Monocyte Production of C1q Potentiates CD8+ T Cell Function Following Respiratory Viral Infection

Respiratory viral infections remain a leading cause of morbidity and mortality. Using a murine model of human metapneumovirus (HMPV), we identified recruitment of a C1q-expressing inflammatory monocyte population concomitant with viral clearance by adaptive immune cells. Genetic ablation of C1q led to reduced CD8+ T cell function. Production of C1q by a myeloid lineage was necessary to enhance CD8+ T cell function. Activated and dividing CD8+ T cells expressed a C1q receptor, gC1qR. Perturbation of gC1qR signaling led to altered CD8+ T cell IFN-γ production, metabolic capacity, and cell proliferation. Autopsy specimens from fatal respiratory viral infections in children demonstrated diffuse production of C1q by an interstitial population. Humans with severe COVID-19 infection also demonstrated upregulation of gC1qR on activated and rapidly dividing CD8+ T cells. Collectively, these studies implicate C1q production from monocytes as a critical regulator of CD8+ T cell function following respiratory viral infection. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Do Not Throw Away Your Shot: Pilot Study in Improving Medical School Curricula Through Focused Vaccine Education

Introduction

With widely prevalent vaccine hesitancy and medical mistrust, future healthcare providers require knowledge of vaccines and comfort in discussing vaccines with patients. However, many U.S. medical schools do not offer formal or elective curricula focused on vaccine education.

Methods

We sought to identify the need for such a curriculum and student gaps in knowledge through a pilot study surveying first- and second-year medical students at a large Pennsylvania medical school to assess knowledge about vaccine initiatives/policies, comfort in discussing vaccines, attitudes toward curricular changes, and effects of COVID-19 on willingness for vaccine education.

Results

Many participants (>40%) reported insufficient knowledge of vaccine policy, vaccine development and testing, and community vaccine initiatives. The majority (>50%) indicated discomfort in discussing vaccines in a clinical setting. Importantly, 79% of participants reported insufficient coverage of vaccine topics in the current curriculum. A total of 54% decisively wanted formal/mandatory education versus 72% who decisively wanted elective education. Desiring formal education was associated with less comfort in discussing vaccines overall and with vaccine-hesitant people in clinical settings. Reassuringly, 74% of participants noted that the COVID-19 pandemic made them want to learn more about vaccines. Guided by these findings, we conducted a pilot elective teaching about vaccines through case studies, interactive discussions, and role-playing scenarios. Pre- and postcourse surveys showed improvement in student knowledge in all vaccine-related topics assessed.

Conclusions

These data can inform the development of formal and elective curricula that effectively prepare medical students for patients' vaccine questions.

IFN-λ drives distinct lung immune landscape changes and antiviral responses in human metapneumovirus infection

Human metapneumovirus (HMPV) is a primary cause of acute respiratory infection, yet there are no approved vaccines or antiviral therapies for HMPV. Early host responses to HMPV are poorly characterized, and further understanding could identify important antiviral pathways. Type III interferon (IFN-λ) displays potent antiviral activity against respiratory viruses and is being investigated for therapeutic use. However, its role in HMPV infection remains largely unknown. Here, we show that IFN-λ is highly upregulated during HMPV infection in vitro in human and mouse airway epithelial cells and in vivo in mice. We found through several immunological and molecular assays that type II alveolar cells are the primary producers of IFN-λ. Using mouse models, we show that IFN-λ limits lung HMPV replication and restricts virus spread from upper to lower airways but does not contribute to clinical disease. Moreover, we show that IFN-λ signaling is predominantly mediated by CD45- non-immune cells. Mice lacking IFN-λ signaling showed diminished loss of ciliated epithelial cells and decreased recruitment of lung macrophages in early HMPV infection along with higher inflammatory cytokine and interferon-stimulated gene expression, suggesting that IFN-λ may maintain immunomodulatory responses. Administration of IFN-λ for prophylaxis or post-infection treatment in mice reduced viral load without inflammation-driven weight loss or clinical disease. These data offer clinical promise for IFN-λ in HMPV treatment.

