Polyester as Antigen Carrier toward Particulate Vaccines

Intranasal Epitope-Polymer Vaccine Lodges Resident Memory T Cells Protecting Against Influenza Virus

Intranasal vaccines, unlike injectable vaccines, boost immunity along the respiratory tract; this can significantly limit respiratory virus replication and shedding. There remains a need to develop mucosal adjuvants and vaccine delivery systems that are both safe and effective following intranasal administration. Here, biopolymer particles (BP) densely coated with repeats of MHC class I restricted immunodominant epitopes derived from influenza A virus namely NP366, a nucleoprotein-derived epitope and PA224, a polymerase acidic subunit derived epitope, are bioengineered. These BP-NP366/PA224 can be manufactured at a high yield and are obtained at ≈93% purity, exhibiting ambient-temperature stability. Immunological characterization includes comparing systemic and mucosal immune responses mounted following intramuscular or intranasal immunization. Immunization with BP-NP366/PA224 without adjuvant triggers influenza-specific CD8+ T cell priming and memory CD8+ T cell development. Co-delivery with the adjuvant poly(I:C) significantly boosts the size and functionality of the influenza-specific pulmonary resident memory CD8+ T cell pool. Intranasal, but not intramuscular delivery of BP-NP366/PA224 with poly(I:C), provides protection against influenza virus challenge. Overall, the BP approach demonstrates as a suitable antigen formulation for intranasal delivery toward induction of systemic protective T cell responses against influenza virus.

Embracing Sustainability: The World of Bio-Based Polymers in a Mini Review

The proliferation of polymer science and technology in recent decades has been remarkable, with synthetic polymers derived predominantly from petroleum-based sources dominating the market. However, concerns about their environmental impacts and the finite nature of fossil resources have sparked interest in sustainable alternatives. Bio-based polymers, derived from renewable sources such as plants and microbes, offer promise in addressing these challenges. This review provides an overview of bio-based polymers, discussing their production methods, properties, and potential applications. Specifically, it explores prominent examples including polylactic acid (PLA), polyhydroxyalkanoates (PHAs), and polyhydroxy polyamides (PHPAs). Despite their current limited market share, the growing awareness of environmental issues and advancements in technology are driving increased demand for bio-based polymers, positioning them as essential components in the transition towards a more sustainable future.

In vivo assembly of epitope-coated biopolymer particles that induce anti-tumor responses

There is an unmet need for antigen delivery systems that elicit efficient T cell priming to prevent infectious diseases or for treatment of cancers. Here, we explored the immunogenic potential of biologically assembled biopolymer particles (BPs) that have been bioengineered to display the antigenic MHC I and MHC II epitopes of model antigen ovalbumin (OVA). Purified dendritic cells (DCs) captured BP-OVA and presented the associated antigenic epitopes to CD4+ T cells and CD8+ T cells. Vaccination with BP-OVA in the absence of adjuvant elicited antigen presentation to OVA-specific CD8+ and CD4+ T cells and cross-primed effective cytotoxic T lymphocyte (CTL) killers. BP-OVA induction of CTL killing did not require CD4+ T cell help, with active CTLs generated in BP-OVA vaccinated I-Ab-/- and CD40-/- mice. In contrast, IL-15 and type I IFN were required, with abrogated CTL activity in vaccinated IL-15-/- and IFNAR1-/- mice. cDC1 and/or CD103+ DCs were not essential for BP-OVA specific CTL with immunization eliciting responses in Batf3-/- mice. Poly I:C, but not LPS or CpG, co-administered as an adjuvant with BP-OVA boosted CTL responses. Finally, vaccination with BP-OVA protected against B16-OVA melanoma and Eμ-myc-GFP-OVA lymphoma inoculation. In summary, we have demonstrated that epitope-displaying BPs represent an antigen delivery platform exhibiting a unique mechanism to effectively engage T cell immune responses.

