Role of dendritic cell phenotype, determinant spreading, and negative costimulatory blockade in dendritic cell-based melanoma immunotherapy

MART-1(27-35)-peptide-pulsed immature dendritic cells (DCs) resulted in immunologic and clinical activity in a prior phase 1 trial. A phase 2 cohort expansion was initiated to further characterize the phenotype and cytokine milieu of the DC vaccines and their immunologic activity in vitro and to further examine a possible link between clinical activity and determinant spreading. In an open-label phase 2 trial, 10(7) autologous ex vivo generated DCs pulsed with the HLA-A*0201 immunodominant peptide MART-1(27-35) were administered to 10 subjects with stage II-IV melanoma. The experimental vaccines were administered intradermally in a biweekly schedule for a total of three injections, and blood for immunologic assays was obtained before each administration and at three time points after. DC vaccine preparations had wide intra- and interpatient variability in terms of cell surface markers and preferential cytokine milieu, but they did not correlate with the levels of antigen-specific T cells after vaccination. Of four patients with measurable disease, one had stable disease for 6 months and another has a continued complete response for over 2 years, which is confounded by receiving a closely sequenced CTLA4 blocking antibody. The DC vaccines induced determinant spreading in this subject, and CTLA4 blockade reactivated T cells with prior antigen exposure. The DC phenotype and cytokine profile do not correlate with the ability to induce antigen-specific T cells, while determinant spreading after DC immunization may be a marker of an efficient antitumor response. Sequential CTLA4 blockade may enhance the immune activity of DC-based immunotherapy.

Antigen presentation by MART-1 adenovirus-transduced interleukin-10-polarized human monocyte-derived dendritic cells

Dendritic cells (DC) play critical roles in generating an immune response and in inducing tolerance. Diverse microenvironmental factors can 'polarize' DC toward an immunogenic or non-immunogenic phenotype. Among the various microenvironmental factors, interleukin-10 (IL-10) exhibits a potent immunosuppressive effect on antigen-presenting cells (APC). Here, we show that monocyte-derived DC generated in the presence of IL-10 exhibit a profound down-regulation of many genes that are associated with immune activation and show that the IL-10-grown DC are poor stimulators of CD8(+) T cells in a strictly autologous and major histocompatibility complex (MHC) class I-restricted melanoma antigen recognized by T cells (MART-1) epitope presentation system. However, these IL-10-grown DC can efficiently activate the epitope-specific CD8(+) T cells when they are made to present the epitope following transduction with an adenoviral vector expressing the MART-1 antigen. In addition, we show that the MART-1 protein colocalizes with the MHC class I protein, equally well, in the iDC and in the DC cultured in presence of IL-10 when both DC types are infected with the viral vector. We also show that the vector transduced DC present the MART-1(27-35) epitope for a sustained period compared to the peptide pulsed DC. These data suggest that although DCs generated in the presence of IL-10 tend to be non-immunogenic, they are capable of processing and presenting an antigen when the antigen is synthesized within the DC.

Immunotherapeutic strategies for hepatocellular carcinoma

There is a continuing need for innovative, alternative therapies for hepatocellular carcinoma (HCC). Immunotherapy for cancer is attractive because of the exquisite specificity of the immune response. Activation of an HCC-specific response can be accomplished by strategies targeting tumor-associated self-antigens (for example, alpha-fetoprotein [AFP]). Gene array studies have added to the list of HCC-specific gene products that can be targeted. Alternatively, the immune response can be targeted against viral antigens in those patients infected with hepatitis B or C virus. Uncharacterized and mutated antigens can also be targeted with whole tumor cell or tumor lysate-based immunization strategies or with vectors coding for genes that make the tumor immunogenic, allowing the immune system to naturally evolve specificity against immunogenic target antigens. Strategies being investigated in animal models include increasing tumor immunogenicity by targeting cytokines or costimulatory molecules to tumor; immunization with tumor cells fused with antigen-presenting cells; adoptive transfer of viral antigen-specific T cells; and targeting AFP-expressing HCC cells by DNA, adenovirus, peptide, and dendritic cell (DC) strategies. Strategies that have been tested in human clinical trials include adoptive transfer of lymphocytes and autologous tumor-pulsed DC as well as 2 AFP-based strategies: AFP-derived peptides in Montanide and AFP peptides pulsed onto autologous DC. These trials, testing novel immune-based interventions in HCC subjects, have resulted in immunologic responses and have impacted recurrence and survival in HCC subjects.

