IgG subclass distribution of antibodies after vaccination of adults with pneumococcal conjugate vaccines

Humoral and cellular immune responses induced by serogroup W135 meningococcal conjugate and polysaccharide vaccines

Investigating the mechanisms by which W135 meningococcal conjugate (PSW135-TT) activates adaptive immune responses in mice can provide a comprehensive understanding of the immune mechanisms of bacterial polysaccharide conjugate vaccines. We compared B-cell and T-cell immune responses immunized with W135 meningococcal capsular polysaccharides (PSW135), tetanus toxoid (TT) and PSW135-TT in mice. The results showed that PSW135-TT could induce higher PSW135-specific and TT-specific IgG antibodies with a significant enhancement after two doses. All serum antibodies immunized with PSW135- TT had strong bactericidal activity, whereas none of the serum antibodies immunized with PSW135 had bactericidal activity. Besides, IgM and IgG antibodies immunized with PSW135-TT after two doses were positively correlated with the titer of bactericidal antibodies. We also found Th cells favored Th2 humoral immune responses in PSW135-TT, PSW135, and TT-immunized mice, especially peripheral blood lymphocytes. Furthermore, PSW135-TT and TT could effectively activate bone marrow derived dendritic cells (BMDCs) and promote BMDCs to highly express major histocompatibility complex Ⅱ (MHCⅡ), CD86 and CD40 molecules in mice, whereas PSW135 couldn't. These data verified the typical characteristics of PSW135-TT and TT as T cell dependent antigen (TD-Ag) and PSW135 as T cell independent antigen (TI-Ag), which will be very helpful for further exploration of the immune mechanism of polysaccharide-protein conjugate vaccines and improvement of the quality of bacterial polysaccharide conjugate vaccines in future.

Disturbances in the IgG Antibody Profile in HIV-Exposed Uninfected Infants Associated with Maternal Factors

Over the last 20 years, the incidence of vertical HIV transmission has decreased from 25%-42% to less than 1%. Although there are no signs of infection, the health of HIV-exposed uninfected (HEU) infants is notoriously affected during the first months of life, with opportunistic infections being the most common disease. Some studies have reported effects on the vertical transfer of antibodies, but little is known about the subclass distribution of these antibodies. We proposed to evaluate the total IgG concentration and its subclasses in HIV+ mothers and HEU pairs and to determine which maternal factors condition their levels. In this study, plasma from 69 HEU newborns, their mothers, and 71 control pairs was quantified via immunoassays for each IgG isotype. Furthermore, we followed the antibody profile of HEUs throughout the first year of life. We showed that mothers present an antibody profile characterized by high concentrations of IgG1 and IgG3 but reduced IgG2, and HEU infants are born with an IgG subclass profile similar to that of their maternal pair. Interestingly, this passively transferred profile could remain influenced even during their own antibody production in HEU infants, depending on maternal conditions such as CD4+ T-cell counts and maternal antiretroviral treatment. Our findings indicate that HEU infants exhibit an altered IgG subclass profile influenced by maternal factors, potentially contributing to their increased susceptibility to infections.

Establishment of an ELISpot Assay to Detect Cellular Immunity against S. pneumoniae in Vaccinated Kidney Transplant Recipients

In organ transplant recipients, the rate of invasive pneumococcal diseases is 25 times greater than in the general population. Vaccination against S. pneumoniae is recommended in this cohort because it reduces the incidence of this severe form of pneumococcal infection. Previous studies indicate that transplant recipients can produce specific antibodies after pneumococcal vaccination. However, it remains unclear if vaccination also induces specific cellular immunity. In the current study on 38 kidney transplant recipients, we established an interferon-γ ELISpot assay that can detect serotype-specific cellular responses against S. pneumoniae. The results indicate that sequential vaccination with the conjugated vaccine Prevenar 13 and the polysaccharide vaccine Pneumovax 23 led to an increase of serotype-specific cellular immunity. We observed the strongest responses against the serotypes 9N and 14, which are both components of Pneumovax 23. Cellular responses against S. pneumoniae correlated positively with specific IgG antibodies (r = 0.32, p = 0.12). In conclusion, this is the first report indicating that kidney transplant recipients can mount specific cellular responses after pneumococcal vaccination. The ELISpot we established will allow for further investigations. These could help to define, for example, factors influencing specific cellular immunity in immunocompromised cohorts or the duration of cellular immunity after vaccination.

Pneumococcal conjugate vaccine dose-ranging studies in humans: A systematic review

BACKGROUND

Streptococcus pneumoniae is one of the most common bacterial pathogens of infants and young children. Antibody responses against the pneumococcal polysaccharide capsule are the basis of vaccine-mediated protection. We examined the relationship between the dose of polysaccharide in pneumococcal conjugate vaccines (PCVs) and immunogenicity.

METHODS

A systematic search of English publications that evaluated the immunogenicity of varying doses of pneumococcal conjugate vaccines was performed in Medline and Embase (Ovid Sp) databases in August 2019. We included only articles that involved administration of pneumococcal conjugate vaccine in humans and assessed the immunogenicity of more than one serotype-specific saccharide dose. Results were synthesised descriptively due to the heterogeneity of product valency, product content and vaccine schedule.

RESULTS

We identified 1691 articles after de-duplication; 9 studies met our inclusion criteria; 2 in adults, 6 in children and 1 in both. Doses of polysaccharide evaluated ranged from 0.44 mcg to 17.6 mcg. In infants, all doses tested elicited IgG geometric mean concentrations (GMCs) above the established correlate of protection (COP; 0.35 mcg/ml). A month after completion of the administered vaccine schedule, 95% confidence intervals of only three out of all the doses evaluated had GMCs that crossed below the COP. In the adult studies, all adults achieved GMCs that would be considered protective in children who have received 3 standard vaccine doses.

CONCLUSION

For some products, the mean antibody concentrations induced against some pneumococcal serotypes increased with increasing doses of the polysaccharide conjugate, but for other serotypes, there were no clear dose-response relationships or the dose response curves were negative. Fractional doses of polysaccharide which contain less than is included in currently distributed formulations may be useful in the development of higher valency vaccines, or dose-sparing delivery for paediatric use.

Neutrophils Are Required During Immunization With the Pneumococcal Conjugate Vaccine for Protective Antibody Responses and Host Defense Against Infection

Neutrophils can shape adaptive immunity; however, their role in vaccine-induced protection against infections in vivo remains unclear. Here, we tested their role in the clinically relevant polysaccharide conjugate vaccine against Streptococcus pneumoniae (pneumococcus). We antibody depleted neutrophils during vaccination, allowed them to recover, and 4 weeks later challenged mice with pneumococci. We found that while isotype-treated vaccinated controls were protected against an otherwise lethal infection in naive mice, full protection was lost upon neutrophil depletion. Compared to vaccinated controls, neutrophil-depleted mice had higher lung bacterial burdens, increased incidence of bacteremia, and lower survival rates. Sera from neutrophil-depleted mice had less antipneumococcal IgG2c and IgG3, were less efficient at inducing opsonophagocytic killing of bacteria by neutrophils in vitro, and were worse at protecting naive mice against pneumococcal pneumonia. In summary, neutrophils are required during vaccination for optimal host protection, which has important implications for future vaccine design against pneumococci and other pathogens.

Vaccination with LytA, LytC, or Pce of Streptococcus pneumoniae Protects against Sepsis by Inducing IgGs That Activate the Complement System

The emergence of non-vaccine serotypes of Streptococcus pneumoniae after the use of vaccines based in capsular polysaccharides demonstrates the need of a broader protection vaccine based in protein antigens and widely conserved. In this study, we characterized three important virulence factors of S. pneumoniae namely LytA, LytC, and Pce as vaccine candidates. These proteins are choline-binding proteins that belong to the cell wall hydrolases’ family. Immunization of mice with LytA, LytC, or Pce induced high titers of immunoglobulins G (IgGs) of different subclasses, with IgG1, IgG2a, and IgG2b as the predominant immunoglobulins raised. These antibodies activated the classical pathway of the complement system by increasing the recognition of C1q on the surface of pneumococcal strains of different serotypes. Consequently, the key complement component C3 recognized more efficiently these strains in the presence of specific antibodies elicited by these proteins, activating, therefore, the phagocytosis. Finally, a mouse sepsis model of infection was established, confirming that vaccination with these proteins controlled bacterial replication in the bloodstream, increasing the survival rate. Overall, these results demonstrate that LytA, LytC, and Pce can be protein antigens to be contained in a future universal vaccine against S. pneumoniae.

