Homologous and Heterologous Covid-19 Booster Vaccinations.

BACKGROUND: Although the three vaccines against coronavirus disease 2019 (Covid-19) that have received emergency use authorization in the United States are highly effective, breakthrough infections are occurring. Data are needed on the serial use of homologous boosters (same as the primary vaccine) and heterologous boosters (different from the primary vaccine) in fully vaccinated recipients. METHODS: In this phase 1-2, open-label clinical trial conducted at 10 sites in the United States, adults who had completed a Covid-19 vaccine regimen at least 12 weeks earlier and had no reported history of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection received a booster injection with one of three vaccines: mRNA-1273 (Moderna) at a dose of 100 µg, Ad26.COV2.S (Johnson & Johnson-Janssen) at a dose of 5×1010 virus particles, or BNT162b2 (Pfizer-BioNTech) at a dose of 30 µg. The primary end points were safety, reactogenicity, and humoral immunogenicity on trial days 15 and 29. RESULTS: Of the 458 participants who were enrolled in the trial, 154 received mRNA-1273, 150 received Ad26.COV2.S, and 153 received BNT162b2 as booster vaccines; 1 participant did not receive the assigned vaccine. Reactogenicity was similar to that reported for the primary series. More than half the recipients reported having injection-site pain, malaise, headache, or myalgia. For all combinations, antibody neutralizing titers against a SARS-CoV-2 D614G pseudovirus increased by a factor of 4 to 73, and binding titers increased by a factor of 5 to 55. Homologous boosters increased neutralizing antibody titers by a factor of 4 to 20, whereas heterologous boosters increased titers by a factor of 6 to 73. Spike-specific T-cell responses increased in all but the homologous Ad26.COV2.S-boosted subgroup. CD8+ T-cell levels were more durable in the Ad26.COV2.S-primed recipients, and heterologous boosting with the Ad26.COV2.S vaccine substantially increased spike-specific CD8+ T cells in the mRNA vaccine recipients. CONCLUSIONS: Homologous and heterologous booster vaccines had an acceptable safety profile and were immunogenic in adults who had completed a primary Covid-19 vaccine regimen at least 12 weeks earlier. (Funded by the National Institute of Allergy and Infectious Diseases; DMID 21-0012 ClinicalTrials.gov number, NCT04889209.).

An mRNA Vaccine against SARS-CoV-2 - Preliminary Report.

BACKGROUND: The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in late 2019 and spread globally, prompting an international effort to accelerate development of a vaccine. The candidate vaccine mRNA-1273 encodes the stabilized prefusion SARS-CoV-2 spike protein. METHODS: We conducted a phase 1, dose-escalation, open-label trial including 45 healthy adults, 18 to 55 years of age, who received two vaccinations, 28 days apart, with mRNA-1273 in a dose of 25 µg, 100 µg, or 250 µg. There were 15 participants in each dose group. RESULTS: After the first vaccination, antibody responses were higher with higher dose (day 29 enzyme-linked immunosorbent assay anti-S-2P antibody geometric mean titer [GMT], 40,227 in the 25-µg group, 109,209 in the 100-µg group, and 213,526 in the 250-µg group). After the second vaccination, the titers increased (day 57 GMT, 299,751, 782,719, and 1,192,154, respectively). After the second vaccination, serum-neutralizing activity was detected by two methods in all participants evaluated, with values generally similar to those in the upper half of the distribution of a panel of control convalescent serum specimens. Solicited adverse events that occurred in more than half the participants included fatigue, chills, headache, myalgia, and pain at the injection site. Systemic adverse events were more common after the second vaccination, particularly with the highest dose, and three participants (21%) in the 250-µg dose group reported one or more severe adverse events. CONCLUSIONS: The mRNA-1273 vaccine induced anti-SARS-CoV-2 immune responses in all participants, and no trial-limiting safety concerns were identified. These findings support further development of this vaccine. (Funded by the National Institute of Allergy and Infectious Diseases and others; mRNA-1273 ClinicalTrials.gov number, NCT04283461).

Memory CD4+ T cells enhance B-cell responses to drifting influenza immunization.

