IgG1, IgG2 and IgM responses to two Haemophilus influenzae type b conjugate vaccines in young infants

Controlled Covalent Conjugation of a Tuberculosis Subunit Antigen (ID93) to Liposome Improved In Vitro Th1-Type Cytokine Recall Responses in Human Whole Blood

Tuberculosis (TB) remains a foremost poverty-related disease with a high rate of mortality despite global immunization with Bacille Calmette-Guérin (BCG). Several adjuvanted recombinant proteins are in clinical development for TB to protect against the disease in infants and adults. Nevertheless, simple mixing of adjuvants with antigens may not be optimal for enhancing the immune response due to poor association. Hence, co-delivery of adjuvants with antigens has been advocated for improved immune response. This report, therefore, presents a strategy of using chemical conjugation to co-deliver an adjuvanted recombinant protein TB vaccine (ID93 + GLA-LSQ). Chemical conjugation involving glutaraldehyde (GA) or 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) was used to associate the antigen (ID93) to the modified liposome (mGLA-LSQ). The physicochemical stability of the formulations was evaluated using high-performance liquid chromatography (HPLC) (adjuvant content), dynamic light scattering (DLS, particle size analysis), and sodium dodecyl sulfate-polyacrylamide gel (SDS) electrophoresis (protein analysis). The bioactivity was assessed by cytokine stimulation using fresh whole blood from 10 healthy donors. The conjugates of ID93 + mGLA_LSQ maintained liposomal and protein integrity with the two protein chemistries. The GLA and QS21 content of the vaccine were also stable for 3 months. However, only the glutaraldehyde conjugates provoked significant secretion of interleukin-2 (210.4 ± 11.45 vs 166.7 ± 9.15; p = 0.0059), interferon-gamma (210.5 ± 14.79 vs 144.1 ± 4.997; p = 0.0011), and tumor necrosis factor alpha (2075 ± 46.8 vs 1456 ± 144.8; p = 0.0082) compared to simple mixing. Conjugation of recombinant protein (ID93) to the liposome (mGLA_LSQ) through chemical conjugation resulted in a stable vaccine formulation, which could facilitate co-delivery of the subunit vaccine to promote a robust immune response.

Antibodies prevalence against Haemophilus influenzae type b in Jeddah population, Saudi Arabia. II. Antibodies subclasses

Our previous reported that Jeddah, Saudi Arabia population have a comparable and protective herd immunity represented by IgG, IgA and IgM against Haemophilus influenzae type b (Hib), by using indirect ELISA test was used to evaluate Haemophilus influenzae type b (Hib) anti-polyribosyl-ribitol phosphate (PRP) total antibodies (IgM, IgG, IgA) in 1,003 sera samples. Current report was evaluated the IgG and IgA subclasses responsible about this protection using same methodology. IgG, IgA, and their subclasses are responsible about this circulating protection. Our study will consider the first report evaluate the levels of IgA subclasses and its relation to ages, as well as the relations between anti-Hib antibody subclass and age. The current results demonstrated that the highest levels concentrated in IgG1 and IgG2, while IgG3 and IgG4 showed the lowest levels. So, their concentrations were arranged in IgG1 > IgG2 > IgG3 > IgG4. The results indicated that the age and gender have no effect on both IgG or IgA subclasses in healthy immunized individuals enrolled. While, IgA1 concentrations were significantly higher than IgA2 in all age categories regardless of gender. It seem that the IgG1, IgG2 and IgA1 subclasses were the main constituent of Jeddah herd immunity against Hib. Finally, to the best of our knowledge, there were no previous reports that focusing on the levels of IgA subclasses and its relation to ages, so our study considers the first worldwide.

