A molecular perspective for the development of antibodies against the human respiratory syncytial virus.

The human respiratory syncytial virus (hRSV) is the leading etiologic agent causing respiratory infections in infants, children, older adults, and patients with comorbidities. Sixty-seven years have passed since the discovery of hRSV, and only a few successful mitigation or treatment tools have been developed against this virus. One of these is immunotherapy with monoclonal antibodies against structural proteins of the virus, such as Palivizumab, the first prophylactic approach approved by the Food and Drug Administration (FDA) of the USA. In this article, we discuss different strategies for the prevention and treatment of hRSV infection, focusing on the molecular mechanisms against each target that underly the rational design of antibodies against hRSV. At the same time, we describe the latest results regarding currently approved therapies against hRSV and the challenges associated with developing new candidates.

Contribution of viral and bacterial infections to senescence and immunosenescence.

Cellular senescence is a key biological process characterized by irreversible cell cycle arrest. The accumulation of senescent cells creates a pro-inflammatory environment that can negatively affect tissue functions and may promote the development of aging-related diseases. Typical biomarkers related to senescence include senescence-associated ß-galactosidase activity, histone H2A.X phosphorylation at serine139 (γH2A.X), and senescence-associated heterochromatin foci (SAHF) with heterochromatin protein 1γ (HP-1γ protein) Moreover, immune cells undergoing senescence, which is known as immunosenescence, can affect innate and adaptative immune functions and may elicit detrimental effects over the host's susceptibility to infectious diseases. Although associations between senescence and pathogens have been reported, clear links between both, and the related molecular mechanisms involved remain to be determined. Furthermore, it remains to be determined whether infections effectively induce senescence, the impact of senescence and immunosenescence over infections, or if both events coincidently share common molecular markers, such as γH2A.X and p53. Here, we review and discuss the most recent reports that describe cellular hallmarks and biomarkers related to senescence in immune and non-immune cells in the context of infections, seeking to better understand their relationships. Related literature was searched in Pubmed and Google Scholar databases with search terms related to the sections and subsections of this review.

Characterization of the humoral and cellular immunity induced by a recombinant BCG vaccine for the respiratory syncytial virus in healthy adults.

Introduction: The human respiratory syncytial virus (hRSV) is responsible for most respiratory tract infections in infants. Even though currently there are no approved hRSV vaccines for newborns or infants, several candidates are being developed. rBCG-N-hRSV is a vaccine candidate previously shown to be safe in a phase I clinical trial in adults (clinicaltrials.gov identifier #NCT03213405). Here, secondary immunogenicity analyses were performed on these samples. Methods: PBMCs isolated from immunized volunteers were stimulated with hRSV or mycobacterial antigens to evaluate cytokines and cytotoxic T cell-derived molecules and the expansion of memory T cell subsets. Complement C1q binding and IgG subclass composition of serum antibodies were assessed. Results: Compared to levels detected prior to vaccination, perforin-, granzyme B-, and IFN-γ-producing PBMCs responding to stimulus increased after immunization, along with their effector memory response. N-hRSV- and mycobacterial-specific antibodies from rBCG-N-hRSV-immunized subjects bound C1q. Conclusion: Immunization with rBCG-N-hRSV induces cellular and humoral immune responses, supporting that rBCG-N-hRSV is immunogenic and safe in healthy individuals. Clinical trial registration: https://classic.clinicaltrials.gov/ct2/show/, identifier NCT03213405.

LAG-3 Contribution to T Cell Downmodulation during Acute Respiratory Viral Infections.

LAG-3 is a type I transmembrane protein expressed on immune cells, such as activated T cells, and binds to MHC class II with high affinity. LAG-3 is an inhibitory receptor, and its multiple biological activities on T cell activation and effector functions play a regulatory role in the immune response. Immunotherapies directed at immune checkpoints, including LAG-3, have become a promising strategy for controlling malignant tumors and chronic viral diseases. Several studies have suggested an association between the expression of LAG-3 with an inadequate immune response during respiratory viral infections and the susceptibility to reinfections, which might be a consequence of the inhibition of T cell effector functions. However, important information relative to therapeutic potential during acute viral lower respiratory tract infections and the mechanism of action of the LAG-3 checkpoint remains to be characterized. In this article, we discuss the contribution of LAG-3 to the impairment of T cells during viral respiratory infections. Understanding the host immune response to respiratory infections is crucial for developing effective vaccines and therapies.

