Distinct T cell responsiveness to different COVID-19 vaccines and cross-reactivity to SARS-CoV-2 variants with age and CMV status

Introduction

Accumulating evidence indicates the importance of T cell immunity in vaccination-induced protection against severe COVID-19 disease, especially against SARS-CoV-2 Variants-of-Concern (VOCs) that more readily escape from recognition by neutralizing antibodies. However, there is limited knowledge on the T cell responses across different age groups and the impact of CMV status after primary and booster vaccination with different vaccine combinations. Moreover, it remains unclear whether age has an effect on the ability of T cells to cross-react against VOCs.

Methods

Therefore, we interrogated the Spike-specific T cell responses in healthy adults of the Dutch population across different ages, whom received different vaccine types for the primary series and/or booster vaccination, using IFNɣ ELISpot. Cells were stimulated with overlapping peptide pools of the ancestral Spike protein and different VOCs.

Results

Robust Spike-specific T cell responses were detected in the vast majority of participants upon the primary vaccination series, regardless of the vaccine type (i.e. BNT162b2, mRNA-1273, ChAdOx1 nCoV-19, or Ad26.COV2.S). Clearly, in the 70+ age group, responses were overall lower and showed more variation compared to younger age groups. Only in CMV-seropositive older adults (>70y) there was a significant inverse relation of age with T cell responses. Although T cell responses increased in all age groups after booster vaccination, Spike-specific T cell frequencies remained lower in the 70+ age group. Regardless of age or CMV status, primary mRNA-1273 vaccination followed by BNT162b2 booster vaccination showed limited booster effect compared to the BNT162b2/BNT162b2 or BNT162b2/mRNA-1273 primary-booster regimen. A modest reduction in cross-reactivity to the Alpha, Delta and Omicron BA.1, but not the Beta or Gamma variant, was observed after primary vaccination.

Discussion

Together, this study shows that age, CMV status, but also the primary-booster vaccination regimen influence the height of the vaccination-induced Spike-specific T cell response, but did not impact the VOC cross-reactivity.

Estimation of the infection attack rate of mumps in an outbreak among college students using paired serology

Mumps virus is a highly transmissible pathogen that is effectively controlled in countries with high vaccination coverage. Nevertheless, outbreaks have occurred worldwide over the past decades in vaccinated populations. Here we analyse an outbreak of mumps virus genotype G among college students in the Netherlands over the period 2009-2012 using paired serological data. To identify infections in the presence of preexisting antibodies we compared mumps specific serum IgG concentrations in two consecutive samples (n=746), whereby the first sample was taken when students started their study prior to the outbreaks, and the second sample was taken 2-5 years later. We fit a binary mixture model to the data. The two mixing distributions represent uninfected and infected classes. Throughout we assume that the infection probability increases with the ratio of antibody concentrations of the second to first sample. The estimated infection attack rate in this study is higher than reported earlier (0.095 versus 0.042). The analyses yield probabilistic classifications of participants, which are mostly quite precise owing to the high intraclass correlation of samples in uninfected participants (0.85, 95%CrI: 0.82-0.87). The estimated probability of infection increases with decreasing antibody concentration in the pre-outbreak sample, such that the probability of infection is 0.12 (95%CrI: 0.10-0.13) for the lowest quartile of the pre-outbreak samples and 0.056 (95%CrI: 0.044-0.068) for the highest quartile. We discuss the implications of these insights for the design of booster vaccination strategies.

SARS-CoV-2 Omicron BA.4/BA.5 Mutations in Spike Leading to T Cell Escape in Recently Vaccinated Individuals

SARS-CoV-2 Omicron (B.1.1.529) lineages rapidly became dominant in various countries reflecting its enhanced transmissibility and ability to escape neutralizing antibodies. Although T cells induced by ancestral SARS-CoV-2-based vaccines also recognize Omicron variants, we showed in our previous study that there was a marked loss of T cell cross-reactivity to spike epitopes harboring Omicron BA.1 mutations. The emerging BA.4/BA.5 subvariants carry other spike mutations than the BA.1 variant. The present study aims to investigate the impact of BA.4/BA.5 spike mutations on T cell cross-reactivity at the epitope level. Here, we focused on universal T-helper epitopes predicted to be presented by multiple common HLA class II molecules for broad population coverage. Fifteen universal T-helper epitopes of ancestral spike, which contain mutations in the Omicron BA.4/BA.5 variants, were identified utilizing a bioinformatic tool. T cells isolated from 10 subjects, who were recently vaccinated with mRNA-based BNT162b2, were tested for functional cross-reactivity between epitopes of ancestral SARS-CoV-2 spike and the Omicron BA.4/BA.5 spike counterparts. Reduced T cell cross-reactivity in one or more vaccinees was observed against 87% of the tested 15 non-conserved CD4+ T cell epitopes. These results should be considered for vaccine boosting strategies to protect against Omicron BA.4/BA.5 and future SARS-CoV-2 variants.

Omicron BA.1 Mutations in SARS-CoV-2 Spike Lead to Reduced T-Cell Response in Vaccinated and Convalescent Individuals

Omicron BA.1 variant can readily infect people with vaccine-induced or naturally acquired SARS-CoV-2 immunity facilitated by escape from neutralizing antibodies. In contrast, T-cell reactivity against the Omicron BA.1 variant seems relatively well preserved. Here, we studied the preexisting T cells elicited by either vaccination with the mRNA-based BNT162b2 vaccine or by natural infection with ancestral SARS-CoV-2 for their cross-reactive potential to 20 selected CD4⁺ T-cell epitopes of spike-protein-harboring Omicron BA.1 mutations. Although the overall memory CD4⁺ T-cell responses primed by the ancestral spike protein was still preserved generally, we show here that there is also a clear loss of memory CD4⁺ T-cell cross-reactivity to immunodominant epitopes across the spike protein due to Omicron BA.1 mutations. Complete or partial loss of preexisting T-cell responsiveness was observed against 60% of 20 nonconserved CD4⁺ T-cell epitopes predicted to be presented by a broad set of common HLA class II alleles. Monitoring such mutations in circulating strains helps predict which virus variants may escape previously induced cellular immunity and could be of concern.

