Analysis of antigens recognized on human melanoma cells by A2-restricted cytolytic T lymphocytes (CTL)

Rational Combination of Parvovirus H1 With CTLA-4 and PD-1 Checkpoint Inhibitors Dampens the Tumor Induced Immune Silencing

The recent therapeutic success of immune checkpoint inhibitors in the treatment of advanced melanoma highlights the potential of cancer immunotherapy. Oncolytic virus-based therapies may further improve the outcome of these cancer patients. A human ex vivo melanoma model was used to investigate the oncolytic parvovirus H-1 (H-1PV) in combination with ipilimumab and/or nivolumab. The effect of this combination on activation of human T lymphocytes was demonstrated. Expression of CTLA-4, PD-1, and PD-L1 immune checkpoint proteins was upregulated in H-1PV-infected melanoma cells. Nevertheless, maturation of antigen presenting cells such as dendritic cells was triggered by H-1PV infected melanoma cells. Combining H-1PV with checkpoint inhibitors, ipilimumab enhanced TNFα release during maturation of dendritic cells; nivolumab increased the amount of IFNγ release. H-1PV mediated reduction of regulatory T cell activity was demonstrated by lower TGF-ß levels. The combination of ipilimumab and nivolumab resulted in a further decline of TGF-ß levels. Similar results were obtained regarding the activation of cytotoxic T cells. H-1PV infection alone and in combination with both checkpoint inhibitors caused strong activation of CTLs, which was reflected by an increased number of CD8⁺GranB⁺ cells and increased release of granzyme B, IFNγ, and TNFα. Our data support the concept of a treatment benefit from combining oncolytic H-1PV with the checkpoint inhibitors ipilimumab and nivolumab, with nivolumab inducing stronger effects on cytotoxic T cells, and ipilimumab strengthening T lymphocyte activity.

Activation of Murine Immune Cells upon Co-culture with Plasma-treated B16F10 Melanoma Cells

Recent advances in melanoma therapy increased median survival in patients. However, death rates are still high, motivating the need of novel avenues in melanoma treatment. Cold physical plasma expels a cocktail of reactive species that have been suggested for cancer treatment. High species concentrations can be used to exploit apoptotic redox signaling pathways in tumor cells. Moreover, an immune-stimulatory role of plasma treatment, as well as plasma-killed tumor cells, was recently proposed, but studies using primary immune cells are scarce. To this end, we investigated the role of plasma-treated murine B16F10 melanoma cells in modulating murine immune cells’ activation and marker profile. Melanoma cells exposed to plasma showed reduced metabolic and migratory activity, and an increased release of danger signals (ATP, CXCL1). This led to an altered cytokine profile with interleukin-1β (IL-1β) and CCL4 being significantly increased in plasma-treated mono- and co-cultures with immune cells. In T cells, plasma-treated melanoma cells induced extracellular signal-regulated Kinase (ERK) phosphorylation and increased CD28 expression, suggesting their activation. In monocytes, CD115 expression was elevated as a marker for activation. In summary, here we provide proof of concept that plasma-killed tumor cells are recognized immunologically, and that plasma exerts stimulating effects on immune cells alone.

Soluble HLA-associated peptide from PSF1 has a cancer vaccine potency

Partner of sld five 1 (PSF1) is an evolutionary conserved DNA replication factor involved in DNA replication in lower species, which is strongly expressed in normal stem cell populations and progenitor cell populations. Recently, we have investigated PSF1 functions in cancer cells and found that PSF1 plays a significant role in tumour growth. These findings provide initial evidence for the potential of PSF1 as a therapeutic target. Here, we reveal that PSF1 contains an immunogenic epitope suitable for an antitumour vaccine. We analysed PSF1 peptides eluted from affinity-purified human leukocyte antigen (HLA) by mass spectrometry and identified PSF1_79-87 peptide (YLYDRLLRI) that has the highest prediction score using an in silico algorithm. PSF1_79-87 peptide induced PSF1-specific cytotoxic T lymphocyte responses such as the production of interferon-γ and cytotoxicity. Because PSF1 is expressed in cancer cell populations and highly expressed in cancer stem cell populations, these data suggest that vaccination with PSF1_79-87 peptide may be a novel therapeutic strategy for cancer treatment.

Immunogenicity of oncolytic vaccinia viruses JX-GFP and TG6002 in a human melanoma in vitro model: studying immunogenic cell death, dendritic cell maturation and interaction with cytotoxic T lymphocytes

Oncolytic virotherapy is an emerging immunotherapeutic modality for cancer treatment. Oncolytic viruses with genetic modifications can further enhance the oncolytic effects on tumor cells and stimulate antitumor immunity. The oncolytic vaccinia viruses JX-594-GFP+/hGM-CSF (JX-GFP) and TG6002 are genetically modified by secreting granulocyte-macrophage colony-stimulating factor (GM-CSF) or transforming 5-fluorocytosine (5-FC) into 5-fluorouracil (5-FU). We compared their properties to kill tumor cells and induce an immunogenic type of cell death in a human melanoma cell model using SK29-MEL melanoma cells. Their influence on human immune cells, specifically regarding the activation of dendritic cells (DCs) and the interaction with the autologous cytotoxic T lymphocyte (CTL) clone, was investigated. Melanoma cells were infected with either JX-GFP or TG6002 alone or in combination with 5-FC and 5-FU. The influence of viral infection on cell viability followed a time- and multiplicity of infection dependent manner. Combination of virus treatment with 5-FU resulted in stronger reduction of cell viability. TG6002 in combination with 5-FC did not significantly strengthen the reduction of cell viability in this setting. Expression of calreticulin and high mobility group 1 protein (HMGB1), markers of immunogenic cell death (ICD), could be detected after viral infection. Accordingly, DC maturation was noted after viral oncolysis. DCs presented stronger expression of activation and maturation markers. The autologous CTL clone IVSB expressed the activation marker CD69, but viral treatment failed to enhance cytotoxicity marker. In summary, vaccinia viruses JX-GFP and TG6002 lyse melanoma cells and induce additional immunostimulatory effects to promote antitumor immune response. Further investigation in vivo is needed to consolidate the data.

Proteomic investigation of the interactome of FMNL1 in hematopoietic cells unveils a role in calcium-dependent membrane plasticity

Formin-like 1 (FMNL1) is a formin-related protein highly expressed in hematopoietic cells and overexpressed in leukemias as well as diverse transformed cell lines. It has been described to play a role in diverse functions of hematopoietic cells such as phagocytosis of macrophages as well as polarization and cytotoxicity of T cells. However, the specific role of FMNL1 in these processes has not been clarified yet and regulation by interaction partners in primary hematopoietic cells has never been investigated. We performed a proteomic screen for investigation of the interactome of FMNL1 in primary hematopoietic cells resulting in the identification of a number of interaction partners. Bioinformatic analysis considering semantic similarity suggested the giant protein AHNAK1 to be an essential interaction partner of FMNL1. We confirmed AHNAK1 as a general binding partner for FMNL1 in diverse hematopoietic cells and demonstrate that the N-terminal part of FMNL1 binds to the C-terminus of AHNAK1. Moreover, we show that the constitutively activated form of FMNL1 (FMNL1γ) induces localization of AHNAK1 to the cell membrane. Finally, we provide evidence that overexpression or knock down of FMNL1 has an impact on the capacitative calcium influx after ionomycin-mediated activation of diverse cell lines and primary cells.

