The current state of tuberculosis vaccines

Next-Generation TB Vaccines: Progress, Challenges, and Prospects

Tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB), is a prevalent global infectious disease and a leading cause of mortality worldwide. Currently, the only available vaccine for TB prevention is Bacillus Calmette-Guérin (BCG). However, BCG demonstrates limited efficacy, particularly in adults. Efforts to develop effective TB vaccines have been ongoing for nearly a century. In this review, we have examined the current obstacles in TB vaccine research and emphasized the significance of understanding the interaction mechanism between MTB and hosts in order to provide new avenues for research and establish a solid foundation for the development of novel vaccines. We have also assessed various TB vaccine candidates, including inactivated vaccines, attenuated live vaccines, subunit vaccines, viral vector vaccines, DNA vaccines, and the emerging mRNA vaccines as well as virus-like particle (VLP)-based vaccines, which are currently in preclinical stages or clinical trials. Furthermore, we have discussed the challenges and opportunities associated with developing different types of TB vaccines and outlined future directions for TB vaccine research, aiming to expedite the development of effective vaccines. This comprehensive review offers a summary of the progress made in the field of novel TB vaccines.

Safety and efficacy of tuberculosis vaccine candidates in low- and middle-income countries: a systematic review of randomised controlled clinical trials

BACKGROUND

Tuberculosis (TB) remains a leading cause of death worldwide, with 98% of cases occurring in low- and middle-income countries (LMICs). The only vaccine licenced for the prevention of TB has limited protection for adolescents, adults and vulnerable populations. A safe and effective vaccine for all populations at risk is imperative to achieve global elimination of TB. We aimed to systematically review the efficacy and safety of TB vaccine candidates in late-phase clinical trials conducted in LMICs.

METHODS

Medline, Embase, CENTRAL, PubMed, Clinicaltrials.gov and Greylit.org were searched in June 2021 to identify phase 2 or later clinical randomised controlled trials that report the efficacy or safety (adverse events) of TB vaccine candidates with participants of any age living in an LMIC. TB vaccine candidates listed in the 2020 WHO Global TB Report were eligible for inclusion aside from BCG revaccination. Trials were excluded if all participants had active TB at baseline. Two reviewers independently assessed papers for eligibility, and for bias and quality using the Risk of Bias 2 tool and GRADE guidelines, respectively. We report efficacy rates and frequencies of adverse events from each included trial where available and qualitatively synthesise the findings.

RESULTS

Thirteen papers representing eleven trials met our inclusion criteria. Seven vaccine candidates were reviewed across seven countries: M72/AS01, RUTI, VPM1002, H56:IC31, MTBVAC, DAR-901 and ID93 + GLA-SE. Two trials reported on efficacy: an efficacy rate of 54% (95% CI 11.5, 76.2) was reported for M72/AS01 in adults with latent TB and 3% (95% CI -13.9, 17.7) for DAR-901 in healthy adolescents. However, the latter trial was underpowered. All vaccine candidates had comparable occurrences of adverse events between treatment arms and demonstrated acceptable safety profiles; though, RUTI resulted in one serious complication in a person living with HIV. M72/AS01 was the only vaccine considered safe across a diverse group of people including people living with HIV or latent TB and healthy infants and adolescents.

CONCLUSION

Further efficacy trials for M72/AS01 are warranted to include additional populations at risk where safety has been demonstrated. Further safety trials are needed for the remaining vaccine candidates to confirm safety in vulnerable populations.

A novel multi-component protein vaccine ECP001 containing a protein polypeptide antigen nPstS1 riching in T-cell epitopes showed good immunogenicity and protection in mice

Tuberculosis (TB) is an infectious disease that seriously affects human health. Until now, the only anti-TB vaccine approved for use is the live attenuated Mycobacterium bovis (M. bovis) vaccine - BCG vaccine, but its protective efficacy is relatively low and does not provide satisfactory protection against TB in adults. Therefore, there is an urgent need for more effective vaccines to reduce the global TB epidemic. In this study, ESAT-6, CFP-10, two antigens full-length and the T-cell epitope polypeptide antigen of PstS1, named nPstS1, were selected to form one multi-component protein antigens, named ECP001, which include two types, one is a mixed protein antigen named ECP001m, the other is a fusion expression protein antigen named ECP001f, as candidates for protein subunit vaccines. were prepared by constructing one novel subunit vaccine by mixing or fusing the three proteins and combining them with aluminum hydroxide adjuvant, and the immunogenicity and protective properties of the vaccine was evaluated in mice. The results showed that ECP001 stimulated mice to produce high titre levels of IgG, IgG1 and IgG2a antibodies; meanwhile, high levels of IFN-γ and a broad range of specific cytokines were secreted by mouse splenocytes; in addition, ECP001 inhibited the proliferation of Mycobacterium tuberculosis in vitro with a capacity comparable to that of BCG. It can be concluded that ECP001 is a novel effective multicomponent subunit vaccine candidate with potential as BCG Initial Immunisation-ECP001 Booster Immunisation or therapeutic vaccine for M. tuberculosis infection.