Ionizing radiation affects human MART-1 melanoma antigen processing and presentation by dendritic cells

Radiation is generally considered to be an immunosuppressive agent that acts by killing radiosensitive lymphocytes. In this study, we demonstrate the noncytotoxic effects of ionizing radiation on MHC class I Ag presentation by bone marrow-derived dendritic cells (DCs) that have divergent consequences depending upon whether peptides are endogenously processed and loaded onto MHC class I molecules or are added exogenously. The endogenous pathway was examined using C57BL/6 murine DCs transduced with adenovirus to express the human melanoma/melanocyte Ag recognized by T cells (AdVMART1). Prior irradiation abrogated the ability of AdVMART1-transduced DCs to induce MART-1-specific T cell responses following their injection into mice. The ability of these same DCs to generate protective immunity against B16 melanoma, which expresses murine MART-1, was also abrogated by radiation. Failure of AdVMART1-transduced DCs to generate antitumor immunity following irradiation was not due to cytotoxicity or to radiation-induced block in DC maturation or loss in expression of MHC class I or costimulatory molecules. Expression of some of these molecules was affected, but because irradiation actually enhanced the ability of DCs to generate lymphocyte responses to the peptide MART-1(27-35) that is immunodominant in the context of HLA-A2.1, they were unlikely to be critical. The increase in lymphocyte reactivity generated by irradiated DCs pulsed with MART-1(27-35) also protected mice against growth of B16-A2/K(b) tumors in HLA-A2.1/K(b) transgenic mice. Taken together, these results suggest that radiation modulates MHC class I-mediated antitumor immunity by functionally affecting DC Ag presentation pathways.

Surveillance of the eye and vision in a clinical trial of MART1-transformed dendritic cells for metastatic melanoma

PURPOSE

To report the protocol for surveillance of the eye and vision in a clinical trial of MART1-transduced dendritic cells for metastatic melanoma.

METHODS

In a phase I/II clinical trial of dendritic cell-based genetic immunotherapy for metastatic cutaneous melanoma, ophthalmic evaluation is performed prior to immunization (Baseline Evaluation), 56+/-7 days after first vaccination (mid-study evaluation), when dendritic cell injections are complete 112+/-7 days after first vaccination (end-study evaluation) and 168+/-7 days after first vaccination (post-study evaluation).

RESULTS

The protocol for baseline, mid-study and end-study evaluations of the eye and vision includes ophthalmic history, comprehensive ophthalmic examination, psychophysical and electrophysiological visual function assessment, fundus photography and fluorescein angiography. Post-study evaluation consists of the 25-item visual functioning questionnaire augmented to elicit autoimmune manifestation with complete ophthalmic evaluation if vision-related symptoms or abnormalities are noted during or after the vaccination.

CONCLUSION

Limited adverse effects on the eye and vision have been reported in melanoma immunotherapy trials, although this novel mode of therapy has the potential to induce melanoma paraneoplastic syndromes known to severely impair vision. Therefore, surveillance of the eye and vision should be considered in melanoma immunotherapy trials.

Enhanced tumor responses to dendritic cells in the absence of CD8-positive cells

Wild-type mice immunized with MART-1 melanoma Ag-engineered dendritic cells (DC) generate strong Ag-specific immunity that has an absolute requirement for both CD8(+) and CD4(+) T cells. DC administration to CD8 alpha knockout mice displayed unexpectedly enhanced levels of protection to tumor challenge despite this deficiency in CD8(+) T cells and the inability to mount MHC class I-restricted immune responses. This model has the following features: 1) antitumor protection is Ag independent; 2) had an absolute requirement for CD4(+) and NK1.1(+) cells; 3) CD4(+) splenocytes are responsible for cytokine production; 4) lytic cells in microcytotoxicity assays express NK, but lack T cell markers (NK1.1(+) alpha beta TCR(-) CD3(-)); and 5) the lytic phenotype can be transferred to naive CD8 alpha knockout mice by NK1.1(+) splenocytes. Elucidation of the signaling events that activate these effective cytotoxic cells and the putative suppressive mechanisms in a wild-type environment may provide means to enhance the clinical activity of DC-based approaches.

