Ken-ichiro Seino

Requirement for natural killer T (NKT) cells in the induction of allograft tolerance

In this study, we investigated the role of Vα14 natural killer T (NKT) cells in transplant immunity. The ability to reject allografts was not significantly different between wild-type (WT) and Vα14 NKT cell-deficient mice. However, in models in which tolerance was induced against cardiac allografts by blockade of lymphocyte function-associated antigen-1/intercellular adhesion molecule-1 or CD28/B7 interactions, long-term acceptance of the grafts was observed only in WT but not Vα14 NKT cell-deficient mice. Adoptive transfer with Vα14 NKT cells restored long-term acceptance of allografts in Vα14 NKT cell-deficient mice. The critical role of Vα14 NKT cells to mediate immunosuppression was also observed in vitro in mixed lymphocyte cultures in which lymphocyte function-associated antigen-1/intercellular adhesion molecule-1 or CD28/B7 interactions were blocked. Experiments using IL-4- or IFN-γ-deficient mice suggested a critical contribution of IFN-γ to the Vα14 NKT cell-mediated allograft acceptance in vivo. These results indicate a critical contribution of Vα14 NKT cells to the induction of allograft tolerance and provide a useful model to investigate the regulatory role of Vα14 NKT cells in various immune responses.

The NKT cell system: bridging innate and acquired immunity

Although natural killer T cells are activated during infection, it is not clear how this process occurs. Closer examination indicates that recognition of endogenous ligands and interleukin 12, rather than bacterial products, may drive the activation process.

Generation of cloned mice by direct nuclear transfer from natural killer T cells

Cloning mammals by nuclear transfer (NT) remains inefficient. One fundamental question is whether clones have really been derived from differentiated cells rather than from rare stem cells present in donor-cell samples. To date, cells, such as mature lymphocytes, with genetic differentiation markers have been cloned to generate mice only via a two-step NT involving embryonic stem (ES) cell generation and tetraploid complementation [1, 2 and 3]. Here, we show that the genome of a unique T-cell population, natural killer T (NKT) cells, can be fully reprogrammed by a single-step NT. The pups and their placentas possessed the rearranged TCR loci specific for NKT cells. The NKT-cell-cloned embryos had a high developmental potential in vitro: Most (71%) developed to the morula/blastocyst stage, in marked contrast to embryos from peripheral blood T cells (12%; p < 1 x 10(-25)). Furthermore, ES cell lines were efficiently established from these NKT-cell blastocysts. These findings clearly indicate a high level of plasticity in the NKT-cell genome. Thus, differentiation of the genome is not always a barrier to NT cloning for either reproductive or therapeutic purposes, so we can now postulate that at least some mammals cloned to date have indeed been derived from differentiated donor cells.

IL-21–induced Bε cell apoptosis mediated by natural killer T cells suppresses IgE responses

Epidemiological studies have suggested that the recent increase in the incidence and severity of immunoglobulin (Ig)E-mediated allergic disorders is inversely correlated with Mycobacterium bovis bacillus Calmette Guerin (BCG) vaccination; however, the underlying mechanisms remain uncertain. Here, we demonstrate that natural killer T (NKT) cells in mice and humans play a crucial role in the BCG-induced suppression of IgE responses. BCG-activated murine Vα14 NKT cells, but not conventional CD4 T cells, selectively express high levels of interleukin (IL)-21, which preferentially induces apoptosis in Bɛ cells. Signaling from the IL-21 receptor increases the formation of a complex between Bcl-2 and the proapoptotic molecule Bcl-2–modifying factor, resulting in Bɛ cell apoptosis. Similarly, BCG vaccination induces IL-21 expression by human peripheral blood mononuclear cells (PBMCs) in a partially NKT cell–dependent fashion. BCG-activated PBMCs significantly reduce IgE production by human B cells. These findings provide new insight into the therapeutic effect of BCG in allergic diseases.

Impaired Proliferative Response of Vα24 NKT Cells from Cancer Patients Against α-Galactosylceramide

Human invariant Vα24+ NKT cells are a relatively new subpopulation of lymphocytes. It has been reported that Vα24 NKT cells are significantly involved in some human diseases. We have evaluated the number and function of Vα24 NKT cells in both healthy volunteers and cancer patients. In this study we found that Vα24 NKT cells in unfractionated PBMCs obtained from cancer patients did not respond efficiently to α-galactosylceramide (α-GalCer) in vitro. Thus, their proportion after stimulation with α-GalCer was smaller than that found in healthy volunteers. However, the cancer patients’ Vα24 NKT cells retained cytotoxic activity against malignant target cells, and they could efficiently proliferate to α-GalCer when fractionated by sorting. Furthermore, we found that addition of G-CSF to the culture could restore the low proliferative response of Vα24 NKT cells from cancer patients. These results suggest that some functions of NKT cells in cancer patients are impaired, and this observation carries significant implications for immunotherapy-based cancer treatments.

