CIGB-247: a VEGF-based therapeutic vaccine that reduces experimental and spontaneous lung metastasis of C57Bl/6 and BALB/c mouse tumors. Vaccine. 2012;30:1790-1799. [PMID: 22240345 DOI: 10.1016/j.vaccine.2012.01.006]

Active immunization with a structurally aggregated PD-L1 antigen breaks T and B immune tolerance in non-human primates and exhibits in vivo anti-tumoral effects in immunocompetent mouse tumor models

Despite the clinical success of the programmed death ligand 1 (PD-L1) blocking therapy in cancer treatment, only a subset of patients exhibits durable responses, therefore further exploration of other immunotherapeutic alternatives are needed. This paper reported the development of the PKPD-L1^Vac vaccine, a new protein vaccine candidate that uses aluminum phosphate as an adjuvant and as an antigen the extracellular domain of human PD-L1 fused to a 47 amino-terminal portion of the LpdA protein from N. meningitides (PKPD-L1). The PKPD-L1 antigen has different physical and biological characteristics than those found in the natural molecule and in others PD-L1 vaccine candidates. The quimeric protein has a reduced binding capacity to the PD-1 and CD80 receptors to decrease their pro-tumoral activity. Besides, the distinctive feature of the PKPD-L1 polypeptide to be structurally aggregated could be desirable for its immunogenic properties. PKPD-L1^Vac elicited anti-PD-L1-specific IgG antibodies and T lymphocyte-mediated immunity in mice and non-human primates. The vaccine administration demonstrated antitumor activity on CT-26 and B16-F10 primary tumor models in mice. Moreover, the immunization with PKPD-L1^Vac increased the tumor-infiltrating lymphocytes and decreased the proportion of CD3⁺CD8⁺PD1^+high anergic T cells in CT-26 tumor tissues, suggesting that the vaccine may remodel the tumor microenvironment. In summary, the PKPD-L1^Vac vaccine exhibits very promising preclinical results and deserves to move forward to a phase I clinical trial.

Mitigating the prevalence and function of myeloid-derived suppressor cells by redirecting myeloid differentiation using a novel immune modulator

BACKGROUND

Immune suppression is common in neoplasia and a major driver is tumor-induced myeloid dysfunction. Yet, overcoming such myeloid cell defects remains an untapped strategy to reverse suppression and improve host defense. Exposure of bone marrow progenitors to heightened levels of myeloid growth factors in cancer or following certain systemic treatments promote abnormal myelopoiesis characterized by the production of myeloid-derived suppressor cells (MDSCs) and a deficiency in antigen-presenting cell function. We previously showed that a novel immune modulator, termed 'very small size particle' (VSSP), attenuates MDSC function in tumor-bearing mice, which was accompanied by an increase in dendritic cells (DCs) suggesting that VSSP exhibits myeloid differentiating properties. Therefore, here, we addressed two unresolved aspects of the mechanism of action of this unique immunomodulatory agent: (1) does VSSP alter myelopoiesis in the bone marrow to redirect MDSC differentiation toward a monocyte/macrophage or DC fate? and (2) does VSSP mitigate the frequency and suppressive function of human tumor-induced MDSCs?

METHODS

To address the first question, we first used a murine model of granulocyte-colony stimulating factor-driven emergency myelopoiesis following chemotherapy-induced myeloablation, which skews myeloid output toward MDSCs, especially the polymorphonuclear (PMN)-MDSC subset. Following VSSP treatment, progenitors and their myeloid progeny were analyzed by immunophenotyping and MDSC function was evaluated by suppression assays. To strengthen rigor, we validated our findings in tumor-bearing mouse models. To address the second question, we conducted a clinical trial in patients with metastatic renal cell carcinoma, wherein 15 patients were treated with VSSP. Endpoints in this study included safety and impact on PMN-MDSC frequency and function.

