With Chronic Fatigue Syndrome
Study Reignites Debate About Viral Agent in Patients
Bridget M. Kuehn
JAMA. 2010;304(15):1653-1656 (doi:10.1001/jama.2010.1421)
A STUDY LINKING CHRONIC Fatigue syndrome (CFS) in humans to a family of retroviruses that cause leukemia in mice appears to validate a controversial study published last fall. But far from settling the debate about the role of viruses in the disease, the new findings raise a host of questions about why other scientists, including a team from the US Centers for Disease Control and Prevention (CDC), have failed to find such a link, and about the potential clinical and public health implications. The study was published in August in the Proceedings of the National Academy of Sciences (Lo S-C et al. Proc Natl Acad Sci U S A. doi:10.1073/pnas .1006901107 [published ahead of print
August 23, 2010]).
“These results raise as many questions as they answer,” said Steve Monroe,
PhD, director of the Division of High-Consequence Pathogens and Pathology at the CDC. As scientists continue to grapple with these questions, the AABB, a nonprofit organization that represents individuals and institutions involved in blood transfusion, recommended in June that patients who have been diagnosed with CFS, chronic fatigue and immune dysfunction syndrome, or myalgic encephalomyelitis refrain from donating blood.
The cause of CFS, a debilitating condition defined by a constellation of clinical
symptoms and the absence of alternate causes, has long eluded scientists. But immune system abnormalities associated with the disorder and the severe flu-like symptoms many patients experience have led scientists to search for infectious agents that might cause the disease.
In a study published in October 2009 (Lombardi VC et al. Science. 2010; 326 :585-589) , a multi -institution team of scientists reported finding an association between CFS and xenotropic murine leukemia virus– related virus (XMRV), which had previously been found in human prostate cancer cells. The team was led by scientists from the Whittemore Peterson Institute, a nonprofit research organization in Reno,Nev, that focuses on diseases involving neurological and immunological symptoms, and included scientists from the National Cancer Institute in Frederick, Md, and the Cleveland Clinic Foundation, in Cleveland, Ohio. The researchers found DNA from the XMRV virus in 68 of 101 patients with CFS (67%) they tested, and in 8 of 218 healthy controls (3.7%). They also found that XMRV derived from patient samples could infect other cells grown in culture.
The findings generated considerable excitement among patients with CFS, who hoped the finding might rapidly lead to definitive diagnostics or new therapies using antiretroviral drugs. However, the finding was cast into question when 4 subsequent studies failed to find XMRV in patients with CFS. Among those studies was one published in July by scientists from the CDC. William M. Switzer, of the National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention at the CDC, and his colleagues tested plasma from 51 individuals with CFS and 53 healthy controls and did not find XMRV in any of the samples (Switzer WM et al. Retrovirology. 2010;7:57).
The newest study, conducted by researchers from the US Food and Drug Administration (FDA), the National Institutes of Health (NIH), and Harvard Medical School, now seems to validate the initial Science study by Lombardi et al. Shyh-Ching Lo, MD, PhD, director of the Tissue Safety Laboratory Program at the FDA, and colleagues did not find the XMRV virus, but did find DNA from what appears to be a family of related viruses in 32 of the samples from37 patients (86.5%) who met strict diagnostic criteria for CFS, and in only 3 of the samples from 44 healthy blood donors (6.8%). Lo said during a press briefing that the variation he and his colleagues found in the murine leukemia virus DNA sequences “is very characteristic for retrovirus infections.” He explained that these viruses often mutate after infecting an individual. In fact, fresh blood samples taken from 8 patients about 15 years after the initial samples examined by Lo and his colleagues contained DNA segments of these viruses with new variations.
Lo and colleagues went to great lengths to ensure that the results were not caused by contamination. For example, the blood samples used came from laboratories that had never worked with mice or retroviral vectors, and testing of the samples was conducted in laboratories that had never worked with mouse cells, tissues, or serum samples, or vectors of the murine leukemia virus. The samples that tested positive for murine leukemia–related viruses were tested to determine whether they were contaminated with mouse DNA. Additionally, the authors noted that if contamination had occurred, the various
samples would likely show the same gene sequence; however, they found at least 6 different murine leukemia virus–related gene sequences that appear distinct from those previously reported. They also used virus-negative controls.
