Identification of a naturally processed HLA-A*02:01-restricted CTL epitope from the human tumor-associated antigen Nectin-4.

Nectin-4 is a tumor antigen present on the surface of breast, ovarian and lung carcinoma cells. It is rarely present in normal adult tissues and is therefore a candidate target for cancer immunotherapy. Here, we identified a Nectin-4 antigenic peptide that is naturally presented to T cells by HLA-A2 molecules. We first screened the 502 nonamer peptides of Nectin-4 (510 amino acids) for binding to and off-rate from eight different HLA class I molecules. We then combined biochemical, cellular and algorithmic assays to select 5 Nectin-4 peptides that bound to HLA-A*02:01 molecules. Cytolytic T lymphocytes were obtained from healthy donors, that specifically lyzed HLA-A2(+) cells pulsed with 2 out of the 5 peptides, indicating the presence of anti-Nectin-4 CD8(+) T lymphocytes in the human T cell repertoire. Finally, an HLA-A2-restricted cytolytic T cell clone derived from a breast cancer patient recognized peptide Nectin-4145-153 (VLVPPLPSL) and lyzed HLA-A2(+) Nectin-4(+) breast carcinoma cells. These results indicate that peptide Nectin-4145-153 is naturally processed for recognition by T cells on HLA-A2 molecules. It could be used to monitor antitumor T cell responses or to immunize breast cancer patients.

A major secretory defect of tumour-infiltrating T lymphocytes due to galectin impairing LFA-1-mediated synapse completion.

Surface galectin has been shown to contribute to dysfunctions of human tumour-infiltrating lymphocytes (TILs). We show here that galectin-covered CD8 TILs produce normal amounts of intracellular cytokines, but fail to secrete them because of defective actin rearrangements at the synapse. The non-secreting TILs also display reduced adhesion to their targets, together with defective LFA-1 recruitment and activation at the synapse. These defects are relieved by releasing surface galectin. As mild LFA-1 blockade on normal blood T cells emulate the defects of galectin-covered TILs, we conclude that galectin prevents the formation of a functional secretory synapse by preventing optimal LFA-1 triggering. Our results highlight a major secretory defect of TILs that is not revealed by widely used intracellular cytokine immunomonitoring assays. They also provide additional insights into the T-cell response, by showing that different thresholds of LFA-1 triggering are required to promote the intracellular production of cytokines and their secretion.

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.

Functions of Anti-MAGE T-cells induced in melanoma patients under different vaccination modalities.

Tumor regressions have been observed in a small proportion of melanoma patients vaccinated with a MAGE-A3 peptide presented by HLA-A1, administered as peptide, ALVAC canarypox virus containing a MAGE-A3 minigene, or peptide-pulsed dendritic cells (DC). There was a correlation between tumor regression and the detection of anti-MAGE-3.A1 CTL responses. These responses were monoclonal and often of a very low magnitude after vaccination with peptide or ALVAC, and usually polyclonal and of a higher magnitude after DC vaccination. These results suggested that, at least in some patients, surprisingly few anti-MAGE-3.A1 T-cells could initiate a tumor regression process. To understand the role of these T cells, we carried out a functional analysis of anti-MAGE-3.A1 CTL clones derived from vaccinated patients who displayed tumor regression. The functional avidities of these CTL clones, evaluated in lysis assays, were surprisingly low, suggesting that high avidity was not part of the putative capability of these CTL to trigger tumor rejection. Most anti-MAGE-3.A1 CTL clones obtained after DC vaccination, but not after peptide or ALVAC vaccination, produced interleukin 10. Transcript profiling confirmed these results and indicated that approximately 20 genes, including CD40L, prostaglandin D2 synthase, granzyme K, and granzyme H, were highly differentially expressed between the anti-MAGE-3.A1 CTL clones derived from patients vaccinated with either peptide-ALVAC or peptide-pulsed DC. These results indicate that the modality of vaccination with a tumor-specific antigen influences the differentiation pathway of the antivaccine CD8 T-cells, which may have an effect on their capacity to trigger a tumor rejection response.

Restoring the association of the T cell receptor with CD8 reverses anergy in human tumor-infiltrating lymphocytes.

For several days after antigenic stimulation, human cytolytic T lymphocyte (CTL) clones exhibit a decrease in their effector activity and in their binding to human leukocyte antigen (HLA)-peptide tetramers. We observed that, when in this state, CTLs lose the colocalization of the T cell receptor (TCR) and CD8. Effector function and TCR-CD8 colocalization were restored with galectin disaccharide ligands, suggesting that the binding of TCR to galectin plays a role in the distancing of TCR from CD8. These findings appear to be applicable in vivo, as TCR was observed to be distant from CD8 on human tumor-infiltrating lymphocytes, which were anergic. These lymphocytes recovered effector functions and TCR-CD8 colocalization after ex vivo treatment with galectin disaccharide ligands. The separation of TCR and CD8 molecules could be one major mechanism of anergy in tumors and other chronic stimulation conditions.