Controlled Human Infection Models To Accelerate Vaccine Development

The timelines for developing vaccines against infectious diseases are lengthy, and often vaccines that reach the stage of large phase 3 field trials fail to provide the desired level of protective efficacy. The application of controlled human challenge models of infection and disease at the appropriate stages of development could accelerate development of candidate vaccines and, in fact, has done so successfully in some limited cases. Human challenge models could potentially be used to gather critical information on pathogenesis, inform strain selection for vaccines, explore cross-protective immunity, identify immune correlates of protection and mechanisms of protection induced by infection or evoked by candidate vaccines, guide decisions on appropriate trial endpoints, and evaluate vaccine efficacy. We prepared this report to motivate fellow scientists to exploit the potential capacity of controlled human challenge experiments to advance vaccine development. In this review, we considered available challenge models for 17 infectious diseases in the context of the public health importance of each disease, the diversity and pathogenesis of the causative organisms, the vaccine candidates under development, and each model's capacity to evaluate them and identify correlates of protective immunity. Our broad assessment indicated that human challenge models have not yet reached their full potential to support the development of vaccines against infectious diseases. On the basis of our review, however, we believe that describing an ideal challenge model is possible, as is further developing existing and future challenge models.

Mycobacterium tuberculosis Rv2005c Induces Dendritic Cell Maturation and Th1 Responses and Exhibits Immunotherapeutic Activity by Fusion with the Rv2882c Protein

Immunotherapy represents a promising approach for improving current antibiotic treatments through the engagement of the host’s immune system. Latency-associated antigens have been included as components of multistage subunit tuberculosis vaccines. We first identified Rv2005c, a DosR regulon-encoded protein, as a seroreactive protein. In this study, we found that Rv2005c induced dendritic cell (DC) maturation and Th1 responses, and its expression by Mycobacterium tuberculosis (Mtb) within macrophages was enhanced by treatment with CoCl₂, a hypoxia-mimetic agent. T cells activated by Rv2005c-matured DCs induced antimycobacterial activity in macrophages under hypoxic conditions but not under normoxic conditions. However, Rv2005c alone did not exhibit any significant vaccine efficacy in our mouse model. The fusion of Rv2005c to the macrophage-activating protein Rv2882c resulted in significant activation of DCs and antimycobacterial activity in macrophages, which were enhanced under hypoxic conditions. Furthermore, the Rv2882c-Rv2005c fusion protein showed significant adjunctive immunotherapeutic effects and led to the generation of long-lasting, antigen-specific, multifunctional CD4⁺ T cells that coproduced TNF-α, IFN-γ and IL-2 in the lungs of our established mouse model. Overall, these results provide a novel fusion protein with immunotherapeutic potential as adjunctive chemotherapy for tuberculosis.

The current status, challenges, and future developments of new tuberculosis vaccines

Mycobacterium tuberculosis complex causes tuberculosis (TB), one of the top 10 causes of death worldwide. TB results in more fatalities than multi-drug resistant (MDR) HIV strain related coinfection. Vaccines play a key role in the prevention and control of infectious diseases. Unfortunately, the only licensed preventive vaccine against TB, bacilli Calmette-Guérin (BCG), is ineffective for prevention of pulmonary TB in adults. Therefore, it is very important to develop novel vaccines for TB prevention and control. This literature review provides an overview of the innate and adaptive immune response during M. tuberculosis infection, and presents current developments and challenges to novel TB vaccines. A comprehensive understanding of vaccines in preclinical and clinical studies provides extensive insight for the development of safer and more efficient vaccines, and may inspire new ideas for TB prevention and treatment.