Inactivated Vaccine-Induced SARS-CoV-2 Variant-Specific Immunity in Children.

Multiple vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have been evaluated in clinical trials. However, trials addressing the immune response in the pediatric population are scarce. The inactivated vaccine CoronaVac has been shown to be safe and immunogenic in a phase 1/2 clinical trial in a pediatric cohort in China. Here, we report interim safety and immunogenicity results of a phase 3 clinical trial for CoronaVac in healthy children and adolescents in Chile. Participants 3 to 17 years old received two doses of CoronaVac in a 4-week interval until 31 December 2021. Local and systemic adverse reactions were registered for volunteers who received one or two doses of CoronaVac. Whole-blood samples were collected from a subgroup of 148 participants for humoral and cellular immunity analyses. The main adverse reaction reported after the first and second doses was pain at the injection site. Four weeks after the second dose, an increase in neutralizing antibody titer was observed in subjects relative to their baseline visit. Similar results were found for activation of specific CD4+ T cells. Neutralizing antibodies were identified against the Delta and Omicron variants. However, these titers were lower than those for the D614G strain. Importantly, comparable CD4+ T cell responses were detected against these variants of concern. Therefore, CoronaVac is safe and immunogenic in subjects 3 to 17 years old, inducing neutralizing antibody secretion and activating CD4+ T cells against SARS-CoV-2 and its variants. (This study has been registered at ClinicalTrials.gov under no. NCT04992260.) IMPORTANCE This work evaluated the immune response induced by two doses of CoronaVac separated by 4 weeks in healthy children and adolescents in Chile. To date, few studies have described the effects of CoronaVac in the pediatric population. Therefore, it is essential to generate knowledge regarding the protection of vaccines in this population. Along these lines, we reported the anti-S humoral response and cellular immune response to several SARS-CoV-2 proteins that have been published and recently studied. Here, we show that a vaccination schedule consisting of two doses separated by 4 weeks induces the secretion of neutralizing antibodies against SARS-CoV-2. Furthermore, CoronaVac induces the activation of CD4+ T cells upon stimulation with peptides from the proteome of SARS-CoV-2. These results indicate that, even though the neutralizing antibody response induced by vaccination decreases against the Delta and Omicron variants, the cellular response against these variants is comparable to the response against the ancestral strain D614G, even being significantly higher against Omicron.

Differences in the immune response elicited by two immunization schedules with an inactivated SARS-CoV-2 vaccine in a randomized phase 3 clinical trial.

Background: The development of vaccines to control the coronavirus disease 2019 (COVID-19) pandemic progression is a worldwide priority. CoronaVac is an inactivated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine approved for emergency use with robust efficacy and immunogenicity data reported in trials in China, Brazil, Indonesia, Turkey, and Chile. Methods: This study is a randomized, multicenter, and controlled phase 3 trial in healthy Chilean adults aged ≥18 years. Volunteers received two doses of CoronaVac separated by 2 (0-14 schedule) or 4 weeks (0-28 schedule); 2302 volunteers were enrolled, 440 were part of the immunogenicity arm, and blood samples were obtained at different times. Samples from a single center are reported. Humoral immune responses were evaluated by measuring the neutralizing capacities of circulating antibodies. Cellular immune responses were assessed by ELISPOT and flow cytometry. Correlation matrixes were performed to evaluate correlations in the data measured. Results: Both schedules exhibited robust neutralizing capacities with the response induced by the 0-28 schedule being better. No differences were found in the concentration of antibodies against the virus and different variants of concern (VOCs) between schedules. Stimulation of peripheral blood mononuclear cells (PBMCs) with Mega pools of Peptides (MPs) induced the secretion of interferon (IFN)-γ and the expression of activation induced markers in CD4+ T cells for both schedules. Correlation matrixes showed strong correlations between neutralizing antibodies and IFN-γ secretion. Conclusions: Immunization with CoronaVac in Chilean adults promotes robust cellular and humoral immune responses. The 0-28 schedule induced a stronger humoral immune response than the 0-14 schedule. Funding: Ministry of Health, Government of Chile, Confederation of Production and Commerce & Millennium Institute on Immunology and Immunotherapy, Chile. Clinical trial number: NCT04651790.

