anti-PRP Response Research Articles

Disparate kinetics in immune response of two different Haemophilus influenzae type b conjugate vaccines: Immunogenicity and safety observations from a randomized controlled phase IV study in healthy infants and toddlers using a 2+1 schedule

ABSTRACT Since the introduction of Haemophilus Influenzae type b (Hib) conjugate vaccines, invasive Hib disease has strongly declined worldwide, yet continued control of Hib disease remains important. In Europe, currently three different hexavalent combination vaccines containing Hib conjugates are marketed. In this phase IV, single-blind, randomized, controlled, multi-country study (NCT04535037), we aimed to compare, in a 2 + 1 vaccination schedule, the immunogenicity and safety and show non-inferiority, as well as superiority, of DTPa-HBV-IPV/Hib (Ih group) versus DTaP5-HB-IPV-Hib (Va group) in terms of anti-polyribosylribitol phosphate (PRP) antibody geometric mean concentrations (GMCs) and proportion of participants reaching anti-PRP antibody concentrations greater than or equal to a threshold of 5 µg/mL. One month after the booster vaccination, the anti-PRP antibody GMC ratio (Ih group/Va group) was 0.917 (95% CI: 0.710–1.185), meeting the non-inferiority criteria. The difference in percentage of participants (Ih group – Va group) reaching GMCs ≥5 µg/mL was -6.3% (95% CI: -14.1% to 1.5%), not reaching the predefined non-inferiority threshold. Interestingly, a slightly higher post-booster antibody avidity was observed in the Ih group versus the Va group. Both vaccines were well tolerated, and no safety concerns were raised. This study illustrates the different kinetics of the anti-PRP antibody response post-primary and post-booster using the two vaccines containing different Hib conjugates and indicates a potential differential impact of concomitant vaccinations on the anti-PRP responses. The clinical implications of these differences should be further studied.

Protective immune responses against Haemophilus influenzae type b elicited by a fully-liquid DTaP-IPV-Hib-HepB vaccine (VAXELIS™)

BackgroundDTaP-IPV-Hib-HepB is a fully-liquid, hexavalent combination vaccine (Vaxelis™) approved for vaccination against diphtheria, tetanus, pertussis, poliomyelitis, hepatitis B, and invasive disease due to Haemophilus influenzae type b (Hib). Hib capsular polysaccharide, polyribosylribitol phosphate (PRP), is conjugated to Neisseria meningitidis outer membrane protein complex (OMPC). Safety and immunogenicity of DTaP-IPV-Hib-HepB were evaluated in 6 Phase III clinical studies including > 5,200 children. Studies included vaccination schedules in the United States (2, 4, 6 months of age) and Europe (2, 3, 4, 12 months of age and 2,4,11–12 months of age). MethodsData pertaining to anti-PRP responses of DTaP-IPV-Hib-Hep B compared to control vaccines from 5 Phase III studies are summarized. ResultsPost-infant series, the percentage of participants that achieved protective antibody thresholds for PRP (anti-PRP titer ≥ 0.15 μg/mL and ≥ 1.0 μg/mL, respectively) were higher in DTaP-IPV-Hib-HepB recipients compared to recipients who received control vaccines. A high level of protective responses (96.6% at ≥ 0.15 μg/mL [95% CI:94.8, 97.9%]; 72.9% at ≥ 1.0 μg/mL [95% CI:69.2,76.4%]) were seen post-dose 2 of the 2 + 1 vaccination schedule and met superiority criteria over comparator, p-value < 0.001.In the same schedule, prior to administration of the toddler dose (in the second year of life), anti-PRP titers were higher in DTaP-IPV-Hib-HepB recipients (91.4% at ≥ 0.15 μg/mL; 46.8% at ≥ 1.0 μg/mL) as compared to recipients who received control vaccines (63.4% at ≥ 0.15 μg/mL; 17.1% at ≥ 1.0 μg/mL).One-month post-toddler dose, high levels of anti-PRP titers were achieved in both DTaP-IPV-Hib-HepB recipients (99.8% at ≥ 0.15 μg/mL; 96.6% at ≥ 1.0 μg/mL) and recipients who received control vaccines (99.5% at ≥ 0.15 μg/mL; 94.9% at ≥ 1.0 μg/mL). ConclusionsThese results support that DTaP-IPV-Hib-HepB induces a robust and sustained early Hib response. During the high-risk period for Hib disease after the infant vaccine and prior to the toddler dose; >90% of recipients maintained superior protective anti-PRP levels compared to control.

