Scientists at Johns Hopkins have taken a less-is-more approach to designing effective drug treatments that are precisely tailored to disease-causing pathogens, such as viruses and bacteria, and cancer cells, any of which can trigger the body's immune system defenses.
In a report to be published in the latest issue of Nature Medicine online Oct. 31, researchers describe a new "epitope-mapping" laboratory test that within three weeks can pinpoint the unique binding site – or epitope – from any antigen where immune system T cells can most securely attach and attack invading germs or errant cells.
Knowing exactly where the best antigen-T-cell fit occurs – at sites where short stretches of proteins, called peptides, bind and are displayed on the surface of antigen-processing immune system cells – is a prerequisite for designing effective and targeted drug therapies, researchers say.
Identifying the best binding site, they say, should speed up cancer vaccine development, lead to new diagnostic tests that detect the first appearance of cancer cells, well before tumors develop, and sort out disorders that are difficult to diagnose, such as Lyme disease.
"Our new, simplified system reproduces what happens in the cells of the immune system when antigens from a pathogen first enter the body and need to be broken down into peptides to become visible to T cells, one of the two immune defender cell types," says immunologist Scheherazade Sadegh-Nasseri, Ph.D., an associate professor of pathology, biophysics and biophysical chemistry at the Johns Hopkins University School of Medicine. "Once T cells recognize an antigen, they latch on, become activated, and call for other immune system cells to enter the fight," adds Sadegh-Nasseri, the senior study investigator for the team of scientists who developed the new epitope-mapping process.
Sadegh-Nasseri says the team's new lab test takes a fraction of the time involved in current methods, which rely on sequencing, or identifying every single peptide in the antigen's make-up, one after another. Such sequencing can take months, or even years, to identify possible T cell binding sites.
"The added beauty of our system is that the entire process can be done in the lab, so we do not have to perform tests in people," says Sadegh-Nasseri, who has a patent pending for the new test.
The Johns Hopkins team, including co-lead investigators AeRyon Kim, Ph.D., and Isamu Hartman, Ph.D., also immunologists, based their test on nearly 20 years of the team's previous research into how immune system cells selectively process antigens and the maze of possible protein combinations inside. That cumulative research led them to narrow their search to five essential and well-described proteins involved in antigen processing by immune system cells.
In their latest series of experiments, the team tested a mix of the selected immune system proteins to see if it could accurately detect two already known epitopes, those of the Texas strain of the influenza virus and type II collagen, both widely used experimental antigens. Then, they used the mix to find unknown epitopes for portions of the influenza virus that causes avian flu and for the parasite involved in malaria.
Chief among the epitope-mapping test's chemical components was a protein molecule common to all the body's immune system cells, called HLA-DR. This molecule is one of the most common binding molecules used in the natural immune system's peptide selection process. HLA stands for human leukocyte antigen, and HLA-DR is produced in a gene-dense region of the body's immune system, the major histocompatibility complex.
Other key chemicals in the make-up were HLA-DM, another protein compound that disrupts the binding of HLA-DR molecules to an antigen if the fit is not perfect, and three of the most common enzymes, so-called cathepsins, involved in breaking up the antigen into its visible, identifiable protein parts.
In the first set of experiments, the team mixed chemical solutions of each antigen with the five key proteins and used mass spectrometry – an electron-beaming device that can measure the exact make-up of molecules – to determine the best-fitting peptide based on precisely which segment of the antigen appeared as mass peaks. Peaks would indicate that HLA-DR had successfully bound to the antigen at a likely epitope.
Next, researchers confirmed their mass spectrometry findings by injecting mice bred to produce human HLA-DR with each antigen to trigger a standard immune response and collecting samples of the resulting T cells. The T cells were then grown in the lab and exposed to various peptides, including the suspect epitopes, to identify and confirm that only one triggered the greatest chemical response from the cultured T cells. The scientists knew that if they could match a peak highlighted by mass spectrometry to the peptide that produced the greatest T cell reaction, they had found the most heavily favored epitope.
When both tests were performed on any of the four disease antigens, researchers were able to narrow the suspect binding sites to one "immunodominant" epitope each for Texas strain of the flu, type II collagen, avian flu and malaria.
Kim, a postdoctoral research fellow at Johns Hopkins, says designing both experiments and completing the verification study took some seven years, noting that adding HLA-DM, which she calls a protein editor, was the pivotal factor in making the initial epitope-selection process work.
Researchers say their next steps are to broaden and refine their chemical mixture for selecting and identifying possible epitopes for other kinds of HLA because the current set of experiments analyzes only one of the most common HLA-type molecules in whites.
Study support was provided with funding from the National Institute of Allergy and Infectious Diseases, a member of the National Institutes of Health. Additional funding came from the Johns Hopkins Malaria Research Institute.
Besides Sadegh-Nasseri, Kim and Hartman, other Hopkins researchers involved in this study were Robert Cotter, Ph.D.; Kimberly Walters, Ph.D.; Sarat Dalai, Ph.D.; Tatiana Boronina, Ph.D.; Wendell Griffith, Ph.D.; and Robert Cole, Ph.D. Hartman is now at University of Texas Southwestern Medical Center. Other investigators were based at the U.S. Walter Reed Army Institute of Research, including Robert Schwenk, Ph.D.; David Lanar, Ph.D.; and Urszula Krzych, Ph.D.For additional information, go to:
David March | EurekAlert!
One gene closer to regenerative therapy for muscular disorders
01.06.2017 | Cincinnati Children's Hospital Medical Center
The gut microbiota plays a key role in treatment with classic diabetes medication
01.06.2017 | University of Gothenburg
An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.
Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...
Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.
Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...
Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.
As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...
Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.
With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...
Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine
Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...
19.06.2017 | Event News
13.06.2017 | Event News
13.06.2017 | Event News
23.06.2017 | Physics and Astronomy
23.06.2017 | Physics and Astronomy
23.06.2017 | Information Technology