T-cell-based IFN-γ release assays for the diagnosis of latent tuberculosis infection: have they met our expectations?

Mycobacteria

The immunocompromised host is at increased risk of Mycobacterium tuberculosis complex and nontuberculous mycobacteria infection. Although Mycobacterium tuberculosis complex is a significant mycobacterial pathogen, nontuberculous mycobacteria causes substantial disease in those with suppressed immune responses. Mycobacterial infections can cause significant morbidity and mortality in this patient population, and rapid identification and susceptibility testing of the mycobacterial species is paramount to patient management and outcomes. Mycobacterial diagnostics has undergone some significant advances in the last two decades with immunodiagnostics (interferon gamma release assay), microscopy (light-emitting diode), culture (automated broth-based systems), identification (direct PCR, sequencing and matrix-assisted laser-desorption ionization–time of flight mass spectrometry) and susceptibility testing (molecular detection of drug resistance from direct specimens or positive cultures). Employing the most rapid and sensitive methods in the mycobacterial laboratory will have a tremendous impact on patient care and, in the case of Mycobacterium tuberculosis complex, in the control of tuberculosis.

The diagnostic potential of MPT63-derived HLA-A*0201-restricted CD8+ T-cell epitopes for active pulmonary tuberculosis

MPT63 protein is found only in Mycobacterium tuberculosis complex, including M. tuberculosis and M. bovis. Detection of MPT63-specific IFN-γ-secreting T cells could be useful for the diagnosis of tuberculosis (TB) diseases. In the present study, the HLA-A*0201 restriction of ten predicted MPT63-derived CD8(+) T-cell epitopes was assessed on the basis of T2 cell line and HLA-A*0201 transgenic mice. The diagnostic potential of immunogenic peptides in active pulmonary TB patients was evaluated using an IFN-γ enzyme-linked immunospot assay. It was found that five peptides bound to HLA-A*0201 with high affinity, whereas the remaining peptides exhibited low affinity for HLA-A*0201. Five immunogenic peptides (MPT6318-26 , MPT6329-37 , MPT6320-28 , MPT635-14 and MPT6310-19 ) elicited large numbers of cytotoxic IFN-γ-secreting T cells in HLA-A*0201 transgenic mice. Each of the five immunogenic peptides was recognized by peripheral blood mononuclear cells from 45% to 73% of 40 HLA-A*0201 positive TB patients. The total diagnostic sensitivity of the five immunogenic peptides was higher than that of a T-SPOT.TB assay (based on ESAT-6 and CFP-10) (93% versus 90%). It is noticeable that the diagnostic sensitivity of the combination of five immunogenic peptides and T-SPOT.TB assay reached 100%. These MPT63-derived HLA-A*0201-restricted CD8(+) T-cell epitopes would likely contribute to the immunological diagnosis of M. tuberculosis infection and may provide the components for designing an effective TB vaccine.