Functionally distinct NKT cell subsets and subtypes.

Natural killer T (NKT) cells are a population of autoreactive cells that mediate both protective and regulatory immune functions. NKT cells comprise several subsets of cells, but it has been unclear whether these different NKT cell subsets possess distinct functions in vivo. New studies now demonstrate that subsets of NKT cells are indeed functionally distinct and that the specific functions of these cells may be dictated in part by organ-specific mechanisms.

A common polymorphism in the interleukin 8 gene promoter is associated with Clostridium difficile diarrhea.

In mouse liver transplantation, tolerance is readily inducible. Recent studies have revealed that CD25+CD4+ regulatory T cells play an important role in regulating various immune responses, including transplant tolerance. However, the contribution of these cells to tolerance in mouse liver transplantation has not been elucidated. We showed here that depletion of CD25+CD4+ T cells increased proliferative response of CD4+ T cells and cytotoxic T lymphocyte induction of CD8+ T cells. Depletion of these cells in the recipient but not in the donor before liver transplantation caused rejection. Furthermore, the number of CD25+CD4+ population and forkhead/winged helix transcription factor expression in liver mononuclear lymphocytes derived from tolerant mice were higher than those from grafts undergoing rejection. In conclusion, these results indicate that CD25+CD4+ regulatory T cells in the recipient but not in the donor of liver transplantation are important for the tolerance induction. Liver Transpl 12:1112–1118, 2006.

Mechanism of NKT cell activation by intranasal coadministration of α-galactosylceramide, which can induce cross-protection against influenza viruses

In a nasal vaccine against influenza, the activation of natural killer T (NKT) cells by intranasal coadministration of α-galactosylceramide (α-GalCer) can potently enhance protective immune responses. The results of this study show that the NKT cell-activated nasal vaccine can induce an effective cross-protection against different strains of influenza virus, including H5 type. To analyze the mechanism of NKT cell activation by this nasal vaccine, we prepared fluorescence-labeled α-GalCer by which we detect a direct interaction between NKT cells and α-GalCer-stored dendritic cells in nasal mucosa-associated tissues. Accordingly, although very few NKT cells exist at mucosa, the nasal vaccination induced a localized increase in NKT cell population, which is partly dependent on CXCL16/CXCR6. Furthermore, we found that NKT cell activation stimulates mucosal IgA production by a mechanism that is dependent on interleukin (IL)-4 production. These results strengthen the basis of nasal vaccination via NKT cell activation, which can induce immune cross-protection.

Differential Role of Thymic Stromal Lymphopoietin in the Induction of Airway Hyperreactivity and Th2 Immune Response in Antigen-Induced Asthma with Respect to Natural Killer T Cell Function

Asthma is an inflammatory lung disease, in which CD1d-restricted natural killer T (NKT) cells play an importantpathogenic role. Also, recent reports indicated that a cytokine, thymic stromal lymphopoietin (TSLP), is essential for the development of antigen-induced asthma. Here we examined the relationship between NKT cells and TSLP in a mouse model of asthma. NKT cells express TSLP receptor as well as IL-7 receptor α-chain. TSLP acts on NKT cells to preferentially increase their IL-13 production but not IFN-γ and IL-4. In an allergen-induced asthma model, the development of airway hyperreactivity, a cardinal feature of asthma, was increased in TSLP transgenic mice, whereas this effect was not observed in TSLP transgenic mice lacking NKT cells. Interestingly, in the NKT cell-lacking TSLP transgenic mice, pulmonary eosinophilia and increase in IgE did not improve. Pulmonary lymphocytes from the NKT cell-lacking TSLP transgenic mice produced much less IL-13 upon CD3 stimulation than those from NKT cell-competent TSLP transgenic mice. These resultssuggest that, in allergen-induced asthma, TSLP acts on NKT cells to enhance airway hyperreactivity by upregulating their IL-13 production, whereas eosinophilia and IgE production are not influenced.

Induction of Regulatory Properties in Dendritic Cells by Vα14 NKT Cells

Vα14 NKT cells exhibit various immune regulatory properties in vivo, but their precise mechanisms remain to be solved. In this study, we demonstrate the mechanisms of generation of regulatory dendritic cells (DCs) by stimulation of Vα14 NKT cells in vivo. After repeated injection of α-galactosylceramide (α-GalCer) into mice, splenic DCs acquired properties of regulatory DCs in IL-10-dependent fashion, such as nonmatured phenotypes and increased IL-10 but reduced IL-12 production. The unique cytokine profile in these DCs appears to be regulated by ERK1/2 and IκBNS. These DCs also showed an ability to suppress the development of experimental allergic encephalomyelitis by generating IL-10-producing regulatory CD4 T cells in vivo. These findings contribute to explaining how Vα14 NKT cells regulate the immune responses in vivo.