Ludovic Martinet

Human Solid Tumors Contain High Endothelial Venules: Association with T- and B-Lymphocyte Infiltration and Favorable Prognosis in Breast Cancer

The mechanisms governing infiltration of lymphocytes into tumors remain poorly characterized, in spite of the critical impact of these cells on patient prognosis and therapeutic responses. High endothelial venules (HEV) are blood vessels found in lymphoid tissues, specialized in lymphocyte recruitment, but their implications in human cancer are unknown. In this article, we report the presence of MECA 79(+) blood vessels displaying all the phenotypic characteristics of HEVs in most of the 319 human primary solid tumors, including melanomas, breast, ovarian, colon, and lung carcinomas, analyzed. Tumor HEVs were specifically located within lymphocyte-rich areas, and their density within the tumor stroma was a strong predictor of infiltration by CD3(+) and CD8(+) T cells as well as B cells. Large-scale flow cytometric and quantitative reverse transcriptase-PCR analyses in freshly operated breast tumors revealed that high densities of tumor HEVs correlated with increased naive, central memory and activated effector memory T-cell infiltration and upregulation of genes related to T-helper 1 adaptive immunity and T-cell cytotoxicity. Finally, in a retrospective cohort of 146 invasive breast cancer patients, we found that high densities of tumor HEVs independently conferred a lower risk of relapse and significantly correlated with longer metastasis-free, disease-free, and overall survival rates. Together, our findings suggest that tumor HEVs function as major gateways for lymphocyte infiltration into human tumors, and may represent attractive targets for cancer diagnosis and therapy.

The receptors CD96 and CD226 oppose each other in the regulation of natural killer cell functions

CD96, CD226 (DNAM-1) and TIGIT belong to an emerging family of receptors that interact with nectin and nectin-like proteins. CD226 activates natural killer (NK) cell–mediated cytotoxicity, whereas TIGIT reportedly counterbalances CD226. In contrast, the role of CD96, which shares the ligand CD155 with CD226 and TIGIT, has remained unclear. In this study we found that CD96 competed with CD226 for CD155 binding and limited NK cell function by direct inhibition. As a result, Cd96−/− mice displayed hyperinflammatory responses to the bacterial product lipopolysaccharide (LPS) and resistance to carcinogenesis and experimental lung metastases. Our data provide the first description, to our knowledge, of the ability of CD96 to negatively control cytokine responses by NK cells. Blocking CD96 may have applications in pathologies in which NK cells are important.

Balancing natural killer cell activation through paired receptors

Natural killer (NK) cells are innate lymphocytes that are crucial for the control of infections and malignancies. NK cells express a variety of inhibitory and activating receptors that facilitate fine discrimination between damaged and healthy cells. Among them, a family of molecules that bind nectin and nectin-like proteins has recently emerged and has been shown to function as an important regulator of NK cell functions. These molecules include CD226, T cell immunoreceptor with immunoglobulin and ITIM domains (TIGIT), CD96, and cytotoxic and regulatory T cell molecule (CRTAM). In this Review, we focus on the recent advances in our understanding of how these receptors regulate NK cell biology and of their roles in pathologies such as cancer, infection and autoimmunity.

Molecular mechanisms of natural killer cell activation in response to cellular stress

Protection against cellular stress from various sources, such as nutritional, physical, pathogenic, or oncogenic, results in the induction of both intrinsic and extrinsic cellular protection mechanisms that collectively limit the damage these insults inflict on the host. The major extrinsic protection mechanism against cellular stress is the immune system. Indeed, it has been well described that cells that are stressed due to association with viral infection or early malignant transformation can be directly sensed by the immune system, particularly natural killer (NK) cells. Although the ability of NK cells to directly recognize and respond to stressed cells is well appreciated, the mechanisms and the breadth of cell-intrinsic responses that are intimately linked with their activation are only beginning to be uncovered. This review will provide a brief introduction to NK cells and the relevant receptors and ligands involved in direct responses to cellular stress. This will be followed by an in-depth discussion surrounding the various intrinsic responses to stress that can naturally engage NK cells, and how therapeutic agents may induce specific activation of NK cells and other innate immune cells by activating cellular responses to stress.

DNAM-1 control of natural killer cells functions through nectin and nectin-like proteins.

