Douglas Girgenti

Vaccine review: "Staphyloccocus aureus vaccines: Problems and prospects"

Staphylococcus aureus is a leading cause of both healthcare- and community-associated infections globally. S. aureus exhibits diverse clinical presentations, ranging from benign carriage and superficial skin and soft tissue infections to deep wound and organ/space infections, biofilm-related prosthesis infections, life-threatening bacteremia and sepsis. This broad clinical spectrum, together with the high incidence of these disease manifestations and magnitude of the diverse populations at risk, presents a high unmet medical need and a substantial burden to the healthcare system. With the increasing propensity of S. aureus to develop resistance to essentially all classes of antibiotics, alternative strategies, such as prophylactic vaccination to prevent S. aureus infections, are actively being pursued in healthcare settings. Within the last decade, the S. aureus vaccine field has witnessed two major vaccine failures in phase 3 clinical trials designed to prevent S. aureus infections in either patients undergoing cardiothoracic surgery or patients with end-stage renal disease undergoing hemodialysis. This review summarizes the potential underlying reasons why these two approaches may have failed, and proposes avenues that may provide successful vaccine approaches to prevent S. aureus disease in the future.

A Recombinant Clumping Factor A-Containing Vaccine Induces Functional Antibodies to Staphylococcus aureus That Are Not Observed after Natural Exposure

ABSTRACT Staphylococcus aureus is a Gram-positive pathogen that causes devastating disease and whose pathogenesis is dependent on interactions with host cell factors. Staphylococcal clumping factor A (ClfA) is a highly conserved fibrinogen (Fg)-binding protein and virulence factor that contributes to host tissue adhesion and initiation of infection. ClfA is being investigated as a possible component of a staphylococcal vaccine. We report the development of an Fg-binding assay that is specific for ClfA-mediated binding. Using the assay, we show that despite the presence of anti-ClfA antibodies, human sera from unvaccinated subjects are unable to prevent the binding of S. aureus to an Fg-coated surface. In contrast, antibodies elicited by a recombinant ClfA-containing vaccine were capable of blocking the ClfA-dependent binding of a diverse and clinically relevant collection of staphylococcal strains to Fg. These functional antibodies were also able to displace S. aureus already bound to Fg, suggesting that the ligand-binding activity of ClfA can be effectively neutralized through vaccination.

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.

Safety and immunogenicity of a 13-valent pneumococcal conjugate vaccine in healthy infants and toddlers given with routine pediatric vaccinations in Canada.

Background: The global distribution of pneumococcal disease and emergence of nonvaccine pneumococcal serotypes prompted the development of a 13-valent pneumococcal conjugate vaccine (PCV13), with broader coverage than 7-valent PCV (PCV7). This study compared compatibility of PCV13 and PCV7 with concurrently administered diphtheria, tetanus, acellular pertussis, inactivated poliovirus, Haemophilus influenzae type b vaccine, and meningococcal C conjugate vaccine (menC), and assessed the safety and immunogenicity of PCV13. Methods: In this double-blind, randomized trial, children received PCV7 or PCV13 at 2, 4, 6, and 12 months with routine vaccinations. One month following the infant series and toddler dose, the responses to Hib, pertussis, menC, and specific pneumococcal serotypes were measured. Safety and tolerability were assessed daily for 4 days by parents. Results: Subjects received PCV13 (n = 300) or PCV7 (n = 303); immunogenicity assessment was completed in 265 and 268 subjects, respectively. There were no statistically significant differences between the groups in responses to Hib, pertussis, or menC after primary or booster vaccinations. More than 95% of subjects in the PCV13 group produced >0.35 &mgr;g/mL antibody to each pneumococcal serotype 1 month after the third dose, except with serotypes 23F (90%), 3 (80%), and 5 (87%). After the fourth dose, 98% to 100% of subjects achieved serotype-specific antibody concentrations >0.35 &mgr;g/mL, except for serotype 3 (85%). Safety and tolerability did not differ between groups with respect to local or systemic side effects. Conclusions: Responses to routine childhood vaccines did not differ with PCV7 or PCV13 coadministration. Serotype-specific pneumococcal antibody concentrations were protective. The safety profile of PCV13 was favorable.

