Interferon-gamma Release Tests

We have previously published systematic and narrative reviews on IGRA accuracy and performance in various subgroups [5] (link), [6] (link), [12] (link), [13] (link), [14] (link)). We updated the database searches that were done in previous systematic reviews and searched the literature for relevant IGRA studies (up to November 2009) that reported data on within-subject variability of IGRAs and/or data on effect of TST on subsequent IGRA results. We searched PubMed, Embase and Biosis and Web of Science, and reviewed citations of all original articles published in all languages.
The search terms used in database searching included: ((interferon-gamma release assay*) OR (T-cell-based assay*) OR (antigen-specific T cell*) OR (T cell response*) OR (T-cell response*) OR (interferon*) OR (interferon-gamma) OR (gamma-interferon) OR (IFN) OR (elispot) OR (ESAT-6) OR (CFP-10) OR (culture filtrate protein) OR (Enzyme Linked Immunosorbent Spot) OR (Quantiferon* OR Quantiferon-TB Gold)) AND ((tuberculosis OR mycobacterium tuberculosis)).
In addition to database searches, we reviewed bibliographies of previous reviews and guidelines on IGRAs, and also screened the citations of relevant original articles. Experts in the field and commercial test manufacturers were also contacted to obtain relevant citations. No language restrictions were imposed and full-length papers as well as conference abstracts were included (to limit potential publication bias).
We included studies of QuantiFERON-TB Gold (QFT-G, also known as QFT-2G), QuantiFERON-TB Gold In-Tube (QFT-GIT, also known as QFT-3G) [Cellestis Limited, Victoria, Australia], and the T-SPOT.TB [Oxford Immunotec, Oxford, UK] or its pre-commercial ELISPOT version. Where relevant, we included in-house, short-incubation (overnight) IFN-γ assays with RD1 antigens as well, to increase the number of relevant studies.
For studies assessing reproducibility (defined as within-subject repeatability over time, under similar conditions), the study had to have repeated (at least two) IGRA assays (same IGRA) done on the same group of subjects, preferably in a setting with limited TB exposure and without an antecedent TST within 6 months. If reproducibility was done in a high TB incidence setting where exposure-related changes are likely, then repeat tests should have been done over a short period of <6 weeks (to avoid the confusion between conversions (or new infections) and natural variations in T-cell responses). For studies assessing boosting of IGRA results due to a prior TST, the study sample must have had at least one IGRA assay done before and after tuberculin skin testing and not performed in the context of a contact or outbreak study in a high incidence setting (again, to avoid the confusion between true conversion and boosting).
We did not consider reproducibility data where two or more tests were done on the same sample at the same time (e.g. two tests done using samples from the same blood draw); this would not have been informative for our objective of determining the within-person variability when the test is repeated over time (serial testing). Also, we did not consider other forms of reproducibility data, such as inter-laboratory variation, variations between lab technologists, batch-to-batch variations, variations due to different incubation times, etc.

We validated specificity of the MTBC nested PCR with IS6110-specific primers using granuloma lung tissues from a naturally M. tuberculosis–infected long-tailed macaque (Figure 1). We confirmed M. tuberculosis infection in the macaque by mycobacterium culture and interferon gamma release assay, using methods reported elsewhere (24 (link)). We collected and extracted granuloma lung tissues for genomic DNA using a QIAGEN Virus/Pathogen Mini Kit. We purified the products obtained from 181-bp nested PCR testing of the naturally M. tuberculosis–infected macaque and the 19 nested PCR–positive samples randomly selected from populations of wild rhesus macaques from Ban Phon Kor and Ban Sang School and Burmese long-tailed macaques from Tham Pra Khayang and Mangrove Forest Research Center using the GenUP Exo Sap Kit (Biotechrabbit, https://www.biotechrabbit.com) and submitted the samples to Macrogen (https://www.macrogen.com) for DNA sequencing. We aligned nucleotide sequences with published M. tuberculosis sequences accessed from GenBank using MEGA X software (25 (link)). After all amplicons from the M. tuberculosis sequences from macaques in our study showed 100% homology with published sequences, we used an IS6110-specific nested PCR protocol to determine the sensitivity of the M. tuberculosis nested PCR technique, using genomic DNA of the M. tuberculosis H37Rv (ATCC27294) strain, serially diluted (1:10) from 1 ng to 1 fg (26 (link)). We designated the lowest concentration of M. tuberculosis H37Rv that we could detect by nested PCR as the limit of detection (LOD) for this technique.

This was a single-center, retrospective study of index patients and close-contact HCWs who were subjected to contact investigation after TB exposure during hospitalization at the NMC (Seoul, South Korea) from January 2018 to July 2021. We reviewed the exposure reports and electronic medical records of index patients and HCWs.
Active TB was diagnosed if any of the following results were present: positive acid-fast bacilli (AFB) culture or Xpert MTB/RIF assay (Cepheid, Sunnyvale, CA, USA), either from sputum or bronchial aspirate. If TB was diagnosed during hospitalization without isolation, the patient was promptly relocated to the isolation unit, and an immediate report to the infection control team was made by the nurse in charge. Each department collects a complete list of HCWs with close contact and sends it to the infection control team, in accordance with the NMC infection control guidelines. The infection control team collects information from the participants on the list through telephone surveys and notifies them to perform chest radiography and interferon gamma-releasing assay (IGRA) at the pulmonology clinic. The test results and the following clinic visits are monitored by the infection control team and are published in exposure reports. The aforementioned information included in exposure reports was thoroughly reviewed by the study.