Human dendritic cell maturation by adenovirus transduction enhances tumor antigen-specific T-cell responses

Dendritic cells (DCs) have been shown to require a degree of maturation to stimulate antigen-specific, type 1 cytotoxic T lymphocytes in numerous murine models. Limited data in humans suggest that immature DCs (DC) can induce tolerance, yet a variety of nonmatured DC used clinically have induced antigen-specific type 1 T cells in vivo to various tumor-associated antigens. Use of adenovirus to engineer DCs is an efficient method for delivery of entire genes to DC, but the data on the biologic effects of viral transduction are contradictory. The authors demonstrate that DCs transduced with adenovirus (AdV) clearly become more mature by the phenotypic criterion of upregulation of CD83 and downregulation of CD14. Transduced DCs also decrease production of IL-10, and a subset of transduced DCs produce increased levels of IL-12 p70. This level of maturation is superior to that achieved by treatment of these cells with tumor necrosis factor-alpha or interferon-alpha but less pronounced than with CD40L trimer or CD40L + interferon-gamma. Maturation by AdV transduction alone leads to efficient stimulation of antigen-specific T cells from both healthy donors and patients with advanced cancer using two defined human tumor-associated antigens, MART-1 and AFP. Given the pivotal role of DCs in immune activation, it is important to understand the direct biologic effects of AdV on DCs, as well as the impact these biologic changes have on the stimulation of antigen-specific T cells. This study has important implications for the design of DC-based clinical trials.

T-cell responses to HLA-A*0201 immunodominant peptides derived from alpha-fetoprotein in patients with hepatocellular cancer

PURPOSE

An existing immunological paradigm is that high concentrations of soluble protein contribute to the maintenance of peripheral tolerance/ignorance to self protein. We tested this hypothesis in a clinical immunotherapy trial using class I-restricted peptide epitopes derived from alpha-fetoprotein (AFP). AFP is a self protein expressed by fetal liver at high levels, but transcriptionally repressed at birth. AFP is de-repressed in a majority of hepatocellular carcinomas (HCCs) and patients with active disease can have plasma levels in the mg/ml range. We previously identified four immunodominant HLA-A*0201-restricted peptides derived from human AFP that could stimulate specific T-cell responses in normal volunteer peripheral blood lymphocytes cultures. We wished to test the hypothesis that AFP peptide-reactive T cells could be expanded in vivo in HCC patients immunized with these four AFP peptides.

EXPERIMENTAL DESIGN

We undertook a pilot Phase I clinical trial in which HLA-A*0201 patients with AFP-positive HCC were immunized with three biweekly intradermal vaccinations of the four AFP peptides (100 microg or 500 microg each) emulsified in incomplete Freund's adjuvant.

RESULTS

All of the patients (n=6) generated T-cell responses to most or all of the peptides as measured by direct IFNgamma enzyme-linked immunospot (ELISPOT) and MHC class I tetramer assays.

CONCLUSIONS

We conclude that the human T-cell repertoire is capable of recognizing AFP in the context of MHC class I even in an environment of high circulating levels of this oncofetal protein.

Regulation of melanoma epitope-specific cytolytic T lymphocyte response by immature and activated dendritic cells, in vitro

Dendritic cell (DC)-based immunization in cancer has proven to be a promising approach. However, just as DCs are crucial accessory cells in generating immune responses, they also seem to participate in tolerance induction, especially against peripheral "self" antigens. The bulk of the evidence that DCs present peripheral self antigens to induce tolerance has, however, come mostly from studies in transgenic animal models. A tolerogenic function of DCs for peripheral self antigens in a human model has not been critically examined. In this study using the Melan-A/MART-1(27-35) peptide as a model for self but melanoma-associated antigen-against which human hosts often harbor CD8(+) CTL precursors with high frequencies-we confirm that although immature dendritic cells (iDCs) are inefficient antigen presenting cells (APCs), fully activated DCs efficiently activate melanoma epitope-specific CD8(+) CTL precursors, in vitro. We, however, show that in a direct epitope presentation schema, iDCs neither delete nor anergize epitope-specific CD8(+) T cells in primary or secondary stimulation. Interestingly, iDCs and activated DCs can delete a large fraction of the epitope-specific CTLs on tertiary stimulation. The deletion is induced in an epitope-specific manner and through apoptosis. These observations, therefore, have implications on the DC-based cancer vaccine designs and are relevant in the inquiry into the role of DCs on tolerance induction.