Natural killer (NK) cells represent key innate immune cells that restrain viral infection and malignant transformation and help mount an adaptive immune response. To perform such complicated tasks, NK cells express a wide set of inhibitory and activating receptors that alert them against cellular stress without damaging healthy cells. A new family of receptors that recognize nectin and nectin‐like molecules has recently emerged as a critical regulator of NK cell functions. The most famous member of this family, DNAX accessory molecule (DNAM‐1, CD226), is an adhesion molecule that control NK cell cytotoxicity and interferon‐γ production against a wide range of cancer and infected cells. Its ligands CD112 and CD155 have been described in different pathological conditions, and recent evidence indicates that their expression is regulated by cellular stress. Additional receptors have been shown to bind DNAM‐1 ligands and modulate NK cell functions bringing another level of complexity. These include CD96 (TACTILE) and TIGIT (WUCAM, VSTM3). Here, we review the role of DNAM‐1, TIGIT and CD96 in NK cell biology summarizing the recent advances made on the role of these receptors in various pathologies, such as cancer, viral infections and autoimmunity.

Suppression of Metastases Using a New Lymphocyte Checkpoint Target for Cancer Immunotherapy

UNLABELLED CD96 has recently been shown as a negative regulator of mouse natural killer (NK)-cell activity, with Cd96(-/-)mice displaying hyperresponsive NK cells upon immune challenge. In this study, we have demonstrated that blocking CD96 with a monoclonal antibody inhibited experimental metastases in three different tumor models. The antimetastatic activity of anti-CD96 was dependent on NK cells, CD226 (DNAM-1), and IFNγ, but independent of activating Fc receptors. Anti-CD96 was more effective in combination with anti-CTLA-4, anti-PD-1, or doxorubicin chemotherapy. Blocking CD96 in Tigit(-/-)mice significantly reduced experimental and spontaneous metastases compared with its activity in wild-type mice. Co-blockade of CD96 and PD-1 potently inhibited lung metastases, with the combination increasing local NK-cell IFNγ production and infiltration. Overall, these data demonstrate that blocking CD96 is a new and complementary immunotherapeutic strategy to reduce tumor metastases. SIGNIFICANCE This article illustrates the antimetastatic activity and mechanism of action of an anti-CD96 antibody that inhibits the CD96-CD155 interaction and stimulates NK-cell function. Targeting host CD96 is shown to complement surgery and conventional immune checkpoint blockade.

Stimulated γδ T Cells Increase the In Vivo Efficacy of Trastuzumab in HER-2+ Breast Cancer

One fourth of women with HER-2+ metastatic breast carcinoma are treated with a combination regimen with trastuzumab, but the frequent resistance to this Ab requires definition of new means to improve its bioactivity. The mechanisms of action of trastuzumab involve several pathways including Ab-dependent cellular cytotoxicity. Because human γδ T lymphocytes mediate Ab-dependent cellular cytotoxicity and can be activated further by phosphoantigens, these cells are prone to improve the efficacy of Abs, as recently demonstrated for CD20+ B cell lymphomas. Whether this concept applies as well with carcinomas remained to be demonstrated in vivo, however. In this study, we asked whether a combination of trastuzumab and phosphoantigen-stimulated γδ lymphocytes increases the efficacy of trastuzumab against HER-2+ breast carcinoma cell lines in vivo. We report that repeated infusions of this combination had a better efficacy than that of trastuzumab alone against HER-2+ mammary carcinoma xenografts in mice. In these models, reduction of tumor growth was observed together with trastuzumab opsonization of HER-2+ cells and tumor infiltration by γδ lymphocytes. In addition in humans, the mammary carcinomas of 27 of 30 patients showed significant γδ T cell infiltrates. Altogether, these findings indicate that combination of trastuzumab and stimulated γδ cells represents a new strategy to improve the efficacy of Herceptin (trastuzumab) in HER-2+ breast cancer.

