A whole blood monokine-based reporter assay provides a sensitive and robust measurement of the antigen-specific T cell response

In vitro responses of multiple cytokines to purified protein derivative in healthy and naturally Mycobacterium tuberculosis-infected rhesus monkeys (Macaca mulatta)

BACKGROUND

As the widely used biomarker of whole-blood stimulation assays for tuberculosis diagnosis, the release of IFN-γ might be affected by multiple factors, such as immunosuppression and some infectious agents. Here, we evaluated additional cytokines as diagnostic biomarkers.

METHODS

Forty-three cytokines were measured by Luminex xMAP technologies in 30 healthy and 10 naturally Mycobacterium tuberculosis (MTB)-infected rhesus monkeys pre- and post-stimulation by purified protein derivative (PPD).

RESULTS

After stimulation, production of 23 and 38 cytokines was markedly increased in healthy and MTB-infected macaques, respectively. A comparison of the stimulation index (SI) between MTB infections and healthy macaques showed that the SIs of 32 cytokines in MTB-infected macaques were significantly higher than those in healthy macaques. Pooling the results, eight cytokines were suggested as ideal biomarkers for a whole-blood stimulation assay for MTB diagnosis.

CONCLUSION

PPD could induce multiple cytokine responses in either healthy or MTB-infected monkeys, and eight cytokines had reliable predictive capacity as diagnostic biomarkers of MTB infection.

Identification of an immunogenic neo-epitope encoded by mouse sarcoma using CXCR3 ligand mRNAs as sensors

The CXCR3 ligands CXCL9, 10, and 11 play critical roles in the amplification of immune responses by recruiting CXCR3⁺ immune effector cells to the tumor site. Taking advantage of this property of CXCR3 ligands, we aimed to establish a novel approach to identify immunogenic mutated-antigens. We examined the feasibility of using CXCR3 ligand mRNAs as sensors for detection of specific immune responses in human and murine systems. We further investigated whether this approach is applicable for the identification of immunogenic mutated-antigens by using murine sarcoma lines. Rapid synthesis of CXCR3 ligand mRNAs occurred shortly after specific immune responses in both human and murine immune systems. Particularly, in CMS5 tumor-bearing mice, we detected specific immune responses to mutated mitogen-activated protein kinase 2 (ERK2), which has previously been identified as an immunogenic mutated-antigen. Furthermore, by combining this approach with whole-exome and transcriptome sequencing analyses, we identified an immunogenic neo-epitope derived from mutated staphylococcal nuclease domain-containing protein 1 (Snd1) in CMS7 tumor-bearing mice. Most importantly, we successfully detected the specific immune response to this neo-epitope even without co-administration of anti-cytotoxic T-lymphocyte protein-4 (CTLA-4), anti-programmed cell death-1 (PD-1) and anti-glucocorticoid-induced TNFR-related protein (GITR) antibodies, which vigorously augmented the immune response and consequently enabled us to detect the specific immune response to this neo-epitope by conventional IFNγ intracellular staining method. Our data indicate the potential usefulness of this strategy for the identification of immunogenic mutated-antigens. We propose that this approach would be of great help for the development of personalized cancer vaccine therapies in future.

The stability of plasma IP-10 enhances its utility for the diagnosis of Mycobacterium bovis infection in African buffaloes (Syncerus caffer)

The measurement of interferon gamma-induced protein 10 (IP-10) in antigen-stimulated whole blood is a sensitive biomarker of Mycobacterium bovis infection in African buffaloes (Syncerus caffer). However, this species often occurs in remote locations and diagnostic samples must be transported to centralised laboratories for processing. In humans, plasma IP-10 is highly stable and this feature contributes to its diagnostic utility; for this reason we aimed to characterize the stability of this molecule in buffaloes. Blood from M. bovis-infected and -uninfected animals was incubated with pathogen-specific peptides, saline and phytohaemagglutinin, respectively. Plasma fractions were harvested and aliquots of selected samples were: (i) stored at different temperatures for various times; (ii) heat treated before storage at RT, and (iii) stored on Protein Saver Cards (PSCs) at RT for either 2 or 8 weeks before measurement of IP-10. Incubation of plasma at 65°C for 20 min caused no loss of IP-10 and this protein could be quantified in plasma stored on PSCs for 2 and 8 weeks. Moreover, for all storage conditions, IP-10 retained its excellent diagnostic characteristics. These features of IP-10 might allow for the heat inactivation of potentially infectious plasma which would facilitate the safe and simple transport of samples.

