Diphtheria Toxoid Conjugate Research Articles

Epitopic overload at the site of injection may result in suppression of the immune response to combined capsular polysaccharide conjugate vaccines

Capsular polysaccharide (CP) conjugate vaccines targeting a variety of bacterial infections are currently under development and clinical evaluation. The inclusion of multiple CP serotypes combined in a single injection is an important maneuver being evaluated. The combination of CP conjugate vaccines into a single multivalent injection may result in competition among the different components and adversely affect the immunogenicity of any individual conjugate. We observed a reduction of 30–90% in antibody responses to several serotypes in mice when immunogenicity of a 12-valent Escherichia coli ( E. coli) lipopolysaccharide (LPS) conjugate vaccine was compared to the immunogenicity of each monovalent vaccine evaluated separately. A reduction of 30% was observed in the Staphylococcus aureus ( S. aureus) type 8 CP antibodies when a type 8-rEPA conjugate was combined with a type 5-rEPA conjugate. S. aureus types 5 and 8-rEPA conjugates were combined with 100 μg of either rEPA (homologous) or diphtheria toxoid (DT) (heterologous) carrier proteins, and evaluated in rEPA or DT primed mice. The addition of the homologous protein resulted in a 64% reduction in type 5 CP antibodies. The heterologous protein did not affect the immunogenicity of the type 5. We postulate that the free protein competed with the conjugate and recruited most of the rEPA primed T cells. In the case of the DT conjugates, the DT targeted different populations of the T cells, thus interference was not observed. These data suggested that the epitopic load rather than the antigenic load at the site of injection caused reduced immunogenicity of the conjugates. We theorize that individual components of multivalent CP vaccines conjugated to the same carrier proteins would compete for a limited number of specific carrier protein primed T cells. This would result in one or more components being unavailable in eliciting a sufficient immune response. The use of multiple carrier proteins should be considered as an approach to reduce interference when multivalent conjugate vaccines are to be formulated into a single injection.

Pneumococcal conjugate vaccination in adults: circulating antibody secreting cell response and humoral antibody responses in saliva and in serum

The results from our previous study showed IgA dominated ASC responses to pneumococcal polysaccharide vaccine and to pneumococcal polysaccharide meningococcal outer membrane protein conjugate vaccine (PncOMPC) in adult volunteers. The results indicated that a high IgA ASC response is a useful indicator of a secretory IgA response in saliva. We believe that the mucosal immune responses is potentially an important characteristic of the pneumococcal vaccines and should thus be measured when the new pneumococcal conjugate vaccines are evaluated. In the present study, we studied two new tetravalent pneumococcal conjugate vaccines: the diphtheria toxoid and tetanus toxoid conjugates. In contrast to PncOMPC, these conjugates induced higher responses than the polysaccharide vaccine. Furthermore, the different structure of the two conjugate vaccines might affect the nature of the response. Thus a different vaccine may be optimal for induction of a mucosal response than is of systemic responses.

Interchangeability of Haemophilus influenzae Type b vaccines in the Primary Series: Evaluation of a Two-dose Mixed Regimen

To evaluate two- or three-dose "mixed" regimens of Haemophilus influenzae type b conjugate vaccines in the priming series. Two randomized clinical trials with 140 and 181 infants, respectively. Private practices in New Orleans and Chicago. In trial I, infants received one of four regimens. Two were recommended regimens for polyribosylribitol phosphate (PRP)-meningococcal protein conjugate (M) and PRP-tetanus toxoid conjugate (T). Two mixed regimens consisted of M at 2 months followed by two doses of T or PRP-diphtheria toxoid conjugate (D) at 4 and 6 months. Trial II consisted of three groups. Two were recommended regimens for M and T. The third was a two-dose mixed regimen consisting of M at 2 months and T at 4 months. Parents were interviewed and instructed to record side effects after each vaccination. Serum was assayed for H influenzae type b anticapsular antibody (anti-PRP). Minor differences in safety profiles likely reflected alpha error. In trial I, M (lot 0884T, one of several known to have had decreased immunogenicity), probably primed for substantial increase in serum antibody when D or T was given at 4 and 6 months. In trial II, infants who received the two-dose mixed regimen (M from immunogenic lot 0116W at 2 months and T at 4 months) had a significantly higher mean area under the curve than recipients of the three-dose TTT regimen when antibody concentration was plotted against age, although the geometric mean anti-PRP antibody concentration for the MT-recipients was significantly lower at 7 months. M used in trial I may have primed infants despite poor immunogenicity. The two-dose mixed regimen (MT-) in trial II produced a mean anti-PRP antibody concentration with higher sustained anti-PRP concentrations from 2 to 7 months, as judged by the area under the curve, but a lower mean anti-PRP antibody concentration at 7 months.

