The CLCF1-CNTFR axis drives an immunosuppressive tumor microenvironment and blockade enhances the effects of established cancer therapies.

Tumors comprise a complex ecosystem consisting of many cell types that communicate through secreted factors. Targeting these intercellular signaling networks remains an important challenge in cancer research. Cardiotrophin-like cytokine factor 1 (CLCF1) is an interleukin-6 (IL-6) family member secreted by cancer-associated fibroblasts (CAFs) that binds to ciliary neurotrophic factor receptor (CNTFR), promoting tumor growth in lung and liver cancer1,2. A high-affinity soluble receptor (eCNTFR-Fc) that sequesters CLCF1 has anti-oncogenic effects3. However, the role of CLCF1 in mediating cell-cell interactions in cancer has remained unclear. We demonstrate that eCNTFR-Fc has widespread effects on both tumor cells and the tumor microenvironment and can sensitize cancer cells to KRAS inhibitors or immune checkpoint blockade. After three weeks of treatment with eCNTFR-Fc, there is a shift from an immunosuppressive to an immunostimulatory macrophage phenotype as well as an increase in activated T, NKT, and NK cells. Combination of eCNTFR-Fc and αPD1 was significantly more effective than single-agent therapy in a syngeneic allograft model, and eCNTFR-Fc sensitizes tumor cells to αPD1 in a non-responsive GEM model of lung adenocarcinoma. These data suggest that combining eCNTFR-Fc with KRAS inhibition or with αPD1 is a novel therapeutic strategy for lung cancer and potentially other cancers in which these therapies have been used but to date with only modest effect. Overall, we demonstrate the potential of cancer therapies that target cytokines to alter the immune microenvironment.

A fast-acting lipid checkpoint in G1 prevents mitotic defects.

Lipid synthesis increases during the cell cycle to ensure sufficient membrane mass, but how insufficient synthesis restricts cell-cycle entry is not understood. Here, we identify a lipid checkpoint in G1 phase of the mammalian cell cycle by using live single-cell imaging, lipidome, and transcriptome analysis of a non-transformed cell. We show that synthesis of fatty acids in G1 not only increases lipid mass but extensively shifts the lipid composition to unsaturated phospholipids and neutral lipids. Strikingly, acute lowering of lipid synthesis rapidly activates the PERK/ATF4 endoplasmic reticulum (ER) stress pathway that blocks cell-cycle entry by increasing p21 levels, decreasing Cyclin D levels, and suppressing Retinoblastoma protein phosphorylation. Together, our study identifies a rapid anticipatory ER lipid checkpoint in G1 that prevents cells from starting the cell cycle as long as lipid synthesis is low, thereby preventing mitotic defects, which are triggered by low lipid synthesis much later in mitosis.

The effect of biomass smoke exposure on quality-of-life among Ugandan patients treated for tuberculosis: A cross-sectional analysis.

More than half the global population burns biomass fuels for cooking and home heating, especially in low-middle income countries. This practice is a prominent source of indoor air pollution and has been linked to the development of a variety of cardiopulmonary diseases, including Tuberculosis (TB). The purpose of this cross-sectional study was to investigate the association between current biomass smoke exposure and self-reported quality of life scores in a cohort of previous TB patients in Uganda. We reviewed medical records from six TB clinics from 9/2019-9/2020 and conducted phone interviews to obtain information about biomass smoke exposure. A random sample of these patients were asked to complete three validated quality-of-life surveys including the St. Georges Respiratory Questionnaire (SGRQ), the EuroQol 5 Dimension 3 Level system (EQ-5D-3L) which includes the EuroQol Visual Analog Scale (EQ-VAS), and the Patient Health Questionnaire 9 (PHQ-9). The cohort was divided up into 3 levels based on years of smoke exposure-no-reported smoke exposure (0 years), light exposure (1-19 years), and heavy exposure (20+ years), and independent-samples-Kruskal-Wallis testing was performed with post-hoc pairwise comparison and the Bonferroni correction. The results of this testing indicated significant increases in survey scores for patients with current biomass exposure and a heavy smoke exposure history (20+ years) compared to no reported smoke exposure in the SGRQ activity scores (adj. p = 0.018) and EQ-5D-3L usual activity scores (adj. p = 0.002), indicating worse activity related symptoms. There was a decrease in EQ-VAS scores for heavy (adj. p = 0.007) and light (adj. p = 0.017) exposure groups compared to no reported exposure, indicating lower perceptions of overall health. These results may suggest worse outcomes or baseline health for TB patients exposed to biomass smoke at the time of treatment and recovery, however further research is needed to characterize the effect of indoor air pollution on TB treatment outcomes.

