Tumor lysate-loaded biodegradable microparticles as cancer vaccines

PLGA-Astragalus Polysaccharide Nanovaccines Exert Therapeutic Effect in Colorectal Cancer

Background

Tumor vaccines have achieved remarkable progress in treating patients with various tumors in clinical studies. Nevertheless, extensive research has also revealed that tumor vaccines are not up to expectations for the treatment of solid tumors due to their low immunogenicity. Therefore, there is an urgent need to design a tumor vaccine that can stimulate a broad anti-tumor immune response.

Methods

In this work, we developed a nanovaccine (NP-TCL@APS), which includes nanoparticles loaded with colorectal cancer tumor cell lysates (TCL) and Astragalus polysaccharides (APS) into poly (lactic-co-glycolic acid) to induce a robust innate immune response. The NP-TCL@APS was identified by transmission electron microscopy and Malvern laser particle size analyzer. The killing and immune activation effects of NP-TCL@APS were evaluated in vitro. Finally, safety and anti-tumor efficacy were evaluated in the colorectal cancer tumor-bearing mouse model.

Results

We found that NP-TCL@APS was preferentially uptaken by DC and further promoted the activation of DC in vitro. Additionally, nanoparticles codelivery of TCL and APS enhanced the antigen-specific CD8+ T cell response and suppressed the growth of tumors in mouse models with good biocompatibility.

Conclusion

We successfully prepared a nanovaccine termed NP-TCL@APS, which can promote the maturation of DC and induce strong responses by T lymphocytes to exert anti-tumor effects. The strategy proposed here is promising for generating a tumor vaccine and can be extended to various types of cancers.

Amplifying Immune Responses: Microparticulate Vaccine Approach Against Breast Cancer

Introduction

The study focuses on evaluating the immune responses generated by a novel microparticulate murine breast cancer vaccine.

Methods

The methodology included the use of a co-culture model of dendritic cells (DCs), and T-cells to evaluate the immunotherapeutic responses generated by the vaccine.

Results

The study observed that the dendritic cells expressed significantly higher levels of MHC I, MHC II, CD 40, and CD 80 cell surface markers in the presence of the vaccine microparticles than the controls (p<0.05). This response was potentiated in the presence of an adjuvant, Poly (I:C). The study also demonstrated that the vaccine microparticles do not elicit inflammatory (TNF-alpha, IFN-gamma, IL-2, and IL-12) or immunosuppressive (IL-10) cytokine production when compared to the control.

Discussion

In conclusion, the study established the role of DCs in stimulating the cancer vaccine's adaptive immune responses.

An updated landscape on nanotechnology-based drug delivery, immunotherapy, vaccinations, imaging, and biomarker detections for cancers: recent trends and future directions with clinical success

The recent development of nanotechnology-based formulations improved the diagnostics and therapies for various diseases including cancer where lack of specificity, high cytotoxicity with various side effects, poor biocompatibility, and increasing cases of multi-drug resistance are the major limitations of existing chemotherapy. Nanoparticle-based drug delivery enhances the stability and bioavailability of many drugs, thereby increasing tissue penetration and targeted delivery with improved efficacy against the tumour cells. Easy surface functionalization and encapsulation properties allow various antigens and tumour cell lysates to be delivered in the form of nanovaccines with improved immune response. The nanoparticles (NPs) due to their smaller size and associated optical, physical, and mechanical properties have evolved as biosensors with high sensitivity and specificity for the detection of various markers including nucleic acids, protein/antigens, small metabolites, etc. This review gives, initially, a concise update on drug delivery using different nanoscale platforms like liposomes, dendrimers, polymeric & various metallic NPs, hydrogels, microneedles, nanofibres, nanoemulsions, etc. Drug delivery with recent technologies like quantum dots (QDs), carbon nanotubes (CNTs), protein, and upconverting NPs was updated, thereafter. We also summarized the recent progress in vaccination strategy, immunotherapy involving immune checkpoint inhibitors, and biomarker detection for various cancers based on nanoplatforms. At last, we gave a detailed picture of the current nanomedicines in clinical trials and their possible success along with the existing approved ones. In short, this review provides an updated complete landscape of applications of wide NP-based drug delivery, vaccinations, immunotherapy, biomarker detection & imaging for various cancers with a predicted future of nanomedicines that are in clinical trials.

Advanced subunit vaccine delivery technologies: From vaccine cascade obstacles to design strategies

Designing and manufacturing safe and effective vaccines is a crucial challenge for human health worldwide. Research on adjuvant-based subunit vaccines is increasingly being explored to meet clinical needs. Nevertheless, the adaptive immune responses of subunit vaccines are still unfavorable, which may partially be attributed to the immune cascade obstacles and unsatisfactory vaccine design. An extended understanding of the crosstalk between vaccine delivery strategies and immunological mechanisms could provide scientific insight to optimize antigen delivery and improve vaccination efficacy. In this review, we summarized the advanced subunit vaccine delivery technologies from the perspective of vaccine cascade obstacles after administration. The engineered subunit vaccines with lymph node and specific cell targeting ability, antigen cross-presentation, T cell activation properties, and tailorable antigen release patterns may achieve effective immune protection with high precision, efficiency, and stability. We hope this review can provide rational design principles and inspire the exploitation of future subunit vaccines.

