Factors affecting SPF in vitro measurement and correlation with in vivo results.

OBJECTIVE: The in vitro evaluation of SPF is still a problem due to the lack of repeatability and correlation between the in vitro and in vivo data, and many authors are currently working to develop an internationally harmonized method. Very recently, the use of several "adjuvant" ingredients such as boosters, antioxidants, immunomodulators, solvents and film-forming ingredients have further complicated the pattern for product developers that should frequently run in vivo test. The aim of this study was to understand whether a simple and cheap in vitro method could be optimized in order to provide both statistically repeatable and predictive SPF measurement. METHODS: In vitro SPF assessments were carried out on 75 commercial products. The SPF was measured according to two laboratory methods (A and B), using different substrates (PMMA and surgical tape Transpore™), quantity of product and spectrophotometers. In order to evaluate whether a standard technique of spreading could lead to a statistically reliable result, we applied different spreading pressure (100 g and 200 g). Furthermore, we investigate whether other parameters characterizing the product (SPF category, filter and texture) might represent statically significant variables affecting the measures. We then compared the results obtained from in vitro SPF measure of 11 products to in vivo SPF, in order to assess the predictability of in vitro methods. RESULTS: Several problems were encountered in confirming the weakness of the in vitro procedures. Pressure, SPF category, filter and texture did not affect significantly the results. Overall best results were obtained with the B2 method that in terms of repeatability and predictivity provided statistically better results. Method A with Transpore™ tape showed better in vitro-in vivo correlation than Method B with PMMA plates. CONCLUSION: In our investigation, we demonstrated that it is possible for a single laboratory to optimize internal methods and protocols to achieve repeatable and predictive in vitro results, but it is extremely difficult to develop methods reproducible and equally reliable in different laboratories, probably due to "external variables" (e.g. environmental, operator), which are difficult to control.

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.

Generation of human T-cell responses to an HLA-A2.1-restricted peptide epitope derived from alpha-fetoprotein.

Alpha-fetoprotein (AFP) is often derepressed in human hepatocellular carcinoma. Peptide fragments of AFP presented in the context of major histocompatibility molecules could serve as potential recognition targets by CD8 T cells, provided these lymphocytes were not clonally deleted in ontogeny. We therefore wished to determine whether the human T-cell repertoire could recognize AFP-derived peptide epitopes in the context of a common class I allele, HLA-A2.1. Dendritic cells genetically engineered to express AFP were capable of generating AFP-specific T-cell responses in autologous human lymphocyte cultures and in HLA-A2.1/Kb transgenic mice. These T cells recognize a 9-mer peptide derived from the AFP protein hAFP(542-550) (GVALQTMKQ). Identified as a potential A2.1-restricted peptide epitope from a computer analysis of the AFP sequence, hAFP(542-550) proved to have low binding affinity to A2.1, but slow off-kinetics. AFP-specific CTL- and IFN-gamma-producing cells recognize hAFP(542-550)-pulsed targets. Conversely, hAFP(542-550) peptide-generated T cells from both human lymphocyte cultures and A2.1/Kb transgenic mice recognized AFP-transfected targets in both cytotoxicity assays and cytokine release assays. These lines of evidence clearly demonstrate that AFP-reactive clones have not been deleted from the human T-cell repertoire and identify one immunodominant A2.1-restricted epitope. These findings also clearly establish AFP as a potential target for T-cell-based immunotherapy.

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.

p53 selective and nonselective replication of an E1B-deleted adenovirus in hepatocellular carcinoma.

An E1B gene-attenuated adenovirus (dl1520) has been proposed to have a selective cytolytic activity in cancer cells with a mutation or deletion in the p53 tumor suppressor gene (p53-null), a defect present in almost half of human hepatocellular carcinomas (HCCs). In this study, the in vitro and in vivo antitumor activity of dl1520 was investigated focusing on two human HCC cell lines, a p53-wild type (p53-wt) cell line and a p53-null cell line. dl1520 was tested for in vitro cytopathic effects and viral replication in the human HCC cell lines Hep3B (p53-null) and HepG2 (p53-wt). The in vivo antitumor effects of dl1520 were investigated in tumors grown s.c. in a severe combined immunodeficient mouse model. In addition, the combination of dl1520 infection with systemic chemotherapy was assessed in these tumor xenografts. At low multiplicities of infection, dl1520 had an apparent p53-dependent in vitro viral growth in HCC cell lines. At higher multiplicities of infection, dl1520 viral replication was independent of the p53 status of the target cells. In vivo, dl1520 significantly retarded the growth of the p53-null Hep3B xenografts, an effect augmented by the addition of cisplatin. However, complete tumor regressions were rare, and most tumors eventually grew progressively. dl1520 had no effect on the in vivo growth of the p53-wt HepG2 cells, with or without cisplatin treatment. The E1B-deleted adenoviral vector dl1520 has an apparent p53-dependent effect in HCC cell lines. However, this effect is lost at higher viral doses and only induces partial tumor regressions without tumor cures in a human HCC xenograft model.

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.

