Skewed distribution of TCR V alpha 7-bearing T cells within tumor-infiltrating lymphocytes of HLA-A24(9)-positive patients with malignant glioma

The biology and functional importance of MAIT cells

In recent years, a population of unconventional T cells called 'mucosal-associated invariant T cells' (MAIT cells) has captured the attention of immunologists and clinicians due to their abundance in humans, their involvement in a broad range of infectious and non-infectious diseases and their unusual specificity for microbial riboflavin-derivative antigens presented by the major histocompatibility complex (MHC) class I-like protein MR1. MAIT cells use a limited T cell antigen receptor (TCR) repertoire with public antigen specificities that are conserved across species. They can be activated by TCR-dependent and TCR-independent mechanisms and exhibit rapid, innate-like effector responses. Here we review evidence showing that MAIT cells are a key component of the immune system and discuss their basic biology, development, role in disease and immunotherapeutic potential.

Human blood MAIT cell subsets defined using MR1 tetramers

Mucosal‐associated invariant T (MAIT) cells represent up to 10% of circulating human T cells. They are usually defined using combinations of non‐lineage‐specific (surrogate) markers such as anti‐TRAV1‐2, CD161, IL‐18Rα and CD26. The development of MR1‐Ag tetramers now permits the specific identification of MAIT cells based on T‐cell receptor specificity. Here, we compare these approaches for identifying MAIT cells and show that surrogate markers are not always accurate in identifying these cells, particularly the CD4⁺ fraction. Moreover, while all MAIT cell subsets produced comparable levels of IFNγ, TNF and IL‐17A, the CD4⁺ population produced more IL‐2 than the other subsets. In a human ontogeny study, we show that the frequencies of most MR1 tetramer⁺ MAIT cells, with the exception of CD4⁺ MAIT cells, increased from birth to about 25 years of age and declined thereafter. We also demonstrate a positive association between the frequency of MAIT cells and other unconventional T cells including Natural Killer T (NKT) cells and Vδ2⁺ γδ T cells. Accordingly, this study demonstrates that MAIT cells are phenotypically and functionally diverse, that surrogate markers may not reliably identify all of these cells, and that their numbers are regulated in an age‐dependent manner and correlate with NKT and Vδ2⁺ γδ T cells.

Immune suppression in tumors as a surmountable obstacle to clinical efficacy of cancer vaccines

Human tumors are usually not spontaneously eliminated by the immune system and therapeutic vaccination of cancer patients with defined antigens is followed by tumor regressions only in a small minority of the patients. The poor vaccination effectiveness could be explained by an immunosuppressive tumor microenvironment. Because T cells that infiltrate tumor metastases have an impaired ability to lyse target cells or to secrete cytokine, many researchers are trying to decipher the underlying immunosuppressive mechanisms. We will review these here, in particular those considered as potential therapeutic targets. A special attention will be given to galectins, a family of carbohydrate binding proteins. These lectins have often been implicated in inflammation and cancer and may be useful targets for the development of new anti-cancer therapies.

Glioblastoma-derived mechanisms of systemic immunosuppression

Abnormalities of cellular immunity are commonly seen in patients with glioblastoma (GBM), and the subsequent relative immunosuppression likely contributes to poor tumor-specific responses in affected individuals. Endogenous immune regulation is likely to limit the efficacy of a wide array of immunotherapeutic strategies, therefore mandating consideration in the continued development of novel treatments for GBM. Various tumor-associated factors have been implicated as potential generators of the immunosuppressive effect. This article outlines relevant experimentation exploring the nature of immune defects in patients with GBM, including a critical discussion of tumor-secreted factors, cell-surface proteins, and more recently described populations of immunoregulatory leukocytes that have potential roles in the subversion of cellular immunity.

Astrocytoma infiltrating lymphocytes include major T cell clonal expansions confined to the CD8 subset

Anaplastic astrocytoma and glioblastoma are frequent and malignant brain tumors that are infiltrated by T lymphocytes. Whether these cells result from non-specific inflammation following blood-brain barrier disruption or an antigen-driven specific immune response is unknown. In this study, an in-depth characterization of TCR diversity in tumor and blood RNA biopsies was performed in a series of 16 patients with malignant astrocytoma. Whilst there was no obvious restriction of the AV and BV gene segment usage, complementarity-determining region 3 size analysis and sequencing of amplified TCR transcripts revealed multiple T cell oligoclonal expansions in all astrocytomas analyzed. Unique T cell clones were present in different adjacent areas of a given tumor, but never detected in the blood. Quantification of the number of TCR clonal transcripts per microg of tumor RNA indicated that certain T cell clonal expansions may represent at least 300 cells/10(6) tumor cells. Furthermore, we demonstrated that the in vivo expanded clones were almost exclusively confined to the CD8(+) subset. Overall, these data suggest that spontaneous antigen-driven immune responses may be elicited against human astrocytoma despite the immunosuppressive microenvironment generated by the brain and the tumor itself. However, the ultimate failure of the immune system to control tumor growth could be the consequence of a deficient CD4 T(h) component of the response. This observation could have important consequences for the development of immunotherapies for astrocytoma patients.

Analysis of TCR usage in human tumors: a new tool for assessing tumor-specific immune responses

Tumor-infiltrating lymphocytes (TILs), through displaying a T-cell receptor (TCR) repertoire as heterogeneous as that of normal peripheral blood T cells, show overexpression of TCR variable-gene segments that include clonally expanded TCR sequences. Here, Marialuisa Sensi and Giorgio Parmiani analyze the available information on TCR usage by T cells present in the infiltrate of histologically different tumors and suggest that the analysis of TCR sequences represents a powerful new tool to assess the in vivo immune response to growing tumors. Ultimately, this strategy may lead to the identification and manipulation of T-cell populations endowed with antitumor reactivity.