Recombinant BCG Expressing LTAK63 Adjuvant induces Superior Protection against Mycobacterium tuberculosis

In order to develop an improved BCG vaccine against tuberculosis we have taken advantage of the adjuvant properties of a non-toxic derivative of Escherichia coli heat labile enterotoxin (LT), LTAK63. We have constructed rBCG strains expressing LTAK63 at different expression levels. Mice immunized with BCG expressing low levels of LTAK63 (rBCG-LTAK63_lo) showed higher Th1 cytokines and IL-17 in the lungs, and when challenged intratracheally with Mycobacterium tuberculosis displayed a 2.0–3.0 log reduction in CFU as compared to wild type BCG. Histopathological analysis of lung tissues from protected mice revealed a reduced inflammatory response. Immunization with rBCG-LTAK63_lo also protected against a 100-fold higher challenge dose. Mice immunized with rBCG-LTAK63_lo produced an increase in TGF-β as compared with BCG after challenge, with a corresponding reduction in Th1 and Th17 cytokines, as determined by Real Time RT-PCR. Furthermore, rBCG-LTAK63_lo also displays protection against challenge with a highly virulent Beijing isolate. Our findings suggest that BCG with low-level expression of the LTAK63 adjuvant induces a stronger immune response in the lungs conferring higher levels of protection, and a novel mechanism subsequently triggers a regulatory immune response, which then limits the pathology. The rBCG-LTAK63_lo strain can be the basis of an improved vaccine against tuberculosis.

Adenovirally-Induced Polyfunctional T Cells Do Not Necessarily Recognize the Infected Target: Lessons from a Phase I Trial of the AERAS-402 Vaccine

The development of a vaccine for Mycobacterium tuberculosis (Mtb) has been impeded by the absence of correlates of protective immunity. One correlate would be the ability of cells induced by vaccination to recognize the Mtb-infected cell. AERAS-402 is a replication-deficient serotype 35 adenovirus containing DNA expressing a fusion protein of Mtb antigens 85A, 85B and TB10.4. We undertook a phase I double-blind, randomized placebo controlled trial of vaccination with AERAS-402 following BCG. Analysis of the vaccine-induced immune response revealed strong antigen-specific polyfunctional CD4⁺ and CD8⁺ T cell responses. However, analysis of the vaccine-induced CD8⁺ T cells revealed that in many instances these cells did not recognize the Mtb-infected cell. Our findings highlight the measurement of vaccine-induced, polyfunctional T cells may not reflect the extent or degree to which these cells are capable of identifying the Mtb-infected cell and correspondingly, the value of detailed experimental medicine studies early in vaccine development.

Tuberculosis vaccine development: Shifting focus amid increasing development challenges

A new tuberculosis vaccine is needed to replace or enhance BCG, which induces variable protection against Mycobacterium tuberculosis pulmonary infections in adults. Development of new TB vaccine candidates is severely hampered by the lack of a correlate of immunity, unproven animal models, and limited funding opportunities. One candidate, MVA85A, recently failed to meet its efficacy endpoint goals despite promising early-phase trial data. As a result, some in the field believe we should now shift our focus away from product development and toward a research-oriented approach. Here, we outline our suggestions for this research-oriented strategy including diversification of the candidate pipeline, expanding measurements of immunity, improving pre-clinical animal models, and investing in combination pre-clinical/experimental medicine studies. As with any evolution, this change in strategy comes at a cost but may also represent an opportunity for advancing the field.

Nucleoside analogs and tuberculosis: new weapons against an old enemy

Purine and pyrimidine nucleoside and nucleotide analogs have been extensively studied as anticancer and antiviral agents. In addition to this, they have recently shown great potential against Mycobacterium Tuberculosis, the causative agent of TB. TB ranks as the tenth most common cause of death in the world. The current treatment for TB infection is limited by side effects and cost of the drugs and most importantly by the development of resistance to the therapy. Therefore the development of novel drugs, capable of overcoming the drawbacks of the existing treatments, has become the focus of many research programs. In parallel to that, a tremendous effort has been made to elucidate the unique metabolism of this pathogen with the aim to identify new possible targets. This review presents the state of the art in nucleoside and nucleotide analogs in the treatment of TB. In particular, we report on the inhibitory activity of this class of compounds, both in enzymatic and whole-cell assays, providing a brief insight to which reported target these novel compounds are hitting.

Increasing Complexity of Vaccine Development

Vaccines already developed have been enormously successful. However, the development of future vaccines requires solution of a number of immunologic problems, including pathogen variability, short effector memory, evoking functional responses, and identification of antigens that generate protective responses. In addition, different populations may respond differently to the same vaccine because of genetic, age, or environmental factors.