IMPORTANCE

Human metapneumovirus (HMPV) is a common respiratory pathogen and often contributes to severe disease, particularly in children, immunocompromised people, and the elderly. There are currently no licensed HMPV antiviral treatments or vaccines. Here, we report novel roles of host factor IFN-λ in HMPV disease that highlight therapeutic potential. We show that IFN-λ promotes lung antiviral responses by restricting lung HMPV replication and spread from upper to lower airways but does so without inducing lung immunopathology. Our data uncover recruitment of lung macrophages, regulation of ciliated epithelial cells, and modulation of inflammatory cytokines and interferon-stimulated genes as likely contributors. Moreover, we found these roles to be distinct and non-redundant, as they are not observed with knockout of, or treatment with, type I IFN. These data elucidate unique antiviral functions of IFN-λ and suggest IFN-λ augmentation as a promising therapeutic for treating HMPV disease and promoting effective vaccine responses.

Distinct roles for type I and type III interferons in virulent human metapneumovirus pathogenesis

Human metapneumovirus (HMPV) is an important cause of acute lower respiratory infection in children and adults worldwide. There are four genetic subgroups of HMPV and both neutralizing antibodies and T cells contribute to protection. However, little is known about mechanisms of pathogenesis and most published work is based on a few extensively passaged, laboratory-adapted strains of HMPV. In this study, we isolated and characterized a panel of low passage HMPV clinical isolates representing all four genetic subgroups. The clinical isolates exhibited lower levels of in vitro replication compared to a lab-adapted strain. We compared disease phenotypes using a well-established mouse model. Several virulent isolates caused severe weight loss, lung pathology, airway dysfunction, and fatal disease in mice, which was confirmed in three inbred mouse strains. Disease severity did not correlate with lung viral titer, as virulent strains exhibited restricted replication in the lower airway. Virulent HMPV isolates were associated with markedly increased proinflammatory cytokine production and neutrophil influx; however, depletion of neutrophils or genetic ablation of inflammasome components did not reverse disease. Virulent clinical isolates induced markedly increased type I and type III interferon (IFN) secretion in vitro and in vivo. STAT1/2-deficient mice lacking both type I and type III IFN signaling showed reduced disease severity and increased lung viral replication. Inhibition of type I IFN signaling using a blocking antibody or genetic ablation of the type I IFN receptor reduced pathology with minimal effect on viral replication. Conversely, blockade of type III IFN signaling with a neutralizing antibody or genetic ablation of the IFN-lambda receptor had no effect on pathogenesis but restored viral replication. Collectively, these results demonstrate distinct roles for type I and type III IFN in HMPV pathogenesis and immunity.

Clinical human metapneumovirus isolates show distinct pathogenesis and inflammatory profiles but similar CD8+ T cell impairment

Human metapneumovirus (HMPV) is a negative-sense single-stranded RNA virus in the Pneumoviridae family and a leading cause of acute upper and lower respiratory infections, particularly in children, immunocompromised patients, and the elderly. Although nearly every person is infected with HMPV during early childhood, re-infections occur often, highlighting difficulty in building long-term immunity. Inflammatory responses, including PD-1-mediated impairment of virus-specific CD8+ T cells (TCD8), contribute to HMPV disease severity. HMPV strains are divided into four lineages: A1, A2, B1, and B2. However, little is known about immune responses to different viral subtypes. Here, we characterize responses to four HMPV clinical isolates-TN/94-344 (A1), TN/94-49 (A2), C2-202 (B1), and TN/96-35 (B2)-in vivo in C57BL/6 (B6) mice. TN/94-49 was avirulent, while TN/94-344, C2-202, and TN/96-35 showed varying degrees of weight loss and clinical disease. Differences in disease did not correlate to virus burden in upper or lower tracts. TN/94-49 HMPV exhibited highest nose titers and delayed lung clearance. Cytokine profiles differed between HMPV isolates, with TN/96-35 inducing the broadest lung inflammatory cytokines. TN/96-35 also showed lower HMPV burden and less weight loss than other virulent isolates, suggesting a more efficient antiviral response. Interestingly, disease correlated with higher expression of T-cell chemoattractant CXCL9. All isolates elicited PD-1 upregulation and decreased IFNγ and CD107a expression in virus-specific TCD8, with little difference between HMPV subtypes. This work uncovers previously uncharacterized variations in immune responses to clinical HMPV isolates of different lineages.IMPORTANCEThis study extensively explored differences in T-cell-mediated immunity between human metapneumovirus (HMPV) clinical isolates. Much existing HMPV research has been done with strains passaged extensively in cell lines, likely acquiring mutations advantageous to in vitro replication. Clinical isolates are collected directly from human patients and have undergone <10 passages, serving as more physiologically relevant models of HMPV infection. Additionally, existing animal studies of HMPV disease mainly focus on lung pathogenesis, while HMPV infects both upper and lower airways of humans. This work highlights distinct differences in HMPV burden in upper and lower tracts between clinical isolates. Lastly, this study uniquely explores differences in host immunity between all four HMPV genetic lineages. The predominant HMPV subtype in circulation varies seasonally; thus, understanding host responses to all subgroups is critical for developing effective HMPV vaccines.

