An integrated molecular and immunological approach towards a meningococcal group B vaccine

Thermodynamics and density of binding of a panel of antibodies to high-molecular-weight capsular polysaccharides

The interaction between antipolysaccharide (anti-PS) antibodies and their antigens was investigated by the use of isothermal titration calorimetry to determine the thermodynamic binding constant (K), the change in the enthalpy of binding (DeltaH), and the binding density (N) to high-molecular-weight PSs. From these values, the change in the entropy of binding (DeltaS) was calculated. The thermodynamic parameters of binding to high-molecular-weight capsular PSs are reported for two monoclonal antibodies (MAbs) with different specificities for meningococcal serogroup C PS, five MAbs specific for different pneumococcal serotypes, and the Fab fragments of two antipneumococcal MAbs. The K values were in the range of 10(6) to 10(7) M(-1), and these values were 1 to 2 orders of magnitude greater than the previously reported K values derived from antibody-oligosaccharide interactions. The DeltaH associated with binding was favorable for each MAb and Fab fragment. The DeltaS associated with binding was also generally favorable for both the MAbs and the Fab fragments, with the exception of the anti-serotype 14 MAb and its Fab fragment. N provides information regarding how densely MAbs or Fabs can bind along PS chains and, as expressed in terms of monosaccharides, was very similar for the seven MAbs, with an average of 12 monosaccharides per bound MAb. The value of N for each Fab was smaller, with five or seven monosaccharides per bound Fab. These results suggest that steric interactions between antibody molecules are a major influence on the values of N of high-affinity MAbs to capsular PSs.

A conjugate vaccine composed of a heat shock protein 60 T-cell epitope peptide (p458) and Neisseria meningitidis type B capsular polysaccharide

Neisseria meningitidis type B is a major world-health problem. The Meningococcus type B capsular polysaccharide (MnB) is very poorly immunogenic and no vaccine to the antigen exists. Here, we conjugated the MnB to a T-cell carrier peptide (p458) derived from the self-60kDa heat shock protein molecule. The conjugate vaccine was effective in inducing long-lasting IgG antibodies to the MnB antigen in mice. The vaccine was also immunogenic when injected in PBS. Thus, the p458 carrier peptide can induce T-cell help for the switch to IgG Ab to the MnB antigen.

Immunogenicity and Protective Efficacy of Bacillus anthracis Poly-γ-d-glutamic Acid Capsule Covalently Coupled to a Protein Carrier Using a Novel Triazine-based Conjugation Strategy

The capsular polypeptide of Bacillus anthracis is composed of a unique polyglutamic acid polymer in which D-glutamate monomers are joined by gamma-peptidyl bonds. The capsule is poorly immunogenic, and efforts at exploiting the polymer for vaccine development have focused on increasing its inherent immunogenicity through chemical coupling to immune-stimulating protein carriers. The usual strategy has employed carbodiimide-based condensing reagents for activation of free alpha-carboxyl groups, despite reports that this chemistry may lead to chain scission. We have purified the high molecular mass capsule to >95% homogeneity and have demonstrated that the polymer contains >99% poly-gamma-D-glutamic acid. The predominant structure of the polymer as assessed by circular dichroism and multiangle laser light scattering was unordered at near-neutral pH. We investigated the effects of various activation chemistries, and we demonstrated that carbodiimide treatment under aqueous conditions results in significant cleavage of the gamma-peptidyl bond, whereas scission is significantly reduced in nonaqueous polar solvents, although undesired side chain modification was still observed. An activation chemistry was developed using the triazine-based reagent 4-(4,6-dimethoxy (1,3,5)triazin-2-yl)-4-methylmorpholinium chloride, which allowed for controlled and reproducible derivatization of alpha-carbonyls. In a two-pot reaction scheme, activated capsule was derivatized with a sulfhydryl-reactive heterobifunctional moiety and was subsequently coupled to thiolated carrier protein. This conjugate elicited very high capsule-specific immune titers in mice. More importantly, mice immunized with conjugated capsule exhibited good protection against lethal challenge from a virulent B. anthracis strain in two models of infection. We also showed, for the first time, that treatment of capsule with carbodiimide significantly reduced recognition by capsule-specific antisera concurrent with the reagent-induced reduction of polymer mass. The data suggested that for vaccine development, maintenance of the high mass of the polymer may be important.

