gp100/pmel 17 is a murine tumor rejection antigen: induction of "self"-reactive, tumoricidal T cells using high-affinity, altered peptide ligand

High vaccination efficiency of low-affinity epitopes in antitumor immunotherapy

Most of the human tumor-associated antigens (TAAs) characterized thus far are derived from nonmutated "self"-proteins. Numerous strategies have been developed to break tolerance to TAAs, combining various forms of antigens with different vectors and adjuvants. However, no study has yet determined how to select epitopes within a given TAA to induce the highest antitumor effector response. We addressed this question by evaluating in HLA-A*0201-transgenic HHD mice the antitumor vaccination efficacy of high- and low-affinity epitopes from the naturally expressed murine telomerase reverse transcriptase (mTERT). Immunity against low-affinity epitopes was induced with heteroclitical variants. We show here that the CTL repertoire against high-affinity epitopes is partially tolerized, while that against low-affinity epitopes is composed of frequent CTLs with high avidity. The high-affinity p797 and p545 mTERT epitopes are not able to protect mice from a lethal challenge with the mTERT-expressing EL4-HHD tumor. In contrast, mice developing CTL responses against the p572 and p988 low-affinity epitopes exhibit potent antitumor immunity and no sign of autoimmune reactivity against TERT-expressing normal tissues. Our results strongly argue for new TAA epitope selection and modification strategies in antitumor immunotherapy applications in humans.

Improved Immunogenicity of an Immunodominant Epitope of the Her-2/neu Protooncogene by Alterations of MHC Contact Residues

The HER-2/neu (HER-2) oncogene is expressed in normal epithelial surfaces at low levels and overexpressed in several types of tumors. The low immunogenicity against this self tumor Ag can be improved by developing epitopes with amino acid replacements in their sequences. In this study, three HER-2/neu.369 (HER-2.369) analogue peptides, produced by modifying both anchor positions by introducing L, V, or T at position 2 and V at the C terminus, were analyzed for their capacity to induce CTLs in vitro from human PBMC and in vivo in HLA-A2.1/Kb transgenic mice. One of the analogues (HER-2.369 V2V9) sensitized target cells for HER-2-specific recognition by human CTLs and induced specific CTLs in vitro at 100-fold lower concentrations than the HER-2.369 wild-type epitope. These CTLs were also able to recognize the wild-type epitope and HER-2-expressing tumors in an MHC-restricted manner. Furthermore, a 100-fold lower amount of the HER-2.369 V2V9 analogue compared with the wild-type epitope was required to induce CTLs in HLA-A2.1/Kb transgenic mice. However, the V2V9 analogue demonstrated only marginally better binding to the MHC class I A2 allele compared with wild type. To establish thermodynamic parameters, we developed radiolabeled F3*Y analogues from both the HER-2.369 epitope and the V2V9 analogue. Our results indicate that the high biological activity of the HER-2.369 V2V9 epitope is associated with a slower dissociation kinetic profile, resulting in an epitope with greater HLA-A2 stability.

Danger, death and DNA vaccines

DNA vaccines, although successful in many animal models of various diseases, remain insufficiently immunogenic in humans. Among the countless approaches to improve them is the stimulation of the innate immune system by promoting the apoptotic death of the transfected host cells, which is the focus of this review.

Inducible Hsp70 as target of anticancer immunotherapy: Identification of HLA-A*0201-restricted epitopes

The design of a broad application tumor vaccine requires the identification of tumor antigens expressed in a majority of tumors of various origins. We questioned whether the major stress-inducible heat shock protein Hsp70 (also known as Hsp72), a protein frequently overexpressed in human tumors of various histological origins, but not in most physiological normal tissues, constitutes a tumor antigen. We selected the p391 and p393 peptides from the sequence of the human inducible Hsp70 that had a high affinity for HLA-A*0201. These peptides were able to trigger a CTL response in vivo in HLA-A*0201-transgenic HHD mice and in vitro in HLA-A*0201+ healthy donors. p391- and p393-specific human and murine CTL recognized human tumor cells overexpressing Hsp70 in a HLA-A*0201-restricted manner. Tetramer analysis of TILs showed that these Hsp70 epitopes are targets of an immune response in many HLA-A*0201+ breast cancer patients. Hsp70 is a tumor antigen and the Hsp70-derived peptides p391 and p393 could be used to raise a cytotoxic response against tumors of various origins.

IL-15 enhances the in vivo antitumor activity of tumor-reactive CD8+ T cells

IL-15 and IL-2 possess similar properties, including the ability to induce T cell proliferation. However, whereas IL-2 can promote apoptosis and limit CD8(+) memory T cell survival and proliferation, IL-15 helps maintain a memory CD8(+) T cell population and can inhibit apoptosis. We sought to determine whether IL-15 could enhance the in vivo function of tumor/self-reactive CD8(+) T cells by using a T cell receptor transgenic mouse (pmel-1) whose CD8(+) T cells recognize an epitope derived from the self/melanoma antigen gp100. By removing endogenous IL-15 by using tumor-bearing IL-15 knockout hosts or supplementing IL-15 by means of exogenous administration, as a component of culture media or as a transgene expressed by adoptively transferred T cells, we demonstrate that IL-15 can improve the in vivo antitumor activity of adoptively transferred CD8(+) T cells. These results provide several avenues for improving adoptive immunotherapy of cancer in patients.

NK and CD8+ T cell-mediated eradication of poorly immunogenic B16-F10 melanoma by the combined action of IL-12 gene therapy and 4-1BB costimulation

In previous reports, systemic administration of a stimulatory monoclonal antibody directed against the 4-1BB receptor had no effect on survival or tumor burden in mice inoculated with the poorly immunogenic B16-F10 melanoma. We combined IL-12 gene transfer with 4-1BB costimulation to explore a previously noted cooperative anti-tumor effect against this model tumor. We hypothesize that the innate immune response mediated by IL-12-activated natural killer (NK) cells initiates the activation of the immune system, leading to the priming of T cells, whereas 4-1BB costimulation enhances the function of primed tumor-specific T cells. The effect of the combination therapy on the growth of subcutaneous (s.c.) tumors and pulmonary metastasis was examined. The combination therapy significantly retarded the growth of subcutaneously-inoculated tumors, and 50% of tumor-bearing mice survived with complete tumor regression. In contrast, neither IL-12 gene transfer nor anti-4-1BB antibody administration alone was as effective. Enhanced CTL activity against both B16-F10 tumor cells and TRP-2-pulsed EL4 syngeneic tumor cells was observed in tumor-bearing animals treated with the combination therapy 2 weeks after treatment and, in long-term survivors from this combination therapy, at >120 days. In a pulmonary metastatic model, only the combination therapy generated significant protection against metastasis. In vivo depletion of NK or CD8(+) but not CD4(+) subsets eliminated the protective immunity. Furthermore, NK cell depletion significantly reduced both tumor-specific CTL activity and the number of tumor-specific IFN-gamma-producing cells, suggesting that this synergistic effect requires the participation of both NK and CD8(+) T cells.

