Polyosides (encapsulated bacteria)

0 1999 Acadkmie

des sciences/Editions

Polyosides

scientifisues

et medicales

(encapsulated

Elsevier

SAS. Tous droits r&e&s

bacteria)

Polyosides (bacthies encapsul6es) Alf A. Lind berg” aPasteur

M&ieux

Connaugh,

1541,

avenue

Marcel-Mhrieux,

69280

Marcy-l’l!toile,

France

Abstract

-The polysaccharide capsule which surrounds bacterial species such as Haemophilus influenzae, Streptococcus pneumoniae, Neisseria meningitidis and Salmonella typhi is a potent virulence factor by protecting the bacteria from phagocytosis. The host responds with antibody production and specific antibodies plus complement binding to the capsule facilitate opsonization of the micro-organism, which is phagocytized and eliminated. Purified capsular polysaccharides elicit T-independent antibody responses without a memory function, but are often poorly immunogenic in infants where much of the invasive H. influenzae type b (Hib) and pneumococcal infections is seen. Therefore purified polysaccharides have found limited use as vaccines. However, covalent linkage of the capsular polysaccharide, or fractions thereof, to immunogenic carrier proteins creates glycoconjugates which are T-dependent antigens and which elicit antibodies also in infants and which prime for boosting either with the glycoconjugate or the capsular polysaccharide. In the last decade Hib glycoconjugate vaccines have been successfully introduced and in countries with very high immunization coverage the disease has been virtually eliminated and a decline of over 95% has been seen in countries with slightly lower vaccine rates. World-wide use of Hib glycoconjugate vaccines offers the possibility of elimination of invasive Hib disease. Pneumococcal (11 serotypes with coverage of approximately 85 % of invasive disease), meningococcal (A, C, W 135, Y but not B) and S. typhi glycoconjugates are in advanced development and offer the prospect of being as successful as the Hib glycoconjugates. 0 1999 Academic des sciences/iditions scientifiques et mgdicales Elsevier SAS encapsulated

f bacteria

J polysaccharide

J glycoconjugate

1. Introduction

target of several it was evident

During the 1990s the introduction of Haemophilus influenzaetype b (Hib) glycoconjugates for vaccination of infants has had a profound effect on the burden of Hib disease, resulting in a virtual elimination in countries with a very high immunization coverage. Thus, it constitutes a highly successful introduction of a new vaccine with a rapid impact and substantial savings in health care costs. The interesting fact is that an efficacious vaccine could have been introduced decades earlier. H. influenzae, Streptococcus pneumoniae and Neisseria meningitidis are examples of bacterial species which can be surrounded by a polysaccharide capsule which protects the bacterium against phagocytosis and therefore is a potent

virulence

factor.

The

medical

impact

of infec-

tions caused by encapsulated bacteria (and in particular pneumococci) was evident in the beginning of the century. The properties of bacterial capsular polysaccharides and their ability to elicit immune responses soon became the C. R. Acad.

Sci. Paris, Sciences

1999,322,925-932

I memory I antibodies

de la vie

/ Life Sciences

- capsular fied’

investigators

and

that: polysaccharides,

preparations,

already

either killed

elicited

antibodies

either

did

after

protective

of bacteria

-

of the

glycoconjugates

valently

linked

antibody

same

types

using

to a carrier

responses which

protected against challenge glycoconjugates had other

haptenic could

infection immunogenic

for making but

been

initiated

molecules

the carrier vaccine [41;

saccharides in rabbits [IO,

had

only

vacci-

coinduce

were high titred, boostable

the polysaccharides. Thus, the basic research not

with

or after

as in the

protein

im-

not respond

disease

nation [5-81; - type-specific antibodies were the effector which conferred protection 17, 91; - vaccination with polysaccharides reduced rate

1940s

cells or ‘puri-

type-specific

mune responses in man [l-4]; - infants and young children type-specific

in the mid

the

and

111, i.e. the properties than

glycoconjugates

foundation

had

been

925

A.A.

Lindberg

Figure 1. Haemophilus influenzae structure of polyribosylribitolphosphate.

laid.

