Development of real-time immuno-PCR for the quantitative detection of mycobacterial PstS1 in tuberculosis patients

Ultrasensitive reporter DNA sensors built on nucleic acid amplification techniques: Application in the detection of trace amount of protein

The detection of protein is of great significance for the study of biological physiological function, early diagnosis of diseases and drug research. However, the sensitivity of traditional protein detection methods for detecting trace amount of proteins was relatively low. By integrating sensitive nucleic acid amplification techniques (NAAT) with protein detection methods, the detection limit of protein detection methods can be substantially improved. The DNA that can specifically bind to protein targets and convert protein signals into DNA signals is collectively referred to reporter DNA. Various NAATs have been used to establish NAAT-based reporter DNA sensors. And according to whether enzymes are involved in the amplification process, the NAAT-based reporter DNA sensors can be divided into two types: enzyme-assisted NAAT-based reporter DNA sensors and enzyme-free NAAT-based reporter DNA sensors. In this review, we will introduce the principles and applications of two types of NAAT-based reporter DNA sensors for detecting protein targets. Finally, the main challenges and application prospects of NAAT-based reporter DNA sensors are discussed.

Antibodies as clinical tools for tuberculosis

Tuberculosis (TB) is a leading cause of morbidity and mortality worldwide. Global research efforts to improve TB control are hindered by insufficient understanding of the role that antibodies play in protective immunity and pathogenesis. This impacts knowledge of rational and optimal vaccine design, appropriate diagnostic biomarkers, and development of therapeutics. Traditional approaches for the prevention and diagnosis of TB may be less efficacious in high prevalence, remote, and resource-poor settings. An improved understanding of the immune response to the causative agent of TB, Mycobacterium tuberculosis (Mtb), will be crucial for developing better vaccines, therapeutics, and diagnostics. While memory CD4+ T cells and cells and cytokine interferon gamma (IFN-g) have been the main identified correlates of protection in TB, mounting evidence suggests that other types of immunity may also have important roles. TB serology has identified antibodies and functional characteristics that may help diagnose Mtb infection and distinguish between different TB disease states. To date, no serological tests meet the World Health Organization (WHO) requirements for TB diagnosis, but multiplex assays show promise for improving the sensitivity and specificity of TB serodiagnosis. Monoclonal antibody (mAb) therapies and serum passive infusion studies in murine models of TB have also demonstrated some protective outcomes. However, animal models that better reflect the human immune response to Mtb are necessary to fully assess the clinical utility of antibody-based TB prophylactics and therapeutics. Candidate TB vaccines are not designed to elicit an Mtb-specific antibody response, but evidence suggests BCG and novel TB vaccines may induce protective Mtb antibodies. The potential of the humoral immune response in TB monitoring and control is being investigated and these studies provide important insight into the functional role of antibody-mediated immunity against TB. In this review, we describe the current state of development of antibody-based clinical tools for TB, with a focus on diagnostic, therapeutic, and vaccine-based applications.

Insight into diagnosis of pleural tuberculosis with special focus on nucleic acid amplification tests

INTRODUCTION

Pleural tuberculosis (TB) is the archetype of extrapulmonary TB (EPTB), which mainly affects the pleural space and leads to exudative pleural effusion. Diagnosis of pleural TB is a difficult task predominantly due to atypical clinical presentations and sparse bacillary load in clinical specimens.

AREA COVERED

We reviewed the current literature on the globally existing conventional/latest modalities for diagnosing pleural TB. Bacteriological examination (smear/culture), tuberculin skin testing/interferon-γ release assays, biochemical testing, imaging and histopathological/cytological examination are the main modalities. Moreover, nucleic acid amplification tests (NAATs), i.e. loop-mediated isothermal amplification, PCR/multiplex-PCR, nested-PCR, real-time PCR and GeneXpert® MTB/RIF are being utilized. Currently, GeneXpert Ultra, Truenat MTB^TM, detection of circulating Mycobacterium tuberculosis (Mtb) cell-free DNA by NAATs, aptamer-linked immobilized sorbent assay and immuno-PCR (I-PCR) have also been exploited.

EXPERT OPINION

Routine tests are not adequate for effective pleural TB diagnosis. The latest molecular/immunological tests as discussed above, and the other tools, i.e. real-time I-PCR/nanoparticle-based I-PCR and identification of Mtb biomarkers within urinary/serum extracellular vesicles being utilized for pulmonary TB and other EPTB types may also be exploited to diagnose pleural TB. Reliable diagnosis and early therapy would reduce the serious complications associated with pleural TB, i.e. TB empyema, pleural fibrosis, etc.

