Attenuated phenotypes and analysis of a herpes simplex virus 1 strain with partial deletion of the UL7, UL41 and LAT genes

Analysis of the Interaction Between the Attenuated HSV-1 Strain M6 and Macrophages Indicates Its Potential as an Effective Vaccine Immunogen

Herpes simplex virus type 1 (HSV-1) is a very concerning pathogen due to its ability to persist in the host's nervous system and continuously interfere with the immune system, which complicates treatment. Therefore, the development of an effective HSV-1 vaccine is crucial. In this study, we focused on an HSV-1 mutant strain, M6, which includes several deleted genes associated with viral infection virulence and latent infection function, and explored its infection of macrophages and immunological characteristics. The study found that both the attenuated strain M6 and the wild-type strain infect macrophages through the binding of the gD protein to the HVEM receptor on the macrophage surface. Compared to the wild-type strain, the attenuated M6 strain induced a milder immune response, characterized by the lower expression of immune signaling molecules and inflammatory cytokine levels. Upon reintroducing macrophages infected with the two strains into mice, the M6 strain induced lower levels of inflammatory cytokines and higher levels of chemokines in spleen cells and also slightly lower humoral and cellular immune responses than the wild-type strain. Further histopathological analysis revealed that mice in the attenuated M6 group showed more stable body weight changes and milder pathological damage in immune organs such as the liver, spleen, and lymph nodes. In conclusion, the attenuated M6 strain exhibits good immunogenicity and mild pathological side effects, suggesting its potential as an effective immunogen.

Control of HSV-1 Infection: Directions for the Development of CRISPR/Cas-Based Therapeutics and Diagnostics

It is estimated that nearly all individuals have been infected with herpesviruses, with herpes simplex virus type 1 (HSV-1) representing the most prevalent virus. In most cases, HSV-1 causes non-life-threatening skin damage in adults. However, in patients with compromised immune systems, it can cause serious diseases, including death. The situation is further complicated by the emergence of strains that are resistant to both traditional and novel antiviral drugs. It is, therefore, imperative that new methods of combating HSV-1 and other herpesviruses be developed without delay. CRISPR/Cas systems may prove an effective means of controlling herpesvirus infections. This review presents the current understanding of the underlying molecular mechanisms of HSV-1 infection and discusses four potential applications of CRISPR/Cas systems in the fight against HSV-1 infections. These include the search for viral and cellular genes that may serve as effective targets, the optimization of anti-HSV-1 activity of CRISPR/Cas systems in vivo, the development of CRISPR/Cas-based HSV-1 diagnostics, and the validation of HSV-1 drug resistance mutations.

Multifunctional Non-Coding RNAs Mediate Latent Infection and Recurrence of Herpes Simplex Viruses

Herpes simplex viruses (HSVs) often cause latent infection for a lifetime, leading to repeated recurrence. HSVs have been engineered as oncolytic HSVs. The mechanism of the latent infection and recurrence remains largely unknown, which brings great challenges and limitations to eliminate HSVs in clinic and engineer safe oHSVs. Here, we systematically reviewed the latest development of the multi-step complex process of HSV latency and reactivation. Significantly, we first summarized the three HSV latent infection pathways, analyzed the structure and expression of the LAT1 and LAT2 of HSV-1 and HSV-2, proposed the regulation of LAT expression by four pathways, and dissected the function of LAT mediated by five LAT products of miRNAs, sRNAs, lncRNAs, sncRNAs and ORFs. We further analyzed that application of HSV LAT deletion mutants in HSV vaccines and oHSVs. Our review showed that deleting LAT significantly reduced the latency and reactivation of HSV, providing new ideas for the future development of safe and effective HSV therapeutics, vaccines and oHSVs. In addition, we proposed that RNA silencing or RNA interference may play an important role in HSV latency and reactivation, which is worth validating in future.

A HSV1 mutant leads to an attenuated phenotype and induces immunity with a protective effect

Herpes simplex virus type 1 (HSV1) is a complicated structural agent with a sophisticated transcription process and a high infection rate. A vaccine against HSV1 is urgently needed. As multiple viral-encoded proteins, including structural and nonstructural proteins, contribute to immune response stimulation, an attenuated or deficient HSV1 vaccine may be relatively reliable. Advances in genomic modification technologies provide reliable means of constructing various HSV vaccine candidates. Based on our previous work, an M6 mutant with mutations in the UL7, UL41, LAT, Us3, Us11 and Us12 genes was established. The mutant exhibited low proliferation in cells and an attenuated phenotype in an animal model. Furthermore, in mice and rhesus monkeys, the mutant can induce remarkable serum neutralizing antibody titers and T cell activation and protect against HSV1 challenge by impeding viral replication, dissemination and pathogenesis.

