Comparative studies of the effects of recombinant GM-CSF and GM-CSF administered via a poxvirus to enhance the concentration of antigen- presenting cells in regional lymph nodes

A First-in-Human Phase I Clinical Study with MVX-ONCO-1, a Personalized Active Immunotherapy, in Patients with Advanced Solid Tumors

Over two decades, most cancer vaccines failed clinical development. Key factors may be the lack of efficient priming with tumor-specific antigens and strong immunostimulatory signals. MVX-ONCO-1, a personalized cell-based cancer immunotherapy, addresses these critical steps utilizing clinical-grade material to replicate a successful combination seen in experimental models: inactivated patient's own tumor cells, providing the widest cancer-specific antigen repertoire and a standardized, sustained, local delivery over days of a potent adjuvant achieved by encapsulated cell technology. We conducted an open-label, single-arm, first-in-human phase I study with MVX-ONCO-1 in patients with advanced refractory solid cancer. MVX-ONCO-1 comprises irradiated autologous tumor cells coimplanted with two macrocapsules containing genetically engineered cells producing granulocyte-macrophage colony-stimulating factor. Patients received six immunizations over 9 weeks without maintenance therapy. Primary objectives were safety, tolerability, and feasibility, whereas secondary objectives focused on efficacy and immune monitoring. Data from 34 patients demonstrated safety and feasibility with minor issues. Adverse events included one serious adverse event possibly related to investigational medicinal product and two moderate-related adverse events. More than 50% of the patients with advanced and mainly nonimmunogenic tumors showed clinical benefits, including partial responses, stable diseases, and prolonged survival. In recurrent/metastatic head and neck squamous cell carcinoma, one patient achieved a partial response, whereas another survived for more than 7 years without anticancer therapy for over 5 years. MVX-ONCO-1 is safe, well tolerated, and beneficial across several tumor types. Ongoing phase IIa trials target patients with advanced recurrent/metastatic head and neck squamous cell carcinoma after initial systemic therapy.

SIGNIFICANCE

This first-in-human phase I study introduces a groundbreaking approach to personalized cancer immunotherapy, addressing limitations of traditional strategies. By combining autologous irradiated tumor cells as a source of patient-specific antigens and utilizing encapsulated cell technology for localized, sustained delivery of granulocyte-macrophage colony-stimulating factor as an adjuvant, the study shows a very good safety and feasibility profile. This innovative approach holds the promise of addressing tumor heterogeneity by taking advantage of each patient's antigenic repertoire.

Adjuvant DNA vaccine pNMM promotes enhanced specific immunity and anti-tumor effects

DNA vaccines containing only antigenic components have limited efficacy and may fail to induce effective immune responses. Consequently, adjuvant molecules are often added to enhance immunogenicity. In this study, we generated a tumor vaccine using a plasmid encoding NMM (NY-ESO-1/MAGE-A3/MUC1) target antigens and immune-associated molecules. The products of the vaccine were analyzed in 293 T cells by western blotting, flow cytometry, and meso-scale discovery electrochemiluminescence. To assess the immunogenicity obtained, C57BL/6 mice were immunized using the DNA vaccine. The results revealed that following immunization, this DNA vaccine induced cellular immune responses in C57BL/6 mice, as evaluated by the release of IFN-γ, and we also detected increases in the percentages of nonspecific lymphocytes, as well as those of antigen-specific T cells. Furthermore, immunization with the pNMM vaccine was found to significantly inhibit tumor growth and prolonged the survival of mice with B16-NMM⁺-tumors. Our data revealed that pNMM DNA vaccines not only confer enhanced immunity against tumors but also provide a potentially novel approach for vaccine design. Moreover, our findings provide a basis for further studies on vaccine pharmacodynamics and pharmacology, and lay a solid foundation for clinical application.

