Identification of adipocyte plasma membrane-associated protein as a novel modulator of human cytomegalovirus infection

Cryptococcus neoformans, a global threat to human health

BACKGROUND

Emerging fungal pathogens pose important threats to global public health. The World Health Organization has responded to the rising threat of traditionally neglected fungal infections by developing a Fungal Priority Pathogens List (FPPL). Taking the highest-ranked fungal pathogen in the FPPL, Cryptococcus neoformans, as a paradigm, we review progress made over the past two decades on its global burden, its clinical manifestation and management of cryptococcal infection, and its antifungal resistance. The purpose of this review is to drive research efforts to improve future diagnoses, therapies, and interventions associated with fungal infections.

METHODS

We first reviewed trends in the global burden of HIV-associated cryptococcal infection, mainly based on a series of systematic studies. We next conducted scoping reviews in accordance with the guidelines described in the Preferred Reporting Items for Systematic Reviews and Meta-analyses extension for Scoping Reviews using PubMed and ScienceDirect with the keyword Cryptococcus neoformans to identify case reports of cryptococcal infections published since 2000. We then reviewed recent updates on the diagnosis and antifungal treatment of cryptococcal infections. Finally, we summarized knowledge regarding the resistance and tolerance of C. neoformans to approved antifungal drugs.

RESULTS

There has been a general reduction in the estimated global burden of HIV-associated cryptococcal meningitis since 2009, probably due to improvements in highly active antiretroviral therapies. However, cryptococcal meningitis still accounts for 19% of AIDS-related deaths annually. The incidences of CM in Europe and North America and the Latin America region have increased by approximately two-fold since 2009, while other regions showed either reduced or stable numbers of cases. Unfortunately, diagnostic and treatment options for cryptococcal infections are limited, and emerging antifungal resistance exacerbates the public health burden.

CONCLUSION

The rising threat of C. neoformans is compounded by accumulating evidence for its ability to infect immunocompetent individuals and the emergence of antifungal-resistant variants. Emphasis should be placed on further understanding the mechanisms of pathogenicity and of antifungal resistance and tolerance. The development of novel management strategies through the identification of new drug targets and the discovery and optimization of new and existing diagnostics and therapeutics are key to reducing the health burden.

A single, improbable B cell receptor mutation confers potent neutralization against cytomegalovirus

Cytomegalovirus (CMV) is a leading cause of infant hearing loss and neurodevelopmental delay, but there are no clinically licensed vaccines to prevent infection, in part due to challenges eliciting neutralizing antibodies. One of the most well-studied targets for CMV vaccines is the viral fusogen glycoprotein B (gB), which is required for viral entry into host cells. Within gB, antigenic domain 2 site 1 (AD-2S1) is a target of potently neutralizing antibodies, but gB-based candidate vaccines have yet to elicit robust responses against this region. We mapped the genealogy of B cells encoding potently neutralizing anti-gB AD-2S1 antibodies from their inferred unmutated common ancestor (UCA) and characterized the binding and function of early lineage ancestors. Surprisingly, we found that a single amino acid heavy chain mutation A33N, which was an improbable mutation rarely generated by somatic hypermutation machinery, conferred broad CMV neutralization to the non-neutralizing UCA antibody. Structural studies revealed that this mutation mediated key contacts with the gB AD-2S1 epitope. Collectively, these results provide insight into potently neutralizing gB-directed antibody evolution in a single donor and lay a foundation for using this B cell-lineage directed approach for the design of next-generation CMV vaccines.

Neutralization Epitopes in Trimer and Pentamer Complexes Recognized by Potent Cytomegalovirus-Neutralizing Human Monoclonal Antibodies

