Protective efficacy of recombinant (Ag85A) BCG Tokyo with Ag85A peptide boosting against Mycobacterium tuberculosis-infected guinea pigs in comparison with that of DNA vaccine encoding Ag85A

Engineering a dual vaccine against COVID-19 and tuberculosis

The COVID-19 pandemic, caused by SARS-CoV-2 virus, has been one of the top public health threats across the world over the past three years. Mycobacterium bovis BCG is currently the only licensed vaccine for tuberculosis, one of the deadliest infectious diseases in the world, that is caused by Mycobacterium tuberculosis. In the past decades, recombinant M.bovis BCG has been studied as a novel vaccine vector for other infectious diseases in humans besides tuberculosis, such as viral infections. In the current study, we generated a recombinant M. bovis BCG strain AspikeRBD that expresses a fusion protein consisting of M. tb Ag85A protein and the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein using synthetic biology technique. Our results show that the recombinant M. bovis BCG strain successfully expressed this fusion protein. Interestingly, the recombinant M. bovis BCG strain AspikeRBD significantly induced SARS-CoV-2 spike-specific T cell activation and IgG production in mice when compared to the parental M.bovis BCG strain, and was more potent than the recombinant M.bovis BCG strain expressing SARS-CoV-2 spike RBD alone. As expected, the recombinant M. bovis BCG strain AspikeRBD activated an increased number of M. tb Ag85A-specific IFNγ-releasing T cells and enhanced IgG production in mice when compared to the parental M.bovis BCG strain or the BCG strain expressing SARS-CoV-2 spike RBD alone. Taken together, our results indicate a potential application of the recombinant M. bovis BCG strain AspikeRBD as a novel dual vaccine against SARS-CoV-2 and M. tb in humans.

Spore-FP1 tuberculosis mucosal vaccine candidate is highly protective in guinea pigs but fails to improve on BCG-conferred protection in non-human primates

Tuberculosis remains a major health threat globally and a more effective vaccine than the current Bacillus Calmette Guerin (BCG) is required, either to replace or boost it. The Spore-FP1 mucosal vaccine candidate is based on the fusion protein of Ag85B-Acr-HBHA/heparin-binding domain, adsorbed on the surface of inactivated Bacillus subtilis spores. The candidate conferred significant protection against Mycobacterium. tuberculosis challenge in naïve guinea pigs and markedly improved protection in the lungs and spleens of animals primed with BCG. We then immunized rhesus macaques with BCG intradermally, and subsequently boosted with one intradermal and one aerosol dose of Spore-FP1, prior to challenge with low dose aerosolized M. tuberculosis Erdman strain. Following vaccination, animals did not show any adverse reactions and displayed higher antigen specific cellular and antibody immune responses compared to BCG alone but this did not translate into significant improvement in disease pathology or bacterial burden in the organs.

Ag85A, As an S2 Vaccine Carrier, Reduces the Toxicity of the S2 Vaccine and Enhances the Protective Ability of Mice against Brucella

Brucella is a globally distributed zoonotic disease that can cause abortion and changes in immune function in humans and animals. At present, there is no good treatment plan for Brucella, and animals can only be treated harmlessly once they become ill, resulting in huge economic losses. Therefore, the prevention of Brucella infection is a very crucial step. Although a variety of Brucella vaccines have been widely used, they have varying degrees of shortcomings. For example, some Brucella vaccines have residual virulence, which leads to the emergence of Brucella in animals during the immunization process. Bacillus infection and other conditions occur. To further reduce the toxicity of the Brucella vaccine and enhance its protective effect on animals, this study used Antigen 85A (Ag85A) as a carrier of the Brucella vaccine to fuse with the Brucella S2 vaccine. The results of the study found that the S2-Ag85A oral Brucella vaccine could effectively reduce the toxicity residue of the S2 vaccine, stimulate the mice to produce a better immunogenic response, and effectively activate the expression levels of Brucella heterozygous IgG1 and IgG2a. Experiments have shown that the expression of IFN-γ in the peripheral blood serum and spleen of mice is significantly increased, and the expression levels of IL-1β, TNF-α, and IL-6 are significantly reduced, which may indicate that S2-Ag85A oral Brucella vaccine could induce the expression of IFN-γ, thus downregulating the expression levels of IL-6 and TNF-α in the spleen tissue. The above results indicate that the S2-Ag85A oral vaccine is an effective attenuated vaccine for preventing Brucella infection.

