Biology subjects

Michailidis, E.

Publications and source records attributed to Michailidis, E..

At least 19 recordsLinked to original sources

bioRxiv2026

A novel proviral mechanism for the ISG, Shiftless, during human coronavirus infection

As highly pathogenic human coronaviruses continue to emerge from zoonotic sources, understanding how host intrinsic immune responses control infection is critical for preventing severe disease. The interferon (IFN) pathway induces antiviral effectors, including the interferon-stimulated gene (ISG) Shiftless (SHFL), which restricts -1 programmed ribosomal frameshifting during SARS-CoV-2 infection. Here, we investigate a novel proviral mechanism for SHFL using loss-of-function and gain-of-function approaches. Despite its established antiviral activity, SHFL enhanced infection by SARS-CoV-2 and the seasonal coronavirus HCoV-229E by increasing cellular susceptibility to infection. SHFL further promoted coronavirus infection by reducing cellular sensitivity to IFN, potentially through modulation of JAK/STAT signaling. Finally, we demonstrate that SHFL-mediated enhancement of baseline viral susceptibility is partially dependent on the domain previously implicated in its antiviral inhibition of -1 programmed ribosomal frameshifting. In contrast, SHFL-mediated regulation of IFN signaling is independent of this domain. Together, these findings establish SHFL as a dual-function ISG with distinct proviral and antiviral activities, highlighting the complex roles of innate immune effectors during coronavirus infection.

microbiology↗

bioRxiv2026

Genetic accessibility, not superior fitness, determines which anti-HBs antibody escape variants are selected in patients

Background and Aims: Genetic diversity within the hepatitis B virus (HBV) surface antigen (HBsAg) drives the emergence of immune escape variants, but studying this diversity in vivo has been limited by the difficulty of establishing infection from patient isolates. We aimed to perform unbiased in vivo screening of variants in the HBs antigenic loop for antibody escape and fitness, using synthetic DNA launch of HBV in human hepatocyte chimeric mice. Approach and Results: Direct intrahepatic injection (IHI) of barcoded, recombinant cccDNA established infection from up to 32,000 independent launch events of a genotype A strain and successfully launched clinical consensus sequences across the major genotypes. Using IHI, we performed deep mutational scanning of 4,608 codon variants across the HBs antigenic loop. Under control antibody treatment, diverse variants expanded, revealing differences in variant fitness in the absence of adaptive immune pressure. Anti-HBs monoclonal antibody treatment suppressed wild-type viremia while permitting breakthrough of resistant variants from the library. Sequencing identified strong enrichment for substitutions at G145 (G145Q, G145H, G145R). Notably, G145Q, rather than the clinically dominant G145R, showed the greatest fitness advantage, indicating that G145R's clinical prevalence does not reflect superior intrinsic fitness. Conclusions: Unbiased in vivo screening reveals that clinically observed HBV escape mutations reflect which substitutions are genetically accessible by single nucleotide change and compatible with the overlapping polymerase reading frame, rather than which confer optimal fitness. This approach establishes a platform for high-resolution mapping of viral variant fitness under antiviral selection pressure.

microbiology↗

bioRxiv2026

The HBV basal core promoter mutation confers a replicative advantage and transcriptionally reprograms hepatocytes toward HCC subtypes

Background: Hepatitis B virus (HBV) basal core promoter (BCP) and precore (PC) mutations occur during chronic HBV infection with the BCP-mutant being associated with increased hepatocellular carcinoma (HCC) risk. Objectives: The effects of these mutants on viral replication, hepatocyte biology, and carcinogenesis remain poorly defined. To address this, we characterized BCP- and PC-mutants using human hepatocyte chimeric mice and asked whether the resulting infection-induced transcriptomes correspond to subsets of human HBV-related hepatocellular carcinomas (HBV-HCCs). Design: Isogenic wild-type (WT), BCP- and PC-mutants of HBV genotypes A, C, and D (HBV-A, -C, -D) were generated from recombinant covalently-closed circular DNA to infect chimeric mice. HBV-HCC transcriptomic datasets from The Cancer Genome Atlas (TCGA) were used to stratify association of HBV variants with HCC subtypes. Results: WT, BCP-mutant, and PC-mutant HBV sequences remained genetically stable. The BCP mutation, but not the PC mutation, accelerated the rise in serum viremia in HBV-D- and HBV-A-infected chimeras; in HBV-C, acceleration required both (PC+BCP) mutations. Further comparisons of HBV-D variants revealed that the BCP-mutant increased intrahepatic viral DNA, viral protein expression, and upregulated cancer-related pathways, including transcripts associated with a subset of HBV-HCCs. Analysis of HBV-HCC samples from the TCGA revealed that tumors often harbor a mixture of WT and mutant transcripts, and that WT- and BCP-mutant-associated HCCs exhibit distinct transcriptional profiles. Conclusions: The HBV BCP-mutant directly perturbs hepatocyte homeostasis via virus-intrinsic mechanisms, selectively activating cancer-related pathways and defining a molecularly distinct subset of HBV-HCC. These findings suggest that HBV variants form distinct subcategories of HBV-HCCs.

