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Human rhinoviruses (HRVs) are the most frequent cause of the common cold and a leading viral cause of acute respiratory illness worldwide. While most infections are mild and self-limiting, HRVs are a major trigger of acute exacerbations of asthma and chronic obstructive pulmonary disease (COPD), and a significant cause of lower respiratory tract disease in infants, the elderly, and immunocompromised individuals. In the United States, HRVs were the most frequently detected viruses among children under five hospitalized for acute respiratory illness, accounting for 25–35% of detections. In China, large-scale surveillance from 2022 to 2024 found HRV to be the most prevalent respiratory pathogen, with a positive rate of 18.7%.
HRVs comprise approximately 180 genetically distinct genotypes classified into three species—HRV-A, HRV-B, and HRV-C. HRV-C, discovered in 2006, is of particular clinical importance: it is strongly associated with severe lower respiratory illness and acute asthma exacerbations in children, and unlike HRV-A and HRV-B, it cannot be readily propagated in conventional cell culture, complicating both study and vaccine production.
Fig. 1 Phylogenetic tree
Despite decades of research, no licensed HRV vaccine exists. The primary obstacle has been the extraordinary antigenic diversity of the virus—neutralizing antibodies are largely serotype-specific, and the number of circulating types far exceeds what a traditional polyvalent inactivated vaccine can practically cover. However, recent advances in structural virology, the discovery of conserved neutralizing epitopes, and the emergence of novel vaccine platforms have revitalized the field, with the first pan-rhinovirus subunit candidate now reporting positive Phase 1 data.
HRVs are non-enveloped, positive-sense single-stranded RNA viruses of the genus Enterovirus, family Picornaviridae. The genome is approximately 7.2 kb and encodes a single polyprotein that is co- and post-translationally cleaved by viral proteases (2A, 3C, 3CD) into 11 mature proteins.
Fig. 2 HRV genomic structure
The icosahedral capsid consists of 60 protomers, each containing four structural proteins: VP1, VP2, VP3, and the internal VP4. VP1, VP2, and VP3 form the outer surface, while VP4 lies beneath the shell and is associated with the RNA genome. A prominent surface feature—the "canyon"—surrounds each fivefold axis and contains the receptor-binding site. Major-group HRVs (most HRV-A and all HRV-B) bind intercellular adhesion molecule 1 (ICAM-1), whereas minor-group HRVs use low-density lipoprotein receptor (LDLR) family members. HRV-C uses cadherin-related family member 3 (CDHR3), a receptor genetically linked to asthma susceptibility.
Antigenic diversity is concentrated in four neutralizing immunogenicity sites (NIm-IA, NIm-IB, NIm-II, NIm-III) located on the exposed loops of VP1, VP2, and VP3 that rim the canyon. These hypervariable regions drive serotype-specific immunity. However, the canyon floor and the internal VP4 protein are more conserved and have emerged as key targets for broadly protective vaccine design.
Several interrelated obstacles have delayed HRV vaccine development:
The earliest HRV vaccine efforts, dating to the 1960s, used formalin-inactivated monovalent (RV13) and later multivalent (10-serotype) preparations. These trials demonstrated that inactivated HRV could induce neutralizing antibodies but provided only minimal protective efficacy, largely due to the narrow serotype coverage and the epitope-damaging effects of formalin inactivation. No adjuvant was used in these early studies, and alum was the only approved adjuvant at the time. These limitations led to the abandonment of whole-virus approaches for several decades.
Recombinant subunit vaccines offer the advantage of focusing the immune response on defined, potentially conserved antigens.
VP0-based vaccines: VP0 is the precursor of VP4 and VP2. Immunization with recombinant VP0 has been shown to induce cross-serotype-reactive antibodies, increase memory CD4+ T-cell numbers, and accelerate viral clearance in vivo following heterologous challenge. The immunodominant epitope maps to the NIm-II region of VP2, which helps explain the residual serotype specificity of this approach.
Conserved VP4 epitopes: The N-terminal region of VP4 is highly conserved across HRV species and is transiently exposed on the virion surface during the capsid "breathing" that precedes uncoating. Antibodies targeting VP4 residues 1–30 exhibit cross-serotypic neutralization. A 2023 study demonstrated that induction of these antibodies depends critically on presenting VP4 peptides in a virus-like conformation, highlighting the importance of structural authenticity in immunogen design.
APL-10456 (Apollo Therapeutics): The most advanced HRV vaccine candidate to date, APL-10456 is a first-in-class adjuvanted recombinant protein subunit vaccine designed as a pan-rhinovirus immunogen to prevent COPD and asthma exacerbations. In August 2026, Apollo Therapeutics announced positive Phase 1 results demonstrating robust immunogenicity and cross-species activity. APL-10456 is the only major pulmonary virus vaccine candidate in clinical development for a pathogen with no licensed vaccine.
VLPs and nanoparticle scaffolds display capsid antigens in a native-like, highly immunogenic particulate conformation without containing infectious genetic material. High-valent VLP formulations incorporating multiple HRV serotypes or conserved antigens are being explored preclinically. VP4-displaying VLPs have shown particular promise by presenting the conserved N-terminal VP4 epitope in a conformation that elicits cross-neutralizing antibodies.
mRNA-LNP technology is being applied to HRV, both as a preventive vaccine and as an immunomodulatory therapy. ETH47 (Ethris) is an intranasally delivered mRNA-LNP therapeutic designed to fortify the respiratory mucosal defense against viral triggers of asthma exacerbations. It entered a Phase IIa trial in August 2025, representing a novel approach to reducing HRV-associated morbidity through innate immune augmentation rather than conventional antigen-specific vaccination.
Computational immunoinformatics approaches have identified conserved B-cell and T-cell epitopes across HRV genotypes, enabling the design of multi-epitope ensemble vaccines. A 2025 observational study protocol is characterizing the immune response to an epitope ensemble vaccine in pediatric asthma and adult COPD populations, while HRV-C-specific multi-epitope constructs have been designed in silico. These strategies aim to overcome serotype diversity by targeting shared epitopes exclusively.
Fig. 3 Rhinovirus vaccine development timeline and clinical pipeline
After more than half a century of frustration driven by the seemingly insurmountable antigenic diversity of HRV, the vaccine landscape has shifted decisively. The recognition that conserved subdominant epitopes—particularly on VP4 and the canyon floor—can elicit cross-serotypic neutralization, combined with rational immunogen design and novel delivery platforms, has transformed what was long considered an intractable problem into an achievable goal. The 2026 Phase 1 success of APL-10456, the first pan-rhinovirus vaccine to report positive clinical data, marks a historic turning point.
Future priorities include establishing validated correlates of cross-protection, ensuring coverage of the difficult-to-culture HRV-C species, and demonstrating that vaccination can meaningfully reduce asthma and COPD exacerbations—the clinical outcomes with the greatest public health impact. With multiple platforms now in or approaching clinical evaluation, the prospect of a licensed HRV vaccine is closer than at any point in history.
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