Influenza A annually infects 5-10% of the world's human population resulting in one million deaths. Influenza causes annual epidemics and reinfects previously exposed individuals because of antigenic drift in the glycoprotein hemagglutinin. Due to antigenic drift, the immune system is simultaneously exposed to novel and conserved parts of the influenza virus via vaccination and/or infection throughout life. Preexisting immunity has long been known to augment subsequent hemagglutination inhibitory antibody (hAb) responses. However, the preexisting immunological contributors that influence hAb responses are not understood. Therefore, we adapted and developed sequential infection and immunization mouse models using drifted influenza strains to show that MHC Class II haplotype and T-cell reactivity influences subsequent hAb responses. We found that CB6F1 mice infected with A/CA followed by immunization with A/PR8 have increased hAb responses to A/PR8 compared to C57BL/6 mice. Increased hAb responses in CB6F1 mice were CD4+  T-cell and B-cell dependent and corresponded to increased germinal center A/PR8-specific B and T-follicular helper cells. These results suggest conserved MHC Class II restricted epitopes within HA are essential for B cells to respond to drifting influenza and could be leveraged to boost hAb responses.

Prophylaxis of Mycobacterium tuberculosis H37Rv Infection in a Preclinical Mouse Model via Inhalation of Nebulized Bacteriophage D29.

Globally, more people die annually from tuberculosis than from any other single infectious agent. Unfortunately, there is no commercially-available vaccine that is sufficiently effective at preventing acquisition of pulmonary tuberculosis in adults. In this study, pre-exposure prophylactic pulmonary delivery of active aerosolized anti-tuberculosis bacteriophage D29 was evaluated as an option for protection against Mycobacterium tuberculosis infection. An average bacteriophage concentration of approximately 1 PFU/alveolus was achieved in the lungs of mice using a nose-only inhalation device optimized with a dose simulation technique and adapted for use with a vibrating mesh nebulizer. Within 30 minutes of bacteriophage delivery, the mice received either a low dose (∼50-100 CFU), or an ultra-low dose (∼5-10 CFU), of M. tuberculosis H37Rv aerosol to the lungs. A prophylactic effect was observed with bacteriophage aerosol pre-treatment significantly decreasing M. tuberculosis burden in mouse lungs 24 hours and 3 weeks post-challenge (p < 0.05). These novel results indicate that a sufficient dose of nebulized mycobacteriophage aerosol to the lungs may be a valuable intervention to provide extra protection to health care professionals and other individuals at risk of exposure to M. tuberculosis.

A Nanostructured Lipid Carrier for Delivery of a Replicating Viral RNA Provides Single, Low-Dose Protection against Zika.

Since the first demonstration of in vivo gene expression from an injected RNA molecule almost two decades ago,1 the field of RNA-based therapeutics is now taking significant strides, with many cancer and infectious disease targets entering clinical trials.2 Critical to this success has been advances in the knowledge and application of delivery formulations. Currently, various lipid nanoparticle (LNP) platforms are at the forefront,3 but the encapsulation approach underpinning LNP formulations offsets the synthetic and rapid-response nature of RNA vaccines.4 Second, limited stability of LNP formulated RNA precludes stockpiling for pandemic readiness.5 Here, we show the development of a two-vialed approach wherein the delivery formulation, a highly stable nanostructured lipid carrier (NLC), can be manufactured and stockpiled separate from the target RNA, which is admixed prior to administration. Furthermore, specific physicochemical modifications to the NLC modulate immune responses, either enhancing or diminishing neutralizing antibody responses. We have combined this approach with a replicating viral RNA (rvRNA) encoding Zika virus (ZIKV) antigens and demonstrated a single dose as low as 10 ng can completely protect mice against a lethal ZIKV challenge, representing what might be the most potent approach to date of any Zika vaccine.

Antigen presentation by B cells guides programing of memory CD4+ T-cell responses to a TLR4-agonist containing vaccine in mice.

