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Monkeypox virus (MPXV), which causes disease in humans, has for many years been restricted to the African continent, with only a handful of sporadic cases in other parts of the world. However, unprecedented outbreaks of monkeypox in non-endemic regions have recently taken the world by surprise. In less than 4 months, the number of detected MPXV infections has soared to more than 48,000 cases, recording a total of 13 deaths. In this Review, we discuss the clinical, epidemiological and immunological features of MPXV infections. We also highlight important research questions and new opportunities to tackle the ongoing monkeypox outbreak.

O'nyongnyong virus (ONNV) is a re-emerging alphavirus previously known to be transmitted by main malaria vectors, thus suggesting the possibility of coinfections with arboviruses in co-endemic areas. However, the pathological outcomes of such infections remain unknown. Using murine coinfection models, we demonstrated that a preexisting blood-stage Plasmodium infection suppresses ONNV-induced pathologies. We further showed that suppression of viremia and virus dissemination are dependent on Plasmodium-induced IFNγ and are associated with reduced infection of CD45- cells at the site of virus inoculation. We further proved that treatment with IFNγ or plasma samples from Plasmodium vivax-infected patients containing IFNγ are able to restrict ONNV infection in human fibroblast, synoviocyte, skeletal muscle, and endothelial cell lines. Mechanistically, the role of IFNγ in restricting ONNV infection was confirmed in in vitro infection assays through the generation of an IFNγ receptor 1 α chain (IFNγR1)-deficient cell line. Agency for Science, Technology and Research (A*STAR) Published version The study was supported by a core research grant provided to A*STAR Infectious Diseases Labs and Singapore Immunology Network by the Biomedical Research Council (BMRC) from the Agency for Science, Technology and Research (A*STAR). A Torres-Ruesta is supported by the A*STAR Singapore International Graduate Award (SINGA) scholarship. Flow cytometry platform is supported by the Health and Biomedical Sciences (HBMS) Open Fund Shared Infrastructure Support Grant under the Immunomonitoring Service Platform project (NRF2017_SISFP09). The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern (VOCs) that have become dominant as the pandemic progresses bear the ORF8 mutation together with multiple spike mutations. A 382-nucleotide deletion (Δ382) in the ORF7b and ORF8 regions has been associated with milder disease phenotype and less systemic inflammation in COVID-19 patients. However, its impact on host immunity against SARS-CoV-2 remains undefined. Here, RNA-sequencing was performed to elucidate whole blood transcriptomic profiles and identify contrasting immune signatures between patients infected with either wildtype or Δ382 SARS-CoV-2 variant. Interestingly, the immune landscape of Δ382 SARS-CoV-2 infected patients featured an increased adaptive immune response, evidenced by enrichment of genes related to T cell functionality, a more robust SARS-CoV-2-specific T cell immunity, as well as a more rapid antibody response. At the molecular level, eukaryotic initiation factor 2 signaling was found to be upregulated in patients bearing Δ382, and its associated genes were correlated with systemic levels of T cell-associated and pro-inflammatory cytokines. This study provides more in-depth insight into the host–pathogen interactions of ORF8 with great promise as a therapeutic target to combat SARS-CoV-2 infection. Supplementary Information The online version contains supplementary material available at 10.1007/s10875-021-01142-z.

Waning antibody levels against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the emergence of variants of concern highlight the need for booster vaccinations. This is particularly important for the elderly population, who are at a higher risk of developing severe coronavirus disease 2019 (COVID-19) disease. While studies have shown increased antibody responses following booster vaccination, understanding the changes in T and B cell compartments induced by a third vaccine dose remains limited. We analyzed the humoral and cellular responses in subjects who received either a homologous messenger RNA(mRNA) booster vaccine (BNT162b2 + BNT162b2 + BNT162b2; ''BBB") or a heterologous mRNA booster vaccine (BNT162b2 + BNT162b2 + mRNA-1273; ''BBM") at Day 0 (prebooster), Day 7, and Day 28 (postbooster). Compared with BBB, elderly individuals (≥60 years old) who received the BBM vaccination regimen display higher levels of neutralizing antibodies against the Wuhan and Delta strains along with a higher boost in immunoglobulin G memory B cells, particularly against the Omicron variant. Circulating T helper type 1(Th1), Th2, Th17, and T follicular helper responses were also increased in elderly individuals given the BBM regimen. While mRNA vaccines increase antibody, T cell, and B cell responses against SARS-CoV-2 1 month after receiving the third dose booster, the efficacy of the booster vaccine strategies may vary depending on age group and regimen combination. Agency for Science, Technology and Research (A*STAR) National Medical Research Council (NMRC) Submitted/Accepted version This study was supported by Biomedical Research Council, A*CRUSE (Vaccine monitoring project), A*ccelerate GAP‐funded project (ACCL/19‐GAP064‐R20H‐H) from Agency of Science, Technology and Research (A*STAR), Singapore National Medical Research Council COVID‐19 Research Fund (COVID19RF‐001; COVID19RF‐007; COVID19RF‐0008; COVID19RF‐060; and OFLCG19May‐0034), U.S. Food and Drug Administration (#75F40120C00085), and A*STAR COVID‐19 Research funding (H/20/04/g1/006).