A Cross-Sectional Analysis of Community Perceptions of Flu and COVID-19 Vaccines at Turtle Creek Primary Care Center

BACKGROUND

Influenza (flu) and COVID-19 vaccination rates are subpar across the US, especially in racial and/or socioeconomic minority groups who are understudied in public health literature.

OBJECTIVE

The objective of this mixed-methods study was to elucidate attitudes of patients at the Turtle Creek Primary Care Center, a clinic that cares for ∼70% non-white patients, towards flu and COVID-19 vaccines, with the goal of establishing vaccine education gaps and increasing vaccine uptake in minority communities.

DESIGN/PATIENTS

This study was conducted as a cross-sectional analysis. Authors completed 123 patient phone surveys of patients cared for at the Turtle Creek clinic inquiring about flu and COVID-19 infection status and vaccination uptake (August 26-October 10, 2021).

APPROACH/KEY RESULTS

We found that rates of vaccination were subpar in the Turtle Creek community, with only 54% having received the COVID-19 vaccine and only 44% receiving the flu vaccine regularly. There was a strong association between COVID-19 and flu vaccine acceptance and a notable correlation between vaccine acceptance and age. When assessing how vaccine acceptance was influenced by trusted sources of information, those who cited trusting "medical professionals" and "word of mouth" had higher odds of COVID-19 vaccine acceptance but those who cited trusting "social media" had decreased odds of acceptance. Finally, we uncovered 14 common factors for either vaccine acceptance or refusal that clustered into four overarching themes of trust, need, safety, and availability.

CONCLUSION

These data highlight the necessity of improved vaccine education and reveal targetable populations and approaches for disseminating vaccine information.

Terminally exhausted CD8+ T cells contribute to age-dependent severity of respiratory virus infection

BACKGROUND

Lower respiratory infections are a leading cause of severe morbidity and mortality among older adults. Despite ubiquitous exposure to common respiratory pathogens throughout life and near universal seropositivity, antibodies fail to effectively protect the elderly. Therefore, we hypothesized that severe respiratory illness in the elderly is due to deficient CD8⁺ T cell responses.

RESULTS

Here, we establish an aged mouse model of human metapneumovirus infection (HMPV) wherein aged C57BL/6 mice exhibit worsened weight loss, clinical disease, lung pathology and delayed viral clearance compared to young adult mice. Aged mice generate fewer lung-infiltrating HMPV epitope-specific CD8⁺ T cells. Those that do expand demonstrate higher expression of PD-1 and other inhibitory receptors and are functionally impaired. Transplant of aged T cells into young mice and vice versa, as well as adoptive transfer of young versus aged CD8⁺ T cells into Rag1^-/- recipients, recapitulates the HMPV aged phenotype, suggesting a cell-intrinsic age-associated defect. HMPV-specific aged CD8⁺ T cells exhibit a terminally exhausted TCF1/7^- TOX⁺ EOMES⁺ phenotype. We confirmed similar terminal exhaustion of aged CD8⁺ T cells during influenza viral infection.