Recombinant rabies virus expressing dog GM-CSF is an efficacious oral rabies vaccine for dogs

Developing efficacious oral rabies vaccines is an important step to increase immunization coverage for stray dogs, which are not accessible for parenteral vaccination. Our previous studies have demonstrated that recombinant rabies virus (RABV) expressing cytokines/chemokines induces robust protective immune responses after oral immunization in mice by recruiting and activating dendritic cells (DCs) and B cells. To develop an effective oral rabies vaccine for dogs, a recombinant attenuated RABV expressing dog GM-CSF, designated as LBNSE-dGM-CSF was constructed and used for oral vaccination in a dog model. Significantly more DCs or B cells were activated in the peripheral blood of dogs vaccinated orally with LBNSE-dGM-CSF than those vaccinated with the parent virus LBNSE, particularly at 3 days post immunization (dpi). As a result, significantly higher levels of virus neutralizing antibodies (VNAs) were detected in dogs immunized with LBNSE-dGM-CSF than with the parent virus. All the immunized dogs were protected against a lethal challenge with 4500 MICLD₅₀ of wild-type RABV SXTYD01. LBNSE-dGM-CSF was found to replicate mainly in the tonsils after oral vaccination as detected by nested RT-PCR and immunohistochemistry. Taken together, our results indicate that LBNSE-dGM-CSF could be a promising oral rabies vaccine candidate for dogs.

Recombinant Poxvirus and the Tumor Microenvironment: Oncolysis, Immune Regulation and Immunization

Oncolytic viruses (OVs) are being extensively studied for their potential roles in the development of cancer therapy regimens. In addition to their direct lytic effects, OVs can initiate and drive systemic antitumor immunity indirectly via release of tumor antigen, as well as by encoding and delivering immunostimulatory molecules. This combination makes them an effective platform for the development of immunotherapeutic strategies beyond their primary lytic function. Engineering the viruses to also express tumor-associated antigens (TAAs) allows them to simultaneously serve as therapeutic vaccines, targeting and amplifying an immune response to TAAs. Our group and others have shown that vaccinating intratumorally with a poxvirus that encodes TAAs, in addition to immune stimulatory molecules, can modulate the tumor microenvironment, overcome immune inhibitory pathways, and drive both local and systemic tumor specific immune responses.

Construction and in vitro evaluation of a recombinant live attenuated PRRSV expressing GM-CSF

Background

Porcine reproductive and respiratory syndrome virus (PRRSV) continues to be an important problem for the swine industry. Inactivated vaccines and modified-live virus vaccines are widely used in the field; however, the efficacy of these PRRSV vaccines is suboptimal due to poor immunogenicity. Granulocyte–macrophage colony stimulating factor (GM-CSF) has been extensively used as an effective genetic and protein adjuvant to enhance the efficiencies vaccines expressing tumor or pathogen antigens. The purpose of this study was to determine if GM-CSF could increase the efficiency of PRRSV vaccine.

Methods

The GM-CSF gene was inserted in the HuN4-F112 vaccine strain by overlap PCR. The expression of GM-CSF by the recombinant virus was confirmed with methods of indirect immunofluorescent assay (IFA) and Western blotting. The stability of recombinant virus was assessed by cDNA sequence and IFA after 20 passages. To detect the biological activity of GM-CSF expressed by the recombinant virus, bone marrow-derived dendritic cells (BMDCs) were isolated and co-cultured with the recombinant virus or parental virus and the surface phenotypes of BMDCs were examined by flow cytometric analysis. The cytokines secreted by BMDCs infected with PRRSV, or treated with LPS, GM-CSF or medium alone were evaluated by ProcartaPlexTM Multiplex Immunoassays and qRT-PCR.

Results

A novel modified-live PRRSV vaccine strain expressing GM-CSF (rHuN4-GM-CSF) was successfully constructed and rescued. The GM-CSF protein was stable expressed in recombinant virus-infected cells after 20 passages. Analysis of virus replication kinetics showed that the novel vaccine strain expressing GM-CSF had a similar replication rate as the parental virus. In vitro studies showed that infection of porcine BMDCs with rHuN4-GM-CSF resulted in increased surface expression of MHCI+, MHCII + and CD80/86+ that was dependent on virus expressed GM-CSF. The expression of representative cytokines was significantly up-regulated when BMDCs were incubated with the recombinant GM-CSF expressing virus.

Conclusions

Our results indicated that the expression of GM-CSF during infection with a vaccine strain could enhance the activation of BMDCs and increase cytokine response, which is expected to result in higher immune responses and may improve vaccine efficacy against PRRSV infection.

