Synaptic release of CCL5 storage vesicles triggers CXCR4 surface expression promoting CTL migration in response to CXCL12.

The lytic function of CTL relies on the polarized release of cytotoxic granules (CG) at the immune synapse (IS) with target cells. CTL also contain CCL5 in cytoplasmic storage vesicles (CCL5V) distinct from CG, the role of which, in regulating T cell effector functions, is not understood. Using human CD8(+) T cells specific to a lung tumor-associated Ag, we show in this article that CTL release both secretory compartments into the immune synapse with autologous tumor cells. Moreover, we demonstrate that disorganization of the T cell microtubule cytoskeleton and defects in hMunc13-4 or Rab27a abrogate CG exocytosis and synaptic secretion of the chemokine. Mechanistically, synaptic release of CCL5 cytoplasmic storage vesicles likely occurs upon their coalescence with the Rab27a-hMunc13-4 compartment and results in autocrine, CCR5-dependent induction of CXCR4 cell surface expression, thereby promoting T cell migration in response to CXCL12. We propose that CCL5 polarized delivery represents a mechanism by which CTL control immune synapse duration.

Alpha E beta 7 integrin interaction with E-cadherin promotes antitumor CTL activity by triggering lytic granule polarization and exocytosis.

Various T cell adhesion molecules and their cognate receptors on target cells promote T cell receptor (TCR)-mediated cell killing. In this report, we demonstrate that the interaction of epithelial cell marker E-cadherin with integrin alpha(E)(CD103)beta(7), often expressed by tumor-infiltrating lymphocytes (TILs), plays a major role in effective tumor cell lysis. Indeed, we found that although tumor-specific CD103(+) TIL-derived cytotoxic T lymphocyte (CTL) clones are able to kill E-cadherin(+)/intercellular adhesion molecule 1(-) autologous tumor cells, CD103(-) peripheral blood lymphocyte (PBL)-derived counterparts are inefficient. This cell killing is abrogated after treatment of the TIL clones with a blocking anti-CD103 monoclonal antibody or after targeting E-cadherin in the tumor using ribonucleic acid interference. Confocal microscopy analysis also demonstrated that alpha(E)beta(7) is recruited at the immunological synapse and that its interaction with E-cadherin is required for cytolytic granule polarization and subsequent exocytosis. Moreover, we report that the CD103(-) profile, frequently observed in PBL-derived CTL clones and associated with poor cytotoxicity against the cognate tumor, is up-regulated upon TCR engagement and transforming growth factor beta1 treatment, resulting in strong potentiation of antitumor lytic function. Thus, CD8(+)/CD103(+) tumor-reactive T lymphocytes infiltrating epithelial tumors most likely play a major role in antitumor cytotoxic response through alpha(E)beta(7)-E-cadherin interactions.

Different expression levels of the TAP peptide transporter lead to recognition of different antigenic peptides by tumor-specific CTL.

Decreased antigenicity of cancer cells is a major problem in tumor immunology. This is often acquired by an expression defect in the TAP. However, it has been reported that certain murine Ags appear on the target cell surface upon impairment of TAP expression. In this study, we identified a human CTL epitope belonging to this Ag category. This epitope is derived from preprocalcitonin (ppCT) signal peptide and is generated within the endoplasmic reticulum by signal peptidase and signal peptide peptidase. Lung cancer cells bearing this antigenic peptide displayed low levels of TAP, but restoration of their expression by IFN-γ treatment or TAP1 and TAP2 gene transfer abrogated ppCT Ag presentation. In contrast, TAP upregulation in the same tumor cells increased their recognition by proteasome/TAP-dependent peptide-specific CTLs. Thus, to our knowledge, ppCT(16-25) is the first human tumor epitope whose surface expression requires loss or downregulation of TAP. Lung tumors frequently display low levels of TAP molecules and might thus be ignored by the immune system. Our results suggest that emerging signal peptidase-generated peptides represent alternative T cell targets, which permit CTLs to destroy TAP-impaired tumors and thus overcome tumor escape from CD8(+) T cell immunity.