CONCLUSIONS

This study identifies terminal CD8⁺ T cell exhaustion as a mechanism of severe disease from respiratory viral infections in the elderly.

Monocyte production of C1q potentiates CD8 + T cell effector function following respiratory viral infection

Respiratory viral infections remain a leading cause of morbidity and mortality. Using a murine model of human metapneumovirus (HMPV), we identified recruitment of a C1q-producing inflammatory monocyte population concomitant with viral clearance by adaptive immune cells. Genetic ablation of C1q led to reduced CD8 ⁺ T cell function. Production of C1q by a myeloid lineage was sufficient to enhance CD8 ⁺ T cell function. Activated and dividing CD8 ⁺ T cells expressed a putative C1q receptor, gC1qR. Perturbation of gC1qR signaling led to altered CD8 ⁺ T cell IFN-γ production and metabolic capacity. Autopsy specimens from fatal respiratory viral infections in children demonstrated diffuse production of C1q by an interstitial population. Humans with severe COVID-19 infection also demonstrated upregulation of gC1qR on activated and rapidly dividing CD8 ⁺ T cells. Collectively, these studies implicate C1q production from monocytes as a critical regulator of CD8 ⁺ T cell function following respiratory viral infection.

A Cross-Sectional Factor Analysis of COVID-19 and Influenza Vaccination Decisions in a Racially Diverse Western Pennsylvania Community

INTRODUCTION

Influenza and COVID-19 vaccination rates remain suboptimal, demanding new community-centric approaches that improve targeted counseling and increase vaccine uptake. Notably, racially diverse communities show high vaccine hesitancy, yet most existing vaccine studies focus on white, college-educated cohorts.

OBJECTIVE

Here, we identify factors influencing vaccination decisions of patients at Turtle Creek Primary Care clinic in Turtle Creek, PA, a racially-diverse borough.

DESIGN

A retrospective mixed-methods study of the predominantly non-white patient population at Turtle Creek Primary Care clinic, a clinic caring for >70% minority patients.

RESULTS

Fourteen factors emerged that patients reported were crucial to vaccine decision-making. Of these factors, top reasons for COVID-19 vaccine hesitancy were trust in vaccines, vaccine side effects, perceived vaccine knowledge, and faith/religion. Top reasons for influenza vaccine hesitancy were perceived need, vaccine side effects, trust in vaccines, and habitual behaviors. We also uncovered correlations between vaccine decision factors and sociodemographic factors. Participants > 65-years-old were more likely to cite personal safety in choosing to get the COVID-19 vaccine, while non-white participants were more likely to cite others' safety. Participants > 65-years-old were also more likely to cite personal safety in influenza vaccine decision-making, and non-female participants were more likely to cite perceived need for influenza vaccines.

CONCLUSIONS

These data uncover targetable factors contributing to vaccine hesitancy and aid in developing community-centered, personalized vaccine education approaches in Turtle Creek and analogous minority communities.

CD8+ T cell impairment drives severe human metapneumovirus respiratory disease in aged mice

Objective

Human metapneumovirus (HMPV) is a leading cause of severe respiratory disease in children &lt;5, adults &gt;65, and the immunocompromised. CD8+ T lymphocytes are the primary cell responsible for clearing HMPV infection in the lung. We tested the hypothesis that CD8+ T cell impairment in the aged host drives severe respiratory infection and delayed viral clearance.

Methods

B6 aged 72–73wk mice and young 6–7wk mice were infected with 2×106 PFU HMPV. Seven days post infection, mice were euthanized and lung, bronchoalveolar lavage (BAL), spleen, and draining lymph nodes were collected for flow cytometry. Lung and BAL supernatant was collected for viral titer, histology, and cytokine measurement.

Results

Aged mice lost more weight, had delayed viral clearance, and increased clinical scores and lung histopathology. Aged mice produced fewer HMPV-tetramer+ cells in lung and BAL. Aged CD8+ T lymphocytes in BAL co-expressed inhibitory receptors PD-1, TIM-3, LAG-3, and 2B4. Aged CD8+ T lymphocytes also upregulated senescence markers, T-bet and EOMES. Upon ex vivo peptide stimulation, aged CD8+ T cells produced significantly less granzyme B compared to young CD8+ T cells. Adoptive transfer of young T cells into aged mice rescued this severe disease phenotype. Young CD8+ cells in the aged host produced more tetramer+ cells and granzyme B and had less senescent marker expression.

