Vaccination of COPD patients with a pneumococcus type 6B tetanus toxoid conjugate vaccine

This paper examines how pneumococcal type 6B polysaccharide conjugated to tetanus toxoid (Pn6B-TT) compares to a 23 valent pneumococcal vaccine (pneumococcal polysaccharide (PPS)-23) with respect to immunogenicity and serum opsonic activity in patients with chronic obstructive pulmonary disease (COPD). Patients with COPD aged 55-75 yrs were vaccinated with Pn6B-TT (n=10) or with PPS-23 (n=9). Healthy young adults (HA) were vaccinated with Pn6B-TT as controls. Total antibodies to serotype 6B polysaccharide were measured by radioimmunoassay and immunoglobulin (Ig)G antibodies by enzyme-linked immunosorbent assay. Opsonic activity was measured by a phagocytosis assay using human neutrophils as effector cells. The patient groups were comparable by age, smoking history, lung function and use of steroids. COPD patients vaccinated with Pn6B-TT or PPS-23 showed an increase in IgG antibodies and a nonsignificant increase in opsonic activity. This was similar to the increase in IgG and opsonic activity seen in HA. There was a significant correlation between antibody levels and opsonic activity in COPD patients vaccinated both with Pn6B-TT and PPS-23. Pneumococcal antibodies have been shown to confer protection from infection. The results of the present study indicate that protective immunity can be expected in elderly chronic obstructive pulmonary disease patients vaccinated with conjugate vaccines.

Production, recovery and immunogenicity of the protective antigen from a recombinant strain of Bacillus anthracis

The protective antigen (PA) is one of the three components of the anthrax toxin. It is a secreted nontoxic protein with a molecular weight of 83 kDa and is the major component of the currently licensed human vaccine for anthrax. Due to limitations found in the existing vaccine formulation, it has been proposed that genetically modified PA may be more effective as a vaccine. The expression and the stability of two recombinant PA (rPA) variants, PA-SNKE-deltaFF-E308D and PA-N657A, were studied. These proteins were expressed in the nonsporogenic avirulent strain BH445. Initial results indicated that PA-SNKE-deltaFF-E308D, which lacks two proteolysis-sensitive sites, is more stable than PA-N657A. Process development was conducted to establish an efficient production and purification process for PA-SNKE-deltaFF-E308D. pH, media composition, growth strategy and protease inhibitors composition were analyzed. The production process chosen was based on batch growth of B. anthracis using tryptone and yeast extract as the only source of carbon, pH control at 7.5, and antifoam 289. Optimal harvest time was 14-18 h after inoculation, and EDTA (5 mM) was added upon harvest for proteolysis control. Recovery of the rPA was performed by expanded-bed adsorption (EBA) on a hydrophobic interaction chromatography (HIC) resin, eliminating the need for centrifugation, microfiltration and diafiltration. The EBA step was followed by ion exchange and gel filtration. rPA yields before and after purification were 130 and 90 mg/l, respectively. The purified rPA, without further treatment, treated with small amounts of formalin or adsorbed on alum, induced, high levels of IgG anti-PA with neutralization activities.

Immunologic and epidemiologic experience of vaccination with a monocomponent pertussis toxoid vaccine

Pertussis re-emerged in Sweden with a cumulative incidence of about 60% during the first 10 years of life, when the locally produced cellular vaccine lost its efficacy around 1970 and general vaccination was discontinued in 1979. The epidemiology, clinical features, and immunology of pertussis and a monocomponent pertussis toxoid vaccine were studied in Göteborg, Sweden. After phase 1 and 2 studies, a randomized, double-blind, placebo-controlled trial of pertussis toxoid (PTox), compounded with diphtheria and tetanus toxoids, was administered to 3450 children according to the Swedish schedule at 3, 5, and 12 months of age. After a mean follow-up of 18 months, the efficacy was 71% overall and 75% in household contacts, respectively. A statistically significant correlation was found between the level of PTox-induced antibodies and protection against pertussis. As observed with cellular and with multicomponent acellular vaccines, PTox reduced the severity of disease and the percent of children with positive cultures. Furthermore, vaccination reduced the transmission of Bordetella pertussis to household contacts in the vaccinees compared with the controls who received only diphtheria and tetanus toxoids. Patients with culture-verified Bordetella parapertussis infection reacted with antibodies to pertactin and to filamentous hemagglutinin but not to pertussis toxin, and some subsequently developed pertussis. The antibody responses of patients with pertussis to the surface polysaccharides of B pertussis and to B parapertussis were cross-reactive serologically. Serosurveys showed that only antibodies to pertussis toxin were related to the occurrence of pertussis in the general population: antibodies to filamentous hemagglutinin and pertactin were probably stimulated by antigens of other bacteria as well as Bordetellae. Mass vaccination of Göteborg children born in the 1990s was started in 1995. In February 1999, about 55% had been vaccinated and both B pertussis and pertussis decreased significantly in individuals of all ages (herd immunity). Similar to diphtheria, PTox-induced immunity to pertussis occurs both on an individual and community basis. The apparent greater efficacy of multicomponent acellular pertussis vaccines compared with monocomponent PTox was proposed to be an artifact created when the diagnosis of pertussis was made by the serologic criteria of the World Health Organization only. Our conclusion is that PTox is both an essential and alone sufficient antigen in acellular pertussis vaccines.

Expression of a Mycobacterium tuberculosis arabinomannan antigen in vitro and in vivo

The outermost layer of Mycobacterium tuberculosis contains two major polysaccharides, arabinomannan (AM) and glucan (GC). We studied the in vitro and in vivo expression of an M. tuberculosis AM antigen using monoclonal antibody (MAb) 9d8 (2a), an isotype-switched variant of the immunoglobulin G3 (IgG3) MAb 9d8. MAb 9d8 had been previously shown to bind M. tuberculosis AM and the M. tuberculosis surface. Our in vitro experiments showed that MAb 9d8(2a) bound strongly to whole-cell M. tuberculosis Erdman but not to the CDC 1551 strain grown in medium for an extended period. However, AM antigen was detected in the culture supernatant of both strains, and its concentration increased in a time-dependent manner. The detection of AM antigen from both strains was decreased in the presence of Tween 80. In mice infected with M. tuberculosis Erdman, AM antigen accumulated in organ homogenates concomitant to an increase in bacterial organ burden and an increase in IgG and IgM titer to AM. These results (i) indicate that the surface expression of AM during in vitro growth changes with culture age, is strain dependent, and is affected by the presence of Tween 80 in the culture media; (ii) show that AM is produced by bacteria growth in vivo; and (iii) demonstrate that the amount of in vivo-detected AM can be dependent on the number of bacteria in the infected organ.