Nature-inspired material binding peptides with versatile polyester affinities and binding strengths

Biodegradable polyesters, such as polyhydroxyalkanoates (PHAs), are having a tremendous impact on biomedicine. However, these polymers lack functional moieties to impart functions like targeted delivery of molecules. Inspired by native GAPs, such as phasins and their polymer-binding and surfactant properties, we generated small material binding peptides (MBPs) for polyester surface functionalization using a rational approach based on amphiphilicity. Here, two peptides of 48 amino acids derived from phasins PhaF and PhaI from Pseudomonas putida, MinP and the novel-designed MinI, were assessed for their binding towards two types of PHAs, PHB and PHOH. In vivo, fluorescence studies revealed selective binding towards PHOH, whilst in vitro binding experiments using the Langmuir-Blodgett technique coupled to ellipsometry showed KD in the range of nM for all polymers and MBPs. Marked morphological changes of the polymer surface upon peptide adsorption were shown by BAM and AFM for PHOH. Moreover, both MBPs were successfully used to immobilize cargo proteins on the polymer surfaces. Altogether, this work shows that by redesigning the amphiphilicity of phasins, a high affinity but lower specificity to polyesters can be achieved in vitro. Furthermore, the MBPs demonstrated binding to PET, showing potential to bind cargo molecules also to synthetic polyesters.

Polymeric epitope-based vaccine induces protective immunity against group A Streptococcus

Group A Streptococcus (Strep A) is a life-threatening human pathogen with no licensed vaccine. Here, we used a biopolymer particle (BP) approach to display repeats of Strep A vaccine candidate peptides p*17 and K4S2 derived from M and non-M protein, respectively. BPs densely displaying both peptides (BP-p*17-S2) were successfully assembled in one-step inside an engineered endotoxin-free Escherichia coli strain. Purified BP-p*17-S2 showed a spherical core-shell morphology with a biopolymer core and peptide shell. Upon formulation with aluminum hydroxide as adjuvant, BP-p*17-S2 exhibited a mean diameter of 2.9 µm and a positive surface charge of 22 mV. No cytotoxicity was detected when tested against HEK-293 cells. Stability studies showed that BP-p*17-S2 is ambient-temperature stable. Immunized mice showed no adverse reactions, while producing high titers of peptide specific antibodies and cytokines. This immune response could be correlated with protective immunity in an animal model of infection, i.e. intranasal challenge of mice with Strep A, where a significant reduction of >100-fold of pathogen burden in nose-associated lymphoid tissue, lung, and spleen was obtained. The cost-effective scalable manufacture of ambient-temperature stable BPs coated with Strep A peptides combined with their immunogenic properties offer an attractive alternative strategy to current Strep A vaccine development.

Enzybiotic-mediated antimicrobial functionalization of polyhydroxyalkanoates

Polymeric nanoparticles (NPs) present some ideal properties as biomedical nanocarriers for targeted drug delivery such as enhanced translocation through body barriers. Biopolymers, such as polyhydroxyalkanoates (PHAs) are gaining attention as nanocarrier biomaterials due to their inherent biocompatibility, biodegradability, and ability to be vehiculized through hydrophobic media, such as the lung surfactant (LS). Upon colonization of the lung alveoli, below the LS layer, Streptococcus pneumoniae, causes community-acquired pneumonia, a severe respiratory condition. In this work, we convert PHA NPs into an antimicrobial material by the immobilization of an enzybiotic, an antimicrobial enzyme, via a minimal PHA affinity tag. We first produced the fusion protein M711, comprising the minimized PHA affinity tag, MinP, and the enzybiotic Cpl-711, which specifically targets S. pneumoniae. Then, a PHA nanoparticulate suspension with adequate physicochemical properties for pulmonary delivery was formulated, and NPs were decorated with M711. Finally, we assessed the antipneumococcal activity of the nanosystem against planktonic and biofilm forms of S. pneumoniae. The resulting system displayed sustained antimicrobial activity against both, free and sessile cells, confirming that tag-mediated immobilization of enzybiotics on PHAs is a promising platform for bioactive antimicrobial functionalization.