Children and Adults With Mild COVID-19: Dynamics of the Memory T Cell Response up to 10 Months

Background

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has led to considerable morbidity/mortality worldwide, but most infections, especially among children, have a mild course. However, it remains largely unknown whether infected children develop cellular immune memory.

Methods

To determine whether a memory T cell response is being developed, we performed a longitudinal assessment of the SARS-CoV-2-specific T cell response by IFN-γ ELISPOT and activation marker analyses of peripheral blood samples from unvaccinated children and adults with mild-to-moderate COVID-19.

Results

Upon stimulation of PBMCs with heat-inactivated SARS-CoV-2 or overlapping peptides of spike (S-SARS-CoV-2) and nucleocapsid proteins, we found S-SARS-CoV-2-specific IFN-γ T cell responses in infected children (83%) and adults (100%) that were absent in unexposed controls. Frequencies of SARS-CoV-2-specific T cells were higher in infected adults, especially in those with moderate symptoms, compared to infected children. The S-SARS-CoV-2 IFN-γ T cell response correlated with S1-SARS-CoV-2-specific serum antibody concentrations. Predominantly, effector memory CD4+ T cells of a Th1 phenotype were activated upon exposure to SARS-CoV-2 antigens. Frequencies of SARS-CoV-2-specific T cells were significantly reduced at 10 months after symptom onset, while S1-SARS-CoV-2-specific IgG concentrations were still detectable in 90% of all children and adults.

Conclusions

Our data indicate that an antigen-specific T cell and antibody response is developed after mild SARS-CoV-2 infection in children and adults. It remains to be elucidated to what extent this SARS-CoV-2-specific response can contribute to an effective recall response after reinfection.

Longitudinal Characterization of the Mumps-Specific HLA-A2 Restricted T-Cell Response after Mumps Virus Infection

Waning of the mumps virus (MuV)-specific humoral response after vaccination has been suggested as a cause for recent mumps outbreaks in vaccinated young adults, although it cannot explain all cases. Moreover, CD8+ T cells may play an important role in the response against MuV; however, little is known about the characteristics and dynamics of the MuV-specific CD8+ T-cell response after MuV infection. Here, we had the opportunity to follow the CD8+ T-cell response to three recently identified HLA-A2*02:01-restricted MuV-specific epitopes from 1.5 to 36 months post-MuV infection in five previously vaccinated and three unvaccinated individuals. The infection-induced CD8+ T-cell response was dominated by T cells specific for the ALDQTDIRV and LLDSSTTRV epitopes, while the response to the GLMEGQIVSV epitope was subdominant. MuV-specific CD8+ T-cell frequencies in the blood declined between 1.5 and 9 months after infection. This decline was not explained by changes in the expression of inhibitory receptors or homing markers. Despite the ongoing changes in the frequencies and phenotype of MuV-specific CD8+ T cells, TCRβ analyses revealed a stable MuV-specific T-cell repertoire over time. These insights in the maintenance of the cellular response against mumps may provide hallmarks for optimizing vaccination strategies towards a long-term cellular memory response.

Nationwide seroprevalence of SARS-CoV-2 and identification of risk factors in the general population of the Netherlands during the first epidemic wave

BACKGROUND

We aimed to detect SARS-CoV-2 serum antibodies in the general population of the Netherlands and identify risk factors for seropositivity amidst the first COVID-19 epidemic wave.

METHODS

Participants (n=3207, aged 2-90 years), enrolled from a previously established nationwide serosurveillance study, provided a self-collected fingerstick blood sample and completed a questionnaire (median inclusion date 3 April 2020). IgG antibodies targeted against the spike S1-protein of SARS-CoV-2 were quantified using a validated multiplex-immunoassay. Seroprevalence was estimated controlling for survey design, individual pre-pandemic concentration, and test performance. Random-effects logistic regression identified risk factors for seropositivity.

RESULTS

Overall seroprevalence in the Netherlands was 2.8% (95% CI 2.1 to 3.7), with no differences between sexes or ethnic background, and regionally ranging between 1.3 and 4.0%. Estimates were highest among 18-39 year-olds (4.9%), and lowest in children 2-17 years (1.7%). Multivariable analysis revealed that persons taking immunosuppressants and those from the Orthodox-Reformed Protestant community had over four times higher odds of being seropositive compared to others. Anosmia/ageusia was the most discriminative symptom between seropositive (53%) and seronegative persons (4%, p<0.0001). Antibody concentrations in seropositive persons were significantly higher in those with fever or dyspnoea in contrast to those without (p=0.01 and p=0.04, respectively).

CONCLUSIONS

In the midst of the first epidemic wave, 2.8% of the Dutch population was estimated to be infected with SARS-CoV-2, that is, 30 times higher than reported. This study identified independent groups with increased odds for seropositivity that may require specific surveillance measures to guide future protective interventions internationally, including vaccination once available.

A Third Dose of Measles-Mumps-Rubella Vaccine to Improve Immunity Against Mumps in Young Adults

BACKGROUND

Waning of vaccine-induced immunity is considered to play a central role in the reemergence of mumps among vaccinated young adults. The aim of the present study was to investigate antibody responses and safety of a third dose of measles-mumps-rubella vaccine (MMR-3) in 150 young adults. Antibody levels were related to a surrogate of protection based on preoutbreak serum antibody levels in 31 persons with and 715 without serological evidence of mumps.

METHODS

Mumps virus-specific immunoglobulin G (IgG) antibody responses and mumps virus-neutralizing antibody responses (based on the focus-reduction neutralizing test) against both the Jeryl Lynn mumps virus vaccine strain (hereafter, the "vaccine strain") and the MuVi/Utrecht.NLD/40.10 outbreak strain (hereafter, the "outbreak strain") were determined, and vaccine safety was evaluated.

