Protective levels of serum antibodies stimulated in infants by two injections of Haemophilus influenzae type b capsular polysaccharide-tetanus toxoid conjugate

An enzyme-linked immunosorbent assay for quantitation of Haemophilus Influenzae type b polysaccharide-specific IgG1 and IgG2 in human and infant rhesus monkey sera

An enzyme-linked immunosorbent assay (ELISA) has been developed and validated to quantitate IgG1 and IgG2 antibody to polyribosyl-ribitol phosphate (PRP), the capsular polysaccharide of Haemophilus influenzae type b (Hib). The sera of children and infant Rhesus monkeys immunized with an Hib conjugate vaccine composed of Hib PRP covalently linked to an outer membrane protein complex (OMPC) from Neisseria meningitidis serogroup B (PedvaxHIB, PRP-OMPC, Merck, Sharp and Dohme Research Laboratories). The solid-phase antigen employed in the ELISA is a conjugate of PRP to human serum albumin. The enzyme-labeled antibody is alkaline phosphatase-conjugated mouse monoclonal (mAb) anti-human IgG1 or IgG2. A human serum standard was calibrated using parallel titrations with a known antibody standard. The geometric mean titer (GMT) of the anti-PRP IgG1 response to one dose of PedvaxHIB was 3.87 micrograms/ml (n = 82), 11.80 micrograms/ml (n = 62) and 14.57 micrograms/ml (n = 74) in infants and children 12 to 17 months, 18 to 23 months and greater than or equal to 24 months old, respectively. Infants 2 to 11 months old responded with an IgG1 anti-PRP response of 7.10 micrograms/ml while infant monkeys responded with a GMT of 150.65 (n = 9) after two doses of vaccine. The anti-PRP IgG2 GMT responses in all groups were less than 0.25 micrograms/ml, except for humans greater than or equal to 18-months old who exhibited a GMT of greater than or equal to 0.40 micrograms/ml (n = 75). PedvaxHIB, immunization of human infants and children and infant Rhesus monkeys elicits primarily an IgG1 response to PRP. The monkey model appears to be a reliable indicator of the human immune response.

Strategies for immunization against invasive Haemophilus influenzae type b infection

Available data on the immunogenicity, safety and efficacy of Hib conjugate vaccines are encouraging and the prospects for having a means to control invasive Hib disease are good. Most of the third generation Hib vaccines seem to prevent invasive Hib disease at a level of efficacy that motivates worldwide mass immunization of infants. The peak incidence of Hib meningitis occurs before the age of 1 year in most industrialized countries and the most desirable time to start vaccination against Hib is at 2-3 months of age. In many countries a Hib conjugate vaccine may ideally be coordinated with the DTP immunization programme. In non-industrialized countries the peak incidence of Hib meningitis occurs earlier than in industrialized countries, which means that in these areas immunization against Hib meningitis should start earlier, for instance at 6 weeks when the first DTP vaccine injection is given in many countries.

Influence of prevaccination immunity on the human B-lymphocyte response to a Haemophilus influenzae type b conjugate vaccine

The purpose of this study was to investigate whether preexisting immunity to components of a polysaccharide-protein conjugate influences the B-lymphocyte response to vaccination with the conjugate. Thirty-two healthy adults were vaccinated once or twice with a conjugate (PRP-D) consisting of Haemophilus influenzae type b capsular polysaccharide (PRP) and diphtheria toxoid (DT), and the response was related to the prevaccination levels of PRP and DT antibodies. Positive correlations were found between increases in plasma PRP (median, 32.0 micrograms/ml) and DT (1.14 IU/ml) antibodies and numbers of circulating PRP and DT antibody-secreting cells (AbSC) (postvaccination days 6 to 9). The B-cell responses (antibody response and AbSC) to both PRP and DT correlated positively with prevaccination levels of anti-DT. DT AbSC appeared earlier (peak, day 7) than PRP AbSC (peak, day 8). Individuals whose PRP AbSC peaked early (day 7) had higher prevaccination anti-DT levels than those who peaked later (P less than 0.05). In contrast, the prevaccination levels of anti-PRP did not correlate significantly with the magnitude of the antibody or AbSC response and did not affect the kinetics of the AbSC. Following revaccination with PRP-D, small increases in the level of PRP antibodies (median, 2.9 micrograms/ml; n = 11) were found; no significant increase in the level of DT antibodies was seen. The numbers of PRP AbSC were lower (P = 0.04) and peaked earlier (day 7) than after the first vaccination. The isotype pattern of PRP AbSC, which was dominated by immunoglobulin A (IgA) after the first vaccination, now showed a more equal distribution between IgG and IgA AbSC. It is concluded that after immunization with PRP-D both the magnitude and the kinetics of the antipolysaccharide B-cell response are influenced by prevaccination immunity to the carrier molecule.

