Aurélie Thedrez

Self/non‐self discrimination by human γδ T cells: simple solutions for a complex issue?

Summary:  Although γδ T cells express clonally distributed T‐cell receptors (TCRs), a hallmark of adaptive immunity, they are classically considered as innate‐like effectors, owing to the high frequency of preactivated γδ T cells, with restricted antigen recognition repertoire in particular tissue locations. Actually, such features are shared only by a fraction of γδ T‐cell subsets located in the skin and reproductive organ mucosa in rodents or in peripheral blood in humans. By contrast, other γδ subsets, e.g. those found in rodent and human spleen, show diverse antigenic reactivity patterns and mixed naive/memory phenotypes. Thus, γδ T cells are made of both ‘primitive’ subsets endowed with innate‐like properties and ‘evolved’ subsets able to mount anamnestic responses like conventional major histocompatibility complex‐restricted αβ T cells. In this article, we show that human γδ T cells, although heterogeneous, do share recurrent innate features that distinguish them from mainstream αβ T cells. In particular, most of them are activated on TCR‐ or natural killer receptor‐mediated recognition of a restricted set of conserved yet poorly defined endogenous stress determinants. This rather simple recognition mechanism allows human γδ T cells to discriminate healthy cells from altered cells and to exert a variety of immunostimulatory or regulatory functions. The recent availability of synthetic γδ T‐cell agonists mimicking these natural stress‐induced ligands have fostered development of immunotherapeutic strategies, with broad indications against infectious and tumor diseases, which are briefly reviewed here.

IL-21-Mediated Potentiation of Antitumor Cytolytic and Proinflammatory Responses of Human Vγ9Vδ2 T Cells for Adoptive Immunotherapy

Vγ9Vδ2 T lymphocytes are a major human γδ T cell subset that react against a wide array of tumor cells, through recognition of phosphorylated isoprenoid pathway metabolites called phosphoantigens. Immunotherapeutic protocols targeting Vγ9Vδ2 T cells have yielded promising, yet limited, signs of antitumor efficacy. To improve these approaches, we analyzed the effects on γδ T cells of IL-21, a cytokine known to enhance proliferation and effector functions of CD8+ T cells and NK cells. IL-21 induced limited division of phosphoantigen-stimulated Vγ9Vδ2 T cells, but did not modulate their sustained expansion induced by exogenous IL-2. Vγ9Vδ2 T cells expanded in the presence of IL-21 and IL-2 showed enhanced antitumor cytolytic responses, associated with increased expression of CD56 and several lytic molecules, and increased tumor-induced degranulation capacity. IL-21 plus IL-2-expanded Vγ9Vδ2 T cells expressed higher levels of inhibitory receptors (e.g., ILT2 and NKG2A) and lower levels of the costimulatory molecule NKG2D. Importantly, these changes were rapidly and reversibly induced after short-term culture with IL-21. Finally, IL-21 irreversibly enhanced the proinflammatory Th1 polarization of expanded Vγ9Vδ2 T cells when added at the beginning of the culture. These data suggest a new role played by IL-21 in the cytotoxic and Th1 programming of precommitted Ag-stimulated γδ T cells. On a more applied standpoint, IL-21 could be combined to IL-2 to enhance γδ T cell-mediated antitumor responses, and thus represents a promising way to optimize immunotherapies targeting this cell subset.

Immunity of human epithelial ovarian carcinoma: the paradigm of immune suppression in cancer

Epithelial ovarian cancer (EOC) is a significant cause of cancer-related mortality in women, and there has been no substantial decrease in the death rates due to EOC in the last three decades. Thus, basic knowledge regarding ovarian tumor cell biology is urgently needed to allow the development of innovative treatments for EOC. Traditionally, EOC has not been considered an immunogenic tumor, but there is evidence of an immune response to EOC in patients. Clinical data demonstrate that an antitumor immune response and immune evasion mechanisms are correlated with a better and lower survival, respectively, providing evidence for the immunoediting hypothesis in EOC. This review focuses on the immune response and immune suppression in EOC. The immunological roles of chemotherapy and surgery in EOC are also described. Finally, we detail pilot data supporting the efficiency of immunotherapy in the treatment of EOC and the emerging concept that immunomodulation aimed at counteracting the immunosuppressive microenvironment must be associated with immunotherapy strategies.