Humoral Responses and Serological Assays in SARS-CoV-2 Infections

In December 2019, the novel betacoronavirus Severe Acute Respiratory Disease Coronavirus 2 (SARS-CoV-2) was first detected in Wuhan, China. SARS-CoV-2 has since become a pandemic virus resulting in hundreds of thousands of deaths and deep socioeconomic implications worldwide. In recent months, efforts have been directed towards detecting, tracking, and better understanding human humoral responses to SARS-CoV-2 infection. It has become critical to develop robust and reliable serological assays to characterize the abundance, neutralization efficiency, and duration of antibodies in virus-exposed individuals. Here we review the latest knowledge on humoral immune responses to SARS-CoV-2 infection, along with the benefits and limitations of currently available commercial and laboratory-based serological assays. We also highlight important serological considerations, such as antibody expression levels, stability and neutralization dynamics, as well as cross-reactivity and possible immunological back-boosting by seasonal coronaviruses. The ability to accurately detect, measure and characterize the various antibodies specific to SARS-CoV-2 is necessary for vaccine development, manage risk and exposure for healthcare and at-risk workers, and for monitoring reinfections with genetic variants and new strains of the virus. Having a thorough understanding of the benefits and cautions of standardized serological testing at a community level remains critically important in the design and implementation of future vaccination campaigns, epidemiological models of immunity, and public health measures that rely heavily on up-to-date knowledge of transmission dynamics.

Humoral response to a 13-valent pneumococcal conjugate vaccine in kidney transplant recipients

BACKGROUND

Vaccination against S. pneumoniae is recommended by national guidelines. Moderate immunogenicity of the 13-valent pneumococcal conjugate vaccine (PCV13) has been reported in adult kidney transplant recipients (KTR). This study further defines the immunogenicity of PCV13 in this cohort.

METHODS

49 KTR were immunized with PCV13. A validated opsonophagocytic killing assay (OPA), a global anti-pneumococcal capsular polysaccharide (anti-PCP) IgG, IgG2, IgM and IgA ELISA, and - for selected patients - a serotype specific anti-PCP WHO reference ELISA were performed pre-vaccination and at month 1 and 12 post-vaccination.

RESULTS

Geometric mean OPA titers increased significantly for 13/13 serotypes at month 1 and for 10/13 serotypes at month 12 post-vaccination. Vaccine response defined as an OPA titer ≥1:8 was reached in 9/13 serotypes (median). 53% reached the vaccine response criteria at month 1 and 45% at month 12. At month 1 after vaccination, the median OPA titer in an age-group matched healthy reference population was 5- to 10-fold higher than in KTR. OPA titers correlated strongly with results to the global and serotype specific anti-PCP IgG ELISA. Lower OPA titers significantly (p < 0.05) correlated with albuminuria, an interval between vaccination and transplantation <12 months, age and treatment with mycophenolate mofetil. Global IgG, IgG2, IgM and IgA, as well as serotype specific anti-PCP antibody concentrations (12/13 serotypes) increased significantly at month 1 and 12 post-vaccination.

CONCLUSIONS

Kidney transplant recipients show a significant humoral response after vaccination with PCV13. Functional antibody response exists, but is not as vigorous as in healthy adults.

Higher mass meningococcal group C-tetanus toxoid vaccines conjugated with carbodiimide correlate with greater immunogenicity

To examine the link between meningococcal C (MenC) vaccine size and immunogenic response, a panel of MenC glycoconjugate vaccines were prepared differing in chain length, molar mass and hydrodynamic volume. The preparations consisted of different lengths of MenC polysaccharide (PS) covalently linked to monomeric purified tetanus toxoid (TT) carrier protein using the coupling reagent ethylcarbodiimide hydrochloride (EDC). Size exclusion chromatography with multi-angle light scattering (SEC-MALS) and viscometry analysis confirmed that the panel of MenC-TT conjugates spanned masses of 191,500 to 2,348,000 g/mol, and hydrodynamic radii ranging from 12.1 to 47.9 nm. The two largest conjugates were elliptical in shape, whereas the two smallest conjugates were more spherical. The larger conjugates appeared to fit a model described by multiple TTs with cross-linked PS, typical of lattice-like networks described previously for TT conjugates, while the smaller conjugates were found to fit a monomeric or dimeric TT configuration. The effect of vaccine conjugate size on immune responses was determined using a two-dose murine immunization. The two larger panel vaccine conjugates produced higher anti-MenC IgG1 and IgG2b titres after the second dose. Larger vaccine conjugate size also stimulated greater T-cell proliferative responses in an in vitro recall assay, although cytokines indicative of a T-helper response were not measurable. In conclusion, larger MenC-TT conjugates up to 2,348,000 g/mol produced by EDC chemistry correlate with greater humoral and cellular murine immune responses. These observations suggest that conjugate size can be an important modulator of immune response.

Response to pneumococcal vaccination in multiple myeloma

Background

Streptococcus pneumoniae infection causes morbidity and mortality in multiple myeloma patients. Pneumococcal vaccination is commonly given to immunocompromised myeloma patients; however response data are sparse. Here, we present longitudinal response data to pneumococcal vaccination in multiple myeloma patients.

Method

Twenty‐eight multiple myeloma patients were included, 25 of whom were newly diagnosed. All the patients received two vaccines Prevnar13® and Pneumo23®. Serotype‐specific IgG was measured by ELISA for all 23 vaccine serotypes at baseline, and then sequentially at different time points postvaccination until treatment ended. Response to vaccination is available for 20 patients. The primary endpoint was the incidence rate of patients who obtained an isotype response serum concentration after vaccination. Secondary endpoints included detailed isotype increase, time to first increase, further assessment of a decreased anti‐pneumococcal serum concentrations following treatment including autologous stem cell transplantation (ASCT), rate of infection with a special attention to pneumococcal infection.

Results

The median age was 66 years and the male to female ratio was 0.6. Anti‐pneumococcal capsular polysaccharide (anti‐PCP23) IgG, IgG2, IgA, and IgM responses were detected within 1 week postvaccination. Response to at least one subtype of antibody was obtained in 85% (n = 17) of patients, for at least two subtypes in 65% (n = 13), for at least three subtypes in 55% (n = 11), and 2 patients responded to all four subtypes. The median increase in the concentration of anti‐PCP23 isotypes was threefold following vaccination, with the highest increase observed when Pneumo23® was given more than 30 days after Prevnar13®. The anti‐pneumococcal geometric mean concentration decreased significantly for all subtypes over time independently of treatment approaches.

Conclusion

Myeloma has the ability to demonstrate a response to pneumococcal vaccine, independently of preexisting hypogammaglobulinemia and possibly of treatment‐induced immunodepression. We also observed a drop in the serum response overtime and following autologous transplantation. Further studies in larger sample are needed to understand the benefit of vaccination strategies in these patients.

A platform for glycoengineering a polyvalent pneumococcal bioconjugate vaccine using E. coli as a host

Chemical synthesis of conjugate vaccines, consisting of a polysaccharide linked to a protein, can be technically challenging, and in vivo bacterial conjugations (bioconjugations) have emerged as manufacturing alternatives. Bioconjugation relies upon an oligosaccharyltransferase to attach polysaccharides to proteins, but currently employed enzymes are not suitable for the generation of conjugate vaccines when the polysaccharides contain glucose at the reducing end, which is the case for ~75% of Streptococcus pneumoniae capsules. Here, we use an O-linking oligosaccharyltransferase to generate a polyvalent pneumococcal bioconjugate vaccine with polysaccharides containing glucose at their reducing end. In addition, we show that different vaccine carrier proteins can be glycosylated using this system. Pneumococcal bioconjugates are immunogenic, protective and rapidly produced within E. coli using recombinant techniques. These proof-of-principle experiments establish a platform to overcome limitations of other conjugating enzymes enabling the development of bioconjugate vaccines for many important human and animal pathogens.

Bioconjugation is a promising process to manufacture conjugate vaccines, but currently employed enzymes cannot generate the full spectrum of bacterial glycoproteins. Here, the authors use an O-linking oligosaccharyltransferase to generate a polyvalent pneumococcal bioconjugate vaccine with polysaccharides containing glucose at their reducing end.

The effect of splenectomy on the levels of PCV-13-induced memory B- and T cells

AIM

Splenectomised patients are associated with lifelong risk of fatal overwhelming post-splenectomy infection (OPSI), which is mostly caused by Streptococcus pneumoniae. Today OPSI cases can still be reported even in patients with appropriate vaccination. In our study, the levels of vaccine-specific memory B- and T cells were compared between control and splenectomised patients to enlighten the underlying reason.

MATERIALS AND METHODS

Five healthy and 14 post-traumatic splenectomised individuals were vaccinated with 13-valent pneumococcal conjugate vaccine (PCV-13) followed by 23-valent pneumococcal polysaccharide vaccine (PPV-23). The levels of memory B- and T cells were compared by ELISPOT analysis.

RESULTS

Splenectomised patients generated reduced levels of memory IgG B cells in response to PCV-13 vaccination, while the memory IFN-γ T-cell levels were undetectable in asplenic patients. This was despite the detection of vaccine-induced memory T-cell levels in control patients, which were analysed simultaneously following the same experimental protocol.

CONCLUSION

Our results suggest that spleen is important, but not essential, for survival and/or generation of memory IgG B cells. In contrast, it seems to be indispensable for PCV-13-specific memory T_H 1-cell levels. Studies enhancing the levels of vaccine-induced memory cells and further enlightening the immune responses in asplenic individuals are required to develop more effective vaccination strategies against OPSI.