However,

the

successful

introduction

of antimicro-

coinciding

with

the

waning

type

of maternal

b repeating

antibodies

unit:

and

bial agents put an effective stop to the further development of both capsular polysaccharide and glycoconjugate vaccines for a few decades. A few things rekindled the interest in vaccination using capsular polysaccharides in the

prior to appearance of anti-capsular antibodies. A pivotal large-scale double-blind study in Finland in 1974 comprising almost a 100 000 children 3 months to 5 years of age showed that after vaccination with a purified Hib

1970s. First, it became increasingly crobials, although largely successful, mate solution to handling infections.

capsular protected months

evident that antimiwere not the ultiTreatment failures

and the emergence of antimicrobial-resistant strains forced a rethinking and the role of prophylactic immunization became one alternative. Advances in immunology with delineation of B- and T-cell responses, and the role of T cells for the immunological memory functions, as well as the structural elucidation of the capsular polysaccharide, opened the way for the rational development of defined

glycoconjugates.

influencae

type b (Hib)

Haemophilus influenzae is a gram-negative coccobacillus which frequently colonizes the oropharynx of man. Most H. influenzae strains are non-encapsulated (nontypable H. influenzae - NTHI), but a few are surrounded by a polysaccharide capsule. Six capsular types, a-f, have been recognized with type b being the most common and virulent. Invasiveness and dissemination is a characteristic trait of Hib infection in the clinical manifestations such as meningitis, epiglottitis, etc. Most Hib infections in the prevaccine era occurred in children. The rates of Hib disease varied, but invasive disease in Europe ranged from 30 to 60 cases per 100 000 children less than 5 years old [I 21. In the US the corresponding figures ranged from 50 to 100 per 100 000 children. Some population groups have been reported to have much higher rates of disease; thus, native Americans and Australian Aborigines have had rates up to 300 per 100 000. Invasive Hib infections are uncommon in adults unless there is predisposing underlying disease: an annual incidence of 0.22 per 100 000 has been

reported

[I 31.

The peak incidence of Hib disease was in children between the ages

926

was seen in the age group 3-12 months [12, 141. This study was certainly a trigger point for the successful development of Hib glycoconjugate vaccines, and consequently brought an end to the use of the capsular polysaccharide as a vaccine. 2.1. Conjugation The contain

2. Haemophilus

in the prevaccine era of 5 and 12 months,

polysaccharide a) children > 18 months were with an efficacy > 90 %, b) children 12-I 8 had questionable protection, and c) no protection

strategies

capsular polysaccharide chemically reactive

carboxyl a protein the ribitol

of groups

moieties that can directly carrier (figure 7). However, and the phosphodiester

Hib (PRP) such as

does amino

not or

be covalently linked to the presence of both in the repeating unit

makes the polysaccharide susceptible to derivatization. The periodate oxidation creates CHO groups which by reductive amination are coupled to a carrier protein. This procedure was used by Anderson and co-workers at Praxis to create HbOC (Hib-Tite@) [I 51. Robbins et al. [I 6, 171 used adipic acid dihydrazide (ADH), a bifunctional nucleophilic spacer, to facilitate binding polysaccharide to the carrier. Cyanogen used to introduce an active group into the the repeating unit. The creation of a Hib

of the capsular bromide is then ribitol moiety of adipic hydrazide

derivative subsequently allows it to be conjugated to tetanus toxoid by carbodiimide-mediated condensation. The resulting conjugate (PRP-T, Act-Hib@) has multipoint attachments between the polysaccharide and the carrier protein and is referred to as a lattice structure. A different conjugate - PRP-OMP - was developed by scientists at Merck, Sharpe and Dohme ]I 81. They conjugated the PRP moiety to an outer membrane protein complex from a Neisseria meningitidis groups B strain (PedVax Hiba). Thus, there are three, currently used, different PRP conjugates on the market with differences in a) carrier protein C. R. Acad.

Sci. Paris,

Sciences

de

la vie / Life Sciences 1999,322,925-932

Polyosides used, b) linkage type with or without polysaccharide size, and linkage at end(s)

spacer, and c) or in the chains.