Alpha-fetoprotein-specific genetic immunotherapy for hepatocellular carcinoma.

The majority of human hepatocellular carcinomas overexpress alpha-fetoprotein (AFP). Two genetic immunization strategies were used to determine whether AFP could serve as a target for T-cell immune responses. Dendritic cells engineered to express AFP produced potent T-cell responses in mice, as evidenced by the generation of AFP-specific CTLs, cytokine-producing T cells, and protective immunity. AFP plasmid-based immunization generated less potent responses. These novel observations demonstrate that this oncofetal antigen can serve as an effective tumor rejection antigen. This provides a rational, gene therapy-based strategy for this disease, which is responsible for the largest number of cancer-related deaths worldwide.

Genetic immunization for the melanoma antigen MART-1/Melan-A using recombinant adenovirus-transduced murine dendritic cells.

Dendritic cells (DCs) are professional antigen-presenting cells that process and present antigenic peptides and are capable of generating potent T-cell immunity. A murine tumor model was developed to evaluate methods of genetic immunization to the human MART-1/Melan-A (MART-1) melanoma antigen. A poorly immunogenic murine fibrosarcoma line (NFSA) was stably transfected with the MART-1 gene. This transfected tumor [NFSA(MART1)] grows progressively in C3Hf/Kam/Sed (H-2k) mice. Partial protection against a challenge with NFSA(MART1) could be achieved with i.m. injections of a MART-1 expression plasmid or with systemic administration of an adenovirus vector expressing MART-1. However, superior protection was achieved when granulocyte macrophage colony-stimulating factor/interleukin-4-differentiated murine DCs transduced with an adenovirus vector expressing MART-1 were used for immunization. Both partial and complete protection could be achieved with i.v. administration of MART-1-engineered DCs. Splenocytes from immunized mice contained MHC class 1-restricted CTLs specific for MART-1. This preclinical model of genetic immunization supports a therapeutic strategy for human melanoma.

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.

Characterization of antitumor immunization to a defined melanoma antigen using genetically engineered murine dendritic cells.

A murine model of dendritic cell (DC)-based genetic immunization to a defined human melanoma antigen (Ag), MART-1/Melan-A (MART-1), was developed. The MART-1 gene was stably transfected into the nonimmunogenic mouse fibrosarcoma cell line NFSA that is syngeneic in C3Hf/Sem/Kam (C3H, H-2k) mice to generate the NFSA(MART1) cell line. In vivo protection from a lethal NFSA(MART1) tumor challenge could be generated by DCs transduced with a recombinant adenovirus (AdV) vector expressing MART-1 (AdVMART1). This model has the following characteristics: (a) immunological specificity and memory, (b) comparable protection for varying transduction multiplicities of infection, cell doses, and sites of DC inoculation but, interestingly, worse protection with increasing numbers of vaccinations, (c) the ability to treat small established tumors, (d) an absolute requirement for CD8 and CD4 T cells, (e) generation of MART-1-specific splenic cytotoxic T lymphocytes, and (f) up-regulation of both T helper type 1 and T helper type 2 cytokines. Genetically engineered DCs presenting defined tumor Ags represent an attractive method to generate effective immune responses.

Long-term expression of a reporter gene from latent herpes simplex virus in the rat hippocampus.

A problem in utilizing herpes simplex virus (HSV) as a vector for expression of foreign genes in CNS neurons has been the inability to facilitate long-term expression of the engineered genes. Previously, we showed that the murine moloney leukemia virus LTR would drive beta-galactosidase (beta-gal) transcription for extended periods from the latent viral genome in sensory, but not motor neurons. In this communication we further evaluate the utility of the LTR promoter for use in long-term expression vectors. Following stereotactic injection of 8117/43 (an ICP4 minus, non-replicating virus with the LTR driving the beta-gal gene, or KD6 (an ICP4 minus non-replicating virus not expressing beta-gal) into the hippocampus of rats, polymerase chain reaction (PCR) analysis of viral DNA after 2 months indicated that latent infections were established. Assaying by both x-gal staining and reverse transcriptase PCR we demonstrate that (1) beta-gal can be detected for at least 6 months in hippocampal neurons, and (2) although the number of beta-gal transcripts in these cells drops considerably by 2 weeks, they can be detected during the period studied. These studies indicate that the LTR promoter is active and affords long-term expression in the CNS, albeit at comparatively low levels compared to those observed at acute times.

Antitumor protection using murine dendritic cells pulsed with acid-eluted peptides from in vivo grown tumors of different immunogenicities.

Peptides extracted from tumor cells after mild acid treatment can function as antigenic epitopes when presented by cultured dendritic cells. Peptides were extracted from four tumors syngeneic to C3H mice, three weakly immunogenic tumors (FSA, MCAK, HCA) and one non-immunogenic tumor (NFSA). Dendritic cells pulsed with peptides extracted from the three weakly immunogenic tumors partially protect mice from a tumor challenge with the parental cell line. This protection was evident by a slower rate of tumor appearance and a slower tumor growth curve when compared to control, non-immunized mice. However, vaccination of mice with dendritic cells pulsed with peptides derived from the non-immunogenic cell line NFSA did not elicit a protective response. Neither the route of immunization, the number of immunizations, nor the amount of peptides significantly affected the antitumor protection. Dendritic cells genetically engineered to produce IL-2 did not increase the protective effect of peptide-pulsed dendritic cells. These results suggest that only a partial protection against immunogenic tumors can be achieved when dendritic cells pulsed with acid-eluted tumor peptides are used as antitumor vaccination.