Prolonged and preferential production of polymeric immunoglobulin A in response to Streptococcus pneumoniae capsular polysaccharides.

Streptococcus pneumoniae is an invasive mucosal pathogen for which host defense is dependent on capsular polysaccharide-specific antibody. Capsule-specific immunoglobulin G (IgG), IgM, and IgA are produced following pneumococcal vaccination and infection. Serum IgA has two molecular forms, polymeric and monomeric. These forms may modulate the avidity of antigen binding and evolve over time as the immune response matures. Therefore, we sequentially characterized the molecular forms of serum IgA to three serotypes of pneumococcal capsular polysaccharides (types 8, 12F, and 14) after pneumococcal vaccination and after natural infection with type 14 S. pneumoniae. Although typically the form of IgA in antigen-specific systemic responses to protein antigens is predominantly polymeric in sera of patients shortly after exposure and shifts to the monomeric form in sera obtained several weeks later, the form of IgA in response to each pneumococcal capsular polysaccharide remained predominantly polymeric 1 month after natural infection and up to I year following vaccination. In contrast, IgA to pneumococcal cell wall polysaccharide was both polymeric and monomeric. Moreover, the form of IgA in response to polyribosyl-ribitol-phosphate (PRP), the capsular polysaccharide of Haemophilus influenzae type b, was predominantly monomeric in the sera of 8 of 10 subjects tested 1 to 3 months after vaccination with either PRP alone or the diphtheria toxoid conjugate of PRP. We conclude that systemic responses to pneumococcal capsular polysaccharides are distinct in the production of predominantly polymeric IgA over time. The persistence of polymeric IgA may facilitate binding and clearance of pneumococci from the systemic circulation or reflect limited maturation of the immune response to pneumococcal capsular polysaccharides.

Eradication of Haemophilus influenzae Type b Disease in Southern California

To assess the effects of Haemophilus influenzae vaccination of infants. We evaluated H influenzae type b (Hib) disease rates in Los Angeles County, California (population, 9 million; 1983 through 1992), and in the Southern California Kaiser Health Plan (2.5 million enrollees; 1988 through 1992) during the past decade. Cases were obtained through active and passive disease surveillance in the two populations. The following vaccines were used during the study period (1983 through 1992): (1) Hib polysaccharide vaccine (polyribosyl ribitol phosphate) (used from 1985 through 1987 for children 24 through 60 months of age); (2) Hib polysaccharide-diphtheria toxoid conjugate, Hib polysaccharide CRM197 mutant diphtheria toxoid conjugate vaccine, and Hib polysaccharide outer-membrane protein of group B meningococcus conjugate vaccine in older children (1988 through 1990; ages 15 through 60 months); and (3) Hib polysaccharide CRM197 mutant diphtheria toxoid conjugate vaccine and Hib polysaccharide outer-membrane protein of group B meningococcus conjugate vaccine used in infants (1991 through 1992). Between 1983 and 1988, the Hib disease incidence in Los Angeles County was unchanged (32.7 to 42.5/100,000 person-years in children younger than 5 years). In 1989 through 1990, before Hib conjugate licensure for infant use, Hib disease rates in all age groups declined. After licensure of Hib vaccines for infants in 1990, there was a further fivefold decrease in infants. More dramatic decreases occurred in the better-immunized Kaiser Health Plan children aged 0 through 60 months (53 cases in 1989, only two cases in 1992). The Hib disease has been nearly eradicated in a fully immunized population (Kaiser Health Plan), and significant reductions have also occurred in Los Angeles County.

Clinical and Serologic Responses of Saudi Children to Hemophilus Influenzae Type B Capsular Polysaccharide Diphtheria Toxoid Conjugate Vaccine

Sixty-eight Saudi children, 17 to 19 months of age, were enrolled in a study to evaluate the safety and immunogenicity of Hemophilus influenzae type B capsular polysaccharide diphtheria toxoid (PRP-D) conjugate vaccine. Adverse reactions to the vaccine were determined through a questionnaire administered to the parents. Local and systemic reactions to the vaccine were mild and resolved within 24 to 48 hours. PRP antibody levels were measured prior to and one to two months following immunization. PRP antibody levels in the pre-immunization sera of 77% of subjects were below the level associated with immediate protection (>/=0.15 microg/ml), and 88% were below the level associated with long-term protection (>/=1 microg/ml) from Hemophilus influenzae type B (HIB) disease. After one dose of PRP-D vaccine, 100% of recipients achieved antibody levels of >/=0.15 microg/ml, and 85% achieved levels of >/=1 microg/ml. The geometric mean level of antibody after immunization (5.66 microg/ml) was significantly higher than that before immunization (0.098 microg/ml). All subjects had a twofold or greater increase in antibody level in response to the vaccine. We conclude that PRP-D is a safe and highly immunogenic vaccine in this age group of Saudi children.

