Protective efficacy of a Treponema pallidum Gpd DNA vaccine vectored by chitosan nanoparticles and fused with interleukin-2

Syphilis vaccine: challenges, controversies and opportunities

Syphilis is a sexually or vertically (mother to fetus) transmitted disease caused by the infection of Treponema pallidum subspecie pallidum (TPA). The incidence of syphilis has increased over the past years despite the fact that this bacterium is an obligate human pathogen, the infection route is well known, and the disease can be successfully treated with penicillin. As complementary measures to preventive campaigns and early treatment of infected individuals, development of a syphilis vaccine may be crucial for controlling disease spread and/or severity, particularly in countries where the effectiveness of the aforementioned measures is limited. In the last century, several vaccine prototypes have been tested in preclinical studies, mainly in rabbits. While none of them provided protection against infection, some prototypes prevented bacteria from disseminating to distal organs, attenuated lesion development, and accelerated their healing. In spite of these promising results, there is still some controversy regarding the identification of vaccine candidates and the characteristics of a syphilis-protective immune response. In this review, we describe what is known about TPA immune response, and the main mechanisms used by this pathogen to evade it. Moreover, we emphasize the importance of integrating this knowledge, in conjunction with the characterization of outer membrane proteins (OMPs), to expedite the development of a syphilis vaccine that can protect against TPA infection.

A clinical perspective of chitosan nanoparticles for infectious disease management

Infectious diseases and their effective management are still a challenge in this modern era of medicine. Diseases, such as the SARS-CoV-2, Ebola virus, and Zika virus, still put human civilization at peril. Existing drug banks, which include antivirals, antibacterial, and small-molecule drugs, are the most advocated method for treatment, although effective but they still flounder in many instances. This calls for finding more effective alternatives for tackling the menace of infectious diseases. Nanoformulations are progressively being implemented for clinical translation and are being considered a new paradigm against infectious diseases. Natural polymers like chitosan are preferred to design nanoparticles owing to their biocompatibility, biodegradation, and long shelf-life. The chitosan nanoparticles (CNPs) being highly adaptive delivers contemporary prevention for infectious diseases. Currently, they are being used as antibacterial, drug, and vaccine delivery vehicles, and wound-dressing materials, for infectious disease treatment. Although the recruitment of CNPs in clinical trials associated with infectious diseases is minimal, this may increase shortly due to the sudden emergence of unknown pathogens like SARS-CoV-2, thus turning them into a panacea for the management of microorganisms. This review particularly focuses on the all-around application of CNPs along with their recent clinical applications in infectious disease management.

Immunization with Tp0954, an adhesin of Treponema pallidum, provides protective efficacy in the rabbit model of experimental syphilis

Syphilis, a chronic multisystemic disease caused by spirochete Treponema pallidum subspecies pallidum infection, continues to be a serious global health problem and congenital syphilis remains a major cause of adverse outcomes in pregnancy in developing countries. The development of an effective vaccine is the most cost-effective way to eliminate syphilis, but so far has been elusive. Here, we evaluated the immunogenicity and protective efficacy of Tp0954, a T. pallidum placental adhesin, as a potential vaccine candidate in a New Zealand White rabbit model of experimental syphilis. Animals immunized with recombinant Tp0954 (rTp0954) produced high titers of Tp0954-specific serum IgG, high levels of IFN-γ from splenocytes and specific splenocyte proliferation response when compared to control animals immunized with PBS and Freund’s adjuvant (FA). Furthermore, rTp0954 immunization significantly delayed the development of cutaneous lesions, promoted inflammatory cellular infiltration at the primary lesion sites, as well as inhibited T. pallidum dissemination to distal tissues or organs when compared with that of the control animals. In addition, the naïve rabbits receiving popliteal lymph nodes from Tp0954-immunized, T. pallidum-challenged animals were not infected by T. pallidum, confirming sterile immunity. These findings suggest that Tp0954 is a potential vaccine candidate against syphilis.

