CD3 hyporesponsiveness and in vitro apoptosis are features of T cells from both malignant and nonmalignant secondary lymphoid organs

Lymphopenia combined with low TCR diversity (divpenia) predicts poor overall survival in metastatic breast cancer patients

Lymphopenia (< 1Giga/L) detected before initiation of chemotherapy is a predictive factor for death in metastatic solid tumors. Combinatorial T cell repertoire (TCR) diversity was investigated and tested either alone or in combination with lymphopenia as a prognostic factor at diagnosis for overall survival (OS) in metastatic breast cancer (MBC) patients. The combinatorial TCR diversity was measured by semi quantitative multi-N-plex PCR on blood samples before the initiation of the first line chemotherapy in a development (n = 66) and validation (n = 67) MBC patient cohorts. A prognostic score, combining lymphocyte count and TCR diversity was evaluated. Univariate and multivariate analyses of prognostic factors for OS were performed in both cohorts. Lymphopenia and severe restriction of TCR diversity called “divpenia” (diversity ≤ 33%) were independently associated with shorter OS. Lympho-divpenia combining lymphopenia and severe divpenia accurately identified patients with poor OS in both cohorts (7.6 and 10.6 vs 24.5 and 22.9 mo). In multivariate analysis including other prognostic clinical factors, lympho-divpenia was found to be an independent prognostic factor in the pooled cohort (p = 0.005) along with lack of HER2 and hormonal receptors expression (p = 0.011) and anemia (p = 0.009). Lympho-divpenia is a novel prognostic factor that will be used to improve quality of MBC patients’ medical care.

Exosomes Represent an Immune Suppressive T Cell Checkpoint in Human Chronic Inflammatory Microenvironments

Background: T cells present in chronic inflammatory tissues such as nasal polyps (from chronic rhinosinusitis patients) have been demonstrated to be hypo-responsive to activation via the TCR, similar to tumor-specific T cells in multiple different human tumor microenvironments. While immunosuppressive exosomes have been known to contribute to the failure of the tumor-associated T cells to respond optimally to activation stimuli, it is not known whether they play a similar role in chronic inflammatory microenvironments. In the current study, we investigate whether exosomes derived from chronic inflammatory microenvironments contribute to the immune suppression of T cells. Methods: Exosomes were isolated by ultracentrifugation and characterized by size and composition using nanoparticle tracking analysis, scanning electron microscopy, antibody arrays and flow exometry. Immunosuppressive ability of the exosomes was measured by quantifying its effect on activation of T cells, using nuclear translocation of NFκB as an activation endpoint. Results: Exosomes were isolated and characterized from two different types of chronic inflammatory tissues - nasal polyps from chronic rhinosinusitis patients and synovial fluid from rheumatoid arthritis patients. These exosomes arrest the activation of T cells stimulated via the TCR. This immune suppression, like that which is seen in tumor microenvironments, is dependent in part upon a lipid, ganglioside GD3, which is expressed on the exosomal surface. Conclusion: Immunosuppressive exosomes present in non-malignant chronic inflammatory tissues represent a new T cell checkpoint, and potentially represent a novel therapeutic target to enhance the response to current therapies and prevent disease recurrences.

Lymphopenia in Cancer Patients and its Effects on Response to Immunotherapy: an opportunity for combination with Cytokines?

Quantitative lymphocyte alterations are frequent in patients with cancer, and strongly impact prognosis and survival. The development of cancers in immunosuppressed patients has demonstrated the contribution of different T cell populations, including CD4⁺ cells, in the control of cancer occurrence.Whereas absolute numbers of neutrophils, platelets and red blood cells are routinely monitored in clinic following treatments, because of possible short-term complications, absolute lymphocyte counts (ALC), their subpopulations or diversity (phenotype, TCR) are rarely analyzed and never used to choose therapy or as prognostic criteria. The recent identification of immune checkpoint inhibitors (ICPi) as powerful therapeutic agents has revitalized immunotherapy of cancer in a broader group of diseases than anticipated. The status of the immune system is now recognized as an important biomarker for response to these novel treatments. Blood ALC values, along with tumor infiltration by CD8⁺T cells, and ICPi and ICPi-ligand expression, are likely to be a potential marker of sensitivity to anti-ICPi therapy.In this article, we review the current knowledge on the incidence and significance of lymphopenia in cancer patients, and discuss therapeutic strategies to restore lymphocyte numbers.

Memory T cells in the chronic inflammatory microenvironment of nasal polyposis are hyporesponsive to signaling through the T cell receptor

A majority of T cells from chronic inflammatory tissues derived from patients with nasal polyposis were found to express an effector memory phenotype. We report here that these memory T cells failed to activate NF-κB in response to TCR stimulation but responded normally when the proximal TCR signaling molecules were bypassed with PMA and ionomycin. The dysfunction of these cells was associated with a decrease in the phosphorylation of several TCR proximal signaling molecules including ZAP70, Lck and SLP-76. In addition to the disruption in the TCR signaling pathway, the nasal polyp-associated T cells were shown to have a defect in their ability to translocate LAMP-1 to the cell surface. The results presented here establish that the phenotype and anergy of the T cells in the nasal polyp are similar to those which is seen in memory T cells derived from human tumors and other sites of chronic inflammation.

Suppression of T-cell expansion by melanoma is exerted on resting cells

BACKGROUND

Immunotherapeutic cancer protocols often rely on the ability to promote proliferative expansion of tumor-specific T-cell, but the influence of cancer on in vivo T-cell expansion remains largely undefined.

