Human Invariant NKT Cells Are Required for Effective In Vitro Alloresponses

The role of natural killer T cells in costimulation blockade-based mixed chimerism

Distinct lymphocyte populations have been identified that either promote or impede the establishment of chimerism and tolerance through allogeneic bone marrow transplantation (BMT). Natural killer T (NKT) cells have pleiotropic regulatory properties capable of either augmenting or downmodulating various immune responses. We investigated in this study whether NKT cells affect outcome in mixed chimerism models employing fully mismatched nonmyeloablative BMT with costimulation blockade (CB). The absence of NKT cells had no detectable effect on chimerism or skin graft tolerance after conditioning with 3Gy total body irradiation (TBI), and a limited positive effect with 1Gy TBI. Stimulation of NKT cells with alpha-galactosylceramide (alpha-gal) at the time of BMT prevented chimerism and tolerance. Activation of recipient (as opposed to donor) NKT cells was necessary and sufficient for the alpha-gal effect. The detrimental effect of NKT activation was also observed in the absence of T cells after conditioning with in vivo T-cell depletion (TCD). NKT cells triggered rejection of BM via NK cells as chimerism and tolerance were not abrogated when NKT cells were stimulated in the absence of both NK cells and T cells. Thus, activation of NKT cells at the time of BMT overcomes the effects of CB, inhibiting the establishment of chimerism and tolerance.

Shaping of iNKT cell repertoire after unrelated cord blood transplantation

Invariant natural killer T (iNKT) cells have a pivotal role in immune regulation, tumor surveillance, and the induction of allograft tolerance. In this report, we analyze the recovery of iNKT cells after unrelated cord blood transplantation (UCBT) of adult patients with high-risk acute myeloid leukemia. We found that iNKT cells were reconstituted within 1 month after UCBT, at the same time as NK cells and before conventional T cells. These iNKT cells displayed a unique primed/central memory CD4(+)CD45RO(+)CCR7(+)CD62L(+) phenotype soon after the transplant. Interestingly, the functional competence of these cells was poor, except for their high GM-CSF production capacity. However, this post-graft functionally immature state was transient and all of the patients tested had fully functional iNKT cells 3 to 6 months post-UCBT and high cytolytic capacity for destroying primary CD1d(+) myeloid blast cells. Our results raise the possibility that iNKT cells might play a key role in graft-versus-leukemia activity after UCBT.

Selected allogeneic dendritic cells markedly enhance human tumour antigen-specific T cell response in vitro

BACKGROUND

Alloreaction is known to accumulate several theoretical advantages that can improve dendritic cell (DC)-based anti-infective or antitumour strategies. Allogeneic DC have already been tested in experimental and clinical studies, but their efficacy compared with their autologous counterparts was rarely investigated and conclusions diverge.

OBJECTIVE

This study compared antigen-specific T cell responses following priming with autologous versus allogeneic DC and examined the possibility of screening these responses in order to select allogeneic DC that lead to a great amplification.

RESULTS

Allogeneic DC obtained from donors matched with the single HLA-A2 allele were efficient in generating in vitro peptide-specific T cell responses. When randomly chosen, allogeneic DC generated a broad range of antigen-specific T cell responses in comparison with autologous DC. When screened and selected, allogeneic DC markedly enhanced peptide-specific T cell priming and allowed a more efficient boosting of resulting T cells. These selected allogeneic DC provided a favourable cytokinic and cellular environment that can help concurrent antigen-specific responses.

CONCLUSION

Ex vivo selected allogeneic DC provide adjuvant effects that lead to amplification of concomitant antigen-specific T cell responses.

Human invariant NKT cells display alloreactivity instructed by invariant TCR-CD1d interaction and killer Ig receptors

Invariant NKT (iNKT) cells are a subset of highly conserved immunoregulatory T cells that modify a variety of immune responses, including alloreactivity. Central to their function is the interaction of the invariant TCR with glycosphingolipid (GSL) ligands presented by the nonpolymorphic MHC class I molecule CD1d and their ability to secrete rapidly large amounts of immunomodulatory cytokines when activated. Whether iNKT cells, like NK and conventional T cells, can directly display alloreactivity is not known. We show in this study that human iNKT cells and APC can establish a direct cross-talk leading to preferential maturation of allogeneic APC and a considerably higher reactivity of iNKT cells cultured with allogeneic rather that autologous APC. Although the allogeneic activation of iNKT cells is invariant TCR-CD1d interaction-dependent, GSL profiling suggests it does not involve the recognition of disparate CD1d/GSL complexes. Instead, we show that contrary to previous reports, iNKT cells, like NK and T cells, express killer Ig receptors at a frequency similar to that of conventional T cells and that iNKT cell allogeneic activation requires up-regulation and function of activating killer Ig receptors. Thus, iNKT cells can display alloreactivity, for which they use mechanisms characteristic of both NK and conventional T cells.