Preprocalcitonin signal peptide generates a cytotoxic T lymphocyte-defined tumor epitope processed by a proteasome-independent pathway.

We identified an antigen recognized on a human non-small-cell lung carcinoma by a cytotoxic T lymphocyte clone derived from autologous tumor-infiltrating lymphocytes. The antigenic peptide is presented by HLA-A2 and is encoded by the CALCA gene, which codes for calcitonin and for the alpha-calcitonin gene-related peptide. The peptide is derived from the carboxy-terminal region of the preprocalcitonin signal peptide and is processed independently of proteasomes and the transporter associated with antigen processing. Processing occurs within the endoplasmic reticulum of all tumoral and normal cells tested, including dendritic cells, and it involves signal peptidase and the aspartic protease, signal peptide peptidase. The CALCA gene is overexpressed in medullary thyroid carcinomas and in several lung carcinomas compared with normal tissues, leading to recognition by the T cell clone. This new epitope is, therefore, a promising candidate for cancer immunotherapy.

Potentiation of NK cell-mediated cytotoxicity in human lung adenocarcinoma: role of NKG2D-dependent pathway.

Natural cytotoxicity receptors and NKG2D correspond to major activating receptors involved in triggering of tumor cell lysis by human NK cells. In this report, we investigated the expression of NKG2D ligands (NKG2DLs), MHC class I-related chain (MIC) A, MICB and UL16-binding proteins 1, 2 and 3, on a panel of human non-small-cell lung carcinoma cell lines, and we analyzed their role in tumor cell susceptibility to NK cell lysis. Although adenocarcinoma (ADC) cells expressed heterogeneous levels of NKG2DLs, they were often resistant to NK cell-mediated killing. Resistance of a selected cell line, ADC-Coco, to allogeneic polyclonal NK cells and autologous NK cell clones correlated with shedding of NKG2DLs resulting from a matrix metalloproteinase (MMP) production. Treatment of ADC-Coco cells with a MMP inhibitor (MMPI) combined with IL-15 stimulation of autologous NK cell clones lead to a potentiation of NK cell-mediated cytotoxicity. This lysis is mainly NKG2D mediated, since it is abrogated by anti-NKG2D-neutralizing mAb. These results suggest that MMPIs, in combination with IL-15, may be useful for overcoming tumor cell escape from the innate immune response.

A three-dimensional tumor cell defect in activating autologous CTLs is associated with inefficient antigen presentation correlated with heat shock protein-70 down-regulation.

We described previously a CTL clone able to lyse the autologous carcinoma cell line IGR-Heu after specific recognition of an HLA-A2/mutated alpha-actinin-4 peptide complex. Here, we used IGR-Heu, cultured either as standard two-dimensional monolayers or as three-dimensional spheroids, to further analyze the influence of target architecture on CTL reactivity. Interestingly, we found that changes in the tumor structure from two- to three-dimensional induced a dramatic decrease in its capacity to activate autologous CTL, as measured by IFN-gamma and tumor necrosis factor-alpha secretion. These functional alterations were attributable neither to MHC class I expression nor to tumor antigen (Ag) down-regulation, because IGR-Heu, cultured as two- or three-dimensional, expressed similar levels of HLA-A2 and alpha-actinin-4. More importantly, incubation of three-dimensional cells with synthetic epitope completely restored cytokine release by CTL. This defective Ag presentation correlated with a decrease in heat shock protein (hsp)70 expression by three-dimensional tumors compared with two-dimensional cells. Furthermore, transfection of the tumor cells with hsp70 cDNA completely restored the Ag-presenting potential of spheroids and, therefore, cytokine production by T cells. These data strongly suggest that hsp70 down-regulation in three-dimensional cells may result in tumor resistance to the immune response.

Mutant alpha-actinin-4 promotes tumorigenicity and regulates cell motility of a human lung carcinoma.