Current developments in cancer vaccines and cellular immunotherapy

This article reviews the immunologic basis of clinical trials that test means of tumor antigen recognition and immune activation, with the goal to provide the clinician with a mechanistic understanding of ongoing cancer vaccine and cellular immunotherapy clinical trials. Multiple novel immunotherapy strategies have reached the stage of testing in clinical trials that were accelerated by recent advances in the characterization of tumor antigens and by a more precise knowledge of the regulation of cell-mediated immune responses. The key steps in the generation of an immune response to cancer cells include loading of tumor antigens onto antigen-presenting cells in vitro or in vivo, presenting antigen in the appropriate immune stimulatory environment, activating cytotoxic lymphocytes, and blocking autoregulatory control mechanisms. This knowledge has opened the door to antigen-specific immunization for cancer using tumor-derived proteins or RNA, or synthetically generated peptide epitopes, RNA, or DNA. The critical step of antigen presentation has been facilitated by the coadministration of powerful immunologic adjuvants, the provision of costimulatory molecules and immune stimulatory cytokines, and the ability to culture dendritic cells. Advances in the understanding of the nature of tumor antigens and their optimal presentation, and in the regulatory mechanisms that govern the immune system, have provided multiple novel immunotherapy intervention strategies that are being tested in clinical trials.

Determinant spreading associated with clinical response in dendritic cell-based immunotherapy for malignant melanoma

PURPOSE

The purpose of this study was to determine the toxicity and immunological effects of three different doses and two routes of administration of autologous dendritic cells (DCs) pulsed with the MART-1(27-35) immunodominant epitope.

EXPERIMENTAL DESIGN

Eighteen HLA-A*0201-positive subjects with stage III-IV melanoma received three biweekly i.v. or intradermal injections of ex vivo generated myeloid DCs pulsed with MART-1(27-35) epitope. Repeated blood samples were processed to obtain peripheral blood mononuclear cells for immunological analysis using IFN-gamma ELISPOT, MHC class I tetramer, intracellular cytokine staining, and microcytotoxicity assays.

RESULTS

The frequency of MART-1/Melan-A (MART-1) antigen-specific T cells in peripheral blood increased in all dose levels as assessed by ELISPOT and MHC class I tetramer assays, but without a clear dose-response effect. The intradermal route generated stronger MART-1 immunity compared with the i.v. route. MART-1-specific immunity did not correlate with clinical outcome in any of the four immunological assays used. However, analysis of determinant spreading to other melanoma antigens was noted in the only subject with complete response to this single-epitope immunization.

CONCLUSIONS

Intradermal immunization with MART-1 peptide-pulsed DCs results in an increase in circulating IFN-gamma-producing, antigen-specific T cells. The frequency of these cells did not correlate with response. In contrast, spreading of immune reactivity to other melanoma antigens was only evident in a subject with a complete response, suggesting that determinant spreading may be an important factor of clinical response to this form of immunotherapy.

Determinant spreading and tumor responses after peptide-based cancer immunotherapy

Modern immunological assays are very sensitive for detection of antigen-specific T cells. These assays are used to detect increased levels of T cells after peptide-based immunotherapy for cancer in an attempt to describe surrogate endpoints correlated with anti-tumor activity. Recent reports demonstrate that determinant spreading develops in a high frequency of subjects with tumor regression responses after this type of immunotherapy and could be valuable for trial monitoring and the design of more effective vaccines.