Expanding the targets available to therapeutic antibodies via novel disease-specific markers

The development of immunotherapies offers significant promise for clinical applications in cancer and infectious diseases. Here the authors describe a novel, integrated approach to immunotherapy that combines novel technologies to discover and target disease-specific peptide/HLA class I complexes. This unique class of markers makes the entire proteome accessible to antibody reagents and offers unsurpassed specificity for targeting cancerous and infected cells. Arm one of the three-armed approach uses an innovative technology for the efficient, direct discovery of new peptide/HLA class I markers. Arm two applies a powerful and inventive strategy to generate T-cell receptor mimics (TCRms), which are antibodies with exquisite binding specificity for peptide/HLA class I markers, and uses TCRms to validate the specific expression of markers on cancerous and infected cells. The third arm uses TCRms to target and kill diseased cells with high sensitivity and specificity. In summary, the combination of two pioneering technologies expands the repertoire of disease-specific markers that can be targeted by therapeutic antibodies and enables a powerful, integrated approach to HLA-based immunotherapy.

Activation by interferon-gamma of expression of ICAM-1 and MHC class II antigens in tumour cells from colorectal carcinomas

Aims-To determine whether lack of MHC class II antigen and intercellular adhesion molecule-1 (ICAM-1) expression in some tumours is due to the inability of the tumour cells to respond to the cytokine interferon-gamma (IFN-gamma), an important activator of these surface molecules.Methods-Cells from 40 colorectal tumours which did not constitutively express class II MHC antigens or ICAM-1 were kept in short term culture after disaggregation for a few days to two weeks without significant loss of viability. These were treated with IFN-gamma. Expression of class II MHC antigens and ICAM-1 was determined using immunohistological techniques.Results-There was clear induction in vitro of both MHC class II antigens and ICAM-1 in cells from eight of the tumours, with between 50 and 80% of the tumour cells in the cultures staining positively. The staining was apparent within 24 hours, appeared maximal at about three days, and declined thereafter. There were no obvious differences in cell morphology or viability between the cultures which were inducible and those which were not, nor were there obvious differences between the tumours from which they were derived.Conclusions-Expression of MHC class II antigens and ICAM-1 may be induced by IFN-gamma in a small proportion of colorectal tumours which do not constitutively express these antigens, showing that only a minority of tumours are capable of responding to this cytokine.

Direct discovery and validation of a peptide/MHC epitope expressed in primary human breast cancer cells using a TCRm monoclonal antibody with profound antitumor properties

The identification and validation of new cancer-specific T cell epitopes continues to be a major area of research interest. Nevertheless, challenges remain to develop strategies that can easily discover and validate epitopes expressed in primary cancer cells. Regarded as targets for T cells, peptides presented in the context of the major histocompatibility complex (MHC) are recognized by monoclonal antibodies (mAbs). These mAbs are of special importance as they lend themselves to the detection of epitopes expressed in primary tumor cells. Here, we use an approach that has been successfully utilized in two different infectious disease applications (WNV and influenza). A direct peptide-epitope discovery strategy involving mass spectrometric analysis led to the identification of peptide YLLPAIVHI in the context of MHC A*02 allele (YLL/A2) from human breast carcinoma cell lines. We then generated and characterized an anti-YLL/A2 mAb designated as RL6A TCRm. Subsequently, the TCRm mAb was used to directly validate YLL/A2 epitope expression in human breast cancer tissue, but not in normal control breast tissue. Moreover, mice implanted with human breast cancer cells grew tumors, yet when treated with RL6A TCRm showed a marked reduction in tumor size. These data demonstrate for the first time a coordinated direct discovery and validation strategy that identified a peptide/MHC complex on primary tumor cells for antibody targeting and provide a novel approach to cancer immunotherapy.

Dendritic cells pulsed with RNA encoding allogeneic MHC and antigen induce T cells with superior antitumor activity and higher TCR functional avidity

Adoptive transfer of T cells expressing transgenic T-cell receptors (TCRs) with antitumor function is a hopeful new therapy for patients with advanced tumors; however, there is a critical bottleneck in identifying high-affinity TCR specificities needed to treat different malignancies. We have developed a strategy using autologous dendritic cells cotransfected with RNA encoding an allogeneic major histocompatibility complex molecule and a tumor-associated antigen to obtain allo-restricted peptide-specific T cells having superior capacity to recognize tumor cells and higher functional avidity. This approach provides maximum flexibility because any major histocompatibility complex molecule and any tumor-associated antigen can be combined in the dendritic cells used for priming of autologous T cells. TCRs of allo-restricted T cells, when expressed as transgenes in activated peripheral blood lymphocytes, transferred superior function compared with self-restricted TCR. This approach allows high-avidity T cells and TCR specific for tumor-associated self-peptides to be easily obtained for direct adoptive T-cell therapy or for isolation of therapeutic transgenic TCR sequences.

Identification of breast cancer peptide epitopes presented by HLA-A*0201

Cellular immune mechanisms detect and destroy cancerous and infected cells via the human leukocyte antigen (HLA) class I molecules that present peptides of intracellular origin on the surface of all nucleated cells. The identification of novel, tumor-specific epitopes is a critical step in the development of immunotherapeutics for breast cancer. To directly identify peptide epitopes unique to cancerous cells, secreted human class I HLA molecules (sHLA) were constructed by deletion of the transmembrane and cytoplasmic domain of HLA A*0201. The resulting sHLA-A*0201 was transferred and expressed in breast cancer cell lines MCF-7, MDA-MB-231, and BT-20 as well as in the immortal, nontumorigenic cell line MCF10A. Stable transfectants were seeded into bioreactors for production of > 25 mg of sHLA-A*0201. Peptides eluted from affinity purified sHLA were analyzed by mass spectroscopy. Comparative analysis of HLA-A*0201 peptides revealed 5 previously uncharacterized epitopes uniquely presented on breast cancer cells. These peptides were derived from intracellular proteins with either well-defined or putative roles in breast cancer development and progression: Cyclin Dependent Kinase 2 (Cdk2), Ornithine Decarboxylase (ODC1), Kinetochore Associated 2 (KNTC2 or HEC1), Macrophage Migration Inhibitory Factor (MIF), and Exosome Component 6 (EXOSC6). Cellular recognition of the MIF, KNTC2, EXOSC6, and Cdk2 peptides by circulating CD8+ cells was demonstrated by tetramer staining and IFN-gamma ELISPOT. The identification and characterization of peptides unique to the class I of breast cancer cells provide putative targets for the development of immune diagnostic tools and therapeutics.

