The Promise and Potential of Metal-Organic Frameworks and Covalent Organic Frameworks in Vaccine Nanotechnology.

The immune system's complexity and ongoing evolutionary struggle against deleterious pathogens underscore the value of vaccination technologies, which have been bolstering human immunity for over two centuries. Despite noteworthy advancements over these 200 years, three areas remain recalcitrant to improvement owing to the environmental instability of the biomolecules used in vaccines─the challenges of formulating them into controlled release systems, their need for constant refrigeration to avoid loss of efficacy, and the requirement that they be delivered via needle owing to gastrointestinal incompatibility. Nanotechnology, particularly metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), has emerged as a promising avenue for confronting these challenges, presenting a new frontier in vaccine development. Although these materials have been widely explored in the context of drug delivery, imaging, and cancer immunotherapy, their role in immunology and vaccine-related applications is a recent yet rapidly developing field. This review seeks to elucidate the prospective use of MOFs and COFs for biomaterial stabilization, eliminating the necessity for cold chains, enhancing antigen potency as adjuvants, and potentializing needle-free delivery of vaccines. It provides an expansive and critical viewpoint on this rapidly evolving field of research and emphasizes the vital contribution of chemists in driving further advancements.

A scalable synthesis of adjuvanting antigen depots based on metal-organic frameworks.

Vaccines have saved countless lives by preventing and even irradicating infectious diseases. Commonly used subunit vaccines comprising one or multiple recombinant proteins isolated from a pathogen demonstrate a better safety profile than live or attenuated vaccines. However, the immunogenicity of these vaccines is weak, and therefore, subunit vaccines require a series of doses to achieve sufficient immunity against the pathogen. Here, we show that the biomimetic mineralization of the inert model antigen, ovalbumin (OVA), in zeolitic imidazolate framework-8 (ZIF-8) significantly improves the humoral immune response over three bolus doses of OVA (OVA 3×). Encapsulation of OVA in ZIF-8 (OVA@ZIF) demonstrated higher serum antibody titers against OVA than OVA 3×. OVA@ZIF vaccinated mice displayed higher populations of germinal center (GC) B cells and IgG1+ GC B cells as opposed to OVA 3×, indicative of class-switching recombination. We show that the mechanism of this phenomenon is at least partly owed to the metalloimmunological effects of the zinc metal as well as the sustained release of OVA from the ZIF-8 composite. The system acts as an antigen reservoir for antigen-presenting cells to traffic into the draining lymph node, enhancing the humoral response. Lastly, our model system OVA@ZIF is produced quickly at the gram scale in a laboratory setting, sufficient for up to 20 000 vaccine doses.

In vivo biocompatibility of ZIF-8 for slow release via intranasal administration.

Zeolitic imidazolate framework-8 (ZIF-8) is becoming popular in research for its potential in antigen protection and for providing a thermally stable, slow-release platform. While papers applying this material for immunological applications are aplenty in the literature, studies that explore the biosafety of ZIF-8 in mammals-especially when administered intranasally-are not well represented. We checked the body clearance of uncoated and ZIF-8-coated liposomes and observed that the release slowed as ZIF-8 is easily degraded by mucosal fluid in the nasal cavity. We delivered varying doses of ZIF-8, checked its short- and long-term effects on diagnostic proteins found in blood serum, and found no noticeable differences from the saline control group. We also studied their lung diffusing capacity and tissue morphology; neither showed significant changes in morphology or function.

Biolistic delivery of liposomes protected in metal-organic frameworks.

Needle-and-syringe-based delivery has been the commercial standard for vaccine administration to date. With worsening medical personnel availability, increasing biohazard waste production, and the possibility of cross-contamination, we explore the possibility of biolistic delivery as an alternate skin-based delivery route. Delicate formulations like liposomes are inherently unsuitable for this delivery model as they are fragile biomaterials incapable of withstanding shear stress and are exceedingly difficult to formulate as a lyophilized powder for room temperature storage. Here we have developed a approach to deliver liposomes into the skin biolistically-by encapsulating them in a nano-sized shell made of Zeolitic Imidazolate Framework-8 (ZIF-8). When encapsulated within a crystalline and rigid coating, the liposomes are not only protected from thermal stress, but also shear stress. This protection from stressors is crucial, especially for formulations with cargo encapsulated inside the lumen of the liposomes. Moreover, the coating provides the liposomes with a solid exterior that allows the particles to penetrate the skin effectively. In this work, we explored the mechanical protection ZIF-8 provides to liposomes as a preliminary investigation for using biolistic delivery as an alternative to syringe-and-needle-based delivery of vaccines. We demonstrated that liposomes with a variety of surface charges could be coated with ZIF-8 using the right conditions, and this coating can be just as easily removed-without causing any damage to the protected material. The protective coating prevented the liposomes from leaking cargo and helped in their effective penetration when delivered into the agarose tissue model and porcine skin tissue.

