Induction of antitumor activity by immunization with fusions of dendritic and carcinoma cells

Ileosigmoid fistulas are found in Crohn's disease and may present a surgical dilemma. PURPOSE: This study was designed to examine surgical practice to determine types of intervention, enumerate complications, and elicit guidelines for surgical management. METHOD: The medical records of patients with ileosigmoid fistula and Crohn's disease from 1975 to 1995 were reviewed. RESULTS: Ninety patients (44 men) were studied. A preoperative diagnosis of ileosigmoid fistula was made in 77 percent of patients. Sigmoid repair was performed in 43 patients (47.8 percent), sigmoid resection in 32 patients (35.6 percent), 12 patients (13.3 percent) underwent more extensive procedures, and 3 patients (3.3 percent) either had surgery elsewhere or were observed. The fistula was never directly responsible for a stoma. The repair and resection groups were similar with respect to age, length of Crohn's disease, and preoperative symptoms. There was no significant difference between groups in the incidence of postoperative complications; there were no postoperative deaths. Average length of stay was 8.3 days following repair and 9.9 days after resection. Reasons for resection included significant purulence or inflammation, a large fistula defect, a defect on the mesenteric border of the sigmoid, and active sigmoid Crohn's disease. Surgeon's assessment of the presence of Crohn's disease in the sigmoid correlated with pathologic examination and was aided by knowledge of recent endoscopic appearance and biopsy results; intraoperative frozen section and colonoscopy were helpful in distinguishing serosal inflammation from active Crohn's disease. CONCLUSION: Contrast studies identified 77 percent of ileosigmoid fistulas preoperatively. Performing repair rather than resection does not increase the risk of complications, if standard surgical principles are followed. Preoperative or intraoperative endoscopy assists the surgical evaluation of the sigmoid.     

Bone marrow-generated dendritic cells pulsed with tumor extracts or tumor RNA induce antitumor immunity against central nervous system tumors

Recent studies have shown that the brain is not a barrier to successful active immunotherapy that uses gene-modified autologous tumor cell vaccines. In this study, we compared the efficacy of two types of vaccines for the treatment of tumors within the central nervous system (CNS): dendritic cell (DC)-based vaccines pulsed with either tumor extract or tumor RNA, and cytokine gene-modified tumor vaccines. Using the B16/F10 murine melanoma (B16) as a model for CNS tumor, we show that vaccination with bone marrow-generated DCs, pulsed with either B16 cell extract or B16 total RNA, can induce specific cytotoxic T lymphocytes against B16 tumor cells. Both types of DC vaccines were able to protect animals from tumors located in the CNS. DC-based vaccines also led to prolonged survival in mice with tumors placed before the initiation of vaccine therapy. The DC-based vaccines were at least as effective, if not more so, as vaccines containing B16 tumor cells in which the granulocytic macrophage colony-stimulating factor gene had been modified. These data support the use of DC-based vaccines for the treatment of patients with CNS tumors.     

Induction of antitumor immunity by interleukin-2 gene-transduced mouse mammary tumor cells versus transduced mammary stromal fibroblasts

BACKGROUND: Tumor cell-targeted cytokine gene transfer has been used to generate tumor cell vaccines, but this approach is limited by the need to establish and implant live tumor cells. PURPOSE: The purpose of this study was to determine if stromal fibroblasts could be used as an alternative vehicle for delivery of the cytokine interleukin-2 (IL-2) into the tumor microenvironment. We attempted to establish the feasibility of (a) genetic immunotherapy in a mammary tumor system and (b) engineering stromal fibroblasts as well as tumor cells. We compared the effects of tumor cell-mediated and stromal fibroblast-mediated local IL-2 expression on the generation of antitumor immune responses. METHODS: Retroviral vectors containing a human IL-2 gene were used to transduce a mouse mammary tumor line, 4TO7, and an immortalized but nontumorigenic fibroblast line established from syngeneic mammary fatpads. Expression of the IL-2 gene in transduced cells was determined by measuring IL-2 secretion, by RNA-polymerase chain reaction, and by immunochemistry. Groups of 5-12 BALB/c mice were injected with either 4TO7 cells or various doses of IL-2-secreting 4TO7 cells (4TO7-IL-2); tumor growth was monitored. To test whether local IL-2 expression by transduced cells could influence the growth of unmodified tumor cells, we determined tumor development in groups of mice treated with 4TO7 cells co-injected with either 4TO7-IL-2 cells or IL-2-secreting fibroblasts. RESULTS: 4TO7-IL-2 cells induced active immunity able to reject the immunizing tumor and to resist challenge with parental 4TO7 cells on the contralateral side. Mice pretreated with 4TO7-IL-2 were significantly protected compared with untreated control animals or mice pretreated with irradiated 4TO7 cells. The immunity induced by 4TO7-IL-2 cells did not protect against challenge with another subline, 4T1, which was derived from the same spontaneously arising mammary tumor as 4TO7. Co-injection of 4TO7 cells with 4TO7-IL-2 cells reduced tumorigenicity, whereas co-injection of 4TO7 cells with IL-2 secreting fibroblasts did not. CONCLUSION: Our results suggest that induction of anti-tumor immune response by local IL-2 production is most effective when the helper cytokine is secreted by the tumor cell. IMPLICATION: Our studies caution against the use of IL-2 gene-transduced syngeneic stromal cells as an alternative strategy of gene therapy for cancer. However, they may allow study of the mechanisms of tumor antigen recognition and the possible involvement of co-stimulatory signals for effective tumor vaccination by gene-modified cells.     