Immune evasion by murine melanoma mediated through CC chemokine receptor-10

Human melanoma cells frequently express CC chemokine receptor (CCR)10, a receptor whose ligand (CCL27) is constitutively produced by keratinocytes. Compared with B16 murine melanoma, cells rendered more immunogenic via overexpression of luciferase, B16 cells that overexpressed both luciferase and CCR10 resisted host immune responses and readily formed tumors. In vitro, exposure of tumor cells to CCL27 led to rapid activation of Akt, resistance to cell death induced by melanoma antigen-specific cytotoxic T cells, and phosphatidylinositol-3-kinase (PI3K)–dependent protection from apoptosis induced by Fas cross-linking. In vivo, cutaneous injection of neutralizing antibodies to endogenous CCL27 blocked growth of CCR10-expressing melanoma cells. We propose that CCR10 engagement by locally produced CCL27 allows melanoma cells to escape host immune antitumor killing mechanisms (possibly through activation of PI3K/Akt), thereby providing a means for tumor progression.

Adoptive-cell-transfer therapy for the treatment of patients with cancer

Adoptive immunotherapy--the isolation of antigen-specific cells, their ex vivo expansion and activation, and subsequent autologous administration--is a promising approach to inducing antitumour immune responses. The molecular identification of tumour antigens and the ability to monitor the persistence and transport of transferred cells has provided new insights into the mechanisms of tumour immunotherapy. Recent studies have shown the effectiveness of cell-transfer therapies for the treatment of patients with selected metastatic cancers. These studies provide a blueprint for the wider application of adoptive-cell-transfer therapy, and emphasize the requirement for in vivo persistence of the cells for therapeutic efficacy.

Effective induction of therapeutic antitumor immunity by dendritic cells coexpressing interleukin-18 and tumor antigen

Dendritic cell (DC) based cancer vaccine can induce potent antitumor immunity in murine models; however, objective clinical responses have been observed only in a minority of cancer patients. To improve the antitumor effect of DC vaccine, Th1-biasing cytokine interleukin (IL) 18 and melanoma-associated antigen gp100 were cotransfected into bone marrow-derived DC (IL-18/gp100-DC), which were used as vaccine to induce the protective and therapeutic immunity in a B16 melanoma model. Immunization with IL-18/gp100-DC resulted in tumor resistance in 87.5% of the mice challenged with B16 cells; however, 12.5% and 25% of mice immunized with gp100 gene-modified DC (gp100-DC) or IL-18 gene-modified DC (IL-18-DC) were tumor free, respectively. Most importantly, IL-18/gp100-DC immunization led to the generation of potent therapeutic immunity that significantly inhibited the tumor growth and improved the survival period of mice bearing established melanoma. Immune cell depletion experiments identified that CD4(+) T cells also played an important role in the priming phase of antitumor immunity and CD8(+) T lymphocytes were the primary effectors. gp100-specific CTL response were induced most markedly in the tumor-bearing mice immunized with IL-18/gp100-DC. Administration with such vaccine also significantly increased the production of Th1 cytokine (IL-2 and interferon-gamma) and induced infiltration of inflammatory cells inside and around the tumors. In addition, natural killer cell activity was also augmented. These results indicate that immunization with DC vaccine coexpressing Th1 cytokine IL-18 and tumor antigen gene may be an effective strategy for a successful therapeutic vaccination.

Tumor regression and autoimmunity after reversal of a functionally tolerant state of self-reactive CD8+ T cells

Many tumor-associated antigens are derived from nonmutated "self" proteins. T cells infiltrating tumor deposits recognize self-antigens presented by tumor cells and can be expanded in vivo with vaccination. These T cells exist in a functionally tolerant state, as they rarely result in tumor eradication. We found that tumor growth and lethality were unchanged in mice even after adoptive transfer of large numbers of T cells specific for an MHC class I-restricted epitope of the self/tumor antigen gp100. We sought to develop new strategies that would reverse the functionally tolerant state of self/tumor antigen-reactive T cells and enable the destruction of large (with products of perpendicular diameters of >50 mm2), subcutaneous, unmanipulated, poorly immunogenic B16 tumors that were established for up to 14 d before the start of treatment. We have defined three elements that are all strictly necessary to induce tumor regression in this model: (a) adoptive transfer of tumor-specific T cells; (b) T cell stimulation through antigen-specific vaccination with an altered peptide ligand, rather than the native self-peptide; and (c) coadministration of a T cell growth and activation factor. Cells, vaccination, or cyto-kine given alone or any two in combination were insufficient to induce tumor destruction. Autoimmune vitiligo was observed in mice cured of their disease. These findings illustrate that adoptive transfer of T cells and IL-2 can augment the function of a cancer vaccine. Furthermore, these data represent the first demonstration of complete cures of large, established, poorly immunogenic, unmanipulated solid tumors using T cells specific for a true self/tumor antigen and form the basis for a new approach to the treatment of patients with cancer.

Immunotherapy of cancer by active vaccination: does allogeneic bone marrow transplantation after non-myeloablative conditioning provide a new option?

The critical role of antigen-specific T cells in cancer immunotherapy has been amply demonstrated in many model systems. Though success of clinical trials still remains far behind expectation, the continuous improvement in our understanding of the biology of the immune response will provide the basis of optimized cancer vaccines and allow for new modalities of cancer treatment. This review focuses on the current status of active therapeutic vaccination and future prospects. The latter will mainly be concerned with allogeneic bone marrow cell transplantation after non-myeloablative conditioning, because it is my belief that this approach could provide a major breakthrough in cancer immunotherapy. Concerning active vaccination protocols the following aspects will be addressed: i) the targets of immunotherapeutic approaches; ii) the response elements needed for raising a therapeutically successful immune reaction; iii) ways to achieve an optimal confrontation of the immune system with the tumor and iv) supportive regimen of immunomodulation. Hazards which one is most frequently confronted with in trials to attack tumors with the inherent weapon of immune defense will only be briefly mentioned. Many question remain to be answered in the field of allogeneic bone marrow transplantation after non-myeloablative conditioning to optimize the therapeutic setting for this likely very powerful tool of cancer therapy. Current considerations to improve engraftment and to reduce graft versus host disease while strengthening graft versus tumor reactivity will be briefly reviewed. Finally, I will discuss whether tumor-reactive T cells can be "naturally" maintained during the process of T cell maturation in the allogeneic host. Provided this hypothesis can be substantiated, a T cell vaccine will meet a pool of virgin T cells in the allogeneically reconstituted host, which are tolerant towards the host, but not anergised towards tumor antigens presented by MHC molecules of the host.