2702. Infants Vaccinated with a Fully-Liquid DTaP-IPV-Hib-HepB Vaccine Are Protected During the High-Risk Period for Haemophilus Influenzae Type B Disease

BackgroundDTaP-IPV-Hib-HepB is a fully-liquid, combination vaccine (Vaxelis™) approved for vaccination in infants and toddlers against diphtheria, tetanus, pertussis, hepatitis B, poliomyelitis and Haemophilus influenzae type b (Hib). Safety and immunogenicity were evaluated in 4 Phase III, randomized, active-comparator controlled clinical trials (Protocols 005 and 006 in the US [Control: PENTACEL™] and Protocols 007 and 008 in the EU [Control: INFANRIX™ hexa]). The vaccine, studied in >6,800 children, has an acceptable safety profile generally similar to that of control vaccines (Xu, PIDJ, 2019; 38:439–43). DTaP-IPV-Hib-HepB includes polyribosylribitol phosphate (PRP) conjugated to outer membrane protein complex of Neisseria meningitidis (OMPC) that elicits a rapid response to Hib.MethodsData from these studies provide a summary of the anti-PRP responses of DTaP-IPV-Hib-HepB compared with Control.ResultsAfter the infant series, the percentage of participants who achieved short-term and long-term protective antibody thresholds for PRP (i.e., anti-PRP titer ≥0.15 μg/mL and ≥1.0 μg/mL, respectively) were higher in DTaP-IPV-Hib-HepB recipients compared with Control. A high level of protective responses (96.6% ≥0.15 μg/mL and 72.9% ≥1.0 μg/mL) were seen after the second dose in the 008 study of the 2 infant series followed by toddler dose hexavalent vaccination schedule (2 + 1). Across all 4 studies, anti-PRP titers were higher in DTaP-IPV-Hib-HepB recipients (91.4% ≥0.15 μg/mL and 46.8% ≥1.0 μg/mL) when compared with Control (63.4% ≥0.15 μg/mL and 17.1% ≥1.0 μg/mL) at the pre-Toddler dose (i.e., prior to the administration of the Toddler dose in the second year of life, between 11–15 months of age). One month after the toddler dose, high levels of anti-PRP titers were achieved in both DTaP-IPV-Hib-HepB recipients (99.8% ≥0.15 μg/mL and 96.6% ≥1.0 μg/mL) and Control (99.5% ≥0.15 μg/mL and 94.9% ≥1.0 μg/mL).ConclusionThese results support that DTaP-IPV-Hib-HepB induces an early Hib response in the first 6 months of life that is sustained until the booster dose is administered in the second year of life. Thus, a high percentage of infants vaccinated with DTaP-IPV-Hib-HepB are protected during the high-risk period for Hib disease. Disclosures All authors: No reported disclosures.

A Phase III randomized, double-blind, clinical trial of an investigational hexavalent vaccine given at 2, 4, and 11–12 months

BackgroundCombination vaccines simplify vaccination visits and improve coverage and timeliness. DTaP5-HB-IPV-Hib is a new investigational, fully-liquid, combination vaccine designed to protect against 6 infectious diseases, including 5 pertussis antigens and OMPC instead of PT as conjugated protein for Hib component. MethodsIn this multicenter, double-blind, comparator-controlled, Phase III study (NCT01480258) conducted in Sweden, Italy, and Finland, healthy infants were randomized 1:1 to receive one two immunization regimens. The DTaP5-HB-IPV-Hib Group received the investigational hexavalent vaccine (DTaP5-HB-IPV-Hib) and the Control Group received Infanrix-hexa (DTPa3-HBV-IPV/Hib) at 2, 4 and 11–12months of age. Both groups received concomitantly Prevnar 13 (PCV13) and Rotateq (RV5) or Rotarix (RV1) at 2, 4months of age and PCV13 at 11–12months. Subjects administered RV5 received a 3rd dose at 5months of age. ResultsA total of 656 subjects were randomized to the DTaP5-HB-IPV-Hib Group and 659 subjects to Control Group. Immune responses to all vaccine antigens post-toddler dose were non-inferior in the DTaP5-HB-IPV-Hib Group as compared to the Control Group. Additionally, the post-dose 2 and pre-toddler DTaP5-HB-IPV-Hib anti-PRP responses were superior. The DTaP5-HB-IPV-Hib Group responses to concomitant RV1 were non-inferior compared to the Control Group.Solicited adverse event rates after any dose were similar in both groups, except for higher rates of pyrexia (6.4% difference; 95% CI: 1.5,11.3) and somnolence (5.8% difference; 95% CI: 1.7,9.8) in the DTaP5-HB-IPV-Hib Group. Vaccine-related serious adverse events occurred infrequently in the DTaP5-HB-IPV-Hib Group (0.3%) and the Control Group (0.5%). ConclusionsThe safety and immunogenicity of DTaP5-HB-IPV-Hib is generally comparable to Control when administered in the 2, 4, 11–12month schedule. Early Hib responses were superior versus Control. DTaP5-HB-IPV-Hib could provide a new hexavalent option for pediatric combination vaccines, aligned with recommended immunizations in Europe.Study identification: V419-008CLINICALTRIALS.GOV identifier: NCT01480258