molecular biology↗

bioRxiv2026

A CRISPR-Cas9 platform for primary human hepatocytes enables arrayed screening and in vivo validation of HBV host factors

More than two million deaths annually are attributed to liver-related conditions, making primary human hepatocytes (PHH) an invaluable in vitro model for studying liver pathophysiology and the molecular mechanisms underlying hepatic diseases. However, because PHH do not proliferate in culture, CRISPR gene editing has been highly inefficient. Here, we report lipofection- and lentivirus-mediated protocols for CRISPR-Cas9 delivery in mouse-passaged primary human hepatocytes (mpPHH), a system that enables PHH expansion in liver-humanized mice. We achieve robust gene editing efficiencies exceeding 90% in mpPHH while maintaining cell viability. We demonstrate the utility of these protocols by disrupting CYP3A4 to impair xenobiotic metabolism and by showing that edited mpPHH efficiently engraft and expand in mice, generating liver-humanized animals. We establish the feasibility of arrayed CRISPR screening in mpPHH using an 85-gene screen to identify host factors influencing hepatitis B virus (HBV) infection, and validate key findings in humanized mice by targeting the HBV entry receptor SLC10A1 (NTCP), which reduced viral infection in vivo. Our methodology enables scalable genetic manipulation of mpPHH, opening new avenues for HBV research and liver disease modeling.

genomics↗

bioRxiv2026

Orthogonal CRISPR screens and human liver chimeric mice identify hepatitis B virus host factors

Hepatitis B virus (HBV) chronically infects approximately 250 million people worldwide, and reliable curative therapies are lacking. A broader understanding of viral-host interactions could accelerate efforts to find new host-centric therapeutic targets. However, inefficient cell culture systems and limited replication markers compatible with pooled screening have precluded the widespread use of genetic perturbation screens. Here, we performed the first pooled, genome-wide CRISPR-Cas9 knockout (KO) screen with authentic HBV infection and integrated these results with two orthogonal pooled screens to identify host factors. We selected 72 genes for a multi-step assessment that included arrayed validation assays using both HBV infection and pgRNA transfection. We then independently tested thirteen genes using high-efficiency bulk KO experiments to guide further investigations of both antiviral and proviral factors. In both KO and siRNA-mediated knockdown experiments, depletion of the top antiviral factor, EXOC1, enhanced multiple HBV replication markers, and transcriptomic analysis revealed activation of hypoxia- and HIF-1 gene signatures. Three proviral factors, IRF2, WDR48, and ZCCHC14, were investigated in vivo using a human liver chimeric mouse model, which demonstrated that ZCCHC14 KO greatly reduced HBV replication and spread. Together, these complementary in vitro and in vivo platforms expand the catalog of HBV host factors and provide a scalable framework for host target discovery.

microbiology↗

bioRxiv2026

Structural and Mechanistic Basis of F227C-Mediated Hypersusceptibility to Islatravir in HIV-1 Reverse Transcriptase