Evaluation of Approaches to Monitor Staphylococcus aureus Virulence Factor Expression during Human Disease

Staphylococcus aureus is a versatile pathogen of medical significance, using multiple virulence factors to cause disease. A prophylactic S. aureus 4-antigen (SA4Ag) vaccine comprising capsular polysaccharide (types 5 and 8) conjugates, clumping factor A (ClfA) and manganese transporter C (MntC) is under development. This study was designed to characterize S. aureus isolates recovered from infected patients and also to investigate approaches for examining expression of S. aureus vaccine candidates and the host response during human infection. Confirmation of antigen expression in different disease states is important to support the inclusion of these antigens in a prophylactic vaccine. Hospitalized patients with diagnosed S. aureus wound (27) or bloodstream (24) infections were enrolled. Invasive and nasal carriage S. aureus isolates were recovered and characterized for genotypic diversity. S. aureus antigen expression was evaluated directly by real-time, quantitative, reverse-transcriptase PCR (qRT-PCR) analysis and indirectly by serology using a competitive Luminex immunoassay. Study isolates were genotypically diverse and all had the genes encoding the antigens present in the SA4Ag vaccine. S. aureus nasal carriage was detected in 55% of patients, and in those subjects 64% of the carriage isolates matched the invasive strain. In swab samples with detectable S. aureus triosephosphate isomerase housekeeping gene expression, RNA transcripts encoding the S. aureus virulence factors ClfA, MntC, and capsule polysaccharide were detected by qRT-PCR. Antigen expression was indirectly confirmed by increases in antibody titer during the course of infection from acute to convalescent phase. Demonstration of bacterial transcript expression together with immunological response to the SA4Ag antigens in a clinically relevant patient population provides support for inclusion of these antigens in a prophylactic vaccine.

Safety, tolerability, and immunogenicity of a 4-antigen Staphylococcus aureus vaccine (SA4Ag): Results from a first-in-human randomised, placebo-controlled phase 1/2 study

BACKGROUND A prophylactic Staphylococcus aureus four-antigen vaccine (SA4Ag) is under development for prevention of invasive S. aureus disease. A preliminary S. aureus three-antigen vaccine (SA3Ag) was reformulated to include a novel manganese transporter protein (MntC or rP305A). This study describes the first-in-human dose-finding, safety, and immunogenicity results for SA4Ag. METHODS In this double-blind, sponsor-unblind, placebo-controlled, phase 1/2 study, 454 healthy adults aged 18-64years were randomised to receive a single dose of one of three formulations of SA4Ag with escalating dose levels of rP305A or placebo. Functional immune responses were measured using opsonophagocytic activity (OPA) killing and fibrinogen-binding inhibition (FBI) assays; antigen-specific immunogenicity was assessed using a four-plex competitive Luminex® immunoassay (cLIA). RESULTS A high proportion of SA4Ag recipients met the pre-defined antibody thresholds for each antigen at Day 29. A substantial and dose-level dependent immune response was observed for rP305A, with up to 18-fold rises in cLIA titres at Day 29. Robust functional responses were demonstrated, with >80-fold and >20-fold rises in OPA assay titres at Day 29 using S. aureus strains expressing capsular polysaccharide serotypes 5 and 8, respectively. Durable antibody responses were observed through month 12, gradually waning from peak levels achieved by days 11-15. SA4Ag was well tolerated, and no vaccine-related serious adverse events were reported. CONCLUSIONS Single-dose vaccination of SA4Ag in healthy adults aged 18-64years safely induced rapid and robust functional immune responses that were durable through month 12, supporting further development of this vaccine. TRIAL REGISTRATION NUMBER NCT01364571.

