Rapid Phenotypic Antibiotic Susceptibility Profiling of Clinical Escherichia coli and Klebsiella pneumoniae Blood Cultures.

Bloodstream infections (BSI) are defined by the presence of viable bacteria or fungi, accompanied by systemic signs of infection. Choosing empirical therapy based solely on patient risk factors and prior antibiotic susceptibility test (AST) may lead to either ineffective treatment or unnecessarily broad-spectrum antibiotic exposure. In general, Clinical & Laboratory Standards Institute guideline-approved ASTs have a turnaround time of 48-72 h from sample to answer, a period that may result in a critical delay in the appropriate selection of therapy. Therefore, reducing the time required for AST is highly advantageous. We have previously shown that our novel rapid AST method, MAPt (Micro-Agar-PCR-test), accurately identifies susceptibility profiles for spiked bioterrorism agents like Bacillus anthracis, Yersinia pestis and Francisella tularensis directly from whole-blood and blood culture samples, even at low bacterial levels (500 CFU/mL). This study evaluated the performance of MAPt on routine bloodstream infection (BSI), focusing on Escherichia coli and Klebsiella pneumoniae isolates from clinical cultures, including resistant strains to some of the six tested antibiotics. Notably, MAPt yielded results exceeding 95% agreement with the standard hospital method within a significantly shorter timeframe of 6 h. These findings suggest significant potential for MAPt as a rapid and reliable BSI management tool.

Visual guidelines and tutoring in pediatric urological surgery.

Background: The aim of this prospective randomized study was to evaluate the impact of visual guidelines (picture book) and parents tutoring on pediatric urological surgery on parent's stress and anxiety, the number of postoperative contacts, and complications. Materials and methods: Following institutional ethical committee approval, a special picture book reflecting different stages of the convalescent period following multiple types of pediatric urological surgery was developed. Parents were randomly divided into 2 groups in which 33 parents in Group 1 received the picture book in addition to routine instructions prior to the surgery and 31 in Group 2 received only routine postoperative instructions. The parents were asked to answer a questionnaire (Amsterdam Preoperative Anxiety and Information Scale) regarding the level of anxiety before surgery and immediately after surgery in the recovery room. The number of postoperative parent's calls, nonplaned emergency room visits, and complications were recorded. Results: No statistically significant difference in perioperative parental anxiety was found (p = 0.88). The visual tutoring group had a significantly lower rate of emergency room admissions (6.6% vs. 18.6%, p = 0.0433), however parents from this group made a higher number of postoperative calls (9.9% vs. 3.1%, p = 0.38). Two (6.6%) from the tutoring group expressed their desire to omit visual counseling in future surgical preparation and 4 (13.2%) did not have an opinion. Overall satisfaction with regards to the preoperative counseling and information and the number of postoperative complications was similar in both groups. Conclusions: Visual tutoring does not add any value to parental anxiety but seems helpful in reducing postoperative emergency room visits. Some parents preferred to exclude visual information from future preoperative counseling.

Immunogenicity of a Third Dose of BNT162b2 Vaccine among Lung Transplant Recipients-A Prospective Cohort Study.

Two doses of mRNA SARS-CoV-2 vaccines elicit an attenuated humoral immune response among immunocompromised patients. Our study aimed to assess the immunogenicity of a third dose of the BNT162b2 vaccine among lung transplant recipients (LTRs). We prospectively evaluated the humoral response by measuring anti-spike SARS-CoV-2 and neutralizing antibodies in 139 vaccinated LTRs ~4-6 weeks following the third vaccine dose. The t-cell response was evaluated by IFNγ assay. The primary outcome was the seropositivity rate following the third vaccine dose. Secondary outcomes included: positive neutralizing antibody and cellular immune response rate, adverse events, and COVID-19 infections. Results were compared to a control group of 41 healthcare workers. Among LTRs, 42.4% had a seropositive antibody titer, and 17.2% had a positive t-cell response. Seropositivity was associated with younger age (t = 3.736, p < 0.001), higher GFR (t = 2.355, p = 0.011), and longer duration from transplantation (t = -1.992, p = 0.024). Antibody titer positively correlated with neutralizing antibodies (r = 0.955, p < 0.001). The current study may suggest the enhancement of immunogenicity by using booster doses. Since monoclonal antibodies have limited effectiveness against prevalent sub-variants and LTRs are prone to severe COVID-19 morbidity, vaccination remains crucial for this vulnerable population.

A single-dose F1-based mRNA-LNP vaccine provides protection against the lethal plague bacterium.

