Safety and immunogenicity of a Pseudomonas aeruginosa O-polysaccharide toxin A conjugate vaccine in humans.

Lipid A-free polysaccharide (PS) isolated from Pseudomonas aeruginosa immunotype 5 lipopolysaccharide (LPS) was covalently coupled to toxin A via reductive amination. The PS-toxin A conjugate was comprised of 29.8% PS and 70.2% toxin A, possessed a molecular weight of greater than 1 X 10(6), was nontoxic for animals and was nonpyrogenic for rabbits at a dose of 50 micrograms/kg body wt when administered intravenously. The conjugate evoked only mild, transient reactions upon subcutaneous administration to human volunteers. Vaccination engendered immunoglobulin G (IgG) antibody, which neutralized the cytotoxic effect of toxin A and promoted the uptake and killing of P. aeruginosa in the presence of human polymorphonuclear leukocytes. Passively transferred IgG isolated from the serum of immunized donors was far more effective at preventing fatal P. aeruginosa burn wound sepsis than paired preimmunization serum. These studies establish the potential usefulness of such a PS-toxin A conjugate as a vaccine against P. aeruginosa.

Safety and immunogenicity of a V3 loop synthetic peptide conjugated to purified protein derivative in HIV-seronegative volunteers.

OBJECTIVES: To develop a peptide-based model for a preventive vaccine for HIV-1 infection. DESIGN: Phase I trial in HIV-1-seronegative volunteers. PARTICIPANTS: Adult healthy subjects HIV-1-antibody-seronegative in an enzyme-linked immunosorbent assay, screened for tuberculin [purified protein derivative (PPD)] reactivity with 2 tuberculin units PPD-administered intradermally. INTERVENTIONS: Submicrogram doses of a PPD conjugate with a peptide of the primary neutralizing domain (PND) of HIV-1MN (PPD-MN-PND) were administered intradermally to tuberculin skin-test-positive and -negative volunteers. RESULTS: Antibodies to the MN-PND were measured after two immunizations in 10 out of 11 PPD skin-test-positive volunteers. After the fourth immunization high-affinity antibodies were detected, which persisted for over 1 year. High titers of MN-PND-specific immunoglobulin (Ig) G and IgA were detected in the serum and saliva of all volunteers tested. Serum antibodies were cross-reactive with PND peptide from some other HIV-1 strains but neutralized only the HIV-1MN prototype. Human leukocyte antigen (HLA)-B7-restricted MN-PND-specific cytotoxic T lymphocytes (CTL) were also detected. CONCLUSIONS: The PPD-MN-PND vaccine at submicrogram doses is safe and immunogenic in PPD skin-test-positive healthy adult volunteers. Long lasting humoral immune responses in the serum and saliva were possibly accompanied by HLA-B7-restricted CTL responses. This is a vaccine prototype that can be rapidly and inexpensively modified to include other peptide epitopes. It is especially suitable for use in a worldwide multibillion Bacillus Calmette-Guérin (BCG)-primed or tuberculosis-exposed population at risk for HIV-1 infection.

Qualitative analysis of antibody binding. An in vitro assay for the evaluation and development of vaccines.

We describe a rapid in vitro assay for the evaluation of in vivo properties of conjugate vaccines. Using human and murine monoclonal antibodies (mAb) specific for lipopolysaccharides (LPS), isolated from Pseudomonas aeruginosa, we determined in a competitive binding assay the amount of LPS or conjugate vaccine which was required to inhibit the antibody binding to LPS by 50% (I50 values). Furthermore, utilizing a murine burn wound sepsis model, we determined the potential of the same conjugates to induce protection in vivo against infection with the corresponding bacteria. Protective mAb have approximately 100-fold lower I50 values for preparations which are highly effective in inducing protection than for preparations which are ineffective. Furthermore, in the case of potent preparations it was noted that protective mAb exhibit similar I50 values for the conjugates and for the corresponding LPS. These results suggest that the fast and easily interpretable in vitro assay described may significantly facilitate the development and optimization of vaccines.

Escherichia coli and Klebsiella vaccines and immunotherapy.