RESULTS

We demonstrated that VSSP diminished PMN-MDSCs by shunting granulocyte-monocyte progenitor differentiation toward monocytes/macrophages and DCs with heightened expression of the myeloid-dependent transcription factors interferon regulatory factor-8 and PU.1. This skewing was at the expense of expansion of granulocytic progenitors and rendered the remaining MDSCs less suppressive. Importantly, these effects were also demonstrated in a clinical setting wherein VSSP monotherapy significantly reduced circulating PMN-MDSCs, and their suppressive function.

CONCLUSIONS

Altogether, these data revealed VSSP as a novel regulator of myeloid biology that mitigates MDSCs in cancer patients and reinstates a more normal myeloid phenotype that potentially favors immune activation over immune suppression.

Synthesis of Four Steroidal Carbamates with Antitumor Activity against Mouse Colon Carcinoma CT26WT Cells: In Vitro and In Silico Evidence

Colorectal cancer (CRC) is one of the most lethal cancers worldwide. If detected on time, surgery can expand life expectations of patients up to five more years. However, if metastasis has grown deliberately, the use of chemotherapy can play a crucial role in CRC control. Moreover, the lack of selectivity of current anticancer drugs, plus mutations that occur in cancerous cells, demands the development of new chemotherapeutic agents. Several steroids have shown their potentiality as anticancer agents, while some other compounds, such as Taxol and its derivatives bearing a carbamate functionality, have reached the market. In this article, the synthesis, characterization, and antiproliferative activity of four steroidal carbamates on mouse colon carcinoma CT26WT cells are described. Carbamate synthesis occurred via direct reaction between diosgenin, its B-ring modified derivative, and testosterone with phenyl isocyanate under a Brønsted acid catalysis. All obtained compounds were characterized by ¹H and ¹³C Nuclear Magnetic Resonance (NMR), High Resolution Mass Spectroscopy (HRMS); their melting points are also reported. Results obtained from antiproliferative activity assays indicated that carbamates compounds have inhibitory effects on the growth of this colon cancer cell line. A molecular docking study carried out on Human Prostaglandin E Receptor (EP4) showed a high affinity between carbamates and protein, thus providing a valuable theoretical explanation of the in vitro results.

Vaccines targeting angiogenesis in melanoma

Angiogenesis has a significant role in metastasis and progression of melanoma. Even small tumors may be susceptible to metastasis and hence lead to a worse outcome in patients with melanoma. One of the anti-angiogenic treatment approaches that is undergoing comprehensive study is specific immunotherapy. While tumor cells are challenging targets for immunotherapy due to their genetic instability and heterogeneity, endothelial cells (ECs) are genetically stable. Therefore, vaccines targeting angiogenesis in melanoma are appropriate choices that target both tumor cells and ECs while capable of inducing strong, anti-tumor immune responses with limited toxicity. The main targets of angiogenesis are VEGFs and their receptors but other potential targets have also been investigated, especially in preclinical studies. Various types of vaccines that target angiogenesis in melanoma have been studied including DNA, peptide, protein, dendritic cell-based, and endothelial cell vaccines. This review outlines a number of target antigens that are important for potential progress in developing vaccines for targeting angiogenesis in melanoma. We also discuss different types of vaccines that have been investigated, delivery mechanisms and popular adjuvants, and suggest ways to improve future clinical outcomes.

Specific humoral response in cancer patients treated with a VEGF-specific active immunotherapy procedure within a compassionate use program

BACKGROUND

CIGB-247 is a cancer therapeutic vaccine that uses as antigen a variant of human vascular endothelial growth factor (VEGF) mixed with the bacterially-derived adjuvant VSSP. CIGB-247 has been already evaluated in two phase I clinical trials (CENTAURO and CENTAURO-2), showing to be safe and immunogenic in advanced cancer patients selected under well-defined and controlled clinical conditions. Surviving patients were submitted to monthly re-immunizations and some of them showed objective clinical benefits. Based on these results, a compassionate use program (CUP) with CIGB-247 was initiated for patients that did not meet the strict entry criteria applied for the CENTAURO and CENTAURO-2 clinical trials, but could potentially benefit from the application of this cancer therapeutic vaccine.