Messenger RNA (mRNA) lipid nanoparticle (LNP) vaccines have emerged as an effective vaccination strategy. Although currently applied toward viral pathogens, data concerning the platform's effectiveness against bacterial pathogens are limited. Here, we developed an effective mRNA-LNP vaccine against a lethal bacterial pathogen by optimizing mRNA payload guanine and cytosine content and antigen design. We designed a nucleoside-modified mRNA-LNP vaccine based on the bacterial F1 capsule antigen, a major protective component of Yersinia pestis, the etiological agent of plague. Plague is a rapidly deteriorating contagious disease that has killed millions of people during the history of humankind. Now, the disease is treated effectively with antibiotics; however, in the case of a multiple-antibiotic-resistant strain outbreak, alternative countermeasures are required. Our mRNA-LNP vaccine elicited humoral and cellular immunological responses in C57BL/6 mice and conferred rapid, full protection against lethal Y. pestis infection after a single dose. These data open avenues for urgently needed effective antibacterial vaccines.

A Novel Approach to Vaccine Development: Concomitant Pathogen Inactivation and Host Immune Stimulation by Peroxynitrite.

The design of efficient vaccines for long-term protective immunity against pathogens represents an objective of utmost public health priority. In general, live attenuated vaccines are considered to be more effective than inactivated pathogens, yet potentially more reactogenic. Accordingly, inactivation protocols which do not compromise the pathogen's ability to elicit protective immunity are highly beneficial. One of the sentinel mechanisms of the host innate immune system relies on the production of reactive nitrogen intermediates (RNI), which efficiently inactivate pathogens. Peroxynitrite (PN) is a prevalent RNI, assembled spontaneously upon the interaction of nitric oxide (NO) with superoxide. PN exerts its bactericidal effect by via the efficient oxidation of a broad range of biological molecules. Furthermore, the interaction of PN with proteins results in structural/chemical modifications, such as the oxidation of tryptophan, tyrosine, and cysteine residues, as well as the formation of carbonyl, dityrosine, and nitrotyrosine (NT). In addition to their role in innate immunity, these PN-mediated modifications of pathogen components may also augment the antigenicity of pathogen peptides and proteins, hence contributing to specific humoral responses. In the study reported here, a novel approach for vaccine development, consisting of pathogen inactivation by PN, combined with increased immunity of NT-containing peptides, is implemented as a proof-of-concept for vaccination against the intracellular pathogen Francisella tularensis (F. tularensis). In vivo experiments in a murine model of tularemia confirm that PN-inactivated F. tularensis formulations may rapidly stimulate innate and adaptive immune cells, conferring efficient protection against a lethal challenge, superior to that elicited by bacteria inactivated by the widely used formalin treatment.

Immune Response to Third Dose BNT162b2 COVID-19 Vaccine Among Kidney Transplant Recipients-A Prospective Study.

Immune response to two SARS-CoV-2 mRNA vaccine doses among kidney transplant recipients (KTRs) is limited. We aimed to evaluate humoral and cellular response to a third BNT162b2 dose. In this prospective study, 190 KTRs were evaluated before and ∼3 weeks after the third vaccine dose. The primary outcomes were anti-spike antibody level >4160 AU/ml (neutralization-associated cutoff) and any seropositivity. Univariate and multivariate analyses were conducted to identify variables associated with antibody response. T-cell response was evaluated in a subset of participants. Results were compared to a control group of 56 healthcare workers. Among KTRs, we found a seropositivity rate of 70% (133/190) after the third dose (37%, 70/190, after the second vaccine dose); and 27% (52/190) achieved levels above 4160 AU/ml after the third dose, compared to 93% of controls. Variables associated with antibody response included higher antibody levels after the second dose (odds ratio [OR] 30.8 per log AU/ml, 95% confidence interval [CI]11-86.4, p < 0.001); and discontinuation of antimetabolite prior to vaccination (OR 9.1,95% CI 1.8-46.5, p = 0.008). T-cell response was demonstrated in 13% (7/53). In conclusion, third dose BNT162b2 improved immune response among KTRs, however 30% still remained seronegative. Pre-vaccination temporary immunosuppression reduction improved antibody response.

Humoral and T-Cell Response before and after a Fourth BNT162b2 Vaccine Dose in Adults ≥60 Years.

Both humoral and cellular anamnestic responses are significant for protective immunity against SARS-CoV-2. In the current study, the responses in elderly people before and after a fourth vaccine dose of BNT162b2 were compared to those of individuals immunized with three vaccine doses. Although a boost effect was observed, the high response following the third administration questions the necessity of an early fourth boost.