Identification of mycobacterial MPT-64 and ESAT-6 proteins in urogenital tuberculosis patients by real-time immuno-PCR

Aim: Diagnosis of urogenital tuberculosis (UGTB) is difficult and there is an immediate need to develop a reliable diagnostic test. Methods: A real-time immuno-PCR (RT-I-PCR) was developed to identify a cocktail of MPT-64 + ESAT-6 in both male/female UGTB patients comprising five confirmed cases, 40 clinically suspected cases and 37 non-TB controls, from whom mid-stream urine specimens were collected, while endometrial biopsies of female patients were obtained on day 1 of their menstrual cycle. Results obtained by RT-I-PCR were compared with I-PCR/ELISA and GeneXpert. Results: A wide range (500 fg/ml-10 ng/ml) of MPT-64 + ESAT-6 was detected in UGTB specimens by RT-I-PCR, although ELISA showed a narrow range (2.5-11 ng/ml). Sensitivities of 80% and 82.2% were obtained by RT-I-PCR in clinically suspected and total UGTB cases, respectively, whereas 94.6% specificity was obtained. Concurrently, RT-I-PCR revealed significantly higher (p < 0.05-0.001) sensitivity than I-PCR/ELISA and GeneXpert. Conclusion: After improving the specificity, the authors may develop RT-I-PCR into a diagnostic kit.

Diagnosis of peritoneal tuberculosis by real-time immuno-PCR assay based on detection of a cocktail of Mycobacterium tuberculosis CFP-10 and HspX proteins

BACKGROUND

Diagnosis of peritoneal TB is difficult owing to unusual clinical manifestations and low sensitivities obtained with most of the available diagnostic modalities. Hence, there is an urgent need to design a reliable diagnostic test so that an early therapy is initiated.

RESEARCH DESIGN AND METHODS

We designed a quantitative real-time immuno-PCR (RT-I-PCR) assay to detect a cocktail of Mycobacterium tuberculosis CFP-10 (Rv3874) and HspX (Rv2031c) proteins in clinical samples (ascitic fluids and peritoneal biopsies) of peritoneal TB patients, and results were compared with I-PCR/ELISA.

RESULTS

A wide range of CFP-10+ HspX (0.6 pg/mL to 9.9 ng/mL) was detected in clinical samples of peritoneal TB patients by RT-I-PCR, whereas ELISA exhibited a narrow range (3 ng/mL to 11.5 ng/mL). Sensitivities of 81.5% and 65.7% and specificities of 92.5% and 90% were obtained in a total of 78 cases (comprising 38 peritoneal TB and 40 non-TB controls) by RT-I-PCR and I-PCR, respectively. Markedly, sensitivity obtained by RT-I-PCR was significantly higher than I-PCR (p = 0.0143) and ELISA (p = 0.0005).

CONCLUSIONS

Our RT-I-PCR revealed good accuracy for the rapid diagnosis of peritoneal TB cases. After further improving the specificity and reducing the cost, this assay may develop into a diagnostic kit.

Diagnosis of osteoarticular tuberculosis by immuno-PCR assay based on mycobacterial antigen 85 complex detection

Diagnosis of osteoarticular tuberculosis (OATB) exhibits serious challenges owing to paucibacillary nature of specimens and localization of disease at sites that are difficult to access. We recently developed indirect immuno-PCR (I-PCR) and real-time I-PCR (RT-I-PCR) assays for the detection of mycobacterial antigen 85 complex (Ag85) in OATB patients. Detection limits for the purified Ag85 protein were found to be 1 and 41 fg ml^-1 by I-PCR and RT-I-PCR, respectively, which were at least 10⁵ -fold lower than respective ELISA. While spiking synovial fluids of non-TB control subjects with the purified Ag85 protein, LODs of 100 and 120 fg ml^-1 were obtained by I-PCR and RT-I-PCR, respectively, thus demonstrating the sample matrix effect. Sensitivities of 87·5 and 70·5% were observed in bodily fluids of confirmed (n = 8) and clinically suspected (n = 51) OATB cases, respectively, by I-PCR, with a specificity of 93·9% (n = 33). Markedly, the sensitivities obtained by I-PCR/RT-I-PCR were significantly higher (P < 0·05-0·01) than ELISA and GeneXpert assay (n = 30). However, no substantial difference in sensitivity was observed between the I-PCR and RT-I-PCR assays. After further improving the accuracy of I-PCR, this test may lead to development of an attractive diagnostic kit.