METHODS

The ability of control and B16F10 melanoma-bearing C57BL/6 mice to expand lymphocytic choriomeningitis virus antigen-specific T-cell populations in response to acute viral infection was compared by using flow cytometric assays of splenocytes.

RESULTS

The ability to expand virus-specific CD8+ and CD4+ T-cells was globally and markedly suppressed in tumor-bearing mice. Expanded cytotoxic T lymphocytes (CTLs) retained in vivo and in vitro functionality, suggesting that melanoma growth did not induce T-cell anergy. The magnitude of suppressed proliferative expansion was proportional to the extent of tumor burden. Melanoma-induced suppression of CTL expansion was correlated with upregulated apoptotic activity and hampered the induction of memory precursor effector cells. Adoptive transfer of resting LCMV antigen-specific T-cells before or after tumor establishment demonstrated that a critical period of in vivo exposure of resting T-cells to growing melanoma was responsible for the induction of suppressed expansion. This suppression was durable; surgical resection of melanoma after in vivo exposure to resting T-cells but before antigenic stimulation did not restore full expansion.

CONCLUSIONS

These data suggest that growing melanoma tumors exert a global, antigen-independent influence on resting T-cells that fundamentally reprograms their ability to undergo proliferative expansion in response to subsequent antigenic stimulation. This finding may have direct implications for T-cell-based immunotherapeutic strategies.

Tumor-resident CD8+ T-cell: the critical catalyst in IL-12-mediated reversal of tumor immune suppression

Tumor-resident T cells display a functionally impaired effector/memory (Tem) phenotype. Sustained intratumoral administration of IL-12, on the other hand, can restore cytolytic function to pre-existing CD8+ Tem, resulting in effective tumor kill. Whereas cytotoxic T lymphocytes (CTL) are generally assumed to mediate tumor regression via direct tumor cytotoxicity, recent work revealed that activated CD8+ Tem mobilize a systemic, multi-component effector cascade that includes both innate and adaptive immune mechanisms. Here we summarize these mechanisms, review how tumor-resident CD8+ Tem orchestrate this cascade and discuss the potential clinical implications of these findings.

T cells and stromal fibroblasts in human tumor microenvironments represent potential therapeutic targets

The immune system of cancer patients recognizes tumor-associated antigens expressed on solid tumors and these antigens are able to induce tumor-specific humoral and cellular immune responses. Diverse immunotherapeutic strategies have been used in an attempt to enhance both antibody and T cell responses to tumors. While several tumor vaccination strategies significantly increase the number of tumor-specific lymphocytes in the blood of cancer patients, most vaccinated patients ultimately experience tumor progression. CD4+ and CD8+ T cells with an effector memory phenotype infiltrate human tumor microenvironments, but most are hyporesponsive to stimulation via the T cell receptor (TCR) and CD28 under conditions that activate memory T cells derived from the peripheral blood of the cancer patients or normal donors. Attempts to identify cells and molecules responsible for the TCR signaling arrest of tumor-infiltrating T cells have focused largely upon the immunosuppressive effects of tumor cells, tolerogenic dendritic cells and regulatory T cells. Here we review potential mechanisms by which human T cell function is arrested in the tumor microenvironment with a focus on the immunomodulatory effects of stromal fibroblasts. Determining in vivo which cells and molecules are responsible for the TCR arrest in human tumor-infiltrating T cells will be necessary to formulate and test strategies to prevent or reverse the signaling arrest of the human T cells in situ for a more effective design of tumor vaccines. These questions are now addressable using novel human xenograft models of tumor microenvironments.

IL-12 delivered intratumorally by multilamellar liposomes reactivates memory T cells in human tumor microenvironments

Using a novel loading technique, IL-12 is reported here to be efficiently encapsulated within large multilamellar liposomes. The preclinical efficacy of the cytokine loaded liposomes to deliver IL-12 into human tumors and to reactive tumor-associated T cells in situ is tested using a human tumor xenograft model. IL-12 is released in vivo from these liposomes in a biologically active form when injected into tumor xenografts that are established by the subcutaneous implantation of non-disrupted pieces of human lung, breast or ovarian tumors into immunodeficient mice. The histological architecture of the original tumor tissue, including tumor-associated leukocytes, tumor cells and stromal cells is preserved anatomically and the cells remain functionally responsive to cytokines in these xenografts. The local and sustained release of IL-12 into the tumor microenvironment reactivates tumor-associated quiescent effector memory T cells to proliferate, produce and release IFN-gamma resulting in the killing of tumor cells in situ. Very little IL-12 is detected in the serum of mice for up to 5 days after an intratumoral injection of the IL-12 liposomes. We conclude that IL-12 loaded large multilamellar liposomes provide a safe method for the local and sustained delivery of IL-12 to tumors and a therapeutically effective way of reactivating existing tumor-associated T cells in human solid tumor microenvironments. The potential of this local in situ T cell re-stimulation to induce a systemic anti-tumor immunity is discussed.

