Adjuvant Potential of Poly-α-l-Glutamine from the Cell Wall of Mycobacterium tuberculosis

Advancements in Vaccine Adjuvants: The Journey from Alum to Nano Formulations

Vaccination is a groundbreaking approach in preventing and controlling infectious diseases. However, the effectiveness of vaccines can be greatly enhanced by the inclusion of adjuvants, which are substances that potentiate and modulate the immune response. This review is based on extensive searches in reputable databases such as Web of Science, PubMed, EMBASE, Scopus, and Google Scholar. The goal of this review is to provide a thorough analysis of the advances in the field of adjuvant research, to trace the evolution, and to understand the effects of the various adjuvants. Historically, alum was the pioneer in the field of adjuvants because it was the first to be approved for use in humans. It served as the foundation for subsequent research and innovation in the field. As science progressed, research shifted to identifying and exploiting the potential of newer adjuvants. One important area of interest is nano formulations. These advanced adjuvants have special properties that can be tailored to enhance the immune response to vaccines. The transition from traditional alum-based adjuvants to nano formulations is indicative of the dynamism and potential of vaccine research. Innovations in adjuvant research, particularly the development of nano formulations, are a promising step toward improving vaccine efficacy and safety. These advances have the potential to redefine the boundaries of vaccination and potentially expand the range of diseases that can be addressed with this approach. There is an optimistic view of the future in which improved vaccine formulations will contribute significantly to improving global health outcomes.

Mycobacterium tuberculosis Rv3628 isan effective adjuvant via activationof dendritic cells for cancer immunotherapy

Tumor antigens (Ags) are weakly immunogenic and elicit inadequate immune responses, thus induction of antigen-specific immune activation via the maturation of dendritic cells (DCs) is a strategy used for cancer immunotherapy. In this study, we examined the effect of Rv3628 from Mycobacterium tuberculosis (Mtb) on activation of DCs and anti-tumor immunity in vivo. Intravenous injection of mice with Rv3628 promoted DC activation of spleen and lymph nodes. More importantly, Rv3628 also induced activation of DCs and enhanced Ag presentation in tumor-bearing mice. In mice bearing ovalbumin (OVA)-expressing tumors, combination treatment with Rv3628 and OVA peptide promoted OVA-specific T cell activation and accumulation of interferon (IFN)-γ and tumor necrosis factor (TNF)-α-producing OT-I and OT-II cells in tumor-draining lymph nodes. Moreover, three different tumor Ags in three different tumor models showed enhanced anti-tumor activity with Rv3628 as adjuvant, including inhibition of growth of OVA-expressing B16 melanoma, CT26 carcinoma, and B16 melanoma tumors, and a synergistic effect with anti-programmed cell death protein 1 (PD-1) antibody treatment. Additionally, potential application against human tumors was indicated by similar activation of human peripheral blood DCs by Rv3628. Taken together, these data demonstrate that Rv3628 could be an effective adjuvant in tumor immunotherapy via enhanced capacity of DC activation and Ag presentation.

Recombinant Lactobacillus plantarum NC8 strain expressing porcine rotavirus VP7 induces specific antibodies in BALB/c mice

The major etiologic agent that causes acute gastroenteritis worldwide in young animals and children is Group A rotavirus. Currently, commercially available vaccines do not often prevent porcine rotavirus (PRV) infection. In this study, we evaluated the efficacy of oral recombinant Lactobacillus vaccine against PRV in a mouse model. Lactobacillus plantarum NC8 was used as the host strain, and bacterial vectors were constructed, because the NC8 isolated has shown the capability to survive gastric transit and to colonize the intestinal tract of humans and other mammals. To explore the immunological mechanisms, lactic acid bacterial vectors were used to express VP7 antigen from PRV. We constructed an L. plantarum strain with surface-displayed VP7, named NC8-pSIP409-pgsA-VP7-DCpep. The expressed recombinant protein had a molecular weight of ∼37 kDa. The strain was used to immunize BALB/c mice to evaluate their immunomodulatory characteristics. Mice were orally immunized with recombinant L. plantarum NC8-pSIP409-pgsA-VP7-DCpep at a dose of 2 × 109 colony forming units/200 µl. The results showed that NC8-pSIP409-pgsA-VP7-DCpep significantly stimulated the differentiation of dendritic cells (DCs) in Peyer's patches (PPs) and increased the serum levels of IL-4 and IFN-γ, as measured by enzyme-linked immunosorbent assay in mice treated with NC8-pSIP409-pgsA-VP7-DCpep. Compared to the empty vector group, NC8-pSIP409-pgsA-VP7-DCpep significantly increased the production of B220+ B cells in mesenteric lymph nodes (MLNs) and PPs and also increased the titer levels of the VP7-specific antibodies, including IgG and sIgA. The administration of NC8-pSIP409-pgsA-VP7-DCpep mediated relatively broad cellular responses. This study reveals that clear alternatives exist for PRV control strategies and provides information on PRV infection.

