Fellow, Stanford University, Infectious Diseases
Residency, Stanford University, Internal Medicine (2018)
Internship, Stanford University, Internal Medicine (2016)
Doctor of Medicine with Honors, University of Washington School of Medicine (2015)
Doctor of Philosophy, University of Washington, Department of Global Health, Pathobiology program, Innate antiviral immunity to HIV-1 (2013)
Bachelor of Science, Stanford University, Biological Sciences (2005)
Progenitor identification and SARS-CoV-2 infection in human distal lung organoids.
The distal lung contains terminal bronchioles and alveoli that facilitate gas exchange. Three-dimensional in vitro human distal lung culture systems would strongly facilitate investigation of pathologies including interstitial lung disease, cancer, and SARS-CoV-2-associated COVID-19 pneumonia. We generated long-term feeder-free, chemically defined culture of distal lung progenitors as organoids derived from single adult human alveolar epithelial type II (AT2) or KRT5+ basal cells. AT2 organoids exhibited AT1 transdifferentiation potential while basal cell organoids developed lumens lined by differentiated club and ciliated cells. Single cell analysis of basal organoid KRT5+ cells revealed a distinct ITGA6+ITGB4+ mitotic population whose proliferation further segregated to a TNFRSF12Ahi subfraction comprising ~10% of KRT5+ basal cells, residing in clusters within terminal bronchioles and exhibiting enriched clonogenic organoid growth activity. Distal lung organoids were created with apical-out polarity to display ACE2 on the exposed external surface, facilitating SARS-CoV-2 infection of AT2 and basal cultures and identifying club cells as a novel target population. This long-term, feeder-free organoid culture of human distal lung, coupled with single cell analysis, identifies unsuspected basal cell functional heterogeneity and establishes a facile in vitro organoid model for human distal lung infections including COVID-19-associated pneumonia.
View details for DOI 10.1038/s41586-020-3014-1
View details for PubMedID 33238290
A single-cell atlas of the peripheral immune response in patients with severe COVID-19.
There is an urgent need to better understand the pathophysiology of Coronavirus disease 2019 (COVID-19), the global pandemic caused by SARS-CoV-2, which has infected more than three million people worldwide1. Approximately 20% of patients with COVID-19 develop severe disease and 5% of patients require intensive care2. Severe disease has been associated with changes in peripheral immune activity, including increased levels of pro-inflammatory cytokines3,4 that may be produced by a subset of inflammatory monocytes5,6, lymphopenia7,8 and T cell exhaustion9,10. To elucidate pathways in peripheral immune cells that might lead to immunopathology or protective immunity in severe COVID-19, we applied single-cell RNA sequencing (scRNA-seq) to profile peripheral blood mononuclear cells (PBMCs) from seven patients hospitalized for COVID-19, four of whom had acute respiratory distress syndrome, and six healthy controls. We identify reconfiguration of peripheral immune cell phenotype in COVID-19, including a heterogeneous interferon-stimulated gene signature, HLA class II downregulation and a developing neutrophil population that appears closely related to plasmablasts appearing in patients with acute respiratory failure requiring mechanical ventilation. Importantly, we found that peripheral monocytes and lymphocytes do not express substantial amounts of pro-inflammatory cytokines. Collectively, we provide a cell atlas of the peripheral immune response to severe COVID-19.