Increased Heme Oxygenase 1 Expression upon a Primary Exposure to the Respiratory Syncytial Virus and a Secondary Mycobacterium bovis Infection.

The human respiratory syncytial virus (hRSV) is the leading cause of severe lower respiratory tract infections in infants. Because recurrent epidemics based on reinfection occur in children and adults, hRSV has gained interest as a potential primary pathogen favoring secondary opportunistic infections. Several infection models have shown different mechanisms by which hRSV promotes immunopathology to prevent the development of adaptive protective immunity. However, little is known about the long-lasting effects of viral infection on pulmonary immune surveillance mechanisms. As a first approach, here we evaluated whether a primary infection by hRSV, once resolved, dampens the host immune response to a secondary infection with an attenuated strain of Mycobacterium bovis (M. Bovis) strain referred as to Bacillus Calmette-Guerin (BCG). We analyzed leukocyte dynamics and immunomodulatory molecules in the lungs after eleven- and twenty-one-days post-infection with Mycobacterium, using previous hRSV infected mice, by flow cytometry and the expression of critical genes involved in the immune response by real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR). Among the latter, we analyzed the expression of Heme Oxygenase (HO)-1 in an immunization scheme in mice. Our data suggest that a pre-infection with hRSV has a conditioning effect promoting lung pathology during a subsequent mycobacterial challenge, characterized by increased infiltration of innate immune cells, including interstitial and alveolar macrophages. Our data also suggest that hRSV impairs pulmonary immune responses, promoting secondary mycobacterial colonization and lung survival, which could be associated with an increase in the expression of HO-1. Additionally, BCG is a commonly used vaccine that can be used as a platform for the generation of new recombinant vaccines, such as a recombinant BCG strain expressing the nucleoprotein of hRSV (rBCG-N-hRSV). Therefore, we evaluated if the immunization with rBCG-N-hRSV could modulate the expression of HO-1. We found a differential expression pattern for HO-1, where a higher induction of HO-1 was detected on epithelial cells compared to dendritic cells during late infection times. This is the first study to demonstrate that infection with hRSV produces damage in the lung epithelium, promoting subsequent mycobacterial colonization, characterized by an increase in the neutrophils and alveolar macrophages recruitment. Moreover, we determined that immunization with rBCG-N-hRSV modulates differentially the expression of HO-1 on immune and epithelial cells, which could be involved in the repair of pulmonary tissue.

Neurotrophin Signaling Impairment by Viral Infections in the Central Nervous System.

Neurotrophins, such as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin 3 (NT-3), NT-4, and NT-5, are proteins involved in several important functions of the central nervous system. The activation of the signaling pathways of these neurotrophins, or even by their immature form, pro-neurotrophins, starts with their recognition by cellular receptors, such as tropomyosin receptor kinase (Trk) and 75 kD NT receptors (p75NTR). The Trk receptor is considered to have a high affinity for attachment to specific neurotrophins, while the p75NTR receptor has less affinity for attachment with neurotrophins. The correct functioning of these signaling pathways contributes to proper brain development, neuronal survival, and synaptic plasticity. Unbalanced levels of neurotrophins and pro-neurotrophins have been associated with neurological disorders, illustrating the importance of these molecules in the central nervous system. Furthermore, reports have indicated that viruses can alter the normal levels of neurotrophins by interfering with their signaling pathways. This work discusses the importance of neurotrophins in the central nervous system, their signaling pathways, and how viruses can affect them.

BCG vaccination induces cross-protective immunity against pathogenic microorganisms.

Bacillus Calmette-Guérin (BCG) is an attenuated Mycobacterium bovis strain used as a vaccine to prevent Mycobacterium tuberculosis (M. tb) infection. Its ability to potentiate the immune response induced by other vaccines and to promote nonspecific immunomodulatory effects has been described. These effects can be triggered by epigenetic reprogramming and metabolic shifts on innate immune cells, a phenomenon known as trained immunity. The induction of trained immunity may contribute to explain why BCG vaccination effectively decreases disease symptoms caused by pathogens different from M. tb. This article explains the importance of BCG immunization and the possible mechanisms associated with the induction of trained immunity, which might be used as a strategy for rapid activation of the immune system against unrelated pathogens.