Comparison of lung dendritic cells and B cells in stimulating naive antigen-specific T cells

Dendritic cells (DCs) are specialized APCs that are important in priming naive T cells and can be manipulated in vitro and in vivo to enhance immunizations against microorganisms and tumors. A limitation in the development of suitable immunotherapeutic vaccines for the lung is incomplete information on the role of DCs and other potential APCs in the lung in priming naive T cells. In the current study, we analyzed the relative contributions of murine lung DCs and B cells to process and present OVA to naive CD4+ OVA323-339-specific (DO11.10) T cells in vitro. We also examined their expression of MHC class II and accessory molecules before and after maturation in culture. Similar to DCs from other sites, freshly isolated lung DCs can process OVA, spontaneously up-regulate MHC class II and accessory molecules during overnight culture, and stimulate naive T cells in an Ag-specific manner. In contrast, freshly isolated lung B cells were unable to both process and present native OVA. Furthermore, under conditions of limited OVA323-339 peptide exposure, B cells had a significantly diminished capacity to stimulate T cells, and this correlated with a decreased density of both MHC class II and important costimulatory molecules as compared with lung DCs.     

Induction of pulmonary allergic responses by antigen-specific Th2 cells

The development of pulmonary allergic responses was examined in mice following pulmonary transfer of Ag (conalbumin)-specific Th2 cells. The levels of serum-specific IgE, cellular infiltrates, airway mucus goblet cells, and airway responsiveness were analyzed and compared with those in Ag-sensitized and -challenged mice. Pulmonary transfer of the conalbumin-specific Th2 clone (D10) induced, in an Ag-specific manner, high levels of the Th2 cytokines IL-4 and IL-5 in the bronchoalveolar lavage fluids and mucosal eosinophils, concomitant with an increase in airway responsiveness. The D10 cell-induced responses were seen in the absence of serum specific IgE. In the presence of Ag, the transferred D10 cells not only remained in the lungs, but also increased in number 72 h post-cell transfer. Although significantly higher levels of IL-4 and IL-5 in the bronchoalveolar lavage fluids were found in D10-transferred mice, the levels of pulmonary eosinophilia, mucus goblet cells, and airway responsiveness were significantly lower than those in Ag-sensitized and -challenged mice. These results demonstrate that although Ag-specific activation of Th2 cells at mucosal sites is able to mediate the recruitment of eosinophils and the subsequent induction of airway hyper-responsiveness, the more severe pulmonary allergic responses were observed only in mice sensitized and challenged with Ag.     

Generation of tumor immunity by bone marrow-derived dendritic cells correlates with dendritic cell maturation stage