Murine cytomegalovirus is present in both chronic active and latent states in persistently infected mice.

Cytomegalovirus induces serious disease in immunosuppressed individuals, often from an "activated" persistent infection. Whether the infection is chronically active or latent is unknown. Using murine cytomegalovirus (MCMV) in mice as a model system, we examined persistent infections in spleen, lung, and bone marrow of infected animals. At 28 days after infection, no virus could be recovered from any organs tested except salivary glands, and here, virus was cleared by 48 days. Virus could be retrieved at all times by cocultivation of spleen or lung with permissive cells. In addition, MCMV DNA was always present in spleen, lung, and bone marrow. After acute infection, RNA from the MCMV immediate early-1 (ie-1) gene was routinely found only in the lung. In spleen and bone marrow, only one sample from each organ examined at these times contained ie-1 RNA, and the RNA in these two samples was present at levels comparable to that found in acute infection. This suggests that the virus had reactivated. The ie-1 RNA found in the lung was present at a much lower RNA:DNA ratio than that found at early times. Taken together, these results indicate that persistent MCMV exists simultaneously in both chronic active and latent states.

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.

A herpes simplex virus transcript abundant in latently infected neurons is dispensable for establishment of the latent state.

We have previously reported that a novel herpes simplex virus RNA transcript partially overlapping the gene encoding ICPO and expressed from the opposite DNA strand is abundant in sensory neurons of mice harboring a latent infection [J.G. Stevens, E.K. Wagner, G.B. Devi-Rao, M.L. Cook, and L.T. Feldman, Science 235, 1056-1059 (1987)]. This finding suggested that this transcript might be involved in establishment, maintenance, or reactivation of latent virus. To determine the function of this latency-associated transcript (LAT), we have examined the latency characteristics of a deletion mutant which is unable to express the LAT gene. Although no viral transcripts could be found in the lumbosacral ganglia of mice surviving rear footpad infection with this deletion virus, a latent infection had been established since infectious virus could be induced and detected after explanation and cocultivation of ganglia with permissive cells in culture. These results indicate that HSV-1 LAT expression is not an absolute requirement for establishment of the latent state.

Generation of melanoma-specific cytotoxic T lymphocytes by dendritic cells transduced with a MART-1 adenovirus.

Dendritic cells (DC) are potent stimulators of primary T cell responses. In this study, we demonstrate that DC, genetically engineered to express the MART-1/Melan-A (MART-1) tumor-associated Ag, express MART-1 mRNA and protein, correctly process and present the HLA-A2.1-restricted immunodominant MART-1 peptide (MART-1(27-35)), and serve as potent stimulators of MART-1-specific CTL in vitro. A replication-defective E1-deleted adenovirus (AdV) was constructed that expresses MART-1 (AdVMART1). Transduced DC produce full length MART-1 mRNA as well as MART-1 protein. AdVMART1 does not significantly down-regulate cell surface class I expression despite having an intact E3 region. Transduction of an HLA-A2-positive/MART-1-negative cell line with AdVMART1 renders these cells sensitive to lysis by CTL specific for the MART-1(27-35) immunodominant peptide. In addition, DC transduced with AdVMART1 stimulated MART-1(27-35)-specific tumor-infiltrating lymphocytes to synthesize IFN-gamma. Finally, AdVMART1-transduced DC were able to generate MART-1(27-35) peptide-specific, class I-restricted CTL in PBL cultures from normal donors. This study supports the use of tumor Ag-engineered DC in genetic immunotherapy.

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.

Generation of T-cell immunity to a murine melanoma using MART-1-engineered dendritic cells.

The murine melanoma B16 expresses the murine counterpart of the human MART-1/Melan-A (MART-1) antigen, sharing a 68.6% amino acid sequence identity. In this study, mice were vaccinated with bone marrow-derived murine dendritic cells genetically modified with a replication-incompetent adenoviral vector to express the human MART-1 gene (AdVMART1). This treatment generated a protective response to a lethal tumor challenge of unmodified murine B16 melanoma cells. The response was mediated by major histocompatibility complex class I-restricted cytotoxic T lymphocytes specific for MART-1 antigen, which produced high levels of interferon-gamma when reexposed to MART-1 in vitro and lysed targets in a calcium-dependent mechanism suggestive of perforin/granzyme B lysis. MART-1 was presented by the dendritic cells used for vaccination and not by epitopes cross-presented by host antigen-presenting cells. In conclusion, dendritic cells genetically modified to express the human MART-1 antigen generate potent murine MART-1-specific protective responses to B16 melanoma.