Proprotein Convertase Subtilisin Kexin Type 9 Inhibition for Autosomal Recessive Hypercholesterolemia - Brief Report

Objective—Proprotein convertase subtilisin kexin type 9 (PCSK9) inhibitors lower low-density lipoprotein (LDL) cholesterol in the vast majority of patients with autosomal dominant familial hypercholesterolemia. Will PCSK9 inhibition with monoclonal antibodies, in particular alirocumab, be of therapeutic value for patients with autosomal recessive hypercholesterolemia (ARH)? Approach and Results—Primary lymphocytes were obtained from 28 genetically characterized ARH patients and 11 controls. ARH lymphocytes treated with mevastatin were incubated with increasing doses of recombinant PCSK9 with or without saturating concentrations of alirocumab. Cell surface LDL receptor expression measured by flow cytometry and confocal microscopy was higher in ARH than in control lymphocytes. PCSK9 significantly reduced LDL receptor expression in ARH lymphocytes albeit to a lower extent than in control lymphocytes (25% versus 76%, respectively), an effect reversed by alirocumab. Fluorescent LDL cellular uptake, also measured by flow cytometry, was reduced in ARH lymphocytes compared with control lymphocytes. PCSK9 significantly lowered LDL cellular uptake in ARH lymphocytes, on average by 18%, compared with a 46% reduction observed in control lymphocytes, an effect also reversed by alirocumab. Overall, the effects of recombinant PCSK9, and hence of alirocumab, on LDL receptor expression and function were significantly less pronounced in ARH than in control cells. Conclusions—PCSK9 inhibition with alirocumab on top of statin treatment has the potential to lower LDL cholesterol in some autosomal recessive hypercholesterolemia patients.

Proprotein Convertase Subtilisin Kexin Type 9 Inhibition for Autosomal Recessive Hypercholesterolemia

Objective—Proprotein convertase subtilisin kexin type 9 (PCSK9) inhibitors lower low-density lipoprotein (LDL) cholesterol in the vast majority of patients with autosomal dominant familial hypercholesterolemia. Will PCSK9 inhibition with monoclonal antibodies, in particular alirocumab, be of therapeutic value for patients with autosomal recessive hypercholesterolemia (ARH)? Approach and Results—Primary lymphocytes were obtained from 28 genetically characterized ARH patients and 11 controls. ARH lymphocytes treated with mevastatin were incubated with increasing doses of recombinant PCSK9 with or without saturating concentrations of alirocumab. Cell surface LDL receptor expression measured by flow cytometry and confocal microscopy was higher in ARH than in control lymphocytes. PCSK9 significantly reduced LDL receptor expression in ARH lymphocytes albeit to a lower extent than in control lymphocytes (25% versus 76%, respectively), an effect reversed by alirocumab. Fluorescent LDL cellular uptake, also measured by flow cytometry, was reduced in ARH lymphocytes compared with control lymphocytes. PCSK9 significantly lowered LDL cellular uptake in ARH lymphocytes, on average by 18%, compared with a 46% reduction observed in control lymphocytes, an effect also reversed by alirocumab. Overall, the effects of recombinant PCSK9, and hence of alirocumab, on LDL receptor expression and function were significantly less pronounced in ARH than in control cells. Conclusions—PCSK9 inhibition with alirocumab on top of statin treatment has the potential to lower LDL cholesterol in some autosomal recessive hypercholesterolemia patients.

A quantitative deficiency in peripheral blood Vγ9Vδ2 cells is a negative prognostic biomarker in ovarian cancer patients.

Vγ9Vδ2 cells are cytotoxic T cells that are able to recognize epithelial ovarian carcinoma (EOC) cells. Therefore, Vγ9Vδ2 cell-based adoptive transfer is an attractive therapy for EOC. However, the inefficient ex vivo expansion after specific stimulation of Vγ9Vδ2 cells from some patients and the relationships between Vγ9Vδ2 cells and clinical course of EOC are issues that remain to be clarified. Herein, peripheral blood mononuclear cells (PBMCs) from 60 EOC patients were stimulated with bromohydrin pyrophosphate (BrHPP) or zoledronate, which are specific agonists of Vγ9Vδ2 cells. The compounds differed in their efficacies to induce ex vivo Vγ9Vδ2 PBMC expansion, but 16/60 samples remained inefficiently expanded with both stimuli. Interestingly, the Vγ9Vδ2 cells in these low-responding PBMCs displayed before expansion (ex vivo PBMCs) an altered production of the pro-inflammatory cytokines IFN-γ and TNF-α, a decreased naive fraction and a reduced frequency. No evidence of an involvement of CD4+CD25+Foxp3+ regulatory cells was observed. Importantly, our data also demonstrate that a Vγ9Vδ2 cell frequency of 0.35% or less in EOC PBMCs could be used to predict low responses to both BrHPP and zoledronate. Moreover, our data highlight that such a deficiency is not correlated with advanced EOC stages but is associated with more refractory states to platinum-based chemotherapy and is an independent predictor of shorter disease-free survival after treatment. These results are the first to suggest a potential contribution of Vγ9Vδ2 cells to the anti-tumor effects of chemotherapeutic agents and they strengthen interest in strategies that might increase Vγ9Vδ2 cells in cancer patients.