Focus on TILs: prognostic significance of tumor infiltrating lymphocytes in human melanoma

Tumors contain variable numbers of lymphocytes, referred to as tumor infiltrating lymphocytes (TILs). In melanoma, the intensity of this lymphocytic infiltrate is believed to correlate with outcome, though there is some debate about the applicability of this finding for all melanomas. Much research has gone into classifying TILs with respect to antigen receptor structure and the antigen to which melanoma-specific T cells react. However, these studies for the most part did not immunophenotype TILs, and recent data has revealed that the composition of tumoral lymphocytes is not homogenous, but rather represents varying contributions from many lymphocytic subsets. Furthermore, the function of TILs is often compromised as a result of the accumulation of immunoregulatory cells and various tumor escape mechanisms. These recent insights stress the need to collect more data on the composition and function of TIL infiltrates before definitive conclusions about the prognostic significance of TILs can be drawn. Advances in immunology have also facilitated the development of immunotherapeutic strategies, examples of which will be discussed with a special emphasis on blocking antibodies against CTLA-4, which are prototypical immunotherapeutic agents. This flurry of novel "biological" therapies will undoubtedly complicate our already incomplete understanding of TIL immunobiology as each of these agents has the potential to uniquely distort the series of immunological events which normally occur in untreated melanoma. Therefore, considerable research is needed to better elucidate the function and prognostic significance of TILs in both untreated melanoma and tumors treated with "biological" therapy.

TGF-beta modulates the functionality of tumor-infiltrating CD8+ T cells through effects on TCR signaling and Spred1 expression

This study demonstrates that CD8+ T cells in the tumor microenvironment display reduced functionality and hyporesponsiveness. TGF-beta contributed markedly to the tumor-infiltrating CD8+ T cells' (TILs) reduced functionality, which could be reversed using a small molecule TGF-beta inhibitor. Upon T-cell receptor (TCR) activation, the activation of ITK and ERK kinases were reduced in CD8+ TILs, as compared to splenic CD8+ T cells: TGF-beta inhibitor could reverse this phenomenon. This study demonstrates for the first time the association of the Spred-1 gene, an inhibitor of the Ras/MAPK pathway, with CD8+ TILs and TGF-beta activity. Spred-1 was upregulated in CD8+ TILs and TGF-beta enhanced the expression of Spred-1 in effector/memory CD8+ T cells and not in rested/memory CD8+ T cells. Based on these findings, this study supports the hypothesis that TGF-beta mediates an inhibitory mechanism on CD8+ TILs involving TCR-signaling blockade and the upregulation of Spred-1, thus implicating Spred-1 as a potential new target for future anti-tumor immune studies.

Exosomes as a tumor immune escape mechanism: possible therapeutic implications

Advances in cancer therapy have been substantial in terms of molecular understanding of disease mechanisms, however these advances have not translated into increased survival in the majority of cancer types. One unsolved problem in current cancer therapeutics is the substantial immune suppression seen in patients. Conventionally, investigations in this area have focused on antigen-nonspecific immune suppressive molecules such as cytokines and T cell apoptosis inducing molecules such as Fas ligand. More recently, studies have demonstrated nanovesicle particles termed exosomes are involved not only in stimulation but also inhibition of immunity in physiological conditions. Interestingly, exosomes secreted by cancer cells have been demonstrated to express tumor antigens, as well as immune suppressive molecules such as PD-1L and FasL. Concentrations of exosomes from plasma of cancer patients have been associated with spontaneous T cell apoptosis, which is associated in some situations with shortened survival. In this paper we place the "exosome-immune suppression" concept in perspective of other tumor immune evasion mechanisms. We conclude by discussing a novel therapeutic approach to cancer immune suppression by extracorporeal removal of exosomes using hollow fiber filtration technology

IDO-expressing regulatory dendritic cells in cancer and chronic infection

Immune evasion and T cell tolerance induction have been associated both with malignant disease and chronic infection. In recent years, increasing evidence has been accumulated that antigen-presenting cells such as dendritic cells (DC) play a major role in immune regulation. They are not only involved in the induction of immunity but also can inhibit immune responses. Interesting parallels for major molecular mechanisms involved in turning DC from stimulatory to regulatory cells have been uncovered between malignant disease and chronic infection. Apparently, not only inhibitory cytokines such as IL-10 seem to play a role, but also metabolic mechanisms dysregulating tryptophan metabolism, thereby, leading to inhibition of T cells and pathogens. We focus here on recent findings establishing the tryptophan catabolizing enzyme indoleamine-pyrrole 2,3 dioxygenase (IDO) as a central feature of DC with regulatory function both in cancer and chronic infection. Induction of enzymatically active IDO can be triggered by various soluble and membrane-bound factors, and in general, require interferon (IFN) signaling. In addition, based on the most recently established link between tumor necrosis factor alpha (TNFalpha), prostaglandin E2 and IDO, a new model of regulation of IDO in context of cancer and infection is proposed. In light of the increasing use of anti-TNFalpha drugs, these findings are also of great interest to the clinician scientist.

Follicular lymphoma intratumoral CD4+CD25+GITR+ regulatory T cells potently suppress CD3/CD28-costimulated autologous and allogeneic CD8+CD25- and CD4+CD25- T cells

Regulatory T cells (T(R)) play a critical role in the inhibition of self-reactive immune responses and as such have been implicated in the suppression of tumor-reactive effector T cells. In this study, we demonstrate that follicular lymphoma (FL)-infiltrating CD8+ and CD4+ T cells are hyporesponsive to CD3/CD28 costimulation. We further identify a population of FL-infiltrating CD4+CD25+GITR+ T(R) that are significantly overrepresented within FL nodes (FLN) compared with that seen in normal (nonmalignant, nonlymphoid hyperplastic) or reactive (nonmalignant, lymphoid hyperplastic) nodes. These T(R) actively suppress both the proliferation of autologous nodal CD8+CD25- and CD4+CD25- T cells, as well as cytokine production (IFN-gamma, TNF-alpha and IL-2), after CD3/CD28 costimulation. Removal of these cells in vitro by CD25+ magnetic bead depletion restores both the proliferation and cytokine production of the remaining T cells, demonstrating that FLN T cell hyporesponsiveness is reversible. In addition to suppressing autologous nodal T cells, these T(R) are also capable of suppressing the proliferation of allogeneic CD8+CD25- and CD4+CD25- T cells from normal lymph nodes as well as normal donor PBL, regardless of very robust stimulation of the target cells with plate-bound anti-CD3 and anti-CD28 Abs. The allogeneic suppression is not reciprocal, as equivalent numbers of CD25+FOXP3+ cells derived from either normal lymph nodes or PBL are not capable of suppressing allogeneic CD8+CD25- and CD4+CD25- T cells, suggesting that FLN T(R) are more suppressive than those derived from nonmalignant sources. Lastly, we demonstrate that inhibition of TGF-beta signaling partially restores FLN T cell proliferation suggesting a mechanistic role for TGF-beta in FLN T(R)-mediated suppression.