The precise role of alpha-actinin-4 encoding gene (ACTN4) is not very well understood. It has been reported to elicit tumor suppressor activity and to regulate cellular motility. To further assess the function of human ACTN4, we studied a lung carcinoma cell line expressing a mutated alpha-actinin-4, which is recognized as a tumor antigen by autologous CD8(+) cytotoxic T lymphocytes (CTL). Confocal immunofluorescence microscopy indicated that, while wild-type (WT) alpha-actinin-4 stains into actin cytoskeleton and cell surface ruffles, the mutated protein is only dispersed in the cytoplasm of the lung carcinoma cells. This loss of association with the cell surface did not appear to correlate with a decrease in in vitro alpha-actinin-4 crosslinking to filamentous (F)-actin. Interestingly, experiments using cell lines stably expressing ACTN4 demonstrated that as opposed to WT gene, mutant ACTN4 was unable to inhibit tumor cell growth in vitro and in vivo. Moreover, the expression of mutant alpha-actinin-4 resulted in the loss of tumor cell capacity to migrate. The identification of an inactivating mutation in ACTN4 emphasizes its role as a tumor suppressor gene and underlines the involvement of cytoskeleton alteration in tumor development and metastasis.

Functional and molecular characterization of a KIR3DL2/p140 expressing tumor-specific cytotoxic T lymphocyte clone infiltrating a human lung carcinoma.

T lymphocytes infiltrating a human lung carcinoma stimulated in vitro with autologous tumor cell line showed a TCRVbeta13.6(+) T-cell expansion. This subset was isolated using TCRVbeta-specific antibody and several T-cell clones were generated. All these clones expressed a unique Vbeta13.6-Jbeta2.7 TCR with the same junctional region strongly suggesting that they derived from the same cell. They were CD8(+)/CD28(-) and expressed the MHC class I binding killer cell Ig-like receptor (KIR)3DL2/p140, but not KIR3DL1/p70, KIR2DL1/p58.1 and KIR2DL2/3/p58.2. Sequence analysis indicated that KIR3DL2/p140 cDNA was identical to the previously reported 3DL2*002 allele except for two nucleic acid substitutions. Functional studies showed that KIR3DL2/p140(+) CTL secrete a significant level of IFNgamma and mediate an HLA-A2-restricted cytotoxicity against the autologous and some allogeneic tumor cells but not towards the autologous EBV-B cells. Strikingly, both the lytic and the cytokine secretion activities induced upon specific cell interactions were unaffected by anti-KIR3DL2/p140 antibody. In addition, crosslinking KIR3DL2/p140 molecules on CTL did not result into the modification of cytotoxicity and cytokine production triggered by anti-CD3 antibody. These results strongly suggest that, as opposed to distinct KIR expressed by CTL, the in vitro KIR3DL2/p140 engagement does not result into inhibitory (nor activatory) effects on tumor-specific CTL.

Generation of diverse mutated tumor antigen-specific cytotoxic T lymphocytes in a lung cancer patient with long survival.

We have identified an antigen recognized on a large cell carcinoma of the lung by tumor-specific cytotoxic T lymphocytes (CTL). The antigenic peptide is encoded by a mutated alpha-actinin-4 gene and presented by human leukocyte antigen (HLA)-A2. Using HLA-A2-peptide tetramers, we have derived from patient peripheral blood lymphocytes (PBL) and autologous tumor infiltrating lymphocytes (TIL) several mutated alpha-actinin-4-specific T cell clones. These clones displayed similar tetramer staining but distinct T cell receptor (TCR) usage and antitumor reactivity. Indeed, TIL clones lysed more efficiently the autologous tumor cells and released higher cytokine levels than PBL clones. Importantly, treatment of cancer cells with interferon-gamma enhanced their susceptibility to PBL clone-mediated lysis correlated with increase in HLA-class I expression. The present findings provide evidence that an immune T cell response took place in a lung cancer patient with favorable clinical evolution and suggest that CTL, recognizing a truly tumor-specific antigen, may contribute to controlling the tumor.