Enhancement of antitumor immunity using a DNA-based replicon vaccine derived from Semliki Forest virus

A DNA-based replicon vaccine derived from Semliki Forest virus, PSVK-shFcG-GM/B7.1 (Fig. 1a) was designed for tumor immunotherapy as previously constructed. The expression of the fusion tumor antigen (survivin and hCGβ-CTP37) and adjuvant molecular protein (Granulocyte-Macrophage Colony-Stimulating Factor/ GM-CSF/B7.1) genes was confirmed by Immunofluorescence assay in vitro, and immunohistochemistry assay in vivo. In this paper, the immunological effect of this vaccine was determined using immunological assays as well as animal models. The results showed that this DNA vaccine induced both humoral and cellular immune responses in C57BL/6 mice after immunization, as evaluated by the ratio of CD4⁺/CD8⁺ cells and the release of IFN-γ. Furthermore, the vaccination of C57BL/6 mice with PSVK-shFcG-GM/B7.1 significantly delayed the in vivo growth of tumors in animal models (survivin⁺ and hCGβ⁺ murine melanoma, B16) when compared to vaccination with the empty vector or the other control constructs (Fig. 1b). These data indicate that this type of replicative DNA vaccine could be developed as a promising approach for tumor immunotherapy. Meanwhile, these results provide a basis for further study in vaccine pharmacodynamics and pharmacology, and lay a solid foundation for clinical application.

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.

Inhibition of TGF-β1 signaling promotes central memory T cell differentiation

This study affirmed that isolated CD8(+) T cells express mRNA and produce TGF-β following cognate peptide recognition. Blockage of endogenous TGF-β with either a TGF-β-blocking Ab or a small molecule inhibitor of TGF-βRI enhances the generation of CD62L(high)/CD44(high) central memory CD8(+) T cells accompanied with a robust recall response. Interestingly, the augmentation within the central memory T cell pool occurs in lieu of cellular proliferation or activation, but with the expected increase in the ratio of the Eomesoderm/T-bet transcriptional factors. Yet, the signal transduction pathway(s) seems to be noncanonical, independent of SMAD or mammalian target of rapamycin signaling. Enhancement of central memory generation by TGF-β blockade is also confirmed in human PBMCs. The findings underscore the role(s) that autocrine TGF-β plays in T cell homeostasis and, in particular, the balance of effector/memory and central/memory T cells. These results may provide a rationale to targeting TGF-β signaling to enhance Ag-specific CD8(+) T cell memory against a lethal infection or cancer.

Distinct effects of saracatinib on memory CD8+ T cell differentiation

Immunologic memory involving CD8(+) T cells is a hallmark of an adaptive Ag-specific immune response and constitutes a critical component of protective immunity. Designing approaches that enhance long-term T cell memory would, for the most part, fortify vaccines and enhance host protection against infectious diseases and, perhaps, cancer immunotherapy. A better understanding of the cellular programs involved in the Ag-specific T cell response has led to new approaches that target the magnitude and quality of the memory T cell response. In this article, we show that T cells from TCR transgenic mice for the nucleoprotein of influenza virus NP68 exhibit the distinct phases--priming, expansion, contraction, and memory--of an Ag-specific T cell response when exposed in vitro to the cognate peptide. Saracatinib, a specific inhibitor of Src family kinases, administered at low doses during the expansion or contraction phases, increased CD62L(high)/CD44(high) central memory CD8(+) T cells and IFN-γ production but suppressed immunity when added during the priming phase. These effects by saracatinib were not accompanied by the expected decline of Src family kinases but were accompanied by Akt-mammalian target of rapamycin suppression and/or mediated via another pathway. Increased central memory cells by saracatinib were recapitulated in mice using a poxvirus-based influenza vaccine, thus underscoring the importance of dose and timing of the inhibitor in the context of memory T cell differentiation. Finally, vaccine plus saracatinib treatment showed better protection against tumor challenge. The immune-potentiating effects on CD8(+) T cells by a low dose of saracatinib might afford better protection from pathogens or cancer when combined with vaccine.

A role for granulocyte-macrophage colony-stimulating factor in the regulation of CD8(+) T cell responses to rabies virus

Inflammatory cytokines have a significant role in altering the innate and adaptive arms of immune responses. Here, we analyzed the effect of GM-CSF on a RABV-vaccine vector co-expressing HIV-1 Gag. To this end, we immunized mice with RABV expressing HIV-1 Gag and GM-CSF and analyzed the primary and recall CD8(+) T cell responses. We observed a statistically significant increase in antigen presenting cells (APCs) in the spleen and draining lymph nodes in response to GM-CSF. Despite the increase in APCs, the primary and memory anti HIV-1 CD8(+) T cell response was significantly lower. This was partly likely due to lower levels of proliferation in the spleen. Animals treated with GM-CSF neutralizing antibodies restored the CD8(+) T cell response. These data define a role of GM-CSF expression, in the regulation of the CD8(+) T cell immune responses against RABV and has implications in the use of GM-CSF as a molecular adjuvant in vaccine development.

