Mycobacterium tuberculosis-reactive CD8+ T lymphocytes:: The relative contribution of classical versus nonclassical HLA restriction

Previous studies in mice and humans models have suggested an important role for CD8(+) T cells in host defense to Mycobacterium tuberculosis (Mtb), In humans, CD8(+) Mtb-reactive T cells have been described that are HLA-A2-, B52-, as well as CD1-restricted, Recently, we have described Mtb-specific CD8(+) T cells that are neither HLA-A-, B-, or C- nor group 1 CD1-restricted, At present, little is known about the relative contribution of each of these restriction specificities to the overall CD8(+) response to Mtb, An IFN-gamma enzyme-linked immunospot assay was used to determine the frequency of Mtb-reactive CD8(+) T cells directly from PBMC, The effector cell frequency among five healthy; purified protein derivative-positive subjects was 1/7,600 +/- 4,300 compared with 1/16,000 +/- 7,000 in six purified protein derivative-negative controls. To determine the frequencies of classically, CD1-, and nonclassically restricted cells, a limiting dilution analysis was performed. In one purified protein derivative-positive subject, 192 clones were generated using Mtb-infected dendritic cells (DC), clones were assessed for reactivity against control autologous DC, Mtb-infected autologous DC, and HLA-mismatched CD1(+) targets (DC), as well as HLA-mismatched CD1(-) targets (macrophages), Of the 96 Mtb-reactive CD8(+) T cell clones, four (4%) were classically restricted and 92 (96%) were nonclassically restricted. CD1-restricted cells were not detected. Of the classically restricted cells, two were HLA-B44 restricted and one was HLA-B14 restricted. These results suggest that while classically restricted CD8(+) lymphocytes can be detected, they comprise a relatively small component of the overall CD8(+) T cell response to Mtb, Further definition of the nonclassical response may aid development of an effective vaccine against tuberculosis.