Immunopotentiator-Loaded Polymeric Microparticles as Robust Adjuvant to Improve Vaccine Efficacy

Development of α-Tocopherol Loaded PLGA Nanoparticles and Its Evaluation as a Novel Immune Adjuvant

With the continuous development of preventive and therapeutic vaccines, traditional adjuvants cannot provide sufficient immune efficacy and it is of high necessity to develop safe and effective novel nanoparticle-based vaccine adjuvants. α-Tocopherol (TOC) is commonly used in oil-emulsion adjuvant systems as an immune enhancer, yet its bioavailability is limited by poor water solubility. This study aims to develop TOC-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles (TOC-PLGA NPs) to explore the potential of TOC-PLGA NPs as a novel nanoparticle-immune adjuvant. TOC-PLGA NPs are prepared by a nanoprecipitation method and their physicochemical properties are characterized. It is shown that TOC-PLGA NPs are 110.8 nm, polydispersity index value of 0.042, and Zeta potential of -13.26 mV. The encapsulation efficiency and drug loading of NPs are 82.57% and 11.80%, respectively, and the cumulative release after 35 days of in vitro testing reaches 47%. Furthermore, TOC-PLGA NPs demonstrate a superior promotion effect on RAW 264.7 cell proliferation compared to PLGA NPs, being well phagocytosed and also promoting antigen uptake by macrophages. TOC-PLGA NPs can strongly upregulate the expression of co-stimulatory surface molecules and the secretion of cytokines. In conclusion, TOC-PLGA NPs can be a novel vaccine adjuvant with excellent biocompatibility and significant immune-enhancing activity.

PLGA Particles in Immunotherapy

Poly(lactic-co-glycolic acid) (PLGA) particles are a widely used and extensively studied drug delivery system. The favorable properties of PLGA such as good bioavailability, controlled release, and an excellent safety profile due to the biodegradable polymer backbone qualified PLGA particles for approval by the authorities for the application as a drug delivery platform in humas. In recent years, immunotherapy has been established as a potent treatment option for a variety of diseases. However, immunomodulating drugs rely on targeted delivery to specific immune cell subsets and are often rapidly eliminated from the system. Loading of PLGA particles with drugs for immunotherapy can protect the therapeutic compounds from premature degradation, direct the drug delivery to specific tissues or cells, and ensure sustained and controlled drug release. These properties present PLGA particles as an ideal platform for immunotherapy. Here, we review recent advances of particulate PLGA delivery systems in the application for immunotherapy in the fields of allergy, autoimmunity, infectious diseases, and cancer.

Nano-Microparticle Platforms in Developing Next-Generation Vaccines

The first vaccines ever made were based on live-attenuated or inactivated pathogens, either whole cells or fragments. Although these vaccines required the co-administration of antigens with adjuvants to induce a strong humoral response, they could only elicit a poor CD8⁺ T-cell response. In contrast, next-generation nano/microparticle-based vaccines offer several advantages over traditional ones because they can induce a more potent CD8⁺ T-cell response and, at the same time, are ideal carriers for proteins, adjuvants, and nucleic acids. The fact that these nanocarriers can be loaded with molecules able to modulate the immune response by inducing different effector functions and regulatory activities makes them ideal tools for inverse vaccination, whose goal is to shut down the immune response in autoimmune diseases. Poly (lactic-co-glycolic acid) (PLGA) and liposomes are biocompatible materials approved by the Food and Drug Administration (FDA) for clinical use and are, therefore, suitable for nanoparticle-based vaccines. Recently, another candidate platform for innovative vaccines based on extracellular vesicles (EVs) has been shown to efficiently co-deliver antigens and adjuvants. This review will discuss the potential use of PLGA-NPs, liposomes, and EVs as carriers of peptides, adjuvants, mRNA, and DNA for the development of next-generation vaccines against endemic and emerging viruses in light of the recent COVID-19 pandemic.

Green preparation of hydrogel particles-in-emulsions for simultaneous enhancement of humoral and cell-mediated immunity

Emulsions are one of the most often used vaccine adjuvant formulations. Although they promote high humoral immunity, the induced cellular immunity is often poor, which restrict their application. To enhance the cellular immunity, some researchers have prepared mixed formulations by adding particles into the aqueous phase of emulsions. However, the particle preparation process usually involves the addition and removal of organic reagents, which is environmentally unfriendly and cumbersome. Moreover, the obtained vaccine adjuvant only induces limited cell-mediated immunity and humoral immunity compared with emulsion-adjuvanted vaccines. Herein, we developed a green and simple method for fabricating a novel nanoparticles-in-emulsions (NPE) formulation. Firstly, a temperature-sensitive hydrogel was used to prepare particles by self-solidification without additional crosslinking reagents. Secondly, the white oil was used as organic phase to avoid the particle washing procedures and organic solvent residues. Moreover, the effect of NPE as vaccine adjuvant was evaluated by using two veterinary vaccines as model antigens. NPE showed advantages than the conventional vaccine formulations in inducing both humoral and cellular immunity. This work provides a facile and broadly applicable approach for preparing nanoparticles-in-emulsions formulation, and presents an effective adjuvant for enhancing immunity against infectious diseases.