Innate immune recognition of poxviral vaccine vectors

The study of poxviruses pioneered the field of vaccinology after Jenner's remarkable discovery that 'vaccination' with the phylogenetically related cowpox virus conferred immunity to the devastating disease of smallpox. The study of poxviruses continues to enrich the field of virology because the global eradication of smallpox provides a unique example of the potency of effective immunization. Other poxviruses have since been developed as vaccine vectors for clinical and veterinary applications and include modified vaccinia virus strains such as modified vaccinia Ankara and NYVAC as well as the avipox viruses, fowlpox virus and canarypox virus. Despite the empirical development of poxvirus-based vectored vaccines, it is only now becoming apparent that we need to better understand how the innate arm of the immune system drives adaptive immunity to poxviruses, and how this information is relevant to vaccine design strategies, which are the topics addressed in this article.

Effect of a small molecule BCL-2 inhibitor on immune function and use with a recombinant vaccine

Small molecule BCL-2 inhibitors are being examined as monotherapy in phase I/II clinical trials for several types of tumors. However, few data are available about the effect of BCL-2 inhibitors on immune function. The aims of our study were to investigate the effect of a small molecule BCL-2 inhibitor on immune function and determine the most effective way of combining this inhibitor with a recombinant vaccine to treat tumors. The in vitro effect of the pan-BCL-2 inhibitor GX15-070 was assessed in mouse CD8 T lymphocytes at 2 different stages of activation as well as regulatory T lymphocytes (Treg). The in vivo effect of GX15-070 after recombinant vaccinia/fowlpox CEA-TRICOM vaccination was analyzed in tumor-infiltrating lymphocytes, and in splenocytes of mice bearing subcutaneous tumors. The therapeutic efficacy of such sequential therapy was measured as a reduction of pulmonary tumor nodules. Activated mature CD8 T lymphocytes were more resistant to GX15-070 as compared to early-activated cells. Treg function was significantly decreased after treatment with the BCL-2 inhibitor. In vivo, GX15-070 was given after vaccination so as to not negatively impact the induction of vaccine-mediated immunity, resulting in increased intratumoral activated CD8:Treg ratio and significant reduction of pulmonary tumor nodules. Our study is the first to show the effect of a small molecule BCL-2 inhibitor on the immune system and following a vaccine. It is also the first to demonstrate the efficacy of this sequence in reducing tumors in mouse models, providing a rationale for the design of combinational clinical studies.

Vaccines against human carcinomas: strategies to improve antitumor immune responses

Multiple observations in preclinical and clinical studies support a role for the immune system in controlling tumor growth and progression. Various components of the innate and adaptive immune response are able to mediate tumor cell destruction; however, certain immune cell populations can also induce a protumor environment that favors tumor growth and the development of metastasis. Moreover, tumor cells themselves are equipped with various mechanisms that allow them to evade surveillance by the immune system. The goal of cancer vaccines is to induce a tumor-specific immune response that ultimately will reduce tumor burden by tipping the balance from a protumor to an antitumor immune environment. This review discusses common mechanisms that govern immune cell activation and tumor immune escape, and some of the current strategies employed in the field of cancer vaccines aimed at enhancing activation of tumor-specific T-cells with concurrent reduction of immunosuppression.

Vaccination with a recombinant Saccharomyces cerevisiae expressing a tumor antigen breaks immune tolerance and elicits therapeutic antitumor responses

PURPOSE

Saccharomyces cerevisiae, a nonpathogenic yeast, has been used previously as a vehicle to elicit immune responses to foreign antigens, and tumor-associated antigens, and has been shown to reduce tumor burden in mice. Studies were designed to determine if vaccination of human carcinoembryonic antigen (CEA)-transgenic (CEA-Tg) mice (where CEA is a self-antigen) with a recombinant S. cerevisiae construct expressing human CEA (yeast-CEA) elicits CEA-specific T-cell responses and antitumor activity.

EXPERIMENTAL DESIGN

CEA-Tg mice were vaccinated with yeast-CEA, and CD4(+) and CD8(+) T-cell responses were assessed after one and multiple administrations or vaccinations at multiple sites per administration. Antitumor activity was determined by tumor growth and overall survival in both pulmonary metastasis and s.c. pancreatic tumor models.

