TLR9 adjuvants enhance immunogenicity and protective efficacy of the SE36/AHG malaria vaccine in nonhuman primate models

Immune tolerance caused by repeated P. falciparum infection against SE36 malaria vaccine candidate antigen and the resulting limited polymorphism

The call for second generation malaria vaccines needs not only the identification of novel candidate antigens or adjuvants but also a better understanding of immune responses and the underlying protective processes. Plasmodium parasites have evolved a range of strategies to manipulate the host immune system to guarantee survival and establish parasitism. These immune evasion strategies hamper efforts to develop effective malaria vaccines. In the case of a malaria vaccine targeting the N-terminal domain of P. falciparum serine repeat antigen 5 (SE36), now in clinical trials, we observed reduced responsiveness (lowered immunogenicity) which may be attributed to immune tolerance/immune suppression. Here, immunogenicity data and insights into the immune responses to SE36 antigen from epidemiological studies and clinical trials are summarized. Documenting these observations is important to help identify gaps for SE36 continued development and engender hope that highly effective blood-stage/multi-stage vaccines can be achieved.

Persistence of Anti-SE36 Antibodies Induced by the Malaria Vaccine Candidate BK-SE36/CpG in 5-10-Year-Old Burkinabe Children Naturally Exposed to Malaria

Information on the dynamics and decline/persistence of antibody titres is important in vaccine development. A recent vaccine trial in malaria-exposed, healthy African adults and children living in a malaria hyperendemic and seasonal area (Ouagadougou, Burkina Faso) was the first study in which BK-SE36/CpG was administered to different age groups. In 5- to 10-year-old children, the risk of malaria infection was markedly lower in the BK-SE36/CpG arm compared to the control arm. We report here data on antibody titres measured in this age-group after the high malaria transmission season of 2021 (three years after the first vaccine dose was administered). At Year 3, 83% of children had detectable anti-SE36 total IgG antibodies. Geometric mean antibody titres and the proportion of children with detectable anti-SE36 antibodies were markedly higher in the BK-SE36/CpG arm than the control (rabies) arm. The information obtained in this study will guide investigators on future vaccine/booster schedules for this promising blood-stage malaria vaccine candidate.

Immunogenicity of Recombinant Lipid-Based Nanoparticle Vaccines: Danger Signal vs. Helping Hand

Infectious diseases are a predominant problem in human health. While the incidence of many pathogenic infections is controlled by vaccines, some pathogens still pose a challenging task for vaccine researchers. In order to face these challenges, the field of vaccine development has changed tremendously over the last few years. For non-replicating recombinant antigens, novel vaccine delivery systems that attempt to increase the immunogenicity by mimicking structural properties of pathogens are already approved for clinical applications. Lipid-based nanoparticles (LbNPs) of different natures are vesicles made of lipid layers with aqueous cavities, which may carry antigens and other biomolecules either displayed on the surface or encapsulated in the cavity. However, the efficacy profile of recombinant LbNP vaccines is not as high as that of live-attenuated ones. This review gives a compendious picture of two approaches that affect the immunogenicity of recombinant LbNP vaccines: (i) the incorporation of immunostimulatory agents and (ii) the utilization of pre-existing or promiscuous cellular immunity, which might be beneficial for the development of tailored prophylactic and therapeutic LbNP vaccine candidates.

Safety and immunogenicity of BK-SE36/CpG malaria vaccine in healthy Burkinabe adults and children: a phase 1b randomised, controlled, double-blinded, age de-escalation trial

Background

BK-SE36/CpG is a recombinant blood-stage malaria vaccine candidate based on the N-terminal Plasmodium falciparum serine repeat antigen5 (SE36), adsorbed to aluminium hydroxide gel and reconstituted, prior to administration, with synthetic oligodeoxynucleotides bearing CpG motifs. In healthy Japanese adult males, BK-SE36/CpG was well tolerated. This study assessed its safety and immunogenicity in healthy malaria-exposed African adults and children.

Methods

A double-blind, randomised, controlled, age de-escalating clinical trial was conducted in an urban area of Ouagadougou, Burkina Faso. Healthy participants (n=135) aged 21-45 years (Cohort 1), 5-10 years (Cohort 2) and 12-24 months (Cohort 3) were randomised to receive three vaccine doses (Day 0, 28 and 112) of BK-SE36/CpG or rabies vaccine by intramuscular injection.

Results

One hundred thirty-four of 135 (99.2%) subjects received all three scheduled vaccine doses. Vaccinations were well tolerated with no related Grade 3 (severe) adverse events (AEs). Pain/limitation of limb movement, headache in adults and fever in younger children (all mild to moderate in intensity) were the most frequently observed local and systemic AEs. Eighty-three of BK-SE36/CpG (91%) recipients and 37 of control subjects (84%) had Grade 1/2 events within 28 days post vaccination. Events considered by the investigator to be vaccine related were experienced by 38% and 14% of subjects in BK-SE36/CpG and control arms, respectively. Throughout the trial, six Grade 3 events (in 4 subjects), not related to vaccination, were recorded in the BK-SE36/CpG arm: 5 events (in 3 subjects) within 28 days of vaccination. All serious adverse events (SAEs) (n=5) were due to severe malaria (52-226 days post vaccination) and not related to vaccination. In all cohorts, BK-SE36/CpG arm had higher antibody titres after Dose 3 than after Dose 2. Younger cohorts had stronger immune responses (12-24-month-old > 5-10 years-old > 21-45 years-old). Sera predominantly reacted to peptides that lie in intrinsically unstructured regions of SE36. In the control arm, there were no marked fold changes in antibody titres and participants' sera reacted poorly to all peptides spanning SE36.

Conclusion

BK-SE36/CpG was well-tolerated and immunogenic. These results pave the way for further proof-of-concept studies to demonstrate vaccine efficacy.

Clinical trial registration

https://pactr.samrc.ac.za/TrialDisplay.aspx?TrialID=1921, PACTR201701001921166.

Advancements and Challenges in Developing Malaria Vaccines: Targeting Multiple Stages of the Parasite Life Cycle

Malaria, caused by Plasmodium species, remains a major global health concern, causing millions of deaths annually. While the introduction of the RTS,S vaccine has shown promise, there is a pressing need for more effective vaccines due to the emergence of drug-resistant parasites and insecticide-resistant vectors. However, the complex life cycle and genetic diversity of the parasite, technical obstacles, limited funding, and the impact of the 2019 pandemic have hindered progress in malaria vaccine development. This review focuses on advancements in malaria vaccine development, particularly the ongoing clinical trials targeting antigens from different stages of the Plasmodium life cycle. Additionally, we discuss the rationale, strategies, and challenges associated with vaccine design, aiming to enhance the immune response and protective efficacy of vaccine candidates. A cost-effective and multistage vaccine could hold the key to controlling and eradicating malaria.