A polyvalent vaccine has been prepared from the capsular polysaccharide of 24 different serotypes of Klebsiella spp. Nearly 200 volunteers have received this vaccine. It is very well tolerated and elicits both binding (ELISA) and functional antibody to 21 of 24 antigens. Antibodies were also detected against 10 serotypes not included in the vaccine. An immunoglobulin for intravenous use (IVIG) was more protective in mouse lethality assays and enhanced opsonophagocytic killing of bacteria more than standard, nonhyperimmune globulin. A monovalent E. coli conjugate vaccine against O18ac antigen was safe and highly immunogenic in humans. A 12-valent conjugate vaccine elicits good levels of antibody in rabbits, and will soon undergo phase I testing in humans. These vaccines might best be used for inducing antibody in donor plasma that could be made into IVIG for passive administration.

Feasibility of prophylaxis and therapy against gram-negative infections by human monoclonal antibodies.

In a murine model of Gram-negative sepsis, we have shown that the prophylactic application of human monoclonal antibodies (HmAbs) with specificity for lipopolysaccharides (LPS) of Pseudomonas aeruginosa protected against bacterial infection. In this paper we show that the therapeutical application of 5 micrograms of these HmAbs up to 6 h after challenge with a lethal dose of live P. aeruginosa results in a protection rate of 70-90%. Administration 18 h after bacterial challenge, diminished the protection to 43% survival rate. Furthermore, using a mixture of HmAbs recognizing a total of six different P. aeruginosa serotypes, no interference in their protective capacities was found. Finally, these HmAbs also protected galactosamine-sensitized mice against lethal challenge with LPS. Our data show that the described HmAbs confer bactericidal activity as well as anti-endotoxic activity in vivo.

Salmonella/mammalian microsome assay with tetranitromethane and 3-nitro-L-tyrosine.

The nitrosating agent tetranitromethane (TNM) and the nitrosation product 3-nitro-L-tyrosine (NT) were tested for mutagenic activity in the Salmonella/mammalian microsome assay. TNM showed strong genotoxic activity: it was mutagenic in all tester strains used (TA97, TA98, TA100, and TA102). The maximum mutagenic activity was reached between 16 and 32 micrograms/plate using the standard plate test; higher amounts led to distinct bactericidal effects. The mutagenicity was independent of an in vitro activation system. In the preincubation assay an increased bactericidal effect was observed. In contrast to TNM, NT, the nitrosation product, was non-mutagenic and non-toxic in the standard plate test and with the preincubation method up to 5000 micrograms/plate with and without S9 mix and with all tester strains used. Although TNM is a strong direct-acting mutagen, its nitrosating effect on proteins does lead to nongenotoxic nitro products of tyrosine in proteins.

Safety and immunogenicity of a Haemophilus influenzae type B polysaccharide-tetanus toxoid conjugate vaccine combined with diphtheria, tetanus and pertussis vaccines in Thai infants.

A randomized, open, multicenter trial was conducted to determine the safety and immunogenicity of a Haemophilus influenzae type b polysaccharide-tetanus toxoid (PRP-T) conjugate vaccine combined with tetanus, diphtheria and pertussis (DTP) vaccine in 271 Thai infants born to mothers immunized against tetanus during pregnancy. Infants were immunized at approximately 2, 4 and 6 months of age with these vaccines. To determine if elevated levels of anti-tetanus toxin antibodies suppressed the anti-PRP antibody response, a second group of infants were immunized with PRP complexed with outer membrane proteins of Neisseria meningitidis (Pedvax HIB) in one limb at 2 and 4 months of age and DTP vaccine in the other limb at 2, 4 and 6 months of age. A third group of infants received only DTP vaccine at 2, 4 and 6 months of age. The occurrence of both local and systemic adverse reactions were comparable in all 3 groups. The geometric mean anti-tetanus antibody titer was > 1 IU/ml at baseline. Approximately 1 month after the administration of the third dose of vaccine, 98.5%, 99.3% and 9.7% of the children immunized with DTP+Pedvax HIB, DTP-PRP-T or DTP possessed > or = 0.15 microgram of anti-PRP antibody per ml. No child in the DTP group achieved > or = 1 microgram/ml while 74.2% and 89.3% did so after immunization with DTP+Pedvax HIB, or DTP-PRP-T, respectively (p < 0.05). Immune responses to diphtheria, tetanus and pertussis antigens were similar in all vaccine groups. These results demonstrate that elevated tetanus antibody titers do not diminish the anti-PRP antibody response following immunization with a PRP-T conjugate combined with DTP vaccine.

Safety and immunogenicity of two Haemophilus influenzae type b polysaccharide-tetanus toxoid conjugate vaccines (PRP-T) given with diphtheria-tetanus-pertussis vaccine to young Papua New Guinean children.