RESULTS

These studies demonstrate that recombinant yeast can break tolerance and that (a) yeast-CEA constructs elicit both CEA-specific CD4(+) and CD8(+) T-cell responses; (b) repeated yeast-CEA administration causes increased antigen-specific T-cell responses after each vaccination; (c) vaccination with yeast-CEA at multiple sites induces a greater T-cell response than the same dose given at a single site; and (d) tumor-bearing mice vaccinated with yeast-CEA show a reduction in tumor burden and increased overall survival compared to mock-treated or control yeast-vaccinated mice in both pulmonary metastasis and s.c. pancreatic tumor models.

CONCLUSIONS

Vaccination with a heat-killed recombinant yeast expressing the tumor-associated antigen CEA induces CEA-specific immune responses, reduces tumor burden, and extends overall survival in CEA-Tg mice. These studies thus form the rationale for the incorporation of recombinant yeast-CEA and other recombinant yeast constructs in cancer immunotherapy protocols.

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.

Chitosan solution enhances the immunoadjuvant properties of GM-CSF

Sustained, local delivery of immunomodulatory cytokines is under investigation for its ability to enhance vaccine and anti-tumor responses both clinically and preclinically. This study evaluates the ability of chitosan, a biocompatible polysaccharide, to (1) control the dissemination of a cytokine, GM-CSF, and (2) enhance the immunoadjuvant properties of GM-CSF. While cytokines have previously been delivered in lipid-based adjuvants and other vehicles, these do not have the clinical safety profile or unique properties of chitosan. We found that chitosan solution maintained a measurable depot of recombinant GM-CSF (rGM-CSF) at a subcutaneous injection site for up to 9 days. In contrast, when delivered in a saline vehicle, rGM-CSF was undetectable in 12-24h. Furthermore, a single s.c. injection of 20 microg rGM-CSF in chitosan solution (chitosan/rGM-CSF(20 microg)) transiently expanded lymph nodes up to 4.6-fold and increased the number of MHC class II expressing cells and dendritic cells by 7.4-fold and 6.8-fold, respectively. These increases were significantly greater than those measured when rGM-CSF was administered in saline at the standard preclinical dose and schedule, i.e. 4 daily s.c. injections of 20 microg. Furthermore, lymph node cells from mice injected with chitosan/rGM-CSF(20 microg) induced greater allogeneic T cell proliferation, indicating enhanced antigen presenting capability, than lymph node cells from mice injected with rGM-CSF alone. Finally, in vaccination experiments, chitosan/rGM-CSF was superior to either chitosan or rGM-CSF alone in enhancing the induction of antigen-specific CD4(+) proliferation, peptide-specific CD8(+) pentamer staining and cytotoxic T cell lysis. Altogether, chitosan/rGM-CSF outperformed standard rGM-CSF administrations in dendritic cell recruitment, antigen presentation and vaccine enhancement. We conclude that chitosan solution is a promising delivery platform for the sustained, local delivery of rGM-CSF.

Combination therapy of an orthotopic renal cell carcinoma model using intratumoral vector-mediated costimulation and systemic interleukin-2

PURPOSE

Interleukin (IL)-2 therapy is currently used for therapy of renal cell carcinoma (RCC). However, it is only effective in approximately 10% to 15% of patients, showing a need for additional therapies. We have previously described a replication-defective fowlpox vector encoding three costimulatory molecules (B7-1, ICAM-1, and LFA-3), designated rF-TRICOM. Here, we show that intratumoral administration of rF-TRICOM in an orthotopic RCC model effectively enhances tumor immunogenicity and reduces tumor burden in mice and the combination of rF-TRICOM and IL-2 is more effective than either therapy alone.

EXPERIMENTAL DESIGN

RCC cells were implanted under the capsule of the kidney, and mice were given rF-TRICOM intratumorally 14 days later. We compared the effect of rF-TRICOM, rF-granulocyte macrophage colony-stimulating factor (GM-CSF), and two doses of IL-2 and combinations of the above on antitumor efficacy and survival. Host CD4(+) and CD8(+) T-cell responses were also evaluated.

