A two-component modular approach for enhancing T-cell activation utilizing a unique anti-FcgammaRI-streptavidin construct and microspheres coated with biotinylated-antigen

Analysis of Nanoparticle Adjuvant Properties

Nanoparticles can be engineered for targeted antigen delivery to immune cells and for stimulating an immune response to improve the antigen immunogenicity. This approach is commonly used to develop nanotechnology-based vaccines. In addition, some nanotechnology platforms may be initially designed for drug delivery, but in the course of subsequent characterization, additional immunomodulatory functions may be discovered that can potentially benefit vaccine efficacy. In both of these scenarios, an in vivo proof of concept study to verify the utility of the nanocarrier for improving vaccine efficacy is needed. Here we describe an experimental approach and considerations for designing an animal study to test adjuvant properties of engineered nanomaterials in vivo.

SARS-CoV-2: Immunity, Challenges with Current Vaccines, and a Novel Perspective on Mucosal Vaccines

The global rollout of COVID-19 vaccines has played a critical role in reducing pandemic spread, disease severity, hospitalizations, and deaths. However, the first-generation vaccines failed to block severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and transmission, partially due to the limited induction of mucosal immunity, leading to the continuous emergence of variants of concern (VOC) and breakthrough infections. To meet the challenges from VOC, limited durability, and lack of mucosal immune response of first-generation vaccines, novel approaches are being investigated. Herein, we have discussed the current knowledge pertaining to natural and vaccine-induced immunity, and the role of the mucosal immune response in controlling SARS-CoV2 infection. We have also presented the current status of the novel approaches aimed at eliciting both mucosal and systemic immunity. Finally, we have presented a novel adjuvant-free approach to elicit effective mucosal immunity against SARS-CoV-2, which lacks the safety concerns associated with live-attenuated vaccine platforms.

Analysis of Nanoparticle-Adjuvant Properties In Vivo

Nanoparticles can be engineered for targeted antigen delivery to the immune cells and for stimulating the immune response to improve the antigen immunogenicity. This approach is commonly used to develop nanotechnology-based vaccines. In addition, some nanotechnology platforms may be initially designed for drug delivery, but in the course of subsequent characterization, their additional immunomodulatory functions may be discovered that can potentially benefit vaccine efficacy. In both of these scenarios, an in vivo proof of concept study to verify the utility of the nanocarrier for improving vaccine efficacy is needed. Here, we describe an experimental approach and considerations for designing an animal study to test adjuvant properties of engineered nanomaterials in vivo.

PLA micro- and nano-particles

Poly(d,l-lactic acid) (PLA) has been widely used for various biomedical applications for its biodegradable, biocompatible, and nontoxic properties. Various methods, such as emulsion, salting out, and precipitation, have been used to make better PLA micro- and nano-particle formulations. They are widely used as controlled drug delivery systems of therapeutic molecules, including proteins, genes, vaccines, and anticancer drugs. Even though PLA-based particles have challenges to overcome, such as low drug loading capacity, low encapsulation efficiency, and terminal sterilization, continuous innovations in particulate formulations will lead to development of clinically useful formulations.

Construction and immunogenicity of a new Fc-based subunit vaccine candidate against Mycobacterium tuberculosis

As an ancient disease, tuberculosis (TB) is a major global health threat. Therefore, there is an urgent need for an effective and safe anti-TB vaccine. In the current study, a delivery system of Fc domain of mouse IgG2a and early secreted antigenic target protein 6 (ESAT-6) was evaluated for the selective uptake of antigens by antigen-presenting cells (APCs). Thus, it was based on the immunogenicity of a fusion protein. The study was initiated by the transfer of recombinant expression vectors of pPICZαA-ESAT-6:Fcγ2a and pPICZαA-ESAT-6: His into Pichia pastoris (P. pastoris). Recombinant proteins were assessed for immunogenicity following the immunoblotting analysis. High levels of IFN-γ and IL-12 were produced to induce Th1-type cellular responses through vaccination with both recombinant proteins [ESAT-6:Fcγ2a (EF) and ESAT-6:His (EH)]. The Fc-tagged recombinant protein induced more effective Th1-type cellular responses with a low increment in IL-4 compared to PBS, BCG, and EH groups. Although in all the immunized groups, the ratio of IFN-γ/IL-4 was in favor of Th1 responses, the highest Th1/Th2 balance was observed in EF immunized group. Fc fragment of mouse IgG2a may induce a selective uptake of APCs towards the cross-presentation and formation of Th1 responses in favor of an appropriate protective anti-tuberculosis reaction. Thus, further research on Fc-fusion proteins is required to develop Fc-based TB vaccines.

