Daily Respiratory Research Analysis

Human metapneumovirus (hMPV) is a significant cause of acute respiratory illness in children and older adults, with most children becoming seropositive by five years of age. The hMPV fusion (F) protein is the sole target of neutralizing antibodies, and while most common B-cell-targeted neutralizing epitopes on the hMPV F protein have been determined in hMPV-infected adults, the antibody response in hMPV-infected children remains undefined. We isolate five human monoclonal antibodies (mAbs) from hMPV-infected children, and evaluate their binding avidity, neutralization potency, epitope specificity, and in vivo efficacy. All mAbs are neutralizing, and epitope binning reveals four different epitopes targeted by the mAbs. Cryo-EM structures of four mAbs in complex with the hMPV F protein reveal epitopes on the hMPV F trimer surface as well as an intratrimer epitope located completely within the hMPV F trimer interface. Furthermore, we determine the prophylactic efficacy of the mAbs in protection against hMPV challenge in mice. These findings provide new insights into the immunodominant antigenic epitopes on the hMPV F protein in children and identify new mAbs for hMPV F disease prevention.

BACKGROUND: Pediatric acute respiratory distress syndrome (PARDS), often triggered by viral infections, is a life-threatening condition. Despite its severity, children demonstrate significantly better survival rates and superior lung repair compared to adults. However, the mechanisms underlying this age-specific advantage remain incompletely understood. PATIENTS AND METHODS: We conducted a pilot multi-omics study of influenza-associated PARDS integrating single-cell RNA sequencing (scRNA-seq) of pediatric lung tissue and bronchoalveolar lavage fluid (BALF), spatial transcriptomics, and plasma proteomics. Analyses were harmonized with the Human Lung Cell Atlas (HLCA) reference, reanalysis of public pediatric PARDS airway scRNA-seq, and contextual comparisons to adult lethal COVID-19 lung. RESULTS: Tissue scRNA-seq and spatial data indicated outcome-linked divergence in PARDS. Survivor showed spatially restricted repair with preserved alveolar type II (AT2) cells, AT2-to-alveolar type I (AT1) differentiation signatures, and higher KRT17, whereas fatal case and adults exhibited diffuse immune activation with pro-fibrotic and pro-apoptotic signaling. In BALF, KRT17-positive airway stress-repair epithelial cells (hillock-like) increased from the acute to recovery phase, and plasma proteomics showed higher circulating KRT17 in survivors. HLCA-based label transfer strengthened cell-type definitions and enabled pediatric-adult comparisons suggesting biological and developmental differences; the adult lethal COVID-19 atlas provided a benchmark with attenuated epithelial repair and prominent collagen CTHRC1-pathologic fibroblasts. Fibroblast programs were regionally compartmentalized, with injury-enriched CTHRC1 CONCLUSIONS: This pilot multi-omics case series outlines putative pediatric lung repair niches in influenza-associated PARDS. KRT17-positive transitional epithelium, preserved AT2 differentiation, and restoration of resident-like macrophages may align with recovery, whereas diffuse immune activation and CTHRC1-enriched fibroblast programs may accompany worse outcomes. HLCA-guided annotations and adult benchmarks indicate possible age-related differences, warranting validation in larger multi-center cohorts.

Respiratory syncytial virus (RSV) causes high hospitalization and mortality in children and the elderly. RSV prefusion conformation-stabilized fusion (F) protein vaccines have been licensed for elderly and maternal vaccination. Nonetheless, a demand exists for an effective RSV vaccine in elderly and young children, avoiding vaccine-enhanced disease. We developed a new prefusion mRNA containing a prototype (DS-Cav1 pre-F) stabilizing and additional fusion domain mutations. The new pre-F mRNA vaccine, encapsulated in lipid nanoparticles (LNP), effectively induced neutralizing antibodies and a preferential Th1-type effector T cell response in mice. Remarkably, a combination of pre-F mRNA-LNP and pre-F protein elicited significantly higher titers of neutralizing antibodies against RSV A and B strains than either pre-F mRNA or protein vaccine alone. Pre-F mRNA and its combination with pre-F protein provided protection by clearing lung viral loads, preventing lung histopathology and inflammation, compared to the prototype pre-F protein. Combination pre-F mRNA and pre-F protein vaccination modulated balanced effector CD8 T cell responses after challenge. This study supports the idea that combining pre-F mRNA and pre-F protein vaccines would provide more effective humoral and balanced cellular immunity than either mRNA or protein vaccine alone.