Human cytomegalovirus (HCMV) infects 36% to almost 100% of adults and causes severe complications only in immunocompromised individuals. HCMV viral surface trimeric (gH/gL/gO) and pentameric (gH/gL/UL128/UL130/UL131A) complexes play important roles in HCMV infection and tropism. Here, we isolated and identified a total of four neutralizing monoclonal antibodies (MAbs) derived from HCMV-seropositive blood donors. Based on their reactivity to HCMV trimer and pentamer, these MAbs can be divided into two groups. MAbs PC0012, PC0014, and PC0035 in group 1 bind both trimer and pentamer and neutralize CMV by interfering with the postattachment steps of CMV entering into cells. These three antibodies recognize antigenic epitopes clustered in a similar area, which are overlapped by the epitope recognized by the known neutralizing antibody MSL-109. MAb PC0034 in group 2 binds only to pentamer and neutralizes CMV by blocking the binding of pentamer to cells. Epitope mapping using pentamer mutants showed that amino acid T94 of the subunit UL128 and K27 of UL131A on the pentamer are key epitope-associated residues recognized by PC0034. This study provides new evidence and insight information on the importance of the development of the CMV pentamer as a CMV vaccine. In addition, these newly identified potent CMV MAbs can be attractive candidates for development as antibody therapeutics for the prevention and treatment of HCMV infection. IMPORTANCE The majority of the global population is infected with HCMV, but severe complications occur only in immunocompromised individuals. In addition, CMV infection is a major cause of birth defects in newborns. Currently, there are still no approved prophylactic vaccines or therapeutic monoclonal antibodies (MAbs) for clinical use against HCMV infection. This study identified and characterized a panel of four neutralizing MAbs targeting the HCMV pentamer complex with specific aims to identify a key protein(s) and antigenic epitopes in the HCMV pentamer complex. The study also explored the mechanism by which these newly identified antibodies neutralize HCMV in order to design better HCMV vaccines focusing on the pentamer and to provide attractive candidates for the development of effective cocktail therapeutics for the prevention and treatment of HCMV infection.

Rescue of Pentamer-Null Strains of Human Cytomegalovirus in Epithelial Cells by Use of Histone Deacetylase Inhibitors Reveals an Additional Postentry Function for the Pentamer Complex

Human cytomegalovirus (HCMV) tropism for epithelial cells is determined by the pentameric glycoprotein complex found on the viral envelope. Laboratory-adapted strains, such as AD169, typically develop loss-of-function mutations for the pentamer, thus losing the ability to efficiently initiate lytic replication in epithelial cells. Using our human salivary gland-derived epithelial (hSGE) cell model, we observed that 3 chemically distinct histone deacetylase (HDAC) inhibitors can rescue infection in hSGE cells using pentamer-null strains of HCMV. Additionally, infection in ARPE-19 epithelial cells was rescued in a similar manner. We isolated nuclei from AD169-infected cells, quantified viral genomes by quantitative PCR (qPCR), and discovered that while HDAC inhibitors increased immediate early (IE) gene expression, they did not increase the amount of viral DNA in the nucleus. Using immunofluorescence microscopy, we observed that pentamer-null strains showed punctate patterning of pp71 in proximity to the nucleus of infected cells, while pp71 was localized to the nucleus after infection with pentamer-containing strains. Upon treatment with HDAC inhibitors, these punctae remained perinuclear, while more cells displayed entry into the lytic cycle, noted by increased IE-positive nuclei. Taken together, our data indicate that HCMV pentamer-null viruses are able to infect epithelial cells (albeit less efficiently than pentamer-positive viruses) and traffic to the nucleus but fail to initiate lytic gene expression once there. These studies reveal a novel postentry function of the pentamer in addition to the recognized role of pentamer in mediating entry. IMPORTANCE Human cytomegalovirus has a wide cellular tropism, which is driven by one of its glycoprotein complexes, the pentamer. Laboratory-adapted strains continuously passaged on fibroblasts readily lose pentamer function and thus lose their ability to infect diverse cell types such as epithelial cells. Pentamer has been attributed an entry function during infection, but mechanistic details as to how this is achieved have not been definitely demonstrated. In this study, we investigate how pharmacological rescue of pentamer-null strains during epithelial infection by histone deacetylase inhibitors implicates a novel role for the pentamer downstream of entry. This work expands on potential functions of the pentamer, will drive future studies to understand mechanistically how it affects tropism, and provides a new target for future therapeutics.

