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D Sesardic

Publications and source records attributed to D Sesardic.

At least 19 recordsLinked to original sources
PubMed2006

Botulinum type A toxin neutralisation by specific IgG and its fragments: a comparison of mouse systemic toxicity and local flaccid paralysis assays.

In this study, we have compared two in vivo assay methods to measure the type A botulinum toxin neutralising activity of specific immunoglobulin G (IgG) and its fragments (F(ab')(2), Fab', Fab) purified from pentavalent botulinum antisera raised in goats. Each assay method was repeated on three separate occasions in mice and relative potencies calculated with respect to a type A equine reference antitoxin. The conventional assay, which measures the number of mice surviving typically after 72 or 96 h following the intraperitoneal administration of a mixture of toxin and antitoxin, gave the following order of potency IgG>F(ab')(2)>Fab'>Fab (6.8>4.7>3.5>2.6 IU/mg). Differences in potency are likely to be due to differences in the pharmacokinetics of the antitoxins, which are related to their molecular weight. The alternative local flaccid paralysis assay, where toxin and antitoxin are injected subcutaneously into the left inguinocrural region, gave results with a narrower range of activities: IgG>Fab'>F(ab')(2)>Fab (6.0>5.9>5.5>4.6 IU/mg). Comparison of the two assay methods showed no significant differences for IgG, F(ab')(2) or Fab', although the Fab fragment was significantly more potent in the non-lethal assay probably because of the reduced influence of antitoxin pharmacokinetics in this localised assay. These findings show that a local flaccid paralysis assay provides a less time consuming and more humane alternative to the lethal assay for the potency testing of botulinum IgG and F(ab')(2) antitoxins.

Animals↗
PubMed2006

Regulatory considerations on new adjuvants and delivery systems.

New and improved vaccines and delivery systems are increasingly being developed for prevention, treatment and diagnosis of human diseases. Prior to their use in humans, all new biological products must undergo pre-clinical evaluation. These pre-clinical studies are important not only to establish the biological properties of the material and to evaluate its possible risk to the public, but also to plan protocols for subsequent clinical trials from which safety and efficacy can be evaluated. For vaccines, evaluation in pre-clinical studies is particularly important as information gained may also contribute to identifying the optimum composition and formulation process and provide an opportunity to develop suitable indicator tests for quality control. Data from pre-clinical and laboratory evaluation studies, which continue during clinical studies, is used to support an application for marketing authorisation. Addition of a new adjuvant and exploration of new delivery systems for vaccines presents challenges to both manufacturers and regulatory authorities. Because no adjuvant is licensed as a medicinal product in its own right, but only as a component of a particular vaccine, pre-clinical and appropriate toxicology studies need to be designed on a case-by-case basis to evaluate the safety profile of the adjuvant and adjuvant/vaccine combination. Current regulatory requirements for the pharmaceutical and pre-clinical safety assessment of vaccines are insufficient and initiatives are in place to develop more specific guidelines for evaluation of adjuvants in vaccines.

Adjuvants, Immunologic↗
PubMed2006

A review of WHO International Standards for botulinum antitoxins.

Clostridium botulinum produces the most potent known toxins, with seven distinct serotypes currently defined (A-G). These toxins can cause a life threatening systemic toxicity whether through natural causes such as food poisoning, infant botulism, wound botulism, or through use as bio-terror agents (e.g. inhalational botulism). It was realised early on that standard reference botulinum antitoxins were required to reduce the variation between assays and ensure a consistent potency of therapeutic antitoxins and vaccines, and to define the serotype. This led to the International Unit being defined by the World Health Organisation (WHO) in the 1960s with the establishment of the first International Standards (IS) for serotypes A-F. Since then botulinum antitoxin ISs have been used world wide as the 'yard stick' to measure the neutralising potency of antitoxins. These primary WHO ISs are used to calibrate in house working reagents that are more extensively utilised. A definition of the International Unit for serotype G antitoxin has yet to be defined or accepted by the WHO and urgently needs addressing. However, before September 11th 2001 there was very little interest in botulinum antitoxin IS and as a result stocks of most of the original preparations are now completely exhausted or depleted and replacements long overdue. We have reviewed the extensive history and availability of the primary WHO ISs and interim materials. All type A and B antitoxin materials were recently assayed and their relative activities confirmed against the original IS preparations. The recent increase in demand for these materials has further exacerbated the shortage. We describe here the production and characterization of stable freeze dried potential candidate replacements along with a new prospective first IS for type G antitoxin. Available toxin A reference preparations are also briefly reviewed.