RESULTS

Polyclonal IgM, IgA and IgG antibodies specific for VEGF were detected by ELISA in serum samples from patients vaccinated with 400 μg of antigen combined with 200 μg of VSSP. Polyclonal antibody response showed no cross reactivity for other VEGF family member molecules like VEGF-C and VEGF-D. Serum from immunized individuals was able to block the binding of VEGF to its receptors VEGFR2 and VEGFR1. IgG fraction purified from immune sera shared the aforementioned characteristics and also inhibited the interaction between VEGF and the therapeutic recombinant antibody bevacizumab, an anti-angiogenic drug approved for the treatment of different tumors. No serious adverse events attributable to CIGB-247 have been documented yet in participants of the CIGB-247 CUP. The present paper is a first report of our findings concerning the humoral response and safety characteristics in treated CIGB-247 CUP cancer patients. The study has provided the unique opportunity of not only testing CIGB-247 in a broader clinical spectrum sample of Cuban cancer patients, but also within the context of the day-to-day clinical practice and treatment settings for these diseases in Cuban medical institutions.

CONCLUSIONS

The CIGB-247 CUP has demonstrated that immunization and follow-up of a variety of cancer patients, under day-to-day clinical practice conditions in several Cuban medical institutions, replicate our previous findings in clinical trials: CIGB-247 is safe and immunogenic.

Xanthium strumarium´s xanthatins induces mitotic arrest and apoptosis in CT26WT colon carcinoma cells

BACKGROUND

Colorectal cancer is one of the most common malignancies worldwide and is associated with high mortality rates. We previously reported that Xanthium strumarium L. induces mitotic arrest in proliferating cells, a process mediated by xanthatins.

HYPOTHESIS/AIM

The aim of this work is to study if xanthatins, isolated from X. strumarium total extract, affect the proliferative capacity of CT26WT colon cancer cells and, in consequence, if tumor growth and proliferation of (lung) metastatic sites can also be arrested in vivo.

STUDY DESIGN

This study consisted of both in vitro and in vivo experiments involving the CT26WT cell line and a subcutaneous mouse model of colon cancer. In vitro cell cycle progression, in vivo tumoral growth and anti-metastatic activity were analyzed to investigate whether xanthatins of X. strumarium induce mitotic arrest in proliferating colorectal carcinoma.

RESULTS

Our in vitro results show that X. strumarium, mediated by xanthatins, induces G₂/M arrest and impair anaphase entrance. This leads to a significant induction of apoptotic and necrotic in CT26WT cells, demonstrating their significant anti-proliferative activity through interfering with the mitotic apparatus. Furthermore, our in vivoresults reveal that X. strumarium inhibits both tumor growth and metastasis progression.

CONCLUSION

X. strumarium antitumor activities are mainly mediated by xanthatins through inhibition of tumor growth and metastasis, inducing mitotic arrest and apoptosis in colon carcinoma cells. These findings further confirm the therapeutic potential of X. strumarium in colorectal cancer.

Evaluation of methodologies to determine the effect of specific active immunotherapy on VEGF levels in phase I clinical trial patients with advanced solid tumors

Two phase I clinical trials were conducted to evaluate, among other parameters, the humoral response elicited by a vascular endothelial growth factor (VEGF)-based therapeutic vaccine in cancer patients with advanced solid tumors. VEGF reduction was studied using an indirect methodology named as “Platelet VEGF”. This methodology is based on the estimation of VEGF within platelets by subtracting the plasma VEGF level from the serum level and dividing this by the platelet count, and then this latter expression is additionally corrected by the hematocrit. However, there is broad debate, whether serum or plasma VEGF or platelet-derived VEGF measurements is the most appropriate strategy to study the changes that occur on ligand bioavailability when patients are submitted to a VEGF-based immunotherapy.