Immunosuppressive effects of interleukin-12 coexpression in melanoma antigen gene-modified dendritic cell vaccines

Genetic immunotherapy with tumor antigen gene-modified dendritic cells (DC) generates robust immunity, although antitumor protection is not complete in all models. Previous experience in a model in which C57BL/6 mice immunized with DC transduced with adenoviral vectors expressing MART-1 demonstrated a 20-40% complete protection to a tumor challenge with B16 melanoma cells. Tumors that did develop in immunized mice had slower growth kinetics compared to tumors implanted in naïve mice. In the present study, we wished to determine if the supraphysiological production of the Th1-skewing cytokine interleukin-12 (IL-12) could enhance immune activation and antitumor protection in this model. In a series of experiments immunizing mice with DC cotransduced with MART-1 and IL-12, antitumor protection and antigen-specific splenocyte cytotoxicity and interferon gamma production inversely correlated with the amount of IL-12 produced by DC. This adverse effect of IL-12 could not be explained by a direct cytotoxic effect of natural killer cells directed towards DC, nor the production of nitric oxide leading to down-regulation of the immune response - the two mechanisms previously recognized to explain immune-suppressive effects of IL-12-based vaccine therapy. In conclusion, in this animal model, IL-12 production by gene-modified DC leads to a cytokine-induced dose-dependent inhibition of antigen-specific antitumor protection.

Rational design of peptide-based tumor vaccines

Administration of synthetic peptides derived from proteins uniquely or overexpressed in tumor cells (tumor-associated antigens) can elicit tumor-specific immune responses in vivo. This is because cytotoxic T lymphocytes can recognize and lyse tumor cells that display peptides derived from tumor-associated antigens (TAAs) in the context of class I major histocompatibility complex (MHC) molecules. TAA peptides, in contrast to peptides of viral origin, generally bind weakly to the MHC molecule. In many cases, this explains the poor magnitude of T cell response directed at the tumor in vivo. Improving MHC binding as a strategy to upregulate antigen recognition can convert low affinity TAA peptides into useful tools in clinical trial settings. High-resolution structures of class I MHC molecules reported over the past two decades provided the framework for designing peptides that can induce optimal T cell response. This review will discuss the basic and clinical aspects of modifying native TAA peptides as tumor vaccines.

Immunotherapy of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the third leading cause of cancer death, with over a million new cases annually. It is generally advanced upon detection due to underlying liver disease, which further complicates treatment. Most of the therapeutic strategies in current use (surgery, transplantation, irradiation or chemotherapy) are either palliative or only of benefit to a small percentage of patients. This article reviews the biology of HCC, including many of the molecular changes and mechanisms leading to HCC development. This article discusses the recent innovative strategies to interfere with the progression of HCC, including novel gene therapy strategies. The most recent data supporting the use of immunotherapy for hepatocellular cancer is reviewed in detail.

Cancer immunotherapy using gene-modified dendritic cells

Gene-engineered dendritic cells (DC) are being tested in cancer immunotherapy. DC are the best equipped antigen-presenting cells (APC) to overcome tolerance/ignorance to self antigens presented by cancer cells. Genetic immunotherapy with DC engineered to express tumor antigens has the potential advantages of endogenous epitope presentation by both major histocompatibility complex (MHC) class I and II molecules. DC can also be gene-modified to express immunostimulatory molecules that further enhance their antigen-presenting function. Review of the literature provided 52 manuscripts where gene-modified DC were being tested in murine models of immunotherapy for cancer. Review of the antitumor effects of gene-modified DC in these preclinical studies provides valuable information on the optimal methods of gene transfer into DC, the schedule of administration, the route, dose and the underlying immunological mechanisms of the antitumor effects. These data may help in the translation of this promising approach to the clinic.

alpha-Fetoprotein-specific tumor immunity induced by plasmid prime-adenovirus boost genetic vaccination

alpha-Fetoprotein (AFP) is a potential target for immunotherapy in hepatocellular carcinoma; both the murine and human T-cell repertoires can recognize AFP-derived epitopes in the context of the MHC. Protective immunity can be generated with AFP-engineered dendritic cell-based vaccines. We now report a DNA-based immunization strategy using a prime-boost approach: coadministration of plasmid DNA encoding murine AFP and murine granulocyte-macrophage colony-stimulating factor followed by boosting with an AFP-expressing nonreplicating adenoviral vector. This immunization strategy can elicit a high frequency of Th1-type AFP-specific cells leading to tumor protective immunity in mice at levels comparable with AFP-engineered dendritic cells. This cell-free mode of immunization is better suited for large-scale vaccine efforts for patients with hepatocellular carcinoma.