Precision-engineering of subunit vaccine particles for prevention of infectious diseases

Vaccines remain the best approach for the prevention of infectious diseases. Protein subunit vaccines are safe compared to live-attenuated whole cell vaccines but often show reduced immunogenicity. Subunit vaccines in particulate format show improved vaccine efficacy by inducing strong immune responses leading to protective immunity against the respective pathogens. Antigens with proper conformation and function are often required to induce functional immune responses. Production of such antigens requiring post-translational modifications and/or composed of multiple complex domains in bacterial hosts remains challenging. Here, we discuss strategies to overcome these limitations toward the development of particulate vaccines eliciting desired humoral and cellular immune responses. We also describe innovative concepts of assembling particulate vaccine candidates with complex antigens bearing multiple post-translational modifications. The approaches include non-covalent attachments (e.g. biotin-avidin affinity) and covalent attachments (e.g. SpyCatcher-SpyTag) to attach post-translationally modified antigens to particles.

Breast cancer vaccines: New insights into immunomodulatory and nano-therapeutic approaches

Breast cancer (BC) is known to be a highly heterogeneous disease that is clinically subdivided into four primary molecular subtypes, each having distinct morphology and clinical implications. These subtypes are principally defined by hormone receptors and other proteins involved (or not involved) in BC development. BC therapeutic vaccines [including peptide-based vaccines, protein-based vaccines, nucleic acid-based vaccines (DNA/RNA vaccines), bacterial/viral-based vaccines, and different immune cell-based vaccines] have emerged as an appealing class of cancer immunotherapeutics when used alone or combined with other immunotherapies. Employing the immune system to eliminate BC cells is a novel therapeutic modality. The benefit of active immunotherapies is that they develop protection against neoplastic tissue and readjust the immune system to an anti-tumor monitoring state. Such immunovaccines have not yet shown effectiveness for BC treatment in clinical trials. In recent years, nanomedicines have opened new windows to increase the effectiveness of vaccinations to treat BC. In this context, some nanoplatforms have been designed to efficiently deliver molecular, cellular, or subcellular vaccines to BC cells, increasing the efficacy and persistence of anti-tumor immunity while minimizing undesirable side effects. Immunostimulatory nano-adjuvants, liposomal-based vaccines, polymeric vaccines, virus-like particles, lipid/calcium/phosphate nanoparticles, chitosan-derived nanostructures, porous silicon microparticles, and selenium nanoparticles are among the newly designed nanostructures that have been used to facilitate antigen internalization and presentation by antigen-presenting cells, increase antigen stability, enhance vaccine antigenicity and remedial effectivity, promote antigen escape from the endosome, improve cytotoxic T lymphocyte responses, and produce humoral immune responses in BC cells. Here, we summarized the existing subtypes of BC and shed light on immunomodulatory and nano-therapeutic strategies for BC vaccination. Finally, we reviewed ongoing clinical trials on BC vaccination and highlighted near-term opportunities for moving forward.

Intranasal Delivery of Antigen-Coated Polymer Particles Protects against Pseudomonas aeruginosa Infection

Pseudomonas aeruginosa is an opportunistic human pathogen that is intrinsically resistant to multiple antibiotics, causing severe and persistent infections in immunocompromised individuals. This bacterium has been listed as a priority pathogen by the WHO in 2017, and there is no vaccine available for human use. In this study, 10 vaccine candidate antigens were selected for particulate vaccine design. We engineered Escherichia coli to assemble biopolymer particles (BPs) that were either coated with epitopes (Ag) derived from OprF/I-AlgE proteins or PopB or PopB-Ag or coated with single or double copies of epitopes (10Ag and 10Ag(2x)) derived from OprF, OprI, AlgE, OprL, PopB, PilA, PilO, FliC, Hcp1, and CdrA. Antigen-coated BPs showed a diameter of 0.93-1.16 μm with negative surface charge. Antigens attached to BPs were identified by mass spectrometry. Vaccination with BP-Ag, BP-PopB, BP-PopBAg, PB-10Ag, and BP-10Ag(2x) with and without Alhydrogel adjuvant induced significant antigen-specific humoral and cell-mediated immune responses in mice. All particulate vaccines with Alhydrogel induced protection in an acute pneumonia murine model of P. aeruginosa infection, contributing to up to 80% survival when administered intramuscularly, and the addition of Alhydrogel boosted immunity. The BP-10Ag(2x) vaccine candidate showed the best performance and even induced protective immunity in the absence of Alhydrogel. Intramuscular administration of the BP-10Ag(2x) without Alhydrogel vaccine resulted in 60% survival. Intranasal vaccination induced immunity, contributing to about 90% survival. Overall, our data suggest that vaccination with BPs coated with P. aeruginosa antigens induce protective immunity against P. aeruginosa infections. The possibility of intranasal delivery will strongly facilitate administration and use of BP vaccines.