Preparation and testing of a Haemophilus influenzae Type b/Hepatitis B surface antigen conjugate vaccine

The majority of conjugate vaccines focus on inducing an antibody response to the polysaccharide antigen and the carrier protein is present primarily to induce a T-cell dependent response. In this study conjugates consisting of poly(ribosylribitolphosphate) (PRP) purified from Haemophilus influenzae Type b bound to Hepatitis B virus surface antigen (HBsAg) virus like particles were prepared with the aim of inducing an antibody response to not only the PRP but also the HBsAg. A conjugate consisting of PRP bound to HBsAg via an adipic acid dihydrazide (ADH) spacer induced strong IgG antibodies to both the PRP and HBsAg. When conjugation was performed without the ADH spacer the induction of an anti-PRP response was equivalent to that seen by conjugate with the ADH spacer, however, a negligible anti-HBsAg response was induced. For comparison, PRP was conjugated to diphtheria toxoid (DT) and Vi polysaccharide purified from Salmonella Typhi conjugated to HBsAg both using an ADH spacer. The PRPAH–DT conjugate induced strong anti-PRP and anti-DT responses, the Vi–AHHBsAg conjugate induced a good anti-HBsAg response but not as strong as that induced by the PRPAH–HBsAg conjugate. This study demonstrated that in mice it was possible to induce robust antibody responses to both polysaccharide and carrier protein provided the conjugate has certain physico-chemical properties. A PRPAH–HBsAg conjugate with the capacity to induce anti-PRP and anti-HBsAg responses could be incorporated into a multivalent pediatric vaccine and simplify formulation of such a vaccine.

Safety and Immunogenicity of 2 Mixed Primary Infant Immunization Schedules of Pentavalent Diphtheria, Tetanus, Acellular Pertussis, Inactivated Poliomyelitis, and Haemophilus influenzae Type b Vaccines at 2, 4, and 6 Months of Age

Two pentavalent infant vaccines that contain either 5 or 3 component acellular pertussis antigens are authorized in Canada. Because of changes in vaccine use by provinces over time and movement of families across jurisdictions, it is possible that children are exposed to different combination vaccines during the primary infant immunization schedule. The safety and immunogenicity of mixed primary infant schedules is unknown. In a double-blind multicenter trial, 2-month-old healthy infants were randomized to 1 of 2 schedules at 2, 4, and 6 months of age (either Pediacel, Pediacel, Infanrix [PPI] or Infanrix, Pediacel, Pediacel [IPP]). Solicited local and systemic adverse events (AEs) were collected by parent diary on days 0 through 7; unsolicited AEs were collected for 31 days after each dose. Immune responses to polypolyribosylribitol phosphate capsular polysaccharide (PRP) (Haemophilus influenzae type b) and pertussis antigens were assessed before the first dose and 28 days after the 6 month (third) dose. In all, 127 infants were randomized to IPP and 126 to PPI. The percentage of children with anti-PRP responses ≥0.15 μg/mL after dose 3 was higher in the IPP than in the PPI group (98.3, 95% CI: 94.1, 99.8 vs. 86.1%, 95% CI: 78.6, 91.7, P < 0.001). Antipertussis toxin and anti-fimbriae 2 and 3 responses were statistically significantly higher in the IPP than in the PPI group. Higher filamentous hemagglutinin responses occurred in PPI than in IPP. No difference between groups was observed in pertactin responses.Systemic AEs were similar between the 2 vaccine schedules. Irritability (67.2 vs. 51.6, P = 0.014) and mild crying (35.2% vs. 23.0%, P = 0.037) were more common after the 6-month dose in the PPI compared with the IPP group, as were overall systemic reactions (any intensity) for the PPI group after this dose (80.0 vs. 68.0, P = 0.042). Mixed 2-, 4-, 6-month pentavalent infant vaccine schedules had different immunogenicity and reactogenicity, with a PPI schedule being more reactogenic, and less immunogenic for PRP and fimbriae 2 and 3 antigens at 7 months. It is preferable to complete the primary infant 3-dose vaccine series with the same vaccine, rather than considering infant vaccines as interchangeable.