The current research is a retrospective study evaluating the changes on VEGF levels in serum and plasma as well as platelet-derived measurements. Changes in VEGF levels were related with the humoral response seen in cancer patients after an active immunotherapy with a VEGF-based vaccine. The present study indicates that “Platelet VEGF” is the most reliable methodology to investigate the effect of VEGF-based immunotherapies on ligand bioavailability. “Platelet VEGF” was associated with those groups of individuals that exhibited the best specific humoral response and the variation of “Platelet VEGF” showed the strongest negative correlation with VEGF-specific IgG antibody levels. This methodology will be very useful for the investigation of this VEGF-based vaccine in phase II clinical trials and could be applied to immunotherapies directed to other growth factors that are actively sequestered by platelets.

Combination therapy of hepatocellular carcinoma by DNA shuffling-based VEGF vaccine and doxorubicin

Antiangiogenic therapy can enhance the efficacy of chemotherapy against solid tumors. This study was to determine whether TT46, a potential VEGF vaccine from DNA shuffling with a helper T-cell epitope of tetanus toxin B subunit, could enhance the efficacy of doxorubicin to combat hepatocellular carcinoma (HCC). Compared with monotherapy, the combination with TT46 vaccination and doxorubicin could significantly reduce microvessel counts and inhibit tumor angiogenesis. Enhanced immunization with TT46 for total six doses could induce long-term response maintenance with high anti-VEGF antibody titers in body. As a result, the combination with enhanced TT46 vaccination and doxorubicin significantly inhibited the HCC growth, and improved the survival rate of HCC-bearing mice in both of subcutaneous tumor model and lung metastasis model. In conclusion, the combined therapy with TT46 vaccination and doxorubicin has antitumor effects in both a prophylactic and therapeutic setting in a mouse model of H22 hepatocellular carcinoma.

Bacterial components as naturally inspired nano-carriers for drug/gene delivery and immunization: Set the bugs to work?

Drug delivery is a rapidly growing area of research motivated by the nanotechnology revolution, the ideal of personalized medicine, and the desire to reduce the side effects of toxic anti-cancer drugs. Amongst a bewildering array of different nanostructures and nanocarriers, those examples that are fundamentally bio-inspired and derived from natural sources are particularly preferred. Delivery of vaccines is also an active area of research in this field. Bacterial cells and their components that have been used for drug delivery, include the crystalline cell-surface layer known as "S-layer", bacterial ghosts, bacterial outer membrane vesicles, and bacterial products or derivatives (e.g. spores, polymers, and magnetic nanoparticles). Considering the origin of these components from potentially pathogenic microorganisms, it is not surprising that they have been applied for vaccines and immunization. The present review critically summarizes their applications focusing on their advantages for delivery of drugs, genes, and vaccines.

Computational study on the origin of the cancer immunotherapeutic potential of B and T cell epitope peptides

Immune therapy is generally seen as the future of cancer treatment. The discovery of tumor-associated antigens and cytotoxic T lymphocyte epitope peptides spurned intensive research into effective peptide-based cancer vaccines. One of the major obstacles hindering the development of peptide-based cancer vaccines is the lack of humoral response induction. As of now, very limited work has been performed to identify epitope peptides capable of inducing both cellular and humoral anticancer responses. In addition, no research has been carried out to analyze the structure and properties of peptides responsible for such immunological activities. This study utilizes a machine learning method together with interpretable descriptors in an attempt to identify parameters determining the immunotherapeutic activity of cancer epitope peptides.