Animals↗
PubMed2005

Effect of skin barrier disruption on immune responses to topically applied cross-reacting material, CRM(197), of diphtheria toxin.

The high accessibility of the skin and the presence of immunocompetent cells in the epidermis makes this surface an attractive route for needle-free administration of vaccines. However, the lining of the skin by the stratum corneum is a major obstacle to vaccine delivery. In this study we examined the effect of skin barrier disruption on the immune responses to the cross-reacting material CRM(197), a nontoxic mutant of diphtheria toxin (DTx) that is considered as a vaccine candidate. Application of CRM(197), together with cholera toxin (CT), onto the tape-stripped skin of mice elicited antibody responses that had anti-DTx neutralizing activity. Vaccine delivery onto mildly ablated skin or intact skin did not elicit any detectable anti-CRM(197) antibodies. Mice immunized with CRM(197) alone onto the tape-stripped skin mounted a vigorous antigen-specific proliferative response. In contrast, the induction of cellular immunity after CRM(197) deposition onto mildly ablated or intact skin was adjuvant dependent. Furthermore, epidermal cells were activated and underwent apoptosis that was more pronounced when the stratum corneum was removed by tape stripping. Overall, these findings highlight the potential for transcutaneous delivery of CRM(197) and establish a correlation between the degree of barrier disruption and levels of antigen-specific immune responses. Moreover, these results provide the first evidence that the development of a transcutaneous immunization strategy for diphtheria, based on simple and practical methods to disrupt the skin barrier, is feasible.

Administration, Topical↗
PubMed2004

Collaborative study for the validation of serological methods for potency testing of diphtheria toxoid vaccines-part 1.

A collaborative study on the evaluation of an alternative functional assay, the Vero cell method, to the Ph. Eur. in vivo challenge procedures for potency determination of diphtheria toxoid in 6 different combined vaccines was initiated in January 2001. The study was an extension of a previous study for the validation of serological methods for potency testing of tetanus toxoid vaccines for human use. To allow interim evaluation of test results and to monitor study progress, the project was divided into three consecutive phases. The results of Phase I and II studies are presented in this report. Pre-validation (Phase I) study, performed in two laboratories, indicated that comparable diphtheria potency estimates were obtained in the Ph. Eur. direct intradermal challenge assay in guinea pigs, in Vero cell assay and in indirect ELISA for five vaccines of different potencies (range of estimates: ca. 20-200 IU/ml). The correlation coefficients between the challenge assay and the Vero cell assay corresponded to those between the challenge assay and ELISA, confirming that the antibodies play an important role in protection and that predominantly protective/neutralising antibodies are present in guinea pigs, at the time point investigated. It was observed, for Vero cell assays, that about 16-35 (9-28 in Phase II study) fold lower titre of individual serum samples were obtained when using equine, rather than guinea pig reference serum. The study also provided preliminary information that sera from the same guinea pigs may be used for potency determination of both diphtheria and tetanus toxoid components of vaccines. In Phase II, another five laboratories analysed a subset of the vaccines included in Phase I study plus an additional vaccine. Four laboratories performed the lethal challenge assay and one laboratory carried out the intradermal challenge assay. All laboratories also performed the Vero cell assay and both ELISA for diphtheria antitoxin and ELISA for tetanus antitoxin. One laboratory also performed the tetanus ToBI assay. The correlation coefficient (r) between Vero cell assay and ELISA for diphtheria antitoxin ranged from 0.76 to 0.91 in the different laboratories. The correlation between diphtheria serological assays and challenge assays were confirmed satisfactory as ca. 90 per cent of serum-estimates lead to correct prediction of mortality. All laboratories had identical rankings of the vaccines in all serological assays and in the valid challenge assays. The ranking order was identical to assumed/provided potency for the highest and the lowest vaccine. Two of the vaccines had an inversion in some assays and laboratories. As these two vaccines have almost identical potencies in all assays, these inversions are not significant. As the vaccine doses were optimised for the diphtheria component, serum anti-tetanus toxoid/toxin activities varied widely between the vaccines, making it questionable to apply a parallel line model to calculate exact potencies. However, the dose levels used showed a clear regression and good linearity in general. DTaP vaccines containing the IPV component did not always meet the present Ph. Eur. requirements in the serological assays. It should be further investigated in the Phase III study if this is a general feature of such combined vaccines. Preliminary investigations on samples from two laboratories indicate that the neutralising activity of type 1, 2 and 3 polioviruses can also be detected, in a dose-dependent way. Further studies are in progress with serum samples from other laboratories. In the light of results obtained in the first two phases, it is recommended to proceed with Phase III study to investigate reliability of the in vitro assays. In Phase III it will also be further investigated whether the serological assays for D and T components are suitable for the control of the multi-component vaccines currently marketed in Europe.