RESULTS

Four weeks following MMR-3 receipt, levels of IgG, anti-vaccine strain, and anti-outbreak strain antibodies increased by a factor of 1.65, 1.34, and 1.35, respectively. Although antibody levels decreased 1 year later, they were still above the baseline level by a factor of 1.37, 1.15, and 1.27, respectively. Based on the surrogate protective antibody cutoff, significantly more participants were protected against mumps virus infection up to 1 year after vaccination (ie, they had antibody levels above the presumed threshold for herd immunity).

CONCLUSIONS

MMR-3 receipt increased antibody levels that may protect against mumps virus infection for longer than previously assumed and is expected to be a good and safe intervention for controlling a mumps outbreak.

CLINICAL TRIALS REGISTRATION

2016-001104-36; NTR5911.

Dynamics of the Antibody Response After a Third Dose of Measles-Mumps-Rubella Vaccine Indicate a Slower Decline Compared With a Second Dose

Background

Breakthrough infections of measles and mumps have raised concerns about the duration of vaccine-induced immunity, which might be improved by a third dose of measles-mumps-rubella vaccine (MMR3).

Methods

Here we compared (IgG) antibody levels against measles, mumps, and rubella in blood samples of 9-year-old children and young adults (18–25 years) following MMR2 and MMR3, respectively.

Results

We found that, in addition to antibody boosting for all 3 vaccine components, MMR3 resulted in lower antibody decay rates than MMR2; the declines were most prominent for mumps and rubella.

Conclusions

This study suggests that MMR3 provides long-lasting seroprotection against measles, mumps, and rubella.

Identification of Naturally Processed Mumps Virus Epitopes by Mass Spectrometry: Confirmation of Multiple CD8+ T-Cell Responses in Mumps Patients

BACKGROUND

The re-emergence of mumps among vaccinated young adults has become a global issue. Besides waning of antibody responses, suboptimal induction of T-cell responses may reduce protection. In a recent study, we observed a dominant polyfunctional CD8+ T-cell response after natural mumps virus (MuV) infection that was not present after vaccination. Unraveling the MuV epitope repertoire can provide insight in the specificity, functionality, and breadth of the T-cell response against MuV.

METHODS

Peptides were eluted from human leukocyte antigen (HLA) class I molecules of MuV-infected cells and characterized by advanced mass spectrometry. Selected identified MuV peptides were tested for in vitro and ex vivo immunogenicity.

RESULTS

In this study, we identified a broad landscape of 83 CD8+ T-cell epitopes of MuV, 41 of which were confirmed based on synthetic peptide standards. For 6 epitopes, we showed induction of an HLA-A*02-restriced CD8+ T-cell response. Moreover, robust T-cell responses against 5 selected MuV epitopes could be detected in all tested mumps patients using peptide/HLA-A*02:01 dextramers.

CONCLUSIONS

The identified CD8+ T-cell epitopes will help to further characterize MuV-specific T-cell immunity after natural MuV infection or vaccination. These MuV epitopes may provide clues for a better understanding of, and possibly for preventing, mumps vaccine failure.We identified for the first time 41 mumps virus (MuV)-specific HLA-A*02 epitopes. For 6 epitopes, CD8+ T-cell responses were confirmed in T cells derived from several mumps cases, and MuV-specific CD8+ T cells could be identified by peptide/dextramer staining.

Are we prepared for emerging flaviviruses in Europe? Challenges for vaccination

Tick-borne encephalitis and West Nile fever are endemic flavivirus diseases in Europe. Climate change, virus evolution, and social factors may increase the risk of these flavivirus infections and may lead to the emergence of other flaviviruses in Europe that are endemic in (sub)tropical regions of the world. Control of the spread of flaviviruses is very difficult considering the cycling of flaviviruses between arthropod vectors and animal reservoir hosts. The increasing threat of flavivirus infections emphasizes the necessity of a sustainable vector surveillance system, an active animal health surveillance system and an adequate human surveillance system for early detection of flavivirus infections. Vaccination is the most important approach to prevent flavivirus infections. Effective inactivated whole virus vaccines against tick-borne encephalitis (TBE) infection are available. Implementation of TBE vaccination based on favorable cost-effectiveness estimates per region and per target group can reduce the disease burden of TBE infection. At present, several West Nile virus (WNV) vaccine candidates are in various stages of clinical development. A major challenge for WNV vaccine candidates is to demonstrate efficacy, because of the sporadic nature of unpredictable WNV outbreaks. Universal WNV vaccination is unlikely to be cost-effective, vaccination of high-risk groups will be most appropriate to protect against WNV infections.

Vaccination against Lyme disease: Are we ready for it?

Lyme disease is the most common tick-borne illness in the Northern hemisphere and is caused by spirochetes of the Borrelia burgdorferi sensu lato complex. A first sign of Borrelia infection is a circular skin rash, erythema migrans, but it can develop to more serious manifestations affecting skin, nervous system, joints, and/or heart. The marked increase in Lyme disease incidence over the past decades, the severity of the disease, and the associated high medical costs of, in particular, the persistent forms of Lyme disease requires adequate measures for control. Vaccination would be the most effective intervention for prevention, but at present no vaccine is available. In the 1990s, 2 vaccines against Lyme disease based on the OspA protein from the predominant Borrelia species of the US showed to be safe and effective in clinical phase III studies. However, failed public acceptance led to the demise of these monovalent OspA-based vaccines. Nowadays, public seem to be more aware of the serious health problems that Lyme disease can cause and seem more ready for the use of a broadly protective vaccine. This article discusses several aspects that should be considered to enable the development and implementation of a vaccine to prevent Lyme disease successfully.

Mumps-specific cross-neutralization by MMR vaccine-induced antibodies predicts protection against mumps virus infection

BACKGROUND

Similar to other recent mumps genotype G outbreaks worldwide, most mumps patients during the recent mumps genotype G outbreaks in the Netherlands had received 2 doses of measles, mumps and rubella (MMR) vaccine during childhood. Here, we investigate the capacity of vaccine-induced antibodies to neutralize wild type mumps virus strains, including mumps virus genotype G.