Plasmodium falciparum infection coinciding with the malaria vaccine candidate BK-SE36 administration interferes with the immune responses in Burkinabe children

Background

A vaccine targeting the erythrocyte stages of Plasmodium falciparum could play a role in preventing clinical disease. BK-SE36 is a promising malaria vaccine candidate that has shown a good safety profile and immunological responses during field evaluations. It was observed that repeated natural infections could result in immune tolerance against SE36 molecule.

Methods

The primary trial was conducted to assess the safety and immunogenicity of the BK-SE36 in two cohorts of children aged 25-60 months (Cohort 1) and 12-24 months (Cohort 2). Immunization was at full dose (1.0 mL) administered at 0, 1, and 6 months. Blood samples were collected before each vaccination for immunological assessments and detection of Plasmodium falciparum infection by microscopy. Blood samples were further collected one month post each vaccination to evaluate immunogenicity.

Results

Of seventy-two (72) subjects that have received BK-SE36 vaccination, 71 had available blood smears during vaccination days. One month post Dose 2, the geometric mean of SE36 antibodies was 263.2 (95% CI: 178.9-387.1) in uninfected individuals compared to 77.1 (95% CI: 47.3-125.7) in infected participants. The same trend was observed one-month post booster dose. Participants uninfected at the time of booster vaccination had significantly higher GMTs compared to those who were infected (424.1 (95% CI: 301.9-595.8) vs. 92.8 (95% CI: 34.9-246.6), p = 0.002. There was a 14.3 (95% CI: 9.7-21.1) and 2.4 (95% CI: 1.3-4.4) fold-change, respectively, in uninfected and infected participants between one-month post Dose 2 and booster. The difference was statistically significant (p < 0.001).

Conclusion

Concomitant infection by P. falciparum during BK-SE36 vaccine candidate administration is associated with reduced humoral responses. However, it is to be noted that the BK-SE36 primary trial was not designed to investigate the influence of concomitant infection on vaccine-induced immune response and should be interpreted cautiously.

Trial registration

WHO ICTRP, PACTR201411000934120.

Vaccination of squirrel monkeys (Saimiri spp.) with nanoparticle based-Toxoplasma gondii antigens: new hope for captive susceptible species

Squirrel monkeys (Saimiri spp.), new world primates from South America, are very susceptible to toxoplasmosis. Numerous outbreaks of fatal toxoplasmosis in zoos have been identified around the world, resulting in acute respiratory distress and sudden death. To date, preventive hygiene measures or available treatments are not able to significantly reduce this mortality in zoos. Therefore, vaccination seems to be the best long-term solution to control acute toxoplasmosis. Recently, we developed a nasal vaccine composed of total extract of soluble proteins of Toxoplasma gondii associated with muco-adhesive maltodextrin-nanoparticles. The vaccine, which generated specific cellular immune responses, demonstrated efficacy against toxoplasmosis in murine and ovine experimental models. In collaboration with six French zoos, our vaccine was used as a last resort in 48 squirrel monkeys to prevent toxoplasmosis. The full protocol of vaccination includes two intranasal sprays followed by combined intranasal and s.c. administration. No local or systemic side-effects were observed irrespective of the route of administration. Blood samples were collected to study systemic humoral and cellular immune responses up to 1 year after the last vaccination. Vaccination induced a strong and lasting systemic cellular immune response mediated by specific IFN-γ secretion by peripheral blood mononuclear cells. Since the introduction of vaccination, no deaths of squirrel monkeys due to T. gondii has been observed for more than 4 years suggesting the promising usage of our vaccine. Moreover, to explain the high susceptibility of naive squirrel monkeys to toxoplasmosis, their innate immune sensors were investigated. It was observed that Toll-like and Nod-like receptors appear to be functional following T. gondii recognition suggesting that the extreme susceptibility to toxoplasmosis may not be linked to innate detection of the parasite.

CpG ODN (K3)-toll-like receptor 9 agonist-induces Th1-type immune response and enhances cytotoxic activity in advanced lung cancer patients: a phase I study

Background

Cytosine-phosphate-guanine oligodeoxynucleotide (CpG ODN) (K3)—a novel synthetic single-stranded DNA immune adjuvant for cancer immunotherapy—induces a potential Th1-type immune response against cancer cells. We conducted a phase I study of CpG ODN (K3) in patients with lung cancer to assess its safety and patients’ immune responses.

Methods

The primary endpoint was the proportion of dose-limiting toxicities (DLTs) at each dose level. Secondary endpoints included safety profile, an immune response, including dynamic changes in immune cell and cytokine production, and progression-free survival (PFS). In a 3 + 3 dose-escalation design, the dosage levels for CpG ODN (K3) were 5 or 10 mg/body via subcutaneous injection and 0.2 mg/kg via intravenous administration on days 1, 8, 15, and 29.

Results

Nine patients (eight non-small-cell lung cancer; one small-cell lung cancer) were enrolled. We found no DLTs at any dose level and observed no serious treatment-related adverse events. The median observation period after registration was 55 days (range: 46–181 days). Serum IFN-α2 levels, but not inflammatory cytokines, increased in six patients after the third administration of CpG ODN (K3) (mean value: from 2.67 pg/mL to 3.61 pg/mL after 24 hours). Serum IFN-γ (mean value, from 9.07 pg/mL to 12.7 pg/m after 24 hours) and CXCL10 levels (mean value, from 351 pg/mL to 676 pg/mL after 24 hours) also increased in eight patients after the third administration. During the treatment course, the percentage of T-bet-expressing CD8⁺ T cells gradually increased (mean, 49.8% at baseline and 59.1% at day 29, p = 0.0273). Interestingly, both T-bet-expressing effector memory (mean, 52.7% at baseline and 63.7% at day 29, p = 0.0195) and terminally differentiated effector memory (mean, 82.3% at baseline and 90.0% at day 29, p = 0.0039) CD8⁺ T cells significantly increased. The median PFS was 398 days.

Conclusions

This is the first clinical study showing that CpG ODN (K3) activated innate immunity and elicited Th1-type adaptive immune response and cytotoxic activity in cancer patients. CpG ODN (K3) was well tolerated at the dose settings tested, although the maximum tolerated dose was not determined.

Trial registration

UMIN-CTR number 000023276. Registered 1 September 2016, https://upload.umin.ac.jp/cgi-open-bin/ctr/ctr_view.cgi?recptno=R000026649

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09818-4.

Plasmodium falciparum Malaria Vaccines and Vaccine Adjuvants

Malaria-a parasite vector-borne disease-is a global health problem, and Plasmodium falciparum has proven to be the deadliest among Plasmodium spp., which causes malaria in humans. Symptoms of the disease range from mild fever and shivering to hemolytic anemia and neurological dysfunctions. The spread of drug resistance and the absence of effective vaccines has made malaria disease an ever-emerging problem. Although progress has been made in understanding the host response to the parasite, various aspects of its biology in its mammalian host are still unclear. In this context, there is a pressing demand for the development of effective preventive and therapeutic strategies, including new drugs and novel adjuvanted vaccines that elicit protective immunity. The present article provides an overview of the current knowledge of anti-malarial immunity against P. falciparum and different options of vaccine candidates in development. A special emphasis has been made on the mechanism of action of clinically used vaccine adjuvants.

