T-bet+ B cells are activated by and control endogenous retroviruses through TLR-dependent mechanisms.

Endogenous retroviruses (ERVs) are an integral part of the mammalian genome. The role of immune control of ERVs in general is poorly defined as is their function as anti-cancer immune targets or drivers of autoimmune disease. Here, we generate mouse-strains where Moloney-Murine Leukemia Virus tagged with GFP (ERV-GFP) infected the mouse germline. This enables us to analyze the role of genetic, epigenetic and cell intrinsic restriction factors in ERV activation and control. We identify an autoreactive B cell response against the neo-self/ERV antigen GFP as a key mechanism of ERV control. Hallmarks of this response are spontaneous ERV-GFP+ germinal center formation, elevated serum IFN-γ levels and a dependency on Age-associated B cells (ABCs) a subclass of T-bet+ memory B cells. Impairment of IgM B cell receptor-signal in nucleic-acid sensing TLR-deficient mice contributes to defective ERV control. Although ERVs are a part of the genome they break immune tolerance, induce immune surveillance against ERV-derived self-antigens and shape the host immune response.

Self-Amplifying RNA Vaccine Candidates: Alternative Platforms for mRNA Vaccine Development.

The present use of mRNA vaccines against COVID-19 has shown for the first time the potential of mRNA vaccines for infectious diseases. Here we will summarize the current knowledge about improved mRNA vaccines, i.e., the self-amplifying mRNA (saRNA) vaccines. This approach may enhance antigen expression by amplification of the antigen-encoding RNA. RNA design, RNA delivery, and the innate immune responses induced by RNA will be reviewed.

Chikungunya Vaccine Candidates: Current Landscape and Future Prospects.

Chikungunya virus (CHIKV) is an alphavirus that has spread globally in the last twenty years. Although mortality is rather low, infection can result in debilitating arthralgia that can persist for years. Unfortunately, no treatments or preventive vaccines are currently licensed against CHIKV infections. However, a large range of promising preclinical and clinical vaccine candidates have been developed during recent years. This review will give an introduction into the biology of CHIKV and the immune responses that are induced by infection, and will summarize CHIKV vaccine development.

A Bivalent Trans-Amplifying RNA Vaccine Candidate Induces Potent Chikungunya and Ross River Virus Specific Immune Responses.

Alphaviruses such as the human pathogenic chikungunya virus (CHIKV) and Ross River virus (RRV) can cause explosive outbreaks raising public health concerns. However, no vaccine or specific antiviral treatment is yet available. We recently established a CHIKV vaccine candidate based on trans-amplifying RNA (taRNA). This novel system consists of a replicase-encoding mRNA and a trans-replicon (TR) RNA encoding the antigen. The TR-RNA is amplified by the replicase in situ. We were interested in determining whether multiple TR-RNAs can be amplified in parallel and if, thus, a multivalent vaccine candidate can be generated. In vitro, we observed an efficient amplification of two TR-RNAs, encoding for the CHIKV and the RRV envelope proteins, by the replicase, which resulted in a high antigen expression. Vaccination of BALB/c mice with the two TR-RNAs induced CHIKV- and RRV-specific humoral and cellular immune responses. However, antibody titers and neutralization capacity were higher after immunization with a single TR-RNA. In contrast, alphavirus-specific T cell responses were equally potent after the bivalent vaccination. These data show the proof-of-principle that the taRNA system can be used to generate multivalent vaccines; however, further optimizations will be needed for clinical application.

Monkeypox Goes North: Ongoing Worldwide Monkeypox Infections in Humans.

In the late 1970s, global vaccination programs resulted in the eradication of smallpox. The Monkeypox virus (MPXV), which is closely related to the smallpox-inducing variola virus, was previously endemic only in Sub-Saharan Africa but is currently spreading worldwide. Only older people who have been vaccinated against smallpox are expected to be sufficiently protected against poxviruses. Here I will summarize current knowledge about the virus, the disease caused by MPXV infections, and strategies to limit its spread.

A taRNA vaccine candidate induces a specific immune response that protects mice against Chikungunya virus infections.

The arthritogenic alphavirus, chikungunya virus (CHIKV), is now present in almost 100 countries worldwide. Further spread is very likely, which raises public health concerns. CHIKV infections cause fever and arthralgia, which can be debilitating and last for years. Here, we describe a CHIKV vaccine candidate based on trans-amplifying RNA (taRNA). The vaccine candidate consists of two RNAs: a non-replicating mRNA encoding for the CHIKV nonstructural proteins, forming the replicase complex and a trans-replicon (TR) RNA encoding the CHIKV envelope proteins. The TR-RNA can be amplified by the replicase in trans, and small RNA amounts can induce a potent immune response. The TR-RNA was efficiently amplified by the CHIKV replicase in vitro, leading to high protein expression, comparable to that generated by a CHIKV infection. In addition, the taRNA system did not recombine to replication-competent CHIKV. Using a prime-boost schedule, the vaccine candidate induced potent CHIKV-specific humoral and cellular immune responses in vivo in a mouse model. Notably, mice were protected against a high-dose CHIKV challenge infection with two vaccine doses of only 1.5 µg RNA. Therefore, taRNAs are a promising safe and efficient vaccination strategy against CHIKV infections.