Ambient Temperature Stable, Scalable COVID-19 Polymer Particle Vaccines Induce Protective Immunity

There is an unmet need for safe and effective severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines that are stable and can be cost-effectively produced at large scale. Here, a biopolymer particle (BP) vaccine technology that can be quickly adapted to new and emerging variants of SARS-CoV-2 is used. Coronavirus antigen-coated BPs are described as vaccines against SARS-CoV-2. The spike protein subunit S1 or epitopes from S and M proteins (SM) plus/minus the nucleocapsid protein (N) are selected as antigens to either coat BPs during assembly inside engineered Escherichia coli or BPs are engineered to specifically ligate glycosylated spike protein (S1-ICC) produced by using baculovirus expression in insect cell culture (ICC). BP vaccines are safe and immunogenic in mice. BP vaccines, SM-BP-N and S1-ICC-BP induced protective immunity in the hamster SARS-CoV-2 infection model as shown by reduction of virus titers up to viral clearance in lungs post infection. The BP platform offers the possibility for rapid design and cost-effective large-scale manufacture of ambient temperature stable and globally available vaccines to combat the coronavirus disease 2019 (COVID-19) pandemic.

A Polyhydroxyalkanoates-Based Carrier Platform of Bioactive Substances for Therapeutic Applications

Bioactive substances (BAS), such as small molecule drugs, proteins, RNA, cells, etc., play a vital role in many therapeutic applications, especially in tissue repair and regeneration. However, the therapeutic effect is still a challenge due to the uncontrollable release and instable physico-chemical properties of bioactive components. To address this, many biodegradable carrier systems of micro-nano structures have been rapidly developed based on different biocompatible polymers including polyhydroxyalkanoates (PHA), the microbial synthesized polyesters, to provide load protection and controlled-release of BAS. We herein highlight the developments of PHA-based carrier systems in recent therapeutic studies, and give an overview of its prospective applications in various disease treatments. Specifically, the biosynthesis and material properties of diverse PHA polymers, designs and fabrication of micro- and nano-structure PHA particles, as well as therapeutic studies based on PHA particles, are summarized to give a comprehensive landscape of PHA-based BAS carriers and applications thereof. Moreover, recent efforts focusing on novel-type BAS nano-carriers, the functionalized self-assembled PHA granules in vivo, was discussed in this review, proposing the underlying innovations of designs and fabrications of PHA-based BAS carriers powered by synthetic biology. This review outlines a promising and applicable BAS carrier platform of novelty based on PHA particles for different medical uses.

Use Intein Cleavable Polyhydroxyalkanoate Synthase Fusions to Improve Protein Solubility

Recombinant E. coli producing intein-cleavable polyhydroxyalkanoate synthase fusions mediates the intracellular formation of polyhydroxyalkanoate (PHA) particles densely coated with intein-cleavable target protein fusion. These PHA particles can be efficiently purified from lysed cells. The self-cleaving intein performs as a bio-linker between the PHA synthase and the target protein. The tagless target protein can be released as pure soluble protein from the PHA particles by a simple pH reduction to 6.0. Here we describe that PHA particles serve as bioseparation resin for purification of soluble target proteins with pharmaceutical grade purity, similar to commercial affinity separation technologies. This cost-effective technique does not involve multiple complicated protein purification procedures, and we have exploited this approach to purify six target proteins: green fluorescent protein (GFP) from A. victoria, antigen Rv1626 from M. tuberculosis, the immunoglobulin G (IgG) binding ZZ domain of protein A derived from Staphylococcus aureus, human tumor necrosis factor alpha (TNFα), human granulocyte colony-stimulating factor (G-CSF), and human interferon alpha 2b (IFNα2b).

