ALBERT

Description: During T cell development, Cd8 expression is controlled via dynamic regulation of its cis-regulatory enhancer elements. Insufficient enhancer activity during initial Cd8 activation is known to cause a variegated CD8 expression, thereby generating a CD4+CD8-TCRb-/low population that should appear as CD4+CD8+ double-positive (DP) thymocytes. However, epigenetic and molecular mechanisms involved in initial Cd8 gene activation remain elusive. We previously reported that Brd1, also known as Brpf2, is responsible for the global acetylation of H3K14 as a subunit of the Hbo1 histone acetyltransferase (HAT) complex. In this study, we generated conditional Brd1 knockout mice (Tie2-Cre;Brd1fl/fl mice), in which Brd1 is inactivated in all hematopoietic cells. Although Tie2-Cre;Brd1fl/fl mice were born and grew normally, detailed analysis revealed an abnormal thymocyte differentiation. Deletion of Brd1 resulted in the appearance of CD4+CD8-TCRβ-/low thymocytes that was indistinguishable from DP thymocytes in their properties. Hierarchical clustering of gene expression profile showed that Brd1Δ/Δ CD4+CD8-TCRβ-/low thymocytes retain an expression profile nearly identical to one observed in DP thymocytes. These results indicate that Brd1Δ/Δ CD4+CD8-TCRβ-/low thymocytes correspond to immature thymocytes that would normally appear as CD4+CD8+ DP thymocytes, and was generated because of a variegated activation of Cd8 gene. Importantly, in the gut intraepithelial lymphocyte (IEL) compartment, the population of CD4+CD8aa+ aβT cells, whose generation requires Cd8 gene reactivation in CD4+CD8− helper T cells, were significantly decreased in Tie2-Cre;Brd1fl/fl mice compared to the Tie2-Cre control mice. In addition, the percentage of CD8aa expressing gdT cells was significantly reduced. These findings suggest that Brd1 is also required to initiate Cd8a activation in gdT cells as well as Cd8 reactivation in CD4+T cells. We further conducted retroviral transduction of Brd1 into Brd1Δ/Δ DN3 cells that were flowed by culture on TSt-4/DLL stromal cells. Upon exogenous Brd1 expression, CD8 expression was completely restored and thereby Brd1Δ/Δ DN3 cells differentiated into DP cells. ChIP analysis demonstrated that Brd1 and Hbo1 co-localize at the known enhancers in the Cd8 locus and that their bindings are responsible for acetylation at H3K14. Biochemical results confirmed a presence of Brd1 in Hbo1 HAT complexes. These findings indicate that the Brd1-mediated HAT activity is crucial for efficient activation of Cd8 expression via acetylation at H3K14, which would serve as an epigenetic mark that promotes the recruitment of transcription machineries to the Cd8 enhancers. Disclosures No relevant conflicts of interest to declare.