Oral S2-Ag85 DNA Vaccine Activated Intestinal Cell dsDNA and RNA Sensors to Promote the Presentation of Intestinal Antigen

Objective

To explore the molecular mechanism by which oral S2-Ag85DNA vaccines present intestinal antigens. The oral S2-Ag85 vaccine has been shown to protect the human body and effectively improve the titration of the vaccine by acting on intestinal mucosa cells and enhancing their immunogenicity.

Method

Mice were immunized with the recombinant S2-Ag85 vaccine, and antibody secretion was then detected in the intestinal tissue. The molecular mechanisms of in vitro detection sensor molecules RIG-1, Pol III, and related conductor transductor molecules DAI, STING, AIM2, IRF3, and IRF7 were determined by separating intestinal IEC, DC, and IELC cells.

Results

The S2-Ag85A vaccine was effective in activating dsDNA and RNA transduction pathways in intestinal cells and improving intestinal antigen presentation in mice.

Peptide-Based Vaccines for Tuberculosis

Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis. As a result of the coronavirus disease 2019 (COVID-19) pandemic, the global TB mortality rate in 2020 is rising, making TB prevention and control more challenging. Vaccination has been considered the best approach to reduce the TB burden. Unfortunately, BCG, the only TB vaccine currently approved for use, offers some protection against childhood TB but is less effective in adults. Therefore, it is urgent to develop new TB vaccines that are more effective than BCG. Accumulating data indicated that peptides or epitopes play essential roles in bridging innate and adaptive immunity and triggering adaptive immunity. Furthermore, innovations in bioinformatics, immunoinformatics, synthetic technologies, new materials, and transgenic animal models have put wings on the research of peptide-based vaccines for TB. Hence, this review seeks to give an overview of current tools that can be used to design a peptide-based vaccine, the research status of peptide-based vaccines for TB, protein-based bacterial vaccine delivery systems, and animal models for the peptide-based vaccines. These explorations will provide approaches and strategies for developing safer and more effective peptide-based vaccines and contribute to achieving the WHO's End TB Strategy.

Recombinant BCG expressing the LTAK63 adjuvant induces increased early and long-term immune responses against Mycobacteria

The development of more effective vaccines against Mycobacterium tuberculosis has become a world priority. Previously, we have shown that a recombinant BCG expressing the LTAK63 adjuvant (rBCG-LTAK63) displayed higher protection than BCG against tuberculosis challenge in mice. In order to elucidate the immune effector mechanisms induced by rBCG-LTAK63, we evaluated the immune response before and after challenge. The potential to induce an innate immune response was investigated by intraperitoneal immunization with BCG or rBCG-LTAK63: both displayed increased cellular infiltration in the peritoneum with high numbers of neutrophils at 24 h and macrophages at 7 d. The rBCG-LTAK63-immunized mice displayed increased production of Nitric Oxide at 24 h and Hydrogen Peroxide at 7 d. The number of lymphocytes was higher in the rBCG-LTAK63 group when compared to BCG. Immunophenotyping of lymphocytes showed that rBCG-LTAK63 immunization increased CD4⁺ and CD8⁺ T cells. An increased long-term Th1/Th17 cytokine profile was observed 90 d after subcutaneous immunization with rBCG-LTAK63. The evaluation of immune responses at 15 d after challenge showed that rBCG-LTAK63-immunized mice displayed increased TNF-α-secreting CD4⁺ T cells and multifunctional IL-2⁺ TNF-α⁺ CD4⁺ T cells as compared to BCG-immunized mice. Our results suggest that immunization with rBCG-LTAK63 induces enhanced innate and long-term immune responses as compared to BCG. These results can be correlated with the superior protection induced against TB.