A review of combination adjuvants for malaria vaccines: a promising approach for vaccine development

It is obvious that there is a critical need for an efficient malaria vaccine to accelerate malaria eradication. Currently, recombinant subunit vaccination against malaria using proteins and peptides is gaining attention. However, one of the major drawbacks of this approach is the lack of an efficient and durable immune response. Therefore, subunit vaccines require adjuvants to make the vaccine sufficiently immunogenic. Considering the history of the RTS,S vaccine, it seems likely that no single adjuvant is capable of eliciting all the protective immune responses required in many malarial subunit vaccines and the use of combination adjuvants will be increasingly important as the science of malaria vaccines advances. In light of this, it appears that identifying the most effective mixture of adjuvants with minimal adverse effects offers tremendous opportunities in improving the efficacy of vaccines against malaria. Owing to the importance of a multi-adjuvanted approach in subunit malaria vaccine development, this review paper outlines some of the best known combination adjuvants used in malaria subunit vaccines, focusing on their proposed mechanisms of action, their immunological properties, and their notable results. The aim of the present review is to consolidate these findings to aid the application of these combination adjuvants in experimental malaria vaccines.

Effects of relocation on immunological and physiological measures in female squirrel monkeys (Saimiri boliviensis boliviensis)

In the present study, we have quantified the effects of transport, relocation and acclimate/adapt to their new surroundings on female squirrel monkey. These responses are measured in blood samples obtained from squirrel monkeys, at different time points relative to their relocation from their old home to their new home. A group of squirrel monkeys we transported, by truck, for approximately 10 hours. Peripheral blood mononuclear cells (PBMCs) were assayed in order to evaluate the phenotype of lymphocyte subsets by flow, mitogen-specific immune responses of PBMCs in vitro, and levels of cytokines at various time points including immediately before transport, immediately upon arrival, and after approximately 150 days of acclimation. We observed significant changes in T cells and subsets, NK and B cells (CD4⁺, CD8⁺, CD4⁺/CD8⁺, CD16⁺, and CD20⁺). Mitogen specific (e.g. PHA, PWM and LPS) proliferation responses, IFN-γ by ELISPOT assay, and cytokines (IL-2, IL-4 and VEGF) significant changes were observed. Changes seen in the serum chemistry measurements mostly complement those seen in the hematology data. The specific goal was to empirically assess the effects of relocation stress in squirrel monkeys in terms of changes in the numbers and functions of various leukocyte subsets in the blood and the amount of time required for acclimating to their new environment. Such data will help to determine when newly arrived animals become available for use in research studies.

First-in-human randomised trial and follow-up study of Plasmodium falciparum blood-stage malaria vaccine BK-SE36 with CpG-ODN(K3)

BACKGROUND

BK-SE36 is blood-stage malaria vaccine candidate that is undergoing clinical trials. Here, the safety and immunogenicity of BK-SE36 with a novel adjuvant, CpG-ODN(K3) (thus, BK-SE36/CpG) was assessed in a phase 1a trial in Japan.

METHODS

An investigator-initiated, randomised, single-blind, placebo-controlled, dose-escalation study was conducted at Osaka University Hospital with 26 healthy malaria naïve Japanese male adults. The trial was conducted in two stages: Stage/Group 1, half-dose (n = 7 for BK-SE36/CpG and n = 3 for control) and Stage/Group 2, full-dose (n = 11 for BK-SE36/CpG and n = 5 for control). There were two intramuscular vaccinations 21 days apart for both half-dose (0.5 ml: 50 µg SE36 + 500 µg aluminum + 500 µg K3) and full-dose (1.0 ml: 100 µg SE36 + 1000 µg aluminum + 1000 µg K3). A one-year follow-up was done to monitor changes in autoimmune markers and vaccine-induced antibody response.

RESULTS

BK-SE36/CpG was well tolerated. Vaccination site reactions were similar to those observed with BK-SE36. During the trial and follow-up period, no subject had clinical evidence of autoimmune disease. The full-dose group had significantly higher titres than the half-dose group (Student's t-test, p = 0.002) at 21 days post-second vaccination. Antibody titres remained above baseline values during 12 months of follow-up. The vaccine induced antibody was mostly composed of IgG1 and IgM, and recognised epitopes close to the polyserine region located in the middle of SE36.

CONCLUSIONS

BK-SE36/CpG has an acceptable safety profile. Use of CpG-ODN(K3) greatly enhanced immunogenicity in malaria naïve Japanese adults when compared to BK-SE36 alone. The utility of BK-SE36/CpG is currently under evaluation in a malaria endemic setting in West Africa.

TRIAL REGISTRATION

JMACCT Clinical Trial Registry JMA-IIA00109.

Characteristic of K3 (CpG-ODN) as a Transcutaneous Vaccine Formulation Adjuvant

Transcutaneous immunization (TCI) is easy to use, minimally invasive, and has excellent efficacy in vaccines against infections. We focused on toll-like receptor (TLR) ligands as applicable adjuvants for transcutaneous formulations and characterized immune responses. TCI was performed using poke-and-patch methods, in which puncture holes are formed with a polyglycolic acid microneedle on the back skin of mice. Various TLR ligands were applied to the puncture holes and covered with an ovalbumin-loaded hydrophilic gel patch. During the screening process, K3 (CpG-oligonucleotide) successfully produced more antigen-specific antibodies than other TLR ligands and induced T helper (Th) 1-type polarization. Transcutaneously administered K3 was detected in draining lymph nodes and was found to promote B cell activation and differentiation, suggesting a direct transcutaneous adjuvant activity on B cells. Furthermore, a human safety test of K3-loaded self-dissolving microneedles (sdMN) was performed. Although a local skin reaction was observed at the sdMN application site, there was no systemic side reaction. In summary, we report a K3-induced Th1-type immune response that is a promising adjuvant for transcutaneous vaccine formulations using MN and show that K3-loaded sdMN can be safely applied to human skin.

Autoinflammation in addition to combined immunodeficiency: SLC29A3 gene defect

INTRODUCTION

H Syndrome is an autosomal recessive (AR) disease caused by defects in SLCA29A3 gene. This gene encodes the equilibrative nucleoside transporter, the protein which is highly expressed in spleen, lymph node and bone marrow. Autoinflammation and autoimmunity accompanies H Syndrome (HS).

AIM

The aim was to further elucidate the mechanisms of disease by molecular studies in a patient with SLC29A3 gene defect.

PATIENT AND METHODS

Mitochondrial dysfunction, lysosomal integrity, cytokine response in response to stimulation with different pattern recognition receptor ligands, and circulating cell-free mitochondrial-DNA(ccf-mtDNA) level in plasma were analyzed compared to controls to understand the cellular triggers of autoinflammation. RNA sequencing (RS) analyses were also performed in monocytes before/after culture with lipopolysaccharide.

