Prospects for active and passive immunization against Staphylococcus aureus

Passive immunotherapy with specific IgG fraction against autolysin: Analogous protectivity in the MRSA infection with antibiotic therapy

Staphylococcus aureus is a leading infectious cause of life-threatening diseases in human beings, with no effective vaccine available to date against this bacterium. Treatment of methicillin-resistant S. aureus (MRSA) infections has become increasingly difficult because of the emergence of multidrug-resistant isolates. Immunotherapy represents a potential approach to prevent S. aureus-related infections. Autolysin is one of the virulence factors, which controls the growth, cell lysis, daughter-cell separation, and biofilm formation. Our study focused on passive immunization against MRSA infection. Herein, rabbit polyclonal IgG was produced following the preparation of r-autolysin. Specificity of IgG against r-autolysin was investigated by ELISA and western blotting assays. IgG fraction was prepared using sulfate ammonium precipitation, and the ability of antiserum to promote phagocytosis of bacteria was assessed by opsonophagocytosis assay. Then, passive immunization of mice was carried out with polyclonal IgG fraction and, mice were sacrificed three days after challenge and their kidneys, liver, and spleen were collected. Results exhibited that the passive immunization with rabbit polyclonal anti-IgG fraction tremendously improved survival rates of mice challenged by S. aureus as well as vancomycin treatment compared with the negative control groups. In addition, a remarkable decrease in bacterial numbers was observed in mice treated with rabbit polyclonal anti-IgG. Importantly, our findings demonstrated that passive immunotherapy and antibiotic therapy lead to decreased histopathological damage in mice infected by S. aureus as compared with control groups. Our results suggested that the passive immunization may result in the introduction of excellent strategies to control infections caused by MRSA, like antibiotic therapy.

Safety of Staphylococcus aureus four-antigen and three-antigen vaccines in healthy adults: A meta-analysis of randomized controlled trials

PURPOSE

Two new Staphylococcus aureus vaccines, S. aureus four-antigen (SA4Ag) and three-antigen (SA3Ag) vaccines, have good immunogenicity and tolerance. However, the safety of these vaccines is worth exploring. Here, we performed a meta-analysis to investigate the safety of SA3Ag and SA4Ag by evaluating systemic and local adverse events.

METHODS

The Medline, EMBASE, and Cochrane databases were searched for randomized clinical trials confirming the safety of SA4Ag and SA3Ag. Two investigators independently selected suitable trials, assessed trial quality, and extracted data.

RESULTS

Three studies comprising a total of 1,148 participants were included in this review. The two S. aureus vaccines did not increase systemic adverse events (relative ratio 1.1 [95% confidence interval 0.98, 1.24]), but increased the incidence of local adverse events (2.89 [2.15, 3.90]). However, the incidence of severe local adverse events (4.06 [0.78, 21.24]) did not rise significantly.

CONCLUSIONS

SA4Ag and SA3Ag have acceptable safety in adults.

Safety and immunogenicity of a booster dose of a 3-antigen Staphylococcus aureus vaccine (SA3Ag) in healthy adults: A randomized phase 1 study

OBJECTIVE

A 2-stage, phase 1, randomized, placebo-controlled study in healthy adults to assess immunogenicity and safety of a booster dose at three dose levels of a 3-antigen Staphylococcus aureus vaccine (SA3Ag) containing recombinant clumping factor A (ClfA) and capsular polysaccharides 5 and 8 (CP5 and CP8) conjugated to a diphtheria toxoid.

METHODS

Six months after initial single vaccination, in Stage 2, SA3Ag recipients were randomized (1:1) to booster vaccination or placebo, while Stage 1 placebo recipients received placebo again. Pre- and post-vaccination blood samples were analyzed.

RESULTS

In Stage 2 (n = 345), pre-booster CP5 and CP8 titers remained high with no increase post-booster. ClfA titers remained high after initial vaccination and increased post-booster, approaching the peak response to the initial dose. Post-booster local reactions were more frequent and of greater severity than reported after the initial vaccination, particularly for the high-dose level recipients. Post hoc analysis showed no dose-response pattern and no obvious association between diphtheria toxoid titers and local reactions after initial or booster vaccination.

CONCLUSION

Immune responses after the initial vaccination persisted for the 12 months studied, with little additional response after the booster dose at 6 months. Post-booster injection site reactions were more frequent and more severe but self-limiting. CLINICALTRIALS.

GOV IDENTIFIER

NCT01018641.