Allorestricted T cells with specificity for the FMNL1-derived peptide PP2 have potent antitumor activity against hematologic and other malignancies

Cell-based immunotherapy in settings of allogeneic stem cell transplantation or donor leukocyte infusion has curative potential, especially in hematologic malignancies. However, this approach is severely restricted due to graft-versus-host disease (GvHD). This limitation may be overcome if target antigens are molecularly defined and effector cells are specifically selected. We chose formin-related protein in leukocytes 1 (FMNL1) as a target antigen after intensive investigation of its expression profile at the mRNA and protein levels. Here, we confirm restricted expression in peripheral blood mononuclear cells (PBMCs) from healthy donors but also observe overexpression in different leukemias and aberrant expression in transformed cell lines derived from solid tumors. We isolated allorestricted T-cell clones expressing a single defined TCR recognizing a particular HLA-A2–presented peptide derived from FMNL1. This T-cell clone showed potent antitumor activity against lymphoma and renal cell carcinoma cell lines, Epstein-Barr virus (EBV)–transformed B cells, and primary tumor samples derived from patients with chronic lymphocytic leukemia (CLL), whereas nontransformed cells with the exception of activated B cells were only marginally recognized. Allorestricted TCRs with specificity for naturally presented FMNL1-derived epitopes may represent promising reagents for the development of adoptive therapies in lymphoma and other malignant diseases.

Antigen recognition and T-cell biology

Despite the wealth of information that has been acquired regarding the way T cells recognize their targets, we are left with far more questions than answers regarding how to manipulate the immune response to better treat cancer patients. Clearly, most patients have a broad repertoire of T cells capable of recognizing their tumor cells. Despite the presence of these tumor reactive T cells and our ability to increase their frequency though vaccination or adoptive transfer, patients still progress. From the T cell side, defects in T cell signaling may account for much of our failure to achieve significant numbers of objective clinical responses. In spite of these negatives, the horizon does remain bright for T cell based immune therapy of cancer. The periodic objective clinical response tells us that immune therapy can work. Now that we know that cancer patients have the capacity to mount immune responses against their tumors, current and future investigations with agents which alter T cell function combined with vaccination or adoptive T cell transfer may help tip the balance towards effective immune therapies.

Superior antitumor in vitro responses of allogeneic matched sibling compared with autologous patient CD8+ T cells

Allogeneic cell therapy as a means to break immunotolerance to solid tumors is increasingly used for cancer treatment. To investigate cellular alloimmune responses in a human tumor model, primary cultures were established from renal cell carcinoma (RCC) tissues of 56 patients. In three patients with stable RCC line and human leukocyte antigen (HLA)-identical sibling donor available, allogeneic and autologous RCC reactivities were compared using mixed lymphocyte/tumor cell cultures (MLTC). Responding lymphocytes were exclusively CD8(+) T cells, whereas CD4(+) T cells or natural killer cells were never observed. Sibling MLTC populations showed higher proliferative and cytolytic antitumor responses compared with their autologous counterparts. The allo-MLTC responders originated from the CD8(+) CD62L(high)(+) peripheral blood subpopulation containing naive precursor and central memory T cells. Limiting dilution cloning failed to establish CTL clones from autologous MLTCs or tumor-infiltrating lymphocytes. In contrast, a broad panel of RCC-reactive CTL clones was expanded from each allogeneic MLTC. These sibling CTL clones either recognized exclusively the original RCC tumor line or cross-reacted with nonmalignant kidney cells of patient origin. A minority of CTL clones also recognized patient-derived hematopoietic cells or other allogeneic tumor targets. The MHC-restricting alleles for RCC-reactive sibling CTL clones included HLA-A2, HLA-A3, HLA-A11, HLA-A24, and HLA-B7. In one sibling donor-RCC pair, strongly proliferative CD3(+)CD16(+)CD57(+) CTL clones with non-HLA-restricted antitumor reactivity were established. Our results show superior tumor-reactive CD8 responses of matched allogeneic compared with autologous T cells. These data encourage the generation of antitumor T-cell products from HLA-identical siblings and their potential use in adoptive immunotherapy of metastatic RCC patients.

A neoepitope generated by an FLT3 internal tandem duplication (FLT3-ITD) is recognized by leukemia-reactive autologous CD8+ T cells

The FLT3 receptor tyrosine kinase is expressed in more than 90% of acute myelogeneous leukemias (AMLs), up to 30% of which carry an internal tandem duplication (ITD) within the FLT3 gene. Although varying duplication sites exist, most FLT3-ITDs affect a single protein domain. We analyzed the FLT3-ITD of an AML patient for encoding HLA class I–restricted immunogenic peptides. One of the tested peptides (YVDFREYEYY) induced in vitro autologous T-cell responses restricted by HLA-A*0101 that were also detectable ex vivo. These peptide-reactive T cells recognized targets transfected with the patient's FLT3-ITD, but not wild-type FLT3, and recognized the patient's AML cells. Our results demonstrate that AML leukemic blasts can in principle process and present immunogenic FLT3-ITD neoepitopes. Therefore, FLT3-ITD represents a potential candidate target antigen for the immunotherapy of AML.

Proteasome-inhibited dendritic cells demonstrate improved presentation of exogenous synthetic and natural HLA-class I peptide epitopes

The design and successful clinical implementation of cancer vaccines targeting the induction of T-cell mediated immunity is a rapidly evolving field that is hampered by an empirical selection of antigen and adjuvant. In particular, vaccines using defined tumor-associated peptide epitopes elicit only a restricted T-cell repertoire in a minority of patients. In this regard, vaccines comprising the whole spectrum of antigens presented by individual autologous tumors would be advantageous. In an in vitro model, we evaluated the capacity of naturally processed Epstein-Barr virus-transformed B-lymphoblastoid-cell line (LCL)-derived peptides to activate virus-specific CD8+ T cells of seropositive healthy individuals. While bulk peptides obtained by mild acid elution from LCL contained multiple T-cell epitopes, this complex mixture of peptides was poorly immunogenic, even when presented by mature dendritic cells (DC). Pretreatment of DC with proteasome inhibitors strongly enhanced the immunogenicity of single viral synthetic as well as bulk LCL peptides. This was most likely achieved by facilitating the loading of exogenous epitopes onto DC-associated HLA-class I complexes in the face of significant inter-peptide competition for such loading. Our results suggest that proteasome inhibitors may be used to increase the antigenicity of mature DC pulsed with exogenous synthetic or naturally processed peptide epitopes in vaccination trials.

