Performance comparison of QuantiFERON-TB Gold In-Tube and QuantiFERON-TB Gold Plus in detecting Mycobacterium tuberculosis infection among HIV patients in China

Introduction

Approximately one-quarter of the world’s population is believed to have Mycobacterium tuberculosis infection, and within this group, 5% to 10% will develop active tuberculosis over the course of their lives (World Health Organization, 2020). In pursuit of the 2035 goal outlined in the End TB Strategy to reduce the tuberculosis incidence rate by 90%, the World Health Organization (WHO) suggests the screening and preventive treatment of Mycobacterium tuberculosis infection among populations at elevated risk including persons living with HIV (PLHIV) (Uplekar et al., 2015). The WHO recommends both the tuberculin skin test (TST) and the interferon gamma release assay (IGRA) for diagnosing Mycobacterium tuberculosis infection (World Health Organization, 2020). However, these tests present significant limitations when applied to PLHIV. TST is often ineffective in detecting Mycobacterium tuberculosis infection in PLHIV, especially in individuals with CD4 lymphocyte counts below 200 cells/mm³ (Fisk et al., 2003; Markowitz et al., 1993). The accuracy of IGRAs in PLHIV is under debate. A systematic review and meta-analysis indicated that IGRAs performed similarly to TSTs in detecting Mycobacterium tuberculosis among PLHIV, suggesting potential insensitivity of IGRAs (Cattamanchi et al., 2011). On June 8, 2017, the Food and Drug Administration (FDA) granted approval to the QuantiFERON-TB Gold Plus (QFT-Plus), a fourth-generation QFT test, replacing the QuantiFERON-TB Gold In-Tube (QFT-GIT). QFT-Plus represents a new-generation iteration of QFT-GIT and has gained widespread utilization in the diagnosis of Mycobacterium tuberculosis infection. The primary distinction between QFT-Plus and QFT-GIT lies in the inclusion of two Mycobacterium tuberculosis-specific antigen-coated tubes within QFT-Plus, designated as TB1 and TB2. While TB1 comprises extended peptides from ESAT-6 and CFP-10 (omitting TB7.7), TB2 incorporates six truncated peptides, alongside the same constituents present in TB1. This design prompts both CD4 and CD8 T-cell immune responses (Nikolova et al., 2013). CD8+ cytotoxic T cells have emerged as a crucial element in the host’s immune response to and regulation of Mycobacterium tuberculosis. Research has demonstrated notably heightened CD8+ T-cell reactions in individuals with smear-positive or active pulmonary TB, in comparison to those with smear-negative or Mycobacterium tuberculosis infection (Day et al., 2011; Rozot et al., 2013). Robust CD8+ T-cell responses have also been observed in individuals recently exposed to patients with active tuberculosis infections (Nikolova et al., 2013). Additionally, patients coinfected with Mycobacterium tuberculosis and PLHIV have exhibited the ability to sustain CD8-positive T-cell antigen responses to Mycobacterium tuberculosis, even in the context of diminished CD4+ T-cell counts. In individuals coinfected with Mycobacterium tuberculosis and HIV, it has been demonstrated that they can sustain CD8+ T-cell antigen responses to Mycobacterium tuberculosis despite having low CD4+ T-cell counts, as evidenced by previous studies (Sutherland et al., 2010). QFT-Plus was expected to amplify sensitivity, specifically among individuals with compromised immune systems. To the best of our knowledge, no direct comparative study has been conducted to evaluate the performance of QFT-GIT and QFT-Plus in diagnosing Mycobacterium tuberculosis infection among PLHIV in China. Thus, we designed this cross-sectional study to directly compare the diagnostic performance of QFT-GIT and QFT-Plus for detecting Mycobacterium tuberculosis infection in this population. Additionally, we assessed the quantitative changes in IFN-γ levels measured by QFT-GIT after preventive treatment to explore its potential role in monitoring treatment response.

Materials and Methods

Results

Discussion

In this research, we assessed the diagnostic potential of both QFT-GIT and QFT-Plus in detecting Mycobacterium tuberculosis infection across PLHIV in a prison hospital. There was no notable distinction observed in FN-γ levels when comparing the QFT-GIT and QFT-Plus assays and the effectiveness of QFT-GIT and QFT-Plus in identifying Mycobacterium tuberculosis infection among PLHIV with relatively higher CD4 count levels was found to be comparable, and the correspondence between these two tests within the PLHIV group demonstrated a strong level of concurrence, exceeding 90%. Furthermore, our investigation revealed that among PLHIV regardless of whether it’s the chemotherapy regimen or the immunotherapy regimen, preventive treatment for Mycobacterium tuberculosis infection would lead to a reduction in IFN-γ levels.

A review and meta-evaluation revealed a 1.3% increase in sensitivity for QFT-Plus compared to QFT-GIT. However, additional evaluation is needed to ascertain the sensitivity of QFT-Plus in individuals with compromised immune systems. In prior research, the agreements rates between QFT-GIT and QFT-Plus in immunocompromised individuals were about 94% (Ryu et al., 2018; Xu et al., 2022). QFT-Plus could potentially offer greater utility in identifying Mycobacterium tuberculosis infection among elderly and immunocompromised individuals, particularly in situations involving limited sample sizes (Chien et al., 2018; Kim, Jo & Shim, 2020). According to a particular study’s conjecture, due to the inclusion of two tubes in the QFT-Plus assay, a positive outcome in either tube is categorized as a positive result. This alteration could potentially lead to an augmentation in the proportion of positive findings (Hogan et al., 2019). Xu et al. (2022) found that among individuals with varying immune statuses, the QFT-Plus assay demonstrated an elevated rate of positive results in comparison to the QFT-GIT assay. Additionally, significant distinctions were observed between the findings of these two assays (Xu et al., 2022). Nevertheless, in our study, the prevalence of Mycobacterium tuberculosis infection measured by QFT-GIT slightly exceeded that of QFT-Plus, albeit without statistical significance. This trend could potentially be attributed to the fact that all PLHIV included in the study exhibited well-maintained CD4 counts, indicating relatively robust immune systems. QFT-Plus could potentially exhibit a significant positivity rate in blood samples collected from individuals with tuberculosis and co-existing HIV infection, even encompassing those with CD4 T-cell counts as low as 100/µ (Telisinghe et al., 2017). Another contributing factor could be the application of preventive treatments for Mycobacterium tuberculosis infection among all PLHIV, which might have contributed to the narrowing of the disparity between QFT-GIT and QFT-Plus results.