The contribution of B cells to immunity against many infectious diseases is unquestionably important and well characterized. Here, we sought to determine the role of B cells in the induction of T-helper 1 (TH 1) CD4+ T cells upon vaccination with a tuberculosis (TB) antigen combined with a TLR4 agonist. We used B-cell deficient mice (µMT-/- ), tetramer-positive CD4+ T cells, markers of memory "precursor" effector cells (MPECs), and T-cell adoptive transfers and demonstrated that the early antigen-specific cytokine-producing TH 1 responses are unaffected in the absence of B cells, however MPEC induction is strongly impaired resulting in a deficiency of the memory TH 1 response in µMT-/- mice. We further show that antigen-presentation by B cells is necessary for their role in MPEC generation using B-cell adoptive transfers from wt or MHC class II knock-out mice into µMT-/- mice. Our study challenges the view that B-cell deficiency exclusively alters the TH 1 response at memory time-points. Collectively, our results provide new insights on the multifaceted roles of B cells that will have a high impact on vaccine development against several pathogens including those requiring TH 1 cell-mediated immunity.

Vaccination Produces CD4 T Cells with a Novel CD154-CD40-Dependent Cytolytic Mechanism.

The discovery of new vaccines against infectious diseases and cancer requires the development of novel adjuvants with well-defined activities. The TLR4 agonist adjuvant GLA-SE elicits robust Th1 responses to a variety of vaccine Ags and is in clinical development for both infectious diseases and cancer. We demonstrate that immunization with a recombinant protein Ag and GLA-SE also induces granzyme A expression in CD4 T cells and produces cytolytic cells that can be detected in vivo. Surprisingly, these in vivo CTLs were CD4 T cells, not CD8 T cells, and this cytolytic activity was not dependent on granzyme A/B or perforin. Unlike previously reported CD4 CTLs, the transcription factors Tbet and Eomes were not necessary for their development. CTL activity was also independent of the Fas ligand-Fas, TRAIL-DR5, and canonical death pathways, indicating a novel mechanism of CTL activity. Rather, the in vivo CD4 CTL activity induced by vaccination required T cell expression of CD154 (CD40L) and target cell expression of CD40. Thus, vaccination with a TLR4 agonist adjuvant induces CD4 CTLs, which kill through a previously unknown CD154-dependent mechanism.

Immune subdominant antigens as vaccine candidates against Mycobacterium tuberculosis.

Unlike most pathogens, many of the immunodominant epitopes from Mycobacterium tuberculosis are under purifying selection. This startling finding suggests that M. tuberculosis may gain an evolutionary advantage by focusing the human immune response against selected proteins. Although the implications of this to vaccine development are incompletely understood, it has been suggested that inducing strong Th1 responses against Ags that are only weakly recognized during natural infection may circumvent this evasion strategy and increase vaccine efficacy. To test the hypothesis that subdominant and/or weak M. tuberculosis Ags are viable vaccine candidates and to avoid complications because of differential immunodominance hierarchies in humans and experimental animals, we defined the immunodominance hierarchy of 84 recombinant M. tuberculosis proteins in experimentally infected mice. We then combined a subset of these dominant or subdominant Ags with a Th1 augmenting adjuvant, glucopyranosyl lipid adjuvant in stable emulsion, to assess their immunogenicity in M. tuberculosis-naive animals and protective efficacy as measured by a reduction in lung M. tuberculosis burden of infected animals after prophylactic vaccination. We observed little correlation between immunodominance during primary M. tuberculosis infection and vaccine efficacy, confirming the hypothesis that subdominant and weakly antigenic M. tuberculosis proteins are viable vaccine candidates. Finally, we developed two fusion proteins based on strongly protective subdominant fusion proteins. When paired with the glucopyranosyl lipid adjuvant in stable emulsion, these fusion proteins elicited robust Th1 responses and limited pulmonary M. tuberculosis for at least 6 wk postinfection with a single immunization. These findings expand the potential pool of M. tuberculosis proteins that can be considered as vaccine Ag candidates.

Interferon γ and Tumor Necrosis Factor Are Not Essential Parameters of CD4+ T-Cell Responses for Vaccine Control of Tuberculosis.