A single heteroclitic epitope determines cancer immunity after xenogeneic DNA immunization against a tumor differentiation antigen

Successful active immunization against cancer requires induction of immunity against self or mutated self Ags. However, immunization against self Ags is difficult. Xenogeneic immunization with orthologous Ags induces cancer immunity. The present study evaluated the basis for immunity induced by active immunization against a melanoma differentiation Ag, gp100. Tumor rejection of melanoma was assessed after immunization with human gp100 (hgp100) DNA compared with mouse gp100 (mgp100). C57BL/6 mice immunized with xenogeneic full-length hgp100 DNA were protected against syngeneic melanoma challenge. In contrast, mice immunized with hgp100 DNA and given i.p. tolerizing doses of the hgp100 D(b)-restricted peptide, hgp100(25-33), were incapable of rejecting tumors. Furthermore, mice immunized with DNA constructs of hgp100 in which the hgp100(25-27) epitope was substituted with the weaker D(b)-binding epitope from mgp100 (mgp100(25-27)) or a mutated epitope unable to bind D(b) did not reject B16 melanoma. Mice immunized with a minigene construct of hgp100(25-33) rejected B16 melanoma, whereas mice immunized with the mgp100(25-33) minigene did not develop protective tumor immunity. In this model of xenogeneic DNA immunization, the presence of an hgp100 heteroclitic epitope with a higher affinity for MHC created by three amino acid (25 to 27) substitutions at predicted minor anchor residues was necessary and sufficient to induce protective tumor immunity in H-2(b) mice with melanoma.

Normal tissue depresses while tumor tissue enhances human T cell responses in vivo to a novel self/tumor melanoma antigen, OA1

Antitumor T cells often recognize targets that are nonmutated "self" tissue differentiation Ags, but the relative impact of Ag expression by normal and transformed tissue for a human self/tumor Ag has not been studied. To examine the influence of self-tolerance mechanisms on the function of self/tumor-specific T cell responses in humans, we sought to identify an Ag that was expressed, processed, and presented in an MHC-restricted fashion by tumor cells, but for which there was the human equivalent of a "knockout." In this study, we report the first immunological characterization of a melanoma/melanocyte differentiation Ag, called OA1, which meets these criteria. This Ag, an X chromosome-encoded melanoma/melanocyte differentiation Ag, was completely deleted in a male patient. Using a newly identified HLA-A*2402-restricted epitope (LYSACFWWL) to study T cell tolerance, we found that OA1-specific T cell reactivity was more than five SD higher in the knockout patient that in normal controls. These data provide compelling evidence for T cell tolerance to OA1 in humans. Most surprisingly, we found elevated levels of OA1-specific T cells in patients with metastatic malignant melanoma, indicating that the tumor-bearing state partially reversed tolerance observed in normal (non-"knockout") individuals. Taken together, these findings indicated that tolerance can exist for self/tumor Ags in humans, and that this tolerance could be partially abrogated by the growth of the tumor, increasing the reactivity of tumor Ag-specific T cells. Thus, the tumor-bearing state reverses, in part, the tolerance of T cells that results from the normal expression of tissue differentiation Ags.

Alphavirus-based DNA vaccine breaks immunological tolerance by activating innate antiviral pathways

Cancer vaccines targeting 'self' antigens that are expressed at consistently high levels by tumor cells are potentially useful in immunotherapy, but immunological tolerance may block their function. Here, we describe a novel, naked DNA vaccine encoding an alphavirus replicon (self-replicating mRNA) and the self/tumor antigen tyrosinase-related protein-1. Unlike conventional DNA vaccines, this vaccine can break tolerance and provide immunity to melanoma. The vaccine mediates production of double-stranded RNA, as evidenced by the autophosphorylation of dsRNA-dependent protein kinase R (PKR). Double-stranded RNA is critical to vaccine function because both the immunogenicity and the anti-tumor activity of the vaccine are blocked in mice deficient for the RNase L enzyme, a key component of the 2',5'-linked oligoadenylate synthetase antiviral pathway involved in double-stranded RNA recognition. This study shows for the first time that alphaviral replicon-encoding DNA vaccines activate innate immune pathways known to drive antiviral immune responses, and points the way to strategies for improving the efficacy of immunization with naked DNA.

Multiple HLA class II-restricted melanocyte differentiation antigens are recognized by tumor-infiltrating lymphocytes from a patient with melanoma

Dramatic clinical responses were observed in patient 888 following the adoptive transfer of autologous tumor-infiltrating lymphocytes (TIL). Previously, extensive analysis of the specificity of class I-restricted T cells from patient 888 TIL has revealed that these T cells recognize a mutated, as well as several nonmutated tumor Ags. Additional studies that were conducted on TIL from patient 888 indicated that they contained CD4-positive T cells that recognized the autologous tumor that had been induced to express HLA class II molecules. Tumor-reactive CD4-positive T cell clones were isolated from TIL and tested for their ability to react with Ags that are recognized by HLA class I-restricted, melanoma-reactive T cells. Using this approach, T cell clones were identified that recognized an epitope expressed in both the tyrosinase-related protein 1 and tyrosinase-related protein 2 Ags in the context of the HLA-DRbeta1*1502 class II gene product. Additional clones were found to recognize an epitope of gp100 in the context of the same HLA-DR restriction element. These observations provide an impetus to develop strategies directed toward generating HLA class II-restricted tumor-reactive T cells.

Clonal deletion of simian virus 40 large T antigen-specific T cells in the transgenic adenocarcinoma of mouse prostate mice: an important role for clonal deletion in shaping the repertoire of T cells specific for antigens overexpressed in solid tumors

In addition to their overexpression in cancer cells, most of the tumor-associated Ags are expressed at low but detectable levels in normal tissues. It is not clear whether the repertoire of T cells specific for unmutated tumor Ags is shaped by negative selection during T cell development. The transgenic adenocarcinoma of mouse prostate (TRAMP) model is transgenic for the SV40 large T Ag (Tag) under the control of the rat probasin regulatory elements. Although it has been established that T lymphocytes from TRAMP mice are tolerant to SV40 Tag, the mechanism of the tolerance is largely unknown. To examine whether the T cell clonal deletion is responsible for the tolerance, we crossed the TRAMP mice with mice transgenic for a rearranged TCR specific for SV40 Tag presented by the H-2K(k). Double transgenic TRAMP/TCR mice showed profound thymic deletion of SV40 Tag-reactive T cells, including a 6- to 10-fold reduction in the total thymocyte numbers and a >50-fold reduction in phenotypically mature T cells. Consistent with this finding, we observed that the SV40 Tag and endogenous mouse probasin genes are expressed at low levels in the thymus. These results demonstrate that clonal deletion is a major mechanism for tolerance to Ags previously regarded as prostate-specific, and provide direct evidence that the T cell repertoire specific for an unmutated tumor Ag can be shaped by clonal deletion in the thymus.