Serum immunoglobulin G antibody responses to Bordetella pertussis lipooligosaccharide and B. parapertussis lipopolysaccharide in children with pertussis and parapertussis

Serum immunoglobulin G (IgG) antibodies against the lipooligosaccharide (LOS) of Bordetella pertussis and the lipopolysaccharide (LPS) of Bordetella parapertussis were measured by enzyme-linked immunosorbent assay in paired sera from 40 children with pertussis and 14 with parapertussis. Wide differences in the individual responses were noted. Both anti-LOS and -LPS IgG levels increased significantly in the children with pertussis, as did anti-LPS but not anti-LOS in those with parapertussis.

The efficacy of a Salmonella typhi Vi conjugate vaccine in two-to-five-year-old children

BACKGROUND

Typhoid fever is common in developing countries. The licensed typhoid vaccines confer only about 70 percent immunity, do not protect young children, and are not used for routine vaccination. A newly devised conjugate of the capsular polysaccharide of Salmonella typhi, Vi, bound to nontoxic recombinant Pseudomonas aeruginosa exotoxin A (rEPA), has enhanced immunogenicity in adults and in children 5 to 14 years old and has elicited a booster response in children 2 to 4 years old.

METHODS

In a double-blind, randomized trial, we evaluated the safety, immunogenicity, and efficacy of the Vi-rEPA vaccine in children two to five years old in 16 communes in Dong Thap Province, Vietnam. Each of the 11,091 children received two injections six weeks apart of either Vi-rEPA or a saline placebo. Cases of typhoid, diagnosed by the isolation of S. typhi from blood cultures after 3 or more days of fever (a temperature of 37.5 degrees C or higher), were identified by active surveillance over a period of 27 months. We estimated efficacy by comparing the attack rate of typhoid in the vaccine group with that in the placebo group.

RESULTS

S. typhi was isolated from 4 of the 5525 children who were fully vaccinated with Vi-rEPA and from 47 of the 5566 children who received both injections of placebo (efficacy, 91.5 percent; 95 percent confidence interval, 77.1 to 96.6; P<0.001). Among the 771 children who received only one injection, there was 1 case of typhoid in the vaccine group and 8 cases in the placebo group. Cases were distributed evenly among all age groups and throughout the study period. No serious adverse reactions were observed. In all 36 children studied four weeks after the second injection of the vaccine, levels of serum IgG Vi antibodies had increased by a factor of 10 or more.

CONCLUSIONS

The Vi-rEPA conjugate typhoid vaccine is safe and immunogenic and has more than 90 percent efficacy in children two to five years old. The antibody responses and the efficacy suggest that this vaccine should be at least as protective in persons who are more than five years old.

Safety and immunogenicity of improved Shigella O-specific polysaccharide-protein conjugate vaccines in adults in Israel

Data suggest that the O-specific polysaccharide (O-SP) domain of the lipopolysaccharide (LPS) of Shigella species is both an essential virulence factor and a protective antigen and that a critical level of serum immunoglobulin G (IgG) to this antigen will confer immunity to shigellosis. Because covalent attachment of polysaccharides to proteins increases their immunogenicity, especially in infants and in young children, the O-SP of Shigella species were bound to medically useful proteins, and the safety and immunogenicity of the resultant conjugates were confirmed in adults and 4- to 7-year-old children. Succinylation of the carrier protein improved the immunogenicity of Shigella conjugates in mice and increased their yield. Based on these results, a clinical trial of O-SP conjugates of Shigella sonnei and Shigella flexneri 2a bound to succinylated mutant Pseudomonas aeruginosa exotoxin A (rEPAsucc) or native or succinylated Corynebacterium diphtheriae toxin mutant (CRM9 or CRM9succ) was conducted in healthy adults. The conjugates were safe and immunogenic. S. sonnei-CRM9, S. sonnei-CRM9succ, and S. sonnei-rEPAsucc elicited significant rises of geometric mean (GM) IgG anti-LPS within 1 week of injection (P < 0.001). At 26 weeks, the GM anti-LPS levels elicited by these three conjugates were similar and higher than their prevaccination levels (P < 0.0001). GM IgG anti-LPS levels elicited by S. flexneri 2a-rEPAsucc were significantly higher than those elicited by S. flexneri 2a-rCRM9succ at all intervals after injection. At 26 weeks, the levels of IgG anti-LPS in vaccinees were higher than their prevaccination levels (P < 0.0001). The serum antibody responses were specific, as there was no significant rise of anti-LPS to the heterologous O-SP in any vaccinee. Both conjugates elicited statistically significant rises of serum antibodies to the injected carrier protein. At 6 months, these five Shigella conjugates elicited higher fold rises than similar conjugates (D. N. Taylor et al., Infect. Immun. 61:3678-3687, 1993). Based on these data, we chose S. sonnei-CRM9 and S. flexneri 2a-rEPAsucc for evaluation in children.

Clostridium difficile recombinant toxin A repeating units as a carrier protein for conjugate vaccines: studies of pneumococcal type 14, Escherichia coli K1, and Shigella flexneri type 2a polysaccharides in mice

Unlike the native protein, a nontoxic peptide (repeating unit of the native toxin designated rARU) from Clostridium difficile toxin A (CDTA) afforded an antigen that could be bound covalently to the surface polysaccharides of pneumococcus type 14, Shigella flexneri type 2a, and Escherichia coli K1. The yields of these polysaccharide-protein conjugates were significantly increased by prior treatment of rARU with succinic anhydride. Conjugates, prepared with rARU or succinylated (rARUsucc), were administered to mice by a clinically relevant dosage and immunization scheme. All conjugates elicited high levels of serum immunoglobulin G both to the polysaccharides and to CDTA. Conjugate-induced anti-CDTA had neutralizing activity in vitro and protected mice challenged with CDTA, similar to the rARU alone. Conjugates prepared with succinylated rARU, therefore, have potential for serving both as effective carrier proteins for polysaccharides and for preventing enteric disease caused by C. difficile.