Protective Efficacy and Mechanism of Passive Immunization with Polyclonal Antibodies in a Sepsis Model of Staphylococcus aureus Infection

Staphylococcus aureus (S. aureus) is an opportunistic bacterial pathogen responsible for a diverse spectrum of human diseases, resulting in considerable yearly mortality rates. Due to its rapid acquisition of antibiotic resistance, it becomes increasingly difficult to cure S. aureus infections with conventional antibiotics. Immunotherapy represents a promising alternative strategy to prevent and/or treat the infection. In the present study, passive immunization with polyclonal antibodies targeting three possible S. aureus antigens, Hla, SEB and MntC (termed "SAvac-pcAb") after challenge with lethal dose of S. aureus resulted in reduced bacterial loads, inflammatory cell infiltration and decreased pathology, and was able to provide nearly complete protection in a murine sepsis model. In vitro studies confirmed the direct interaction of SAvac-pcAb with S. aureus bacteria. Additional studies validated that SAvac-pcAb contained both opsonic and neutralizing antibodies that contributed to its protective efficacy. The former mediated opsonophagocytosis in a neutrophil-dependent manner, while the later inhibited the biological functions of Hla and SEB, two major virulence factors secreted by S. aureus. Critically, we demonstrated that SAvac-pcAb was cross-reactive with different clinical strains of S. aureus. These results confirmed the efficacy for treatment of S. aureus infection by passive immunization as an important therapeutic option.

A randomized phase I study of the safety and immunogenicity of three ascending dose levels of a 3-antigen Staphylococcus aureus vaccine (SA3Ag) in healthy adults

BACKGROUND

Staphylococcus aureus is a common cause of healthcare-acquired morbidity and mortality and increased healthcare resource utilization. A prophylactic vaccine is being developed that may reduce this disease burden.

METHODS

Volunteers in good general health aged 50-85 (n=312) and 18-24 (n=96) years were randomized to receive a single intramuscular dose of one of three dose levels of a non-adjuvanted, 3-antigen S. aureus vaccine (SA3Ag) or placebo. SA3Ag antigens included capsular polysaccharides 5 and 8 (CP5 and CP8), each conjugated to cross-reactive material 197 (CRM197), and recombinant clumping factor A (ClfA). Safety, tolerability, and immunogenicity were evaluated.

RESULTS

At day 29 post-vaccination, robust immune responses were observed in both age cohorts at all three SA3Ag dose levels. In the primary analysis population, the 50- to 85-year age stratum, geometric mean-fold-rises in competitive Luminex(®) immunoassay antibody titers from baseline ranged from 29.2 to 83.7 (CP5), 14.1 to 31.0 (CP8), and 37.1 to 42.9 (ClfA), all (P<0.001) exceeding the pre-defined two-fold rise criteria. Similar rises in opsonophagocytic activity assay titers demonstrated functionality of the immune response. Most injection-site reactions were mild in severity and there were no substantial differences (SA3Ag vs. placebo) with regard to systemic or adverse events.

CONCLUSIONS

In this study of healthy adults aged 50-85 and 18-24 years, SA3Ag elicited a rapid and robust immune response and was well tolerated, with no notable safety concerns.

Progress in the development of effective vaccines to prevent selected gram-positive bacterial infections

Infections caused by virulent Gram-positive bacteria, such as Staphylococcus aureus, group B streptococci and group A streptococci, remain significant causes of morbidity and mortality despite progress in antimicrobial therapy. Despite significant advances in the understanding of the pathogenesis of infection caused by these organisms, there are only limited strategies to prevent infection. In this article, we review efforts to develop safe and effective vaccines that would prevent infections caused by these 3 pathogens.

The potential economic value of a Staphylococcus aureus vaccine for neonates

The continuing morbidity and mortality associated with Staphylococcus aureus (S. aureus) infections, especially methicillin-resistant S. aureus (MRSA) infections, have motivated calls to make S. aureus vaccine development a research priority. We developed a decision analytic computer simulation model to determine the potential economic impact of a S. aureus vaccine for neonates. Our results suggest that a S. aureus vaccine for the neonatal population would be strongly cost-effective (and in many situations dominant) over a wide range of vaccine efficacies (down to 10%) for vaccine costs (or=1%).

Staphylococcus aureus vaccine for orthopedic patients: an economic model and analysis

To evaluate the potential economic value of a Staphylococcus aureus vaccine for pre-operative orthopedic surgery patients, we developed an economic computer simulation model. At MRSA colonization rates as low as 1%, a $50 vaccine was cost-effective [<or=$50,000 per quality-adjusted life year (QALY) saved] at vaccine efficacy >or=30%, and a $100 vaccine at vaccine efficacy >or=70%. High MRSA prevalence (>or=25%) could justify a vaccine price as high as $1000. Our results suggest that a S. aureus vaccine for the pre-operative orthopedic population would be very cost-effective over a wide range of MRSA prevalence and vaccine efficacies and costs.