Recombinant BCG Expressing Mycobacterium ulcerans Ag85A Imparts Enhanced Protection against Experimental Buruli ulcer

Buruli ulcer, an emerging tropical disease caused by Mycobacterium ulcerans (MU), is characterized by disfiguring skin necrosis and high morbidity. Relatively little is understood about the mode of transmission, pathogenesis, or host immune responses to MU infection. Due to significant reduction in quality of life for patients with extensive tissue scarring, and that a disproportionately high percentage of those affected are disadvantaged children, a Buruli ulcer vaccine would be greatly beneficial to the worldwide community. Previous studies have shown that mice inoculated with either M. bovis bacille Calmette–Guérin (BCG) or a DNA vaccine encoding the M. ulcerans mycolyl transferase, Ag85A (MU-Ag85A), are transiently protected against pathology caused by intradermal challenge with MU. Building upon this principle, we have generated quality-controlled, live-recombinant strains of BCG and M. smegmatis which express the immunodominant MU Ag85A. Priming with rBCG MU-Ag85A followed by an M. smegmatis MU-Ag85A boost strongly induced murine antigen-specific CD4⁺ T cells and elicited functional IFNγ-producing splenocytes which recognized MU-Ag85A peptide and whole M. ulcerans better than a BCG prime-boost vaccination. Strikingly, mice vaccinated with a single subcutaneous dose of BCG MU-Ag85A or prime-boost displayed significantly enhanced survival, reduced tissue pathology, and lower bacterial load compared to mice vaccinated with BCG. Importantly, this level of superior protection against experimental Buruli ulcer compared to BCG has not previously been achieved. These results suggest that use of BCG as a recombinant vehicle expressing MU antigens represents an effective Buruli ulcer vaccine strategy and warrants further antigen discovery to improve vaccine efficacy.

Buruli ulcer, caused by subcutaneous infection with Mycobacterium ulcerans, is a highly disfiguring flesh-eating skin disease with significant morbidity. Besides surgical intervention, 8-week combination antibiotics is the standard of care. However, problems with resistance and toxicity warrant their replacement with efficacious vaccines. Several attempts to generate a vaccine have met with limited success and, to date, BCG remains the only vaccine capable of conferring transient protection. Here we demonstrate that a recombinant BCG-based vaccine expressing the immunodominant M. ulcerans Ag85A is capable of significantly enhancing protection in experimental Buruli ulcer compared to standard BCG, with a decrease in bacterial burden, pathology, and increase in survival. These results support further Buruli ulcer vaccine development using the highly safe and well-established BCG vehicle.

Comparative evaluation of booster efficacies of BCG, Ag85B, and Ag85B peptides based vaccines to boost BCG induced immunity in BALB/c mice: a pilot study

Purpose

In the present study booster efficacies of Ag85 B, Bacillus Calmette-Guerin (BCG), and Ag85B peptides were evaluated using prime boost regimes in BALB/c mice.

Materials and Methods

Mice were primed with BCG vaccine and subsequently boosted with Ag85B, BCG and cocktail of Ag85B peptides.

Results

Based on analysis of immune response it was observed mice boosted with Ag85B peptides showed significant (p < 0.001) cytokines levels (interferon γ, interleukin 12) and BCG specific antibodies (anti-BCG and anti-purified protein derivative titre) compared to booster dose of BCG, Ag85B and BCG alone.

Conclusion

Our pilot results suggest that prime boost regimes with Ag85B peptides can boost waning BCG induced immunity and may improve immunogenicity of BCG vaccine. However, lot of work is further needed using experimental model of tuberculosis infection to justify the result.