Islatravir (ISL; 4'-ethynyl-2-fluoro-2'-deoxyadenosine (EFdA)), a first-in-class nucleoside reverse transcriptase (RT) translocation inhibitor (NRTTI), was recently approved by the FDA for the treatment of HIV-1 infection in combination with the non-nucleoside RT inhibitor (NNRTI), doravirine (DOR). Notably, the RT mutation F227C, which confers clinical resistance to multiple NNRTIs, including DOR, unexpectedly increases susceptibility to ISL. To elucidate the mechanistic basis of this hypersusceptibility, we determined a 1.8 angstrom crystal structure of F227C RT in complex with a ddGMP-terminated primer/template and ISL-triphosphate. The structure reveals conformational rearrangements that propagate into a cleft, thereby affecting ATP-mediated unblocking of chain-terminating antivirals. Complementary biochemical assays showed that although F227C does not significantly affect ISL incorporation, it alters RT translocation and impairs ATP-dependent phosphorolytic excision of ISL-terminated primers, thereby enhancing ISL susceptibility. These findings establish direct structural and mechanistic links between NNRTI resistance and ISL hypersusceptibility, providing a structural foundation for rationally designed, resistance-informed combination regimens that exploit this unique collateral sensitivity.

biochemistry↗

bioRxiv2026

Unraveling the Mechanism of HIV-1 Hypersusceptibility to Tenofovir Imparted by Islatravir Resistance Mutations

In response to the newly approved antiretroviral therapy (ART) islatravir (ISL), the M184V and A114S resistance mutations have emerged in the human immunodeficiency virus type 1 reverse transcriptase (HIV-1 RT). These mutations markedly hypersensitize RT to the globally administered ART tenofovir disoproxil fumarate (TDF). We have solved six structures - four by X-ray crystallography and two by cryo-EM - that capture the single- and double-mutant RTs during inhibitor incorporation and demonstrate the role of the mutations in altering protein-antiviral interactions. These snapshots reveal that the smaller, more flexible TDF diphosphate (TDF-DP) can better accommodate mutation-induced active site changes than ISL triphosphate (ISL-TP). Structural differences between the two inhibitors are consistent with biochemical determination of inhibitory constants (Kis), highlighting differences at the step of inhibitor incorporation. Virological evaluation of ISL and TDF combinations reveals additive inhibition of HIV-1. Given the converse ISL hypersusceptibility imparted by the TDF-resistant K65R mutation, we propose ISL and TDF as a combination that can inspire future therapeutic options.

biochemistry↗

bioRxiv2024

A Genome-Wide Arrayed CRISPR Screen Reveals PLSCR1 as an Intrinsic Barrier to SARS-CoV-2 Entry

Interferons (IFNs) play a crucial role in the regulation and evolution of host-virus interactions. Here, we conducted a genome-wide arrayed CRISPR knockout screen in the presence and absence of IFN to identify human genes that influence SARS-CoV-2 infection. We then performed an integrated analysis of genes interacting with SARS-CoV-2, drawing from a selection of 67 large-scale studies, including our own. We identified 28 genes of high relevance in both human genetic studies of COVID-19 patients and functional genetic screens in cell culture, with many related to the IFN pathway. Among these was the IFN-stimulated gene PLSCR1. PLSCR1 did not require IFN induction to restrict SARS-CoV-2 and did not contribute to IFN signaling. Instead, PLSCR1 specifically restricted spike-mediated SARS-CoV-2 entry. The PLSCR1-mediated restriction was alleviated by TMPRSS2 over-expression, suggesting that PLSCR1 primarily restricts the endocytic entry route. In addition, recent SARS-CoV-2 variants have adapted to circumvent the PLSCR1 barrier via currently undetermined mechanisms. Finally, we investigate the functional effects of PLSCR1 variants present in humans and discuss an association between PLSCR1 and severe COVID-19 reported recently.

immunology↗

bioRxiv2020

Human hepatocyte PNPLA3 148M exacerbates rapid non-alcoholic steatohepatitis development in chimeric mice

Advanced non-alcoholic fatty liver disease (NAFLD) is a rapidly emerging global health problem associated with pre-disposing genetic polymorphisms, most strikingly an isoleucine to methionine substitution in patatin-like phospholipase domain-containing protein 3 (PNPLA3-I148M). Here, we study how human hepatocytes with PNPLA3 148I and 148M variants engrafted in the livers of chimeric mice respond to a hypercaloric Western-style diet. As early as 4 weeks, mice developed dyslipidemia, impaired glucose tolerance, and steatohepatitis selectively in the human graft, followed by pericellular fibrosis after 8 weeks of hypercaloric feeding. The PNPLA3 148M variant, either from a homozygous 148M human donor or overexpressed in a homozygous 148I donor background, caused widespread microvesicular steatosis and even more severe steatohepatitis. We conclude that PNPLA3 148M in human hepatocytes exacerbates NAFLD. These models will facilitate mechanistic studies into human genetic variants associated with advanced fatty liver diseases.