Augmented interferon regulatory factor 7 axis in whole tumor cell vaccines prevents tumor recurrence by inducing interferon gamma-secreting B cells

Among cancer immunotherapy, which has received great attention in recent years, cancer vaccines can potentially prevent recurrent tumors by using the exquisite power and specificity of the immune system. Specifically, whole tumor cell vaccines (WTCVs) based on surgically resected tumors have been considered to elicit robust anti-tumor immune responses by exposing various tumor-associated antigens to host immunity. However, most tumors have little immunogenicity because of immunoediting by continuous interactions with host immunity; thus, preparing WTCVs based on patient-derived non-modified tumors cannot prevent tumor onset. Hence, the immunogenicity of tumor cells must be improved for effective WTCVs. In this study, we indicate the importance of the interferon regulatory factor 7 (Irf7) axis, including Irf7 and its downstream factors, within tumor cells in regulating immunogenicity. Indeed, WTCVs that augmented the Irf7 axis have exerted remarkable recurrence-preventive effects when vaccinated after tumor inactivation by radiation. Most notably, vaccination with murine colon cancer cells that enhanced the Irf7 axis prevented the development of challenged tumors in all mice and resulted in a 100% survival rate during the observation period. Furthermore, the mechanism leading to vaccine effectiveness was mediated by interferon-gamma-producing B cells. This study provides novel insights into how to enhance tumor immunogenicity and use WTCVs as recurrence prophylaxis.

Adjuvant properties of IFN-γ and GM-CSF in the scFv6.C4 DNA vaccine against CEA-expressing tumors

Tumor-associated carcinoembryonic antigen (CEA) is a natural target for vaccines against colorectal cancers. Our previous experience with a DNA vaccine with scFv6.C4, a CEA surrogate, showed a CEA-specific immune response with 40% of tumor-free mice after challenge with B16F10-CEA and 47% with MC38-CEA cells. These percentages increased to 63% after using FrC as an adjuvant. To further enhance the vaccine efficacy, we tested GM-CSF and IFNγ as adjuvants. C57BL/6J-CEA2682 mice were immunized 4 times with uP-PS/scFv6.C4, uP-PS/scFv6.C4 + uP-IFNγ, or uP-PS/scFv6.C4 + uP-GMCSF. After one week, the mice were challenged with MC38-CEA, and tumor growth was monitored over 100 days. Immunization with scFv6.C4 and scFv6.C4 + GM-CSF resulted in a gradual increase in the anti-CEA antibody titer, while scFv6.C4 + IFNγ immunization led to a rapid and sustained increase in the titer. The addition of IFNγ also induced higher CD4 + and CD8 + responses. When challenged, almost 80% of the scFv6.C4 + IFNγ-vaccinated mice did not develop tumors, while the others had a significant tumor growth delay. The probability of being tumor-free was 2700% higher using scFv6.C4 + IFNγ than scFv6.C4. The addition of GM-CSF had no additional effect on tumor protection. DNA immunization with scFv6.C4 + IFNγ, but not GM-CSF, increased the antitumor effect via readily sustained specific humoral and cytotoxic responses to CEA.

Engineered implantable vaccine platform for continuous antigen-specific immunomodulation

Cancer vaccines harness the host immune system to generate antigen-specific antitumor immunity for long-term tumor elimination with durable immunomodulation. Commonly investigated strategies reintroduce ex vivo autologous dendritic cells (DCs) but have limited clinical adoption due to difficulty in manufacturing, delivery and low clinical efficacy. To combat this, we designed the "NanoLymph", an implantable subcutaneous device for antigen-specific antitumor immunomodulation. The NanoLymph consists of a dual-reservoir platform for sustained release of immune stimulants via a nanoporous membrane and hydrogel-encapsulated antigens for local immune cell recruitment and activation, respectively. Here, we present the development and characterization of the NanoLymph as well as efficacy validation for immunomodulation in an immunocompetent murine model. Specifically, we established the NanoLymph biocompatibility and mechanical stability. Further, we demonstrated minimally invasive transcutaneous refilling of the drug reservoir in vivo for prolonging drug release duration. Importantly, our study demonstrated that local elution of two drugs (GMCSF and Resiquimod) generates an immune stimulatory microenvironment capable of local DC recruitment and activation and generation of antigen-specific T lymphocytes within 14 days. In summary, the NanoLymph approach can achieve in situ immunomodulation, presenting a viable strategy for therapeutic cancer vaccines.