View details for DOI 10.1038/s41591-020-0944-y
View details for PubMedID 32514174
Innate Antiviral Immune Signaling, Viral Evasion and Modulation by HIV-1
JOURNAL OF MOLECULAR BIOLOGY
2014; 426 (6): 1161-1177
The intracellular innate antiviral response in human cells is an essential component of immunity against virus infection. As obligate intracellular parasites, all viruses must evade the actions of the host cell's innate immune response in order to replicate and persist. Innate immunity is induced when pathogen recognition receptors of the host cell sense viral products including nucleic acid as "non-self". This process induces downstream signaling through adaptor proteins to activate latent transcription factors that drive the expression of genes encoding antiviral and immune modulatory effector proteins that restrict virus replication and regulate adaptive immunity. The interferon regulatory factors (IRFs) are transcription factors that play major roles in innate immunity. In particular, IRF3 is activated in response to infection by a range of viruses including RNA viruses, DNA viruses and retroviruses. Among these viruses, human immunodeficiency virus type 1 (HIV-1) remains a major global health problem mediating chronic infection in millions of people wherein recent studies show that viral persistence is linked with the ability of the virus to dysregulate and evade the innate immune response. In this review, we discuss viral pathogen sensing, innate immune signaling pathways and effectors that respond to viral infection, the role of IRF3 in these processes and how it is regulated by pathogenic viruses. We present a contemporary overview of the interplay between HIV-1 and innate immunity, with a focus on understanding how innate immune control impacts infection outcome and disease.
View details for DOI 10.1016/j.jmb.2013.12.003
View details for Web of Science ID 000333487600004
View details for PubMedID 24326250
Two new monoclonal antibodies for biochemical and flow cytometric analyses of human interferon regulatory factor-3 activation, turnover, and depletion
2013; 59 (2): 225-232
Interferon regulatory factor-3 (IRF-3) is a master transcription factor that drives the host intracellular innate immune response to virus infection. The importance of IRF-3 in innate immune responses is highlighted by the fact that pathogenic viruses have developed strategies for antagonism of IRF-3. Several tools exist for evaluation of viral regulation of IRF-3 activation and function, but high-quality monoclonal antibodies that mark the differential activation states of human IRF-3 are lacking. To study IRF-3 activation, turnover, and depletion in a high-throughput manner in the context of virus infection, we have developed two new monoclonal antibodies to human IRF-3. These antibodies detect IRF-3 in virus-infected cells in a wide variety of assays and provide a new tool to study virus-host interactions and innate immune signaling.
View details for DOI 10.1016/j.ymeth.2012.05.011
View details for Web of Science ID 000316651100008
View details for PubMedID 22705311
View details for PubMedCentralID PMC3568209
Occurrence and Timing of Subsequent Severe Acute Respiratory Syndrome Coronavirus 2 Reverse-transcription Polymerase Chain Reaction Positivity Among Initially Negative Patients.
Clinical infectious diseases : an official publication of the Infectious Diseases Society of America
2021; 72 (2): 323–26
Using data for 20 912 patients from 2 large academic health systems, we analyzed the frequency of severe acute respiratory syndrome coronavirus 2 reverse-transcription polymerase chain reaction test discordance among individuals initially testing negative by nasopharyngeal swab who were retested on clinical grounds within 7 days. The frequency of subsequent positivity within this window was 3.5% and was similar across institutions.
View details for DOI 10.1093/cid/ciaa722
View details for PubMedID 33501950
Profiling of the Human Natural Killer Cell Receptor-Ligand Repertoire.
Journal of visualized experiments : JoVE
Natural killer (NK) cells are among the first responders to viral infections. The ability of NK cells to rapidly recognize and kill virally infected cells is regulated by their expression of germline-encoded inhibitory and activating receptors. The engagement of these receptors by their cognate ligands on target cells determines whether the intercellular interaction will result in NK cell killing. This protocol details the design and optimization of two complementary mass cytometry (CyTOF) panels. One panel was designed to phenotype NK cells based on receptor expression. The other panel was designed to interrogate expression of known ligands for NK cell receptors on several immune cell subsets. Together, these two panels allow for the profiling of the human NK cell receptor-ligand repertoire. Furthermore, this protocol also details the process by which we stain samples for CyTOF. This process has been optimized for improved reproducibility and standardization. An advantage of CyTOF is its ability to measure over 40 markers in each panel, with minimal signal overlap, allowing researchers to capture the breadth of the NK cell receptor-ligand repertoire. Palladium barcoding also reduces inter-sample variation, as well as consumption of reagents, making it easier to stain samples with each panel in parallel. Limitations of this protocol include the relatively low throughput of CyTOF and the inability to recover cells after analysis. These panels were designed for the analysis of clinical samples from patients suffering from acute and chronic viral infections, including dengue virus, human immunodeficiency virus (HIV), and influenza. However, they can be utilized in any setting to investigate the human NK cell receptor-ligand repertoire. Importantly, these methods can be applied broadly to the design and execution of future CyTOF panels.