Safety and Immunogenicity of an Inactivated Severe Acute Respiratory Syndrome Coronavirus 2 Vaccine in a Subgroup of Healthy Adults in Chile.

BACKGROUND: The development of effective vaccines against coronavirus disease 2019 is a global priority. CoronaVac is an inactivated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine with promising safety and immunogenicity profiles. This article reports safety and immunogenicity results obtained for healthy Chilean adults aged ≥18 years in a phase 3 clinical trial. METHODS: Volunteers randomly received 2 doses of CoronaVac or placebo, separated by 2 weeks. A total of 434 volunteers were enrolled, 397 aged 18-59 years and 37 aged ≥60 years. Solicited and unsolicited adverse reactions were registered from all volunteers. Blood samples were obtained from a subset of volunteers and analyzed for humoral and cellular measures of immunogenicity. RESULTS: The primary adverse reaction in the 434 volunteers was pain at the injection site, with a higher incidence in the vaccine than in the placebo arm. Adverse reactions observed were mostly mild and local. No severe adverse events were reported. The humoral evaluation was performed on 81 volunteers. Seroconversion rates for specific anti-S1-receptor binding domain (RBD) immunoglobulin G (IgG) were 82.22% and 84.44% in the 18-59 year age group and 62.69% and 70.37% in the ≥60 year age group, 2 and 4 weeks after the second dose, respectively. A significant increase in circulating neutralizing antibodies was detected 2 and 4 weeks after the second dose. The cellular evaluation was performed on 47 volunteers. We detected a significant induction of T-cell responses characterized by the secretion of interferon-γ (IFN-γ) upon stimulation with Mega Pools of peptides from SARS-CoV-2. CONCLUSIONS: Immunization with CoronaVac in a 0-14 schedule in Chilean adults aged ≥18 years is safe, induces anti-S1-RBD IgG with neutralizing capacity, activates T cells, and promotes the secretion of IFN-γ upon stimulation with SARS-CoV-2 antigens.

The Causes and Long-Term Consequences of Viral Encephalitis.

Reports regarding brain inflammation, known as encephalitis, have shown an increasing frequency during the past years. Encephalitis is a relevant concern to public health due to its high morbidity and mortality. Infectious or autoimmune diseases are the most common cause of encephalitis. The clinical symptoms of this pathology can vary depending on the brain zone affected, with mild ones such as fever, headache, confusion, and stiff neck, or severe ones, such as seizures, weakness, hallucinations, and coma, among others. Encephalitis can affect individuals of all ages, but it is frequently observed in pediatric and elderly populations, and the most common causes are viral infections. Several viral agents have been described to induce encephalitis, such as arboviruses, rhabdoviruses, enteroviruses, herpesviruses, retroviruses, orthomyxoviruses, orthopneumovirus, and coronaviruses, among others. Once a neurotropic virus reaches the brain parenchyma, the resident cells such as neurons, astrocytes, and microglia, can be infected, promoting the secretion of pro-inflammatory molecules and the subsequent immune cell infiltration that leads to brain damage. After resolving the viral infection, the local immune response can remain active, contributing to long-term neuropsychiatric disorders, neurocognitive impairment, and degenerative diseases. In this article, we will discuss how viruses can reach the brain, the impact of viral encephalitis on brain function, and we will focus especially on the neurocognitive sequelae reported even after viral clearance.

Modulation of Adaptive Immunity and Viral Infections by Ion Channels.

Most cellular functions require of ion homeostasis and ion movement. Among others, ion channels play a crucial role in controlling the homeostasis of anions and cations concentration between the extracellular and intracellular compartments. Calcium (Ca2+) is one of the most relevant ions involved in regulating critical functions of immune cells, allowing the appropriate development of immune cell responses against pathogens and tumor cells. Due to the importance of Ca2+ in inducing the immune response, some viruses have evolved mechanisms to modulate intracellular Ca2+ concentrations and the mobilization of this cation through Ca2+ channels to increase their infectivity and to evade the immune system using different mechanisms. For instance, some viral infections require the influx of Ca2+ through ionic channels as a first step to enter the cell, as well as their replication and budding. Moreover, through the expression of viral proteins on the surface of infected cells, Ca2+ channels function can be altered, enhancing the pathogen evasion of the adaptive immune response. In this article, we review those ion channels and ion transporters that are essential for the function of immune cells. Specifically, cation channels and Ca2+ channels in the context of viral infections and their contribution to the modulation of adaptive immune responses.