BACKGROUND: Mycobacterium tuberculosis infects one third of the world's population and causes >8 million cases of tuberculosis annually. New vaccines are necessary to control the spread of tuberculosis. T cells, interferon γ (IFN-γ), and tumor necrosis factor (TNF) are necessary to control M. tuberculosis infection in both humans and unvaccinated experimental animal models. However, the immune responses necessary for vaccine efficacy against M. tuberculosis have not been defined. The multifunctional activity of T-helper type 1 (TH1) cells that simultaneously produce IFN-γ and TNF has been proposed as a candidate mechanism of vaccine efficacy. METHODS: We used a mouse model of T-cell transfer and aerosolized M. tuberculosis infection to assess the contributions of TNF, IFN-γ, and inducible nitric oxide synthase (iNOS) to vaccine efficacy. RESULTS: CD4(+) T cells were necessary and sufficient to transfer protection against aerosolized M. tuberculosis, but neither CD4(+) T cell-produced TNF nor host cell responsiveness to IFN-γ were necessary. Transfer of Tnf(-/-) CD4(+) T cells from vaccinated donors to Ifngr(-/-) recipients was also sufficient to confer protection. Activation of iNOS to produce reactive nitrogen species was not necessary for vaccine efficacy. CONCLUSIONS: Induction of TH1 cells that coexpress IFN-γ and TNF is not a requirement for vaccine efficacy against M. tuberculosis, despite these cytokines being essential for control of M. tuberculosis in nonvaccinated animals.

Protection against tuberculosis with homologous or heterologous protein/vector vaccine approaches is not dependent on CD8+ T cells.

Considerable effort has been directed to develop Mycobacterium tuberculosis vaccines to boost bacille Calmette-Guérin or for those who cannot be immunized with bacille Calmette-Guérin. We hypothesized that CD4(+) and CD8(+) T cell responses with a heterologous prime/boost vaccine approach could induce long-lived vaccine efficacy against M. tuberculosis in C57BL/6 mice. We produced an adenovirus vector expressing ID93 (Ad5-ID93) for induction of CD8 T cells to use with our candidate tuberculosis vaccine, ID93/glucopyranosyl lipid adjuvant (GLA)-stable emulsion (SE), which induces potent Th1 CD4 T cells. Ad5-ID93 generates ID93-specific CD8(+) T cell responses and induces protection against M. tuberculosis. When Ad5-ID93 is administered in a prime-boost strategy with ID93/GLA-SE, both CD4(+) and CD8(+) T cells are generated and provide protection against M. tuberculosis. In a MHC class I-deficient mouse model, all groups including the Ad5-ID93 group elicited an Ag-specific CD4(+) T cell response and significantly fewer Ag-specific CD8(+) T cells, but were still protected against M. tuberculosis, suggesting that CD4(+) Th1 T cells could compensate for the loss of CD8(+) T cells. Lastly, the order of the heterologous immunizations was critical. Long-lived vaccine protection was observed only when Ad5-ID93 was given as the boost following an ID93/GLA-SE prime. The homologous ID93/GLA-SE prime/boost regimen also induced long-lived protection. One of the correlates of protection between these two approaches was an increase in the total number of ID93-specific IFN-γ-producing CD4(+) T cells 6 mo following the last immunization. Our findings provide insight into the development of vaccines not only for tuberculosis, but other diseases requiring T cell immunity.

Protection against Mycobacterium leprae infection by the ID83/GLA-SE and ID93/GLA-SE vaccines developed for tuberculosis.

Despite the dramatic reduction in the number of leprosy cases worldwide in the 1990s, transmission of the causative agent, Mycobacterium leprae, is still occurring, and new cases continue to appear. New strategies are required in the pursuit of leprosy elimination. The cross-application of vaccines in development for tuberculosis may lead to tools applicable to elimination of leprosy. In this report, we demonstrate that the chimeric fusion proteins ID83 and ID93, developed as antigens for tuberculosis (TB) vaccine candidates, elicited gamma interferon (IFN-γ) responses from both TB and paucibacillary (PB) leprosy patients and from healthy household contacts of multibacillary (MB) patients (HHC) but not from nonexposed healthy controls. Immunization of mice with either protein formulated with a Toll-like receptor 4 ligand (TLR4L)-containing adjuvant (glucopyranosyl lipid adjuvant in a stable emulsion [GLA-SE]) stimulated antigen-specific IFN-γ secretion from pluripotent Th1 cells. When immunized mice were experimentally infected with M. leprae, both cellular infiltration into the local lymph node and bacterial growth at the site were reduced relative to those of unimmunized mice. Thus, the use of the Mycobacterium tuberculosis candidate vaccines ID83/GLA-SE and ID93/GLA-SE may confer cross-protection against M. leprae infection. Our data suggest these vaccines could potentially be used as an additional control measure for leprosy.