IP-10 Is a Sensitive Biomarker of Antigen Recognition in Whole-Blood Stimulation Assays Used for the Diagnosis of Mycobacterium bovis Infection in African Buffaloes (Syncerus caffer)

African buffaloes (Syncerus caffer) are maintenance hosts of Mycobacterium bovis, the causative agent of bovine tuberculosis. They act as reservoirs of this infection for a wide range of wildlife and domestic species, and the detection of infected animals is important to control the geographic spread and transmission of the disease. Interferon gamma (IFN-γ) release assays (IGRAs) utilizing pathogen-derived peptide antigens are highly specific tests of M. bovis infection; however, the diagnostic sensitivities of these assays are suboptimal. We evaluated the diagnostic utility of measuring antigen-dependent interferon gamma-induced protein 10 (IP-10) release as an alternative to measuring IFN-γ levels. M. bovis-exposed buffaloes were tested using the Bovigam PC-EC and Bovigam PC-HP assays and a modified QuantiFERON TB-Gold (mQFT) assay. IP-10 was measured in the harvested plasma and was produced in significantly greater abundance in response to M. bovis antigens in Bovigam-positive than in Bovigam-negative animals. For each assay, using the Bovigam results as a reference, receiver operating characteristic curve analysis was done to determine diagnostically relevant cutoff values for IP-10. Thereafter, mQFT test results derived from measurement of IP-10 and IFN-γ were compared and a larger number of Bovigam-positive animals were detected using IP-10 as a diagnostic marker. Moreover, using IP-10, agreement between the mQFT assay and the Bovigam assays was increased, while the excellent agreement between the Bovigam assays was retained. We conclude that IP-10 is a sensitive marker of antigen recognition and that measurement of this cytokine in antigen-stimulated whole blood might increase the sensitivity of conventional IGRAs in African buffaloes.

Diagnosing latent tuberculosis in immunocompromised patients measuring blood IP-10 production capacity: an analysis of chronic renal failure patients

OBJECTIVE

Patients undergoing haemodialysis for chronic renal failure-hemodialysis (CRF-HD) are at risk of latent tuberculosis infection (LTBI). The effectiveness of using blood IP-10 production capacity to diagnose LTBI in CRF-HD patients was analysed.

METHODS

The study enrolled 50 CRF-HD patients. Interferon-γ release assay (IGRA) was done using QuantiFERON-TB Gold In Tube (QFG-IT) system. Blood IP-10 production capacity was measured using the QFG-IT system tubes. Tuberculin skin testing (TST) was performed on the same day and the test results were compared.

RESULTS

TST turned out to be positive in 36.4% of the patients and QFG-IT in 54% of them. After stimulation with specific tuberculosis antigens, blood IP-10 levels increased noticeably. The antigen-stimulated blood IP-10 level was significantly higher in patients who were either TST or QFG-IT positive than in patients whose tests were negative (p=0.0001). Using 4.02 pg/mL as the threshold for stimulated blood log-transformed IP-10 level, good agreement was observed between IP-10 and QFG-IT results (κ=1).

CONCLUSION

Blood IP-10 level, which can be measured simply, provides results equivalent to IGRAs for the diagnosis of LTBI in CRF-HD patients.

CMV specific cytokine release assay in whole blood is optimized by combining synthetic CMV peptides and toll like receptor agonists

BACKGROUND

Interferon gamma release assays (IGRAs) are widely used to detect pathogen specific cellular immunity. Cytomegalovirus (CMV) is the foremost problematic viral infection in immunocompromised patients such as transplant or HIV infected patients. CMV antibody ELISAs are not able to predict CMV specific cellular immunity during immunosuppression. We developed a CMV specific IGRA comparing synthetic CMV peptides, native lysate and recombinant antigen. In addition, TLR agonists were tested to enhance CMV antigen immunogenicity.

METHODS

397 healthy controls (HC) were stratified according to CMV IgM and IgG serostatus and subsequently tested for IFNγ- and IL2-secretion in whole blood after challenge with synthetic, native or recombinant CMV antigens and TLR agonists by ELISA. The selected TLR agonists were lipopolysaccharide (LPS), lipoteichoic acid (LTA), peptidoglycan (PGN), zymosan (Zym), polyinosinic-polycytidylic acid (Poly(I:C)), flagellin (Fla), R848, loxoribine (Lox) and bropirimine (Bro).