Novel Approach for Transdermal Delivery of Rifampicin to Induce Synergistic Antimycobacterial Effects Against Cutaneous and Systemic Tuberculosis Using a Cationic Nanoemulsion Gel

Purpose

This study demonstrated improved transdermal delivery of rifampicin-loaded cationic nanoemulsion gel to treat systemic and cutaneous tuberculosis using capmul, labrasol, and acconon, which exert anti-Mycobacterium activities. This approach enhanced drug permeation across the skin, increased therapeutic efficacy, and reduced dose-related side effects.

Methods

Design Expert^® was used to optimize formulations (S_mix ratio and capmul as independent factors), which were prepared using a slow spontaneous titration method. The optimized nanoemulsion was incorporated into carbopol gel to allow for topical application and comparative assessments. Nanoemulsions and gels were evaluated for size, size distribution, shape, zeta potential, percent spread, viscosity, in vitro hemolysis, in vitro release, and ex vivo skin permeation and deposition. A mechanistic evaluation was performed using scanning electron microscopy. Furthermore, in vivo pharmacokinetic and irritation studies were performed.

Results

The optimized cationic nanoemulsion (OCNE-1) was characterized by small particle size (≤100 nm), had optimal viscosity, percent spread, zeta potential, and percent drug release, and was hemocompatible. The OCNE-1T gel exhibited higher permeation flux (51.32 ± 0.5 µg/cm² hr), permeation coefficient (2.566 ± 0.08 cm/hr), drug deposition (994.404 µg/cm²), and enhancement ratio (7.16) than those of the OCNE-1 nanoemulsion or drug solution. Scanning electron microscopy was used to characterize the mechanism of enhanced permeation. An In vivo study showed that the C_max and area under the curve following transdermal application were 4.34- and 4.74-fold higher than those following oral administration.

Conclusion

Transdermal delivery of rifampicin could be a promising alternative to conventional approaches to treat systemic and local tuberculosis, and other bacterial infections.

The effect of adjuvants and delivery systems on Th1, Th2, Th17 and Treg cytokine responses in mice immunized with Mycobacterium tuberculosis-specific proteins

Tuberculosis (TB) is a major health problem of global concern. The control of this disease requires appropriate preventive measures, including vaccines. In TB, T helper (Th)1 cytokines provide protection whereas Th2 and T regulatory (Treg) cytokines contribute to the pathogenesis and Th17 cytokines play a role in both protection and pathogenesis. Previous studies with Mycobacterium tuberculosis-specific proteins have identified seven low molecular weight proteins, PE35, ESXA, ESXB, Rv2346c, Rv2347c, Rv3619c, and Rv3620c, as immunodominant antigens inducing Th1-cell responses in humans following natural infection with M. tuberculosis. The aim of this study was to characterize the cytokine responses induced in mice immunized with these proteins, using various adjuvants and delivery systems, i.e. chemical adjuvants (Alum and IFA), non-pathogenic mycobacteria (M. smegmatis and M. vaccae) and a DNA vaccine plasmid (pUMVC6). The immune responses were monitored by quantifying the marker cytokines secreted by Th1 (IFN-ɣ), Th2 (IL-5), Treg (IL-10), and Th17 (IL-17A) cells. DNA corresponding to pe35, esxa, esxb, rv2346c, rv2347c, rv3619c, and rv3620c genes were cloned into the expression vectors pGES-TH-1, pDE22 and pUMVC6 for expression in Escherichia coli, mycobacteria and eukaryotic cells, respectively. Mice were immunized with the recombinants using different adjuvants and delivery systems, and spleen cells were stimulated in vitro with peptides of immunizing proteins to investigate antigen-specific secretion of Th1 (IFN-ɣ), Th2 (IL-5), Treg (IL-10), and Th17 (IL-17A) cytokines. The results showed that spleen cells, from mice immunized with all antigens, secreted the protective Th1 cytokine IFN-ɣ, except ESXB, with one or more adjuvants and delivery systems. However, only Rv3619c consistently induced Th1-biased responses, without the secretion of significant concentrations of Th2, Th17 and Treg cytokines, with all adjuvants and delivery systems. Rv3619c also induced antigen-specific IgG antibodies in immunized mice.

