Identification of gp100-derived, melanoma-specific cytotoxic T-lymphocyte epitopes restricted by HLA-A3 supertype molecules by primary in vitro immunization with peptide-pulsed dendritic cells

Immunogenicity of Non-Mutated Ovarian Cancer-Specific Antigens

Epithelial ovarian cancer (EOC) has not significantly benefited from advances in immunotherapy, mainly because of the lack of well-defined actionable antigen targets. Using proteogenomic analyses of primary EOC tumors, we previously identified 91 aberrantly expressed tumor-specific antigens (TSAs) originating from unmutated genomic sequences. Most of these TSAs derive from non-exonic regions, and their expression results from cancer-specific epigenetic changes. The present study aimed to evaluate the immunogenicity of 48 TSAs selected according to two criteria: presentation by highly prevalent HLA allotypes and expression in a significant fraction of EOC tumors. Using targeted mass spectrometry analyses, we found that pulsing with synthetic TSA peptides leads to a high-level presentation on dendritic cells. TSA abundance correlated with the predicted binding affinity to the HLA allotype. We stimulated naïve CD8 T cells from healthy blood donors with TSA-pulsed dendritic cells and assessed their expansion with two assays: MHC-peptide tetramer staining and TCR Vβ CDR3 sequencing. We report that these TSAs can expand sizeable populations of CD8 T cells and, therefore, represent attractive targets for EOC immunotherapy.

Therapeutic Cancer Vaccines—Antigen Discovery and Adjuvant Delivery Platforms

For decades, vaccines have played a significant role in protecting public and personal health against infectious diseases and proved their great potential in battling cancers as well. This review focused on the current progress of therapeutic subunit vaccines for cancer immunotherapy. Antigens and adjuvants are key components of vaccine formulations. We summarized several classes of tumor antigens and bioinformatic approaches of identification of tumor neoantigens. Pattern recognition receptor (PRR)-targeting adjuvants and their targeted delivery platforms have been extensively discussed. In addition, we emphasized the interplay between multiple adjuvants and their combined delivery for cancer immunotherapy.

Know thy immune self and non-self: Proteomics informs on the expanse of self and non-self, and how and where they arise

T cells play an important role in the adaptive immune response to a variety of infections and cancers. Initiation of a T cell mediated immune response requires antigen recognition in a process termed MHC (major histocompatibility complex) restri ction. A T cell antigen is a composite structure made up of a peptide fragment bound within the antigen‐binding groove of an MHC‐encoded class I or class II molecule. Insight into the precise composition and biology of self and non‐self immunopeptidomes is essential to harness T cell mediated immunity to prevent, treat, or cure infectious diseases and cancers. T cell antigen discovery is an arduous task! The pioneering work in the early 1990s has made large‐scale T cell antigen discovery possible. Thus, advancements in mass spectrometry coupled with proteomics and genomics technologies make possible T cell antigen discovery with ease, accuracy, and sensitivity. Yet we have only begun to understand the breadth and the depth of self and non‐self immunopeptidomes because the molecular biology of the cell continues to surprise us with new secrets directly related to the source, and the processing and presentation of MHC ligands. Focused on MHC class I molecules, this review, therefore, provides a brief historic account of T cell antigen discovery and, against a backdrop of key advances in molecular cell biologic processes, elaborates on how proteogenomics approaches have revolutionised the field.

Immune targets and neoantigens for cancer immunotherapy and precision medicine

Harnessing the immune system to eradicate malignant cells is becoming a most powerful new approach to cancer therapy. FDA approval of the immunotherapy-based drugs, sipuleucel-T (Provenge), ipilimumab (Yervoy, anti-CTLA-4), and more recently, the programmed cell death (PD)-1 antibody (pembrolizumab, Keytruda), for the treatment of multiple types of cancer has greatly advanced research and clinical studies in the field of cancer immunotherapy. Furthermore, recent clinical trials, using NY-ESO-1-specific T cell receptor (TCR) or CD19-chimeric antigen receptor (CAR), have shown promising clinical results for patients with metastatic cancer. Current success of cancer immunotherapy is built upon the work of cancer antigens and co-inhibitory signaling molecules identified 20 years ago. Among the large numbers of target antigens, CD19 is the best target for CAR T cell therapy for blood cancer, but CAR-engineered T cell immunotherapy does not yet work in solid cancer. NY-ESO-1 is one of the best targets for TCR-based immunotherapy in solid cancer. Despite the great success of checkpoint blockade therapy, more than 50% of cancer patients fail to respond to blockade therapy. The advent of new technologies such as next-generation sequencing has enhanced our ability to search for new immune targets in onco-immunology and accelerated the development of immunotherapy with potentially broader coverage of cancer patients. In this review, we will discuss the recent progresses of cancer immunotherapy and novel strategies in the identification of new immune targets and mutation-derived antigens (neoantigens) for cancer immunotherapy and immunoprecision medicine.