The SARS-CoV-2 Variant Omicron Is Able to Escape Vaccine-Induced Humoral Immune Responses, but Is Counteracted by Booster Vaccination.

The SARS-CoV-2 variant Omicron has spread world-wide and is responsible for rapid increases in infections, including in populations with high vaccination rates. Here, we analysed in the sera of vaccinated individuals the antibody binding to the receptor-binding domain (RBD) of the spike protein and the neutralization of wild-type (WT), Delta (B.1.617.2), and Omicron (B.1.1.529; BA.1) pseudotyped vectors. Although sera from individuals immunized with vector vaccines (Vaxzevria; AZ and COVID-19 Janssen, Ad26.COV2.S; J&J) were able to bind and neutralize WT and Delta, they showed only background levels towards Omicron. In contrast, mRNA (Comirnaty; BNT) or heterologous (AZ/BNT) vaccines induced weak, but detectable responses against Omicron. While RBD-binding antibody levels decreased significantly six months after full vaccination, the SARS-CoV-2 RBD-directed avidity remained constant. However, this still coincided with a significant decrease in neutralization activity against all variants. A third booster vaccination with BNT significantly increased the humoral immune responses against all tested variants, including Omicron. In conclusion, only vaccination schedules that included at least one dose of mRNA vaccine and especially an mRNA booster vaccination induced sufficient antibody levels with neutralization capacity against multiple variants, including Omicron.

Longitudinal Analysis of Coronavirus-Neutralizing Activity in COVID-19 Patients.

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic has now been continuing for more than two years. The infection causes COVID-19, a disease of the respiratory and cardiovascular system of variable severity. Here, the humoral immune response of 80 COVID-19 patients from the University Hospital Frankfurt/Main, Germany, was characterized longitudinally. The SARS-CoV-2 neutralization activity of serum waned over time. The neutralizing potential of serum directed towards the human alpha-coronavirus NL-63 (NL63) also waned, indicating that no cross-priming against alpha-coronaviruses occurred. A subset of the recovered patients (n = 13) was additionally vaccinated with the mRNA vaccine Comirnaty. Vaccination increased neutralization activity against SARS-CoV-2 wild-type (WT), Delta, and Omicron, although Omicron-specific neutralization was not detectable prior to vaccination. In addition, the vaccination induced neutralizing antibodies against the more distantly related SARS-CoV-1 but not against NL63. The results indicate that although SARS-CoV-2 humoral immune responses induced by infection wane, vaccination induces a broad neutralizing activity against multiple SARS-CoVs, but not to the common cold alpha-coronavirus NL63.

Comparative Investigation of Methods for Analysis of SARS-CoV-2-Spike-Specific Antisera.

In light of an increasing number of vaccinated and convalescent individuals, there is a major need for the development of robust methods for the quantification of neutralizing antibodies; although, a defined correlate of protection is still missing. Sera from hospitalized COVID-19 patients suffering or not suffering from acute respiratory distress syndrome (ARDS) were comparatively analyzed by plaque reduction neutralization test (PRNT) and pseudotype-based neutralization assays to quantify their neutralizing capacity. The two neutralization assays showed comparable data. In case of the non-ARDS sera, there was a distinct correlation between the data from the neutralization assays on the one hand, and enzyme-linked immune sorbent assay (ELISA), as well as biophysical analyses, on the other hand. As such, surface plasmon resonance (SPR)-based assays for quantification of binding antibodies or analysis of the stability of the antigen-antibody interaction and inhibition of syncytium formation, determined by cell fusion assays, were performed. In the case of ARDS sera, which are characterized by a significantly higher fraction of RBD-binding IgA antibodies, there is a clear correlation between the neutralization assays and the ELISA data. In contrast to this, a less clear correlation between the biophysical analyses on the one hand and ELISAs and neutralization assays on the other hand was observed, which might be explained by the heterogeneity of the antibodies. To conclude, for less complex immune sera-as in cases of non-ARDS sera-combinations of titer quantification by ELISA with inhibition of syncytium formation, SPR-based analysis of antibody binding, determination of the stability of the antigen-antibody complex, and competition of the RBD-ACE2 binding represent alternatives to the classic PRNT for analysis of the neutralizing potential of SARS-CoV-2-specific sera, without the requirement for a BSL3 facility.