Two tandem repeats of mHSP70407-426 enhance therapeutic antitumor effects of a recombined vascular endothelial growth factor (VEGF) protein vaccine

AIMS

Active immunization with human vascular endothelial growth factor (hVEGF) vaccines provides a therapeutic option instead of bevacizumab therapy. However, the immunity to self-molecule is difficult to elicit due to immune tolerance. A bioactive peptide of two tandem repeats of mHSP70_407-426 (M₂) has exhibited potent adjuvant ability in our previous study, and the aim of this study was to explore whether M₂ could assist hVEGF to display enhanced therapeutic anti-tumor effects.

MAIN METHODS

The anti-tumor effects of hVEGF-M₂ vaccine were evaluated in both H22 hepatocellular carcinoma and Lewis lung tumor models. CD31 analysis of excised tumors was used to evaluate anti-angiogenesis effects. The titers of anti-VEGF antibody was detected by ELISA and verified by western blot analyses, and the effects of immune sera on HUVEC differentiation were investigated by tube formation assay.

KEY FINDINGS

M₂ could assist hVEGF to exhibit more favorable therapeutic anti-tumor growth and metastasis effects than hVEGF. Meanwhile, high titer of anti-VEGF antibody was detected in hVEGF-M₂ immunized mice sera by ELISA and verified by western blot analysis. Sera from hVEGF-M₂ immunized mice could more significantly inhibit HUVEC tube formation than hVEGF immune serum. The hVEGF-M₂-immune sera could more effectively inhibit H22 tumor growth and extend the survival rates of H22 tumor bearing mice than hVEGF-immune sera. CD31 analysis of the excised tumors verified a significant reduction in vessel density after hVEGF-M₂ vaccination.

SIGNIFICANCE

M₂ could assist hVEGF to display enhanced anti-tumor effects, which are important for the further application of M₂ to enhance antigen-specific immune responses.

Characteristics of the specific humoral response in patients with advanced solid tumors after active immunotherapy with a VEGF vaccine, at different antigen doses and using two distinct adjuvants

Background

CIGB-247, a VSSP-adjuvanted VEGF-based vaccine, was evaluated in a phase I clinical trial in patients with advanced solid tumors (CENTAURO). Vaccination with the maximum dose of antigen showed an excellent safety profile, exhibited the highest immunogenicity and was the only one showing a reduction on platelet VEGF bioavailability. However, this antigen dose level did not achieve a complete seroconversion rate in vaccinated patients. These clinical results led us to the question whether a “reserve” of untapped immune response potential against VEGF could exist in cancer patients. To address this matter, CENTAURO-2 clinical trial was conducted where antigen and VSSP dose scale up were studied, and also incorporated the exploration of aluminum phosphate as adjuvant. These changes were made with the aim to increase immune response against VEGF.

Results

The present study reports the characterization of the humoral response elicited by CIGB-247 from the combining of different antigen doses and adjuvants. Cancer patients were immunologically monitored for approximately 1 year. Vaccination with different CIGB-247 formulations exhibited a very positive safety profile. Cancer patients developed IgM, IgG or IgA antibodies specific to VEGF. Elicited polyclonal antibodies had the ability to block the interaction between VEGF and its receptors, VEGFR1 and VEGFR2. The highest humoral response was detected in patients immunized with 800 μg of antigen + 200 μg of VSSP. Off-protocol long-term vaccination did not produce negative changes in humoral response.

Conclusions

Vaccination with a human VEGF variant molecule as antigen in combination with VSSP or aluminum phosphate is immunogenic. The results of this study could contribute to the investigation of this vaccine therapy in an adequately powered efficacy trial.

Trial registration

Trial registration number: RPCEC00000155. Cuban Public Clinical Trial Registry. Date of registration: June 06, 2013. Available from: http://registroclinico.sld.cu/.

Electronic supplementary material

The online version of this article (doi:10.1186/s12865-017-0222-z) contains supplementary material, which is available to authorized users.

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.