The number of tumour-infiltrating TIA-1+ cytotoxic T cells but not FOXP3+ regulatory T cells predicts outcome in diffuse large B-cell lymphoma

The prognostic significance of tumour-infiltrating lymphocytes (TILs) in patients with diffuse large B-cell lymphoma (DLBCL) remains controversial. Furthermore, the possible impact of regulatory T cells (T(regs)) on survival in DLBCL is still unknown. We performed a retrospective study on the immunohistochemical expression of cytotoxic cells and T(regs), and their correlation with survival in 195 DLBCL patients. Patients with a small number of cytotoxic T-cell intracytoplasmic antigen-1 (TIA-1)+ T cells (< or =260 cells/mm(2) tumour area; n = 52) had significantly better outcome than patients with a large number (>260 cells/mm(2); n = 143); progression-free survival (PFS) at 5 years was 67% vs. 50% (P = 0.03) and overall survival (OS) was 73% vs. 57% (P = 0.03). In multivariate analysis, the low TIA-1+ group still had a better PFS (relative risk 0.75, 95% confidence interval 0.31-0.99; P = 0.05). The number of forkhead box protein 3 (FOXP3)+ T(regs) had no influence on PFS (P = 0.89) or OS (P = 0.75). These results suggest that immunohistochemical analysis of cytotoxic T cells at time of diagnosis could provide additional prognostic information. The lack of correlation between the number of FOXP3+ cells and survival could possibly indicate that tumour-infiltrating T(regs) are of less clinical importance in DLBCL. However, these findings need to be explored in functional studies.

Cancer immunoediting from immune surveillance to immune escape

Cancer immune surveillance is considered to be an important host protection process to inhibit carcinogenesis and to maintain cellular homeostasis. In the interaction of host and tumour cells, three essential phases have been proposed: elimination, equilibrium and escape, which are designated the 'three E's'. Several immune effector cells and secreted cytokines play a critical role in pursuing each process. Nascent transformed cells can initially be eliminated by an innate immune response such as by natural killer cells. During tumour progression, even though an adaptive immune response can be provoked by antigen-specific T cells, immune selection produces tumour cell variants that lose major histocompatibility complex class I and II antigens and decreases amounts of tumour antigens in the equilibrium phase. Furthermore, tumour-derived soluble factors facilitate the escape from immune attack, allowing progression and metastasis. In this review, the central roles of effector cells and cytokines in tumour immunity, and the escape mechanisms of tumour cells during tumour progression are discussed.

Cancer immunoediting from immune surveillance to immune escape

Cancer immune surveillance is considered to be an important host protection process to inhibit carcinogenesis and to maintain cellular homeostasis. In the interaction of host and tumour cells, three essential phases have been proposed: elimination, equilibrium and escape, which are designated the 'three E's'. Several immune effector cells and secreted cytokines play a critical role in pursuing each process. Nascent transformed cells can initially be eliminated by an innate immune response such as by natural killer cells. During tumour progression, even though an adaptive immune response can be provoked by antigen-specific T cells, immune selection produces tumour cell variants that lose major histocompatibility complex class I and II antigens and decreases amounts of tumour antigens in the equilibrium phase. Furthermore, tumour-derived soluble factors facilitate the escape from immune attack, allowing progression and metastasis. In this review, the central roles of effector cells and cytokines in tumour immunity, and the escape mechanisms of tumour cells during tumour progression are discussed.

Memory T cells in human tumor and chronic inflammatory microenvironments: sleeping beauties re-awakened by a cytokine kiss

Human tumors often progress and spread in spite of the presence of large numbers of CD4+ and CD8+ T cells with activated or memory cell phenotypes. The T cells in the microenvironment of human lung tumors fail to be activated in response to stimulation via the T cell receptor and CD28 under conditions that fully activate T cells derived from the peripheral blood of the cancer patients. A combination of regulatory mechanisms which are also observed in a variety of different chronic inflammatory conditions may contribute to the T cell unresponsiveness, and to their inability to respond to and kill tumor cells. The non-responsiveness of memory T cells isolated from human lung tumors and non-malignant chronic inflammatory tissues can be reversed in vitro by a brief pulse with IL-12, and the local and sustained release of exogenous IL-12 into the microenvironment of human tumor xenografts in SCID mice re-activates the tumor-associated T cells in situ. In the later case, the T cells proliferate, secrete interferon-gamma and initiate a cascade of events that culminate in the eradication of tumor cells from the xenograft. In transplantable and spontaneously developing tumors of mice the injection of a single tumor nodule with IL-12 loaded biodegradable microspheres activates tumor-associated T cells to kill tumor cells in situ, and provokes a systemic anti-tumor response that results in the eradication of distant metastatic tumor nodules that are not treated with the cytokine. These mice exhibit a systemic tumor specific immunity as they resist a second challenge with the same (but not a different) tumor. These findings suggest that it will be possible to provoke a systemic anti-tumor immunity in cancer patients by the direct injection of IL-12 loaded biodegradable microspheres or liposomes to locally deliver very low but sustained doses of IL-12 into a single tumor site. This strategy which is based upon the ability of IL-12 to re-activate tumor-associated T cells is termed in situ tumor vaccination.