Immunogenicity of four Haemophilus influenzae type b conjugate vaccines in 17- to 19-month-old children

OBJECTIVE

To compare the immunogenicity of four Haemophilus influenzae type b (Hib) conjugate vaccines in different populations of 17- to 19-month-old children in the United States.

DESIGN

Four immunogenicity trials with sera were assayed in one laboratory. Trials 1 and 2 each compared one vaccine in two regions, and trials 3 and 4 were randomized comparisons of multiple vaccines within a region.

SUBJECTS

A convenience sample of 313 healthy children recruited from pediatric practices in Minneapolis, Minn., Dallas and Houston, Tex., and Sellersville, Pa.

MEASUREMENTS AND RESULTS

Children with prevaccination antibody greater than 0.15 microgram/ml showed higher antibody responses to vaccination than children with less than or equal to 0.15 microgram/ml (p less than 0.001). Among the former, there were no significant differences in antibody response to vaccination with the different conjugates within any of the trials. Among children with less than or equal to 0.15 microgram/ml of antibody before vaccination, there were no significant differences in the geometric mean antibody responses of children in trial 1 vaccinated with polyribosylribitol phosphate-diphtheria toxoid (PRP-D) in Dallas or in Minneapolis, or of children in trial 3 in Dallas randomly assigned to receive Hib oligosaccharide-CRM197 (HbOC) or PRP-D. In contrast, in trial 2, children given PRP-tetanus toxoid (PRP-T) in Pennsylvania had a significantly higher geometric mean antibody response than children given PRP-T in Houston (13.5 vs 3.0 micrograms/ml; p = 0.005). In trial 4 in Minneapolis, the geometric mean antibody response was highest in children randomly assigned to receive PRP-outer membrane protein (OMP) (9.3 micrograms/ml), followed by PRP-D (5.0 micrograms/ml) and HbOC (2.3 micrograms/ml) (PRP-OMP vs HbOC; p = 0.005). In all four trials, IgG1 responses predominated compared with IgG2 responses.

CONCLUSIONS

All four conjugate vaccines are immunogenic in children 17 to 19 months of age. However, the magnitude of the anticapsular antibody response varied by vaccine type, the level of antibody in prevaccination sera, and geographic location.

Clinical and immunologic responses to Haemophilus influenzae type b-tetanus toxoid conjugate vaccine in infants injected at 3, 5, 7, and 18 months of age

The safety and immunogenicity of Haemophilus influenzae type b-tetanus toxoid conjugate vaccine (Hib-TT) were evaluated in 77 healthy infants receiving injections at 3, 5, 7, and 18 months of age. No serious local or systemic reactions were noted. After the first injection the geometric mean Hib antibody level rose to 0.55 micrograms/ml, and each subsequent injection elicited a statistically significant rise in the geometric mean. The percentage of vaccinees with Hib antibody levels greater than 0.15 micrograms/ml serum was 75.5% after the first, 97.4% after the second, and 100% after the third Hib-TT injection. This percentage fell to 90.9% at 18 months of age but rose again to 100% after the fourth injection. Control infants (n = 10) injected with diphtheria-tetanus toxoid-pertussis vaccine only had nondetectable levels after the second injection. Hib-TT elicited increases of Hib antibody in all isotypes: IgG greater than IgM greater than IgA. Among IgG subclasses the highest increases were of IgG1. All vaccinated subjects had greater than 0.01 U/ml of TT antibody (estimated protective level) throughout the study. We conclude that Hib-TT, injected at 3, 5, 7, and 18 months, is safe and induces protective levels of antibodies during the age of highest incidence of meningitis caused by Hib.

