Identification of potent biodegradable adjuvants that efficiently break self-tolerance--a key issue in the development of therapeutic vaccines

Vaccination against galectin-1 promotes cytotoxic T-cell infiltration in melanoma and reduces tumor burden

Galectin-1 (Gal1) is a glycan-binding protein that promotes tumor progression by several distinct mechanisms. Through direct binding to vascular endothelial growth factor (VEGF)-receptor 2, Gal1 is able to induce VEGF-like signaling, which contributes to tumor angiogenesis. Furthermore, several studies have demonstrated an immunosuppressive function of Gal1 through effects on both effector and regulatory T cells. Elevated Gal1 expression and secretion have been shown in many tumor types, and high Gal1 serum levels have been connected to poor prognosis in cancer patients. These findings suggest that therapeutic strategies directed against Gal1 would enable simultaneous targeting of angiogenesis, immune evasion and metastasis. In the current study, we have analyzed the potential of Gal1 as a cancer vaccine target. We show that it is possible to generate high anti-Gal1 antibody levels in mice immunized with a recombinant vaccine protein consisting of bacterial sequences fused to Gal1. Growth of Gal1 expressing melanomas was significantly impaired in the immunized mice compared to the control group. This was associated with improved perfusion of the tumor vasculature, as well as increased infiltration of macrophages and cytotoxic T cells (CTLs). The level of granzyme B, mainly originating from CTLs in our model, was significantly elevated in Gal1 vaccinated mice and correlated with a decrease in tumor burden. We conclude that vaccination against Gal1 is a promising pro-immunogenic approach for cancer therapy that could potentially enhance the effect of other immunotherapeutic strategies due to its ability to promote CTL influx in tumors.

Cancer Vaccination against Extracellular Vimentin Efficiently Adjuvanted with Montanide ISA 720/CpG

Simple Summary

Vaccination against specific proteins in the tumor vasculature has already shown promising results in several preclinical studies. However, the efficacy of vaccination highly depends on the adjuvant used. This study aimed to assess the potential use of the biodegradable adjuvant Montanide ISA 720 in combination with our vaccine against extracellular vimentin, a protein specifically secreted by the tumor vasculature. Compared to the potent but toxic Freund’s adjuvant, Montanide showed a comparable immune response and tumor growth inhibition in a preclinical vaccination experiment in mice, especially when supplemented with the immune stimulatory molecule CpG. We also observed that vaccination reduced the blood vessel count and increased the infiltration of immune cells. We conclude that Montanide ISA 720 shows potential to be used as an adjuvant for vaccination against extracellular vimentin for future clinical studies in cancer patients.

Abstract

Extracellular vimentin is a specific marker of the tumor vasculature, where it is secreted by tumor endothelial cells. Vaccination with a conjugate vaccine targeting extracellular vimentin was previously shown to induce a potent humoral immune response and tumor growth inhibition in mice. These data were obtained by vaccination using the toxic Freund’s adjuvant (FA) and are therefore not directly translatable into the clinic. In the present study, we aimed to investigate the potential of the biodegradable Montanide ISA 720 adjuvant. We tested Montanide either alone (MN) or supplemented with CpG 1826 (MN-C). Both adjuvant compositions, as well as FA, resulted in a significant tumor growth inhibition and decreased vessel density in the B16F10 melanoma tumor model. Vaccination of mice with either FA or MN-C resulted in an equally potent humoral immune response towards vimentin, while the antibody titers obtained with MN alone were significantly lower compared to FA. Vaccination coincided with the infiltration of immune cells. The highest number of intratumoral immune cells was seen in tumors from the MN-C group. Therefore, we conclude that Montanide ISA 720 supplemented with CpG allows efficient vaccination against extracellular vimentin, which is a prerequisite for the transfer of the vaccine into the clinic.