Mannosylated polylactic-co-glycolic acid (MN-PLGA) nanoparticles induce potent anti-tumor immunity in murine model of breast cancer

Nanoparticle-based cancer immunotherapy is considered a novel and promising therapeutic strategy aimed at stimulating host immune responses against tumors. To this end, in the present study, mannan-decorated polylactic-co-glycolic acid (PLGA) nanoparticles containing tumor cell lysate (TCL) and poly riboinosinic polycytidylic acid (poly I:C) were used as antigen delivery systems to immunize breast tumor-bearing Balb/c mice. PLGA nanoparticles were fabricated employing a double emulsion solvent evaporation method. The formation of spherical and uniform nanoparticles (NPs) ranging 150-250 nm was detected by field emission scanning electron microscopy (FESEM) and dynamic light scattering (DLS). Four nanoformulation were used to treat mice and vaccination-induced immunological responses. Tumor regression and overall survival rate were evaluated in four experimental groups. Tumor cell lysate and poly I:C loaded mannan-decorated nanoparticles (TCL-Poly I:C) NP-MN caused a significant decrease in tumor growth and 2- to 3-fold improvement in survival times of the treated mice. The NPs with or without mannan decoration elicited stronger responses in terms of lymphocyte proliferation, delayed-type hypersensitivity and CD107a expression. Moreover, our data indicated that the production of IFN-γ and IL-2 increased while the production of IL-4 and IL-10 decreased in splenocytes culture supernatants. In the pathological evaluations, we found that necrosis and immune cells infiltration rate in the tumor tissue of the treated mice was elevated, while tumor cellularity and lung metastases significantly decreased in particular in the group that received (TCL-Poly I:C) NP-MN. Altogether, our findings suggested that the mannan-decorated PLGA NPs antigen delivery system had significant anti-tumor effects against the murine model of breast cancer and it could be considered as a step forward to human breast cancer immunotherapy.

Synthetic bacterial vesicles combined with tumour extracellular vesicles as cancer immunotherapy

Bacterial outer membrane vesicles (OMV) have gained attention as a promising new cancer vaccine platform for efficiently provoking immune responses. However, OMV induce severe toxicity by activating the innate immune system. In this study, we applied a simple isolation approach to produce artificial OMV that we have named Synthetic Bacterial Vesicles (SyBV) that do not induce a severe toxic response. We also explored the potential of SyBV as an immunotherapy combined with tumour extracellular vesicles to induce anti-tumour immunity. Bacterial SyBV were produced with high yield by a protocol including lysozyme and high pH treatment, resulting in pure vesicles with very few cytosolic components and no RNA or DNA. These SyBV did not cause systemic pro-inflammatory cytokine responses in mice compared to naturally released OMV. However, SyBV and OMV were similarly effective in activation of mouse bone marrow-derived dendritic cells. Co-immunization with SyBV and melanoma extracellular vesicles elicited tumour regression in melanoma-bearing mice through Th-1 type T cell immunity and balanced antibody production. Also, the immunotherapeutic effect of SyBV was synergistically enhanced by anti-PD-1 inhibitor. Moreover, SyBV displayed significantly greater adjuvant activity than other classical adjuvants. Taken together, these results demonstrate a safe and efficient strategy for eliciting specific anti-tumour responses using immunotherapeutic bacterial SyBV.

Therapeutic efficacy of cancer vaccine adjuvanted with nanoemulsion loaded with TLR7/8 agonist in lung cancer model

Although immune checkpoint inhibitors have significantly improved clinical outcomes in various malignant cancers, only a small proportion of patients reap benefits, likely due to the low number of T cells and high number of immunosuppressive cells in the tumor microenvironment (TME) of patients with advanced disease. We developed a cancer vaccine adjuvanted with nanoemulsion (NE) loaded with TLR7/8 agonist (R848) and analyzed its therapeutic effect alone or in combination with immune checkpoint inhibitors, on antitumor immune responses and the reprogramming of suppressive immune cells in the TME. NE (R848) demonstrated robust local and systemic antitumor immune responses in both subcutaneous and orthotopic mouse lung cancer models, inducing tumor-specific T cell activation and mitigating T cell exhaustion. Combination with anti-PD-1 antibodies showed synergistic effects with respect to therapeutic efficacy and survival rate. Thus, NE (R848)-based cancer vaccines could prevent tumor recurrence and prolong survival by activating antitumor immunity and reprogramming immunosuppression.

Hitchhiking on Controlled-Release Drug Delivery Systems: Opportunities and Challenges for Cancer Vaccines

Cancer vaccines represent among the most promising strategies in the battle against cancers. However, the clinical efficacy of current cancer vaccines is largely limited by the lack of optimized delivery systems to generate strong and persistent antitumor immune responses. Moreover, most cancer vaccines require multiple injections to boost the immune responses, leading to poor patient compliance. Controlled-release drug delivery systems are able to address these issues by presenting drugs in a controlled spatiotemporal manner, which allows co-delivery of multiple drugs, reduction of dosing frequency and avoidance of significant systemic toxicities. In this review, we outline the recent progress in cancer vaccines including subunit vaccines, genetic vaccines, dendritic cell-based vaccines, tumor cell-based vaccines and in situ vaccines. Furthermore, we highlight the efforts and challenges of controlled or sustained release drug delivery systems (e.g., microparticles, scaffolds, injectable gels, and microneedles) in ameliorating the safety, effectiveness and operability of cancer vaccines. Finally, we briefly discuss the correlations of vaccine release kinetics and the immune responses to enlighten the rational design of the next-generation platforms for cancer therapy.