Correlation between pertussis toxin IgG antibodies in postvaccination sera and subsequent protection against pertussis

All acellular pertussis vaccines contain pertussis toxoid and induce protection against pertussis. This study investigated the relation between the postvaccination levels of pertussis toxin (PT) serum IgG and protection against pertussis. PT IgG was determined in sera obtained 21-77 days after the third vaccination from 813 children who received 3 doses of pertussis toxoid. The children were followed for 21-33 months after vaccination for the occurrence of pertussis. Of the children, 126 were exposed to pertussis in their households. The median PT IgG concentration was 79 U/mL in those who developed severe pertussis (>/=21 day of paroxysmal cough), 156 U/mL with mild pertussis (<21 days of paroxysmal cough), and 246 U/mL in those who did not develop pertussis (79 vs. 246, P<.0001). Corresponding values in the 687 children with no household exposure were 99, 124, and 155 U/mL, respectively (99 vs. 155, P<.0001). Thus, there is a highly significant correlation between the level of vaccine-induced serum PT IgG and protection against pertussis.

Safety and immunogenicity of Vi conjugate vaccines for typhoid fever in adults, teenagers, and 2- to 4-year-old children in Vietnam

The capsular polysaccharide of Salmonella typhi, Vi, is an essential virulence factor and a protective vaccine for people older than 5 years. The safety and immunogenicity of two investigational Vi conjugate vaccines were evaluated in adults, 5- to 14-year-old children, and 2- to 4-year-old children in Vietnam. The conjugates were prepared with Pseudomonas aeruginosa recombinant exoprotein A (rEPA) as the carrier, using either N-succinimidyl-3-(2-pyridyldithio)-propionate (SPDP; Vi-rEPA(1)) or adipic acid dihydrazide (ADH; Vi-rEPA(2)) as linkers. None of the recipients experienced a temperature of >38.5 degrees C or significant local reactions. One injection of Vi-rEPA(2) into adults elicited a geometric mean (GM) increase in anti-Vi immunoglobulin G (IgG) from 9.62 enzyme-linked immunosorbent assay units/ml (EU) to 465 EU at 6 weeks; this level fell to 119 EU after 26 weeks. In the 5- to 14-year-old children, anti-Vi IgG levels at 6 weeks elicited by Vi-rEPA(2), Vi-rEPA(1), and Vi were 169, 22.8, and 18.9 EU, respectively (P = 0.0001 for Vi-rEPA(1) and Vi with respect to Vi-rEPA(2)). At 26 weeks, the anti-Vi IgG levels for recipients of Vi-rEPA(2), Vi-rEPA(1), and Vi were 30.0, 10.8, and 13.4 EU, respectively (P < 0.001 for Vi-rEPA(1) and Vi with respect to Vi-rEPA(2)); all were higher than the preinjection levels (P = 0. 0001). Vi-rEPA(2) also elicited the highest anti-Vi IgM and IgA levels of the three vaccines. In the 2- to 4-year-old children at 6 weeks following the first injection, Vi-rEPA(2) elicited an anti-Vi IgG level of 69.9 EU compared to 28.9 EU for Vi-rEPA(1) (P = 0.0001). Reinjection increased Vi antibody levels from 69.9 to 95.4 EU for Vi-rEPA(2) and from 28.9 to 83.0 EU for Vi-rEPA(1). At 26 weeks, anti-Vi IgG levels remained higher than those at preinjection (30.6 versus 0.18 for Vi-rEPA(2) and 12.8 versus 0.33 for Vi-rEPA(1); P = 0.0001 for both). Vi vaccine is recommended for individuals of 5 years of age or older. In the present study, the GM level of anti-Vi IgG elicited by two injections of Vi-rEPA(2) in the 2- to 4-year-old children was higher than that elicited by Vi in the 5- to 14-year-old children (30.6 versus 13.4; P = 0.0001). The safety and immunogenicity of the Vi-rEPA(2) conjugate warrant further investigation.

Treatment with succinic anhydride improves the immunogenicity of Shigella flexneri type 2a O-specific polysaccharide-protein conjugates in mice

Seroepidemiological data and a clinical trial with a Shigella sonnei O-specific polysaccharide (O-SP)-Pseudomonas aeruginosa recombinant exoprotein A (rEPA) conjugate provide evidence that a critical level of immunoglobulin G (IgG) lipopolysaccharide (LPS) antibodies in serum confers protection against shigellosis. We evaluated the immunogenicity of conjugates whose carrier proteins and O-SPs were treated with succinic anhydride (SA), which reacts with amino groups at neutral pH to form amide-linked carboxyls (succinylation). Conjugates were synthesized with either of two genetically inactivated medically useful toxins, the diphtheria protein CRM9 or rEPA, bound to the O-SP of Shigella flexneri type 2a. Conjugates composed of the succinylated protein, succinylated O-SP, or both succinylated components were administered to mice by a clinically relevant scheme, and their levels of serum IgG anti-LPS and anti-proteins were assayed 7 days after the second and third injections. CRM9 served as a more immunogenic carrier than rEPA. Conjugates composed of succinylated components were more immunogenic than the conjugates composed of the native components. SA treatment of both the carrier protein and the O-SP did not confer an advantage over the succinylated protein alone. Conjugates prepared with native proteins, in general, elicited slightly higher levels of IgG protein antibodies than conjugates composed of the SA-treated proteins.

Safety and immunogenicity of Shigella sonnei and Shigella flexneri 2a O-specific polysaccharide conjugates in children

O-specific polysaccharide conjugates of shigellae were safe and immunogenic in young adults, and a Shigella sonnei conjugate conferred protection [1-3]. Shigellosis is primarily a disease of children; therefore, the safety and immunogenicity of S. sonnei and Shigella flexneri 2a conjugates were studied in 4- to 7-year-old children. Local and systemic reactions were minimal. The first injection of both conjugates elicited significant rises in geometric mean levels of serum IgG only to the homologous lipopolysaccharide (LPS) (S. sonnei, 0.32-8.25 ELISA units [EU]; S. flexneri 2a, 1.15-20.5 EU; P<.0001). Revaccination at 6 weeks induced a booster response to S. flexneri 2a LPS (20.5-30.5 EU, P=.003). Six months later, the geometric mean levels of IgG anti-LPS for both groups were higher than the prevaccination levels (P<.0001). Similar, but lesser, rises were observed for IgM and IgA anti-LPS. The investigational Shigella conjugates were safe and immunogenic in children and merit evaluation of their efficacy.