Homozygous Familial Hypercholesterolemia Patients With Identical Mutations Variably Express the LDLR (Low-Density Lipoprotein Receptor)Highlights: Implications for the Efficacy of Evolocumab

Objective— Evolocumab, a PCSK9 (proprotein convertase subtilisin kexin type 9)–neutralizing antibody, lowers low-density lipoprotein cholesterol (LDL-C) in homozygous familial hypercholesterolemic (HoFH) patients with reduced LDLR (low-density lipoprotein receptor) function. However, their individual responses are highly variable, even among carriers of identical LDLR genetic defects. We aimed to elucidate why HoFH patients variably respond to PCSK9 inhibition. Approach and Results— Lymphocytes were isolated from 22 HoFH patients enrolled in the TAUSSIG trial (Trial Assessing Long Term Use of PCSK9 Inhibition in Subjects With Genetic LDL Disorders). Ten patients were true homozygotes (FH1/FH1) and 5 identical compound heterozygotes (FH1/FH2). Lymphocytes were plated with or without mevastatin, recombinant PCSK9 (rPCSK9), or a PCSK9-neutralizing antibody. Cell surface LDLR expression was analyzed by flow cytometry. All HoFH lymphocytes had reduced cell surface LDLR expression compared with non-FH lymphocytes, for each treatment modality. Lymphocytes from FH1/FH2 patients (LDLR defective/negative) displayed the lowest LDLR expression levels followed by lymphocytes from FH1/FH1 patients (defective/defective). Mevastatin increased, whereas rPCSK9 reduced LDLR expression. The PCSK9-neutralizing antibody restored LDLR expression. Lymphocytes displaying higher LDLR expression levels were those isolated from patients presenting with lowest levels of LDL-C and apolipoprotein B, before and after 24 weeks of evolocumab treatment. These negative correlations remained significant in FH1/FH1 patients and appeared more pronounced when patients with apolipoprotein E3/E3 genotypes were analyzed separately. Significant positive correlations were found between the levels of LDLR expression and the percentage reduction in LDL-C on evolocumab treatment. Conclusions— Residual LDLR expression in HoFH is a major determinant of LDL-C levels and seems to drive their individual response to evolocumab.

CRTAM Receptor Engagement by Necl-2 on Tumor Cells Triggers Cell Death of Activated Vγ9Vδ2 T Cells

Human Vγ9Vδ2 T cells exert potent in vitro and in vivo antitumor activities, making them promising candidates for immunotherapy strategies. Recognition of tumor cells by Vγ9Vδ2 T cells requires engagement of the TCR and/or NK receptors. Recently, one of the novel NK receptors, the class I–restricted T cell–associated molecule (CRTAM), has been described to promote cytotoxic function of NK cells and to lead to IFN-γ secretion by CD8+ T cells through interaction with its ligand, Necl-2. A better understanding of the role of CRTAM in Vγ9Vδ2 T cell functions is highly relevant to optimize innate-like T cell–based cancer immunotherapy. In this article, we report that CRTAM is transiently expressed on activated Vγ9Vδ2 T lymphocytes following TCR engagement. However, CRTAM–Necl-2 interaction does not modify the cytotoxic function or IFN-γ secretion of Vγ9Vδ2 T cells. The expression of CRTAM in activated Vγ9Vδ2 T cells is quickly downregulated following interaction with Necl-2 on tumor cells. Of interest, CRTAM is concurrently acquired at the cell surface of Necl-2+ tumor cells through Vγ9Vδ2 T cell membrane capture. Finally, we highlight that coculture experiments with tumor cells expressing Necl-2 result in significant cell death of CRTAM+ Vγ9Vδ2 T cells. CRTAM-mediated cell death is dependent on an autophagic process, but not on apoptosis or necroptosis, as attested by the expression of characteristic markers and blocking experiments with specific inhibitors. On the basis of these findings, we propose that Necl-2 on tumor cells represents a new tumor counterattack mechanism and a potential target to improve efficiency of γδ T cell–based immunotherapy.

[Nectins and nectin-like receptors DNAM-1 and CRTAM: new ways for tumor escape].

Nectin and nectin-like (Necl) are cell adhesion molecules expressed in various tumors. They were alternatively reported as involved in tumor suppressor or oncogenic functions that led to their use as histological or serological cancer markers. Gene inactivation in lung carcinoma but overexpression in leukemia were reported for Necl-2. DNAM-1 and CRTAM are emerging NK receptors of immune cells that were described to interact with nectin and Necl. DNAM-1, constitutively expressed by CD8(+) T cells, NK or γδ T lymphocytes, is a ligand of Necl-5. It participates to tumor immunosurveillance promoting Necl-5 expressing tumor cell lysis. CRTAM, only expressed after lymphocyte activation, is a ligand of Necl-2. Engagement of CRTAM with Necl-2 has opposite effects depending on the type of lymphocyte. For NK or CD8(+) T cells, it promotes cytotoxicity and IFNγ secretion favoring immunosurveillance. By contrast, CRTAM/Necl-2 interaction triggers cell death of activated TVg9Vd2 γδ T cells favoring immune escape. Nectin and Necl-mediated interactions appear to be crucial for the delicate balance between tumor escape and antitumor response.