Jon and Teddy Yewdell join the TWiV team to talk about their careers, their research, and the problems with biomedical research.
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Patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS)Â showed clinical improvement after extended treatment withÂ the anti-B-cell monoclonal antibody rituximab. This result suggests that in a subset of patients, ME/CFS might be an autoimmune disease.
Rituximab is a monoclonal antibody against a protein on the surface of B cells known as CD20. When the antibody is given to patients, it leads to destruction of B cells, which are the producers of antibodies, proteins that are madeÂ by the immune system toÂ counter infections. The drug has been approved by the US Food and Drug administration to treat diseases of B cells such as lymphomas, leukemias, and autoimmune conditions.
ME/CFS is a disease of unknown etiology and mechanism that includes symptoms of severe fatigue, post-exertional malaise, pain, cognitive and sleep problems that affects 0.1-0.2% of the population. A previous randomized, phase II trial of rituximab treatment showed clinical benefit in 20 ofÂ 30Â patients. The improvements were evident 2-8 months after treatment, leading the study authors to suggest that remission requires elimination of long-lived antibodies after depletion of B cells.
The current study was done to determine the effects of sustained treatment with rituximab. Included patients (29) wereÂ 18-66 years of age andÂ diagnosed with ME/CFS according to Fukuda 1994 criteria. All were given rutiximab infusions two weeks apart, then at 3, 6, 10, and 15 months, and followed up for 36 months. Self-reported symptoms were recorded every second week and used to calculate scores for fatigue (comprising post-exertional malaise, need for rest, daily functioning), pain (muscle, joint, and cutaneous painÂ and headache)Â and cognitive scores (concentration ability, memory disturbance, mental tiredness).
Clinically significant responsesÂ were found in 18/29 patients (64%), with a lag of 8-66 weeks. After 36 weeks 11 of 18 responding patients were still in clinical remission. Nine patients from the placebo group in the previous study were included in this trial; of these, six had clinical improvement.
These results show that some ME/CFS patients benefit from ablating B cells. The delayed response, coupled with the relapse after cessation of treatment and B cell regeneration, suggests that antibodies are involved in the pathogenesis of the disease. Because onset of ME/CFS in many patients correlates with a viral infection, it is possible that antibodies to viral proteins may cross-react with self proteins, leading to autoimmune reactions that cause disease. Treatment with rituximab would lead to reduced levels of such antibodies, thereby reducing symptoms.
These results warrant trials of larger numbers of ME/CFS patients in other countries (this study was carried out in Norway) to determine if ablation of B cells would have a similar effects elsewhere. It would also be useful to determine the total repertoire of antiviral antibodies produced by ME/CFS patients. Such antibodies can be identified using the newly developed VirScan assay, which requires a small amount of blood and is relatively inexpensive. The results will indicate whether certain viral infections in a large population of ME/CFS patients predispose to the illness. Furthermore, the results may also be used to guide efforts toÂ determine whether such antibodies react with human cellular proteins. A similar approach was used to determine that antibodies to an influenza virus protein cross react with a neuropeptide receptor, leading to narcolepsy.
While these findings are promising, they also show that not all ME/CFS may involve autoimmune pathogenesis. Other creative approaches will be needed to determine the cause of disease in individuals who do not respond to rituximab.
On episode #314 of the science show This Week in Virology,Â VincentÂ travels to Albert Einstein College of Medicine where he speaksÂ with Kartik, Ganjam, and Margaret about their work on Ebolavirus entry, a tumor suppressorÂ that binds the HIV-1 integrase, and the entry of togaviruses and flaviviruses into cells.
You can find TWiV #314 at www.microbe.tv/twiv.
ZMapp, a mixture of three antibodiesÂ againstÂ Ebola virus, became a household name after it wasÂ used to treat twoÂ Americans who wereÂ infected while working in Liberia. The structure of these antibodies bound to the Ebola virus glycoprotein suggestÂ how they inhibit infection and ways to improveÂ ZMapp.
The three monoclonal antibodies that comprise ZMapp (called c13C6, c2G4, and c4G7) were produced by immunizing mice withÂ a recombinant vesicular stomatitis virus in which the glycoprotein was replaced with that from Ebola virus. Antibodies that bound the viral glycoprotein and protected mice from infection were identified, and three were made to resemble human antibodies and produced in tobacco plants. Ecco Zmapp!
Embedded in the membrane of the filamentous Ebola virus particle are many copies of the glycoprotein, seen as club-shaped spikesÂ in the image toÂ the right (image credit: ViralZone). The viral glycoprotein is essential for entry of the virus into cells. The antibodies in ZMapp are directed against the viral glycoprotein.
To determine how the antibodies bind the virus particle, they were individually mixed with purified Ebola virus glycoprotein, and the structures were determined by electron microscopy and image reconstruction. The results, shown in the illustration, indicate precisely where each antibody binds to the Ebola virus glycoprotein. The individual antibodiesÂ coloredÂ red (c2G4), yellow (c4G7), and purple (c13C6) are bound to a single Ebola virus glycoprotein in white, withÂ the viral membrane below (Image credit).
The structures reveal that c13C6 (purple) binds at the tip of the viral glycoprotein, perpendicular to the plane of the viral membrane. The other two antibodies (red, yellow) bind at the base of the viral glycoprotein. Their binding sites overlap but are not identical (the Ebola virus glycoprotein is a trimer, and in the image, the yellow and red antibodies are shown binding to different subunits for clarity). Two other antibodies that block Ebola virus infection also bind at the base of the glycoprotein.
Antibody c13C6, which binds to the tip of the viral glycoprotein, does not neutralize viral infectivity. Nevertheless, it can protect animals from Ebola virus infection. This observation suggests that the c13C6 antibody may work in concert with complement, a collection of serum proteins, to block virus infection. It is not known why c13C6 antibody is non-neutralizing, but one possibility is that it binds to a part of the viral glycoprotein that is removed by an endosomal protease, cathepsin, before receptor binding in late endosomes.
Antibodies c2G4 and c4G7, which bind to the membrane-proximal part of the viral glycoprotein, neutralize viral infectivity. How they do so is not known, but one possibility is that they prevent structural changes of the viral protein that are essential for the fusion with the endosomal membrane, a process that delivers the viral nucleic acid into the cell cytoplasm.
These studies reveal two general areas of the Ebola virus glycoprotein that are important targets for antibodies that protect animals from Ebola virus infection. Those directed at the base ofÂ the glycoprotein neutralize infectivity while those that bind the tip do not. This information can now be used to isolate additional antibodies that bind either site. These can be used in animal protection studiesÂ to design mixturesÂ that are even more potent than ZMapp.
On episode #292 of the science show This Week in Virology,Â Vincent visits Medimmune and speaks with Wade, Matt, Nicole, and Ken about why they work in industry and their daily roles in a biotechnology company.
You can find TWiV #292 at www.microbe.tv/twiv.