Meningococcal vaccination in pregnancy

Invasive meningococcal disease causes meningitis and septicemia worldwide with highest rates of disease occurring in children <2 years of age, and in particular young infants. Vaccination during pregnancy has been a successful strategy for prevention of other infections in young infants, most notably tetanus, pertussis and influenza. However, few studies of meningococcal vaccines in pregnancy have been undertaken, and none include the most commonly used current vaccines to prevent disease by capsular groups A, B, C, W and Y. The limited data suggest that the older polysaccharide vaccines are immunogenic, but the impact on prevention of infant disease has not been measured. Further studies of MenB protein vaccines and MenA protein-polysaccharide conjugate vaccines in particular are needed if vaccination in pregnancy is to be utilized as an approach to prevention of meningococcal disease in young infants.

Novel Intervention in the Aging Population: A Primary Meningococcal Vaccine Inducing Protective IgM Responses in Middle-Aged Adults

Introduction

Vaccine responses are often reduced in the elderly, leaving part of the elderly population vulnerable to infectious diseases. Timely vaccination may offer a solution for strengthening memory immunity before reaching old age, which classifies middle-aged persons as a target age group for vaccine interventions. However, knowledge regarding the immunogenicity of primary immunizations in middle-aged adults is lacking. We determined the immunogenicity of a primary meningococcal vaccine towards which no or (very) low pre-vaccination immunity exists in middle-aged adults (NTR4636).

Methods

A vaccine containing multiple meningococcal groups (tetravalent) conjugated to tetanus toxoid (MenACWY-TT) was administered to middle-aged adults (50–65 years of age, N = 204) in a phase IV single-center and open-label study. Blood samples were taken pre-, 7 days, 28 days, and 1 year post-vaccination. Functional antibody titers were measured with the serum bactericidal assay (SBA). Meningococcal- and tetanus-specific antibody responses were determined with a fluorescent bead-based multiplex immunoassay. A bi-exponential decay model was used to estimate long-term protection.

Results

In the majority of the participants, the meningococcal vaccine clearly induced naïve responses to meningococci W (MenW) and meningococci Y (MenY) as compared to a booster response to meningococci C (MenC). After 28 days, 94, 99, and 97% of the participants possessed a protective SBA titer for MenC, MenW, and MenY, respectively, which was maintained in 76, 94, and 86% 1 year post-vaccination. At this 1-year time point, significantly lower SBA titers were found in participants without a pre-vaccination SBA titer. Overall, protective antibody titers were predicted to persist after 10 years in 40–60% of the participants. The SBA titers correlated well with the meningococcal-specific IgM responses, especially for MenW and MenY. Interestingly, these IgM responses were negatively correlated with age.

Conclusion

Primary immunization with a tetravalent meningococcal vaccine was highly immunogenic in middle-aged adults, inducing protective antibody titers in the vast majority of the participants lasting for at least 1 year. The age-related decrease in highly functional IgM responses argues in favor of vaccination against de novo antigens before reaching old age and, hence, middle-aged persons are an age group of interest for future vaccine interventions to protect the aging population.

Measurement of the IgG2 response to Pneumococcal capsular polysaccharides may identify an antibody deficiency in individuals referred for immunological investigation

IgG2 is the most efficient subclass for providing protection against pneumococcal pathogens. We hypothesised that some individuals may be unable to mount an effective pneumococcal capsular polysaccharide (PCP) IgG2 response despite having a normal PCP IgG concentration (PCP IgG2 deficient). The median pre-vaccination PCP IgG2 concentration was significantly lower in individuals referred for immunological investigation compared to healthy controls (2.8 mg/L range, 95% CI 1.1-88 vs. 29.5mg/L, 95% CI 13.5-90, p = 0.0002). PCP IgG:IgG2 ratios were significantly higher for the referral population than for healthy controls suggesting the increased production of PCP specific subclasses other than IgG2. The percentage of individuals with PCP IgG2 deficiency was significantly higher in referral groups compared to controls (31% vs. 5%; p = 0.0009) and in an individual with PCP IgG2 deficiency, the balance of PCP specific IgG subclass antibodies post vaccination changed from IgG2>IgG1>IgG3>IgG4 to IgG1>IgG3>IgG2>IgG4. The median PCP IgG2 concentration in those with PCP IgG2 deficiency was significantly lower in the referral groups compared to controls (7.8 mg/L, 95% CI 1.1-12 vs. 12.7 mg/L, 95% CI 11.8-13.1; p = 0.006). The data suggests a defect in the production PCP IgG2 may be present in individuals with normal PCP IgG referred for immunological investigation.

Production of IgG antibodies to pneumococcal polysaccharides is associated with expansion of ICOS+ circulating memory T follicular-helper cells which is impaired by HIV infection

Dysfunction of T follicular-helper (T_FH) cells is a possible cause of impaired germinal centre (GC) and IgG antibody responses in individuals with human immunodeficiency virus-1 (HIV-1) infection and might contribute to decreased magnitude and isotype diversification of IgG antibodies to pneumococcal polysaccharides (PcPs). We examined the production of IgG1 and IgG2 antibodies to PcPs 4, 6B, 9V and 14 by enumerating antibody secreting cells (ASCs) at day (D) 7 and determining fold-increase in serum antibody levels at D28 after vaccination with unconjugated PcPs in HIV seronegative subjects (n = 20) and in HIV patients who were receiving antiretroviral therapy (ART) (n = 28) or who were ART-naive (n = 11) and determined their association with ICOS⁺ and ICOS^- circulating memory T_FH (cmT_FH) cells (CD4⁺CD45RA^-CD27⁺CXCR5⁺PD-1⁺) and short lived plasmablasts (SPBs) at D7, and with PcP-specific and total IgM⁺ and IgG⁺ memory B cells at D0. In HIV seronegative subjects, production of IgG1⁺ and IgG2⁺ ASCs was consistently associated with the frequency of ICOS⁺ cmT_FH cells but not ICOS^- cmT_FH cells or memory B cells. In contrast, post-vaccination ASCs in HIV patients, regardless of ART status, were lower than in HIV seronegative subjects and not associated with ICOS⁺ cmT_FH cells, the expansion of which was absent (ART-naive patients) or much lower than in HIV seronegative subjects (ART-treated patients). Production of SPBs was also lower in ART-naive patients. Fold-increase in IgG2 antibodies at D28 also correlated with ICOS⁺ cmT_FH cells at D7 in HIV seronegative subjects but not in HIV patients. These novel findings provide evidence that ICOS⁺ cmT_FH cells contribute to the regulation of PcP-specific IgG antibody responses, including isotype diversification, and that T_FH cell dysfunction may be a cause of impaired PcP-specific IgG antibody responses and increased susceptibility to pneumococcal disease in HIV patients.

Immunization with LytB protein of Streptococcus pneumoniae activates complement-mediated phagocytosis and induces protection against pneumonia and sepsis

The cell wall glucosaminidase LytB of Streptococcus pneumoniae is a surface exposed protein involved in daughter cell separation, biofilm formation and contributes to different aspects of the pathogenesis process. In this study we have characterized the antibody responses after immunization of mice with LytB in the presence of alhydrogel as an adjuvant. Enzyme-linked immunosorbent assays measuring different subclasses of immunoglobulin G, demonstrated that the antibody responses to LytB were predominantly IgG1 and IgG2b, followed by IgG3 and IgG2a subclasses. Complement-mediated immunity against two different pneumococcal serotypes was investigated using sera from immunized mice. Immunization with LytB increased the recognition of S. pneumoniae by complement components C1q and C3b demonstrating that anti-LytB antibodies trigger activation of the classical pathway. Phagocytosis assays showed that serum containing antibodies to LytB stimulates neutrophil-mediated phagocytosis against S. pneumoniae. Animal models of infection including invasive pneumonia and sepsis were performed with two different clinical isolates. Vaccination with LytB increased bacterial clearance and induced protection demonstrating that LytB might be a good candidate to be considered in a future protein-based vaccine against S. pneumoniae.

Antibody and T-cell responses associated with experimental human malaria infection or vaccination show limited relationships

This study examined specific antibody and T-cell responses associated with experimental malaria infection or malaria vaccination, in malaria-naive human volunteers within phase I/IIa vaccine trials, with a view to investigating inter-relationships between these types of response. Malaria infection was via five bites of Plasmodium falciparum-infected mosquitoes, with individuals reaching patent infection by 11-12 days, having harboured four or five blood-stage cycles before drug clearance. Infection elicited a robust antibody response against merozoite surface protein-119 , correlating with parasite load. Classical class switching was seen from an early IgM to an IgG1-dominant response of increasing affinity. Malaria-specific T-cell responses were detected in the form of interferon-γ and interleukin-4 (IL-4) ELIspot, but their magnitude did not correlate with the magnitude of antibody or its avidity, or with parasite load. Different individuals who were immunized with a virosome vaccine comprising influenza antigens combined with P. falciparum antigens, demonstrated pre-existing interferon-γ, IL-2 and IL-5 ELIspot responses against the influenza antigens, and showed boosting of anti-influenza T-cell responses only for IL-5. The large IgG1-dominated anti-parasite responses showed limited correlation with T-cell responses for magnitude or avidity, both parameters being only negatively correlated for IL-5 secretion versus anti-apical membrane antigen-1 antibody titres. Overall, these findings suggest that cognate T-cell responses across a range of magnitudes contribute towards driving potentially effective antibody responses in infection-induced and vaccine-induced immunity against malaria, and their existence during immunization is beneficial, but magnitudes are mostly not inter-related.