Conclusion

Aged mice exhibit more severe respiratory disease when infected with HMPV. Aged CD8+ T cells appear to be impaired and upregulate senescence markers that contribute to severe HMPV infection in the aged host.

Supported by: NIH/NIAID 5R01 AI085062-09, John V. Williams, MD  NIH T32GM008208 Medical Scientist Training Program, University of Pittsburgh School of Medicine  

Identification and Characteristics of HLA-restricted HMPV-specific CD8+ T cells

Human metapneumovirus (HMPV) is a leading cause of respiratory tract infection in pediatric, elderly, and immunocompromised populations. All individuals have been exposed to HMPV by the age of 5, but humoral immunity does not fully protect against reinfection of adults. Despite the clinical burden, there are currently no FDA-approved vaccines or therapeutics for HMPV. T cell responses are important for protection and viral clearance. The aim of this study was to better understand the human T cell response to HMPV and guide vaccine development. To accomplish these goals, we sought to identify HLA class I-restricted viral epitopes. In this study, 5 transgenic mouse strains that express human HLA-A*01:03, HLA-A*24:01, HLA-B*35:01, HLA-B*15:02, or HLA-Cw*07:01 were used to map HMPV-specific epitopes and characterize HMPV-specific CD8+ T cells. We used ELISpot screening of overlapping peptides and predictopes to discover several epitopes and generate MHC-I tetramers for each genetic background. We found that human CD8+ T cells of subjects expressing the same HLA types could recognize viral epitopes by ELISpot and tetramer staining. Our results suggest that the transgenic mouse is a useful model to identify HLA-restricted viral-specific epitopes and novel targets for vaccination against HMPV.

Supported by grants from NIH (R01 AI085062)

Reovirus infection is regulated by NPC1 and endosomal cholesterol homeostasis

Cholesterol homeostasis is required for the replication of many viruses, including Ebola virus, hepatitis C virus, and human immunodeficiency virus-1. Niemann-Pick C1 (NPC1) is an endosomal-lysosomal membrane protein involved in cholesterol trafficking from late endosomes and lysosomes to the endoplasmic reticulum. We identified NPC1 in CRISPR and RNA interference screens as a putative host factor for infection by mammalian orthoreovirus (reovirus). Following internalization via clathrin-mediated endocytosis, the reovirus outer capsid is proteolytically removed, the endosomal membrane is disrupted, and the viral core is released into the cytoplasm where viral transcription, genome replication, and assembly take place. We found that reovirus infection is significantly impaired in cells lacking NPC1, but infection is restored by treatment of cells with hydroxypropyl-β-cyclodextrin, which binds and solubilizes cholesterol. Absence of NPC1 did not dampen infection by infectious subvirion particles, which are reovirus disassembly intermediates that bypass the endocytic pathway for infection of target cells. NPC1 is not required for reovirus attachment to the plasma membrane, internalization into cells, or uncoating within endosomes. Instead, NPC1 is required for delivery of transcriptionally active reovirus core particles from endosomes into the cytoplasm. These findings suggest that cholesterol homeostasis, ensured by NPC1 transport activity, is required for reovirus penetration into the cytoplasm, pointing to a new function for NPC1 and cholesterol homeostasis in viral infection.

Genetic screens are useful strategies to identify host factors required for viral infection. NPC1 was identified in independent CRISPR and RNA interference screens as a putative host factor required for reovirus replication. We discovered that NPC1-mediated cholesterol transport is dispensable for reovirus attachment, internalization, and disassembly but required for penetration of the viral disassembly intermediate from late endosomes into the cytoplasm. These findings uncover an essential function for cholesterol in the entry of reovirus and raise the possibility that cholesterol homeostasis regulates the entry of other viruses that penetrate late endosomes to initiate replication.