Rapid and Sensitive SERS-Based Lateral Flow Test for SARS-CoV2-Specific IgM/IgG Antibodies.

As an immune response to COVID-19 infection, patients develop SARS-CoV-2-specific IgM/IgG antibodies. Here, we compare the performance of a conventional lateral flow assay (LFA) with a surface-enhanced Raman scattering (SERS)-based LFA test for the detection of SARS-CoV-2-specific IgM/IgG in sera of COVID-19 patients. Sensitive detection of IgM might enable early serological diagnosis of acute infections. Rapid detection in serum using a custom-built SERS reader is at least an order of magnitude more sensitive than the conventional LFAs with naked-eye detection. For absolute quantification and the determination of the limit of detection (LOD), a set of reference measurements using purified (total) IgM in buffer was performed. In this purified system, the sensitivity of SERS detection is even 7 orders of magnitude higher: the LOD for SERS was ca. 100 fg/mL compared to ca. 1 µg/mL for the naked-eye detection. This outlines the high potential of SERS-based LFAs in point-of-care testing once the interference of serum components with the gold conjugates and the nitrocellulose membrane is minimized.

Development of a Sensitive Detection Method for Alphaviruses and Its Use as a Virus Neutralization Assay.

Alphaviruses have a single-stranded, positive-sense RNA genome that contains two open reading frames encoding either the non-structural or the structural genes. Upon infection, the genomic RNA is translated into the non-structural proteins (nsPs). NsPs are required for viral RNA replication and transcription driven from the subgenomic promoter (sgP). Transfection of an RNA encoding the luciferase gene under the control of the sgP into cells enabled the detection of replication-competent chikungunya virus (CHIKV) or Mayaro virus (MAYV) with high sensitivity as a function of the induced luciferase activity. This assay principle was additionally used to analyze virus-neutralizing antibodies in sera and might be an alternative to standard virus neutralization assays based on virus titration or the use of genetically modified tagged viruses.

The green tea catechin epigallocatechin gallate inhibits SARS-CoV-2 infection.

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection has caused a pandemic with tens of millions of cases and more than a million deaths. The infection causes COVID-19, a disease of the respiratory system of divergent severity. No treatment exists. Epigallocatechin-3-gallate (EGCG), the major component of green tea, has several beneficial properties, including antiviral activities. Therefore, we examined whether EGCG has antiviral activity against SARS-CoV-2. EGCG blocked not only the entry of SARS-CoV-2, but also MERS- and SARS-CoV pseudotyped lentiviral vectors and inhibited virus infections in vitro. Mechanistically, inhibition of the SARS-CoV-2 spike-receptor interaction was observed. Thus, EGCG might be suitable for use as a lead structure to develop more effective anti-COVID-19 drugs.

Comparison of potency assays to assess SARS-CoV-2 neutralizing antibody capacity in COVID-19 convalescent plasma.

Convalescent plasma is plasma collected from individuals after resolution of an infection and the development of antibodies. Passive antibody administration by transfusion of convalescent plasma is currently in clinical evaluations to treat COVID-19 patients. The level of neutralizing antibodies vary among convalescent patients and fast and simple methods to identify suitable plasma donations are needed. We compared three methods to determine the SARS-CoV-2 neutralizing activity of human convalescent plasma: life virus neutralization by plaque reduction assay, a lentiviral vector based pseudotype neutralization assay and a competition ELISA-based surrogate virus neutralization assay (sVNT). Neutralization activity correlated among the different assays; however the sVNT assay was overvaluing the low neutralizing plasma. On the other hand, the sVNT assay required the lowest biosafety level, is fast and is sufficient to identify highly neutralizing plasma samples. Though weakly neutralizing samples were more reliable detected by the more challenging lentiviral vector based assays or virus neutralization assays. Spike receptor binding competition assays are suitable to identify highly neutralizing plasma samples under low biosafety requirements. Detailed analysis of in vitro neutralization activity requires more sophisticated methods that have to be performed under higher biosafety levels.

Analysis of Humoral Immune Responses in Patients With Severe Acute Respiratory Syndrome Coronavirus 2 Infection.