Viremic HIV Controllers Exhibit High Plasmacytoid Dendritic Cell-Reactive Opsonophagocytic IgG Antibody Responses against HIV-1 p24 Associated with Greater Antibody Isotype Diversification

Identifying the mechanisms of natural control of HIV-1 infection could lead to novel approaches to prevent or cure HIV infection. Several studies have associated natural control of HIV-1 infection with IgG Abs against HIV-1 Gag proteins (e.g., p24) and/or production of IgG2 Abs against HIV-1 proteins. These Abs likely exert their effect by activating antiviral effector cell responses rather than virus neutralization. We hypothesized that an opsonophagocytic IgG Ab response against HIV-1 p24 that activates plasmacytoid dendritic cells (pDCs) through FcγRIIa would be associated with control of HIV and that this would be enhanced by Ab isotype diversification. Using the Gen2.2 pDC cell line, we demonstrated that pDC-reactive opsonophagocytic IgG Ab responses against HIV-1 p24 were higher in HIV controllers (HIV RNA < 2000 copies/ml) than noncontrollers (HIV RNA > 10,000 copies/ml), particularly in controllers with low but detectable viremia (HIV RNA 75-2000 copies/ml). Opsonophagocytic Ab responses correlated with plasma levels of IgG1 and IgG2 anti-HIV-1 p24 and, notably, correlated inversely with plasma HIV RNA levels in viremic HIV patients. Phagocytosis of these Abs was mediated via FcγRIIa. Isotype diversification (toward IgG2) was greatest in HIV controllers, and depletion of IgG2 from Ig preparations indicated that IgG2 Abs to HIV-1 p24 do not enhance phagocytosis, suggesting that they enhance other aspects of Ab function, such as Ag opsonization. Our findings emulate those for pDC-reactive opsonophagocytic Ab responses against coxsackie, picorna, and influenza viruses and demonstrate a previously undefined immune correlate of HIV-1 control that may be relevant to HIV vaccine development.

Impaired haemophilus influenzae type b transplacental antibody transmission and declining antibody avidity through the first year of life represent potential vulnerabilities for HIV-exposed but -uninfected infants

To determine whether immune function is impaired among HIV-exposed but -uninfected (HEU) infants born to HIV-infected mothers and to identify potential vulnerabilities to vaccine-preventable infection, we characterized the mother-to-infant placental transfer of Haemophilus influenzae type b-specific IgG (Hib-IgG) and its levels and avidity after vaccination in Ugandan HEU infants and in HIV-unexposed U.S. infants. Hib-IgG was measured by enzyme-linked immunosorbent assay in 57 Ugandan HIV-infected mothers prenatally and in their vaccinated HEU infants and 14 HIV-unexposed U.S. infants at birth and 12, 24, and 48 weeks of age. Antibody avidity at birth and 48 weeks of age was determined with 1 M ammonium thiocyanate. A median of 43% of maternal Hib-IgG was transferred to HEU infants. Although its level was lower in HEU infants than in U.S. infants at birth (P < 0.001), Hib-IgG was present at protective levels (>1.0 μg/ml) at birth in 90% of HEU infants and all U.S. infants. HEU infants had robust Hib-IgG responses to a primary vaccination. Although Hib-IgG levels declined from 24 to 48 weeks of age in HEU infants, they were higher than those in U.S. infants (P = 0.002). Antibody avidity, comparable at birth, declined by 48 weeks of age in both populations. Early vaccination of HEU infants may limit an initial vulnerability to Hib disease resulting from impaired transplacental antibody transfer. While initial Hib vaccine responses appeared adequate, the confluence of lower antibody avidity and declining Hib-IgG levels in HEU infants by 12 months support Hib booster vaccination at 1 year. Potential immunologic impairments of HEU infants should be considered in the development of vaccine platforms for populations with high maternal HIV prevalence.

Pneumococcal vaccine development

A 7-valent pneumococcal conjugate vaccine has demonstrated an impact on pneumococcal bacteremia in the immunized pediatric population, extending to nonimmunized adults via herd immunity. A considerable reduction of all-cause pediatric pneumonia has also been found. The impact on all-cause pediatric otitis is limited, but postlicensure data suggests stronger reductions. Higher valency conjugate vaccines are now under development (11V or more). Licensed 23-valent pneumococcal polysaccharide vaccines have been available since 1983 with a demonstrated impact on adult pneumococcal bacteremia. The burden of adult nonbacteremic pneumococcal pneumonia has remained high and efforts to develop improved adult pneumococcal vaccines have been initiated that include conjugates and pneumococcal proteins.

Neonatal infections in Saudi Arabia: association with C-reactive protein, CRP -286 (C>T>A) gene polymorphism and IgG antibodies

Background

C-reactive protein (CRP) is a nonspecific, acute-phase protein that rises in response to infectious and non-infectious inflammatory processes. Infections are the single largest cause of neonatal deaths globally.

The primary aim of this study is to examine the association between CRP gene polymorphism and serum levels of CRP in correlation with early onset sepsis (EOS) infection in newborns living in Taif city, Saudi Arabia. The second aim is to examine the relationship between specific IgG/IgG subclasses and early onset sepsis (EOS) infection among these newborns.

Methods

Staphylococcus aureus (S. aureus) is one of the most common organisms related to sepsis infection in the newborn at King Abdel Aziz Specialist Hospital (KAASH). This study was conducted in Taif city, at KAASH’s neonatal intensive care unit between March and August 2012. Neonates were consecutively enrolled onto the study having met our inclusion criteria (as per our research protocol).

The CRP concentration level was analysed using NycoCard® CRP Single Test. CRP -286 (C>T>A) A polymorphisms were analyzed using Pyrosequencing technology for CRP genotyping. IgG subclasses were analysed in the study population using ELISA.

Result

Logistic regression analyses showed that the AA and AC genotypes were negatively associated amongst EOS neonates compared to suspected neonates. The frequency of CC and CT were significantly associated with the EOS neonates compared to the suspected group. The levels of specific IgG1, IgG2 and IgG3 antibodies were significantly lower amongst EOS compared to the suspected group.

Conclusions

Taken together, the CRP-286 (C>T>A) A genotype polymorphism and specific IgG antibodies isotype levels can contribute to a reduced risk of EOS. Furthermore, CRP has a potential use in detecting EOS in neonates, which may mean earlier detection and management of EOS and subsequently better clinical outcome.

Reference ranges and cutoff levels of pneumococcal antibody global serum assays (IgG and IgG2) and specific antibodies in healthy children and adults

Pneumococcal antibodies represent the acquisition of natural immunity. Determination of pneumococcal antibodies is an important screening tool for immunodeficiencies. Our study generated reference ranges and cutoff levels for pneumococcal antibody global serum assays correlated to a specific pneumococcal antibody ELISA. Specific pneumococcal antibody levels were measured from 457 children undergoing elective surgery and 46 healthy adult volunteers (88 with previous pneumococcal immunization from both groups), 22 severe immunodeficient subjects with ataxia telangiectasia (A-T, negative controls), and age-matched 36 healthy allergic asthmatics. We determined a representative panel of serotype-specific pneumococcal antibodies (serotype 4, 5, 6B, 7F, 14, 18C, 19F, 23F) by ELISA and global pneumococcal IgG and IgG2 antibodies by EIA. In vaccine-naïve healthy subjects, initial pneumococcal IgG geometric mean concentrations of 13.1 μg/ml were low in the first year of life and increased over the time, reaching adult levels (70.5 μg/ml) at age 8-12 years. In parallel, IgG2 antibodies increased from 20.7 % (0.5-1 year old) to adult proportions (>30 %) in preschoolers. Correlation between the pneumococcal IgG screening assay and specific pneumococcal antibody levels was acceptable (Pearson's coefficient r = 0.4455; p = 0.001). Cutoff levels showed high sensitivity, whereas specificity was high to moderate calculated from correlations with the specific ELISA. We provide reference ranges and cutoff levels for the interpretation of specific antibody determinations in the clinical setting. The global pneumococcal IgG/IgG2 assay is a suitable screening tool and correlates with the ELISA serotype-specific pneumococcal antibodies. However, results below our cutoff values should be re-evaluated by serotype-specific ELISA testing.

Transplacental transport of IgG antibodies to preterm infants: a review of the literature

Newborn infants, especially preterm infants, have an immature immune system, which is not capable to actively protect against vaccine-preventable infections. Therefore, the newborn is dependent on transplacental transport of Immunoglobulin G (IgG), an active, FcRn receptor mediated process. Fetal IgG rises from approximately 10% of the maternal concentration at 17-22weeks of gestation to 50% at 28-32weeks of gestation. If transplacental acquired IgG is lower in preterm than in term infants, preterm infants are especially at risk for these vaccine-preventable diseases. The aim of this study was to review the transplacental transfer of IgG against vaccine-preventable diseases (measles, rubella, varicella-zoster, mumps, Haemophilus influenza type B, diphtheria, tetanus, pertussis and polio) to (pre)term infants and to identify factors that influence the transplacental transfer of these antigens. After selection, 18 studies on transplacental transport to preterm infants were included. In general, these studies showed for all antibodies that preterm infants have lower antibody concentrations compared with term infants. Maternal and infants antibody concentrations showed a strong correlation in 7 of the included studies. Infant antibody concentration was not associated with parity, maternal age, height or weight. Infants of vaccinated mothers had lower anti-measles antibody titers than infants of natural immunized mothers. IgG titers of preterm infants decrease earlier in life below protective antibody titers than term infants. Combined with their immature immune system, this puts preterm infants at increased risk for vaccine-preventable diseases.