MHC class I and class II presentation of tumor antigen in retrovirally and adenovirally transduced dendritic cells

The unique antigen-presenting capabilities of dendritic cells (DCs) make them an attractive means with which to initiate an antitumor immune response. Using DCs transduced with tumor antigens for immunotherapy has several theoretical advantages over peptide-pulsed DCs including the possibility that transduced DCs are capable of presenting epitopes on both class I and class II MHC molecules. To test this theory, we inserted the human tumor antigen gp100 into mouse DCs transgenic for HLA-DRbeta1*0401 using either adenoviral vector or a VSV-G pseudotyped retroviral vector. DCs transduced with tumor antigen were able to be recognized by both a murine CD8(+) T-cell clone and a murine CD4(+) T-cell line in a cytokine release assay, thereby demonstrating presentation of both MHC class I and class II gp100 epitopes. This study describes the simultaneous presentation of a tumor-associated antigen to both CD4(+) and CD8(+) T cells and lends support to the use of gene-modified DCs as a means to initiate both CD4(+) and CD8(+) antitumor responses.

Modification of a tumor-derived peptide at an HLA-A2 anchor residue can alter the conformation of the MHC-peptide complex: probing with TCR-like recombinant antibodies

A common assumption about peptide binding to the class I MHC complex is that each residue in the peptide binds independently. Based on this assumption, modifications in class I MHC anchor positions were used to improve the binding properties of low-affinity peptides (termed altered peptide ligands), especially in the case when tumor-associated peptides are used for immunotherapy. Using a new molecular tool in the form of recombinant Abs endowed with Ag-specific MHC-restricted specificity of T cells, we show that changes in the identity of anchor residues may have significant effects, such as altering the conformation of the peptide-MHC complex, and as a consequence, may affect the TCR-contacting residues. We herein demonstrate that the binding of TCR-like recombinant Abs, specific for the melanoma differentiation Ag gp100 T cell epitope G9-209, is entirely dependent on the identity of a single peptide anchor residue at position 2. An example is shown in which TCR-like Abs can recognize the specific complex only when a modified peptide, G9-209-2 M, with improved affinity to HLA-A2 was used, but not with the unmodified natural peptide. Importantly, these results demonstrate, using a novel molecular tool, that modifications at anchor residues can dramatically influence the conformation of the MHC peptide groove and thus may have a profound effect on TCR interactions. Moreover, these results may have important implications in designing modifications in peptides for cancer immunotherapy, because most such peptides studied are of low affinity.

Induction of Tumor-Reactive CTL by C-Side Chain Variants of the CTL Epitope HER-2/neu Protooncogene (369-377) Selected by Molecular Modeling of the Peptide: HLA-A2 Complex

To design side chain variants for modulation of immunogenicity, we modeled the complex of the HLA-A2 molecule with an immunodominant peptide, E75, from the HER-2/neu protooncogene protein recognized by CTL. We identified the side chain orientation of E75. We modified E75 at the central Ser(5) (E75 wild-type), which points upward, by removing successively the HO (variant S5A) and the CH2-OH (variant S5G). Replacement of the OH with an aminopropyl (CH2)3-NH3 (variant S5K) maintained a similar upward orientation of the side chain. S5A and S5G were stronger stimulators while S5K was a weaker stimulator than E75 for induction of lytic function, indicating that the OH group and its extension hindered TCR activation. S5K-CTL survived longer than did CTL induced by E75 and the variants S5A and S5G, which became apoptotic after restimulation with the inducer. S5K-CTL also recognized E75 endogenously presented by the tumor by IFN-gamma production and specific cytolysis. S5K-CTL expanded at stimulation with E75 or with E75 plus agonistic anti-Fas mAb. Compared with S5K-CTL that had been restimulated with the inducer S5K, S5K-CTL stimulated with wild-type E75 expressed higher levels of E75(+) TCR and BCL-2. Activation of human tumor-reactive CTL by weaker agonists than the nominal Ag, followed by expansion with the nominal Ag, is a novel approach to antitumor CTL development. Fine tuning of activation of tumor-reactive CTL by weak agonists, designed by molecular modeling, may circumvent cell death or tolerization induced by tumor Ag, and thus, may provide a novel approach to the rational design of human cancer vaccines.

Fas ligand breaks tolerance to self-antigens and induces tumor immunity mediated by antibodies

The role of Fas ligand (FasL) in programmed cell death via interaction with its receptor Fas is well characterized. It has been proposed that expression of FasL can confer immune privilege to some organs, allowing them to kill infiltrating lymphocytes and inflammatory cells. However, a number of studies have shown that when tumors or transplants express FasL, rejection often occurs as a consequence of proinflammatory functions of FasL. Here we demonstrate that FasL elicits tumor immunity in a murine melanoma model with weak immunogenicity and low expression of major histocompatibility complex (MHC) class I. We show that protected mice recognize melanocyte differentiation self-antigens. Importantly, tumor immunity is mediated by antibodies, as it can be transferred by serum from protected mice.

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.

Identification of a human telomerase reverse transcriptase peptide of low affinity for HLA A2.1 that induces cytotoxic T lymphocytes and mediates lysis of tumor cells

Telomerase reverse transcriptase (TRT) is a tumor-associated antigen expressed in the vast majority of human tumors and is presently one of the most promising target candidates for a therapeutic cancer vaccine. TRT is also expressed at low level in selected tissues and should be considered a self antigen. In the present study we sought to develop cytotoxic T lymphocytes (CTL) responses directed against human (h)TRT peptides with low relative affinity for which the available repertoire is to be preferentially spared from tolerance. This was accomplished by using analogue peptides of hTRT whose relative affinity for the MHC was increased by a targeted (-->Tyr) substitution in position one. By immunizing HLA A2.1 transgenic mice with these analogue peptides, we identified one such low relative affinity peptide (p572) that is endogenously processed and presented by HLA A2.1 in tumor cells, and is recognized by specific CTL. We used the highly immunogenic analogue peptide to successfully induce TRT-specific CTL in cancer patients and normal donors. CTL against p572-lysed human and mouse tumor cells but not activated autologous B cells. This peptide represents, therefore, an important candidate component of a cancer vaccine based on a TRT substrate and validates the strategy of targeting peptides with low affinity for the MHC for cancer immunotherapy.