Combined meningococcal serogroup A and W135 outer-membrane vesicles activate cell-mediated immunity and long-term memory responses against non-covalent capsular polysaccharide A

Outer-membrane vesicles (OMVs) have inherent adjuvant properties, and many vaccines use OMV as vaccine components. Utilizing the adjuvant properties of OMV could lead to the formulation of vaccines that are less expensive and potentially more immunogenic than covalently conjugated polysaccharide vaccines. We evaluated the adjuvant effect in Balb/c mice of combinations of OMV from Neisseria meningitidis serogroup A and W135 as compared to that of the non-covalently conjugated capsular polysaccharide A. Both antigens were adsorbed onto aluminum hydroxide. The mice were given a booster dose of plain polysaccharide A to stimulate an immunologic memory response. Subclasses determination and cytokine assays demonstrated the capacity of OMV to induce a IgG2a/IgG2b isotype profile and IFN-γ production, suggesting the induction of a Th1 pattern immune response. Lymphoproliferative responses to OMVs were high, with affinity maturation of antibodies observed. Bactericidal titers after the booster dose were also observed. Memory B cells and long-term memory T cells were also detected. The results of this study indicate that combined meningococcal serogroup A and W135 OMV can activate cell-mediated immunity and induce a long-term memory response.

Hyporesponsiveness and its clinical implications after vaccination with polysaccharide or glycoconjugate vaccines

Hyporesponsiveness (immune tolerance) follows vaccination with meningococcal polysaccharide and many pneumococcal polysaccharide serotypes. Hyporesponsiveness after Haemophilus influenzae type b polysaccharide vaccination has not been directly observed, but may follow exposure during disease in some individuals. Use of currently licensed conjugate vaccines has not been associated with hyporesponsiveness to date, with the possible exception of pneumococcal serotype 3. Introduction of polysaccharide vaccines anywhere into a conjugate vaccination schedule may result in reduced immune responses on subsequent exposure. This review of vaccine-induced hyporesponsiveness and its potential clinical implications considers recent evidence suggesting that hyporesponsiveness may occur for specific components of combined conjugate vaccines, such as pneumococcal serotype 3. These data have implications for the development of new multivalent vaccines.

Safety, tolerability and immunogenicity of low dose Haemophilus influenzae type b conjugated to the outer membrane protein complex of Neisseria meningitidis group B

Infants vaccinated with three doses followed by a booster of either 1.0 microg of Haemophilus influenzae type b conjugated to the outer membrane protein complex of Neisseria meningitidis group B or H. influenzae 10-microg oligosaccharide vaccine conjugated to 25 microg mutant toxin (CRM197) isolated from Corynebacterium diphtheriae had protective antipolyribosylribitol phosphate concentrations.

Neonatal and early life vaccinology

Preclinical and human vaccine studies indicate that, although neonatal immunisation does not generally lead to rapid and strong antibody responses, it may result in an efficient immunological priming, which can serve as an excellent basis for future responses. The apparent impairment of CD4 and CD8 T-cell function in early life seems to result from suboptimal antigen-presenting cells-T cell interactions, which can be overcome by use of specific adjuvants or delivery systems. Although persistence of maternal antibodies may limit infant antibody responses, induction of T-cell responses largely remain unaffected by these passively transferred antibodies. Thus, neonatal priming and early boosting with vaccine formulations optimised for sufficient early life immunogenicity and maximal safety profiles, could allow better control of the huge infectious disease burden in early life.

Clinical and immunological risk factors associated with Haemophilus influenzae type b conjugate vaccine failure in childhood

Haemophilus influenzae type b (Hib) conjugate vaccines have proved extremely efficacious in healthy children. True Hib vaccine failures are rare. Hib conjugate vaccines were introduced for routine immunization in the United Kingdom and the Republic of Ireland in 1992. Coincident with this, active prospective and national surveillance via pediatricians, microbiologists, and public health physicians was commenced to assess the clinical and immunological factors associated with vaccine failure. During the 6 years of the study, 115 children with true vaccine failure were reported. Of the children who were vaccinated before 12 months of age, a clinical risk factor was detected in 20%, an immunological deficiency was detected in 30%, and one or both were detected in 44%. Children who were vaccinated after 12 months of age were more likely to have one or both factors (67%). Thirty percent (33 of 105) of children with true vaccine failure had a low Hib antibody response (concentration, <1.0 microg/mL) after disease, but the majority then responded to a further dose of Hib vaccine. Children who develop Hib disease despite vaccination deserve further clinical and immunological evaluation.

