Granulocyte/macrophage-colony-stimulating factor released by adenovirally transduced CT26 cells leads to the local expression of macrophage inflammatory protein 1alpha and accumulation of dendritic cells at vaccination sites in vivo

Granulocyte-Macrophage Colony Stimulating Factor: An Adjuvant for Cancer Vaccines

Granulocyte-macrophage colony stimulating factor (GM-CSF) enhances immune responses by inducing the proliferation, maturation, and migration of dendritic cells, and the expansion and differentiation of B and T lymphocytes. There is significant data in pre-clinical animal models demonstrating the adjuvant effects of GM-CSF in a variety of cancer vaccine approaches, including cellular vaccines, viral vaccines, peptide and protein vaccines, and DNA vaccines. GM-CSF is an attractive vaccine adjuvant because of its immune modulation effects and low toxicity profile. The results in animal models have been confirmed in pilot clinical trials and several clinical trials are currently ongoing.

Autologous CLL cell vaccination early after transplant induces leukemia-specific T cells

BACKGROUND

Patients with advanced hematologic malignancies remain at risk for relapse following reduced-intensity conditioning (RIC) allogeneic hematopoietic stem cell transplantation (allo-HSCT). We conducted a prospective clinical trial to test whether vaccination with whole leukemia cells early after transplantation facilitates the expansion of leukemia-reactive T cells and thereby enhances antitumor immunity.

METHODS

We enrolled 22 patients with advanced chronic lymphocytic leukemia (CLL), 18 of whom received up to 6 vaccines initiated between days 30 and 45 after transplantation. Each vaccine consisted of irradiated autologous tumor cells admixed with GM-CSF-secreting bystander cells. Serial patient PBMC samples following transplantation were collected, and the impact of vaccination on T cell activity was evaluated.

RESULTS

At a median follow-up of 2.9 (range, 1-4) years, the estimated 2-year progression-free and overall survival rates of vaccinated subjects were 82% (95% CI, 54%-94%) and 88% (95% CI, 59%-97%), respectively. Although vaccination only had a modest impact on recovering T cell numbers, CD8+ T cells from vaccinated patients consistently reacted against autologous tumor, but not alloantigen-bearing recipient cells with increased secretion of the effector cytokine IFN-γ, unlike T cells from nonvaccinated CLL patients undergoing allo-HSCT. Further analysis confirmed that 17% (range, 13%-33%) of CD8+ T cell clones isolated from 4 vaccinated patients by limiting dilution of bulk tumor-reactive T cells solely reacted against CLL-associated antigens.

CONCLUSION

Our studies suggest that autologous tumor cell vaccination is an effective strategy to advance long-term leukemia control following allo-HSCT.

TRIAL REGISTRATION

Clinicaltrials.gov NCT00442130.

FUNDING

NCI (5R21CA115043-2), NHLBI (5R01HL103532-03), and Leukemia and Lymphoma Society Translational Research Program.

Role of GM-CSF signaling in cell-based tumor immunization

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a potent adjuvant in cancer vaccination; however, the specific role of endogenous GM-CSF remains unknown. We performed cell-based vaccination in 2 tumor models. First, we vaccinated C57BL/6 mice lacking either GM-CSF, IL-5, or beta-common chain (betac), a receptor subunit essential for GM-CSF and IL-5 signaling, with melanoma cells engineered to produce GM-CSF. Tumor vaccination was effective in both GM-CSF(-/-) and IL-5(-/-) mice, showing that protective immunization is independent of both endogenous cytokines. However, all betac(-/-) animals developed tumor. Loss of tumor immunity in betac(-/-) mice does not reflect global impairment in cell-mediated immunity, as contact hypersensitivity reaction to haptens is unaltered. The importance of tumor cell-derived GM-CSF was highlighted by recruitment of dendritic cells at the vaccination site in wild-type, GM-CSF(-/-), and IL-5(-/-) but not in betac(-/-) mice. In the second model, vaccination with unmodified RENCA cells showed similar results with efficient immunization in BALB/c wild-type and GM-CSF(-/-), whereas all betac(-/-) animals died. Altogether, our results strongly suggest that although endogenous GM-CSF and IL-5 are not required to induce tumor immunity, signaling through betac receptor is critically needed for efficient cancer vaccination in both genetically modified GM-CSF-secreting tumor cells and a spontaneously immunogenic models.