View details for DOI 10.3791/61912
View details for PubMedID 33283785
- Evaluating the Utility of UV Lamps to Mitigate the Spread of Pathogens in the ICU APPLIED SCIENCES-BASEL 2020; 10 (18)
Cytokine profile in plasma of severe COVID-19 does not differ from ARDS and sepsis.
BACKGROUND: Elevated levels of inflammatory cytokines have been associated with poor outcomes among COVID-19 patients. It is unknown, however, how these levels compare to those observed in critically ill patients with ARDS or sepsis due to other causes.METHODS: We used a luminex assay to determine expression of 76 cytokines from plasma of hospitalized COVID-19 patients and banked plasma samples from ARDS and sepsis patients. Our analysis focused on detecting statistical differences in levels of 6 cytokines associated with cytokine storm (IL-1b, IL-1RA, IL-6, IL-8, IL-18, and TNFalpha) between patients with moderate COVID-19, severe COVID-19, and ARDS or sepsis.RESULTS: 15 hospitalized COVID-19 patients, 9 of whom were critically ill, were compared to critically ill patients with ARDS (n = 12) or sepsis (n = 16). There were no statistically significant differences in baseline levels of IL-1b, IL-1RA, IL-6, IL-8, IL-18, and TNFalpha between patients with COVID-19 and critically ill controls with ARDS or sepsis.CONCLUSIONS: Levels of inflammatory cytokines were not higher in severe COVID-19 patients than in moderate COVID-19 or critically ill patients with ARDS or sepsis in this small cohort. Broad use of immunosuppressive therapies in ARDS has failed in numerous Phase 3 studies; use of these therapies in unselected patients with COVID-19 may be unwarranted.FUNDING: A.J.R.: Stanford ICU Biobank NHLBI K23 HL125663. C.A.B.: Burroughs Wellcome Fund Investigators in the Pathogenesis of Infectious Diseases #1016687; NIH/NIAID U19AI057229-16 (PI MM Davis); Stanford Maternal Child Health Research Institute; Chan Zuckerberg Biohub.
View details for DOI 10.1172/jci.insight.140289
View details for PubMedID 32706339
Defining the features and duration of antibody responses to SARS-CoV-2 infection associated with disease severity and outcome.
2020; 5 (54)
SARS-CoV-2-specific antibodies, particularly those preventing viral spike receptor binding domain (RBD) interaction with host angiotensin-converting enzyme 2 (ACE2) receptor, can neutralize the virus. It is, however, unknown which features of the serological response may affect clinical outcomes of COVID-19 patients. We analyzed 983 longitudinal plasma samples from 79 hospitalized COVID-19 patients and 175 SARS-CoV-2-infected outpatients and asymptomatic individuals. Within this cohort, 25 patients died of their illness. Higher ratios of IgG antibodies targeting S1 or RBD domains of spike compared to nucleocapsid antigen were seen in outpatients who had mild illness versus severely ill patients. Plasma antibody increases correlated with decreases in viral RNAemia, but antibody responses in acute illness were insufficient to predict inpatient outcomes. Pseudovirus neutralization assays and a scalable ELISA measuring antibodies blocking RBD-ACE2 interaction were well correlated with patient IgG titers to RBD. Outpatient and asymptomatic individuals' SARS-CoV-2 antibodies, including IgG, progressively decreased during observation up to five months post-infection.
View details for DOI 10.1126/sciimmunol.abe0240
View details for PubMedID 33288645
Human B Cell Clonal Expansion and Convergent Antibody Responses to SARS-CoV-2.