Structural basis for HCMV Pentamer recognition by neuropilin 2 and neutralizing antibodies

Human cytomegalovirus (HCMV) encodes multiple surface glycoprotein complexes to infect a variety of cell types. The HCMV Pentamer, composed of gH, gL, UL128, UL130, and UL131A, enhances entry into epithelial, endothelial, and myeloid cells by interacting with the cell surface receptor neuropilin 2 (NRP2). Despite the critical nature of this interaction, the molecular determinants that govern NRP2 recognition remain unclear. Here, we describe the cryo-EM structure of NRP2 bound to Pentamer. The high-affinity interaction between these proteins is calcium dependent and differs from the canonical carboxyl-terminal arginine (CendR) binding that NRP2 typically uses. We also determine the structures of four neutralizing human antibodies bound to the HCMV Pentamer to define susceptible epitopes. Two of these antibodies compete with NRP2 binding, but the two most potent antibodies recognize a previously unidentified epitope that does not overlap the NRP2-binding site. Collectively, these findings provide a structural basis for HCMV tropism and antibody-mediated neutralization.

APMAP Promotes Epithelial-Mesenchymal Transition and Metastasis of Cervical Cancer Cells by Activating the Wnt/β-catenin Pathway

Cervical cancer is a malignant tumor of the female reproductive system. At present, its occurrence, development and transfer mechanism are not entirely clear. APMAP (Adipocyte Plasma Membrane Associated Protein) is a glycosyl type II transmembrane protein that is mainly distributed in the plasma membrane and endoplasmic reticulum of adipocytes. APMAP has been reported to be involved in lipid transport and can induce epithelial-mesenchymal transition of prostate cancer and the liver metastasis of colorectal cancer. However, the role of APMAP in cervical cancer is still unknown. We analyzed the expression and prognosis of APMAP using data in both the GEO and the TCGA databases. We analyzed the function of APMAP using Transwell, wound healing assay and flow cytometry, and assessed the main mechanisms of APMAP by RT-PCR and Western blotting. We found that APMAP was highly expressed in cervical cancer tissues, and patients with high expression had poor prognosis. The functional in vitro experiments demonstrated that APMAP knockdown significantly inhibited the migration ability of cervical cancer cells, but had little effect on cell apoptosis. Mechanically, APMAP promotes cervical cancer cell migration and epithelial-mesenchymal transition by activating the Wnt/β-catenin pathway. Overall, APMAP is a potential prognostic marker as well as a therapeutic target of cervical cancer.

A conditionally replication-defective cytomegalovirus vaccine elicits potent and diverse functional monoclonal antibodies in a phase I clinical trial

A conditionally replication-defective human cytomegalovirus (HCMV) vaccine, V160, was shown to be safe and immunogenic in a two-part, double-blind, randomized, placebo-controlled phase I clinical trial (NCT01986010). However, the specificities and functional properties of V160-elicited antibodies remain undefined. Here, we characterized 272 monoclonal antibodies (mAbs) isolated from single memory B cells of six V160-vaccinated subjects. The mAbs bind to diverse HCMV antigens, including multiple components of the pentamer, gB, and tegument proteins. The most-potent neutralizing antibodies target the pentamer-UL subunits. The binding sites of the antibodies overlap with those of antibodies responding to natural HCMV infection. The majority of the neutralizing antibodies target the gHgL subunit. The non-neutralizing antibodies predominantly target the gB and pp65 proteins. Sequence analysis indicated that V160 induced a class of gHgL antibodies expressing the HV1-18/KV1-5 germline genes in multiple subjects. This study provides valuable insights into primary targets for anti-HCMV antibodies induced by V160 vaccination.

Recognition of a highly conserved glycoprotein B epitope by a bivalent antibody neutralizing HCMV at a post-attachment step