BACKGROUND: In view of high mortality and morbidity from Haemophilus influenzae type b (Hib) in young Papua New Guinean children, the incorporation of a Hib conjugate vaccine into a nationwide immunization program would be of major public health benefit. METHODS: We evaluated the safety and immunogenicity of a lyophilized and a liquid form of Hib polysaccharide-tetanus toxoid conjugate vaccines (PRP-T) given in the same syringe as diphtheria-tetanus-pertussis (DTP) vaccine to children in Goroka, Eastern Highlands Province. In Part 1 of the study 209 children were randomized to receive at ages 1, 2 and 3 months either DTP alone or a liquid formulation of DTP/PRP-T or lyophilized PRP-T dissolved in DTP suspension. A further 75 children were given the liquid DTP/PRP-T formulation at ages 2, 3 and 4 months (Part 2). 54 children aged 15-18 months were given a booster of the same preparation of PRP-T/DTP as they had received during Part 1. Blood for antibody assays was collected at enrolment, before (Part 1 only) and one month after the third dose, then just before and 3 weeks after the booster dose. RESULTS: Follow-up to age of 12 months showed that PRP-T was safe with no evidence of impaired response to individual vaccine components when combined with DTP. Geometric mean titres (GMTs) of anti-PRP antibody before vaccination (n = 64, mean age 41 days), after 2 doses (mean age 99 days) and after 3 doses (mean age 132 days) of the lyophilized formulation were 0.21, 1.48 and 5.04 microg/ml, respectively, with 58% and 89% having anti-PRP antibody titres > or = 1.0 microg/ml after 2 and 3 doses, respectively. Anti-PRP antibody responses to the liquid Hib vaccine formulation were lower (GMT post-dose 3 = 0.48 microg/ml) than to the lyophilized formulation, but better responses were elicited from older children (Part 2; GMT post-dose 3 = 0.78 microg/ml, with 79% > or = 0.15 microg/ml). Both PRP-T preparations elicited excellent booster responses suggesting that children are likely to be protected if exposed to Hib infection. CONCLUSIONS: Lyophilized PRP-T given together with DTP is safe and immunogenic when given to young infants. The liquid DTP/PRP-T formulation showed a lower immunogenicity than in earlier studies with this vaccine, which might have been due to exposure to low temperature during shipment or the younger age at immunization.

Immunity in experimental salmonellosis. II. Basis for the avirulence and protective capacity of gal E mutants of Salmonella typhimurium.

Salmonella typhimurium strains which are deficient in uridine diphosphate (UDP)-galactose-4-epimerase (gal E mutants) owe their outstanding protective capacity when used as live vaccine to the fact that when galactose is supplied exogenously, such as occurs in vivo, smooth cell wall lipopolysaccharides are synthesized. The mutants lose most of their protective capacity when this phenotypic curing is prevented by a second mutation of the kind found in strains LT(2)M(1)A (deficient in galactokinase) or E(32) (deficient in UDP-galactose-lipopolysaccharide transferase). Despite such phenotypic reversion, the gal E mutants are rendered avirulent as a result of galactose-induced bacteriolysis. Secondary mutants have been isolated which differ from each other with respect to the extent of galactose-induced lysis. The differences in galactose sensitivity are attributable to different activities of the other Leoloir pathway enzymes, namely, galactokinase and galactose-1-phosphate-uridyl transferase. The influence of these enzymes on lipopolysaccharide composition and galactose sensitivity and thus on virulence and immunogenicity of gal E mutants has been studied.

Characteristics of the attenuated oral vaccine strain "S. typhi" Ty 21a.

The lack of a reliable in vitro test or animal model that can predict the potency of typhoid vaccines in man makes it extremely difficult to develop guidelines for the quality control of these vaccines. Attenuated S. typhi strain Ty 21a that has been shown to be safe and efficacious as live oral vaccine in clinical studies and in a controlled field trial, has been extensively characterized by genetical, biochemical and biological data. Production of live oral typhoid vaccine Ty 21a is based on a parent and working seed lot system. Characteristics of the seed lot cultures have to correspond with the original strain. Characteristics of strain Ty 21a relevant to its avirulence and potency are discussed.

Immunization with a Pseudomonas aeruginosa immunotype 5 O polysaccharide-toxin A conjugate vaccine: effect of a booster dose on antibody levels in humans.