Effects of CHO-expressed recombinant lactoferrins on mouse dendritic cell presentation and function

Lactoferrin (LF), a natural iron-binding protein, has previously demonstrated effectiveness in enhancing the Bacillus Calmette-Guérin (BCG) tuberculosis vaccine. This report investigates immune modulatory effects of Chinese hamster ovary (CHO) cell-expressed recombinant mouse and human LFs on mouse bone marrow-derived dendritic cells (BMDCs), comparing homologous and heterologous functions. BCG-infected BMDCs were cultured with LF, and examined for class II presentation molecule expression. Culturing of BCG-infected BMDCs with either LF decreased the class II molecule-expressing population. Mouse LF significantly increased the production of IL-12p40, IL-1β and IL-10, while human LF-treated BMDCs increased only IL-1β and IL-10. Overlaying naïve CD4 T-cells onto BCG-infected BMDCs cultured with mouse LF increased IFN-γ, whereas the human LF-exposed group increased IFN-γ and IL-17 from CD4 T cells. Overlay of naïve CD8 T cells onto BCG-infected BMDCs treated with mouse LF increased the production of IFN-γ and IL-17, while similar experiments using human LF only increased IL-17. This report is the first to examine mouse and human recombinant LFs in parallel experiments to assess murine DC function. These results detail the efficacy of the human LF counterpart used in a heterologous system to understand LF-mediated events that confer BCG efficacy against Mycobacterium tuberculosis challenge.

Unmet needs in respiratory diseases : "You can't know where you are going until you know where you have been"--Anonymous

The care of patients with respiratory diseases has improved vastly in the past 50 years. In spite of that, there are still massive challenges that have not been resolved. Although the incidence of tuberculosis has decreased in the developed world, it is still a significant public health problem in the rest of the world. There are still over 2 million deaths annually from tuberculosis, with most of these occurring in the developing world. Even with the development of new pharmaceuticals to treat tuberculosis, there is no indication that the disease will be eradicated. Respiratory syncytial virus, severe acute respiratory syndrome, and pertussis are other respiratory infectious diseases with special problems of their own, from vaccine development to vaccine coverage. Asthma, one of the most common chronic diseases in children, still accounts for significant mortality and morbidity, as well as high health care costs worldwide. Even in developed countries such as the USA, there are over 4,000 deaths per year. Severe asthma presents a special problem, but the question is whether there can be one treatment pathway for all patients with severe asthma. Severe asthma is a heterogeneous disease with many phenotypes and endotypes. The gene for cystic fibrosis was discovered over 24 years ago. The promise of gene therapy as a cure for the disease has fizzled out, and while new antimicrobials and other pharmaceuticals promise improved longevity and better quality of life, the average life span of a patient with cystic fibrosis is still at about 35 years. What are the prospects for gene therapy in the twenty-first century? Autoimmune diseases of the lung pose a different set of challenges, including the development of biomarkers to diagnose and monitor the disease and biological modulators to treat the disease.

A peptide fragment from the human COX3 protein disrupts association of Mycobacterium tuberculosis virulence proteins ESAT-6 and CFP10, inhibits mycobacterial growth and mounts protective immune response

Background

Tuberculosis (TB) is one of the most prevalent infectious diseases affecting millions worldwide. The currently available anti-TB drugs and vaccines have proved insufficient to contain this scourge, necessitating an urgent need for identification of novel drug targets and therapeutic strategies. The disruption of crucial protein-protein interactions, especially those that are responsible for virulence in Mycobacterium tuberculosis – for example the ESAT-6:CFP10 complex – are a worthy pursuit in this direction.

Methods

We therefore sought to improvise a method to attenuate M. tuberculosis while retaining the latter’s antigenic properties. We screened peptide libraries for potent ESAT-6 binders capable of dissociating CFP10 from ESAT-6. We assessed the disruption by a peptide named HCL2, of the ESAT-6:CFP10 complex and studied its effects on mycobacterial survival and virulence.

Results

We found that HCL2, derived from the human cytochrome c oxidase subunit 3 (COX3) protein, disrupts ESAT-6:CFP10 complex, binds ESAT-6 potently, disintegrates bacterial cell wall and inhibits extracellular as well as intracellular mycobacterial growth. In addition, an HCL2 expressing M. tuberculosis strain induces both Th1 and Th17 host protective responses.

Conclusions

Disruption of ESAT-6:CFP10 association could, therefore, be an alternate method for attenuating M. tuberculosis, and a possible route towards future vaccine generation.