Human cytomegalovirus (HCMV) is one of the main causative agents of congenital viral infection in neonates. HCMV infection also causes serious morbidity and mortality among organ transplant patients. Glycoprotein B (gB) is a major target for HCMV neutralizing antibodies, yet the underlying neutralization mechanisms remain largely unknown. Here we report that 3–25, a gB-specific monoclonal antibody previously isolated from a healthy HCMV-positive donor, efficiently neutralized 14 HCMV strains in both ARPE-19 cells and MRC-5 cells. The core epitope of 3–25 was mapped to a highly conserved linear epitope on antigenic domain 2 (AD-2) of gB. A 1.8 Å crystal structure of 3–25 Fab in complex with the peptide epitope revealed the molecular determinants of 3–25 binding to gB at atomic resolution. Negative-staining electron microscopy (EM) 3D reconstruction of 3–25 Fab in complex with de-glycosylated postfusion gB showed that 3–25 Fab fully occupied the gB trimer at the N-terminus with flexible binding angles. Functionally, 3–25 efficiently inhibited HCMV infection at a post-attachment step by interfering with viral membrane fusion, and restricted post-infection viral spreading in ARPE-19 cells. Interestingly, bivalency was required for HCMV neutralization by AD-2 specific antibody 3–25 but not the AD-4 specific antibody LJP538. In contrast, bivalency was not required for HCMV binding by both antibodies. Taken together, our results reveal the structural basis of gB recognition by 3–25 and demonstrate that inhibition of viral membrane fusion and a requirement of bivalency may be common for gB AD-2 specific neutralizing antibody.

HCMV infection is usually asymptomatic in healthy individuals. However, life-threatening diseases frequently accompany HCMV infection in individuals with under-developed or compromised immune systems. Glycoprotein B antigenic domain 2 (AD-2) is a major target for HCMV-neutralizing antibodies that potentially provide immune protection. We report the structure-based study of gB recognition by a potent neutralizing antibody named 3–25 that binds a highly conserved epitope on AD-2. Functionally, 3–25 efficiently inhibited HCMV infection at a post-attachment step by interfering with viral membrane fusion, and restricted post-infection viral spreading. Furthermore, bivalency of 3–25 is required for viral neutralization but not for binding. Our findings advance understanding of gB antibody-mediated HCMV neutralization and facilitate development of gB-targeted vaccines and antibody drugs against HCMV infection.

Adipocyte Plasma Membrane Protein (APMAP) promotes JC Virus (JCPyV) infection in human glial cells

The demyelinating disease progressive multifocal leukoencephalopathy (PML) is caused by the human polyomavirus, JCPyV, under conditions of prolonged immunosuppression. Initial infection is asymptomatic, and the virus establishes lifelong persistence in the host. Following the loss of immune surveillance, the virus can traffic to the central nervous system and infect oligodendrocytes to cause demyelination and PML. The mechanisms involved in glial cell infection are not completely understood. In a screen for N-glycosylated proteins that influence JCPyV pathology, we identified Adipocyte Plasma Membrane Associated Protein (APMAP) as a host cell modulator of JCPyV infection. The removal of APMAP by small interfering siRNA as well as by CRISPR-Cas9 gene editing resulted in a significant decrease in JCPyV infection. Exogenous expression of APMAP in APMAP knockout cell lines rescued susceptibility to infection. These data suggest that virus infection of glial cells is dependent on APMAP.

Virus-Like Particles and Nanoparticles for Vaccine Development against HCMV

Human cytomegalovirus (HCMV) infects more than 70% of the human population worldwide. HCMV is responsible for high morbidity and mortality in immunocompromised patients and remains the leading viral cause of congenital birth defects. Despite considerable efforts in vaccine and therapeutic development, HCMV infection still represents an unmet clinical need and a life-threatening disease in immunocompromised individuals and newborns. Immune repertoire interrogation of HCMV seropositive patients allowed the identification of several potential antigens for vaccine design. However, recent HCMV vaccine clinical trials did not lead to a satisfactory outcome in term of efficacy. Therefore, combining antigens with orthogonal technologies to further increase the induction of neutralizing antibodies could improve the likelihood of a vaccine to reach protective efficacy in humans. Indeed, presentation of multiple copies of an antigen in a repetitive array is known to drive a more robust humoral immune response than its soluble counterpart. Virus-like particles (VLPs) and nanoparticles (NPs) are powerful platforms for multivalent antigen presentation. Several self-assembling proteins have been successfully used as scaffolds to present complex glycoprotein antigens on their surface. In this review, we describe some key aspects of the immune response to HCMV and discuss the scaffolds that were successfully used to increase vaccine efficacy against viruses with unmet medical need.