Enhancing cancer immunotherapy by intracellular delivery of cell-penetrating peptides and stimulation of pattern-recognition receptor signaling

The importance of T-cell-mediated antitumor immunity has been demonstrated in both animal models and human cancer immunotherapy. In the past 30 years, T-cell-based immunotherapy has been improved with an objective clinical response rate of up to 72%. Identification of MHC class I- and II-restricted tumor antigens recognized by tumor-reactive T cells has generated a resurgence of interest in cancer vaccines. Although clinical trials with cancer peptide/protein vaccines have only met a limited success, several phase II/III clinical trials are either completed or ongoing with encouraging results. Recent advances in immunotherapy have led to the approval of two anticancer drugs (sipuleucel-T vaccine and anti-CTLA-4 antibody) by the US FDA for the treatment of metastatic castration-resistant prostate cancer and melanoma, respectively. Intracellular delivery of antigenic peptides into dendritic cells (DCs) prolongs antigen presentation of antigen-presenting cells to T cells, thus further improving clinical efficacy of peptide/protein cancer vaccines. Because innate immune responses are critically important to provide sensing and initiating of adaptive immunity, combined use of cell-penetrating peptide vaccines with stimulation of innate immune signaling may produce potent antitumor immune responses. We will discuss the recent progress and novel strategies in cancer immunotherapy.

Peptide epitope identification for tumor-reactive CD4 T cells

Because T lymphocytes have the capacity to recognize tumor cells, significant efforts are being devoted towards the development of T cell-based immunotherapy for cancer. Most of this work has centered in the induction of anti-tumor CD8 T cells, which exhibit cytolytic activity towards tumor cells expressing tumor-specific or tumor associated antigens. Unfortunately to this day, T cell-based immunotherapy for cancer remains suboptimal. One of the possible explanations is that these immunotherapies have ignored the role that CD4 T helper lymphocytes play in the generation and persistence of CD8 T cell responses. Thus, we believe that in order to obtain clinical benefits T cell-based immunotherapy must stimulate both CD8 and CD4 tumor-reactive T cell responses. During the past seven years our group has focused on the identification of CD4 T cell epitopes from tumor-associated and tumor-specific antigens that could be used to complement the already identified CD8 T cell epitopes to produce effective vaccination strategies against numerous tumor types. We will describe here the strategy we used that resulted in the identification and characterization of numerous CD4 T cell epitopes that are applicable to developing therapies against hematological malignancies and solid tumors.

Conditional MHC class I ligands and peptide exchange technology for the human MHC gene products HLA-A1, -A3, -A11, and -B7

Major histocompatibility complex (MHC) class I multimer technology has become an indispensable immunological assay system to dissect antigen-specific cytotoxic CD8(+) T cell responses by flow cytometry. However, the development of high-throughput assay systems, in which T cell responses against a multitude of epitopes are analyzed, has been precluded by the fact that for each T cell epitope, a separate in vitro MHC refolding reaction is required. We have recently demonstrated that conditional ligands that disintegrate upon exposure to long-wavelength UV light can be designed for the human MHC molecule HLA-A2. To determine whether this peptide-exchange technology can be developed into a generally applicable approach for high throughput MHC based applications we set out to design conditional ligands for the human MHC gene products HLA-A1, -A3, -A11, and -B7. Here, we describe the development and characterization of conditional ligands for this set of human MHC molecules and apply the peptide-exchange technology to identify melanoma-associated peptides that bind to HLA-A3 with high affinity. The conditional ligand technology developed here will allow high-throughput MHC-based analysis of cytotoxic T cell immunity in the vast majority of Western European individuals.