Vaccination as infection control: a pilot study to determine the impact of Staphylococcus aureus vaccination on nasal carriage

BACKGROUND

There is a critical need for an effective Staphylococcus aureus vaccine for the prevention of staphylococcal disease. In this study, we investigated the impact of S. aureus conjugate vaccine comprised of capsular polysaccharides 5 and 8 (CP5, CP8) on nasal colonization with S. aureus.

METHODS

Healthy adults recruited from one academic medical center to participate in a lot consistency trial of StaphVAX (S. aureus capsular polysaccharide 5 and 8 conjugate vaccine) were assessed for S. aureus nasal colonization at two weekly points prior to vaccination and again at six weeks post-vaccination. Serum anti-capsular antibody titers to CP5 and CP8 were obtained prior to vaccination and 42 days post-vaccination and measured by ELISA.

RESULTS

Thirty of 88 enrolled subjects (34%) had S. aureus isolated from at least one of the pre-immunization cultures. Of these, 20 were termed persistent carriers due to two positive cultures one week apart; 19 of the 20 were evaluable at Day 42. Baseline anti-CP8 concentrations were higher in persistent carriers of CP8+ S. aureus; however, baseline anti-CP5 levels were not significantly higher in individuals persistently colonized with CP5+ S. aureus. Statistically significant rises in antibody concentrations were noted after vaccination. At Day 42, 14 of 19 persistent carriers remained colonized; 5 subjects did not have evidence of S. aureus colonization. Ten additional subjects were positive for S. aureus at Day 42 who were not persistently colonized at baseline. Serum antibody concentrations were not statistically different between those with persistent carriage vs. those that lost carriage or those with newly acquired carriage.

CONCLUSIONS

Immune responses to vaccine were brisk and comparable in subjects with or without persistent colonization. Despite a substantial rise in anti-CP5 and anti-CP8 antibody concentrations post-vaccination, S. aureus nasal colonization rates did not significantly change.

Vaccines under study: non-HIV vaccines

The development of effective vaccines has been an amazing public health achievement and has resulted in countless lives being saved. Dermatologic therapy has recently been greatly advanced by the licensure of an effective human papillomavirus vaccine and herpes zoster vaccine. Despite these successes, many infectious diseases do not currently have a preventive vaccine. We review potential vaccines against selected infectious agents, including viruses, bacteria, fungi, and protozoa that have cutaneous and mucocutaneous manifestations. The road to licensure of a new vaccine begins with exhaustive preclinical and clinical studies, and many of these will fail before a successful vaccine candidate is approved. This article focuses on vaccines that have yet to be approved for licensure.

Vaccination with clumping factor A and fibronectin binding protein A to prevent Staphylococcus aureus infection of an aortic patch in mice

Staphylococcus aureus is a leading cause of ventricular assist device-related infections. This study evaluated the protective effect against S. aureus infection of active and passive immunization that targeted 3 proteins involved in bacterial attachment to a murine intra-aortic polyurethane patch. Active immunization of mice with a combination of the A domains of clumping factor A (ClfA), fibronectin-binding protein A (FnBPA) and fibronectin-binding protein B or passive immunization with monoclonal antibodies against ClfA and FnBPA resulted in a higher level of protection than that obtained by vaccination with either protein or antibody alone. The combination of antibodies or protein antigens appears to provide enhanced protection against prosthetic-device infection.

Investigational treatments for postoperative surgical site infections

Surgical site infections rank third among nosocomial infections, representing a global threat, associated with the emergence of multi-drug-resistant bacteria. The pharmaceutical industry has recently curtailed developmental programmes; however, the need for new compounds is extremely important. This article reviews new antimicrobials and immunointerventional targets for their potential to treat surgical site infections in comparison with recently licensed compounds. Daptomycin, dalbavancin, oritavancin, telavancin, iclaprim and ranbezolid seem to be promising agents against infections caused by Gram-positive pathogens and effectively address the present problems of multi-resistance in Gram-positive infections. Peptide deformylase inhibitors and immunostimulating agents open new perspectives in this field; however, very few compounds targeting Gram-negative problematic pathogens are in the pipeline of the future. Tigecycline (recently marketed) ceftobiprole, ceftaroline and doripenem seem to possess an extended anti-Gram-positive and -negative spectrum. Among these compounds, only doripenem demonstrates activity against Pseudomonas aeruginosa, for which there is a clear unmet need for new compounds, focusing on new targets.