Non-myeloablative transplants for congenital diseases

The morbidity and mortality associated with postnatal HSCT, toxicity of HSCT conditioning regimens, lifelong immunosuppressive therapy, and lack of compatible donors discourages many patients and physicians from utilizing postnatal HSCT as a treatment for congenital disease. Non-myeloblative in utero HSCT is now being considered as an alternate treatment with the hope that it will be more therapeutic with less toxicity to a wider spectrum of patients with congenital disorders. Prenatal stem cell transfer may eliminate many of the risks and hazards associated with postnatal HSCT, as the fetus may be less reactive than an immunologically mature individual such that tolerance to donor cells could be developed. GVHD and rejection of postnatal therapeutic grafts may be minimized thus reducing or eliminating altogether the need for postnatal myeloablation and immunosuppression. Much work must be done both in animal studies as well as in clinical trials. By using well-designed murine models such as the beta-thalassemic mouse outlined above, we believe we can determine the optimal conditions for non-myeloablative postnatal transplants with allogeneic or haplocompatible HSC following prenatal tolerance induction with these cells. In addition, we may answer basic immunology questions regarding the development and regulation of immunity and tolerance in both mice and humans.

Amino acid modifications in the wild type sequence p53 232-240 overcome the poor immunogenicity of this self tumour epitope

A major limitation in antigen-specific cancer vaccines is that most of the tumour antigens that are potent candidates for broad applicability originate from self proteins. The peptides presented by tumour cells are derived from tissue-specific differentiation proteins, from proteins altered by genetic mutation or by non mutated proteins that are normally silent in most adult tissues. As a consequence, T-cell responses elicited against those antigens are rather weak. Several data showed that amino acid modifications could enhance the immunogenicity of such antigens by priming T-cells that have escaped central tolerance based on a poor avidity. In this regard, this strategy could be powerful for inducing immunity against tumours. The present report focuses on the murine wild type epitope p53 232-240 that is poorly immunogenic. It shows that substitution of the two cysteine residues by serine or amino butyric acid derivatives and substitution of the two methionine residues by norleucine residues resulted in enhanced stability of the MHC/peptide complex. The MHC binding affinity of analogue peptides was enhanced between 10 and 100 fold. They were also potent immunogens, stronger than was the original wild type epitope; T-cell responses were increased up to 50 times. Moreover, the effector T-cells elicited by three of these peptides cross reacted with the natural epitope. These observations have important implications for strategies that use the modified-peptide epitope.

HER-2/neu and hTERT cryptic epitopes as novel targets for broad spectrum tumor immunotherapy

Tolerance to tumor-nonmutated self proteins represents a major obstacle for successful cancer immunotherapy. Since this tolerance primarily concerns dominant epitopes, we hypothesized that targeting cryptic epitopes that have a low affinity for HLA could be an efficient strategy to breach the tolerance to tumor Ags. Using the P1Y heteroclitic peptide approach, we identified low affinity cryptic HLA-A*0201-restricted epitopes derived from two widely expressed tumor Ags, HER-2/neu and hTERT. The P1Y variants of four HER-2/neu (neu(391), neu(402), neu(466), neu(650))- and two hTERT (hTERT(572) and hTERT(988))-derived low affinity peptides exhibited strong affinity for HLA-A*0201 and stimulated specific CTL from healthy donor PBMCs. These CTL specifically recognized HER-2/neu- and hTERT-expressing tumor cells of various histological origins. In vivo studies showed that HLA-A*0201 transgenic HHD mice vaccinated with the P1Y variant peptides generated CTL that specifically lysed Ag-expressing tumor cells, thus recognizing the cognate endogenous Ags. These results suggest that heteroclitic variants of low affinity, cryptic epitopes of widely expressed tumor Ags may serve as valid tools for tumor immunotherapy.

Lymphotactin cotransfection enhances the therapeutic efficacy of dendritic cells genetically modified with melanoma antigen gp100

Lymphotactin (Lptn) is a C chemokine that attracts T cells and NK cells. Dendritic cells (DC) are highly efficient, specialized antigen-presenting cells and antigen-pulsed DC has been regarded as promising vaccines in cancer immunotherapy. The aim of our present study is to improve the therapeutic efficacy of DC-based tumor vaccine by increasing the preferential chemotaxis of DC to T cells. In this study, Lptn and/or melanoma-associated antigen gp100 were transfected into mouse bone marrow-derived DC, which were used as vaccines in B16 melanoma model. Immunization of C57BL/6 mice with DC adenovirally cotransfected with Lptn and gp100 (Lptn/gp100-DC) could enhance the cytotoxicities of CTL and NK cells, increase the production of IL-2 and interferon-gamma significantly, as compared with immunization with gp100-DC, Lptn-DC, LacZ-DC, DC or PBS counterparts. The Lptn/gp100-DC immunized mice exhibited resistance to tumor challenge most effectively. It was found that the tumor mass of mice vaccinated by Lptn/gp100-DC showed obvious necrosis and inflammatory cell infiltration. In vivo depletion analysis demonstrated that CD8(+) T cells are the predominant T cell subset responsible for the antitumor effect of Lptn/gp100-DC and CD4(+) T cells were necessary in the induction phase of tumor rejection, while NK cells were less important although they participated in the antitumor response either in the induction phase or in the effector phase. In the murine model with the pre-established subcutaneous B16 melanoma, immunization with Lptn/gp100-DC inhibited the tumor growth most significantly when compared with other counterparts. These findings provide a potential strategy to improve the efficacy of DC-based tumor vaccines.

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.

The potential of DNA vaccination against tumor-associated antigens for antitumor therapy

Conventional treatment approaches for malignant tumors are highly invasive and sometimes have only a palliative effect. Therefore, there is an increasing demand to develop novel, more efficient treatment options. Increased efforts have been made to apply immunomodulatory strategies in antitumor treatment. In recent years, immunizations with naked plasmid DNA encoding tumor-associated antigens have revealed a number of advantages. By DNA vaccination, antigen-specific cellular as well as humoral immune responses can be generated. The induction of specific immune responses directed against antigens expressed in tumor cells and displayed e.g., by MHC class I complexes can inhibit tumor growth and lead to tumor rejection. The improvement of vaccine efficacy has become a critical goal in the development of DNA vaccination as antitumor therapy. The use of different DNA delivery techniques and coadministration of adjuvants including cytokine genes may influence the pattern of specific immune responses induced. This brief review describes recent developments to optimize DNA vaccination against tumor-associated antigens. The prerequisite for a successful antitumor vaccination is breaking tolerance to tumor-associated antigens, which represent "self-antigens." Currently, immunization with xenogeneic DNA to induce immune responses against self-molecules is under intensive investigation. Tumor cells can develop immune escape mechanisms by generation of antigen loss variants, therefore, it may be necessary that DNA vaccines contain more than one tumor antigen. Polyimmunization with a mixture of tumor-associated antigen genes may have a synergistic effect in tumor treatment. The identification of tumor antigens that may serve as targets for DNA immunization has proceeded rapidly. Preclinical studies in animal models are promising that DNA immunization is a potent strategy for mediating antitumor effects in vivo. Thus, DNA vaccines may offer a novel treatment for tumor patients. DNA vaccines may also be useful in the prevention of tumors with genetic predisposition. By DNA vaccination preventing infections, the development of viral-induced tumors may be avoided.