METHODS

In this study, we tested 105 pre-outbreak serum samples from students who had received 2 MMR vaccine doses and who had no mumps virus infection (n=76), symptomatic mumps virus infection (n=10) or asymptomatic mumps virus infection (n=19) during the mumps outbreaks. In all samples, mumps-specific IgG concentrations were measured by multiplex immunoassay and neutralization titers were measured against the Jeryl Lynn vaccine strain and against wild type genotype G and genotype D mumps virus strains.

RESULTS

The correlation between mumps-specific IgG concentrations and neutralization titers against Jeryl Lynn was poor, which suggests that IgG concentrations do not adequately represent immunological protection against mumps virus infection by antibody neutralization. Pre-outbreak neutralization titers in infected persons were significantly lower against genotype G than against the vaccine strain. Furthermore, antibody neutralization of wild type mumps virus genotype G and genotype D was significantly reduced in pre-outbreak samples from infected persons as compared with non-infected persons. No statistically significant difference was found for the vaccine strain. The sensitivity/specificity ratio was largest for neutralization of the genotype G strain as compared with the genotype D strain and the vaccine strain.

CONCLUSIONS

The reduced neutralization of wild type mumps virus strains in MMR vaccinated persons prior to infection indicates that pre-outbreak mumps virus neutralization is partly strain-specific and that neutralization differs between infected and non-infected persons. Therefore, we recommend the use of wild type mumps virus neutralization assays as preferred tool for surveillance of protection against mumps virus infection.

Development of an IFNγ ELISPOT for the analysis of the human T cell response against mumps virus

In the last decade, mumps virus (MuV) causes outbreaks in highly vaccinated populations. Sub-optimal T cell immunity may play a role in the susceptibility to mumps in vaccinated individuals. T cell responses to mumps virus have been demonstrated, yet the quality of the MuV-specific T cell response has not been analyzed using single cell immunological techniques. Here we developed an IFNγ ELISPOT assay to assess MuV-specific T cell responses in peripheral blood mononuclear cells (PBMC) of healthy (vaccinated) donors and mumps patients. Various in vitro MuV-specific stimulation methods of PBMC were compared, using either live or inactivated MuV alone or MuV-infected autologous antigen presenting cells, i.e. Epstein Barr Virus-transformed B lymphoblastoid cell lines (EBV-BLCL) or (mitogen pre-activated) PBMC, for their ability to recall IFNγ-producing responder cells measured by ELISPOT. For the detection of MuV-specific T cell responses, direct exposure (24h) to live MuV was the preferred stimulation method when assay sensitivity and practical reasons were considered. Notably, flowcytometric confirmation of data revealed that primarily T cells and NK cells produce IFNγ upon live MuV stimulation. Depleting PBMC from CD56(+) NK cells prior to stimulation with live MuV led to the enumeration of MuV-specific T cell responses by ELISPOT. Our assay constitutes a tool to evaluate memory MuV-specific T cell responses in MuV vaccinated or infected persons. Furthermore, this study provides evidence that live MuV not only induces IFNγ production by T cells, but also by NK cells.

Parents' attitude toward multiple vaccinations at a single visit with alternative delivery methods

Last decades, the number of routine childhood vaccinations has increased considerably, which consequently has led to multiple vaccine injections per consultation. Implementation of additional vaccines will probably lead to more than 2 vaccine injections per consult, which might be a barrier for parents to vaccinate their child. A decrease in vaccination coverage, however, increases the risk of disease outbreaks. Less stressful alternative methods for vaccine delivery might lead to an increased acceptance of multiple childhood vaccinations by parents. The present questionnaire study was set up to explore the maximum number of vaccine injections per visit that is acceptable for parents, as well as to gauge parents’ attitude toward alternative needle-free methods for vaccine delivery. For this purpose, the parents’ opinion toward a jet injector, a patch, a microneedle system, and nasal spray device as methods for vaccine delivery was assessed. The majority of the 1154 participating parents indicated that 3 vaccine injections per visit was perceived as too much. Most participants had a positive attitude with respect to the jet injector and the patch as alternative vaccine delivery method, whereas the microneedle device and an intranasal spray device were not perceived as better than the conventional syringe by the parents. Parents indicated that both the jet injector and the patch might increase their acceptance of giving their children more than 2 vaccinations at the same time. This should encourage vaccine developers and manufacturers to put efforts in developing these delivery methods for their vaccines.

Dynamics of the serologic response in vaccinated and unvaccinated mumps cases during an epidemic

In the last decade, several mumps outbreaks were reported in various countries despite high vaccination coverage. In most cases, young adults were affected who have acquired immunity against mumps solely by vaccination and not by previous wild-type mumps virus infection. To investigate mumps-specific antibody levels, functionality and dynamics during a mumps epidemic, blood samples were obtained longitudinally from 23 clinical mumps cases, with or without a prior history of vaccination, and from 20 healthy persons with no serological evidence of recent mumps virus infection. Blood samples from mumps cases were taken 1-2 months and 7-10 months after onset of disease. Both vaccinated and unvaccinated mumps cases had significantly higher geomean concentrations of mumps-specific IgG (resp. 13,617 RU/ml (95% CI of 9,574-19,367 RU/ml) vs. 1,552 (445-5412) RU/ml at 1-2 months; and 6,514 (5,247-8,088) RU/ml vs. 1,143 (480-2,725) RU/ml at 7-10 months) than healthy controls (169 (135-210) RU/ml) (p = 0.001). Patterns in virus-neutralizing (VN) antibody responses against the mumps vaccine virus were similar, vaccinated and unvaccinated mumps cases had significantly higher ND50 values at both time points of sampling (resp 4,695 (3,779-5,832) RU/ml vs. 1,533 (832-2,825) RU/ml at 1-2 months; 2,478 (1,968-3,122) RU/ml vs. 1,221 (1,029-1,449) RU/ml at 7-10 months) compared with (previously vaccinated) healthy controls (122 (196-76)) RU/ml) (p = 0.001) The unvaccinated mumps cases had significantly lower mumps-specific IgG and VN antibody concentrations at both sampling points compared with previously vaccinated cases, but their antibody concentrations did not differ significantly at the 2 time points. In contrast, the mumps-specific IgG and VN antibody concentrations of the previously vaccinated mumps cases were significantly higher within the first 2 months after onset of mumps and declined thereafter, characteristic for a secondary response. A moderate correlation was found between the level of mumps-specific IgG serum antibodies and VN antibodies for the mumps cases (r = 0.64; p<0.001).

