Performance of a simple flow cytometric assay in diagnosing active tuberculosis

Area of Science:

• Immunology
• Infectious Diseases
• Diagnostics

Background:

• Tuberculosis (TB) remains a global health challenge, necessitating improved diagnostic tools.
• Accurate diagnosis is crucial for effective treatment and control, particularly in populations with high HIV prevalence.
• Current diagnostic methods have limitations, driving the search for more sensitive and specific assays.

Purpose of the Study:

• To evaluate a novel flow cytometric assay measuring Mycobacterium tuberculosis-specific CD4 T-cell responses (OX40 assay) as a diagnostic tool for active TB.
• To assess the assay's performance in a Thai population, including individuals with and without HIV infection.
• To compare the OX40 assay's diagnostic accuracy with the Xpert MTB/RIF assay.

Main Methods:

• Peripheral blood mononuclear cells (PBMC) from 133 participants with suspected active TB were cryopreserved.
• CD4 T-cell responses were measured using the OX40 assay after stimulation with RD-1 antigens (CFP-10 + ESAT-6).
• Assay performance (sensitivity, specificity) was calculated and compared to culture-confirmed TB and Xpert MTB/RIF results.

Main Results:

• The OX40 assay demonstrated an overall sensitivity of 94.7% and specificity of 71.9% for active TB.
• In HIV-infected participants, the assay achieved a sensitivity of 100% and a specificity of 92.9%.
• The assay performed exceptionally well in individuals with active TB and HIV coinfection.

Conclusions:

• The OX40 assay is a highly sensitive diagnostic tool for active tuberculosis.
• The assay shows particular promise for diagnosing TB in HIV-infected individuals.
• This flow cytometric approach offers a valuable addition to TB diagnostic strategies, especially in resource-limited settings.