The response of autologous T cells to a human melanoma is dominated by mutated neoantigens

Our understanding of pathways leading to antitumor immunity may depend on an undistorted knowledge of the primary antigenic targets of patients' autologous T cell responses. In the melanoma model derived from patient DT, we applied cryopreserved short-term autologous mixed lymphocyte-tumor cell cultures (MLTCs) in combination with an IFN-gamma enzyme-linked immunospot (ELISPOT) assay to cDNA expression screening. We identified three previously unknown peptides processed from melanosomal proteins tyrosinase (presented by HLA-A(*)2601 and -B(*)3801) and gp100 (presented by HLA-B(*)07021) and five neoantigens generated by somatic point mutations in the patient's melanoma. The mutations were found in the genes SIRT2, GPNMB, SNRP116, SNRPD1, and RBAF600. Peptides containing the mutated residues were presented by HLA-A(*)03011, -B(*)07021, and -B(*)3801. Mutation-induced functional impairment was so far demonstrated for SIRT2. Within MLTC responder populations that were independently expanded from the patient's peripheral blood lymphocytes of different years, T cells against mutated epitopes clearly predominated. These results document a high degree of individuality for the cellular antitumor response and support the need for individualizing the monitoring and therapeutic approaches to the primary targets of the autologous T cell response, which may finally lead to a more effective cancer immunotherapy.

T cell avidity and tumor recognition: implications and therapeutic strategies

In the last two decades, great advances have been made studying the immune response to human tumors. The identification of protein antigens from cancer cells and better techniques for eliciting antigen specific T cell responses in vitro and in vivo have led to improved understanding of tumor recognition by T cells. Yet, much remains to be learned about the intricate details of T cell – tumor cell interactions. Though the strength of interaction between T cell and target is thought to be a key factor influencing the T cell response, investigations of T cell avidity, T cell receptor (TCR) affinity for peptide-MHC complex, and the recognition of peptide on antigen presenting targets or tumor cells reveal complex relationships. Coincident with these investigations, therapeutic strategies have been developed to enhance tumor recognition using antigens with altered peptide structures and T cells modified by the introduction of new antigen binding receptor molecules. The profound effects of these strategies on T cell – tumor interactions and the clinical implications of these effects are of interest to both scientists and clinicians. In recent years, the focus of much of our work has been the avidity and effector characteristics of tumor reactive T cells. Here we review concepts and current results in the field, and the implications of therapeutic strategies using altered antigens and altered effector T cells.

Cytokine gene single nucleotide polymorphisms and susceptibility to and prognosis in cutaneous malignant melanoma

Cutaneous malignant melanoma (CMM) is a potentially fatal malignancy in which exposure to UV light is the most important risk factor. Several lines of evidence suggest that CMM patients develop an immune response to their tumours, although, in most cases, anti-tumour immune responses are insufficient to abrogate tumour development. Polymorphism in genes regulating the immune response and cell growth may result in increased susceptibility to and/or poorer prognosis in certain individuals. In this study, we addressed whether single nucleotide polymorphisms (SNPs) associated with differential expression of selected pro- and anti-inflammatory cytokines and growth factors [interleukin (IL)-1beta-35 and -511, IL-2 -330, IL-4 -590, IL-6 -174, IL-8 -251, interferon (IFN)-gamma+874 and transforming growth factor (TGF)beta1 +915] or as markers of candidate cytokine genes (IL-12 +1188) are associated with susceptibility to or known prognostic indicators (e.g. initial tumour growth phase, Breslow thickness, mitotic count in vertical growth phase tumours, tumour regression) in CMM. One hundred and sixty-nine British caucasian CMM patients and 261 controls were included in the study and all SNPs were genotyped by ARMS-PCR. No SNP genotypes or alleles showed significant associations with CMM susceptibility and only the IL-1beta-511 TT genotype was associated with thinner invasive tumours at presentation, as assessed by Breslow thickness at the clinically significant cut-off point of 1.5 mm [occurring in 2/51 (3.9%) thicker vs. 14/78 (17.9%) thinner tumours (P = 0.03; relative risk = 0.29 (95% confidence interval 0.05-0.95)]. These findings suggest that - with the possible exception of IL-1beta- genetic variation associated with differential expression of the selected pro- and anti-inflammatory cytokines is unlikely to play a major role in susceptibility to and prognosis in CMM.

Melanoma-reactive class I-restricted cytotoxic T cell clones are stimulated by dendritic cells loaded with synthetic peptides, but fail to respond to dendritic cells pulsed with melanoma-derived heat shock proteins in vitro

Immunization with heat shock proteins (hsp) isolated from cancer cells has been shown to induce a protective antitumor response. The mechanism of hsp-dependent cellular immunity has been attributed to a variety of immunological activities mediated by hsp. Hsp have been shown to bind antigenic peptides, trim the bound peptides by intrinsic enzymatic activity, improve endocytosis of the chaperoned peptides by APCs, and enhance the ability of APCs to stimulate peptide-specific T cells. We have investigated the potential capacity of hsp70 and gp96 to function as a mediator for Ag-specific CTL stimulation in an in vitro model for human melanoma. Repetitive stimulation of PBLs by autologous DCs loaded with melanoma-derived hsp did not increase the frequency of T cells directed against immunodominant peptides of melanoma-associated Ags Melan-A and tyrosinase. In contrast, repeated T cell stimulation with peptide-pulsed DCs enhanced the number of peptide-specific T cells, allowing HLA/peptide multimer-guided T cell cloning. We succeeded in demonstrating that the established HLA-A2-restricted CTL clones recognized HLA-A2(+) APCs exogenously loaded with the respective melanoma peptide as well as melanoma cells processing and presenting these peptides in the context of HLA-A2. We were not able to show that these melanoma-reactive CTL clones were stimulated by autologous dendritic cells pulsed with melanoma-derived hsp. These results are discussed with respect to various models for proving the role of hsp in T cell stimulation and to recent findings that part of the immunological antitumor activities reported for hsp are independent of the chaperoned peptides.

The use of clonal mRNA as an antigenic format for the detection of antigen-specific T lymphocytes in IFN-γ ELISPOT assays

Most assay systems for the quantification of antigen-specific T-cell responses in infectious, malignant and autoimmune disease depend on the peptide antigen format and are therefore restricted to known epitopes and their presenting HLA molecules. Here we tested in ELISPOT assays the application of in vitro-transcribed clonal mRNA as an alternative antigen format covering all potential epitopes of a given antigen. As model antigens, we chose pp65 of human cytomegalovirus (HCMV) and human tyrosinase (hTyr). Antigen-presenting cells (APC) were K562 cells stably transfected with single HLA class I alleles and autologous dendritic cells (DC). As effectors, we applied in vitro-generated anti-tyrosinase T-cell populations as well as ex vivo-CD8(+) lymphocytes from HCMV-seropositive donors. APC electroporated with clonal mRNA were efficient inducers of spot formation by antigen-experienced CD8(+) T cells. They were equivalent to peptide-loaded targets. mRNA electroporation did not induce non-specific spot formation. While the use of autologous mRNA-electroporated DC can uncover the complete individual T-cell response towards an antigen, mRNA-electroporated K562 cells stably transfected with single HLA class I alleles help to detect CD8(+) T-cell responses restricted by single HLA class I molecules.