Routine vaccination against MenB: considerations for implementation

Effective polysaccharide(conjugate) vaccines against Neisseria meningitidis serogroups A, C, W, and Y have been widely used, but serogroup B meningococci remain a major cause of severe invasive meningococcal disease (IMD) worldwide, especially in infants. Recently, a vaccine, 4CMenB (Bexsero^®), containing three recombinant proteins, and outer membrane vesicles (OMV) derived from a serogroup B meningococcal strain (MenB) has been licensed in Europe and Australia and is indicated for persons aged 2 mo or older. This article discusses what should be considered to enable a successful implementation of a broad coverage MenB vaccine in national immunization programs. Epidemiology data, vaccine characteristics including vaccine coverage, immunogenicity, post-implementation surveillance and costs are relevant aspects that should be taken into account when selecting an appropriate immunization strategy. The potential impact on strain variation and carriage, as well as monitoring vaccine effectiveness, and rare but potentially serious adverse events are points that need to be included in a post-implementation surveillance plan.

Preclinical evaluation of MenB vaccines: prerequisites for clinical development

Despite the widespread use of polysaccharide and conjugate vaccines against disease caused by several serogroups of Neisseria meningitidis, vaccines targeting meningococci expressing the serogroup B capsule (MenB) have focused on subcapsular antigens, due to crossreactivity of the polysaccharide with human glycoproteins. Protein vaccines composed of outer membrane vesicles have been used successfully to control epidemics of MenB disease in several countries; however, these are specific for epidemic strains. Currently, a single serogroup B vaccine, aiming to provide comprehensive coverage, has been approved for use, and several others are undergoing clinical trials. Data on potential new vaccine candidates, from discovery to initial preclinical evaluation, are regularly published. In this review, the data required to progress from preclinical to clinical development of MenB vaccines are outlined, with reference to relevant regulatory guidelines. The issues caused by a lack of reliable animal models, particularly with respect to determination of protective efficacy, are also discussed.

Improved production process for native outer membrane vesicle vaccine against Neisseria meningitidis

An improved detergent-free process has been developed to produce vaccine based on native outer membrane vesicles (NOMV) against Neisseria meningitidis serogroup B. Performance was evaluated with the NonaMen vaccine concept, which provides broad coverage based on nine distinct PorA antigens. Scalable aseptic equipment was implemented, replacing undesirable steps like ultracentrifugation, inactivation with phenol, and the use of preservatives. The resulting process is more consistent and gives a higher yield than published reference processes, enabling NOMV production at commercial scale. Product quality met preliminary specifications for 9 consecutive batches, and an ongoing study confirmed real-time stability up to 12 months after production. As the NOMV had low endotoxic activity and induced high bactericidal titres in mice, they are expected to be safe and effective in humans. The production process is not limited to NonaMen and may be applicable for other N. meningitidis serogroups and other gram-negative pathogens. The current results therefore facilitate the late-stage development and clinical evaluation of NOMV vaccines.

Vaccination against RSV: is maternal vaccination a good alternative to other approaches?

The respiratory syncytial virus (RSV) is the major cause of lower respiratory tract illness (LRI) in infants worldwide. Also persons with heart/lung disease or an immunodeficiency disorder, and the elderly are at increased risk for severe LRI upon RSV infection. Although there is at present no licensed RSV vaccine available, it is a priority target for several vaccine developers. For the implementation of a future RSV vaccination within national immunization schemes, various strategies can be considered even without the availability of extended clinical data on RSV vaccines. For this purpose, the extensive knowledge on RSV with respect to disease pathology, epidemiology and immunology can be used. This article discusses different aspects that should be considered to enable a successful implementation of a new RSV vaccine in national immunization programs. In addition, gaps in knowledge that needs further attention are identified. The maternal immunization strategy is highlighted, but also vaccination in the youngest infants and specific risk group immunization strategies are evaluated in this paper. Key factors such as the seasonality of RSV disease, interference of maternal antibodies and the immaturity of the infants’ immune system are addressed.

Nonclinical vaccine safety evaluation: advantages of continuous temperature monitoring using abdominally implanted data loggers

Fever has been reported as the most common adverse event after vaccination in infants and children. For this reason it is important that, prior to clinical testing of a new vaccine, change in body temperature following vaccination is tested carefully in nonclinical animal studies. Since both the timing and the height of the temperature peak after vaccination may differ from vaccine to vaccine, it is important that the time point for body temperature measurement should be chosen on a case-by-case basis with sufficient knowledge of the specific vaccine. In order to determine the best time point for rectal body temperature measurement after vaccination with a new vaccine candidate against N. meningitidis serogroup B, to be applied in a formal Good Laboratory Practice (GLP) toxicology study, miniature temperature data loggers were implanted into the peritoneal cavity of rabbits. The continuous body temperature monitoring appeared to give a complete picture of the entire body temperature kinetics after vaccination. The body temperature peaked at 4 h after vaccination, and this time point was subsequently applied in the toxicology study. Measured body temperature values at the selected time point of 4 h after vaccination were comparable in the continuous temperature setting and in the formal toxicology study, i.e. rectal temperature measurement at one time point. In the present study implanted temperature loggers were successfully used to define an adequate time point to be applied in determining rectal body temperature in a formal GLP toxicology study with a new vaccine candidate.