Age-Related Immunoreactivity Profiles to Diverse Mycobacterial Antigens in BCG-Vaccinated Chinese Population

Long-term immunoreactivity to mycobacterial antigens in Bovis Calmette-Guérin (BCG)-vaccinated population is not well investigated. Herein, 361 volunteer healthy donors (HDs) with neonatal BCG vaccination from Shanghai region (China) were enrolled. They were subdivided into ESAT-6/CFP10^- (E6C10^-) and ESAT-6/CFP10⁺ (E6C10⁺) groups based on gamma-interferon release assays (IGRAs). Three mycobacterial antigens, including Rv0934, Rv3006, and Rv3841, were subjected to the determination of immunoreactivity by ELISPOT assay. The immunoreactivities to three mycobacterial antigens were firstly compared among TB patients (N=39), E6C10⁺ HDs (N=78, 21.61% of HDs) and E6C10^- HDs (N=283, 78.39% of HDs). It was revealed that Rv3006 was dominant upon M.tb infection, while Rv3841 was likely to be more responsive upon latent TB infection. In E6C10^- population, the immunoreactivity to Rv3841 maintained along with aging, whereas those to Rv3006 and Rv0934 attenuated in E6C10^- HDs older than 45 years old. Our study implies the shift of dominant antigens at different infection statuses, providing the clues for the selection of mycobacterial antigens in vaccine development and precision revaccination in the future.

Human antibodies targeting a Mycobacterium transporter protein mediate protection against tuberculosis

Mycobacterium tuberculosis (Mtb) exposure drives antibody responses, but whether patients with active tuberculosis elicit protective antibodies, and against which antigens, is still unclear. Here we generate monoclonal antibodies from memory B cells of one patient to investigate the B cell responses during active infection. The antibodies, members of four distinct B cell clones, are directed against the Mtb phosphate transporter subunit PstS1. Antibodies p4-36 and p4-163 reduce Mycobacterium bovis-BCG and Mtb levels in an ex vivo human whole blood growth inhibition assay in an FcR-dependent manner; meanwhile, germline versions of p4-36 and p4-163 do not bind Mtb. Crystal structures of p4-36 and p4-170, complexed to PstS1, are determined at 2.1 Å and 2.4 Å resolution, respectively, to reveal two distinctive PstS1 epitopes. Lastly, a prophylactic p4-36 and p4-163 treatment in Mtb-infected Balb/c mice reduces bacterial lung burden by 50%. Our study shows that inhibitory anti-PstS1 B cell responses arise during active tuberculosis.

Detection of mycobacterial CFP-10 (Rv3874) protein in tuberculosis patients by gold nanoparticle-based real-time immuno-PCR

Aim: Timely and reliable diagnostic test for tuberculosis (TB) is immediately required. Attempts were made to improve the technology and diagnostic potential of real-time immuno-PCR (RT-I-PCR). Methods: We designed gold nanoparticle (GNP)-based RT-I-PCR (GNP-RT-I-PCR) assay for the detection of Mycobacterium tuberculosis CFP-10 (Rv3874) protein in clinical samples of TB patients. Results: A wide quantitative detection range of CFP-10 was found to be 0.5-5 × 10⁴ pg/ml in bodily fluids of TB patients, which can evaluate the progression of disease. Moreover, sensitivities of 83.7 and 76.2% were observed in pulmonary (n = 49) and extrapulmonary TB (n = 42) patients, respectively, with specificities of 93.5-93.8% (n = 63). Conclusion: Conjugation of detection antibodies and oligonucleotides to functionalized GNPs of GNP-RT-I-PCR is relatively easier, compared with streptavidin-biotin/succinimidyl-4-(N-maleimidomethyl) cyclohexane-1-carboxylate system employed in RT-I-PCR. Our assay also showed better diagnostic performance than RT-I-PCR, which may provide a viable platform for the development of an efficient TB diagnostic test.

Quantitative detection of a cocktail of mycobacterial MPT64 and PstS1 in tuberculosis patients by real-time immuno-PCR

AIM

There is an urgent need to design a reliable diagnostic test for tuberculosis (TB).

METHODS

Real-time immuno-PCR (RT-I-PCR) assay was devised for the quantitative detection of a cocktail of mycobacterial MPT64 (Rv1980c) and PstS1 (Rv0934) in TB patients.

RESULTS

A broad dynamic range of 0.95 pg/ml-95 ng/ml of MPT64+PstS1 was detected in TB patients. In smear-positive (n = 59) and smear-negative (n = 42) pulmonary TB cases, sensitivities of 93.2 and 83.3% were observed, respectively with 92.8% specificity, whereas a sensitivity of 77.9% and a specificity of 91.3% were observed in extrapulmonary TB cases (n = 86). Furthermore, significantly reduced MPT64+PstS1 concentrations (p < 0.001) were noticed in patients on therapy by RT-I-PCR as compared with untreated patients.