Engineering a sustained release vaccine with a pathogen-mimicking manner for robust and durable immune responses

Sustained release vaccine carriers can facilitate an increased interaction time between the antigen and immune system to strengthen immune responses, but their promotion on adaptive immune responses, especially cellular immunity, are still unfavorable. Herein, we report a sustained antigen delivery vector, which carries abundant antigens, a nucleic acid adjuvant and pathogen-associated molecular patterns to simulate a natural pathogen to reinforce immune responses. Specifically, murine colorectal cancer cells MC38 lysate and Toll-like receptor 9 agonist CpG are loaded into yeast derived β-glucan particles (GPs). After vaccination, these particles can form a vaccine depot that continuously release the antigen similar to the traditional aluminum hydroxide gel, but recruit more immune cells and induce more cytokine secretion at the injection site. Stronger antibody responses, Th1 and Th17 biased cellular immunity and immune memory are achieved compared with aluminum hydroxide gel. More importantly, treatment with these particles significantly suppress tumor growth in a therapeutic tumor model. This work shed light on the efficacy of combining sustained antigen release with pathogen-mimicking manner in vaccine design.

Cyclophosphamide loaded thermo-responsive hydrogel system synergize with a hydrogel cancer vaccine to amplify cancer immunotherapy in a prime-boost manner

Although neoantigen-based cancer vaccines show great potential in cancer immunotherapy due to their ability to induce effective and long-lasting anti-tumor immunity, their development is hindered by the limitations of neoantigens identification, low immunogenicity, and weak immune response. Cyclophosphamide (CTX) not only directly kills tumors but also causes immunogenic cell death, providing a promising source of antigens for cancer vaccines. Herein, a combined immunotherapy strategy based on temperature-sensitive PLEL hydrogel is designed. First, CTX-loaded hydrogel is injected intratumorally into CT26 bearing mice to prime anti-tumor immunity, and then 3 days later, PLEL hydrogels loaded with CpG and tumor lysates are subcutaneously injected into both groins to further promote anti-tumor immune responses. The results confirm that this combined strategy reduces the toxicity of CTX, and produces the cytotoxic T lymphocyte response to effectively inhibit tumor growth, prolong survival, and significantly improve the tumor cure rate. Moreover, a long-lasting immune memory response is observed in the mice. About 90% of the cured mice survive for at least 60 days after being re-inoculated with tumors, and the distant tumor growth is also well inhibited. Hence, this PLEL-based combination therapy may provide a promising reference for the clinical promotion of chemotherapy combined with cancer vaccines.

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PLEL based-CTX hydrogel system avoided the rapid clearance of CTX and reduced systemic toxicity.

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PLEL-assisted tumor lysate vaccine was cheap, safe, and contained all tumor antigens.

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This strategy promoted the maturation and activation of DCs, enhanced cancer-specific CD8⁺ T cell responses.

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PLEL-assisted combination strategy achieved a good tumor inhibition effect and generate a lasting immune memory. .

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This local administration strategy could kill tumors that could not be detected or removed surgically in the clinic.

Engineered Nanoparticles for Cancer Vaccination and Immunotherapy

The immune system has evolved over time to protect the host from foreign microorganisms. Activation of the immune system is predicated on a distinction between self and nonself. Unfortunately, cancer is characterized by genetic alterations in the host's cells, leading to uncontrolled cellular proliferation and evasion of immune surveillance. Cancer immunotherapy aims to educate the host's immune system to not only recognize but also attack and kill mutated cancer cells. While immune checkpoint blockers have been proven to be effective against multiple types of advanced cancer, the overall patient response rate still remains below 30%. Therefore, there is an urgent need to improve current cancer immunotherapies. In this Account, we present an overview of our recent progress on nanoparticle-based strategies for improving cancer vaccines and immunotherapies. We also present other complementary strategies to give a well-rounded snapshot of the field of combination cancer immunotherapy. The versatility and tunability of nanoparticles make them promising platforms for addressing individual challenges posed by various cancers. For example, nanoparticles can deliver cargo materials to specific cells, such as vaccines delivered to antigen-presenting cells for strong immune activation. Nanoparticles also allow for stimuli-responsive delivery of various therapeutics to cancer cells, thus forming the basis for combination cancer immunotherapy. Here, we focus on nanoparticle platforms engineered to deliver tumor antigens, whole tumor cells, and chemotherapeutic or phototherapeutic agents in a manner to effectively and safely trigger the host's immune system against tumor cells. For each work, we discuss the nanoparticle platform developed, synthesis chemistry, and in vivo applications. Nanovaccines offer a unique platform for codelivery of personalized tumor neoantigens and adjuvants and elicitation of robust immune responses against aggressive tumors. Nanovaccines either delivering whole tumor cell lysate or formed from tumor cell lysate may increase the repertoire of tumor antigens as immune targets while exploiting immunogenic cell death to prime antitumor immune responses. We also discuss how antigen- and whole tumor cell-based approaches may open the door for personalized cancer vaccination and immunotherapy. On the other hand, chemotherapy, phototherapy, and radiotherapy are more standardized cancer therapies, and nanoparticle-based approaches may promote their ability to initiate T cell activation against tumor cells and improve antitumor efficacy with minimal toxicity. Finally, building on the recent progress in nanoparticle-based cancer immunotherapy, the field should set the ultimate goal to be clinical translation and clinical efficacy. We will discuss regulatory, analytical, and manufacturing hurdles that should be addressed to expedite the clinical translation of nanomedicine-based cancer immunotherapy.

