nature paper on the association between a cytokine receptor gene, IL27RA, and EBV infection. Researchers from INSERM in Paris have encountered a handful of children with severe EBV infection, who turned out to be knockouts for IL27RA. The gene encodes one of the two subunits of interleukin 27's receptor (IL27RA stands for interleukin 27 receptor subunit alpha). This is the first time researchers are learning about the role of IL27 signaling in EBV infection.
Genetic defects in immune genes increasing the susceptibility to EBV infection is not new. Scientists have known many genes that when lost result in severe EBV infection. But the case of IL27RA is special.
As you might remember learning in high school or in college that EBV is an oncogenic virus, meaning, it causes cancer. Not in everyone it infects. That would be crazy, as more than 95% of the population gets infected with EBV at some point in their life. Most wouldn't even know they did get infected. The virus can silently enter the human body through exchange of body fluids (often through kissing, hence the name 'kissing disease' for infectious mononucleosis) and reach their home that is B cells and live there for the rest of the human’s life. But a subset of humans, typically those with a weak immune system, develops cancer after EBV infection. EBV can cause different types of cancer: lymphomas, gastric cancer, nasopharyngeal cancer etc.
All previously known inborn errors of immunity linked to severe EBV infection have almost always led to cancer. And this is the first time, scientists are coming across a genetic defect that has resulted in severe EBV infection but hasn't resulted in cancer. Perhaps, these patients could be holding the answers to discovering medicines to prevent EBV-infected, immunocompromised individuals from developing cancer.
The discovery story of EBV
In this short YouTube video, Dorothy Crawford and Alan Rickinson, the authors of the book 'Cancer Virus', tell the story of the EBV discovery. The story begins sometime in the late 1950s in Kampala in Uganda, when an African child caught the attention of a British surgeon, Denis Burkitt, working in a local hospital. Fascinated by the facial appearance of the child, Burkitt examined the child. The child had a swollen jaw. The swelling was caused by multiple tumors. Burkitt had never seen such a case before. He made a note of the case in his personal diary and went on his business. Two weeks later, he noticed another kid on the street with a swollen jaw. This cannot be a coincidence, he felt. He dropped everything and went searching for more such cases around the area and found 38 individuals. In some cases, the tumors grew so big they knocked the teeth out and distorted the face severely. He didn't know what caused the tumor, but he felt it must be the most common tumor in that region of Africa. The occurrence appeared to be geographically restricted to areas with high rainfall and hot weather. He published his observations in the British Journal of Surgery in 1958.
On March 22, 1961, Burkitt visited London Medical School and gave a lecture on his recent work titled “The Commonest Children’s Cancer in Tropical Africa — A Hitherto Unrecognised Syndrome”. Among the audience was Anthony Epstein, a young cancer researcher from Middlesex Hospital in London. As a scientist researching the role of virus in cancer, Epstein got excited learning about Burkitt’s work, particularly Burkitt’s intuition that the tumors may have a viral etiology. He proposed to collaborate with Burkitt and requested him to send biopsy samples of the tumors for electron microscopic studies. It seemed that for almost two years, sample after sample, Epstein and Yvonne Barr, his graduate student who helped Epstein on the project, couldn't find anything. By the time they were almost about to give up, the 26th sample flew from Kampala to London on a Friday in December 1963. It was a foggy day, the Heathrow Airport was closed, and the biopsy sample was sent wrongly to Manchester and as result, the delivery was delayed by 12 hours. It was afternoon by the time the sample reached the lab. When they opened the package, they found that the fluid containing the biopsy was cloudy. They almost threw it away as the sample appeared to be contaminated with bacterial infection. But when looked through a microscope, they realized that the cloudiness was because of free tumor cells floating around in the medium. They fished out the tumor cells and dropped them in a Petri dish containing cell culture medium. The tumor cells began to grow. In about six weeks, they had a fully grown tumor cell culture containing malignant lymphoid cells. Sometime in February 1964, Epstein examined the grown tumor cells using electron microscope. He couldn't believe his sight. He switched off the microscope and walked around the block for 20 minutes. Then returned to the lab and looked at it again. It hit him what he saw was real: small virus particles lurking inside the tumor cells. And that's how the first human tumor virus was discovered, says Crawford and Rickinson.