RESULTS

Patient had progressive destructive arthropathy in addition to clinical findings due to combined immunodeficiency. Pure red cell aplasia (PRCA), vitiligo, diabetes, multiple autoantibody positivity, lymphopenia, increased acute phase reactants were present. Recent thymic emigrants (RTE), naïve T cells were decreased, effector memory CD4 + T cells, nonclassical inflammatory monocytes were increased. Patient's peripheral blood mononuclear cells secreted more IL-1β and IL-6, showed lysosomal disruption and significant mitochondrial dysfunction compared to healthy controls. Plasma ccf-mtDNA level was significantly elevated compared to age-matched controls (p < 0.05). RNA sequencing studies revealed decreased expression of NLR Family Caspase Recrument-Domain Containing 4(NLRC4), 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 4(PFKFB4), serine dehydratase(SDS), heparan sulfate(Glucosamine) 3-O-sulfotransferase 1(HS3ST1), neutral cholesterol ester hydrolase 1 (NCEH1), and interleukin-8 (IL-8) in patient's monocytes compared to controls. Longstanding PRCA, which is possibly autoimmune, resolved after initiating monthly intravenous immunoglobulins (IVIG) and low dose steroids to the patient.

CONCLUSION

Although autoinflammation and autoimmunity are reported in HS, by functional analyses we here show in the present patient that over-active inflammasome pathway in HS might be related with mitochondrial and lysosomal dysfunction. Increased plasma ccf-mtDNA may be used as a biomarker of inflammasomopathy in HS. HS should be included in the classification of primary immunodeficiency diseases.

Class C CpG Oligodeoxynucleotide Immunomodulatory Response in Aged Squirrel Monkey (Saimiri Boliviensis Boliviensis)

One means of stimulating the mammalian innate immune system is via Toll-like receptor 9 (TLR9) being exposed to unmethylated cytosine-phosphate-guanine (CpG) DNA, also known as pathogen-associated molecular patterns (PAMPs) of microbial origin. Synthetic CpG oligodeoxynucleotides (ODNs) with defined CpG motifs possess broad immunostimulatory properties that make CpG ODNs suitable as therapeutic interventions in a variety of human disease conditions, including Alzheimer's disease (AD). Rodent models are often used to preclinically test the effectiveness of CpG ODN therapeutic agents for AD and other disorders. However, the translatability of findings in such models is limited due to the significant difference of the expression of TLR9 between primates and rodents. The squirrel monkey (SQM), a New World non-human primate (NHP), is known to be phylogenetically proximate to humans, and develops extensive age-dependent cerebral amyloid angiopathy (CAA), a key pathological feature of AD. Hence, this model is currently being used to test AD therapeutics. In the present study, we conducted the first examination of Class C CpG ODN's immunomodulatory role in elderly SQMs. We documented the effectiveness of CpG ODN to trigger an immune response in an aged cohort whose immune system is senescent. The specific immune response patterns detected here closely resembled CpG ODN-induced immunostimulatory patterns observed in prior human studies. Overall, our findings provide critical data regarding the immunomodulatory potential of CpG ODN in this NHP model, allowing for future translational studies of innate immunity stimulation via TLR9 agonists for diverse indications, including AD therapeutics.

B cell-intrinsic MyD88 signaling controls IFN-γ-mediated early IgG2c class switching in mice in response to a particulate adjuvant

Adjuvants improve the potency of vaccines, but the modes of action (MOAs) of most adjuvants are largely unknown. TLR-dependent and -independent innate immune signaling through the adaptor molecule MyD88 has been shown to be pivotal to the effects of most adjuvants; however, MyD88's involvement in the TLR-independent MOAs of adjuvants is poorly understood. Here, using the T-dependent antigen NIPOVA and a unique particulate adjuvant called synthetic hemozoin (sHZ), we show that MyD88 is required for early GC formation and enhanced antibody class-switch recombination (CSR) in mice. Using cell-type-specific MyD88 KO mice, we found that IgG2c class switching, but not IgG1 class switching, was controlled by B cell-intrinsic MyD88 signaling. Notably, IFN-γ produced by various cells including T cells, NK cells, and dendritic cells was the primary cytokine for IgG2c CSR and B-cell intrinsic MyD88 is required for IFN-γ production. Moreover, IFN-γ receptor (IFNγR) deficiency abolished sHZ-induced IgG2c production, while recombinant IFN-γ administration successfully rescued IgG2c CSR impairment in mice lacking B-cell intrinsic MyD88. Together, our results show that B cell-intrinsic MyD88 signaling is involved in the MOA of certain particulate adjuvants and this may enhance our specific understanding of how adjuvants and vaccines work.

CpG enhances the immunogenicity of heterologous DNA-prime/protein-boost vaccination with the heavy chain myosin of Brugia malayi in BALB/c mice

The recombinant heavy chain myosin of Brugia malayi (Bm-Myo) has earlier been reported as a potent vaccine candidate in our lab. Subsequently, we further enhanced its efficacy employing heterologous DNA prime/protein boost (Myo-pcD+Bm-Myo) immunization approach that produced superior immune-protection than protein or DNA vaccination. In the present study, we evaluated the efficacy of heterologous prime boost vaccination in combination with CpG, synthetic oligodeoxynucleotides (ODN) adjuvant in BALB/c mice. The results showed that CpG/Myo-pcD+Bm-Myo conferred 84.5 ± 0.62% protection against B. malayi infective larval challenge which was considerably higher than Myo-pcD+Bm-Myo (75.6 ± 1.10%) following immunization. Although, both the formulations of immunization elicited robust production of specific IgG antibody and their isotypes (IgG1, IgG2a, IgG2b, and IgG3); however, CpG/Myo-pcD+Bm-Myo predominantly enhanced the level of IgG2a suggesting Th1 biased immune response in presence of CpG. Furthermore, spleen isolated from mice that immunized with CpG/Myo-pcD+Bm-Myo had greater accumulation of CD4+, CD8+, and CD19+ B cells and there was an augmented expression of co-stimulatory molecules CD40, CD86 on host dendritic cells (DCs). In contrast to Myo-pcD+Bm-Myo group, the splenocytes of CpG/Myo-pcD+Bm-Myo immunized mice developed comparatively higher pro-inflammatory cytokines IL-2 and IFN-γ leaving anti-inflammatory cytokine levels unchanged. Moreover, CpG formulation also upregulated the RNA expression of IL-12 and TNF-α in spleenocytes. The current findings suggest that the use of CpG would be more advantageous as an adjuvant predominantly in DNA/protein prime boost vaccine against Bm-Myo and presumably also for filarial infection.

