Treatment of Multi-Drug-Resistant Tuberculosis in Mice with DNA Vaccines Alone or in Combination with Chemotherapeutic Drugs

Mechanisms of ag85a/b DNA vaccine conferred immunotherapy and recovery from Mycobacterium tuberculosis-induced injury

Our previous research developed a novel tuberculosis (TB) DNA vaccine ag85a/b that showed a significant therapeutic effect on the mouse tuberculosis model by intramuscular injection (IM) and electroporation (EP). However, the action mechanisms between these two vaccine immunization methods remain unclear. In a previous study, 96 Mycobacterium tuberculosis (MTB) H₃₇ Rv-infected BALB/c mice were treated with phosphate-buffered saline, 10, 50, 100, and 200 μg ag85a/b DNA vaccine delivered by IM and EP three times at 2-week intervals, respectively. In this study, peripheral blood mononuclear cells (PBMCs) from three mice in each group were isolated to extract total RNA. The gene expression profiles were analyzed using gene microarray technology to obtain differentially expressed (DE) genes. Finally, DE genes were validated by real-time reverse transcription-quantitive polymerase chain reaction and the GEO database. After MTB infection, most of the upregulated DE genes were related to the digestion and absorption of nutrients or neuroendocrine (such as Iapp, Scg2, Chga, Amy2a5), and most of the downregulated DE genes were related to cellular structural and functional proteins, especially the structure and function proteins of the alveolar epithelial cell (such as Sftpc, Sftpd, Pdpn). Most of the abnormally upregulated or downregulated DE genes in the TB model group were recovered in the 100 and 200 μg ag85a/b DNA IM groups and four DNA EP groups. The pancreatic secretion pathway downregulated and the Rap1 signal pathway upregulated had particularly significant changes during the immunotherapy of the ag85a/b DNA vaccine on the mouse TB model. The action targets and mechanisms of IM and EP are highly consistent. Tuberculosis infection causes rapid catabolism and slow anabolism in mice. For the first time, we found that the effective dose of the ag85a/b DNA vaccine immunized whether by IM or EP could significantly up-regulate immune-related pathways and recover the metabolic disorder and the injury caused by MTB.

B21 DNA vaccine expressing ag85b, rv2029c, and rv1738 confers a robust therapeutic effect against latent Mycobacterium tuberculosis infection

Latent tuberculosis infection (LTBI) treatment is known to accelerate the decline in TB incidence, especially in high-risk populations. Mycobacterium tuberculosis (M. tb) expression profiles differ at different growth periods, and vaccines protective and therapeutic effects may increase when they include antigenic compositions from different periods. To develop a post-exposure vaccine that targets LTBI, we constructed four therapeutic DNA vaccines (A39, B37, B31, and B21) using different combinations of antigens from the proliferation phase (Ag85A, Ag85B), PE/PPE family (Rv3425), and latent phase (Rv2029c, Rv1813c, Rv1738). We compared the immunogenicity of the four DNA vaccines in C57BL/6j mice. The B21 vaccine stimulated the strongest cellular immune responses, namely Th1/Th17 and CD8⁺ cytotoxic T lymphocyte responses. It also induced the generation of strengthened effector memory and central memory T cells. In latently infected mice, the B21 vaccine significantly reduced bacterial loads in the spleens and lungs and decreased lung pathology. In conclusion, the B21 DNA vaccine can enhance T cell responses and control the reactivation of LTBI.

Modulation of immune responses using adjuvants to facilitate therapeutic vaccination