The Mutation of the Genes Related to Neurovirulence in HSV-2 Produces an Attenuated Phenotype in Mice

HSV-2 (Herpes simplex virus type 2) is a critical viral agent that mainly causes genital herpes and life-long latent infection in the dorsal root ganglia. Gene modification via CRISPR/Cas9 Clustered regularly interspaced short palindromic repeat sequences/CRISPR associated 9) was used here to construct HSV-2 mutant strains through the deletion of fragments of the RL1 (Repeat Long element 1) and/or LAT (Latency-associated Transcript) genes. The HSV-2 mutant strains LAT-HSV-2 and RL1-LAT-HSV-2 present different biological properties. The proliferation of RL1-LAT-HSV-2 in nerve cells was decreased significantly, and the plaques induced by RL1-LAT-HSV-2 in Vero cells were smaller than those induced by LAT-HSV-2 mutant and wild-type strains. The observation of mice infected with these two mutants compared to mice infected with the wild-type strain indicated that the mutant RL1-LAT-HSV-2 has an attenuated phenotype with reduced pathogenicity during both acute and latent infections and induces a stronger specific immune response than the wild-type strain, whereas the attenuation effect was not found in mice infected with the LAT-HSV-2 mutant containing the LAT gene deletion. However, the simultaneous mutation of both the RL1 and LAT genes did not completely restrict viral proliferation in nerve cells, indicating that multiple HSV genes are involved in viral replication in the neural system. This work suggests that the HSV-2 genes RL1 and/or LAT might be involved in the virulence mechanisms in mouse infections.

Distinct infection process of SARS-CoV-2 in human bronchial epithelial cell lines

Coronavirus disease 2019, caused by severe acute respiratory syndrome coronavirus‐2 (SARS‐CoV‐2), leads to a series of clinical symptoms of respiratory and pulmonary inflammatory reactions via unknown pathologic mechanisms related to the viral infection process in tracheal or bronchial epithelial cells. Investigation of this viral infection in the human bronchial epithelial cell line (16HBE) suggests that SARS‐CoV‐2 can enter these cells through interaction between its membrane‐localized S protein with the angiotensin‐converting enzyme 2 molecule on the host cell membrane. Further observation indicates distinct viral replication with a dynamic and moderate increase, whereby viral replication does not lead to a specific cytopathic effect but maintains a continuous release of progeny virions from infected cells. Although messenger RNA expression of various innate immune signaling molecules is altered in the cells, transcription of interferons‐α (IFN‐α), IFN‐β, and IFN‐γ is unchanged. Furthermore, expression of some interleukins (IL) related to inflammatory reactions, such as IL‐6, IL‐2, and IL‐8, is maintained at low levels, whereas that of ILs involved in immune regulation is upregulated. Interestingly, IL‐22, an IL that functions mainly in tissue repair, shows very high expression. Collectively, these data suggest a distinct infection process for this virus in respiratory epithelial cells, which may be linked to its clinicopathological mechanism.

SARS‐CoV‐2 does not lead to a specific cytopathic effect in 16HBE cells, but maintains continuous release of progeny virions from infected cells. During infection, IL‐22, an interleukin that functions mainly in tissue repair, showed very high expression.

Reducing Viral Inhibition of Host Cellular Apoptosis Strengthens the Immunogenicity and Protective Efficacy of an Attenuated HSV-1 Strain

Herpes simplex virus 1 (HSV-1), a member of α herpesviruses, shows a high infectivity rate of 30%-60% in populations of various ages. Some herpes simplex (HSV) vaccine candidates evaluated during the past 20 years have not shown protective efficacy against viral infection. An improved understanding of the immune profile of infected individuals and the associated mechanism is needed. HSV uses an immune evasion strategy during viral replication, and various virus-encoded proteins, such as ICP47 and Vhs, participate in this process through limiting the ability of CD8⁺ cytotoxic T lymphocytes to recognize target cells. Other proteins, e.g., Us3 and Us5, also play a role in viral immune evasion via interfering with cellular apoptosis. In this work, to study the mechanism by which HSV-1 strain attenuation interferes with the viral immune evasion strategy, we constructed a mutant strain, M5, with deletions in the Us3 and Us5 genes. M5 was shown to induce higher neutralizing antibody titers and a stronger cellular immune response than our previously reported M3 strain, and to prevent virus infection more effectively than the M3 strain in an in vivo mouse challenge test.