Tracing the Origins of IgE, Mast Cells, and Allergies by Studies of Wild Animals

In most industrialized countries, allergies have increased in frequency quite dramatically during the past 50 years. Estimates show that 20–30% of the populations are affected. Allergies have thereby become one of the major medical challenges of the twenty-first century. Despite several theories including the hygiene hypothesis, there are still very few solid clues concerning the causes of this increase. To trace the origins of allergies, we have studied cells and molecules of importance for the development of IgE-mediated allergies, including the repertoire of immunoglobulin genes. These studies have shown that IgE and IgG most likely appeared by a gene duplication of IgY in an early mammal, possibly 220–300 million years ago. Receptors specific for IgE and IgG subsequently appeared in parallel with the increase in Ig isotypes from a subfamily of the recently identified Fc receptor-like molecules. Circulating IgE levels are generally very low in humans and laboratory rodents. However, when dogs and Scandinavian wolfs were analyzed, IgE levels were found to be 100–200 times higher compared to humans, indicating a generally much more active IgE synthesis in free-living animals, most likely connected to intestinal parasite infections. One of the major effector molecules released upon IgE-mediated activation by mast cells are serine proteases. These proteases, which belong to the large family of hematopoietic serine proteases, are extremely abundant and can account for up to 35% of the total cellular protein. Recent studies show that several of these enzymes, including the chymases and tryptases, are old. Ancestors for these enzymes were most likely present in an early mammal more than 200 million years ago before the separation of the three extant mammalian lineages; monotremes, marsupials, and placental mammals. The aim is now to continue these studies of mast cell biology and IgE to obtain additional clues to their evolutionary conserved functions. A focus concerns why the humoral immune response involving IgE and mast cells have become so dysregulated in humans as well as several of our domestic companion animals.

The revival of cancer vaccines - The eminent need to activate humoral immunity

In light of the increasing number of approved monoclonal antibodies for the treatment of cancer, it seems peculiar that the development of antibody inducing vaccines gets so little attention. In our view there is a tremendous opportunity in the development of cancer vaccines inducing humoral immune responses, involving a couple of major advantages. Firstly, the effectivity of a polyclonal antibody response is expected to exceed the one of monoclonal antibodies. This is supported by preclinical data that show pronounced anti-tumor responses and early clinical trials in which benefit is observed in patients with advanced cancer. Secondly, vaccination strategies are expected to reduce hospital visits, resulting in enhanced quality of life. And last but not least, vaccination strategies are extremely cost effective, alleviating the socioeconomic problems of prohibitively high drug costs. To reach further clinical success, efforts should focus on target identification, optimization of vaccination strategies and adjuvant development.

Development of a novel therapeutic vaccine carrier that sustains high antibody titers against several targets simultaneously

With the aim to improve the efficacy of therapeutic vaccines that target self-antigens, we have developed a novel fusion protein vaccine on the basis of the C-terminal multimerizing end of the variable lymphocyte receptor B (VLRB), the Ig equivalent in jawless fishes. Recombinant vaccines were produced in Escherichia coli by fusing the VLRB sequence to 4 different cancer-associated target molecules. The anti-self-immune response generated in mice that were vaccinated with VLRB vaccines was compared with the response in mice that received vaccines that contained bacterial thioredoxin (TRX), previously identified as an efficient carrier. The anti-self-Abs were analyzed with respect to titers, binding properties, and duration of response. VLRB-vaccinated mice displayed a 2- to 10-fold increase in anti-self-Ab titers and a substantial decrease in Abs against the foreign part of the fusion protein compared with the response in TRX-vaccinated mice (P < 0.01). VLRB-generated Ab response had duration similar to the corresponding TRX-generated Abs, but displayed a higher diversity in binding characteristics. Of importance, VLRB vaccines could sustain an immune response against several targets simultaneously. VLRB vaccines fulfill several key criteria for an efficient therapeutic vaccine that targets self-antigens as a result of its small size, its multimerizing capacity, and nonexposed foreign sequences in the fusion protein.-Saupe, F., Reichel, M., Huijbers, E. J. M., Femel, J., Markgren, P.-O., Andersson, C. E., Deindl, S., Danielson, U. H., Hellman, L. T., Olsson, A.-K. Development of a novel therapeutic vaccine carrier that sustains high antibody titers against several targets simultaneously.

The Density Code for the Development of a Vaccine?

The development of prophylactic vaccines remains largely empirical in nature and rarely have general rules been applied in the strategic decision and the formulation of a viral vaccine. Currently, there are a total of 15 virus agents from 12 unique virus families with vaccines licensed by the U.S. Food and Drug Administration. Extensive structural information on these viral particles and potential mechanisms of protection are available for the majority of these virus pathogens and their respective vaccines. Here I review the quantitative features of these viral surface antigens in relation to the molecular mechanisms of B-cell activation and point out a potential correlation between the density of immunogenic proteins displayed on the surface of the vaccine antigen carrier and the success of a vaccine. These features help us understand the humoral immunity induced by viral vaccines on a quantitative ground and re-emphasize the importance of antigen density on the activation of the immune system. Although the detailed mechanisms behind this phenomenon remain to be explored, it implies that both the size of antigen carriers and the density of immunogenic proteins displayed on these carriers are important parameters that may need to be optimized for the formulation of a vaccine.