Social and economic dimensions of food sustainability - a background paper for the Nordic Nutrition Recommendations.

This review seeks to demonstrate how the social and economic dimensions of sustainability need to be considered alongside its environmental dimensions. This is particularly important when, as in the case of the Nordic Nutrition Recommendations (NNRs), policymakers are attempting to address the twin goals of health and sustainability. For a policy that might make good sense when seen in purely environmental terms, it might not prove sustainable in social and economic terms - if it is too costly, it exacerbates existing inequalities or has detrimental effects on public health. There are some 'win-wins' in the field of health and sustainability policy. However, difficult choices between competing policy options will occur, similar to those facing ordinary consumers in their everyday lives. Being clear about the way food is framed as an issue and how different framings shape policy outcomes is a useful way forward in addressing the inevitable trade-offs and compromises between competing objectives.

Patient level barriers to accessing TB care services during the COVID-19 pandemic in Uganda, a mixed methods study.

INTRODUCTION: Lockdown measure has been utilized widely to mitigate COVID-19 pandemic transmission and recently during the 2022 Sudan Ebola Virus Disease outbreak in Uganda. These have setback effects on the continuity of essential health services such as tuberculosis (TB) care, reversing progress made in the fight against tuberculosis (TB) over the past decade. We set out to understand patient-reported barriers to accessing TB care services during the COVID-19 pandemic in Uganda. METHODS: Mixed methods study involving review of medical records of TB patients who received TB care from January to September 2020. We used quantitative and qualitative methods including phone questionnaires and in-depth interviews. We carried out descriptive statistics, a chi-square test and conducted a thematic analysis. RESULTS: We carried out phone interviews with 672 participants. The majority (60%) were male and with an average of 35 years (SD:11). A significantly higher proportion of patients reported a barrier to TB care access during the COVID-19 lockdown than pre-lockdown (79.9% vs. 68.1% p = 0.027). We carried out in-depth interviews with 28 participants (54% (15/28): male). Barriers experienced by these participants included lack of a means of transport to reach the health facility, lack of money to pay the transport fares, long distances to the facility, fear of COVID-19 infection, stigma due to overlap between TB and COVID-19 symptoms, and few health care workers available during the lockdown period. CONCLUSION: Lockdown measures instituted to mitigate the transmission of COVID1-19 affected access to TB care services in Uganda. Uganda is at risk of future emerging and re-emerging diseases of epidemic potential. Therefore, there should be measures to ensure the continuity of essential services such as tuberculosis care during the implementation of future epidemic response interventions such as a lockdown.

Increasing fibre intake in the UK: lessons from the Danish Whole Grain Partnership.

Diets deficient in fibre are reported globally. The associated health risks of insufficient dietary fibre are sufficiently grave to necessitate large-scale interventions to increase population intake levels. The Danish Whole Grain Partnership (DWP) is a public-private enterprise model that successfully augmented whole-grain intake in the Danish population. The potential transferability of the DWP model to Slovenia, Romania and Bosnia-Herzegovina has recently been explored. Here, we outline the feasibility of adopting the approach in the UK. Drawing on the collaborative experience of DWP partners, academics from the Healthy Soil, Healthy Food, Healthy People (H3) project and food industry representatives (Food and Drink Federation), this article examines the transferability of the DWP approach to increase whole grain and/or fibre intake in the UK. Specific consideration is given to the UK's political, regulatory and socio-economic context. We note key political, regulatory, social and cultural challenges to transferring the success of DWP to the UK, highlighting the particular challenge of increasing fibre consumption among low socio-economic status groups - which were also most resistant to interventions in Denmark. Wholesale transfer of the DWP model to the UK is considered unlikely given the absence of the key 'success factors' present in Denmark. However, the DWP provides a template against which a UK-centric approach can be developed. In the absence of a clear regulatory context for whole grain in the UK, fibre should be prioritised and public-private partnerships supported to increase the availability and acceptability of fibre-rich foods.

A scoping study on the social determinants of health and sugar consumption in the context of policy approaches for improving population health.