Healthy adult volunteers were vaccinated on day 0 and 28 and at 15 months with a Pseudomonas aeruginosa immunotype 5 O polysaccharide-toxin A conjugate vaccine. Immunization resulted in mild, transient local reactions in less than 20% of the subjects. Maximal immunoglobulin G (IgG) antibody titers to both toxin A and lipopolysaccharide (LPS) as determined by enzyme-linked immunosorbent assay were seen at day 42, at which time 50% of the vaccinees showed a fourfold or greater rise in toxin A-neutralizing titers. By 15 months postvaccination, both antitoxin A and anti-LPS IgG antibodies had markedly declined. A booster dose of vaccine administered at 15 months evoked a vigorous anti-toxin A IgG antibody response with 100% of the volunteers showing a fourfold or greater rise in neutralizing antibody titer compared with preimmunization levels. In contrast, there was no significant elevation of anti-LPS IgG antibody levels. At 24 months postimmunization, only anti-toxin A antibody levels were significantly higher than preimmunization levels.

[Effectiveness of oral, attenuated live Salmonella typhi Ty 21a vaccine in controlled field trials]. / Zur Wirksamkeit des oralen, attenuierten Lebendimpfstoffes Salmonella typhi Ty 21a in kontrollierten Feldversuchen.

The first live oral typhoid vaccine (strain Salmonella typhi Ty 21a) distributed under the trade name of "Vivotif" has been evaluated for safety and efficacy in volunteer studies and in large-scale, placebo-controlled, double-blind field trials. While the data demonstrated that the vaccine was well tolerated, the level of efficacy varied distinctly. It is probable that the differences observed can be chiefly attributed to the various vaccine formulations evaluated to facilitate the passage of the acid-sensitive vaccine strain through the acid environment of the stomach. Based upon these results, the initially marketed formulation (2 bicarbonate capsules + vaccine capsule) was changed to an acid-resistant capsule which was subsequently evaluated in a field trial conducted in Chile and involving 44,000 school age children. Following 4 years of surveillance, a protection rate of 70% was obtained. To further optimize the means of delivering the vaccine, a formulation consisting of lyophilized vaccine reconstituted in a buffer solution is now being evaluated in a Chilean and Indonesian field trial. A similar though less practicable formulation showed excellent efficacy (approximately 95%) in a previous Egyptian field trial.

Safety and immunogenicity of Klebsiella pneumoniae K1 capsular polysaccharide vaccine in humans.

The safety and immunogenicity of two Klebsiella pneumoniae K1 capsular polysaccharide (CPS) vaccines were evaluated in humans. Trace quantities of lipopolysaccharide present in vaccine preparations were detoxified by treatment of K1 CPS in a 95% ethanol-0.1 N NaOH solution. This procedure greatly reduced the pyrogenicity of K1 CPS but did not markedly alter its antigenicity, molecular size, or immunogenicity for animals. Volunteers received either 25 or 50 micrograms of untreated or NaOH-treated K1 CPS vaccine subcutaneously. Systemic reactions on primary vaccination were infrequent with both vaccine preparations. However, the frequency and severity of local reactions were substantially reduced after immunization with NaOH-treated vaccine as compared with untreated K1 CPS. All vaccinees responded with a fourfold or greater rise in IgG and IgM titers. IgG antibody to K1 CPS isolated from immune sera was highly effective in preventing fatal experimental burn wound sepsis due to K. pneumoniae K1 in mice.

Purification and vaccine potential of Klebsiella capsular polysaccharides.

Capsular polysaccharide (CPS) from 18 Klebsiella strains of different capsular types was isolated and characterized. Purified CPSs were composed primarily of carbohydrate with trace quantities of protein, nucleic acids, and lipopolysaccharide. All CPSs were of a high molecular weight, possessing a Kd of 0.01 to 0.11 as determined by gel filtration over Sepharose CL-4B. Low levels of lipopolysaccharide present in all preparations were responsible for the highly pyrogenic nature of one-half of the CPS preparations. Treatment of capsular material with dilute NaOH in 95% ethanol markedly reduced the pyrogenicity of all preparations and had a negligible effect on their molecular weight. The immunogenicity of the various native CPSs for mice varied considerably from serotype to serotype, but all evoked an anticapsular immunoglobulin G response. Five of 18 NaOH-treated polysaccharides were significantly (P less than 0.05) less immunogenic than their native counterparts. Human immunoglobulin G prepared from volunteers immunized with either native or NaOH-treated KP1-0 capsular polysaccharide was equally effective at preventing experimental fatal Klebsiella pneumoniae burn wound sepsis in mice.