Several studies have highlighted a substantial increase in IFN-γ levels within TB2 tubes when contrasted with TB and TB1 tubes. Moreover, TB1 tubes have shown noticeably higher IFN-γ levels than TB tubes (Won et al., 2020). Notably, some investigations have indicated that there is no statistically significant difference in IFN-γ levels among TB, TB1, and TB2 tubes (Xu et al., 2022). Nevertheless, in our study, the IFN-γ levels observed in TB tubes were comparable to those in TB2 tubes, yet they were higher than the levels in TB1 tubes. This discrepancy could potentially be attributed to the omission of the TB7.7 peptide in TB1 tubes as opposed to TB tubes (Hoffmann et al., 2016; Pieterman et al., 2018).

We made another intriguing discovery during our research, revealing a noteworthy trend in the IFN-γ levels of QFT-GIT after the implementation of preventive treatment. Impressively, these levels exhibited a distinct decrease, demonstrating a significant response to the intervention. Additionally, it is noteworthy that approximately 23.1% of the subjects underwent a revision, further underscoring the impact of the preventive measures. Effector T-cell responses following brief incubation with Mycobacterium tuberculosis-specific antigens, as employed in custom-made IGRAs, exhibited a correlation with both antigen presence and bacillary burden. This suggests their potential utility as a treatment response marker (Carrara et al., 2004). Reversion of IGRA scores following treatment for Mycobacterium tuberculosis infection has been noted in various studies. In the most extensive cohort reported to date by Chee et al. (2007) among 226 treated close contacts, approximately 38% of the scores reverted based on the manufacturer’s criteria for the T-SPOT.TB assay. In a more recent study involving 74 individuals who were QFT-IT-positive tuberculosis contacts, Lee et al. (2010) observed a comparable reversion rate of 42%. In our study, the IFN-γ levels of post-treatment was much lower than that of pre-treatment, which could stem from the observation that tuberculosis infection in PLHIV in prison is more prone to being recently acquired like younger subjects (Goletti et al., 2007). Furthermore, the decrease in IFN-γ response is achieved with greater ease and rapidity following the treatment of recent contacts who have not been previously exposed to Mycobacterium tuberculosis (Goletti et al., 2007). However, Xin et al. (2022) conducted a comprehensive randomized controlled study involving 910 individuals. These participants were categorized into three groups: Group A received 8 weeks of once-weekly rifapentine plus isoniazid, Group B received 6 weeks of twice-weekly rifapentine plus isoniazid, and Group C served as untreated controls. Remarkably, their findings indicated comparable rates of persistent QFT-GIT reversion across all three groups (P = 0.512). Indeed, in the absence of a parallel control group, the task of determining whether the decline signified a treatment’s influence, the organic resolution of the condition, or intrinsic oscillations in T-cell reactions within the same persons became a formidable challenge. These oscillations might arise from elements such as immune senescence or mere variability around the predefined threshold, owing to the reproducibility of the testing procedure (Banaei, Gaur & Pai, 2016; van Zyl-Smit et al., 2009). Further investigations were required to determine whether reduced IFN-γ levels should be employed as a means to monitor the host’s reaction to treatment for Mycobacterium tuberculosis infection.

Our study has several limitations that should be acknowledged. Firstly, the absence of a control group limits the robustness of our conclusions, as it restricts our ability to attribute observed effects solely to the interventions studied. Future studies incorporating well-defined control groups are essential to validate our results and strengthen the evidence base. Secondly, we did not conduct the T-SPOT.TB or TST assays concurrently, which could have served as reference standards for assessing the precision of the QFT-GIT and QFT-Plus assays. This omission limits our ability to fully evaluate the comparative accuracy of these assays. Thirdly, we were unable to differentiate whether the decline in IFN-γ levels resulted from preventive treatment, natural clearance, or within-subject variability in T-cell responses, given the absence of a parallel control group. This uncertainty complicates the interpretation of changes in IFN-γ levels over time. Lastly, while IGRA has acknowledged limitations in high-risk settings, we employed it as a practical tool for evaluating treatment efficacy due to the lack of more definitive biomarkers for Mycobacterium tuberculosis infection management. This approach, although widely used, introduces inherent uncertainties that should be considered when interpreting our findings.

In conclusion, the diagnostic performance of QFT-GIT and QFT-Plus for detecting Mycobacterium tuberculosis infection among PLHIV with relatively higher CD4 counts was comparable. The concordance between these two assays within the PLHIV group exhibited a robust agreement, surpassing the 90% threshold. Furthermore, our investigation revealed that irrespective of whether the treatment involved a chemotherapy regimen or an immunotherapy regimen, preventive Mycobacterium tuberculosis infection interventions among PLHIV led to a consistent decrease in IFN-γ levels.

Supplemental Information