The imitation game: a viral strategy to subvert the complement system

Kaposi sarcoma-associated herpesvirus complement control protein (KCP) and glycoprotein K8.1 are not required for viral infection in vitro or in vivo

Kaposi sarcoma-associated herpesvirus (KSHV), also known as human herpesvirus-8, is the causal agent of Kaposi sarcoma, a cancer that appears as tumors on the skin or mucosal surfaces, as well as primary effusion lymphoma and KSHV-associated multicentric Castleman disease, which are B-cell lymphoproliferative disorders. Effective prophylactic and therapeutic strategies against KSHV infection and its associated diseases are needed. To develop these strategies, it is crucial to identify and target viral glycoproteins involved in KSHV infection of host cells. Multiple KSHV glycoproteins expressed on the viral envelope are thought to play a pivotal role in viral infection, but the infection mechanisms involving these glycoproteins remain largely unknown. We investigated the role of two KSHV envelope glycoproteins, KSHV complement control protein (KCP) and K8.1, in viral infection in various cell types in vitro and in vivo. Using our newly generated anti-KCP antibodies, previously characterized anti-K8.1 antibodies, and recombinant mutant KSHV viruses lacking KCP, K8.1, or both, we demonstrated the presence of KCP and K8.1 on the surface of both virions and KSHV-infected cells. We showed that KSHV lacking KCP and/or K8.1 remained infectious in KSHV-susceptible cell lines, including epithelial, endothelial, and fibroblast, when compared to wild-type recombinant KSHV. We also provide the first evidence that KSHV lacking K8.1 or both KCP and K8.1 can infect human B cells in vivo in a humanized mouse model. Thus, these results suggest that neither KCP nor K8.1 is required for KSHV infection of various host cell types and that these glycoproteins do not determine KSHV cell tropism.

IMPORTANCE

Kaposi sarcoma-associated herpesvirus (KSHV) is an oncogenic human gamma-herpesvirus associated with the endothelial malignancy Kaposi sarcoma and the lymphoproliferative disorders primary effusion lymphoma and multicentric Castleman disease. Determining how KSHV glycoproteins such as complement control protein (KCP) and K8.1 contribute to the establishment, persistence, and transmission of viral infection will be key for developing effective anti-viral vaccines and therapies to prevent and treat KSHV infection and KSHV-associated diseases. Using newly generated anti-KCP antibodies, previously characterized anti-K8.1 antibodies, and recombinant mutant KSHV viruses lacking KCP and/or K8.1, we show that KCP and K8.1 can be found on the surface of both virions and KSHV-infected cells. Furthermore, we show that KSHV lacking KCP and/or K8.1 remains infectious to diverse cell types susceptible to KSHV in vitro and to human B cells in vivo in a humanized mouse model, thus providing evidence that these viral glycoproteins are not required for KSHV infection.

Gene therapy for liver diseases - progress and challenges

Gene therapy is poised to revolutionize modern medicine, with seemingly unlimited potential for treating and curing genetic disorders. For otherwise incurable indications, including most inherited metabolic liver disorders, gene therapy provides a realistic therapeutic option. In this Review, we discuss gene supplementation and gene editing involving the use of recombinant adeno-associated virus (rAAV) vectors for the treatment of inherited liver diseases, including updates on several ongoing clinical trials that are producing promising results. Clinical testing has been essential in highlighting many key translational challenges associated with this transformative therapy. In particular, the interaction of a patient's immune system with the vector raises issues of safety and the duration of treatment efficacy. Furthermore, several serious adverse events after the administration of high doses of rAAVs suggest greater involvement of innate immune responses and pre-existing hepatic conditions than initially anticipated. Finally, permanent modification of the host genome associated with rAAV genome integration and gene editing raises concerns about the risk of oncogenicity that require careful evaluation. We summarize the main progress, challenges and pathways forward for gene therapy for liver diseases.

Progressive multifocal leukoencephalopathy genetic risk variants for pharmacovigilance of immunosuppressant therapies

Background

Progressive multifocal leukoencephalopathy (PML) is a rare and often lethal brain disorder caused by the common, typically benign polyomavirus 2, also known as JC virus (JCV). In a small percentage of immunosuppressed individuals, JCV is reactivated and infects the brain, causing devastating neurological defects. A wide range of immunosuppressed groups can develop PML, such as patients with: HIV/AIDS, hematological malignancies (e.g., leukemias, lymphomas, and multiple myeloma), autoimmune disorders (e.g., psoriasis, rheumatoid arthritis, and systemic lupus erythematosus), and organ transplants. In some patients, iatrogenic (i.e., drug-induced) PML occurs as a serious adverse event from exposure to immunosuppressant therapies used to treat their disease (e.g., hematological malignancies and multiple sclerosis). While JCV infection and immunosuppression are necessary, they are not sufficient to cause PML.