Cell host & microbe
B cells are critical for the production of antibodies and protective immunity to viruses. Here we show that patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) who develop coronavirus disease 2019 (COVID-19) display early recruitment of B cells expressing a limited subset of IGHV genes, progressing to a highly polyclonal response of B cells with broader IGHV gene usage and extensive class switching to IgG and IgA subclasses with limited somatic hypermutation in the initial weeks of infection. We identify convergence of antibody sequences across SARS-CoV-2-infected patients, highlighting stereotyped naive responses to this virus. Notably, sequence-based detection in COVID-19 patients of convergent B cell clonotypes previously reported in SARS-CoV infection predicts the presence of SARS-CoV/SARS-CoV-2 cross-reactive antibody titers specific for the receptor-binding domain. These findings offer molecular insights into shared features of human B cell responses to SARS-CoV-2 and SARS-CoV.
View details for DOI 10.1016/j.chom.2020.09.002
View details for PubMedID 32941787
- Eremothecium coryli bloodstream infection in a patient with acute myeloid leukemia: first case report of human infection DIAGNOSTIC MICROBIOLOGY AND INFECTIOUS DISEASE 2019; 95 (1): 77–79
Deltex2 represses MyoD expression and inhibits myogenic differentiation by acting as a negative regulator of Jmjd1c
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2017; 114 (15): E3071-E3080
The myogenic regulatory factor MyoD has been implicated as a key regulator of myogenesis, and yet there is little information regarding its upstream regulators. We found that Deltex2 inhibits myogenic differentiation in vitro, and that skeletal muscle stem cells from Deltex2 knockout mice exhibit precocious myogenic differentiation and accelerated regeneration in response to injury. Intriguingly, Deltex2 inhibits myogenesis by suppressing MyoD transcription, and the Deltex2 knockout phenotype can be rescued by a loss-of-function allele for MyoD In addition, we obtained evidence that Deltex2 regulates MyoD expression by promoting the enrichment of histone 3 modified by dimethylation at lysine 9 at a key regulatory region of the MyoD locus. The enrichment is attributed to a Deltex2 interacting protein, Jmjd1c, whose activity is directly inhibited by Deltex2 and whose expression is required for MyoD expression in vivo and in vitro. Finally, we find that Deltex2 causes Jmjd1c monoubiquitination and inhibits its demethylase activity. Mutation of the monoubiquitination site in Jmjd1c abolishes the inhibitory effect of Deltex2 on Jmjd1c demethylase activity. These results reveal a mechanism by which a member of the Deltex family of proteins can inhibit cellular differentiation, and demonstrate a role of Deltex in the epigenetic regulation of myogenesis.
View details for DOI 10.1073/pnas.1613592114
View details for Web of Science ID 000398789800012
View details for PubMedID 28351977
Vpu Mediates Depletion of Interferon Regulatory Factor 3 during HIV Infection by a Lysosome-Dependent Mechanism
JOURNAL OF VIROLOGY
2012; 86 (16): 8367-8374
HIV has evolved sophisticated mechanisms to avoid restriction by intracellular innate immune defenses that otherwise serve to control acute viral infection and virus dissemination. Innate defenses are triggered when pattern recognition receptor (PRR) proteins of the host cell engage pathogen-associated molecule patterns (PAMPs) present in viral products. Interferon regulatory factor 3 (IRF3) plays a central role in PRR signaling of innate immunity to drive the expression of type I interferon (IFN) and interferon-stimulated genes (ISGs), including a variety of HIV restriction factors, that serve to limit viral replication directly and/or program adaptive immunity. Productive infection of T cells by HIV is dependent upon the targeted proteolysis of IRF3 that occurs through a virus-directed mechanism that results in suppression of innate immune defenses. However, the mechanisms by which HIV controls innate immune signaling and IRF3 function are not defined. Here, we examined the innate immune response induced by HIV strains identified through their differential control of PRR signaling. We identified viruses that, unlike typical circulating HIV strains, lack the ability to degrade IRF3. Our studies show that IRF3 regulation maps specifically to the HIV accessory protein Vpu. We define a molecular interaction between Vpu and IRF3 that redirects IRF3 to the endolysosome for proteolytic degradation, thus allowing HIV to avoid the innate antiviral immune response. Our studies reveal that Vpu is an important IRF3 regulator that supports acute HIV infection through innate immune suppression. These observations define the Vpu-IRF3 interface as a novel target for therapeutic strategies aimed at enhancing the immune response to HIV.