pathology↗

bioRxiv2020

Genome-scale identification of SARS-CoV-2 and pan-coronavirus host factor networks

The COVID-19 pandemic has claimed the lives of more than one million people worldwide. The causative agent, SARS-CoV-2, is a member of the Coronaviridae family, which are viruses that cause respiratory infections of varying severity. The cellular host factors and pathways co-opted by SARS-CoV-2 and other coronaviruses in the execution of their life cycles remain ill-defined. To develop an extensive compendium of host factors required for infection by SARS-CoV-2 and three seasonal coronaviruses (HCoV-OC43, HCoV-NL63, and HCoV-229E), we performed parallel genome-scale CRISPR knockout screens. These screens uncovered multiple host factors and pathways with pan-coronavirus and virus-specific functional roles, including major dependency on glycosaminoglycan biosynthesis, SREBP signaling, and glycosylphosphatidylinositol biosynthesis, as well as an unexpected requirement for several poorly characterized proteins. We identified an absolute requirement for the VTT-domain containing protein TMEM41B for infection by SARS-CoV-2 and all other coronaviruses. This human Coronaviridae host factor compendium represents a rich resource to develop new therapeutic strategies for acute COVID-19 and potential future coronavirus spillover events. HIGHLIGHTSGenome-wide CRISPR screens for SARS-CoV-2, HCoV-OC43, HCoV-NL63, and HCoV-229E coronavirus host factors. Parallel genome-wide CRISPR screening uncovered host factors and pathways with pan-coronavirus and virus-specific functional roles. Coronaviruses co-opt multiple biological pathways, including glycosaminoglycan biosynthesis, SREBP signaling, and glycosylphosphatidylinositol biosynthesis and anchoring, among others. TMEM41B - a poorly understood factor with roles in autophagy and lipid mobilization - is a critical pan-coronavirus host factor.

microbiology↗

bioRxiv2020

Functional interrogation of a SARS-CoV-2 host protein interactome identifies unique and shared coronavirus host factors

The ongoing SARS-CoV-2 pandemic has devastated the global economy and claimed nearly one million lives, presenting an urgent global health crisis. To identify host factors required for infection by SARS-CoV-2 and seasonal coronaviruses, we designed a focused high-coverage CRISPR-Cas9 library targeting 332 members of a recently published SARS-CoV-2 protein interactome. We leveraged the compact nature of this library to systematically screen four related coronaviruses (HCoV-229E, HCoV-NL63, HCoV-OC43 and SARS-CoV-2) at two physiologically relevant temperatures (33 {degrees}C and 37 {degrees}C), allowing us to probe this interactome at a much higher resolution relative to genome scale studies. This approach yielded several new insights, including unexpected virus and temperature specific differences in Rab GTPase requirements and GPI anchor biosynthesis, as well as identification of multiple pan-coronavirus factors involved in cholesterol homeostasis. This coronavirus essentiality catalog could inform ongoing drug development efforts aimed at intercepting and treating COVID-19, and help prepare for future coronavirus outbreaks. HIGHLIGHTSFocused CRISPR screens targeting host factors in the SARS-CoV-2 interactome were performed for SARS-CoV-2, HCoV-229E, HCoV-NL63, and HCoV-OC43 coronaviruses. Focused interactome CRISPR screens achieve higher resolution compared to genome-wide screens, leading to the identification of critical factors missed by the latter. Parallel CRISPR screens against multiple coronaviruses uncover host factors and pathways with pan-coronavirus and virus-specific functional roles. The number of host proteins that interact with a viral bait protein is not proportional to the number of functional interactors. Novel SARS-CoV-2 host factors are expressed in relevant cell types in the human airway.