Effectiveness of a nationwide infant immunization program against Haemophilus influenzae b. The Israeli Pediatric Bacteremia and Meningitis Group

An ongoing nationwide prospective surveillance program for invasive H. influenzae b (Hib) disease in Israel enabled us to study the effectiveness of a national infant Hib immunization program, which included all infants born since January 1994. The vaccine used was Hib polysaccharide conjugated to outer membrane protein complex of Neisseria meningitidis b (PRP-OMPC). For the cohort born during the 3 years since January 1994, the vaccine effectiveness was 94.9% for all invasive Hib diseases and 96.6% for meningitis. The efficacy in fully immunized subjects was 98.7 and 99.5%, respectively. A herd immunity effect could be observed, since a reduction in cases also occurred among infants too young to be immunized. No increase in invasive cases caused by S. pneumoniae and N. meningitidis was observed during the study period. This is the first report outside North America and Western Europe that demonstrates a nationwide extensive reduction of invasive Hib disease within a short time of the introduction of Hib conjugate vaccines to the infant immunization program.

Protective immunogenicity of Haemophilus influenzae type b polysaccharide-tetanus protein conjugate vaccine in children who failed to respond to prior invasive H. influenzae type b disease

A polyribosylribitol phosphate (polysaccharide)-tetanus protein conjugate vaccine (PRP-T) against Haemophilus influenzae type b (Hib) was evaluated for protective immunogenicity in 25 previously PRP-unimmunized children who had failed to develop protective PRP antibody levels (< 1 microg/ml) after prior invasive Hib disease at median age 10 months. Children under 21 months of age at time of PRP-T immunization received one, two or three doses. Serum was obtained for total PRP antibody, complement mediated bactericidal activity and specific IgG1 and IgG2 PRP antibodies before (n = 25), 1 to 2 months (n = 24) and > 5 months (n = 13) after completed vaccination. One to 2 months after immunization, all but one patient developed > 1 microg/ml of antibody (geometric mean level 50.7 microg/ ml). The non-responder developed protective antibody levels when tested at 6 months after vaccination. Twenty out of 22 sera had detectable complement mediated bactericidal activity (median dilution titer 1:24), 1-2 months after vaccination. Three patients failed to demonstrate PRP antibodies in the IgG1 or IgG2 subclasses, although two of them had protective (> 1 microg/ml) total antibody levels. The second post immunization sera showed persistence of the total PRP antibody levels (geometric mean level 38.2 microg/ml) as well as of the bactericidal activity (median dilution titer 1:32).

CONCLUSION

PRP-T conjugate vaccine is able to elicit a protective immune response in children who have low or unmeasurable PRP antibody levels after a systemic Hib infection.

Immunization with Haemophilus influenzae type b conjugate vaccine in children given bone marrow transplantation: comparison with healthy age-matched controls

Forty-seven patients (age range, 7 months-18 years) with malignant (38 cases) and nonmalignant (9 cases) disorders given an allogeneic or an autologous bone marrow transplantation (BMT) were immunized with Haemophilus influenzae type b (Hib) polysaccharide-diphtheria toxoid conjugate vaccine administered in a single dose at different time points after transplantation. Results were compared with those of 13 healthy children matched for age and sex who received the same immunization schedule. Serum and saliva samples for measurement of total IgG subclass and specific antibody levels were obtained from patients and healthy controls before and 3 weeks after vaccination. Twenty-five of the 47 patients (53%) had a specific anti-Hib IgG response, while an effective IgA and IgM response was mounted by 23 (49%) and 11 (23%) children, respectively. In the control group, 13 of 13 subjects mounted a specific IgG antibody production (P < 0.005 in comparison to the patients' response rate), while an IgA and IgM response was demonstrated in 12 (92%; P < 0.01 compared to transplanted patients) and 7 (54%; P < 0.05 in comparison to BMT recipients) children, respectively. Lapse of time from BMT to immunization was the most important factor predicting antibody response, as proved by an effective increase in prevaccination specific IgG levels in the majority of patients vaccinated after 2 years from transplant. Our data demonstrate that BMT recipients have a reduced capacity to mount an antibody response to polysaccharide antigens compared to normal controls, even when a protein-conjugated vaccine is employed. Since time after transplant is the major factor influencing the recovery of immune reactivity to polysaccharide antigens, the ontogeny of the B cell repertoire seems to follow a predetermined sequential program of development.