Unexpected induction of unresponsiveness by vaccination with transformed Salmonella typhimurium

Rats vaccinated with attenuated Salmonella typhimurium transformed with a vector containing the v2 exon of CD44 (SL-v2) were not protected and developed thymic metastases at a high rate. This was surprising because there was evidence for concomitant induction of a CD44v2-specific helper and cytotoxic T-cell response. The inefficacy of vaccination was partly caused by tumor escape and tumor-induced immunosuppression. More important were the facts that (i) BSpl2v2 cells migrated from the intraperitoneal implantation site to the thymus and (ii) after vaccination with transformed attenuated Salmonella typhimurium, a small number of dendritic cells, which had transcribed the cDNA insert, were detected in the thymus. In the thymic environment, these v2 presenting dendritic cells, as well as the BSp12v2 tumor cells, supported tolerance induction. Thus, vaccination with tumor-associated differentiation antigens, which in many instances have induced antitumor response, may deteriorate survival time and rate if vaccination is accompanied by presentation of the antigen during intrathymic T-cell selection.

Assumptions of the tumor 'escape' hypothesis

The reasons why cancer cells are not destroyed by the immune system are likely to be similar, in most cases, to the reasons why normal cells are not destroyed by the immune system. Unfortunately for tumor immunologists, these reasons have not yet been fully elucidated. What is known, however, is that the lack of autoimmune destruction of normal tissue after immune activation is a finely regulated, highly orchestrated sequence of events. Viewed in this light, it is interesting to conceptualize the derangement of the tumor genome not merely as an engine that enables cancer cells to dodge immune recognition. The dysregulation characteristic of the transformed genome is also what makes tumor immunity, a specialized form of autoimmunity, possible.

Can the low-avidity self-specific T cell repertoire be exploited for tumor rejection?

Can self-specific T cells that have escaped intrathymic deletion be exploited to generate antitumor immunity? To determine whether antitumor immunity to a self-Ag for which central tolerance exists can be generated, a mouse model is used in which a fragment of the influenza nucleoprotein (NP) is expressed as a transgene under the control of the H-2K promoter in C57BL/10 mice (B10NP mice). In these mice an oligoclonal population of NP-specific T cells escapes thymic and peripheral deletion and can be activated upon immunization. The main hallmark of these self-specific CD8(+) T cells is diminished avidity for the pertinent MHC/peptide complex. We show in this study that intranasal infection with influenza virus can stimulate low-avidity NP-specific T cells to recognize and destroy NP-expressing microtumors in the lung, but not NP-expressing tumors growing s.c. Only a memory NP-specific CD8(+) T cell response can suppress the growth of an s.c. growing NP-expressing tumor. This delay in tumor growth is associated with a dramatic increase in the number of circulating NP-specific CD8(+) T cells. In addition, cultured memory NP-specific T cells require approximately 100-fold less Ag to induce NP-specific lysis than primary T cells, consistent with the observation that memory T cells have an increased avidity due to affinity maturation. Finally, during an NP-specific memory response, substantial numbers of low-avidity NP-specific T cells can be recovered from s.c. growing tumors. Together, these findings indicate that, when only a low-avidity repertoire is available to generate antitumor immunity, the best strategy may be to enhance memory responses.

The efficacy of genetic vaccination is dependent upon the nature of the vector system and antigen

Genetic immunisation is emerging as a safe and specific means of eliciting prophylactic and therapeutic immune responses. Just as the immune response to various infectious agents will differ based on the aetiology of the infection and nature of antigenic determinants, so does the immune response following genetic immunisation. This review will discuss the impact of vector selection and antigen structure on genetic immunisation. Comparative analyses of plasmid DNA (pDNA), adenovirus (Ad) and vaccinia virus vaccines have demonstrated that each vector system is associated with a unique outcome following immunisation. Similarly, re-targeting cytosolic protein to different cellular compartments can dramatically affect the subsequent immune response. Thus, to design an effective genetic vaccine, one must consider both the biology of the vaccine vector/antigen combination and the biology of the pathogen.

Dendritic cell-based xenoantigen vaccination for prostate cancer immunotherapy

Many tumor-associated Ags represent tissue differentiation Ags that are poorly immunogenic. Their weak immunogenicity may be due to immune tolerance to self-Ags. Prostatic acid phosphatase (PAP) is just such an Ag that is expressed by both normal and malignant prostate tissue. We have previously demonstrated that PAP can be immunogenic in a rodent model. However, generation of prostate-specific autoimmunity was seen only when a xenogeneic homolog of PAP was used as the immunogen. To explore the potential role of xenoantigen immunization in cancer patients, we performed a phase I clinical trial using dendritic cells pulsed with recombinant mouse PAP as a tumor vaccine. Twenty-one patients with metastatic prostate cancer received two monthly vaccinations of xenoantigen-loaded dendritic cells with minimal treatment-associated side effects. All patients developed T cell immunity to mouse PAP following immunization. Eleven of the 21 patients also developed T cell proliferative responses to the homologous self-Ag. These responses were associated with Ag-specific IFN-gamma and/or TNF-alpha secretion, but not IL-4, consistent with induction of Th1 immunity. Finally, 6 of 21 patients had clinical stabilization of their previously progressing prostate cancer. All six of these patients developed T cell immunity to human PAP following vaccination. These results demonstrate that xenoantigen immunization can break tolerance to a self-Ag in humans, resulting in a clinically significant antitumor effect.

Mining the melanosome for tumor vaccine targets: P.polypeptide is a novel tumor-associated antigen

To identify novel, tumor-specific target antigens for vaccine development, we studied immune responses to P.polypeptide, an M(r) 110,000 integral melanosomal membrane protein associated with the Prader-Willi syndrome. Together with expressed sequence tag (EST) and serial analyses of gene expression (SAGE) library analyses, reverse transcription-PCR and Northern blotting verified that P.polypeptide expression was limited to melanoma and melanocytes. A single dominant epitope corresponding to positions 427-435 (IMLCLIAAV) was identified using allele-specific epitope forecasting combined with work in HLA-A*0201/K(b) transgenic mice. This epitope was then used to generate de novo human P.polypeptide-specific CD8+ T cells capable of recognizing P.polypeptide expressing human tumor cell lines in an HLA-A*0201-restricted fashion. Thus, P.polypeptide may be valuable in the creation of novel therapeutic anticancer vaccines.