Evaluation of a Frozen Micro-Agar Plates of MAPt Antibiotic Susceptibility Test for Enhanced Bioterror Preparedness.

There is an urgent need for rapid antibiotic susceptibility tests to improve clinical treatment and to support antibiotic stewardship, especially concerning the emergence of multi-drug-resistant bacteria. Nowadays this need is even more profound due to progress in synthetic biology procedures that may facilitate the malicious preparation of engineered antibiotic-resistant pathogens. We recently described a novel, rapid, simple, specific, and sensitive method named a Micro-Agar-PCR-test (MAPt) and showed its performance on clinical as well as environmental samples. The method does not require any isolation or purification steps and is applicable to a wide range of bacterial concentrations, thus allowing a short time to respond within a bioterror event (5-7 h for B. anthracis, 10-12 h for Y. pestis, and 16 h for F. tularensis). Ready-to-use reagents for this assay may add a level of preparedness. We examined the option of freezing pre-prepared MAPt agar plates and thawing them upon need. Our results show that adequate minimal inhibitory concentration (MIC) values are obtained with the use of thawed 6- and 12-month frozen agar plates. The ability to store MAPt micro-agar plates at -70 °C for a year, together with all other reagents required for MAPt, holds a great advantage for bioterror preparedness.

Genome-wide CRISPR screens identify GATA6 as a proviral host factor for SARS-CoV-2 via modulation of ACE2.

The global spread of SARS-CoV-2 led to major economic and health challenges worldwide. Revealing host genes essential for infection by multiple variants of SARS-CoV-2 can provide insights into the virus pathogenesis, and facilitate the development of novel therapeutics. Here, employing a genome-scale CRISPR screen, we provide a comprehensive data-set of cellular factors that are exploited by wild type SARS-CoV-2 as well as two additional recently emerged variants of concerns (VOCs), Alpha and Beta. We identified several host factors critical for SARS-CoV-2 infection, including various components belonging to the Clathrin-dependent transport pathway, ubiquitination, Heparan sulfate biogenesis and host phosphatidylglycerol biosynthesis. Comparative analysis of the different VOCs revealed the host factors KREMEN2 and SETDB1 as potential unique candidates required only to the Alpha variant. Furthermore, the analysis identified GATA6, a zinc finger transcription factor, as an essential proviral gene for all variants inspected. We show that GATA6 directly regulates ACE2 transcription and accordingly, is critical for SARS-CoV-2 cell entry. Analysis of clinical samples collected from SARS-CoV-2 infected individuals shows elevated levels of GATA6, suggesting a role in COVID-19 pathogenesis. Finally, pharmacological inhibition of GATA6 resulted in down-modulation of ACE2 and inhibition of viral infectivity. Overall, we show GATA6 may represent a target for the development of anti-SARS-CoV-2 therapeutic strategies and reaffirm the value of the CRISPR loss-of-function screens in providing a list of potential new targets for therapeutic interventions.

Whole genome sequencing and taxonomic profiling of two Pantoea sp. isolated from environmental samples in Israel.

OBJECTIVE: As part of a research aiming at the isolation of bacteria secreting growth inhibiting compounds, cultures of Francisella tularensis were implanted in environmental samples and monitored for inhibition zones on agar. Two antibiotic-like secreting bacteria were isolated, their genomic sequence was deciphered and taxonomic profiling analysis classified them as belonging to the Pantoea genus. DATA DESCRIPTION: Two bacterial isolates exhibiting growth inhibition zones to F. tularensis (LVS) were analyzed using the Oxford Nanopore Technology (ONT). Preliminary de novo assembly of the reads was performed, followed by taxonomic profiling based on Multi Locus Sequence Analysis (MLSA) and implementation of the Average Nucleotide Identity (ANI) measure. The genomic sequences resulted in the identification of two different Pantoea species, denoted EnvD and EnvH. Subsequent de novo genome assembly generated 5 and 10 contigs for EnvD and EnvH, respectively. The largest contig (4,008,183 bps and 3,740,753 bps for EnvD and EnvH, respectively), overlaps to a major extent to the chromosome of closely related Pantoea species. ANI values calculated for both isolates revealed two apparently new species of the Pantoea genus. Our study deciphered the identity of two bacteria producing antibiotic-like compounds, and the genomic sequence revealed they represent distinct Pantoea species.

Phage Therapy Potentiates Second-Line Antibiotic Treatment against Pneumonic Plague.

