Development of an HSV-1 neutralization test with a glycoprotein D specific antibody for measurement of neutralizing antibody titer in human sera

Immuno-Colorimetric Neutralization Test: A Surrogate for Widely Used Plaque Reduction Neutralization Tests in Public Health Virology

Since their first documentation in 1952, plaque reduction neutralization tests (PRNTs) have become the choice of test for the measurement of neutralizing antibodies against a particular virus. However, PRNTs can be performed only against viruses that cause cytopathic effects (CPE). PRNTs also require skilled personnel and can be time-consuming depending on the time required for the virus to cause CPE. Hence, their application limits large-scale studies or epidemiological and laboratory investigations. Since 1978, many surrogate PRNTs or immunocolorimetric assay (ICA)-based focus reduction neutralization tests (FRNT) have been developed. In this article, ICAs and their utility in FRNTs for the characterization of neutralizing antibodies, homologous or heterologous cross-neutralization, and laboratory diagnosis of viruses of public health importance have been discussed. Additionally, possible advancements and automations have been described that may help in the development and validation of novel surrogate tests for emerging viruses.

Promotion of the resistance of human oral epithelial cells to herpes simplex virus type I infection via N6-methyladenosine modification

OBJECTIVE

This study aimed to explore the mechanism behind N6-methyladenosine (m6A) modification of the total ribonucleic acid (RNA) involved in the resistance to herpes simplex virus type I (HSV-1) infection in oral epithelial cells.

METHOD

The variation in m6A modification level on messenger RNA following HSV-1 infection was determined using the RNA dot blot method. The expression levels of alpha-ketoglutarate-dependent dioxygenase lab homolog 5 (ALKBH5) protein and fatty mass and obesity-associated genes (FTO) were determined using real-time fluorescence quantification polymerase chain reaction and the western blot technique, respectively. Next, after suppressing the expression of ALKBH5 or FTO via small interfering RNA, human immortalised oral epithelial cells (HIOECs) were infected with HSV-1, followed by measurement of the viral load or expression level of type I interferon (I-IFN) and interferon-stimulated genes (ISGs).

RESULTS

The m6A modification level was significantly increased following HSV-1 infection of the HIOECs (P < 0.05), while the expression of ALKBH5 and FTO genes was reduced (P < 0.01). Moreover, the suppression of ALKBH5 or FTO increased the production of I-IFN and ISGs during the HSV-1 infection of the HIOECs (P < 0.01), and the viral load was significantly reduced (P < 0.01).

CONCLUSION

During oral HSV-1 infection, the m6A level was increased through the down-regulation of ALBHK5 and FTO expression, increasing I-IFN production and the promotion of HSV-1 clearing in HIOECs.

Development of a rapid neutralization testing system for Rhinovirus C15 based on the enzyme-linked immunospot assay

Human Rhinoviruses (RVs) are dominant pathogens causing a wide range of respiratory tract diseases, posing a huge threat to public health worldwide. Viruses belonging to the RV-C species are more likely to cause severe illnesses and are strongly associated with asthma onset or exacerbations than RV-A or RV-B. Rapid and sensitive detection of neutralizing antibodies (NAbs) against RV-C can promote the development of vaccines and antiviral drugs and help in the diagnosis of viral infection. In this study, a rapid neutralization testing system for RV-C15, based on an enzyme-linked immunospot assay (Nt-ELISPOT) was developed. A monoclonal antibody (MAb), named 9F9, with high binding efficacy for RV-C15 conjugated to horseradish peroxidase (HRP), was used to detect RV-C15-infected cells at a concentration of 2 μg/ml. The optimal infectious dose of RV-C15 was set at 1 × 10⁴ TCID₅₀/well and the cells were fixed with 0.5% formaldehyde diluted in PBS after incubation for 20 h. Compared with the traditional cytopathic effect (CPE)-based neutralization assay (Nt-CPE), Nt-ELISPOT significantly shortened the detection period and showed good consistency with the detection of neutralizing titers of both sera and NAbs. Using Nt-ELISPOT, three anti-RV-C15 NAbs were obtained with IC₅₀ values of 0.16, 0.27, and 11.8 μg/ml, respectively. Moreover, 64 human serum samples collected from a wide range of age groups were tested for NAb against RV-C15 by Nt-ELISPOT. The total seroprevalence was 48.4% (31/64) and the positive rate was lowest in the group under 6 years old. Thus, the Nt-ELISPOT established in this study can be used as a high-throughput and rapid neutralization assay for the screening of NAbs and for seroepidemiological investigation against RV-C15.