Phase I/II study of GM-CSF DNA as an adjuvant for a multipeptide cancer vaccine in patients with advanced melanoma

Granulocyte-macrophage colony-stimulating factor (GM-CSF) enhances immune responses by inducing dendritic cell proliferation, maturation, and migration and B and T lymphocyte expansion and differentiation. The potency of DNA vaccines can be enhanced by the addition of DNA encoding cytokines, acting as molecular adjuvants. We conducted a phase I/II trial of human GM-CSF DNA in conjunction with a multipeptide vaccine (gp100 and tyrosinase) in stage III/IV melanoma patients. Nineteen human leukocyte antigen (HLA)-A*0201(+) patients were treated. Three dose levels were studied: 100, 400, and 800 mcg DNA/injection, administered subcutaneously (SQ) every month with 500 mcg of each peptide. In the dose-ranging study, 3 patients were treated at each dose level. The remaining patients were then treated at the highest dose. Most toxicities were grade 1 injection site reactions. Eight patients (42%) developed CD8+ T-cell responses, defined by a ≥3 SD increase in baseline reactivity to tyrosinase or gp100 peptide in tetramer or intracellular cytokine staining assays. There was no relationship between dose and T-cell response. Responding T cells had an effector memory cell phenotype. Polyfunctional T cells were also demonstrated. At a median of 31 months follow-up, median survival has not been reached. Human GM-CSF DNA was found to be a safe adjuvant.

Cell based cancer vaccines: regulatory and commercial development

There is both clinical and regulatory drive to expedite development of safe, efficacious cancer therapies. Stimulation of the patients immune system through vaccination with tumour cells has long been at the vanguard of cancer therapeutic vaccines, and several have been demonstrated to be safe and to have efficacy in early clinical trials for a range of cancers including melanoma, renal cell carcinoma, prostate and colorectal cancers. A number of development-stage vaccines and strategies are currently being tested, utilising either autologous or allogeneic tumour cells, which may also have been ex vivo manipulated (e.g. cytokine transfected cells). It seems likely that clinical trial success, and hence patient benefit, could be improved through better patient identification, possibly by the discovery and use of novel immune response biomarkers. In this review, we aim to summarise the state of tumour cell vaccines in commercial development and to explore not only the difficulties of determining efficacy, but also the production challenges faced when developing a vaccine from proof of principle to pivotal phase III trials.

Intratumoral delivery of vector mediated IL-2 in combination with vaccine results in enhanced T cell avidity and anti-tumor activity

Systemic IL-2 is currently employed in the therapy of several tumor types, but at the price of often severe toxicities. Local vector mediated delivery of IL-2 at the tumor site may enhance local effector cell activity while reducing toxicity. To examine this, a model using CEA-transgenic mice bearing established CEA expressing tumors was employed. The vaccine regimen was a s.c. prime vaccination with recombinant vaccinia (rV) expressing transgenes for CEA and a triad of costimulatory molecules (TRICOM) followed by i.t. boosting with rF-CEA/TRICOM. The addition of intratumoral (i.t.) delivery of IL-2 via a recombinant fowlpox (rF) IL-2 vector greatly enhanced anti-tumor activity of a recombinant vaccine, resulting in complete tumor regression in 70-80% of mice. The anti-tumor activity was shown to be dependent on CD8(+) cells and NK1.1(+). Cellular immune assays revealed that the addition of rF-IL-2 to the vaccination therapy enhanced CEA-specific tetramer(+) cell numbers, cytokine release and CTL lysis of CEA(+) targets. Moreover, tumor-bearing mice vaccinated with the CEA/TRICOM displayed an antigen cascade, i.e., CD8(+) T cell responses to two other antigens expressed on the tumor and not the vaccine: wild-type p53 and endogenous retroviral antigen gp70. Mice receiving rF-IL-2 during vaccination demonstrated higher avidity CEA-specific, as well as higher avidity gp70-specific, CD8(+) T cells when compared with mice vaccinated without rF-IL-2. These studies demonstrate for the first time that the level and avidity of antigen specific CTL, as well as the therapeutic outcome can be improved with the use of i.t. rF-IL-2 with vaccine regimens.