CD40 cross-linking bypasses the absolute requirement for CD4 T cells during immunization with melanoma antigen gene-modified dendritic cells

Genetic immunization of mice with dendritic cells (DCs) engineered to express a melanoma antigen generates antigen-specific, MHC-restricted, CD4-dependent protective immune responses. We wanted to determine the role of CD4 cells and CD40 ligation of MART-1 gene-modified DC in an animal model of immunotherapy for murine melanoma. CD4 knock-out (CD4KO) or antibody-depleted mice were immunized with DC adenovirally transduced with the MART-1 gene (AdVMART1/DC) with or without CD40 cross-linking. Tumor protection was absent in CD4-depleted mice, but protection was reestablished when the CD40 receptor was engaged using three different constructs. Transduction of DCs with vectors expressing the Th1 cytokines interleukin (IL)-2, IL-7, or IL-12 could not reproduce the CD40-mediated maturation signal in this model. CD8 T-cell depletion in CD4KO mice immunized with CD40-ligated DCs abrogated the protective response. Pooled analysis of CD40 cross-linking of AdVMART1/DC administered to wild-type C57BL/6 mice revealed an overall enhancement of antitumor immunity. However, this effect was inconsistent between replicate studies. In conclusion, maturation of AdVMART1-transduced DCs through the CD40 ligation pathway can promote a protective CD8 T-cell-mediated immunity that is independent of CD4 T-cell help.

T cell responses to HLA-A*0201-restricted peptides derived from human alpha fetoprotein

alpha fetoprotein (AFP)-derived peptide epitopes can be recognized by human T cells in the context of MHC class I. We determined the identity of AFP-derived peptides, presented in the context of HLA-A*0201, that could be recognized by the human (h) T cell repertoire. We screened 74 peptides and identified 3 new AFP epitopes, hAFP(137-145), hAFP(158-166), and hAFP(325-334), in addition to the previously reported hAFP(542-550.) Each possesses two anchor residues and stabilized HLA-A*0201 on T2 cells in a concentration-dependent class I binding assay. The peptides were stable for 2-4 h in an off-kinetics assay. Each peptide induced peptide-specific T cells in vitro from several normal HLA-A*0201 donors. Importantly, these hAFP peptide-specific T cells also were capable of recognizing HLA-A*0201(+)/AFP(+) tumor cells in both cytotoxicity assays and IFN-gamma enzyme-linked immunospot assays. The immunogenicity of each peptide was tested in vivo with HLA-A*0201/K(b)-transgenic mice. After immunization with each peptide emulsified in CFA, draining lymph node cells produced IFN-gamma on recognition of cells stably transfected with hAFP. Furthermore, AFP peptide-specific T cells could be identified in the spleens of mice immunized with dendritic cells transduced with an AFP-expressing adenovirus (AdVhAFP). Three of four AFP peptides could be identified by mass spectrometric analysis of surface peptides from an HLA-A*0201 human hepatocellular carcinoma (HCC) cell line. Thus, compelling immunological and physiochemical evidence is presented that at least four hAFP-derived epitopes are naturally processed and presented in the context of class I, are immunogenic, and represent potential targets for hepatocellular carcinoma immunotherapy.

Immunosensitization of melanoma tumor cells to non-MHC Fas-mediated killing by MART-1-specific CTL cultures

The discovery of human melanoma rejection Ags has allowed the rational design of immunotherapeutic strategies. One such Ag, MART-1, is expressed on >90% of human melanomas, and CTL generated against MART-1(27-35) kill most HLA A2.1(+) melanoma cells. However, variant tumor cells, which do not express MART-1, down-regulate MHC, or become resistant to apoptosis, will escape killing. Cytotoxic lymphocytes kill by two main mechanisms, the perforin/granzyme degranulation pathway and the TNF/Fas/TNF-related apoptosis-inducing ligand superfamily of apoptosis-inducing ligands. In this study, we examined whether cis-diaminedichloroplatinum (II) cisplatin (CDDP) sensitizes MART-1/HLA A2.1(+) melanoma and melanoma variant tumor cells to non-MHC-restricted, Fas ligand (FasL)-mediated killing by CTL. MART-1(27-35)-specific bulk CTL cultures were generated by pulsing normal PBL with MART-1(27-35) peptide. These CTL cultures specifically kill M202 melanoma cells (MART-1(+), HLA A2.1(+), FasR(-)), and MART-1(27-35) peptide-pulsed T2 cells (FasR(+)), but not M207 melanoma cells (MART-1(+), HLA A2.1(-), FasR(-)), FLU(58-66) peptide-pulsed T2 cells, or DU145 and PC-3 prostate cells (MART-1(-), HLA A2.1(-), FasR(+)). CDDP (0.1-10 microg/ml) sensitized non-MART-1(27-35) peptide-pulsed T2 to the CD8(+) subset of bulk MART-1-specific CTL, and killing was abolished by neutralizing anti-Fas Ab. Furthermore, CDDP up-regulated FasR expression and FasL-mediated killing of M202, and sensitized PC-3 and DU145 to killing by bulk MART-1-specific CTL cultures. These findings demonstrate that drug-mediated sensitization can potentiate FasL-mediated killing by MHC-restricted CTL cell lines, independent of MHC and MART-1 expression on tumor cells. This represents a novel approach for potentially controlling tumor cell variants found in primary heterogeneous melanoma tumor cell populations that would normally escape killing by MART-1-specific immunotherapy.