Immunogenicity of Routinely Used Childhood Vaccines When Coadministered With the 10-Valent Pneumococcal Non-typeable Haemophilus influenzae Protein D Conjugate Vaccine (PHiD-CV)

The choice of non-typeable Haemophilus influenzae Protein D as main carrier protein in the candidate 10-valent pneumococcal conjugate vaccine (PHiD-CV, GlaxoSmithKline Biologicals), was driven in part to avoid carrier-mediated suppression and possible bystander interference with coadministered vaccines. Immunogenicity data from 3 primary and 2 booster vaccination studies were assessed for possible impacts of PHiD-CV coadministration on immune responses to routinely administered childhood vaccines, in comparison to 7-valent pneumococcal conjugate vaccine (7vCRM) coadministration. Randomized, controlled studies in which PHiD-CV or 7vCRM vaccines were coadministered with DTPa-[HBV]-IPV/Hib, DTPa-[HBV]-IPV, DTPw-HBV/Hib, IPV, and OPV, combined Hib-Neisseria meningitidis serogroup C vaccine (Hib-MenC-TT), standalone MenC-TT or MenC-CRM vaccines. One month after primary vaccination, >96% of PHiD-CV recipients had seroprotective antibody concentrations against diphtheria, tetanus, poliovirus types 1 and 3, Hib (>or=0.15 microg/mL), SBA-MenC (>or=1:8), and >94% were seropositive for antibodies against pertussis antigens. Somewhat lower responses against poliovirus type 2 in study A (compared with poliovirus type 1 and 2 responses) and hepatitis B in the 6-, 10-, and 14-week schedule in the Philippines (compared with hepatitis B responses in the other studies) were observed after coadministration of both PHiD-CV and 7vCRM vaccines. Antitetanus and anti-PRP antibody geometric mean concentrations (GMCs) tended to be higher after PHiD-CV coadministration, probably because of the TT carrier protein for serotype 18C in PHiD-CV. Booster vaccination induced substantial increases in antibody GMCs for all coadministered antigens. These responses were generally within the same range in PHiD-CV and 7vCRM groups. Observed anti-PRP responses remained higher in PHiD-CV recipients after the booster dose. Coadministration of PHiD-CV with commonly used childhood vaccines induced high levels of seroprotection/seropositivity against all targeted diseases. No evidence of negative interference on the immune response to any of the coadministered vaccine antigens was observed when compared with the current routine practice of 7vCRM coadministration.

Evaluation of a diphtheria–tetanus–acellular pertussis–inactivated poliovirus–Haemophilus influenzae type b vaccine given concurrently with meningococcal group C conjugate vaccine at 2, 3 and 4 months of age

Background and objective: In view of the possible introduction of diphtheria–tetanus–acellular pertussis–inactivated poliovirus–Haemophilus influenzae type b (DTaP-IPV-Hib, eg Pediacel) vaccine in the UK, a study of the immunogenicity of Pediacel...