CD40-mediated death and cytokine secretion in colorectal cancer: a potential target for inflammatory tumour cell killing

CD40, a member of the tumour necrosis factor family, is expressed in a variety of epithelial cells. Although soluble CD40 agonists are growth-inhibitory, membrane-presented CD40 ligand (CD40L) induces extensive apoptosis in carcinoma cells. This study investigated whether CD40 is expressed in human colorectal carcinoma (CRC) cells and explored the functional consequences of CD40 ligation. CD40 expression in a panel of CRC lines was assessed by flow cytometry and in resected human CRCs by immunohistochemistry. CRC cells were treated in vitro with soluble CD40 agonists or cocultured with fibroblasts expressing membrane-bound CD40 ligand. Apoptosis was determined by flow cytometry using Annexin V/propidium iodide labelling and by a DNA fragmentation assay. Cytokine secretion induced by CD40 ligation was quantified by a multiplex-bead array approach. We show that CD40 is expressed in a proportion of established CRC lines in culture and that receptor expression is functional. Activation of CD40 by membrane-presented CD40L, but not soluble agonists, causes high levels of death in CD40-positive CRC cells and induces secretion of proinflammatory cytokines. In agreement with our in vitro observations, immunohistochemical studies demonstrated that CD40 is highly expressed in a proportion of colorectal cancer specimens. The high level of susceptibility of CRC cells to CD40-killing combined with the ability of CD40 to induce concomitant secretion of proinflammatory cytokines suggest that CD40 ligation may represent a novel mechanism for elimination of CRC cells and render CD40 a promising therapeutic target for the eradication of colorectal tumours.

Vascular endothelial growth factor blockade reduces intratumoral regulatory T cells and enhances the efficacy of a GM-CSF-secreting cancer immunotherapy

PURPOSE

The purpose of the present study was to evaluate granulocyte macrophage colony-stimulating factor (GM-CSF)-secreting tumor cell immunotherapy in combination with vascular endothelial growth factor (VEGF) blockage in preclinical models.

EXPERIMENTAL DESIGN

Survival and immune response were monitored in the B16 melanoma and the CT26 colon carcinoma models. VEGF blockade was achieved by using a recombinant adeno-associated virus vector expressing a soluble VEGF receptor consisting of selected domains of the VEGF receptors 1 and 2 (termed sVEGFR1/R2). Dendritic cell and tumor infiltrating lymphocyte activation status and numbers were evaluated by fluorescence-activated cell sorting analysis. Regulatory T cells were quantified by their CD4+CD25hi and CD4+FoxP3+ phenotype.

RESULTS

The present study established that GM-CSF-secreting tumor cell immunotherapy with VEGF blockade significantly prolonged the survival of tumor-bearing mice. Enhanced anti-tumor protection correlated with an increased number of activated CD4+ and CD8+ tumor-infiltrating T cells and a pronounced decrease in the number of suppressive regulatory T cells residing in the tumor. Conversely, overexpression of VEGF from tumors resulted in elevated numbers of regulatory T cells in the tumor, suggesting a novel mechanism of VEGF-mediated immune suppression at the tumor site.