Transplacental transport of IgG antibodies specific for pertussis, diphtheria, tetanus, haemophilus influenzae type b, and Neisseria meningitidis serogroup C is lower in preterm compared with term infants

BACKGROUND

Maternal antibodies, transported through the placenta during pregnancy, contribute to the protection of infants from infectious diseases during the first months of life. The aim of this study was to measure the concentration of antibodies against several vaccine-preventable diseases in paired maternal and cord blood serum samples in preterm and term infants and to assess placental transfer ratios and infant antibody concentrations against vaccine-preventable diseases.

METHODS

Antibody concentrations specific against pertussis proteins (pertussis toxin, filamentous hemagglutinin, pertactin, and fimbriae), diphtheria and tetanus toxins, and antibody concentrations specific against polysaccharides from Haemophilus influenzae type b and Neisseria meningitidis serogroup C were measured in cord blood samples from preterm (<32 weeks and 1500 g) and term infants and maternal serum samples, using a fluorescent bead-based multiplex immunoassay.

RESULTS

A total of 96 preterm and 42 term infants and their mothers were included in the study. Placental transfer ratios of antibodies against all vaccine antigens were significantly lower in preterm infants (medians varied from 0.26 to 0.86) compared with term infants (medians, 0.74-1.89; all antibodies P < 0.05). Furthermore, polysaccharide-vaccine-specific antibodies showed lower transplacental transport ratios than protein-vaccine-specific antibodies. Maternal concentrations are the most important determinants of infant antibody concentrations against vaccine-preventable diseases.

CONCLUSIONS

Preterm infants benefit to a lesser extent from maternal antibodies against vaccine-preventable diseases than term infants, posing them at higher risk for infectious diseases in the first months of life.

Vaccine-induced IgG2 anti-HIV p24 is associated with control of HIV in patients with a 'high-affinity' FcgammaRIIa genotype

OBJECTIVES

We have previously shown that vaccination with a recombinant fowlpox virus carrying the genes for HIV Gag-Pol and interferon-gamma (IFN-gamma) was associated with partial control of HIV replication after antiretroviral therapy (ART) was ceased but not with increased anti-HIV T-cell responses. Because IFN-gamma enhances IgG2 production, and IgG2 antibodies to HIV antigens and the 'high-affinity' polymorphism of FcgammaRIIa (the major Fc receptor for IgG2) have been associated with a favourable outcome of HIV infection, we examined the association of IgG2 antibodies to HIV p24 and 'high-affinity' polymorphisms of FcgammaRIIa with control of HIV replication in these patients.

METHODS

Plasma from weeks 0 (cessation of ART 1 week after the last vaccination), 9 and 20 was available from patients who had received the full construct vaccine, a partial construct (without IFN-gamma) or placebo. IgG2 and IgG1 anti-p24 and anti-gp41 were assayed and all patients were genotyped for the FcgammaRIIa 131 R/H polymorphism that affects IgG2 binding.

RESULTS

At week 0, IgG2 anti-p24 was present in five of nine full construct patients but none of 14 partial construct or placebo patients and was associated with a smaller increase in plasma HIV RNA over 20 weeks. Patients with IgG2 anti-p24 and the 'high-affinity' polymorphism of FcgammaRIIa exhibited lower HIV replication than other patients at week 20.

CONCLUSION

The role of IgG2 anti-HIV antibodies and FcgammaRIIa in the control of HIV replication should be investigated further. Inclusion of an IFN-gamma gene in DNA vaccine constructs might be a means of enhancing IgG2 antibody production.

Development of a fluorescent-bead-based multiplex immunoassay to determine immunoglobulin G subclass responses to Neisseria meningitidis serogroup A and C polysaccharides

A fluorescent-particle-based multiplex flow cytometric immunoassay (MIA) for the detection of serum immunoglobulin G (IgG) and two IgG subclasses, IgG1 and IgG2, specific for Neisseria meningitidis serogroup A (MenA) and C (MenC) polysaccharides (PS) was developed. The assay comprised three separate duplex assays, one for the detection of the IgG response to MenA and MenC PS, another for the detection of the IgG1 response to MenA and MenC PS, and a third for the detection of the IgG2 response to MenA and MenC PS. Next, the three separate duplex assays were combined and analyzed as a hexaplex assay. No interference between monoplex, duplex, and hexaplex assays was observed, and the assay was found to have low intra- and interassay variation (<9.0% and <27%, respectively). Comparison of the meningococcal subclass MIA to the in-house enzyme-linked inmmunosorbent assays showed a good correlation (R >or= 0.85) for each of the subclasses. We conclude that the hexaplex meningococcal subclass MIA is an easy and specific assay for the determination of anti-MenA and anti-MenC PS subclass IgG, requiring minimal amounts of serum to study IgG subclass responses to vaccines.

Estimating the protective concentration of anti-pneumococcal capsular polysaccharide antibodies

Estimates of minimum protective antibody concentrations for vaccine preventable diseases are of critical importance in assessing whether new vaccines will be as effective as those for which clinical efficacy was shown directly. We describe a method for correlating pneumococcal anticapsular antibody responses of infants immunized with pneumococcal conjugate (PnC) vaccine (Prevenar) with clinical protection from invasive pneumococcal disease (IPD). Data from three double blind controlled trials in Northern Californian, American Indian and South African infants were pooled in a meta-analysis to derive a protective concentration of 0.35 microg/ml for anticapsular antibodies to the 7 serotypes in Prevenar. This concentration has been recommended by a WHO Working Group as applicable on a global basis for assessing the efficacy of future pneumococcal conjugate vaccines. The WHO Working Groups anticipated that modifications in antibody assays for pneumococcal anticapsular antibodies would occur. The principles for determining whether such assay modifications should change the protective concentration are outlined. These principles were applied to an improvement in the ELISA for anticapsular antibodies, i.e. absorption with 22F pneumococcal polysaccharide, which increases the specificity of the assay for vaccine serotype anticapsular antibodies by removing non-specific antibodies. Using sera from infants in the pivotal efficacy trial in Northern California Kaiser Permanente (NCKP), 22F absorption resulted in minimal declines in pneumococcal antibody in Prevenar immunized infants but significant declines in unimmunized controls. Recalculation of the protective concentration after 22F absorption resulted in only a small decline from 0.35 microg/ml to 0.32 microg/ml. These data support retaining the 0.35 microg/ml minimum protective concentration recommended by WHO for assessing the efficacy of pneumococcal conjugate vaccines in infants.

Immunoglobulin G subclass response to a meningococcal quadrivalent polysaccharide-diphtheria toxoid conjugate vaccine

Changes in the immunoglobulin G1 (IgG1)/IgG2 ratio following vaccination can indicate the activation of cellular control mechanisms typical of a T-cell-dependent response. We examined IgG subclass ratios in 17 healthy adults (26 to 55 years of age) before and 4 to 6 weeks following immunization with a quadrivalent meningococcal-polysaccharide diphtheria toxoid conjugate vaccine against serogroups A, C, Y, and W135. Serologic responses were determined by serum bactericidal antibody assay and serogroup-specific IgG, IgG1, and IgG2 enzyme-linked immunosorbent assay. Prevaccination serogroup A-specific IgG1/IgG2 ratios were <1 for all subjects and differed by subject for C, Y, and W-135. Postvaccination, significant increases in IgG, IgG1, and IgG2, were observed for all serogroups. Serogroup-specific IgG1/IgG2 ratios increased for group A (14/17 subjects, 88%), decreased in more than half of subjects for groups C (9/17, 53%) and W135 (12/17, 71%) and decreased for serogroup Y (16/17, 94%). IgG1/IgG2 ratios differed between individual vaccinees and were similar to the responses of adults who received pneumococcal conjugate vaccines or a monovalent C conjugate vaccine. Further studies on IgG subclasses following meningococcal polysaccharide and conjugate vaccination are needed.

Pneumococcal vaccine efficacy for mucosal pneumococcal infections depends on Fcγ receptor IIa polymorphism

IgG2 antibodies are the main antibody subclass produced after pneumococcal polysaccharide vaccination. For these antibodies to be effective, interaction with FcgammaIIa receptors on phagocytic cells is necessary. FcgammaRIIa displays a functional polymorphism with either a histidine (H) or arginine (R) at position 131. Interaction of IgG2 antibodies depends on the H131 allele, whereas this interaction is low to absent with the R131 allele. We tested the clinical efficacy of combined pneumococcal conjugate and pneumococcal polysaccharide vaccination according to FcgammaIIa-H/R131 genotype in a randomized double blind placebo controlled vaccination trial in children with a history of acute otitis media. We found a decisive role for the FcgammaIIa-H/R131 polymorphism on the clinical vaccine efficacy of combined pneumococcal conjugate and polysaccharide vaccinations. RR homozygotes showed a significant increase in recurrence of acute otitis media after pneumococcal vaccinations. This cannot be explained by differences in the pneumococcal specific antibody response or differences in nasopharyngeal pneumococcal carriage, but may be explained by less efficient interaction of FcgammaRIIa with polysaccharide-induced IgG2 anti-pneumococcal antibodies in RR homozygotes. Our data show that the genetic make-up of individuals or populations under study should be considered while evaluating vaccine efficacy trials.

