Background: The identification and treatment of individuals with tuberculosis (TB) is a global public health priority. Accurate diagnosis of pulmonary active TB (ATB) disease remains challenging and relies on extensive medical evaluations and detection of Mycobacterium tuberculosis (Mtb) in the patients' sputum. Further, the response to treatment is monitored by sputum culture conversion, which takes several weeks for results. Here, we sought to identify blood-based host biomarker associated with ATB and hypothesized that the frequencies of Mtb-specific CD4+ T cells expressing active caspase-3 would be associated with Mtb load in vivo and could thus provide a gauge of Mtb infection. Caspase-3, a member of the caspase family of cysteine proteases, is highly expressed in CD4 effector T cells downstream of anti-CD3 mediated T cell receptor (TCR) activation and has been shown to regulate T cell activation, cell cycle entry, proliferation and apoptosis.
Methods: Using polychromatic flow cytometry, we evaluated the expression of active caspase-3 on Mtb-specific CD4+ T cells from individuals with asymptomatic latent Mtb infection (LTBI) (n=22), ATB (n=18), and from ATB patients undergoing anti-TB treatment (n=7).
Results: Frequencies of Mtb-specific IFN-g+CD4+ T cells that expressed active caspase-3 were substantially higher in subjects with ATB compared to those with LTBI (Figure 1) suggesting that apoptotic pathways are operant during pulmonary active. This marker accurately classified ATB and LTBI status with cutoff value of 3% (black dot line) with 95% specificity and greater than 100% sensitivity.
This marker also distinguished individuals with untreated ATB from those who had successfully completed anti-TB treatment and correlated with decreasing mycobacterial loads during treatment (Figure 2).
Conclusion: We have identified a host blood-based biomarker on Mtb-specific CD4+ T cells that discriminate between ATB and LTBI and provide a tool for monitoring treatment response and cure.
S. Cagle, None
S. M. Ray, None
J. Rengarajan, None