Bruno Silva-Santos

CD27 is a thymic determinant of the balance between interferon-gamma- and interleukin 17-producing gammadelta T cell subsets.

The production of cytokines such as interferon-γ and interleukin 17 by αβ and γδ T cells influences the outcome of immune responses. Here we show that most γδ T lymphocytes expressed the tumor necrosis factor receptor family member CD27 and secreted interferon-γ, whereas interleukin 17 production was restricted to CD27− γδ T cells. In contrast to the apparent plasticity of αβ T cells, the cytokine profiles of these distinct γδ T cell subsets were essentially stable, even during infection. These phenotypes were established during thymic development, when CD27 functions as a regulator of the differentiation of γδ T cells at least in part by inducing expression of the lymphotoxin-β receptor and genes associated with trans-conditioning and interferon-γ production. Thus, the cytokine profiles of peripheral γδ T cells are predetermined mainly by a mechanism involving CD27.

The inter-relatedness and interdependence of mouse T cell receptor γδ + and αβ + cells

Although T cell receptor (TCR)γδ+ and TCRαβ+ cells are commonly viewed as functionally independent, their relatedness and potential interdependence remain enigmatic. Here we have identified a gene profile that distinguishes mouse γδ cell populations from conventional αβ T cells. However, this profile was also expressed by sets of unconventional αβ T cells. Therefore, whereas TCR specificity determines the involvement of a T cell in an immune response, the cells functional potential, as assessed by gene expression, does not segregate with the TCR. By monitoring the described gene profile, we show that γδ T cell development and function in TCRβ-deficient mice was impaired because of the absence of αβ T cell progenitors. Thus, normal γδ cell development is dependent on the development of conventional αβ T cells.

γδ T cells in cancer.

With the promise of T cell-based therapy for cancer finally becoming reality, this Review focuses on the less-studied γδ T cell lineage and its diverse responses to tumours. γδ T cells have well-established protective roles in cancer, largely on the basis of their potent cytotoxicity and interferon-γ production. Besides this, recent studies have revealed a series of tumour-promoting functions that are linked to interleukin-17-producing γδ T cells. Here, we integrate the current knowledge from both human and mouse studies to highlight the potential of γδ T cell modulation to improve cancer immunotherapy.

Identification of Regulatory Foxp3+ Invariant NKT Cells Induced by TGF-β

Invariant NKT (iNKT) cells were shown to prevent the onset of experimental autoimmune encephalomyelitis in mice following administration of their specific TCR agonist α-galactosylceramide. We found that this protection was associated with the emergence of a Foxp3+ iNKT cell population in cervical lymph nodes. We demonstrate that the differentiation of these cells is critically dependent on TGF-β in both mice and humans. Moreover, in vivo generation of Foxp3+ iNKT cells was observed in the TGF-β–rich environment of the murine gut. Foxp3+ iNKT cells displayed a phenotype similar to that of Foxp3+ regulatory T cells, and they suppress through a contact-dependent, glucocorticoid-induced TNFR-mediated mechanism. Nevertheless, Foxp3+ iNKT cells retain distinctive NKT cell characteristics, such as promyelocytic leukemia zinc finger protein expression and preferential homing to the liver following adoptive transfer, where they stably maintained Foxp3 expression. Our data thus unveil an unexpected capacity of iNKT cells to acquire regulatory functions that may contribute to the establishment of immunological tolerance.

Early events in the thymus affect the balance of effector and regulatory T cells

In cellular immunology the critical balance between effector and regulatory mechanisms is highlighted by serious immunopathologies attributable to mutations in Foxp3, a transcription factor required for a major subset of regulatory T (Tr) cells. Thus, many studies have focused on the developmental origin of Tr cells, with the prevailing view that they emerge in the thymus from late-stage T-cell progenitors whose T-cell receptors (TCRs) engage high affinity (agonist) ligands. This study questions the completeness of that interpretation. Here we show that without any obvious effect on TCR-mediated selection, the normal differentiation of mouse γδ T cells into potent cytolytic and interferon-γ-secreting effector cells is switched towards an aggregate regulatory phenotype by limiting the capacity of CD4+CD8+ T-cell progenitors to influence in trans early γδ cell progenitors. Unexpectedly, we found that the propensity of early TCR-αβ+ progenitors to differentiate into Foxp3+ Tr cells is also regulated in trans by CD4+CD8+ T-cell progenitor cells, before agonist selection.