EBV and multiple sclerosis
Sixty years have passed since the EBV discovery, still the virus surprises scientists year after year. Just a couple of years back, there were two studies, one published in Science and the other in Nature, which revisited the long-suspected link between EBV and MS and gave a compelling proof on the causal role of EBV in MS.1 In the Science paper, using 20 years longitudinal health data of US military recruits, researchers from Harvard T.H. Chan School of Public Health reported an epidemiological analysis, proving the causality of EBV's association with MS with near certainty. In the Nature paper, Stanford researchers reported a follow-up analysis on the EBV's association with MS, detailing the molecular mechanisms through which EBV infections might lead to MS. The authors found that one of the EBV antigen is a doppelgänger of a central nervous system (CNS) protein called glial cell adhesion molecule (GlialCAM). As a result, CNS glial cells become victims in the war between the body's immune system and EBV, leading to autoimmune-mediated myelin destruction. An mRNA vaccine against the viral antigen EBNA1 that mimics the GlialCAM is currently trialed as a means to prevent MS after EBV infection.
EBV and IL27 signaling
A bulk of the research on EBV over the past half a century went into understanding immune signaling pathways that are involved in the EBV infection and the development of complications such as cancer. Naturally occurring genetic mutations in humans, resulting in a breach in the immune defense against EBV has helped scientists to trace the EBV-related immune signaling pathways. Below is a illustration of the cross talks between EBV-infected B cells and T cells at initial and later stages of immune defense. The proteins highlighted in red are the ones identified to play key roles in the immune response against EBV infection through inborn errors of immunity. The IL27RA adds to this list of genes.
The authors of the current Nature paper, researchers from the INSERM in Paris, studied three children with severe acute EBV infection, unusual for their age. EBV infection in children are usually asymptomatic. Clinical and lab investigations suggested that the children might have some immune-related genetic defects. As suspected, the authors found recessive deleterious mutations in an immune-gene, IL27RA, encoding the receptor of cytokine interleukin 27 (IL27). Two of the children were homozygote and one, compound heterozygote. Referencing the variants with public databases, the authors found that the variants were not reported before, except one, rs201107107, which occurred in relatively higher frequency (MAF=0.7%) in the Finnish population. There were 15 homozygotes of this variant in the Finngen. This motivated the authors to collaborate with the Finngen team to find out if any of these 15 homozygotes have got severe EBV infection. Two of them turned out to have been hospitalized for infectious mononucleosis, which is 50-fold enrichment compared to the non-carriers.
Through in vitro experiments in the blood cells from the three patients, the authors found that T cells of the patients indeed do not express IL27 receptors or up regulate IL27RA expression upon activation, unlike healthy controls. Stimulating the T cells with IL27 did not activate the downstream cell signaling events either. In the paper, the authors present further a wide range of functional experiments, highlighting the role of IL27 signaling in the T cell response to EBV infection. The bottom line: the three patients with IL27RA mutations have helped scientists learn about the role of IL27 signaling in the EBV infection. Particularly, its possible role in EBV-mediated oncogenic transformation of B cells. It seems the same receptor that is required for T cells to respond to EBV-infected B cells to fight against infection, is also required for T cells to transform the EBV-infected B cells into tumor cells. As a result, even though loss of IL27RA results in severe EBV-infection, it doesn't further lead to cancer development. This opens up the possibility of targeting IL27 signaling pathway to treat or prevent cancer in individuals at high risk of developing severe EBV infection, such as those with weak immune system. But it also makes me wonder if IL27 signaling plays a role in MS development. If so, it will also open up therapeutic opportunities for the treatment of MS. Time will tell.
I felt lucky to have bumped into this YouTube video of the lecture by Jeffrey Dunn, a Stanford neuroscientist who was involved in the work published in Nature in 2022 on the molecular mimicry of EBV in MS. I have never seen such a clarity in a research presentation before. I strongly recommend watching this video.