Renal-cell carcinoma: tumour markers, T-cell epitopes, and potential for new therapies

Advanced renal-cell carcinoma is a very difficult tumour to treat, and response rates to biological therapies are less than 20%. The identification of various molecular and cellular markers has led to the development of novel therapies. Despite evaluation of their association with histological subtype, immune infiltration, molecular markers of cell proliferation, p53 mutation, and growth-factor-receptor expression, none of these markers has proved better predictive factors than tumour stage and histological grade. The identification of tumour-associated antigens and the specificity of cellular immune responses have led to the development of targeted immunotherapy with monoclonal antibodies, radioimmunotherapy, and T-cell therapies. In this review, we evaluate a range of markers associated with renal-cell carcinoma and new treatment approaches based on tumour-associated antigens and, in particular, T-cell epitopes.

Specific immunotherapy of cancer in elderly patients

The concept of immunotherapy of cancer is more than a century old, but only recently have molecularly defined therapeutic approaches been developed. In this review, we focus on the most promising approach, active therapeutic vaccination. The identification of tumour antigens can now be accelerated by methods allowing the amplification of gene products selectively or preferentially transcribed in the tumour. However, determining the potential immunogenicity of such gene products remains a demanding task, since major histocompatibility complex (MHC) restriction of T cells implies that for any newly defined antigen, immunogenicity will have to be defined for any individual MHC haplotype. Tumour-derived peptides eluted from MHC molecules of tumour tissue are also a promising source of antigen. Tumour antigens are mostly of weak immunogenicity, because the vast majority are tumour-associated differentiation antigens already 'seen' by the patient's immune system. Effective therapeutic vaccination will thus require adjuvant support, possibly by new approaches to immunomodulation such as bispecific antibodies or antibody-cytokine fusion proteins. Tumour-specific antigens, which could be a more potent target for immunotherapy, mostly arise by point mutations and have the disadvantage of being not only tumour-specific, but also individual-specific. Therapeutic vaccination will probably focus on defined antigens offered as protein, peptide or nucleic acid. Irrespective of the form in which the antigen is applied, emphasis will be given to the activation of dendritic cells as professional antigen presenters. Dendritic cells may be loaded in vitro with antigen, or, alternatively, initiation of an immune response may be approached in vivo by vaccination with RNA or DNA, given as such or packed into attenuated bacteria. The importance of activation of T helper cells has only recently been taken into account in cancer vaccination. Activation of cytotoxic T cells is facilitated by the provision of T helper cell-derived cytokines. T helper cell-dependent recruitment of elements of non-adaptive defence, such as leucocytes, natural killer cells and monocytes, is of particular importance when the tumour has lost MHC class I expression. Barriers to successful therapeutic vaccination include: (i) the escape mechanisms developed by tumour cells in response to immune attack; (ii) tolerance or anergy of the evoked immune response; (iii) the theoretical possibility of provoking an autoimmune reaction by vaccination against tumour-associated antigens; and (iv) the advanced age of many patients, implying reduced responsiveness of the senescent immune system.

Influence of TNFalpha and LTalpha single nucleotide polymorphisms on susceptibility to and prognosis in cutaneous malignant melanoma in the British population

Cutaneous malignant melanoma (CMM) is a potentially fatal malignancy in which exposure to UV light is the most important risk factor. Several lines of evidence suggest that increased expression of tumour necrosis factor (TNF) alpha, upregulated by UV exposure, may contribute to tumour escape from the immune response. In this study, we addressed whether single nucleotide polymorphisms (SNPs) in the TNFalpha promoter and lymphotoxin (LT) alpha gene are associated with susceptibility to or known prognostic indicators (e.g. initial tumour growth phase, Breslow thickness, mitotic count in vertical growth phase tumours, and tumour regression) in CMM. One hundred and forty-six British Caucasian CMM patients and 220 controls were typed for TNFalpha-376, -308 and -238 and LTalpha+252 SNPs by ARMS-PCR. Only the TNFalpha -238 GG (P = 0.05) and GA (P = 0.03) genotypes showed slight, but significant, associations with CMM, while LTalpha+252 AA was associated with a higher mitotic count in vertical growth phase tumours (P = 0.02). Both TNFalpha-238 and LTalpha+252 SNPs showed linkage disequilibrium with HLA-DQB1*0303 and *0301 alleles, variably implicated in CMM susceptibility/prognosis. In addition, TNFalpha-238, -308, LTalpha+252 haplotypes were assigned and compared. The GGA haplotype showed a modest association with CMM (P = 0.04) and with stage of disease (P = 0.03) and initial growth phase in CMM (P = 0.02), but these associations were only significant when P-values were uncorrected. Unlike basal cell carcinoma, these preliminary findings suggest that genetic variation associated with differential TNFalpha and LTalpha production is unlikely to play a major, independent role in susceptibility to, and perhaps prognosis in, CMM.

The use of HLA-A*0201-transfected K562 as standard antigen-presenting cells for CD8(+) T lymphocytes in IFN-gamma ELISPOT assays

ELISPOT assays are increasingly used for a direct detection and quantification of single antigen-specific T cells in freshly isolated peripheral blood mononuclear cells (PBMC). They are particularly attractive for the monitoring of specific T lymphocyte responses in clinical trials assessing antigen-specific immunizations in patients with cancer or chronic viral infections. However, one major limitation for the broad clinical implementation of ELISPOT assays is the lack of an inexhaustible source of suitable HLA-matched antigen-presenting cells (APC). Currently available allogeneic or xenogeneic APC (such as the human lymphoid hybrid T2 or HLA-transfected insect cells) can either lead to strong background spot production by APC-reactive T lymphocytes or have a low antigen presentation capability. Both phenomena can prevent the detection of low frequency T cell responses in PBMC. In search of alternative APC for ELISPOT assays, the human chronic myelogenous leukemia cell line K562 that per se does not express HLA class I and class II molecules on the cell surface was transfected with the HLA-A*0201 gene. Clonal HLA-A*0201-expressing K562 (K562/A*0201) cells were able to process and present endogenously expressed and exogenously loaded melanoma peptide antigens to HLA-A*0201-restricted cytolytic T lymphocyte clones in cytotoxicity and IFN-gamma ELISPOT assays. K562/A*0201 cells were then used as APC in IFN-gamma spot assays to detect ex vivo CD8(+) T lymphocytes responsive to known HLA-A*0201-binding peptide epitopes derived from cytomegalovirus, Epstein-Barr virus, influenza virus and melanoma in PBMC from HLA-A*0201-positive donors. In the majority of cases, peptide-pulsed K562/A*0201 cells were similarly efficient in the ability to visualize single antigen-specific CD8(+) T lymphocytes when compared to T2 cells. However, in contrast to T2, background reactivity of CD8(+) T cells responsive to unpulsed K562/A*0201 was regularly found to be negligible, thereby enhancing the sensitivity of the ELISPOT assay, particularly in donors with strong anti-T2 reactivity. K562 cells transfected with HLA-A*0201 or other HLA genes can serve as standard APC for monitoring T lymphocyte responses against tumor and viral peptide antigens.