Therapeutic vaccination offers great promise as an intervention for a diversity of infectious and non-infectious conditions. Given that most chronic health conditions are thought to have an immune component, vaccination can at least in principle be proposed as a therapeutic strategy. Understanding the nature of protective immunity is of vital importance, and the progress made in recent years in defining the nature of pathological and protective immunity for a range of diseases has provided an impetus to devise strategies to promote such responses in a targeted manner. However, in many cases, limited progress has been made in clinical adoption of such approaches. This in part results from a lack of safe and effective vaccine adjuvants that can be used to promote protective immunity and/or reduce deleterious immune responses. Although somewhat simplistic, it is possible to divide therapeutic vaccine approaches into those targeting conditions where antibody responses can mediate protection and those where the principal focus is the promotion of effector and memory cellular immunity or the reduction of damaging cellular immune responses as in the case of autoimmune diseases. Clearly, in all cases of antigen-specific immunotherapy, the identification of protective antigens is a vital first step. There are many challenges to developing therapeutic vaccines beyond those associated with prophylactic diseases including the ongoing immune responses in patients, patient heterogeneity, and diversity in the type and stage of disease. If reproducible biomarkers can be defined, these could allow earlier diagnosis and intervention and likely increase therapeutic vaccine efficacy. Current immunomodulatory approaches related to adoptive cell transfers or passive antibody therapy are showing great promise, but these are outside the scope of this review which will focus on the potential for adjuvanted therapeutic active vaccination strategies.

Immunotherapeutic effects of Mycobacterium tuberculosis rv3407 DNA vaccine in mice

Tuberculosis (TB) is a major global public health problem. Latent TB infection (LTBI) is a major source of active TB. New vaccines to treat LTBI are urgently demanded. In this study, the gene encoding latency-associated antigen Rv3407 of Mycobacterium tuberculosis (MTB) rv3407 DNA vaccine was used to prepare and the immunogenicity and therapeutic effects were evaluated. Normal mice were immunized intramuscularly three times at two-week intervals with sterile water for injection, plasmid vector pVAX1, M. vaccae vaccine, ag85a DNA or rv3407 DNA. TB-infected mice were immunized intramuscularly three times at two-week intervals with phosphate-buffered saline (PBS) and rv3407 DNA. The normal mice immunized with rv3407 DNA or ag85a DNA showed higher levels of interferon-gamma (IFN-γ) in stimulated spleen lymphocyte culture supernatants, and had more Th1 cells and an elevated ratio of Th1/Th2 immune cells in whole blood, indicating that a Th1-type immune response was predominant. The levels of anti-Ag85A or anti-Rv3407 IgG antibody were significantly increased in the ag85a DNA and rv3407 DNA groups compared to the sterile water for injection, vector, and M. vaccae groups (p < .0001). Compared with the PBS group, the rv3407 DNA group had pulmonary bacterial loads that were lower by 0.56 log₁₀ (p < .01)_. The mice vaccinated with rv3407 DNA developed antigen-specific cellular and humoral responses. The rv3407 DNA is a potential DNA vaccine candidate against TB.

Meeting report: 5th Global Forum on TB Vaccines, 20-23 February 2018, New Delhi India

The 5th Global Forum on TB Vaccines was held in New Delhi, India from 20 to 23 February 2018. This was the largest Global Forum on TB Vaccines to date with nearly 350 participants from more than 30 countries. The program included over 60 speakers in 12 special, plenary and breakout sessions and 72 posters. This Global Forum brought a great sense of momentum and excitement to the field. New vaccines are in clinical trials, new routes of delivery are being tested, novel assays and biomarker signatures are being developed, and the results from the first prevention of infection clinical trial with the H4:IC31 vaccine candidate and BCG revaccination were presented. Speakers and participants acknowledged the significant challenges that the TB vaccine R&D field continues to face - including limited funding, and the need for novel effective vaccine candidates and tools such as improved diagnostics and biomarkers to accurately predict protective efficacy. New solutions and approaches to address these challenges were discussed. The following report presents highlights from talks presented at this Global Forum. A full program, abstract book and presentations (where publicly available) from the Forum may be found at tbvaccinesforum.org.

Immunogenicity and therapeutic effects of recombinant Ag85AB fusion protein vaccines in mice infected with Mycobacterium tuberculosis

