Natural killer cell and hepatic cell interaction via NKG2A leads to dendritic cell-mediated induction of CD4 CD25 T cells with PD-1-dependent regulatory activities

Changes to the natural killer cell repertoire after therapeutic hepatitis B DNA vaccination

BACKGROUND

Improvements to the outcome of adaptive immune responses could be achieved by inducing specific natural killer (NK) cell subsets which can cooperate with dendritic cells to select efficient T cell responses. We previously reported the induction or reactivation of T cell responses in chronic hepatitis B patients vaccinated with a DNA encoding hepatitis B envelope proteins during a phase I clinical trial.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we examined changes in the peripheral NK cell populations occurring during this vaccine trial using flow cytometry analysis. Despite a constant number of NK cells in the periphery, a significant increase in the CD56(bright) population was observed after each vaccination and during the follow up. Among the 13 different NK cell markers studied by flow cytometry analysis, the expression of CD244 and NKG2D increased significantly in the CD56(bright) NK population. The ex vivo CD107a expression by CD56(bright) NK cells progressively increased in the vaccinated patients to reach levels that were significantly higher compared to chronically HBV-infected controls. Furthermore, modifications to the percentage of the CD56(bright) NK cell population were correlated with HBV-specific T cell responses detected by the ELISPOT assay.

CONCLUSIONS/SIGNIFICANCE

These changes in the CD56(bright) population may suggest a NK helper effect on T cell adaptive responses. Activation of the innate and adaptive arms of the immune system by DNA immunization may be of particular importance to the efficacy of therapeutic interventions in a context of chronic infections.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00988767.

Blockade of PD-1/B7-H1 interaction restores effector CD8+ T cell responses in a hepatitis C virus core murine model

The impaired function of CD8(+) T cells is characteristic of hepatitis C virus (HCV) persistent infection. HCV core protein has been reported to inhibit CD8(+) T cell responses. To determine the mechanism of the HCV core in suppressing Ag-specific CD8(+) T cell responses, we generated a transgenic mouse, core(+) mice, where the expression of core protein is directed to the liver using the albumin promoter. Using a recombinant adenovirus to deliver Ag, we demonstrated that core(+) mice failed to clear adenovirus-LacZ (Ad-LacZ) infection in the liver. The effector function of LacZ-specific CD8(+) T cells was particularly impaired in the livers of core(+) mice, with suppression of IFN-gamma, TNF-alpha, and granzyme B production by CD8(+) T cells. In addition, the impaired CD8(+) T cell responses in core(+) mice were accompanied by the enhanced expression of the inhibitory receptor programmed death-1 (PD-1) by LacZ-specific CD8(+) T cells and its ligand B7-H1 on liver dendritic cells following Ad-LacZ infection. Importantly, blockade of the PD-1/B7-H1 inhibitory pathway (using a B7-H1 blocking antibody) in core(+) mice enhanced effector function of CD8(+) T cells and cleared Ad-LacZ-infection as compared with that in mice treated with control Ab. This suggests that the regulation of the PD-1/B7-H1 inhibitory pathway is crucial for HCV core-mediated impaired T cell responses and viral persistence in the liver. This also suggests that manipulation of the PD-1/B7-H1 pathway may be a potential immunotherapy to enhance effector T cell responses during persistent HCV infection.

Regulatory T cells: what role do they play in antitumor immunity in patients with head and neck cancer?

Advances in the treatment modalities for head and neck squamous cell carcinoma (HNSCC) over the last 20 years involving surgery, radiotherapy, chemotherapy, and immunotherapy are not fully reflected in increases in the 5-year survival rates, mainly due to locoregional recurrences and to a lesser extent, distant metastasis. This can, in part, be attributed to the fact that HNSCC induces severe depression of a patient's immune system. Recent advances in understanding the complex host-tumor interactions have led to the identification of a distinct suppressor cell population known as regulatory T cells that play a crucial role in maintaining T-cell tolerance to self-antigens. Here, we present a critical review of our understanding of the involvement of regulatory T cells in controlling the T-cell immune response in tumor occurrence and progression in HNSCC with an emphasis on current and future immunotherapeutic approaches involving regulatory T cells.

Dendritic cells, the liver, and transplantation

Interstitial liver dendritic cells (DCs) exhibit phenotypic diversity and functional plasticity. They play important roles in both innate and adaptive immunity. Their comparatively low inherent T cell stimulatory ability and the outcome of their interactions with CD4(+) and CD8(+) T cells, as well as with natural killer (NK) T cells and NK cells within the liver, may contribute to regulation of hepatic inflammatory responses and liver allograft outcome. Liver DCs migrate in the steady state and after liver transplantation to secondary lymphoid tissues, where the outcome of their interaction with antigen-specific T cells determines the balance between tolerance and immunity. Systemic and local environmental factors that are modulated by ischemia-reperfusion injury, liver regeneration, microbial infection, and malignancy influence hepatic DC migration, maturation, and function. Current research in DC biology is providing new insights into the role of these important antigen-presenting cells in the complex events that affect liver transplant outcome.

Frontiers in Nephrology: The Varied Faces of Natural Killer Cells in Transplantation—Contributions to Both Allograft Immunity and Tolerance

Natural killer (NK) cells are recognized for providing an important early innate immune response to viral and bacterial pathogens and for the surveillance of stressed and transformed autologous cells. However, with the exception of a pronounced role in allogeneic hematopoietic stem cell rejection, it has been challenging to ascribe the precise roles for NK cells in reactivity to tissue and solid-organ transplants. In general, NK cells initiate a rapid, proinflammatory environment that is conducive to many forms of effective immune host defense. This reactivity is often considered deleterious to allograft survival because NK cells are implicated in promoting both acute and chronic graft injury. However, more recent findings indicate that NK cells can also play a surprisingly profound role in allograft tolerance induction. This duality of function requires a reconsideration of the nature and consequence of NK cell reactivity during the allograft response. This review focuses on the differing "faces" of NK cells, especially the unexpected role of NK cells in allograft tolerance induction.