Stimulation of immune systems by conjugated polymers and their potential as an alternative vaccine adjuvant

Tailoring biomaterials for vaccine delivery

Biomaterials are substances that can be injected, implanted, or applied to the surface of tissues in biomedical applications and have the ability to interact with biological systems to initiate therapeutic responses. Biomaterial-based vaccine delivery systems possess robust packaging capabilities, enabling sustained and localized drug release at the target site. Throughout the vaccine delivery process, they can contribute to protecting, stabilizing, and guiding the immunogen while also serving as adjuvants to enhance vaccine efficacy. In this article, we provide a comprehensive review of the contributions of biomaterials to the advancement of vaccine development. We begin by categorizing biomaterial types and properties, detailing their reprocessing strategies, and exploring several common delivery systems, such as polymeric nanoparticles, lipid nanoparticles, hydrogels, and microneedles. Additionally, we investigated how the physicochemical properties and delivery routes of biomaterials influence immune responses. Notably, we delve into the design considerations of biomaterials as vaccine adjuvants, showcasing their application in vaccine development for cancer, acquired immunodeficiency syndrome, influenza, corona virus disease 2019 (COVID-19), tuberculosis, malaria, and hepatitis B. Throughout this review, we highlight successful instances where biomaterials have enhanced vaccine efficacy and discuss the limitations and future directions of biomaterials in vaccine delivery and immunotherapy. This review aims to offer researchers a comprehensive understanding of the application of biomaterials in vaccine development and stimulate further progress in related fields.

Synthesis and Characterization of Thiolated Nanoparticles Based on Poly (Acrylic Acid) and Algal Cell Wall Biopolymers for the Delivery of the Receptor Binding Domain from SARS-CoV-2

The COVID-19 pandemic required great efforts to develop efficient vaccines in a short period of time. However, innovative vaccines against SARS-CoV-2 virus are needed to achieve broad immune protection against variants of concern. Polymeric-based particles can lead to innovative vaccines, serving as stable, safe and immunostimulatory antigen delivery systems. In this work, polymeric-based particles called thiolated PAA/Schizo were developed. Poly (acrylic acid) (PAA) was thiolated with cysteine ethyl ester and crosslinked with a Schizochytrium sp. cell wall fraction under an inverse emulsion approach. Particles showed a hydrodynamic diameter of 313 ± 38 nm and negative Zeta potential. FT-IR spectra indicated the presence of coconut oil in thiolated PAA/Schizo particles, which, along with the microalgae, could contribute to their biocompatibility and bioactive properties. TGA analysis suggested strong interactions between the thiolated PAA/Schizo components. In vitro assessment revealed that thiolated particles have a higher mucoadhesiveness when compared with non-thiolated particles. Cell-based assays revealed that thiolated particles are not cytotoxic and, importantly, increase TNF-α secretion in murine dendritic cells. Moreover, immunization assays revealed that thiolated PAA/Schizo particles induced a humoral response with a more balanced IgG2a/IgG1 ratio. Therefore, thiolated PAA/Schizo particles are deemed a promising delivery system whose evaluation in vaccine prototypes is guaranteed.

Synergetic Effect of Electrical and Topographical Cues in Aniline Trimer-Based Polyurethane Fibrous Scaffolds on Tissue Regeneration

Processibility and biodegradability of conductive polymers are major concerns when they are applied to tissue regeneration. This study synthesizes dissolvable and conductive aniline trimer-based polyurethane copolymers (DCPU) and processes them into scaffolds by using electrospinning with different patterns (random, oriented, and latticed). The effects of topographic cue changes on electrical signal transmission and further regulation of cell behaviors concerning bone tissue are researched. Results show that DCPU fibrous scaffolds possessed good hydrophilicity, swelling capacity, elasticity, and fast biodegradability in enzymatic liquid. In addition, the conductivity and efficiency of electrical signal transmission can be tuned by changing the surface’s topological structure. Among them, oriented DCPU scaffolds (DCPU-O) showed the best conductivity with the lowest ionic resistance value. Furthermore, the viability and proliferation results of bone mesenchymal stem cells (BMSCs) demonstrate a significant increase on three DCPU scaffolds compared to AT-free scaffolds (DPU-R). Especially, DCPU-O scaffolds exhibit superior abilities to promote cell proliferation because of their unique surface topography and excellent electroactivity. Concurrently, the DCPU-O scaffolds can synergistically promote osteogenic differentiation in terms of osteogenic differentiation and gene expression levels when combined with electrical stimulation. Together, these results suggest a promising use of DCPU-O fibrous scaffolds in the application of tissue regeneration.