A combined subunit vaccine comprising BP26, Omp25 and L7/L12 against brucellosis

The current vaccines against brucellosis, namely Brucella abortus strains 19 and RB51, prevent infection in animals but pose potential risks like virulence and attenuation reversal. In this milieu, although subunit vaccination using a single potent immunogen of B. abortus, e.g. BP26 or Omp25 or L7/L12 etc., appears as a safer alternative, nonetheless it confers inadequate protection against the zoonosis compared to attenuated vaccines. Hence, we have investigated the prophylactic potential of a combined subunit vaccine (CSV) comprising the BP26, Omp25 and L7/L12 antigens of B. abortus, in mice model. Sera obtained from CSV immunized mice groups showed heightened IgG titers against all the three components and exhibited specificity upon immunoblotting, reiterating their authenticity. Further, the IgG1/IgG2a ratio obtained against each antigen revealed a predominant Th2 immune response in CSV immunized mice group. However, on assessing the levels of Th1-dependent (IFN-γ and TNF-α) and Th2-dependent (IL-4 and IL-10) cytokines in different formulations, prominent IFN-γ levels were elicited in CSV immunized mice. Further, upon infection with virulent B. abortus 544, the combined subunit vaccinated mice displayed superior degree of protection (Log10 reduction) than the individual vaccines; however, B. abortus S19 showed the highest protection. Altogether, this study suggests that co-immunization of three B. abortus immunogens as a CSV complements and triggers a mixed Th1/Th2 immune response leading to superior degree of protection against pathogenic B. abortus 544 infection.

Crystalline and Amorphous Preparation of Aluminum Hydroxide Nanoparticles Enhances Protective Antigen Domain 4 Specific Immunogenicity and Provides Protection Against Anthrax

Introduction

Aluminum salts, although they have been used as adjuvants in many vaccine formulations since 1926, exclusively induce a Th2-biased immune response, thereby limiting their use against intracellular pathogens like Mycobacterium tuberculosis.

Methods and Results

Herein, we synthesized amorphous and crystalline forms of aluminum hydroxide nanoparticles (AH nps) of 150–200 nm size range. Using Bacillus anthracis protective antigen domain 4 (D4) as a model antigen, we demonstrated that both amorphous and crystalline forms of AH nps displayed enhanced antigen D4 uptake by THP1 cells as compared to commercial adjuvant aluminum hydroxide gel (AH gel). In a mouse model, both amorphous and crystalline AH nps triggered an enhanced D4-specific Th2- and Th1-type immune response and conferred superior protection against anthrax spore challenge as compared to AH gel. Physicochemical characterization of crystalline and amorphous AH nps revealed stronger antigen D4 binding and release than AH gel.

Conclusion

These results demonstrate that size and crystallinity of AH nps play important roles in mediating enhanced antigen presenting cells (APCs) activation and potentiating a strong antigen-specific immune response, and are critical parameters for the rational design of alum-based Th1-type adjuvant to induce a more balanced antigen-specific immune response.

Tuberculosis vaccine candidates based on mycobacterial cell envelope components

Even after decades searching for a new and more effective vaccine against tuberculosis, the scientific community is still pursuing this goal due to the complexity of its causative agent, Mycobacterium tuberculosis (Mtb). Mtb is a microorganism with a robust variety of survival mechanisms that allow it to remain in the host for years. The structure and nature of the Mtb envelope play a leading role in its resistance and survival. Mtb has a perfect machinery that allows it to modulate the immune response in its favor and to adapt to the host's environmental conditions in order to remain alive until the moment to reactivate its normal growing state. Mtb cell envelope protein, carbohydrate and lipid components have been the subject of interest for developing new vaccines because most of them are responsible for the pathogenicity and virulence of the bacteria. Many indirect evidences, mainly derived from the use of monoclonal antibodies, support the potential protective role of Mtb envelope components. Subunit and DNA vaccines, lipid extracts, liposomes and membrane vesicle formulations are some examples of technologies used, with encouraging results, to evaluate the potential of these antigens in the protective response against Mtb.