OBJECTIVES: To conduct a scoping review of existing research on the social determinants of health, sugar consumption and public health policy responses to address or improve health outcomes. METHODS: A total of 13 categories were developed to reflect the authors' interest in the overall focus on the social determinants of health, sugar as an independent risk factor, upstream policy action ('whole populations'), downstream policy action ('targeted') and two contemporary policy strategies (namely 'Vulnerable populations' and 'Proportionate Universalism'). The search strategy was then performed on MEDLINE (via Ovid) and Web of Science, and was limited to the English language. No time limits prior to when the database search was conducted in 2022 were set to explore the full extent of the literature in this field. RESULTS: Five hundred and sixty articles were retrieved, of which 181 met the criteria for review. When all categories were applied, the findings showed that 76% of papers focusing on sugar consumption as a risk factor for non-communicable diseases (NCDs) mentioned the social determinants of health. The majority of studies (60%) recommended downstream interventions, with 40% recommending 'upstream' interventions. A limited proportion (12%) of research work was published in dental journals. Research had been done using predominantly quantitative methods (66% of articles), with 24% of studies adopting a mixed methods approach, and 8% being exclusively qualitative. Research on contemporary strategies for sugar reduction were focused on the 'Global North' and 98% of papers used individual level data focused on targeted approaches, highlighting that there is little direct evidence for contemporary strategies aimed at reducing sugar consumption. CONCLUSIONS: Whilst the majority of public and dental health research argues that there is a need to address the social determinants of health, the findings from this study highlight that very few empirical studies have been designed to directly inform contemporary strategies for sugar reduction. More research is therefore needed that can directly assess the evidence for contemporary strategies in public health policy.

Inulin-type fructans and 2'fucosyllactose alter both microbial composition and appear to alleviate stress-induced mood state in a working population compared to placebo (maltodextrin): the EFFICAD Trial, a randomized, controlled trial.

BACKGROUND: There is increasing interest in the bidirectional relationship existing between the gut and brain and the effects of both oligofructose and 2'fucosyllactose to alter microbial composition and mood state. Yet, much remains unknown about the ability of oligofructose and 2'fucosyllactose to improve mood state via targeted manipulation of the gut microbiota. OBJECTIVES: We aimed to compare the effects of oligofructose and 2'fucosyllactose alone and in combination against maltodextrin (comparator) on microbial composition and mood state in a working population. METHODS: We conducted a 5-wk, 4-arm, parallel, double-blind, randomized, placebo-controlled trial in 92 healthy adults with mild-to-moderate levels of anxiety and depression. Subjects were randomized to oligofructose 8 g/d (plus 2 g/d maltodextrin); maltodextrin 10 g/d; oligofructose 8 g/d plus 2'fucosyllactose (2 g/d) or 2'fucosyllactose 2 g/d (plus 8 g/d maltodextrin). Changes in microbial load (fluorescence in situ hybridization-flow cytometry) and composition (16S ribosomal RNA sequencing) were the primary outcomes. Secondary outcomes included gastrointestinal sensations, bowel habits, and mood state parameters. RESULTS: There were significant increases in several bacterial taxa including Bifidobacterium, Bacteroides, Roseburia, and Faecalibacterium prausnitzii in both the oligofructose and oligofructose/2'fucosyllactose interventions (all P ≤ 0.05). Changes in bacterial taxa were highly heterogenous upon 2'fuscoyllactose supplementation. Significant improvements in Beck Depression Inventory, State Trait Anxiety Inventory Y1 and Y2, and Positive and Negative Affect Schedule scores and cortisol awakening response were detected across oligofructose, 2'fucosyllactose, and oligofructose/2'fucosyllactose combination interventions (all P ≤ 0.05). Both sole oligofructose and oligofructose/2'fuscosyllactose combination interventions outperformed both sole 2'fucosyllactose and maltodextrin in improvements in several mood state parameters (all P ≤ 0.05). CONCLUSION: The results of this study indicate that oligofructose and combination of oligofructose/2'fucosyllactose can beneficially alter microbial composition along with improving mood state parameters. Future work is needed to understand key microbial differences separating individual responses to 2'fucosyllactose supplementation. This trial was registered at clinicaltrials.gov as NCT05212545.

The IFT81-IFT74 complex acts as an unconventional RabL2 GTPase-activating protein during intraflagellar transport.