The immune function of tuberculosis (TB) patients is disordered. By using immune regulators to assist chemotherapy for TB the curative effect might be improved. In this study, a vaccine containing Mycobacterium tuberculosis (M. tuberculosis) recombinant Ag85AB fusion protein (rAg85AB) was constructed and evaluated. The mice were immunized intramuscularly three times at two-week intervals with Ag85AB fusion protein combined with Corynebacterium parvum adjuvant (rAg85AB+CP). In comparison to control mice that received either CP alone or saline, the mice that received rAg85AB+CP had significantly higher number of T cells secreting IFN-γ and higher levels of specific antibodies of IgG, IgG1 and IgG2a isotypes in sera. The specific antibodies also had higher ratios of IgG2a to IgG1, indicating a predominant Th1 immune response. To test for immunotherapy of TB, M. tuberculosis infected mice were given three intramuscular doses of 20μg, 40μg or 60μg of rAg85AB in rAg85AB+CP, or phosphate-buffered saline (PBS), or CP or Mycobacterium phlei (M. Phlei) F.U.36. Compared with the PBS group, 20µg, 40µg and 60µg rAg85AB+CP and M. phlei F.U.36 groups reduced the pulmonary bacterial loads by 0.13, 0.15, 0.42 and 0.40 log₁₀, and the liver bacterial loads by 0.64, 0.64, 0.53 and 0.61 log₁₀, respectively. Pathological changes of lungs were less, and the lesions were limited to a certain extent in 40µg and 60µg rAg85AB+CP and M. phlei F.U.36 groups. These results showed that rAg85AB+CP had immunotherapeutic effect on TB, significantly increasing the cellular immune response, and inhibiting the growth of M. tuberculosis.

Immunogenicity and therapeutic effects of a Mycobacterium tuberculosis rv2190c DNA vaccine in mice

Background

Tuberculosis (TB) is a major global public health problem. New treatment methods on TB are urgently demanded. In this study, Mycobacterium tuberculosis (MTB) rv2190c DNA vaccine was prepared and its immunogenicity and therapeutic effects were evaluated.

Results

Non-infected mice immunized with rv2190c DNA or ag85a DNA showed higher levels of interferon-gamma (IFN-γ) in stimulated spleen lymphocyte culture supernatants, and had more Th1 cells and an elevatory ratio of Th1/Th2 immune cells in whole blood, indicating that Th1-type immune response was predominant. Compared with the saline group, ag85a DNA group and rv2190c DNA group in the infected mice decreased the lung colony-forming units (CFUs) by 0.533 and 0.283 log₁₀, and spleen CFUs by 0.425 and 0.321 log₁₀ respectively, and pathological lesion.

Conclusions

The rv2190c DNA had some immunotherapeutic effect on TB.

Electronic supplementary material

The online version of this article (doi:10.1186/s12865-017-0196-x) contains supplementary material, which is available to authorized users.

Boosting BCG-primed mice with chimeric DNA vaccine HG856A induces potent multifunctional T cell responses and enhanced protection against Mycobacterium tuberculosis

The tuberculosis pandemic continues to rampage despite widespread use of the current Bacillus Calmette-Guerin (BCG) vaccine. Because DNA vaccines can elicit effective antigen-specific immune responses, including potent T cell-mediated immunity, they are promising vehicles for antigen delivery. In a prime-boost approach, they can supplement the inadequate anti-TB immunological memory induced by BCG. Based on this, a chimeric DNA vaccine HG856A encoding Mycobacterium tuberculosis (M. tuberculosis) immunodominant antigen Ag85A plus two copies of ESAT-6 was constructed. Potent humoral immune responses, as well as therapeutic effects induced by this DNA vaccine, were observed previously in M. tuberculosis-infected mice. In this study, we further evaluated the antigen-specific T cell immune responses and showed that repeated immunization with HG856A gave modest protection against M. tuberculosis challenge infection and significantly boosted the immune protection primed by BCG vaccination. Enhanced protection was accompanied by increased multifunctional Th1 CD4(+) T cell responses, most notably by an elevated frequency of M. tuberculosis antigen-specific IL-2-producing CD4(+) T cells post-vaccination. These data confirm the potential of chimeric DNA vaccine HG856A as an anti-TB vaccine candidate.