Epitope-coated polymer particles elicit neutralising antibodies against Plasmodium falciparum sporozoites

The current Malaria RTS,S vaccine is based on virus-like particles (VLPs) comprising the NANP repetitive epitopes from the cicumsporozoite protein (CSP) of Plasmodium falciparum. This vaccine has limited efficacy, only preventing severe disease in about 30% of vaccinated individuals. A more efficacious vaccine is urgently needed to combat malaria. Here we developed a particulate malaria vaccine based on the same CSP epitopes but using biopolymer particles (BPs) as an antigen carrier system. Specific B- and T-cell epitope-coated BPs were assembled in vivo inside an engineered endotoxin-free mutant of Escherichia coli. A high-yield production process leading to ~27% BP vaccine weight over biomass was established. The epitope-coated BPs were purified and their composition, i.e., the polymer core and epitope identity, was confirmed. Epitope-coated BPs were used alongside soluble peptide epitopes and empty BPs to vaccinate sheep. Epitope-coated BPs showed enhanced immunogenicity by inducing anti-NANP antibody titre of EC50 > 150,000 that were at least 20 times higher than induced by the soluble peptides. We concluded that the additional T-cell epitope was not required as it did not enhance immunogenicity when compared with the B-cell epitope-coated BPs. Antibodies specifically bound to the surface of Plasmodium falciparum sporozoites and efficiently inhibited sporozoite motility and traversal of human hepatocytes. This study demonstrated the utility of biologically self-assembled epitope-coated BPs as an epitope carrier for inclusion in next-generation malaria vaccines.

Engineering Antigens to Assemble into Polymer Particle Vaccines for Prevention of Streptococcus suis Infection

Streptococcus suis is a zoonotic pathogen affecting pigs and humans. This bacterium causes severe economic losses in the swine industry and poses a serious threat to public health and food safety. There is no effective commercial vaccine available for pigs or humans. In this study, we applied the biopolymer particle (BP) vaccine technology to incorporate seven conserved S. suis antigens (38 kDa protein (38), enolase (Enol), SSU1915, SSU1355, SSU0185, SSU1215, and SSU1773 (SSU1 and SSU2)). Two combinations of these antigens (38 and Enol; all SSU antigens designated as SSU1 and SSU2) were engineered to mediate production of BPs coated with either antigens 38 and Enol or SSU1 and SSU2 inside recombinant Escherichia coli. The isolated and purified empty BPs, 38-BP-Enol and SSU1-BP-SSU2, showed size ranges of 312-428 nm and 292-344 nm with and without the QuilA® adjuvant, respectively, and all showed a negative surface charge. Further characterization of purified BPs confirmed the presence of the expected antigen-comprising fusion proteins as assessed by tryptic peptide fingerprinting analysis using quadrupole time-of-flight mass spectrometry and immunoblotting. Vaccination with 38-BP-Enol and SSU1-BP-SSU2 formulated with and without QuilA® adjuvant induced significant antigen-specific humoral immune responses in mice. Antigen-coated BPs induced significant and specific Ig (IgM + IgG) and IgG immune responses (1.0 × 106-1.0 × 107) when compared with mice vaccinated with empty BPs. Functionality of the immune response was confirmed in challenge experiments using an acute murine S. suis infection model, which showed 100% survival of the 38-BP-Enol and SSU1-BP-SSU2 vaccinated mice compared to 70% survival when vaccinated with empty BPs. Overall, our data suggest that S. suis antigen-coated BPs could be developed into particulate vaccines that induce protective immunity against S. suis infections.

Particulate Mycobacterial Vaccines Induce Protective Immunity against Tuberculosis in Mice