Immunization with nontreponemal antigen alters the course of experimental syphilis in the rabbit model

The role of nontreponemal antibodies in the Treponema pallidum infection course is unclear. We investigated the effect of immunization with nontreponemal antigen on T. pallidum-challenged rabbits. Nontreponemal antigen was injected intravenously into rabbits in the nontreponemal group (n = 12) to elicit antibodies (≥1:64), and normal saline-injected rabbits were used as controls (n = 12). Then, rabbits were challenged with 10⁶T. pallidum per site along their back. Lesion development was observed, and the injection sites were biopsied for mRNA analysis every week. Six rabbits from both groups were euthanized at 14 d and 28 d. The popliteal lymph nodes were extracted to assess infectivity using a rabbit infectivity test. The maximum lesion diameters were not different between the two groups (12.4 ± 0.9 mm in the nontreponemal group vs. 12.5 ± 1.0 mm in the control group, P = 0.386), but the time to maximum diameter appearance was delayed by approximately 4 d in the nontreponemal group (14.4 ± 1.6 d vs. 10.8 ± 1.9 d, P = 0.000). There were no significant differences in the proportions of lesions (58/60 (96.7%) vs. 59/60 (98.3%), P = 0.500) or ulcers (55/60 (91.7%) vs. 57/60 (95.0%), P = 0.359) between the two groups. An ulcer development delay of 5 d was observed in the nontreponemal group (19.3 ± 2.0 d vs. 14.0 ± 1.8 d, P = 0.000). IL-2 and IFN-γ mRNA expression in the nontreponemal group was significantly higher than that in the control group at 7 d and 14 d post-challenge. flaA mRNA expression and the rabbit infectivity test positive rate were not different between the two groups. Immunization with nontreponemal antigen altered the syphilis course in rabbits, resulting in delayed maximal lesion diameter and ulcer development, but it could not inhibit the spread of T. pallidum from primary lesion sites to viscera.

Intramuscular primary immunization by nucleic acid vaccine pcDNA/Gpd-IL-2 and enhanced immunization with mucosal adjuvant CpG-ODN and Gpd-IL-2 recombinant protein effectively induced strong mucosal immune responses and immune protective effects against Treponema pallidum skin infection

The present study aimed to evaluate the immune effect of intramuscular primary immunization by the nucleic acid vaccine pcDNA/glycerophosphodiester phosphodiesterase-interleukin-2 (pcDNA/Gpd-IL-2) and enhanced immunization 2 weeks later with the combination of mucosal adjuvant CpG-oligodeoxynucleotides (ODN) and Gpd-IL-2 recombinant protein on skin infection caused by Treponema pallidum (Tp) in New Zealand rabbits. At week 8 following immunization, MTT assay was used to detect spleen cell proliferation, while enzyme-linked immunosorbent assay was performed to detect the cytokine and secretory immunoglobulin A (SIgA) levels. At week 10 after primary immunization, rabbits were inoculated with 10⁵ Tp (Nichols strain). Alterations in the skin redness, swelling and ulceration were recorded for 0-60 days. In addition, positive rate of Tp in skin lesions and ulcer formation rate were examined using dark field and silver staining. The results indicated that intramuscular primary immunization by nucleic acid vaccine pcDNA/Gpd-IL-2 followed by enhanced immunization via nasal feeding with mucosal adjuvant CpG-ODN and Gpd-IL-2 recombinant protein induced the higher levels of Tp Gpd specific antibodies, increased the secretion of IL-2 and interferon-γ, and promoted the proliferation of T cells in the first 8 weeks after immunization. Furthermore, this immunization strategy stimulated the production of mucosa specific SIgA antibody. Thus, this strategy led to the lowest Tp positive and ulcer formation rates at the Tp infection sites, as well as healing of skin lesions on the earliest time point (day 42). In conclusion, immunization by nucleic acid vaccine pcDNA/Gpd-IL-2 followed by enhanced immunization with a combination of mucosal adjuvant CpG-ODN and Gpd-IL-2 recombinant protein is an effective immune strategy to induce strong mucosal immune responses and immune protective effects.