MyD88 and TRIF synergistic interaction is required for TH1-cell polarization with a synthetic TLR4 agonist adjuvant.

Glucopyranosyl lipid adjuvant-stable emulsion (GLA-SE) is a synthetic adjuvant TLR4 agonist that promotes potent poly-functional T(H)1 responses. Different TLR4 agonists may preferentially signal via MyD88 or TIR-domain-containing adapter inducing IFN-beta (TRIF) to exert adjuvant effects; however, the contribution of MyD88 and TRIF signaling to the induction of polyclonal T(H)1 responses by TLR4 agonist adjuvants has not been studied in vivo. To determine whether GLA-SE preferentially signals through MyD88 or TRIF, we evaluated the immune response against a candidate tuberculosis (TB) vaccine Ag following immunization of mice lacking either signaling adapter compared with that of wild-type mice. We find that both MyD88 and TRIF are necessary for GLA-SE to induce a poly-functional T(H)1 immune response characterized by CD4(+) T cells producing IFN-γ, TNF, and IL-2, as well as IgG2c class switching, when paired with the TB vaccine Ag ID93. Accordingly, the protective efficacy of ID93/GLA-SE immunization against aerosolized Mycobacterium tuberculosis was lost when either signaling molecule was ablated. We demonstrate that MyD88 and TRIF must be expressed in the same cell for the in vivo T(H)1-skewing adjuvant activity, indicating that these two signaling pathways cooperate on an intracellular level. Thus engagement of both the MyD88 and TRIF signaling pathways are essential for the effective adjuvant activity of this TLR4 agonist.

The importance of adjuvant formulation in the development of a tuberculosis vaccine.

An effective protein-based vaccine for tuberculosis will require a safe and effective adjuvant. There are few adjuvants in approved human vaccines, including alum and the oil-in-water-based emulsions MF59 (Novartis Vaccines and Diagnostics), AS03 and AS04 (GlaxoSmithKline Biologics), AF03 (Sanofi), and liposomes (Crucell). When used with pure, defined proteins, both alum and emulsion adjuvants are effective at inducing primarily humoral responses. One of the newest adjuvants in approved products is AS04, which combines monophosphoryl lipid A, a TLR-4 agonist, with alum. In this study, we compared two adjuvants: a stable oil-in-water emulsion (SE) and a stable oil-in-water emulsion incorporating glucopyranosyl lipid adjuvant, a synthetic TLR-4 agonist (GLA-SE), each together with a recombinant protein, ID93. Both the emulsion SE and GLA-SE adjuvants induce potent cellular responses in combination with ID93 in mice. ID93/SE induced Th2-biased immune responses, whereas ID93/GLA-SE induced multifunctional CD4(+) Th1 cell responses (IFN-γ, TNF-α, and IL-2). The ID93/GLA-SE vaccine candidate induced significant protection in mice and guinea pigs, whereas no protection was observed with ID93/SE, as assessed by reductions in bacterial burden, survival, and pathology. These results highlight the importance of properly formulating subunit vaccines with effective adjuvants for use against tuberculosis.

Therapeutic immunization against Mycobacterium tuberculosis is an effective adjunct to antibiotic treatment.

BACKGROUND: Recent advances in rational adjuvant design and antigen selection have enabled a new generation of vaccines with potential to treat and prevent infectious disease. The aim of this study was to assess whether therapeutic immunization could impact the course of Mycobacterium tuberculosis infection with use of a candidate tuberculosis vaccine antigen, ID93, formulated in a synthetic nanoemulsion adjuvant, GLA-SE, administered in combination with existing first-line chemotherapeutics rifampicin and isoniazid. METHODS: We used a mouse model of fatal tuberculosis and the established cynomolgus monkey model to design an immuno-chemotherapeutic strategy to increase long-term survival and reduce bacterial burden, compared with standard antibiotic chemotherapy alone. RESULTS: This combined approach induced robust and durable pluripotent antigen-specific T helper-1-type immune responses, decreased bacterial burden, reduced the duration of conventional chemotherapy required for survival, and decreased M. tuberculosis-induced lung pathology, compared with chemotherapy alone. CONCLUSIONS: These results demonstrate the ability of therapeutic immunization to significantly enhance the efficacy of chemotherapy against tuberculosis and other infectious diseases, with implications for treatment duration, patient compliance, and more optimal resource allocation.