IL-12 reverses anergy to T cell receptor triggering in human lung tumor-associated memory T cells

Memory T cells in human non-small cell lung cancer are unresponsive to progressing tumors. T cells were evaluated at the single cell level by imaging the nuclear translocation of NF-kappaB and NFAT via immunofluorescence confocal microscopy as an early measure of responsiveness to T cell receptor triggering. Little translocation of NF-kappaB or NFAT occurred in tumor-associated T cells in response to CD3+CD28 cross-linking under conditions which led to maximal translocation in normal donor peripheral blood T cells. TNF-alpha induced maximal NF-kappaB translocation in these T cells, indicating that they remain receptive to alternative signaling pathways, and pulsing with IL-12 prior to TCR triggering reversed their apparent anergy. T cells from additional chronic inflammatory microenvironments demonstrated a similar refractoriness to TCR activation, suggesting either that a common regulatory mechanism present within the microenvironment controls these cells or that with continuous antigen exposure, they remain refractory to activation via the TCR.

Skewed T-cell differentiation in patients with indolent non-Hodgkin lymphoma reversed by ex vivo T-cell culture with gammac cytokines

The unfavorable clinical evolution in indolent non-Hodgkin lymphomas suggests defective control of neoplastic growth by the immune system. To address this issue, we evaluated phenotype, function, and maturation profile of CD4(+) and CD8(+) T cells from peripheral-blood, lymph nodes, or bone marrow of patients with B-cell non-Hodgkin lymphoma (NHL) at diagnosis. T cells from these patients frequently showed an activated but apoptosis-prone phenotype with low frequency of tumor-reactive T cells showing a TH2/Tc2 functional profile in the response to autologous tumor. In peripheral blood or in lymph nodes and bone marrow, and, in comparison to healthy donors, patients' T cells showed a skewed differentiation toward Tnaive and Tcentral memory stages, with low expression of granzyme B and perforin. T-cell culture with autologous tumor in the presence of IL-2, IL-15, and autologous bone marrow-derived cells led to massive T-cell expansion and to differentiation of cytotoxic factor(+) CD8(+) T cells releasing IFN-gamma and killing autologous B-cell tumor in an HLA-class I-restricted fashion. These results suggest impaired T-cell differentiation to effector stage in patients with B-cell NHL, but indicate that T-cell responsiveness to gammac cytokines is retained, thus allowing to promote generation of antitumor T cells for immune intervention.

Current concepts of tumor-infiltrating lymphocytes in human malignancies

Tumor-infiltrating lymphocytes (TILs) develop as manifestations of the recognition and defense against malignant cells by the host immune system. TILs were literally defined as "tumor-infiltrating lymphocytes", which a posteriori locate within the tumor tissues. Although such cells can be found, they fail to control the growth of tumor. Many have proposed diverse mechanisms for dysfunction of TILs with regard to the roles of immunosurveillance against cancer. However, only a few cancer types, e.g. melanoma, have seen the benefits brought by activating these cells for immunotherapy. Functional defects of TILs have been linked to abnormalities of signaling molecules; however, there is conflicting data. The death of TILs was attributed to expression of cancer-derived FasL, PD-1 and RCAS1, and cancer-induced activation-induced cell death (AICD). Confirmed by studies using TILs and animal models, the compromise of tumor-specific immune responses was thought to result from not only mechanisms of clonal anergy but also exhaustion and/or deletion. Furthermore, functional cytotoxic CD8(+) TILs might be rendered incompetent by cancer-induced up-regulation of inhibitory NK receptors or proximal signaling abnormalities. Additionally, immune privilege was partly attributed to recruitment of regulatory T cells to the tumor sites. The failure of IL-2 signaling, which stands at the center of T cell functionalities, had been linked to the enzymatic activity of cancer-derived matrix metalloproteinases (MMPs). Finally, the exploitation of IDO expression, an important enzyme in pregnancy-related immunosuppression, by cancer cells might play a role in tumor immunity. The disparity of cancer types, origin, developmental stages and individual genetic backgrounds likely account for differences, or even contradictions, which might be the reason why immunotherapy works only on a few cancer types. Delineating the mechanisms behind functional defects of TILs can help not only boost chances of the development of a successful cure but understand the not fully identified roles played by immune system in the face of malignancies.

Characterization of Defective CD4−CD8−T Cells in Murine Tumors Generated Independent of Antigen Specificity

Immune-based therapy confers limited benefits to hosts bearing late-stage tumors. Mounting evidence points to local suppression of T cell function as the most substantial barrier to effective antitumor immunity in hosts with large tumor burdens. Despite this, events responsible for locally defective T cells and immune suppression in tumors remain unclear. We describe in this study a predominant T cell population localized within two murine tumors that is characterized by expression of apoptotic markers and TCRalphabeta/CD3, but not CD4, CD8, or NK-associated markers. These defective cells resembled double negative (DN) T cells in lpr mice, harbored defects in the expression of T cell signaling molecules, and produced the anti-inflammatory cytokine, IL-10. Conditions known to increase or decrease the accumulation of lpr DN T cells had corresponding effects on local DN tumor infiltrating lymphocyte (TIL) levels and inversely impacted host survival. Adoptive transfer into s.c. tumors demonstrated that naive CD8(+) T cells were highly susceptible to becoming DN TIL, and local supplementation of tumors with nontumor Ag-bearing MHC class I-expressing fibroblasts decreased both this susceptibility and endogenous DN TIL levels. These findings identify a major defective T cell population with suppressive potential within tumors. The data also suggest that local T cell defectiveness is controlled by the tumor environment independent of cognate Ag specificity per se. Decreasing defective DN TIL levels by increasing noncognate peptide MHC class I availability, or modulating TCR or cytokine signaling may facilitate host survival by bolstering endogenous immunity to late-stage tumors, and may help improve therapeutic tumor vaccines.