Old Dog New Tricks: PLGA Microparticles as an Adjuvant for Insulin Peptide Fragment-Induced Immune Tolerance against Type 1 Diabetes

Poly[lactic-co-(glycolic acid)] (PLGA) is arguably one of the most versatile synthetic copolymers used for biomedical applications. In vivo delivery of multiple substances including cells, pharmaceutical compounds, and antigens has been achieved by using PLGA-based micro-/nanoparticles although, presently, the exact biological impact of PLGA particles on the immune system remains controversial. Type 1 diabetes (T1D) is one subtype of diabetes characterized by the attack of immune cells against self-insulin-producing pancreatic islet cells. Considering the autoimmune etiology of T1D and the recent use of PLGA particles for eliciting desired immune responses in various aspects of immunotherapy, for the present study, a combination of Ins2_9-23 peptide (a known autoantigen of T1D) and PLGA microparticles was selected for T1D prevention assessment in nonobese diabetic (NOD) mice, a well-known animal model with spontaneous development of T1D. Thus, inoculation of PLGA microparticles + Ins2_9-23 completely prevented T1D development, significantly better than untreated controls and mice treated by either PLGA microparticles or Ins2_9-23 per se. Subsequent mechanistic investigation further revealed a facilitative role of PLGA microparticles in immune tolerance induction. In summary, our data demonstrate an adjuvant potential of PLGA microparticles in tolerance induction and immune remodulation for effective prevention of autoimmune diseases such as T1D.

Technological Approaches for Improving Vaccination Compliance and Coverage

Vaccination has been well recognised as a critically important tool in preventing infectious disease, yet incomplete immunisation coverage remains a major obstacle to achieving disease control and eradication. As medical products for global access, vaccines need to be safe, effective and inexpensive. In line with these goals, continuous improvements of vaccine delivery strategies are necessary to achieve the full potential of immunisation. Novel technologies related to vaccine delivery and route of administration, use of advanced adjuvants and controlled antigen release (single-dose immunisation) approaches are expected to contribute to improved coverage and patient compliance. This review discusses the application of micro- and nano-technologies in the alternative routes of vaccine administration (mucosal and cutaneous vaccination), oral vaccine delivery as well as vaccine encapsulation with the aim of controlled antigen release for single-dose vaccination.

Harnessing Dendritic Cells for Poly (D,L-lactide-co-glycolide) Microspheres (PLGA MS)-Mediated Anti-tumor Therapy

With emerging success in fighting off cancer, chronic infections, and autoimmune diseases, immunotherapy has become a promising therapeutic approach compared to conventional therapies such as surgery, chemotherapy, radiation therapy, or immunosuppressive medication. Despite the advancement of monoclonal antibody therapy against immune checkpoints, the development of safe and efficient cancer vaccine formulations still remains a pressing medical need. Anti-tumor immunotherapy requires the induction of antigen-specific CD8+ cytotoxic T lymphocyte (CTL) responses which recognize and specifically destroy tumor cells. Due to the crucial role of dendritic cells (DCs) in initiating anti-tumor immunity, targeting tumor antigens to DCs has become auspicious in modern vaccine research. Over the last two decades, micron- or nanometer-sized particulate delivery systems encapsulating tumor antigens and immunostimulatory molecules into biodegradable polymers have shown great promise for the induction of potent, specific and long-lasting anti-tumor responses in vivo. Enhanced vaccine efficiency of the polymeric micro/nanoparticles has been attributed to controlled and continuous release of encapsulated antigens, efficient targeting of antigen presenting cells (APCs) such as DCs and subsequent induction of CTL immunity. Poly (D, L-lactide-co-glycolide) (PLGA), as one of these polymers, has been extensively studied for the design and development of particulate antigen delivery systems in cancer therapy. This review provides an overview of the current state of research on the application of PLGA microspheres (PLGA MS) as anti-tumor cancer vaccines in activating and potentiating immune responses attempting to highlight their potential in the development of cancer therapeutics.