HLA class I supertypes: a revised and updated classification

BACKGROUND

Class I major histocompatibility complex (MHC) molecules bind, and present to T cells, short peptides derived from intracellular processing of proteins. The peptide repertoire of a specific molecule is to a large extent determined by the molecular structure accommodating so-called main anchor positions of the presented peptide. These receptors are extremely polymorphic, and much of the polymorphism influences the peptide-binding repertoire. However, despite this polymorphism, class I molecules can be clustered into sets of molecules that bind largely overlapping peptide repertoires. Almost a decade ago we introduced this concept of clustering human leukocyte antigen (HLA) alleles and defined nine different groups, denominated as supertypes, on the basis of their main anchor specificity. The utility of this original supertype classification, as well several other subsequent arrangements derived by others, has been demonstrated in a large number of epitope identification studies.

RESULTS

Following our original approach, in the present report we provide an updated classification of HLA-A and -B class I alleles into supertypes. The present analysis incorporates the large amount of class I MHC binding data and sequence information that has become available in the last decade. As a result, over 80% of the 945 different HLA-A and -B alleles examined to date can be assigned to one of the original nine supertypes. A few alleles are expected to be associated with repertoires that overlap multiple supertypes. Interestingly, the current analysis did not identify any additional supertype specificities.

CONCLUSION

As a result of this updated analysis, HLA supertype associations have been defined for over 750 different HLA-A and -B alleles. This information is expected to facilitate epitope identification and vaccine design studies, as well as investigations into disease association and correlates of immunity. In addition, the approach utilized has been made more transparent, allowing others to utilize the classification approach going forward.

Dendritic cells loaded with killed allogeneic melanoma cells can induce objective clinical responses and MART-1 specific CD8+ T-cell immunity

Dendritic cells (DCs) loaded with killed allogeneic tumors can cross-prime tumor-specific naive CD8 T cells in vitro, thereby providing an option to overcome human leukocyte antigen restriction inherent to loading DC vaccines with peptides. We have vaccinated 20 patients with stage IV melanoma with autologous monocyte-derived DCs loaded with killed allogeneic Colo829 melanoma cell line. DCs were generated by culturing monocytes with granulocyte macrophage-colony stimulating factor (granulocyte macrophage-colony stimulating factor) and interleukin (IL-4) and activated by additional culture with tumor necrosis factor and CD40 ligand. A total of 8 vaccines were administered at monthly intervals. The first patient was accrued December 2002 and the last November 2003. Fourteen patients were alive at 12 months, 9 patients were alive at 24 months, and 8 patients are alive as of January 2006. The estimated median overall survival is 22.5 months with a range of 2 to 35.5 months. Vaccinations were safe and tolerable. They induced, in 2 patients who failed previous therapy, durable objective clinical responses, 1 complete regression (CR) and 1 partial regression (PR) lasting 18 and 23 months, respectively. Three out of 13 analyzed patients showed T-cell immunity to melanoma antigen recognized by autologous T cells (MART-1) tissue differentiation antigen. Two of 3 patients showed improved immune function after vaccinations demonstrated by improved secretion of interferon (IFN)-gamma or T-cell proliferation in response to MART-1 derived peptides. In one of these patients, vaccination led to elicitation of CD8 T-cell immunity specific to a novel peptide-derived from MART-1 antigen, suggesting that cross-priming/presentation of melanoma antigens by DC vaccine had occurred. Thus, the present results justify the design of larger follow-up studies to assess the clinical response to DC vaccines loaded with killed allogeneic tumor cells in patients with metastatic melanoma.

T cell receptor cross-recognition of an HIV-1 CD8+ T cell epitope presented by closely related alleles from the HLA-A3 superfamily

HLA-A3 and -A11 share similar peptide-binding motifs, however, it is unclear if promiscuous epitope presentation by HLA-A3 or HLA-A11 is associated with promiscuous TCR recognition. Here, we show that despite widespread cross-presentation of identical HIV-1 peptides in HIV-1-infected individuals expressing HLA-A3 or HLA-A11, peptides presented by HLA-A3 or HLA-A11 commonly exhibited clear immune distinctiveness with exclusive TCR recognition. Yet, using HLA-A3 and HLA-A11 tetramers for testing T cell cross-recognition of the HIV-1 Nef QK10 epitope, we observed in two study persons that specific CD8+ T cell populations were able to cross-recognize this peptide in the context of both HLA-A3 and HLA-A11. This cross-recognition was mediated by single cross-reactive TCRs, as shown by TCR sequencing in conjunction with TCR Vbeta chain immunostaining. In each cross-reactive cell population, multiple TCR beta chain variants were detected in the presence of only one TCR alpha chain variant. Thus, despite distinct TCR recognition of HLA-A3 or HLA-A11 presented HIV-1 peptides in the vast majority of cases, specific TCRs can cross-recognize their antigen in the context of both HLA-A3 and HLA-A11.