Differentiation of human peripheral blood Vδ1+ T cells expressing the natural cytotoxicity receptor NKp30 for recognition of lymphoid leukemia cells

The success of cancer immunotherapy depends on productive tumor cell recognition by killer lymphocytes. γδ T cells are a population of innate-like lymphocytes endowed with strong, MHC-unrestricted cytotoxicity against tumor cells. This notwithstanding, we recently showed that a large proportion of human hematologic tumors is resistant to γδ peripheral blood lymphocytes (PBLs) activated with specific agonists to the highly prevalent Vγ9Vδ2 TCR. Although this probably constitutes an important limitation to current γδ T cell-mediated immunotherapy strategies, we describe here the differentiation of a novel subset of Vδ2(-) Vδ1(+) PBLs expressing natural cytotoxicity receptors (NCRs) that directly mediate killing of leukemia cell lines and chronic lymphocytic leukemia patient neoplastic cells. We show that Vδ1(+) T cells can be selectively induced to express NKp30, NKp44 and NKp46, through a process that requires functional phosphatidylinositol 3-kinase (PI-3K)/AKT signaling on stimulation with γ(c) cytokines and TCR agonists. The stable expression of NCRs is associated with high levels of granzyme B and enhanced cytotoxicity against lymphoid leukemia cells. Specific gain-of-function and loss-of-function experiments demonstrated that NKp30 makes the most important contribution to TCR-independent leukemia cell recognition. Thus, NKp30(+) Vδ1(+) T cells constitute a novel, inducible and specialized killer lymphocyte population with high potential for immunotherapy of human cancer.

Targeting γδ T Lymphocytes for Cancer Immunotherapy: From Novel Mechanistic Insight to Clinical Application

Abundant interferon-γ secretion, potent cytotoxicity, and major histocompatibility complex-independent targeting of a large spectrum of tumors make γδ T cells attractive mediators of cancer immunotherapy. However, a better understanding of the molecular mechanisms involved in tumor cell recognition and γδ T-cell activation is required to improve the limited success of γδ T-cell-mediated treatments. Here, we review key advances in basic knowledge made over the past 3 years, and summarize the results of γδ T-cell-based clinical trials concluded to date. We also highlight new research directions on the basis of the modulation of receptors that control the function of γδ T cells.

The MHC class Ib protein ULBP1 is a nonredundant determinant of leukemia/lymphoma susceptibility to γδ T-cell cytotoxicity

On the path to successful immunotherapy of hematopoietic tumors, gammadelta T cells offer great promise because of their human leukocyte antigen (HLA)-unrestricted targeting of a wide variety of leukemias/lymphomas. However, the molecular mechanisms underlying lymphoma recognition by gammadelta T cells remain unclear. Here we show that the expression levels of UL16-binding protein 1 (ULBP1) determine lymphoma susceptibility to gammadelta T cell-mediated cytolysis. Consistent with this, blockade of NKG2D, the receptor for ULBP1 expressed on all Vgamma9(+) T cells, significantly inhibits lymphoma cell killing. Specific loss-of-function studies demonstrate that the role of ULBP1 is nonredundant, highlighting a thus far unique physiologic relevance for tumor recognition by gammadelta T cells. Importantly, we observed a very wide spectrum of ULBP1 expression levels in primary biopsies obtained from lymphoma and leukemia patients. We suggest this will impact on the responsiveness to gammadelta T cell-based immunotherapy, and therefore propose ULBP1 to be used as a leukemia/lymphoma biomarker in upcoming clinical trials.

The split nature of tumor-infiltrating leukocytes: Implications for cancer surveillance and immunotherapy.

An important development in tumor immunology was the identification of highly diverse tumor-infiltrating leukocyte subsets that can play strikingly antagonistic functions. Namely, “anti-tumor” vs. “pro-tumor” roles have been suggested for Th1 and Th17 subsets of CD4+ T cells, Type I or Type II NKT cells, M1 and M2 macrophages, or N1 and N2 neutrophils, respectively. While these findings are being validated in cancer patients, it is also clear that the balance between infiltrating CD8+ cytotoxic and Foxp3+ regulatory T cells has prognostic value. Here we review the pre-clinical and clinical data that have shaped our current understanding of tumor-infiltrating leukocytes.

Epithelial and dendritic cells in the thymic medulla promote CD4+Foxp3+ regulatory T cell development via the CD27-CD70 pathway

CD27–CD70 signals are required for optimal development of natural regulatory T cells from the thymus.