Manipulation of avidity to improve effectiveness of adoptively transferred CD8(+) T cells for melanoma immunotherapy in human MHC class I-transgenic mice

The adoptive transfer of tumor-reactive CD8(+) T cells into tumor-bearing hosts provides an attractive alternative to vaccination-based active immunotherapy of melanoma. The development of techniques that result in the preferential expansion of tumor-reactive T cells is therefore of great importance. In this study, we report the generation of HLA-A*0201-restricted CD8(+) T cell populations that recognize either tyrosinase(369-376) or gp100(209-217) from tolerant human class I MHC-transgenic mice by using single amino acid-substituted variant peptides. Low peptide concentration or restimulation with the parent peptide was used to enhance the functional avidity, defined by stimulation of IFN-gamma accumulation, and cross-reactivity of the resulting T cell populations. We found a direct correlation between the ability of a T cell population to respond in vitro to low concentrations of the precise peptide expressed on the tumor and its ability to delay the outgrowth of B16 melanoma after adoptive transfer. Surprisingly, we found that some T cells that exhibited high functional avidity and were effective in controlling tumor outgrowth exhibited low structural avidity, as judged by MHC-tetramer staining. Our results establish strategies for the development and selection of CD8(+) T cell populations that persist despite peripheral tolerance, and that can control melanoma outgrowth. Furthermore, they support the use of human MHC class I-transgenic mice as a preclinical model for developing effective immunotherapies that can be rapidly extended into therapeutic settings.

Immune responses to the HLA-A*0201-restricted epitopes of tyrosinase and glycoprotein 100 enable control of melanoma outgrowth in HLA-A*0201-transgenic mice

Many of the Ags recognized by human melanoma-reactive CTL are derived from proteins that are also expressed in melanocytes. The possibility of self-tolerance to these epitopes has led to questions about their utility for antitumor immunotherapy. To investigate the issue, we established a preclinical model based on transgenic mice expressing a recombinant HLA-A*0201 molecule and B16 melanoma transfected to express this molecule. HLA-A*0201-restricted epitopes from the melanocyte differentiation proteins (MDP) tyrosinase and gp100 are expressed in both tumor cells and melanocytes, and the former is associated with self-tolerance. However, adoptive transfer of tyrosinase or gp100-reactive CTL developed from tolerant mice delayed tumor outgrowth, as did immunization with MDP peptide-pulsed dendritic cells. Protection was enhanced by the use of peptide ligands containing conservative substitutions that were cross-reactive with the original Ags. These data establish that CTL populations reactive against MDP-derived self-Ags can be activated to mount effective antitumor immunity and strongly support their continued development for tumor immunotherapy in humans.

Low-avidity self-specific T cells display a pronounced expansion defect that can be overcome by altered peptide ligands

Thymic expression of self-Ags results in the deletion of high-avidity self-specific T cells, but, at least for certain Ags, a residual population of self-specific T cells with low-affinity TCRs remains after negative selection. Such self-specific T cells are thought to play a role in the induction of T cell-mediated autoimmunity, but may also be used for the induction of antitumor immunity against self-Ags. In this study, we examine the functional competence of a polyclonal population of self-specific CD8+ T cells. We show that low-affinity interactions between TCR and peptide are associated with selective loss of critical T cell functions. Triggering of low levels of IFN-gamma production and cytolytic activity through low-affinity TCRs readily occurs provided high Ag doses are used, but IL-2 production and clonal expansion are severely reduced at all Ag doses. Remarkably, a single peptide variant can form an improved ligand for the highly diverse population of low-avidity self-specific T cells and can improve their proliferative capacity. These data provide insight into the inherent limitations of self-specific T cell responses through low-avidity TCR signals and the effect of modified peptide ligands on self-specific T cell immunity.

Processing and presentation of antigens by dendritic cells: implications for vaccines

Dendritic cells (DCs) are potent antigen-presenting cells that are specialized in initiation of T-cell immunity. DCs induce promising anti-tumor T-cell and clinical responses, apparently without significant toxicity. Under certain conditions, DCs even silence T-cell immune responses in vivo. This dual capacity to modulate the immune system uniquely positions DCs for the treatment of autoimmunity, cancer and chronic viral infections.

Evidence of the extrathymic development of tyrosinase-related protein-2-recognizing CD8+ T cells with low avidity

The majority of the human tumour-associated antigens characterized to date are derived from non-mutated self-proteins. However, nothing is known about the development of autoreactive and tumour-associated antigen-recognizing T cells. Tyrosinase-related protein (TRP)-2 is a non-mutated melanocyte differentiation antigen and TRP-2-recognizing CD8+ T cells are known to show responses to melanoma both in humans and mice. In addition, TRP-2-reactive T cells with low avidity have been suggested to be readily induced from the spleen cells of naïve mice. On the other hand, recent reports suggest that self antigen-reactive CD8+ T cells can be positively selected in the periphery. In this study, we tested the possibility that TRP-2-reactive CD8+ T cells in naïve mice could develop via the extrathymic pathway. As a consequence, TRP-2-reactive CD8+ T cell precursors in naïve C57BL/6 mice were suggested to express both interleukin-2 (IL-2) receptor beta chain (IL-2Rbeta) and CD44 molecules, in a manner similar to that of extrathymically developed T cells. Furthermore, IL-2Rbeta+ CD44+ CD8+ T cells were detected in the adult thymectomized and bone marrow-reconstituted mice, and functional TRP-2-reactive T cells were generated from their spleen cells. Overall, these results suggest that low avidity CD8+ T cells recognizing TRP-2 can be developed extrathymically.

Elucidating the autoimmune and antitumor effector mechanisms of a treatment based on cytotoxic T lymphocyte antigen-4 blockade in combination with a B16 melanoma vaccine: comparison of prophylaxis and therapy

We have previously shown that small B16 melanomas can be successfully treated using a combination of anti-cytotoxic T lymphocyte antigen (CTLA)-4 monoclonal antibody with a granulocyte/macrophage colony-stimulating factor (GM-CSF) producing irradiated tumor cell vaccine. Regression of tumors results in long-lasting immunity and is frequently accompanied by autoimmune depigmentation. Here we examine the cellular and molecular mechanisms of this combined treatment. Histological examination of depigmented lesions revealed infiltration of polymorphonuclear cells and deposition of antibody. The combination therapy also induced tumor rejection and skin depigmentation in B cell-deficient and in CD4(+) T cell-depleted mice. Both effects of the treatment absolutely required CD8(+) T cells. Analysis of the response in successfully treated mice revealed elevated levels of CD8(+) T cells specific for a nonameric peptide consisting of residues 180-188 of the melanocyte differentiation antigen tyrosinase-related protein (TRP)2. There was no evidence of reactivity to the melanocyte antigens gp100, tyrosinase, Mart1/MelanA, or TRP1. Fas-FasL interactions and perforin played a role in mounting the effector response, whereas the tumor necrosis factor pathway was not required. The cellular requirements for tumor rejection in this therapeutic setting were strikingly different from those in a prophylactic setting. In particular, if mice received a prophylactic vaccine consisting of anti-CTLA-4 and B16-GM-CSF before tumor challenge, full protection was obtained even in the absence of CD8(+) T cells. Our data demonstrate that therapeutic autoreactive CD8(+) T cell responses can effectively be generated in tumor-bearing mice and stresses the value of studying tumor immunity in a therapeutic rather than a prophylactic setting.