Is a single dose of meningococcal serogroup C conjugate vaccine sufficient for protection? experience from the Netherlands

BACKGROUND

The first meningococcal serogroup C (MenC) conjugate vaccine was licensed in 1999 and introduced in the United Kingdom. Countries that have implemented the MenC vaccine since then in their national immunisation programmes use different schedules. Nevertheless, all involved countries seem to experience substantial declines in the incidence of MenC disease.

DISCUSSION

Since 2001, the MenC conjugate vaccine has been implemented in the Netherlands by offering a single dose to all children aged 14 months. Prior to the introduction of the vaccine into the national immunisation programme, a catch-up vaccination campaign was initiated in which a single dose of the MenC conjugate vaccine was offered to all children aged from 14 months up to and including 18 years. Since then, there has been no report of any case of MenC disease among immunocompetent vaccinees. Administration of a single dose of MenC conjugate vaccine after infancy could be beneficial considering the already complex immunisation schedules with large numbers of vaccinations in the first year of life. The present paper deals with the advantages and critical aspects of a single dose of the MenC conjugate vaccine.

SUMMARY

A single dose of MenC conjugate vaccine at the age of 14 months in combination with a catch up vaccine campaign appeared to be a successful strategy to prevent MenC disease in the Netherlands, thereby confirming that a single dose of the vaccine could sufficiently protect against disease. Nevertheless, this approach can only be justified in countries with a relatively low incidence of serogroup C meningococcal disease in the first year of life. Furthermore, a good surveillance programme is recommended for timely detection of vaccine breakthroughs and outbreaks among non-vaccinees, since long-term protection after a single dose in the second year of life cannot currently be guaranteed.

Hepatitis B vaccination strategies tailored to different endemicity levels: some considerations

Hepatitis B is a serious public health problem. Worldwide three different levels of hepatitis B endemicity (high, intermediate and low) can be distinguished. Areas with different levels of endemicity require tailored vaccination strategies to fit the needs for individuals at risk and/or countries, depending on the infection risk per age group, vaccination rate, duration of protection after vaccination, cost effectiveness of vaccination strategies and ease of implementation in the national immunization schedules.This opinion paper evaluates these factors and proposes a combination of infant risk group and universal adolescent vaccination for low endemic countries thus targeting the different groups at risk. A universal infant vaccination schedule starting with a newborn vaccination within 24h after birth is more appropriate in intermediate- and high-endemic regions.

Increased mumps incidence in the Netherlands: Review on the possible role of vaccine strain and genotype

As reported in a recent issue of Eurosurveillance, a mumps outbreak is ongoing in the Netherlands despite high vaccination coverage of 90-95% [1]. The reported mumps cases are restricted to geographic regions with a high percentage of residents who are members of a religious community that rejects vaccination. Consequently, two thirds of the mumps patients were not vaccinated. However, also vaccinated individuals in these regions were affected [1]. Since 1987, the measles-mumps-rubella (MMR) combination vaccine produced by the Netherlands Vaccine Institute (NVI) is part of the Dutch national immunisation programme and administered at the ages of 14 months and nine years.

In vitro sensitivity and cross-resistance to deoxynucleoside analogs in childhood acute leukemia

BACKGROUND AND OBJECTIVES

Cytarabine (ara-C) is a key drug in the treatment of acute leukemia. Resistance to ara-C might be circumvented by the use of other deoxynucleoside analogs.

DESIGN AND METHODS

Using the MTT assay, we determined in vitro sensitivity and cross-resistance to deoxynucleoside analogs in 362 acute leukemia samples from untreated children and 32 normal bone marrow mononuclear cell samples.

RESULTS

Normal bone marrow samples were significantly more resistant to ara-C, cladribine and fludarabine than were acute myeloid leukemia (AML) samples and significantly more resistant to ara-C and fludarabine than were acute lymphoblastic leukemia (ALL) samples. The only drug to which AML samples were more sensitive in vitro than ALL was cladribine. AML FAB M5 was significantly more sensitive in vitro to ara-C and cladribine than FAB M1/2 or FAB M4. T-ALL was significantly more resistant to cladribine than B-cell precursor ALL. A paired analysis of 60 AML and 99 ALL samples demonstrated significant cross-resistance between all four deoxynucleoside analogs. Cross-resistance was also observed between ara-C and etoposide (Rp=0.54, p<0.0001), and ara-C and daunorubicin (Rp=0.48, p<0.0001) in AML. In ALL blasts, cross-resistance was observed between ara-C and vincristine (Rp=0.50; p<0.0001), and between ara-C and daunorubicin and L-asparaginase (Rp=0.25; p=0.01; Rp=0.28; p=0.005).

INTERPRETATION AND CONCLUSIONS

Cladribine appears to be a useful drug in AML, particularly in FAB M5. We observed cross-resistance between ara-C and other deoxynucleoside analogs, as well as between ara-C and drugs with different modes of action in childhood acute leukemia.

Expression of a natural tumor antigen by thymic epithelial cells impairs the tumor-protective CD4+ T-cell repertoire

A variety of antigens that display a highly tissue-specific expression pattern have recently found to be also expressed in medullary thymic epithelial cells (mTEC). This unique feature of mTEC plays an important role in preventing hazardous autoimmune responses through thymic tolerization of T-cell subsets directed against autoantigens but could also limit the possibility of exploiting tumor-associated antigens for immune-mediated targeting of cancers. Our present study shows that expression of carcinoembryonic antigen (CEA) in thymic epithelial cells of CEA-transgenic mice results in tolerization of a major fraction of the CD4+ T-cell repertoire against this antigen, thereby markedly limiting the effect of CEA-specific immunization against CEA-overexpressing tumors. The expression of CEA in mTEC of CEA-transgenic mice is mirrored by its expression in human mTEC, arguing that promiscuous gene expression in these thymic stromal cells needs to be considered as a potential hurdle for immunotherapies of cancer that target tissue-specific autoantigens.