Controlled trial of Haemophilus influenzae type B diphtheria toxoid conjugate combined with diphtheria, tetanus and pertussis vaccines, in 18-month-old children, including comparison of arm versus thigh injection

A randomized, controlled comparison was made in 175 healthy 18-month-old children given either diphtheria and tetanus toxoids and pertussis vaccine, adsorbed (DTP) and haemophilus b diphtheria toxoid conjugate vaccine (PRP/D) concurrently at separate sites (66 children) or a new vaccine combining these products (109 children). Rates of local or systemic adverse effects postimmunization and antibody responses to each component did not differ significantly between groups. DTP-containing vaccines were better tolerated when given in the thigh than in the arm. The combination DTP-PRP/D vaccine performed satisfactorily at 18 months of age, avoiding the inconvenience of two injections.

Protective immunization with invariant peptides of the Plasmodium falciparum antigen MSA2.

Three octapeptides from the N and C terminal C regions of the merozoite surface Ag 2 (MSA2) of Plasmodium falciparum elicit anti-MSA2 antibody when given as diphtheria toxoid conjugates. These antibodies also bind to the MSA2 homolog from the rodent malaria Plasmodium berghei. All mice vaccinated with these conjugates and challenged with an otherwise lethal inoculum of P. berghei showed substantial protection with most surviving. There was a inverse correlation between the development of the parasitemia and the antibody titer, with alum, algammulin, and CFA giving comparable results. These observations show that the conserved region of MSA2 could form the basis of a malaria vaccine when presented in a suitably immunogenic form, thus avoiding the problems of antigenic diversity [corrected].

Antibody Responses toHaemophilus influenzaeType b Vaccines in Men with Human Immunodeficiency Virus Infection

Persons with human immunodeficiency virus (HIV) infection are at increased risk for serious infections caused by Haemophilus influenzae, yet there are few data on their antibody responses to the H. influenzae type b vaccines. We evaluated antibody responses in 248 men who were randomly assigned to receive a single dose of either the H. influenzae type b polysaccharide (PRP) vaccine or the polysaccharide-mutant diphtheria toxoid conjugate vaccine (PRP-CRM). The subjects were stratified into four groups: seronegative men (67 subjects), men with asymptomatic HIV infection (79), men with symptomatic HIV infection (47), and men with the acquired immunodeficiency syndrome (AIDS) (55). Before immunization, the subjects with AIDS had the lowest PRP-antibody titers; 40 percent had titers below the putative protective level (less than 0.15 micrograms per milliliter). In the seronegative subjects, those with asymptomatic HIV infection, and those with symptomatic HIV infection, the PRP-CRM vaccine led to a threefold greater increase in geometric mean antibody titers than did the PRP vaccine (P less than 0.01). However, the subjects with AIDS had a greater antibody response to the PRP vaccine. The antibody response of HIV-seropositive men to the PRP-CRM vaccine correlated significantly with the number of CD4 lymphocytes (r = 0.47, P less than 0.0001, as compared with r = -0.01 for the PRP vaccine). In these HIV-infected men, both vaccines elicited the dominant anti-PRP idiotype described previously in populations not infected with HIV. Immunization with the PRP-CRM conjugate vaccine early in the course of HIV infection is likely to confer protection against disease caused by H. influenzae type b.

Efficacy of Haemophilus influenzae type b polysaccharide-diphtheria toxoid conjugate vaccine in US children aged 18-59 months

Vaccines prepared from the polyribosylribitol phosphate (PRP) capsule of Haemophilus influenzae b (Hib) have not consistently shown good efficacy in protecting children aged over 18 months from invasive Hib disease. To evaluate the efficacy of conjugate-PRP vaccines in this age-group, and to compare their effect with that of PRP vaccines, a post-marketing case-control study was conducted among 10 400 000 persons. Between Oct 1,1988, and Feb 28, 1990, 75 patients with Hib disease and 161 control children between 18 and 60 months of age were enrolled. To minimise potentially confounding socioeconomic variables, controls were selected either from among patients' classmates at their day-care centre or from among family acquaintances. 9 of the 75 patients had received the diphtheria toxoid conjugate Hib vaccine more than 2 weeks before onset of illness. After adjusting for age and household crowding, the efficacy of PRP Hib vaccine was 64% (95% Cl = -20, 89) and efficacy of the diphtheria toxoid conjugate Hib vaccine was 74% (95% Cl = 30, 90). The study shows that the protective efficacy of this conjugate vaccine is less than ideal and highlights the need for additional post-licensing studies to confirm and expand understanding of the efficacy of these new products.