View details for DOI 10.1128/JVI.00423-12
View details for Web of Science ID 000307198300003
View details for PubMedID 22593165
HIV infection of dendritic cells subverts the IFN induction pathway via IRF-1 and inhibits type 1 IFN production
2011; 118 (2): 298-308
Many viruses have developed mechanisms to evade the IFN response. Here, HIV-1 was shown to induce a distinct subset of IFN-stimulated genes (ISGs) in monocyte-derived dendritic cells (DCs), without detectable type I or II IFN. These ISGs all contained an IFN regulatory factor 1 (IRF-1) binding site in their promoters, and their expression was shown to be driven by IRF-1, indicating this subset was induced directly by viral infection by IRF-1. IRF-1 and -7 protein expression was enriched in HIV p24 antigen-positive DCs. A HIV deletion mutant with the IRF-1 binding site deleted from the long terminal repeat showed reduced growth kinetics. Early and persistent induction of IRF-1 was coupled with sequential transient up-regulation of its 2 inhibitors, IRF-8, followed by IRF-2, suggesting a mechanism for IFN inhibition. HIV-1 mutants with Vpr deleted induced IFN, showing that Vpr is inhibitory. However, HIV IFN inhibition was mediated by failure of IRF-3 activation rather than by its degradation, as in T cells. In contrast, herpes simplex virus type 2 markedly induced IFNβ and a broader range of ISGs to higher levels, supporting the hypothesis that HIV-1 specifically manipulates the induction of IFN and ISGs to enhance its noncytopathic replication in DCs.
View details for DOI 10.1182/blood-2010-07-297721
View details for Web of Science ID 000292735100015
View details for PubMedID 21411754
Enhanced gene repair mediated by methyl-CpG-modified single-stranded oligonucleotides
NUCLEIC ACIDS RESEARCH
2009; 37 (22): 7468-7482
Gene editing mediated by oligonucleotides has been shown to induce stable single base alterations in genomic DNA in both prokaryotic and eukaryotic organisms. However, the low frequencies of gene repair have limited its applicability for both basic manipulation of genomic sequences and for the development of therapeutic approaches for genetic disorders. Here, we show that single-stranded oligodeoxynucleotides (ssODNs) containing a methyl-CpG modification and capable of binding to the methyl-CpG binding domain protein 4 (MBD4) are able to induce >10-fold higher levels of gene correction than ssODNs lacking the specific modification. Correction was stably inherited through cell division and was confirmed at the protein, transcript and genomic levels. Downregulation of MBD4 expression using RNAi prevented the enhancement of gene correction efficacy obtained using the methyl-CpG-modified ssODN, demonstrating the specificity of the repair mechanism being recruited. Our data demonstrate that efficient manipulation of genomic targets can be achieved and controlled by the type of ssODN used and by modulation of the repair mechanism involved in the correction process. This new generation of ssODNs represents an important technological advance that is likely to have an impact on multiple applications, especially for gene therapy where permanent correction of the genetic defect has clear advantages over viral and other nonviral approaches currently being tested.