CD103 or LFA-1 engagement at the immune synapse between cytotoxic T cells and tumor cells promotes maturation and regulates T-cell effector functions.

T-cell adhesion/costimulatory molecules and their cognate receptors on target cells play a major role in T-cell receptor (TCR)-mediated activities. Here, we compared the involvement of CD103 and LFA-1, and their respective ligands, in the maturation of the cytotoxic immune synapse (cIS) and in the activation of CTL effector functions. Our results indicate that cytotoxicity toward cancer cells and, to a lesser extent, cytokine production by specific CTL require, together with TCR engagement, the interaction of either CD103 with E-cadherin or LFA-1 with ICAM-1. Flow-based adhesion assay showed that engagement of CD103 or LFA-1, together with TCR, enhances the strength of the T-cell/target cell interaction. Moreover, electron microscopic analyses showed that integrin-dependent mature cIS (mcIS) displays a cohesive ultrastructure, with tight membrane contacts separated by extensive clefts. In contrast, immature cIS (icIS), which is unable to trigger target cell lysis, is loose, with multiple protrusions in the effector cell membrane. Experiments using confocal microscopy revealed polarized cytokine release and degranulation at the mcIS associated with target cell killing, whereas icIS is characterized by failure of IFN-γ and granzyme B relocalization. Thus, interactive forces between CTL and epithelial tumor cells, mainly regulated by integrin engagement, correlate with maturity and the ultrastructure of the cIS and influence CTL effector functions. These results provide new insights into molecular mechanisms regulating antitumor CTL responses and may lead to the development of more efficient cancer immunotherapy strategies.

Minimal engagement of CD103 on cytotoxic T lymphocytes with an E-cadherin-Fc molecule triggers lytic granule polarization via a phospholipase Cgamma-dependent pathway.

Interaction of the integrin αE(CD103)ß7 expressed on tumor-infiltrating lymphocytes (TIL) with E-cadherin on epithelial tumor cells is required to trigger polarized exocytosis of cytotoxic granules in TIL that elicit tumor cell lysis. In this study, we investigated the functional and signaling properties of CD103 and its individual contribution to T-cell-mediated cancer-cell killing. Our results indicated that the binding of CD103 on tumor-specific CTL to immobilized recombinant E-cadherin-Fc is sufficient to induce the polarization of cytolytic granules, whereas the degranulation of cytolytic granules also requires the coengagement of the T-cell receptor. Moreover, minimal CD103 triggering promotes the phosphorylation of the ERK1/2 kinases and phospholipase Cγ1 (PLCγ1). Inhibiting PLCγ blocks granule relocalization, decreasing T-cell receptor-mediated cytotoxicity. Thus, our results emphasize a unique costimulatory role of CD103 in tumor-specific CTL activation by providing signals that promote T-cell effector functions needed to specifically target and lyse cancer cells.

Intratumoral induction of CD103 triggers tumor-specific CTL function and CCR5-dependent T-cell retention.

We have reported previously that the interaction of alpha(E)(CD103)beta(7) integrin, expressed on a CD8(+) tumor-infiltrating lymphocyte (TIL) clone but not on a peripheral blood lymphocyte (PBL) counterpart, with the epithelial marker E-cadherin on human lung tumor cells plays a crucial role in T-cell receptor-mediated cytotoxicity. We show here that both TIL and PBL clones are able to migrate toward autologous tumor cells and that chemokine receptor CCR5 is involved in this process. Adoptive transfer of the PBL clone in the cognate tumor engrafted in nonobese diabetic/severe combined immunodeficient mice and subsequent coengagement of T-cell receptor and transforming growth factor-beta1 receptor triggers CD103 expression on T-cell surface resulting in strong potentiation of antitumor lytic function. Moreover, interaction of alpha(E)beta(7) integrin with E-cadherin, but not lymphocyte function-associated antigen-1 with intercellular adhesion molecule-1, promotes CCR5 recruitment at the immunologic synapse formed between TIL and tumor cells, leading to inhibition of T-cell sensitivity to CCL5 chemotactic gradient. These results provide evidence for a role of tumor microenvironment, namely MHC class I-restricted antigen presentation and transforming growth factor-beta1 secretion, in regulating the effector phase of tumor-specific CTL response. They also suggest a unique role of CD103 in T-cell retention at the tumor site by a CCR5-dependent mechanism.