CONCLUSION

Our RT-I-PCR assay revealed high sensitivity especially for the rapid diagnosis of smear-negative pulmonary TB and paucibacillary extrapulmonary TB samples, which could also monitor the dynamics of disease in patients on therapy.

Detection of Mycobacterium tuberculosis purified ESAT-6 (Rv3875) by magnetic bead-coupled gold nanoparticle-based immuno-PCR assay

PURPOSE

Immuno-PCR (I-PCR), an ultrasensitive method, combines the versatility of ELISA with the exponential amplification capacity of PCR. Coupling of detection antibodies with the reporter DNA is a critical step of I-PCR. Gold nanoparticles (GNPs) and magnetic beads (MBs) are relatively easy to attach with the antibodies and DNA. Therefore, we designed MB-coupled GNP-based I-PCR (MB-GNP-I-PCR) assay for the detection of Mycobacterium tuberculosis antigen.

METHODS

GNPs were synthesized by chemical reduction and seed-mediated synthesis. Functionalized GNPs were prepared by coupling GNPs with the detection antibodies and reporter DNA and were characterized. Detection limit of M. tuberculosis-specific purified early secreted antigenic target-6 (ESAT-6) (Rv3875) was determined by MB-GNP-I-PCR.

RESULTS

Transmission electron microscopy revealed spherical and slightly polydispersed GNPs of ~20 and ~60 nm size. Coupling of antibodies to GNPs was indicated by a shift in absorption maxima from 524 to 534 nm, which was confirmed by transmission electron microscopy. A color reaction with ELISA and the presence of 76 bp product by PCR further validated the coupling of detection antibodies and signal DNA to the functionalized GNPs. Also, attachment of capture antibodies with MBs was confirmed by magneto-ELISA. Detection limit of purified ESAT-6 by MB-GNP-I-PCR was determined to be 10 fg/mL, 105-fold lower than analogous ELISA. Notably, no sample matrix effect was observed in the saliva samples of healthy individuals spiked with the purified ESAT-6.

CONCLUSION

Unlike conventional I-PCR (solid format), MB-GNP-I-PCR (liquid format) is relatively simple with the reduced background signals, which can be further exploited for the clinical diagnosis of tuberculosis.

Role of Immuno-Polymerase Chain Reaction (I-PCR) in Resolving Diagnostic Dilemma Between Tuberculoma and Neurocysticercosis: A Case Report

BACKGROUND Tuberculoma and neurocysticercosis (NCC) often show similar clinical and neuroimaging features. Differential diagnosis of these 2 diseases is imperative, as tuberculoma is an active infection that requires immediate anti-tubercular therapy (ATT). CASE REPORT We present the case of a 17-year-old Indian girl with fever, severe headache, and right 6th cranial nerve palsy. Brain magnetic resonance imaging (MRI) showed multiple tiny ring-enhancing lesions in bilateral cerebral parenchyma with mild perilesional edema, which were initially thought to be NCC, but subsequently were diagnosed as brain tuberculomas. Based on clinical findings, mildly increased choline/creatine ratio (1.35) with slight prominent lipid lactate peak and absence of alanine, succinate peak by magnetic resonance spectroscopy (MRS), and the detection of Mycobacterium tuberculosis (Mtb)-specific early-secreted antigenic target-6 (ESAT-6, Rv3875) protein from the cerebrospinal fluid (CSF) by indirect ELISA, as well as indirect immuno-PCR (I-PCR) assay, diagnosis of brain tuberculomas associated with tuberculous meningitis (TBM) was confirmed, which was followed by ATT. The patient responded well and the symptoms resolved. CONCLUSIONS In this case, multiple ring-enhancing lesions of the brain by MRI were diagnosed as tuberculomas associated with TBM by MRS and indirect ELISA/I-PCR method, thus resolving the diagnostic dilemma.

Immuno-PCR, a new technique for the serodiagnosis of tuberculosis

Rapid and accurate diagnosis of tuberculosis (TB) is essential to control the disease. The conventional microbiological tests have limitations and there is an urgent need to devise a simple, rapid and reliable point-of-care (POC) test. The failure of TB diagnostic tests based on antibody detection due to inconsistent and imprecise results has stimulated renewed interest in the development of rapid antigen detection methods. However, the World Health Organization (WHO) has emphasized to continue research for designing new antibody-based detection tests with improved accuracy. Immuno-polymerase chain reaction (I-PCR) combines the simplicity and versatility of enzyme-linked immunosorbent assay (ELISA) with the exponential amplification capacity and sensitivity of PCR thus leading to several-fold increase in sensitivity in comparison to analogous ELISA. In this review, we have described the serodiagnostic potential of I-PCR assays for an early diagnosis of TB based on the detection of potential mycobacterial antigens and circulating antibodies in body fluids of TB patients.