Immunogenicity and reactogenicity of Haemophilus influenzae type b-meningococcus group B outer membrane protein conjugate vaccine in children 2-60 months of age

Haemophilus influenzae b - Neisseria meningitidis group B outer membrane protein conjugate vaccine (Hib-OMP) was given to 571 children 2-60 months of age. Two doses of Hib-OMP were given, 2 months apart, to 2-11 month old infants, and a single dose to children 12-60 month old. Sera were obtained from a subset of vaccinees at each immunization, and at follow-up 1 month and 1 year after immunization. Geometric mean antibody concentration (micrograms/ml) before and after full immunization were respectively 0.111 and 3.549 for 2-3 month old, 0.108 and 5.048 for 4-5 month old, 0.082 and 6.933 for 6-11 month old; they were 0.103 and 3.500 for 12-17 month old, 0.167 and 7.791 for 18-23 month old and 0.243 and 12.781 for children greater than or equal to 24 months. Detectable antibody (greater than or equal to 0.125 micrograms/ml) failed to develop in 2/399 (0.5%) after primary immunization, and 12/252 (4.8%) lost detectable antibody 1 year later. Six of these 12 infants were less than 12 month old. The vaccine was immunogenic as early as 3-5 months of age. The need for booster immunization needs to be assessed.

Limited efficacy of a Haemophilus influenzae type b conjugate vaccine in Alaska Native infants. The Alaska H. influenzae Vaccine Study Group

BACKGROUND

The prevention of invasive Haemophilus influenzae type b disease requires a vaccine that is effective when administered during the first six months of life. The infants of Alaska Natives are at particularly high risk of invasive H. influenzae type b disease.

METHODS

To evaluate the protective efficacy of a H. influenzae type b polysaccharide-diphtheria toxoid conjugate vaccine (polyribosylribitol phosphate-diphtheria toxoid [PRP-D]), we enrolled 2102 Alaska Native infants in a randomized, double-blind, placebo-controlled trial in which either the vaccine or a saline placebo was administered at approximately two, four, and six months of age.

RESULTS

After 3969 subject-years of follow-up and 32 episodes of H. influenzae type b disease, the overall incidence of invasive disease was not reduced significantly in the vaccinated subjects (6.0 cases per 1000 patient-years), as compared with the placebo controls (9.6) or with other Alaska Native infants (6.0). After one, two, or three doses there was no significant protective efficacy with the vaccine; after three doses the efficacy was only 35 percent (95 percent confidence interval, -57 to 73). The lack of efficacy was not related to the age at onset of disease, age at immunization, type of disease, degree of Alaska Native heritage, time after immunization, or year of the study. Levels of H. influenzae type b anticapsular antibody in recipients of the vaccine became significantly higher than levels in those who received placebo only after the second and third doses. Even after the third dose, only 48 percent of the vaccinated infants had antibody levels of more than 0.1 microgram per milliliter (geometric mean titer, 0.18). Antibody responses did not vary with the level of maternally acquired antibody, degree of Alaska Native ancestry, or age at time of the first or second immunizations, but they increased with increasing age at time of the third dose (P less than 0.001).

CONCLUSIONS

We found no evidence that the PRP-D vaccine provides significant protection, at least for Alaska Native infants, against invasive diseases caused by H. influenzae type b. The ineffectiveness of the vaccine paralleled its limited immunogenicity.

Effect of breast-feeding on antibody response to conjugate vaccine

Infants were immunised at the ages of 2, 4, and 6 months with conjugate Haemophilus influenzae type b vaccine, and their responses to the vaccine were evaluated by feeding method (breast or formula). There were no significant differences between the groups in antibody levels at early ages. However the antibody levels were significantly higher in the breast-fed (57 infants) than the formula-fed group (24 infants) at 7 months (mean [SD] 29.8 [32.0] vs 17.5 [14.8] micrograms/ml) and at 12 months (55 vs 26 infants; 4.8 [4.4] vs 3.0 [2.3] micrograms/ml). These findings are strong evidence that breast-feeding enhances the active immune response in the first year of life, and therefore the feeding method must be taken into account in the evaluation of vaccine studies in infants.