CONCLUSION

GM-CSF-secreting cancer immunotherapy and VEGF blockade increases the i.t. ratio of effector to regulatory T cells to provide enhanced antitumor responses. This therapeutic combination may prove to be an effective strategy for the treatment of patients with cancer.

Multiple costimulatory modalities enhance CTL avidity

Recent studies in both animal models and clinical trials have demonstrated that the avidity of T cells is a major determinant of antitumor and antiviral immunity. In this study, we evaluated several different vaccine strategies for their ability to enhance both the quantity and avidity of CTL responses. CD8(+) T cell quantity was measured by tetramer binding precursor frequency, and avidity was measured by both tetramer dissociation and quantitative cytolytic function. We have evaluated a peptide, a viral vector expressing the Ag transgene alone, with one costimulatory molecule (B7-1), and with three costimulatory molecules (B7-1, ICAM-1, and LFA-3), with anti-CTLA-4 mAb, with GM-CSF, and combinations of the above. We have evaluated these strategies in both a foreign Ag model using beta-galactosidase as immunogen, and in a "self" Ag model, using carcinoembryonic Ag as immunogen in carcinoembryonic Ag transgenic mice. The combined use of several of these strategies was shown to enhance not only the quantity, but, to a greater magnitude, the avidity of T cells generated; a combination strategy is also shown to enhance antitumor effects. The results reported in this study thus demonstrate multiple strategies that can be used in both antitumor and antiviral vaccine settings to generate higher avidity host T cell responses.

Comparative studies of Avipox-GM-CSF versus recombinant GM-CSF protein as immune adjuvants with different vaccine platforms

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a potent immune stimulant when administered with different vaccines. Optimal use of GM-CSF resides in its ability to act locally to stimulate the proliferation and maturation of professional antigen-presenting cells (APCs) (i.e., Langerhans' cells) at the injection site. GM-CSF was engineered into a replication-incompetent recombinant avian (fowlpox) virus (rF-GM-CSF) and a single subcutaneous injection resulted in a sustained enrichment of activated dendritic cells within the regional draining lymph nodes. Those changes were attributed to local GM-CSF production at the injection site by rF-GM-CSF-infected cells. Studies were carried out in which mice were administered different types of beta-galactosidase (beta-gal)-based vaccines--whole protein, peptide, recombinant poxviruses--and GM-CSF was administered either as a single injection of rF-GM-CSF or four daily bolus injections of the recombinant protein. The use of rF-GM-CSF either improved the immune adjuvant effect, as observed for poxvirus-based vaccines, or was equivalent to rGM-CSF, as observed with the beta-gal protein vaccine. It is important to note that with either the replication-competent (vaccinia) or replication-incompetent (fowlpox) vaccines expressing LacZ, strong CTL responses directed against beta-gal were induced only when rF-GM-CSF was used as the immune adjuvant. Engineering GM-CSF into a recombinant fowlpox virus offers an excellent vehicle for the delivery of this cytokine as an immune adjuvant with specific vaccine platforms. In particular, delivery of GM-CSF via the rF-GM-CSF construct would be preferred over bolus injections of rGM-CSF when used as an immune adjuvant with whole protein or recombinant poxvirus-based vaccines. The study underscores the importance of defining the appropriate delivery form of an immune adjuvant, such as GM-CSF, relative to the immunization strategy to maximize the host immune responses against a specific antigen.

Intratumoral immunotherapy: using the tumour against itself

Summary Diverse immunotherapy approaches have achieved success in controlling individual aspects of immune responses in animal models. Transfer of such immunotherapies to clinical trials has obtained some success in patients, with clinical responses observed or effective antigen specific immune responses achieved, but has had limited impact on patient survival. Key elements required to generate de novo cell-mediated antitumour immune responses in vivo include recruitment of antigen-presenting cells to the tumour site, loading these cells with antigen, and their migration and maturation to full antigen-presenting function. In addition, it is essential for antigen-specific T cells to locate the tumour to mediate cytotoxicity, emphasizing the need for local inflammation to target effector cell recruitment. We review those therapies that involve the tumour site as a target and source of antigen for the initiation of immune responses, and discuss strategies to generate and co-ordinate an optimal cell-mediated immune response to control tumours locally.