Immune Mechanisms Involved in Schistosoma mansoni-Cathepsin B Vaccine Induced Protection in Mice

A vaccine against schistosomiasis would contribute to a long-lasting decrease in disease spectrum and transmission. Our previous protection studies in mice using Schistosoma mansoni Cathepsin B (Sm-Cathepsin B) resulted in 59 and 60% worm burden reduction with CpG oligodeoxynucleotides and Montanide ISA720 VG as adjuvants, respectively. While both formulations resulted in significant protection in a mouse model of schistosomiasis, the elicited immune responses differed. Therefore, in this study, we aimed to decipher the mechanisms involved in Sm-Cathepsin B vaccine-mediated protection. We performed in vitro killing assays using schistosomula stage parasites as targets for lung-derived leukocytes and serum obtained from mice immunized with Sm-Cathepsin B adjuvanted with either Montanide ISA 720 VG or CpG and from non-vaccinated controls. Lung cells and immune sera from the Sm-Cathepsin B + Montanide group induced the highest killing (63%) suggesting the importance of antibodies in cell-mediated parasite killing. By contrast, incubation with lung cells from Sm-Cathepsin B + CpG immunized animals induced significant parasite killing (53%) independent of the addition of immune serum. Significant parasite killing was also observed in the animals immunized with Sm-Cathepsin B alone (41%). For the Sm-Cathepsin B + Montanide group, the high level killing effect was lost after the depletion of CD4⁺ T cells or natural killer (NK) cells from the lung cell preparation. For the Sm-Cathepsin B + CpG group, high parasite killing was lost after CD8⁺ T cell depletion, and a reduction to 39% was observed upon depletion of NK cells. Finally, the parasite killing in the Sm-Cathepsin B alone group was lost after the depletion of CD4⁺ T cells. Our results demonstrate how the different Sm-Cathepsin B formulations influence the immune mechanisms involved in parasite killing and protection against schistosomiasis.

Carbonate Apatite Nanoparticles Act as Potent Vaccine Adjuvant Delivery Vehicles by Enhancing Cytokine Production Induced by Encapsulated Cytosine-Phosphate-Guanine Oligodeoxynucleotides

Vaccine adjuvants that can induce not only antigen-specific antibody responses but also Th1-type immune responses and CD8⁺ cytotoxic T lymphocyte responses are needed for the development of vaccines against infectious diseases and cancer. Of many available adjuvants, oligodeoxynucleotides (ODNs) with unmethylated cytosine-phosphate-guanine (CpG) motifs are the most promising for inducing the necessary immune responses, and these adjuvants are currently under clinical trials in humans. However, the development of novel delivery vehicles that enhance the adjuvant effects of CpG ODNs, subsequently increasing the production of cytokines such as type-I interferons (IFNs), is highly desirable. In this study, we demonstrate the potential of pH-responsive biodegradable carbonate apatite (CA) nanoparticles as CpG ODN delivery vehicles that can enhance the production of type-I IFNs (such as IFN-α) relative to that induced by CpG ODNs and can augment the adjuvant effects of CpG ODNs in vivo. In contrast to CpG ODNs, CA nanoparticles containing CpG ODNs (designated CA-CpG) induced significant IFN-α production by mouse dendritic cells and human peripheral blood mononuclear cells in vitro; and production of interleukin-12, and IFN-γ was higher in CA-CpG-treated groups than in CpG ODNs groups. In addition, treatment with CA-CpG resulted in higher cytokine production in draining lymph nodes than did treatment with CpG ODNs in vivo. Furthermore, vaccination with CA-CpG plus an antigen, such as ovalbumin or influenza virus hemagglutinin, resulted in higher antigen-specific antibody responses and CD8⁺ cytotoxic T lymphocyte responses in vivo, in an interleukin-12- and type-I IFN-dependent manner, than did vaccination with the antigen plus CpG ODNs; in addition, the efficacy of the vaccine against influenza virus was higher with CA-CpG as the adjuvant than with CpG ODNs as the adjuvant. These data show the potential of CA nanoparticles to serve as CpG ODN delivery vehicles that increase the production of cytokines, especially IFN-α, induced by CpG ODNs and thus augment the efficacy of CpG ODNs as adjuvants. We expect that the strategy reported herein will facilitate the design and development of novel adjuvant delivery vehicles for vaccines.

Immunization with the outer membrane proteins OmpK17 and OmpK36 elicits protection against Klebsiella pneumoniae in the murine infection model

Klebsiella pneumoniae is a Gram-negative bacterium that is increasingly reported as a serious nosocomial and community-acquired pathogen. In the current study, two K. pneumoniae antigens, OmpK17 and OmpK36, as well as their fusion protein cognate F36/17 were investigated as potential vaccine candidates in a murine infection model. Three immunoadjuvants, namely the Gram-positive Enhancer Matrix (GEM) adjuvant, synthetic hemozoin (Hz) adjuvant and incomplete Freund's adjuvant (IFA) were evaluated. Genes of OmpK17 and OmpK36 antigens as well as their fusion protein were cloned in Escherichia coli for recombinant expression. Mice were immunized thrice with the individual recombinant purified antigens adjuvanted with one of the three adjuvants. Two weeks after the last booster, animals were challenged with a lethal dose of K. pneumoniae and immune protection parameters were assessed. Animals immunized with GEM- or Hz-adjuvanted K. pneumoniae antigens did not show significant protection upon bacterial challenge. Animals immunized with subcutaneous IFA-adjuvanted antigens showed the best results with survival percentages of 50, 60 and 50% for groups immunized with OmpK17, OmpK36 and F36/17, respectively. Serum IgG1, rather than IgG2a, antibodies were the most prevalent following vaccination indicating bias towards T helper type 2 (Th2) immune response. Opsonophagocytic assays demonstrated significant percentage killing in case of animals immunized with IFA-adjuvanted antigens. Overall, OmpK17 and OmpK36 are promising vaccine antigens which are worthy of further optimization of the immunization conditions, particularly the used immunoadjuvants, in order to achieve full protection against K. pneumoniae.

An Antigen-Free, Plasmacytoid Dendritic Cell-Targeting Immunotherapy To Bolster Memory CD8+ T Cells in Nonhuman Primates

The priming, boosting, and restoration of memory cytotoxic CD8⁺ T lymphocytes by vaccination or immunotherapy in vivo is an area of active research. Particularly, nucleic acid-based compounds have attracted attention due to their ability to elicit strong Ag-specific CTL responses as a vaccine adjuvant. Nucleic acid-based compounds have been shown to act as anticancer monotherapeutic agents even without coadministration of cancer Ag(s); however, so far they have lacked efficacy in clinical trials. We recently developed a second-generation TLR9 agonist, a humanized CpG DNA (K3) complexed with schizophyllan (SPG), K3-SPG, a nonagonistic Dectin-1 ligand. K3-SPG was previously shown to act as a potent monoimmunotherapeutic agent against established tumors in mice in vivo. In this study we extend the monoimmunotherapeutic potential of K3-SPG to a nonhuman primate model. K3-SPG activated monkey plasmacytoid dendritic cells to produce both IFN-α and IL-12/23 p40 in vitro and in vivo. A single injection s.c. or i.v. with K3-SPG significantly increased the frequencies of activated memory CD8⁺ T cells in circulation, including Ag-specific memory CTLs, in cynomolgus macaques. This increase did not occur in macaques injected with free CpG K3 or polyinosinic-polycytidylic acid. Injection of 2 mg K3-SPG induced mild systemic inflammation, however, levels of proinflammatory serum cytokines and circulating neutrophil influx were lower than those induced by the same dose of polyinosinic-polycytidylic acid. Therefore, even in the absence of specific Ags, we show that K3-SPG has potent Ag-specific memory CTL response-boosting capabilities, highlighting its potential as a monoimmunotherapeutic agent for chronic infectious diseases and cancer.