PGE2 inhibits natural killer and γδ T cell cytotoxicity triggered by NKR and TCR through a cAMP-mediated PKA type I-dependent signaling

Natural killer (NK) and unconventional gammadelta T cells, by their ability to sense ligands induced by oncogenic stress on cell surface and to kill tumor cells without a need for clonal expansion, show a great therapeutic interest. They use numerous activating and inhibitory receptors which can function with some independence to trigger or inhibit destruction of target cells. Previous reports demonstrated that PGE(2) is able to suppress the destruction of some tumor cell lines by NK and gammadelta T cells but it remained uncertain if PGE(2) interferes with the different activating receptors governing the cytolytic responses of NK and gammadelta T cells. In this report, using the model of specific redirected lysis of the mouse FcgammaR(+) cell line P815, we clearly demonstrate that the major NK receptors (NKR): NKG2D, CD16 and natural cytotoxicity receptors (NCR: NKp30, NKp44, NKp46) and gammadelta T cell receptors TCR Vgamma9Vdelta2, NKG2D and CD16 are all inhibited by PGE(2). As is the case with gammadelta T cells, we show that PGE(2) binds on E-prostanoid 2 (EP2) and EP4 receptors on NK cells. Finally, we delineate that the signaling of the blockade by PGE(2) is mediated through a cAMP-dependent activation of PKA type I which inhibits early signaling protein of cytotoxic cells. In the discussion, we focused on how these data should impact particular approaches in the treatment of cancer.

High Endothelial Venule Blood Vessels for Tumor-Infiltrating Lymphocytes Are Associated with Lymphotoxin β–Producing Dendritic Cells in Human Breast Cancer

Blood vessels and tumor angiogenesis are generally associated with tumor growth and poor clinical outcome of cancer patients. However, we recently discovered that some blood vessels present within the tumor microenvironment can be associated with favorable prognosis. These vessels, designated tumor high endothelial venules (HEVs), appear to facilitate tumor destruction by allowing high levels of lymphocyte infiltration into tumors. In this study, we investigated the mechanisms regulating HEV blood vessels in human breast cancer. We found that lymphotoxin β was overexpressed in tumors containing high densities of HEVs (HEVhigh) and correlated to DC-LAMP, a marker of mature DCs. DCs were the main producers of lymphotoxin β in freshly resected HEVhigh breast tumor samples, and the density of DC-LAMP+ DCs clusters was strongly correlated with the density of tumor HEVs, T and B cell infiltration, and favorable clinical outcome in a retrospective cohort of 146 primary invasive breast cancer patients. Densities of tumor HEVs and DC-LAMP+ DCs were strongly reduced during breast cancer progression from in situ carcinoma to invasive carcinoma, suggesting that loss of tumor HEVs is a critical step during breast cancer progression. Finally, an increase in the infiltration of regulatory T cells was observed in HEVhigh breast tumors, indicating that tumor HEVs can develop in the presence of regulatory T cells. Together, our results support a key role for DCs and DC-derived lymphotoxin in the formation of tumor HEVs. These findings are important because novel therapeutic strategies based on the modulation of tumor HEVs could have a major impact on clinical outcome of cancer patients.

Natural killer cells are essential for the ability of BRAF inhibitors to control BRAFV600E-mutant metastatic melanoma.

BRAF(V600E) is a major oncogenic mutation found in approximately 50% of human melanoma that confers constitutive activation of the MAPK pathway and increased melanoma growth. Inhibition of BRAF(V600E) by oncogene targeting therapy increases overall survival of patients with melanoma, but is unable to produce many durable responses. Adaptive drug resistance remains the main limitation to BRAF(V600E) inhibitor clinical efficacy and immune-based strategies could be useful to overcome disease relapse. Tumor microenvironment greatly differs between visceral metastasis and primary cutaneous melanoma, and the mechanisms involved in the antimetastatic efficacy of BRAF(V600E) inhibitors remain to be determined. To address this question, we developed a metastatic BRAF(V600E)-mutant melanoma cell line and demonstrated that the antimetastatic properties of BRAF inhibitor PLX4720 (a research analogue of vemurafenib) require host natural killer (NK) cells and perforin. Indeed, PLX4720 not only directly limited BRAF(V600E)-induced tumor cell proliferation, but also affected NK cell functions. We showed that PLX4720 increases the phosphorylation of ERK1/2, CD69 expression, and proliferation of mouse NK cells in vitro. NK cell frequencies were significantly enhanced by PLX4720 specifically in the lungs of mice with BRAF(V600E) lung metastases. Furthermore, PLX4720 also increased human NK cell pERK1/2, CD69 expression, and IFNγ release in the context of anti-NKp30 and IL2 stimulation. Overall, this study supports the idea that additional NK cell-based immunotherapy (by checkpoint blockade or agonists or cytokines) may combine well with BRAF(V600E) inhibitor therapy to promote more durable responses in melanoma.