Antibodies as key mediators of protection against Mycobacterium tuberculosis.

Tuberculosis (TB) is caused by infection with the bacterial pathogen Mycobacterium tuberculosis (M.tb) in the respiratory tract. There was an estimated 10.6 million people newly diagnosed with TB, and there were approximately 1.3 million deaths caused by TB in 2022. Although the global prevalence of TB has remained high for decades and is an annual leading cause of death attributed to infectious diseases, only one vaccine, Bacillus Calmette-Guérin (BCG), has been approved so far to prevent/attenuate TB disease. Correlates of protection or immunological mechanisms that are needed to control M.tb remain unknown. The protective role of antibodies after BCG vaccination has also remained largely unclear; however, recent studies have provided evidence for their involvement in protection against disease, as biomarkers for the state of infection, and as potential predictors of outcomes. Interestingly, the antibodies generated post-vaccination with BCG are linked to the activation of innate immune cascades, providing further evidence that antibody effector functions are critical for protection against respiratory pathogens such as M.tb. In this review, we aim to provide current knowledge of antibody application in TB diagnosis, prevention, and treatment. Particularly, this review will focus on 1) The role of antibodies in preventing M.tb infections through preventing Mtb adherence to epithelium, antibody-mediated phagocytosis, and antibody-mediated cellular cytotoxicity; 2) The M.tb-directed antibody response generated after vaccination and how humoral profiles with different glycosylation patterns of these antibodies are linked with protection against the disease state; and 3) How antibody-mediated immunity against M.tb can be further explored as early diagnosis biomarkers and different detection methods to combat the global M.tb burden. Broadening the paradigm of differentiated antibody profiling and antibody-based detection during TB disease progression offers new directions for diagnosis, treatment, and preventative strategies. This approach involves linking the aforementioned humoral responses with the disease state, progression, and clearance.

Backtranslation of human RNA biosignatures of tuberculosis disease risk into the preclinical pipeline is condition dependent.

It is not clear whether human progression to active tuberculosis disease (TB) risk signatures are viable endpoint criteria for evaluations of treatments in clinical or preclinical development. TB is the deadliest infectious disease globally and more efficacious vaccines are needed to reduce this mortality. However, the immune correlates of protection for either preventing infection with Mycobacterium tuberculosis or preventing TB disease have yet to be completely defined, making the advancement of candidate vaccines through the pipeline slow, costly, and fraught with risk. Human-derived correlate of risk (COR) gene signatures, which identify an individual's risk to progressing to active TB disease, provide an opportunity for evaluating new therapies for TB with clear and defined endpoints. Though prospective clinical trials with longitudinal sampling are prohibitively expensive, characterization of COR gene signatures is practical with preclinical models. Using a 3Rs (Replacement, Reduction and Refinement) approach we reanalyzed heterogeneous publicly available transcriptional datasets to determine whether a specific set of COR signatures are viable endpoints in the preclinical pipeline. We selected RISK6, Sweeney3 and BATF2 human-derived blood-based RNA biosignatures because they require relatively few genes to assign a score and have been carefully evaluated across several clinical cohorts. Excitingly, these data provide proof-of-concept that human COR signatures seem to have high fidelity across several tissue types in the preclinical TB model pipeline and show best performance when the model most closely reflected human infection or disease conditions. Human-derived COR signatures offer an opportunity for high-throughput preclinical endpoint criteria of vaccine and drug therapy evaluations. One Sentence Summary: Human-derived biosignatures of tuberculosis disease progression were evaluated for their predictive fidelity across preclinical species and derived tissues using available public data sets.

Protective interplay: Mycobacterium tuberculosis diminishes SARS-CoV-2 severity through innate immune priming.

