PRF1 and tuberculosis: Nevertheless, to date, most new TB vaccines have been reported to induce reasonable CD4+ T-cell responses, but relatively negligible CD8+ T-cell responses, despite evidence from recent studies indicating that CD8+ T cells mediate essential roles in protective immunity against TB (5, 37–39) including cytolytic functions to kill Mtb-infected cells via granule-mediated function (via perforin, granzymes, and granulysin) and Fas-Fas ligand interaction to induce apoptosis.