Adenovirus-interleukin-12-mediated tumor regression in a murine hepatocellular carcinoma model is not dependent on CD1-restricted natural killer T cells

The cytokine interleukin-12 (IL-12) has shown potent antitumor activity in several tumor models. Recently, natural killer (NK) T cells have been proposed to mediate the antitumor effects of IL-12. In this study, the antitumor response of IL-12 was investigated in a gene therapeutic model against s.c. growing mouse hepatocellular carcinomas using an adenoviral vector expressing murine IL-12 (AdVmIL-12). An adenoviral-based system was chosen because of the ability of adenoviruses to transduce dividing and nondividing cells and because of their high transduction efficiencies. Our goals were to examine the efficacy of AdVmIL-12 in a hepatocellular carcinoma model and to investigate the mechanism of the AdVmIL-12-mediated antitumor response with specific interest in the role of NK T cells. Our studies demonstrate that intratumoral AdVmIL-12-mediated regression of s.c. hepatocellular tumors is associated with rapid antitumor responses. AdVmIL-12 treatment was associated with an immune cellular infiltrate consisting of CD4 and CD8 T lymphocytes, macrophages, NK cells, and NK T cells. Antibody ablation of CD4 and CD8 T cells and use of NK cell-defective beige mice failed to abrogate the response to AdVmIL-12. Studies in T-cell- and B-cell-deficient severe combined immunodeficient and recombinase activating gene-2-deficient mice and T-cell-, B-cell-, and NK cell-defective severe combined immunodeficient/beige mice also failed to abrogate this response. AdVmIL-12 retained potent antitumor activity in mice with specific genetic defects in immune cellular cytotoxicity (perforin knockout mice) and costimulation (CD28 knockout mice). Use of mice with specific NK T cell deficiencies, Valpha14 T-cell receptor and CD1 knockout mice, also failed to abrogate the response to AdVmIL-12. Histological and immunohistochemical studies of AdVmIL-12-treated tumors showed extensive inhibition of neovascularization and a marked decrease in factor VIII-stained endothelial cells. Our studies indicate that the antitumor response of AdVmIL-12 is independent of direct cytotoxic cellular immunity (specifically, the function of NK T cells) and suggest that the initial mechanisms of AdVmIL-12-mediated tumor regression involve inhibition of angiogenesis.

Fine specificity analysis of an HLA-A2.1-restricted immunodominant T cell epitope derived from human alpha-fetoprotein

Human alpha-fetoprotein (AFP) is a potentially important target for the immunotherapy of hepatocellular carcinoma (HCC). AFP(542-550) (GVALQTMKQ) is one of several HLA-A2.1-restricted immunodominant AFP peptides that consistently generate AFP-specific T cell responses in human T cell cultures and in HLA-A2.1/K(b) transgenic (A2.1 tg) mice. We performed a fine specificity analysis of this nonamer to determine which amino acid side chains were critical for T cell priming and recognition. Using peptide-pulsed dendritic cells (DC) as an immunization strategy, we characterized the effects of AFP(542-550) amino acid substitutions on priming and recognition in A2.1 tg mice. Replacing the glutamine at anchor position 9 with a leucine enhanced MHC binding and AFP-specific T cell responses. Substitution of leucine at non-anchor position 4 with an alanine did not alter binding but greatly diminished T cell recognition. Computer-generated three-dimensional models provided the structural rationale for these observed effects in MHC binding and T cell responses resulted from the modifications in the AFP(542-550) sequence.