Induction of humoural and cellular immunity by immunisation with HCV particle vaccine in a non-human primate model

OBJECTIVE

Although HCV is a major cause of chronic liver disease worldwide, there is currently no prophylactic vaccine for this virus. Thus, the development of an HCV vaccine that can induce both humoural and cellular immunity is urgently needed. To create an effective HCV vaccine, we evaluated neutralising antibody induction and cellular immune responses following the immunisation of a non-human primate model with cell culture-generated HCV (HCVcc).

DESIGN

To accomplish this, 10 common marmosets were immunised with purified, inactivated HCVcc in combination with two different adjuvants: the classically used aluminum hydroxide (Alum) and the recently established adjuvant: CpG oligodeoxynucleotide (ODN) wrapped by schizophyllan (K3-SPG).

RESULTS

The coadministration of HCVcc with K3-SPG efficiently induced immune responses against HCV, as demonstrated by the production of antibodies with specific neutralising activity against chimaeric HCVcc with structural proteins from multiple HCV genotypes (1a, 1b, 2a and 3a). The induction of cellular immunity was also demonstrated by the production of interferon-γ mRNA in spleen cells following stimulation with the HCV core protein. These changes were not observed following immunisation with HCVcc/Alum preparation. No vaccination-related abnormalities were detected in any of the immunised animals.

CONCLUSIONS

The current preclinical study demonstrated that a vaccine included both HCVcc and K3-SPG induced humoural and cellular immunity in marmosets. Vaccination with this combination resulted in the production of antibodies exhibiting cross-neutralising activity against multiple HCV genotypes. Based on these findings, the vaccine created in this study represents a promising, potent and safe prophylactic option against HCV.

Increased Plasmodium falciparum Parasitemia in Non-splenectomized Saimiri sciureus Monkeys Treated with Clodronate Liposomes

A major constraint in the study of Plasmodium falciparum malaria, including vaccine development, lies on the parasite's strict human host specificity and therefore the shortage of animal experimental models able to harbor human plasmodia. The best experimental models are neo-tropical primates of the genus Saimiri and Aotus, but they require splenectomy to reduce innate defenses for achieving high and consistent parasitemias, an important limitation. Clodronate-liposomes (CL) have been successfully used to deplete monocytes/macrophages in several experimental models. We investigated whether a reduction in the numbers of phagocytic cells by CL would improve the development of P. falciparum parasitemia in non-splenectomized Saimiri sciureus monkeys. Depletion of S. sciureus splenocytes after in vitro incubation with CL was quantified using anti-CD14 antibodies and flow cytometry. Non-infected and P. falciparum-infected S. sciureus were injected intravenously twice a week with either CL at either 0.5 or 1 mL (5 mg/mL) or phosphate buffered saline (PBS). Animals were monitored during infection and treated with mefloquine. After treatment and euthanasia, spleen and liver were collected for histological analysis. In vitro CL depleted S. sciureus splenic monocyte/macrophage population in a dose- and time-dependent manner. In vivo, half of P. falciparum-infected S. sciureus treated with CL 0.5 mL, and two-thirds of those treated with CL 1 mL developed high parasitemias requiring mefloquine treatment, whereas all control animals were able to self-control parasitemia without the need for antimalarial treatment. CL-treated infected S. sciureus showed a marked decrease in the degree of splenomegaly despite higher parasitemias, compared to PBS-treated animals. Histological evidence of partial monocyte/macrophage depletion, decreased hemozoin phagocytosis and decreased iron recycling was observed in both the spleen and liver of CL-treated infected S. sciureus. CL is capable of promoting higher parasitemia in P. falciparum-infected S. sciureus, associated with evidence of partial macrophage depletion in the spleen and liver. Macrophage depletion by CL is therefore a practical and viable alternative to surgical splenectomy in this experimental model.

Evaluation of marker gene expression as a potential predictive marker of leukopenic toxicity for inactivated influenza vaccines

The leukopenic toxicity test (LTT) is used to evaluate the safety and lot-to-lot consistency of influenza hemagglutinin split vaccine (HAv) and is included in the Japanese Minimum Requirements for Biological Products. LTT assesses the reduced leukocyte levels in murine peripheral blood after HAv administration. However, they require large numbers of animals, and therefore it would be beneficial to develop a more accurate and sensitive alternative method. In this study, we selected biomarkers of leukocyte reduction from 18 previously identified marker genes that were associated with an abnormal toxicity test (ATT). Among these 18 genes, the expressions of 15 marker genes were strongly associated with leukocyte reduction levels. A stepwise single addition multiple regression analysis was used to further extract the genes responsible for leukocyte reduction, with significant (p < 0.25) regression coefficients. The expression of 7 genes significantly predicted the leukocyte reduction. The prediction accuracy of this approach was approximately >90% (mean) for the direct measurement of leukocyte numbers. These results indicate that the expression of these 18 previously identified genes can provide information for both ATT and LTT.

Understanding malarial toxins

Recognized since antiquity, malaria is one of the most infamous and widespread infectious diseases in humans and, although the death rate during the last century has been diminishing, it still accounts for more than a half million deaths annually. It is caused by the Plasmodium parasite and typical symptoms include fever, shivering, headache, diaphoresis and nausea, all resulting from an excessive inflammatory response induced by malarial toxins released into the victim's bloodstream. These toxins are hemozoin and glycosylphosphatidylinositols. The former is the final product of the parasite's detoxification of haeme, a by-product of haemoglobin catabolism, while the latter anchor proteins to the Plasmodium cell surface or occur as free molecules. Currently, only two groups of antimalarial toxin drugs exist on the market, quinolines and artemisinins. As we describe, they both target biosynthesis of hemozoin. Other substances, currently in various phases of clinical trials, are directed towards biosynthesis of glycosylphosphatidylinositol, formation of hemozoin, or attenuation of the inflammatory response of the patient. Among the innovative approaches to alleviating the effects of malarial toxins, is the development of antimalarial toxin vaccines. In this review the most important lessons learned from the use of treatments directed against the action of malarial toxins in antimalarial therapy are emphasized and the most relevant and promising directions for future research in obtaining novel antimalarial agents acting on malarial toxins are discussed.