Overcoming immunogenicity issues of HIV p24 antigen by the use of innovative nanostructured lipid carriers as delivery systems: evidences in mice and non-human primates

HIV is one of the deadliest pandemics of modern times, having already caused 35 million deaths around the world. Despite the huge efforts spent to develop treatments, the virus cannot yet be eradicated and continues to infect new people. Spread of the virus remains uncontrolled, thus exposing the worldwide population to HIV danger, due to the lack of efficient vaccines. The latest clinical trials describe the challenges associated with developing an effective prophylactic HIV vaccine. These immunological obstacles will only be overcome by smart and innovative solutions applied to the design of vaccine formulations. Here, we describe the use of nanostructured lipid carriers (NLC) for the delivery of p24 protein as a model HIV antigen, with the aim of increasing its immunogenicity. We have designed vaccine formulations comprising NLC grafted with p24 antigen, together with cationic NLC optimized for the delivery of immunostimulant CpG. This tailored system significantly enhanced immune responses against p24, in terms of specific antibody production and T-cell activation in mice. More importantly, the capacity of NLC to induce specific immune responses against this troublesome HIV antigen was further supported by a 7-month study on non-human primates (NHP). This work paves the way toward the development of a future HIV vaccine, which will also require the use of envelope antigens.

To date, HIV vaccines have resulted in poor or absent protection. A team led by Fabrice P. Navarro at the CEA LETI use the conserved HIV capsid protein p24 vectorized into cationic nanostructured lipid carriers (NLC-p24) along with NLC-delivered CpG. Owing to their small size, NLCs gain access to lymph nodes and deliver antigen directly to antigen presenting cells. Anti-p24 responses have been associated with effective HIV control, making them an attractive vaccine antigen, but they are poorly immunogenic. NLC-p24 shows a good safety profile while at the same time being able to elicit robust humoral and cellular immune responses in both mice and Cynomolgus macaques. NLC-mediated delivery of both p24 and CpG results in more effective immune stimulation than delivery of free antigen and adjuvant. These findings demonstrate the possibility of priming effective responses to a potent but otherwise poorly immunogenic HIV antigen.

An immunopotentiator, ophiopogonin D, encapsulated in a nanoemulsion as a robust adjuvant to improve vaccine efficacy

As an ingredient of vaccines, adjuvants are indispensable for enhancing and directly inducing robust and extensive adaptive immune responses associated with vaccine antigens. In this study, we initially determined that a new molecular immunopotentiator, ophiopogonin D (OP-D), enhanced the antibody response to antigen. Because OP-D has certain disadvantages, including poor solubility, we next encapsulated OP-D in a nanoemulsion adjuvant (nanoemulsion-encapsulated OP-D, NOD) using low-energy emulsification methods. The NOD thus produced was small, with an average size of 76.45 nm, and exhibited good distribution (PdI value 0.16), significantly increasing the solubility of OP-D. Furthermore, NOD exhibited reduced cellular toxicity and acute toxicity. Our results showed that a fusion antigen of MRSA (HlaH_35LIsdB_348-465) formulated with NOD significantly improved humoral and cellular immune responses compared to those observed in the antigen/OP-D and antigen/AlPO₄ groups. Compared with antigen/OP-D, the antigen formulated with NOD more effectively promoted antigen uptake by dendritic cells (DCs) and the activation of antigen-presenting cells (APCs). Moreover, the NOD-formulated antigen had ideal protective efficacy in a MRSA sepsis model by inducing more potent antibody responses and a Th1/Th17-biased CD4⁺ T cell immune response. Therefore, these results suggest that NOD is a promising and robust adjuvant platform for a MRSA vaccine.

STATEMENT OF SIGNIFICANCE

We first identified a new powerful immunopotentiator, Ophiopogonin D, among dozens of natural products and then used nanotechnology to construct a highly efficient and low toxic adjuvant system (NOD). Our approach intersects natural medicinal chemistry, nanomaterials and immunology, revealing that a strong adjuvant activity of this adjuvant system was verified in vitro and in vivo, and the application of MRSA subunit vaccine model for survival experiments achieved a 100% protection rate. This research illustrate that NOD is a promising and robust adjuvant platform for subunit vaccines.

Adjuvanticity Regulation by Biodegradable Polymeric Nano/microparticle Size

Polymeric nano/microparticles as vaccine adjuvants have been researched in experimental and clinical studies. A more profound understanding of how the physicochemical properties regulate specific immune responses has become a vital requirement. Here we prepared poly(d,l-lactic-co-glycolic acid) (PLGA) nano/microparticles with uniform sizes (500 nm, 900 nm, 2.1 μm, and 4.9 μm), and the size effects on particle uptake, activation of macrophages, and antigen internalization were evaluated. Particle uptake kinetic studies demonstrated that 900 nm particles were the easiest to accumulate in cells. Moreover, they could induce macrophages to secrete NO and IL-1β and facilitate antigen internalization. Furthermore, 900 nm particles, mixed with antigen, could exhibit superior adjuvanticity in both humoral and cellular immune responses in vivo, including offering the highest antibody protection, promoting the maximum secretion levels of IFN-γ and IL-4 than particles with other sizes. Overall, 900 nm might be the optimum choice for PLGA particle-based vaccine adjuvants especially for recombinant antigens. Understanding the effect of particle size on the adjuvanticity based immune responses might have important enlightenments for rational vaccine design and applications.