Effect of single dose irradiation on human glioblastoma spheroids in vitro

Investigation of the predictive value of a radiosurgery-relevant treatment of glioblastoma spheroids. Organotypic multicellular spheroids were cultured and irradiated (20 Gy). Morphology, apoptosis and immunohistochemical expression of p53, p21, MIB-1, TGF-beta and VEGF were examined 4 h, 24 h, 7 days, and 14 days following treatment. Cell proliferation decreased, while apoptosis was increased. No morphological damage was observed. p53 expression was significantly increased after 4 h. TGF-beta and VEGF expression were only slightly altered. Particularly early changes in proliferation and apoptosis can be observed in spheroids. Individual response differences suggest spheroids of human gliomas to be useful for monitoring radiosurgery effects.

In vitro cytotoxicity of aplidin and crossresistance with other cytotoxic drugs in childhood leukemic and normal bone marrow and blood samples: a rational basis for clinical development

To determine the potential of aplidin as a cytotoxic agent in pediatric leukemia, we tested bone marrow (BM) and peripheral blood (PB) samples (n=72) of children with different types of leukemia and healthy children in the methyl-thiazol-tetrazolium assay. Also, we compared these results with other cytotoxic drugs. Aplidin was cytotoxic in vitro at nanomolar concentrations, in a dose-dependent fashion. L-carnitine, that is applied in clinical studies to prevent myotoxicity caused by aplidin, had no effect on aplidin cytotoxicity in vitro. Aplidin cytotoxicity in vitro was not different when initial and relapsed acute lymphoblastic leukemia (ALL) or initial ALL and initial acute myeloid leukemia were compared. However, normal BM (n=19) and PB (n=13) cells were more resistant to aplidin than leukemic cells (median two- to seven-fold, P=0.001 and median four- to 11-fold, P&<0.0001, respectively). In leukemia samples, no significant crossresistance between aplidin and other cytotoxic drugs was found, except for a trend for correlation with 2',2'-difluorodeoxycytidine (rho=0.71, P=0.02). In normal BM samples, significant crossresistance with the epipodophyllotoxins was found, which is not readily explained by the currently known mechanisms of action of aplidin. In conclusion, we show that aplidin has selective cytotoxicity in vitro towards childhood leukemia cells and generally lacks crossresistance with other known cytotoxic drugs, which warrants clinical studies.

Cell proliferation is related to in vitro drug resistance in childhood acute leukaemia

Bone marrow and peripheral blood samples from 362 patients with acute lymphoblastic leukaemia (ALL) proliferating cell and 90 patients with acute myeloid leukaemia (AML) were analysed for S-phase fractions, Ki67 antigen, and proliferating cell nuclear antigen expression. The S-phase fractions were correlated with in vitro drug resistance to 15 different anticancer agents. Leukaemia cells isolated from bone marrow had higher S-phase fractions than leukaemia cells isolated from peripheral blood (in initial ALL, median values resp. 6.9 and 2.7%, in initial AML resp. 5.3 and 1.3%; both P<0.01). Relapse ALL samples derived from bone marrow showed increased S-phase fractions (median 9.9%) compared with initial ALL samples (median 6.9%; P<0.01). ALL samples obtained at initial diagnosis showed higher S-phase fractions (median 6.9%) and higher Ki67 expression (median 30%) than initial AML samples (median resp. 5.3 and 14%; both P<0.05). The S-phase fractions were not related to white blood cell count, age, or gender. Within initial ALL, the S-phase fraction correlated significantly but modestly strong (rho=0.3-0.5; P<0.05) with sensitivity to antimetabolites (cytarabine, mercaptopurine, thioguanine), L-asparaginase, teniposide, and vincristine. Similar results were found within subgroups of initial ALL (nonhyperdiploid and common/precursor-B-lineage ALL). In relapsed ALL and AML such correlations were not found. In conclusion, cell proliferation differs between leukaemia subgroups and increased proliferation is associated with increased in vitro sensitivity to several anticancer agents in initial ALL.

Oxygenation and response to irradiation of organotypic multicellular spheroids of human glioma

PURPOSE

Investigation of the oxygenation status of organotypic multicellular spheroids (OMS) and their response to irradiation.

MATERIALS AND METHODS

Tumour specimens of glioblastoma multiforme patients (n = 16) were initiated as OMS. Following 20 Gy gamma-irradiation, the cell migratory capacity was evaluated. Spheroid oxygenation was determined by micro-electrode pO2 measurements and pimonidazole immunostaining. Spheroids prepared from established human glioma cell lines were used as a reference.

RESULTS

Irradiation inhibited spheroid outgrowth by 12 to 88% relative to the non-irradiated controls. A large interpatient variation was noticed. Oxygen measurements revealed a gradual decrease in pO2 level from the periphery to the core of the spheroids, but the pO2 values remained within an oxygenated range. However, in the cell line spheroids an intermediate layer of hypoxia surrounding the central core was observed.

CONCLUSION

Cell line spheroids with a hypoxic cell fraction and well-oxygenated OMS both show high resistance to irradiation, indicating that hypoxia may not be the biological factor determining the radioresistance of glioma spheroids in vitro.

Past, current and future protocols for combined modality therapy in childhood medulloblastoma

Radiotherapy plays a major role in the management of brain tumors, together with surgical resection and more recently, chemotherapy. Improved efficacy of radiotherapy, ranging from novel techniques of radiotherapy to combination with (new) chemotherapeutic drugs or agents that selectively target tumor cells, are currently being explored and offer some hope for improvement of the prognosis of primary brain tumors. This approach might also enable reducing radiation doses, thereby potentially decreasing the risk of severe late effects in pediatric brain tumor patients. This review will evaluate past, current and future treatment approaches of combined modality therapy in childhood medulloblastoma.

High concentration of Daunorubicin and Daunorubicinol in human malignant astrocytomas after systemic administration of liposomal Daunorubicin

The value of chemotherapy in patients with malignant astrocytoma remains controversial. In our laboratories in vitro experiments with organotypic spheroid cultures showed superior effectiveness of anthracyclines. Systemic administration did not provide in therapeutic concentrations so far. Because recent studies on Daunorubicin in liposomes in the treatment of Kaposi sarcoma have shown effectiveness with diminished systemic toxicity, we administered intravenously a single dose of Daunorubicin in liposomes in eight patients at different intervals prior to surgery (12-50 h). In samples taken from tumor, tumor-edge and where possible from adjacent brain, the levels of Daunorubicin and its active metabolite Daunorubicinol were assessed with high performance liquid chromatography. Here we report that high concentrations of Daunorubicin and Daunorubicinol were found in malignant gliomas after systemic administration of liposomal Daunorubicin.