Substance P/Heparin-Conjugated PLCL Mitigate Acute Gliosis on Neural Implants and Improve Neuronal Regeneration via Recruitment of Neural Stem Cells

The inflammatory host tissue response, characterized by gliosis and neuronal death at the neural interface, limits signal transmission and longevity of the neural probe. Substance P induces an anti-inflammatory response and neuronal regeneration and recruits endogenous stem cells. Heparin prevents nonspecific protein adsorption, suppresses the inflammatory response, and is beneficial to neuronal behavior. Poly(l-lactide-co-ε-caprolactone) (PLCL) is a soft and flexible polymer, and PLCL covalently conjugated with biomolecules has been widely used in tissue engineering. Coatings of heparin-conjugated PLCL (Hep-PLCL), substance P-conjugated PLCL (SP-PLCL), and heparin/substance P-conjugated PLCL (Hep/SP-PLCL) reduced the adhesion of astrocytes and fibroblasts and improved neuronal adhesion and neurite development compared to bare glass. The effects of these coatings are evaluated using immunohistochemistry analysis after implantation of coated stainless steel probes in rat brain for 1 week. In particular, Hep/SP-PLCL coating reduced the activation of microglia and astrocytes, the neuronal degeneration caused by inflammation, and indicated a potential for neuronal regeneration at the tissue-device interface. Suppression of the acute host tissue response by coating Hep/SP-PLCL could lead to improved functionality of the neural prosthesis.

All-polymeric transient neural probe for prolonged in-vivo electrophysiological recordings

Transient bioelectronics has grown fast, opening possibilities never thought before. In medicine, transient implantable devices are interesting because they could eliminate the risks related to surgical retrieval and reduce the chronic foreign body reaction. Despite recent progress in this area, the potential of transient bioelectronics is still limited by their short functional lifetime owed to the fast dissolution rate of degradable metals, which is typically a few days or weeks. Here we report that a switch from degradable metals to an entirely polymer-based approach allows for a slower degradation process and a longer lifetime of the transient probe, thus opening new possibilities for transient medical devices. As a proof-of-concept, we fabricated all-polymeric transient neural probes that can monitor brain activity in mice for a few months, rather than a few days or weeks. Also, we extensively evaluated the foreign body reaction around the implant during the probe degradation. This kind of devices might pave the way for several applications in neuroprosthetics.

Chemical Strategies to Boost Cancer Vaccines

Personalized cancer vaccines (PCVs) are reinvigorating vaccine strategies in cancer immunotherapy. In contrast to adoptive T-cell therapy and checkpoint blockade, the PCV strategy modulates the innate and adaptive immune systems with broader activation to redeploy antitumor immunity with individualized tumor-specific antigens (neoantigens). Following a sequential scheme of tumor biopsy, mutation analysis, and epitope prediction, the administration of neoantigens with synthetic long peptide (SLP) or mRNA formulations dramatically improves the population and activity of antigen-specific CD4+ and CD8+ T cells. Despite the promising prospect of PCVs, there is still great potential for optimizing prevaccination procedures and vaccine potency. In particular, the arduous development of tumor-associated antigen (TAA)-based vaccines provides valuable experience and rational principles for augmenting vaccine potency which is expected to advance PCV through the design of adjuvants, delivery systems, and immunosuppressive tumor microenvironment (TME) reversion since current personalized vaccination simply admixes antigens with adjuvants. Considering the broader application of TAA-based vaccine design, these two strategies complement each other and can lead to both personalized and universal therapeutic methods. Chemical strategies provide vast opportunities for (1) exploring novel adjuvants, including synthetic molecules and materials with optimizable activity, (2) constructing efficient and precise delivery systems to avoid systemic diffusion, improve biosafety, target secondary lymphoid organs, and enhance antigen presentation, and (3) combining bioengineering methods to innovate improvements in conventional vaccination, "smartly" re-educate the TME, and modulate antitumor immunity. As chemical strategies have proven versatility, reliability, and universality in the design of T cell- and B cell-based antitumor vaccines, the union of such numerous chemical methods in vaccine construction is expected to provide new vigor and vitality in cancer treatment.

