James J. Mond

Towards a comprehensive view of immunoglobulin class switching

While it is well established that T cells play a prominent role in regulating Ig isotype switching in response to T-cell-dependent (TD) antigens, the events which control this process in response to antigens that do not recruit antigen-specific T cells (T-cell-independent (TI) antigens) is less clear. In this article, Clifford Snapper and James Mond suggest that the nature of the B-cell activator, in combination with cytokines produced by antigen non-specific cells, including macrophages, NK cells, and polyclonally activated B cells, may play an important role in the process leading to Ig isotype switching in response to TI antigens.

Lysostaphin Disrupts Staphylococcus aureus and Staphylococcus epidermidis Biofilms on Artificial Surfaces

ABSTRACT Staphylococci often form biofilms, sessile communities of microcolonies encased in an extracellular matrix that adhere to biomedical implants or damaged tissue. Infections associated with biofilms are difficult to treat, and it is estimated that sessile bacteria in biofilms are 1,000 to 1,500 times more resistant to antibiotics than their planktonic counterparts. This antibiotic resistance of biofilms often leads to the failure of conventional antibiotic therapy and necessitates the removal of infected devices. Lysostaphin is a glycylglycine endopeptidase which specifically cleaves the pentaglycine cross bridges found in the staphylococcal peptidoglycan. Lysostaphin kills Staphylococcus aureus within minutes (MIC at which 90% of the strains are inhibited [MIC90], 0.001 to 0.064 μg/ml) and is also effective against Staphylococcus epidermidis at higher concentrations (MIC90, 12.5 to 64 μg/ml). The activity of lysostaphin against staphylococci present in biofilms compared to those of other antibiotics was, however, never explored. Surprisingly, lysostaphin not only killed S. aureus in biofilms but also disrupted the extracellular matrix of S. aureus biofilms in vitro on plastic and glass surfaces at concentrations as low as 1 μg/ml. Scanning electron microscopy confirmed that lysostaphin eradicated both the sessile cells and the extracellular matrix of the biofilm. This disruption of S. aureus biofilms was specific for lysostaphin-sensitive S. aureus, as biofilms of lysostaphin-resistant S. aureus were not affected. High concentrations of oxacillin (400 μg/ml), vancomycin (800 μg/ml), and clindamycin (800 μg/ml) had no effect on the established S. aureus biofilms in this system, even after 24 h. Higher concentrations of lysostaphin also disrupted S. epidermidis biofilms.

Identification of In Vivo–Expressed Antigens of Staphylococcus aureus and Their Use in Vaccinations for Protection against Nasal Carriage

A spectrum of in vivo-expressed Staphylococcus aureus antigens was identified by probing bacteriophage expression libraries of S. aureus with serum samples from infected and uninfected individuals. Eleven recombinant antigenic proteins were produced, and specific antibody titers in a large collection of human serum samples were determined. Significantly increased concentrations of reactive immunoglobulin G (IgG) to 7 antigens were found in serum samples from ill individuals, compared with those in healthy individuals. Significantly higher concentrations of reactive IgG to 4 antigens, including iron-responsive surface determinant (Isd) A and IsdH, were found in serum samples from healthy individuals who were not nasal carriers of S. aureus, compared with those in healthy carriers. Vaccination of cotton rats with IsdA or IsdH protected against nasal carriage. Also, IsdA is involved in adherence of S. aureus to human desquamated nasal epithelial cells and is required for nasal colonization in the cotton rat model. Thus, vaccination with these antigens may prevent S. aureus carriage and reduce the prevalence of human disease.