Octavalent Pseudomonas aeruginosa O-polysaccharide-toxin A conjugate vaccine.

An octavalent Pseudomonas aeruginosa conjugate vaccine was synthesized by covalently coupling the O-polysaccharide (O-PS) moiety derived from lipopolysaccharides of Habs serotypes 1, 2, 3, 4, 5, 6, 11 and 12 to toxin A. Adipic acid dihydrazide was used as a spacer molecule to facilitate conjugation. The vaccine was composed of 37% (w/w) O-PS and 63% toxin A, devoid of enzymatic activity characteristic of toxin A, non-toxic for mice and guinea pigs, and non-pyrogenic. The vaccine elicited a significant rise in immunoglobulin G antibody levels to all serotypes of lipopolysaccharide contained in the vaccine and to toxin A. Serotypes 6, 10 and 11 were most immunogenic in mice whereas serotypes 1 and 5 engendered the lowest antibody response. Antitoxin A antibody was able to neutralize the cytotoxicity of toxin A. Immunization of mice with the vaccine conferred significant protection against subsequent challenge with all P. aeruginosa serotype strains contained in the vaccine.

Immunization against fatal experimental Klebsiella pneumoniae pneumonia.

The ability of serospecific anti-capsular polysaccharide (CPS) antibody to prevent fatal Klebsiella pneumoniae pneumonia was evaluated in a rat lung model. Rats were immunized intramuscularly with 100 micrograms of purified serotype 2 CPS and challenged intrabronchially 14 days later with a serotype 2 strain of K. pneumoniae. Vaccination engendered high levels of serum anti-CPS antibody which afforded significant protection (P less than 0.01) against fatal pneumonia. Immunization promoted clearance of the challenge bacteria from the lungs and prevented bacteremia. Histological examination of lung tissue from infected control animals showed pronounced inflammatory cellular infiltrate in the alveolar spaces, intra- and peribronchial inflammation, and tissue necrosis. In contrast, pathological changes noted in lungs from immunized animals were restricted to infrequent intra- and peribronchial involvement.

Synthesis and characterization of a Pseudomonas aeruginosa alginate-toxin A conjugate vaccine.

Alginate from Pseudomonas aeruginosa 3064 was depolymerized by controlled heating in dilute acid. The resulting depolymerized alginate (Mr less than 60,000) was covalently coupled to toxin A with adipic acid dihydrazide as a spacer molecule and carbodiimide as a linker. The resulting conjugate was composed of toxin A and depolymerized alginate at a ratio of 4:1 and possessed an Mr of 260,000. The conjugate was nontoxic and nonpyrogenic. While native alginate (Mr greater than 640,000) given in a range of doses was poorly immunogenic in mice and rabbits, the conjugate induced high levels of antibody which bound to native alginate. Rabbits, but not mice, also produced an antitoxin immunoglobulin antibody response. Alginate derived from three other strains of P. aeruginosa competed with the homologous 3064 alginate for binding to anticonjugate antibody. This indicates that the conjugate elicits an antibody response able to recognize heterologous alginates. The serum from rabbits immunized with the conjugate was effective at promoting the uptake and killing of mucoid strains of P. aeruginosa by human polymorphonuclear leukocytes. In contrast, immunization with native alginate did not engender an opsonic antibody response. Rabbit anticonjugate antibody also neutralized the cytotoxic potential of toxin A.

Preparation of a purified antigenic cholera toxoid.

Purified cholera enterotoxin was prepared by methods described by Finkelstein and Lo Spalluto (1970). This toxin was detoxified by treatment with heat and formaldehyde. Heating cholera toxin at 60 C for 25 min resulted in the formation of a polymer named procholeragenoid by Finkelstein et al. (1971). The weak toxic activity of this product was removed by treatment with formalin. No residual toxicity could be demonstrated in formalinized procholeragenoid by the rabbit ileal loop assay and the highly sensitive rabbit skin tests. This toxoid was nevertheless at least as antigenic in the rabbit as was the toxin. No reversion to toxicity was observed in vivo and in vitro at 4 C. The toxicity of formalinized procholeragenoid never exceeded 1/5,000 to 1/10,000 that of the toxin.