Similarities between the pathogenesis of and immunity to diphtheria and pertussis: the complex nature of serum antitoxin-induced immunity to these two diseases

Despite data from animal studies, seroepidemiological surveys, and controlled clinical trials, skepticism persists about immunity to pertussis conferred by serum IgG neutralizing antibodies (antitoxin). This is largely prompted by the absence of a "protective" level of antitoxin. Examination of the similarities between the pathogenesis and immunity to pertussis and diphtheria provides an explanation for this dilemma. As with pertussis, diphtheria toxoid vaccination confers only approximately 70% immunity on an individual basis, individuals with protective levels of antitoxin may contract diphtheria, and about 50% of the entire population, especially adults, have less than protective levels of antitoxin. The virtual disappearance of diphtheria followed vaccination of the entire population with diphtheria toxoid, which blocked transmission of toxigenic Corynebacterium diphtheriae and thus reduced the pathogen to almost undetectable levels. The individual and community-based immunity induced by diphtheria toxoid, we hypothesize, is similar to that of pertussis and pertussis toxoid.

Protein conjugates of synthetic saccharides elicit higher levels of serum IgG lipopolysaccharide antibodies in mice than do those of the O-specific polysaccharide from Shigella dysenteriae type 1

Our development of vaccines to prevent shigellosis is based on the hypothesis that a critical (protective) level of serum IgG to the O-specific polysaccharide (O-SP) domain of Shigella lipopolysaccharide (LPS) confers immunity. The O-SP is a hapten and must be conjugated to a protein to induce serum antibodies. The O-SP of Shigella dysenteriae type 1 (approximately 27 tetrasaccharide repeat units), prepared by acid hydrolysis of the LPS, was bound to human serum albumin (HSA) by multiple point attachment (O-SP-HSA): The molar ratio of HSA to O-SP was 1.0. Synthetic saccharides, composed of one or multiples of the O-SP tetrasaccharide, equipped with a spacer at their reducing end, were bound to HSA by a single point attachment: The average molar ratios of the saccharides to HSA ranged from 4 to 24. Serum IgG anti-LPS, elicited in mice by O-SP-HSA or synthetic tetra-, octa-, dodeca-, and hexadecasaccharide fragments, was measured by ELISA. Outbred 6-week-old female mice were injected s.c. three times at biweekly intervals with 2.5 micrograms of saccharide as a conjugate and were bled 7 days after the second and third injections. Excepting the tetramer, conjugates of the octamer, dodecamer and hexadecamer elicited IgG LPS antibodies after the second injection, a statistically significant rise (booster) after the third injection, and higher levels than those vaccinated with O-SP-HSA (P = 0.0001). The highest geometric mean levels of IgG anti-LPS were elicited by the hexadecamer with 9 chains or 9 moles of saccharide/HSA (15.5 ELISA units) followed by the octamer with 20 chains (11.1 ELISA units) and the dodecamer with 10 chains (9.52 ELISA units). Clinical evaluation of these synthetic saccharides bound to a medically useful carrier is planned.

Serum IgG antibody responses to pertussis toxin and filamentous hemagglutinin in nonvaccinated and vaccinated children and adults with pertussis

Levels of IgG antibody to pertussis toxin (PT) and filamentous hemagglutinin (FHA) were measured in paired serum samples from 781 patients fulfilling at least one laboratory criterion for pertussis that was suggested by an ad hoc committee sponsored by the World Health Organization. The patients were participants or family members of participants in a double-blind efficacy trial of a monocomponent pertussis toxoid vaccine. Of 596 nonvaccinated children, 90% had significant (two-fold or more) rises in PT IgG and FHA IgG levels. Only 17 (32%) of 53 children previously vaccinated with three doses of pertussis toxoid had rises in PT IgG levels because they already had elevated PT IgG levels in their acute-phase serum samples. PT IgG and FHA IgG levels were significantly higher in acute-phase serum samples from 29 adults than in acute-phase serum samples from the nonvaccinated children. Nevertheless, significant rises in levels of PT IgG (79% of samples) and FHA IgG (90%) were demonstrated in adults. In conclusion, assay of PT IgG and FHA IgG in paired serum samples is highly sensitive for diagnosing pertussis in nonvaccinated individuals. Assay of PT IgG levels in paired sera is significantly less sensitive for diagnosis of pertussis for children vaccinated with pertussis toxoid.

Immunity to pertussis. Not all virulence factors are protective antigens

As with diphtheria, immunity to pertussis is complex because it involves both individual and community protection against infection with B. pertussis. Although B. pertussis has at least five proteins required for virulence and an additional two "toxic" components, only serum neutralizing antibodies to PT (antitoxin) have been shown to confer immunity to pertussis.

Standardization of acellular pertussis vaccine by assay of serum neutralizing antibodies to pertussis toxin (antitoxin): analogy with diphtheria toxoid

Immunity conferred by vaccination with cellular pertussis vaccines and pertussis wanes so that adults are now the main reservoir of B. pertussis. Similar to diphtheria toxoid, acellular pertussis vaccines are suitable for vaccination of adults and it is probable that addition of pertussis toxoid to DT will be recommended for this age group. If this can be achieved, it is easy to predict that pertussis will be eliminated and the possibility of eradicating B. pertussis will become feasible. We propose that, despite the relative inaccuracy of correlating levels of antitoxin with individual immunity, a standardized assay and reference antiserum for pertussis toxoid will control acellular pertussis vaccines as was achieved with diphtheria toxoid.