A potent neutralizing and protective antibody against a conserved continuous epitope on HSV glycoprotein D

Infections caused by herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) remain a serious global health issue, and the medical countermeasures available thus far are limited. Virus-neutralizing monoclonal antibodies (NAbs) are crucial tools for studying host-virus interactions and designing effective vaccines, and the discovery and development of these NAbs could be one approach to treat or prevent HSV infection. Here, we report the isolation of five HSV NAbs from mice immunized with both HSV-1 and HSV-2. Among these were two antibodies that potently cross-neutralized both HSV-1 and HSV-2 with the 50% virus-inhibitory concentrations (IC₅₀) below 200 ng/ml, one of which (4A3) exhibited high potency against HSV-2, with an IC₅₀ of 59.88 ng/ml. 4A3 neutralized HSV at the prebinding stage and prevented HSV infection and cell-to-cell spread. Significantly, administration of 4A3 completely prevented weight loss and improved survival of mice challenged with a lethal dose of HSV-2. Using structure-guided molecular modeling combined with alanine-scanning mutagenesis, we observed that 4A3 bound to a highly conserved continuous epitope (residues 216 to 220) within the receptor-binding domain of glycoprotein D (gD) that is essential for viral infection and the triggering of membrane fusion. Our results provide guidance for developing NAb drugs and vaccines against HSV.

Intratumoral Virotherapy with Wild-Type Newcastle Disease Virus in Carcinoma Krebs-2 Cancer Model

The results of experimental and clinical trials of the agents based on oncolytic Newcastle disease virus (NDV) strains provided hope for the development of virotherapy as a promising method for treating human tumors. However, the mechanism of the antitumor effect of NDV and realization of its cytotoxic potential in a cancer cell remains to be elucidated. In the current work, we have studied the antitumor effect of NDV in a syngeneic model of mouse Krebs-2 carcinoma treated with intratumoral injections of a wild-type strain NDV/Altai/pigeon/770/2011. Virological methods were used for preparation of a virus-containing sample. Colorimetric MTS assay was used to assess the viability of Krebs-2 tumor cells infected with a viral strain in vitro. In vivo virotherapy was performed in eight-week-old male BALB/c mice treated with serial intratumoral injections of NDV in an experimental model of Krebs-2 solid carcinoma. Changes in the tumor nodes of Krebs-2 carcinoma after virotherapy were visualized by MRI and immunohistological staining. Light microscopy examination, immunohistochemical and morphometric analyses have shown that intratumoral viral injections contribute to the inhibition of tumor growth, appearance of necrosis-like changes in the tumor tissue and the antiangiogenic effect of the virus. It has been established that a course of intratumoral virotherapy with NDV/Altai/pigeon/770/2011 strain in a mouse Krebs-2 carcinoma resulted in increased destructive changes in the tumor tissue, in the volume density of necrotic foci and numerical density of endothelial cells expressing CD34 and VEGFR. These results indicate that intratumoral NDV injection reduces tumor progression of an aggressive tumor.

Rapid Neutralization Testing System for Zika Virus Based on an Enzyme-Linked Immunospot Assay

Zika virus (ZIKV) is a mosquito-borne flavivirus that has been associated with neuropathology in fetuses and adults, imposing a serious health concern. Therefore, the development of a vaccine is a global health priority. Notably, neutralization tests have a significant value for vaccine development and virus diagnosis. The cytopathic effect (CPE)-based neutralization test (Nt-CPE) is a common neutralization method for ZIKV. However, this method has some drawbacks, such as being time-consuming and labor-intensive and having low-throughput, which precludes its application in the detection of large numbers of specimens. To improve this problem, we developed a neutralization test based on an enzyme-linked immunospot assay (Nt-ELISPOT) for ZIKV and performed the assay in a 96-well format. A monoclonal antibody (mAb), 11C11, with high affinity and reactivity to ZIKV was used to detect ZIKV-infected cells. To optimize this method, the infectious dose of ZIKV was set at a multiplicity of infection (MOI) of 0.0625, and a detection experiment was performed after incubating for 24 h. As a result, under these conditions, the Nt-ELISPOT had good consistency with the traditional Nt-CPE to measure neutralizing titers of sera and neutralizing antibodies. Additionally, three neutralizing antibodies against ZIKV were screened by this method. Overall, we successfully developed an efficient neutralization test for ZIKV that is high-throughput and rapid. This Nt-ELISPOT can potentially be applied to detecting neutralizing titers of large numbers of specimens in vaccine evaluation and neutralizing antibody screening for ZIKV.