Bacterial and Viral Coinfections with the Human Respiratory Syncytial Virus.

The human respiratory syncytial virus (hRSV) is one of the leading causes of acute lower respiratory tract infections in children under five years old. Notably, hRSV infections can give way to pneumonia and predispose to other respiratory complications later in life, such as asthma. Even though the social and economic burden associated with hRSV infections is tremendous, there are no approved vaccines to date to prevent the disease caused by this pathogen. Recently, coinfections and superinfections have turned into an active field of study, and interactions between many viral and bacterial pathogens have been studied. hRSV is not an exception since polymicrobial infections involving this virus are common, especially when illness has evolved into pneumonia. Here, we review the epidemiology and recent findings regarding the main polymicrobial infections involving hRSV and several prevalent bacterial and viral respiratory pathogens, such as Staphylococcus aureus, Pseudomonas aeruginosa, Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Klebsiella pneumoniae, human rhinoviruses, influenza A virus, human metapneumovirus, and human parainfluenza viruses. As reports of most polymicrobial infections involving hRSV lack a molecular basis explaining the interaction between hRSV and these pathogens, we believe this review article can serve as a starting point to interesting and very much needed research in this area.

Host Components That Modulate the Disease Caused by hMPV.

Human metapneumovirus (hMPV) is one of the main pathogens responsible for acute respiratory infections in children up to 5 years of age, contributing substantially to health burden. The worldwide economic and social impact of this virus is significant and must be addressed. The structural components of hMPV (either proteins or genetic material) can be detected by several receptors expressed by host cells through the engagement of pattern recognition receptors. The recognition of the structural components of hMPV can promote the signaling of the immune response to clear the infection, leading to the activation of several pathways, such as those related to the interferon response. Even so, several intrinsic factors are capable of modulating the immune response or directly inhibiting the replication of hMPV. This article will discuss the current knowledge regarding the innate and adaptive immune response during hMPV infections. Accordingly, the host intrinsic components capable of modulating the immune response and the elements capable of restricting viral replication during hMPV infections will be examined.

Contribution of Pro-Inflammatory Molecules Induced by Respiratory Virus Infections to Neurological Disorders.

Neurobehavioral alterations and cognitive impairment are common phenomena that represent neuropsychiatric disorders and can be triggered by an exacerbated immune response against pathogens, brain injury, or autoimmune diseases. Pro-inflammatory molecules, such as cytokines and chemokines, are produced in the brain by resident cells, mainly by microglia and astrocytes. Brain infiltrating immune cells constitutes another source of these molecules, contributing to an impaired neurological synapse function, affecting typical neurobehavioral and cognitive performance. Currently, there is increasing evidence supporting the notion that behavioral alterations and cognitive impairment can be associated with respiratory viral infections, such as human respiratory syncytial virus, influenza, and SARS-COV-2, which are responsible for endemic, epidemic, or pandemic outbreak mainly in the winter season. This article will review the brain's pro-inflammatory response due to infection by three highly contagious respiratory viruses that are the leading cause of acute respiratory illness, morbidity, and mobility in infants, immunocompromised and elderly population. How these respiratory viral pathogens induce increased secretion of pro-inflammatory molecules and their relationship with the alterations at a behavioral and cognitive level will be discussed.

Type I Natural Killer T Cells as Key Regulators of the Immune Response to Infectious Diseases.

