IFN-γ Release Assays in the Diagnosis of Latent Tuberculosis Infection among Immunocompromised Adults Gil Redelman-Sidi and Kent A. Sepkowitz Am J Respir Crit Care Med 2013;188: 호흡기 내과 / R4 이민혜 Concise Clinical Review

Introduction Tuberculosis(TB) Initial infection Active TB within the 1 st year Latent tuberculosis infection(LTBI) Lifetime risk of progressing to active TB 3~4% 5%5% ~10%: active TB ~90%: LTBI

Introduction Tuberculin skin test (TST): several limitations –False positive Prior bacillus Calmette-Guérin(BCG) vaccination Exposure to other nontuberculous mycobacteria(NTM) Variability in results due to the operator bias that is inherent to the test –False negative Anergy Recent live virus vaccination (measles, mumps, polio) Recent or overwhelming active TB infection Improper administration of TST Repeatedly tested by TST: booster phenomenon –Sensitivity↑: detection of prior false negative –Specificity↓: false positive(prior BCG vaccination, exposure to NTM)

Introduction Immunocompromised persons with LTBI –↑Risk of progression to active TB –Treatment of LTBI: ↓risk of progression –Already receiving complicated medical regimens  empiric treatment for LTBI impractical –TST: ↑false negative –Alternative methods for diagnosing LTBI

IFN-γ Release Assays IFN- γ release assays (IGRAs) –In vitro blood tests –Cell-mediated immune response that measure T-cell release of IFN- γ after stimulation by antigens unique to Mycobacterium tuberculosis Two IGRAs –T-SPOT.TB assay (Oxford Immunotec, Abingdon, UK) –QuantiFERON-TB Gold In-Tube (QFT-GIT) assay (Cellestis Limited, Carnegie, Australia) Immunocompetent persons: both assays, equal sensitivity to the TST, with improved specificity

IFN-γ Release Assays QFT-GIT –3 rd -generation enzyme-linked immunosorbent assay –Measures the amount of IFN-γ released in response to in vitro stimulation of whole blood with peptides from three TB-specific antigens (ESAT-6, CFP-10, and TB7.7) –International units (IU) per milliliter T-SPOT.TB –Enzyme-linked immunospot (ELISPOT) assay –Count the number of IFN-γ–producing cells (spot-forming cells) in response to stimulation with the TB-specific antigens ESAT-6 and CFP-10 –Performed on separated and counted peripheral blood mononuclear cells

IFN-γ Release Assays Both T-SPOT.TB and QFT-GIT: negative and positive controls –Negative control: measures response in the absence of antigen –Positive control: measures response in the presence of a known mitogen –Indeterminate (1) the negative control tests positive regardless of the response to TB-specific antigens (2) the positive control tests negative, as does the response to TB-specific antigens The response to TB-specific antigens cannot be interpreted in the presence of an indeterminate result –Borderline: T-SPOT.TB Uncertainty for results near the defined cut point, and to increase the certainty that a conversion from a negative to a positive result truly represents newly acquired infection Centers for Disease Control and Prevention

IFN-γ Release Assays Centers for Disease Control and Prevention

IFN-γ Release Assays Aadvantages of IGRAs –Results are numerical  less subject to reader bias –No need for a follow-up visit for reading of results –Not affected by BCG vaccination status Disadvantages of IGRAs –Costs More expensive reagents Need for laboratory Blood-drawing equipment and expertise –Clinical experience is relatively short Prognostic value with respect to the subsequent development of active TB is not as well defined as for TST

Use of IGRAs to Diagnose LTBI in Immunocompromised Patients

LTBI in immunocompromised patients –High risk for TB reactivation –Impaired immunity  low sensitivity of TST  more difficult to diagnose IGRAs have been studied in various populations of immunocompromised patients in the hope that they would perform more reliably than TST

Use of IGRAs to Diagnose LTBI in Immunocompromised Patients

HIV-infected Patients HIV-infected patients with LTBI: annual risk of TB reactivation as high as 10% The risk of reactivation decreases in patients treated with antiretrovirals, but it is still twice that of the general population HIV-infected patients –CD4 + lymphocyte count<100–200 cells/mm3: frequently anergic to skin testing –TST: unreliable method –Both QFT-GIT and T-SPOT.TB: alternative methods to diagnose LTBI

HIV-infected Patients Birth or long-term residence in a TB-endemic country Contact with a patient with active TB Lifestyle-related risk factors (homelessness, incarceration, injection drug use, or work in health care) Chest X-ray findings suggestive of past TB or a history of prior active TB

HIV-infected Patients QFT-GIT: increase in indeterminate results(1.5~16%) – Lower CD4 + lymphocyte counts – Injection drug use – Elevated viral load – Clinical history of prior manifestations of acquired immunodeficiency syndrome (AIDS)