Peripheral blood progenitor cell product contains Th1-biased noninvariant CD1d-reactive natural killer T cells: implications for posttransplant survival

OBJECTIVE

Bone marrow (BM) Th1 populations can contribute to graft-vs-leukemia responses. Granulocyte/granulocyte macrophage colony-stimulating factor (CSF)-mobilized peripheral blood progenitor cells (PBPC) have become widely accepted alternatives to BM transplantation. T cells coexpressing natural killer cell proteins (NKT) include a CD1d-reactive subset that influences immunity by rapidly producing large amounts of Th1 and/or Th2 cytokines dependent upon microenvironment and disease. There are two types of CD1d-reactive NKT. iNKT express a semi-invariant T-cell receptor-alpha. Other noninvariant CD1d-reactive NKT from BM and liver produce large amounts of interleukin-4 or interferon-gamma, respectively, and within the intestine can be biased in either direction. Recent data suggests that NKT might contribute to clinical benefits of PBPC.

MATERIALS AND METHODS

To address these issues, we phenotypically and functionally studied PBPC NKT.

RESULTS

Similarly to BM, NKT-like cells were common in allogeneic and autologous PBPC, there were relatively few classical iNKT, but high CD1d-reactivity concentrated in NKT fractions. Significantly, PBPC CD1d-reactive cells were relatively Th1-biased and their presence was associated with better prognosis. Granulocyte CSF treatment of BM to yield PBPC in vivo as well as in vitro Th2-polarizes conventional T cells and iNKT. However, granulocyte CSF treatment of BM in vitro produced Th1-biased NKT, providing a mechanism for opposite polarization of NKT from BM vs PBPC.

CONCLUSIONS

These results suggest distinct Th1 CD1d-reactive NKT cells could stimulate anti-tumor responses from those previously described, which can suppress graft-vs-host disease.

Human invariant Valpha24+ natural killer T cells acquire regulatory functions by interacting with IL-10-treated dendritic cells

Glycolipid-reactive Valpha24(+) invariant natural killer T (iNKT) cells have been implicated in regulating a variety of immune responses and in the induction of immunologic tolerance. Activation of iNKT cells requires interaction with professional antigen-presenting cells, such as dendritic cells (DCs). We have investigated the capacity of distinct DC subsets to modulate iNKT cell functions. We demonstrate that tolerogenic DCs (tolDCs), generated by treatment of monocyte-derived DC with interleukin (IL)-10, induced regulatory functions in human iNKT cells. tolDCs, compared with immunogenic DCs, had reduced capacity to induce iNKT-cell proliferation, but these cells produced large amounts of IL-10 and acquired an anergic phenotype. These anergic Valpha24(+) iNKT cells were able to potently inhibit allogeneic CD4(+) T-cell proliferation in vitro. Furthermore, the anergic Valpha24(+) iNKT cells could suppress DC maturation in vitro. We conclude that the interaction of iNKT cells with tolDCs plays an important role in the immune regulatory network, which might be exploited for therapeutic purposes.

Low levels of circulating invariant natural killer T cells predict poor clinical outcome in patients with head and neck squamous cell carcinoma

PURPOSE

Evading antitumor immune responses is an important aspect of the pathogenesis of head and neck squamous cell carcinoma (HNSCC). Invariant CD1d-restricted natural killer T (iNKT) cells play an allegedly pivotal role in such responses via transactivation of immune effector cells. It has been reported that iNKT cells are reduced in peripheral blood of cancer patients compared with healthy controls. Here, we investigated whether the extent of this deficiency affected disease outcome in HNSCC patients.

PATIENTS AND METHODS

In a prospective study, circulating iNKT cell numbers were evaluated in 47 patients before radiotherapy. Patients were stratified in three groups based on iNKT cell levels, and clinical data were obtained during a median follow-up period of 31 months.

RESULTS

A small, compared with an intermediate or large, circulating iNKT cell fraction was significantly associated with decreased 3-year overall survival rate (39% v 75% and 92%, respectively), disease-specific survival rate (43% v 87% and 92%, respectively), and locoregional control rate (31% v 74% and 92%, respectively) in HNSCC patients. Cox regression revealed that the iNKT cell level, as well as clinical T stage, was an independent prognostic parameter even after correction for the confounding effect of age.

CONCLUSION

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.

Natural killer T cells and haemopoiesis

Invariant natural killer T (iNKT) cells are a small but powerful subset of regulatory T cells involved in the modulation of a variety of normal and pathological immune responses. In contrast to conventional or other types of regulatory T cells, they are activated by glycolipid and phospholipid ligands that are presented to them by the non-polymorphic, major histocompatibility complex class I-like molecule CD1d. The in-depth understanding of their function has resulted in successful, iNKT cell-centred experimental therapeutic interventions including prevention of graft-versus-host disease and anti-leukaemia effects. Extending these successes into the clinical arena will require better understanding of their contribution to the pathogenesis of human, including haematological, diseases.