RESULTS

Synthetic pp65 peptides elicited strong IFNγ responses in CMV seropositive, but not seronegative HC (6418 vs. 13 pg/ml). Native lysates and recombinant pp65 induced equally high IFNγ responses in seropositive (35,877 and 26,428 pg/ml) and increased background IFNγ expression in seronegative HC (43 and 1148 pg/ml). Diagnostic sensitivity and specificity with regard to anti-CMV serology reached 100% for synthetic pp65 and native CMV lysate, but 57% and 100% for recombinant pp65, respectively. TLR agonists LTA and Poly(I:C) augmented IFNγ responses after challenge with synthetic pp65 peptide, native lysate or recombinant pp65 in seropositive HC. Seronegative HC remained unaffected. IL2 production was negligible compared to IFNγ.

CONCLUSION

IGRAs using synthetic CMV peptides or native lysate showed the best cytokine signal to noise ratio compared to recombinant antigen and TLR agonists LTA and Poly(I:C) constitute potential costimulating reagents.

The evaluation of candidate biomarkers of cell-mediated immunity for the diagnosis of Mycobacterium bovis infection in African buffaloes (Syncerus caffer)

We evaluated commercially available bovine enzyme linked immunosorbent assays (ELISA) and a human IP-10 ELISA to measure IP-10, MIG, MCP-1, MCP-2, MCP-3 and IL1-RA in buffalo plasma in order to identify sensitive markers of the immune response to Mycobacterium bovis-specific peptides. Additionally, we found that all coding mRNA sequences of these cytokines showed very high homology with their homologues in domestic cattle (97-99%) as did the derived amino acid sequences (97-99%). This high sequence homology between cattle and buffaloes supports the use of bovine ELISAs for the detection these cytokines in buffaloes. MCP-1 concentration showed a positive correlation with that of IFN-γ (p=0.0077) and appears to occur in far greater abundance in buffaloes when compared to humans. Using a bovine IP-10 ELISA, levels of this cytokine were found to be significantly increased in antigen-stimulated blood samples from M. bovis test positive buffaloes (p<0.0001) and IP-10 was detected in far greater abundance than IFN-γ. Measurement of IP-10 with this ELISA may prove to be a sensitive marker of M. bovis infection in African buffaloes.

Development of a one-step probe based molecular assay for rapid immunodiagnosis of infection with M. tuberculosis using dried blood spots

Background

Antigen specific release of IP-10 is the most promising alternative marker to IFN-γ for infection with M. tuberculosis. Compared to Interferon-γ release assays (IGRA), IP-10 is released in high levels enabling novel approaches such as field friendly dried blood spots (DBS) and molecular detection.

Aim

To develop a robust IP-10 based molecular assay for the diagnosis of infection with M. tubercuolsis from whole blood and DBS.

Method

We developed a one-step probe based multiplex RT-qPCR assay for detecting IP-10 and IFN-γ mRNA expression from whole blood and DBS samples. The assay was validated and applied for the diagnosis of M. tuberculosis infection in DBS samples from 43 patients with confirmed TB, 13 patients with latent TB and 96 presumed uninfected controls. In parallel, IP-10 and INF-γ levels were measured in Quantiferon (QFT-TB) plasma supernatants.

Results

IP-10 mRNA upregulation was detectable at 4 hours after stimulation (6 fold upregulation) peaking at 8 hours (108 fold upregulation). IFN-γ expression occurred in concert but levels were lower (peak 6.7 fold upregulation). IP-10 gene expression level was significantly higher in patients with tuberculosis (median 31.2, IQR 10.7–67.0) and persons with latent tuberculosis infection (LTBI) (41.2, IQR 9.8–64.9) compared to healthy controls (1.6, IQR 1.1–2.4; p<0.0001). The IP-10 mRNA and protein based tests had comparable diagnostic accuracy to QFT-TB, sensitivity (85% and 88% vs 85%) and specificity (96% and 96% vs 97%, p = ns.).

Conclusion

We developed a rapid, robust and accurate molecular immunodiagnostic test for M. tuberculosis infection. By combining DBS based sample acquisition, mail or currier based sample transport with centralized molecular detection, this immunodiagnostic test concept can reduce the local technological requirements everywhere and make it possible to offer highly accurate immunodiagnostic tests in low resource settings.

Screening vaccine formulations for biological activity using fresh human whole blood

Understanding the relevant biological activity of any pharmaceutical formulation destined for human use is crucial. For vaccine-based formulations, activity must reflect the expected immune response, while for non-vaccine therapeutic agents, such as monoclonal antibodies, a lack of immune response to the formulation is desired.