Current understanding of interactions between nanoparticles and the immune system

The delivery of drugs, antigens, and imaging agents benefits from using nanotechnology-based carriers. The successful translation of nanoformulations to the clinic involves thorough assessment of their safety profiles, which, among other end-points, includes evaluation of immunotoxicity. The past decade of research focusing on nanoparticle interaction with the immune system has been fruitful in terms of understanding the basics of nanoparticle immunocompatibility, developing a bioanalytical infrastructure to screen for nanoparticle-mediated immune reactions, beginning to uncover the mechanisms of nanoparticle immunotoxicity, and utilizing current knowledge about the structure-activity relationship between nanoparticles' physicochemical properties and their effects on the immune system to guide safe drug delivery. In the present review, we focus on the most prominent pieces of the nanoparticle-immune system puzzle and discuss the achievements, disappointments, and lessons learned over the past 15years of research on the immunotoxicity of engineered nanomaterials.

Active immunity induced by passive IgG post-exposure protection against ricin

Therapeutic antibodies can confer an instant protection against biothreat agents when administered. In this study, intact IgG and F(ab')2 from goat anti-ricin hyperimmune sera were compared for the protection against lethal ricin mediated intoxication. Similar ricin-binding affinities and neutralizing activities in vitro were observed between IgG and F(ab')2 when compared at the same molar concentration. In a murine ricin intoxication model, both IgG and F(ab')2 could rescue 100% of the mice by one dose (3 nmol) administration of antibodies 1 hour after 5 × LD50 ricin challenge. Nine days later, when the rescued mice received a second ricin challenge (5 × LD50), only the IgG-treated mice survived; the F(ab')2-treated mice did not. The experimental design excluded the possibility of residual goat IgG responsible for the protection against the second ricin challenge. Results confirmed that the active immunity against ricin in mice was induced quickly following the passive delivery of a single dose of goat IgG post-exposure. Furthermore, it was demonstrated that the induced active immunity against ricin in mice lasted at least 5 months. Therefore, passive IgG therapy not only provides immediate protection to the victim after ricin exposure, but also elicits an active immunity against ricin that subsequently results in long term protection.

Mucosal immunization with an unadjuvanted vaccine that targets Streptococcus pneumoniae PspA to human Fcγ receptor type I protects against pneumococcal infection through complement- and lactoferrin-mediated bactericidal activity

Targeting an antigen to Fc receptors (FcR) can enhance the immune response to the antigen in the absence of adjuvant. Furthermore, we recently demonstrated that intranasal immunization with an FcγR-targeted antigen enhances protection against a category A intracellular mucosal pathogen, Francisella tularensis. To determine if a similar strategy could be applied to the important pathogen Streptococcus pneumoniae, we used an improved mucosal FcR-targeting strategy that specifically targets human FcγR type I (hFcγRI). A humanized single-chain antibody component in which the variable domain binds to hFcγRI [anti-hFcγRI (H22)] was linked in a fusion protein with the pneumococcal surface protein A (PspA). PspA is known to elicit protection against pneumococcal sepsis, carriage, and pneumonia in mouse models when administered with adjuvants. Anti-hFcγRI-PspA or recombinant PspA (rPspA) alone was used to intranasally immunize wild-type (WT) and hFcγRI transgenic (Tg) mice in the absence of adjuvant. The hFcγRI Tg mice receiving anti-hFcγRI-PspA exhibited elevated S. pneumoniae-specific IgA, IgG2c, and IgG1 antibodies in serum and bronchoalveolar lavage fluid. Neither immunogen was effective in protecting WT mice in the absence of adjuvant, but when PspA was targeted to hFcγRI as the anti-hFcγRI-PspA fusion, enhanced protection against lethal S. pneumoniae challenge was observed in the hFcγRI Tg mice compared to mice given nontargeted rPspA alone. Immune sera from the anti-hFcγRI-PspA-immunized Tg mice showed enhanced complement C3 deposition on bacterial surfaces, and protection was dependent upon an active complement system. Immune serum also showed an enhanced bactericidal activity directed against S. pneumoniae that appears to be lactoferrin mediated.