Therapeutic vaccination against fibronectin ED-A attenuates progression of metastatic breast cancer

Therapeutic vaccination targeting self-molecules is an attractive alternative to monoclonal antibody-based therapies for cancer and various inflammatory diseases. However, development of cancer vaccines targeting self-molecules has proven difficult. One complicating factor is that tumor cells have developed strategies to escape recognition by the immune system. Antigens specifically expressed by the tumor vasculature can therefore provide alternative targets. The alternatively spliced extra domain-A and B (ED-A and ED-B) of fibronectin are expressed during vasculogenesis in the embryo, but essentially undetectable under normal conditions in the adult. However, these domains are re-expressed during tumor angiogenesis and matrix remodeling, which renders them highly interesting for targeted cancer therapies.

Using the MMTV-PyMT transgenic model of metastatic mammary carcinoma, we show that tumor burden can be significantly decreased by immunization against ED-A in a therapeutic setting. Furthermore, we found that in mice carrying anti-ED-A antibodies the number of metastases was reduced. ED-A immunization increased infiltration of macrophages and compromised tumor blood vessel function. These findings implicate an attack of the tumor vasculature by the immune system, through a polyclonal antibody response. We conclude that tumor vascular antigens are promising candidates for development of therapeutic vaccines targeting growth of primary tumors as well as disseminated disease.

Vaccination against IL-33 Inhibits Airway Hyperresponsiveness and Inflammation in a House Dust Mite Model of Asthma

In several clinical and experimental studies IL-33 and its receptor have been found to play important roles in the development of asthma and allergic airway inflammation. We evaluated the effects of vaccination against IL-33 in a mouse model of airway inflammation induced by house dust mite (HDM) allergen. Balb/c mice received the IL-33 vaccine subcutaneously, followed by intranasal administration of HDM for up to six weeks. Vaccination against IL-33 induced high titers of specific anti-IL-33 IgG antibodies that inhibited HDM-induced airway hyperresponsiveness (AHR) in the conducting airways and tissue damping. The vaccination also attenuated the HDM-induced elevation in the numbers of eosinophils in bronchoalveolar lavage fluid (BALF) and suppressed the accumulation of inflammatory cells in the airways. Furthermore, the levels of IL-17A, IL-25, IL-33 and TSLP in lung tissue homogenates were reduced by vaccination against IL-33. These observations demonstrate that vaccination against IL-33 inhibits HDM-induced development of AHR, airway inflammation and production of inflammatory cytokines. The results also indicate an important role of IL-33 in the regulation of AHR of the distal lung compartments. Thus, administration of such a vaccine is potentially an effective therapeutic tool for treating allergic asthma.

Therapeutic vaccination targeting the tumour vasculature

Therapeutic vaccination targeting self-molecules could provide a cost-efficient alternative to monoclonal antibody-based therapies for cancer and various inflammatory diseases. However, development of cancer vaccines targeting self-molecules has proven difficult. One complicating factor is that tumour cells have developed strategies to escape recognition by the immune system. Antigens specifically expressed by the tumour vasculature can therefore provide alternative targets. The present mini-review highlights potential target molecules associated with tumour angiogenesis and the approaches made to direct an immune response against them. Furthermore, the requirements on a vaccine targeting self-molecules, in contrast with those directed against virus or bacteria, are discussed.

Vaccines targeting self-antigens: mechanisms and efficacy-determining parameters

We recently showed that it is possible to compromise tumor vessel function and, as a consequence, suppress growth of aggressive preclinical tumors by immunizing against the tumor vascular markers extra domain-A (ED-A) or -B (ED-B) of fibronectin, using a fusion protein consisting of the ED-A or ED-B peptide fused to bacterial thioredoxin. To address the mechanism behind fusion protein-induced immunization and the specific contribution of the different vaccine constituents to elicit an anti-self-antibody response, we immunized mice with modified or unmodified self-antigens, combined with different adjuvant components, and analyzed antibody responses by ELISA in sera. Several essential requirements to circumvent tolerance were identified: (1) a potent pattern recognition receptor agonist like an oligonucleotide containing unmethylated cytosine and guanine dinucleotides (CpG); (2) a depot adjuvant to keep the CpG at the site of injection; and (3) the presence of foreign sequences in the vaccine protein. Lack of either of these factors abolished the anti-self-response (P = 0.008). In mice genetically deficient for type I IFN signaling, there was a 60% reduction in the anti-self-response compared with wild-type (P = 0.011), demonstrating a key role of this pathway in CpG-induced circumvention of self-tolerance. Identification of these mechanistic requirements to generate a potent anti-self-immune response should significantly aid the design of efficient, specific, and safe therapeutic cancer vaccines.