Both soluble and membrane-bound forms of Flt3 ligand enhance tumor immunity following "suicide" gene therapy in a murine colon carcinoma model

In prodrug-activated ("suicide") gene therapy, tumor cells are transfected with the gene for an enzyme that converts an inactive prodrug, such as ganciclovir (GCV), to a toxic compound. Transfected cells are killed on administration of GCV, as also are untransfected "bystander" cells. The ability of the dendritic cell stimulatory cytokine Flt3 ligand (Flt3-L) to modulate prodrug-activated gene therapy has been investigated. Transfectants of the murine colon carcinoma MC26 were generated expressing soluble (FLS) and membrane-bound forms of Flt3-L. They were inoculated together with wild-type MC26 cells and cells expressing herpes simplex virus-1 (HSV1) thymidine kinase into BALB/c mice, which were then administered GCV. Expression of Flt3-L or FLS prevented regrowth of tumor in most mice, which was comparable to the effect of granulocyte-macrophage colony-stimulating factor (GM-CSF), while tumors recurred in all mice receiving "suicide" gene therapy alone. Recurring tumor cells were resistant to direct killing by GCV but sensitive to "bystander" killing in vitro. Mice without tumor recurrence were rechallenged with unmodified MC26 cells. Of those mice given transfectants expressing GM-CSF, Flt3-L, or FLS, approximately 50% were immune to rechallenge. These mice also showed cytotoxic and proliferative responses to MC26 cells. These experiments show that both soluble and membrane-bound forms of Flt3-L were able to induce a protective immune response to colon carcinoma cells in a fashion similar to GM-CSF.

Role of immature myeloid Gr-1+ cells in the development of antitumor immunity

One of the mechanisms by which tumor cells evade the immune system is the lack of proper antigen-presenting cells. Improvement in host immunity against tumor cells can be achieved by promoting the differentiation of dendritic cells (DCs) from immature myeloid cells (Gr-1(+)Ly-6C(+)F4/80(+)) that accumulate in the bone marrow and lymphoid organs of mice with large tumor burdens. The enriched immature myeloid cells inhibit T-cell proliferation and tumor-specific T-cell response, which can be reversed by the differentiation of immature myeloid cells or depletion of F4/80(+) cells. Sorted Gr-1(+)/F4/80(+) immature myeloid cells differentiated into CD11c(+) cells that express CD80 and I-A/I-E (MHC class II) in the presence of recombinant murine granulocyte macrophage colony-stimulating factor (GM-CSF). Furthermore, intratumoral gene delivery of GM-CSF not only promoted the differentiation of carboxyfluoroscein succinimidyl ester-labeled immature myeloid cells into CD11c(+) cells with the characteristics of mature DCs (CD80(+), I-A/I-E(+)) but also enhanced innate natural killer and adaptive cytolytic T-cell activities in mice treated with interleukin (IL)-12 and anti-4-1BB combination therapy. More importantly, intratumoral delivery of GM-CSF and IL-12 genes in combination with 4-1BB costimulation greatly improved the long-term survival rate of mice bearing large tumors and eradicated the untreated existing hepatic tumor. The results suggest that inducing the maturation of immature myeloid cells, thus preventing their inhibitory activity and enhancing their antigen-presenting capability, by GM-CSF gene therapy is a critically important step in the development of effective antitumor responses in hosts with advanced tumors.