Carrier gas triggered controlled biolistic delivery of DNA and protein therapeutics from metal-organic frameworks.

The efficacy and specificity of protein, DNA, and RNA-based drugs make them popular in the clinic; however, these drugs are often delivered via injection, requiring skilled medical personnel, and producing biohazardous waste. Here, we report an approach that allows for their controlled delivery, affording either a burst or slow release without altering the formulation. We show that when encapsulated within zeolitic-imidazolate framework eight (ZIF-8), the biomolecules are stable in powder formulations and can be inoculated with a low-cost, gas-powered "MOF-Jet" into living animal and plant tissues. Additionally, their release profiles can be modulated through judicious selection of the carrier gas used in the MOF-Jet. Our in vitro and in vivo studies reveal that when CO2 is used, it creates a transient and weakly acidic local environment that causes a near-instantaneous release of the biomolecules through an immediate dissolution of ZIF-8. Conversely, when air is used, ZIF-8 biodegrades slowly, releasing the biomolecules over a week. This is the first example of controlled-biolistic delivery of biomolecules using ZIF-8, which provides a powerful tool for fundamental and applied science research.

Rip it, stitch it, click it: A Chemist's guide to VLP manipulation.

Viruses are some of nature's most ubiquitous self-assembled molecular containers. Evolutionary pressures have created some incredibly robust, thermally, and enzymatically resistant carriers to transport delicate genetic information safely. Virus-like particles (VLPs) are human-engineered non-infectious systems that inherit the parent virus' ability to self-assemble under controlled conditions while being non-infectious. VLPs and plant-based viral nanoparticles are becoming increasingly popular in medicine as their self-assembly properties are exploitable for applications ranging from diagnostic tools to targeted drug delivery. Understanding the basic structure and principles underlying the assembly of higher-order structures has allowed researchers to disassemble (rip it), reassemble (stitch it), and functionalize (click it) these systems on demand. This review focuses on the current toolbox of strategies developed to manipulate these systems by ripping, stitching, and clicking to create new technologies in the biomedical space.

Lactate during ex-situ heart perfusion does not predict the requirement for mechanical circulatory support following donation after circulatory death (DCD) heart transplants.

BACKGROUND: Ex-situ heart perfusion (ESHP) is commonly used for the reanimation and preservation of hearts following donation after circulatory determined death (DCD). The only commercially available existing ESHP device promotes perfusate lactate levels for assessment of heart viability. The reliability of this marker is yet to be confirmed for DCD heart transplantation. METHODS: This is a single center, retrospective study examining DCD heart transplants from March 1, 2015 to June 30, 2020. Recipients were divided into 2 groups dependent upon their requirement for or absence of mechanical circulatory support post-transplant. Lactate profiles obtained during ESHP were analyzed. Hearts were procured using the direct procurement and perfusion (DPP) method. RESULTS: Fifty-one DCD heart transplant recipients were studied, of which 20 (39%) were dependent on mechanical circulatory support (MCS) following transplantation, (2% Ventricular Assist Device (VAD), 16% Extra Corporeal Membrane Oxygenation (ECMO) and 21% Intra-aortic balloon pumps (IABP). There was no difference in arterial lactate profiles on ESHP at any time point for those dependent upon MCS support (MCS) and those that were not (no MCS) post-transplant. After 3 hours of ESHP, the arterial lactate was >5mmol/L in 80% upon MCS vs 62% no MCS, p = .30. There was also no difference in ESHP rising arterial lactate concentrations, (15% MCS vs 13% non MCS, p = 1.00). CONCLUSION: For DCD hearts transplants retrieved using the DPP technique, lactate profiles do not seem to be a reliable predictor of mechanical circulatory support requirement post-transplant.