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.

A listing of human tumor antigens recognized by T cells: March 2004 update

The technological advances occurred in the last few years have led to a great increase in the number of tumor associated antigens (TAA) that are currently available for clinical applications. In this review we provide a comprehensive list of human tumor antigens as reported in the literature updated at February 2004. The list includes all T cell-defined epitopes, while excluding analogs or artificially modified epitopes, as well as virus-encoded and antibodies-recognized antigens. TAAs are listed in alphabetical order along with the epitope sequence and the HLA allele which restricts recognition by T cells. Data on the tissue distribution of each antigen are also provided together with an extensive bibliography that allows a rapid search for any additional information may be needed on each single antigen or epitope. Overall, the updated list is a database tool for clinicians, scientists and students who have an interest in the field of tumor immunology and immunotherapy.

Biochemical and structural impact of natural polymorphism in the HLA-A3 superfamily

Class I alleles of the HLA-A3 superfamily (-A*0301, -A*1101, -A*3101, -A*3301, and -Aw*6801) share largely overlapping peptide repertoires. Cross-reactive T cell responses between HLA-A3-like molecule/peptide complexes have been demonstrated in vitro and during natural diseases. In spite of this immune relatedness, HLA-A3-like molecules exhibit noticeable differences in their antigen-selecting and -presenting properties. Identifying molecular and structural features responsible for these differences is important for understanding how natural polymorphism leads to functional divergence within the HLA-A3 superfamily. Towards this goal, we used an approach that combines thermal stability data on recombinant, soluble HLA-A3-like molecules complexed with a nonamer and decamer HIV-1 peptide, together with a detailed structural analysis of these HLA-A3-like molecule/peptide complexes based on crystal and molecular model structures. Our studies revealed the importance of residues 9 and 67 for modulating peptide selection within the B pocket; of residue 97 for modulating peptide selection within the F pocket interdependently with the presence (or absence) of a middle, secondary anchor residue; and of residues 70, 73, 97, 152, and 156 for modulating peptide presentation in the central region of the groove that leads to altered antigenic surfaces. Overall, our detailed assessment of the biochemical and structural impact of natural polymorphism within the HLA-A3 superfamily has permitted to understand how HLA-A3-like molecules differ at the level of their primary and secondary anchor pockets causing fine differences in their peptide-selecting and -presenting properties. A better understanding of the molecular immunological properties of HLA-A3-like molecules is significantly important for the rationale design of broad peptide-based vaccines.

Identification and characterization of a T-helper peptide from carcinoembryonic antigen

PURPOSE

The purpose of this research was to identify promiscuous T-helper cell determinants (THd) from carcinoembryonic antigen (CEA) to be used to prime T-cell help for cancer therapy. CEA was selected because this antigen is expressed in an important variety of carcinomas.

EXPERIMENTAL DESIGN

Potential promiscuous THd from CEA were predicted using available computer algorithms. Predicted peptides were synthesized and tested in binding experiments to different HLA-DR molecules. Binder peptides were then used to prime T-cell responses both in vitro and in vivo.

RESULTS

Twenty 15-mer peptides from CEA were predicted to bind to different HLA-DR molecules. The promiscuous character of these peptides was demonstrated in binding experiments. Fifteen of 20 peptides tested were able to bind to HLA-DR4, but only CEA (625-639) was shown to be presented after processing of recombinant CEA. CEA (625-639) was also found to be presented by HLA-DR53. Moreover, immunization of HLA-DR4 transgenic mice with CEA (625-639) in conjunction with class I epitope OVA (257-264), induced a CTL response specific of OVA (257-264).

CONCLUSIONS

CEA (625-639) might be a relevant promiscuous THd peptide for cancer therapy.