Currently available vaccines fail to provide consistent protection against tuberculosis (TB). New, improved vaccines are urgently needed for controlling the disease. The mycobacterial antigen fusions H4 (Ag85B-TB10.4) and H28 (Ag85B-TB10.4-Rv2660c) have been shown to be very immunogenic and have been considered as potential candidates for TB vaccine development. However, soluble protein vaccines are often poorly immunogenic, but augmented immune responses can be induced when selected antigens are delivered in particulate form. This study investigated whether the mycobacterial antigen fusions H4 and H28 can induce protective immunity when assembled into particulate vaccines (polyester nanoparticle-H4, polyester nanoparticle-H28, H4 nanoparticles and H28 nanoparticles). The particulate mycobacterial vaccines were assembled inside an engineered endotoxin-free production strain of Escherichia coli at high yield. Vaccine nanoparticles were purified and induced long-lasting antigen-specific T cell responses and protective immunity in mice challenged by aerosol with virulent Mycobacterium tuberculosis. A significant reduction of M. tuberculosis CFU, up to 0.7-log₁₀ protection, occurred in the lungs of mice immunized with particulate vaccines in comparison to placebo-vaccinated mice (p < 0.0001). Polyester nanoparticles displaying the mycobacterial antigen fusion H4 induced a similar level of protective immunity in the lung when compared to M. bovis bacillus Calmette-Guérin (BCG), the currently approved TB vaccine. The safe and immunogenic polyester nanoparticle-H4 vaccine is a promising subunit vaccine candidate, as it can be cost-effectively manufactured and efficiently induces protection against TB.

PM2.5 collected using cyclonic separation causes stronger biological responses than that collected using a conventional filtration method

Evaluation of the health effects of particulate matter with aerodynamic dias. ≤ 2.5 μm (PM2.5) should reflect realistic condition in ambient atmosphere. However, using conventional filtration methods, only extracts from PM2.5 collected on the filter can be analyzed and not the particle itself. Cyclonic separation is a technique that enables the direct analysis of the effects of the crude "powder form" of PM2.5 on respiratory health. Airway epithelial cells and antigen-presenting cells were exposed to PM2.5 collected during the same period using a conventional filtration method or cyclonic separation. PM2.5 collected using cyclonic separation led to a higher secretion of interleukins 6 and 8 (IL-6, IL-8) from airway epithelial cells, and IL-6, IL-1β, tumor necrosis factor-α (TNF-α) secretion, cluster of differentiation 86 (CD86), and dendritic and epithelial cells 205 (DEC205) expression on antigen-presenting cells, compared with the effects of filter-collected PM2.5. Furthermore, PM2.5 collected using cyclonic separation increased inflammatory cytokine levels and induced lung inflammation in vivo. These results suggest that crude PM2.5 collected using cyclonic separation causes stronger biological responses than filter-collected PM2.5. Hence, PM2.5 collected using cyclonic separation can be utilized for a reliable evaluation of the health effects of ambient PM2.5.

Engineered Mycobacterium tuberculosis antigen assembly into core-shell nanobeads for diagnosis of tuberculosis

Despite recent advances in diagnosis, tuberculosis (TB) remains one of the ten leading causes of death worldwide. Here, we engineered Mycobacterium tuberculosis (Mtb) proteins (ESAT6, CFP10, and MTB7.7) to self-assemble into core-shell nanobeads for enhanced TB diagnosis. Respective purified Mtb antigen-coated polyester beads were characterized and their functionality in TB diagnosis was tested in whole blood cytokine release assays. Sensitivity and specificity were studied in 11 pulmonary TB patients (PTB) and 26 healthy individuals composed of 14 Tuberculin Skin Test negative (TSTn) and 12 TST positive (TSTp). The production of 6 cytokines was determined (IFNγ, IP10, IL2, TNFα, CCL3, and CCL11). To differentiate PTB from healthy individuals (TSTp + TSTn), the best individual cytokines were IL2 and CCL11 (>80% sensitivity and specificity) and the best combination was IP10 + IL2 (>90% sensitivity and specificity). We describe an innovative approach using full-length antigens attached to biopolyester nanobeads enabling sensitive and specific detection of human TB.