Fc receptor-targeted mucosal vaccination as a novel strategy for the generation of enhanced immunity against mucosal and non-mucosal pathogens

Numerous studies have demonstrated that targeting immunogens to Fcgamma receptors (FcgammaR) on antigen (Ag)-presenting cells (APC) can enhance humoral and cellular immunity in vitro and in vivo. FcgammaR are classified based on their molecular weight, IgG-Fc binding affinities, IgG subclass binding specificity, and cellular distribution and they consist of activating and inhibitory receptors. However, despite the potential advantages of targeting Ag to FcR at mucosal sites, very little is known regarding the role of FcR in mucosal immunity or the efficacy of FcR-targeted mucosal vaccines. In addition, recent work has suggested that FcRn is present in the lungs of adult mice and humans and can transport FcRn-targeted Ag to FcgammaR-bearing APC within mucosal lymphoid tissue. In this review we will discuss the need for new vaccine strategies, the potential for FcR-targeted vaccines to fill this need, the impact of activating versus inhibitory FcgammaR on FcR-targeted vaccination, the significance of focusing on mucosal immunity, as well as caveats that could impact the use of FcR targeting as a mucosal vaccine strategy.

Enhanced Antigen-Specific Antibody and Cytokine Responses When Targeting Antigen to Human FcGAMMA Receptor Type I Using an Anti-Human FcGAMMA Receptor Type I-Streptavidin Fusion Protein in an Adjuvant-Free System

There is a continuing need for alternatives to current human adjuvants. Recombinant protein vaccines, which target antigen to human Fc gamma receptor type I (hFcgammaRI) on hFcgammaRI-expressing antigen presenting cells, provide one potential alternative. Using a recombinant anti-hFcgammaRI-antigen fusion protein and adjuvant independent mouse model, we demonstrate enhanced antigen-specific antibody responses to low doses of antigen, when targeting antigen to hFcgammaRI in vivo. Enhanced antibody production to hFcyRI-targeted antigen is evident in both primary and secondary immune responses, as compared to that of non-targeted antigen. Furthermore, antibody isotype and cytokine responses following immunization with hFcgammaRI-targeted antigen, suggest enhancement of both Th1 and Th2 responses.

Utilization of Fc receptors as a mucosal vaccine strategy against an intracellular bacterium, Francisella tularensis

Numerous studies have demonstrated that targeting Ag to Fc receptors (FcR) on APCs can enhance humoral and cellular immunity. However, studies are lacking that examine both the use of FcR-targeting in generating immune protection against infectious agents and the use of FcRs in the induction of mucosal immunity. Francisella tularensis is a category A intracellular mucosal pathogen. Thus, intense efforts are underway to develop a vaccine against this organism. We hypothesized that protection against mucosal infection with F. tularensis would be significantly enhanced by targeting inactivated F. tularensis live vaccine strain (iFt) to FcRs at mucosal sites, via intranasal immunization with mAb-iFt complexes. These studies demonstrate for the first time that: 1) FcR-targeted immunogen enhances immunogen-specific IgA production and protection against subsequent infection in an IgA-dependent manner, 2) FcgammaR and neonatal FcR are crucial to this protection, and 3) inactivated F. tularensis, when targeted to FcRs, enhances protection against the highly virulent SchuS4 strain of F. tularensis, a category A biothreat agent. In summary, these studies show for the first time the use of FcRs as a highly effective vaccination strategy against a highly virulent mucosal intracellular pathogen.