Dose response of CRM 197 and tetanus toxoid-conjugated Haemophilus influenzae type b vaccines

High vaccine cost has limited use of conjugate vaccines in the developing world where the disease burden is greatest. Fixed fractional doses of Haemophilus influenzae type b (Hib) vaccines have been shown to be immunogenic, but dose responses of these vaccines in humans are needed to determine the lowest immunogenic dose as an option for lowering vaccine cost. We randomized children to receive one of five doses (0.625, 1.25, 2.5, 5.0 and 10 μg) of either a diphtheria CRM 197 or tetanus toxoid-conjugated Hib vaccine. The children received a primary three-dose series at 6, 10, and 14 weeks of age and a booster dose at 9 months. Anti-PRP IgG antibodies were measured at each vaccination, at 18 weeks, and at one week following the booster dose. Concentrations of ≥1.25 μg of HibCRM 197 vaccine produced mean anti-PRP responses at 18 weeks of ≥5.72 μg/ml and ≥0.15 μg/ml was achieved in >98% of the children with at least 79% reaching anti-PRP concentrations of ≥1.0 μg/ml. Concentrations of ≥1.25 μg of Hib-tetanus vaccine produced mean anti-PRP responses at 18 weeks of ≥8.63 μg/ml and ≥0.15 μg/ml was achieved in 100% of the children with at least 88.9% reaching anti-PRP concentrations of ≥1.0 μg/ml. While mean antibody concentrations after either vaccine decreased over time, the proportion of children with antibody levels of ≥0.15 μg/ml had not changed significantly at the 9 month measurement. Immunologic memory was demonstrated by significant increases in mean antibody concentrations one week after the booster dose for doses ≥1.25 μg of HibCRM 197 and Hib-tetanus to mean concentrations ≥37.71 and 16.07 μg/ml, respectively. There were no differences in antibody responses for vaccine doses ≥1.25 μg of the same vaccine or between the same concentrations of the two different vaccines. Our data suggest that doses of these vaccines of ≥1.25 μg may be sufficient to stimulate an immune response that offers both short and longer term protection from invasive Hib disease.

A combined liquid Hib (PRP-OMPC), hepatitis B, diphtheria, tetanus and whole-cell pertussis vaccine: controlled studies of immunogenicity and reactogenicity

We evaluated the immunogenicity and reactogenicity of a new liquid pentavalent combination vaccine, which incorporates a diphtheria, tetanus and whole-cell pertussis vaccine (DTP) with Hib (PRP-OMPC) and hepatitis B vaccine (HB), in a series of three studies involving 2156 infants. The vaccination schedule was 2, 4, 6 and 18 months for all studies. In addition, subjects in the third study also received a dose of monovalent hepatitis B vaccine at birth. The principal study was a randomised double blind trial of two separate, but concurrently administered vaccines in each of three groups: pentavalent vaccine [DTP-Hib-HB] plus placebo (Group A, n=619); quadrivalent vaccine [DTP-HB] plus Hib vaccine (Group B, n=620); and bivalent vaccine [Hib-HB] plus DTP (Group C, n=226). The second study (Group D, n=231) was an open trial of three separate, but concurrently administered licenced control vaccines (DTP, Hib and HB). The third study (Group E, n=460) administered a dose of monovalent hepatitis B vaccine at birth followed by pentavalent vaccine as for Group A. Subjects were bled prior to the 2- and 18-month vaccinations, and a month after the 6- and 18-month vaccinations. A diary card was used to record subject temperatures and other systemic and local clinical signs for 7 days after each vaccination. The pentavalent vaccine, whether or not preceded by a birth dose of hepatitis B vaccine, was generally well tolerated at all administration times, and had a reactogenicity profile similar to that observed for licenced vaccine controls. Diphtheria and tetanus antibody levels were substantially above protective levels in all study groups. The anti-HBs responses (%≥10 mIU/ml) following the 6-month dose of vaccines were, respectively, for Groups A–E: 83.2, 91.7, 96.5, 98.8 and 93.9%, and following the 18-month doses: 87.9, 97.5, 98.8, 98.8 and 92.8%. Anti-PRP responses (%≥1.0 μg/ml) following the 6-month dose for Groups A–D were 86.0, 90.5, 91.2, and 74.4%, and after the 18-month dose for Groups A–E were 97.3, 98.3, 98.1, 97.0, and 99.5%. Consistently higher geometric mean titres (GMTs) for pertussis antibodies to agglutinogens (Agg2, Agg3) and pertactin were recorded for the pentavalent vaccine compared to the licenced control vaccine, though they were somewhat lower for pertussigen (PT). Except for the hepatitis B response, antibody responses induced by the pentavalent vaccine to all antigens with a schedule commencing at 2 months of age and completed at 18 months were equivalent to responses to the same antigens induced by the separate, but concurrently administered licenced control vaccines. A regimen of a birth dose of hepatitis B vaccine followed by pentavalent vaccine at 2, 4, 6 and 18 months was not countered by any clinically significant decrease in seroresponses.