Cilia are important cellular organelles for signaling and motility and are constructed via intraflagellar transport (IFT). RabL2 is a small GTPase that localizes to the basal body of cilia via an interaction with the centriolar protein CEP19 before downstream association with the IFT machinery, which is followed by initiation of IFT. We reconstituted and purified RabL2 with CEP19 or IFT proteins to show that a reconstituted pentameric IFT complex containing IFT81/74 enhances the GTP hydrolysis rate of RabL2. The binding site on IFT81/74 that promotes GTP hydrolysis in RabL2 was mapped to a 70-amino-acid-long coiled-coil region of IFT81/74. We present structural models for RabL2-containing IFT complexes that we validate in vitro and in cellulo and demonstrate that Chlamydomonas IFT81/74 enhances GTP hydrolysis of human RabL2, suggesting an ancient evolutionarily conserved activity. Our results provide an architectural understanding of how RabL2 is incorporated into the IFT complex and a molecular rationale for why RabL2 dissociates from anterograde IFT trains soon after departure from the ciliary base.

A Longitudinal Study of Multimodal Bronchoscopy Training in Uganda.

Background: Flexible bronchoscopy is an essential tool in diagnosing and managing pulmonary diseases. However, there is limited capacity for bronchoscopy in low and middle income countries (LMICs). In 2019, a pilot program for flexible bronchoscopy training was launched for local physicians in Kampala, Uganda. We then conducted a follow up multimodal bronchoscopy course after 2 years. Objective: The aim of this study is to assess a longitudinal multimodal bronchoscopy training in an LMIC setting. Methods: A multimodal follow up curriculum was developed with pulmonologists from Uganda and the United States. The training was delivered to Ugandan providers who attended previous bronchoscopy training and new participants. The training included a prepared curriculum consisting of lectures, simulations, and deliberate practice-based proctoring. A 12-question multiple-choice exam was administered at the beginning and end of the course, assessing knowledge. Procedural competency was measured using a validated assessment tool called the BSTAT (Bronchoscopic Skills and Tasks Assessment Tool). Results were analyzed to evaluate the retention of knowledge among those who took part in previous training and the efficacy of the follow-up curriculum for participants without previous training. Results: Among the participants who attended didactic training in 2022 (11), mean exam scores were improved after training, from 43.9 (standard deviation [SD], 11.3) to 59.8 (SD, 16.1) (mean difference [MD], +15.9; SD, 13.9; P = 0.008), but were lower compared with post didactic scores in 2019: 90.8 (SD, 6.1; MD, -31; P < 0.0001). Participants who completed BSTAT assessments (8) had mean scores similar in 2019 and 2022, at 72.1 and 75.2, respectively (MD, 3.1; P = 0.38). Conclusion: This study provides an example of how a longitudinal multimodal bronchoscopy curriculum can improve competency and proficiency for local physicians in an LMIC.

Oligofructose alone and in combination with 2'fucosyllactose induces physiologically relevant changes in γ-aminobutyric acid and organic acid production compared to sole 2'fucosyllactose supplementation: an in vitro study.

We explored the potential for the prebiotic oligofructose and prebiotic candidate 2'fucosyllactose, alone and in combination (50:50 blend) to induce physiologically relevant increases in neurotransmitter (γ-aminobutyric acid, serotonin, tryptophan, and dopamine) and organic acid (acetate, propionate, butyrate, lactate, and succinate) production as well as microbiome changes using anaerobic pH-controlled in vitro batch culture fermentations over 48 h. Changes in organic acid and neurotransmitter production were assessed by gas chromatography and liquid chromatography and, bacterial enumeration using fluorescence in situ hybridization, respectively. Both oligofructose and oligofructose/2'fucosyllactose combination fermentations induced physiologically relevant concentrations of γ-aminobutyric acid, acetate, propionate, butyrate, and succinate at completion (all P ≤ .05). A high degree of heterogeneity was seen amongst donors in both neurotransmitter and organic acid production in sole 2'FL fermentations suggesting a large responder/nonresponder status exists. Large increases in Bifidobacterium, Lactobacillus, and Bacteroides numbers were detected in oligofructose fermentation, smallest increases being detected in 2'fucosyllactose fermentation. Bacterial numbers in the combined oligofructose/2'fucosyllactose fermentation were closer to that of sole oligofructose. Our results indicate that oligofructose and oligofructose/2'fucosyllactose in combination have the potential to induce physiologically relevant increases in γ-aminobutyric and organic acid production along with offsetting the heterogenicity seen in response to sole 2'fucosyllactose supplementation.

UHRF1 is a mediator of KRAS driven oncogenesis in lung adenocarcinoma.