The immune system must work in an orchestrated way to achieve an optimal response upon detection of antigens. The cells comprising the immune response are traditionally divided into two major subsets, innate and adaptive, with particular characteristics for each type. Type I natural killer T (iNKT) cells are defined as innate-like T cells sharing features with both traditional adaptive and innate cells, such as the expression of an invariant T cell receptor (TCR) and several NK receptors. The invariant TCR in iNKT cells interacts with CD1d, a major histocompatibility complex class I (MHC-I)-like molecule. CD1d can bind and present antigens of lipid nature and induce the activation of iNKT cells, leading to the secretion of various cytokines, such as gamma interferon (IFN-γ) and interleukin 4 (IL-4). These cytokines will aid in the activation of other immune cells following stimulation of iNKT cells. Several molecules with the capacity to bind to CD1d have been discovered, including α-galactosylceramide. Likewise, several molecules have been synthesized that are capable of polarizing iNKT cells into different profiles, either pro- or anti-inflammatory. This versatility allows NKT cells to either aid or impair the clearance of pathogens or to even control or increase the symptoms associated with pathogenic infections. Such diverse contributions of NKT cells to infectious diseases are supported by several publications showing either a beneficial or detrimental role of these cells during diseases. In this article, we discuss current data relative to iNKT cells and their features, with an emphasis on their driving role in diseases produced by pathogenic agents in an organ-oriented fashion.

Potential Neurocognitive Symptoms Due to Respiratory Syncytial Virus Infection.

Respiratory infections are among the major public health burdens, especially during winter. Along these lines, the human respiratory syncytial virus (hRSV) is the principal viral agent causing acute lower respiratory tract infections leading to hospitalization. The pulmonary manifestations due to hRSV infection are bronchiolitis and pneumonia, where the population most affected are infants and the elderly. However, recent evidence suggests that hRSV infection can impact the mother and fetus during pregnancy. Studies have indicated that hRSV can infect different cell types from the placenta and even cross the placenta barrier and infect the fetus. In addition, it is known that infections during the gestational period can lead to severe consequences for the development of the fetus due not only to a direct viral infection but also because of maternal immune activation (MIA). Furthermore, it has been described that the development of the central nervous system (CNS) of the fetus can be affected by the inflammatory environment of the uterus caused by viral infections. Increasing evidence supports the notion that hRSV could invade the CNS and infect nervous cells, such as microglia, neurons, and astrocytes, promoting neuroinflammation. Moreover, it has been described that the hRSV infection can provoke neurological manifestations, including cognitive impairment and behavioral alterations. Here, we will review the potential effect of hRSV in brain development and the potential long-term neurological sequelae.

Interim report: Safety and immunogenicity of an inactivated vaccine against SARS-CoV-2 in healthy chilean adults in a phase 3 clinical trial.

Background: The ongoing COVID-19 pandemic has had a significant impact worldwide, with an incommensurable social and economic burden. The rapid development of safe and protective vaccines against this disease is a global priority. CoronaVac is a vaccine prototype based on inactivated SARS-CoV-2, which has shown promising safety and immunogenicity profiles in pre-clinical studies and phase 1/2 trials in China. To this day, four phase 3 clinical trials are ongoing with CoronaVac in Brazil, Indonesia, Turkey, and Chile. This article reports the safety and immunogenicity results obtained in a subgroup of participants aged 18 years and older enrolled in the phase 3 Clinical Trial held in Chile. Methods: This is a multicenter phase 3 clinical trial. Healthcare workers aged 18 years and older were randomly assigned to receive two doses of CoronaVac or placebo separated by two weeks (0-14). We report preliminary safety results obtained for a subset of 434 participants, and antibody and cell-mediated immunity results obtained in a subset of participants assigned to the immunogenicity arm. The primary and secondary aims of the study include the evaluation of safety parameters and immunogenicity against SARS-CoV-2 after immunization, respectively. This trial is registered at clinicaltrials.gov ( NCT04651790 ). Findings: The recruitment of participants occurred between November 27 th , 2020, until January 9 th , 2021. 434 participants were enrolled, 397 were 18-59 years old, and 37 were ≥60 years old. Of these, 270 were immunized with CoronaVac, and the remaining 164 participants were inoculated with the corresponding placebo. The primary adverse reaction was pain at the injection site, with a higher incidence in the vaccine arm (55.6%) than in the placebo arm (40.0%). Moreover, the incidence of pain at the injection site in the 18-59 years old group was 58.4% as compared to 32.0% in the ≥60 years old group. The seroconversion rate for specific anti-S1-RBD IgG was 47.8% for the 18-59 years old group 14 days post immunization (p.i.) and 95.6% 28 and 42 days p.i. For the ≥60 years old group, the seroconversion rate was 18.1%, 100%, and 87.5% at 14, 28, and 42 days p.i., respectively. Importantly, we observed a 95.7% seroconversion rate in neutralizing antibodies for the 18-59 years old group 28 and 42 days p.i. The ≥60 years old group exhibited seroconversion rates of 90.0% and 100% at 28 and 42 days p.i. Interestingly, we did not observe a significant seroconversion rate of anti-N-SARS-CoV-2 IgG for the 18-59 years old group. For the participants ≥60 years old, a modest rate of seroconversion at 42 days p.i. was observed (37.5%). We observed a significant induction of a T cell response characterized by the secretion of IFN-γ upon stimulation with Mega Pools of peptides derived from SARS-CoV-2 proteins. No significant differences between the two age groups were observed for cell-mediated immunity. Interpretation: Immunization with CoronaVac in a 0-14 schedule in adults of 18 years and older in the Chilean population is safe and induces specific IgG production against the S1-RBD with neutralizing capacity, as well as the activation of T cells secreting IFN-γ, upon recognition of SARS-CoV-2 antigens. Funding: Ministry of Health of the Chilean Government; Confederation of Production and Commerce, Chile; Consortium of Universities for Vaccines and Therapies against COVID-19, Chile; Millennium Institute on Immunology and Immunotherapy.