Nanoparticle cancer vaccines: Design considerations and recent advances

Vaccines therapeutics manipulate host's immune system and have broad potential for cancer prevention and treatment. However, due to poor immunogenicity and limited safety, fewer cancer vaccines have been successful in clinical trials. Over the past decades, nanotechnology has been exploited to deliver cancer vaccines, eliciting long-lasting and effective immune responses. Compared to traditional vaccines, cancer vaccines delivered by nanomaterials can be tuned towards desired immune profiles by (1) optimizing the physicochemical properties of the nanomaterial carriers, (2) modifying the nanomaterials with targeting molecules, or (3) co-encapsulating with immunostimulators. In order to develop vaccines with desired immunogenicity, a thorough understanding of parameters that affect immune responses is required. Herein, we discussed the effects of physicochemical properties on antigen presentation and immune response, including but not limited to size, particle rigidity, intrinsic immunogenicity. Furthermore, we provided a detailed overview of recent preclinical and clinical advances in nanotechnology for cancer vaccines, and considerations for future directions in advancing the vaccine platform to widespread anti-cancer applications.

Harnessing T-cell activity against prostate cancer: A therapeutic microparticulate oral cancer vaccine

Prostate Cancer specific immunotherapy in combination with immune stimulating adjuvants may serve as a viable strategy for facilitating tumor regression and preventing recurrence. In this study, an oral microparticulate vaccine encapsulating tumor associated antigens (TAA) extracted from a murine prostate cancer cell line, TRAMP-C2, was formulated with the help of a spray dryer. Microparticles were characterized in vitro to determine their physicochemical properties and antigenicity. Formulated microparticles had an average size of 4.92 ± 0.5 μm with a zeta potential of 7.92 ± 1.2 mV. In order to test our formulation for its ability to demonstrate adequate antigen presentation and co-stimulation, microparticles were tested in vitro on murine dendritic cells. In vitro biological characterization demonstrated the activation of specific immune system markers such as CD80/86, CD40, MHC-I and MHC-II. Following in vitro characterization, in vivo anti-tumor efficacy of the oral microparticulate vaccine was evaluated in C57BL/6 male mice. Combination therapy of vaccine microparticles with cyclophosphamide and granulocyte macrophage-colony stimulating factor (GM-CSF) demonstrated a five-fold reduction in tumor volume as compared to non-vaccinated mice. At the cellular level, cyclophosphamide and GM-CSF augmented the vaccine response as indicated by the reduced tumor volume and significant elevation of cytotoxic T-cell (CTL) CD8+ and (T-helper) CD4+ T-cells compared to mice receiving vaccine microparticles alone. Furthermore, our studies indicate a significant reduction in T-regulatory cells (T-regs) in mice receiving vaccine along with GM-CSF and cyclophosphamide, one of the immune escape mechanisms linked to tumor growth and progression. Thus, oral microparticulate vaccines have the potential to trigger a robust anti-tumor cellular response, and in combination with clinically relevant agents, significantly resist tumor growth and progression.

Evaluation of a Particulate Breast Cancer Vaccine Delivered via Skin

Breast cancer impacts female population globally and is the second most common cancer for females. With various limitations and adverse effects of current therapies, several immunotherapies are being explored. Development of an effective breast cancer vaccine can be a groundbreaking immunotherapeutic approach. Such approaches are being evaluated by several clinical trials currently. On similar lines, our research study aims to evaluate a particulate breast cancer vaccine delivered via skin. This particulate breast cancer vaccine was prepared by spray drying technique and utilized murine breast cancer whole cell lysate as a source of tumor-associated antigens. The average size of the particulate vaccine was 1.5 μm, which resembled the pathogenic species, thereby assisting in phagocytosis and antigen presentation leading to further activation of the immune response. The particulate vaccine was delivered via skin using commercially available metal microneedles. Methylene blue staining and confocal microscopy were used to visualize the microchannels. The results showed that microneedles created aqueous conduits of 50 ± 10 μm to deliver the microparticulate vaccine to the skin layers. Further, an in vivo comparison of immune response depicted significantly higher concentration of serum IgG, IgG2a, and B and T cell (CD4+ and CD8+) populations in the vaccinated animals than the control animals (p < 0.001). Upon challenge with live murine breast cancer cells, the vaccinated animals showed five times more tumor suppression than the control animals confirming the immune response activation and protection (p < 0.001). This research paves a way for individualized immunotherapy following surgical tumor removal to prolong relapse episodes.