Simultaneous prediction of binding capacity for multiple molecules of the HLA B44 supertype

We selected for study a set of B44-supertype molecules collectively represented in >40% of the individuals in all major ethnicities (B*1801, B*4001, B*4002, B*4402, B*4403, and B*4501). The peptide-binding specificity of each molecule was characterized using single amino acid substitution analogues and nonredundant peptide libraries. In all cases, only peptide ligands with glutamic acid in position 2 were preferred. At the C terminus, each allele was associated with a unique but broad pattern of preferences, but all molecules tolerated hydrophobic/aliphatic (leucine, isoleucine, valine, methionine), aromatic (tyrosine, phenylalanine, tryptophan), and small (alanine, glycine, threonine) residues. Secondary anchor motifs were also defined for all molecules. Together, these features were used to define a B44 supermotif and a novel algorithm for calculating degeneracy scores that can be used to predict B44-supertype degenerate binders. Approximately 90% of the peptides with a B44 supermotif degeneracy score of >10 bound at least three of the six B44-supertype molecules studied with high affinity. Finally, a number of peptides derived from hepatitis B and C viruses, HIV, and Plasmodium falciparum have been identified that have degenerate B44 supertype-binding capacity. Taken together, these findings have important implications for epitope-based approaches to vaccination, immunotherapy, and the monitoring of immune responses.

Identification of Peptide Vaccine Candidates Sharing among HLA-A3+, -A11+, -A31+, and -A33+ Cancer Patients

PURPOSE

Only a few studies have been reported on CTL epitope peptides restricted with alleles other than HLA-A2 and -A24. The HLA-A11, -A31, and -A33 alleles share similar binding motifs with HLA-A3 and -A68 alleles, and, thus, are classified as an HLA-A3 supertype. This study tried to identify CTL epitope peptides as vaccine candidates sharing by HLA-A3(+), -A11(+), -A31(+), and -A33(+) cancer patients.

EXPERIMENTAL DESIGN

Seven peptides possessing the ability to induce HLA-A31-restricted and tumor-reactive CTLs were examined for their ability to induce HLA-A3-, -A11-, and -A33-restricted and tumor-reactive CTLs from peripheral blood mononuclear cells (PBMCs) of 18 epithelial cancer patients. The five reference peptides all have the ability to induce CTL activity restricted with one of the HLA-A3 supertypes, and, thus, were also examined as positive controls.

RESULTS

Three peptides (2 from beta-tublin5- and 1 from CGI37-derived peptides) induced tumor-reactive CTLs in PBMCs of HLA-A3(+), -A11(+), and -A33(+) cancer patients with various frequencies (17-50%). One RLI- or KIAA0036-derived peptide induced tumor-reactive CTLs in PBMCs of HLA-A3(+) and -A11(+) or HLA-A11(+) and -A33(+) cancer patients also with various frequencies (22-67%), respectively, whereas the other peptide induced CTL activity in only HLA-A33(+) patients. Among the five reference peptides tested, one peptide, TRP2-197, induced CTL activity in both HLA-A11(+)- and -A33(+)-restricted manners.

CONCLUSIONS

We identified new peptide vaccine candidates for HLA-A3, -A11, -A31, and -A33 positive cancer patients. This study may facilitate the development of both basic and clinical studies of peptide-based immunotherapy for cancer patients with other alleles of HLA-A2 and -A24.

HLA-A3 supermotif defined by quantitative structure-activity relationship analysis

Activation of a cytotoxic T cell requires specific binding of antigenic peptides to major histocompatibility complex (MHC) molecules. This paper reports a study of peptides binding to members of the HLA-A3 superfamily using a recently developed 2D-QSAR method, called the additive method. Four alleles with high phenotype frequency were included in the study: A*0301, A*1101, A*3101 and A*6801. The influence of each of the 20 amino acids at each position of the peptide on binding was studied. A refined A3 supertype motif was defined in the study.

Antigens derived from melanocyte differentiation proteins: self-tolerance, autoimmunity, and use for cancer immunotherapy

A large set of peptide antigens presented by class I major histocompatibility complex (MHC) molecules on human and murine melanomas and recognized by CD8+ T cells have been defined. These peptides represent attractive candidates for the development of therapeutic and/or prophylactic approaches to treat this cancer. However, the majority of the peptides that are presented by multiple tumors and recognized by T cells from multiple patients arise from proteins that are also expressed in normal melanocytes. It is expected that immune responses to such peptides will be compromised by self-tolerance or, alternatively, that stimulation of effective immune responses will be accompanied by autoimmune vitiligo. In this review, we describe a preclinical model to evaluate these issues and recent data to suggest that tolerance can be overcome to generate effective antitumor responses. This model also allows the rapid and systematic examination of parameters for the effective use of synthetic peptide vaccines.