RESULTS

The results show that (a) systemic IL-2 therapy was moderately effective in the reduction of tumor burden in an orthotopic RCC model; (b) a single intratumoral injection of rF-TRICOM and rF-GM-CSF significantly reduced tumor burden; (c) the addition of systemic IL-2 to intratumoral rF-TRICOM/rF-GM-CSF administration resulted in further reduction of tumor burden, decrease in the incidence of metastasis, and extended survival in tumor-bearing mice above that seen with either treatment alone; and (d) CD8(+) T cells played a critical role in the antitumor effect seen with rF-TRICOM/rF-GM-CSF + IL-2 therapy. Finally, the addition of systemic recombinant IL-15 or intratumoral vector-delivered IL-15 to intratumoral rF-TRICOM/rF-GM-CSF administration resulted in substantially more tumor-free mice than either therapy alone.

CONCLUSIONS

These studies show that intratumoral administration of rF-TRICOM admixed with rF-GM-CSF is effective at reducing tumor burden in mice and the addition of IL-2 further contributes to this effect. These studies thus form the rationale for combination immunotherapy clinical trials in patients with RCC.

Chemotherapy enhances CD8(+) T cell-mediated antitumor immunity induced by vaccination with vaccinia virus

The use of immunotherapy or chemotherapy alone is generally ineffective against well-established tumors. To overcome this intrinsic resistance against therapy for tumors, we have attempted to combine immunotherapy with chemotherapy. In this study, we tried to induce a rapid antitumor effect via chemoimmunotherapy using a vaccinia viral vaccine as an immunotherapeutic agent with anticancer agents including epigallocatechin-3-gallate (EGCG) and conventional anticancer drugs. Although a combination of vaccinia-mediated vaccination and chemotherapy led to a strong inhibition of tumor growth, monotherapy alone failed to completely cure tumors. In contrast, intravenous injection of cisplatin (CDDP) or cyclophosphamide (CTX) after vaccinia virus vaccination led to complete regression of the established tumors. Interestingly, anticancer drugs appear to augment the antitumor effect of the vaccinia virus-mediated immunotherapy. This effect is mainly associated with the enhanced tumor-specific CD8(+) T cell immune response induced by vaccinia virus, which was demonstrated by antibody depletion. However, anticancer drugs alone failed to induce a significant enhancement of the tumor-specific CD8(+) T cell immune response. Taken together, these results suggest that combining vaccinia virus-based immunotherapy with anticancer drugs is particularly effective against established tumors by increasing the tumor antigen-specific CD8(+) T cell immune response, which is primed by vaccinia virus-mediated vaccination.

PANVAC-VF: poxviral-based vaccine therapy targeting CEA and MUC1 in carcinoma

PANVAC is a cancer vaccine therapy delivered through two viral vectors--recombinant vaccinia and recombinant fowlpox--which are given sequentially. Both vectors contain transgenes for the tumor-associated antigens epithelial mucin 1 and carcinoembryonic antigen, which are altered or overexpressed in most carcinomas. The vectors also contain transgenes for three human T cell costimulatory molecules required to enhance immune response: B7.1, intracellular adhesion molecule-1 and leukocyte function-associated antigen-3. PANVAC is injected subcutaneously and processed by the body's antigen-presenting cells. Preclinical studies have demonstrated the efficacy of PANVAC in inducing both carcinoembryonic antigen- and mucin 1-specific cytotoxic T lymphocyte responses in vitro and in murine models. Other strategies that enhance the immune response include the use of granulocyte-macrophage colony-stimulating factor and a prime-boost administration sequence. Clinical trials have demonstrated PANVAC's safety and its ability to induce antigen-specific T cell responses. Early clinical trials are evaluating PANVAC alone and in combination with conventional chemotherapy and/or radiation. Studies to date hold promise for the use of PANVAC as a means to stimulate the immune system against malignancies and to provide clinical benefit.

Expression of CCL20 and granulocyte-macrophage colony-stimulating factor, but not Flt3-L, from modified vaccinia virus ankara enhances antiviral cellular and humoral immune responses