microbiology↗

bioRxiv2020

Enhanced SARS-CoV-2 Neutralization by Secretory IgA in vitro

SARS-CoV-2 primarily infects cells at mucosal surfaces. Serum neutralizing antibody responses are variable and generally low in individuals that suffer mild forms of the illness. Although potent IgG antibodies can neutralize the virus, less is known about secretory antibodies such as IgA that might impact the initial viral spread and transmissibility from the mucosa. Here we characterize the IgA response to SARS-CoV-2 in a cohort of 149 individuals. IgA responses in plasma generally correlate with IgG responses and clones of IgM, IgG and IgA producing B cells that are derived from common progenitors are evident. Plasma IgA monomers are 2-fold less potent than IgG equivalents. However, IgA dimers, the primary form in the nasopharynx, are on average 15 times more potent than IgA monomers. Thus, secretory IgA responses may be particularly valuable for protection against SARS-CoV-2 and for vaccine efficacy.

immunology↗

bioRxiv2020

Development of Resistance to 4'-Ethynyl-2-Fluoro-2'-Deoxyadenosine (EFdA) by Wild-Type and Nucleoside Reverse Transcriptase Inhibitor Resistant Human Immunodeficiency Virus Type 1

4-ethynyl-2-fluoro-2-deoxyadenosine (EFdA, MK-8591, islatravir) is a nucleoside reverse transcriptase translocation inhibitor (NRTTI) with exceptional potency against WT and drug-resistant HIV strains. However, HIV resistance to EFdA is not well characterized. We therefore developed resistance to EFdA by serial passages using progressively increasing concentrations of EFdA. The starting virus was either WT or clinically relevant NRTI-resistant viruses K65R, M184V, and D67N/K70R/T215F/K219Q). In all cases, the selected mutations included M184V. Additional mutations in the RT connection domain (R358K and E399K) and one mutation in the RNase H domain (A502V) were noted. Site-specific mutagenesis validated the role for M184V as the primary determinant for resistance to EFdA; none of the connection domain mutations contributed significantly to phenotypic resistance to EFdA. A novel EFdA resistance mutation was also observed in the background of M184V. The A114S/M184V combination of mutations imparted higher resistance to EFdA (~24-fold) than M184V (-8-fold) or A114S (~2-fold) alone. Virus fitness data suggested that A114S affects HIV fitness by itself and in the presence of M184V. This is consistent with biochemical experiments that showed decreases in the enzymatic efficiency (kcat/Km) of WT RT vs. A114S (2.1-fold) and A114S/M184V/502V (6.5-fold), whereas there was no significant effect of A502V on RT or virus fitness. The observed EFdA resistance of M184V by itself and in combination with A114S combined with the strong published in vitro and in vivo data, confirm that EFdA is an excellent candidate as a potential HIV therapeutic.

microbiology↗

bioRxiv2020

Escape from neutralizing antibodies by SARS-CoV-2 spike protein variants

Neutralizing antibodies elicited by prior infection or vaccination are likely to be key for future protection of individuals and populations against SARS-CoV-2. Moreover, passively administered antibodies are among the most promising therapeutic and prophylactic anti-SARS-CoV-2 agents. However, the degree to which SARS-CoV-2 will adapt to evade neutralizing antibodies is unclear. Using a recombinant chimeric VSV/SARS-CoV-2 reporter virus, we show that functional SARS-CoV-2 S protein variants with mutations in the receptor binding domain (RBD) and N-terminal domain that confer resistance to monoclonal antibodies or convalescent plasma can be readily selected. Notably, SARS-CoV-2 S variants that resist commonly elicited neutralizing antibodies are now present at low frequencies in circulating SARS-CoV-2 populations. Finally, the emergence of antibody-resistant SARS-CoV-2 variants that might limit the therapeutic usefulness of monoclonal antibodies can be mitigated by the use of antibody combinations that target distinct neutralizing epitopes.

microbiology↗

bioRxiv2020

Measuring SARS-CoV-2 neutralizing antibody activity using pseudotyped and chimeric viruses