Maternal Immunization With Haemophilus influenzae Type b Polysaccharide—Tetanus Protein Conjugate Vaccine in The Gambia

To evaluate maternal responses to Haemophilus influenzae type b (Hib) polysaccharide-tetanus protein conjugate (polyribosylribitol phosphate-tetanus or PRP-T) given to pregnant Gambian women, the transplacental transfer of antibody, and the effect of maternal immunization on infant responses to the vaccine. An open, randomized immunogenicity study. A busy urban health center in The Gambia. A total of 451 pregnant women enrolled during the third trimester of pregnancy. Study participants were randomized to three groups. In one group, mothers were given PRP-T during the third trimester and their infants were given PRP-T at 2, 3, and 4 months of age. In the second group, mothers received PRP-T and infants were given inactivated poliovirus vaccine. In the third group, mothers received meningococcal A and C vaccine, and their infants received PRP-T. Anti-PRP antibody measurements of maternal cord, and infant blood. Vaccinated women had a marked increase in total anti-PRP antibody (geometric mean titer 9.0 micrograms/mL), which was greatest in women in their first or second pregnancy. Previous tetanus vaccination during the same pregnancy and high concentrations of antitetanus antibody were associated with lower anti-PRP responses. In infants of PRP-T recipients, cord blood anti-PRP IgG concentrations were 61% of simultaneous maternal concentrations. In vaccinated infants of vaccinated mothers, geometric mean anti-PRP antibody concentrations at birth, 2 months of age, and 5 months of age were 1.92, 0.35 and 2.84 micrograms/mL, respectively, while in vaccinated infants of unvaccinated mothers, the corresponding concentrations were 0.29, 0.12, and 3.91 micrograms/mL. At 2 months of age, 60% of infants of vaccinated mothers and 26% of infants of unvaccinated mothers had anti-PRP antibody concentrations considered to be protective (>0.15 micrograms/mL). In areas where much invasive Hib disease occurs in infants younger than 6 months, maternal immunization may help to reduce the risk of Hib disease in infants too young for immunization.

Anti-PRP antibody levels after a primary series of PRP-OMPC and persistence of antibody titres following primary and booster doses

The Haemophilus influenzae capsular polysaccharide-outer membrane protein conjugate, PRP-OMPC (PedvaxHIB) elicits very good antibody responses in infants ≥ 2 months of age after the first dose. Increasing age at time of first vaccination correlates with higher antibody responses. Anti-PRP responses are consistently high with the first injection among all population groups studied. Booster doses stimulate anamnestic antibody responses after one year of age. Among US children (excluding Navajo and Apache children) given a primary injection at 14–18 months of age, the geometric mean titre (GMT) after 2 to 3 years was >1 μg/ml. US children (excluding Navajo and Apache children) given a primary series at 2 and 4 months of age and a booster at 18 months of age also had an anti-PRP GMT >1 μg/ml 2.5 years later. Navajo and Apache children given a primary series at 2 and 4 months of age and a booster at 12–15 months had antibody levels of 1.50 μg/ml one year later. Antibody persistence data suggest there will be long-term protection against Haemophilus influenzae b disease following immunization with PRP-OMPC.

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.

EFFECT OF OLIGOSACCHARIDE (OS) CHAIN LENGTH, TERMINAL GROUP, AND HAPTEN LOADING ON THE SERUM ANTIBODY (Ab) RESPONSE OF 1-YR-OLD INFANTS TO H. INFLUENZAE B CAPSULAR ANTIGEN (PRP) CONJUGATED TO THE DIPHTHERIA PROTEIN CRM197

Vaccines consisting of OS derived from PRP and conjugated by reductive amination to the nontoxic diphtheria mutant toxin CRM 197 (C) were previously shown to elicit memory-type serum anti-PRP responses in human infants. Here we seek to define structural variables that control the infant's response. In the coupled OS, the nonreducing (and hence exposed) terminal group can be ribitol (r), ribose (R), or phosphate (p). A series of r-terminal OS of mean length 4, 6, or 12 repeat units were coupled to C at ca. 10 ribose/protein, and OS of 12 repeat units terminating in R or p were coupled at ca. 30 ribose/protein. A 2-injection sequence was given to healthy infants aged 9-15 mo (groups of 8-10). Anti-PRP Ab was assayed by radioantigen binding; at 1 mo after the 2° the geometric means (GM) and 95% confidence intervals (CI) were:Series C4r, C6r, C12r (all at low hapten loading) induced similar titers regardless of OS chain length. C12R and C12p (both with high loadings) induced similar titers that were >10-fold the r series.