Standardization may suffice for licensure of conjugate vaccines

Standardization schemes devised by Control Agencies have followed clinical trials of experimental vaccines. The wealth of information about the pathogenesis of and immunity to bacteria, whose surface polysaccharides are protective antigens, now permits standardization to predict the efficacy of polysaccharide-based vaccines. There has been tacit acceptance of this notion with the licensure of groups Y and W135 meningococcal vaccines and of many of the pneumococcal types whose frequency in patients was too low for statistical significance to be assigned for their clinical efficacy. In fact, this was also the case for licensure of polio virus type 2 vaccine. We can reliably measure the level of anti-polysaccharide antibodies for meningococci, pneumococci, GBS and the Vi of S. typhi. Haemophilus type b conjugates have been reliably standardized by physico-chemical assays. New conjugates, therefore, may be licensed by data provided by standardization without awaiting the results of costly and time-consuming efficacy trials. Adoption of this scientifically-based approach to licensure will hasten the implementation of new and more effective vaccines.

Isotypes and opsonophagocytosis of pneumococcus type 6B antibodies elicited in infants and adults by an experimental pneumococcus type 6B-tetanus toxoid vaccine

Streptococcus pneumoniae is a major respiratory pathogen of infants, children, and the elderly. Polysaccharide vaccines have been useful in adult populations but do not elicit protective immunity in infants and young children. To enhance their immunogenicity, vaccines of pneumococcal polysaccharides conjugated to proteins are being developed. In this study antibody levels and opsonic activities were compared in sera of infants and adults injected with pneumococcal polysaccharide type 6B (Pn6B) conjugated to tetanus toxoid (TT) (Pn6B-TT). Healthy infants were injected with Pn6B-TT; group A was injected at 3, 4, and 6 months of age, and group B was injected at 7 and 9 months of age. A booster injection was given at 18 months. Adults were injected once. Antibodies were measured by enzyme-linked immunosorbent assay and radioimmunoassay, and their functional activities were measured by opsonophagocytosis of radiolabelled pneumococci. In adults, increases in immunoglobulin M (IgM), IgG, IgA, IgG1, and IgG2 to Pn6B were observed. Infants reached adult levels of IgG1 anti-Pn6B after the primary injections. After the booster injection the infant groups had total IgG- and IgM-Pn6B antibody levels similar to those of adults. After the booster injection, IgG1 was the dominant infant anti-Pn6B isotype and at a level higher than in vaccinated adults, but IgA and IgG2 antibodies remained at very low levels. Opsonic activity increased significantly after Pn6B-TT injections; the highest infant sera showed opsonic activity comparable to that of vaccinated adults. Overall, opsonic activity correlated best with total and IgG anti-Pn6B antibodies (r = 0.741, r = 0.653, respectively; n = 35) and was highest in sera with high levels of all Pn6B antibody isotypes. The results indicate the protective potential of a pneumococcal 6B polysaccharide protein conjugate vaccine for young infants.

Immunization of children with pertussis toxoid decreases spread of pertussis within the family

OBJECTIVE

In a previously reported double blind placebo-controlled trial it was shown that vaccination with pertussis toxoid during infancy reduced the incidence of pertussis in the vaccinees. Parents and siblings of participants in the trial were followed for pertussis to determine whether vaccination provided indirect protection of close contacts in a nonvaccinating country with a high incidence of pertussis.

STUDY DESIGN

A group of 3450 infants were randomized to vaccination with diphtheria, tetanus and pertussis toxoids (DTPtxd) or to diphtheria and tetanus toxoids (DT). Pertussis cases were actively sought and diagnosed by cultures and serology in vaccinees (previously reported) and in family members during 2 years after the third vaccination.

RESULTS

Pertussis as defined by the World Health Organization (paroxysmal cough of > or = 21 days and certain laboratory criteria) was diagnosed in 11 parents of DTPtxd recipients and in 26 parents of DT recipients; indirect protection was 60% (95% confidence intervals, 16 to 82%). In nonvaccinated younger siblings of DTPtxd and DT recipients there were 10 and 18 cases of pertussis, respectively; indirect protection was 43% (95% confidence intervals, -31 to 76%). When all cases of pertussis with cough > or = 7 days were included, the indirect protection was 44% (95% confidence intervals, 7 to 67%) in parents and 56% (95% confidence intervals, 9 to 81%) in younger siblings.

CONCLUSION

Vaccination of children with pertussis toxoid reduces spread of pertussis to close contacts, which suggests that mass vaccination with pertussis toxoid would induce herd immunity.

Conformational stabilization of the altruronic acid residue in the O-specific polysaccharide of Shigella sonnei/Plesiomonas shigelloides

Complete assignments for the 1H- and the 13C-NMR spectra of the O-specific polysaccharide of S. sonnei/Plesiomonas shigelloides are reported. Evidence is presented that in this polysaccharide both pyranose residues exist preferentially in the 4C1 chair conformation and that the polysaccharide exists in the zwitterion form.

Immune responses of infants vaccinated with serotype 6B pneumococcal polysaccharide conjugated with tetanus toxoid

BACKGROUND

Streptococcus pneumoniae is a major cause of meningitis, bacteremia, pneumonia and otitis media. Pneumococcal polysaccharides are not immunogenic in infants, but improved immunogenicity of polysaccharide-protein conjugates has been demonstrated. Antibiotic-resistant pneumococci have increased the need for an effective vaccine.

OBJECTIVE

To study the safety and immunogenicity of a pneumococcal type 6B polysaccharidetetanus toxoid conjugate (Pn6B-TT) in infants and to assess the function of antibodies.

METHODS

Healthy infants were injected, Group A at 3, 4 and 6 months (n = 21) and Group B at 7 and 9 months (n = 19). Booster injection was given at 18 months. Antibodies were measured by enzyme-linked immunosorbent assay and radioimmunoassay, and functional activity was measured by opsonization of radiolabeled pneumococci. Nasopharyngeal cultures were obtained.

RESULTS

No significant adverse reactions were observed. Pn6B-IgG (enzyme-linked immunosorbent assay) increased to a geometric mean of 0.62 microgram/ml (P = 0.367, compared with prevaccination titers) in Group A at 7 months and 1.22 micrograms/ml (P < 0.001) in Group B at 10 months. Total Pn6B antibodies (radioimmunoassay) were 44 ng of antibody N/ml (P < 0.053) in Group A and 211 ng of antibody N/ml (P < 0.001) in Group B. A smaller increase in IgM and IgA anti-Pn6B was observed. Reinjection at 18 months elicited booster responses in total and IgG anti-Pn6B; 62% of those in Group A and 79% of those in Group B had > 300 ng of antibody N/ml. Opsonic activity, after initial and booster vaccinations, correlated with Pn6B-antibody titers. Three infants with nasopharyngeal cultures repeatedly positive for serogroup 6 had poor serum IgG responses.