The three vaccine types, not unexpectedly, immunogenicity. HbOC and PRP-T behave manner each requiring two or three doses

differ in their in the same to generate

2.2.

Correlates

PRP-OMP

can

of protection

be used

after

The protective role of antibodies polysaccharide was known already the inverse correlation of disease

in two-dose

regularly that Hib

have antibodies disease is rare

vaccination

to PRP. Based on the in adults as a conse-

be to establish a marker are characterized by antibody, i.e. antibodies

and in

as a surrogate of it was shown that following primary following boost-

glycoconjugate

The

introduction

vaccine of Hib

conjugate

has had

a

profound effect on the overall burden of Hib disease. There has been > 97 % reduction in Finland, the UK and USA where different Hib conjugates have been used: in Finland, PRP-D followed by HbOC [22], in the UK, PRPT [23]

and

in the

US,

HbOC

(> 90 % up to 1994)

1241.

In Finland and in the US a primary series with three doses at 2,4 and 6 months of age were used with a booster dose in the second year of life. In the UK the primary series C. R. Acad. Sci. Paris, Sciences 1999,322,925-932

de la vie / Life Sciences

from Genetic

1 week basis

for

after vaccine

just

one

and a

dose

of vaccine

[23].

failure

Gm and Km genes code for the antigenic determinants of the heavy and light chains of immunoglobulins, respectively. Cm groups are localized to the constant region of the y heavy chain each are exclusive

and thus are limited to one of the four

Gm allotypes are located Cm factors are inherited present on x light chains classes of immunoglobulins. on chromosome 2.

to IgG classes IgG subclasses.

and The

on chromosome 14. Many of the together. The Km factors are and therefore represented in all The Km allotypes are found

is significant variation of Cm and different races in human populations

important allelic associations with in the genetic predisposition to eases [30, 311. The biological role of Cm and Km is not understood,

efficacy vaccines

vacanother

There among

jugate in the same formulation highlight a need for a better understanding of the relationship between primary antibody responses and long-term protection. Hib

The use of a carrier protein in the glycoconjugate cine may improve the immune response in yet

2.4.

ing [21]. Most of the increase in avidity was seen in the months after primary immunization. The concern with ‘too low’ anti-PRP titres after vaccination with combination vaccines containing acellular pertussis and Hib con-

2.3.

have

protection

of priming. Memory rethe production of highstrongly binding to the

antigen. Thus, avidity can be considered successful priming. In a recent study, antibody avidity was relatively low immunization and significantly higher

immunized children most likely reduces transmission hence children who lack protective antibodies reduced probability of being infected.

way. If the infant is primed by a prior tetanus toxoid vaccination the antibody response to PRP-T was found to be improved [27, 281. In the British study young infants (3-11 months of age) were found to have a high level of

quence of ‘protective antibodies’ and that 95 % of adult sera analysed had 0.04 u/mL of anti PRP antibodies, a limit of > 0.15 p/mL was arbitrarily set as a level for short-term protection [14, 191. In studies of the post-immunization antibody concentrations seen in vaccines of the Finnish PRP study a concentration of > 1 .O p/mL predicted protec-

should sponses avidity

of for

ably > 90 %) with a resulting herd immunity. An added and unexpected benefit of the routine use of Hib conjugate vaccines is a substantial reduction in oropharyngeal carriage of Hib [25, 261. The reduced colonization in

to the Hib capsular in the 1930s as was occurrence and the

tion over the following year [20]. Thus, the concentrations > 0.15 and > 10 p/mL are used as correlates for shortlong-term protection, respectively. A better approach the evaluation of glycoconjugate vaccine immunogenicity

also contained three doses given at 2, 3 and 4 months age but with no booster [23]. The reported efficacy infants 5-l 1 months of age was 99.1 %, for 12-23-month-

high at about 95 %. The authors challenged the concept that a booster may be required in the second year of life to ensure that protection persists until school age (more than 95 % of invasive Hib disease occurs before the age of 5). A basis for this proposal is a high vaccine coverage (prob-

pri-

presence of bactericidal antibodies in serum of individuals of different ages. The pivotal Finnish study with purified PRP as vaccine demonstrated the same relationship for type b-specific anticapsular antibodies [12]. Adults argument

bacteria)

old infants 97.3 % and for 24-35-month-old children it was 94.4 %. Although this shows a gradual fall in the efficacy as children approach the age of 3 years, the 95 % confidence limits for efficacy in each age group were found to overlap [23]. The estimated protection remained

substantial antibody titres. PRP-OMP elicits strong antibody responses even after a single dose, and subsequent doses add little to the immune response. Thus, PRP-T and HbOC are used in three-dose primary immunization series, whereas mary series.