Vaccination of a melanoma patient with mature dendritic cells pulsed with MAGE-3 peptides triggers the activity of nonvaccine anti-tumor cells.

We previously characterized the CTL response of a melanoma patient who experienced tumor regression following vaccination with an ALVAC virus coding for a MAGE-A3 Ag. Whereas anti-vaccine CTL were rare in the blood and inside metastases of this patient, anti-tumor CTL recognizing other tumor Ags, mainly MAGE-C2, were 100 times more frequent in the blood and considerably enriched in metastases following vaccination. In this study we report the analysis of the CTL response of a second melanoma patient who showed a mixed tumor response after vaccination with dendritic cells pulsed with two MAGE-A3 antigenic peptides presented, respectively, by HLA-A1 and HLA-DP4. Anti-MAGE-3.A1 CD8 and anti-MAGE-3.DP4 CD4 T cells became detectable in the blood after vaccination at a frequency of approximately 10(-5) among the CD8 or CD4 T cells, respectively, and they were slightly enriched in slowly progressing metastases. Additional anti-tumor CTL were present in the blood at a frequency of 2x10(-4) among the CD8 T cells and, among these, an anti-MAGE-C2 CTL clone was detected only following vaccination and was enriched by >1,000-fold in metastases relative to the blood. The striking similarity of these results with our previous observations further supports the hypothesis that the induction of a few anti-vaccine T cells may prime or restimulate additional anti-tumor T cell clones that are mainly responsible for the tumor regression.

A new tumor-specific antigen encoded by MAGE-C2 and presented to cytolytic T lymphocytes by HLA-B44.

A panel of cytolytic T lymphocyte (CTL) clones was isolated from metastases and blood samples of a melanoma patient vaccinated with MAGE-3.A1-pulsed autologous dendritic cells. We report here the identification of a new antigen encoded by the MAGE-C2 cancer-germline gene. This antigen is recognized by some of these CTL on HLA-B*4403. The sequence of the peptide is SESIKKKVL. It is processed in various melanoma cell lines expressing MAGE-C2 and HLA-B*4403. Because of the expression pattern of gene MAGE-C2, this new antigen is strictly tumor-specific and could therefore be used for peptide-based antitumoral vaccination.

CD45RA on human CD8 T cells is sensitive to the time elapsed since the last antigenic stimulation.

The expression of CD45RA on CCR7- human CD8+ memory T cells is widely considered to be a marker of terminal differentiation. We studied the time course of CD45RA and CCR7 expression on human antitumoral cytotoxic T lymphocyte (CTL) clones and blood CD8+ T cells after antigenic stimulation. Our results indicate that CD45RA+ CCR7- CD8+ T cells are resting memory cells that, upon antigenic stimulation and during the next 10 days, proliferate, lose CD45RA, and transiently acquire CCR7. In the absence of further antigenic stimulation, they progressively re-express CD45RA and become CD45RA+ CCR7-. We conclude that the expression of CD45RA on these cells is indicative of the time elapsed since the last antigenic stimulation rather than the incapacity to proliferate or particularly high lytic potential. This concept leads to a reinterpretation of the significance of the presence of CD45RA+ CD8+ memory cells in patients affected by viral infections or by cancer.

Phase 1/2 study of subcutaneous and intradermal immunization with a recombinant MAGE-3 protein in patients with detectable metastatic melanoma.

The purpose of this phase 1/2 study was to evaluate toxicity, tumor evolution and immunologic response following administration of a fixed dose of a recombinant MAGE-3 protein by subcutaneous and intradermal routes in the absence of immunologic adjuvant. Thirty-two patients with detectable metastatic melanoma expressing gene MAGE-3 were included and 30 received at least one injection with a fixed dose of a ProtD-MAGE-3 fusion protein. The immunization schedule included 6 intradermal and subcutaneous injections at 3-week intervals. Afterward, patients without major tumor progression who required other treatments received additional vaccinations at increasing time intervals. The vaccine was generally well tolerated. Among the 26 patients who received at least 4 vaccinations, we observed 1 partial response and 4 mixed responses. For these 5 responding patients, time to progression varied from 3.5 to 51+ months. An anti-MAGE-3 CD4 T-lymphocyte response was detected in 1 out of the 5 responding patients. The majority of patients had no anti-MAGE-3 antibody response. The clinical and immunologic responses generated by the vaccine are rather limited. Nevertheless, given the potential antitumor efficacy and the very mild toxicity of vaccinations, further studies combining MAGE proteins and/or peptides with potent immunologic adjuvants are warranted, not only in metastatic melanoma, but also in the adjuvant setting.