Biomaterials for vaccine-based cancer immunotherapy

The development of therapeutic cancer vaccines as a means to generate immune reactivity against tumors has been explored since the early discovery of tumor-specific antigens by Georg Klein in the 1960s. However, challenges including weak immunogenicity, systemic toxicity, and off-target effects of cancer vaccines remain as barriers to their broad clinical translation. Advances in the design and implementation of biomaterials are now enabling enhanced efficacy and reduced toxicity of cancer vaccines by controlling the presentation and release of vaccine components to immune cells and their microenvironment. Here, we discuss the rational design and clinical status of several classes of cancer vaccines (including DNA, mRNA, peptide/protein, and cell-based vaccines) along with novel biomaterial-based delivery technologies that improve their safety and efficacy. Further, strategies for designing new platforms for personalized cancer vaccines are also considered.

Nanoparticles: augmenting tumor antigen presentation for vaccine and immunotherapy treatments of cancer

The major goal of immunity is maintaining host survival. Toward this, immune cells recognize and eliminate targets that pose a danger. Primarily, these are external invaders (pathogens) and internal invaders (cancers). Their recognition relies on distinguishing foreign components (antigens) from self-antigens. Since cancer cells are the host's own cells that are harmfully altered, they are difficult to distinguish from normal self. Furthermore, the antigens least resembling the host are often sequestered in parts of the tumor least accessible to immune responses. Therefore, to sufficiently boost immunity, these tumor antigens must be exposed to the immune system. Toward this, nanoparticles provide an innovating means of tumor antigen presentation and are destined to become an integral part of cancer immunotherapy.

A simple, clinically relevant therapeutic vaccine shows long-term protection in an aggressive, delayed-treatment B lymphoma model

Despite initial remission after successful treatments, B lymphoma patients often encounter relapses and resistance causing high mortality. Thus, there is a need to develop therapies that prevent relapse by providing long-term protection and, ultimately, lead to functional cure. In this study, our goal was to develop a simple, clinically relevant, and easily translatable therapeutic vaccine that provides durable immune protection against aggressive B cell lymphoma and identify critical immune biomarkers that are predictive of long-term survival. In a delayed-treatment, aggressive, murine model of A20 B lymphoma that mimics human diffuse large B cell lymphoma, we show that therapeutic A20 lysate vaccine adjuvanted with an NKT cell agonist, α-galactosylceramide (α-GalCer), provides long-term immune protection against lethal tumor challenges and the antitumor immunity is primarily CD8 T cell dependent. Using experimental and computational methods, we demonstrate that the initial strength of germinal center reaction and the magnitude of class-switching into a Th1 type humoral response are the best predictors for the long-term immunity of B lymphoma lysate vaccine. Our results not only provide fundamentally insights for successful immunotherapy and long-term protection against B lymphomas, but also present a simple, therapeutic vaccine that can be translated easily due to the facile and inexpensive method of preparation.

Recent progress in GM-CSF-based cancer immunotherapy

Cancer immunotherapy is a growing field. GM-CSF, a potent cytokine promoting the differentiation of myeloid cells, can also be used as an immunostimulatory adjuvant to elicit antitumor immunity. Additionally, GM-CSF is essential for the differentiation of dendritic cells, which are responsible for processing and presenting tumor antigens for the priming of antitumor cytotoxic T lymphocytes. Some strategies have been developed for GM-CSF-based cancer immunotherapy in clinical practice: GM-CSF monotherapy, GM-CSF-secreting cancer cell vaccines, GM-CSF-fused tumor-associated antigen protein-based vaccines, GM-CSF-based DNA vaccines and GM-CSF combination therapy. GM-CSF also contributes to the regulation of immunosuppression in the tumor microenvironment. This review provides recommendations regarding GM-CSF-based cancer immunotherapy.