The immune responses and mechanisms limiting symptom progression in asymptomatic cases of SARS‐CoV‐2 infection remain unclear. We comprehensively characterized transcriptomic profiles, cytokine responses, neutralization capacity of antibodies, and cellular immune phenotypes of asymptomatic patients with acute SARS‐CoV‐2 infection to identify potential protective mechanisms. Compared to symptomatic patients, asymptomatic patients had higher counts of mature neutrophils and lower proportion of CD169+ expressing monocytes in the peripheral blood. Systemic levels of pro‐inflammatory cytokines were also lower in asymptomatic patients, accompanied by milder pro‐inflammatory gene signatures. Mechanistically, a more robust systemic Th2 cell signature with a higher level of virus‐specific Th17 cells and a weaker yet sufficient neutralizing antibody profile against SARS‐CoV‐2 was observed in asymptomatic patients. In addition, asymptomatic COVID‐19 patients had higher systemic levels of growth factors that are associated with cellular repair. Together, the data suggest that asymptomatic patients mount less pro‐inflammatory and more protective immune responses against SARS‐CoV‐2 indicative of disease tolerance. Insights from this study highlight key immune pathways that could serve as therapeutic targets to prevent disease progression in COVID‐19., We show that asymptomatic patients elicit a different repertoire of immune responses from symptomatic patients. Our data suggest that asymptomatic patients could limit symptom development with a well‐balanced inflammatory response and more protective immune responses against SARS‐CoV‐2.

Alphaviruses are mosquito-borne pathogens distributed worldwide in tropical and temperate areas causing a wide range of symptoms ranging from inflammatory arthritis-like manifestations to the induction of encephalitis in humans. Historically, large outbreaks in susceptible populations have been recorded followed by the development of protective long-lasting antibody responses suggesting a potential advantageous role for a vaccine. Although the current understanding of alphavirus antibody-mediated immunity has been mainly gathered in natural and experimental settings of chikungunya virus (CHIKV) infection, little is known about the humoral responses triggered by other emerging alphaviruses. This knowledge is needed to improve serology-based diagnostic tests and the development of highly effective cross-protective vaccines. Here, we review the role of antibody-mediated immunity upon arthritogenic and neurotropic alphavirus infections, and the current research efforts for the development of vaccines as a tool to control future alphavirus outbreaks.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern (VOCs) that have become dominant as the pandemic progresses bear the ORF8 mutation together with multiple spike mutations. A 382-nucleotide deletion (Δ382) in the ORF7b and ORF8 regions has been associated with milder disease phenotype and less systemic inflammation in COVID-19 patients. However, its impact on host immunity against SARS-CoV-2 remains undefined. Here, RNA-sequencing was performed to elucidate whole blood transcriptomic profiles and identify contrasting immune signatures between patients infected with either wildtype or Δ382 SARS-CoV-2 variant. Interestingly, the immune landscape of Δ382 SARS-CoV-2 infected patients featured an increased adaptive immune response, evidenced by enrichment of genes related to T cell functionality, a more robust SARS-CoV-2-specific T cell immunity, as well as a more rapid antibody response. At the molecular level, eukaryotic initiation factor 2 signaling was found to be upregulated in patients bearing Δ382, and its associated genes were correlated with systemic levels of T cell-associated and pro-inflammatory cytokines. This study provides more in-depth insight into the host-pathogen interactions of ORF8 with great promise as a therapeutic target to combat SARS-CoV-2 infection.

Key immune signatures of SARS-CoV-2 infection may associate with either adverse immune reactions (severity) or simply an ongoing anti-viral response (temporality); how immune signatures contribute to severe manifestations and/or temporal progression of disease and whether longer disease duration correlates with severity remain unknown. Patient blood was comprehensively immunophenotyped via mass cytometry and multiplex cytokine arrays, leading to the identification of 327 basic subsets that were further stratified into more than 5000 immunotypes and correlated with 28 plasma cytokines. Low-density neutrophil abundance was closely correlated with hepatocyte growth factor levels, which in turn correlated with disease severity. Deep analysis also revealed additional players, namely conventional type 2 dendritic cells, natural killer T cells, plasmablasts and CD16+ monocytes, that can influence COVID-19 severity independent of temporal progression. Herein, we provide interactive network analysis and data visualization tools to facilitate data mining and hypothesis generation for elucidating COVID-19 pathogenesis.

