Lethal-7 (let-7) microRNAs are the most abundant in the genome but their role in developing thymocytes is unclear. We now report that let-7 miRNAs target Zbtb16 mRNA, which encodes the lineage-specific transcription factor PLZF, to post-transcriptionally regulate PLZF expression and NKT cell effector function. Dynamic up-regulation of let-7 miRNAs during NKT thymocyte development down-regulates PLZF expression and directs terminal differentiation into interferon-γ-producing NKT1 cells. Without let-7 up-regulation, NKT thymocytes maintain high PLZF expression and terminally differentiate into IL-4-producing NKT2 and IL-17-producing NKT17 cells. Let-7 up-regulation in developing NKT thymocytes can be signaled by IL-15, vitamin D and retinoic acid. Such miRNA targeting of a lineage-specific transcription factor constitutes a new level of developmental regulation in the thymus.

Type I diabetes is associated with bone loss and marrow adiposity. To identify early events involved in the etiology of diabetic bone loss, diabetes was induced in mice by multiple low dose streptozotocin injections. Serum markers of bone metabolism and inflammation as well as tibial gene expression were examined between 1 and 17 days post-injection (dpi). At 3 dpi, when blood glucose levels were significantly elevated, body, fat pad and muscle mass were decreased. Serum markers of bone resorption and formation significantly decreased at 5 dpi in diabetic mice and remained suppressed throughout the time course. An osteoclast gene, TRAP5 mRNA, was suppressed at early and late time points. Suppression of osteogenic genes (runx2 and osteocalcin) and induction of adipogenic genes (PPARgamma2 and aP2) were evident as early as 5 dpi. These changes were associated with an elevation of serum cytokines, but more importantly we observed an increase in the expression of cytokines in bone, supporting the idea that bone, itself, exhibits an inflammatory response during diabetes induction. This inflammation could in turn contribute to diabetic bone pathology. IFN-gamma (one of the key cytokines elevated in bone and known to be involved in bone regulation) deficiency did not prevent diabetic bone pathology. Taken together, our findings indicate that bone becomes inflamed with the onset of T1-diabetes and during this time bone phenotype markers become altered. However, inhibition of one cytokine, IFN-gamma was not sufficient to prevent the rapid bone phenotype changes.

Preselection thymocytes are normally retained in the thymic cortex, but the mechanisms responsible remain incompletely understood. We now report that deletion of genes encoding the E-protein transcription factors E2A and HEB disorders chemokine receptor expression on developing thymocytes to allow escape of preselection TCR−CD8+ thymocytes into the periphery. We document that CXCR4 expression normally anchors preselection thymocytes to the thymic cortex via interaction with its ligand CXCL12 on cortical thymic epithelial cells, and that disruption of CXCR4–CXCL12 engagements release preselection thymocytes from the thymic cortex. We further document that CXCR4 expression must be extinguished by TCR-mediated positive selection signals to allow migration of TCR-signaled thymocytes out of the thymic cortex into the medulla. Thus, E-protein transcription factors regulate the ordered expression pattern of chemokine receptors on developing thymocytes, and the interaction of the chemokine receptor CXCR4 with its ligand adheres TCR-unsignaled preselection thymocytes to the thymic cortex.

T cell antigen receptor (TCR) signaling in the thymus initiates positive selection but CD8 lineage fate is thought to be induced by cytokines after TCR signaling has ceased, although this remains controversial and unproven. We now identify four non-common gamma chain (γc) receptor-signaling cytokines (IL-6, IFN-γ, TSLP, TGF-β) that, like IL-7 and IL-15, induce expression of the lineage-specifying transcription factor Runx3d and signal the generation of CD8 T cells. Remarkably, elimination of in vivo signaling by all ‘lineage-specifying cytokines’ during positive selection eliminated Runx3d expression and completely abrogated CD8 single-positive thymocyte generation. Thus, this study proves that signaling during positive selection by lineage-specifying cytokines is responsible for all CD8 lineage fate decisions in the thymus.

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T cell receptor (TCR) gene-engineered T cells have shown promise in the treatment of melanoma and synovial cell sarcoma, but their application to epithelial cancers has been limited. The identification of novel therapeutic TCRs for the targeting of these tumors is important for the development of new treatments. Here, we describe the preclinical characterization of a TCR directed against Kita-Kyushu Lung Cancer Antigen-1 (KK-LC-1, encoded by CT83 ), a cancer germline antigen with frequent expression in human epithelial malignancies including gastric cancer, breast cancer, and lung cancer. Gene-engineered T cells expressing the KK-LC-1 TCR (KK-LC-1 TCR-Ts) demonstrated recognition of CT83 + tumor lines in vitro and mediated regression of established CT83+ xenograft tumors in immunodeficient mouse models. Cross-reactivity studies based on experimental determination of the recognition motifs for the target epitope did not demonstrate cross-reactivity against other human proteins. CT83 gene expression studies in 51 non-neural tissues and 24 neural tissues showed expression restricted exclusively to germ cells. CT83 was however expressed by a range of epithelial cancers, with the highest expression noted in gastric cancer. Collectively, these findings support the further investigation and clinical testing of KK-LC-1 TCR-Ts for gastric cancer and possibly other malignancies. Electronic supplementary material The online version of this article (10.1186/s40425-019-0678-x) contains supplementary material, which is available to authorized users.

Thymocytes bearing autoreactive T cell receptors (TCRs) are agonist-signaled by TCR/co-stimulatory molecules to either undergo clonal deletion or to differentiate into specialized regulatory T (Treg) or effector T (Teff) CD4+ cells. How these different fates are achieved during development remains poorly understood. We now document that deletion and differentiation are agonist-signaled at different times during thymic selection and that Treg and Teff cells both arise after clonal deletion as alternative lineage fates of agonist-signaled CD4+CD25+ precursors. Disruption of agonist signaling induces CD4+CD25+ precursors to initiate Foxp3 expression and become Treg cells, whereas persistent agonist signaling induces CD4+CD25+ precursors to become IL-2+ Teff cells. Notably, we discovered that transforming growth factor-β induces Foxp3 expression and promotes Treg cell development by disrupting weaker agonist signals and that Foxp3 expression is not induced by IL-2 except under non-physiological in vivo conditions. Thus, TCR signaling disruption versus persistence is a general mechanism of lineage fate determination in the thymus that directs development of agonist-signaled autoreactive thymocytes.

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+ PLZFhi innate precursors for their retention in the thymus and completion of their differentiation into mature NKT2 cells. By contrast, CD69-deficient CD24+ PLZFhi innate precursors express S1P1 and prematurely exit the thymus, while S1P1 inhibitor treatment of CD69-deficient mice retains CD24+ PLZFhi innate precursors in the thymus and restores NKT2 cell differentiation. Thus, CD69 prevents S1P1 expression on CD24+ PLZFhi 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.