Serum antibody response in adult volunteers elicited by injection of Streptococcus pneumoniae type 12F polysaccharide alone or conjugated to diphtheria toxoid

Conjugates of an uronic acid-containing capsular polysaccharide (CP), pneumococcous type 12F (Pn12F) bound to diphtheria toxoid (DT), were studied for safety and immunogenicity in adult volunteers. In mice, these conjugates, prepared with the same lot of DT and Pn12F-40234-006, a homogenous CP of high molecular weight, or Pn12-812408, a polydisperse CP with lower-molecular-weight material, were more immunogenic than the Pn12F alone and had T-cell dependent properties (A. Fattom, W. F. Vann, S.C. Szu, A. Sutton, X. Li, B. Bryla, G. Schiffman, J. B. Robbins, and R. Schneerson, Infect. Immun. 56:2292-2298, 1988). Adult volunteers, randomized into three groups, were injected either with one of these two conjugates or with Pnu-Imune, the 23 valent pneumococcus vaccine containing 25 micrograms of Pn12F as one of its components. Volunteers were injected two times, 4 weeks apart, with the Pn12F-DT conjugates and once with the Pnu-Imune. Side reactions following injection of the conjugates of Pnu-Imune were mild and short-lived. At 4 weeks and at 7 months after the first injection, higher levels of Pn12F antibodies were found in the volunteers injected with the conjugates than in the Pnu-Imune group (P less than 0.001). The conjugate prepared with the higher-molecular-weight Pn12F elicited higher levels of antibodies than the conjugate prepared with a lower-molecular-weight Pn12F preparation (P = 0.05). Both conjugates elicited about a 13-fold rise in DT antibodies.

New vaccines against Haemophilus influenzae type b

Recently, great progress has been made in the development of vaccines against Hib. Four polysaccharide-protein conjugate vaccines are actively being tested. Three of these (PRP-D, HbOC, and PRP-OMP) are currently licensed for use in children at 15-18 months of age. Clinical trials of these vaccines in infants are currently being conducted in the United States. If these show the vaccines to be efficacious, licensure for infants will follow. Although much work remains to be done, it seems likely that the effective prevention of serious Hib infections in infants, as well as in older children, is a goal that may be within our reach in the next several years.

Response to a Haemophilus influenzae type b diphtheria CRM197 conjugate vaccine in children with a defect of antibody production to Haemophilus influenzae type b polysaccharide

A defect in antibody response to immunization with Haemophilus influenzae type b (Hib) capsular polysaccharide vaccine has been reported in children with recurrent infections and normal immunoglobin levels. We identified 15 children, aged 2 to 6 years, with this defect, and we evaluated their response to immunization with an Hib capsular oligosaccharide diphtheria CRM197 protein-conjugate vaccine (HbOC). The children received a series of three vaccines: HbOC at 0 and 8 weeks, and the Hib polysaccharide vaccine at 16 weeks. Levels of antibody to the Hib capsular polysaccharide (polyribosyl ribitol phosphate, PRP) and to diphtheria toxoid were obtained before and 4 weeks after each vaccination. The geometric mean serum anti-PRP concentration was 0.17 microgram/ml before immunization and 29.3 micrograms/ml after the second HbOC immunization (week 12). All 15 children had postvaccination anti-PRP antibody levels greater than 1.0 microgram/ml after receiving the second HbOC (week 12). In addition, booster responses were observed after the second Hib conjugate in 13 of the patients and after the Hib polysaccharide in four of the patients. All patients with low preimmunization diphtheria titers had a response to the diphtheria toxoid. These results suggest that conjugation of Hib polysaccharide with diphtheria CRM197 overcomes the defective antibody response to Hib oligosaccharide in children who are initially observed with recurrent infections and inability to respond to the Hib polysaccharide vaccine.

Synthesis and immunological properties of conjugates composed of group B streptococcus type III capsular polysaccharide covalently bound to tetanus toxoid

A synthetic scheme for covalently binding group B streptococcus type III to tetanus toxoid (TT), using adipic acid dihydrazide as a spacer, is described. Type III alone or as a conjugate with TT was injected subcutaneously into laboratory mice, and the type-specific and TT antibody responses elicited by these immunogens were assayed. Type III-TT elicited significantly higher levels of type-specific antibodies after each immunization than did the type III alone. These levels were related to the dosage of the conjugate, enhanced by Freund adjuvant, and exhibited booster responses. Type III alone elicited only immunoglobulin M (IgM) antibodies in Swiss albino mice and mostly IgM and low levels of IgG antibodies of the IgG3 subclass in BALB/c mice. Type III-TT conjugates, in contrast, elicited mostly IgG antibodies in both strains of mice. IgA type III antibodies were not detected. The first two immunizations with the conjugates elicited type III antibodies in the IgG1 and in the IgG3 subclasses. Low levels of IgG2a type III antibodies were detected after a third injection of type III-TT. Conjugate-induced antibodies facilitated opsonization of group B streptococcus type III organisms and did not react with the structurally related pneumococcus type 14. TT alone or as a component of type III-TT induced mostly antibodies of the IgG class: IgG1 levels were the highest of the four subclasses. No IgA TT antibodies were detected. The conjugation procedure, therefore, enhanced the immunogenicity of and conferred T-cell dependent properties to the type III while preserving the immunogenicity of the TT component. The T-cell dependent properties of the conjugates were responsible for stimulating IgG type III antibodies which could be boosted. Evaluation of type III-TT conjugates in antibody-negative women of child-bearing age is planned.

