Invariant natural killer T (NKT) cells are a highly conserved subset of T lymphocytes expressing a semi-invariant T cell receptor (TCR), which is restricted to CD1d and specific for the glycosphingolipid antigen α-galactosylceramide. Their ability to secrete a variety of cytokines, which in turn modulate the activation of cells of both innate and acquired immune responses, suggests that invariant NKT cells exert a regulatory role mainly via indirect mechanisms. A relevant question is whether invariant NKT cells can directly help B cells. We document here that human invariant NKT cells are as efficient as conventional CD4+ Th0 lymphocytes in promoting proliferation of autologous memory and naive B lymphocytes in vitro, and in inducing immunoglobulin production. Help to B cells by invariant NKT cells is CD1d-dependent and delivered also in the absence of α-galactosylceramide, suggesting that NKT cells recognize an endogenous ligand presented by CD1d on B cells. The two major subsets of invariant NKT cells, CD4+ and double negative (CD4−CD8−), express comparable levels of CD40 ligand and cytokines, but differ in helper functions. Indeed, both subsets induce similar levels of B cell proliferation, whereas CD4+ NKT cells induce higher levels of immunoglobulin production. These results suggest a direct role for invariant NKT cells in regulating B lymphocyte proliferation and effector functions.

CD1 molecules present lipid antigens to T cells. An intriguing subset of human T cells recognize CD1-expressing cells without deliberately added lipids. Frequency, subset distribution, clonal composition, naïve-to-memory dynamic transition of these CD1 selfreactive T cells remain largely unknown. By screening libraries of T-cell clones, generated from CD4 1 or CD4 À CD8 À double negative (DN) T cells sorted from the same donors, and by limiting dilution analysis, we find that the frequency of CD1 self-reactive T cells is unexpectedly high in both T-cell subsets, in the range of 1/10-1/300 circulating T cells. These T cells predominantly recognize CD1a and CD1c and express diverse TCRs. Frequency comparisons of T-cell clones from sorted naïve and memory compartments of umbilical cord and adult blood show that CD1 self-reactive T cells are naïve at birth and undergo an age-dependent increase in the memory compartment, suggesting a naïve/ memory adaptive-like population dynamics. CD1 self-reactive clones exhibit mostly Th1 and Th0 functional activities, depending on the subset and on the CD1 isotype restriction. These findings unveil the unanticipated relevance of self-lipid T-cell response in humans and clarify the basic parameters of the lipid-specific T-cell physiology. IntroductionConventional TCR-a/b 1 T lymphocytes recognize peptides presented by MHC molecules and are key players in the adaptive immune response. Thymic selection maximizes the generation of conventional mature T-cell repertoires specific for foreign Ags while minimizing autoreactivity [1]. A key feature of the adaptive immune response is that newly generated conventional T cells are naïve and acquire an effector/memory phenotype upon Ag encounter [2].There exists also an unconventional population of TCR-a/b 1 T lymphocytes that are restricted for CD1 molecules and recognize self-and microbial lipid antigens [3]. CD1 are non-polymorphic MHC class I-like molecules classified into three groups based on the sequence homology: group 1 comprises CD1a, CD1b and CD1c; group 2 CD1d; group 3 CD1e [4]. The best characterized CD1-restricted T cells are the CD1d-restricted invariant Natural Killer à These authors contributed equally to this work. 602Frontline T (iNKT) cells that express, in humans, an invariant Va24-Ja18 TCR paired with Vb11, together with NK-cell receptors [5][6][7]. iNKT cells can be unequivocally identify through their peculiar TCR: they are overly autoreactive, display an innate-like (constitutive) effector/ memory phenotype already at birth [8], unlike conventional T cells, and are divided in two main and functionally distinct CD4 1 and CD4 À CD8 À double negative (DN) subsets [9,10].A second type of CD1-restricted T lymphocytes does not express the invariant TCR and is mainly restricted for group 1 CD1 [3]. Because of the lack of specific markers, this T-cell type has been investigated using sporadically isolated T-cell clones, which provided fundamental hints on the microbial lipids and lipopeptides Ags recognized by these T cells...