Animals↗
PubMed2004

Collaborative study for the validation of serological methods for potency testing of diphtheria toxoid vaccines - extended study: correlation of serology with in vivo toxin neutralisation.

Phase I of BSP034 collaborative study was extended in two laboratories to include correlation of serology with in vivo toxin neutralisation test (TNT) using 2 separate sets of 20 serum pools, produced in-house. The study investigated the extent to which the in vitro methods for diphtheria antibodies, Vero cell assay and diphtheria enzyme-linked immunosorbent assay for diphtheria antitoxin (D-ELISA), can detect neutralising antibodies by comparison with TNT in guinea pigs. The study was also performed to compare the antibody neutralising potency obtained in relation to guinea pig (GP) or equine (DI) antitoxin standard. In addition, the study provided an opportunity to compare ELISA for tetanus antitoxin (T-ELISA) and TNT assay for detection of anti-tetanus antibodies, from the same set of serum pools. The data obtained show that antitoxin potency obtained by Vero cell assay, D-ELISA and T-ELISA using the same GP standard, highly correlated with neutralising potency as determined in respective TNT assays. Vero cell assay with DI provided estimates that also correlated with neutralising potency, but were of significantly lower titre. Since reference to DI standard is widely used in serodiagnosis, as well as in clinical studies where diphtheria antitoxin titres obtained in the Vero cell method are taken as surrogate markers for vaccine efficacy, it should be investigated if a similar difference is also observed for human serology.

Animals↗
PubMed2003

Collaborative study for establishment of the European Pharmacopoeia BRP batch 1 for diphtheria toxin.

A stable liquid candidate Biological Reference Preparation (BRP) for diphtheria toxin was prepared in peptone buffer (nominal content of diphtheria toxin: 1 Lf/ml, 0.4 micro g/ml), filled in ampoules (filling volume: 1 ml) and characterised in a collaborative study. The toxin is to be used in the test "Absence of toxin and irreversibility of toxoid" as described in the current European Pharmacopoeia (Ph. Eur.) monograph Diphtheria Vaccine (Adsorbed) (2002:0443). Eleven laboratories assessed the specific activity of the preparation by in vivo and in vitro assays. The material is assumed to have satisfactory stability with a calculated predicted loss of activity of <1% per year at 4-8 degrees C. From the collaborative study, the specific activity was calculated as 77.6 (45-113) LD( 50)/ml (lethal challenge) and >75 000 Lr/Lf (intradermal challenge). The candidate BRP was successfully used in nine laboratories and confirmed suitable for use in the Vero cell test for "Absence of toxin and irreversibility of toxoid" as described in the Ph. Eur. monograph 2002:0443; i.e., concentrations of 5 x 10( -5) Lf/ml and below caused cytotoxic effects in the Vero cell test. Due to its liquid nature, the stability of the material will be monitored at regular intervals and preparation of a stable freeze-dried formulation will be considered for long-term use. Additional studies will be performed to confirm suitability of this BRP for other applications. The candidate BRP was adopted as the Ph. Eur. reference material for Diphtheria Toxin Batch 1 by the Ph. Eur. Commission at its session in March 2003.

Animals↗
PubMed2002

Calibration of replacement international standard and European pharmacopoeia biological reference preparation for tetanus toxoid, adsorbed.