Safety, tolerability, and immunogenicity of a single dose 4-antigen or 3-antigen Staphylococcus aureus vaccine in healthy older adults: Results of a randomised trial

BACKGROUND The decline in immune function with age is a challenge to vaccine development. Following an initial study in adults aged 18-64years, this study evaluated the safety and immunogenicity of Staphylococcus aureus (S. aureus) 4-antigen (SA4Ag) and 3-antigen (SA3Ag) vaccine in older adults. SA3Ag included capsular polysaccharide serotypes 5 and 8 (CP5 and CP8) conjugated to the nontoxic mutant form of diphtheria toxin (CRM197) and a recombinant version of clumping factor A (ClfA). SA4Ag included these antigens, with the addition of a recombinant manganese transporter C (rP305A or MntC). Both vaccines were unadjuvanted. METHODS In this double-blind, sponsor-unblinded, placebo-controlled, phase 1/2 study, 284 healthy adults (aged 65-85years) were randomised to receive a single dose of one of three formulations of SA4Ag with escalating dose levels of rP305A, SA3Ag, or placebo. Functional immune responses were measured using opsonophagocytic activity (OPA) killing and fibrinogen-binding inhibition (FBI) assays; immunogenicity was also assessed using a competitive Luminex® immunoassay (cLIA). T-cell responses were measured in a small subgroup of subjects using intracellular cytokine staining (ICS) assays. RESULTS The results demonstrated rapid and robust functional immune responses to all antigens in healthy older adults. A high proportion of active vaccine recipients met the pre-defined antibody thresholds for each antigen at Day 29. SA4Ag elicited a dose-level response to rP305A with up to a 13-fold rise in cLIA titres at Day 29. Opsonophagocytic activity (OPA) assays showed >50- and >20-fold rises in functional titres using S. aureus strains expressing CP5 and CP8, respectively, at Day 29. T-cell cytokine responses were not substantially above background levels. There were no safety concerns in this study population and no increases in adverse events with higher rP305A dose levels. CONCLUSIONS Single-dose vaccination of SA4Ag and SA3Ag in healthy adults aged 65-85years safely induced rapid and robust functional immune responses, supporting further development of SA4Ag for the prevention of S. aureus disease in adults up to age 85years. TRIAL REGISTRATION NUMBER NCT01643941.

Immunogenicity, safety and tolerability of 3 lots of 13-valent pneumococcal conjugate vaccine given with routine pediatric vaccinations in the United States.

Background: The 7-valent pneumococcal conjugate vaccine (PCV7; serotypes 4, 6B, 9V, 14, 18C, 19F and 23F) has decreased invasive pneumococcal disease incidence. This study was performed to support licensure of a 13-valent pneumococcal conjugate vaccine (PCV13), which expands serotype coverage to include serotypes 1, 3, 5, 6A, 7F and 19A. This study assessed the immunogenicity, safety and manufacturing consistency of PCV13. Methods: Randomized, double-blind, multicenter trial. Healthy United States infants were randomized 2:2:2:1 to receive 1 of 3 lots of PCV13 or PCV7, along with routine US pediatric vaccines at ages 2, 4 and 6 months (infant series), and 12 months (toddler dose). Results: Among 1709 vaccinated infants, 1 month postinfant series and 1 month posttoddler dose, immunoglobulin G geometric mean concentrations (GMCs) were within 2-fold among the PCV13 lots, meeting equivalence criteria for all 13 serotypes. In a post hoc analysis, based on percent responders at ≥0.35 &mgr;g/mL postinfant series and immunoglobulin G GMC ratios postinfant series and posttoddler dose, noninferiority criteria were met for combined PCV13 lots compared with PCV7 for all common serotypes. Posttoddler dose immunoglobulin G GMCs were higher than postinfant series GMCs for all serotypes. Local reactions and fevers were generally mild; incidences of local reactions, systemic events and adverse events were generally similar between groups. Conclusions: PCV13 can be manufactured in a manner that elicits consistent immune responses. PCV13 provides increased serotype coverage and immunogenicity that is noninferior to PCV7 and has a safety profile similar to PCV7 when given with routine pediatric vaccines.