In situ recruitment of antigen-presenting cells by intratumoral GM-CSF gene delivery

Proper antigen presentation is paramount to the induction of effective and persistent antitumor immune responses. In a murine model of hepatic metastasis of colon cancer, we found that the numbers of in situ mature dendritic cells (DCs) and macrophages in tumor-infiltrating leukocytes (TILs) were significantly increased in mice treated with the combination therapy of herpes simplex virus thymidine kinase, interleukin 2, and GM-CSF genes when compared with control groups without GM-CSF treatment. Significantly higher levels of IFN-gamma, MIP-1 alpha, mIL-12, and GM-CSF were detected in the tumor after the combination therapy. T cells isolated from the combination therapy-treated mice exhibited higher ex vivo direct CTL activity than those from other treatment groups. Antigen-presenting cells (APCs) enriched from the TILs and liver of the combination therapy-treated mice induced higher levels of proliferation by the splenocytes from long-term surviving mice that had been cured of tumors at early time points (days 4 and 7) whereas significant APC activity was only observed in the spleen at the latter time point (day 7, 14) after the combination therapy. In contrast, APCs isolated from tk or tk + IL-2-treated mice did not induce any significant proliferation. Subcutaneous injection of fluorescence-labeled latex microspheres followed by the combination therapy showed a similar sequential trafficking of microspheres, day 4 after the combination therapy to tumor and day 14 to spleen. The results suggest that APCs recruited by intratumoral gene delivery of GM-CSF can capture antigens, mature to a stage suitable for antigen presentation, and subsequently migrate to the spleen where they can efficiently stimulate antigen-specific T cells.

Cytokines and antitumor immunity

Currently, the notion of immunosurveillance against tumors is enjoying something of a renaissance. Even if we still refuse to accept that tumors arising in the normal host are unable to trigger an immune response because of the lack of initiation ("danger") signals, there is no doubt that the immune system can be manipulated experimentally and by implication therapeutically to exert anti-tumor effects. For this activity to be successful, the appropriate cytokine milieu has to be provided, making cytokine manipulation central to immunotherapy. On the other hand, the major hurdle currently preventing successful immunotherapy is the ability of tumors to evolve resistant variants under the pressure of immune selection. Here, too, the cytokine milieu plays an essential role. The purpose of this brief review is to consider the current status of the application of cytokines in facilitating antitumor immunity, as well their role in inhibiting responses to tumors. Clearly, encouraging the former but preventing the latter will be the key to the effective clinical application of cancer immunotherapy.

GM-CSF-based cancer vaccines

The crafting of genetic and biochemical techniques to identify cancer antigens yielded the unexpected discovery that immune recognition of tumors regularly accompanies cancer development. The failure of the host to suppress tumor formation or attenuate disease progression may thus reflect the limited immunogenicity of nascent tumors. One critical determinant of host immunity is the mixture of cytokines produced in the tumor microenvironment. We have compared a large number of secreted and surface molecules for their relative abilities to augment tumor immunity following gene transfer into cancer cells. In multiple murine models, granulocyte-macrophage colony stimulating factor (GM-CSF) proved to be the most potent immunostimulatory product. Vaccination with irradiated tumor cells engineered to secrete GM-CSF involves enhanced tumor antigen presentation by recruited dendritic cells (DCs) and macrophages; the coordinated functions of CD4+ and CD8+ T cells, CD1d-restricted NKT cells and antibodies mediate protective immunity. The evaluation of this vaccination strategy in patients with advanced melanoma revealed the consistent induction of cellular and humoral antitumor responses capable of effectuating substantial necrosis of distant metastases. The formulation of simplified methods for manufacturing autologous, GM-CSF-secreting tumor cells has enabled more extensive clinical testing in diverse patient settings.