Structural and antigenic conservation of the P2 porin protein among strains of Haemophilus influenzae type b

The P2 porin protein is the most abundant protein in the outer membrane of Haemophilus influenzae type b (Hib). Biochemical and immunochemical techniques were used to characterize the P2 proteins from a number of different Hib strains. P2 proteins from Hib outer membrane vesicles were resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transferred to nitrocellulose for in situ tryptic digestion. Solid-phase tryptic digests of P2 from eight Hib strains were resolved by high-pressure liquid chromatography and shown to be similar if not identical. Radioimmunoprecipitation analysis involving Hib cells (containing intrinsically radiolabeled proteins or lipooligosaccharide) and Western blot (immunoblot) analysis were used to identify two P2-specific murine monoclonal antibodies (MAbs). These MAbs were shown to be reactive with 120 Hib strains tested in a colony blot radioimmunoassay. One of these MAbs bound to a surface-exposed P2 epitope that was antibody accessible on all Hib strains tested; the other MAb was directed against a P2 epitope that either was not exposed on the cell surface or was otherwise inaccessible to antibody.

Childhood acute bacterial meningitis in the Sudan: an epidemiological, clinical and laboratory study

The aims of the present study were to document the epidemiology, clinical features and complications of childhood acute bacterial meningitis (ABM) in The Sudan during both an inter-epidemic (endemic) period (1985-1986), and the 1988 serogroup A epidemic; and to examine the phenotypic and genetic similarities and differences of Neisseria meningitidis strains isolated in The Sudan and Sweden. A new enzyme immunoassay test (Pharmacia Meningitis EIA-Test) was evaluated as a potential rapid diagnostic method for the detection of Haemophilus influenzae (HI) type b, Neisseria meningitidis (MC) and Streptococcus pneumoniae (PNC). The test was found to have good sensitivity (0.86) and specificity (0.95) in the inter-epidemic period; and to be adaptable to the field work in The Sudan during the 1988 MC epidemic. During inter-epidemic (endemic) situations in The Sudan, greater than 90% of childhood ABM was caused by one of the three organisms, HI type b, MC and PNC. HI accounted for 57% of the cases. The peak incidence (76%) of HI cases was in infants (less than 12 months) similar to the situation in other African countries. The overall case fatality ratio was 18.6%. Prospective follow-up of survivors for 3-4 years revealed that an additional 43% either died or had permanent neurological complications, the most prevalent and persistent of which was sensorineural hearing loss recorded in 22% of long term survivors. Post-meningitic children were found to have significantly lower intelligence quotients (92.3 +/- 13.9) than their sibling controls (100.7 +/- 10.2, P = 0.029). Features of the large serogroup A sulphonamide resistant MC epidemic (February-August 1988) in Khartoum are described. An estimated annual incidence of 1,679/100,000 was recorded at the peak of the epidemic. The highest attack rate was in young children less than 5 years, as in many other African countries; nevertheless, a high morbidity was observed in adults (31% of the cases greater than or equal to 20 years). The clinical features, mortality (6.3%) and short term sequelae in Sudanese children were generally within the framework described for MC disease elsewhere. Detailed analysis of MC isolates from Sudan and Sweden by characterizing their electrophoretic enzyme types, DNA restriction endonuclease pattern and outer membrane proteins, revealed that serogroup A MC clone III-1 was responsible of The Sudan epidemic in 1988 and has been the dominant serogroup A organism in Sweden since 1973. The Sudanese strains isolated prior to the epidemic (1985) were clone IV-1.(ABSTRACT TRUNCATED AT 250 WORDS)