The mutational pattern of IgVH and IgVL genes from synovial tissue B cell hybridomas (n = 8) of patients (n = 4) with rheumatoid arthritis (RA) was analysed, which had been produced by the electrofusion technique without prior in vitro stimulation. The molecular data were correlated with immunohistopathological data and parameters of local disease activity. The IgVH genes of the B cell hybridomas belonged to the VH3 family (DP42; DP47, n = 2; DP53), the VH1 family (DP75), the VH4 family (DP71) and the VH5 family (DP73); 7/7 IgVH genes showed somatic mutations, the R/S ratio (CDR) was > 3 in 4/7 IgVH genes and the mean R/S ratio of all IgVH genes was 9.3 (CDR) and 1.0 (FR), suggesting an antigen-dependent selection. The IgVL/lambda genes belonged to the Vlambda1 family (DPL2, DPL5, DPL8nf), the Vlambda2 family (DPL11, n = 2) and to the Vlambda6 family (IGLV6S1); 6/6 IgVL genes showed somatic mutations, the R/S ratio (CDR) was > 3 in 3/6 IgVL genes and the mean R/S ratio of all IgVL was 3.0 (CDR) and 2.3 (FR), suggesting an antigen-dependent selection. The synovial tissue exhibited germinal centres in the follicles (3/4), with the unique distribution of Ki-M4+ follicular dendritic cells and Ki-67+ proliferating cells and a dominance of IgA+ plasma cells (3/3). All patients were positive for RF in serum and exhibited severe local symptoms (swelling 4/4; warmth 4/4; effusion 2/4), whereas the hybridomas were negative for RF. Since B cell hybridomas showed hypermutation and affinity selection for IgVH and IgVL/lambda genes and the patients exhibited severe local symptoms with germinal centres in synovial tissue, this study indicates that an antigen-driven process is behind the B cell expansion in the synovial tissue of clinically affected joints. These mutated B hybridomas were negative for RF, thus suggesting that antigens different from RF are also involved in the local B cell expansion and in the chronic synovitis of RA.     

Genetically modified bone marrow-derived dendritic cells expressing tumor-associated viral or "self" antigens induce antitumor immunity in vivo

The clinical application of synthetic tumor peptide-based vaccines is currently limited to patients with specified major histocompatibility complex (MHC) class I alleles. Such logistic limitations may be overcome using tumor gene-based approaches. Here we describe the effective generation of dendritic cells (DC) expressing tumor peptide-MHC complexes as a result of particle-mediated transfer of genes encoding tumor-associated antigens (TAA). Bone marrow-derived DC were transfected with plasmid DNA encoding the tumor-associated viral antigen E7 derived from human papilloma virus (HPV) 16. When applied as a vaccine, these genetically modified DC induced antigen-specific CD8+ cytotoxic T lymphocytes (CTL) in vivo and promoted the rejection of a subsequent, normally lethal challenge with an HPV 16-transformed tumor cell line. Of greatest interest, immunization of mice with syngeneic DC genetically modified to enhance their presentation of a constitutive "self" epitope derived from the tumor-suppressor gene product p53 caused a significant reduction in the in vivo growth of a chemically induced p53-positive sarcoma. These results suggest that cancer vaccines consisting of DC genetically modified to express TAA of viral or "self" origin effectively induce antitumor immunity in vivo.     

Lymphotactin gene-modified bone marrow dendritic cells act as more potent adjuvants for peptide delivery to induce specific antitumor immunity

Dendritic cells (DC) are regarded as attractive candidates for cancer immunotherapy. Our aim is to improve the therapeutic efficacy of DC-based tumor vaccine by augmenting DC preferential chemotaxis on T cells. Mouse bone marrow-derived DC were transduced with lymphotactin (Lptn) gene by adenovirus vector. The supernatants from Lptn gene-modified DC (Lptn-DC) were capable of attracting CD4+ and CD8+ T cells in a chemotaxis assay, whereas their mock control could not. Lptn expression of Lptn-DC was further confirmed by RT-PCR. Lptn-DC were pulsed with Mut1 peptide and used for vaccination. Immunization with the low dose (1 x 10(4)) of Mut1 peptide-pulsed DC induced weak CTL activity, whereas the same amounts of Mut1 peptide-pulsed Lptn-DC markedly induced specific CTL against 3LL tumor cells. A single immunization with 1 x 10(4) Mut1 peptide-pulsed Lptn-DC could render mice resistant to a 5 x 10(5) 3LL tumor cell challenge completely, but their counterpart could not. The protective immunity induced by Mut1 peptide-pulsed Lptn-DC depends on both CD4+ T cells and CD8+ T cells rather than NK cells in the induction phase and depends on CD8+ T cells rather than CD4+ T cells and NK cells in the effector phase. Moreover, the involvement of CD28/CTLA4 costimulation pathway and IFN-gamma are also necessary. When 3LL tumor-bearing mice were treated with 1 x 10(4) Mut1 peptide-pulsed Lptn-DC, their pulmonary metastases were significantly reduced, whereas the same low dose of Mut1 peptide-pulsed DC had no obvious therapeutic effects. Our data suggest that Lptn-DC are more potent adjuvants for peptide delivery to induce protective and therapeutic antitumor immunity.     