Ex vivo-generated dendritic cell-based vaccines in melanoma: the role of nanoparticulate delivery systems

Melanoma is a poor immunogenic cancer and many treatment strategies have been used to enhance specific or nonspecific immunity against it. Dendritic cell (DC)-based cancer vaccine is the most effective therapies that have been used so far. Meanwhile, the efficacy of DC-based immunotherapy relies on critical factors relating to DCs such as the state of maturation and proper delivery of antigens. In this regard, the use of nanoparticulate delivery systems for effective delivery of antigen to ex vivo-generated DC-based vaccines that also poses adjuvanticity would be an ideal approach. In this review article, we attempt to summarize the role of different types of nanoparticulate antigen delivery systems used in the development of ex vivo-generated DC-based vaccines against melanoma and describe their adjuvanticity in mediation of DC maturation, cytoplasmic presentation of antigens to MHC class I molecules, which led to potent antigen-specific immune responses. As were represented, cationic liposomes were the most used approach, which suggest its potential applicability as delivery systems for further experiments in combination with either adjuvants or monoclonal antibodies.

Immunomodulatory Nanosystems

Immunotherapy has emerged as an effective strategy for the prevention and treatment of a variety of diseases, including cancer, infectious diseases, inflammatory diseases, and autoimmune diseases. Immunomodulatory nanosystems can readily improve the therapeutic effects and simultaneously overcome many obstacles facing the treatment method, such as inadequate immune stimulation, off-target side effects, and bioactivity loss of immune agents during circulation. In recent years, researchers have continuously developed nanomaterials with new structures, properties, and functions. This Review provides the most recent advances of nanotechnology for immunostimulation and immunosuppression. In cancer immunotherapy, nanosystems play an essential role in immune cell activation and tumor microenvironment modulation, as well as combination with other antitumor approaches. In infectious diseases, many encouraging outcomes from using nanomaterial vaccines against viral and bacterial infections have been reported. In addition, nanoparticles also potentiate the effects of immunosuppressive immune cells for the treatment of inflammatory and autoimmune diseases. Finally, the challenges and prospects of applying nanotechnology to modulate immunotherapy are discussed.

Facile syntheses of conjugated polymers for photothermal tumour therapy

Development of photothermal materials which are able to harness sunlight and convert it to thermal energy seems attractive. Besides carbon-based nanomaterials, conjugated polymers are emerging promising photothermal materials but their facile syntheses remain challenging. In this work, by modification of a CBT-Cys click condensation reaction and rational design of the starting materials, we facilely synthesize conjugated polymers poly-2-phenyl-benzobisthiazole (PPBBT) and its dihexyl derivative with good photothermal properties. Under the irradiation of either sunlight-mimicking Xe light or near-infrared laser, we verify that PPBBT has comparable photothermal heating-up speed to that of star material single-wall carbon nanotube. Moreover, PPBBT is used to fabricate water-soluble NPPPBBT nanoparticles which maintain excellent photothermal properties in vitro and photothermal therapy effect on the tumours exposed to laser irradiation. We envision that our synthetic method provides a facile approach to fabricate conjugated polymers for more promising applications in biomedicine or photovoltaics in the near future.

Interactions Between Nanoparticles and Dendritic Cells: From the Perspective of Cancer Immunotherapy

Dendritic cells (DCs) are the primary antigen-presenting cells and play key roles in the orchestration of the innate and adaptive immune system. Targeting DCs by nanotechnology stands as a promising strategy for cancer immunotherapy. The physicochemical properties of nanoparticles (NPs) influence their interactions with DCs, thus altering the immune outcome of DCs by changing their functions in the processes of maturation, homing, antigen processing and antigen presentation. In this review, we summarize the recent progress in targeting DCs using NPs as a drug delivery carrier in cancer immunotherapy, the recognition of NPs by DCs, and the ways the physicochemical properties of NPs affect DCs' functions. Finally, the molecular pathways in DCs that are affected by NPs are also discussed.

Cancer Cell Membrane-Coated Adjuvant Nanoparticles with Mannose Modification for Effective Anticancer Vaccination

Tumor vaccines for cancer prevention and treatment have attracted tremendous interests in the area of cancer immunotherapy in recent years. In this work, we present a strategy to construct cancer vaccines by encapsulating immune-adjuvant nanoparticles with cancer cell membranes modified by mannose. Poly(d,l-lactide- co-glycolide) nanoparticles are first loaded with toll-like receptor 7 agonist, imiquimod (R837). Those adjuvant nanoparticles (NP-R) are then coated with cancer cell membranes (NP-R@M), whose surface proteins could act as tumor-specific antigens. With further modification with mannose moiety (NP-R@M-M), the obtained nanovaccine shows enhanced uptake by antigen presenting cells such as dendritic cells, which would then be stimulated to the maturation status to trigger antitumor immune responses. With great efficacy to delay tumor development as a prevention vaccine, vaccination with such NP-R@M-M in combination with checkpoint-blockade therapy further demonstrates outstanding therapeutic efficacy to treat established tumors. Therefore, our work presents an innovative way to fabricate cancer nanovaccines, which in principle may be applied for a wide range of tumor types.

