Natural killer T (NKT) cells are CD1d-restricted lymphoid cells and are characterized by an invariant T-cell receptor, which in humans consists of a Va24 chain paired with a Vb11 chain. These cells are known for their rapid production of large amounts of cytokines (e.g., Vb11+ NKT cell numbers in both healthy controls and cancer patients and demonstrate that in both groups females have higher NKT cell levels compared to males. In a large group of 120 cancer patients, we show that circulating Va24+ NKT cell numbers are about 50% lower than in ageand gender-matched healthy controls and that this decrease is independent of tumor type or tumor load. This decrease was not restored upon tumor removal by means of surgery or radiotherapy. Even though the percentage of NKT cells that secrete IFN-g, as detected by ELISPOT, is normal in cancer patients, the absolute number of circulating IFN-g-secreting NKT cells is reduced. Together, our results suggest that the reduced circulating Va24 + Vb11+ NKT cell numbers in cancer patients are not affected by tumor load, but might actually reflect a risk factor for tumor development, e.g., by hampering efficient tumor immunosurveillance. ' 2005 Wiley-Liss, Inc.

A severe circulating iNKT cell deficiency was related to poor clinical outcome in HNSCC patients, suggesting their critical contribution to antitumor immune responses. Furthermore, screening for iNKT cell levels may be useful for determining which patients can benefit from immunotherapeutic adjuvant therapies aimed at reconstitution of the circulating iNKT cell pool.

Local TLR stimulation is an attractive approach to induce antitumor immunity. In this study, we compared various TLR ligands for their ability to affect murine GL261 cells in vitro and to eradicate established intracerebral murine gliomas in vivo. Our data show that GL261 cells express TLR2, TLR3, and TLR4 and respond to the corresponding TLR ligands with increasing MHC class I expression and inducing IL-6 secretion in vitro, while TLR5, TLR7, and TLR9 are essentially absent. Remarkably, CpG-oligonucleotides (CpG-ODN, TLR9) appeared to inhibit GL261 cell proliferation in a cell-type specific, but CpG-motif and TLR9-independent manner. A single intratumoral injection of CpG-ODN most effectively inhibited glioma growth in vivo and cured 80% of glioma-bearing C57BL/6 mice. Intratumoral injection of Pam3Cys-SK4 (TLR1/2) or R848 (TLR7) also produced a significant survival benefit, whereas poly(I:C) (TLR3) or purified LPS (TLR4) stimulation alone was not effective. Additional studies using TLR9+/+ wild-type and TLR9−/− knockout mice revealed that the efficacy of local CpG-ODN treatment in vivo required TLR9 expression on nontumor cells. Additional experiments demonstrated increased frequencies of tumor-infiltrating IFN-γ producing CD4+ and CD8+ effector T cells and a marked increase in the ratio of CD4+ effector T cells to CD4+FoxP3+ regulatory T cells upon CpG-ODN treatment. Surviving CpG-ODN treated mice were also protected from a subsequent tumor challenge without further addition of CpG-ODN. In summary, this study underlines the potency of local TLR treatment in antiglioma therapy and demonstrates that local CpG-ODN treatment most effectively restores antitumor immunity in a therapeutic murine glioma model.