During early formulation development, various biochemical and biophysical characteristics can be monitored in a high-throughput screening (HTS) format. However, it remains impractical and arguably unethical to screen samples in this way for immunological functionality in animal models. Furthermore, data for immunological functionality lag formulation design by months, making it cumbersome to relate back to formulations in real-time. It is also likely that animal testing may not accurately reflect the response in humans.

For a more effective formulation screen, a human whole blood (hWB) approach can be used to assess immunological functionality. The functional activity relates directly to the human immune response to a complete formulation (adjuvant/antigen) and includes adjuvant response, antigen response, adjuvant-modulated antigen response, stability, and potentially safety.

The following commentary discusses the hWB approach as a valuable new tool to de-risk manufacture, formulation design, and clinical progression.

Evaluation of the diagnostic potential of IP-10 and IL-2 as biomarkers for the diagnosis of active and latent tuberculosis in a BCG-vaccinated population

BACKGROUND

The Mycobacterium tuberculosis (Mtb)-specific T-cell interferon gamma release assays (IGRAs) are useful in detecting Mtb infection but perform poorly at distinguishing active tuberculosis disease (ATB) and latent tuberculosis infection (LTBI). This study is aimed at evaluating additional cytokines as biomarkers besides interferon-gamma (IFN-γ) to improve the identification of ATB and LTBI.

METHODOLOGY/PRINCIPAL FINDINGS

Sixty-six patients with ATB, 73 household contacts (HHC) of ATB patients and 76 healthy controls (HC) were recruited to undergo QuantiFERON TB GOLD in-tube assay (QFT) and the enzyme-linked immunosorbent assay (ELISA) where the release of IFN-γ, IFN-γ inducible protein 10 (IP-10), Interleukin 2 (IL-2) and Tumor Necrosis Factor-α (TNF-α) was determined in the whole blood with or without antigen-stimulation. The positive rates of the QFT, IP-10 and IL-2 tests were 86.4%, 89.4% and 86.4% for the ATB group with no difference between them (p>0.05). However, QFT in combination with IP-10 and IL-2 significantly increased the detection rate to 95.5% in the ATB group (p = 0.03) and the indeterminate rate of all samples decreased from 2.3% (5/215) to 0.4% (1/215). The un-stimulated level of IP-10 was significantly higher in the HHC than the ATB and HC groups. The IP-10 responses were strongly associated with extended Mtb exposure time and the degree of smear-positivity of the index cases. The IL-2/IFN-γ ratio in the antigen-stimulated plasma could discriminate LTBI from ATB with a sensitivity of 77.2% and a specificity of 87.2%.

CONCLUSION

The increased Mtb-specific antigen-stimulated expression of IP-10 and IL-2 may be useful for detecting both ATB and LTBI. Combining the QFT with IP-10 and IL-2 could increase the detection accuracy of active TB over the QFT alone.

IP-10 release assays in the diagnosis of tuberculosis infection: current status and future directions

The current state-of-the-art tests for infection with Mycobacterium tuberculosis - the IFN-γ release assays - rely on accurate measurement of the cytokine IFN-γ. Many other potential biomarkers are expressed in concert with IFN-γ, and IP-10 in particular has shown promising results. IP-10 is produced in large amounts, allowing for the development of new and simplified test platforms, such as lateral flow. In this review, we summarize the results of 22 clinical studies exploring the use of IP-10 as an alternative marker to IFN-γ. The studies report that diagnostic accuracy of IP-10 is on par with IFN-γ, but also that IP-10 may be more robust in young children and in HIV-infected individuals with low CD4 cell counts. We conclude the review by presenting limitations of the published works and outline recent developments and future directions.

MIGRAs: are they the new IGRAs? Development of monokine-amplified IFN-γ release assays

IFN-γ release by antigen-specific T cells can be used to track immune responses to infections and vaccines. In recent years, there have been substantial advances in the techniques available to measure IFN-γ release and a generation of such assays are now available for clinical use, as well as in a research setting. Interferon release leads to subsequent release of interferon-responsive chemokines such as MIG and IP-10, thus amplifying the original signal. A number of investigators have assessed whether measurement of these chemokines might provide a sensitive platform for detection of infection and antigen-specific T-cell responses. In this article, we assess the potential of these new approaches. We have termed the new antigen-specific T-cell assays monokine-amplified IFN-γ release assays (MIGRAs). Overall, it seems likely that improvements in the detection threshold could be made by analysis of antigen-triggered chemokines and potentially of other molecules in the future, although whether MIGRAs will provide additional clinical utility still remains to be determined.