Assignment of weight-based immunoglobulin G1 (IgG1) and IgG2 units in antipneumococcal reference serum lot 89-S(F) for pneumococcal polysaccharide serotypes 1, 4, 5, 7F, 9V, and 18C

Weight-based assignments for immunoglobulin G1 (IgG1) and IgG2 subclass antibodies to Streptococcus pneumoniae capsular polysaccharides (PnPs) in antipneumococcal standard reference serum lot 89-S (lot 89-S), also known as lot 89-SF, have been determined for serotypes 1, 4, 5, 7F, 9V, and 18C. This extends the usefulness of lot 89-S beyond the IgG1 and IgG2 subclass assignments for serotypes 3, 6B, 14, 19F, and 23F made previously (A. Soininen, H. Kayhty, I. Seppala, and T. Wuorimaa, Clin. Diagn. Lab. Immunol. 5:561-566, 1998) to cover 11 major serotypes associated with the highest percentage of pneumococcal disease worldwide. A method of equivalence of absorbances in enzyme immunosorbent assays was used to determine the IgG1 and IgG2 antibody concentrations for the additional serotypes in lot 89-S, based on the subclass values previously assigned for PnPs serotypes 6B, 14, and 23F. This cross-standardization method assures consistency with previous antibody assignments in that reference serum. The newly assigned subclass values for serotype 9V, and previously assigned values for serotype 14, were used to quantitate PnPs antibodies in sera from adult and pediatric subjects immunized with a pneumococcal conjugate vaccine. There was a predominance of IgG1 anti-PnPs antibodies in pediatric sera and IgG2 anti-PnPs antibodies in the adult sera. The IgG1 and IgG2 subclass assignments for the 11 PnPs serotypes in antipneumococcal standard reference serum lot 89-S are useful for quantitating and characterizing immune responses to pneumococcal infection and vaccination regimens.

Assignment of weight-based antibody units for 13 serotypes to a human antipneumococcal standard reference serum, lot 89-S(f)

Weight-based immunoglobulin G (IgG), IgM, IgA, and total Ig antibody assignments were made to human antipneumococcal standard reference serum lot 89-S, also known as lot 89-SF, for Streptococcus pneumoniae capsular polysaccharide (PnPs) serotypes 2, 6A, 8, 9N, 10A, 11A, 12F, 15B, 19A, 17F, 20, 22F, and 33F, as well as for C-polysaccharide (C-Ps), extending the standard's usefulness for pneumococcal vaccine evaluation beyond the original serotype 1, 3, 4, 5, 6B, 7F, 9V, 14, 18C, 19F, and 23F assignments (S. A. Quataert, C. S. Kirch, L. J. Quackenbush Wiedl, D. C. Phipps, S. Strohmeyer, C. O. Cimino, J. Skuse, and D. V. Madore, Clin. Diagn. Lab. Immunol. 2:590-597, 1995). The additional 14 assignments were determined using an equivalence of absorbance method with an anti-PnPs serotype 6B reference enzyme-linked immunosorbent assay (EIA). To assure accuracy, anti-PnPs EIA for serotype 14 antibodies, a previously assigned serotype, was performed concurrently. This method assures consistency of the new microgram-per-microliter assignments with previous antiserotype assignments to lot 89-S. The sum of the experimentally derived isotype assignments for anti-PnPs serotypes in lot 89-S agrees well with the separately determined total Ig assignment for each serotype. The lot 89-S assignments for serotypes 1, 5, 6B, 14, 18C, 19F, and 23F were used for pneumococcal conjugate vaccine clinical trial evaluation and to generate data in efficacy trials where serological correlates for protection have been proposed. The assignment of antibody concentrations to additional pneumococcal serotypes in this reference reagent facilitates the consistent and accurate comparison of serum antibody concentrations across clinical trials.

Delineation of the role of platelet-activating factor in the immunoglobulin G2 antibody response

Localized aggressive periodontitis (LAgP) is a chronic inflammatory disease characterized by severe destruction of periodontal tissues surrounding the first molars and incisors. LAgP subjects produce large amounts of immunoglobulin G2 (IgG2) antibody against oral pathogens, and this response is inversely correlated with the severity of disease. We previously demonstrated that platelet-activating factor (PAF) is required for optimal IgG2 responses. The present investigation was designed to determine the mechanism of IgG2 induction by PAF. Exogenous PAF acetylhydrolase suppressed approximately 80% of pokeweed mitogen-stimulated IgG2 production, confirming that PAF is essential for optimal responses. PAF-activated leukocytes produced gamma interferon (IFN-gamma), a Th1 cytokine that has been associated with IgG2 responses in previous studies. The monocyte-derived cytokines interleukin-12 (IL-12) and IL-18 are upstream of IFN-gamma production, and IgG2 production was suppressed by neutralizing antibodies against these proteins. In addition, PAF induced monocyte-derived dendritic cells (DC) but not macrophages (MPhi) to secrete IL-12 and IL-18. This observation was interesting because monocyte differentiation in LAgP subjects is skewed to the DC phenotype. Although other investigators have implicated IFN-gamma in IgG2 production, its precise role in this response is controversial. Our studies suggest that IFN-gamma induces isotype switching to IgG2 but only in concert with the Th2 cytokine IL-4. Thus, it appears that the unique PAF metabolism of LAgP monocytes or DC promotes Th1 responses that are essential for optimal IgG2 antibody production. As IgG2 antibodies opsonize oral bacteria and promote their clearance and destruction, these alterations in PAF metabolism may be essential for limiting disease severity in LAgP patients.

A peptide mimotope of type 8 pneumococcal capsular polysaccharide induces a protective immune response in mice

Increasing antibiotic resistance and a rising patient population at risk for infection due to impaired immunity underscore the importance of vaccination against pneumococci. However, available capsular polysaccharide vaccines are often poorly immunogenic in patients at risk for pneumococcal disease. The goal of this study was to explore the potential of peptide mimotopes to function as alternative vaccine antigens to elicit a type-specific antibody response to pneumococci. We used a human monoclonal immunoglobulin A (IgA) antibody (NAD) to type 8 Streptococcus pneumoniae capsular polysaccharide (type 8 PS) to screen a phage display library, and the phage PUB1 displaying the peptide FHLPYNHNWFAL was selected after three rounds of biopanning. Inhibition studies with phage-displayed peptide or the peptide PUB1 and type 8 PS showed that PUB1 is a mimetic of type 8 PS. PUB1 conjugated to tetanus toxoid (PUB1-TT) induced a type 8 PS-specific antibody response in BALB/c mice, further defining it as a mimotope of type 8 PS. The administration of immune sera obtained from PUB1-TT-immunized mice earlier (days 14 and 21) and later (days 87 and 100) after primary and reimmunization resulted in a highly significant prolongation of the survival of naive mice after pneumococcal challenge compared to controls. The survival of PUB1-TT-immunized mice was also prolonged after pneumococcal challenge nearly 4 months after primary immunization. The efficacy of PUB1-TT-induced immune sera provides proof of principle that a mimotope-induced antibody response can protect against pneumococci and suggests that peptide mimotopes selected by type-specific human antibodies could hold promise as immunogens for pneumococci.

Advances in Pneumococcal Vaccines

The introduction of Haemophilus influenzae type b (Hib) vaccine into the universal immunisation schedules of many industrialised countries and the subsequent remarkable decline in the incidence of invasive Hib disease has further highlighted the impact of invasive pneumococcal diseases. Streptococcus pneumoniae is now the leading cause of bacterial meningitis in children in many settings and a leading cause of vaccine-preventable bacterial disease in children worldwide. The currently marketed 23-valent pneumococcal polysaccharide vaccine provides large serotype coverage at a relatively low cost. However, it is not efficacious in young children. Pneumococcal conjugate vaccines (PCVs) are highly effective in preventing invasive disease in infants and young children, with favourable safety and immunogenicity profiles. These vaccines have also shown efficacy in reducing cases of non-invasive disease (i.e. otitis media), nasopharyngeal acquisition of vaccine-specific serotypes of S. pneumoniae, and protection against pneumococcal disease caused by resistant strains. However, PCV contains a limited number of pneumococcal serotypes and, given adequate ecological pressure, replacement disease by non-vaccine serotypes remains a threat, particularly in areas with very high disease burden. Furthermore, although capsular-specific antibodies have been shown to be highly protective, it remains unclear what concentration of these serotype-specific antibodies protect against disease and, more recently, it has become clear that opsonic activity and avidity of these antibodies are more critical determinants of protection than concentration. Therefore, monitoring disease burden and defining immune correlates of protection after widespread use of conjugate vaccines are crucial for the evaluation of these new generation vaccines. Furthermore, a need exists to develop pneumococcal vaccines with lower cost and larger serotype coverage. Development of one or more protein vaccines that might be easier and, thus, less expensive to manufacture, and which might provide protection against multiple serotypes, is in progress. This article reviews the current state of pneumococcal disease and pneumococcal vaccines in clinical use.