Methods

We hypothesized that patients may also have a genetic susceptibility from the presence of rare deleterious genetic variants in immune-relevant genes (e.g., those that cause inborn errors of immunity). In our prior genetic study of 184 PML cases, we discovered 19 candidate PML risk variants. In the current study of another 152 cases, we validated 4 of 19 variants in both population controls (gnomAD 3.1) and matched controls (JCV+ multiple sclerosis patients on a PML-linked drug ≥ 2 years).

Results

The four variants, found in immune system genes with strong biological links, are: C8B, 1-57409459-C-A, rs139498867; LY9 (alias SLAMF3), 1-160769595-AG-A, rs763811636; FCN2, 9-137779251-G-A, rs76267164; STXBP2, 19-7712287-G-C, rs35490401. Carriers of any one of these variants are shown to be at high risk of PML when drug-exposed PML cases are compared to drug-exposed matched controls: P value = 3.50E-06, OR = 8.7 [3.7-20.6]. Measures of clinical validity and utility compare favorably to other genetic risk tests, such as BRCA1 and BRCA2 screening for breast cancer risk and HLA-B^*15:02 pharmacogenetic screening for pharmacovigilance of carbamazepine to prevent Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis.

Conclusion

For the first time, a PML genetic risk test can be implemented for screening patients taking or considering treatment with a PML-linked drug in order to decrease the incidence of PML and enable safer use of highly effective therapies used to treat their underlying disease.

Nonstructural Protein 1 of Variant PEDV Plays a Key Role in Escaping Replication Restriction by Complement C3

Zoonotic coronaviruses represent an ongoing threat to public health. The classical porcine epidemic diarrhea virus (PEDV) first appeared in the early 1970s. Since 2010, outbreaks of highly virulent PEDV variants have caused great economic losses to the swine industry worldwide. However, the strategies by which PEDV variants escape host immune responses are not fully understood. Complement component 3 (C3) is considered a central component of the three complement activation pathways and plays a crucial role in preventing viral infection. In this study, we found that C3 significantly inhibited PEDV replication in vitro, and both variant and classical PEDV strains induced high levels of interleukin-1β (IL-1β) in Huh7 cells. However, the PEDV variant strain reduces C3 transcript and protein levels induced by IL-1β compared with the PEDV classical strain. Examination of key molecules of the C3 transcriptional signaling pathway revealed that variant PEDV reduced C3 by inhibiting CCAAT/enhancer-binding protein β (C/EBP-β) phosphorylation. Mechanistically, PEDV nonstructural protein 1 (NSP1) inhibited C/EBP-β phosphorylation via amino acid residue 50. Finally, we constructed recombinant PEDVs to verify the critical role of amino acid 50 of NSP1 in the regulation of C3 expression. In summary, we identified a novel antiviral role of C3 in inhibiting PEDV replication and the viral immune evasion strategies of PEDV variants. Our study reveals new information on PEDV-host interactions and furthers our understanding of the pathogenic mechanism of this virus. IMPORTANCE The complement system acts as a vital link between the innate and the adaptive immunity and has the ability to recognize and neutralize various pathogens. Activation of the complement system acts as a double-edged sword, as appropriate levels of activation protect against pathogenic infections, but excessive responses can provoke a dramatic inflammatory response and cause tissue damage, leading to pathological processes, which often appear in COVID-19 patients. However, how PEDV, as the most severe coronavirus causing diarrhea in piglets, regulates the complement system has not been previously reported. In this study, for the first time, we identified a novel mechanism of a PEDV variant in the suppression of C3 expression, showing that different coronaviruses and even different subtype strains differ in regulation of C3 expression. In addition, this study provides a deeper understanding of the mechanism of the PEDV variant in immune escape and enhanced virulence.

SARS-CoV-2 Omicron variant: Immune escape and vaccine development

New genetic variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) constantly emerge through unmitigated spread of the virus in the ongoing Coronavirus disease 2019 pandemic. Omicron (B.1.1.529), the latest variant of concern (VOC), has so far shown exceptional spread and infectivity and has established itself as the dominant variant in recent months. The SARS-CoV-2 spike glycoprotein is a key component for the recognition and binding to host cell angiotensin-converting enzyme 2 receptors. The Omicron variant harbors a cluster of substitutions/deletions/insertions, and more than 30 mutations are located in spike. Some noticeable mutations, including K417N, T478K, N501Y, and P681H, are shared with the previous VOCs Alpha, Beta, Gamma, or Delta variants and have been proven to be associated with higher transmissibility, viral infectivity, and immune evasion potential. Studies have revealed that the Omicron variant is partially resistant to the neutralizing activity of therapeutic antibodies and convalescent sera, which poses significant challenges for the clinical effectiveness of the current vaccines and therapeutic antibodies. We provide a comprehensive analysis and summary of the epidemiology and immune escape mechanisms of the Omicron variant. We also suggest some therapeutic strategies against the Omicron variant. This review, therefore, aims to provide information for further research efforts to prevent and contain the impact of new VOCs during the ongoing pandemic.

