T-CELL RESPONSES TO A MIXTURE OF MYCOBACTERIUM-TUBERCULOSIS PEPTIDES WITH COMPLEMENTARY HLA-DR BINDING PROFILES

The T cell response to a mixture of eight peptides derived from sequen ces of the Mycobacterium tuberculosis 16-, 19- and 38-kD antigens (MTB mix-8) has been studied. The peptides were selected on the basis of co mplementary binding to nine HLA-DR molecules (HLA-DR1 to DR9). MTBmix- 8 at 625 and 50 mu g/ml gave rise to significant stimulation (P < 0.05 ) of peripheral blood mononuclear cells (PBMC) from healthy tuberculin -positive and both untreated and treated diseased subjects, but not in ally of a control group of healthy tuberculin-negative subjects, MTBm ix-8 stimulated proliferation of PBMC from healthy tuberculin-positive individuals at lower concentrations than the individual component pep tides. However, the maximal stimulation achieved was only slightly hig her than that achieved with individual peptides. MTBmix-8 also stimula ted the production of interferon-gamma (IFN-gamma) in vitro. Using the mean +/-2 s.d. of the values for IFN-gamma production in the tubercul in-negative population as a cut-off, MTBmix-8 at 6.25 mu g/ml was able to detect infection with a sensitivity of 100% in untreated patients, 87% in treated patients, and 82% in tuberculin-positive controls. The corresponding figures for the most potent single peptide (16p91-110) were: 66% in untreated patients, 71% in treated patients and only 42% in controls. Thus, using the IFN-gamma-based assay, which has the addi tional advantages of speed and does not require radioactivity, the mix ture of peptides is more sensitive than single peptides in diagnosing infection.