Catalase (KatA) and Alkyl Hydroperoxide Reductase (AhpC) Have Compensatory Roles in Peroxide Stress Resistance and Are Required for Survival, Persistence, and Nasal Colonization in Staphylococcus aureus

Oxidative-stress resistance in Staphylococcus aureus is linked to metal ion homeostasis via several interacting regulators. In particular, PerR controls the expression of a regulon of genes, many of which encode antioxidants. Two PerR regulon members, ahpC (alkylhydroperoxide reductase) and katA (catalase), show compensatory regulation, with independent and linked functions. An ahpC mutation leads to increased H2O2 resistance due to greater katA expression via relief of PerR repression. Moreover, AhpC provides residual catalase activity present in a katA mutant. Mutation of both katA and ahpC leads to a severe growth defect under aerobic conditions in defined media (attributable to lack of catalase activity). This results in the inability to scavenge exogenous or endogenously produced H2O2, resulting in accumulation of H2O2 in the medium. This leads to DNA damage, the likely cause of the growth defect. Surprisingly, the katA ahpC mutant is not attenuated in two independent models of infection, which implies reduced oxygen availability during infection. In contrast, both AhpC and KatA are required for environmental persistence (desiccation) and nasal colonization. Thus, oxidative-stress resistance is an important factor in the ability of S. aureus to persist in the hospital environment and so contribute to the spread of human disease.

Lysostaphin Cream Eradicates Staphylococcus aureus Nasal Colonization in a Cotton Rat Model

ABSTRACT The anterior nares are a primary ecologic niche for Staphylococcus aureus, and nasal colonization by this opportunistic pathogen increases the risk of development of S. aureus infection. Clearance of S. aureus nasal colonization greatly reduces this risk. Mupirocin ointment is the current standard of care for clearance of S. aureus nasal colonization, but resistance to this antibiotic is emerging. Lysostaphin is a glycylglycine endopeptidase which specifically cleaves the cross-linking pentaglycine bridges in the cell walls of staphylococci. Lysostaphin is extremely staphylocidal (MIC at which 90% of isolates are inhibited, 0.001 to 0.064 μg/ml) and rapidly lyses both actively growing and quiescent S. aureus. This study demonstrates that a single application of 0.5% lysostaphin (actual dose, ∼150 μg of lysostaphin), formulated in a petrolatum-based cream, dramatically reduces S. aureus nasal colonization in 100% of animals tested and eradicates S. aureus nasal colonization in 93% of animals in a cotton rat model. A single dose of lysostaphin cream is more effective than a single dose of mupirocin ointment in eradicating S. aureus nasal colonization in this animal model. The lantibiotic peptide nisin, which has potent in vitro antistaphylococcal activity, was ineffective in reducing staphylococcal nasal carriage in this model. Nasal colonization was not reduced after three treatments with 5% nisin (∼1,500 μg/dose) in any of the treated animals. Lysostaphin formulated in cream may prove to be a superior alternative to mupirocin ointment for clearance of S. aureus nasal colonization.

Activation of soluble polysaccharides with 1-cyano-4-dimethylaminopyridinium tetrafluoroborate for use in protein—polysaccharide conjugate vaccines and immunological reagents

Neonates have poor immune responses to type 2 T-cell independent antigens (TI-2), such as polysaccharides and immunization of human infants with these antigens does not induce protective levels of serum antibodies. Conjugating proteins to TI-2 antigens converts the immune response to one which is T-cell dependent. We used an organic cyanylating reagent, 1-cyano-4-dimethylaminopyridinium tetrafluroborate (CDAP), to activate polysaccharides, in water, and subsequently react them with hexanediamine, in preparation for coupling proteins to the polysaccharide. CDAP activation of polysaccharide is rapid (< 2 min) and efficient. CDAP can be used to activate polysaccharides of diverse chemical natures, including dextrans and pneumococcal types 6, 14, 19 and 23. The critical parameters in CDAP activation of polysaccharides were the reagent concentrations and the pH. Activation can be performed over a broad alkaline pH range, with an optimum of pH 9-10. Furthermore, proteins can be coupled to CDAP-activated polysaccharides without the use of a spacer. Direct conjugation of protein to CDAP-activated polysaccharides can be performed under mildly alkaline conditions (pH 7-9). These conditions allow CDAP to be used with alkaline-sensitive polysaccharides and proteins. Mice immunized with BSA-pneumococcal type 14 polysaccharides (Pn14) conjugates, prepared either by direct conjugation or via a spacer, had high anti-Pn14 and anti-BSA serum antibody IgG1 titers, whereas no IgG1 antibody was induced to the unconjugated components. The ease of use and mild activating conditions should prove of value in using CDAP to prepare conjugate vaccines, as well as other immunologically useful reagents.