Recombinant Neisseria surface protein A is a potential vaccine candidate against Neisseria meningitides serogroup B

Neisseria meningitidis is the pathogen of epidemic encephalomyelitis and is responsible for permanent damage to the brain and nervous system. In the present study, the prokaryotic expression vector pGEX-6p-1/neisseria surface protein A (NspA) was constructed and the immune protective effect was investigated with the purified recombinant rNspA. Female BALB/c mice were immunized by intraperitoneal inoculation of rNspA, glutathione S-transferase (GST) or phosphate-buffered saline (PBS). The protection experiment in mice demonstrated that the protection rate of the rNspA group was 85% against the N. meningitidis strain MC58, and a serum bactericidal assay in vitro revealed that the serum bactericidal titer of the rNspA group reached 1:64 following three immunizations. The levels of specific immunoglobulin (Ig) A (SIgA), IgG, IgG1, IgG2a, IgG2b and IgG3 of mice in the rNspA group peaked at week six and were higher than those in the mice in the GST and PBS groups. The levels of stimulation index, interleukin-4 and interferon-γ in the culture supernatant of the spleen lymphocytes of the rNspA group increased in a time-dependent manner and were higher than those of the mice in the GST and PBS groups over the same period. The results suggested that rNspA may induce increased specific humoral and cellular immune responses, and that it is effectively protective against N. meningitidis serogroup B in mice. The present study offered novel evidence that may lead to the development of a novel effective N. meningitidis serogroup B vaccine.

The emerging physiological roles of the glycerophosphodiesterase family

The glycerophosphodiester phosphodiesterases are evolutionarily conserved proteins that have been linked to several patho/physiological functions, comprising bacterial pathogenicity and mammalian cell proliferation or differentiation. The bacterial enzymes do not show preferential substrate selectivities among the glycerophosphodiesters, and they are mainly dedicated to glycerophosphodiester hydrolysis, producing glycerophosphate and alcohols as the building blocks that are required for bacterial biosynthetic pathways. In some cases, this enzymatic activity has been demonstrated to contribute to bacterial pathogenicity, such as with Hemophilus influenzae. Mammalian glyerophosphodiesterases have high substrate specificities, even if the number of potential physiological substrates is continuously increasing. Some of these mammalian enzymes have been directly linked to cell differentiation, such as GDE2, which triggers motor neuron differentiation, and GDE3, the enzymatic activity of which is necessary and sufficient to induce osteoblast differentiation. Instead, GDE5 has been shown to inhibit skeletal muscle development independent of its enzymatic activity.

Co-expression of S. Typhi GroEL and IL-22 gene augments immune responses against Salmonella infection

Recombinant DNA vaccines represent a novel method for generating in situ expression of vaccine antigens. Intramuscular injections of naked DNA are able to elicit potent humoral and cellular immune responses but still numerous factors limit the immunogenicity of DNA vaccines. Co-expression of cytokines with antigen encoding genes in DNA vectors can improve the immune responses and modify Th1/Th2 balance. In this study, the immunomodulatory effect of Interleukin 22 (IL-22) as an adjuvant was studied by DNA vaccination with S. Typhi Heat shock protein 60 (HSP60/GroEL) in mice. Further, DNA construct of IL-22 gene fused with GroEL was developed and immunization studies were carried out in mice. DNA vaccination with GroEL alone stimulated humoral and cell-mediated immune responses. Co-immunization (IL-22+GroEL) further resulted in increase in T-cell proliferative responses, antibody titres (IgG, IgG1, IgG2a) and secretion of IFNγ (Th1), IL-1β and Th2 (IL-4, IL-6) cytokines. Co-expression (IL-22-GroEL DNA) also promoted antibody titres and cytokine levels were significantly higher as compared to co-immunized group. A reduction in bacterial load in spleen, liver and intestine was seen in all the immunized groups as compared to control, with least organ burden in fusion DNA construct group (co-expression). Improved protective efficacy (90%) against lethal challenge by Salmonella was observed with IL-22-GroEL co-expressing DNA vector as compared with plasmid encoding GroEL only (50-60%) or co-immunization group (75-80%). This study thus shows that co-expression of IL-22 and GroEL genes enhances the immune responses and protective efficacy, circumventing the need of any adjuvant.

CpG adjuvant enhances the mucosal immunogenicity and efficacy of a Treponema pallidum DNA vaccine in rabbits

OBJECTIVES

The protective response against Treponema pallidum (Tp) infection of a DNA vaccine enhanced by an adjuvant CpG ODN was investigated.