Peptide vaccines for cancer

The revelation that immune cytolytic and helper T-cells recognize intracellularly degraded peptides processed via the proteosome apparatus, inserted into the endoplasmic reticulum and transported to the surface for association with major histocompatibility locus (MHC) molecules on specialized antigen-presenting cells has revolutionized the cancer vaccine field. Understanding the science of antigen processing and presentation has provided new reagents, delivery systems, and new investigative leads for the generation of immune responses against cancer. The cloning of tumor antigen genes has proceeded rapidly in melanoma, due to the ease with which melanoma-specific T-cells can be propagated in vitro, but breast, cervix, and lung cancer are not far behind. The cloning and identification of tumor antigens recognized by T-cells and data from initial clinical trials with peptides vaccines derived from those antigens are presented.

Challenges in the development of effective peptide vaccines for cancer

The ability of the immune system to recognize malignant cells has opened the door to development of tumor vaccines to treat or prevent various types of cancer. In the era of molecular biology, the tumor antigens recognized by the immune system have been identified, allowing the generation of subunit vaccines that may improve safety and efficacy compared with more crude vaccines such as irradiated tumor cells and tumor cell lysates. Synthetic peptides corresponding to defined antigenic epitopes for tumor-reactive lymphocytes represent one of the new types of vaccines currently being developed to treat or prevent various types of malignant disorders. The design of peptide-based vaccines to stimulate antitumor T-cell responses has many attractive features such as ease of manufacturing and characterization (ie, quality control), as well as an excellent safety profile in past clinical studies. However, ambiguous results from initial clinical trials indicate that these vaccines are far from optimal and that considerable efforts for their optimization lie ahead. We attempt to address the 8 most important challenges we currently face for developing peptide-based vaccines that would effectively induce immune responses leading to antitumor effects.

Inhibiting effects on the induction of cytotoxic T lymphocytes by dendritic cells pulsed with lysates from acute myeloid leukemia blasts

Dendritic cells (DCs) were established from 25 patients in complete remission of acute myeloid leukemia (AML). In patients during hematopoietic regeneration following chemotherapy the yield of DC was comparable to that of healthy donors. In patients, more than 2 months after chemotherapy, significantly less DC were generated. Comparison of the antigen-presenting capacity using tetanus toxoid of six AML patients and six healthy volunteers did not show significant differences. In six AML patients, lymphocytes stimulated with blast cell lysate pulsed DC were analyzed for cytotoxic activity against autologous blast cells. 8.4-35.6% of autologous blast cells were lysed by DC stimulated lymphocytes. In three of the six patients maximum lysis of target cells was achieved by unpulsed DC. Thus, it seems that in some patients blast cell lysates mediate inhibitory effects, which may explain to some extend immune escape mechanisms in AML.

Immunotherapy for melanoma

BACKGROUND

Immunotherapy for cancers is based on the principle that the host's immune system is capable of generating immune responses against tumor cells. Currently available treatments for melanoma patients are limited by poor response rates. Interferon-a has been approved for adjuvant treatment of stage III melanoma with improved survival. New and more innovative approaches with improved efficacy are needed.

METHODS

We reviewed the various new approaches and strategies for immunotherapy for the treatment of melanoma.

RESULTS

Immunotherapy for melanoma includes a number of different strategies with vaccines utilizing whole cell tumors, peptides, cytokine-mediated dendritic cells, DNA and RNA, and antibodies.

CONCLUSIONS

A variety of approaches can be used to enhance immune reactivity in patients with melanoma. Preclinical studies and initial clinical trials have shown promising results. Additional clinical trials are currently ongoing to evaluate the clinical efficacy and the associated toxicities of these novel treatment strategies.

Direct evidence to support the role of antigen-specific CD8(+) T cells in melanoma-associated vitiligo

Vitiligo is a cutaneous pigmentary disorder characterized by the loss of melanocytes. An autoimmune mechanism is strongly suspected to be involved in this affection given that it is frequently associated with autoimmune hormonal disorders, and because antibodies directed against melanocytic antigens are found in the serum of patients with vitiligo. We examined the role of cellular immunity in melanoma-associated vitiligo by expanding infiltrating lymphocytes from fresh biopsy specimens of vitiligo patches in melanoma patients. The vitiligo-infiltrating lymphocytes were almost exclusively T lymphocytes, and most were CD8(+). Following in vitro expansion, vitiligo-infiltrating lymphocytes remained predominantly CD8(+) and expressed the cutaneous homing receptor CLA. Furthermore, vitiligo-infiltrating lymphocytes had a clonal or oligoclonal T cell receptor profile, possibly reflecting specific antigenic stimulation. Finally, vitiligo- infiltrating lymphocytes specifically recognized differentiation antigens shared by normal melanocytes and melanoma cells. This direct demonstration of CD8(+) T cell involvement in vitiligo suggests that, in melanoma patients, vitiligo may be a visible effect of a spontaneous antitumoral immune response.