KRAS is a frequent driver in lung cancer. To identify KRAS-specific vulnerabilities in lung cancer, we performed RNAi screens in primary spheroids derived from a Kras mutant mouse lung cancer model and discovered an epigenetic regulator Ubiquitin-like containing PHD and RING finger domains 1 (UHRF1). In human lung cancer models UHRF1 knock-out selectively impaired growth and induced apoptosis only in KRAS mutant cells. Genome-wide methylation and gene expression analysis of UHRF1-depleted KRAS mutant cells revealed global DNA hypomethylation leading to upregulation of tumor suppressor genes (TSGs). A focused CRISPR/Cas9 screen validated several of these TSGs as mediators of UHRF1-driven tumorigenesis. In vivo, UHRF1 knock-out inhibited tumor growth of KRAS-driven mouse lung cancer models. Finally, in lung cancer patients high UHRF1 expression is anti-correlated with TSG expression and predicts worse outcomes for patients with KRAS mutant tumors. These results nominate UHRF1 as a KRAS-specific vulnerability and potential target for therapeutic intervention.

Health Equity and Respiratory Diseases in Low- and Middle-Income Countries.

Over 80% of the morbidity and mortality related to acute and chronic respiratory diseases occur in low- and middle-income countries (LMICs), a reflection of vast disparities in care for these conditions. Over the next decade, the prevalence of respiratory diseases is expected to increase, as population growth in LMICs exceeds high-income countries (HICs). Pediatric morbidity and mortality from lower respiratory tract infections and asthma occur almost exclusively in LMICs, contributing to a greater loss of quality adjusted life years from these conditions when compared with HICs.

Risk factors for disruptions in tuberculosis care in Uganda during the COVID-19 pandemic.

BACKGROUND: During the COVID-19 pandemic, TB mortality increased while diagnoses decreased, likely due to care disruption. In March, 2020, Uganda-a country with high TB burden, implemented a COVID-19 lockdown with associated decrease in TB diagnoses. This study aims to examine patient level risk factors for disruption in TB care during the COVID-19 pandemic in Uganda. This retrospective cross-sectional cohort study included six TB clinics in Uganda. Clustered sampling included phases of TB care and three time-periods: pre-lockdown, lockdown and post-lockdown. Characteristics of patients with TB care disruption (TBCD), defined as those with > 2 months of symptoms prior to diagnosis or who missed a TB clinic, and those without TB care disruption (non-TBCD) were analyzed between time-periods. 1,624 charts were reviewed; 1322 were contacted, 672 consented and completed phone interview; pre-lockdown (n = 213), lockdown (n = 189) and post-lockdown (n = 270). TBCD occurred in 57% (385/672) of patients. There was an increase in the proportion of urban patients in the TBCD and non-TBCD groups during post-lockdown (p <0.001). There was no difference in demographics, HIV co-infection, socioeconomic status, or distance to TB clinic between TBCD and non-TBCD groups or within TBCD by time-period. There were few differences amongst TBCD and all TB patients by time-period. The increase in urban patients' post-lockdown may represent a portion of urban patients who delayed care until post-lockdown. Insignificant trends suggesting more TBCD amongst those who lived further from clinics and those without HIV-coinfection require more investigation.

Single-molecule imaging in the primary cilium.

The primary cilium is an important signaling organelle critical for normal development and tissue homeostasis. Its small dimensions and complexity necessitate advanced imaging approaches to uncover the molecular mechanisms behind its function. Here, we outline how single-molecule fluorescence microscopy can be used for tracking molecular dynamics and interactions and for super-resolution imaging of nanoscale structures in the primary cilium. Specifically, we describe in detail how to capture and quantify the 2D dynamics of individual transmembrane proteins PTCH1 and SMO and how to map the 3D nanoscale distributions of the inversin compartment proteins INVS, ANKS6, and NPHP3. This protocol can, with minor modifications, be adapted for studies of other proteins and cell lines to further elucidate the structure and function of the primary cilium at the molecular level.

Developing and Evaluating the Fidelity of Patient Specific Kidney Emulating Phantoms for Image-guided Intervention Applications.