CONCLUSION

Our results demonstrate that Pn6B-TT is safe, elicits functional antibodies and memory responses in infants.

Double-blind vaccine-controlled randomised efficacy trial of an investigational Shigella sonnei conjugate vaccine in young adults

BACKGROUND

The aim of this double-blind randomised vaccine-controlled trial was to assess the efficacy of a conjugate vaccine composed of Shigella sonnei O-specific polysaccharide bound to Pseudomonas aeruginosa recombinant exoprotein A (S sonnei-rEPA) and of an oral, live-attenuated Escherichia coli/S flexneri 2a (EcSf2a-2) hybrid vaccine among military recruits in Israel at high risk of exposure to Shigella spp. We report here our preliminary findings on the efficacy of S sonnei-rEPA; we have not documented sufficient cases to assess the efficacy of EcSf2a-2.

METHODS

Between April, 1993, and August, 1994, male Israeli Military recruits aged 18-22 years were asked to take part in our study. We enrolled 1446 soldiers from seven separate field sites (groups A-G). Soldiers were randomly allocated one injection of S sonnei-rEPA and four doses of oral placebo (n = 576), four oral doses of EcSf2a-2 and one injection of saline placebo (n = 580), or one injection of meningococcal tetravalent control vaccine and four doses of oral placebo (n = 290). Because there were no cases of S flexneri 2a, the EcSf2a-2 and meningococcal vaccines were the control group. We defined S sonnei shigellosis as diarrhoea with a positive faecal culture for S sonnei. Each group of soldiers was followed up for 2.5-7.0 months. The primary endpoint was protective efficacy of S sonnei-rEPA against S sonnei shigellosis.

FINDINGS

Cases of culture-proven S sonnei shigellosis occurred in four groups of soldiers (groups A-D), which comprised 787 volunteers (312 received S sonnei-rEPA, 316 received EcSf2a-2, and 159 received meningococcal control vaccine). In groups A-C, cases of shigellosis occurred 70-155 days after vaccination, whereas in group D cases occurred after 1-17 days. In groups A-C, the attack rate of shigellosis was 2.2% in recipients of S sonnei-rEPA compared with 8.6% in controls (protective efficacy 74% [95% CI 28-100], p = 0.006). S sonnei-rEPA also showed significant protection against shigellosis in group D (43% [4-82], p = 0.039). Prevaccination and postvaccination ELISA measurements of antibody to S sonnei lipopolysaccharide among recipients of S sonnei-rEPA showed that the vaccinees who developed S sonnei shigellosis had significantly lower serum IgG and IgA responses to the homologous lipopolysaccharide than those who did not (p = < 0.05).

INTERPRETATION

One injection of S sonnei-rEPA confers type-specific protection against S sonnei shigellosis. The high antibody concentration induced by the conjugate vaccine in volunteers who did not develop shigellosis suggests that there is an association between serum antibody titre and protection.

Of four murine, anti-Shigella dysenteriae type 1 O-polysaccharide antibodies, three employ V-genes that differ extensively from those of the fourth

Three murine, monoclonal antibodies, IgM 5286 F2, IgM 5297 C1, and IgG 5338 H4 were generated against Shigella dysenteriae type 1 O-specific polysaccharide (O-SP)-conjugate. They are specific for the O-SP, which is a poly-[alpha-L-rhamnopyranosyl-(1-->3)-alpha-L-rhamnopyranosyl-(1-->2)-al pha-D-galactopyranosyl-(1-->3)-2-deoxy-2-amino-N-acetyl-alpha-D-glucopyr anosyl]. The VH and VL genes of these antibodies were cloned and their sequences determined. They showed 93% homology, but were quite different to the primary sequence of IgM 3707 E9, of the same O-SP-specificity, previously reported. The fine-specificities of both IgG 5338 H4 and IgM 3707 E9 were for the same disaccharide moiety in the O-SP, while IgMs 5286 F2 and 5297 C1 showed fine-specificity for the entire repeating unit of the O-SP. Therefore, divergent sequences can confer upon antibodies similar-, or even identical-carbohydrate-epitope fine-specificity. In addition, close primary sequence-homology does not preclude differences in antibody fine-specificity.

The 1996 Albert Lasker Medical Research Awards. Prevention of systemic infections, especially meningitis, caused by Haemophilus influenzae type b. Impact on public health and implications for other polysaccharide-based vaccines

The development of Haemophilus influenzae type b (Hib) conjugate vaccines has led to the virtual elimination of systemic infections caused by that pathogen, has provided insights into the pathogenesis of and immunity to other capsulated bacteria, and has contributed to the development of new vaccines. Meningitis, a common and serious infection of children, and other infections caused by Hib have been virtually eliminated in countries that have achieved widespread vaccination with Hib conjugates, including the United States, Canada, the United Kingdom, Iceland, Scandinavia, France, and Germany. Hib conjugates have also been shown to be highly effective in developing countries. The principles derived from the use of these vaccines, along with studies of other capsulated pathogens, should allow the rapid inclusion of new polysaccharide-based conjugates into routine vaccination schedules of infants, and should help to realize further reductions in serious systemic infectious diseases.