COVID-19, Pre-Eclampsia, and Complement System

COVID-19 is characterized by virus-induced injury leading to multi-organ failure, together with inflammatory reaction, endothelial cell (EC) injury, and prothrombotic coagulopathy with thrombotic events. Complement system (C) via its cross-talk with the contact and coagulation systems contributes significantly to the severity and pathological consequences due to SARS-CoV-2 infection. These immunopathological mechanisms overlap in COVID-19 and pre-eclampsia (PE). Thus, mothers contracting SARS-CoV-2 infection during pregnancy are more vulnerable to developing PE. SARS-CoV-2 infection of ECs, via its receptor ACE2 and co-receptor TMPRSS2, can provoke endothelial dysfunction and disruption of vascular integrity, causing hyperinflammation and hypercoagulability. This is aggravated by bradykinin increase due to inhibition of ACE2 activity by the virus. C is important for the progression of normal pregnancy, and its dysregulation can impact in the form of PE-like syndrome as a consequence of SARS-CoV-2 infection. Thus, there is also an overlap between treatment regimens of COVID-19 and PE. C inhibitors, especially those targeting C3 or MASP-2, are exciting options for treating COVID-19 and consequent PE. In this review, we examine the role of C, contact and coagulation systems as well as endothelial hyperactivation with respect to SARS-CoV-2 infection during pregnancy and likely development of PE.

Emerging roles of the complement system in host-pathogen interactions

The complement system has historically been entertained as a fluid-phase, hepatically derived system which protects the intravascular space from encapsulated bacteria. However, there has been an increasing appreciation for its role in protection against non-encapsulated pathogens. Specifically, we have an improved understanding of how pathogens are recognized by specific complement proteins, as well as how they trigger and evade them. Additionally, we have an improved understanding of locally derived complement proteins, many of which promote host defense. Moreover, intracellular complement proteins have been identified that facilitate local protection and barrier function despite pathogen invasion. Our review aims to summarize these advances in the field as well as provide an insight into the pathophysiological changes occurring when the system is dysregulated in infection.

A double edged-sword - The Complement System during SARS-CoV-2 infection

In the past 20 years, infections caused by coronaviruses SARS-CoV, MERS-CoV and SARS-CoV-2 have posed a threat to public health since they may cause severe acute respiratory syndrome (SARS) in humans. The Complement System is activated during viral infection, being a central protagonist of innate and acquired immunity. Here, we report some interactions between these three coronaviruses and the Complement System, highlighting the central role of C3 with the severity of these infections. Although it can be protective, its role during coronavirus infections seems to be contradictory. For example, during SARS-CoV-2 infection, Complement System can control the viral infection in asymptomatic or mild cases; however, it can also intensify local and systemic damage in some of severe COVID-19 patients, due to its potent proinflammatory effect. In this last condition, the activation of the Complement System also amplifies the cytokine storm and the pathogenicity of coronavirus infection. Experimental treatment with Complement inhibitors has been an enthusiastic field of intense investigation in search of a promising additional therapy in severe COVID-19 patients.

Virus-Encoded Complement Regulators: Current Status

Viruses require a host for replication and survival and hence are subjected to host immunological pressures. The complement system, a crucial first response of the host immune system, is effective in targeting viruses and virus-infected cells, and boosting the antiviral innate and acquired immune responses. Thus, the system imposes a strong selection pressure on viruses. Consequently, viruses have evolved multiple countermeasures against host complement. A major mechanism employed by viruses to subvert the complement system is encoding proteins that target complement. Since viruses have limited genome size, most of these proteins are multifunctional in nature. In this review, we provide up to date information on the structure and complement regulatory functions of various viral proteins.

Potential Cross-Links of Inflammation With Schizophreniform and Affective Symptoms: A Review and Outlook on Autoimmune Encephalitis and COVID-19

Based on current implications of the SARS-CoV-2 pandemic with regards to mental health, we show that biological links exist between inflammation and mental illness in addition to psychoreactive effects. We describe key principles of the biological interaction of the immune system and the mind, as well as the possible routes of viral entry into the brain. In addition, we provide a stepwise scheme for the diagnosis and therapy of autoimmune-encephalitis with schizophrenia-like symptomatology as a general guide for clinical practice and in the specialized scenario of infections, such as those caused by the SARS-CoV-2 virus.