Targeting Myeloid-Derived Suppressor Cells in Cancer

Myeloid derived suppressor cells (MDSC) represent only a minor fraction of circulating blood cells but play an important role in tumor formation and progression. They are a heterogeneous group of cells that influence the tumor microenvironment by depletion of amino acids, oxidative stress, decreased trafficking of antitumor effector cells, and increased regulatory T and regulatory dendritic cell responses. Investigational treatment strategies targeting MDSCs have attempted to inhibit MDSC development and expansion (stem cell factor blockade, modulate of cell signaling, and target MDSC migration and recruitment), inhibit MDSC function (nitric oxide inhibition and reactive oxygen and nitrogen species inhibition), differentiate MDSCs into more mature cells (Vitamins A and D, all-trans retinoic acid, interleukin-2, toll-like receptor 9 inhibitors, taxanes, beta-glucan particles, tumor-derived exosome inhibition, and very small size proteoliposomes), and destroy MDSCs (cytotoxic agents, ephrin A2 degradation, anti-interleukin 13, and histamine blockers). To date, there are no Food and Drug Administration approved therapies selectively targeting MDSCs, but such therapies are likely to be implemented in the future, due to the key role of MDSCs in antitumor immunity.

Indirect and competitive enzyme-linked immunosorbent assays for monitoring the humoral response against human VEGF

CIGB-247, a VEGF-based vaccine, was studied in a clinical trial. This advance demands the refinement of the methodologies for assessment of vaccine immune responses. This study aimed to improve the performance of ELISAs for detecting IgG antibodies against human VEGF and the blocking activity of the serum to inhibit the VEGF/VEGFR2 interaction. The best experimental conditions were established through the evaluation of several blocking buffers, immobilization surfaces, and plate suppliers using human sera as test samples. As a result, two controlled ELISAs were used in testing of elicited immune response against VEGF in patients immunized with CIGB-247.

Experimental studies of a vaccine formulation of recombinant human VEGF antigen with aluminum phosphate

CIGB-247 is a cancer vaccine that is a formulation of a recombinant protein antigen representative of the human vascular endothelial growth factor (VEGF) with a bacterially-derived adjuvant (VSSP). The vaccine has shown an excellent safety profile in mice, rats, rabbits, not-human primates and in recent clinical trials in cancer patients. Response to the vaccine is characterized by specific antibody titers that neutralize VEGF/VEGFR2 binding and a cytotoxic tumor-specific response. To expand our present anti-VEGF active immunotherapy strategies, we have now studied in mice and non-human primates the effects of vaccination with a formulation of our recombinant VEGF antigen and aluminum phosphate adjuvant (hereafter denominated CIGB-247-A). Administered bi-weekly, CIGB-247-A produces high titers of anti-VEGF IgG blocking antibodies in 2 mice strains. Particularly in BALB/c, the treatment impaired subcutaneous F3II mammary tumor growth and reduced the number of spontaneous lung macro metastases, increasing animals' survival. Spleen cells from specifically immunized mice directly killed F3II tumor cells in vitro. CIGB-247-A also showed to be immunogenic in non-human primates, which developed anti-VEGF blocking antibodies and the ability for specific direct cell cytotoxic responses, all without impairing the healing of deep skin wounds or other side effect. Our results support consideration of aluminum phosphate as a suitable adjuvant for the development of new vaccine formulations using VEGF as antigen.

Vaccination approach to anti-angiogenic treatment of cancer

Improvement of patient survival by anti-angiogenic therapy has proven limited. A vaccination approach inducing an immune response against the tumor vasculature combines the benefits of immunotherapy and anti-angiogenesis, and may overcome the limitations of current anti-angiogenic drugs. Strategies to use whole endothelial cell vaccines and DNA- or protein vaccines against key players in the VEGF signaling axis, as well as specific markers of tumor endothelial cells, have been tested in preclinical studies. Current clinical trials are now testing the promise of this specific anti-cancer vaccination approach. This review will highlight the state-of-the-art in this exciting field of cancer research.

