Mortality among recipients of the Merck V710 Staphylococcus aureus vaccine after postoperative S. aureus infections: an analysis of possible contributing host factors.

In a blinded randomized trial, preoperative receipt of the Merck V710 Staphylococcus aureus vaccine was associated with a higher mortality rate than placebo in patients who later developed postoperative S. aureus infections. Of the tested patients, all 12 V710 recipients (but only 1 of 13 placebo recipients) with undetectable serum IL2 levels prior to vaccination and surgery died after postoperative S. aureus infection. The coincidence of 3 factors (low prevaccination IL-2 levels, receipt of V710, and postoperative S. aureus infection) appeared to substantially increase mortality in our study population after major cardiothoracic surgery. Furthermore, 9 of the 10 V710 recipients with undetectable preoperative IL17a levels and postoperative S. aureus infections died. Although the current study is hypothesis-generating and the exact pathophysiology remains speculative, these findings raise concern that immune predispositions may adversely impact the safety and efficacy of staphylococcal vaccines actively under development. The potential benefits of an effective vaccine against S. aureus justify continued but cautious pursuit of this elusive goal.

Effect of an investigational vaccine for preventing Staphylococcus aureus infections after cardiothoracic surgery: a randomized trial.

IMPORTANCE: Infections due to Staphylococcus aureus are serious complications of cardiothoracic surgery. A novel vaccine candidate (V710) containing the highly conserved S. aureus iron surface determinant B is immunogenic and generally well tolerated in volunteers. OBJECTIVE: To evaluate the efficacy and safety of preoperative vaccination in preventing serious postoperative S. aureus infection in patients undergoing cardiothoracic surgery. DESIGN, SETTING, AND PARTICIPANTS: Double-blind, randomized, event-driven trial conducted between December 2007 and August 2011 among 8031 patients aged 18 years or older who were scheduled for full median sternotomy within 14 to 60 days of vaccination at 165 sites in 26 countries. INTERVENTION: Participants were randomly assigned to receive a single 0.5-mL intramuscular injection of either V710 vaccine, 60 µg (n = 4015), or placebo (n = 4016). MAIN OUTCOME MEASURES: The primary efficacy end point was prevention of S. aureus bacteremia and/or deep sternal wound infection (including mediastinitis) through postoperative day 90. Secondary end points included all S. aureus surgical site and invasive infections through postoperative day 90. Three interim analyses with futility assessments were planned. RESULTS: The independent data monitoring committee recommended termination of the study after the second interim analysis because of safety concerns and low efficacy. At the end of the study, the V710 vaccine was not significantly more efficacious than placebo in preventing either the primary end points (22/3528 V710 vaccine recipients [2.6 per 100 person-years] vs 27/3517 placebo recipients [3.2 per 100 person-years]; relative risk, 0.81; 95% CI, 0.44-1.48; P = .58) or secondary end points despite eliciting robust antibody responses. Compared with placebo, the V710 vaccine was associated with more adverse experiences during the first 14 days after vaccination (1219/3958 vaccine recipients [30.8%; 95% CI, 29.4%-32.3%] and 866/3967 placebo recipients [21.8%; 95% CI, 20.6%-23.1%], including 797 [20.1%; 95% CI, 18.9%-21.4%] and 378 [9.5%; 95% CI, 8.6%-10.5%] with injection site reactions and 66 [1.7%; 95% CI, 1.3%-2.1%] and 51 [1.3%; 95% CI, 1.0%-1.7%] with serious adverse events, respectively) and a significantly higher rate of multiorgan failure during the entire study (31 vs 17 events; 0.9 [95% CI, 0.6-1.2] vs 0.5 [95% CI, 0.3-0.8] events per 100 person-years; P = .04). Although the overall incidence of vaccine-related serious adverse events (1 in each group) and the all-cause mortality rate (201/3958 vs 177/3967; 5.7 [95% CI, 4.9-6.5] vs 5.0 [95% CI, 4.3-5.7] deaths per 100 person-years; P = .20) were not statistically different between groups, the mortality rate in patients with staphylococcal infections was significantly higher among V710 vaccine than placebo recipients (15/73 vs 4/96; 23.0 [95% CI, 12.9-37.9] vs 4.2 [95% CI, 1.2-10.8] per 100 person-years; difference, 18.8 [95% CI, 8.0-34.1] per 100 person-years). CONCLUSIONS AND RELEVANCE: Among patients undergoing cardiothoracic surgery with median sternotomy, the use of a vaccine against S. aureus compared with placebo did not reduce the rate of serious postoperative S. aureus infections and was associated with increased mortality among patients who developed S. aureus infections. These findings do not support the use of the V710 vaccine for patients undergoing surgical interventions. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT00518687.