Polyhydroxyalkanoates (PHAs): Biopolymers for Biofuel and Biorefineries

Fossil fuels are energy recourses that fulfill most of the world's energy requirements. However, their production and use cause severe health and environmental problems including global warming and pollution. Consequently, plant and animal-based fuels (also termed as biofuels), such as biogas, biodiesel, and many others, have been introduced as alternatives to fossil fuels. Despite the advantages of biofuels, such as being renewable, environmentally friendly, easy to source, and reducing the dependency on foreign oil, there are several drawbacks of using biofuels including high cost, and other factors discussed in the fuel vs. food debate. Therefore, it is imperative to produce novel biofuels while also developing suitable manufacturing processes that ease the aforementioned problems. Polyhydroxyalkanoates (PHAs) are structurally diverse microbial polyesters synthesized by numerous bacteria. Moreover, this structural diversity allows PHAs to readily undergo methyl esterification and to be used as biofuels, which further extends the application value of PHAs. PHA-based biofuels are similar to biodiesel except for having a high oxygen content and no nitrogen or sulfur. In this article, we review the microbial production of PHAs, biofuel production from PHAs, parameters affecting the production of fuel from PHAs, and PHAs biorefineries. In addition, future work on the production of biofuels from PHAs is also discussed.

Polymeric nanoparticle vaccines to combat emerging and pandemic threats

Subunit vaccines are more advantageous than live attenuated vaccines in terms of safety and scale-up manufacture. However, this often comes as a trade-off to their efficacy. Over the years, polymeric nanoparticles have been developed to improve vaccine potency, by engineering their physicochemical properties to incorporate multiple immunological cues to mimic pathogenic microbes and viruses. This review covers recent advances in polymeric nanostructures developed toward particulate vaccines. It focuses on the impact of microbe mimicry (e.g. size, charge, hydrophobicity, and surface chemistry) on modulation of the nanoparticles’ delivery, trafficking, and targeting antigen-presenting cells to elicit potent humoral and cellular immune responses. This review also provides up-to-date progresses on rational designs of a wide variety of polymeric nanostructures that are loaded with antigens and immunostimulatory molecules, ranging from particles, micelles, nanogels, and polymersomes to advanced core-shell structures where polymeric particles are coated with lipids, cell membranes, or proteins.

What Has Been Trending in the Research of Polyhydroxyalkanoates? A Systematic Review

Over the past decades, enormous progress has been achieved with regard to research on environmentally friendly polymers. One of the most prominent families of such biopolymers are bacterially synthesized polyhydroxyalkanoates (PHAs) that have been known since the 1920s. However, only as recent as the 1990s have extensive studies sprung out exponentially in this matter. Since then, different areas of exploration of these intriguing materials have been uncovered. However, no systematic review of undertaken efforts has been conducted so far. Therefore, we have performed an unbiased search of up-to-date literature to reveal trending topics in the research of PHAs over the past three decades by data mining of 2,227 publications. This allowed us to identify eight past and current trends in this area. Our study provides a comprehensive review of these trends and speculates where PHA research is heading.

Recent Advances in Crosslinked Nanogel for Multimodal Imaging and Cancer Therapy

Nanomaterials have been widely applied in the field of cancer imaging and therapy. However, conventional nanoparticles including micelles and liposomes may suffer the issue of dissociation in the circulation. In contrast, crosslinked nanogels the structures of which are covalently crosslinked have better physiological stability than micelles and liposomes, making them more suitable for cancer theranostics. In this review, we summarize recent advances in crosslinked nanogels for cancer imaging and therapy. The applications of nanogels in drug and gene delivery as well as development of novel cancer therapeutic methods are first introduced, followed by the introduction of applications in optical and multimodal imaging, and imaging-guided cancer therapy. The conclusion and future direction in this field are discussed at the end of this review.

Bacterial biopolymers: from pathogenesis to advanced materials

Bacteria are prime cell factories that can efficiently convert carbon and nitrogen sources into a large diversity of intracellular and extracellular biopolymers, such as polysaccharides, polyamides, polyesters, polyphosphates, extracellular DNA and proteinaceous components. Bacterial polymers have important roles in pathogenicity, and their varied chemical and material properties make them suitable for medical and industrial applications. The same biopolymers when produced by pathogenic bacteria function as major virulence factors, whereas when they are produced by non-pathogenic bacteria, they become food ingredients or biomaterials. Interdisciplinary research has shed light on the molecular mechanisms of bacterial polymer synthesis, identified new targets for antibacterial drugs and informed synthetic biology approaches to design and manufacture innovative materials. This Review summarizes the role of bacterial polymers in pathogenesis, their synthesis and their material properties as well as approaches to design cell factories for production of tailor-made bio-based materials suitable for high-value applications.