Toll-like receptor 9 ligand D-type oligodeoxynucleotide D35 as a broad inhibitor for influenza A virus replication that is associated with suppression of neuraminidase activity

The most effective drugs available to treat influenza are neuraminidase (NA) inhibitors, which provide important additional measures for the control of influenza virus infections. However, since the emergence of NA inhibitor-resistant viruses may compromise the clinical utility of this class of anti-influenza agents, it is very important to develop new anti-influenza agents which target a different region in NA responsible for its sensitivity from that for NA inhibitors and could be used to treat NA inhibitors-resistant isolates. The oligodeoxynucleotide D35, multimerized and aggregated, suppressed replication of influenza A viruses except A/WSN/33 (WSN). The suppressive viral replication by D35 depended on G-terad and multimer formation. The range of the suppressive viral replication at the late stage, including virus assembly and release from infected cells, was much larger than that at the initial stage, viral attachment and entry. D35 suppressed NA activity of influenza A viruses. Furthermore, replacing the NA gene of A/Puerto Rico/8/34 (PR8), in which viral replication was inhibited by D35 at the late stage, with the NA gene from WSN, in which viral replication was not inhibited, eliminated the D35-dependent suppression. D35 showed an additive anti-influenza effect with oseltamivir. It was also effective in vivo. These results suggest that the influenza virus NA mainly contributse to the D35-suppressible virus release from infected cells at the late stage. In addition, because administration of D35 into the virus-infected mice suppressed viral replication and weight loss, clinical application of D35 could be considered.

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The oligodeoxynucleotide D35 suppressed replication of some influenza A viruses.

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D35 inhibits viral replication at the late step which is dependent on NA activity.

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Antiviral mechanism by D35 is different from that by oseltamivir.

TLR 9 involvement in early protection induced by immunization with rPb27 against Paracoccidioidomycosis

Paracoccidioidomycosis is caused by fungi of the Paracoccidioides genus and constitutes the most prevalent deep mycosis in Latin America. Toll-like receptors promote immune response against infectious agents. Recently, it was reported that TLR9 is crucial for mice survival during the first 48 h of P. brasiliensis infection. In this study, we used CPG oligodeoxynucleotide motif as an adjuvant with and without rPb27 to immunize mice against Paracoccidioidomycosis. CPG adjuvant induced differential recruitment of lymphocytes in the inflammatory process and a lower recruitment of neutrophils. In addition, CPG induced the production of pro-inflammatory cytokines such as IL-1β, TNF-α, IL-6 and IL-12; increased phagocytic ability and microbicidal activity by macrophages; and induced differential production of lgG2a and lgG2b, subtypes of Ig. Knockout mice for TLR9 and IL-12 showed higher fungal loads and rates of mortality compared to control mice after 30 days of infection. The association between CPG and rPb27 induced a high level of protection against Paracoccidioidomycosis after the first 30 days of infection but not at 60 days. Our findings demonstrate that TLR 9 plays a role in the protection induced by immunization with rPb27 and confirms the importance of TLR9 in the initial protection against Paracoccidioidomycosis.

Recent advances in recombinant protein-based malaria vaccines

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Protein-based vaccines remain the cornerstone approach for B cell and antibody induction against leading target malaria antigens.

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Advances in antigen selection, immunogen design and epitope-focusing are advancing the field.

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New heterologous expression platforms are enabling cGMP production of next-generation protein vaccines.

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Next-generation antigens, protein-based immunogens and virus-like particle (VLP) delivery platforms are in clinical development.

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Protein-based vaccines will form part of a highly effective multi-component/multi-stage/multi-antigen subunit formulation against malaria.

Plasmodium parasites are the causative agent of human malaria, and the development of a highly effective vaccine against infection, disease and transmission remains a key priority. It is widely established that multiple stages of the parasite's complex lifecycle within the human host and mosquito vector are susceptible to vaccine-induced antibodies. The mainstay approach to antibody induction by subunit vaccination has been the delivery of protein antigen formulated in adjuvant. Extensive efforts have been made in this endeavor with respect to malaria vaccine development, especially with regard to target antigen discovery, protein expression platforms, adjuvant testing, and development of soluble and virus-like particle (VLP) delivery platforms. The breadth of approaches to protein-based vaccines is continuing to expand as innovative new concepts in next-generation subunit design are explored, with the prospects for the development of a highly effective multi-component/multi-stage/multi-antigen formulation seeming ever more likely. This review will focus on recent progress in protein vaccine design, development and/or clinical testing for a number of leading malaria antigens from the sporozoite-, merozoite- and sexual-stages of the parasite's lifecycle–including PfCelTOS, PfMSP1, PfAMA1, PfRH5, PfSERA5, PfGLURP, PfMSP3, Pfs48/45 and Pfs25. Future prospects and challenges for the development, production, human delivery and assessment of protein-based malaria vaccines are discussed.

Development of Nonaggregating Poly-A Tailed Immunostimulatory A/D Type CpG Oligodeoxynucleotides Applicable for Clinical Use

Immunostimulatory CpG ODNs have been developed and utilized as TLR9-dependent innate immune activators and vaccine adjuvants. Four different types of immunostimulatory CpG ODNs (A/D, B/K, C, and P type) have been reported. A/D type ODNs are characterized by high IFN-α production but intrinsically form aggregates, hindering its good manufacturing practice grade preparation. In this study, we developed several D35-derived ODNs (a commonly used A/D type ODN), which were modified with the addition of a phosphorothioate polynucleotide tail (such as dAs40), and examined their physical properties, solubility in saline, immunostimulatory activity on human PBMCs, and vaccine adjuvant potential in monkeys. We found that two modified ODNs including D35-dAs40 and D35core-dAs40 were immunostimulatory, similar to original D35 in human PBMCs, resulting in high IFN-α secretion in a dose-dependent manner. Physical property analysis by dynamic light scattering revealed that both D35-dAs40 and D35core-dAs40 did not form aggregates in saline, which is currently impossible for the original D35. Furthermore, D35-dAs40 and D35core-dAs40 worked as better vaccine adjuvant in monkeys. These results suggested that D35-dAs40 and D35core-dAs40 are two promising prototypes of nonaggregating A/D type ODN with advantages of ease of drug preparation for clinical applications as vaccine adjuvants or IFN-α inducing immunomodifiers.

Evaluation of the immune response and protective efficacy of Schistosoma mansoni Cathepsin B in mice using CpG dinucleotides as adjuvant

Schistosomiasis is the most important human helminth infection due to its impact on public health. Worldwide, schistosomiasis is estimated to infect at least 200 million individuals while 700 million are at risk. The clinical manifestations are chronic and significantly decrease an individual's quality of life. Infected individuals suffer from long-term organ pathologies including fibrosis which eventually leads to organ failure. The development of a vaccine against this parasitic disease would contribute to a long-lasting decrease in disease spectrum and transmission. Our group has chosen to target Schistosoma mansoni Cathepsin B as a prospective vaccine candidate. The recombinant protein was tested in the presence of synthetic oligodeoxynucleotides containing unmethylated CpG dinucleotides, which are Toll-like receptor 9 agonists known to stimulate a Th1 response. This formulation conferred a 59% decrease in worm burden as well as a reduction in egg burden. Hepatic egg burden and intestinal egg burden were decreased by 56% and 54% respectively. Immunizations with the formulation elicited robust production of Sm-Cathepsin B specific antibodies, both IgG1 and IgG2c but with the latter predominating. Furthermore, splenocytes isolated from the immunized animals, compared to control animals, had increased secretion levels of key Th1 cytokines, IFN-γ and TNF-α, as well as the chemokine CCL5 when stimulated with recombinant Sm-Cathepsin B. These results highlight the potential of Sm-Cathepsin B/CpG as a vaccine candidate against schistosomiasis.