The bi-specific CD3 x NCAM antibody: a model to preactivate T cells prior to tumour cell lysis

To target the neural cell adhesion molecule (NCAM, CD56) on neuroblastoma by T cell-based immunotherapy we have generated a bi-specific CD3 x NCAM antibody (OE-1). This antibody can be used to redirect T cells to NCAM+ cells. Expectedly, the antibody binds specifically to NCAM+ neuroblastoma cells and CD3+ T cells. OE-1 induces T cell activation, expansion and effector function in peripheral blood mononuclear cell (PBMC)-derived CD4+ and CD8+ T cells. T cell activation was shown to depend on the presence of normal natural killer (NK) cells in the culture. Interestingly, while PBMC- derived T cells were activated by OE-1, NK cells were almost completely depleted, suggesting that T cells activated by OE-1 deleted the NK cells. Activated CD4+ and CD8+ T cells differentiate into a larger CCR7+ central memory and a smaller CCR7- effector memory cell population. Most importantly, preactivated T cells were highly cytotoxic for neuroblastoma cells. In eight of 11 experiments tumour-directed cytotoxicity was enhanced when NK cells were present during preactivation with OE-1. These data strongly support a bi-phasic therapeutic concept of primarily stimulating T cells with the bi-specific antibody in the presence of normal NCAM+ cells to induce T cell activation, migratory capacity and finally tumour cell lysis.

Expression of mutant non-cleavable Fas ligand on retrovirus packaging cells causes apoptosis of immunocompetent cells and improves prodrug activation gene therapy in a malignant glioma model

Recombinant retroviruses (RV) have been widely used as vectors for clinical gene therapy of malignant brain tumors. Because of the very limited stability of these vectors in vivo, RV producing cells (VPC) are routinely used for intratumoral RV release. The host immune system, however, recognizes the intratumorally grafted allogeneic or xenogeneic VPC, and mounts an immune response against them. Humoral and cellular immune responses eventually result in reduction of VPC numbers and in limited success of RV mediated gene therapy approaches. This study presents a non-pharmacological and spatially limited approach for protection of VPC grafted in the CNS against destruction by host immune responses. Murine fibroblast-derived VPC expressing herpes-simplex-virus type I thymidine kinase (HSV-tk) were genetically modified to co-express a human Fas ligand (CD95L) deletion mutant (DeltaFasL) resistant to enzymatic cleavage and shedding. Direct interactions between Fas (CD95) on lymphocytes and DeltaFasL on VPC upon cell-cell contact rapidly caused apoptosis in lymphocytes. In addition, cultured malignant brain tumor cells (U87, LN18, LN229) transduced with DeltaFasL-RV were rendered apoptotic by Fas/DeltaFasL interaction. DeltaFasL-expressing VPC grafted in a 9L rat brain tumor model survived in significantly higher numbers compared with control VPC, and did not cause an increase in neutrophil infiltration of tumors. Gene therapy of tumor bearing animals grafted with the modified DeltaFasL-VPC and given the prodrug Ganciclovir resulted in significantly increased survival rates compared to treatment with control VPC and Ganciclovir. In conclusion, prolonged intratumoral presence of DeltaFasL-VPC seems to be a direct consequence of the expression of the membrane-bound mutant FasL, and may result in increased total RV output and improved tumor transduction with RV.

Apoptosis underlies immunopathogenic mechanisms in acute silicosis

We investigated immunopathogenic roles for apoptosis in acute murine silicosis. Intratracheal silica instillation induced pulmonary inflammation and enlarged thoracic lymph nodes. Lymphocytes from silica-exposed lymph nodes showed reduced mitogenic responses to T cell receptor (TCR) stimulation, and markedly increased activation-induced cell death, compared with control lymphocytes from saline-exposed lymph nodes. CD4(+) T cell death was mediated by Fas ligand, because CD4(+) T cells from Fas ligand-deficient gld mice did not undergo activation-induced apoptosis. Silica deposition also resulted in increased apoptosis associated with inflammatory infiltrates in lung parenchyma. In vivo treatment with caspase inhibitors reduced neutrophil accumulation, and alleviated inflammation in the lungs of silica-treated mice. These results suggest that silica-induced apoptosis plays an inflammatory role in the lung parenchyma, and creates immunologic abnormalities in regional lymph nodes, with pathogenic implications for the host.