Human melanoma cells secrete and respond to placenta growth factor and vascular endothelial growth factor

The vascular endothelial growth factor is produced by a large variety of human tumors, including melanoma, in which it appears to play an important role in the process of tumor-induced angiogenesis. Little information is available on the role of placenta growth factor, a member of the vascular endothelial growth factor family of cytokines, in tumor angiogenesis, even though placenta growth factor/vascular endothelial growth factor heterodimers have been recently isolated from tumor cells. To investigate the role of placenta growth factor and vascular endothelial growth factor homodimers and heterodimers in melanoma angiogenesis and growth, 19 human melanoma cell lines derived from primary or metastatic tumors were characterized for the expression of these cytokines and their receptors. Release of placenta growth factor and vascular endothelial growth factor polypeptides into the supernatant of human melanoma cells was demonstrated. Reverse transcriptase polymerase chain reaction analysis showed the presence of mRNAs encoding at least three different vascular endothelial growth factor isoforms (VEGF(121), VEGF(165), and VEGF(189)) and transcripts for two placenta growth factor isoforms (PlGF-1 and PlGF-2) in human melanoma cells. In addition, placenta growth factor expression in human melanoma in vivo was detected by immunohistochemical staining of tumor specimens. Both primary and metastatic melanoma cells were found to express the mRNAs encoding for vascular endothelial growth factor and placenta growth factor receptors (KDR, Flt-1, neuropilin-1, and neuropilin-2), and exposure of melanoma cells to these cytokines resulted in a specific proliferative response, supporting the hypothesis of a role of these angiogenic factors in melanoma growth. J Invest Dermatol 115:1000-1007 2000

CD4(+), HLA class I-restricted, cytolytic T-lymphocyte clone against primary malignant melanoma cells

The involvement of HLA-class I in target cell lysis by CD4(+) cytolytic T cells (CTL) has been a controversial issue. A CTL clone of CD4 phenotype was derived from the peripheral blood lymphocytes of a patient with primary melanoma. The CTL clone stably lysed the autologous primary melanoma cells for approximately 9 months in culture. Both the Valpha2/Vbeta8 T-cell receptor and CD4 were involved in CTL cytotoxicity. Of a large panel of allogeneic primary and metastatic melanoma or colorectal carcinoma cells, autologous and allogeneic Epstein-Barr virus-transformed B cells and autologous fibroblasts, only allogeneic metastatic melanoma cells matched with the autologous tumor cells for HLA-class I (B57[17]) were lysed and induced IFN-gamma secretion by the CTL clone. Lysis of the autologous tumor cells was significantly blocked by monoclonal antibody to HLA-B17. Importantly, allogeneic, HLA-class I- and class II-unmatched melanoma cells were lysed by the CTL only following transfection of the cells with B57[17] cDNA. Our results provide direct evidence for the involvement of both CD4 and HLA-class I in tumor cell lysis by CD4(+) CTL.

A CTL assay requiring only 150 microliter of mouse blood

In this paper, we present a method for measuring antigen specific cytotoxic T lymphocyte (CTL) activity from individual mouse peripheral blood samples without animal sacrifice. Peripheral blood cells are stimulated in vitro with a cocktail of antigen, cytokines, costimulatory molecules and irradiated feeder cells resulting, 7 days later, in a readily detectable antigen specific signal from a well plated under limiting dilution conditions. This highly sensitive and antigen specific assay is more efficient than conventional CTL assays and thus increases the number of mice that can be tested in a single assay. Since blood samples can be assayed from an individual mouse at multiple times during the course of an in vivo study, the assay can facilitate and strengthen correlative studies on CTL responses and in vivo results.

Consequences of antigen self-presentation by tumor-specific cytotoxic T cells

CD8-positive cytotoxic T cells (CTL) recognize antigenic peptides in combination with major histocompatibility complex (MHC) class I molecules on the surface of syngeneic antigen presenting cells (APC). In the present paper we show that cells from tumor antigen-specific CTL clones present their cognate antigenic peptide to other CTL from the same clone. Inter-CTL peptide presentation resulted in activation of the cells of one CTL clone to MHC-unrestricted lysis of bystander cells. In contrast to the behaviour of this clone, another CTL clone did not lyse bystander cells after incubation with the cognate peptide, but was activated to self-destruction. The human herpes virus Epstein-Barr virus is involved in the pathogenesis of a broad spectrum of human neoplasias. Using freshly established non-clonal T cells with specificity for a peptide derived from an Epstein-Barr virus encoded antigen we found again lysis of MHC mismatched bystander cells as a consequence of inter-CTL peptide presentation, indicating that bystander lysis following antigen self-presentation is not a phenomenon restricted to long-term in vitro cultured T cell clones. The potential implications for immunosurveillance against cancer and for tumor escape mechanisms are discussed.

Enhanced susceptibility to cytotoxic T lymphocytes without increase of MHC class I antigen expression after conditional overexpression of heat shock protein 70 in target cells

Antigenic peptides have been found associated with heat shock proteins (HSP) including cytoplasmic HSP70 and heat shock cognate protein 70 as well as the endoplasmic reticulum-resident glucose-regulated protein 94. Recently, HSP70 transfection has been reported to increase MHC class I cell surface expression and antigen presentation on mouse melanoma B16 cells (Wells et al., Int. Immunol. 1998. 10: 609). To analyze the effect of HSP70 on MHC class I cell surface expression and lysability of target cells we transfected a human melanoma cell line with the rat Hsp70-1 gene using the Tet-On system for conditional overexpression of HSP70. Induction of HSP70 did not increase cell surface expression of HLA class I molecules in general or individual HLA-A and B antigens in particular. Nonetheless, induction of HSP70 enhanced susceptibility of these cells to lysis by allospecific CTL. The same effect was observed using an HLA-A2-restricted tyrosinase-specific CTL clone after pulsing the tyrosinase-negative target cells with the specific peptide. Thus, HSP70 induction can increase killing by CTL without affecting MHC class I cell surface expression or antigen processing. This effect of HSP70 appears to be different from the commonly found protection exerted by HSP70 against stress like heat shock, and might be mediated by improving CTL-induced apoptosis.