MAGE-A1 interacts with adaptor SKIP and the deacetylase HDAC1 to repress transcription.

MAGE-A1 belongs to a family of 12 genes that are active in various types of tumors and silent in normal tissues except in male germ-line cells. The MAGE-encoded antigens recognized by T cells are highly tumor-specific targets for T cell-oriented cancer immunotherapy. The function of MAGE-A1 is currently unknown. To analyze it, we attempted to identify protein partners of MAGE-A1. Using yeast two-hybrid screening, we detected an interaction between MAGE-A1 and Ski Interacting Protein (SKIP). SKIP is a transcriptional regulator that connects DNA-binding proteins to proteins that either activate or repress transcription. We show that MAGE-A1 inhibits the activity of a SKIP-interacting transactivator, namely the intracellular part of Notch1. Deletion analysis indicated that this inhibition requires the binding of MAGE-A1 to SKIP. Moreover, MAGE-A1 was found to actively repress transcription by binding and recruiting histone deacetylase 1 (HDAC1). Our results indicate that by binding to SKIP and by recruiting HDACs, MAGE-A1 can act as a potent transcriptional repressor. MAGE-A1 could therefore participate in the setting of specific gene expression patterns for tumor cell growth or spermatogenesis.

Polyclonal CTL responses observed in melanoma patients vaccinated with dendritic cells pulsed with a MAGE-3.A1 peptide.

Vaccination with mature, monocyte-derived dendritic cells (DC) pulsed with the MAGE-3(168-176) peptide, which is presented by HLA-A1, has been reported to induce tumor regressions and CTL in some advanced stage IV melanoma patients. We present here a precise evaluation of the level of some of these anti-MAGE-3.A1 CTL responses and an analysis of their clonal diversity. Blood lymphocytes were stimulated with the MAGE-3.A1 peptide under limiting dilution conditions and assayed with an A1/MAGE-3 tetramer. This was followed by the cloning of the tetramer-positive cells and by TCR sequence analysis of the CTL clones that lysed targets expressing MAGE-3.A1. We also used direct ex vivo tetramer staining of CD8 cells, sorting, and cloning of the positive cells. In three patients who showed regression of some of their metastases after vaccination, CTL responses were observed with frequencies ranging from 7 x 10(-6) to 9 x 10(-4) of CD8(+) blood T lymphocytes, representing an increase of 20- to 400-fold of the frequencies found before immunization. A fourth patient showed neither tumor regression nor an anti-MAGE-3.A1 CTL response. In each of the responses, several CTL clones were amplified. This polyclonality contrasts with the monoclonality of the CTL responses observed in patients vaccinated with MAGE-3.A1 peptide or with an ALVAC recombinant virus coding for this antigenic peptide.

Cytolytic T-cell responses of cancer patients vaccinated with a MAGE antigen.

'Cancer-germline' genes such as the MAGE gene family are expressed in many tumors and in male germline cells but not in normal tissues. They encode shared tumor-specific antigens, which have been used in therapeutic vaccination trials of metastatic melanoma patients. To establish whether there is a correlation between tumoral regressions and T-cell responses against the vaccine antigen, we evaluated the responses of patients vaccinated with a MAGE-3 antigenic peptide or a recombinant virus coding for the peptide. Blood lymphocytes were stimulated with antigenic peptide followed by detection with tetramer, T-cell cloning, and TCR analysis. In 4/9 regressor patients and in 1/14 progressors we found a low level, usually monoclonal cytolytic T lymphocyte response against the MAGE-3 peptide.

A reversible functional defect of CD8+ T lymphocytes involving loss of tetramer labeling.

We have observed that human CTL clones lose their specific cytolytic activity and cytokine production under certain stimulation conditions, while retaining an antigen-dependent growth pattern. These inactive CTL simultaneously lose their labeling by an HLA-peptide tetramer, even though the amount of TCR-CD3 at their surface is not reduced. The tetramer-negative cells recover tetramer staining and cytolytic activity after stimulation with tumor cells in the presence of a supernatant of activated lymphocytes. Our results suggest the existence of a new type of functional defect of CTL. They also indicate that tetramers may fail to reveal some CTL bearing the relevant TCR, even when such functionally arrested CTL retain the potential to participate in immune responses because their defect is reversible.