Vaccines consisting of periodate-cleaved oligosaccharides from the capsule of Haemophilus influenzae type b coupled to a protein carrier: structural and temporal requirements for priming in the human infant.

Reducing oligosaccharides from the Haemophilus influenzae type b capsular polymer (PRP) coupled by reductive amination to diphtheria toxoids (DTd) had been shown to elicit potentially protective serum anti-PRP antibodies (Ab) in infants too young for an adequate response to PRP vaccine. Here we report that cleavage of PRP with periodate gives antigenic oligosaccharides that couple with high efficiency. DTd-coupled saccharides of mean length eight or 20 repeat units (Dpo8 and Dpo20, respectively) were tested for immunogenicity in young adults (single injection) and in infants 9 to 15 mo old who received a sequence of primary (1 degree) and secondary (2 degrees) injections. Both vaccines consistently induced high anti-PRP Ab responses in adults. In infants, Dpo8 elicited only modest anti-PRP responses, whereas Dpo20 gave consistently high titers; post-2 degrees responses were higher when the interval between 1 degree and 2 degrees injections was 6 to 14 wk than with an interval of 2 to 4 wk. Thus with this type of immunogen, priming responses in infancy has more stringent structural requirements than does triggering responses in adults, and the priming appears to maximize more slowly than the Ab level.

1102 FURTHER STUDIES OF THE RESPONSES TO HAEMOPHILUS INFLUENZAE TYPE b VACCINE IN RELATION TO THE KM(1) AND GM(23) Ig ALLOTYPES

In experimental animals, there are genes associated with Ig allotypes which regulate immune responses. We examined the responses of children immunized with Haemophilus influenzae type b polysaceharide vaccine (PRP). 97 children, ages 12 to 83 mos (M=36.8±19), were immunized. Sera were obtained prior to immunization and 2 mos later. Total antiPRP was measured by a radioantigen-binding assay. IgG antiPRP was measured by ELISA. AntiPRP responses were lower in blacks lacking the Km(l) Ig allotype.In whites, there were no significant differences in antibody response in relation to the Km(1) or Gm(23) allotypes. In conclusion, blacks with Km(l) but not whites have higher IgG responses to PRP vaccine. Our findings corroborate previous results with a different Hib vaccine (PRP complexed to pertussis vaccine) (J.clin.Invest. 74:1708, 1984). The present data support a genetic basis for immune response to the PS component of the vaccine. Further, the children found in our previous study to be genetically at greatest risk of Hib disease [Blacks lacking Km(l)] are the group least likely to benefit from immunization.

1184 SERUM ANTIBODY (Ab) KINETICS FOLLOWING H. INFLUENZAE TYPE B POLYRIBOSEPHOSPHATE (PRP)-DIPHTHERIA TOXOID CONJUGATE (PRP-D) VACCINE GIVEN TO INFANTS: 1 YR FOLLOW-UP AND BOOSTER DOSE RESPONSE

We have previously reported a 90% (28/31) anti-PRP Ab response following administration of 3 doses of PRP-D to 3 mo. old infants. The resulting group geometric mean (GM) Ab cone was 0.99 μg/ml (1.4 μg/ml in responders). Sera has been obtained from 25 subjects at 6 mos., and 8 subjects at 12 mos. postvaccine. As expected, anti-PRP cone had dropped in 24/25 at the 6 mo. followup, but was still ≥0.15 μg/ml in 60% (12/20) of those who had previously achieved a titer of ≥0.15 yg one month after dose 3. The 6 mos. GM Ab conc for these 25 subjects decreased from 0.883 μg/ml to 0.163 μg/ml (p<0.01). At 12 mos. post-vaccination, 5/7 children had a further drop (one 6 mos. sera not obtained), but 62% (5/8) had an anti-PRP conc. ≥0.15 μg/ml (group GMT - 0.163 μg/ml). All 8 subjects received a 4th dose of PRP-D at 18 mos. of age (12 month follow-up) without adverse reactions. Excellent anti-PRP responses have developed in the 3 subjects studied to date, a 23 to 137-fold increase over their previous peak Ab cone (2.7 μg/ml, 5.6 μg/ml and 31.3 μg/ml). In summary, anti-PRP Ab cone ≥0.15 μg/ml was present in 60% of subjects vaccinated at age 3 mos. when evaluated at 6 and 12 mos. postvaccine. A 4th booster dose at 18 mos. did not result in any adverse reaction and induced excellent anti-PRP responses. The remaining subjects are being revaccinated and Ab evaluated.