Plague pandemics and outbreaks have killed millions of people during the history of humankind. The disease, caused by the bacteria Yersinia pestis, is currently treated effectively with antibiotics. However, in the case of multidrug-resistant (MDR) bacteria, alternative treatments are required. Bacteriophage (phage) therapy has shown efficient antibacterial activity in various experimental animal models and in human patients infected with different MDR pathogens. Here, we evaluated the efficiency of фA1122 and PST phage therapy, alone or in combination with second-line antibiotics, using a well-established mouse model of pneumonic plague. Phage treatment significantly delayed mortality and limited bacterial proliferation in the lungs. However, the treatment did not prevent bacteremia, suggesting that phage efficiency may decrease in the circulation. Indeed, in vitro phage proliferation assays indicated that blood exerts inhibitory effects on lytic activity, which may be the major cause of treatment inefficiency. Combining phage therapy and second-line ceftriaxone treatment, which are individually insufficient, provided protection that led to the survival of all infected animals-a synergistic protective effect that represents a proof of concept for efficient combinatorial therapy in an emergency event of a plague outbreak involving MDR Y. pestis strains.

T Cell Response following Anti-COVID-19 BNT162b2 Vaccination Is Maintained against the SARS-CoV-2 Omicron B.1.1.529 Variant of Concern.

The progression of the COVID-19 pandemic has led to the emergence of variants of concern (VOC), which may compromise the efficacy of the currently administered vaccines. Antigenic drift can potentially bring about reduced protective T cell immunity and, consequently, more severe disease manifestations. To assess this possibility, the T cell responses to the wild-type Wuhan-1 SARS-CoV-2 ancestral spike protein and the Omicron B.1.1.529 spike protein were compared. Accordingly, peripheral blood mononuclear cells (PBMC) were collected from eight healthy volunteers 4-5 months following a third vaccination with BNT162b2, and stimulated with overlapping peptide libraries representing the spike of either the ancestral or the Omicron SARS-CoV-2 virus variants. Quantification of the specific T cells was carried out by a fluorescent ELISPOT assay, monitoring cells secreting interferon-gamma (IFNg), interleukin-10 (IL-10) and interleukin-4 (IL-4). For all the examined individuals, comparable levels of reactivity to both forms of spike protein were determined. In addition, a dominant Th1 response was observed, manifested mainly by IFNg-secreting cells and only limited numbers of IL-10- and IL-4-secreting cells. The data demonstrate stable T cell activity in response to the emerging Omicron variant in the tested individuals; therefore, the protective immunity to the variant following BNT162b2 vaccination is not significantly affected.

Preliminary nonclinical safety and immunogenicity of an rVSV-ΔG-SARS-CoV-2-S vaccine in mice, hamsters, rabbits and pigs.

rVSV-ΔG-SARS-CoV-2-S is a clinical stage (Phase 2) replication competent recombinant vaccine against SARS-CoV-2. To evaluate the safety profile of the vaccine, a series of non-clinical safety, immunogenicity and efficacy studies were conducted in four animal species, using multiple doses (up to 108 Plaque Forming Units/animal) and dosing regimens. There were no treatment-related mortalities or any noticeable clinical signs in any of the studies. Compared to unvaccinated controls, hematology and biochemistry parameters were unremarkable and no adverse histopathological findings. There was no detectable viral shedding in urine, nor viral RNA detected in whole blood or serum samples seven days post vaccination. The rVSV-ΔG-SARS-CoV-2-S vaccination gave rise to neutralizing antibodies, cellular immune responses, and increased lymphocytic cellularity in the spleen germinal centers and regional lymph nodes. No evidence for neurovirulence was found in C57BL/6 immune competent mice or in highly sensitive type I interferon knock-out mice. Vaccine virus replication and distribution in K18-human Angiotensin-converting enzyme 2-transgenic mice showed a gradual clearance from the vaccination site with no vaccine virus recovered from the lungs. The nonclinical data suggest that the rVSV-ΔG-SARS-CoV-2-S vaccine is safe and immunogenic. These results supported the initiation of clinical trials, currently in Phase 2.

Is Ultrasound-Guided Single-Shot Quadratus Lumborum Block a Viable Alternative to a Caudal Block in Pediatric Urological Surgery?