Human CD5 protects circulating tumor antigen-specific CTL from tumor-mediated activation-induced cell death.

We previously characterized several tumor-specific T cell clones from PBL and tumor-infiltrating lymphocytes of a lung cancer patient with identical TCR rearrangements and similar lytic potential, but with different antitumor response. A role of the TCR inhibitory molecule CD5 to impair reactivity of peripheral T cells against the tumor was found to be involved in this process. In this report, we demonstrate that CD5 also controls the susceptibility of specific T cells to activation-induced cell death (AICD) triggered by the tumor. Using a panel of tumor-infiltrating lymphocytes and PBL-derived clones expressing different levels of CD5, our results indicate that T lymphocyte AICD in response to the cognate tumor is inversely proportional to the surface expression level of CD5. They also suggest a direct involvement of CD5 in this process, as revealed by an increase in tumor-mediated T lymphocyte AICD following neutralization of the molecule with specific mAb. Mechanistically, our data indicate that down-regulation of FasL expression and subsequent inhibition of caspase-8 activation are involved in CD5-induced T cell survival. These results provide evidence for a role of CD5 in the fate of peripheral tumor-specific T cells and further suggest its contribution to regulate the extension of CTL response against tumor.

Identification of target actin content and polymerization status as a mechanism of tumor resistance after cytolytic T lymphocyte pressure.

To investigate tumor resistance to T cell lysis, a resistant variant was selected after specific cytolytic T lymphocytes (CTL) selection pressure. Although the resistant variant triggered perforin and granzyme B transcription in specific CTLs, as well as their degranulation, it exhibited a dramatic resistance to cytotoxic T cell killing. It also displayed strong morphological changes with alterations of the actin cytoskeleton. Electron microscopy analysis revealed a loosen interaction between CTLs and the resistant variant despite the formation of apparently normal conjugates. Transcriptional profiling identified a gene expression signature that distinguished sensitive from resistant tumor targets. More notably, we found that actin-related genes ephrin-A1 and scinderin were overexpressed in resistant target. Silencing of these genes using RNA interference resulted in a restoration of normal cell morphology and a significant attenuation of variant resistance to CTL killing. Our present study shows that a shift in cytoskeletal organization can be used, by tumor cells, as a strategy to promote their resistance after CTL selection pressure.

p53 potentiation of tumor cell susceptibility to CTL involves Fas and mitochondrial pathways.

In this study, we have investigated the mechanisms used by wild-type p53 (wtp53) to potentiate tumor cell susceptibility to CTL-mediated cell death. We report that wtp53 restoration in a human lung carcinoma cell line Institut Gustave Roussy (IGR)-Heu, displaying a mutated p53, resulted in up-regulation of Fas/CD95 receptor expression associated with an increase of tumor cell sensitivity to the autologous CTL clone, Heu127. However, when IGR-Heu cells were transfected with Fas cDNA, no potentiation to Heu127-mediated lysis was observed, indicating that induction of CD95 is not sufficient to sensitize target cells to CTL killing. Importantly, our data indicate that the effect of wtp53 on the Fas-mediated pathway involves a degradation of short cellular FLICE inhibitory protein resulting in subsequent caspase 8 activation. Furthermore, we demonstrate that wtp53 restoration also resulted in CTL-induced Bid translocation into mitochondria and a subsequent mitochondrial membrane permeabilization leading to cytochrome c release. These results indicate that tumor cell killing by autologous CTL can be enhanced by targeting degranulation-independent mechanisms via restoration of wtp53, a key determinant of apoptotic machinery regulation.