Pneumococcal conjugate vaccines for preventing vaccine-type invasive pneumococcal disease and pneumonia with consolidation on x-ray in children under two years of age

BACKGROUND

Pneumonia, most commonly caused by Streptococcus pneumoniae (Pnc), is a major cause of morbidity and mortality among young children especially in developing countries. Recently, the prevalence of antibiotic-resistant Pnc has increased worldwide such that the effectiveness of preventive strategies, like the new pneumococcal conjugate vaccines (PCV) on rates of invasive pneumococcal disease (IPD) and pneumonia, needs to be evaluated.

OBJECTIVES

To determine the efficacy of PCV in reducing the incidence of IPD due to vaccine serotypes (VT) and x-ray confirmed pneumonia with consolidation of unspecified etiology in children who received PCV before 12 months of age.

SEARCH STRATEGY

We searched the following databases: the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, Issue 1 2004), MEDLINE (1990 to March 2004) and EMBASE (1990 to December 2003). Reference list of articles, and books of abstracts of relevant symposia, were hand searched. Researchers in the field were also contacted.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing PCV with placebo, or another vaccine, among children below two years with IPD and clinical/radiographic pneumonia as outcomes.

DATA COLLECTION AND ANALYSIS

Two reviewers independently identified eligible studies, assessed trial quality, and extracted data. Differences were resolved by discussion. The inverse variance method was used to pool effect sizes.

MAIN RESULTS

We identified four trials assessing the efficacy of PCV in reducing the incidence of IPD, two on x-ray confirmed pneumonia as outcome, and one on clinical pneumonia, with or without x-ray confirmation. Results from pooling HIV-1 negative children from the South African study with the other studies were as follows: the pooled vaccine efficacy (VE) for vaccine-type IPD was 88% (95% confidence interval (CI) 73% to 94%; fixed effect and random effects models), the effect measure was statistically significant (p <0.00001) and there was no heterogeneity (p = 0.77I2 0%); the pooled VE for all-serotype IPD was 66% (95% CI 46% to 79%; fixed effect model), the effect measure was statistically significant (p <0.00001) and there was no statistical heterogeneity (p = 0.09, I2 51%); the pooled VE for x-ray confirmed pneumonia was 22% (95% CI 11% to 31%; both fixed effect and random effects models) and there was no statistical heterogeneity (p = 0.80, I2 0%). Analyses that included all the children in the South African study (HIV-1 negative and HIV-1 positive children) and pooled with data from the other studies gave very similar results.

REVIEWERS' CONCLUSIONS

PCV is effective in reducing the incidence of IPD from all serotypes but exerts a greater effect in reducing VT IPD. Although PCV is also effective in reducing the incidence of x-ray confirmed pneumonia, there are still uncertainties about the definition of this outcome. Additional randomised controlled trials are currently in progress.

Central role of complement in passive protection by human IgG1 and IgG2 anti-pneumococcal antibodies in mice

Streptococcus pneumoniae is an important cause of morbitity and mortality worldwide. Capsule-specific IgG1 and IgG2 Abs are induced upon vaccination with polysaccharide-based vaccines that mediate host protection. We compared the protective capacity of human recombinant serogroup 6-specific IgG1 and IgG2 Abs in mice deficient for either leukocyte FcR or complement factors. Human IgG1 was found to interact with mouse leukocyte FcR in vitro, whereas human IgG2 did not. Both subclasses induced complement activation, resulting in C3c deposition on pneumococcal surfaces. Passive immunization of C57BL/6 mice with either subclass before intranasal challenge with serotype 6A induced similar degrees of protection. FcgammaRI- and III-deficient mice, as well as the combined FcgammaRI, II, and III knockout mice, were protected by passive immunization, indicating FcR not to be essential for protection. C1q or C2/factor B knockout mice, however, were not protected by passive immunization. Passively immunized C2/factor B(-/-) mice displayed higher bacteremic load than C1q(-/-) mice, supporting an important protective role of the alternative complement pathway. Spleens from wild-type and C1q(-/-) mice showed hyperemia and thrombotic vessel occlusion, as a result of septicemic shock. Notably, thrombus formation was absent in spleens of C2/factor B(-/-) mice, suggesting that the alternative complement pathway contributes to shock-induced intravascular coagulation. These studies demonstrate complement to play a central role in Ab-mediated protection against pneumococcal infection in vivo, as well as in bacteremia-associated thrombotic complications.

Disparity in functional activity between serum anticapsular antibodies induced in adults by immunization with an investigational group A and C Neisseria meningitidis-diphtheria toxoid conjugate vaccine and by a polysaccharide vaccine

Polysaccharide-protein conjugate vaccines elicit higher concentrations of serum anticapsular antibody in infants and children than do unconjugated polysaccharide vaccines. The conjugate-induced antibodies also have higher avidity and complement-mediated bactericidal activity. Similar vaccine-related differences in the magnitude or functional activity of antibody are observed infrequently in immunized adults. We compared the antibody responses of adults immunized with an investigational group A and C meningococcal conjugate vaccine to those elicited by an unconjugated meningococcal polysaccharide vaccine. Although there were no significant differences between the respective geometric mean bactericidal titers of the two vaccine groups, it took, on average, three- to fourfold higher concentrations of polysaccharide-induced serum anticapsular antibody to achieve 50% complement-mediated bacteriolysis than conjugate-induced antibody (P < 0.001 for groups A and C). At limiting doses, the polysaccharide-induced anticapsular antibodies also were less effective in conferring passive protection against meningococcal bacteremia in infant rats challenged with a group C strain (P < 0.04). The avidity index of the group C antibodies was higher in the conjugate vaccine group than in the polysaccharide vaccine group (P < 0.005). The disparities in the functional activity of the anticapsular antibodies elicited in adults by the two vaccines imply fundamental differences in the respective B-cell populations stimulated.

Immunization with Porphyromonas gingivalis capsular polysaccharide prevents P. gingivalis-elicited oral bone loss in a murine model

The capsular polysaccharide (CPS) of the periodontal pathogen Porphyromonas gingivalis is an important virulence factor for this organism. We purified P. gingivalis CPS, immunized mice with this antigen, and assessed the vaccine potential of P. gingivalis CPS by using the murine oral challenge model. Animals immunized with P. gingivalis CPS developed elevated levels of immunoglobulin M (IgM) and IgG in serum that reacted with whole P. gingivalis organisms. The mice immunized with P. gingivalis CPS were protected from P. gingivalis-elicited oral bone loss. These data demonstrate that P. gingivalis CPS is a vaccine candidate for prevention of P. gingivalis-elicited oral bone loss.

Perspectives on hepatitis B infections and the efficacy of vaccination (hepatitis B and pneumococci) in dialysis patients

Hepatitis B is a well known problem in dialysis units. We therefore examined the historical frequency of hepatitis B carriers in our unit, our vaccination program to hepatitis B virus (HBV), the response to hepatitis B vaccine, the IgG subclass response of anti-HBs and the response and IgG subclass response to pneumococcal vaccination (another vaccine) in dialysis patients. From 1970 and onwards 23 HBV carriers were found, but no new cases of hepatitis B occurred during the study period, i.e. from 1980 and onwards. Only one of the carriers was alive by the end of 2001. In four patients liver disease (in one of them liver cirrhosis) may have been a concomitant cause of death. The antibody response to hepatitis B vaccine was significantly lower in patients than in staff. In four patients a fourth injection was cancelled due to transplantation and bad health, while such data were lacking in 8 cases. In anti-HBs positive patients and controls a significant difference in the response of healthy adults was observed in anti-HBs IgG1 (p < 0.001) vs all other IgG subclasses. Dialysis patients had low levels, or negative findings, in all cases, with IgG1 as the highest proportion found (3/11 patients). An antibody response to pneumococcal vaccination was registered in 25 out of 29 dialysis patients (in all 86%). The IgG-subclass vaccination response to pneumococci in 28 dialysis patients was mainly IgG2 and IgG1 but also occurred in IgG3 and IgG4. Prevaccination antibody levels of the controls were higher in IgG1 and IgG2 (p < 0.01) (n = 21) than in dialysis patients (n = 28). Hepatitis B is nowadays a rare, but still dangerous disease in nephrology units. Dialysis patients have a reduced response to hepatitis B vaccine and vaccination schedules should be started early as some patients otherwise may not receive a fourth injection. The adequate antibody response to pneumococcal vaccination mainly due to IgG2 and IgG1 antibodies indicates that the antigen involved is important in vaccination responses in dialysis patients.