Here we report the characterisation of a preparation of tetanus toxoid, adsorbed, and its calibration by 27 laboratories in 19 countries in a joint international collaborative study co-sponsored by World Health Organization (WHO) Expert Committee of Biological Standardization (ECBS) and the European Biological Standardisation Programme of European Directorate for the Quality of Medicines (EDQM), Council of Europe. Calibration was in terms of the Second International Standard (I.S.) for Tetanus Toxoid, Adsorbed, by the established WHO/European Pharmacopoeia (Ph Eur) challenge methods. The replacement standard preparation was found to have a unitage of 469 IU/ampoule on the basis of its calibration in guinea-pigs and 496 IU/ampoule on the basis of its calibration in mice. Assessment, both within the collaborative study and as part of candidate characterisation, indicated satisfactory stability of the candidate preparation. This study also provided some information on the effect of mouse strain on potency testing of tetanus vaccines. A limited assessment of the impact of the replacement standard on testing of current production batches of vaccines was also carried out by four manufacturers. This study did not directly address the serological approaches to potency testing. However, one laboratory offered data from mouse serology assay, which gave comparable estimates to in vivo mouse bioassay. Based on the results of this study and with the agreement of participants, the candidate standard was established as the Third International Standard for Tetanus Toxoid, Adsorbed (coded 98/552) by the WHO Expert Committee of Biological Standardization (ECBS) in November 2000. The same preparation was also established as the second Ph Eur Biological Reference Preparation (Ph Eur BRP, batch no. 2) by the Steering Committee of the Biological Standardisation Programme of the EDQM and approved by the European Pharmacopoeia Commission.

Animals↗
PubMed2002

Alternatives in testing of bacterial toxins and antitoxins.

The potency of several novel toxin-derived biological therapeutic products now in routine medical use is determined exclusively by in vivo methods. In addition, large numbers of animals continue to be used for the potency and safety testing of therapeutic antitoxins. There is thus an increasing need to develop acceptable alternative assays for toxicity testing which would reduce the need for a mouse lethality assay in quality control. Scientific advances in the understanding of the mode of action of clostridial neurotoxins have now provided the basis for improving conventional testing procedures for both therapeutic toxins and antitoxins.

Animal Testing Alternatives↗
PubMed2002

A Vero cell method for potency testing of diphtheria vaccines.

A collaborative study on the evaluation of an alternative functional assay to the Ph. Eur. in vivo challenge procedure for potency determination of diphtheria toxoid vaccines was initiated in January 2001. This study is an extension of the collaborative study for the validation of serological methods for potency testing of tetanus toxoid vaccines for human use. The primary aim was to examine whether a Vero cell assay is a valid alternative to the Ph. Eur. in vivo challenge methods for potency determination of the diphtheria toxoid component of combined vaccines. The study also investigated whether sera from the same immunised guinea pigs can be used for potency determination of both the diphtheria and the tetanus toxoid components. The project was divided into three parts. In part I, summarised in this publication, the operating procedures for the methods and the optimal vaccine dilutions for the immunisation of guinea pigs were established. From the results of the part I study, performed in two laboratories, the correlation co-efficients between the Vero cell method and the challenge assay were considered satisfactory to warrant continuing with the next phase. Comparable diphtheria potency estimates were obtained in the two assays for four vaccines of different activities (range ca. 20-200 IU/ml). The study also provided preliminary information that sera from the same guinea pigs may also be used for potency determination of both diphtheria and tetanus toxoid components of vaccines by ELISA.

Animal Testing Alternatives↗
PubMed2002

Application of an in vitro endopeptidase assay for detection of residual toxin activity in tetanus toxoids.

Tetanus vaccine is composed of chemically denatured tetanus toxin (TeNT), thus safety testing requires confirmation of freedom from residual and reversible toxicity. Currently, TeNT activity is estimated using in vivo assay models. Information that TeNT acts by selectively inactivating protein leading to the blocking of release of neurotransmitters has provided the opportunity to develop in vitro biochemical assay for toxin activity. In this study we describe development and use of an in vitro endopeptidase assay for detection of TeNT activity in toxoid vaccine formulations.

Animal Testing Alternatives↗
PubMed2001

Immunogenicity and reactogenicity of acellular diphtheria/tetanus/pertussis vaccines given as a pre-school booster: effect of simultaneous administration of MMR.