Endogenous granulocyte-macrophage colony-stimulating factor overexpression in vivo results in the long-term recruitment of a distinct dendritic cell population with enhanced immunostimulatory function

GM-CSF is critical for dendritic cell (DC) survival and differentiation in vitro. To study its effect on DC development and function in vivo, we used a gene transfer vector to transiently overexpress GM-CSF in mice. We found that up to 24% of splenocytes became CD11c+ and the number of DC increased up to 260-fold to 3 x 10(8) cells. DC numbers remained substantially elevated even 75 days after treatment. The DC population was either CD8alpha+CD4- or CD8alpha-CD4- but not CD8alpha+CD4+ or CD8alpha-CD4+. This differs substantially from subsets recruited in normal or Flt3 ligand-treated mice or using GM-CSF protein injections. GM-CSF-recruited DC secreted extremely high levels of TNF-alpha compared with minimal amounts in DC from normal or Flt3 ligand-treated mice. Recruited DC also produced elevated levels of IL-6 but almost no IFN-gamma. GM-CSF DC had robust immune function compared with controls. They had an increased rate of Ag capture and caused greater allogeneic and Ag-specific T cell stimulation. Furthermore, GM-CSF-recruited DC increased NK cell lytic activity after coculture. The enhanced T cell and NK cell immunostimulation by GM-CSF DC was in part dependent on their secretion of TNF-alpha. Our findings show that GM-CSF can have an important role in DC development and recruitment in vivo and has potential application to immunotherapy in recruiting massive numbers of DC with enhanced ability to activate effector cells.

Transfection of macrophage inflammatory protein 1 alpha into B16 F10 melanoma cells inhibits growth of pulmonary metastases but not subcutaneous tumors

Macrophage inflammatory protein 1 alpha (MIP-1 alpha), a CC chemokine, is a chemoattractant for T cells and immature dendritic cells. Plasmacytoma cells expressing MIP-1 alpha generate a cytotoxic T cell response without affecting tumor growth. To understand this discrepancy, we compared a local tumor model with a metastatic one using MIP-1 alpha-transfected B16 F10 melanoma cells. Clonal idiosyncrasies were controlled by selecting three lipotransfected tumor clones and two pcDNA vector transfected control clones with equivalent in vitro proliferative capacities. No significant differences were seen between the MIP-1 alpha-producing and control melanoma cells after s.c. injection in the hind leg. All animals had a leg diameter of 10 cm in 18.5-21.5 days. However, after i.v. injection the number of pulmonary foci was significantly reduced in the MIP-1 alpha-producing clones. Injection of 10(6) control transfected cells resulted in a median of 98.5 tumor foci in 2 wk, whereas the injection of the MIP-1 alpha-producing clones resulted in 89.5, 26.5, and 0 foci. The number of metastatic foci was inversely proportional to the amount of MIP-1 alpha produced by the clone in vitro. Flow cytometry showed a significant increase in CD8(+) cells in lungs of mice with MIP-1 alpha-transfected tumors 3 days after injection. This increase was not maintained 10 days later despite continued production of MIP-1 alpha. The protection offered by transfection with MIP-1 alpha was significantly impaired in beta(2)-microglobulin(-/-) mice. Our findings suggest that MIP-1 alpha is effective in preventing the initiation of metastasis, but not at sustaining an effective antitumor response.

Induction of effective antitumor immune responses in a mouse bladder tumor model by using DNA of an alpha antigen from mycobacteria

One of the main objectives of cancer immunotherapy is the activation and increase in number of antitumor effector cells. Recently, genetically modified tumor cell vaccines have been proposed for elicitation of antitumor effector cells. Native alpha antigen (alpha Ag) (also known as MPT59 and antigen 85B) of mycobacteria, which cross-reacts among mycobacteria species, may play an important biological role in host-pathogen interaction because it elicits various helper T-cell type 1 immune responses. To assess the induction of antitumor immune responses by alpha Ag, mouse tumor cell lines transfected with cDNA of alpha Ag from Mycobacterium kansasii were established, and the possibility of producing a tumor cell vaccine for induction of antitumor effects was explored. Transfection of tumor cell lines with an alpha Ag gene lead to primary tumor rejection and the establishment of protective immunity to nontransfected original tumor cell lines in Mycobacterium bovis bacillus Calmette-Gurin (BCG)-primed and unprimed mice. Mice immunized with tumor cell lines transfected with the alpha Ag gene showed delayed-type hypersensitivity responses in vivo and proliferative responses together with induction of interferon-gamma of spleen cells against nontransfected wild-type tumor cell lines in in vitro experiments. Moreover, immunization of mice with alpha Ag-expressing tumor cells elicited tumor-specific and cytotoxic T lymphocyte (CTL) epitope peptide-specific CD8+ CTLs. The results of this study provided evidence of the potential usefulness of alpha Ag in tumor cell vaccines.