View details for DOI 10.1093/nar/gkp757
View details for Web of Science ID 000272935000020
View details for PubMedID 19854937
View details for PubMedCentralID PMC2794159
- Enhanced Level of Gene Correction Mediated by Oligonucleotides Containing CpG Modification in the mdx Mouse Model for Duchenne Muscular Dystrophy NATURE PUBLISHING GROUP. 2006: S221
An inwardly rectifying potassium channel in apical membrane of Calu-3 cells
JOURNAL OF BIOLOGICAL CHEMISTRY
2004; 279 (45): 46558-46565
Patch clamp methods and reverse transcription-polymerase chain reaction (RT-PCR) were used to characterize an apical K+ channel in Calu-3 cells, a widely used model of human airway gland serous cells. In cell-attached and excised apical membrane patches, we found an inwardly rectifying K+ channel (Kir). The permeability ratio was PNa/PK = 0.058. In 30 patches with both cystic fibrosis transmembrane conductance regulator and Kir present, we observed 79 cystic fibrosis transmembrane conductance regulator and 58 Kir channels. The average chord conductance was 24.4 +/- 0.5 pS (n = 11), between 0 and -200 mV, and was 9.6 +/- 0.7 pS (n = 8), between 0 and 50 mV; these magnitudes and their ratio of approximately 2.5 are most similar to values for rectifying K+ channels of the Kir4.x subfamilies. We attempted to amplify transcripts for Kir4.1, Kir4.2, and Kir5.1; of these only Kir4.2 was present in Calu-3 lysates. The channel was only weakly activated by ATP and was relatively insensitive to internal pH. External Cs+ and Ba2+ blocked the channel with Kd values in the millimolar range. Quantitative modeling of Cl- secreting epithelia suggests that secretion rates will be highest and luminal K+ will rise to 16-28 mm if 11-25% of the total cellular K+ conductance is placed in the apical membrane (Cook, D. I., and Young, J. A. (1989) J. Membr. Biol. 110, 139-146). Thus, we hypothesize that the K+ channel described here optimizes the rate of secretion and is involved in K+ recycling for the recently proposed apical H+ -K+ -ATPase in Calu-3 cells.
View details for DOI 10.1074/jbc.M406058200
View details for Web of Science ID 000224832400028
View details for PubMedID 15328350
Regulation of antiprotease and antimicrobial protein secretion by airway submucosal gland serous cells
JOURNAL OF BIOLOGICAL CHEMISTRY
2004; 279 (37): 38854-38860
Airway submucosal gland serous cells express the cystic fibrosis transmembrane conductance regulator (CFTR) and secrete antimicrobial, anti-inflammatory, and antioxidant molecules. In cystic fibrosis, diminished gland secretion may impair innate airway host defenses. We used Calu-3 cells as a serous cell model to study the types of proteins released, the pathways that release them, and the possible involvement of CFTR activity in protein release. Many proteins were secreted constitutively into the apical fluid and showed increased release to agonists. We identified some of them by high pressure liquid chromatography-mass spectrometry and reverse transcriptase PCR, including lysozyme, siderocalin (the protein NGAL), which inhibits bacterial growth by binding iron-containing siderophores, HSC-71, which is thought to have anti-inflammatory properties, and the serine protease inhibitors alpha-1-antitrypsin and alpha-1-antichymotrypsin, which may function as antimicrobials as well as play a potential role in diminishing the activation of epithelial Na(+) channels by serine proteases. We used an enzyme-linked immunosorbent assay to quantify lysozyme secretion by Calu-3 cells in response to various agonists and inhibitors. Forskolin increased the lysozyme secretion rate (J(lyz)) from 32 to 77 ng/hr/cm(2) (n = 36, p < 0.005). Thapsigargin increased J(lyz) from 40 to 63 ng/h/cm(2) (n = 16, p < 0.005), and forskolin plus thapsigargin further increased the forskolin-stimulated J(lyz) by 48% (n = 9, p < 0.05). 1-Ethyl-benzimidazolinone and carbachol were less effective. Glibenclamide inhibited basal and stimulated J(lyz), but clotrimazole was without effect. CFTR(inh)172 caused a small (15%) but significant inhibition of forskolin-stimulated J(lyz) without affecting basal J(lyz). Thus, Calu-3 cells secrete diverse proteins that in aggregate would be expected to suppress microbial growth, protect the airways from damage, and limit the activation of epithelial Na(+) channels via serine proteases.
View details for DOI 10.1074/jbc.M407077200
View details for Web of Science ID 000223684100098
View details for PubMedID 15234967