SARS-CoV-2: Immune Response Elicited by Infection and Development of Vaccines and Treatments.

The World Health Organization (WHO) announced in March a pandemic caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). This new infectious disease was named Coronavirus Disease 19 (COVID-19), and at October 2020, more than 39,000,000 cases of SARS-CoV-2 have been detected worldwide leading to near 1,100,000 deaths. Clinically, COVID-19 is characterized by clinical manifestations, such as fever, dry cough, headache, and in more severe cases, respiratory distress. Moreover, neurological-, cardiac-, and renal-related symptoms have also been described. Clinical evidence suggests that migration of immune cells to the affected organs can produce an exacerbated release of proinflammatory mediators that contribute to disease and render the immune response as a major player during the development of the COVID-19 disease. Due to the current sanitary situation, the development of vaccines is imperative. Up to the date, 42 prototypes are being tested in humans in different clinical stages, with 10 vaccine candidates undergoing evaluation in phase III clinical trials. In the same way, the search for an effective treatment to approach the most severe cases is also in constant advancement. Several potential therapies have been tested since COVID-19 was described, including antivirals, antiparasitic and immune modulators. Recently, clinical trials with hydroxychloroquine-a promising drug in the beginning-were suspended. In addition, the Food and Drug Administration (FDA) approved convalescent serum administration as a treatment for SARS-CoV-2 patients. Moreover, monoclonal antibody therapy is also under development to neutralize the virus and prevent infection. In this article, we describe the clinical manifestations and the immunological information available about COVID-19 disease. Furthermore, we discuss current therapies under study and the development of vaccines to prevent this disease.

The Role of Dendritic Cells During Infections Caused by Highly Prevalent Viruses.

Dendritic cells (DCs) are a type of innate immune cells with major relevance in the establishment of an adaptive response, as they are responsible for the activation of lymphocytes. Since their discovery, several reports of their role during infectious diseases have been performed, highlighting their functions and their mechanisms of action. DCs can be categorized into different subsets, and each of these subsets expresses a wide arrange of receptors and molecules that aid them in the clearance of invading pathogens. Interferon (IFN) is a cytokine -a molecule of protein origin- strongly associated with antiviral immune responses. This cytokine is secreted by different cell types and is fundamental in the modulation of both innate and adaptive immune responses against viral infections. Particularly, DCs are one of the most important immune cells that produce IFN, with type I IFNs (α and ß) highlighting as the most important, as they are associated with viral clearance. Type I IFN secretion can be induced via different pathways, activated by various components of the virus, such as surface proteins or genetic material. These molecules can trigger the activation of the IFN pathway trough surface receptors, including IFNAR, TLR4, or some intracellular receptors, such as TLR7, TLR9, and TLR3. Here, we discuss various types of dendritic cells found in humans and mice; their contribution to the activation of the antiviral response triggered by the secretion of IFN, through different routes of the induction for this important antiviral cytokine; and as to how DCs are involved in human infections that are considered highly frequent nowadays.