Clinical evaluation of a group B meningococcal N-propionylated polysaccharide conjugate vaccine in adult, male volunteers

The safety and immunogenicity of a group B meningococcal vaccine, consisting of N-propionylated (NPr) B capsular polysaccharide conjugated to tetanus toxoid, was tested for the first time, in 17 healthy male volunteers aged between 18 and 40 years. Four escalating dosages of vaccine were tested and each was given as three intramuscular injections at 4-week intervals. The vaccine was well tolerated and induced only mild and transient, dose-dependent, injection-site reactions. One month after the last injection, there was no evidence of the production of autoantibodies or antibodies binding to PSA-NCAM. The vaccine induced an increase in the pre-existing titres of IgM specific to B polysaccharide and NPr B polysaccharide. Moreover, it induced IgG antibodies specific to NPr B polysaccharide, which were undetectable before vaccination. However, no functional activity of vaccine-induced antibodies was demonstrated in bactericidal assays, opsonophagocytic tests or passive protection tests.

Serosubtypes and PorA types of Neisseria meningitidis serogroup B isolated in Brazil during 1997--1998: overview and implications for vaccine development

Meningococcal disease caused by N. meningitidis serogroup B (MenB) has been endemic in Brazil since 1997. In this study, we determined the prevalence of serosubtypes of MenB isolated in 10 Brazilian states and the Federal District during 1997 and 1998 and investigated the extent of PorA VR sequence variation among the most prevalent serosubtypes to evaluate the possible use of an outer membrane vesicle (OMV)-, PorA-based vaccine to prevent meningococcal disease in Brazil. During this period, a total of 8,932 cases of meningococcal disease were reported. Only 42% (n = 3,751) of the reported cases were laboratory confirmed, and about 60% (n = 2,255) of those were identified as MenB. Among 1,297 MenB strains selected for this study, the most prevalent serosubtypes were P1.19,15 (66%), P1.7,1 (11%), and P1.7,16 (4%). PorA VR typing showed that 91% of the P1.19,15 strains analyzed had VR1 and VR2 sequences identical to those of the prototype strain. No sequence variation was detected among the 40 strains representing all isolated MenB P1.7,16 strains in the three southern states, where this serosubtype accounts for 75% of the serosubtypes identified. Similarly, all P1.7,1 strains were identified by PorA typing as P1.7-1,1. Although further improvements in the reporting of cases and collection of strains in Brazil are needed, our data suggest that a trivalent OMV-based vaccine prepared with PorA types P1.19,15, P1.7-1,1, and P1.7,16 may be appropriate to control serogroup B meningococcal disease in most of the Brazilian states.

Modulation of the serological response to meningococcal polysaccharides by cytokines

Meningococcal A and C but not B capsular polysaccharides stimulated a low level primary antibody response, predominantly IgM, and no secondary response in 21-day-old CBA/A mice. However, in 56-day-old mice a higher proportion of IgG antibody and a secondary response were produced. When the polysaccharides were injected in conjunction with rDNA derived human interleukin 2 (IL-2) the IgG antibody responses were increased in both age groups and memory cells were primed in the younger mice. IL-2 increased significantly the IgG antibody response to conjugates of A and C polysaccharides with diphtheria mutant protein but exerted a minimal effect on the IgG response to B polysaccharide complexed with aluminium hydroxide and outer membrane proteins. The stimulatory effect of IL-2 on the antibody responses to the polysaccharide antigens was not mediated by T-cells as similar results were obtained in athymic (nu/nu) and thymocompetent (nu/+) mice. However, the response to the A and C oligosaccharide conjugates was T-cell dependent and occurred only in the heterozygotes. In this case the adjuvant effect of IL-2 was seen only in the response to the C polysaccharide conjugate and was transferable with T-lymphocytes from primed animals.