BACKGROUND: The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has caused a pandemic with tens of millions of cases and hundreds of thousands of deaths. The infection causes coronavirus disease 2019 (COVID-19), a disease of the respiratory system of divergent severity. In the current study, humoral immune responses were characterized in a cohort of 143 patients with COVID-19 from the University Hospital Frankfurt am Main, Germany. METHODS: SARS-CoV-2-specific-antibodies were detected by enzyme-linked immunosorbent assay (ELISA). SARS-CoV-2 and human coronavirus NL63 neutralization activity was analyzed with pseudotyped lentiviral vectors. RESULTS: The severity of COVID-19 increased with age, and male patients encountered more serious symptoms than female patients. Disease severity was correlated with the amount of SARS-CoV-2-specific immunoglobulin (Ig) G and IgA and the neutralization activity of the antibodies. The amount of SARS-CoV-2-specific IgG antibodies decreased with time after polymerase chain reaction conformation of the infection, and antibodies directed against the nucleoprotein waned faster than spike protein-directed antibodies. In contrast, for the common flu coronavirus NL63, COVID-19 disease severity seemed to be correlated with low NL63-neutralizing activities, suggesting the possibility of cross-reactive protection. CONCLUSION: The results describe the humoral immune responses against SARS-CoV-2 and might aid the identification of correlates of protection needed for vaccine development.

A highly immunogenic and effective measles virus-based Th1-biased COVID-19 vaccine.

The COVID-19 pandemic is caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and has spread worldwide, with millions of cases and more than 1 million deaths to date. The gravity of the situation mandates accelerated efforts to identify safe and effective vaccines. Here, we generated measles virus (MeV)-based vaccine candidates expressing the SARS-CoV-2 spike glycoprotein (S). Insertion of the full-length S protein gene in two different MeV genomic positions resulted in modulated S protein expression. The variant with lower S protein expression levels was genetically stable and induced high levels of effective Th1-biased antibody and T cell responses in mice after two immunizations. In addition to neutralizing IgG antibody responses in a protective range, multifunctional CD8+ and CD4+ T cell responses with S protein-specific killing activity were detected. Upon challenge using a mouse-adapted SARS-CoV-2, virus loads in vaccinated mice were significantly lower, while vaccinated Syrian hamsters revealed protection in a harsh challenge setup using an early-passage human patient isolate. These results are highly encouraging and support further development of MeV-based COVID-19 vaccines.

[Monoclonal antibodies for anti-infective therapy]. / Monoklonale Antikörper zur antiinfektiven Therapie.

Sera of animal origin and hyperimmunoglobulins have dominated serum therapy for a century. Although numerous monoclonal antibodies (MABs) have been developed since the end of the 1980s, particularly for the treatment of immunological and oncological diseases, it will take 20 years before the first anti-infective MAB is approved in the European Union. Interestingly, to combat the COVID-19 pandemic, numerous MABs, which are approved in particular for immunological indications, are currently being used to treat the consequences of SARS-CoV­2 infection, such as pneumonia or hyperimmune reactions.The approved monoclonal antibodies for the treatment of infectious diseases are presented here. In addition, an overview of the current developments, in particular in the treatment of SARS-CoV­2 infection, is provided.

A New Host Factor Essential for Chikungunya Virus.

FHL1 has been identified as a host protein that is essential for chikungunya virus (CHIKV) replication. FHL1 interacts with the chikungunya non-structural protein 3, which is thought to recruit cellular proteins to the viral replication complex. Inhibition of this interaction is a promising target for drug development.

Analysis of Humoral Immune Responses in Chikungunya Virus (CHIKV)-Infected Patients and Individuals Vaccinated With a Candidate CHIKV Vaccine.

BACKGROUND: Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus that causes severe flu-like symptoms. The acute symptoms disappear after 1 week, but chronic arthralgia can persist for years. In this study, humoral immune responses in CHIKV-infected patients and vaccinees were analyzed. METHODS: Alphavirus neutralization activity was analyzed with pseudotyped lentiviral vectors, and antibody epitope mapping was performed with a peptide array. RESULTS: The greatest CHIKV neutralization activity was observed 60-92 days after onset of symptoms. The amount of CHIKV-specific antibodies and their binding avidity and cross-reactivity with other alphaviruses increased over time. Chikungunya virus and o'nyong-nyong virus (ONNV) were both neutralized to a similar extent. Linear antibody binding epitopes were mainly found in E2 domain B and the acid-sensitive regions (ASRs). In addition, serum samples from healthy volunteers vaccinated with a measles-vectored chikungunya vaccine candidate, MV-CHIK, were analyzed. Neutralization activity in the samples from the vaccine cohort was 2- to 6-fold lower than in samples from CHIKV-infected patients. In contrast to infection, vaccination only induced cross-neutralization with ONNV, and the E2 ASR1 was the major antibody target. CONCLUSIONS: These data could assist vaccine design and enable the identification of correlates of protection necessary for vaccine efficacy.

Cellular Attachment and Entry Factors for Chikungunya Virus.

Chikungunya virus (CHIKV) is clinically the most relevant member of the Alphavirus genus. Like alphaviruses in general, CHIKV has the capacity to infect a large variety of cells, tissues, and species. This broad host tropism of CHIKV indicates that the virus uses a ubiquitously expressed receptor to infect cells. This review summarizes the current knowledge available on cellular CHIKV receptors and the attachment factors used by CHIKV.