Invariant (inv)NKT cells are a subset of autoreactive lymphocytes that recognize endogenous lipid ligands presented by CD1d, and are suspected to regulate the host response to cell stress and tissue damage via the prompt production of cytokines. We investigated invNKT cell response during the progression of chronic viral hepatitis caused by hepatitis B or C virus infection, a major human disease characterized by a diffused hepatic necroinflammation with scarring fibrotic reaction, which can progress toward cirrhosis and cancer. Ex vivo frequency and cytokine production were determined in circulating and intrahepatic invNKT cells from controls (healthy subjects or patients with nonviral benign or malignant focal liver damage and minimal inflammatory response) or chronic viral hepatitis patients without cirrhosis, with cirrhosis, or with cirrhosis and hepatocellular carcinoma. invNKT cells increase in chronically infected livers and undergo a substantial modification in their effector functions, consisting in the production of the type 2 profibrotic IL-4 and IL-13 cytokines, which characterizes the progression of hepatic fibrosis to cirrhosis. CD1d, nearly undetectable in noncirrhotic and control livers, is strongly expressed by APCs in cirrhotic ones. Furthermore, in vitro CD1d-dependent activation of invNKT cells from healthy donors elicits IL-4 and IL-13. Together, these findings show that invNKT cells respond to the progressive liver damage caused by chronic hepatitis virus infection, and suggest that these cells, possibly triggered by the recognition of CD1d associated with viral- or stress-induced lipid ligands, contribute to the pathogenesis of cirrhosis by expressing a set of cytokines involved in the progression of fibrosis.

CD1c self-reactive T cells recognize a novel class of self-lipids that are accumulated on leukemia cells.

Invariant NK T (iNKT) cells are a separate lineage of T lymphocytes with innate effector functions. They express an invariant TCR specific for lipids presented by CD1d and their development and effector differentiation rely on a unique gene expression program. We asked whether this program includes microRNAs, small noncoding RNAs that regulate gene expression posttranscriptionally and play a key role in the control of cellular differentiation programs. To this aim, we investigated iNKT cell development in mice in which Dicer, the RNase III enzyme that generates functional microRNAs, is deleted in cortical thymocytes. We find that Dicer deletion results in a substantial reduction of iNKT cells in thymus and their disappearance from the periphery, unlike mainstream T cells. Without Dicer, iNKT cells do not complete their innate effector differentiation and display a defective homeostasis due to increased cell death. Differentiation and homeostasis of iNKT cells require Dicer in a cell-autonomous fashion. Furthermore, we identify a miRNA profile specific for iNKT cells, which exhibits features of activated/effector T lymphocytes, consistent with the idea that iNKT cells undergo agonist thymic selection. Together, these results define a critical role of the Dicer-dependent miRNA pathway in the physiology of iNKT cells.

NKT cells are a small subset of T lymphocytes which express an invariant Vα24JαQ TCR and recognize glycolipids presented by CD1d. In adults, NKT cells have a memory phenotype, frequently associated with oligoclonal expansion, express NK cell markers, and produce T0 cytokines upon primary stimulation. Because of these features, NKT cells are regarded as lymphocytes of innate immunity. We investigated NKT cells from cord blood to see how these cells appear in the absence of exogenous stimuli. We found that NKT cells are present at comparable frequencies in cord blood and adult peripheral blood mononuclear cells and in both cases display a memory (CD45RO+CD62L–) phenotype. However, neonatal NKT cells differ from their adult counterparts by the following characteristics: (1) they express markers of activation, such as CD25; (2) they are polyclonal; (3) they do not produce cytokines in response to primary stimulation. Together, our data show that human NKT cells arise in the newborn with an activated memory phenotype, probably due to recognition of an endogenous ligand(s). The absence of oligoclonal expansion and primary effector functions also suggest that neonatal NKT cells, despite their activated memory phenotype, require a further priming / differentiation event to behave as fully functional cells of innate immunity.

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Immune reconstitution plays a crucial role on the outcome of patients given T cell-depleted HLA-haploidentical hematopoietic stem cell transplantation (hHSCT) for hematological malignancies. CD1d-restricted invariant NKT (iNKT) cells are innate-like, lipid-reactive T lymphocytes controlling infections, cancer, and autoimmunity. Adult mature iNKT cells are divided in two functionally distinct CD4+ and CD4− subsets that express the NK receptor CD161 and derive from thymic CD4+CD161− precursors. We investigated iNKT cell reconstitution dynamics in 33 pediatric patients given hHSCT for hematological malignancies, with a follow-up reaching 6 y posttransplantation, and correlated their emergence with disease relapse. iNKT cells fully reconstitute and rapidly convert into IFN-γ–expressing effectors in the 25 patients maintaining remission. CD4+ cells emerge earlier than the CD4− ones, both displaying CD161− immature phenotypes. CD4− cells expand more slowly than CD4+ cells, though they mature with significantly faster kinetics, reaching full maturation by 18 mo post-hHSCT. Between 4 and 6 y post-hHSCT, mature CD4− iNKT cells undergo a substantial expansion burst, resulting in a CD4+<CD4− NKT cell ratio similar to that found in healthy adults. In contrast with patients maintaining remission, iNKT cells failed to reconstitute in all eight patients experiencing disease relapse. These findings define the peripheral dynamics of human iNKT cells and suggest a contribution of these cells to maintain remission, possibly via early IFN-γ provision. Adoptive transfer of donor-derived iNKT cells into HLA-haploidentical patients failing to reconstitute these cells might represent a novel therapeutic option to prevent leukemia recurrence.