Bactericidal antibody responses of juvenile rhesus monkeys immunized with group B Neisseria meningitidis capsular polysaccharide-protein conjugate vaccines

Reports on the bactericidal activities of antibodies to group B Neisseria meningitidis capsular polysaccharide (B PS) are conflicting. Using three different complement sources, we analyzed the bactericidal activities of sera of juvenile rhesus monkeys immunized with five conjugate vaccines of B PS synthesized by different schemes, an Escherichia coli K92 conjugate, and a noncovalent complex of B PS with group B meningococcal outer membrane vesicles (B+OMV) (S. J. N. Devi, W. D. Zollinger, P. J. Snoy, J. Y. Tai, P. Costantini, F. Norelli, R. Rappuoli, and C. E. Frasch, Infect. Immun. 65:1045-1052, 1997). With rabbit complement, nearly all preimmune sera showed relatively high bactericidal titers, and all vaccines, except the K92 conjugate, induced a fourfold or greater increase in bactericidal titers in most of the monkeys vaccinated. In contrast, with human complement, most prevaccination sera showed no bactericidal activity and in most of the vaccine groups, little or no increase in bactericidal titer was observed. However, the covalent conjugation of P BS and OMV (B-OMV) administered with and without the Ribi adjuvant induced relatively high bactericidal titers which persisted up to 30 weeks. An analysis of the specificities of bactericidal antibodies revealed that absorption with E. coli K1 cells did not change the bactericidal titer with human complement but reduced the titers observed with the rabbit and monkey complements. A significant increase in anti-lipopolysaccharide (LPS) antibodies was elicited by the B-OMV conjugates, and nearly all of the bactericidal activity with human complement could be inhibited with the purified group B meningococcal L3,7,8 LPS. B-OMV covalently coupled via adipic acid dihydrazide elicited significantly elevated levels (P < or = 0.02) of anti-OMV antibodies compared to those of the noncovalently complexed B+OMV. An initial small-scale evaluation of B PS conjugates in adult human males appears feasible, with careful monitoring, to settle the inconsistent reports of the importance of source of complement in eliciting bacteriolysis. Subsequent analysis of resultant human antibodies for bacteriolysis, opsonophagocytosis, and protective efficacy in animal models may be the first step toward answering safety- and efficacy-related concerns about B PS conjugate vaccines.

Preclinical evaluation of group B Neisseria meningitidis and Escherichia coli K92 capsular polysaccharide-protein conjugate vaccines in juvenile rhesus monkeys

We reported the first use of group B meningococcal conjugate vaccines in a nonhuman primate model (S. J. N. Devi, C. E. Frasch, W. Zollinger, and P. J. Snoy, p. 427-429, in J. S. Evans, S. E. Yost, M. C. J. Maiden, and I. M. Feavers, ed., Proceedings of the Ninth International Pathogenic Neisseria Conference, 1994). Three different group B Neisseria meningitidis capsular polysaccharide (B PS)-protein conjugate vaccines and an Escherichia coli K92 capsular polysaccharide-tetanus toxoid (K92-TT) conjugate vaccine are here evaluated for safety and relative immunogenicities in juvenile rhesus monkeys with or without adjuvants. Monkeys were immunized intramuscularly with either B PS-cross-reactive material 197 conjugate, B PS-outer membrane vesicle (B-OMV) conjugate, or N-propionylated B PS-outer membrane protein 3 (N-pr. B-OMP3) conjugate vaccine with or without adjuvants at weeks 0, 6, and 14. A control group of monkeys received one injection of the purified B PS alone, and another group received three injections of B PS noncovalently complexed with OMV. Antibody responses as measured by enzyme-linked immunosorbent assay varied among individual monkeys. All vaccines except B PS and the K92-TT conjugate elicited a twofold or greater increase in total B PS antibodies after one immunization. All vaccines, including the K92-TT conjugate, elicited a rise in geometric mean B PS antibody levels of ninefold or more over the preimmune levels following the third immunization. Antibodies elicited by N-pr. B-OMP3 and B-OMV conjugates were directed to the N-propionylated or to the spacer-containing B PS antigens as well as to the native B PS complexed with methylated human serum albumin. None of the vaccines caused discernible safety-related symptoms.