Recombinant BCG: Innovations on an Old Vaccine. Scope of BCG Strains and Strategies to Improve Long-Lasting Memory

Bacille Calmette-Guérin (BCG), an attenuated vaccine derived from Mycobacterium bovis, is the current vaccine of choice against tuberculosis (TB). Despite its protection against active TB in children, BCG has failed to protect adults against TB infection and active disease development, especially in developing countries where the disease is endemic. Currently, there is a significant effort toward the development of a new TB vaccine. This review article aims to address publications on recombinant BCG (rBCG) published in the last 5 years, to highlight the strategies used to develop rBCG, with a focus on the criteria used to improve immunological memory and protection compared with BCG. The literature review was done in April 2013, using the key words TB, rBCG vaccine, and memory. This review discusses the BCG strains and strategies currently used for the modification of BCG, including: overexpression of Mycobacterium tuberculosis (Mtb) immunodominant antigens already present in BCG; gene insertion of immunodominant antigens from Mtb absent in the BCG vaccine; combination of introduction and overexpression of genes that are lost during the attenuation process of BCG; BCG modifications for the induction of CD8+ T-cell immune responses and cytokines expressing rBCG. Among the vaccines discussed, VPM1002, also called rBCGΔureC:hly, is currently in human clinical trials. Much progress has been made in the effort to improve BCG, with some promising candidates, but considerable work is still required to address functional long-lasting memory.

Immunogenicity and protective efficacy of a novel recombinant BCG strain overexpressing antigens Ag85A and Ag85B

Recombinant Bacillus Calmette-Guérin (rBCG) strain is the promising vaccine candidate for tuberculosis (TB) prevention, which aims at providing more enduring and enhanced protection than the parental BCG vaccine. In this study, three rBCG strains overexpressing immunodominant antigens Ag85B (rBCG::85B), Ag85A (rBCG::85A), or both (rBCG::AB) of Mycobacterium tuberculosis were constructed, respectively. rBCG strains showed higher level of overexpression of Ag85A and/or Ag85B proteins than BCG containing empty vector pMV261(rBCG::261), which had low levels of endogenous expression of both proteins as expected. rBCG::AB strain could provide the strongest short-term and long-term protection in the lung against intravenous infection with virulent M. tuberculosis than rBCG::261 control and other two rBCG strains overexpressing single antigen. The stronger and longer-lasting protection provided by rBCG::AB than rBCG::261 was correlated with systemic in vitro antigen-specific IFN-γ responses. Therefore, our results indicate that rBCG::AB could be a very promising TB vaccine candidate and should be further evaluated for the preclinical test.

Boosting BCG to protect against TB

Given that TB still constitutes a tremendous public health problem at the start of the 21st Century, it may come as a surprise that Bacillus Calmette-Guérin (BCG), developed nearly 100 years ago, is today still the only vaccine available against TB. Owing to its limited efficiency in controlling TB, much effort has been deployed to develop new, improved vaccines, with initial preclinical models showing encouraging results. However, since most individuals worldwide have been vaccinated with BCG, new vaccine developments have to be placed in that context. Consequently, several approaches explore the heterologous prime-boost strategy. In this strategy, BCG-primed immunity will be strengthened or prolonged by the administration of antigens present in BCG but formulated in a different manner; either as purified antigens in the presence of appropriate adjuvants, as DNA vaccines or as viral-encoded mycobacterial antigens.

Protective efficacy of recombinant BCG Tokyo (Ag85A) in rhesus monkeys (Macaca mulatta) infected intratracheally with H37Rv Mycobacterium tuberculosis

We have reported previously that recombinant BCG Tokyo (Ag85A) (rBCG-Ag85A[Tokyo]) shows promise as a tuberculosis vaccine, demonstrating protective efficacy in cynomolgus monkeys. As a next step, rhesus monkeys were utilized because they are also susceptible to Mycobacterium tuberculosis and show a continuous course of infection resembling human tuberculosis. The recombinant BCG vaccine (5x10(5) CFU per monkey) was administered once intradermally into the back skin to three groups of rhesus monkeys, and its protective efficacy was compared for 4months with that of its parental BCG Tokyo strain. Eight week vaccination of the monkeys with rBCG-Ag85A[Tokyo] resulted in a reduction of tubercle bacilli CFU (p<0.01) and lung pathology in animals infected intratracheally with 3000 CFU H37Rv M. tuberculosis. Vaccination prevented an increase in the old tuberculin test after challenge with M. tuberculosis and reaction of M. tuberculosis-derived antigen. Thus, it was shown that even in rhesus monkeys rBCG-Ag85A[Tokyo] induced higher protective efficacy than BCG Tokyo.