Objectives The emergence of a SARS‐CoV‐2 variant with a point mutation in the spike (S) protein, D614G, has taken precedence over the original Wuhan isolate by May 2020. With an increased infection and transmission rate, it is imperative to determine whether antibodies induced against the D614 isolate may cross‐neutralise against the G614 variant. Methods Antibody profiling against the SARS‐CoV‐2 S protein of the D614 variant by flow cytometry and assessment of neutralising antibody titres using pseudotyped lentiviruses expressing the SARS‐CoV‐2 S protein of either the D614 or G614 variant tagged with a luciferase reporter were performed on plasma samples from COVID‐19 patients with known D614G status (n = 44 infected with D614, n = 6 infected with G614, n = 7 containing all other clades: O, S, L, V, G, GH or GR). Results Profiling of the anti‐SARS‐CoV‐2 humoral immunity reveals similar neutralisation profiles against both S protein variants, albeit waning neutralising antibody capacity at the later phase of infection. Of clinical importance, patients infected with either the D614 or G614 clade elicited a similar degree of neutralisation against both pseudoviruses, suggesting that the D614G mutation does not impact the neutralisation capacity of the elicited antibodies. Conclusions Cross‐reactivity occurs at the functional level of the humoral response on both the S protein variants, which suggests that existing serological assays will be able to detect both D614 and G614 clades of SARS‐CoV‐2. More importantly, there should be negligible impact towards the efficacy of antibody‐based therapies and vaccines that are currently being developed., A single point mutation from aspartic acid (D) to glycine (G) at position 614 of the SARS‐CoV‐2 spike (S) protein, termed D614G, has garnered global attention due to the observed increase in transmissibility and infection rate. Given that a majority of the developing antibody‐mediated therapies and serological assays are based on the S antigen of the original Wuhan reference sequence, it is crucial to determine whether humoral immunity acquired from the original SARS‐CoV‐2 isolate is able to induce cross‐detection and cross‐protection against the novel prevailing D614G variant. In this study, we demonstrated an overall equivalent neutralising capacity against both the D614 and G614 pseudoviruses, suggesting negligible impact towards the efficacy of antibody‐based therapies and vaccines that are currently being developed.

Background: Given the unceasing worldwide surge in COVID-19 cases, there is an imperative need to develop highly specific and sensitive serology assays to define exposure to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Methods: Pooled plasma samples from PCR positive COVID-19 patients were used to identify linear B-cell epitopes from a SARS-CoV-2 peptide library of spike (S), envelope (E), membrane (M), and nucleocapsid (N) structural proteins by peptide-based ELISA. Hit epitopes were further validated with 79 COVID-19 patients with different disease severity status, 13 seasonal human CoV, 20 recovered SARS patients and 22 healthy donors. Findings: Four immunodominant epitopes, S14P5, S20P2, S21P2 and N4P5, were identified on the S and N viral proteins. IgG responses to all identified epitopes displayed a strong detection profile, with N4P5 achieving the highest level of specificity (100%) and sensitivity (>96%) against SARS-CoV-2. Furthermore, the magnitude of IgG responses to S14P5, S21P2 and N4P5 were strongly associated with disease severity. Interpretation: IgG responses to the peptide epitopes can serve as useful indicators for the degree of immunopathology in COVID-19 patients, and function as higly specific and sensitive sero-immunosurveillance tools for recent or past SARS-CoV-2 infections. The flexibility of these epitopes to be used alone or in combination will allow for the development of improved point-of-care-tests (POCTs). Agency for Science, Technology and Research (A*STAR) National Medical Research Council (NMRC) Published version Biomedical Research Council (BMRC), the A*ccelerate GAP-funded project (ACCL/19-GAP064-R20H-H) from Agency of Science, Technology and Research (A*STAR), and National Medical Research Council (NMRC) COVID-19 Research fund (COVID19RF-001) and CCGSFPOR20002. ATR is supported by the Singapore International Graduate Award (SINGA), A*STAR.

Given the ongoing SARS-CoV-2 pandemic, identification of immunogenic targets against the coronavirus spike glycoprotein will provide crucial advances towards the development of sensitive diagnostic tools and potential vaccine candidate targets. In this study, using pools of overlapping linear B-cell peptides, we report two IgG immunodominant regions on SARS-CoV-2 spike glycoprotein that are recognised by sera from COVID-19 convalescent patients. Notably, one is specific to SARS-CoV-2, which is located in close proximity to the receptor binding domain. The other region, which is localised at the fusion peptide, could potentially function as a pan-SARS target. Functionally, antibody depletion assays demonstrate that antibodies targeting these immunodominant regions significantly alter virus neutralisation capacities. Taken together, identification and validation of these neutralising B-cell epitopes will provide insights towards the design of diagnostics and vaccine candidates against this high priority coronavirus., Characterisation of the human antibody response to SARS-CoV-2 can help the design of serological tests and vaccines. Here, the authors identify two linear epitopes in SARS-CoV-2 spike protein that elicit neutralising antibodies in several patients and could thus be useful for serology and vaccine development.

