Scientists pinpoint mechanisms associated with severe COVID-19 blood clotting

After studying blood samples from 244 patients hospitalized for COVID-19, a group of researchers, including those who work at the National Institutes of Health, identified “rogue antibodies” that correlate with severe illness and may help explain mechanisms associated with severe blood clotting.

The researchers found circulating antiphospholipid antibodies, which can be more common among people with autoimmune disorders, such as lupus. However, these “autoantibodies,” which target a person’s own organs and systems, can also be activated in response to viral infections and activate other immune responses.
 

Scientists compared the blood samples to those from healthy controls and found the COVID-19 samples contained higher levels of the antibody IgG, which works with other immune cells, such as IgM, to respond to immune threats. Higher levels of IgG were also associated with COVID-19 disease severity, such as in patients who required breathing assistance. The researchers observed similar patterns, but to a lesser extent, after analyzing blood samples from 100 patients hospitalized for sepsis, which can leave the body in inflammatory shock following a bacterial or viral infection.  

IgG helps bridge a gap between innate and adaptive immune responses – a process that helps the body recognize, respond to, and remember danger. In normal cases, these features help protect the body from illness and infection. However, in some cases, this response can become hyperextended or altered and exacerbate illness. A unique finding from this study is that when researchers removed IgG from the COVID-19 blood samples, they saw molecular indicators of “blood vessel stickiness” fall. When they added these same IgG antibodies to the control samples, they saw a blood vessel inflammatory response that can lead to clotting.  
 
Since every organ has blood vessels in it, circulating factors that lead to the “stickiness” of healthy blood vessels during COVID-19 may help explain why the virus can affect many organs, including the heart, lungs, and brain. A query of this study was evaluating “upstream” factors involved with severe blood clotting and inflammation among people with severe COVID-19 illness.   
 

The researchers note future studies could explore the potential benefits of screening patients with COVID-19 or other forms of critical illness for antiphospholipids and other autoantibodies and at earlier points of infection. This may help identify patients at risk for extreme blood clotting, vascular inflammation, and respiratory failure. Corresponding studies could then assess the potential benefits of providing these patients with treatments to protect blood vessels or fine-tune the immune system.  

Monoclonal Antibodies Against MERS Coronavirus Show Promise in Phase 1 NIH-Sponsored Trial

A randomized, placebo-controlled Phase 1 clinical trial of two monoclonal antibodies (mAbs) directed against the coronavirus that causes Middle East respiratory syndrome (MERS) found that they were well tolerated and generally safe when administered simultaneously to healthy adults.

The experimental mAbs, REGN3048 and REGN3051, target the MERS coronavirus (MERS CoV) spike protein used by the virus to attach to and infect target cells. The mAbs were discovered and developed by scientists at the biopharmaceutical company Regeneron, located in Tarrytown, New York. The trial was sponsored by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health. 

The trial was the first to test the experimental antibodies in people. Conducted at WCCT Global, a clinical trial site in California, the study enrolled 48 healthy adults, 36 of whom received the mAbs. All volunteers were followed for 121 days after receiving mAbs (or placebo) by intravenous infusion. No serious adverse events occurred.

In preclinical studies, investigators at Regeneron and the University of Maryland, College Park, also administered REGN3048 and REGN3051 sequentially and in combination to genetically modified mice that, unlike wild-type mice, can be infected with MERS CoV. When administered one day prior to coronavirus exposure, both REGN3048 and REGN3051 reduced the levels of virus later detected in the lungs, with co-administration providing more potent protective effects than either mAb alone. Similarly, co-administering the mAbs one day after MERS CoV exposure provided a therapeutic benefit in mice by lowering viral levels and lessening tissue damage in the lungs as compared to mice that received placebo.

Together, the findings from the clinical trial and the preclinical mouse studies “demonstrate the potential efficacy and utility of monoclonal antibody therapy for the prevention or treatment of MERS-CoV and lays the groundwork for the development of spike-targeted mAb therapies for other infectious disease threats, including SARS-CoV-2,” which causes COVID-19, the authors conclude. 

Broadly protective antibodies could lead to better flu treatments and vaccines

A newly identified set of three antibodies could lead to better treatments and vaccines against influenza, according to a paper published this week in Science. 

Researchers supported by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, isolated the antibodies from a person sick with the flu five days after the onset of symptoms.

They found that the antibodies, which bind to neuraminidase (NA) proteins on the surface of influenza viruses, provided broad protection against several different strains of influenza when tested both in vitro and in mice.