Robo4 vaccines induce antibodies that retard tumor growth

Tumor endothelial specific expression of Robo4 in adults identifies this plasma membrane protein as an anti-cancer target for immunotherapeutic approaches, such as vaccination. In this report, we describe how vaccination against Robo4 inhibits angiogenesis and tumor growth. To break tolerance to the auto-antigen Robo4, mice were immunised with the extracellular domain of mouse Robo4, fused to the Fc domain of human immunoglobulin within an adjuvant. Vaccinated mice show a strong antibody response to Robo4, with no objectively detectable adverse effects on health. Robo4 vaccinated mice showed impaired fibrovascular invasion and angiogenesis in a rodent sponge implantation assay, as well as a reduced growth of implanted syngeneic Lewis lung carcinoma. The anti-tumor effect of Robo4 vaccination was present in CD8 deficient mice but absent in B cell or IgG1 knockout mice, suggesting antibody dependent cell mediated cytotoxicity as the anti-vascular/anti-tumor mechanism. Finally, we show that an adjuvant free soluble Robo4-carrier conjugate can retard tumor growth in carrier primed mice. These results point to appropriate Robo4 conjugates as potential anti-angiogenic vaccines for cancer patients.

The non-toxic and biodegradable adjuvant Montanide ISA 720/CpG can replace Freund's in a cancer vaccine targeting ED-B--a prerequisite for clinical development

We have recently shown that immunization against the extra domain-B (ED-B) of fibronectin, using Freund's adjuvant, reduces tumor growth in mice by 70%. In the present study we compare the immune response generated against ED-B using the non-toxic and biodegradable adjuvant Montanide ISA 720/CpG with the response elicited by Freund's adjuvant. Montanide ISA 720/CpG induced anti-ED-B antibodies with higher avidity and less variable levels between individuals than Freund's. Moreover, the duration of the immune response was longer and the generation of anti-ED-B antibodies in naïve mice was faster, when Montanide ISA 720/CpG was used. We conclude that it is possible to replace the mineral oil based adjuvant Freund's with an adjuvant acceptable for human use, which is a prerequisite for transfer of the ED-B vaccine to the clinic.

Immunodrugs: breaking B- but not T-cell tolerance with therapeutic anticytokine vaccines

Pathology in most chronic inflammatory diseases is characterized by an imbalance in cytokine expression. Targeting cytokines with monoclonal antibodies has proven to be a highly effective treatment. However, monoclonal antibody therapy has disadvantages such as high production costs, generation of antimonoclonal antibodies and the inconvenience of frequent injections. Therapeutic vaccines have the potential to overcome these limitations. The aim of active vaccination is to induce B-cell responses and obtain autoantibodies capable of neutralizing the interaction of the targeted cytokine with its receptor. In order to achieve this, therapeutic vaccines need to circumvent the potent tolerance mechanisms that exist to prevent immune responses against self-molecules. This article focuses on the tolerance mechanisms of the B- and T-cell compartments and how these may be manipulated to obtain high-affinity autoantibodies without inducing potentially dangerous autoreactive T-cell responses.

Vaccination against the extra domain-B of fibronectin as a novel tumor therapy

Monoclonal antibody-based therapies have made an important contribution to current treatment strategies for cancer and autoimmune disease. However, the cost for these new drugs puts a significant strain on the health-care economy, resulting in limited availability for patients. Therapeutic vaccination, defined as induction of immunity against a disease-related self-molecule, is therefore an attractive alternative. To analyze the potential of such an approach, we have developed a vaccine against the extra domain-B (ED-B) of fibronectin. This 91-aa domain, inserted by alternative splicing, is expressed during vasculogenesis in the embryo, but essentially undetectable under normal conditions in the adult. However, ED-B is highly expressed around angiogenic vasculature, such as in tumorigenesis. Here, we demonstrate that it is possible to break self-tolerance and induce a strong antibody response against ED-B by vaccination. Nineteen of 20 vaccinated mice responded with production of anti-ED-B antibodies and displayed a 70% reduction in tumor size compared to those lacking anti-ED-B antibodies. Analysis of the tumor tissue revealed that immunization against ED-B induced several changes, consistent with an attack by the immune system. These data show that tumor vascular antigens are highly interesting candidates for development of therapeutic vaccines targeting solid tumors.