In Vivo Synthesis of Cyclic-di-GMP Using a Recombinant Adenovirus Preferentially Improves Adaptive Immune Responses against Extracellular Antigens

There is a compelling need for more effective vaccine adjuvants to augment induction of Ag-specific adaptive immune responses. Recent reports suggested the bacterial second messenger bis-(3'-5')-cyclic-dimeric-guanosine monophosphate (c-di-GMP) acts as an innate immune system modulator. We recently incorporated a Vibrio cholerae diguanylate cyclase into an adenovirus vaccine, fostering production of c-di-GMP as well as proinflammatory responses in mice. In this study, we recombined a more potent diguanylate cyclase gene, VCA0848, into a nonreplicating adenovirus serotype 5 (AdVCA0848) that produces elevated amounts of c-di-GMP when expressed in mammalian cells in vivo. This novel platform further improved induction of type I IFN-β and activation of innate and adaptive immune cells early after administration into mice as compared with control vectors. Coadministration of the extracellular protein OVA and the AdVCA0848 adjuvant significantly improved OVA-specific T cell responses as detected by IFN-γ and IL-2 ELISPOT, while also improving OVA-specific humoral B cell adaptive responses. In addition, we found that coadministration of AdVCA0848 with another adenovirus serotype 5 vector expressing the HIV-1-derived Gag Ag or the Clostridium difficile-derived toxin B resulted in significant inhibitory effects on the induction of Gag and toxin B-specific adaptive immune responses. As a proof of principle, these data confirm that in vivo synthesis of c-di-GMP stimulates strong innate immune responses that correlate with enhanced adaptive immune responses to concomitantly administered extracellular Ag, which can be used as an adjuvant to heighten effective immune responses for protein-based vaccine platforms against microbial infections and cancers.

Diaminosulfide based polymer microparticles as cancer vaccine delivery systems

The aim of the research presented here was to determine the characteristics and immunostimulatory capacity, in vivo, of antigen and adjuvant co-loaded into microparticles made from a novel diaminosulfide polymer, poly(4,4'-trimethylenedipiperdyl sulfide) (PNSN), and to assess their potential as cancer vaccine vectors. PNSN microparticles co-loaded with the antigen, ovalbumin (OVA), and adjuvant, CpG 1826, (PNSN(OVA + CpG)) were fabricated and characterized for size (1.64 μm diameter; PDI=0.62), charge (-23.1 ± 0.3), and loading efficiencies of antigen (7.32 μg/mg particles) and adjuvant (0.95 μg/mg particles). The ability of PNSN(OVA + CpG) to stimulate cellular and humoral immune responses in vivo was compared with other PNSN microparticle formulations as well as with poly(lactic-co-glycolic acid)(PLGA)-based microparticles, co-loaded with OVA and CpG (PLGA(OVA + CpG)), an adenovirus encoding OVA (Ad5-OVA), and OVA delivered with incomplete Freund's adjuvant (IFA(OVA)). In vivo OVA-specific IgG1 responses, after subcutaneous prime/boosts in mice, were similar when PNSN(OVA + CpG) and PLGA(OVA + CpG) were compared and the presence of CpG 1826 within the PNSN microparticles demonstrated significantly improved responses when compared to PNSN microparticles loaded with OVA alone (PNSN(OVA)), plus or minus soluble CpG 1826. Cellular immune responses to all particle-based vaccine formulations ranged from being negligible to modest with PNSN(OVA + CpG) generating the greatest responses, displaying significantly increased levels of OVA-specific CD8+ T lymphocytes compared to controls and IFA(OVA) treated mice. Finally, it was shown that of all vaccination formulations tested PNSN(OVA + CpG) was the most protective against subsequent challenge with an OVA-expressing tumor cell line, E.G7. Thus, microparticles made from poly(diaminosulfide)-based macromolecules possess promising potential as vaccine vectors and, as demonstrated here, may have impact as cancer vaccines in particular.

Personalized approaches to active immunotherapy in cancer

Immunotherapy is emerging as a promising anti-cancer curative modality. However, in contrast to recent advances obtained employing checkpoint blockade agents and T cell therapies, clinical efficacy of therapeutic cancer vaccines is still limited. Most vaccination attempts in the clinic represent "off-the shelf" approaches since they target common "self" tumor antigens, shared among different patients. In contrast, personalized approaches of vaccination are tailor-made for each patient and in spite being laborious, hold great potential. Recent technical advancement enabled the first steps in the clinic of personalized vaccines that target patient-specific mutated neo-antigens. Such vaccines could induce enhanced tumor-specific immune response since neo-antigens are mutation-derived antigens that can be recognized by high affinity T cells, not limited by central tolerance. Alternatively, the use of personalized vaccines based on whole autologous tumor cells, overcome the need for the identification of specific tumor antigens. Whole autologous tumor cells could be administered alone, pulsed on dendritic cells as lysate, DNA, RNA or delivered to dendritic cells in-vivo through encapsulation in nanoparticle vehicles. Such vaccines may provide a source for the full repertoire of the patient-specific tumor antigens, including its private neo-antigens. Furthermore, combining next-generation personalized vaccination with other immunotherapy modalities might be the key for achieving significant therapeutic outcome.