Harvey J. Alter, MD, chief of clinical studies and associate director for research in the Department of Transfusion Medicine at the NIH Clinical Center in Bethesda, Md, and a member of the research group, cautioned at the press briefing that it is still uncertain whether XMRV-related viruses have a causal role in CFS or whether infection may be a consequence of immune deficiencies related to the disease. “We haven’t studied enough people, we don’t know enough of the mechanisms, we don’t how the virus might cause these symptoms,” he said. William Schaffner, MD, chair of the department of preventive medicine at Vanderbilt University School of Medicine and secretary of the Infectious Disease Society of America, called the results from Lo and his colleagues “provocative,” particularly their findings that the viruses persist in patients over time. But he noted that attempts to link a complex condition to an infectious agent have proved difficult in the past. For example, a series of infectious agents linked to multiple sclerosis initially looked promising but ultimately did not pan out.
“We’re in for a bit of rollercoaster ride,” he said. “We don’t yet have a definitive answer.” Schaffner explained there may be many reasons for the conflicting results so far. One is that there is no laboratory test for CFS, so different scientists may have defined cases differently. In fact, many patients criticized the study by the CDC researchers because it relied on an older and less restrictive case definition (http://www.retrovirology.com/content/7/1/57 /comments).
There may also be an array of causes for CFS, including a subset of patients whose disease is related to infection with this family of viruses, suggested Alter. Such diversity might help explain why researchers in different regions of the United States and the world have had differing results. “Perhaps the relative contribution of causes varies over the US and abroad,” said Schaffner. Additionally, differences in the sensitivity and specificity of the gene probes used by different laboratories may have contributed to different findings, Lo noted. So may the fact that the viruses are present in very low titers in the blood.
MORE STUDIES NEEDED
Scientists do agree that more studies are needed. Among the matters still to be determined are how these viruses interact with humans and whether they cause disease, said Monroe. Lo noted that he and his colleagues have already begun designing studies that may help answer such questions. The NIH has recruited W. Ian Lipkin, MD, an epidemiologist at Columbia University’s Mailman School of Public Health, to lead a new study that will examine blood samples from 100 patients and 100 controls at 4 sites and have blinded samples tested at the Whittemore Peterson Institute, the FDA, and the CDC.
Meanwhile, scientists from the National Heart, Lung, and Blood Institute have begun developing a standardized process for testing samples for this family of viruses, which may help to reduce variation in the results of future studies, said Hira Nakhasi, PhD, director of the Division of Emerging and Transfusion Transmitted Disease at the FDA. A group of scientists who published a commentary alongside the newest study suggested that rigorous clinical trials of reverse transcriptase inhibiters, which have been demonstrated to inhibit XMRV in the laboratory, could help to demonstrate whether the virus is causal and whether such therapies offer clinical benefits to patients with CFS (Courgnaud V et al. ProcNatl Acad Sciences U S A. doi:10.1073/pnas .1007944107 [published ahead of print August 23, 2010]). They note that such interventional studies were key to establishing the relationship between Helicobacter pylori and peptic ulcer disease.
Schaffner cautioned that the potential adverse effects of antiretroviral drugs are not trivial, but that such trials should be discussed by advisors to the FDA and the NIH. During the press briefing, Celia Witten, MD, PhD, director of the Office of Cellular, Tissue, and Gene Therapies at the FDA, said the agency had no comment on whether to conduct such trials at this time. Studies have also begun to probe whether this family of viruses may pose a threat to the blood supply. “There has been no demonstration, yet, of the transfusion association of the virus or the disease,” said Nakhasi. However, FDA regulations require blood donors to be in good health, which is consistent with the AABB recommendation that patients with CFS abstain from donating.
Alter said his group has a study in progress looking for the virus and antibodies to it in samples from 1000 donors. They also have frozen samples taken from blood recipients before and after transfusion and have linked them to donors. “We will be looking at those samples to see if we can demonstrate any transmission,” he said. Schaffner said it would be helpful for the NIH to recruit additional well qualified researchers to the CFS field. He explained that many investigators may have shied away from the area in the past because they were uncertain about the disease or were concerned about dealing with passionate members of support organizations devoted to the illness.
“We have to keep our minds open,” Schaffner said. “I empathize enormously with patients and families dealing with CFS and their desire to understand the disorder and have treatment options, but we can’t let that trump the investigation to understand the etiology.”