Bioengineered Polyhydroxyalkanoates as Immobilized Enzyme Scaffolds for Industrial Applications

Enzymes function as biocatalysts and are extensively exploited in industrial applications. Immobilization of enzymes using support materials has been shown to improve enzyme properties, including stability and functionality in extreme conditions and recyclability in biocatalytic processing. This review focuses on the recent advances utilizing the design space of in vivo self-assembled polyhydroxyalkanoate (PHA) particles as biocatalyst immobilization scaffolds. Self-assembly of biologically active enzyme-coated PHA particles is a one-step in vivo production process, which avoids the costly and laborious in vitro chemical cross-linking of purified enzymes to separately produced support materials. The homogeneous orientation of enzymes densely coating PHA particles enhances the accessibility of catalytic sites, improving enzyme function. The PHA particle technology has been developed into a remarkable scaffolding platform for the design of cost-effective designer biocatalysts amenable toward robust industrial bioprocessing. In this review, the PHA particle technology will be compared to other biological supramolecular assembly-based technologies suitable for in vivo enzyme immobilization. Recent progress in the fabrication of biological particulate scaffolds using enzymes of industrial interest will be summarized. Additionally, we outline innovative approaches to overcome limitations of in vivo assembled PHA particles to enable fine-tuned immobilization of multiple enzymes to enhance performance in multi-step cascade reactions, such as those used in continuous flow bioprocessing.

Covalent Functionalization of Bioengineered Polyhydroxyalkanoate Spheres Directed by Specific Protein-Protein Interactions

Bioengineered polyhydroxyalkanoate (PHA) spheres assembled in engineered bacteria are showing promising potential in protein immobilization for high-value applications. Here, we have designed innovative streamlined approaches to add functional proteins from complex mixtures (e.g., without prior purification) to bioengineered PHA spheres directly harnessing the specificity of the SpyTag/SpyCatcher mediated protein ligation. Escherichia coli was engineered to assemble PHA spheres displaying the SpyCatcher domain while simultaneously producing a SpyTagged target protein, which was in vivo specifically ligated to the PHA spheres. To further demonstrate the specificity of this ligation reaction, we incubated isolated SpyCatcher-coated PHA spheres with cell lysates containing SpyTagged target protein, which also resulted in specific ligation mediating surface functionalization. An even cruder approach was used by lysing a mixture of cells, either producing PHA spheres or target protein, which resulted in specific surface functionalization suggesting that ligation between the SpyCatcher-coated PHA spheres and the SpyTagged target proteins is highly specific. To expand the design space of this general modular approach toward programmable multifunctionalization, e.g., one-pot construction of immobilized multienzyme cascade systems on PHA spheres, we designed various recombinant bimodular PHA spheres utilizing alternative Tag/Catcher pairs (e.g., SnoopTag/SnoopCatcher and SdyTag/SdyCatcher systems). One of our bimodular PHA spheres resulted in simultaneous multifunctionalization of plain PHA spheres in one-step with two differently tagged proteins under in vitro and ex vivo reaction conditions while remaining functional. Our bimodular PHA spheres also showed high orthogonality with the non-target peptide tag and exhibited decent robustness against repeated freeze-thaw treatment. We demonstrated the utility of these approaches by using a fluorescent protein, a monomeric amylase, and a dimeric organophosphate hydrolase as target proteins. We established a versatile toolbox for dynamic functionalization of PHA spheres for biomedical and industrial applications.

Recent Approaches for Solid Dose Vaccine Delivery

Recent studies on vaccine delivery systems are exploring the possibility of replacing liquid vaccines with solid dose vaccines due to the many advantages that solid dose vaccines can offer. These include the prospect of a needle-free vaccine delivery system leading to better patient compliance, cold chain storage, less-trained vaccinators and fewer chances for needle stick injury hazards. Some studies also indicate that vaccines in a solid dosage form can result in a higher level of immunogenicity compared to the liquid form, thus providing a dose-sparing effect. This review outlines the different approaches in solid vaccine delivery using various routes of administration including, oral, pulmonary, intranasal, buccal, sublingual, and transdermal routes. The various techniques and their current advancements will provide a knowledge base for future work to be carried out in this arena.