Improved Pharmacokinetics and Reduced Antibody Reactivity of Lysostaphin Conjugated to Polyethylene Glycol

ABSTRACT Lysostaphin is a 27-kDa endopeptidase that enzymatically disrupts the cell wall of Staphylococcus aureus and is a promising candidate for treating S. aureus blood-borne infections. It would be extremely useful to define conditions that would both increase lysostaphins in vivo half-life to allow for more effective tissue distribution and reduce its immunogenicity. Conjugation of polyethylene glycol (PEG) to lysostaphin (PEGylation) was investigated as a means to accomplish these goals. Rather than using linear forms of PEG, branched PEGs were chosen as the initial candidates because their large spatial volumes prevent entry of the polymer into the enzymes active sites, which could potentially reduce enzymatic function. Enzymatic activity for most PEGylated lysostaphins was reduced, but these compounds were still considerably active compared to unconjugated lysostaphin, with conjugates that had lower degrees of PEG modification having greater activity than those with higher degrees. PEGylated lysostaphin injected intravenously had a serum drug half-life of up to 24 h and resulted in much higher plasma drug concentrations than an equal dose of unconjugated lysostaphin, which had a half-life of less than 1 h. Finally, reduced binding affinity was shown for PEGylated lysostaphin in an antilysostaphin capture enzyme-linked immunosorbent assay, with some PEG-lysostaphin conjugates having binding affinities that were reduced more than 10-fold compared to unconjugated lysostaphin. These findings demonstrate that PEGylation of lysostaphin, while diminishing its S. aureus killing activity, results in prolonged serum drug persistence and reduced antibody binding. These features should significantly enhance lysostaphins therapeutic value as an intravenous “antibiotic” against S. aureus.

A randomized study of a monoclonal antibody (pagibaximab) to prevent staphylococcal sepsis

BACKGROUND: Pagibaximab, a human chimeric monoclonal antibody developed against lipoteichoic acid, was effective against staphylococci preclinically and seemed safe and well tolerated in phase 1 studies. OBJECTIVE: To evaluate the clinical activity, pharmacokinetics, safety, and tolerability of weekly pagibaximab versus placebo infusions in very low birth weight neonates. PATIENTS AND METHODS: A phase 2, randomized, double-blind, placebo-controlled study was conducted at 10 NICUs. Patients with a birth weight of 700 to 1300 g and 2 to 5 days old were randomly assigned to receive 3 once-a-week pagibaximab (90 or 60 mg/kg) or placebo infusions. Blood was collected for pharmacokinetics, bacterial killing, and safety analyses. Adverse event and clinical outcome data were collected. RESULTS: Eighty-eight patients received pagibaximab at 90 (n = 22) or 60 (n = 20) mg/kg or placebo (n = 46). Groups were not different in demography, mortality, or morbidity. Pagibaximab demonstrated linear pharmacokinetics, a 14.5-day half-life, and nonimmunogenicity. Definite staphylococcal sepsis occurred in 0%, 20%, and 13% (P < .11) and nonstaphylococcal sepsis occurred in 0%, 10%, and 15% (P < .15) of patients in the 90 mg/kg, 60 mg/kg, and placebo groups, respectively. In all patients with staphylococcal sepsis, estimated or observed pagibaximab levels were <500 μg/mL (target level) at infection. CONCLUSIONS: Three once-a-week 90 or 60 mg/kg pagibaximab infusions, in high-risk neonates, seemed safe and well tolerated. No staphylococcal sepsis occurred in infants who received 90 mg/kg. Target levels were only consistently achieved after 2 to 3 doses. Dose optimization should enhance protection.