(encapsulated

Km

allotypes [29], and

Cm and Km allotypes some infectious disof the polymorphisms but evidence suggests

that the polymorphism is protective at the population level: lack of it is associated with higher levels of infectious disease [32] and is specifically associated with lower immune responses to certain infections [33]. The responsiveness of healthy white to Hib PRP is significantly associated negative allotype [34, 351. When the was used the association between allotype and the PRP disappeared

adults and children with the Km (l)Hib glycoconjugate

the [36].

Km

(I)-negative

It appears that the responsiveness, or lack thereof, is specific to the particular type of polysaccharide. A woman unresponsive to PRP, responded readily to pneumococcal

927

A.A. Lindberg and

meningococcal

capsular

polysaccharides

as well

as

H. influenzae outer membrane proteins [37]. Immunization with PRP-T elicited only a minimal response, and not until multiple doses were given at 0,2,4,8 and 15 months did she reach a concentration of 3.1 &mL. Thus, a selective deficiency of antibody repeated injections with vidual vaccination scheme immunizations. Response (23)-positive persistent

to PRP allotype association

to PRP could be overcome by PRP-T, i.e. a need for an indibeyond what is used in routine

has also been 1381. However, across racial

linked to the G2m there is a lack of a or ethnic groups re-

garding Cm and Km. Hence other factors must interact with the roles of the products of the Cm and Km allotypes. Although the use of glycoconjugate vaccines may overcome some of the allotype associations with the T-cellindependent responses to polysaccharide vaccines, it may not be the panacea we hoped for. However, herd immunity and a substantial reduction in transmission of bacteria may be more than adequate as seen with the introduction of the

Hib

vaccine.

respiratory dren [4244].

infections

compared

with

healthy

chil-

Clinical illness is a result of the spread of the pneumococci to tissues from the oropharynx. Although carriage may result in infection it appears as if the period just after acquisition is a period of high risk [42]. Epidemiological studies in the 1980s have pneumococcal bacteriaemia cases per 100 000 persons

found an annual incidence of to vary between 9 and 18 of all ages ]411. In children

there were 105 and 234 cases per 100 000 individuals, white and black, respectively. There appear to be racial differences with black and native Americans having rates approximately 2.5 times those of whites and Hispanics. Even higher rates have been found among the native population of Alaska. It has been estimated that in the US there is on an annual basis 3 50 000 of bacteriaemia, 500 7 000 000 cases of acute otitis mately 40 000 deaths caused by

000 cases of meningitis, 000 of pneumonia and media [41, 451. Approxipneumococci occur each

year in the US and it has been estimated mately half are potentially preventable with

that approxipneumococ-

cat vaccines.

3. Streptococcus Streptococcus

pneumoniae

pneumoniae

an

continues

to

be

a major

cause of morbidity and mortality in adults and children despite the availability of effective antimicrobial therapy. As for Hib the virulence is caused by a capsular polysaccharide, and there are now 90 different capsular types described 1391. Invasiveness is dependent on the capsular structure rather than the amount being produced. The polysaccharide tosis.

is not

toxic

in itself,

but

inhibits

phagocy-

In developing even more

estimated that by pneumococci annually, most

countries significant

pneumococcal infections cause disease burden. It has been

acute lower respiratory infections caused account for more than 4 million deaths of them in children < 5 years of age [46].