Immunogenicity of Haemophilus influenzae type b polysaccharide—diphtheria toxoid conjugate vaccine in 3- to 17-month-old infants with sickle cell diseases

Immunogenicity of Haemophilus influenzae type b polysaccharide—diphtheria toxoid conjugate vaccine in 3- to 17-month-old infants with sickle cell diseases

Persistence of Antibody and Booster Responses to Reimmunization With Haemophilus influenzae Type b Polysaccharide and Polysaccharide Diphtheria Toxoid Conjugate Vaccines in Children Initially Immunized at 15 to 24 Months of Age

To evaluate the persistence of antibody after Haemophilus influenzae type b polysaccharide vaccine (PRP) and H influenzae type b polysaccharide diphtheria toxoid conjugate vaccine (PRP-D), a group of 141 infants initially immunized between 15 and 24 months of age were studied 1 year later. One month after immunization with PRP, the man anti-PRP antibody level was 0.27 microgram/mL and 1 year later was 0.29 microgram/mL (not significant). In the group immunized with PRP-D, the levels were 1.34 micrograms/mL and 1.20 micrograms/mL (not significant), respectively. To evaluate immunogenicity and safety of a booster immunization 1 year after initial vaccination, subjects were randomly assigned to receive saline, PRP, or PRP-D. In addition, 73 age-matched previously unimmunized subjects were vaccinated with PRP or PRP-D. In all groups, adverse reactions were minor and resolved by 48 hours. Subjects receiving booster immunization with PRP or PRP-D had significantly greater antibody responses than children of the same age receiving their first dose of vaccine. The highest antibody levels were achieved in children initially immunized with PRP-D, regardless of whether the booster vaccine was PRP (112.8 micrograms/mL) or PRP-D (122.0 micrograms/mL) (not significant). Antibody levels after booster vaccine were significantly lower in those initially given PRP compared with those initially given PRP-D but significantly higher than in age-matched previously unimmunized control subjects (PRP booster 3.16 micrograms/mL vs control of 0.62 microgram/mL [P less than .05]; PRP-D booster 12.31 micrograms/mL vs control 2.31 micrograms/mL [P less than .01]).

The use of maleimidocaproyloxysuccinimide to prepare malarial peptide carrier immunogens immunogenicity of the linking region

Malarial peptides synthesized with an added N terminal cysteine were conjugated to purified diphtheria toxoid (DT) protein using the bifunctional reagent maleimidocaproyloxysuccinimide (MCS). The molar ratio of peptide to carrier was determined by subtractive sulphydryl titration and confirmed by sodium dodecyl sulphate (SDS) electrophoresis. For enzyme-linked immunoabsorbent (ELISA) analysis of sera from animals immunized with the DT conjugates, peptides were conjugated to bovine serum albumin (BSA) using MCS as well as a glutaraldehyde based coupling procedure. Western blotting analysis shows that both DT and BSA adducts were recognized by monoclonal antibodies (Mabs) directed against the peptide epitopes in the native sequences. Animals immunized with the DT-peptide conjugates produced antibodies to the coupling reagent (MCS) as well as diphtheria toxoid and peptide specific antibodies. This MCS specificity could be largely abolished by pre-incubation of sera with a soluble MCS homologue, a thiosuccinimidocaproylamide (TSC).