At the beginning of the COVID-19 pandemic those with underlying chronic lung conditions, including tuberculosis (TB), were hypothesized to be at higher risk of severe COVID-19 disease. However, there is inconclusive clinical and preclinical data to confirm the specific risk SARS-CoV-2 poses for the millions of individuals infected with Mycobacterium tuberculosis (M.tb). We and others have found that compared to singly infected mice, mice co-infected with M.tb and SARS-CoV-2 leads to reduced SARS-CoV-2 severity compared to mice infected with SARS-CoV-2 alone. Consequently, there is a large interest in identifying the molecular mechanisms responsible for the reduced SARS-CoV-2 infection severity observed in M.tb and SARS-CoV-2 co-infection. To address this, we conducted a comprehensive characterization of a co-infection model and performed mechanistic in vitro modeling to dynamically assess how the innate immune response induced by M.tb restricts viral replication. Our study has successfully identified several cytokines that induce the upregulation of anti-viral genes in lung epithelial cells, thereby providing protection prior to challenge with SARS-CoV-2. In conclusion, our study offers a comprehensive understanding of the key pathways induced by an existing bacterial infection that effectively restricts SARS-CoV-2 activity and identifies candidate therapeutic targets for SARS-CoV-2 infection.

Tuberculosis vaccines update: Is an RNA-based vaccine feasible for tuberculosis?

OBJECTIVES: Despite concerted efforts, Mycobacterium tuberculosis (M.tb), the pathogen that causes tuberculosis (TB), continues to be a burden on global health, regaining its dubious distinction in 2022 as the world's biggest infectious killer with global COVID-19 deaths steadily declining. The complex nature of M.tb, coupled with different pathogenic stages, has highlighted the need for the development of novel immunization approaches to combat this ancient infectious agent. Intensive efforts over the last couple of decades have identified alternative approaches to improve upon traditional vaccines that are based on killed pathogens, live attenuated agents, or subunit recombinant antigens formulated with adjuvants. Massive funding and rapid advances in RNA-based vaccines for immunization have recently transformed the possibility of protecting global populations from viral pathogens, such as SARS-CoV-2. Similar efforts to combat bacterial pathogens such as M.tb have been significantly slower to implement. METHODS: In this review, we discuss the application of a novel replicating RNA (repRNA)-based vaccine formulated and delivered in nanostructured lipids. RESULTS: Our preclinical data are the first to report that RNA platforms are a viable system for TB vaccines and should be pursued with high-priority M.tb antigens containing cluster of differentiation (CD4+) and CD8+ T-cell epitopes. CONCLUSION: This RNA vaccine shows promise for use against intracellular bacteria such as M.tb as demonstrated by the feasibility of construction, enhanced induction of cell-mediated and humoral immune responses, and improved bacterial burden outcomes in in vivo aerosol-challenged preclinical TB models.

SARS-CoV-2 infection and immune responses.

The recent pandemic caused by the SARS-CoV-2 virus continues to be an enormous global challenge faced by the healthcare sector. Availability of new vaccines and drugs targeting SARS-CoV-2 and sequelae of COVID-19 has given the world hope in ending the pandemic. However, the emergence of mutations in the SARS-CoV-2 viral genome every couple of months in different parts of world is a persistent danger to public health. Currently there is no single treatment to eradicate the risk of COVID-19. The widespread transmission of SARS-CoV-2 due to the Omicron variant necessitates continued work on the development and implementation of effective vaccines. Moreover, there is evidence that mutations in the receptor domain of the SARS-CoV-2 spike glycoprotein led to the decrease in current vaccine efficacy by escaping antibody recognition. Therefore, it is essential to actively identify the mechanisms by which SARS-CoV-2 evades the host immune system, study the long-lasting effects of COVID-19 and develop therapeutics targeting SARS-CoV-2 infections in humans and preclinical models. In this review, we describe the pathogenic mechanisms of SARS-CoV-2 infection as well as the innate and adaptive host immune responses to infection. We address the ongoing need to develop effective vaccines that provide protection against different variants of SARS-CoV-2, as well as validated endpoint assays to evaluate the immunogenicity of vaccines in the pipeline, medications, anti-viral drug therapies and public health measures, that will be required to successfully end the COVID-19 pandemic.