Commercially available pneumococcal vaccines are composed of the 23 most coccal serotypes and represent 85-90

polysaccharide common pneumo% of the serotypes

that cause invasive infections in adults in industrialized countries. As for Hib young children do respond poorly most serotypes up to the age of 2 years, and against

to the

The immunological defense against pneumococcal infection depends on type-specific anticapsular polysaccharide antibody interacting with complement to opsonize the bacteria and have them prepared for phagocytosis and

least immunogenic serotypes (6B, 14, 19F, 23F) up to the age of 5-l 0 years [47,48]. Consequently the polysaccharide vaccine has found a market in the elderly population alone.

clearance. defense, ficiency, individuals, increased

The seven most commonly isolated (pneumococcal) serotypes covered up to 85 % of all pneumococci-causing invasive infections in Finnish, Israeli and USchildren [49]. A nonovalent glycoconjugate vaccine for global use including serotypes 1, 5, 6B, 7F, 9V, 14, 18C, 19F and 23F

Defects in any of these components of the host i.e. antibody production, complement factor desplenic dysfunction, including splenectomized or neutropenia are usually associated with an risk of serious pneumococcal infection. Of the

components type-specific anticapsular antibodies are by far the most important. The importance of antibodies to recovery from pneumococcal infection was demonstrated as early as the 1930s. The immunogenicity and immunochemistry of pneumococcal capsular polysaccharides was

recently

reviewed

Pneumococci

cause

[40, a wide

411. variety

of infections

ranging

from relatively mild mucosal infections such as acute otitis media, to more serious invasive diseases such as bronchopneumonia with septicaemia and potentially lifethreatening meningitis. Pneumococci frequently colonize the respiratory mucosa of both healthy and sick individuals with carrier rates being higher in children than in adults, even higher in children attending day care centres than

928

those

staying

at homes,

and

still

higher

in those

with

would cover approximately 80 % of strains causing tions in industrialized countries and approximately of strains in developing countries [50].

infec70 %

The structure of each polysaccharide serotype differs from that of others serotypes and from that of PRP. Hence different coupling strategies have to be devised for each polysaccharide, either in its native or sized form (often incorrectly called oligosaccharide). The manufacturers are using the same overall strategies as for the Hib conjugates, i.e. reductive amination, ADH spacer and linkage to a N. meningitidis OMP complex. The carriers used are the same as for Hib conjugates, i.e. tetanus and diphtheria toxoids [17], the genetically toxoided diphtheria toxin CRM 197 [51], and the N. meningitidis OMP complex [18]. C. R. Acad.

Sci. Paris, Sciences

de

la vie

/ Life Sciences 1999,322,925-932

Polyosides The future probably

development of several different conjugates in a pneumococcal vaccine, seven in the first and 11 in the second generation, raises the question

of carrier protein overload. Too much carrier may impair the antibody response to the polysaccharides by antigen competition or carrier-mediated epitope suppression [52, 531. Conjugates

have

been

through

phase

1, 2 and

3 trials

and several conclusions can already be drawn. a) In adults the conjugates have been well tolerated although local reactions at the injection site appear to be more common than after vaccination with capsular polysaccharides [54]. b) In toddlers all conjugates tested have been immunogenic. c) In infants all conjugates tested have been well tolerated and no immediate, serious vaccine-related adverse events have been reported; the reaction rates have been lower and their intensity less marked in young infants than in adults. IgG antibody polysaccharide

d) The infants are primed for anamnestic responses to subsequent boosting with vaccine [55,56]. The highest dose (10 pLg/

mL) of each polysaccharide induced the strongest response after primary immunization (2,4,6 months of age), but the booster response was greatest in the group primed with the lowest dose (1 pg/rnL of each polysaccharide). e) A significant reduction in the carriage of vaccine-related strains was observed after primary immunization. This suggests that transmission of specific pneumococcal types can be reduced after immunization [57, Wyeth-Lederle’s heptavalent Pnc-CRM vaccine

sero581. f) was

100 % efficacious against invasive disease in a study in northern California: 17 cases in the control group and 0 in the vaccine group (2, 4, 6 month primary series) (pers. comm.). g) No antibody correlates for protection are yet available. The

results

so far are very

encouraging

and

suggest

that

the first 7-valent pneumococcal vaccine will be marketed around year 2000. The first indication will be for invasive infections (pneumonia with bacteriaemia and meningitis). Efficacy against mucosal infections, i.e. acute otitis media, has not yet been demonstrated but a pivotal phase 3 trial is ongoing 3.1.