Patients with Immune-mediated Inflammatory Diseases and Candidates for Treatment with Tumor Necrosis Factor-α Inhibitors Patients receiving tumor necrosis factor(TNF)-α inhibitors, which are used in an increasing number of IMIDs –Particularly high risk of TB reactivation –As high as 12 times that of the normal population Adalimumab(Humira ® )and infliximab(Remicade ® ): greatest risk LTBI treatment with isoniazid before beginning TNF-α inhibitor therapy: 74% reduction in the risk of TB activation

Patients with Immune-mediated Inflammatory Diseases and Candidates for Treatment with Tumor Necrosis Factor-a Inhibitors In patients with IMID, use of immunosuppressive medications, particularly corticosteroids: negative and indeterminate QFT-GIT results/not with a negative or indeterminate T-SPOT.TB

Patients Receiving Dialysis for End-Stage Renal Disease Uremia is associated with impaired immunity Chronic renal failure, whether or not they are receiving dialysis: increased risk for reactivation of latent TB, estimated to be 2.4-fold higher than the risk of a healthy person Patients receiving dialysis frequently exhibit anergy to skin testing

Patients Receiving Dialysis for End-Stage Renal Disease In patients receiving dialysis for ESRD, QFT-GIT may be more sensitive for diagnosing LTBI than TST and perhaps T-SPOT.TB A systematic review evaluated 30 studies comparing the IGRAs with TST in patients with ESRD – QuantiFERON assays were more strongly associated with clinical risk factors for TB than TST – T-SPOT.TB did not significantly differ from TST regarding association with clinical risk factors

Other Immunocompromised Populations, Including Cancer and Transplant Hematologic malignancies or head and neck cancers: increased risk of developing active TB compared with the general population Solid organ transplant recipients: risk of developing active TB may be 20- to 74- fold higher than in the general population

Other Immunocompromised Populations, Including Cancer and Transplant One of the studies: T-SPOT.TB may be more sensitive than TST in the presence of leukopenia, and that it may correlate better than TST with clinical risk factors for LTBI

Other Immunocompromised Populations, Including Cancer and Transplant In a one study, all solid organ transplant candidates were tested by QuantiFERON Gold or QFT-GIT –IGRA positivity correlated with the presence of clinical risk factors for LTBI –Interestingly, more than 40% of liver transplant candidates had an indeterminate result, compared with only 10% of kidney transplant candidates

Other Immunocompromised Populations, Including Cancer and Transplant Given the paucity of data, it is difficult to make any definite recommendations regarding the use of IGRAs to diagnose LTBI in these populations As TST remains the best studied test in these populations, we would suggest that it be the test of choice pending further data

Available Guidelines The CDC(US) –Use of IGRAs in place of (but not in addition to) TST in any situation in which TST is recommended –High-risk population, if initial testing by TST or IGRA is negative  performance of both tests should be considered  positive result on either sufficient to diagnose LTBI The ECDC(Europe) –Immunocompromised patients  TST+IGRAs The CDC and the ECDC both guidelines –Repeating testing in the case of an indeterminate result (in either T-SPOT.TB or QFT-GIT) or a borderline result (in T-SPOT.TB) in all patients

Available Guidelines The U.K. guidelines –HIV and CD4 + cell counts<200 cells/mm3: TST+IGRA  consider LTBI treatment if either test is positive –HIV and CD4 + cell counts of 200–500 cells/mm3: TST+IGRA or IGRA alone –HIV-infected persons with higher CD4 + cell counts: treated as immunocompetent individuals –For other immunocompromised persons: IGRA alone or TST+IGRA  consider LTBI treatment if either test is positive The Canadian guidelines –Immunocompromised patients: initially by TST –If TST is negative and the clinician is still concerned about the possibility of LTBI  IGRA can be performed: positive result considered diagnostic for LTBI –T-SPOT.TB: preferable to QFT-GIT retain sensitivity in immunocompromised patients

Available Guidelines The WHO guideline: discourage the use of IGRAs among HIV-infected patients in resource limited settings –Neither IGRA is consistently more sensitive than the TST –More data are available supporting the predictive value of TST –Cost of IGRAs –Need for well-equipped laboratories with trained personnel –May not be readily available in resource-limited settings

Available Guidelines The Korean guidelines (2011)

Use of IGRAs to Diagnose Active TB Two meta-analyses: IGRAs were neither sensitive nor specific in diagnosing active TB among HIV-infected patients Discourage use of IGRAs as stand alone tests to diagnose active TB

Conclusions Current data do not suggest that IGRAs have a clear across-the-board advantage over TST in immunocompromised patients, and they are unlikely to entirely replace TST in this role However, data do suggest that IGRAs have specific advantages in certain patient populations and in particular situations –T-SPOT.TB: less affected by low CD4 + cell count in HIV-infected persons, and by corticosteroid use in patients with IMID –QFT-GIT: retain sensitivity in patients with dialysis compared with TST and, perhaps, T-SPOT.TB Better studies are needed to more accurately define the usefulness of IGRAs in immunocompromised patients