IL-12 secreting dendritic cells are required for optimum activation of human secondary lymphoid tissue T cells

Successful immunization requires that mature dendritic cells (mDCs) prime T cells in secondary lymphoid tissue (LT). Previously, the authors have shown that LT T cell activation has an increased costimulatory threshold for a proliferative response as compared with peripheral blood (PB) T cells. Therefore, to optimize mDC immunogenicity, DC maturation was studied using LT T cells as responders. While mDCs obtained with soluble CD40Ligand (sCD40L) or a sCD40L/IFNgamma combination similarly expressed the CD83 and CCR7 molecules on their membrane, only the latter secreted IL-12. sCD40L/IFNgamma mDCs, as compared with sCD40L mDCs, enhanced allogeneic LT T cell proliferation, LT CD4+ cell IFNgamma production and LT CD8+ cell cytotoxicity. Enhancement could be predominantly ascribed to IL-12 secreted by sCD40L/IFNgamma mDCs and to additional costimulatory signals as shown remarkably in the IFNgamma response when IL-12 was neutralized. Therefore, in addition to their membrane phenotype, mDCs to be used in immunization protocols should be assessed for IL-12 secretion as a surrogate marker for an optimum costimulatory potential.

CD3-zetachain expression of intratumoral lymphocytes is closely related to survival in gastric carcinoma patients

BACKGROUND

Impaired or reduced CD3 zeta chain (CD3-zeta) expression in T cells has been identified in various cancers and may be associated with an ineffective immune response. The clinical significance of CD3-zeta chain expression in tumor-infiltrating lymphocytes (TILs) in gastric carcinoma remains unclear.

METHODS

The authors immunohistochemically investigated CD3-zeta expression in TILs in 185 patients who had undergone curative gastrectomy. CD3-zeta/CD3 epsilon (CD3-epsilon) ratios were calculated. Patients were divided into two groups: a normal CD3-zeta group (n = 121) and a reduced CD3-zeta group (n = 64). Patients with a zeta per epsilon ratio of greater than 66% were placed in the normal CD3-zeta group.

RESULTS

Patients in the normal CD3-zeta group had fewer lymph node metastasis (P < 0.01) and a shallower depth of invasion (P < 0.05) than those in the reduced CD3-zeta group. The 5-year survival rate was 72% in the normal CD3-zeta group, which was significantly better than that in the reduced CD3-zeta group (55%; P < 0.01). When stratified according to clinical stage, the prognostic value was significantly different only in Stage IV patients. Multivariate analysis showed that CD3-zeta expression was an independent prognostic factor (P = 0.03) next to depth of invasion and lymph node involvement.

CONCLUSIONS

Reduced CD3-zeta expression in TILs was strongly correlated with progressive disease in gastric carcinomas. CD3-zeta expression in TILs is considered an immunologic, independent prognostic marker in gastric carcinoma patients. CD3-zeta normalization with cytokine treatment may lead to prolonged survival in advanced gastric carcinoma patients.

Abnormal expression of various molecular forms and distribution of T cell receptor zeta chain in patients with systemic lupus erythematosus

OBJECTIVE

T cells from the majority of patients with systemic lupus erythematosus (SLE) display antigen receptor-mediated signaling aberrations associated with defective T cell receptor (TCR) zeta chain expression. The TCR zeta chain, a critical signaling molecule, exists in multiple molecular forms and membrane fractions with distinct functions in antigen-mediated signaling processes. This study was undertaken to investigate the complete spectrum of expression of the different forms and distribution of the TCR zeta chain in SLE T cells.

METHODS

T cells were isolated from 48 SLE patients and 21 healthy subjects. The expression of various forms of the TCR zeta chain was investigated by immunoblotting with specific antibodies. The lipid raft-associated form of the zeta chain was determined by quantitating the solubilized zeta chain after disruption of the lipid rafts by cholesterol depletion using methyl-betacyclodextrin. The distribution of the zeta chain was investigated by fluorescence microscopy.

RESULTS

The phosphorylated 21- and 23-kd forms and the detergent-insoluble membrane-associated form of the TCR zeta chain and alternatively spliced zeta chain were significantly decreased in SLE T cells. In contrast, major ubiquitinated forms of the zeta chain were increased in these cells. We also identified up-regulation of a novel 14-kd form of the zeta chain in SLE T cells. Resting SLE T cell membranes had an increased percentage of the residual membrane-bound zeta chain in the lipid rafts. Fluorescence microscopy findings indicated that the residual zeta chain is more clustered on the cell membranes of SLE T cells.

CONCLUSION

These results suggest that, in addition to the 16-kd form, expression of other molecular forms and fractions of the TCR zeta chain as well as its membrane distribution are abnormal in SLE T cells. Increased lipid raft association and surface clustering of the zeta chain may explain the molecular mechanisms underlying the signaling abnormalities in these cells.

T-cell analysis in identical twins reveals an impaired anti-follicular lymphoma immune response in the patient but not in the healthy twin

In lymphomas an innate defect in the T-cell repertoire could account for the impaired tumour-specific immune response; alternatively, the tumour itself could exert an inhibitory effect on the immune system. To address this issue we analysed the T-cell responses against follicular lymphoma (FL) in identical twins as it can be postulated that their overall T-cell repertoire is identical. While differences between the T-cell response of the patient and the healthy twin would point to a tumour-induced T-cell unresponsiveness, impaired responses in both would point to a defective T-cell repertoire. We demonstrated an impaired tumour-specific proliferation (P = 0.035 and P = 0.013) and cytokine release (P = 0.004 and P = 0.0008) of both peripheral blood and tumour-derived T-cells, respectively, in the FL patient compared with the T-cell response of the healthy twin. Moreover, only syngeneic primed T cells were able to directly lyse unmodified FL cells of the patient. These data support previous findings in murine lymphomas and suggest that inhibitory mechanisms during tumour growth, rather than a defective T-cell repertoire, are responsible for the insufficient T-cell response in lymphoma.