in Finland. Genetic

regulation

of immune

responses

Healthy adults have a varying ability to respond to pneumococcal polysaccharides with antibody production. A study of 61 ashkenazic family members showed that the capacity to generate anti-pneumococcal polysaccharide IgG was inherited in a mixed, codominant fashion [59]. However, no association between G2m (23) allotype and antibody to the polysaccharide was found. Revaccination either with the 23-valent polysaccharide vaccine (single, double dose of 20 times higher dose of a single polysaccharide) or with either Pnc-OMPC or PncCRM failed to elicit antibody production to the relevant polysaccharide in a subject who had initially shown no measurable IgG after vaccination. These individuals also failed to elicit IgG antibody production, and hence the C. R. Acad. 1999,322,925-932

Sci. Paris, Sciences

de la vie / Life Sciences

failure from The

to respond IgM

not

caused

by

bacteria)

a failure

to switch

to IgG.

data

mediated recognition occasional charide

was

(encapsulated

suggest

that

a not

yet

understood

defect in pneumococcal is responsible. It is tempting vaccine failures with the vaccine may be caused at

genetically determined capsular polysaccharides. cance of these defects

4. Neisseria Meningitis feared disease.

incapacity to make IgG The extent and potential remains to be elucidated.

to the signifi-

meningitidis

caused by Neisseria Although the total

meningitidis is still a number of cases is small

it is a disease which because of its mortality attention. Here, as for Hib and pneumococci charide capsule is an important virulence prospects for prophylactic immunization N. meningitidis

genetically

polysaccharide to speculate that 23-valent polysacleast in part by a

is an exclusive

There are 12 serogroups capsular polysaccharide: Y and Z. Approximately

human

attracts much a polysacfactor, and are good.

pathogen.

based on the structure A, B, C, 29E, H, I, K, L. WI 90 % of cases of meningitis

of the 35, X, are

caused by strains belonging to serotypes A, B and C. All three serotypes can cause epidemics, but it is usually group A strains that are the causative agent in repeating epiderrlics in sub-Saharan Africa [59]. Presently, serogroup B is most prevalent in Europe and Latin America causing more than 50 % of the cases, whereas serogroup C is most

prevalent

Meningococcal one-third occurs to 9 years old,

in North

America

[60,

611.

meningitis is spread over all age groups: from 0 to 4 years of age, one-third from 5 and the final one-third at age 20 and

above 1621. Therefore, there is a need to vaccinate the whole population. As early as 1913 Flexner published convincing data that serum therapy decreased the fatality rate of meningococcal meningitis [63], and 20 years later Fothergill and Wright observed that there was an inverse relationship between the incidence of meningitis at different ages and the causative agent [I vaccines available in the adolescent

presence of serum antibodies to the 71. There are capsular polysaccharide which show a good protective efficacy and adult populations but the lack of

immune responses in the very young elicit memory makes the development vaccines imperative. 4.1.

Meningococcal

and the inability of glycoconjugate

to

glycoconjugates

Purified capsular polysaccharides WI 35 and Y are marketed products, antigens elicit antibody responses

from serogroups A, C, and asT-independent with no memory func-

tion, with the possible exception of serogroup A [14]. The polysaccharide vaccine from serogroup A elicits an antibody response in infants which even below the age of 6 months appears to be primed [14]. The serogroup C polysaccharide is not immunogenic in children < 2 years

929

A.A. Lindberg of age,

and

development

of antibody

titres

is slow

[61].