Therapeutic cancer vaccines

The clinical benefit of therapeutic cancer vaccines has been established. Whereas regression of lesions was shown for premalignant lesions caused by HPV, clinical benefit in cancer patients was mostly noted as prolonged survival. Suboptimal vaccine design and an immunosuppressive cancer microenvironment are the root causes of the lack of cancer eradication. Effective cancer vaccines deliver concentrated antigen to both HLA class I and II molecules of DCs, promoting both CD4 and CD8 T cell responses. Optimal vaccine platforms include DNA and RNA vaccines and synthetic long peptides. Antigens of choice include mutant sequences, selected cancer testis antigens, and viral antigens. Drugs or physical treatments can mitigate the immunosuppressive cancer microenvironment and include chemotherapeutics, radiation, indoleamine 2,3-dioxygenase (IDO) inhibitors, inhibitors of T cell checkpoints, agonists of selected TNF receptor family members, and inhibitors of undesirable cytokines. The specificity of therapeutic vaccination combined with such immunomodulation offers an attractive avenue for the development of future cancer therapies.

Applying biodegradable particles to enhance cancer vaccine efficacy

One of the primary goals of our group and our collaborators here at the University of Iowa is to develop therapeutic cancer vaccines using biodegradable and biocompatible polymer-based vectors. A major advantage of using discretely packaged immunogenic cargo over non-encapsulated vaccines is that they promote enhanced cellular immunity, a key requirement in achieving antitumor activity. We discuss the importance of co-encapsulation of tumor antigen and adjuvant, with specific focus on the synthetic oligonucleotide adjuvant, cytosine-phosphate-guanine oligodeoxynucleotides. We also discuss our research using a variety of polymers including poly(α-hydroxy acids) and polyanhydrides, with the aim of determining the effect that parameters, such as size and polymer type, can have on prophylactic and therapeutic tumor vaccine formulation efficacy. Aside from their role as vaccine vectors per se, we also address the research currently underway in our group that utilizes more novel applications of biodegradable polymer-based particles in facilitating other types of immune-based therapies.

Microencapsulation of tumor lysates and live cell engineering with MIP-3α as an effective vaccine

The combination of several potential strategies so as to develop new tumor vaccines is an attractive field of translational medicine. Pulsing tumor lysates with dendritic cells (DCs), in-vivo attraction of DCs by macrophage inflammatory protein 3α (MIP-3α), and reversion of the tumor suppressive microenvironment have been tested as strategies to develop tumor vaccines. In this study, we generated an alginate microsphere (named PaLtTcAdMIP3α) that encapsulated tumor lysates, live tumor cells engineering with a recombinant MIP-3α adenovirus and BCG. We used PaLtTcAdMIP3α as a model vaccine to test its antitumor activities. Our results showed that PaLtTcAdMIP3α expressed and excreted MIP-3α, which effectively attracted DCs ex vivo and in vivo. Injection of PaLtTcAdMIP3α into tumor-bearing mice effectively induced both therapeutic and prophylactic antitumor immunities in CT26, Meth A, B16-F10 and H22 models, but without any ensuing increase in adverse effects. Both tumor-specific cellular and humoral immune responses, especially the CD8(+) T cell-dependent cytotoxic T immunity, were found in the mice injected with PaLtTcAdMIP3α. The anti-tumor activity was abrogated completely by depletion of CD8(+) and partially by CD4(+) T lymphocytes. In addition, the number of IFN-γ-producing CD8(+) T cells in spleen and tumor tissues was significantly increased; but the number of CD4(+)CD25(+)FOXP3(+) regulatory T cells (Treg) in tumor tissues was decreased. These data strongly suggest that a combination of multi-current-using strategies such as the novel approach of using our PaLtTcAdMIP3α microspheres could be an effective tumor model vaccine.

A therapeutic microparticle-based tumor lysate vaccine reduces spontaneous metastases in murine breast cancer

Metastatic breast cancer is currently incurable, and available therapies are associated with severe toxicities. Induction of protective anti-tumor immunity is a promising therapeutic approach for disseminated breast cancer, as immune responses are (i) systemic; (ii) antigen-specific; and (iii) capable of generating long-lived "memory" populations that protect against future tumor recurrences. Pursuant with this approach, we have developed a novel heterologous prime/boost vaccination regimen that reduces spontaneous lung metastases in mice with established murine 4T1 adenocarcinoma breast tumors. In our studies, mice were orthotopically challenged with luciferase-expressing 4T1 tumor cells; luciferase expression was retained in vivo, enabling us to quantitatively track metastatic tumor growth via bioluminescent imaging. On day 6 post-challenge, mice received a therapeutic "prime" consisting of bulk tumor lysates encapsulated in poly(lactic-co-glycolic) acid (PLGA) microparticles (MPs). On day 11, mice received a "boost" composed of free tumor lysates plus a cocktail of Toll-like receptor (TLR)-stimulating adjuvants. Tumor progression was monitored in vaccinated and untreated mice for 25 days, a time at which 100% of untreated mice had detectable lung tumors. PLGA MPs injected subcutaneously trafficked to draining lymph nodes and were efficiently phagocytosed by dendritic cells (DCs) within 48 h. Our combination therapy reduced metastatic lung tumor burdens by 42% and did not induce autoimmunity. These findings illustrate that vaccines based upon MP delivery of tumor lysates can form the basis of an effective treatment for metastatic breast cancer and suggest that similar approaches may be both efficacious and well-tolerated in the clinic.