Immunogenicity and safety of Haemophilus influenzae type b polysaccharide-Neisseria meningitidis conjugate vaccine in 7.5 micrograms liquid formulation: a comparison of three lots with the 15.0 micrograms lyophilized formulation. Study Group for 7.5 micrograms Liquid PedvaxHIB

We conducted a multicenter, single-blind, randomized comparisons of the immunogenicity and safety of three manufacturing-scale lots of 7.5 micrograms liquid Haemophilus influenzae type b polysaccharide- Neisseria meningitidis conjugate vaccine (PRP-OMPC) and a single lot of 15.0 micrograms lyophilized PRP OMPC. A total of 908 infants were entered into the study. Each infant received two primary injections intramuscularly 2 months apart beginning at age 2-6 months and a booster injection at 12-15 months. Blood samples for serology were obtained before each injection and 1 month after the second and the booster dose. Immune responses were measured by radioimmunoassay. Approximately 80% of the infants achieved a titer > 1.0 micrograms ml-1 after the second primary dose of all four lots tested: the geometric mean titer (GMT) was ca 3 micrograms ml-1 for each vaccine group. After the booster dose, more than 90% of infants from each vaccine group had a titer > 1.0 microgram ml-1;GMTs ranged from 8 to 10 micrograms ml-1. No serious vaccine-associated adverse reactions were reported. Thus the 7.5 liquid PRP OMPC vaccine was at least as immunogenic and well tolerated as the 15.0 micrograms lyophilized vaccine.

Characteristics of immune responses to native and protein conjugated pneumococcal polysaccharide type 14

The immune response to pneumococcal polysaccharide type 14 (PPS-14), induced by native PPS-14 was compared with the response induced by PPS-14 conjugated with CRM197 (PPS-14-CRM197). In our animal model, immunization with PPS-14-CRM197 gave a significant enhancement of anti-PPS-14 serum titres for IgM and IgG, but not for IgA. Also an increase in total number of anti-PPS-14 antibody-secreting cells was found. Using immunohistochemical techniques, a different distribution pattern of specific antibody-containing cells in spleen section after immunization with PPS-14-CRM197 was observed. Furthermore, a higher number of IFN-gamma producing cells was found after immunization with PPS-14-CRM197, as compared with immunization with PPS-14. This enhanced IFN-gamma production may be the cause for enhanced IgG response observed after immunization with PPS-14-CRM197. The specific immune response was less affected by splenectomy in animals immunized with PPS-14-CRM197 than with PPS-14. However, an age-related response to the native as well as the conjugated form of the PPS-14 was observed, since no effect of conjugation with CRM197 was seen in the onset of the immune response to PPS-14 in young animals. In conclusion, our results affirm the hypothesis that conjugation of polysaccharides changes the characteristics of the antigen towards a thymus-dependent antigen.

Current status of meningococcal group B vaccine candidates: capsular or noncapsular?

Meningococcal meningitis is a severe, life-threatening infection for which no adequate vaccine exists. Current vaccines, based on the group-specific capsular polysaccharides, provide short-term protection in adults against serogroups A and C but are ineffective in infants and do not induce protection against group B strains, the predominant cause of infection in western countries, because the purified serogroup B polysaccharide fails to elicit human bactericidal antibodies. Because of the poor immunogenicity of group B capsular polysaccharide, different noncapsular antigens have been considered for inclusion in a vaccine against this serogroup: outer membrane proteins, lipooligosaccharides, iron-regulated proteins, Lip, pili, CtrA, and the immunoglobulin A proteases. Alternatively, attempts to increase the immunogenicity of the capsular polysaccharide have been made by using noncovalent complexes with outer membrane proteins, chemical modifications, and structural analogs. Here, we review the strategies employed for the development of a vaccine for Neisseria meningitidis serogroup B; the difficulties associated with the different approaches are discussed.