Cytokine-secreting tumor cell vaccines

Modification of the tumor microenvironment with gene transfer techniques stimulates two immune mechanisms that effectuate tumor destruction. One involves improved tumor-antigen presentation for the development of specific cellular and humoral immunity. The second involves compromise of the tumor vasculature by soluble factors and leukocytes.

Plasmid vaccine expressing granulocyte-macrophage colony-stimulating factor attracts infiltrates including immature dendritic cells into injected muscles

Plasmid-encoded GM-CSF (pGM-CSF) is an adjuvant for genetic vaccines; however, little is known about how pGM-CSF enhances immunogenicity. We now report that pGM-CSF injected into mouse muscle leads to a local infiltration of potential APCs. Infiltrates reached maximal size on days 3 to 5 after injection and appeared in several large discrete clusters within the muscle. Immunohistological studies in muscle sections from mice injected with pGM-CSF showed staining of cells with the macrophage markers CD11b, Mac-3, IA(d)/E(d) and to the granulocyte marker GR-1 from day 1 through day 14. Cells staining with the dendritic cell marker CD11c were detected only on days 3 to 5. Muscles injected with control plasmids did not stain for CD11c but did stain for CD11b, Mac-3, IA(d)/E(d), and GR-1. No staining was observed with the APC activation markers, B7.1 or CD40, or with markers for T or B cells. These findings are consistent with the infiltrating cells in the pGM-CSF-injected muscles being a mixture of neutrophils, macrophages, and immature dendritic cells and suggest that the i.m. APCs may be enhancing immune responses to coinjected plasmid Ags. This hypothesis is supported by data showing that 1) separation of injections with pGM-CSF and Ag-expressing plasmid into different sites did not enhance immune responses and 2) immune enhancement was associated with the presence of CD11c+ cells in the infiltrates. Thus, pGM-CSF enhancement may depend on APC recruitment to the i.m. site of injection.

Proinflammatory cytokine, chemokine, and cellular adhesion molecule expression during the acute phase of experimental brain abscess development

Brain abscess represents the infectious disease sequelae associated with the influx of inflammatory cells and activation of resident parenchymal cells in the central nervous system. However, the immune response leading to the establishment of a brain abscess remains poorly defined. In this study, we have characterized cytokine and chemokine expression in an experimental brain abscess model in the rat during the acute stage of abscess development. RNase protection assay revealed the induction of the proinflammatory cytokines interleukin (IL)-1alpha, IL-1beta, IL-6, and tumor necrosis factor-alpha as early as 1 to 6 hours after Staphylococcus aureus exposure. Evaluation of chemokine expression by reverse transcription-polymerase chain reaction demonstrated enhanced levels of the CXC chemokine KC 24 hours after bacterial exposure, which correlated with the appearance of neutrophils in the abscess. In addition, two CC chemokines, monocyte chemoattractant protein-1 and macrophage inflammatory protein-1alpha were induced within 24 hours after S. aureus exposure and preceded the influx of macrophages and lymphocytes into the brain. Analysis of abscess lesions by in situ hybridization identified CD11b+ cells as the source of IL-1beta in response to S. aureus. Both intercellular adhesion molecule-1 and platelet endothelial cell adhesion molecule expression were enhanced on microvessels in S. aureus but not sterile bead-implanted tissues at 24 and 48 hours after treatment. These results characterize proinflammatory cytokine and chemokine expression during the early response to S. aureus in the brain and provide the foundation to assess the functional significance of these mediators in brain abscess pathogenesis.