Adjunctive immunotherapy with α-crystallin based DNA vaccination reduces Tuberculosis chemotherapy period in chronically infected mice

By employing modified Cornell model, we have evaluated the potential of adjunctive immunotherapy with DNA vaccines to shorten the tuberculosis chemotherapy period and reduce disease reactivation. We demonstrate that α-crystallin based DNA vaccine (DNAacr) significantly reduced the chemotherapy period from 12 weeks to 8 weeks when compared with the chemotherapy alone. Immunotherapy with SodA based DNA vaccine (DNAsod) reduced the pulmonary bacilli only as much as DNAvec. Both DNAacr and DNAsod, although significantly delayed the reactivation in comparison to the chemotherapy alone, this delay was associated with the immunostimulatory sequences present in the vector backbone and was not antigen specific. Both DNA vaccines resulted in the production of significantly higher number of T_EM cells than the chemotherapy alone, however, only in the case of DNAsod, this enhancement was significant over the DNAvec treatment. Overall, our findings emphasize the immunotherapeutic potential of DNAacr in shortening the duration of TB chemotherapy.

Immunogenicity and therapeutic effects of Ag85A/B chimeric DNA vaccine in mice infected with Mycobacterium tuberculosis

The situation of tuberculosis (TB) is very severe in China. New therapeutic agents or regimens to treat TB are urgently needed. In this study, Mycobacterium tuberculosis-infected mice were given immunotherapy intramuscularly with Ag85A/B chimeric DNA or saline, plasmid vector pVAX1, or Mycobacterium vaccae vaccine. The mice treated with Ag85A/B chimeric DNA showed significantly higher numbers of T cells secreting interferon-gamma (IFN-γ), more IFN-γ in splenocyte culture supernatant, more Th1 and Tc1 cells, and higher ratios of Th1/Th2 and Tc1/Tc2 cells in whole blood, indicating a predominant Th1 immune response to treatment. Infected mice treated with doses of 100 μg Ag85A/B chimeric DNA had an extended time until death of 50% of the animals that was markedly longer than the saline and vector control groups, and the death rate at 1 month after the last dose was lower than that in the other groups. Compared with the saline group, 100 μg Ag85A/B chimeric DNA and 100 μg Ag85A DNA reduced the pulmonary bacterial loads by 0.79 and 0.45 logs, and the liver bacterial loads by 0.52 and 0.50 logs, respectively. Pathological changes in the lungs were less, and the lesions were more limited. These results show that Ag85A/B chimeric DNA was effective for the treatment of TB, significantly increasing the cellular immune response and inhibiting the growth of M. tuberculosis.

Tuberculosis vaccine research in China

It is now privately acknowledged that there may be little if any perceptible impact of the national Bacille Calmette-Guerin (BCG) vaccination program on disease prevalence, despite the extensive coverage of the newborn infant population and likely benefit in the early years of life. A better preventive vaccine than BCG is now being sought by Chinese researchers. Urgency has been added to the control problem by the emergence of multidrug-resistant tuberculosis (TB). Furthermore, expensive second-line drugs seem unlikely to be made available by the government to treat drug-resistant cases, so attention in addition has turned to the potential of immunotherapy as an adjunct to chemotherapy. Research trends are summarized here.

Immunotherapy for TB

Mycobacterium tuberculosis was one of the first human pathogens to be identified as the cause of a specific disease – TB. TB was also one of the first specific diseases for which immunotherapy was attempted. In more than a century since, multiple different immunotherapies have been attempted, alongside vaccination and antibiotic treatment, with varying degrees of success. Despite this, TB remains a major worldwide health problem that causes nearly 2 million deaths annually and has infected an estimated 2 billion people. A major reason for this is that M. tuberculosis is an ancient human pathogen that has evolved complex strategies for persistence in the human host. It has thus been long understood that, to effectively control TB, we will need to address the ability of the pathogen to establish a persistent, latent infection in most infected individuals. This review discusses what is presently known about the interaction of M. tuberculosis with the immune system, and how this knowledge has been used to design immunotherapeutic strategies.

Vaccines against tuberculosis: where are we and where do we need to go?

In this review we discuss recent progress in the development, testing, and clinical evaluation of new vaccines against tuberculosis (TB). Over the last 20 years, tremendous progress has been made in TB vaccine research and development: from a pipeline virtually empty of new TB candidate vaccines in the early 1990s, to an era in which a dozen novel TB vaccine candidates have been and are being evaluated in human clinical trials. In addition, innovative approaches are being pursued to further improve existing vaccines, as well as discover new ones. Thus, there is good reason for optimism in the field of TB vaccines that it will be possible to develop better vaccines than BCG, which is still the only vaccine available against TB.