Biased activation of human T lymphocytes due to low extracellular pH is antagonized by B7/CD28 costimulation

As T cell response to tumor-associated antigens may be impaired by the acidic microenvironment typical of solid tumors, we assessed the effect of extracellular pH (pH(e)) on the activation and proliferation of human T lymphocytes and generation of the cytotoxic response. T lymphocytes stimulated with anti-CD3 mAb or PHA at low pH(e) were unable to secrete IL-2 and IFN-gamma and their ability to progress through the cell cycle was impaired. T lymphocytes also displayed up-regulation of IFN-gammaR2 chain and CTLA-4 expression, rendering them sensitive to negative regulatory signals. Agonistic mAb against CD28, but not against CD2, completely restored cytokine production and cell cycle progression, but down-regulated IFN-gammaR2 and CTLA-4 expression. The anti-CD28mAb rescued the CTL response of allogeneic anti-tumor cultures generated at low pH(e). Following anti-CD28 mAb treatment, T cells synthesized cyclooxygenase-2 (Cox-2) protein, which is involved in the early phases of T cell activation. This rescue of T cell activation was independent of the inducible 6-phosphofructo-2-kinase (iPFK-2) pathway, which stimulates proliferation in hypoxic and acidic conditions. The restoration of proliferative and cytotoxic T cell responses by CD28-triggering provides insight into the mechanisms by which B7 enhances the T cell anti-tumor response in vivo.

Multiple co-stimulatory signals are required for triggering proliferation of T cells from human secondary lymphoid tissue

Vaccine-based therapies are being developed for a variety of cancers and their efficacy will be determined by their ability to stimulate T cells in the secondary lymphoid tissue. We found that T cells isolated from human secondary lymphoid organs (LT-T), in contrast to peripheral blood T cells (PB-T) are hyporesponsive to cross-linked anti-CD3 mAb (CD3c) even in the presence of exogenous IL-2. Using mAb to trigger CD2 and CD28 co-stimulatory molecules, we found that such dual co-stimulation of LT-T induces profound and sustained responses including CD25 expression, IL-2 secretion and proliferation. Different levels of co-stimulation produced a hierarchical pattern of responses in LT-T, which correlated with the degree of CD3-TCR down-regulation. Mature antigen-presenting cells (APC) restored the capacity of LT-T to proliferate to stimulation of the CD3-TCR complex. Blocking studies demonstrated that optimal proliferation was critically dependent on co-stimulation via CD2 and CD28 engaged by their ligands on the APC. Therefore, LT-T have increased co-stimulatory requirements as compared to PB-T, i.e. multiple co-stimulatory signals coupled to CD3-TCR triggering. Furthermore, LT-T were found to be dependent on APC for survival, in contrast to PB-T. Clearly, LT-T do not behave in a comparable way to PB-T and in vitro experiments assessing novel cancer vaccines should therefore use LT-T as the most appropriate population of responder T cells.

The CD7(-) subset of CD4(+) memory T cells is prone to accelerated apoptosis that is prevented by interleukin-15 (IL-15)

The CD7(-) subset of CD4(+) T cells reflects a stable differentiation state of post-thymic helper T cells with CD45R0(+)CD45RA(-) 'memory' phenotype. Here we report that CD4(+)CD7(-) T cells are prone to increased spontaneous apoptosis in vitro compared to CD4(+)CD7(+) T cells. Spontaneous apoptosis is prevented by IL-15, but not by IL-2. Moreover, IL-15 increases Bcl-2 and decreases CD95/Fas expression of CD7(-), but not of CD7(+) T cells. Because IL-15 is physiologically not secreted but expressed in a membrane-bound form, we cocultured T cells with TNF-alpha stimulated fibroblasts that expose membrane IL-15. TNF-alpha stimulated fibroblasts rescue CD4(+)CD7(-) T cells from apoptosis whereas unstimulated fibroblasts do not. Rescue from apoptosis requires cell-cell contact and is abolished by addition of neutralizing antibodies to IL-15. We conclude that membrane IL-15 prevents accelerated apoptosis of CD4(+)CD7(-) T cells. This mechanism may contribute to accumulation of CD7(-) T cells in chronic inflammatory skin lesions.

From the study of tumor cell immunogenicity to the generation of antitumor cytotoxic cells in non-Hodgkin's lymphomas

The question of the immunogenicity of non-Hodgkin's lymphoma (NHL) B cells has been investigated in an attempt to support the development of new immunotherapeutic treatments for this disorder, which remains resistant to conventional treatments in most cases. In the present review, we report and discuss our new findings in the field of NHL B cell immunogenicity. One aspect of our work is the description of the expression and functions of membrane molecules associated with antigen presentation. The expression levels of adhesion molecules was measured, and the relevance of this expression to the sensitivity of malignant B cells to cell-mediated lysis was studied. Since the T cell response relies on the expression of both HLA class I and II molecules, we also investigated whether or not these molecules were present at the surface of NHL B cells. Subsequently, we asked whether antitumor CTL and LAK cells could be developed and analyzed the mechanisms of cell lysis involved. Since the generation of a T cell response requires the expression of the costimulatory molecules CD80 and CD86, we investigated their in vivo expression and their modulation in vitro during contact with responding T lymphocytes. The understanding of the immunogenicity of NHL B cells has enabled us to develop a new culture protocol to induce antitumor specific autologous CTL. The originality of NHL B cells--unlike most other tumor cells--is to be able to function as antigen presenting cells (APC) and to activate a T cell response in the absence of other professional APC. Over the next few years, these findings should allow the generation of anti-NHL specific T cells for adoptive immunotherapy and for the identification of NHL-associated antigens.