Morgan S. A. Gilman, Carlos Castellanos, Man Chen, Joan O. Ngwuta, Eileen Goodwin, Syed M. Moin, Vicente Mas, Jose A. Melero, Peter F. Wright, Barney S. Graham, Jason S. McLellan, Laura M. Walker
December 23, 2016
Overview of study and research significance
Respiratory syncytial virus (RSV) remains a major cause of morbidity and mortality in infants and older adults. In a collaboration with other institutions, Adimab researchers performed the first large-scale donor-level dissection of the human RSV antibody repertoire using a single-cell, recombinant expression platform. By cloning and characterizing antibodies from memory B cells of three healthy adult donors, they defined the genetic, functional, and structural features of antibodies recognizing the RSV fusion (F) glycoprotein, the principal target of neutralizing antibodies. These insights gained from understanding the relationship between neutralization potency and epitope specificity directly inform rational vaccine and therapeutic antibody design.
Research goal and core hypothesis
This study was designed to leverage Adimab’s yeast-based single-B-cell cloning and high-throughput IgG expression platform, enabling rapid recovery and characterization of hundreds of RSV antibodies. The authors sought to determine how naturally acquired antibodies target epitopes comprising the prefusion (preF) and postfusion (postF) conformations of the RSV F glycoprotein, whether particular germline genes or mutation levels correlate with neutralization potency, and to what extent preF-specific antibodies dominate the neutralizing response.
Experimental approach and analytical techniques
Peripheral memory B cells were stained with a mixture of fluorescently labeled preF and postF probes, single cells were sorted by flow cytometry, and 364 recombinant monoclonal antibodies were expressed and analyzed.
Characterization and functional profiling included:
Diversity and genetic features of RSV antibody repertoires
From the 364 recombinant antibodies recovered, 70–98 clonal lineages were identified per donor. The repertoires were genetically diverse, showing heavy-chain germlines such as VH1-18, VH1-2, VH1-69, VH3-23, and VH5-51. Compared with non-reactive repertoires, the distribution of CDRH3 lengths in RSV F-specific antibodies skewed toward 14–18 amino acids. In addition, the average level of somatic hypermutation (SHM) varied between the three donor repertoires, ranging from 16 to 30 nucleotide substitutions per VH gene (excluding CDRH3), consistent with extensive affinity maturation through recurrent RSV exposure. Approximately 50% of all antibodies bound exclusively to preF, confirming its immunodominance in these memory responses.
Mapping of dominant antigenic sites on RSV F
In addition to confirming the five major preF antigenic known epitopes (Ø, I, II, III, IV), this study identified the previously undescribed pre-fusion F-specific neutralizing site V. Patch mutant analysis revealed that site V antibodies interact with the α3 helix and β3/β4 hairpin of preF. Approximately 51% of antibodies were preF-specific, and nearly all potent neutralizers targeted sites Ø and V at the trimer apex, regions unique to the prefusion form. A significant proportion of antibodies targeting site V used the germline pair VH1-18 with VK2-30, reflecting convergent genetic solutions for recognizing this vulnerable epitope and offers the potential to rapidly detect these types of antibodies in human samples using high-throughput sequencing technology.
Potency of prefusion-specific antibodies and cross-neutralization
Across all donors, 64–80% of cloned antibodies neutralized RSV A and B, with 19–38% achieving high potency (IC₅₀ < 0.05 µg/mL). Prefusion-specific antibodies were on average ~10-fold more potent than cross-reactive F-binders and ~80-fold more potent than postF-restricted antibodies. Several preF mAbs matched or exceeded the benchmark neutralizers D25 and palivizumab in potency. There was no correlation between neutralization potency and level of SHM.
A subset of nine antibodies also neutralized human metapneumovirus (HMPV), including two with strong cross-reactive potency, revealing highly conserved pneumovirus epitopes that could be leveraged for broad antiviral designs.
Implications for RSV vaccine and antibody therapeutic development
Unlike broadly neutralizing antibodies to pathogens such as HIV, the vast majority of RSV F–specific antibodies lacked measurable polyreactivity, indicating strong therapeutic developability. The data validate stabilized preF as the optimal antigenic target for eliciting potent neutralizing antibodies. Sites Ø and V emerge as dominant neutralizing determinants, offering concrete templates for vaccine engineering. Recurrent germline pairings, particularly VH1-18/VK2-30, suggest measurable repertoire signatures that could serve as biomarkers of effective vaccine-induced immunity. Cross-neutralizing mAbs highlight opportunities for universal prophylactic or therapeutic antibodies against pneumoviruses.
Broader impact and future perspectives
This molecular-level repertoire analysis defines the architecture of naturally acquired RSV immunity. The integrated workflow, which includes single-cell isolation, recombinant expression, and parallel functional and epitope mapping, provides a high-resolution framework for evaluating vaccine responses and for studying antibody repertoires against other viral fusion proteins. The findings support the use of stabilized prefusion F as a central antigen for RSV vaccine and antibody discovery.
For full details of the study, read the article in Science Immunology.
Post-study note: These findings directly informed the later development of the prefusion F–based antibody nirsevimab (MEDI8897), now approved for RSV prevention, validating preF stabilization as a key design principle.