Correlates of protection have not been firmly established. However, data suggest that for protection against serogroups A and C serum concentrations of anti-capsular antibodies should be > 2.0 pg/mL [14, 611. A and C glycoconjugate vaccines under development are safe and well tolerated in infants and toddlers and using a 2-, 4-, 6-month schedule for primary immunization all infants had elicited specific anti-A and anti-C polysaccharide antibody titres > 2.0 ug/mL [64-661. A functional assay is to estimate bactericidal titre of 1 :8 was seen in all those vaccinated, having equally high titres 1 year later [65].

gate [671. So far, all data indicate that meningococcal glycoconjugate vaccines will have as great a chance of being successful as the Hib and pneumococcal conjugates and licensure is expected within the coming years. Most likely, meningococcal A + C and meningococcal A + C + WI 35 + Y glycoconjugates will be marketed. B polysaccharide, a sialic acid residues, is Since the same struc-

ture is found in embryonic neural cell adhesion molecules, man is probably tolerant to the polysaccharide structure. It has been suggested that vaccine-induced antibodies may interfere with the causing injury [69], a theory which lenged [70]. The uncertainties have

adhesion has also definitely

molecules been chalslowed the

vaccine, proteins However,

and instead and protein antibodies

elicited against the serogroup B polysaccharide, although low in titre, are bactericidal [71]. Jennings has modified the group B polysaccharide by replacing the N-acetyl groups with N-propionyl groups before its conjugation to tetanus toxoid [72]. a unique protective group B meningococci

antibodies. A with 47 %

In a study in Gambia an interesting and as yet unexplained observation was made: whereas the serogroup C conjugate, as expected, induced memory, no such observation was seen with the serogroup A conju-

The meningococcal serogroup homopolymer of alpha-2,8-linked poorly immunogenic in man [68].

development of a glycoconjugate focused interest on outer membrane complexes such as immunogens.

5. Other

glycoconjugates

The spectacular probable success cal glycoconjugates converting T-independent Group meningitis

The resulting polysaccharide mimics epitope on the surface of the native and elicits antibodies [73].

other

success of the Hib conjugates and of the pneumococcal and meningocochave obviously focused an interest capsular to T-dependent

B streptococci and sepsis

polysaccharide vaccines.

antigens

the on from

(CBS) are the leading cause in neonates in the US. At least

of six

capsular types have been associated with human disease, and type-specific antibodies are responsible for protection via opsonization of the bacteria by antibodies and complement. Kasper and Jennings have developed immunogenic glycoconjugates which *in animal models elicit protective antibodies rently in phase 1 and and

Similar attempts safe vaccines

Salmonella

The

typhi ]76]

and

capsular

Escherichia sonnei.

of and

conjugates

are under way to make against the Vi polysaccharide

lipopolysaccharide

gel/a flexneri

[74, 751. 2 studies.

5.

are

cur-

immunogenic capsule

polysaccharide co/i [77, 781

of and

and

Shi-

References

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111 Finland M.D., Dowling H.F., A study of the cutaneous reactions and antibody responses to intramuscular injection of pneumococcus polysaccharides, J. Immunol. 29 (1935) 285-299.

1121 Peltola H., Kayhty H., Sivonen A., ffaemophilus infiuenzae type b capsular polysaccharide vaccine in children: a double-blind field trial of 100, 000 vaccines 3 months to 5 years of age in Finland, Paediatrics 60 (1977) 730-737.

[2] Ruegsegger J.M., Finland M., The influence injection on the antibody response of human carbohydrate of the type VIII pneumococcus, 833-836. I31 Lister

S., Ordman

D., South

African

of dosage and route of subjects to the specific J. Clin. Invest. 14 (1935)

Inst. Med.

Res. 7 (1935).

[41 Macleod C.M., Hodge S.R.C., Heidelberger M., Bernhard W.C., Prevention of pneumococcal pneumonia by immunization with specific capsular polysaccharides, J. Exp. Med. 82 (1945) 445-465. [5] Sutliff W.D., Finland M., Antipneumococcal reactions of human subjects of different ages, J. Exp. Med. 55 (1932)‘837-852. [6]

Davis

J.A.V.,

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33 (1939)

171 Fothergill L.D., Wright J.J., Relation cidal power of blood against the causal 273-284. [SJ Ward H.K., Lyons C., J. Exp. Med.

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191 Pittman M., The action of type-specific antiserum, J. Exp. Med. 58 (1933) 683-706.

515. Haemophilus

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930

studies specificity

iniluenzae on conjuof syn-

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