Genetic immunotherapy for cancer

Genetic immunization refers to treatment strategies where gene transfer methods are used to generate immune responses against cancer. Our growing knowledge of the mechanisms regulating the initiation and maintenance of cytotoxic immune responses has provided the rationale for the design of several genetic immunization strategies. Tumor cells have been gene-modified to express immune stimulatory genes and are then administered as tumor vaccines, in an attempt to overcome tumor cell ignorance by the immune system. With the description of well-characterized tumor antigens, multiple strategies have been proposed mainly aimed at optimal tumor antigen presentation by antigen-presenting cells (APC). Among APC, the dendritic cells have been recognized as the most powerful cells in this class, and have become the target for introducing tumor antigen genes to initiate antitumor immune responses. The detailed knowledge of how the immune system can be activated to specifically recognize tumor antigens, and the mechanisms involved in the control of this immune response, provide the basis for modern genetic immunization strategies for cancer treatment.

Immune deviation and Fas-mediated deletion limit antitumor activity after multiple dendritic cell vaccinations in mice

Genetic immunization with a single injection of dendritic cells (DCs) expressing a model melanoma antigen generates antigen-specific, MHC-restricted, protective immune responses. After initiating the immune response, additional vaccinations may increase the protection or conversely downregulate the immune response. Groups of mice were vaccinated several times with DCs transduced with the MART-1 gene, and the anti-tumor protection was compared with that of mice receiving a single vaccination. C3H mice had poorer protection from a syngeneic MART-1-expressing tumor challenge with multiple vaccinations. This was accompanied by lower levels of splenic CTL effectors and a shift from a type 1 to a type 2 cytokine profile. On the contrary, multiple vaccinations in C57BL/6 mice generated greater in vivo antitumor protection with no decrease in splenic CTLs and no cytokine shift. Antiadenoviral humoral or cellular immune responses did not seem to contribute to these effects. When studies were performed in Fas receptor-negative C3H.(lpr) mice, the adverse effect of multiple vaccinations disappeared, and there was no cytokine shift pattern. In conclusion, C3H mice but not C57BL/6 mice receiving multiple vaccinations with DCs expressing the MART-1 tumor antigen show decreased protection associated with deviation from a type 1 to a type 2 cytokine response attributable to a Fas-receptor mediated clearance of antigen-specific IFN-gamma-producing cells.

Intratumoral administration of adenoviral interleukin 7 gene-modified dendritic cells augments specific antitumor immunity and achieves tumor eradication

In two murine lung cancer models adenoviral interleukin 7-transduced dendritic cells (DC-AdIL-7) were administered intratumorally, resulting in complete tumor regression. Intratumoral DC-AdIL-7 therapy was as effective as DCs pulsed with specific tumor peptide antigens. Comparison with other intratumoral therapies including recombinant IL-7, AdIL-7 vector alone, unmodified DCs, IL-7-transduced fibroblasts, or DCs pulsed with tumor lysates revealed DC-AdIL-7 therapy to be superior in achieving antitumor responses and augmenting immunogenicity. Mice with complete tumor eradication as a result of either DC-AdIL-7 or AdIL-7 therapy were rechallenged with parental tumor cells 30 days or more after complete tumor eradication. All the DC-AdIL-7-treated mice completely rejected a secondary rechallenge, whereas the AdIL-7-treated mice had sustained antitumor effects in only 20-25% of the mice. DC-AdIL-7 therapy was more effective than AdIL-7 in achieving systemic antitumor responses and enhancing immunogenicity. After complete tumor eradication, those mice treated with DC-AdIL-7 evidenced significantly greater release of splenocyte GM-CSF and IFN-gamma than did controls or AdIL-7-treated mice. After intratumoral injection, gene-modified DCs trafficked from the tumor to lymph node sites and spleen. DCs were detected in nodal tissues for up to 7 days after intratumoral injection. We report that intratumoral DC-AdIL-7 leads to significant systemic immune responses and potent antitumor effects in murine lung cancer models.