Immune response enhancement by in vivo administration of B7.2Ig, a soluble costimulatory protein

The identification of both class I- and class II-restricted tumor-associated peptides recognized by T cells has led to the test of these peptides as immunogens in experimental immunotherapy for cancer patients. However, optimal T cell activation requires signaling both through the T cell receptor for antigen and through costimulatory pathways. B7.1 and B7.2 are powerful costimulatory molecules expressed on the surface of antigen-presenting cells. Using a mouse model, we have sought to optimize costimulatory signals during antipeptide responses by administering a soluble form of B7.2 at the time of peptide immunization. Administration of B7. 2Ig fusion protein significantly enhanced T helper cell and CTL responses. These findings suggest that soluble forms of human B7.2 protein may provide a straightforward and practical method of supplying optimal costimulation during clinical immunotherapy.

Cancer therapy: new concepts on active immunization

There is increasing evidence that tumors express putative target molecules for a therapeutic immune reaction. Yet, tumor cells lack the prerequisites for appropriate antigen presentation and--hence--the immune system does not respond. This difficulty can probably be circumvented when tumor antigens are processed by conventional antigen presenting cells. Thus, the identification of immunogenic tumor-associated antigens may allow new modes of vaccination with the hope of adding a fourth and hopefully powerful weapon to surgery, radiation and chemotherapy in the fight against cancer.

Human leukocyte antigens and cancer: is it in our genes?

Human leukocyte antigens (HLAs) are widely expressed cell surface molecules which present antigenic peptides to T-lymphocytes, thus modulating the immune response. The efficiency of peptide presentation by HLAs is dependent on the extreme polymorphism in the HLA-encoding loci within the major histocompatibility complex (MHC). HLA polymorphism is known to alter disease susceptibility and progression in a range of predominantly inflammatory conditions, many of which are T-lymphocyte-mediated. More recently, the importance of alterations in HLA expression and polymorphisms within HLA-encoding loci has emerged in the development of malignancy. This review concentrates on the role of HLA polymorphism in malignant disease, with discussion of the major cancers in which HLA associations have become clear, as well as the potential mechanisms by which HLA polymorphisms may act as important factors, or cofactors, in the pathogenesis of malignant disease. In addition, the role of certain non-HLA genes within the MHC in the pathogenesis of malignancy is also considered briefly.

Cytolytic T Lymphocytes Recognize an Antigen Encoded by MAGE-A10 on a Human Melanoma

From melanoma patient LB1751, cytolytic T lymphocytes (CTL) were generated that lysed specifically autologous tumor cells. To establish whether these CTL recognized one of the Ags that had previously been defined, a CTL clone was stimulated with cells expressing various MAGE genes. It produced TNF upon stimulation with target cells expressing MAGE-A10. The Ag was found to be nonapeptide GLYDGMEHL (codons 254–262), which is presented by HLA-A2.1. This is the first report on the generation of anti-MAGE CTL by autologous mixed lymphocyte-tumor cell culture (MLTC) from a melanoma patient other than patient MZ2, from whom the first MAGE gene was identified. MAGE genes are expressed in many tumors but not by normal tissues except male germline cells and placenta, which do not express HLA molecules. Therefore, the identification of an antigenic peptide derived from MAGE-A10 adds to the repertoire of tumor-specific shared Ags available for anti-tumoral vaccination trials.

Antitumor immunity at work in a melanoma patient

This review covers the results obtained so far with a chronological analysis of the antitumor cytolytic T lymphocyte (CTL) cell response of a melanoma patient who enjoys an unusually favorable evolution. Two melanoma cell lines, MEL.A and MEL.B, were derived from metastases removed from the patient in 1988 and 1993, respectively. The patient developed a very strong CTL response against the MEL.A cells. Several antigens on these cells, presented by various HLA class I molecules, result from point mutations present in the genome of the tumor. The MEL.B cells, on the other hand, resist lysis by these CTLs because they have lost expression of most HLA class I molecules, suggesting that they were selected in vivo by the anti-MEL.A CTLs. New CTLs recognize MEL.B cells specifically, however. Analysis of their specificity indicates that they carry inhibitory receptors similar to those present on natural killer (NK) cells. These results illustrate the relationship between a tumor and the immune system in vivo over a period of several years. They are discussed in the context of the recent identification of many human tumor antigens recognized by CTLs, and the perspectives of specific immunotherapy opened up by these discoveries.

HLA-DQB1*0303 and *0301 alleles influence susceptibility to and prognosis in cutaneous malignant melanoma in the British Caucasian population

The presence of lymphocytic infiltrates within primary cutaneous malignant melanoma (CMM), documented spontaneous tumour regression and genetic linkage with chromosome six in familial cases all suggest that immunogenetic factors may modulate disease progression. An association has been suggested between HLA DQB1*0301 and CMM in US patients but no such investigation has been performed in the UK population. Polymerase chain reaction-based HLA class II DRB1, DQA1 and DQB1 typing of 99 UK-based CMM patients was performed using DNA extracted from archival formalin-fixed and paraffin wax-embedded surgical biopsies, enabling retrospective access to clinical follow-up data. An increase in frequency of the HLA DQB1*0303 genotype among CMM patients was identified compared to control subjects (19.2% vs 5.8%; Pc=0.003; RR=3.9) while HLA DQB1*0301 was associated with more advanced and therefore poorer prognosis primary tumours (e.g. HLA DQB1*0301 allele frequency: 20.1% vertical growth phase vs 4.0% horizontal growth phase; Pc=0.03; RR=6.1). These findings suggest that the HLA DQB1 locus, and in particular the HLA DQB1*0303 and *0301 alleles, may play an important role in determining the risk of development and the prognosis of CMM within the UK population.

Broadened clinical utility of gene gun-mediated, granulocyte-macrophage colony-stimulating factor cDNA-based tumor cell vaccines as demonstrated with a mouse myeloma model

Effective immunization against the murine B16 melanoma by a nonviral approach in which a gene gun is used to transfer GM-CSF cDNA into tumor cells has been described. We have extended this nonviral approach by using the poorly immunogenic murine myeloma MPC11 model. Vaccination with the transfected, GM-CSF-expressing MPC11 cells induced a potent antitumor cytotoxic T lymphocyte response associated with tumor rejection in the majority of the test mice. Furthermore, nearly 100% (27 of 28) of the tumor-free mice were able to reject a tumor rechallenge. While this approach is clinically attractive because of minimal tissue manipulation/culturing and the absence of infectious agents, a number of tested human primary tumors, including myeloma cells, have failed to produce high levels of GM-CSF after gene gun transfection. To circumvent the low transfection efficiency in certain human tumor cells, we showed that combining irradiated tumor cells to provide tumor antigens together with gene gun-transfected fibroblasts to provide GM-CSF induced effective tumor rejection. We also report that normal human skin fibroblasts transfected by the gene gun produce high levels of human GM-CSF (250 ng/10(6) cells/24 hr). These results suggest that combining irradiated tumor cells with gene gun-transfected fibroblasts results in antitumor immune responses and may allow for a wider application of this approach to cancer immunotherapy.