TLR3 and TLR9 agonists improve postexposure vaccination efficacy of live smallpox vaccines

Eradication of smallpox and discontinuation of the vaccination campaign resulted in an increase in the percentage of unvaccinated individuals, highlighting the need for postexposure efficient countermeasures in case of accidental or deliberate viral release. Intranasal infection of mice with ectromelia virus (ECTV), a model for human smallpox, is curable by vaccination with a high vaccine dose given up to 3 days postexposure. To further extend this protective window and to reduce morbidity, mice were vaccinated postexposure with Vaccinia-Lister, the conventional smallpox vaccine or Modified Vaccinia Ankara, a highly attenuated vaccine in conjunction with TLR3 or TLR9 agonists. We show that co-administration of the TLR3 agonist poly(I:C) even 5 days postexposure conferred protection, avoiding the need to increase the vaccination dose. Efficacious treatments prevented death, ameliorated disease symptoms, reduced viral load and maintained tissue integrity of target organs. Protection was associated with significant elevation of serum IFNα and anti-vaccinia IgM antibodies, modulation of IFNγ response, and balanced activation of NK and T cells. TLR9 agonists (CpG ODNs) were less protective than the TLR3 agonist poly(I:C). We show that activation of type 1 IFN by poly(I:C) and protection is achievable even without co-vaccination, requiring sufficient amount of the viral antigens of the infective agent or the vaccine. This study demonstrated the therapeutic potential of postexposure immune modulation by TLR activation, allowing to alleviate the disease symptoms and to further extend the protective window of postexposure vaccination.

Protective properties of a fusion pneumococcal surface protein A (PspA) vaccine against pneumococcal challenge by five different PspA clades in mice

An increase in the appearance of nonvaccine serotypes in both children and adults with invasive pneumococcal disease (IPD) after introduction of pneumococcal conjugate vaccine represents a limitation of this vaccine. In this study, we generated three recombinant pneumococcal surface protein A (PspA) proteins comprising PspA families 1 and 2, and we examined the reactivity of antisera raised in mice immunized with a PspA fusion protein in combination with CpG oligonucleotides plus aluminum hydroxide gel. The protective effects of immunization with PspA fusion proteins against pneumococcal challenge by strains with five different PspA clades were also examined in mice. Flow cytometry demonstrated that PspA3+2-induced antiserum showed the greatest binding of PspA-specific IgG to all five challenge strains with different clades. PspA2+4- or PspA2+5-induced antiserum showed the lowest binding of PspA-specific IgG to clade 3. Immunization with PspA3+2 afforded significant protection against pneumococcal challenge by five strains with different clades in mice, but immunization with PspA2+4 or PspA2+5 failed to protect mice from pneumococcal challenge by strains with clades 1 and 3. The binding of PspA-specific IgG in antisera raised by three PspA fusion proteins was examined in 68 clinical isolates from adult patients with IPD. Immunization of mice with PspA3+2-induced antiserum with a high binding capacity for clinical isolates expressing clades 1-4, but not clade 5. Our results suggest that the PspA3+2 vaccine has an advantage over the PspA2+4 or PspA2+5 vaccine in terms of a broad range of cross-reactivity with clinical isolates and cross-protection against pneumococcal challenge in mice.

Immune Adjuvant Effect of Molecularly-defined Toll-Like Receptor Ligands

Vaccine efficacy is optimized by addition of immune adjuvants. However, although adjuvants have been used for over a century, to date, only few adjuvants are approved for human use, mostly aimed at improving vaccine efficacy and antigen-specific protective antibody production. The mechanism of action of immune adjuvants is diverse, depending on their chemical and molecular nature, ranging from non-specific effects (i.e., antigen depot at the immunization site) to specific activation of immune cells leading to improved host innate and adaptive responses. Although the detailed molecular mechanism of action of many adjuvants is still elusive, the discovery of Toll-like receptors (TLRs) has provided new critical information on immunostimulatory effect of numerous bacterial components that engage TLRs. These ligands have been shown to improve both the quality and the quantity of host adaptive immune responses when used in vaccine formulations targeted to infectious diseases and cancer that require both humoral and cell-mediated immunity. The potential of such TLR adjuvants in improving the design and the outcomes of several vaccines is continuously evolving, as new agonists are discovered and tested in experimental and clinical models of vaccination. In this review, a summary of the recent progress in development of TLR adjuvants is presented.

Hemozoin is a potent adjuvant for hemagglutinin split vaccine without pyrogenicity in ferrets

BACKGROUND

Synthetic hemozoin (sHZ, also known as β-hematin) from monomeric heme is a particle adjuvant which activates antigen-presenting cells (APCs), such as dendritic cells and macrophages, and enhances humoral immune responses to several antigens, including ovalbumin, human serum albumin, and serine repeat antigen 36 of Plasmodium falciparum. In the present study, we evaluated the adjuvanticity and pyrogenicity of sHZ as an adjuvant for seasonal trivalent hemagglutinin split vaccine (SV) for humans using the experimental ferret model.

METHOD

Ferrets were twice immunized with trivalent SV, SV with sHZ (SV/sHZ) or Fluad, composed of trivalent SV with MF59. Serum hemagglutination inhibition (HI) titers against three viral hemagglutinin (HA) antigens were measured at every week after the immunization. The pyrogenicity of SV/sHZ was examined by monitoring the body temperature of the immunized ferrets. To evaluate the protective efficacy of SV/sHZ, the immunized ferrets were challenged with influenza virus B infection, followed by measurement of viral titers in the nasal cavity and body temperature.

RESULTS

sHZ enhanced HI titers against three viral HA antigens in a dose-dependent manner, to an extent comparable to that of Fluad. The highest dose of sHZ (800 μg) immunized with SV conferred sterile protection against infection with heterologous Influenza B virus, without causing any pyrogenic reaction such as high fever.

CONCLUSION

In the present study, sHZ enhanced the protective efficacy of SV against influenza infection without inducing pyrogenic reaction, suggesting sHZ to be a promising adjuvant candidate for human SV.

An overview of adjuvant formulations and delivery systems

Adjuvants may promote immune responses: by recruiting professional antigen-presenting cells (APCs) to the vaccination site, increasing the delivery of antigens to APCs, or by activating APCs to produce cytokines and by triggering T cell responses. Aluminium salts have been effective at promoting protective humoral immunity; however, they are not effective in generating cell-mediated immunity. A number of different approaches have been developed to potentiate immune response and they have been partially successful. Research has been conducted into vaccine delivery systems (VDS); enhancing cross-presentation by targeting antigens to (APCs). Antigen discovery has increased over the past decade, and consequently, it has accelerated vaccine development demanding a new generation of VDS that combines different types of adjuvants into specific formulations with greater activity. The new approaches offer a wide spectrum of opportunities in vaccine research with direct applications in the near future.