The emergence of SARS-CoV-2 and the ensuing explosive epidemic of COVID19 disease has generated a need for assays to rapidly and conveniently measure the antiviral activity of SARS-CoV-2-specific antibodies. Here, we describe a collection of approaches based on SARS-CoV-2 spike-pseudotyped, single-cycle, replication-defective human immunodeficiency virus type-1 (HIV-1) and vesicular stomatitis virus (VSV), as well as a replication-competent VSV/SARS-CoV-2 chimeric virus. While each surrogate virus exhibited subtle differences in the sensitivity with which neutralizing activity was detected, the neutralizing activity of both convalescent plasma and human monoclonal antibodies measured using each virus correlated quantitatively with neutralizing activity measured using an authentic SARS-CoV-2 neutralization assay. The assays described herein are adaptable to high throughput and are useful tools in the evaluation of serologic immunity conferred by vaccination or prior SARS-CoV-2 infection, as well as the potency of convalescent plasma or human monoclonal antibodies.

microbiology↗

bioRxiv2020

Convergent Antibody Responses to SARS-CoV-2 Infection in Convalescent Individuals

During the COVID-19 pandemic, SARS-CoV-2 infected millions of people and claimed hundreds of thousands of lives. Virus entry into cells depends on the receptor binding domain (RBD) of the SARS-CoV-2 spike protein (S). Although there is no vaccine, it is likely that antibodies will be essential for protection. However, little is known about the human antibody response to SARS-CoV-21-5. Here we report on 149 COVID-19 convalescent individuals. Plasmas collected an average of 39 days after the onset of symptoms had variable half-maximal neutralizing titers ranging from undetectable in 33% to below 1:1000 in 79%, while only 1% showed titers >1:5000. Antibody cloning revealed expanded clones of RBD-specific memory B cells expressing closely related antibodies in different individuals. Despite low plasma titers, antibodies to three distinct epitopes on RBD neutralized at half-maximal inhibitory concentrations (IC50s) as low as single digit ng/mL. Thus, most convalescent plasmas obtained from individuals who recover from COVID-19 do not contain high levels of neutralizing activity. Nevertheless, rare but recurring RBD-specific antibodies with potent antiviral activity were found in all individuals tested, suggesting that a vaccine designed to elicit such antibodies could be broadly effective.

immunology↗

bioRxiv2020

LY6E impairs coronavirus fusion and confers immune control of viral disease

Zoonotic coronaviruses (CoVs) are significant threats to global health, as exemplified by the recent emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)1. Host immune responses to CoV are complex and regulated in part through antiviral interferons. However, the interferon-stimulated gene products that inhibit CoV are not well characterized2. Here, we show that interferon-inducible lymphocyte antigen 6 complex, locus E (LY6E) potently restricts cellular infection by multiple CoVs, including SARS-CoV, SARS-CoV-2, and Middle East respiratory syndrome coronavirus (MERS-CoV). Mechanistic studies revealed that LY6E inhibits CoV entry into cells by interfering with spike protein-mediated membrane fusion. Importantly, mice lacking Ly6e in hematopoietic cells were highly susceptible to murine CoV infection. Exacerbated viral pathogenesis in Ly6e knockout mice was accompanied by loss of hepatic and splenic immune cells and reduction in global antiviral gene pathways. Accordingly, we found that Ly6e directly protects primary B cells and dendritic cells from murine CoV infection. Our results demonstrate that LY6E is a critical antiviral immune effector that controls CoV infection and pathogenesis. These findings advance our understanding of immune-mediated control of CoV in vitro and in vivo, knowledge that could help inform strategies to combat infection by emerging CoV.

microbiology↗

bioRxiv2020

Public broadly neutralizing antibodies against hepatitis B virus in individuals with elite serologic activity

SUMMARYAlthough there is no effective cure for chronic hepatitis B virus (HBV) infection, antibodies are protective and constitute clinical correlates of recovery from infection. To examine the human neutralizing antibody response to HBV in elite neutralizers we screened 144 individuals. The top individuals produced shared clones of broadly neutralizing antibodies (bNAbs) that targeted 3 non-overlapping epitopes on the HBV S antigen (HBsAg). Single bNAbs protected humanized mice against infection, but selected for resistance mutations in mice with established infection. In contrast, infection was controlled by a combination of bNAbs targeting non-overlapping epitopes with complementary sensitivity to mutations that commonly emerge during human infection. The co-crystal structure of one of the bNAbs with a peptide epitope containing residues frequently mutated in human immune escape variants revealed a loop anchored by oppositely charged residues. The structure provides a molecular explanation for why immunotherapy for HBV infection may require combinations of complementary bNAbs.

immunology↗