Some viruses, like HIV, influenza viruses and respiratory syncytial virus (RSV), effectively conceal the part of their structure that is vulnerable to antibodies, which makes it hard to design effective vaccines against them.
Team leader William R. Schief (left), shown here with coauthor Research Associate Bruno E. Correia.
TSRI scientists have invented a new method for designing artificial proteins and have used it to make key ingredients for a candidate vaccine against RSV, a significant cause of infant mortality. Their new “rational design” approach could also help develop vaccines for other viruses that have also been resistant to current vaccine-design strategies.
“RSV is estimated to cause nearly seven percent of all human deaths worldwide in children ages one month to one year,” said William R. Schief, associate professor of immunology at TSRI. “So we are going to push hard to see if we can make an RSV vaccine for infants and children using these new technologies. We're also trying to improve this protein design method further and apply it to other vaccine projects including HIV and influenza vaccines.”
Virtually all existing viral vaccines use whole particles or entire proteins to naturally stimulate antibody reactions. However, viruses like RSV display mostly “decoy” structures to prevent the antibodies from binding to them, and only vaccines that can artificially stimulate large numbers of antibodies – against rare binding areas (epitopes) that are vulnerable – are likely to provide broad protection against such viruses.
With the help of collaborating laboratories, the TSRI scientists were able to apply the new method to make vaccines focused on specific RSV epitopes. This resulted in designer vaccine proteins that stimulate the production of the desired virus-neutralizing antibodies in rhesus macaques.
Scientists know how to sift through blood samples of virus-exposed patients to find the rare, “broadly neutralizing” antibodies that hit those vulnerable epitopes. In many cases, they also know how to map the precise atomic structures of these antibodies and their corresponding epitopes, using X-ray crystallography.
“What we haven't been able to do is to take that information about broadly neutralizing antibodies and their epitopes and translate it into effective, epitope-focused vaccines,” said TSRI Research Associate Bruno E. Correia, a member of Dr. Schief's laboratory at the time of the study and lead author of the new report.
The team used a new software app to design proteins that incorporate and stabilize a broadly neutralizing epitope on RSV, which stimulates the production of antibodies that can bind to it. Winnowing thousands of design possibilities down to four, the team then turned them over to collaborating laboratories for preclinical testing and analysis. In rhesus macaque monkeys, whose immune systems are quite similar to humans', the designer “immunogen” proteins showed great promise. After five immunizations, 12 of 16 macaques were producing robust amounts of antibodies that could neutralize RSV in the lab dish.
Analyses of the animals' immune responses were conducted at the laboratories of Philip Johnson at Children's Hospital in Philadelphia, James E. Crowe, Jr., at Vanderbilt University Medical Center and Barney Graham at the NIH/NIAID Vaccine Research Center. At the laboratory of Roland K. Strong at Fred Hutchinson Cancer Research Center in Seattle, researchers performed X-ray crystallography of two neutralizing monoclonal antibodies produced by the macaques and confirmed that each hit the desired virus epitope.
“The achievement represents the confluence of recent technological advances in computational biology, structural biology and immune monitoring, and offers great potential for accelerating development of next generation vaccines against major global diseases,” said Wayne C. Koff, chief scientific officer at the International AIDS Vaccine Initiative, which helped fund the studies.
Dr. Schief and his colleagues hope to continue this line of research and produce a working RSV vaccine.