Genes coding for melanoma antigens recognised by cytolytic T lymphocytes

It is now well established that human melanoma cells express antigens that are recognised by cytolytic T lymphocytes derived from the tumour-bearing patient. The molecular definition of these antigens is progressing at an accelerated pace. The currently characterised melanoma antigens can be classified into three categories: differentiation antigens, antigens encoded by genes that are specifically expressed in tumours, and antigens encoded by mutated genes. Several of these antigens are sufficiently tumour-specific to qualify them as candidate anti-cancer vaccines in melanoma patients.

Overlapping peptides of melanocyte differentiation antigen Melan-A/MART-1 recognized by autologous cytolytic T lymphocytes in association with HLA-B45.1 and HLA-A2.1

From the peripheral blood lymphocytes (PBLs) of melanoma patient SK29(AV) we have previously isolated 2 independent cytolytic T lymphocyte (CTL) clones (CTL7/147 and CTL13/211), which lysed autologous tumor cells in association with HLA-B45.1. As demonstrated here, both CTL clones were directed against melanocyte differentiation antigen Melan-A/MART-1, which also was recognized by HLA-A2.1-restricted CTLs from the same patient. By generating and transfecting 3'-deletion mutants of Melan-A/MART-1 cDNA, we localized its peptide-coding regions. The HLA-B45.1-presented peptides were derived from a hydrophobic region of the protein and largely overlapped the peptides recognized by CTLs from the same patient in association with HLA-A2.1. We determined the fine specificity of these CTL clones with synthetic peptides. CTL clone CTL7/147 recognized the 11-mer peptide AEEAAGIGILT (residues 24-34) at the lowest concentrations. The absence of threonine-34 abrogated the recognition by CTL7/147. The truncated peptide AEEAAGIGIL (residues 24-33) proved to be the optimal synthetic peptide for sensitization against lysis by CTL13/211. This indicated that C-terminal threonine-34 was not involved in binding to HLA-B45.1 but, rather, was part of the epitope for CTL7/147. HLA-B45.1-associated peptides of Melan-A/MART-1 were regularly processed and presented by other melanomas and other cell types. Three of 4 independent HLA-A2.1-restricted SK29-CTL clones recognized the 10-mer peptide EAAGIGILTV (residues 26-35) at 10- to 100-fold lower concentrations than the nonamer AAGIGILTV (residues 27-35), previously described as the common immunodominant peptide antigen for all known anti-Melan-A/MART-1 CTLs restricted by HLA-A2.1. Different melanoma peptide antigens currently are applied in therapeutic vaccination studies. Our findings emphasize that restricting to peptides of minimal length might exclude relevant T-cell epitopes.

Identification of genes coding for tumor antigens recognized by cytolytic T lymphocytes

Strategies have been developed to characterize tumor antigens recognized by cytolytic T lymphocytes (CTL). We use a genetic approach based on the transfection of HLA genes and cDNA libraries in COS cells to isolate the gene producing the antigenic peptide. The tumor-specific expression of this gene can be evaluated by cDNA synthesis and quantitative PCR amplification. Transfection of fragments of the isolated gene allows the identification of the region encoding the antigenic peptide. Peptides are synthesized and tested for their ability to sensitize target cells to lysis by the CTL.

Cytotoxicity of histocompatibility leukocyte antigen-DR8-restricted CD4 killer T cells against human autologous squamous cell carcinoma

Although CD8+ killer T cells reacting against human autologous tumor cells have recently been studied in detail, little is known about the cytotoxic mechanism of CD4+ T cells against such tumor cells. In order to investigate this, we have established CD4+ cytotoxic T lymphocyte TcOSC-20 lines. TcOSC-20 showed selective cytotoxic activity against autologous OSC-20 cells, derived from a cancer of the tongue, in an HLA-DR-restricted fashion. HLA-DR8 (DRB1*08032) is the only DR molecule expressed on OSC-20 cells, and anti-DR8 monoclonal antibody could inhibit the cytotoxicity, suggesting that HLA-DRB1*08032 is the tumor rejection antigen-presenting molecule to TcOSC-20. The Fas ligand was expressed on TcOSC-20 lines, and its expression was induced upon mixed lymphocyte-tumor cell culture of autologous peripheral blood lymphocytes. Furthermore, the cytotoxicity of TcOSC-20 was inhibited by anti-Fas ligand antibody. These data imply that TcOSC-20 lines recognize the tumor antigenic peptide presented by HLA-DR8, and exert cytotoxicity against autologous tumor cells via a Fas-mediated cytotoxic pathway.

HLA-C revisited. Ten years of change

During the past 10 years knowledge about the interactions between major histocompatibility complex (MHC) class I molecules and the T-cell receptor (TCR) complex of cytotoxic T-cells (CTL) has developed dramatically. But the primary interest, both with respect to structure as well as function, has concentrated on HLA-A and -B molecules because of their high sequence polymorphism and their dominating presence at the cell surface. In contrast, HLA-C molecules seemed to be of only minor importance in the cascade of immune reactions owing to their more limited polymorphism and reduced levels of surface expression. The inability to define a number of antigen specificities had the result that HLA-C molecules were often neglected in studies of immune response, transplantation, and disease association. More recently a new function has been identified for HLA class I molecules where they act as inhibitors of the lytic capacity of natural killer (NK) cells and non-MHC-restricted T-cells. Moreover, the understanding of this novel mode of negative regulation of cytotoxicity was remarkably influenced by HLA-C since these were the first HLA class I molecules found to have such inhibitory potential. With this new inhibitory function serving as an essential component of the immune system, HLA-C molecules can no longer be neglected.

The majority of autologous cytolytic T-lymphocyte clones derived from peripheral blood lymphocytes of a melanoma patient recognize an antigenic peptide derived from gene Pmel17/gp100

Anti-melanoma cytolytic T-lymphocyte (CTL) clones were derived from peripheral blood lymphocytes of HLA-A2 melanoma patient LB265 after stimulation with the autologous tumor cell line LB265-MEL, which showed high expression of melanocyte-lineage specific genes. Of 55 CTL clones, 46 recognized HLA-A2-restricted antigens. These 46 CTL clones were studied for their ability to specifically release tumor necrosis factor in the presence of COS cells cotransfected with the HLA-A2 gene and the cDNA of either tyrosinase, Melan-A/MART1, Pmel17/gpl00, gp75/TRP1, or MSH receptor. Six CTL clones recognized the Melan-A/MART1 antigen, whereas the remaining 40 CTL clones recognized a Pmel17/gp100 antigen. These 40 anti-PmelI7/gpl00 CTL clones were all able to lyse T2 cells pulsed with the antigenic peptide YLEPGPVTA, as previously reported. The T-cell receptor beta chain hypervariable region was sequenced and found to be identical in the 15 CTL clones analyzed. Taken together, these data show a high frequency of Pmell7/gp100-specific T cells in autologous antitumor CTL clones derived from peripheral blood of a melanoma patient.