RESULTS

The mucosal adjuvant CpG ODN enhanced the production of higher levels of anti-TpGpd antibodies induced by pcD/Gpd-IL-2 in rabbits. It also resulted in higher levels of secretion of IL-2 and IFN-γ, and facilitated T cell proliferation and differentiation (p<0.05). No significant difference about testing index above-mentioned was found in the intranasal immunization group of pcD/Gpd-IL-2 vaccine adjuvanted by CpG ODN when compared with the immunization by pcD/Gpd-IL-2 vaccine intramuscular injection alone (p>0.05). Furthermore, CpG ODN stimulated the production of mucosa-specific anti-sIgA antibodies and resulted in the lowest Tp-positive rate (6.7%) for Tp-infection of skin lesions and the lowest rates (8.3%) of ulceration lesions, thus achieving better protective effects.

METHODS

New Zealand rabbits were immunized with the eukaryotic vector encoding recombinant pcD/Gpd-IL-2 using intramuscular multi-injection or together with mucosal enhancement via a nasal route. The effect of the mucosal adjuvant CpG ODN was examined.

CONCLUSIONS

The CpG ODN adjuvant significantly enhances the humoral and cellular immune effects of the immunization by pcD/Gpd-IL-2 with mucosal enhancement via nasal route. It also stimulates strong mucosal immune effects, thus initiating more efficient immune-protective effects.

Preparation and efficacy of a live newcastle disease virus vaccine encapsulated in chitosan nanoparticles

BACKGROUND

Newcastle disease (ND) is a highly contagious viral disease of poultry caused by pathogenic strains of the Newcastle disease virus (NDV). Live NDV vaccines are administered by drinking water, eyedrops or coarse aerosol spray. To further enhance mucosal immune responses, chitosan nanoparticles were developed for the mucosal delivery of a live NDV vaccine.

METHODOLOGY/PRINCIPAL FINDINGS

A lentogenic live-virus vaccine (strain LaSota) against NDV encapsulated in chitosan nanoparticles were developed using an ionic crosslinking method. Chitosan nanoparticles containing the lentogenic live-virus vaccine against NDV (NDV-CS-NPs) were produced with good morphology, high stability, a mean diameter of 371.1 nm, an encapsulation rate of 77% and a zeta potential of +2.84 mV. The Western blotting analysis showed that NDV structural proteins were detected in NDV-CS-NPs. The virus release assay results of NDV-CS-NPs indicated that NDV was released from NDV-CS-NPs. Chickens immunized orally or intranasally with NDV-CS-NPs were fully protected whereas one out of five chickens immunized with the LaSota live NDV vaccine and three out of five chickens immunized with the inactivated NDV vaccine were dead after challenge with the highly virulent NDV strain F48E9.

CONCLUSIONS/SIGNIFICANCE

NDV-CS-NPs induced better protection of immunized specific pathogen free chickens compared to the live NDV vaccine strain LaSota and the inactivated NDV vaccine. This study lays a foundation for the further development of mucosal vaccines and drugs encapsulated in chitosan nanoparticles.

Protective immune responses in mice induced by intramuscular and intranasal immunization with a Mycoplasma pneumoniae P1C DNA vaccine

Mycoplasma pneumoniae is an important causative agent of atypical pneumonia. This study was to determine the ability of a DNA expression vector, which encodes the carboxy terminal region of the M. pneumoniae P1 protein (P1C), to induce humoral and cellular immune responses and to protect against M. pneumoniae infection in BALB/c mice. Mice were immunized with pcDNA3.1/P1C by either intramuscular injection (i.m.) or intranasal inoculation (i.n.). Our results showed that p1c DNA immunization generates detectable antibodies specific to M. pneumoniae, and elicits high levels of IgG1, IgG2a, and IgG2b isotypes (P < 0.01). The levels of IFN-γ and IL-4 in spleen cells of the immunized mice were significantly elevated by immunization via both the i.m. and i.n. methods. Moreover, p1c DNA-immunized mice exhibited detectable protection against M. pneumoniae infection. The lung tissue inflammation was relieved and the histopathologic score (HPS) of pcDNA3.1/P1C-immunized mice was significantly decreased than those in phosphate-buffed saline (PBS) or vaccine-vector-immunized mice (P < 0.01), whereas there were no significant differences in HPS between i.m. and i.n. vaccination (P > 0.05). Our results suggest that pcDNA3.1/P1C could be useful for developing a vaccine against M. pneumoniae infection.