Safety and immunogenicity of investigational Shigella conjugate vaccines in Israeli volunteers

The safety and immunogenicity of investigational conjugates, composed of the O-specific polysaccharides of Shigella sonnei and Shigella flexneri type 2a covalently bound to Pseudomonas aeruginosa recombinant exoprotein A (rEPA), were evaluated in 192 Israeli soldiers. None had significant local reactions or fever. Fourteen days after injection, 90% of S. sonnei-rEPA recipients and 73 to 77% of S. flexneri-rEPA recipients had a fourfold or greater increase in serum immunoglobulin G (IgG) and IgA anti-lipopolysaccharide (anti-LPS) levels; at 2 years, these remained higher than at prevaccination (P < 0.01). There was a fourfold or greater increase in IgM anti-LPS in 20% of vaccinees at 2 weeks, but levels returned to prevaccination values at 6 to 12 months. IgG was the highest and most sustained class of LPS antibodies. Reinjection at day 42 did not boost antibody levels. Eighteen of 23 (78%) who received S. sonnei-rEPA and 13 of 19 (68%) who received S. flexneri-rEPA. had significant IgA-secreting cell responses. Significant IgG antibody-secreting cell responses were detected in 19 of 23 (83%) and 11 of 19 (58%) volunteers following vaccination with S. sonnei-rEPA and S. flexneri 2a-rEPA, respectively. On the basis of these data, further evaluation of the Shigella conjugates for protective efficacy in field trials in Israel was started.

Safety and immunogenicity of Staphylococcus aureus type 5 capsular polysaccharide-Pseudomonas aeruginosa recombinant exoprotein A conjugate vaccine in patients on hemodialysis

Seventeen volunteers with ESRD on hemodialysis, negative for infection with HIV or hepatitis B and C and not receiving immunosuppressive therapy, were injected two times 6 wk apart with 25 micrograms of Staphylococcus aureus Type 5 capsular polysaccharide-Pseudomonas aeruginosa exoprotein A (rEPA) conjugate. Controls were healthy adults, 18 to 44 yr old, injected previously with the same vaccine. None of the patients had fever or significant elevations in their SGOT or SGPT attributable to the vaccine. Two vaccinees had transient induration > 1 cm in diameter at the injection site. The preimmunization geometric mean (GM) Type 5 antibody levels of the ESRD patients and controls were similar. Type 5 antibody levels of the three major immunoglobulin (lg) classes rose at 2 and 6 wk after immunization (P < 0.001 for lgG, P < 0.005 for lgM, and P = 0.0001 for lgA). Reimmunization at 6 wk did not elicit a booster response. At 6 months, the GM lgG level of the patients was approximately 50% of that of the healthy volunteers and 14 of 17 had a more than fourfold higher antibody level than the preimmune value. The GM lgM level, in contrast, declined to the preimmunization value. Vaccine-induced Type 5 antibodies had opsonophagocytic activity. There was a slight increase of lgG antibodies to the heterologous S. aureus Type 8 polysaccharide (P < 0.01) that was sustained at 6 months. The S. aureus Type 5-rEPA vaccine is safe and immunogenic in ESRD patients, and evaluation of its effectiveness against S. aureus bacteremia in this at-risk group is planned.

Hypothesis: how licensed vaccines confer protective immunity

By examining experience with evaluation of licensed vaccines we theorize that a critical level of serum IgG confers protection against infectious diseases by killing or inactivating the inoculum. We found that efficacy is reliably predicted by measurement of serum antibodies elicited by vaccines, that serum IgG antibodies alone account for the protection conferred by passive immunization, that vaccine-induced "herd" immunity is best explained by inactivation of the inoculum on epithelial surfaces by serum antibodies and that serum antibodies induced by active immunization will neither treat disease symptoms nor eliminate the pathogen. If valid, this theory should facilitate research because knowledge of the pathogenesis of the disease symptoms may not be essential for vaccine development.

Interlaboratory study evaluating quantitation of antibodies to Haemophilus influenzae type b polysaccharide by enzyme-linked immunosorbent assay

An interlaboratory study was conducted to determine whether an enzyme-linked immunosorbent assay (ELISA) with an antigen preparation composed of various-sized fragments of Haemophilus influenzae type b polysaccharide conjugated to human serum albumin could be standardized across laboratories and whether the ELISA-derived results from different laboratories are equivalent to those obtained by the standard radioactive antigen binding assay (RABA) for quantitation of anti-H, influenzae type b polysaccharide antibodies. Twenty coded human serum samples were quantitated by ELISA in 11 laboratories and by RABA in 5 laboratories. The mean RABA-derived values served as the basis for all comparisons. While the overall correspondence of antibody values between the two methods was good, significant differences were found among some of the 11 ELISA data sets and among the mean RABA values. Seven laboratories generated higher ELISA antibody values for low-titered sera. Four laboratories generated antibody concentrations that were not statistically different between the two assay methods. The results therefore indicate that the ELISA can tolerate substantial variations in protocol, such as the use of different plates and different antibody reagents, without affecting the quantitation of serum antibodies. However, attention should be focused on low-titered sera, as some assay conditions may yield spurious results. This ELISA is a serologic assay which can serve as an alternative to the RABA for quantitation of antibodies to H. influenzae type h polysaccharide.

Characterization of a human monoclonal immunoglobulin M (IgM) antibody (IgMBEN) specific for Vi capsular polysaccharide of Salmonella typhi

A search for human monoclonal antibodies to protective antigens of bacteria revealed an immunoglobulin M lambda chain [IgM(lambda); designated IgMBEN] reactive with the Vi capsular polysaccharide of Salmonella typhi. Vi, a linear homopolymer of alpha(1-->4)GalApNAc that is O acetylated at C-3, is a licensed vaccine for typhoid fever. Immunologic properties of IgMBEN were compared to those of burro globulin prepared by intravenous injections of S. typhi (B339-340). IgMBEN and B339-340 yielded identical precipitin lines with Vi by double immunodiffusion. IgMBEN and B339-340 produced similar precipitation results with Vi and its derivatives prepared by de-O-acetylation, carboxyl reduction, and removal or replacement of the N-acetyl at C-2 with O-acetyl. B339-340 yielded maximal precipitation with Vi (0.41 mg of antibody per ml with 1.4 micrograms of Vi); next was carboxyl-reduced, O-acetylated Vi, which precipitated 0.325 mg of antibody per ml with 2.5 micrograms of Vi. IgMBEN yielded maximal precipitation with de-O-acetylated, carboxyl-reduced Vi (approximately 11.0 mg of antibody per ml with approximately 1.3 micrograms of antigen); next were de-O-acetylated Vi (9.89 mg/ml) and Vi (9.19 mg/ml). The precipitin curves and equivalence points of these three antigens were similar. Pneumococcus type 1, which contains GalApNAc, did not precipitate with Vi or its derivatives. These slight differences in specificity between IgMBEN and B339-340 were related to our proposed structure of Vi. We plan to use IgMBEN as a reference for measurement of vaccine-induced Vi antibodies.