Tailoring Biomaterials for Cancer Immunotherapy: Emerging Trends and Future Outlook

Cancer immunotherapy, as a paradigm shift in cancer treatment, has recently received tremendous attention. The active cancer vaccination, immune checkpoint blockage (ICB) and chimeric antigen receptor (CAR) for T-cell-based adoptive cell transfer are among these developments that have achieved a significant increase in patient survival in clinical trials. Despite these advancements, emerging research at the interdisciplinary interface of cancer biology, immunology, bioengineering, and materials science is important to further enhance the therapeutic benefits and reduce side effects. Here, an overview of the latest studies on engineering biomaterials for the enhancement of anticancer immunity is given, including the perspectives of delivery of immunomodulatory therapeutics, engineering immune cells, and constructing immune-modulating scaffolds. The opportunities and challenges in this field are also discussed.

Strong in vivo antitumor responses induced by an antigen immobilized in nanogels via reducible bonds

Cancer vaccines are at present mostly based on tumor associated protein antigens but fail to elicit strong cell-mediated immunity in their free form. For protein-based vaccines, the main challenges to overcome are the delivery of sufficient proteins into the cytosol of dendritic cells (DCs) and processing by, and presentation through, the MHC class I pathway. Recently, we developed a cationic dextran nanogel in which a model antigen (ovalbumin, OVA) is reversibly conjugated via disulfide bonds to the nanogel network to enable redox-sensitive intracellular release. In the present study, it is demonstrated that these nanogels, with the bound OVA, were efficiently internalized by DCs and were capable of maturating them. On the other hand, when the antigen was just physically entrapped in the nanogels, OVA was prematurely released before the particles were taken up by cells. When combined with an adjuvant (polyinosinic-polycytidylic acid, poly(I:C)), nanogels with conjugated OVA induced a strong protective and curative effect against melanoma in vivo. In a prophylactic vaccination setting, 90% of the mice vaccinated with nanogels with conjugated OVA + poly(I:C) did not develop a tumor. Moreover, in a therapeutic model, 40% of the mice showed clearance of established tumors and survived for the duration of the experiment (80 days) while the remaining mice showed substantial delay in tumor progression. In conclusion, our results demonstrate that conjugation of antigens to nanogels via reducible covalent bonds for intracellular delivery is a promising strategy to induce effective antigen-specific immune responses against cancer.

Lipid core peptide/poly(lactic-co-glycolic acid) as a highly potent intranasal vaccine delivery system against Group A streptococcus

Rheumatic heart disease represents a leading cause of mortality caused by Group A Streptococcus (GAS) infections transmitted through the respiratory route. Although GAS infections can be treated with antibiotics these are often inadequate. An efficacious GAS vaccine holds more promise, with intranasal vaccination especially attractive, as it mimics the natural route of infections and should be able to induce mucosal IgA and systemic IgG immunity. Nanoparticles were prepared by either encapsulating or coating lipopeptide-based vaccine candidate (LCP-1) on the surface of poly(lactic-co-glycolic acid) (PLGA). In vitro study showed that encapsulation of LCP-1 vaccine into nanoparticles improved uptake and maturations of antigen-presenting cells. The immunogenicity of lipopeptide incorporated PLGA-based nanoparticles was compared with peptides co-administered with mucosal adjuvant cholera toxin B in mice upon intranasal administration. Higher levels of J14-specific salivary mucosal IgA and systemic antibody IgG titres were observed for groups immunized with encapsulated LCP-1 compared to LCP-1 coated nanoparticles or free LCP-1. Systemic antibodies obtained from LCP-1 encapsulated PLGA NPs inhibited the growth of bacteria in six different GAS strains. Our results show that PLGA-based lipopeptide delivery is a promising approach for rational design of a simple, effective and patient friendly intranasal GAS vaccine resulting in mucosal IgA response.