Whole genome identification of Mycobacterium tuberculosis vaccine candidates by comprehensive data mining and bioinformatic analyses

Background

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), infects ~8 million annually culminating in ~2 million deaths. Moreover, about one third of the population is latently infected, 10% of which develop disease during lifetime. Current approved prophylactic TB vaccines (BCG and derivatives thereof) are of variable efficiency in adult protection against pulmonary TB (0%–80%), and directed essentially against early phase infection.

Methods

A genome-scale dataset was constructed by analyzing published data of: (1) global gene expression studies under conditions which simulate intra-macrophage stress, dormancy, persistence and/or reactivation; (2) cellular and humoral immunity, and vaccine potential. This information was compiled along with revised annotation/bioinformatic characterization of selected gene products and in silico mapping of T-cell epitopes. Protocols for scoring, ranking and prioritization of the antigens were developed and applied.

Results

Cross-matching of literature and in silico-derived data, in conjunction with the prioritization scheme and biological rationale, allowed for selection of 189 putative vaccine candidates from the entire genome. Within the 189 set, the relative distribution of antigens in 3 functional categories differs significantly from their distribution in the whole genome, with reduction in the Conserved hypothetical category (due to improved annotation) and enrichment in Lipid and in Virulence categories. Other prominent representatives in the 189 set are the PE/PPE proteins; iron sequestration, nitroreductases and proteases, all within the Intermediary metabolism and respiration category; ESX secretion systems, resuscitation promoting factors and lipoproteins, all within the Cell wall category. Application of a ranking scheme based on qualitative and quantitative scores, resulted in a list of 45 best-scoring antigens, of which: 74% belong to the dormancy/reactivation/resuscitation classes; 30% belong to the Cell wall category; 13% are classical vaccine candidates; 9% are categorized Conserved hypotheticals, all potentially very potent T-cell antigens.

Conclusion

The comprehensive literature and in silico-based analyses allowed for the selection of a repertoire of 189 vaccine candidates, out of the whole-genome 3989 ORF products. This repertoire, which was ranked to generate a list of 45 top-hits antigens, is a platform for selection of genes covering all stages of M. tuberculosis infection, to be incorporated in rBCG or subunit-based vaccines.

Recombinant BCG Tokyo (Ag85A) protects cynomolgus monkeys (Macaca fascicularis) infected with H37Rv Mycobacterium tuberculosis

One tuberculosis vaccine candidate that has shown a promising degree of protective efficacy in guinea pigs is recombinant BCG Tokyo (Ag85A)(rBCG-Ag85A[Tokyo]). As a next step, cynomolgus monkeys were utilized because they are susceptible to Mycobacterium tuberculosis and develop a continuous course of infection that resembles that in humans both clinically and pathologically. The recombinant BCG vaccine was administered once intradermally in the back skin to three groups of cynomolgus monkeys, and its protective efficacy was compared for 4 months with that of its parental BCG Tokyo strain. Vaccination of the monkeys with the rBCG-Ag85A[Tokyo] resulted in a reduction of tubercle bacilli CFU (p<0.01) and lung pathology in animals challenged intratracheally with 3000 CFU H37Rv M. tuberculosis. Vaccination prevented an increase in the old tuberculin test after challenge with M. tuberculosis and reaction of M. tuberculosis-derived antigen. Thus, it was shown in monkeys that rBCG-Ag85A[Tokyo] induced higher protective efficacy than BCG Tokyo. This warrants further clinical evaluation.