Induction of transplantation immunity by dansylated tumor cells

Tumor cells were coupled with fluorecent dansyl group in aqueous medium by dansyl chloride-cycloheptaamylose complex (CDC) without destruction of the cells. C57BL/6 mice and Donryu rats pretreated respectively with dansylated EL4 leukemia cells and with dansylated Yoshida sarcoma cells acquired transplantation immunity to the corresponding tumor cells. Serum and spleen cells obtained from EL4 immune mice showed cytotoxicity to EL4 cells but not to other allogeneic leukemia cells. Hapten-specific cytotoxicity of immune serum and spleen cells was not observed in the present immune system.     

Retrovirally transduced bone marrow-derived dendritic cells require CD4+ T cell help to elicit protective and therapeutic antitumor immunity

It has been extensively documented that murine dendritic cells loaded with tumor-associated Ag (TAA)-derived peptides or protein can prime Ag-specific CD8+ cytotoxic T cells in vivo and can elicit Ag-specific immunity. Optimal presentation of TAA might be achieved by retroviral transduction of DCs allowing long term and stable expression of the TAA-peptides as well as the presentation of multiple epitopes in the context of MHC class I and/or class II molecules. Here we show that retroviral transduction of bone marrow-derived dendritic cells (DCs) with chicken OVA cDNA or the reporter gene green fluorescent protein retained their potent stimulatory capacity and that the transduced DCs could process and present the endogenously expressed OVA protein. The DCs transduced with cDNA encoding native OVA protein presented OVA-derived peptides in the context of MHC class I as well as MHC class II and induced a strong Ag-specific CTL response. DCs expressing a cytosolic form of OVA presented OVA peptides only in the context of MHC class I and failed to induce an OVA-specific CTL response in vivo when they had been cultured in the absence of exogenous protein. Immunization with retrovirally transduced DCs resulted in an Ag-specific immunity and rejection of a tumor cell challenge and a significant survival advantage in tumor-bearing mice. These results obtained in this rapidly lethal tumor model suggest that DCs transduced with TAA may be useful for tumor immunotherapy and underscore the importance of the simultaneous delivery of T cell help in the development of Ag-specific cytotoxic T-cells.     

Induction of tolerance by IL-10-treated dendritic cells

Dendritic cells (DC) form a specialized system for presenting Ag to naive or quiescent T cells and consequently play a central role in the induction of T and B cell immunity. In this study we used DC generated from peripheral progenitors to analyze the effect of IL-10 on the accessory function of human DC. We demonstrate that immature DC, harvested on days 9 to 11 and exposed to IL-10 for the last 2 days of culture, show a strongly reduced capacity to stimulate a CD4+ T cell response in an allogeneic MLR in a dose-dependent manner. In contrast, fully mature DC are completely resistant to the effects of IL-10. These results were obtained in both an alloantigen-induced MLR and an anti-CD3 mAb-induced response of primed and naive (CD45RA+) CD4+ T cells. FACS analysis revealed inhibition of the up-regulation of the costimulatory molecules CD58 and CD86 and the specific DC marker CD83 in DC pretreated with IL-10. These data suggest that IL-10 inhibited the development of fully mature DC. Furthermore, DC precultured with IL-10, but not controls, induced a state of alloantigen-specific anergy in CD4+ T cells and of peptide-specific anergy in the influenza hemagglutinin-specific T cell clone HA1.7. Analysis of the supernatants of these anergic T cells revealed a reduced production of IL-2 and IFN-gamma compared with that in control cells. Collectively, these data suggest that IL-10 converts immature DC into tolerogenic APC, which might be a useful tool in the therapy of patients with autoimmune or allergic diseases.     

Dual role of dendritic cells in the induction and down-regulation of antigen-specific cutaneous inflammation

We have previously reported that contact sensitivity (CS) to dinitrofluorobenzene (DNFB) in C57BL/6 mice was mediated by MHC class I-restricted CD8+ T cells and down-regulated by MHC class II-restricted CD4+ T cells. In this study, we analyzed the contribution of dendritic cells (DC) in the induction of these two T cell subsets endowed with opposite functions. Hapten-pulsed skin- and bone marrow-derived DC, obtained from either normal C57BL/6 mice or from MHC class II (I+ II-) and MHC class I (I- II+)-deficient mice, were tested for their ability to prime normal mice for CS to dinitrofluorobenzene. Expression of MHC class I molecules by transferred DC was mandatory both for the induction of CS and for the generation of hapten-specific CD8+ T cells in lymphoid organs. I+ II- DC were as potent as I+ II+ DC in priming for CS, demonstrating that activation of effector CD8+ T cells can occur independently of CD4+ T cell help. I- II+ DC could not immunize for CS, although they could sensitize for a delayed-type hypersensitivity reaction to protein Ags. Moreover, I- II+ DC injected simultaneously with cutaneous sensitization down-regulated the inflammatory response, suggesting that hapten presentation by MHC class II molecules could prime regulatory CD4+ T cells. These results indicate that DC can present haptenated peptides by both MHC class I and class II molecules and activate Ag-specific CD8+ effector and CD4+ regulatory T cell subsets, concurrently and independently.     