Objectives Zika virus (ZIKV) is a mosquito‐borne flavivirus that re‐emerged in 2015. The association between ZIKV and neurological complications initiated the development of relevant animal models to understand the mechanisms underlying ZIKV‐induced pathologies. Transient inhibition of the type I interferon (IFN) pathway through the use of an IFNAR1‐blocking antibody, MAR1‐5A3, could efficiently permit active virus replication in immunocompetent animals. Type I IFN signalling is involved in the regulation of humoral responses, and thus, it is crucial to investigate the potential effects of type I IFN blockade towards B‐cell responses. Methods In this study, comparative analysis was conducted using serum samples collected from ZIKV‐infected wild‐type (WT) animals either administered with or without MAR1‐5A3. Results Serological assays revealed a more robust ZIKV‐specific IgG response and subtype switching upon inhibition of type I IFN due to the abundance of antigen availability. This observation was corroborated by an increase in germinal centres, plasma cells and germinal centre B cells. Interestingly, although both groups of animals recognised different B‐cell linear epitopes in the E and NS1 regions, there was no difference in neutralising capacity. Further characterisation of these epitopes in the E protein revealed a detrimental role of antibodies that were generated in the absence of type I IFN. Conclusion This study highlights the role of type I IFN in shaping the anti‐ZIKV antibody response to generate beneficial antibodies and will help guide development of better vaccine candidates triggering efficient neutralising antibodies and avoiding detrimental ones., Type I IFN signalling is involved in the regulation of humoral responses, and thus, it is crucial to investigate the potential effects of type I IFN blockade towards ZIKV‐induced B‐cell responses. In this study, comparative analysis was conducted using serum samples collected from ZIKV‐infected wild‐type (WT) animals either administered with or without MAR1‐5A3. Results showed animals that have their type I IFN response transiently suppressed displayed a more robust ZIKV‐specific IgG response and subtype switching, which was corroborated by a higher number of germinal centres in the spleen. In addition, several linear B‐cell epitopes were identified from the envelope and non‐structural 1 proteins; however, interestingly, the dominant regions recognised between both groups of animals are different. Further characterisation of these dominant epitopes revealed a detrimental role of antibodies that were generated in the absence of type I IFN.

Background: Given the unceasing worldwide surge in COVID-19 cases, there is an imperative need to develop highly specific and sensitive serology assays to define exposure to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Methods: Pooled plasma samples from PCR positive COVID-19 patients were used to identify linear B-cell epitopes from a SARS-CoV-2 peptide library of spike (S), envelope (E), membrane (M), and nucleocapsid (N) structural proteins by peptide-based ELISA. Hit epitopes were further validated with 79 COVID-19 patients with different disease severity status, 12 seasonal human CoV, 20 recovered SARS patients and 22 healthy donors. Findings: Four immunodominant epitopes, S14P5, S20P2, S21P2 and N4P5, were identified on the S and N viral proteins. IgG responses to all identified epitopes displayed a strong detection profile, with N4P5 achieving the highest level of specificity (100%) and sensitivity (>96%) against SARS-CoV-2. Furthermore, the magnitude of IgG responses to S14P5, S21P2 and N4P5 were strongly associated with disease severity. Interpretation: IgG responses to the peptide epitopes can serve as useful indicators for the degree of immunopathology in COVID-19 patients, and function as higly specific and sensitive sero-immunosurveillance tools for recent or past SARS-CoV-2 infections. The flexibility of these epitopes to be used alone or in combination will allow for the development of improved point-of-care-tests (POCTs). Funding Statement: Biomedical Research Council (BMRC), the A*ccelerate GAP-funded project (ACCL/19-GAP064-R20H-H) from Agency of Science, Technology and Research (A*STAR), and National Medical Research Council (NMRC) COVID-19 Research fund (COVID19RF-001). ATR is supported by the Singapore International Graduate Award (SINGA), A*STAR. Declaration of Interests: The authors declare no conflict of interest. Ethics Approval Statement: The study design and protocols for COVID-19, recovered SARS and seasonal hCoV patient cohorts were evaluated by National Healthcare Group (NHG) Domain Specific Review Board (DSRB) and approved under study numbers 2012/00917, 2020/00091 and 2020/00076, respectively. Healthy donor samples were collected under study numbers 2017/2806 and NUS IRB 04-140. Residual serum sample from National Healthy Survey (NHS) collected in 2010 under study number 006/2010 was used as a positive control in peptide-based ELISA (13). Written informed consent was obtained from participants in accordance with the Declaration of Helsinki for Human Research.