Four acellular diphtheria/tetanus/pertussis (aDTP) vaccines were compared with two diphtheria/tetanus (DT) vaccines given as a pre-school booster to 1033 children aged 4 to < 6 years who had completed primary immunisation with DTP vaccine according to the UK 2, 3 and 4 month schedule; 71 children had received aDTP vaccine and the remaining 962 a whole cell DTP vaccine for primary immunisation. The effect of simultaneous administration of a second dose of MMR vaccine was evaluated in 374 (37%). Overall, there was little difference in the frequency of post-vaccination symptoms in DT and aDTP vaccinees, although local reactions occurred more quickly in the aDTP group. The concomitant administration of MMR had no effect on local reactions or fever within 10 days, or on the proportions requiring a doctor's visit in the 4--6 week post-vaccination period. Local reactions > or = 3 cm were higher on day 2 in children who had received aDTP for primary immunisation (erythema 32.4% vs. 17.4% for wDTP, P = 0.0012; swelling 28.2% vs. 15.5%, P = 0.0027). Pertussis antibody responses were consistent with the antigen content of the aDTP vaccines. All were more immunogenic with respect to PT -- the only pertussis antigen which by itself has been shown to be protective in clinical trials -- than a wDTP pre-school booster given in an earlier trial. MMR vaccine had no significant effect on antibody responses to either the pertussis or diphtheria and tetanus antigens. Diphtheria antibody responses in children who had received wDTP for primary immunisation were 2.8 times higher than in those who had received aDTP vaccine (P < 0.0001); they were also higher in children who had received a single dose of a Haemophilus influenzae type b vaccine containing CRM(197) conjugate after 12 months of age. For countries currently using DT vaccines as a pre-school booster, replacement with an aDTP vaccine is unlikely to have a perceptible effect on reactogenicity, at least in children given wDTP for primary immunisation, and would boost antibody levels to antigens known to be associated with protection.

Child, Preschool↗
PubMed2001

Calibration of replacement international standard and European Pharmacopoeia Biological Reference Preparation for Diphtheria Toxoid, Adsorbed.

We report here the characterisation of a preparation of diphtheria toxoid, adsorbed, and its calibration by twenty laboratories in fourteen countries in terms of the Second International Standard (I.S.) for Diphtheria Toxoid, Adsorbed, coded sample A (DIXA) using the established World Health Organisation (WHO)/European Pharmacopoeia (Ph Eur) challenge methods. The replacement standard preparation was found to have a unitage of 160 IU/ampoule on the basis of its calibration by in vivo bioassay. Stability was assessed within the collaborative study, and as part of candidate characterisation. Results suggest that the replacement standard will have satisfactory stability. This study also provided an opportunity to investigate serology as alternative to in vivo bioassay for potency testing of diphtheria vaccines. Six laboratories participated by performing serology according to in-house protocol. The calibration of the replacement standard in a mouse Vero cell assay gave a significantly higher results than in the established WHO/Ph Eur methods. Based on the results of this study and with the agreement of participants, the candidate standard was established as the Third International Standard for Diphtheria Toxoid, Adsorbed (coded 98/560) by the WHO Expert Committee of Biological Standardization in October 1999. The same preparation was also established as the second Ph Eur Biological Reference Preparation (Ph Eur BRP, batch no. 3) by the Steering Committee of the Biological Standardisation Programme of the European Directorate for the Quality of Medicines and approved by the European Pharmacopoeia Commission.

Adsorption↗
PubMed2001

Collaborative study for the establishment of tetanus vaccine (adsorbed) Third International Standard and European Pharmacopoeia Biological Reference Preparation batch no. 2.