Dendritic cells require maturation via CD40 to generate protective antitumor immunity

A critical role for CD40/CD154 interactions in the generation of protective cell-mediated tumor immunity has been demonstrated previously. Herein, we show that the failure to generate systemic tumor immunity in the absence of CD40/CD154 interactions correlates with an inhibition of Th1-type cytokine production following tumor vaccination. Furthermore, protective antitumor responses can be restored in CD40-deficient mice by the coadministration of CD40+/+ but not CD40-/- dendritic cells (DCs) with tumor Ag, suggesting that CD40 is critical for the maturation and function of DCs in vivo. Finally, we demonstrate that an IL-12-transduced but not a mock-transduced tumor vaccine induces systemic tumor immunity in anti-CD154-treated and CD154-deficient mice. These data suggest that impaired antitumor responses in the absence of CD40/CD154 interactions are the result of a lesion in APC function, namely IL-12 production, and that CD40 plays a critical role in the maturation of DCs in vivo.     

CD1 expression by dendritic cells in human leprosy lesions: correlation with effective host immunity

A potential role for the CD1 family of lipid Ag-presenting molecules in antimicrobial immunity in vivo was investigated in human leprosy skin lesions. Strong induction of three CD1 proteins (CD1a, -b, and -c) was observed in dermal granulomas in biopsy samples of involved skin from patients with the tuberculoid form of leprosy or with reversal reactions, which represent clinical patterns of disease associated with active cellular immunity to Mycobacterium leprae. In contrast, lesions from patients with the lepromatous form of the disease who lack effective cell-mediated immunity to the pathogen did not show induction of CD1 proteins. Thus, expression of CD1 correlated directly with effective immunity to M. leprae, as assessed by the clinical course of infection. CD1a, -b, and -c could be induced to similar levels on monocytes from the blood of either tuberculoid or lepromatous leprosy patients. This suggested that the absence of expression in lepromatous lesions was most likely due to local factors at the site of infection as opposed to a primary defect of the CD1 system itself. The majority of cells expressing CD1 in leprosy lesions were identified as a population of CD83+ dendritic cells. Initial in vitro studies of the Ag-presenting function of CD1+CD83+ monocyte-derived dendritic cells showed that such cells were highly efficient APCs for CD1-restricted T cells. These results indicate that the CD1 system can be up-regulated in human infectious diseases in vivo, and may play a role in augmenting host defense against microbial pathogens.     

Perforin-deficient CD8+ T cells: in vivo priming and antigen-specific immunity against Listeria monocytogenes

CD8+ T cells require perforin to mediate immunity against some, but not all, intracellular pathogens. Previous studies with H-2b MHC perforin gene knockout (PO) mice revealed both perforin-dependent and perforin-independent pathways of CD8+ T cell-mediated immunity to Listeria monocytogenes (LM). In this study, we address two previously unresolved issues regarding the requirement for perforin in antilisterial immunity: 1) Is CD8+ T cell-mediated, perforin-independent immunity specific for a single Ag or generalizable to multiple Ags? 2) Is there a deficiency in the priming of the CD8+ T cell compartment of PO mice following an immunizing challenge with LM? We used H-2d MHC PO mice to generate CD8+ T cell lines individually specific for three known Ags expressed by a recombinant strain of virulent LM. Adoptive transfer experiments into BALB/c host mice revealed that immunity can be mediated by PO CD8+ T cells specific for all Ags examined, indicating that perforin-independent immunity is not limited to CD8+ T cells that recognize listeriolysin O. Analysis of epitope-specific CD8+ T cell expansion by MHC class I tetramer staining and ELISPOT revealed no deficiency in either the primary or secondary response to LM infection in PO mice. These results demonstrate that the perforin-independent pathway of antilisterial resistance mediated by CD8+ T cells is generalizable to multiple epitopes. Furthermore, the results show that reduced antilisterial resistance observed with polyclonal PO CD8+ T cells is a consequence of a deficiency in effector function and not a result of suboptimal CD8+ T cell priming.     