Intratumoral Delivery of a PD-1-Blocking scFv Encoded in Oncolytic HSV-1 Promotes Antitumor Immunity and Synergizes with TIGIT Blockade

Oncolytic virotherapy can lead to systemic antitumor immunity, but the therapeutic potential of oncolytic viruses in humans is limited due to their insufficient ability to overcome the immunosuppressive tumor microenvironment (TME). Here, we showed that locoregional oncolytic virotherapy upregulated the expression of PD-L1 in the TME, which was mediated by virus-induced type I and type II IFNs. To explore PD-1/PD-L1 signaling as a direct target in tumor tissue, we developed a novel immunotherapeutic herpes simplex virus (HSV), OVH-aMPD-1, that expressed a single-chain variable fragment (scFv) against PD-1 (aMPD-1 scFv). The virus was designed to locally deliver aMPD-1 scFv in the TME to achieve enhanced antitumor effects. This virus effectively modified the TME by releasing damage-associated molecular patterns, promoting antigen cross-presentation by dendritic cells, and enhancing the infiltration of activated T cells; these alterations resulted in antitumor T-cell activity that led to reduced tumor burdens in a liver cancer model. Compared with OVH, OVH-aMPD-1 promoted the infiltration of myeloid-derived suppressor cells (MDSC), resulting in significantly higher percentages of CD155⁺ granulocytic-MDSCs (G-MDSC) and monocytic-MDSCs (M-MDSC) in tumors. In combination with TIGIT blockade, this virus enhanced tumor-specific immune responses in mice with implanted subcutaneous tumors or invasive tumors. These findings highlighted that intratumoral immunomodulation with an OV expressing aMPD-1 scFv could be an effective stand-alone strategy to treat cancers or drive maximal efficacy of a combination therapy with other immune checkpoint inhibitors.

Fighting Cancer with Viruses: Oncolytic Virus Therapy in China

As part of oncolytic virotherapy to treat cancer, oncolytic viruses (OVs) can selectively infect tumor cells to promote oncolysis of cancer cells, local immunological reactions, and systemic antitumor immunity with minimal toxicity to normal tissues. The immunostimulatory properties of OVs provide enormous benefits for the treatment of cancer. A variety of OVs, including genetically engineered and natural viruses, have shown promise in preclinical models and clinical studies. In 2005, the China Food and Drug Administration approved its first OV drug, Oncorine (H101), for treatment of advanced head and neck cancer. To explore new treatment strategies, >200 recombinant or natural OVs are undergoing in-depth investigation in China, and >250 oncolytic virotherapy-related reports from the OV community in China have been published in the past 5 years. These studies investigated a variety of exogenous genes and combination therapeutic strategies to enhance the treatment effects of OVs. To date, five clinical trials covering four OV agents (Oncorine, OrienX010, KH901, and H103) are ongoing, and additional OV agents are awaiting approval for clinical trials in China. Overall, this research emphasizes that combination therapy, especially tumor immunotherapy coupled with effective system administration strategies, can promote the development of oncolytic virotherapies. This article focuses on studies that were carried out in China in order to give an overview of the past, present, and future of oncolytic virotherapy in China.

Development of an efficient neutralization assay for Coxsackievirus A10

Coxsackievirus A10 (CVA10) recently has become one of the major pathogens of hand, foot, and mouth disease (HFMD) in children worldwide, but no cure or vaccine against CVA10 is available yet. Serological evaluation of herd immunity to CVA10 will promote the development of vaccine. The traditional neutralization assay based on inhibition of cytopathic effect (Nt-CPE) is a common method for measuring neutralizing antibody titer against CVA10, which is time-consuming and labor-intensive. In this study, an efficient neutralization test based on a monoclonal antibody (mAb) 3D1 against CVA10, called Elispot-based neutralization test (Nt-Elispot), was developed. In the Nt-Elispot, the mAb 3D1 labeled with horseradish peroxidase (HRP) was used to detect the CVA10-infected RD cells at a 1:4000 dilution and the optimal infectious dose of CVA10 was set at 10⁵ TCID₅₀/well when combined with a fixed incubation time of 14 h. Compared with the Nt-CPE, the Nt-Elispot method effectively shortened the detection period and presented a good correlativity with it. Using the Nt-Elispot, a total of 123 sera from healthy children were tested for neutralizing antibody against CVA10, demonstrating that the overall seroprevalence was 49.3% (54/123) and the geometric mean titer (GMT) had been calculated as 574.2. Furthermore, 2 anti-CVA10 neutralizing mAbs were obtained by screening via the Nt-Elispot. Overall, the established Nt-Elispot could be used as an efficient and high-throughput method for evaluating immunity to CVA10 and screening the neutralizing antibodies.