Current state of pneumococcal vaccines

Streptococcus pneumoniae is a leading cause of bacterial pneumonia, meningitis, and acute otitis media in children and adults worldwide. According to World Health Organization estimates, at least 1 million children under 5 years of age die each year from pneumococcal pneumonia. The emergence of resistant strains necessitates the development of an effective vaccine with a large serotype coverage. The 11 most common serotypes cause 72-83% of all serious pneumococcal diseases worldwide. Currently marketed 23-valent pneumococcal polysaccharide vaccine provides large serotype coverage and offers a less expensive option. However, it is efficacious only in adults but not in infants. Conjugate vaccines offer a solution by generating immunological memory already at early age. A recently licensed 7-valent conjugate vaccine is immunogenic and efficacious in infants. Its serotype coverage might be sufficient in Europe and North America, but not in Africa, Asia and Oceania. A need exists to develop pneumococcal vaccines with lower cost and larger serotype coverage. Several 11-valent pneumococcal conjugate vaccines are being evaluated in phase I-III trials. This study reviews the current state of pneumococcal problem and pneumococcal vaccines in clinical use.

Bridging phase 2 and phase 3 pneumococcal immunologic data for future combination vaccines

Pneumococcal conjugate vaccines (PncCs) will be introduced into childhood vaccination programs now that the first PncC has been licensed for use. The next generation of PncCs and possible combination vaccines containing PncC will most probably be approved on the basis of phase 2 immunogenicity and safety data. PncCs are combination vaccines that include, at present, 7-11 components. Immune response to different components may vary. Furthermore, there seem to be population-based differences in immune response. Whether these differences are due to the other vaccines that are given simultaneously or due to the genetic background remains to be seen. Immune response can be evaluated by determining both the quantity and the quality of antibodies after vaccination. However, data are still missing on the minimal protective immune response and serologic correlates or surrogates of protection.

Polysaccharides, mimotopes and vaccines for fungal and encapsulated pathogens

Vaccination is a rational alternative to treatment for Cryptococcus neoformans infections, as these infections are currently intractable in immunocompromised (including HIV-infected) individuals. Vaccines composed of the cryptococcal capsular polysaccharide glucuronoxylomannan (GXM), the key C. neoformans virulence factor, elicit protective antibodies in mice, although deleterious antibodies can also be induced. By contrast, polysaccharides are poor immunogens in HIV-infected humans and others with B-cell defects. Peptide mimotopes of GXM can induce protective immunity to C. neoformans in mice, however, our knowledge of the mechanisms of mimotope-induced protection is incomplete and further work is needed if polysaccharide- or mimotope-based vaccines are to be used to manage C. neoformans infection.

Activation of cell-mediated immunity following immunization with pneumococcal conjugate or polysaccharide vaccine

The immunogenicity of pneumococcal polysaccharide (PS) vaccines can be improved by conjugating PS to a polypeptide carrier that alters the immune response from T-cell independent to T-cell dependent. In order to study the influence of PS or protein antigens as inducers of cell-mediated responses, 30 adults were immunized with a 23-valent pneumococcal PS vaccine (PS-group) or an 11-valent, tetanus and diphtheria mixed carrier conjugate vaccine with (adjuvant group) or without aluminium adjuvant (nonadjuvant group). Cell-mediated responses were analyzed on days 0, 14 and 28 after vaccination by measuring lymphocyte proliferation and production of interferon (IFN)-gamma (Th1 marker) or interleukin (IL)-4 and IL-5 (Th2 markers) cytokines after in vitro stimulation with the PS and protein components of the vaccines. Tetanus and diphtheria proteins were the main inducers of lymphocyte proliferative and cytokine responses. Conjugate vaccines induced increased proliferative responses to the tetanus or diphtheria protein, but not to the PS components. In the PS-group, a lymphocyte proliferative response to protein antigens was not observed. The number of antigen-specific and nonspecific IFN-gamma-secreting cells detected by ELISPOT tended to increase in all three groups in response to protein or to PS antigen. No major differences were detected in the number of IL-4-secreting cells measured 14 and 28 days after vaccination. The conjugate vaccine with adjuvant was associated with Th2 type of activation indicated by an enhanced IL-5 secretion in response to the tetanus and diphtheria protein antigens.

Tolerability and immunogenicity of an 11-valent pneumococcal conjugate vaccine in adults

We studied the safety and immunogenicity in healthy adults of an 11-valent pneumococcal conjugate vaccine. Capsular polysaccharides (PS) of serotypes 1, 4, 5, 7F, 9V, 19F and 23F were conjugated to tetanus toxoid, and of serotypes 3, 6B, 14 and 18C to diphtheria toxoid. Ten subjects received the conjugate vaccine with and the other ten subjects without aluminium hydroxide adjuvant. The reference vaccine was a marketed 23-valent PS vaccine. Safety data were recorded over 5 days after the immunisation. IgG antibody concentrations, avidity and subclass distribution were measured by EIA. The conjugate without aluminium induced more local adverse effects than the conjugate with aluminium or PS vaccine. All vaccines evoked significant antibody increases to all vaccine specific antigens. Both conjugate vaccines induced antibodies mainly of IgG(2) subclass, and adjuvanted conjugate vaccine induced IgG antibodies with increased avidity. This first administration, to man, of a mixed protein carrier 11-valent pneumococcal conjugate vaccine demonstrated its ability to induce an immune response without significant adverse effects, enabling further study on its use in paediatric populations.

Are the enzyme immunoassays for antibodies to pneumococcal capsular polysaccharides serotype specific?

The specificity of antibody binding to pneumococcal capsular polysaccharides (Pnc PSs) measured by enzyme immunoassay (EIA) was studied by inhibition of antibody binding by homologous and heterologous PSs. We found extensive cross-reactivity of antibody binding to type 6B, 19F, and 23F PSs but not to type 14 PS, even after treatment with cell wall PS (CPS). The cross-reactive antibody was highly prevalent in sera of infants and adults with naturally acquired antibody, but not in sera of infants and adults immunized with pneumococcal vaccines. However, a type 11A antibody response was seen after vaccination with heterologous PSs. Monoclonal antibodies prepared against a type 6B PS-tetanus toxoid conjugate recognized also other than the specific type of PS in the EIA, implying the possible existence of a cross-reactive epitope. Remarkable differences in specificity among type 6B PS preparations from different manufacturers were found. Moreover, different lots of type 11A PS from the same manufacturer showed differences in specificity. The results suggest that some Pnc PS preparations may contain cross-reactive epitopes or impurities, other than CPS, that are common to many types of Pnc PS. The specificity of antibodies, especially in sera from nonimmunized subjects, measured by EIA can be questioned.

Immunogenicity of pneumococcal conjugate vaccines

BACKGROUND

Prevention of pneumococcal infections is a public health priority because of the high impact of the disease and because of the increasing problems due to antimicrobial resistance. Traditional vaccines, consisting of purified capsular polysaccharides (PSs) of Streptococcus pneumoniae, are not immunogenic in young children. In addition they confer only limited protection in patients with immunodeficiencies and hematologic malignancies.

IMMUNOGENICITY OF PNEUMOCOCCAL CONJUGATE VACCINES

Immunogenicity of the PS vaccine has been enhanced by coupling pneumococcal PSs to proteins to produce a conjugate vaccine. Conjugate molecules are designed to possess T cell dependent properties, such as immunogenicity in early infancy, stimulation of high levels of IgG isotype antibodies and enhanced immunologic memory responses. In the clinical studies multivalent pneumococcal conjugate vaccines have been shown to induce an IgG-dominating serum antibody response against common pneumococcal serotypes causing infections in children. A booster dose later in life creates a robust and rapid antibody response, indicating the existence of immunologic memory in primed children. Antibodies induced by conjugate vaccines are functionally active, as demonstrated by their high avidity and opsonophagocytic activity.

Polyclonal antibodies from patients immunized with a globo H-keyhole limpet hemocyanin vaccine: isolation, quantification, and characterization of immune responses by using totally synthetic immobilized tumor antigens

We have previously reported on a carbohydrate-based vaccine program for immunotherapy in cancer patients. One such vaccine, based on the globo H antigen conjugated to the protein keyhole limpet hemocyanin (KLH), has been in clinical evaluation. Although this and other carbohydrate vaccines have been shown to induce antibody responses, there are currently no quantitative data on the antibody levels achieved in immunized patients by these or other anti-cancer vaccines. We report herein an efficient route to complex synthetic oligosaccharides attached to an affinity matrix for identifying and isolating antibodies elicited against such a carbohydrate-based vaccine in humans. Pre- and postvaccination profiles from serum samples of patients immunized with globo H-KLH were compared. All anti-globo H antibody activity was efficiently separated from other serum constituents. The isolated antibodies were readily quantified, and their specificities were analyzed. Since no comparable data were available on antibodies resulting from the vaccination of other cancer patients, we compared the observed levels with those quoted in studies with bacterial polysaccharide vaccines that had been quantified. Remarkably, cancer patients immunized with globo H-KLH produce anti-globo H antibody levels often exceeding those formed by immunization with bacterial polysaccharides. In addition, substantial quantities of both IgG and IgM antibodies were elicited, clearly indicating a class switch to IgG. Taken together, these analyses serve to clarify several aspects of the immune response to the vaccine and give several new insights to the carbohydrate-based vaccination strategy. Furthermore, antibodies so isolated could well have applications in clinical therapy.