Perspective: hypothesis: serum IgG antibody is sufficient to confer protection against infectious diseases by inactivating the inoculum

The theory proposed is that a critical level of specific serum IgG is sufficient to confer protection against infectious diseases by inactivating the inoculum of the pathogen. This theory relies heavily on evaluation of licensed vaccines and includes the following: Measurement of serum antibodies only reliably predicts the efficacy of vaccines, according to regulatory agencies. Serum IgG antibodies alone account for the protection conferred by passive immunization. "Herd" immunity conferred by vaccines on viral and bacterial diseases is best explained by serum antibodies that inactivate the inoculum on mucosal surfaces, thus reducing the pathogen's transmission. Once the disease is manifest, serum antibodies induced by active immunization will neither relieve symptoms nor eliminate the pathogen; specific IgG must be present when the host encounters the pathogen in order to confer protective immunity. Information about the initial pathogen-host contact is vital, whereas knowledge of the symptomatology of the disease may not be essential for vaccine development.

Qualitative and quantitative analyses of the antibody response elicited by Haemophilus influenzae type b capsular polysaccharide-tetanus toxoid conjugates in adults with IgG subclass deficiencies and frequent infections

Twenty-one IgG subclass-deficient adult patients with repeated infections of the respiratory tract, were immunized with Haemophilus influenzae type b capsular polysaccharide (HibCP) covalently bound to tetanus toxoid (TT). Specific immunoglobulin and IgG subclasses to HibCP and TT were quantified; the biological activities of HibCP antibodies were also investigated. Most patients showed an antibody response similar to that observed in healthy adults, and the bactericidal activity related to the post-immunization levels of HibCP antibodies. No relation was found between immunoglobulin isotype deficiency, the clinical symptoms and the IgG subclass responsiveness, and no relation was observed between HibCP and TT antibody responses. Our data indicate that some, but not all, patients with recurrent infections and IgG subclass deficiency have an abnormal serum antibody response to polysaccharide and protein epitopes of Hib-TT conjugate vaccine. Analysis of the antibody response after vaccination with HibCP-TT conjugate vaccine did not seem to predict the clinical course of such patients.

Comparison of conjugates composed of lipopolysaccharide from Shigella flexneri type 2a detoxified by two methods and bound to tetanus toxoid

Shigella flexneri type 2a lipopolysaccharide (LPS) was detoxified with acetic acid (O-SP) or with hydrazine (DeALPS). DeALPS, but not O-SP, retained part of its lipid A. Both gave an identical line of precipitation with typing antiserum by double immunodiffusion, and both had low levels of LPS activity by the Limulus amoebocyte lysate assay. O-SP had an M(r) of approximately 17,000. DeALPS had two components of M(r)s approximately 30,00 (major and approximately 10,000 (minor). Adipic acid hydrazide derivatives of O-SP and DeALPS were conjugated to tetanus toxoid (TT), purified by gel filtration through CL-6B Sepharose, and designated O-SP-TT and DeALPS-TT, respectively. Saccharide (2.5 micrograms) as O-SP, DeALPS, or their conjugates was injected subcutaneously into 5-week-old mice three times 2 weeks apart. The mice were bled before the second injection and 7 days after the second and third. O-SP alone did not elicit immunoglobulin M (IgM) or IgG LPS antibodies. DeALPS elicited low levels of IgM LPS antibodies after the third injection only. Two of three lots of O-SP-TT induced significant levels of IgM LPS antibodies after the third injection. One O-SP-TT lot elicited IgG LPS antibodies after the second injection, and all three lots elicited significant levels of IgG after the third. DeALPS-TT induced low levels of anti-LPS IgM and IgG only after the third injection. The geometric mean antibody titers of both immunoglobulin classes induced by O-SP-TT were higher than those induced by DeALPS-TT. By these criteria, O-SP provided a more immunogenic saccharide than DeALPS for S. flexneri type 2a conjugates.

Binding of the O-antigen of Shigella dysenteriae type 1 and 26 related synthetic fragments to a monoclonal IgM antibody

Shigella dysenteriae type 1 possesses an O-antigen whose repeating unit is -->3)-alpha-L-Rhap-(1-->3)-alpha-L-Rhap-(1-->2)-alpha-D-Galp -(1-->3)-alpha-D- GlcpNAc-(1-->, where Rhap is rhamnopyranosyl, Galp is galactopyranosyl, and Glcp is glucopyranosyl. Using ligand-induced protein fluorescence change, we have measured the affinities of a monoclonal murine IgM for 26 fragments of, or related to, the structure of the O-polysaccharide and of the IgM Fab for the intact O-specific bacterial polysaccharide. Synthetic saccharides used were methyl glycosides to ensure an anomerically defined pyranosyl ring conformation. The galactosyl residue is the only monosaccharide of the antigenic epitope that shows quantifiable binding: approximately 3.0 kcal/mol of binding free energy, depending on the structure and conformation of the fragment it is a part of. Addition of an alpha-(1-->2)-linked rhamnosyl residue increases the free energy of binding significantly. We propose this rhamnopyranosyl-alpha-(1-->2)-galactopyranosyl disaccharide to be the basic determinant of the Shigella O-polysaccharide. Further extension (by linkages as in the natural antigen) of this oligosaccharidic ligand toward the upstream end (in an oligo- (or poly-)saccharide, such as A-->B-->C-->D-->E-->m, where A, B, C, D, and E are sugars and m is any moiety, such as methyl, we define A as the glycosyl- or upstream terminus, and E as the glycoside- or downstream terminus) by rhamnosyl and N-acetylglucosaminyl moieties improves the binding only minimally. The antibody is quite specific for the rhamnosyl-alpha-(1-->2)-galactosyl sequence but less so for the nature of the attachment to the galactosyl residue on the downstream side. Measurements using IgM Fab and the intact O-specific polysaccharide show that the antibody can bind internal segments on the antigen chain. The free energy of binding of this antibody for the disaccharide determinant varies from -delta G of 4.7 to 5.1 kcal/mol, depending on its flanking residues.