Human immune response to epitopes on the meningococcal outer membrane class 5 protein following natural infection

Two monoclonal antibodies (mAbs) were produced against a serogroup B Neisseria meningitidis strain. These mAbs recognized two epitopes in the class 5 outer membrane proteins (OMP), designated P5.7 and P5.Bm, and were able to kill the homologous strain through complement activation. Both epitopes were surface exposed and 68% of group B meningococcal clinical isolates had one or both epitopes present in their class 5 OMP. Antibodies to one or both epitopes were demonstrated in 17 patients with meningococcal meningitis using an ELISA inhibition assay. Of the 17 paired sera, 41% and 29% of the acute-phase sera had antibodies to the P5.7 and P5.Bm epitopes, respectively. Immunoglobulin G to P5.Bm were found in all 17 convalescent-phase sera while specific antibodies against P5.7 were only found in 6 of these sera. These results demonstrate the potential importance of the P5.Bm and P5.7 epitopes on the class 5 OMP as candidates for vaccine composition.

Binding diversity of monoclonal antibodies to alpha(2-->8) polysialic acid conjugated to outer membrane vesicle via adipic acid dihydrazide

Murine monoclonal antibodies (mAbs) were generated using group B Neisseria meningitidis and Escherichia coli K1 polysaccharides (PSs) conjugated to outer membrane vesicle (OMV) via adipic acid dihydrazide, and were used to identify the immunodeterminants expressed on these capsular PSs. Ten mAbs representative of IgM and all subclasses of IgG were obtained which recognized diverse immunodeterminants on alpha(2-->8) polysialic acid (PSA). The specificity of mAbs to different antigenic determinants was assessed by their differential binding to PSA attached to a solid phase by different methods and confirmed by absorption studies. Two mAbs from the E. coli K1 fusion were directed to the O-acetyl epitope and the rest reacted with both the PSs only when attached to a solid phase by certain means. The methods by which PSA was coated on the solid phase had an impact on the epitope expression and binding pattern. At the concentrations used, the O-acetyl-specific mAbs, IgG1 and IgG3 mAbs were not bactericidal against group B N. meningitidis, whereas other mAbs were. The conjugates B and K1 PSs present to the murine immune system different antigenic determinants, some of which elicit bactericidal antibodies.

Haemophilus influenzae type b conjugate vaccines

In summary, all of the Hib conjugate vaccines are highly immunogenic and efficacious in children older than 12-15 months of age, and HbOC, PRP-OMPC, and PRP-T are highly immunogenic and demonstrated to be efficacious in infants as young as 2 months old. HbOC, PRP-OMPC, and PRP-T have been licensed in numerous countries for infants and are recommended for infant immunization. However, perhaps the greatest tribute one can pay to all four Hib vaccines described in this review is to note the dramatic decrease in the incidence of Hib disease that has occurred since their introduction. In fact, according to the Morbidity and Mortality Weekly Report (March 4, 1994), the incidence of Hib disease in children less than 5 years old has declined by 95% from 41 cases per 100,000 in 1987 to 2 cases per 100,000 in 1993, timing that coincides with the availability and use of the Hib conjugate vaccines (Anderson, 1994). As universal administration is achieved and the apparent vaccine-induced reduction in carriage of Hib by the population continues, Hib vaccines may follow the lead of past vaccines (such as smallpox, measles, mumps, rubella, and polio) toward eradication of disease or at least a high degree of medical control, thereby virtually eliminating the mortality and insidious morbidity associated with invasive Hib diseases.

Molecular recognition of antigenic polysaccharides: a conformational comparison of capsules from Streptococcus pneumoniae serogroup 9

Aqueous solution conformations of three antigenic bacterial capsular polysaccharides (CPS) from S. pneumoniae serogroup 9 were determined using a combination of NMR data (NOE build-up rates and conformation-dependent chemical shifts), simulated annealing, and molecular dynamics simulations. Each polymer adopts a flexible extended ribbon conformation in solution. Conformations of structural elements shared by each PS are indistinguishable. Differences in conformations are minor and localised at the sites of structural variations; there is no evidence of long-range stabilisation of a secondary structure. It is likely that antigenic specificity of Group 9 PS is dominated by local structural variation rather than by conformational differences.