Patient specific organ and tissue mimicking phantoms are used routinely to develop and assess new image-guided intervention tools and techniques in laboratory settings, enabling scientists to maintain acceptable anatomical relevance, while avoiding animal studies when the developed technology is still in its infancy. Gelatin phantoms, specifically, offer a cost-effective and readily available alternative to the traditional manufacturing of anatomical phantoms, and also provide the necessary versatility to mimic various stiffness properties specific to various organs or tissues. In this study, we describe the protocol to develop patient specific anthropomorphic gelatin kidney phantoms and we also assess the faithfulness of the developed phantoms against the patient specific CT images and corresponding virtual anatomical models used to generate the phantoms. We built the gelatin phantoms by first using additive manufacturing to generate a kidney mold based on patient specific CT images, into which the gelatin was poured. We then evaluated the fidelity of the phantoms (i.e., children) against the virtual kidney model generated from the patient specific CT image (i.e., parent) by comparing it to the surface model of the mold and gelatin phantoms (i.e., children) following their CT imaging post-manufacturing using various registration metrics. Our experiments showed a 0.58 ± 0.48 mm surface-to-surface distance between the phantoms and mold models following landmark-based registration, and 0.52 ± 0.40 mm surface-to-surface distance between the phantoms and the mold model following iterative closest point (ICP) registration. These experiments confirm that the described protocol provides a reliable, fast, and cost-effective method for manufacturing faithful patient specific organ emulating gelatin phantoms and can be applied or extended to other image-guided intervention applications.

Exhaled breath condensate identifies metabolic dysregulation in patients with radiation-induced lung injury.

Radiation-induced lung injury (RILI) is a consequence of therapeutic thoracic irradiation (TR) for many cancers, and there are no FDA-approved curative strategies. Studies report that 80% of patients who undergo TR will have CT-detectable interstitial lung abnormalities, and strategies to limit the risk of RILI may make radiotherapy less effective at treating cancer. Our lab and others have reported that lung tissue from patients with idiopathic pulmonary fibrosis (IPF) exhibits metabolic defects including increased glycolysis and lactate production. In this pilot study, we hypothesized that patients with radiation-induced lung damage will exhibit distinct changes in lung metabolism that may be associated with the incidence of fibrosis. Using liquid chromatography/tandem mass spectrometry to identify metabolic compounds, we analyzed exhaled breath condensate (EBC) in subjects with CT-confirmed lung lesions after TR for lung cancer, compared with healthy subjects, smokers, and cancer patients who had not yet received TR. The lung metabolomic profile of the irradiated group was significantly different from the three nonirradiated control groups, highlighted by increased levels of lactate. Pathway enrichment analysis revealed that EBC from the case patients exhibited concurrent alterations in lipid, amino acid, and carbohydrate energy metabolism associated with the energy-producing tricarboxylic acid (TCA) cycle. Radiation-induced glycolysis and diversion of lactate to the extracellular space suggests that pyruvate, a precursor metabolite, converts to lactate rather than acetyl-CoA, which contributes to the TCA cycle. This TCA cycle deficiency may be compensated by these alternate energy sources to meet the metabolic demands of chronic wound repair. Using an "omics" approach to probe lung disease in a noninvasive manner could inform future mechanistic investigations and the development of novel therapeutic targets.NEW & NOTEWORTHY We report that exhaled breath condensate (EBC) identifies cellular metabolic dysregulation in patients with radiation-induced lung injury. In this pilot study, untargeted metabolomics revealed a striking metabolic signature in EBC from patients with radiation-induced lung fibrosis compared to patients with lung cancer, at-risk smokers, and healthy volunteers. Patients with radiation-induced fibrosis exhibit specific changes in tricarboxylic acid (TCA) cycle energy metabolism that may be required to support the increased energy demands of fibroproliferation.

COVID-19 Stay-At-Home Orders and Secondhand Smoke in Public Housing.

INTRODUCTION: This study aimed to better understand the inequitable impact of the pandemic by examining the associations between stay-at-home orders and indoor smoking in public housing, measured by ambient particulate matter at the 2.5-micron threshold, a marker for secondhand smoke. METHODS: Particulate matter at the 2.5-micron threshold was measured in 6 public-housing buildings in Norfolk, VA from 2018 to 2022. Multilevel regression was used to compare the 7-week period of the Virginia stay-at-home order in 2020 with that period in other years. RESULTS: Indoor particulate matter at the 2.5-micron threshold was 10.29 µg/m3 higher in 2020 (95% CI=8.51, 12.07) than in the same period in 2019, a 72% increase. Although particulate matter at the 2.5-micron threshold improved in 2021 and 2022, it remained elevated relative to the level in 2019. CONCLUSIONS: Stay-at-home orders likely led to increased indoor secondhand smoke in public housing. In light of evidence linking air pollutants, including secondhand smoke, with COVID-19, these results also provide further evidence of the disproportionate impact of the pandemic on socioeconomically disadvantaged communities. This consequence of the pandemic response is unlikely to be isolated and calls for a critical examination of the COVID-19 experience to avoid similar policy failures in future public health crises.