While modified vaccinia virus Ankara (MVA) is currently in clinical development as a safe vaccine against smallpox and heterologous infectious diseases, its immunogenicity is likely limited due to the inability of the virus to replicate productively in mammalian hosts. In light of recent data demonstrating that vaccinia viruses, including MVA, preferentially infect antigen-presenting cells (APCs) that play crucial roles in generating antiviral immunity, we hypothesized that expression of specific cytokines and chemokines that mediate APC recruitment and activation from recombinant MVA (rMVA) vectors would enhance the immunogenicity of these vectors. To test this hypothesis, we generated rMVAs that express murine granulocyte-macrophage colony-stimulating factor (mGM-CSF), human CCL20/human macrophage inflammatory protein 3alpha (hCCL20/hMIP-3alpha), or human fms-like tyrosine kinase 3 ligand (hFlt3-L), factors predicted to increase levels of dendritic cells (DCs), to recruit DCs to sites of immunization, or to promote maturation of DCs in vivo, respectively. These rMVAs also coexpress the well-characterized, immunodominant lymphocytic choriomeningitis virus nucleoprotein (NP) antigen that enabled sensitive and quantitative assessment of antigen-specific CD8(+) T-cell responses following immunization of BALB/c mice. Our results demonstrate that immunization of mice with rMVAs expressing mGM-CSF or hCCL20, but not hFlt3-L, results in two- to fourfold increases of cellular immune responses directed against vector-encoded antigens and 6- to 17-fold enhancements of MVA-specific antibody titers, compared to those responses elicited by nonadjuvanted rMVA. Of note, cytokine augmentation of cellular immune responses occurs when rMVAs are given as primary immunizations but not when they are used as booster immunizations, suggesting that these APC-modulating proteins, when used as poxvirus-encoded adjuvants, are more effective at stimulating naïve T-cell responses than in promoting recall of preexisting memory T-cell responses. Our results demonstrate that a strategy to express specific genetic adjuvants from rMVA vectors can be successfully applied to enhance the immunogenicity of MVA-based vaccines.

Mouse models expressing human carcinoembryonic antigen (CEA) as a transgene: evaluation of CEA-based cancer vaccines

In recent years, investigators have carried out several studies designed to evaluate whether human tumor-associated antigens might be exploited as targets for active specific immunotherapy, specifically human cancer vaccines. Not too long ago such an approach would have been met with considerable skepticism because the immune system was believed to be a rigid discriminator between self and non-self which, in turn, protected the host from a variety of pathogens. That viewpoint has been challenged in recent years by a series of studies indicating that antigenic determinants of self have not induced absolute host immune tolerance. Moreover, under specific conditions that evoke danger signals, peptides from self-antigen can be processed by the antigen-presenting cellular machinery, loaded onto the major histocompatibility antigen groove to serve as targets for immune intervention. Those findings provide the rationale to investigate a wide range of tumor-associated antigens, including differentiation antigens, oncogenes, and tumor suppressor genes as possible immune-based targets. One of those tumor-associated antigens is the carcinoembryonic antigen (CEA). Described almost 40 years ago, CEA is a M(r) 180-200,000 oncofetal antigen that is one of the more widely studied human tumor-associated antigens. This review will provide: (i) a brief overview of the CEA gene family, (ii) a summary of early preclinical findings on overcoming immune tolerance to CEA, and (iii) the rationale to develop mouse models which spontaneously develop gastrointestinal tumors and express the CEA transgene. Those models have been used extensively in the study of overcoming host immune tolerance to CEA, a self, tumor-associated antigen, and the experimental findings have served as the rationale for the design of early clinical trials to evaluate CEA-based cancer vaccines.

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.

Immunotherapy for colorectal cancer

There have been significant improvements in the diagnosis and treatment of colorectal cancer over the past 15 years. However, some 30% of patients with colorectal cancer have disseminated disease at presentation, and furthermore, 50% of patients initially believed to be cured by surgery subsequently relapse and die of the disease. Novel treatment concepts based on understanding the molecular signatures that separate tumor from normal epithelium, such as immunotherapy, are aimed at abolishing microscopic residual disease post standard treatment. The authors provide an overview of progress in the development of specific and nonspecific immunotherapies and explain why definition of end-points and early translation of immunotherapy into the adjuvant field are key to effective use of such agents in the clinical setting.

Granulocyte-macrophage-colony-stimulating factor added to a multipeptide vaccine for resected Stage II melanoma

BACKGROUND

Forty-eight patients with resected Stages IIA and IIB melanoma were immunized with two tumor antigen epitope peptides derived from gp100(209-217) (210M) (IMDQVPSFV) and tyrosinase(368-376) (370D) (YMDGTMSQV) emulsified with incomplete Freund's adjuvant (IFA). Patients were assigned randomly to receive either peptides/IFA alone or with 250 microm of granulocyte-macrophage-colony-stimulating factor (GM-CSF) subcutaneously daily for 5 days to evaluate the toxicities and immune responses in either arm. Time to recurrence and survival were secondary end points.

METHODS

Immunizations were administered every 2 weeks x 4, then every 4 weeks x 3, and once 8 weeks later. A leukapheresis to obtain peripheral blood mononuclear cells for immune analyses and skin testing with peptides and recall reagents was performed before and after eight vaccinations.

