Recombinant antigen production for assays of intradermoreaction for diagnosis and surveillance of tuberculosis

Immunomodulation by epigenome alterations in Mycobacterium tuberculosis infection

Mycobacterium tuberculosis (MTB) has co-evolved with humans for decades and developed several mechanisms to evade host immunity. It can efficiently alter the host epigenome, thus playing a major role in immunomodulation by either activating or suppressing genes responsible for mounting an immune response against the pathogen. Epigenetic modifications such as DNA methylation and chromatin remodelling regulate gene expression and influence several cellular processes. The involvement of epigenetic factors in disease onset and development had been overlooked upon in comparison to genetic mutations. It is now believed that assessment of epigenetic changes hold great potential in diagnosis, prevention and treatment strategies for a wide range of diseases. In this review, we unravel the principles of epigenetics and the numerous ways by which MTB re-shapes the host epigenetic landscape as a strategy to overpower the host immune system for its survival and persistence.

High-yield production of major T-cell ESAT6-CFP10 fusion antigen of M. tuberculosis complex employing codon-optimized synthetic gene

Translation engineering and bioinformatics have accelerated the rate at which gene sequences can be improved to generate multi-epitope proteins. Strong antigenic proteins for tuberculosis diagnosis include individual ESAT6 and CFP10 proteins or derived peptides. Obtention of heterologous multi-component antigens in E. coli without forming inclusion bodies remain a biotechnological challenge. The gene sequence for ESAT6-CFP10 fusion antigen was optimized by codon bias adjust for high-level expression as a soluble protein. The obtained fusion protein of 23.7 kDa was observed by SDS-PAGE and Western blot analysis after Ni-affinity chromatography and the yield of expressed soluble protein reached a concentration of approximately 67 mg/L in shake flask culture after IPTG induction. Antigenicity was evaluated at 4 μg/mL in whole blood cultures from bovines, and protein stimuli were assessed using a specific in vitro IFN-γ release assay. The hybrid protein was able to stimulate T-cell specific responses of bovine TB suspects. The results indicate that improved E. coli codon usage is a good and cost-effective strategy to potentialize large scale production of multi-epitope proteins with sustained antigenic properties for diagnostic purposes.

Application of transdermal patches with new skin test reagents for detection of latent tuberculosis

Introduction. Current intradermal tuberculin skin tests for latent tuberculosis infection (LTBI) based on purified protein derivative (PPD) have poor specificity.Aims. Developing a better skin test antigen as well as a simple skin patch test may improve and facilitate diagnostic performance.Methodology. Defined recombinant antigens that were unique to Mycobacterium tuberculosis (MTB), including two potential latency-associated antigens (ESAT-6 and Rv2653c) and five DosR-encoded latency proteins (Rv1996, Rv2031c, Rv2032, DevR and Rv3716c), were used as diagnostic skin test reagents in comparison with a standard PPD. The performance of the skin tests based on the detection of delayed-type hypersensitivity (DTH) reaction in guinea pigs sensitized to MTB and M. bovis bacille Calmette-Guérin (BCG) vaccine was evaluated.Results. The latency antigens Rv1996, Rv2031c, Rv2032 and Rv2653c and the ESAT-6 protein elicited less reactive DTH skin responses in MTB-sensitized guinea pigs than those resulting from PPD, but elicited no response in BCG-vaccinated guinea pigs. The remaining two latency antigens (DevR and Rv3716c) elicited DTH responses in both groups of animals, as did PPD. The reactivity of PPD in BCG-vaccinated guinea pigs was greater than that of any of the selected skin test reagents. Using stronger concentrations of selected skin test reagents in the patch test led to increased DTH responses that were comparable to those elicited by PPD in guinea pigs sensitized with MTB.Conclusion. Transdermal application of defined purified antigens might be a promising method for LTBI screening.