NK cells infiltrating a MHC class I-deficient lung adenocarcinoma display impaired cytotoxic activity toward autologous tumor cells associated with altered NK cell-triggering receptors.

NK cells are able to discriminate between normal cells and cells that have lost MHC class I (MHC-I) molecule expression as a result of tumor transformation. This function is the outcome of the capacity of inhibitory NK receptors to block cytotoxicity upon interaction with their MHC-I ligands expressed on target cells. To investigate the role of human NK cells and their various receptors in the control of MHC-I-deficient tumors, we have isolated several NK cell clones from lymphocytes infiltrating an adenocarcinoma lacking beta2-microglobulin expression. Unexpectedly, although these clones expressed NKG2D and mediated a strong cytolytic activity toward K562, Daudi and allogeneic MHC-class I+ carcinoma cells, they were unable to lyse the autologous MHC-I- tumor cell line. This defect was associated with alterations in the expression of natural cytotoxicity receptor (NCR) by NK cells and the NKG2D ligands, MHC-I-related chain A, MHC-I-related chain B, and UL16 binding protein 1, and the ICAM-1 by tumor cells. In contrast, the carcinoma cell line was partially sensitive to allogeneic healthy donor NK cells expressing high levels of NCR. Indeed, this lysis was inhibited by anti-NCR and anti-NKG2D mAbs, suggesting that both receptors are required for the induced killing. The present study indicates that the MHC-I-deficient lung adenocarcinoma had developed mechanisms of escape from the innate immune response based on down-regulation of NCR and ligands required for target cell recognition.

In situ sensory adaptation of tumor-infiltrating T lymphocytes to peptide-MHC levels elicits strong antitumor reactivity.

We have isolated from tumor-infiltrating lymphocytes (TIL) and PBL of a lung carcinoma patient several tumor-specific T cell clones displaying similar peptide-MHC tetramer staining and expressing a unique TCR. Although these clones elicited identical functional avidity and similar cytolytic potential, only T cell clones derived from TIL efficiently lysed autologous tumor cells. Interestingly, all of these clones expressed the same T cell surface markers except for the TCR inhibitory molecule CD5, which was expressed at much lower levels in TIL than in PBL. Video-imaging recordings demonstrated that, although both T cell clones could form stable conjugates with tumor cells, the Ca(2+) response occurred in TIL clones only. Significantly, analysis of a panel of circulating clones indicated that antitumor cytolytic activity was inversely proportional to CD5 expression levels. Importantly, CD5 levels in TIL appeared to parallel the signaling intensity of the TCR/peptide-MHC interaction. Thus, in situ regulation of CD5 expression may be a strategy used by CTL to adapt their sensitivity to intratumoral peptide-MHC levels.

Cytotoxic T lymphocytes directed against a tumor-specific mutated antigen display similar HLA tetramer binding but distinct functional avidity and tissue distribution.

We have previously identified an antigen (Ag) recognized on a human large cell carcinoma of the lung by a tumor-specific cytotoxic T lymphocyte clone derived from autologous tumor infiltrating lymphocytes (TILs). The antigenic peptide is presented by HLA-A2 molecules and is encoded by a mutated alpha-actinin-4 (ACTN4) gene. In the present report, we have isolated two anti-alpha-actinin-4 T cell clones from the same patient TIL and from his peripheral blood lymphocytes (PBLs) by using tetramers of soluble HLA-A2 molecules loaded with the mutated peptide. Although all of the clones displayed similar tetramer labeling, those isolated from PBL showed lower avidity of Ag recognition and killed the specific target much less efficiently, indicating that tetramer staining does not correlate with clone avidity/tumor reactivity. T cell receptor (TCR) analysis revealed that alpha-actinin-4-reactive clones used distinct alpha and beta chain rearrangements, demonstrating TCR repertoire diversity. Interestingly, TCR beta chain gene usage indicated that only Ag-specific clones with high functional avidity were expanded at the tumor site, whereas a low-avidity clone was exclusively amplified in patient peripheral blood. Our results point to the existence of distinct but overlapping antitumor TCR repertoires in TIL and PBL and suggest a selective in situ expansion of tumor-specific cytotoxic T lymphocyte with high avidity/tumor reactivity.

