T cells that spot TB by sensing lipid signals

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), remains the world’s leading infectious killer, yet many parts of the human immune response to this pathogen are still unclear. One understudied route involves non-classical T-cell pathways that recognise lipids rather than the protein fragments more commonly discussed in vaccine design. CD1c-autoreactive T-cells, which respond to self-lipids presented by the antigen-presenting molecule CD1c, are commonly found in human blood, but researchers have not known how these cells behave during TB. In work led by Salah Mansour, investigators set out to test whether CD1c-expressing antigen-presenting cells (APCs) and Mtb infection influence these T cells. Using engineered human APC systems and complementary single-cell transcriptomic profiling of cells taken directly from people, the team mapped where CD1c appears in disease and how Mtb affects its display. They found CD1c present within human TB granulomas, the organized immune structures that form around Mtb, but also observed that Mtb reduces CD1c expression on the APCs it infects — a change consistent with an immune evasion strategy by the bacterium.

To see how CD1c-autoreactive T-cells respond, the researchers used engineered human APC systems alongside single-cell RNA-sequencing to define the ex vivo phenotypic landscape of these T cells. Across those approaches they showed that CD1c-autoreactive T-cells react more strongly when presented with Mtb-infected CD1c+ APCs than with uninfected cells. This heightened response depended on CD1c-dependent recognition and involved increased activation, signs of cytotoxicity, and secretion of a range of cytokines. In laboratory assays the CD1c-autoreactive T-cells were able to reduce the relative Mtb burden inside infected phagocytes, indicating an ability to control bacterial levels in vitro. At the single-cell level, transcriptomic profiles revealed cytotoxic effector-memory programmes and the expression of antimicrobial molecules, giving a molecular explanation for how these T-cells can attack infected APCs and contribute to killing or suppressing Mtb.

Together the findings define a human CD1c-restricted T-cell response to Mtb-infected APCs and point to autoreactive CD1c-restricted T-cells as a candidate cellular axis for lipid-directed immunity in TB. The observation that Mtb down-modulates CD1c on infected APCs suggests the bacterium may evade this lipid-based surveillance, highlighting an interaction that could be important to disease progression or control. By linking functional assays with single-cell transcriptomics, the study provides a clearer view of the cells’ cytotoxic and antimicrobial programmes, and where they sit within infected tissue. While more work will be needed to translate these insights into treatments or vaccines, the results open a path for future research that focuses on lipid presentation and CD1c biology as potential targets to boost immunity against TB.