CD4 1 CD25 hi CTLA4 1 FoxP3 1 regulatory T cells (Treg) have been shown to maintain immune tolerance against self antigens and increased circulating frequencies have been reported in various types of cancers. Circulating invariant natural killer T-cells (iNKT) are reduced in cancer patients and low iNKT frequency is related to poor prognosis. It is not yet clear whether high Treg numbers and low iNKT cell numbers pose an increased risk for the progression of premalignant lesions or whether Treg and iNKT cell numbers are influenced by dysplasia. We therefore studied prospectively the relation between iNKT cell and Treg frequencies and the natural course of human papillomavirus type 16 (HPV16) induced pre-malignant cervical dysplasia in 82 patients who participated in a nonintervention cohort study of women with abnormal cytology. Treg frequencies were significantly increased in women who had persistent HPV16 infection. Within the HPV16 persistence group there was no difference in Treg frequencies among patients who developed a CIN3 lesion and patients who did not progress to CIN3. Furthermore, Treg frequencies were increased in patients who had detectable HPV16 E7 specific IL-2 producing T-helper cells, which suggests a causal role of HPV infection in Treg development in parallel with HPV16 specific T helper cells. No evidence was found for a role for iNKT cells in persistence of HPV16 and progression of HPV16 induced CIN lesions. However, HPV-persistence-associated Tregs may explain the inefficacy of concomitant persistence associated immunity and may contribute to subsequent progression to neoplasia. ' 2007 Wiley-Liss, Inc.Key words: regulatory T cells; invariant NKT cells; HPV type 16; persistence; CIN Specific immune responses against viruses and cancer are controlled by various regulatory cells. This negative regulation occurs by naturally occurring CD4 1 CD25 hi regulatory T cells (Tregs), induced antigen specific regulatory T-cells (Tr1 and TH3 cells) or CD4 1 CD25 hi cells developing from CD4 1 CD25 2 T-cells. Unlike naturally occurring Tregs, which can be identified by intracellular cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) and forkhead box (Fox)P3 expression, antigen specific regulatory T-cells have no discriminating phenotype. 1-3 Increased numbers of circulating Tregs have been detected in patients with solid tumors 4 and hematologic malignancies. 5 While there is evidence for an influence of tumor associated factors, 6 it has also been suggested that an age related increase in Treg frequencies is associated with an increased risk to develop cancer. 7 Another regulatory T cell is the invariant natural killer T (iNKT) cell, which is characterized by expression of the Va24Vb11 invariant T-cell receptor and NK cell receptors. iNKT cells have the capacity to either enhance or suppress immuneresponses by secreting proinflammatory or anti-inflammatory cytokines respectively upon activation via antigenic recognition of the glycolipid a-galactosylceramide (a-GalCer) in the context of the non-polymo...

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CD1d-restricted NKT cells play important regulatory roles in various immune responses and are rapidly and selectively depleted upon infection with HIV-1. The cause of this selective depletion is incompletely understood, although it is in part due to the high susceptibility of CD4+ NKT cells to direct infection and subsequent cell death by HIV-1. Here, we demonstrate that highly active antiretroviral therapy (HAART) results in the rapid recovery of predominantly CD4− NKT cells with kinetics that are strikingly similar to those of mainstream T cells. As it is well known that the early recovery of mainstream T cells in response to HAART is due to their redistribution from tissues to the circulation, our data suggest that the selective depletion of circulating NKT cells is likely due to a combination of cell death and tissue sequestration and indicates that HAART can improve immune functions by reconstituting both conventional T cells and immunoregulatory NKT cells.

Circulating invariant natural killer T-cell numbers predict outcome in head and neck squamous cell carcinoma: Updated analysis with 10-year follow-up

CD1d-restricted invariant NKT (iNKT) cells can enhance immunity to cancer or prevent autoimmunity, depending on the cytokine profile secreted. Antitumor effects of the iNKT cell ligand α-galactosylceramide (αGC) and iNKT cell adoptive transfer have been demonstrated in various tumor models. Together with reduced numbers of iNKT cells in cancer patients, which have been linked to poor clinical outcome, these data suggest that cancer patients may benefit from therapy aiming at iNKT cell proliferation and activation. Herein we present results of investigations on the effects of human iNKT cells on Ag-specific CTL responses. iNKT cells were expanded using αGC-pulsed allogeneic DC derived from the acute myeloid leukemia cell line MUTZ-3, transduced with CD1d to enhance iNKT cell stimulation, and with IL-12 to stimulate type 1 cytokine production. Enhanced activation and increased IFN-γ production was observed in iNKT cells, irrespective of CD4 expression, upon stimulation with IL-12-overexpressing dendritic cells. IL-12-stimulated iNKT cells strongly enhanced the MART-1 (melanoma Ag recognized by T cell 1)-specific CD8+ CTL response, which was dependent on iNKT cell-derived IFN-γ. Furthermore, autologous IL-12-overexpressing dendritic cells, loaded with Ag as well as αGC, was superior in stimulating both iNKT cells and Ag-specific CTL. This study shows that IL-12-overexpressing allogeneic dendritic cells expand IFN-γ-producing iNKT cells, which may be more effective against tumors in vivo. Furthermore, the efficacy of autologous Ag-loaded DC vaccines may well be enhanced by IL-12 overexpression and loading with αGC.