OBJECTIVE: To review our experience with quadratus lumborum block (QLB) in pediatric urology. MATERIALS AND METHODS: This mixed prospective-retrospective study included 41 patients who received QLB following induction of general anesthesia. Data collected included: the duration of block induction, surgery, hospitalization, postoperative pain score, and the use of rescue analgesia. The results were compared with a matched cohort of patients who received caudal block (CB) during similar surgeries from our retrospectively acquired data registry. RESULTS: There was no difference between the type and length of surgery, weight, sex, and age of the patients between the two groups. The duration of block induction was significantly shorter in the CB group compared with the QLB group (35.6 ± 14.6 vs. 239 ± 33.4 seconds [p < 0.0001]). There was no difference between the groups in pain scores at 1, 4, and 24 hours postoperatively, in the time to first rescue analgesia, or in the postoperative opioid requirements. However, the QLB group required more rescue analgesia compared with CB group (p = 0.016). Finally, no differences were found in the use of rescue analgesics at home, pain record behavior, and overall satisfaction. CONCLUSION: Our data show that QLB might serve as a viable alternative to CB in pediatric urological surgery.

Beating the Bio-Terror Threat with Rapid Antimicrobial Susceptibility Testing.

A bioterror event using an infectious bacterium may lead to catastrophic outcomes involving morbidity and mortality as well as social and psychological stress. Moreover, a bioterror event using an antibiotic resistance engineered bacterial agent may raise additional concerns. Thus, preparedness is essential to preclude and control the dissemination of the bacterial agent as well as to appropriately and promptly treat potentially exposed individuals or patients. Rates of morbidity, death, and social anxiety can be drastically reduced if the rapid delivery of antimicrobial agents for post-exposure prophylaxis and treatment is initiated as soon as possible. Availability of rapid antibiotic susceptibility tests that may provide key recommendations to targeted antibiotic treatment is mandatory, yet, such tests are only at the development stage. In this review, we describe the recently published rapid antibiotic susceptibility tests implemented on bioterror bacterial agents and discuss their assimilation in clinical and environmental samples.

Implementation of Adenovirus-Mediated Pulmonary Expression of Human ACE2 in HLA Transgenic Mice Enables Establishment of a COVID-19 Murine Model for Assessment of Immune Responses to SARS-CoV-2 Infection.

HLA transgenic mice are instrumental for evaluation of human-specific immune responses to viral infection. Mice do not develop COVID-19 upon infection with SARS-CoV-2 due to the strict tropism of the virus to the human ACE2 receptor. The aim of the current study was the implementation of an adenovirus-mediated infection protocol for human ACE2 expression in HLA transgenic mice. Transient pulmonary expression of the human ACE2 receptor in these mice results in their sensitisation to SARS-CoV-2 infection, consequently providing a valuable animal model for COVID-19. Infection results in a transient loss in body weight starting 3 days post-infection, reaching 20-30% loss of weight at day 7 and full recovery at days 11-13 post-infection. The evolution of the disease revealed high reproducibility and very low variability among individual mice. The method was implemented in two different strains of HLA immunized mice. Infected animals developed strong protective humoral and cellular immune responses specific to the viral spike-protein, strictly depending on the adenovirus-mediated human ACE2 expression. Convalescent animals were protected against a subsequent re-infection with SARS-CoV-2, demonstrating that the model may be applied for assessment of efficacy of anti-viral immune responses.

Rapid Antibiotic Susceptibility Testing of Tier-1 Agents Bacillus anthracis, Yersinia pestis, and Francisella tularensis Directly From Whole Blood Samples.

Rapid antibiotic susceptibility tests, performed directly on whole blood samples, will offer great clinical advantages. This issue is of considerable importance when it comes to bioterror pathogens where prompt antibiotic treatment should be offered to infected patients as well as prophylaxis to suspected exposed individuals. Herein, we describe a novel and rapid method, named MAPt, that is based on the direct application of a blood sample onto solid agar that has been embedded with different concentrations of the tested antibiotic. Following a short incubation, bacterial growth is monitored by qPCR. The method was applied on blood cultures and whole blood samples inoculated with the Tier-1 pathogens Bacillus anthracis, Yersinia pestis, and Francisella tularensis. The use of agar medium, which better supports the growth of bacteria at low concentrations, together with the use of qPCR, which provides sensitivity and specificity, allowed minimal inhibitory concentration (MIC) determination to a wide range of bacterial concentrations, ranging from ∼5 × 102 cfu/ml up to 108 cfu/ml. The omission of the enrichment procedure in blood culture and the isolation step, both required in standard antibiotic susceptibility tests (ASTs), allowed a dramatic reduction in time to answer, from a few days to a few hours. The total time required for MIC determination was ∼6 h for fast-growing bacteria, such as B. anthracis, and 12-16 h for slow-growing bacteria, represented by Y. pestis and F. tularensis. Accordingly, MAPt may offer health authorities means for public preparedness in the case of a bioterror attack as well as prompt clinical treatment options in common blood stream infections.