GM3-containing nanoparticles in immunosuppressed hosts: Effect on myeloid-derived suppressor cells

Cancer vaccines to date have not broadly achieved a significant impact on the overall survival of patients. The negative effect on the immune system of the tumor itself and conventional anti-tumor treatments such as chemotherapy is, undoubtedly, a key reason for these disappointing results. Myeloid-derived suppressor cells (MDSCs) are considered a central node of the immunosuppressive network associated with tumors. These cells inhibit the effector function of natural killer and CD8⁺ T cells, expand regulatory T cells and can differentiate into tumor-associated macrophages within the tumor microenvironment. Thus, overcoming the suppressive effects of MDSCs is likely to be critical for cancer immunotherapy to generate effective anti-tumor immune responses. However, the capacity of cancer vaccines and particularly their adjuvants to overcome this inhibitory population has not been well characterized. Very small size proteoliposomes (VSSP) is a nanoparticulated adjuvant specifically designed to be formulated with vaccines used in the treatment of immunocompromised patients. This adjuvant contains immunostimulatory bacterial signals together with GM3 ganglioside. VSSP promotes dendritic cell maturation, antigen cross-presentation to CD8⁺ T cells, Th1 polarization, and enhances CD8⁺ T cell response in tumor-free mice. Currently, four cancer vaccines using VSSP as the adjuvant are in Phase I and II clinical trials. In this review, we summarize our work characterizing the unique ability of VSSP to stimulate antigen-specific CD8⁺ T cell responses in two immunocompromised scenarios; in tumor-bearing mice and during chemotherapy-induced leukopenia. Particular emphasis has been placed on the interaction of these nanoparticles with MDSCs, as well as comparison with other cancer vaccine adjuvants currently in preclinical or clinical studies.

Very small size proteoliposomes abrogate cross-presentation of tumor antigens by myeloid-derived suppressor cells and induce their differentiation to dendritic cells

Background

Myeloid-derived suppressor cells (MDSCs) are among the major obstacles that adjuvants for cancer vaccines have to overcome. These cells cross-present tumor-associated antigens (TAA) to naive T lymphocytes with a tolerogenic outcome. Very Small Size Proteoliposomes (VSSP) is used as adjuvant by four therapeutic cancer vaccines currently in Phase I and II clinical trials. We previously found that VSSP reduces the suppressive function of MDSCs, then activating antigen-specific CTL responses in tumor-bearing (TB) mice, with the consequent reduction of tumor growth. However the mechanistic explanation for the immunomodulatory effect of this adjuvant in TB hosts has not been addressed before.

Methods

TB mice were inoculated with VSSP and MDSCs isolated and characterized by their expression of Arg1 and Nos2 genes by RT-PCR. The effect of VSSP on antigen cross-presentation by MDSCs, regulatory T cells (Tregs) expansion and MDSCs differentiation towards dendritic cells (DCs) was analyzed by FACS. Student’s t test or ANOVA and Tukey’s tests were used for statistical analyses.

Results

After inoculating VSSP into TB mice, a significant reduction of Arg1 and Nos2 gene expression was observed in recovered MDSCs. Concurrently the ability of these cells to induce down-regulation of CD3ζ chain on T cells was lost. Likewise in mice inoculated with the adjuvant lower percentages of Tregs were detected. In vitro, VSSP treatment was enough to differentiate MDSCs into phenotypically mature DCs, eliminating the former suppressive effect. Noteworthy, in vivo administration of VSSP to OVA-expressing (EG.7) TB mice abrogated this model antigen cross-presentation by splenic MDSCs. Similar results were obtained even when OVA antigen was administered into these TB mice formulated in VSSP. On the contrary, immunization with the same protein in polyI:C did not change the percentage of MDSCs expressing SIINFEKL/H-2K^b complexes, whereas a concomitant injection of VSSP aborted the limitations of polyI:C in this setting.