The aim of the present collaborative study was to calibrate two candidate replacement standards for tetanus vaccine for human use in the terms of the Second International Standard (IS) for Tetanus Toxoid, Adsorbed (TEXA-2) using challenge potency assays in guinea pigs and mice and to establish the 3rd IS and the Ph. Eur. BRP batch 2. Two test preparations (coded B and C) were included as candidate replacement for TEXA-2 and Ph. Eur. BRP batch 1 (EBRP-1). This project was run as a joint WHO/Ph. Eur. study. Twenty-seven laboratories representing nineteen countries participated in the study. Twenty-three laboratories performed assays in mice (11 laboratories performed lethal, 11 paralysis, and one serology assays) and fourteen laboratories performed assays in guinea pigs (10 laboratories performed lethal and 4 paralysis assays). Estimates of potency, expressed in ampoule of TEXA-2 per ampoule of candidate replacement standards were two-fold higher in mice than in guinea pigs. However, using the assumed relationship between TEXA-1 and TEXA-2 in mice and guinea pigs (Lyng and Nyerges, 1984), potency estimates for candidate replacement standards (sample coded B and C), in terms of TEXA-1, gives estimates which are similar in both animal models. Stability was assessed within the collaborative study for candidate standard B. On the basis of this collaborative study, the ECBS of WHO has established the candidate material coded B as the Third IS for Tetanus Toxoid, Adsorbed, with an assigned unitage of 469 IU/ampoule, based on its calibration by guinea pig challenge assays (WHO report BS/00.1932). Further studies were organised to assess which of the two candidate standards is most suitable as replacement for EBRP-1. Manufacturers were asked to include candidate B and candidate C in their routine quality control potency assays of tetanus vaccines in order to assess the impact of the use of either preparation on their calibration results. The features and results of this additional phase are described at the end of this report in a separate section entitled "Choice of replacement batch for EBRP-1". Based on these results, at the session in March 2001, the Ph. Eur. Commission adopted candidate B as the Tetanus vaccine (adsorbed) Ph. Eur. BRP Batch 2 with assigned potencies of 469 IU/ampoule for the guinea pig assays and 496 IU/ampoule for the mouse assays.

Animals↗
PubMed2000

Comparison of in vitro and in vivo methods to study stability of PLGA microencapsulated tetanus toxoid vaccines.

The purpose of this study was to investigate the utility of various in vitro and in vivo methods to assess the stability of experimental vaccines containing tetanus toxoid (TT) within PLGA microspheres. In vitro, the breakdown of the encapsulating polymers into their acid components led to changes in the structure of TT, as determined by the physico-chemical methods, rendering it undetectable by capture ELISA and altering its structural integrity. The changes in TT were directly related to increasing acidity of the vaccine supernate. Purified toxoid (not encapsulated) exposed to low pH (2.5) underwent similar changes but re-neutralisation of buffer containing free toxoid, even after one week at pH 2.5 led to some re-folding of protein as determined by fluorescence spectroscopy and gel filtration chromatography. The microencapsulated vaccines were still able to generate an antibody response in mice even after prolonged pre-incubation at 37 degrees C and the apparent absence of detectable toxoid in the vaccine supernate. Electron microscopy demonstrated differences in the amount of degradation between different formulations of microspheres. Vaccines that had retained their spherical morphology after incubation in vitro for up to 28 days were able to induce protective antibodies response equal to that of freshly prepared vaccines, which indicates that the toxoid within intact microspheres remained immunogenic. Immunochemical and physico-chemical detection methods, performed on antigen released from PLGA vaccines in vitro, are valuable in providing information on product characteristics but may not be able to predict effectiveness and should be used with in vivo methods to evaluate the stability of such formulations.

Animals↗
PubMed2000

Ambiguities in the preclinical quality assessment of microparticulate vaccines.

Vaccination techniques do not always stimulate immunity because of the inappropriate mobilization of immune responses, and the frequency of vaccinations required is impractical in many developing countries. Such limitations have spurred the development of new vaccine-delivery approaches. Microparticles made of poly(lactide-co-glycolide) can induce adaptive immunity after a single administration of a vaccine. However, the preclinical assessment of such vaccines is not standardized, making it difficult to compare pharmaceutical with immunological data. The relevance of and the ambiguity in the assessment of microparticulate vaccines with respect to the current knowledge on immunity are discussed, in addition to the application of this knowledge to rational vaccine design.

Antigens↗
PubMed2000

Monitoring of diphtheria, pertussis and tetanus toxoids by circular dichroism, fluorescence spectroscopy and size-exclusion chromatography.

A combination of spectroscopic and chromatographic methods has been used to monitor the quality and integrity of diphtheria, pertussis and tetanus toxoids (DTxd, PTxd and TTxd) which have been prepared from the toxins by formaldehyde treatment. Different processes for detoxifying all three toxins have yielded toxoids varying in their molecular size, including oligomers (associated monomers) and aggregates (high molecular weight complexes of non-specifically associated monomers). Changes in the intrinsic fluorescence spectra of the polypeptides have been observed in some sized fractions of DTxd and PTxd. Some physico-chemical changes have been observed to correlate with a loss of antigenicity. Spectroscopic and chromatographic methods are useful not only in monitoring the stability and consistency of vaccine starting materials, but can also be used to dissect heterogeneous toxoid preparations.

Chemical Phenomena↗