A recombinant 63-kDa form of Bacillus anthracis protective antigen produced in the yeast Saccharomyces cerevisiae provides protection in rabbit and primate inhalational challenge models of anthrax infection.

Infection by Bacillus anthracis is preventable by prophylactic vaccination with several naturally derived and recombinant vaccine preparations. Existing data suggests that protection is mediated by antibodies directed against the protective antigen (PA) component of the anthrax toxin complex. PA is an 83-kDa protein cleaved in vivo to yield a biologically active 63-kDa protein. In an effort to evaluate the potential of yeast as an expression system for the production of recombinant PA, and to determine if the yeast-purified rPA63 can protect from a lethal inhalational challenge, the sequence of the 63-kDa form of PA was codon-optimized and expressed in the yeast Saccharomyces cerevisiae. Highly purified rPA63 isolated from Saccharomyces under denaturing conditions demonstrated reduced biological activity in a macrophage-killing assay compared to non-denatured rPA83 purified from Escherichia coli. Rabbits and non-human primates (NHP) immunized with rPA63 and later challenged with a lethal dose of B. anthracis spores were generally protected from infection. These results indicate that epitopes present in the 63-kDa from of PA can protect rabbits and non-human primates from a lethal spore challenge, and further suggest that a fully functional rPA63 is not required in order to provide these epitopes.

Isolation, structural characterization, and immunological evaluation of a high-molecular-weight exopolysaccharide from Staphylococcus aureus.

Colonization of implanted medical devices by coagulase-negative staphylococci such as Staphylococcus epidermidis is mediated by the bacterial polysaccharide intercellular adhesin (PIA), a polymer of beta-(1-->6)-linked glucosamine substituted with N-acetyl and O-succinyl constituents. The icaADBC locus containing the biosynthetic genes for production of PIA has been identified in both S. epidermidis and S. aureus. Whereas it is clear that PIA is a constituent that contributes to the virulence of S. epidermidis, it is less clear what role PIA plays in infection with S. aureus. Recently, identification of a novel polysaccharide antigen from S. aureus termed poly N-succinyl beta-(1-->6)-glucosamine (PNSG) has been reported. This polymer was composed of the same glycan backbone as PIA but was reported to contain a high proportion of N-succinylation rather than acetylation. We have isolated a glucosamine-containing exopolysaccharide from the constitutive over-producing MN8m strain of S. aureus in order to prepare polysaccharide-protein conjugate vaccines. In this report we demonstrate that MN8m produced a high-molecular-weight (>300,000 Da) polymer of beta-(1-->6)-linked glucosamine containing 45-60% N-acetyl, and a small amount of O-succinyl (approx 10% mole ratio to monosaccharide units). By detailed NMR analyses of polysaccharide preparations, we show that the previous identification of N-succinyl was an analytical artifact. The exopolysaccharide we have isolated is active in in vitro hemagglutination assays and is immunogenic in mice when coupled to a protein carrier. We therefore conclude that S. aureus strain MN8m produces a polymer that is chemically and biologically closely related to the PIA produced by S. epidermidis.