Description: Background: Invariant natural killer T (iNKT) cells are known as CD1d-restricted T cells that express the invariant T-cell receptors (TCR) Vα24 and Vβ11 in humans and specifically recognize glycolipid antigens such as α-galactosylceramide (αGalCer) presented by CD1d. iNKT cells show direct cytotoxicity toward CD1d-positive tumor cells presenting glycolipid antigens and indirect cytotoxicity by activating other cytotoxic immune cells or regulating CD1d-positive immunosuppressive cells in the tumor microenvironment. Although we previously reported that αGalCer-activated NKT cells exert a potent perforin-dependent cytotoxic activity against a wide variety of human tumor cell lines, the direct recognition of CD1d-negative tumors is controversial and the mechanism is unknown. Here we clarify whether iNKT cells recognize and exhibit cytotoxicity toward leukemia cells in a CD1d-independent manner and identify the molecule that recognizes CD1d-negative leukemia cells. Methods: Purified iNKT cells were generated from peripheral blood mononuclear cells (PBMCs) of healthy adult volunteer donors. PBMCs were cultured in complete RPMI 1640 medium for 9-14 days in the presence of 100 U/mL of recombinant human IL-2 and 200 ng/mL of αGalCer. The iNKT cells were then isolated with an autoMACS Pro separator using FITC-labeled anti-Vα24 antibody (clone, C15) and anti-FITC microbeads. We evaluated the cytotoxic activity of iNKT cells toward CD1d-negative leukemia cells within four days after isolation using a CD107a assay for degranulation, cytometric bead array for cytokine production, and cytotoxicity assay in vitro and in vivo. For in vivo cytotoxicity assays, NOG mice were inoculated with 1 × 106 K562-luc cells on day 0 and with 4 × 106 human iNKT cells on day 1. Gene knock-out (KO) was performed using a CRISPR/Cas9 system. T-cell or NK receptor-KO iNKT cells were used for experiments three or four days after electroporation of the Cas9 protein and guide RNA CRISPR ribonucleoprotein complex. Patient-derived leukemia cells were obtained from PBMCs or bone marrow mononuclear cells of pre-treatment pediatric patients. All studies were approved by the institutional review board and the Animal Care and Use Committee of Chiba University. Results: We observed that iNKT cells degranulated and released Th1 cytokines when co-cultured with CD1d-negative leukemia cells (K562, HL-60, REH, and CD1d-KO U937) as well as αGalCer-loaded CD1d-positive leukemia cells (Jurkat), and showed in vitro cytotoxicity toward these CD1d-negative leukemia cells. This CD1d-independent degranulation decreased over time after isolation and was not restored with re-stimulation by αGalCer. The cytotoxicity of iNKT cells toward K562 cells was confirmed in vivo by comparsion with survival curves of K562-inoculated NOG mice given iNKT cells or PBS alone (log-rank, p= 0.016). To identify the receptors contributing to the CD1d-independent recognition and cytotoxicity against CD1d-negative leukemia cells, we first focused on costimulatory receptors, which are also known as activating NK receptors and are expressed on iNKT cells such as NKG2D, DNAM-1, 2B4, LFA-1, and CD2, and analyzed cytotoxicity after blocking these receptors with antibodies. We found that all costimulatory receptors that we assessed contributed to cytotoxicity toward CD1d-negative leukemia cells. Next, we analyzed cytotoxicity of TCR-KO iNKT cells toward CD1d-negative leukemia cells to confirm the contribution of TCR to CD1d-independent recognition. Notably, TCR-KO iNKT cells showed decreased degranulation, Th1 cytokine release, and cytotoxicity toward K562 cells more so than iNKT cells with KO of NK receptors such as LFA-1(CD11a) or CD2. To assess the clinical application potential of adoptive iNKT cell immunotherapy for leukemia treatment, we analyzed degranulation of iNKT cells using patient-derived leukemia cells. We found iNKT cells degranulation using cells from four out of five myeloid leukemia cases, but only one out of eight BCP-ALL cases (p = 0.032). Conclusion: Primary iNKT cells activated by αGalCer can recognize and show anti-tumor effects toward leukemia cells in an unrestricted manner via CD1d. The TCR also has an important role in recognizing CD1d-negative leukemia cells and multiple NK receptors assist in cytotoxicity. Adoptive iNKT cell immunotherapy may be effective in treating myeloid leukemia. Disclosures No relevant conflicts of interest to declare.

Description: Natural killer (NK) cells play a pivotal role in the immune reaction during the bone marrow allograft rejection. Little is known, however, about the molecular mechanisms underlying the NK cell–mediated allograft recognition and rejection. In this report, we assessed the role of a recently identified NK receptor, killer cell lectinlike receptor 1 (KLRE-1), by generating knock-out mice. KLRE-1–deficient mice were born at an expected frequency and showed no aberrant phenotype on growth and lymphoid development. Nevertheless, KLRE-1–deficient cells showed a severely compromised allogeneic cytotoxic activity compared with the wild-type cells. Furthermore, allogeneic bone marrow transfer culminated in colony formation in the spleen of KLRE-1–deficient mice, whereas no colony formation was observed in wild-type recipient mice. These results demonstrate that KLRE-1 is a receptor mediating recognition and rejection of allogeneic target cells in the host immune system.

Description: It has recently been shown that CD4+CD25+ T cells are immunoregulatory T cells that prevent CD4+ T-cell–mediated organ-specific autoimmune diseases. In this study, the regulatory mechanism of CD4+CD25+ T-cell development were investigated using T-cell receptor (TCR) transgenic mice. It was found that CD4+CD25+ T cells preferentially expressed the endogenous TCRα chain in DO10+ TCR transgenic mice compared with CD4+CD25− T cells. Moreover, it was found that CD4+CD25+ thymocytes were severely decreased in DO10+ TCR-α−/− mice in positively selecting and negatively selecting backgrounds, whereas CD4+CD25− thymocytes efficiently developed by transgenic TCR in DO10+ TCR-α−/− mice in positively selecting backgrounds, indicating that the appropriate affinity of TCR to major histocompatibility complex (MHC) for the development of CD4+CD25+ thymocytes is different from that of CD4+CD25− thymocytes and that a certain TCR–MHC affinity is required for the development of CD4+CD25+ thymocytes. Finally, it was found that, in contrast to thymus, CD4+CD25+ T cells were readily detected in spleen of DO10+TCR-α−/− mice in positively selecting backgrounds and that splenic CD4+CD25+ T cells, but not CD4+CD25+ thymocytes, were significantly decreased in B-cell–deficient mice, suggesting that B cells may control the peripheral pool of CD4+CD25+ T cells. Together, these results indicate that the development of CD4+CD25+ T cells in thymus and the homeostasis of CD4+CD25+ T cells in periphery are regulated by distinct mechanisms.