Summary Cellular plasticity contributes to the regenerative capacity of plants, invertebrates, teleost fishes, and amphibians. In vertebrates, differentiated cells are known to revert into replicating progenitors, but these cells do not persist as stable stem cells. We now present evidence that differentiated airway epithelial cells can revert into stable and functional stem cells in vivo. Following the ablation of airway stem cells, we observed a surprising increase in the proliferation of committed secretory cells. Subsequent lineage tracing demonstrated that the luminal secretory cells had dedifferentiated into basal stem cells. Dedifferentiated cells were morphologically indistinguishable from stem cells and they functioned as well as their endogenous counterparts to repair epithelial injury. Indeed, single secretory cells clonally dedifferentiated into multipotent stem cells when they were cultured ex vivo without basal stem cells. In contrast, direct contact with a single basal stem cell was sufficient to prevent secretory cell dedifferentiation. In analogy to classical descriptions of amphibian nuclear reprogramming, the propensity of committed cells to dedifferentiate was inversely correlated to their state of maturity. This capacity of committed cells to dedifferentiate into stem cells may play a more general role in the regeneration of many tissues and in multiple disease states, notably cancer.

Angiotensin-converting enzyme 2 (ACE2) and accessory proteases (TMPRSS2 and CTSL) are needed for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) cellular entry, and their expression may shed light on viral tropism and impact across the body. We assessed the cell-type-specific expression of ACE2, TMPRSS2 and CTSL across 107 single-cell RNA-sequencing studies from different tissues. ACE2, TMPRSS2 and CTSL are coexpressed in specific subsets of respiratory epithelial cells in the nasal passages, airways and alveoli, and in cells from other organs associated with coronavirus disease 2019 (COVID-19) transmission or pathology. We performed a meta-analysis of 31 lung single-cell RNA-sequencing studies with 1,320,896 cells from 377 nasal, airway and lung parenchyma samples from 228 individuals. This revealed cell-type-specific associations of age, sex and smoking with expression levels of ACE2, TMPRSS2 and CTSL. Expression of entry factors increased with age and in males, including in airway secretory cells and alveolar type 2 cells. Expression programs shared by ACE2 + TMPRSS2 + cells in nasal, lung and gut tissues included genes that may mediate viral entry, key immune functions and epithelial-macrophage cross-talk, such as genes involved in the interleukin-6, interleukin-1, tumor necrosis factor and complement pathways. Cell-type-specific expression patterns may contribute to the pathogenesis of COVID-19, and our work highlights putative molecular pathways for therapeutic intervention.

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The inability to visualize airway smooth muscle (ASM) cells in vivo is a major obstacle in understanding their role in normal physiology and diseases. At present, there is no imaging modality available to assess ASM in vivo. Confocal endomicroscopy lacks the penetration depth and field of view, and conventional optical coherence tomography (OCT) does not have sufficient contrast to differentiate ASM from surrounding tissues. We have developed a birefringence microscopy platform which leverages the micro-organization of tissue to add further dimension to traditional OCT. We have utilized this technology to validate ASM measurements in ex vivo swine and canine studies, visualize and characterize volumetric representations of ASM in vivo, and to quantify and predict ASM contractile force as a function of optical retardation. We provide in vivo images and volumetric assessments of ASM in living humans and document structural disease variations in subjects with mild asthma. The opportunity to link inflammatory responses to ASM responses, and to link ASM responses to clinical responses and outcomes could lead to an increased understanding of diseases of the airway and ultimately to improved patient outcomes.

In asthma, the relationship among airway inflammation, airway hyperresponsiveness, and lung function is poorly understood. Methods to noninvasively assess these relationships in human subjects are needed. We sought to determine whether 18F-FDG uptake rate (Ki, min−1) could serve as a biomarker of eosinophilic inflammation and local lung function. Methods We used PET/CT to assess regional pulmonary perfusion (Q̇), specific ventilation per unit volume (sV̇A), fractional gas content (Fgas), airway wall thickness, and regional Ki 10 h after segmental allergen challenge to the right middle lobe in 6 asthmatic subjects with demonstrated atopy. Q̇, sV̇A, and Fgas in the allergen-challenged lobe were compared with the right upper lobe, where diluent was applied as a control. The airway wall thickness aspect ratio (ω) of the allergen-challenged airway was compared with those of similarly sized airways from unaffected areas of the lung. Differences in Ki between allergen and diluent segments were compared with those in cell counts obtained 24 h after the allergen challenge by a bronchoalveolar lavage of the respective segments. Results We found systematic reductions in regional Q̇, sV̇A, and Fgas and increased ω in all subjects. The ratio of eosinophil count (allergen to diluent) was linearly related (R2 = 0.9917, P < 0.001) to the ratio of Ki. Conclusion Regional Ki measured with PET is a noninvasive and highly predictive biomarker of eosinophilic airway inflammation and its functional effects. This method may serve to help in the understanding of allergic inflammation and test the therapeutic effectiveness of novel drugs or treatments.