Safety and immunogenicity of Haemophilus influenzae type b polysaccharide and polysaccharide diphtheria toxoid conjugate vaccines in children 15 to 24 months of age

To evaluate the safety and immunogenicity of the Haemophilus influenzae type b polysaccharide vaccine, PRP, and a new polysaccharide-diphtheria toxoid conjugate vaccine, PRP-D, a collaborative study was carried out in six centers in five states. Subjects were 585 infants 15 to 24 months of age. They were randomly assigned to receive a single dose of PRP or PRP-D vaccine. There were no significant differences in the rate of adverse reactions between the two vaccine groups. Minor local reactions occurred in 10.3% of PRP and 12.5% of PRP-D recipients, and fever in 27.4% of PRP and 23.8% of PRP-D recipients. All reactions resolved within 48 hours. Serum samples were obtained just before vaccination and after 1 month. Prevaccination antibody levels were similar for the PRP (0.035 micrograms/mL) and PRP-D (0.027 micrograms/mL) groups, with no differences in levels by age, sex, race, vaccine lot, or study site. Both groups had significant rises in geometric mean levels, but this difference was significantly greater for PRP-D (2.166 micrograms/mL) than for PRP (0.154 micrograms/mL). In addition, the percentage of responders as determined by three definitions (twofold titer rise, greater than 0.15 micrograms/mL, and greater than 1.0 micrograms/mL) was also significantly greater for PRP-D than PRP. In contrast to a marked age-related immunogenicity to PRP (P less than 0.001), there was no significant variation in immune response to PRP-D by age. PRP-D conjugate vaccine appears to be as safe and significantly more immunogenic than PRP vaccine for children vaccinated at 15 to 24 months of age.

Persistence of antibody and response to booster dose of Haemophilus influenzae type b polysaccharide diphtheria toxoid conjugate vaccine in infants immunized at 9 to 15 months of age

At approximately 2 years of age, 27 infants previously immunized at 9 to 15 months of age with two doses of polyribosylribitol phosphate-diphtheria toxoid conjugate vaccine (PRP-D) and 23 infants immunized with polyribosylribitol phosphate (PRP) vaccine were given a single injection of PRP-D. Pre- and post-immunization sera were obtained. No serious local or systemic reactions were observed. The PRP-D recipients had a geometric mean anti-PRP antibody level of 4.8 micrograms/ml 1 month after the second primary injection, retained 1.2 microgram/ml 1 year later, and had a level of 71 micrograms/ml after the booster immunization. In contrast, PRP recipients had a geometric mean level of 0.083 microgram/ml 1 month after the second primary injection, retained 0.042 microgram/ml 1 year later, and after a single dose of PRP-D at approximately 2 years of age had a geometric mean level of 8.6 micrograms/ml. The significantly higher antibody response in the prior PRP-D recipients suggests the recall of immunologic memory induced by the PRP-D vaccine.

ANTIBODY LEVELS ACHIEVED IN INFANTS BY COURSE OF HAEMOPHILUS INFLUENZAE TYPE B POLYSACCHARIDE/DIPHTHERIA TOXOID CONJUGATE VACCINE

A Haemophilus influenzae type b (Hib) capsular polysaccharide (polyribosylribitol phosphate, PRP)/diphtheria toxoid (D) conjugate vaccine was given to 71 infants. The level of anti-PRP antibody believed to predict long-term protection, 1·0 μg/ml, was reached in 50% of the infants who were vaccinated at 3, 5, and 7 months, and in 57% of the infants who received PRP-D at 7 and 9 months of age. A lower level of antibody, 0·15 μg/ml, which has been associated with protection at the time of assay, was reached in 92% and 87% of the two groups. Thus, the seroresponse was dependent upon both the frequency of immunisation and age of the infant. Comparison of these results with previous experience with PRP immunisation in Finland showed that PRP-D induced substantial antibody rises at an earlier age than did PRP.

Safety and immunogenicity of haemophilus influenzae type b-polysaccharide diphtheria toxoid conjugate vaccine in infants 9 to 15 months of age

Sixty 9- to 15-month-old infants were randomly assigned to receive two doses, 1 month apart, of a Haemophilus influenzae type b capsular polysaccharide-diphtheria toxoid conjugate vaccine (PRP-D) or PRP vaccine, each containing 20 micrograms PRP. There were no significant local or systemic reactions. After one dose of PRP-D, 93% of the subjects attained levels of greater than or equal to 0.15 microgram/ml and 59% achieved greater than or equal to 1 microgram/ml antibody protein. These percentages rose to 100% and 86%, respectively, after the second dose, at which time the geometric mean titer of anti-PRP antibody was 4.8 micrograms/ml. IgG anti-PRP levels were 4.3 times higher than IgM. The proportion of IgG to IgM antibody induced by PRP-D increased with age. After two doses, 33% of the PRP recipients responded with a level of greater than or equal to 0.15 microgram/ml and only 19% responded to a level of greater than or equal to 1.0 microgram/ml. One year later, all of the PRP-D recipients tested still had greater than or equal to 0.15 microgram/ml and more than half had greater than or equal to 1.0 microgram/ml antibody protein.