RESULTS

Local pain and granuloma formation, fever, and lethargy of Grade 1 or 2 were observed. Transient vaccine-related Grade III and no Grade IV toxicity was observed. Seventeen of the 40 patients for whom posttreatment skin tests were performed developed a positive skin test response to the gp100 peptide, but only 1 of the 40 patients developed a positive skin test response to tyrosinase. Immune responses were measured by release of interferon-gamma (IFN-gamma) in an enzyme-linked immunosorbent assay (ELISA) by effector cells in the presence of peptide-pulsed antigen-presenting cells, by cytokine release of IFN-gamma, GM-CSF, and tumor necrosis factor-alpha in a Luminex assay, or by an antigen-specific tetramer flow cytometry assay. Thirty-four of the 39 patients for whom the ELISA data were performed demonstrated an immune response after vaccination, as did 37 of 42 patients by tetramer assay. Enzyme-linked immunosorbent assay, Luminex, and tetramer responses in the GM-CSF/peptide/IFA group were higher than in the peptide/IFA group. Epitope spreading to the MART-1/MelanA 27-35 and 26-35 (27L) epitopes was detected by tetramer assay in 10 patients. Seven of 48 patients experienced disease recurrence with a median of 24 months of follow-up and 2 patients in this intermediate to high risk group have died.

CONCLUSION

These data suggest a significant number of patients with resected melanoma mount an antigen-specific immune response against a peptide vaccine. There is a trend for GM-CSF to modestly increase the immune response and support further development of GM-CSF as a vaccine adjuvant.

Selective induction of apoptosis in antigen-presenting cells in mice by Parapoxvirus ovis

Viruses have evolved numerous mechanisms to avoid host immune reactions. Here we report a mechanism by which Parapoxvirus ovis (PPVO) interferes with antigen presentation. PPVO (orf virus) causes orf, an acute skin disease of sheep and goats worldwide. Importantly, PPVO can repeatedly infect its host in spite of a vigorous inflammatory and host immune response to the infection. We demonstrate in a mouse system that PPVO induces apoptosis in a significant number of antigen-presenting cells after intraperitoneal injection using the CD95 pathway, thus preventing a primary T-cell response. We also show that PPVO induces a compensatory activation of the immune system. Our results may help to explain the phenomenon that natural PPVO infections in sheep occur repeatedly even after short intervals. They also suggest that the combination of immunosuppressive and immunostimulatory mechanisms is an effective survival strategy that might be used in other viruses as well.

Phase I study in advanced cancer patients of a diversified prime-and-boost vaccination protocol using recombinant vaccinia virus and recombinant nonreplicating avipox virus to elicit anti-carcinoembryonic antigen immune responses

PURPOSE

This trial sought to determine, for the first time, the validity in human vaccinations of using two different recombinant vaccines in diversified prime-and-boost regimens to enhance T-cell responses to a tumor antigen.

PATIENTS AND METHODS

Eighteen patients with advanced tumors expressing carcinoembryonic antigen (CEA) were randomized to receive either recombinant vaccinia (rV)-CEA followed by three avipox-CEA vaccinations, or avipox-CEA (three times) followed by one rV-CEA vaccination. Subsequent vaccinations in both cohorts were with avipox-CEA. Immunologic monitoring was performed using a CEA peptide and the enzyme-linked immunospot assay for interferon gamma production.

RESULTS

rV-CEA followed by avipox-CEA was superior to the reverse order in the generation of CEA-specific T-cell responses. Further increases in CEA-specific T-cell precursors were seen when local granulocyte-macrophage colony-stimulating factor (GM-CSF) and low-dose interleukin (IL)-2 were given with subsequent vaccinations. The treatment was extremely well tolerated. Limited clinical activity was seen using vaccines alone in this patient population. Antibody production against CEA was also observed in some of the treated patients.

CONCLUSION

rV-CEA was more effective in its role as a primer of the immune system; avipox-CEA could be given up to eight times with continued increases in CEA T-cell precursors. Future trials should use rV-CEA first followed by avipox-CEA. Vaccines specific to CEA are able to generate CEA-specific T-cell responses in patients without significant toxicity. T-cell responses using vaccines alone may be inadequate to generate significant anticancer objective responses in patients with advanced disease. Cytokines such as GM-CSF and IL-2 may play a key role in generating such responses.