Biological evaluation of mimetic peptides as active molecules for a new and simple skin test in an animal model

A skin test is a widely used tool in diagnostic evaluations to investigate cutaneous leishmaniases (CL). The actual antigen (Montenegro skin test [MST] antigen) presents some difficulties that pertain to its manufacturing and validation. To contribute to overcoming this problem, we propose the application of new-generation molecules that are based on skin antigen tests. These antigens were obtained through biotechnology pathways by manufacturing synthetic mimetic peptides. Three peptides, which were selected by phage display, were tested as skin test antigens in an animal model (Cavia porcellus) that was immunized with Leishmania amazonensis or Leishmania braziliensis. The peptide antigens, individually (PA1, PA2, PA3) or in a mix (PAMix), promoted induration reactions at 48 and 72 h after the test was performed. The indurations varied from 0.5 to 0.7 cm. In the animals immunized with L. amazonensis, the PA3 antigen showed better results than the standard MST antigen. In animals immunized with L. braziliensis, two peptide antigens (PA2 and PAMix) promoted induration reactions for a longer period of time than the standard MST antigen. These results validate our hypothesis that peptides could be used as antigens in skin tests and may replace the current antigen for CL diagnosis.

Process parameters optimization to produce the recombinant protein CFP10 for the diagnosis of tuberculosis

The aim of this study was to evaluate the parameters that affect the production of the recombinant 10 kDa culture filtrate protein (CFP10), a promising reagent of high specificity for intradermoreaction and other antigen-based methods used in the diagnosis of tuberculosis. Conditions of Escherichia coli growth temperature, induction temperature and IPTG-inducer concentration were evaluated in shake flasks and dissolved O₂ concentrations of 15 and 30% were evaluated in a bioreactor. The process parameters defined on small scale were: growth temperature between 30 and 37 °C, induction temperature of 26 °C and IPTG concentration of 0.12 mM. The process conducted with 15% dissolved O₂ presented a recombinant protein yield of 78.6 mg g^-1 biomass and a proportion of recombinant protein (insoluble fraction) in relation to total insoluble protein of 72%, at the time of maximum productivity. The operation with 30% dissolved O₂ resulted in lower recombinant protein yields of 62.9 mg g^-1 biomass and 20% in relation to total insoluble protein, but in higher overall concentration in the culture broth (69.2 mg L^-1versus 48.3 mg L^-1). The protein identity was confirmed by mass spectrometry, showing high similarity to CFP10, 10 kDa of Mycobacterium tuberculosis H37Rv (score 95), and the purified antigen presented reactivity by the Western blotting assay.

New strategy to improve quality control of Montenegro skin test at the production level

INTRODUCTION

The production of the Montenegro antigen for skin test poses difficulties regarding quality control. Here, we propose that certain animal models reproducing a similar immune response to humans may be used in the quality control of Montenegro antigen production.

METHODS

Fifteen Cavia porcellus (guinea pigs) were immunized with Leishmania amazonensis or Leishmania braziliensis , and, after 30 days, they were skin tested with standard Montenegro antigen. To validate C. porcellus as an animal model for skin tests, eighteen Mesocricetus auratus (hamsters) were infected with L. amazonensis or L. braziliensis , and, after 45 days, they were skin tested with standard Montenegro antigen.

RESULTS

Cavia porcellus immunized with L. amazonensis or L. braziliensis , and hamsters infected with the same species presented induration reactions when skin tested with standard Montenegro antigen 48-72h after the test.

CONCLUSIONS

The comparison between immunization methods and immune response from the two animal species validated C. porcellus as a good model for Montenegro skin test, and the model showed strong potential as an in vivo model in the quality control of the production of Montenegro antigen.

Polymorphisms in the PE35 and PPE68 antigens in Mycobacterium tuberculosis strains may affect strain virulence and reflect ongoing immune evasion