Metal-Organic Framework Encapsulated Whole-Cell Vaccines Enhance Humoral Immunity against Bacterial Infection.

The increasing rate of resistance of bacterial infection against antibiotics requires next generation approaches to fight potential pandemic spread. The development of vaccines against pathogenic bacteria has been difficult owing, in part, to the genetic diversity of bacteria. Hence, there are many potential target antigens and little a priori knowledge of which antigen/s will elicit protective immunity. The painstaking process of selecting appropriate antigens could be avoided with whole-cell bacteria; however, whole-cell formulations typically fail to produce long-term and durable immune responses. These complications are one reason why no vaccine against any type of pathogenic E. coli has been successfully clinically translated. As a proof of principle, we demonstrate a method to enhance the immunogenicity of a model pathogenic E. coli strain by forming a slow releasing depot. The E. coli strain CFT073 was biomimetically mineralized within a metal-organic framework (MOF). This process encapsulates the bacteria within 30 min in water and at ambient temperatures. Vaccination with this formulation substantially enhances antibody production and results in significantly enhanced survival in a mouse model of bacteremia compared to standard inactivated formulations.

Transition from a 1D Coordination Polymer to a Mixed-Linker Layered MOF.

A novel copper(II) metal-organic framework (MOF) has been synthesized by modifying the reaction conditions of a 1D coordination polymer. The 1D polymer is built by the coordination between copper and 2,2'-(1 H-imidazole-4,5-diyl)di-1,4,5,6-tetrahydropyrimidine (H-L1). The geometry of H-L1 precludes its ability to form extended 3D framework structures. By adding 1,4-benzenedicarboxylic acid (H2BDC), a well-studied linker in MOF synthesis, we achieved the transition from a 1D polymer chain into porous 2D layered structures. Hydrogen bonding between L1 and BDC directs the parallel stacking of these layers, resulting in a 3D structure with one-dimensional channels accessible by two different pore windows. The preferred growth orientation of the crystal produces prolonged channels and a disparity in pore size distribution. This in turn results in slow diffusion processes in the material. Furthermore, an isoreticular MOF was prepared by substituting the BDC linker by 2,6-naphthalenedicarboxylic acid (H2NDC).

Effects of lidocaine and steroids on breast milk-induced lung injury in rabbits.

BACKGROUND: Local anesthetics inhibit mediator and free radical release from polymorphonuclear granulocytes and migration to their site of action. In a recent study, lidocaine significantly improved the alveolar-arterial oxygen difference gradients (A-aDO2) after tracheal instillation of acid in rabbits. The purpose of the current study was to evaluate the effects of lidocaine and pulse-dose steroids on human breast milk (HBM)-induced lung injury in rabbits. METHODS: After Animal Care Committee approval, six adult rabbits were assigned to each of three treatments: control, lidocaine, and steroids. After induction of anesthesia and controlled ventilation, acidified HBM at pH 1.8 and volume 1.2 ml.kg(-1) was instilled into the trachea. Rabbits in the lidocaine group received lidocaine 2 mg.kg(-1) i.v. before tracheal instillation and then 2 mg.kg(-1).h(-1) i.v. continuously. Rabbits in the steroid group received 30 mg.kg(-1) methylprednisolone before tracheal instillation. A-aDO2, static compliance and blood for white cell count, and cytokine interleukin-8 (IL-8) concentration were obtained at baseline and at 1 and 4 h postinstillation. After 4 h, the rabbits were killed. The left upper lobe was isolated and excised to determine the wet/dry ratio. The right lung was lavaged with 30 ml normal saline to determine the white cell count and the concentrations of albumin and IL-8. Data were analyzed using one- or two-way anova with repeated measures and an Student-Newman-Keuls (SNK) posthoc test (P < 0.05). RESULTS: All rabbits completed the protocol. A-aDO2 and CO2 tensions increased significantly at 1 and 4 h compared with baseline, although there were no differences among the treatments (P < 0.05). Compliance in the control group decreased compared with lidocaine and steroids. CONCLUSION: We conclude that preemptive lidocaine and steroids attenuate in part HBM-induced lung injury in rabbits.