1149 PERSISTENCE OF ANTIBODY IN CHILDREN IMMUNIZED WITH HEMOPHILUS INFLUENZAE, B POLYSACCHARIDE (PRP) COMBINED WITH DTP VACCINE (PRP-DTP) AT 18 MONTHS OF AGE

PRP-DTP vaccine given to children at 18 mos. of age who have previously received this vaccine results in enhanced serum anti-PRP responses at 19 mos. of age, as measured by RIA. To assess the duration of elevated serum anti-PRP concentrations, antibody titers at 36-42 mos. of age in 31 prior recipients of PRP-DTP at 18 mos., 17 of whom had also received PRP-DTP in infancy, were compared with those at 19 mos. The mean GMTs (ug/ml) in the two groups did not change significantly in the interval. In groups A and B, anti-PRP titer decreases of twofold or more occurred in 4/17 and 6/14 (p = 0.44), respectively. The frequency of anti-PRP concentration ≥ 0.15 and ≥ 1.0 ug/ml at 19 mos. and at 36-42 mos. in each group did not differ: These findings indicate that anti-PRP titers in 3 to 3½ year old children immunized with PRP-DTP at 18 mos. of age reflect immunological responses at that age; and for those achieving high titers at 19 mos., subsequent doses of PRP may not be necessary to sustain protection.

1103 IgG1 ANTIBODY RESPONSES OF CHILDREN AND ADULTS IMMUNIZED WITH HAEMOPHILUS INFLUENZAE TYPE b (Hib) POLYSACCHARIDE VACCINE (PRP)

IgG was purified by gel filtration of sera from 3 adults immunized with PRP. The ratio of IgGl to IgG2 anti-PRP was determined in affinity purified anti-PRP. We also determined IgG1 anti-PRP by measuring anti-PRP radioantigen binding activity before and after column immunoabsorption of IgGl employing a highly specific monoclonal prepared locally (HG-11). 38–46% of the post-vaccine serum IgG anti-PRP was of the IgGl subclass. An ELISA was then used to measure IgG and IgGl anti-PRP antibody in sera from 16 normal adults; and from 97 children 12 to 83 mos of age and 8 adults immunized with PRP. Only 2 of 16 unimmunized adults had IgGl liters >1:49. The IgGl anti-PRP antibody 2 mo after immunization was age-dependent.12 of 35 children had high IgG antiPRP responses (post vaccine titers >1:400) but no detectable IgGl antibody (IgGl titer <1:49). Thus, IgGl is an important component of the IgG antiPRP response of some but not all immunized subjects. In addition, although serum IgGl reaches adult concentrations in the first year of life, most children of this age cannot respond to immunization with IgGl anti-PRP whereas many older children can.

AUGMENTED ANTIBODY (Ab) RESPONSES IN INFANTS ADMINISTERED A NEW HAEMOPHILUS INFLUENZAE TYPE B CAPSULAR POLYSACCHARIDE (PRP) DIPHTHERIA TOXOID CONJUGATE VACCINE (PRP-D)

PRP-D, a hapten-carrier conjugate containing 20μg PRP/0.5cc, has previously been shown to be highly immunogenic in adults and young children (<18 mo.) given 2 doses. Ab responses in sera taken 1 mo. post-vac were evaluated in 90 infants administered PRP-D, PRP, or placebo at ages 3, 5 & 7 months. No significant adverse reactions occurred. Anti-PRP responses for the vaccinees shown (Farr assay with SK standard) developed in 14%, 53%,& 100% of PRP-D vaccinees respectively, following the first three doses as compared to 0, 7%, and 60% in PRP vaccinees respectively. A sequential increase in the mean anti-PRP titer was see in the PRP-D group and final mean titers were 5-fold greater than that following PRP:This new PRP-D conjugate vaccine appears to have resulted in an enhanced response since the seroconversion rate and Ab titers were higher than those seen following PRP.