Summary Background Influenza continues to have a significant socioeconomic and health impact despite a long established vaccine program and approved antivirals. Preclinical data suggest combination antivirals might be more effective than oseltamivir alone in the treatment of influenza. Methods We conducted a randomized, double-blinded, multicenter phase 2 trial of combination antivirals versus monotherapy for the treatment of influenza. Participants ≥18 years with influenza at increased risk of complications from influenza were randomized by an online computer-generated randomization system to receive either oseltamivir, amantadine, and ribavirin or oseltamivir alone for 5 days, and followed for 28 days. The primary endpoint was the percentage of participants with virus detectable by polymerase chain reaction in nasopharyngeal swab at Day 3. Among the secondary outcomes, there were safety and time to alleviation of influenza clinical symptoms. ClinicalTrials.gov Identifier: NCT01227967. Findings Between March 2011 and April 2016 we randomized 633 participants. Seven participants were excluded from analysis: 3 were given treatment without randomization, 3 withdrew before taking any medication, and 1 was lost to follow-up. The primary analysis included 394 participants, excluding 47 in the pilot phase, 172 without confirmed influenza, and 13 without an endpoint sample. 80 of 200 (40.0%) participants in the combination arm had virus detectable at Day 3 compared to 97 of 194 (50.0%) (95%C.I. 0.2–19.8%, p=0.046) in the control arm. There was no benefit, however, in multiple clinical secondary endpoints, such as median duration of symptoms (4.5 days in the combination arm vs 4.0 days in the oseltamivir arm; p = 0.21). Interpretation Although oseltamivir, amantadine, and ribavirin showed a statistically significant decrease in viral shedding at Day 3 relative to oseltamivir, this difference was not associated with improved clinical benefit. More work is needed to understand the lack of clinical benefit when a difference in virologic outcome was identified. Funding National Institute of Allergy and Infectious Diseases, National Institutes of Health, United States.

Mass cytometry (CyTOF), a mass spectrometry-based single cell phenotyping technology, allows utilization of over 35 antibodies in a single sample and is a promising tool for translational human immunology studies. Although several analysis tools are available to interpret the complex data sets generated, a robust method for standardization and quality control within and across studies is needed. Here we report an efficient and easily adaptable method to monitor quality of individual samples in human immunology studies and to facilitate reproducible data analysis. Samples to be assessed are spiked with a defined amount of reference peripheral blood mononuclear cells from a healthy donor, derived from a single large blood draw. The presence of known standardized numbers and phenotypic profiles of these reference cells greatly facilitates sample analysis by allowing for: 1) quality control for consistent staining of each antibody in the panel, 2) identification of potential batch effects, and 3) implementation of a robust gating strategy. We demonstrate the utility of this method using peripheral blood and bronchoalveolar lavage samples from HIV+ patients by characterizing their CD8+ T-cell phenotypes and cytokine expression, respectively. Our results indicate that this method allows quality control of experimental conditions and results in highly reproducible population frequencies through a robust gating strategy.

Foxp3 + regulatory T (T reg ) cells expressing the interleukin (IL)-33 receptor ST2 mediate tissue repair in response to IL-33. Whether T reg cells also respond to the alarmin IL-33 to regulate specific aspects of the immune response is not known. Here we describe an unexpected function of ST2 + T reg cells in suppressing the innate immune response in the lung to environmental allergens without altering the adaptive immune response. Following allergen exposure, ST2 + T reg cells were activated by IL-33 to suppress IL-17-producing γδ T cells. ST2 signaling in T reg cells induced Ebi3, a component of the heterodimeric cytokine IL-35 that was required for T reg cell-mediated suppression of γδ T cells. This response resulted in less eosinophil-attracting chemokines and reduced eosinophil recruitment into the lung, which was beneficial to the host in reducing inflammation induced by allergen. Thus, we define a fundamental role for ST2 + T reg cells in the lung as a negative regulator of the early innate γδ T cell response to mucosal injury.