Efficient presentation of multivalent antigens targeted to various cell surface molecules of dendritic cells and surface Ig of antigen-specific B cells

To study the relation between the form of an Ag and the response to it, we compared presentation in vitro with hen egg lysozyme (HEL)-specific T cells from TCR transgenic mice of free HEL and liposome-encapsulated HEL by different APC. HEL-specific splenic B cells or bone marrow-derived dendritic cells were incubated with free HEL or HEL-containing liposomes targeted by Ab to either surface Ig, the Fc receptor, or MHC class I and II molecules. Ag presentation by HEL-specific B cells was at least 100-fold more efficient for HEL in surface Ig-targeted liposomes than free HEL taken up by the same receptor or HEL in liposomes targeted to class I or II molecules. Ag presentation by dendritic cells from Fc receptor-targeted vesicles was augmented 1,000-10,000-fold compared with free Ag or nontargeted liposomes, but presentation was also efficient when Ag was targeted to class I or II molecules. These results indicate that Ag-specific B cells and dendritic cells can be equally efficient in stimulating IL-2 production by Ag-specific T cells from unimmunized TCR transgenic mice when the Ag is multivalent and taken up by appropriate receptors. In contrast to B cells, which require engagement of surface Ig for optimal presentation, dendritic cells may present Ag by means of several different cell surface molecules.     

High titer, prostate specific antigen-specific human IgG production by hu-PBL-SCID mice immunized with antigen-mouse IgG2a complex-pulsed autologous dendritic cells

We report here that immunization of human PBMC reconstituted SCID mice (hu-PBL-SCID mice) with in vitro cultured autologous dendritic cells (DC) pulsed with prostate specific antigen (PSA) complexed to a PSA-specific mouse IgG2a (PSA-IgG2a) consistently and reproducibly stimulates PSA-specific human IgG production. On day 0, female PBMC were used to reconstitute SCID mice and to generate DC in vitro. DC cultures were pulsed with PSA or PSA-IgG2a on day 6. The previously reconstituted hu-PBL-SCID mice were immunized with either PSA-pulsed DC and PSA, PSA-IgG2a-pulsed DC and PSA-IgG2a, or additional PBMC and PSA-IgG2a on day 7. Mice immunized with PSA-IgG2a-pulsed DC had, on the average, up to 31.5 times greater PSA-specific IgG serum concentrations than control mice. Competition ELISA confirmed the PSA specificity of serum IgG. Immunoblot analysis suggested that sera IgG preferentially recognized conformational epitopes on PSA. Therefore, our results represent a major step toward cloning human tumor-associated Ag-specific human mAbs from hu-PBL-SCID mice. In addition, flow cytometry showed that PSA-pulsed DC express significantly more B7.1, B7.2, CD40, and MHC class II surface molecules than mock-treated DC, but PSA-IgG2a-pulsed DC only had significantly enhanced B7.2 surface expression. Interestingly, PSA-specific IgG responses were reproducibly stimulated by DC expressing more B7.2, a molecule associated with Th2-type immune deviation, but not by those expressing more B7.1 and CD40, molecules associated with Th1-type immune deviation. Thus, our results show that stimulation with either Ag or Ag complexed to mAb yields DC with different phenotypes and APC effector functions.     

Costimulation provided by DNA immunization enhances antitumor immunity

The interaction of the TCR with MHC class I-bound Ag is insufficient for the priming of CTL unless secondary costimulatory signals are provided. To ascertain the minimum elements required to activate an Ag-specific CTL response in vivo, we injected mice intradermally or i.m. with plasmid DNA encoding a MHC class I-restricted peptide Ag (minigene) and different membrane-bound costimulatory ligands. The minigene-encoded epitope only primed a specific CTL response if injected in the vicinity of an ectopically expressed costimulatory ligand. Vector encoding B7-1 was repeatedly more potent at stimulating a cytolytic response than vector encoding B7-2. In contrast the B7-2-encoding plasmid preferentially enhanced Ag-specific Ab responses when injected with either protein or a cDNA expression vector. Gene vaccination with plasmids encoding OVA and B7-1, but not B7-2, prolonged survival in mice challenged with an OVA-transfected tumor. These results show that functional B7-1 transfection can be achieved in vivo and induces the selective induction of CTL. The data suggest that B7-1 plasmids should be coadministered with naked DNA vaccines that aim to induce tumor-specific cellular immunity.