Detailed characterization of human Mycobacterium tuberculosis specific HLA-E restricted CD8⁺ T cells

HLA-E presented antigens are interesting targets for vaccination given HLA-Es' essentially monomorphic nature. We have shown previously that Mycobacterium tuberculosis (Mtb) peptides are presented by HLA-E to CD8⁺ effector T cells, but the precise phenotype and functional capacity of these cells remains poorly characterized. We have developed and utilized in this study a new protocol combining HLA-E tetramer with intracellular staining for cytokines, transcription factors and cytotoxic molecules to characterize these cells in depth. We confirm in this study the significantly increased ex vivo frequency of Mtb-peptide/HLA-E-TM⁺ CD8⁺ T cells in the circulation of patients with active tuberculosis (TB). HLA-E restricted CD8⁺ T cells from TB patients produced more IL-13 than cells from controls or subjects with latent tuberculosis infection (LTBI). Compared to total CD8⁺ T cells, HLA-E restricted cells produced more IFNγ, IL-4, IL-10, and granulysin but less granzyme-A. Moreover, compared to "classical" Mtb specific HLA-A2 restricted CD8⁺ T cells, HLA-E restricted CD8⁺ T cells produced less TNFα and perforin, but more IL-4. In conclusion, HLA-E restricted- Mtb specific cells can produce Th2 cytokines directly.