Reporter-Phage-Based Detection and Antibiotic Susceptibility Testing of Yersinia pestis for a Rapid Plague Outbreak Response.

Pneumonic plague is a lethal infectious disease caused by Yersinia pestis, a Tier-1 biothreat agent. Antibiotic treatment can save infected patients; however, therapy should begin within 24 h of symptom onset. As some Y. pestis strains showed an antibiotic resistance phenotype, an antibiotic susceptibility test (AST) must be performed. Performing the Clinical and Laboratory Standards Institute (CLSI)-recommended standard process, which includes bacterial isolation, enumeration and microdilution testing, lasts several days. Thus, rapid AST must be developed. As previously published, the Y. pestis-specific reporter phage ϕA1122::luxAB can serve for rapid identification and AST (ID-AST). Herein, we demonstrate the ability to use ϕA1122::luxAB to determine minimal inhibitory concentration (MIC) values and antibiotic susceptibility categories for various Y. pestis therapeutic antibiotics. We confirmed the assay by testing several nonvirulent Y. pestis isolates with reduced susceptibility to doxycycline or ciprofloxacin. Moreover, the assay can be performed directly on positive human blood cultures. Furthermore, as Y. pestis may naturally or deliberately be spread in the environment, we demonstrate the compatibility of this direct method for this scenario. This direct phage-based ID-AST shortens the time needed for standard AST to less than a day, enabling rapid and correct treatment, which may also prevent the spread of the disease.

Evaluation of the European Committee on Antimicrobial Susceptibility Testing Guidelines for Rapid Antimicrobial Susceptibility Testing of Bacillus anthracis-, Yersinia pestis- and Francisella tularensis-Positive Blood Cultures.

Rapid determination of bacterial antibiotic susceptibility is important for proper treatment of infections. The European Committee on Antimicrobial Susceptibility Testing (EUCAST) has recently published guidelines for rapid antimicrobial susceptibility testing (RAST) performed directly from positive blood culture vials. These guidelines, however, were only published for a limited number of common pathogenic bacteria. In this study, we evaluated the applicability of these guidelines to three Tier 1 bioterror agents (Bacillus anthracis, Yersinia pestis and Francisella tularensis) that require prompt antibiotic treatment to mitigate morbidity and mortality. We used spiked-in human blood incubated in a BACTEC™ FX40 system to determine the proper conditions for RAST using disc-diffusion and Etest assays. We found that reliable disc-diffusion inhibition diameters and Etest MIC values could be obtained in remarkably short times. Compared to the EUCAST-recommended disc-diffusion assays that will require adjusted clinical breakpoint tables, Etest-based RAST was advantageous, as the obtained MIC values were similar to the standard MIC values, enabling the use of established category breakpoint tables. Our results demonstrate the promising applicability of the EUCAST RAST for B. anthracis-, Y. pestis- or F. tularensis-positive blood cultures, which can lead to shorter diagnostics and prompt antibiotic treatment of these dangerous pathogens.

Lipid Nanoparticle RBD-hFc mRNA Vaccine Protects hACE2 Transgenic Mice against a Lethal SARS-CoV-2 Infection.

The COVID-19 pandemic led to development of mRNA vaccines, which became a leading anti-SARS-CoV-2 immunization platform. Preclinical studies are limited to infection-prone animals such as hamsters and monkeys in which protective efficacy of vaccines cannot be fully appreciated. We recently reported a SARS-CoV-2 human Fc-conjugated receptor-binding domain (RBD-hFc) mRNA vaccine delivered via lipid nanoparticles (LNPs). BALB/c mice demonstrated specific immunologic responses following RBD-hFc mRNA vaccination. Now, we evaluated the protective effect of this RBD-hFc mRNA vaccine by employing the K18 human angiotensin-converting enzyme 2 (K18-hACE2) mouse model. Administration of an RBD-hFc mRNA vaccine to K18-hACE2 mice resulted in robust humoral responses comprising binding and neutralizing antibodies. In correlation with this response, 70% of vaccinated mice withstood a lethal SARS-CoV-2 dose, while all control animals succumbed to infection. To the best of our knowledge, this is the first nonreplicating mRNA vaccine study reporting protection of K18-hACE2 against a lethal SARS-CoV-2 infection.