Phase 1/2 Double-Blind, Placebo-Controlled, Dose Escalation, Safety, and Pharmacokinetic Study of Pagibaximab (BSYX-A110), an Antistaphylococcal Monoclonal Antibody for the Prevention of Staphylococcal Bloodstream Infections, in Very-Low-Birth-Weight Neonates

ABSTRACT Staphylococcal sepsis is a major cause of morbidity and mortality in very-low-birth-weight (VLBW) infants. A human chimeric monoclonal antibody, pagibaximab, was developed against staphylococcal lipoteichoic acid. We evaluated the safety, tolerability, and pharmacokinetics of pagibaximab in VLBW neonates. A phase 1/2, randomized, double-blind, placebo-controlled, dose escalation study was conducted in VLBW infants (700 to 1,300 g) 3 to 7 days old. Patients received two doses 14 days apart of intravenous pagibaximab (10, 30, 60, or 90 mg/kg of body weight) or placebo in a 2:1 ratio. Blood and urine samples were obtained pre- and postinfusion for analysis of safety and pharmacokinetics, and data on adverse events were gathered. Staphylococcal organisms causing sepsis were collected and evaluated. Fifty-three patients received at least one dose of pagibaximab or placebo. The average gestational age was 27.6 weeks; the average birth weight was 1,003 g. All serious adverse events were deemed unrelated or probably not drug related. Morbidity and mortality were similar across treatment groups. No evidence of immunogenicity of pagibaximab was detected. Pagibaximab pharmacokinetics was linear. The mean clearance (CL), volume of distribution, and elimination half-life of pagibaximab were independent of dose. The serum half-life was 20.5 ± 6.8 days. Pagibaximab enhanced serum opsonophagocytic activity. All staphylococci causing sepsis were opsonizable by pagibaximab. Two infusions of pagibaximab, administered 2 weeks apart to high-risk neonates appeared safe and tolerable, and pharmacokinetics were linear. Evaluation of more frequent doses, at the highest doses tested, in neonates at high-risk of staphylococcal sepsis, is warranted.

Lysostaphin eradicates established Staphylococcus aureus biofilms in jugular vein catheterized mice

OBJECTIVES Staphylococcus aureus infections associated with indwelling devices can be very difficult to treat due to the recalcitrant nature of bacterial biofilms to conventional antibiotics. Lysostaphin has been shown to clear S. aureus biofilms in vitro, and in this study we determined whether lysostaphin could also eradicate established S. aureus biofilms on implanted jugular vein catheters in mice. METHODS Jugular vein catheterized mice (four to six per group) challenged with S. aureus developed multiorgan infection and biofilm infections on the catheters. The infected mice with established biofilms received various doses of recombinant lysostaphin through the catheters, administered up to three times daily for up to 4 days. Some mice also received lysostaphin combined with nafcillin. Following treatment, mice were sacrificed and cfu on the catheter and in the liver and heart were determined. In another set of experiments, implanted jugular vein catheters in mice were pre-instilled with lysostaphin to determine whether this pre-treatment would protect the mice from biofilm infection. RESULTS AND CONCLUSIONS Lysostaphin administered at 15 mg/kg in combination with 50 mg/kg nafcillin three times per day for 4 days eradicated established S. aureus, including methicillin-resistant S. aureus, biofilms from implanted catheters and sterilized heart and liver infections of S. aureus-infected mice. Furthermore, a single pre-instillation of 10 mg/kg lysostaphin in catheters completely protected catheterized mice from a subsequent biofilm infection. These results demonstrate that lysostaphin is an effective treatment as well as prophylaxis for S. aureus biofilms on indwelling catheters.