Autologous dendritic cells for treatment of advanced cancer--an update

Dendritic cells (DC) are commonly viewed as the professional antigen-presenting cell. They capture antigens, migrate to appropriate lymphoid organs and initiate an antigen-specific CD4 and CD8 T cell response. Much is known about DC physiology, and it is now possible to culture, maintain and expand DC from different human sources, including hematopoietic progenitors in bone marrow and peripheral blood. Combined with the detection of an increasing number of tumor-associated antigens and T cell-recognized peptide epitopes, this has led to a new enthusiasm in the field of tumor immunotherapy and to various clinical applications in phase I/II studies on the treatment of different malignancies. This chapter will review the latest developments and give a brief update of the results obtained in studies of advanced melanoma, as well as provide a short overview of published results for other tumors.

Reverse immunogenetic and polyepitopic approaches for the induction of cell-mediated immunity against bovine viral pathogens

The control of several infectious diseases of animals by vaccination is perhaps the most outstanding accomplishment of veterinary medicine in the last century. Even the eradication of some pathogens is in sight, at least in some parts of the world. However, infectious diseases continue to cost millions of dollars to the livestock industry. One of the reasons for the failure to control certain pathogens is the limited emphasis placed on cell-mediated immunity (CMI) in the design of vaccines against these pathogens. Traditionally, vaccine-induced immunity has been studied in relation to antibody-mediated protection. More recent studies, however, have focused on understanding CMI and developing means of inducing CMI. This review focuses on recent advances made in the study of CMI in general and of cytotoxic T lymphocytes in particular. Parallels from studies in human and mouse immunology are drawn in order to point out implications to bovine immunology, specifically for immunity against bovine herpesvirus 1.

Identification of HLA-A*03, A*11 and B*07-restricted melanoma-associated peptides that are immunogenic in vivo by vaccine-induced immune response (VIIR) analysis

With the discovery of increasing numbers of tumor antigens, there is a need to rapidly determine whether these antigens and the individual peptides they express are able to stimulate immune responses in vivo and thus, can be used to construct cancer vaccines. In this study we used the method of vaccine-induced immune response (VIIR) analysis to identify multiple immunogenic peptide epitopes derived from several melanoma associated antigens and presented by HLA-A*03, A*11 and B*07. Thirty-one patients with melanoma were immunized to a polyvalent vaccine containing multiple antigens, including MAGE-3, Melan A/MART-1, gp100 and tyrosinase. Their peripheral blood was tested for peptide-specific, vaccine-induced CD8+ T cell responses before and after immunization using an enzyme-linked immune spot (ELISPOT) assay with panels of peptides restricted by these three alleles. The peptides were selected for immunogenic potential based on their strong binding affinity in vitro to HLA-A*03, A*11 or B*07. Overall, 60% of the 20 peptides studied were recognized by at least one patient and 50% of the patients showed a vaccine-induced CD8+ T cell response to at least one peptide that matched their HLA specificity. We conclude that VIIR analysis is an effective strategy to directly identify immunogenic peptides that are good candidates for vaccine construction.

In vitro and in vivo induction of a Th cell response toward peptides of the melanoma-associated glycoprotein 100 protein selected by the TEPITOPE program

The melanoma-associated Ag glycoprotein 100 was analyzed by the T cell epitope prediction software TEPITOPE. Seven HLA-DR promiscuous peptides predicted with a stringent threshold were used to load dendritic cells (DC), and induction of a proliferative response was monitored. PBMC of all nine donors including two patients with malignant melanoma responded to at least one of the peptides. The proliferative response was defined as a Th response by the selective expansion of CD4(+) cells, up-regulation of CD25 and CD40L, and IL-2 and IFN-gamma expression. Peptide-loaded DC also initiated a T helper response in vivo (i.e., tumor growth in the SCID mouse was significantly retarded by the transfer of PBMC together with peptide-loaded DC). Because the use of the TEPITOPE program allows for a prediction of T cell epitopes; because the predicted peptides can be rapidly confirmed by inducing a Th response in the individual patient; and because application of peptide-loaded DC suffices for the in vivo activation of helper cells, vaccination with MHC class II-binding peptides of tumor-associated Ags becomes a feasible and likely powerful tool in the immunotherapy of cancer.

