Imagine the last time you went to the doctor feeling miserable with a cold. If you have ever heard “you have a virus” from your physician, you know exactly what that means. There are no antibiotics that can help you feel better, and usually only cold remedies can help ease your symptoms. Respiratory viruses, which are usually little more than a nuisance for healthy adults, can cause devastating complications for patients who are immunocompromised. “There is a need for safe and effective treatments for these viruses that afflict immunocompromised patients” said Dr. Jim Boonyaratanakornkit, an Associate Professor in the Vaccine, and Infection Disease Division. Dr. Boonyaratanakornkit is especially interested in “drug development against infectious diseases traditionally neglected in immunosuppressed populations.” Respiratory viruses, including respiratory syncytial virus (RSV), human metapneumovirus (HMPV), and human parainfluenza virus types one (HPIV1) and three (HPIV3), are leading causes of death among patients who are immunocompromised. Antibodies are one type of treatment for respiratory viruses. "Our research advances the preclinical development of two cross-protective antibodies against the viruses,” said Dr. Boonyaratanakornkit. A recent study published in Nature Communications, led by Madeline Caban, a post-baccalaureate student in Dr. Boonyaratanakornkit’s lab, identified two cross-neutralizing antibodies against these respiratory viruses: the antibody MxR which neutralizes both RSV and HMPV, and the antibody 3x1which neutralizes HPIV1 and HPIV3.
In RSV, HMPV, HPIV1 and 3 virus particles, genetic material is tightly packed into the core and enclosed in a lipid membrane containing attachment proteins and fusion proteins, essential for viral entry. The fusion (F) protein undergoes a transition from a prefusion (preF) to a postfusion (postF) conformation. Since preF is the most abundant conformation of infectious virions, antibodies to preF tend to be the most effective at neutralizing them. Researchers developed a bait-and-switch strategy to identify cross-neutralizing antibodies by assuming that B cells capable of binding to one virus while neutralizing another virus are more likely to neutralize them both. Briefly, the authors isolated B cells that bind specifically to the preF conformation of recombinant fusion protein but not to the postF conformation by magnetic enrichment and cell sorting. Identified B cells were then cultured with feeder cells expressing CD40L, IL2 and IL21 to stimulate antibody production. Next, the supernatant containing antibodies were incubated with live viruses and tested for neutralization by plaque assay (measures virus infection).
Following the bait-and-switch strategy, the authors isolated HPIV3-binding B cells. Supernatants were incubated with live HPIV1, and one antibody (called 3x1) was found to neutralize HPIV1. 3x1 antibody showed a high neutralization potency against both HPIV1 and HPIV3 by plaque assay. "These results describe an antigenic site in HPIV3 that is conserved in HPIV1, which we have named site X," said Dr. Boonyaratanakornkit. In addition, the authors investigated HPIV3 preFbinding to the 3x1 antibody using cryo-electron microscopy. Dr. Boonyaratanakornkit explained that "we could see how 3x1 could block both HPIV3 and HPIV1 infection by binding to a heptad repeat and preventing the viral fusion protein from transitioning between the prefusion and postfusion conformations.” The authors also isolated RSV and HMPV binding B cells from human blood and isolated an antibody that binds to RSV and HMPV (named MxR). MxR showed high neutralization potency against RSV and HMPV. Additionally, cryo-electron microscopy was used to validate the interaction between RSV preF and MxR antibody.
Lastly, the authors assessed the efficacy of both antibodies as prophylaxis agents against viral infection in vivo. To do so, hamsters were injected with either 3x1 or MxR antibody two days before intranasal infection with RSV, HPMV, or HPIV1. The lungs and nasal turbinates were harvested after 5 days. In lungs and nasal turbinates, prophylactic administration of MxR reduced RSV and HPMV replication. Replication of HPIV1 was completely blocked in the lungs and reduced in the nasal turbinates. Moreover, the authors tested whether both antibodies could provide broader protection against RSV, HMPV, HPIV1 and HPIV3. It is particularly relevant for patients who are immunocompromised since co-infection with multiple respiratory viruses has been linked to the worse outcomes. Hamsters were injected with both 3x1 and MxR antibodies two days before intranasal co-infection with RSV and HPIV3. The cocktail of antibodies reduced HPIV3 viral load in lungs significantly, but not in nasal turbinates. RSV viral load in lungs and nasal turbinates was significantly reduced by the cocktail of antibodies.
Overall, these results suggest that prophylactic administration of both antibodies against HPIV3 and RSV co-infection in vivo was effective. “Our antibodies are cross-protective because they bind to evolutionarily conserved antigenic sites,” said Dr. Boonyaratanakornkit. However, “this conserved binding site is not an iron-clad guarantee against viral escape and the development of resistance” he added. Dr. Boonyaratanakornkit's team is working on “developing an immunocompromised hamster model to test our antibodies,” because “this model would more closely recapitulate the target population of immunocompromised patients" he said.
This spotlighted research was supported by the Vaccine and Infectious Disease Division Faculty Initiative and Evergreen Beyond Pilot Award from the Fred Hutchinson Cancer Center, the American Society for Transplantation and Cellular Therapy, and the Amy Strelzer Manasevit Award from the National Marrow Donor Program and National Institute of Health.
Fred Hutch/University of Washington/Seattle Children's Cancer Consortium member Dr. Marie Pancera contributed to this work.
Cabán M, Rodarte JV, Bibby M, Gray MD, Taylor JJ, Pancera M, Boonyaratanakornkit J. Cross-protective antibodies against common endemic respiratory viruses. Nat Commun. 2023 Feb 13;14(1):798. doi: 10.1038/s41467-023-36459-3.