Previous studies have demonstrated that the Pro‑Glu/Pro‑Pro‑Glu (PE/PPE) genes in strains of Mycobacterium tuberculosis exhibit high sequence variation and may be involved in antigenic variation and immune evasion. Region of Difference 1 (RD1), encoding genes from Rv3871 to Rv3879, was observed to be lost during the original derivation of Bacillus Calmette‑Guérin between 1908 and 1921. It has been previously demonstrated that two PE/PPE proteins, PE35 (Rv3872) and PPE68 (Rv3873), are encoded by RD1 and exhibit immunodominance. To explore the genetic diversity of PE35 and PPE68, and to evaluate the impact of sequence variation on the immune recognition of these proteins, 161 clinical M. tuberculosis strains were selected from China and comparative sequence analysis of PE35 and PPE68 was performed. The results indicated that polymorphisms in PE35 and PPE68 may lead to alterations in the function of these proteins, which may potentially affect strain virulence. In addition, the human T‑cell epitopes of PE35 and PPE68 were highly variable, suggesting that the two antigens may be involved in diversifying selection to evade host immunity. The prevalence of strains with PE35 mutations in the non‑Beijing family was significantly greater compared with the Beijing family, indicating that Beijing strains may be more conservative than non‑Beijing strains in this gene.

Animal models of tuberculosis: Guinea pigs

The progression of the disease that follows infection of guinea pigs with Mycobacterium tuberculosis displays many features of human tuberculosis (TB), and the guinea pig model of TB has been used for more than 100 years as a research tool to understand and describe disease mechanisms. Changes in the bacterial burden and pathology following infection can be readily monitored and used to evaluate the impact of TB interventions. Demonstration of the protective efficacy of vaccines in the low-dose aerosol guinea pig model is an important component of the preclinical data package for novel vaccines in development, and there is a continual need to improve the model to facilitate progression of vaccines to the clinic. Development of better tools with which to dissect the immune responses of guinea pigs is a focus of current research.

Evaluation of cocktails with recombinant proteins of Mycobacterium bovis for a specific diagnosis of bovine tuberculosis

The Delayed type hypersensitivity skin test (DTH) and interferon-gamma assay are used for the diagnosis of bovine tuberculosis (TBB). The specificity of these diagnoses, however, is compromised because both are based on the response against purified protein derivative of Mycobacterium bovis (PPD-B). In this study, we assessed the potential of two cocktails containing M. bovis recombinant proteins: cocktail 1 (C1): ESAT-6, CFP-10 and MPB83 and cocktail 2 (C2): ESAT-6, CFP-10, MPB83, HspX, TB10.3, and MPB70. C1, C2, and PPD-B showed similar response by DTH in M. bovis-sensitized guinea pigs. Importantly, C1 induced a lower response than PPD-B in M. avium-sensitized guinea pigs. In cattle, C1 displayed better performance than PPD-B and C2; indeed, C1 showed the least detection of animals either vaccinated or Map-infected. To optimize the composition of the cocktails, we obtained protein fractions from PPD-B and tested their immunogenicity in experimentally M. bovis-infected cattle. In one highly reactive fraction, seven proteins were identified. The inclusion of FixB in C1 enhanced the recognition of M. bovis-infected cattle without compromising specificity. Our data provide a promising basis for the future development of a cocktail for TBB detection without interference by the presence of sensitized or infected animals with other mycobacteria.

Tuberculosis diagnosis using immunodominant, secreted antigens of Mycobacterium tuberculosis

Tuberculosis (TB) remains a major public health concern in most low-income countries. Hence, rapid and sensitive TB diagnostics play an important role in detecting and preventing the disease. In addition to established diagnostic methods, several new approaches have been reported. Some techniques are simple but time-consuming, while others require complex instrumentation. One prominent and readily available approach is to detect proteins that Mycobacterium tuberculosis secretes, such as Mpt64, the 6-kDa early secreted antigenic target (Esat6), the 10-kDa culture filtrate protein (Cfp10), and the antigen 85 (Ag85) complex. Although their functions are not fully understood, a growing body of molecular evidence implicates them in M. tuberculosis virulence. Currently these biomarkers are either being used or investigated for use in skin patch tests, biosensor analyses, and immunochromatographic, immunohistochemical, polymerase chain reaction-based, and enzyme-linked immunosorbent assays. This review provides a comprehensive discussion of the roles these immunodominant antigens play in M. tuberculosis pathogenesis and compares diagnostic methods based on the detection of these proteins with more established tests for TB.