Tumor-specific CD4+ T lymphocytes from cancer patients are required for optimal induction of cytotoxic T cells against the autologous tumor

This study focuses on the specific CD4+ T cell requirement for optimal induction of cytotoxicity against MHC class II negative autologous tumors (AuTu) collected from patients with various types of cancer at advanced stages. CD4+ T cells were induced in cultures of cancer patients' malignant effusion-associated mononuclear cells with irradiated AuTu (mixed lymphocyte tumor cultures (MLTC)) in the presence of recombinant IL-2 and recombinant IL-7. Tumor-specific CD4+ T cells did not directly recognize the AuTu cells, but there was an MHC class II-restricted cross-priming by autologous dendritic cells (DCs), used as APC. CD8+ CTL, also induced during the MLTC, lysed specifically AuTu cells or DCs pulsed with AuTu peptide extracts (acid wash extracts (AWE)) in an MHC class I-restricted manner. Removal of CD4+ T cells or DCs from the MLTC drastically reduced the CD8+ CTL-mediated cytotoxic response against the AuTu. AWE-pulsed DCs preincubated with autologous CD4+ T cells were able, in the absence of CD4+ T cells, to stimulate CD8+ T cells to lyse autologous tumor targets. Such activated CD8+ T cells produced IL-2, IFN-gamma, TNF-alpha, and GM-CSF. The process of the activation of AWE-pulsed DCs by CD4+ T cells could be inhibited with anti-CD40 ligand mAb. Moreover, the role of CD4+ T cells in activating AWE-pulsed DCs was undertaken by anti-CD40 mAb. Our data demonstrate for the first time in patients with metastatic cancer the essential role of CD4+ Th cell-activated DCs for optimal CD8+ T cell-mediated killing of autologous tumors and provide the basis for the design of novel protocols in cellular adoptive immunotherapy of cancer, utilizing synthetic peptides capable of inducing T cell help in vivo.

Melanoma vaccines

Remarkable advances in tumor vaccination have been made since Coley first deliberately infected cancer patients with both live and heat-killed bacteria. Melanoma is the most immunogenic solid tumor and, as such, has served as the major model for tumor vaccine investigation in both the laboratory and the clinic. Many advances in the field of melanoma vaccination have been based on an improved understanding of the cellular interaction required to induce a specific antitumor immune response. As a result of this new knowledge, many clinical trials of melanoma vaccines are now under way, and vaccines for metastatic melanoma have shown evidence of clinical effectiveness. This paper outlines the current status of melanoma vaccination.

Melanoma peptide vaccines: from preclinical background to clinical trials

The discovery that immune T-cells recognize intracellularly processed peptides associated with major histocompatibility locus molecules has revolutionized the cancer vaccine field by providing new reagents for the generation of immune responses against cancer. The cloning of tumor antigen genes has proceeded most rapidly in melanoma because of the ease with which melanoma-specific T-cells can be propagated in vitro. The cloning and identification of tumor regression antigens and data from the initial clinical trials with peptides vaccines derived from those antigens are presented here.

Advances in cancer vaccine development

Traditionally, cancer vaccines have used whole tumour cells administered in adjuvant or infected with viruses to increase the immunogenicity of the cells. With the identification of tumour-associated and tumour-specific antigens (TAA, TSA), antigen and epitope-specific vaccines have been designed. Compared to tumour cell vaccines, antigen and epitope vaccines are more specific and easier to produce in large quantities but may display lower immunogenicity and lead to the in vivo selection of antigen or epitope-negative escape tumour variant cells. The optimal vaccine will elicit both humoral and cellular immunity in the patients as both parameters have been positively correlated with the induction of beneficial clinical responses. The choice of adjuvant, costimulation and delivery mode greatly determines the outcome of vaccinations and may favour the induction of T-cell responses of T helper (Th)1, Th2, or both Th1 and Th2 types. Animal models of TAA vaccines must take into account the normal tissue expression of TAA, which may induce immunological tolerance to TAA. With the identification of homologues of human TAA in animals, novel experimental models of cancer vaccines which mimic the condition in patients are now available. Several vaccines comprising tumour cells, TAA or anti-idiotypic antibodies mimicking TAA have recently entered phase III of clinical evaluation.