Antitumor cytotoxic T-lymphocyte response in human lung carcinoma: identification of a tumor-associated antigen.

We have isolated several cytotoxic T lymphocyte (CTL) clones from lymphocytes infiltrating a lung carcinoma of a patient with long survival. These clones showed a CD3+, CD8+, CD4-, CD28- phenotype and expressed a T-cell receptor (TCR) encoded either by Vbeta8-Jbeta1.5 or Vbeta22-Jbeta1.4 rearrangements. Functional studies indicated that these clones mediated a high human leukocyte antigen (HLA)-A2.1-restricted cytotoxic activity against the autologous tumor cell line. Interestingly, TCRbeta chain gene usage indicated that CTL clones identified in vitro were selectively expanded in vivo at the tumor site as compared to autologous peripheral blood lymphocytes (PBL). These findings provide evidence that an immune response may take place in non-small cell lung carcinoma and that effector T cells may contribute to tumor regression. Further study indicated that the CTL clones recognized the same decamer peptide encoded by a mutated alpha-actinin-4 gene. Using tetramers of soluble HLA-A2 molecules loaded with the mutated antigenic peptide, we have derived several anti-alpha-actinin-4 T-cell clones from patient PBL. These CTL, recognizing a truly tumor-specific antigen, may play a role in the clinical evolution of this lung cancer patient. Adoptive transfer of CTL clones in a SCID/NOD mice model transplanted with autologous tumor supported their antitumor effect in vivo.

Tumor-infiltrating CD4+ T lymphocytes express APO2 ligand (APO2L)/TRAIL upon specific stimulation with autologous lung carcinoma cells: role of IFN-alpha on APO2L/TRAIL expression and -mediated cytotoxicity.

In the present report, we have investigated TRAIL/APO2 ligand (APO2L) expression, regulation, and function in human lung carcinoma tumor-infiltrating lymphocytes. Using a panel of non-small cell lung carcinoma cell lines, we first showed that most of them expressed TRAIL-R1/DR4, TRAIL-R2/DR5, but not TRAIL-R3/DcR1 and TRAIL-R4/DcR2, and were susceptible to APO2L/TRAIL-induced cell death. Two APO2L/TRAIL-sensitive tumor cell lines (MHC class I(+)/II(+) or I(+)/II(-)) were selected and specific CD4(+) HLA-DR- or CD8(+) HLA-A2-restricted CTL clones were respectively isolated from autologous tumor-infiltrating lymphocytes. Interestingly, although the established T cell clones did not constitutively express detectable levels of APO2L/TRAIL, engagement of their TCR via activation with specific tumor cells selectively induced profound APO2L/TRAIL expression on the CD4(+), but not on the CD8(+), CTL clones. Furthermore, as opposed to the CD8(+) CTL clone which mainly used granule exocytosis pathway, the CD4(+) CTL clone lysed the specific target via both perforin/granzymes and APO2L/TRAIL-mediated mechanisms. The latter cytotoxicity correlated with APO2L/TRAIL expression and was significantly enhanced in the presence of IFN-alpha. More interestingly, in vivo studies performed in SCID/nonobese diabetic mice transplanted with autologous tumor and transferred with the specific CD4(+) CTL clone in combination with IFN-alpha resulted in an important APO2L/TRAIL-mediated tumor growth inhibition, which was prohibited by soluble TRAIL-R2. Our findings suggest that APO2L/TRAIL, specifically induced by autologous tumor and up-regulated by IFN-alpha, may be a key mediator of tumor-specific CD4(+) CTL-mediated cell death and point to a potent role of this T cell subset in tumor growth control.