Gene delivery by attenuated Salmonella typhimurium: comparing the efficacy of helper versus cytotoxic T cell priming in tumor vaccination

Using the murine B16F1 melanoma, we compared a CTL- versus helper T cell (TH)-directed vaccination approach. Mice were either orally vaccinated with attenuated Salmonella typhimurium (SL) or subcutaneously with dendritic cells (DCs) loaded with gp100 peptides predicted to bind to H2-Kb/H2-Db molecules. SL were transformed with the murine gp100 cDNA (SL-gp100) or with a fusion construct of gp100 and a fragment of invariant chain cDNA (SL-gp100/Ii). Transcription of these genes in vivo has been readily observed in monocytes and DC. Retardation of B16F1 growth was more efficiently achieved by vaccination with SL-gp100 than with DC. Vaccination with SL-gp100/Ii aiming at preferential presentation by MHC II molecules provided some further improvement due to a stronger expansion of TH and CTL. The importance of help was further sustained by a prolongation of the survival time when mice concomitantly received IL2. Notably, prophylactic, compared to therapeutic, vaccination had no additional impact on survival time/rate. This was due to a striking decrease in frequencies of gp100-specific TH, CTL, and cytokine-expressing cells during tumor growth. Thus, the efficacy of vaccination was limited by tumor-induced immunosuppression. Our data demonstrate the oral route of vaccination via Salmonella as a most convenient transfer regimen and confirm the superiority of protocols aiming at preferential activation of TH.

Dendritic cells: immunological features and utilisation for tumour immunotherapy

The prospect of developing 'magic bullets' to attack tumour cells has been a goal of biologists for decades. Abundant experimental and clinical observations demonstrating that an effective specific immune response may engender tumour regression has prompted efforts to find an immunotherapeutic approach to this problem. The most important arm of cellular immunity for such responses appears to be cytotoxic T-lymphocytes (CTL) which can recognise antigen on virtually all cell types and which are key to the elimination of virally-infected cells. The specific activation and maintenance of activity of these cells is therefore the major goal of designing a therapeutic cancer vaccine. Advances in our understanding of the role of dendritic cells (DC) in priming and modifying immune responses suggest that they should be potent adjuvants for vaccination. The use of antigens targeted to the major histocompatibility complex (MHC) molecules expressed on these cells as an approach to tumour immunotherapy has already been tested in the treatment of many malignancies, and recent findings shed light on additional directions through which their efficacy may be improved.

Class I major histocompatibility complex anchor substitutions alter the conformation of T cell receptor contacts

An immunogenic peptide (GP2) derived from HER-2/neu binds to HLA-A2.1 very poorly. Some altered-peptide ligands (APL) of GP2 have increased binding affinity and generate improved cytotoxic T lymphocyte recognition of GP2-presenting tumor cells, but most do not. Increases in binding affinity of single-substitution APL are not additive in double-substitution APL. A common first assumption about peptide binding to class I major histocompatibility complex is that each residue binds independently. In addition, immunologists interested in immunotherapy frequently assume that anchor substitutions do not affect T cell receptor contact residues. However, the crystal structures of two GP2 APL show that the central residues change position depending on the identity of the anchor residue(s). Thus, it is clear that subtle changes in the identity of anchor residues may have significant effects on the positions of the T cell receptor contact residues.

The Role of Adoptively Transferred CD8 T Cells and Host Cells in the Control of the Growth of the EG7 Thymoma: Factors That Determine the Relative Effectiveness and Homing Properties of Tc1 and Tc2 Effectors

We had previously examined the factors that regulate the response of OVA-specific TCR-transgenic CD8 T cells to the B16 OVA melanoma, growing as lung metastases. We examine here whether the same parameters operate for EG7, growing intradermally. Tc1 or Tc2 CD8 effector cells from OT-1 mice were injected either mixed with the tumor or i.v. at day 0 or 7. Tc2 were one-fifth to one-tenth as effective as Tc1 when injected with the tumor, in controlling tumor growth, but were only 1/20 to 1/100 injected i.v. Tc1 injected i.v. entered the draining lymph nodes faster than Tc2 and caused a faster accumulation of host cells. Both caused an abrupt termination of host cell entry into lymph nodes and spleen after tumor elimination, but this occurred earlier for Tc1 than for Tc2. Host responses were ineffective in the absence of adoptive transfer but were essential after transfer. Perforin expression in the donor cells plays no role in adoptively transferred Tc1 or Tc2 control of the tumor, and neither IL-4 nor IL5 is needed for Tc1 or Tc2 function. Tc1 cells from mice lacking IFN-gamma, however, control tumor growth less well, whereas Tc2 effectors lacking IFN-gamma are unaffected. Tc1 from IFN-gamma-deficient mice attract fewer host cells to the draining lymph node, whereas Tc1 cells from perforin-deficient donors are unimpaired. We conclude that host cell recruitment is a crucial element in adoptive immunotherapy. The differences between the EG7 and the previous B16 melanoma model are discussed.

B16 as a mouse model for human melanoma

This unit details protocols for in vivo models of subcutaneous growth and pulmonary metastases of B16 melanoma. Therapeutic approaches include the use of B16.GM-CSF and rVVmTRP-1 to induce autoimmune vitiligo and tumor protection. The induction and use of gp 100-specific therapeutic cytotoxic T lymphocytes (CTL) are discussed. Methods are also included for CTL induction, isolation and testing, CTL maintenance, and adoptive transfer. Support protocols detail the testing of mouse sera for presence of MDA-specific antibodies by immunoblotting and ELISA, respectively. Additional sections, including growing B16 melanoma, enumerating pulmonary metastases, and use of recombinant viruses for vaccination, are discussed together with safety concerns.

Immunity against cancer: lessons learned from melanoma

Most major advances in human cancer immunology and immunotherapy have come from studies in melanoma. We are beginning to understand the immune repertoire of T cells and antibodies that are active against melanoma, with recent glimpses of the CD4(+) T cell repertoire. The view of what the immune system can see is extending to mutations and parts of the genome that are normally invisible.