Immune response of Brazilian children to a Neisseria meningitidis serogroup B outer membrane protein vaccine: comparison with efficacy

Since 1986, serogroup B Neisseria meningitidis has caused approximately 80% of the meningococcal disease in Brazil. In 1988, an epidemic caused by N. meningitidis B:4:P1.15 was recognized in the greater São Paulo area of Brazil. The São Paulo state government decided to vaccinate children from 3 to 83 months of age with a vaccine consisting of serotype 4 outer membrane protein and group C meningococcal polysaccharide that was produced in Cuba. About 2.7 million children were vaccinated during two immunization campaigns conducted in 1989 and 1990. Because of this, a case-control study was designed to determine vaccine efficacy against group B meningococcal disease. The purpose of our study was to compare the antibody response with the protection from disease estimated from the case-control study. We measured the immune responses of vaccinees by enzyme-linked immunosorbent assay (ELISA), immunoblot, and bactericidal assay. The development of bactericidal antibodies was age dependent and in good agreement with the results of the case-control study. Only 40% of vaccinees showed fourfold or greater increases in bactericidal antibody titers after vaccination. A poor correlation between antibody levels detected by ELISA and those by bactericidal assay was found. Immunoblot analysis showed that about 50% of the serum samples with bactericidal titers higher than 1:4 were reactive with class 1 outer membrane protein. We conclude that the bactericidal assay is a good, laboratory-based, functional assay for the study of vaccine immunogenicity and that an effective solution to group B meningococcal disease remains to be demonstrated.

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.

Hereditary deficiency of the seventh component of complement and recurrent meningococcal infection: investigations of an Irish family using a novel haemolytic screening assay for complement activity and C7 M/N allotyping

Terminal complement component deficiency predisposes to meningococcal infection and is inherited in an autosomal co-dominant manner. An Irish family is described, in which 2 of 3 brothers had recurrent meningococcal infection. A novel screening assay was used to investigate for terminal complement deficiency and the 2 affected brothers were found to be completely deficient in the seventh component of complement (C7). Enzyme-linked immunosorbent assay for C7 revealed lower than normal levels in the remaining brother and parents. C7 M/N protein polymorphism allotyping, used to investigate the segregation of the C7 deficiency genes, showed that the apparently complement sufficient brother was heterozygous C7 deficient and a carrier of one of the deficiency genes. Complement screening should be carried out in any individual suffering recurrent meningococcal infection or infection with an uncommon meningococcal serogroup. Identification of complement deficient patients allows the implementation of strategies to prevent recurrent infection.

[Immune response to anti-meningococcal vaccines]

In view of a recent epidemic of meningococcal disease caused by serogroup B N. meningitidis in the Greater S. Paulo area (Brazil), a review of the epidemics that occurred in Brazil during the period from 1900 to 1990 is presented. The current status of vaccines against N. meningitidis A.C.Y. and W135 is analysed. The recent advances in the development and effectiveness of B. meningococci vaccines are discussed.

Dramatic reduction of meningococcal meningitis among military recruits in Italy after introduction of specific vaccination

Meningococcal meningitis is still a serious infectious disease with a mortality rate that can be as high as 10% even in developed countries. Military recruits are generally a high-risk group for meningococcal disease, with a reported incidence of four to ten times greater than that of the general population. In Italy the results of the National Meningitis Surveillance Programme showed a high attack rate of the disease among recruits in 1985 as well as in 1986, with 92 and 95% of the cases, respectively, caused by serogroup C and thus preventable. These findings led to the authorities' decision to make vaccination against meningococcal disease mandatory for recruits starting from January 1987. After almost 5 years from the introduction of meningococcal vaccination, we here sum up the epidemiological and immunological effects of the vaccination. From the epidemiological point of view we have observed a dramatic reduction of the prevalence of the disease. In 1987, the year in which we had 150,000 unvaccinated and 150,000 vaccinated recruits, the protective efficacy was 91.2%. From the immunological point of view, vaccination is highly effective, as seroconversion against polysaccharide (PS) A and C is 84 and 91%, respectively. The spectrotypic analysis of the sera before and after vaccination shows that the type of response is mainly oligoclonal, like the majority of the responses to PSs, and the antibodies induced by a sole PS are not qualitatively different from the antibodies induced by natural immunization. In addition, the efficacy is not modified by environmental factors like hypoxia, as demonstrated during permanence at 16,174 feet for 20 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of meningococcal group B monoclonal antibody and its Fab fragment with alpha 2-8-linked sialic acid polymers: requirement of a long oligosaccharide segment for binding