Antibody responses to routine pediatric vaccines administered with 13-valent pneumococcal conjugate vaccine.

Background: A 13-valent pneumococcal conjugate vaccine (PCV13) has been licensed in >100 countries to broaden coverage against pneumococcal disease. We assessed whether PCV13 interferes with immune responses to concomitantly administered routine pediatric vaccines. Methods: Healthy US infants were randomly assigned in 2 studies to receive PCV13 or 7-valent PCV (PCV7) at age 2, 4 and 6 months concomitantly with diphtheria, tetanus, acellular pertussis, inactivated polio virus, hepatitis B and Haemophilus influenzae type b, and at age 12–15 months with measles, mumps, rubella, varicella and hepatitus A. Antibodies to pertussis antigens, diphtheria, tetanus toxoid, poliovirus types 1–3, Haemophilus influenzae type b polyribosylribitol phosphate capsular polysaccharide and polyribosylribitol phosphate capsular polysaccharide were measured 1 month after the infant series; measles, mumps, rubella, varicella and polyribosylribitol phosphate capsular polysaccharide were determined 1 month after the toddler dose. Both the percentages of responders (subjects reaching a prespecified antibody concentration) and immunoglobulin G antibody geometric mean concentrations/titers were calculated for each concomitant vaccine antigen. Results: Not all assays were performed on all subjects. Data were available from 153 to 239 infants and 163–230 toddlers in the PCV13 group and 173–240 infants and 167–214 toddlers in the PCV7 group. One month after both infant series and the toddler dose, noninferiority criteria were met for all antigens with respect to percentage of responders in both PCV7 and PCV13 groups. Immunoglobulin G antibody geometric mean concentration/titer ratios (PCV13/PCV7) were 0.91–1.33 and 0.83–1.03 at 1 month after the infant series and toddler dose, respectively, and met predetermined noninferiority criteria. Conclusions: Immune responses to routine pediatric vaccines concomitantly administered with PCV13 were noninferior to responses achieved when administered with PCV7.

A CCR2/5 Inhibitor, PF-04634817, Is Inferior to Monthly Ranibizumab in the Treatment of Diabetic Macular Edema

Purpose Ligands for the proinflammatory C-C chemokine receptor types 2 and 5 (CCR2 and CCR5) are elevated in the eyes of patients with diabetic macular edema (DME). We evaluated the efficacy and safety of PF-04634817, an oral CCR2/5 dual antagonist, versus intravitreal ranibizumab, in adult subjects with DME. Methods In this phase II, randomized, placebo-controlled, double-masked study, eligible subjects (≥18 years of age) had type 1 or 2 diabetes and DME with best-corrected visual acuity (BCVA) of 20/32 or worse (letter score ≤ 78), and up to 20/320 or better (≥24 letter score), in the study eye. Subjects were assigned randomly 1:1 to once-daily (QD) oral PF-04634817 200 mg plus masked sham therapy as placebo or monthly intravitreal ranibizumab 0.3/0.5 mg plus QD oral placebo. The primary objective was to evaluate the efficacy of PF-04634817 compared with ranibizumab in change from baseline in BCVA after 12 weeks in a noninferiority design. Noninferiority was based on BCVA 80% confidence interval (CI): there had to be a less than three letter loss in the PF-04634817 arm compared with the ranibizumab arm. Results A total of 199 subjects were randomized. Least squares mean difference in change in BCVA from baseline to week 12 in the study eye for the PF-04634817 arm was -2.41 letters (80% CI: -3.91, -0.91; P = 0.04) compared with ranibizumab. PF-04634817 was well tolerated. Conclusions Treatment with oral CCR2/5 receptor dual antagonist PF-04634817 was associated with a modest improvement in BCVA, but did not meet the predefined noninferiority criteria compared with intravitreal ranibizumab.