Altered thymic differentiation and modulation of arthritis by invariant NKT cells expressing mutant ZAP70

RORγt inhibition selectively targets IL-17 producing iNKT and γδ-T cells enriched in Spondyloarthritis patients

Dysregulated IL-23/IL-17 responses have been linked to psoriatic arthritis and other forms of spondyloarthritides (SpA). RORγt, the key Thelper17 (Th17) cell transcriptional regulator, is also expressed by subsets of innate-like T cells, including invariant natural killer T (iNKT) and γδ-T cells, but their contribution to SpA is still unclear. Here we describe the presence of particular RORγt⁺T-bet^loPLZF^- iNKT and γδ-hi T cell subsets in healthy peripheral blood. RORγt⁺ iNKT and γδ-hi T cells show IL-23 mediated Th17-like immune responses and were clearly enriched within inflamed joints of SpA patients where they act as major IL-17 secretors. SpA derived iNKT and γδ-T cells showed unique and Th17-skewed phenotype and gene expression profiles. Strikingly, RORγt inhibition blocked γδ17 and iNKT17 cell function while selectively sparing IL-22⁺ subsets. Overall, our findings highlight a unique diversity of human RORγt⁺ T cells and underscore the potential of RORγt antagonism to modulate aberrant type 17 responses.

Unveiling the regulation of NKT17 cell differentiation and function

Invariant natural killer T cells (iNKTs) are distinct from conventional T cells. iNKT cells express a semi-invariant T cell receptor (TCR) that can specifically recognize lipid antigens presented by CD1d, an MHC class I-like antigen-presenting molecule. Currently, iNKT cells are distinguished in three functionally distinct subsets. Each subset is defined by lineage-specifying factors: T-bet shapes the fate of NKT1 subset that mainly secretes IFNγ, Gata3 specifies the NKT2 subset that produces robustly IL-4 whereas RORγt seals the differentiation of NKT17 subset that secretes IL-17. In the present review, the focus is placed on the regulation of NKT17 specification and their function.

The Role of Autophagy in iNKT Cell Development

CD1d-restricted invariant natural killer T (iNKT) cells are innate-like T cells that express an invariant T cell receptor (TCR) α-chain and recognize self and foreign glycolipid antigens. They can rapidly respond to agonist activation and stimulate an extensive array of immune responses. Thymic development and function of iNKT cells are regulated by many different cellular processes, including autophagy, a self-degradation mechanism. In this mini review, we discuss the current understanding of how autophagy regulates iNKT cell development and effector lineage differentiation. Importantly, we propose that iNKT cell development is tightly controlled by metabolic reprogramming.

CD69 prevents PLZFhi innate precursors from prematurely exiting the thymus and aborting NKT2 cell differentiation

While CD69 may regulate thymocyte egress by inhibiting S1P₁ expression, CD69 expression is not thought to be required for normal thymocyte development. Here we show that CD69 is in fact specifically required for the differentiation of mature NKT2 cells, which do not themselves express CD69. Mechanistically, CD69 expression is required on CD24⁺ PLZF^hi innate precursors for their retention in the thymus and completion of their differentiation into mature NKT2 cells. By contrast, CD69-deficient CD24⁺ PLZF^hi innate precursors express S1P₁ and prematurely exit the thymus, while S1P₁ inhibitor treatment of CD69-deficient mice retains CD24⁺ PLZF^hi innate precursors in the thymus and restores NKT2 cell differentiation. Thus, CD69 prevents S1P₁ expression on CD24⁺ PLZF^hi innate precursor cells from aborting NKT2 differentiation in the thymus. This study reveals the importance of CD69 to prolong the thymic residency time of developing immature precursors for proper differentiation of a T cell subset.

CD69 competes with S1P₁, a chemokine receptor mediating thymocyte egress, for surface expression on thymocytes, but whether CD69 is required for normal thymic development is unclear. Here the authors show that CD69 and S1P₁ synergize to control type 2 natural killer (NKT2) cells differentiation by modulating the thymic egress of NKT2 precursor.