A novel approach for rapid high-throughput selection of recombinant functional rat monoclonal antibodies

Background

Most monoclonal antibodies against mouse antigens have been derived from rat spleen-mouse myeloma fusions, which are valuable tools for purposes ranging from general laboratory reagents to therapeutic drugs, and yet selecting and expressing them remains a time-consuming and inefficient process. Here, we report a novel approach for the rapid high-throughput selection and expression of recombinant functional rat monoclonal antibodies with different isotypes.

Results

We have developed a robust system for generating rat monoclonal antibodies through several processes involving simultaneously immunizing rats with three different antigens expressing in a mixed cell pools, preparing hybridoma cell pools, in vitro screening and subsequent cloning of the rearranged light and heavy chains into a single expression plasmid using a highly efficient assembly method, which can decrease the time and effort required by multiple immunizations and fusions, traditional clonal selection and expression methods. Using this system, we successfully selected several rat monoclonal antibodies with different IgG isotypes specifically targeting the mouse PD-1, LAG-3 or AFP protein from a single fusion. We applied these recombinant anti-PD-1 monoclonal antibodies (32D6) in immunotherapy for therapeutic purposes that produced the expected results.

Conclusions

This method can be used to facilitate an increased throughput of the entire process from multiplex immunization to acquisition of functional rat monoclonal antibodies and facilitate their expression and feasibility using a single plasmid.

Electronic supplementary material

The online version of this article (10.1186/s12865-018-0274-8) contains supplementary material, which is available to authorized users.

A direct quantitative PCR-based measurement of herpes simplex virus susceptibility to antiviral drugs and neutralizing antibodies

Herpes simplex viruses (HSV) are common human pathogens that can cause painful but benign manifestations and recurrent complaints, but can also cause significant morbidity and mortality on infection of the eye or brain and with disseminated infection of an immunosuppressed patient or a neonate. HSV growth inhibition measurement by plaque or yield reduction is a key task in the development of novel antiviral compounds but the manual methods are very labour intensive. The sensitive and specific PCR technology could be an effective method for quantitation of HSV DNA related to virus replication; however the currently described PCR approaches have a major limitation, namely the requirement of purification of DNA from the infected cells. This limitation makes this approach unfeasible for high-throughput screenings. The monitoring of HSV specific antibody titre is essential in vaccination trials and in the improvement of HSV-based oncolytic virotherapy. Usually, conventional cytopathic effect-based and plaque reduction neutralization tests are applied to measure the neutralization titre, but these methods are also time-consuming. To overcome this, we developed a quantitative PCR (qPCR) method for the detection of HSV-2 DNA directly from the infected cells (direct qPCR) and the method was further adapted to measure the titre of HSV specific neutralizing antibody in human sera. The conditions of direct qPCR assay were optimized to measure the antiviral activity of known and novel antiviral substances. Using HSV-2 seronegative and seropositive patients' sera, the validity of the direct qPCR neutralization test was compared to traditional cytopathic effect-based assay. The direct qPCR method was able to detect the HSV-2 DNA quantitatively between multiplicity of infection 1/64 and 1/4194304, indicating that the dynamic range of the detection was approximately 65,500 fold with high correlation between the biological and technical replicates. As a proof of the adaptability of the method, we applied the direct qPCR for antiviral inhibitory concentration 50 (IC₅₀) measurements of known and novel antiviral compounds. The measured IC₅₀ of acyclovir was ∼0.28μg/ml, similar to the previously published IC₅₀ value. The IC₅₀ of novel antiviral candidates was between 1.6-3.1μg/ml. The direct qPCR-based neutralization titres of HSV positive sera were 1:32-1:64, identical to the neutralization titres determined using a traditional neutralization assay. The negative sera did not inhibit the HSV-2 replication in either of the tests. Our direct qPCR method for the HSV-2 growth determination of antiviral IC₅₀ and neutralization titre is less time-consuming, less subjective and a more accurate alternative to the traditional plaque titration and growth reduction assays.