Conclusions

Altogether, these results indicate that VSSP has the peculiar capacity of inhibiting TAA cross-presentation and certain suppressive mechanisms on MDSCs which in turn, combined with the ability to induce differentiation of these cells into antigen-presenting cells (APCs), sustains this adjuvant as an ideal immunomodulator for cancer immunotherapy.

Specific active immunotherapy with a VEGF vaccine in patients with advanced solid tumors. results of the CENTAURO antigen dose escalation phase I clinical trial

CIGB-247 is a novel cancer therapeutic vaccine that uses a human VEGF variant molecule as antigen, in combination with a bacterial adjuvant. In mice, CIGB-247 has anti-tumor and anti-metastatic effects. The vaccine induces anti-VEGF blocking antibodies and a cellular response targeting tumor cells producing VEGF, and has proven to be safe in mice, rats, rabbits and non-human primates. Herein we report the results of a Phase I clinical trial (code name CENTAURO) where safety, tolerance, and immunogenicity of CIGB-247 were studied in 30 patients with advanced solid tumors, at three antigen dose levels. Individuals were subcutaneously immunized for 8 consecutive weeks with 50, 100 or 400 μg of antigen, and re-immunized on week twelve. On week sixteen, evaluations of safety, tolerance, clinical status, and immunogenicity (seroconversion for anti-VEGF IgG, serum VEGF/KDR-Fc blocking ability, and gamma-IFN ELISPOT with blood cells stimulated in vitro with mutated VEGF) were done. Surviving patients were eligible for off-trial additional 4-week re-immunizations with 400 μg of antigen. Immunogenicity and clinical status were again studied on weeks 25 and 49. Vaccination was shown to be safe at the three dose levels, with only grade 1-2 adverse events. CIGB-247 was immunogenic and higher numbers of individuals positive to the three immune response tests were seen with increasing antigen dose. Off-protocol long-term vaccination produced no additional adverse events or negative changes in immunogenicity. Eleven patients are still alive, with overall survivals ranging from 20 to 24 months. Twelve of the thirty patients exhibited objective clinical benefits, and two individuals have complete responses. Most patients with higher survivals are positive in the three immune response tests. In summary, this is the first clinical testing report of a cancer therapeutic vaccine based on a human VEGF related molecule as antigen. The CIGB-247 vaccine is safe, immunogenic, and merits further clinical development.

REGISTRATION NUMBER AND NAME OF TRIAL REGISTRY

RPCEC00000102. Cuban Public Clinical Trial Registry (WHO accepted Primary Registry). Available from: http://registroclinico.sld.cu/.

Humoral immune responses to CTL epitope peptides from tumor-associated antigens are widely detectable in humans: a new biomarker for overall survival of patients with malignant diseases

Both cellular and humoral immune responses are crucial to induce potent anti-tumor immunity, but most of currently conducted peptide-based cancer vaccines paid attention to cellular responses alone, and none of them are yet approved as a therapeutic modality against cancer patients. We investigated humoral immune responses to CTL epitope peptides derived from tumor-associated antigens in healthy donors and patients with various diseases to facilitate better understanding of their distribution patterns and potential roles. Bead-based multiplex assay, ELISA, and Western blotting were used to measure immunoglobulins reactive to each of 31 different CTL epitope peptides. Importantly, the sums of anti-peptide IgG levels specific to 31 CTL epitope peptides were well correlated with better overall survival (OS) in patients with malignant diseases. Our results suggested that humoral immune responses to CTL epitope peptides were widely detectable in humans. Measurement of immunoglobulins specific to CTL epitope peptides may provide a new biomarker for OS of patients with malignant diseases, although it still remains to be determined whether the correlations between humoral immune responses to epitope peptides and OS are observed only for the CTL epitopes used, or also for other panels of peptides. Quantity of circulating IgG reactive to these peptides was also discussed.