Recent developments in tuberculosis vaccines

Substantial efforts have been made over the past decade to develop vaccines against tuberculosis. We review recent developments in tuberculosis vaccines in the global portfolio, including those designed for use in a prophylactic setting, either alone or as boosts to Bacille Calmette-Guérin, and therapeutic vaccines designed to improve chemotherapy. While there is no doubt that progress is still being made, there are limitations to our animal model screening processes, which are further amplified by the lack of understanding of the immunological responses involved and the precise type of long-lived immunity that new vaccines need to induce. The challenge ahead is to optimize the planning for advanced clinical trials in poor endemic settings, which could be greatly facilitated by identifying correlates of protection.

Immunotherapy of tuberculosis with Mycobacterium leprae Hsp65 as a DNA vaccine triggers cross-reactive antibodies against mammalian Hsp60 but not pathological autoimmunity

Despite substantial efforts in recent years toward the development of new vaccines and drugs against tuberculosis (TB), success has remained elusive. Immunotherapy of TB with mycobacterial Hsp65 as a DNA vaccine (DNA-hsp65) results in a reduction of systemic bacterial loads and lung tissue damage, but the high homology of Hsp65 with the mammalian protein raises concern that pathological autoimmune responses may also be triggered. We searched for autoimmune responses elicited by DNA-hsp65 immunotherapy in mice chronically infected with TB by evaluating the humoral immune response and comprehensive histopathology using stereology. Cross-reactive antibodies between mycobacterial and mammalian Hsp60/65 were detected; however, no signs of pathological autoimmunity were found up to 60 days after the end of the therapy.

Update on the diagnosis and management of tuberculous meningitis in children

Tuberculous meningitis (TBM), the most devastating manifestation of tuberculosis, is often missed or overlooked because of nonspecific symptoms and difficulties in diagnosis. It continues to be an important cause of neurologic handicap in resource-poor countries. Owing to the suboptimal performance of diagnostic tests of TBM, diagnosis relies on thorough history, clinical examination, and relevant investigations. The development of affordable, accurate diagnostic tests for TBM in resource-poor settings remains a priority. Short intensified treatment is safe and effective in both human immunodeficiency virus (HIV)-infected and HIV-uninfected children. Treatment of tuberculous hydrocephalus depends on the level of the cerebrospinal fluid obstruction. Corticosteroids reduce risk of neurodisability and death in HIV-uninfected children. Thalidomide should be considered in children compromised by tuberculosis abscesses and tuberculous-related optochiasmic arachnoiditis. In resource-poor countries, home-based TBM treatment after initial in-hospital stabilization is feasible in carefully selected patients. Early diagnosis and treatment of TBM is the single most important factor determining outcome.

Comparative analysis of Bacillus subtilis spores and monophosphoryl lipid A as adjuvants of protein-based mycobacterium tuberculosis-based vaccines: partial requirement for interleukin-17a for induction of protective immunity

The development of adjuvants for vaccines has become an important area of research as the number of protein-based vaccines against infectious pathogens increases. Currently, there are a number of adjuvant-based Mycobacterium tuberculosis vaccines in clinical trials that have shown efficacy in animal models. Despite these novel adjuvants, there is still a need to design new and more versatile adjuvants that have minimal adverse side effects but produce robust long-lasting adaptive immune responses. To this end, we hypothesized that Bacillus subtilis spores may provide the appropriate innate signals that are required to generate such vaccine-mediated responses, which would be sufficient to reduce the mycobacterial burden after infection with M. tuberculosis. In addition, we compared the response generated by B. subtilis spores to that generated by monophosphoryl lipid A (MPL), which has been used extensively to test tuberculosis vaccines. The well-characterized, 6-kDa early secretory antigenic target of M. tuberculosis (ESAT-6; Rv3875) was used as a test antigen to determine the T cell activation potential of each adjuvant. Inoculated into mice, B. subtilis spores induced a strong proinflammatory response and Th1 immunity, similar to MPL; however, unlike MPL formulated with dimethyldioctadecylammonium (DDA) bromide, it failed to induce significant levels of interleukin-17A (IL-17A) and was unable to significantly reduce the mycobacterial burden after pulmonary infection with M. tuberculosis. Further analysis of the activity of MPL-DDA suggested that IL-17A was required for protective immunity. Taken together, the data emphasize the requirement for a network of cytokines that are essential for protective immunity.