Most influenza vaccines are designed to stimulate an immune response against another protein found on the surface of the influenza virus called hemagglutinin (HA). However, HA proteins change frequently as the virus evolves. As a result, people must receive a new seasonal influenza vaccination every year to be protected against currently circulating influenza viruses. NA proteins change more slowly than HA proteins and thus could be a good target for an influenza vaccine that provides long-term protection.

In the new study, the researchers took antibody-producing cells from the blood of a volunteer sick with H3N2 influenza and screened for monoclonal antibodies (mAbs). Monoclonal antibodies are antibodies which are designed to bind to a single target. The mAbs the researchers found were tested in the laboratory for their ability to bind to different kinds of influenza proteins. Of 45 mAbs tested, three bound to NA proteins of an H3N2 influenza virus strain. Upon further testing, these three mAbs also bound to NA proteins from multiple other types of influenza viruses.

To see whether these three mAbs could help prevent the influenza virus from infecting mammalian cells, the researchers treated mice with the mAbs and then infected them with different types of influenza viruses. The mAbs inhibited many kinds of NA proteins from different types of influenza viruses, and protected most of the mice from severe influenza infections. Mice given lethal doses of H3N2 influenza virus survived when treated with low doses of the three antibodies.

If additional testing supports these early results, the researchers suggest that these potent mAbs could become the basis for a new antiviral treatment. Additionally, the antibodies could inform development of new influenza vaccines designed to induce similar antibodies that could provide broader and longer-lasting immunity than current HA-based influenza vaccines.

HIV vaccine elicits antibodies in animals that neutralize dozens of HIV strains

NIH study results represent major advance for structure-based HIV vaccine design.

This protein structure diagram illustrates the location of the fusion peptide epitope (red) on the HIV spike (green), which projects out of the viral membrane (grey). The diagram also shows how a broadly neutralizing antibody (yellow) binds to the fusion peptide. NIAID

An experimental vaccine regimen based on the structure of a vulnerable site on HIV elicited antibodies in mice, guinea pigs and monkeys that neutralize dozens of HIV strains from around the world. The findings were reported today in the journal Nature Medicine by researchers at the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, and their colleagues.

Peter D. Kwong, Ph.D., and John R. Mascola, M.D., led the study. Dr. Kwong is chief of the Structural Biology Section at the NIAID Vaccine Research Center, and Dr. Mascola is the center director.

“NIH scientists have used their detailed knowledge of the structure of HIV to find an unusual site of vulnerability on the virus and design a novel and potentially powerful vaccine,” said NIAID Director Anthony S. Fauci, M.D. “This elegant study is a potentially important step forward in the ongoing quest to develop a safe and effective HIV vaccine.”

A preliminary human trial of the new vaccine regimen is anticipated to begin in the second half of 2019.

Today’s report reflects one of two broad, complementary approaches NIAID is pursuing to develop an HIV vaccine. In one approach, scientists first identify powerful HIV antibodies that can neutralize many strains of the virus, and then try to elicit those antibodies with a vaccine based on the structure of the HIV surface protein where the antibodies bind. In other words, scientists start with the most promising part of the immune response and work to develop a vaccine that will induce it. This method was used to design the vaccine described today.

The other, empiric approach to HIV vaccine development begins by evaluating the most encouraging vaccine candidates for efficacy in people through clinical trials. Then scientists try to build on successful trial results by, for example, examining blood and other clinical specimens from study participants who received the vaccine to identify the most promising parts of the immune response. Researchers subsequently use this information to improve vaccination approaches for future trials. This method was used to develop the HIV vaccine regimen tested in the RV144 clinical trial and the HIV vaccine regimens currently under study in the HVTN 702 and Imbokodo clinical trials.

Over the past several years, HIV researchers have discovered many powerful, naturally occurring antibodies that can prevent multiple HIV strains from infecting human cells in the laboratory. About half of people living with HIV make these so-called “broadly neutralizing” antibodies(link is external), but usually only after several years of infection — long after the virus has established a foothold in the body. Scientists have identified and characterized the sites, or epitopes, on HIV where each known broadly neutralizing antibody binds. Many laboratories around the world are developing HIV vaccine candidates based on the structure of these epitopes with the goal of coaxing the immune systems of HIV-negative people to make protective antibodies after vaccination.