Mouse monoclonal IgG2a antibody (735D4) and other antibodies to the capsular polysaccharide of group B meningococci have been shown to require an unusually long segment of the alpha 2-8-linked N-acetylneuraminic acid polymer for binding. This property may be due to a conformational nature of the polysaccharide epitope recognized, or alternatively due to the requirement of bivalent binding of the antibody to the polysaccharide. In order to study the binding requirements, Fab fragments were prepared from the monoclonal antibody and their binding to alpha 2-8-linked sialic acid polymers of different lengths was studied. Both the intact antibody and its Fab fragment bound to sialic acid poly- and oligomers to similar extents, the critical chain length being about 10 sialyl units for both molecules. This excluded bivalency as the explanation for the requirement of a long oligosaccharide segment for binding. Although the binding was enhanced with increasing chain length, the first 10 monosaccharides were calculated to contribute to more than 90% of the total binding energy. This is in agreement with an oligosaccharide segment with defined conformational epitope binding to the antibody combining site. The antibody preparations also bound polysialic acid containing glycopeptides isolated from developing human and rat brain, suggesting, in quantitative binding assay, an average chain length of 10 or more sialic acid residues. The interaction of the antibody with both the bacterial and the tissue derived polysialic acids suggests that the conformational epitope critical for the interaction is formed by both classes of compounds.

Passive transfer of meningococcal group B polysaccharide antibodies to the offspring of pregnant rabbits and their protective role against infection with Escherichia coli K1

Pregnant rabbits vaccinated with meningococcal group B polysaccharide complexed to outer membrane proteins (serotype 6) responded to produce IgG, IgM and IgA anti-B polysaccharide antibodies, which were passively transferred to the offspring (IgG preferentially) and could be detected in their sera immediately after birth. These antibody levels were sustained in the mothers but diminished in the offspring to background levels at day 22 after birth. In a subsequent experiment, rabbits immunized with the group B vaccine had offspring that proved considerably more resistant to infection with Escherichia coli K1 than the control litters from non-immune mothers. Although not complete, protection was statistically of high significance and correlated well with the anti-B polysaccharide titres obtained in the mothers.

Immune responses in mice to different noncovalent complexes of meningococcal B polysaccharide and outer membrane proteins

Noncovalent complexes of meningococcal group B polysaccharide and outer membrane proteins (OMPs) from serotypes 2a, 2b, 6, 8, and 15 were made either by coextraction of the two components from culture supernatants or by separate preparation of both OMPs and B polysaccharide with subsequent mixing of the two components. The former method showed a markedly greater degree of binding of B polysaccharide to OMPs, a less heterogeneous composition of OMPs, and a lower lipopolysaccharide content. Immunization of mice with these complexes showed that a higher degree of binding of B polysaccharide to OMPs resulted in a higher anti-B response. Western blotting (immunoblotting) and solid-phase radioimmunoassay techniques confirmed that antibody cross-reactions occur among OMP serotypes. The occurrence of common T-cell determinants between OMP serotypes was suggested when mice primed with a type 6 OMP complex and challenged with a homologous or heterologous serotype complex responded with significantly higher anti-B titers than unprimed animals. These memory T cells persisted for at least 12 months in mice.

Vaccine development reconsidered

This paper briefly reviews work on vaccine development since the early 1950s with special emphasis on identification of immunogens and their presentation to the host so as to elicit an immune response. This is illustrated primarily by a discussion of the development of a candidate meningococcal B vaccine based on a capsular carbohydrate outer membrane protein complex. Work on malaria and living Salmonella typhi vaccine is also discussed.