Pathogen recognition and development of particulate vaccines: does size matter?

The use of particulate carriers holds great promise for the development of effective and affordable recombinant vaccines. Rational development requires a detailed understanding of particle up-take and processing mechanisms to target cellular pathways capable of stimulating the required immune responses safely. These mechanisms are in turn based on how the host has evolved to recognize and process pathogens. Pathogens, as well as particulate vaccines, come in a wide range of sizes and biochemical compositions. Some of these also provide 'danger signals' so that antigen 'senting cells (APC), usually dendritic cells (DC), acquire specific stimulatory activity. Herein, we provide an overview of the types of particles currently under investigation for the formulation of vaccines, discuss cellular uptake mechanisms (endocytosis, macropinocytosis, phagocytosis, clathrin-dependent and/or caveloae-mediated) for pathogens and particles of different sizes, as well as antigen possessing and presentation by APC in general, and DC in particular. Since particle size and composition can influence the immune response, inducing humoral and/or cellular immunity, activating CD8 T cells and/or CD4 T cells of T helper 1 and/or T helper 2 type, particle characteristics have a major impact on vaccine efficacy. Recently developed methods for the formulation of particulate vaccines are presented in this issue of Methods, showcasing a range of "cutting edge" particulate vaccines that employ particles ranging from nano to micro-sized. This special issue of Methods further addresses practical issues of production, affordability, reproducibility and stability of formulation, and also includes a discussion of the economic and regulatory challenges encountered in developing vaccines for veterinary use and for common Third World infectious diseases.

Microspheres for Drug Delivery

With advances in biotechnology, genomics, and combinatorial chemistry, a wide variety of new, more potent and specific therapeutics are being created. Because of common problems such as low solubility, high potency, and/or poor stability of many of these new drugs, the means of drug delivery can impact efficacy and potential for commercialization as much as the nature of the drug itself. Thus, there is a corresponding need for safer and more effective methods and devices for drug delivery. Indeed, drug delivery systems—designed to provide a therapeutic agent in the needed amount, at the right time, to the proper location in the body, in a manner that optimizes efficacy, increases compliance and minimizes side effects—were responsible for $47 billion in sales in 2002, and the drug delivery market is expected to grow to $67 billion by 2006.

Production of genetically engineered biotinylated interleukin-2 and its application in a rapid nonradioactive assay for T-cell activation

The development of reliable assay systems that can measure lymphocyte activation in vitro has been a major goal of immunodiagnostics. Traditionally, tritiated thymidine incorporation has been used to monitor T-cell activation. Other methods include enzyme-linked immunosorbent assay (ELISA), enzyme-linked immunospot assay, and colorimetric assays. We have established a lymphocyte activation assay that utilizes fluorescein isothiocyanate (FITC)-streptavidin bound to recombinant biotinylated human interleukin-2 (IL-2). Utilizing recombinant DNA technology, a unique monobiotinylated human IL-2 has been created and isolated using the Promega PinPoint vector system. ELISA has been used to demonstrate streptavidin binding and recognition by a human IL-2-specific antibody. IL-2 function has been demonstrated using a murine IL-2-dependent T-cell line, CTLL-2, responsive to human IL-2. Recombinant biotinylated human IL-2 conjugated to streptavidin-FITC or streptavidin-horseradish peroxidase has been used to monitor T-cell activation in the presence of antigen as well as mitogen. The sensitivity and convenience of this method make this lymphocyte activation assay an attractive alternative to tritiated thymidine incorporation as a method for monitoring T-cell activation. In addition, the availability of a recombinant biotinylated human IL-2 will permit the production of a uniform product suitable for diagnostic and clinical application.