The experimental vaccine described in today’s report is based on an epitope called the HIV fusion peptide, identified by NIAID scientists in 2016. The fusion peptide, a short string of amino acids, is part of the spike on the surface of HIV that the virus uses to enter human cells. According to the scientists, the fusion peptide epitope is particularly promising for use as a vaccine because its structure is the same across most strains of HIV, and because the immune system clearly “sees” it and makes a strong immune response to it. The fusion peptide lacks sugars that obscure the immune system’s view of other HIV epitopes.

To make the vaccine, the researchers engineered many different immunogens — proteins designed to activate an immune response. These were designed using the known structure of the fusion peptide. The scientists first assessed the immunogens using a collection of antibodies that target the fusion peptide epitope, and then tested in mice which immunogens most effectively elicited HIV-neutralizing antibodies to the fusion peptide. The best immunogen consisted of eight amino acids of the fusion peptide bonded to a carrier that evoked a strong immune response. To improve their results, the scientists paired this immunogen with a replica of the HIV spike.

The researchers then tested different combinations of injections of the protein plus HIV spike in mice and analyzed the antibodies that the vaccine regimens generated. The antibodies attached to the HIV fusion peptide and neutralized up to 31 percent of viruses from a globally representative panel of 208 HIV strains.

Based on their analyses, the scientists adjusted the vaccine regimen and tested it in guinea pigs and monkeys. These tests also yielded antibodies that neutralized a substantial fraction of HIV strains, providing initial evidence that the vaccine regimen may work in multiple species.

The scientists are now working to improve the vaccine regimen, including making it more potent and able to achieve more consistent outcomes with fewer injections. The researchers also are isolating additional broadly neutralizing antibodies generated by the vaccine in monkeys, and they will assess these antibodies for their ability to protect the animals from a monkey version of HIV. The NIAID scientists will use their findings to optimize the vaccine and then manufacture a version of it suitable for safety testing in human volunteers in a carefully designed and monitored clinical trial.

Research offers clues for improved influenza vaccine design

Influenza vaccines that better target the influenza surface protein called neuraminidase (NA) could offer broad protection against various influenza virus strains and lessen the severity of illness, according to new research published in Cell.

3D print of influenza virus. The virus surface (yellow) is covered with proteins called hemagglutinin (blue) and neuraminidase (red). NIH

Current seasonal influenza vaccines mainly target a different, more abundant influenza surface protein called hemagglutinin (HA). However, because influenza vaccines offer varying and sometimes limited protection, scientists are exploring ways to improve vaccine effectiveness. The new research builds on previous studies of NA and was conducted by a team of scientists including investigators from the Centers of Excellence for Influenza Research and Surveillance (CEIRS)(link is external) program, which is organized and funded by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.

Investigators analyzed blood samples from people vaccinated against influenza and people diagnosed with either the 2009 H1N1 influenza virus or H3N2 influenza viruses. The volunteers were recruited for this study or had taken part in prior influenza research studies. The analyses indicate that influenza vaccines rarely induce NA-reactive antibodies, whereas natural influenza infection induces these types of antibodies at least as often as they induce HA-reactive antibodies. Additional studies in mice reinforced the human data, indicating that current influenza vaccines do not induce NA-reactive antibodies efficiently.

Additional laboratory experiments show that the NA-reactive antibodies induced during natural influenza infection are broadly reactive, meaning they could potentially protect against diverse strains of influenza. To test this theory, scientists isolated NA-reactive monoclonal antibodies from the H3N2 and H1N1 influenza patients (N2-reactive antibodies and N1-reactive antibodies, respectively). They administered 13 N2-reactive antibodies to mice and subsequently infected the mice with a different H3N2 virus strain. Eleven of the 13 N2-reactive antibodies partially or fully protected the mice. They also administered eight N1-reactive antibodies to mice and subsequently infected the mice with a similar H1N1 virus strain or an H5N1-like virus strain. Four of the eight antibodies completely protected the mice against both virus strains.

The authors note that the findings suggest that influenza vaccines should be optimized to better target NA for broad protection against diverse influenza strains. In this regard, NIAID is supporting research to characterize NA responses in infected and vaccinated individuals and to determine the mechanism of action of NA protection. NIAID also supports “NAction!” a CEIRS working group that identifies knowledge gaps in our understanding of NA and sets NA research priorities for improved influenza vaccines(link is external). These efforts contribute to NIAID’s larger plan to develop a universal influenza vaccine — a vaccine that can durably protect all age groups against multiple influenza virus strains.

NIH, the nation’s medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research, and is investigating the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit www.nih.gov.