Characteristics of herpes simplex virus infection and pathogenesis suggest a strategy for vaccine development

Herpes simplex virus (HSV) can cause oral or genital ulcerative lesions and even encephalitis in various age groups with high infection rates. More seriously, HSV may lead to a wide range of recurrent diseases throughout a lifetime. No vaccines against HSV are currently available. The accumulated clinical research data for HSV vaccines reveal that the effects of HSV interacting with the host, especially the host immune system, may be important for the development of HSV vaccines. HSV vaccine development remains a major challenge. Thus, we focus on the research data regarding the interactions of HSV and host immune cells, including dendritic cells (DCs), innate lymphoid cells (ILCs), macrophages, and natural killer (NK) cells, and the related signal transduction pathways involved in immune evasion and cytokine production. The aim is to explore possible strategies to develop new effective HSV vaccines.

Traditional Chinese Medicine as a Potential Source for HSV-1 Therapy by Acting on Virus or the Susceptibility of Host

Herpes simplex virus type 1 (HSV-1) is the most common virus, with an estimated infection rate of 60–95% among the adult population. Once infected, HSV-1 can remain latent in the host for a lifetime and be reactivated in patients with a compromised immune system. Reactivation of latent HSV-1 can also be achieved by other stimuli. Though acyclovir (ACV) is a classic drug for HSV-1 infection, ACV-resistant strains have been found in immune-compromised patients and drug toxicity has also been commonly reported. Therefore, there is an urge to search for new anti-HSV-1 agents. Natural products with potential anti-HSV-1 activity have the advantages of minimal side effects, reduced toxicity, and they exert their effect by various mechanisms. This paper will not only provide a reference for the safe dose of these agents if they are to be used in humans, referring to the interrelated data obtained from in vitro experiments, but also introduce the main pharmacodynamic mechanisms of traditional Chinese medicine (TCM) against HSV-1. Taken together, TCM functions as a potential source for HSV-1 therapy by direct (blocking viral attachment/absorption/penetration/replication) or indirect (reducing the susceptibility to HSV-1 or regulating autophagy) antiviral activities. The potential of these active components in the development of anti-HSV-1 drugs will also be described.

Attenuated Phenotype and Immunogenic Characteristics of a Mutated Herpes Simplex Virus 1 Strain in the Rhesus Macaque

Herpes simplex virus type 1(HSV-1) presents a conundrum to public health worldwide because of its specific pathogenicity and clinical features. Some experimental vaccines, such as the recombinant viral glycoproteins, exhibit the viral immunogenicity of a host-specific immune response, but none of these has achieved a valid epidemiological protective efficacy in the human population. In the present study, we constructed an attenuated HSV-1 strain M3 through the partial deletion of UL7, UL41, and the latency-associated transcript (LAT) using the CRISPR/Cas9 system. The mutant strain exhibited lowered infectivity and virulence in macaques. Neutralization testing and ELISpot detection of the specific T-cell responses confirmed the specific immunity induced by M3 immunization and this immunity defended against the challenges of the wild-type strain and restricted the entry of the wild-type strain into the trigeminal ganglion. These results in rhesus macaques demonstrated the potential of the attenuated vaccine for the prevention of HSV-1 in humans.

Immune mechanisms induced by an HSV-1 mutant strain: Discrepancy analysis of the immune system gene profile in comparison with a wild-type strain

Herpes simplex virus is a prevalent pathogen of humans of various age groups. The fact that no prophylactic or therapeutic vaccine is currently available suggests a significant need to further investigate the immune mechanisms induced by the virus and various vaccine candidates. We previously generated an HSV-1 mutant strain, M3, with partial deletions in ul7, ul41 and LAT that produced an attenuated phenotype in mice. In the present study, we performed a comparative analysis to characterize the immune responses induced by M3 versus wild-type HSV-1 in a mouse model. Infection with wild-type HSV-1 triggered an inflammatory-dominated response and adaptive immunity suppression and was accompanied by severe pathological damage. In contrast, infection with M3 induced a systematic immune response involving full activation of both innate and adaptive immunity and was accompanied by no obvious pathological changes. Furthermore, the immune response induced by M3 protected mice from lethal challenge with wild-type strains of HSV-1 and restrained virus proliferation and impaired latency. These data are useful for further HSV-1 vaccine development using a mutant strain construction strategy.