The failure of current immunotherapy for malignant glioma. Tumor-derived TGF-beta, T-cell apoptosis, and the immune privilege of the brain

Human malignant gliomas are rather resistant to all current therapeutic approaches including surgery, radiotherapy and chemotherapy as well as antibody-guided or cellular immunotherapy. The immunotherapy of malignant glioma has attracted interest because of the immunosuppressed state of malignant glioma patients which resides mainly in the T-cell compartment. This T-cell suppression has been attributed to the release by the glioma cells of immunosuppressive factors like transforming growth factor-beta (TGF-beta) and prostaglandins. TGF-beta has multiple effects in the immune system, most of which are inhibitory. TGF-beta appears to control downstream elements of various cellular activation cascades and regulates the expression of genes that are essential for cell cycle progression and mitosis. Since TGF-beta-mediated growth arrest of T-cell lines results in their apoptosis in vitro, glioma-derived TGF-beta may prevent immune-mediated glioma cell elimination by inducing apoptosis of tumor-infiltrating lymphocytes in vivo. T-cell apoptosis in the brain may be augmented by the absence of professional antigen-presenting cells and of appropriate costimulating signals. Numerous in vitro studies predict that tumor-derived TGF-beta will incapacitate in vitro-expanded and locally administered lymphokine-activated killer cells (LAK-cells) or tumor-infiltrating lymphocytes. Thus, TGF-beta may be partly responsible for the failure of current adoptive cellular immunotherapy of malignant glioma. Recent experimental in vivo studies on non-glial tumors have corroborated that neutralization of tumor-derived TGF-beta activity may facilitate immune-mediated tumor rejection. Current efforts to improve the efficacy of immunotherapy for malignant glioma include various strategies to enhance the immunogenicity of glioma cells and the cytotoxic activity of immune effector cells, e.g., by cytokine gene transfer. Future strategies of cellular immunotherapy for malignant glioma will have to focus on rendering glioma cell-targeting immune cells resistent to local inactivation and apoptosis which may be induced by TGF-beta and other immunosuppressive molecules at the site of neoplastic growth. Cytotoxic effectors targeting Fas/APO-1, the receptor protein for perforin-independent cytotoxic T-cell killing, might be promising, since Fas/APO-1 is expressed by glioma cells but not by untransformed brain cells, and since Fas/APO-1-mediated killing in vitro is not inhibited by TGF-beta.

Shared amino acid sequences in the ND beta N and N alpha regions of the T cell receptors of tumor-infiltrating lymphocytes within malignant glioma

The purpose of this study was to assess the V-(D)-J junctional region of the T cell receptor (TCR), the CDR3 region, which is responsible for glioma-specific antigen contact in alpha beta TCR-mediated recognition. We sequenced the TCR alpha and beta chains of V alpha 7, and V beta 13.1 cDNA derived from tumor-infiltrating lymphocytes (TIL) of 12 glioma patients and also the corresponding clones from the patients' peripheral blood lymphocytes (PBL). A shared V beta 13.1 DJ sequence of the CDR3 region, ND beta N, was demonstrated in 49 of 66 V beta 13.1+ clones (74.2%) from the glioma TIL, whereas only 4 of 33 clones (12.1%) were observed in the V beta 13.1+ clones from the PBL (p < 0.001). A common VDJ sequence, FCASS (V beta 13.1)-YRLPWGTSDS (ND beta N)-GELFF (J beta 2.2), was observed not only in the gliomas from each patient, but also among all the patients with a preference for V beta 13.1. In contrast, the amino acid sequences of the V beta 13.1+ PBL clones were diverse and random. Next, we sequenced subclones from other V beta subfamilies randomly selected to compare their VDJ region rearrangements (V beta 3 and V beta 5.1). In contrast to V beta 13.1, the amino acid sequences of these junctional regions were completely different in these subclones. The V-J junctional region of the alpha chain is dominated by a few clones in some patients, and no shared amino acid sequences were detected in the TCR V alpha junctional region. However, in the N alpha region of the V alpha 7-bearing TIL clones, arginine was used in 27 of 44 clones (61.4%) compared to only 3 of 12 clones from the PBL (p < 0.05). These results are consistent with the hypothesis that a clonal expansion/accumulation of glioma lineage-specific T cells occurred in vivo at the tumor site and that these T cells may be recognizing glioma-specific antigens.

Association of malignant glioma with the human leukocyte antigen, HLA-A24(9)

Many immune responses are controlled by genes of the major histocompatibility complex (MHC). In humans these include the loci encoding the HLA-A, -B, -C, -DR, -DQ, and -DP antigens, and many diseases have been linked with these. However, little information is available about any connection between malignant tumors and HLA. In this study the possible association of HLA-A, -B, -C and -DR specificities with susceptibilities to malignant glioma was investigated in 42 patients with malignant glioma and 42 controls with non-glial intracranial tumors using the Terasaki-NIH standard method. The data were also compared with those of the 11th International HLA Workshop. The result showed that a high frequency of HLA-24(9) was observed in patients with intracranial malignant gliomas, which was not common in other, non-glial patient groups. In animals the MHC acts in defense against virally induced tumors, but until now there has been no evidence that they do so in human gliomas. Our discovery of its association with an HLA antigen is important for understanding the immunogenetic basis of susceptibility to glioma.