In vitro and in vivo models for the study of brain tumour invasion

Since it is difficult to study the dynamic biological aspects of brain tumour invasion using histological sections of surgical biopsy and autopsy tissues, various laboratory systems have been devised. Animal models are less than ideal as chemically-induced brain tumours suffer from the fact that they have a low incidence and a long latency, while transplanted tumours grow predominantly by expansion, due to high proliferative activity, and not by diffuse local invasion as in human brain tumours. Various in vitro assays have, therefore, been established for both migration and invasion. These include the simple scratch technique in a confluent cell monolayer, the use of cloning rings and the "Transwell" modified Boyden chamber technique. More complex, three-dimensional culture model systems have also been developed, using chick heart, optic nerve or reaggregated fetal brain as "targets" for the invasion of neoplastic glia. Each method has yielded important information on the mechanisms which underlie brain tumour invasion. Moreover, individual microenvironmental factors may be modulated in these laboratory systems to determine their influence on the migration/invasion process.

Hypofractionated radiation induces a decrease in cell proliferation but no histological damage to organotypic multicellular spheroids of human glioblastomas

The aim of this study was to examine the effect of radiation on glioblastoma, using an organotypic multicellular spheroid (OMS) model. Most glioblastoma cell lines are, in contrast to glioblastomas in vivo, relatively radiosensitive. This limits the value of using cell lines for studying the radiation effect of glioblastomas. The advantage of OMS is maintenance of the characteristics of the original tumour, which is lost in conventional cell cultures. OMS prepared from four glioblastomas were treated with hypofractionated radiation with a radiobiologically equivalent dose to standard radiation treatment for glioblastoma patients. After treatment, the histology as well as the cell proliferation of the OMS was examined. After radiation, a significant decrease in cell proliferation was found, although no histological damage to the OMS was observed. The modest effects of radiation on the OMS are in agreement with the limited therapeutic value of radiotherapy for glioblastoma patients. Therefore, OMS seems to be a good alternative for cell lines to study the radiobiological effect on glioblastomas.

Differential expression of CD44 splice variants in the normal human central nervous system

Cluster of differentiation 44 (CD44) is a broadly distributed group of glycoproteins that are involved in many functions related to cell-cell and cell-matrix interactions. In the present study, the expression of the standard form of CD44 (CD44s) and of CD44 variants (CD44v) was explored immunohistochemically on frozen sections of various areas of the human CNS. The results demonstrate that CD44s epitopes are expressed predominantly by white matter astrocytes, whereas different CD44 variant molecules are present in neurons, on axonal membranes, on endothelium or on choroid plexus epithelium. Interestingly, neurons and axons differentially expressed CD44 variant epitopes but consistently lack immunoreactivity for CD44s epitopes. Another interesting finding was that some CD44 variant epitopes expressed by neurons were localized in the cytoplasm instead of on the cell membrane. The broad distribution of variant CD44 molecules in the human CNS suggests that CD44 may play an important role in many biological processes in the CNS.

Cryopreservation of organotypic multicellular spheroids from human gliomas

Fresh human glioma tissue can be cultured on agarose to form organotypic multicellular spheroids (OMS). The major advantage of OMS is the preservation of the cellular heterogeneity and the tumour architecture, which is lost in conventional monolayer cultures. The present study was undertaken to assess the possibilities of storing frozen OMS from seven gliomas which were frozen to determine the viability after thawing. OMS were frozen slowly to -196 degrees C using a programmable freezing machine in culture medium containing 45% serum and 10% of the cryopreservative agent dimethyl sulphoxide (DMSO). After 2 weeks storage at -196 degrees C, quick thawing, and culturing for another week, it appeared that the frozen-thawed OMS were viable and retained their histological characteristics. In addition, it is demonstrated that the cellular constituents of the OMS resumed metabolic and proliferative activities. It is concluded that it is possible to establish frozen stocks of viable glioma OMS. This will enable extensive studies on OMS, such as investigation of the biological behaviour of gliomas by using OMS obtained from primary and corresponding recurrent gliomas. In addition, cryopreservation of OMS makes it possible to correlate the results of in vitro tests on OMS with the patients' responses to similar therapeutic approaches.

Daunorubicin and doxorubicin but not BCNU have deleterious effects on organotypic multicellular spheroids of gliomas

In the present study organotypic multicellular spheroids (OMS) were used to study the effects of chemotherapeutic agents on malignant gliomas. Compared with the frequently used cell line models, OMS have several advantages with respect to the preservation of the cellular heterogeneity and the structure of the original tumour. OMS prepared from seven glioma specimens were treated with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), daunorubicin or doxorubicin. After exposure to these drugs, the histology and cell proliferation of the OMS were analysed by immunohistochemistry and image analysis. Furthermore, the expression of P-glycoprotein (P-gp) and multidrug resistance-related protein (MRP), which both can contribute to resistance to daunorubicin and doxorubicin, were immunohistochemically investigated. We found that OMS from gliomas are sensitive for daunorubicin and doxorubicin but not for BCNU in terms of tissue destruction and decrease in cell proliferation. In addition, all gliomas were P-gp and MRP negative, which is in accordance with the sensitivity for daunorubicin and doxorubicin. Considering the potential use of several new alternative drug delivery methods, such as intratumoural implantation of drug-impregnated polymers or liposomal encapsulation of cytostatic drugs, daunorubicin and doxorubicin might be effective in the treatment of malignant gliomas.

Expression of CD44 splice variants in human primary brain tumors

Expression of CD44, particularly of certain splice variants, has been linked to tumor progression and metastatic potential in a number of different animal and human cancers. Although differential expression of CD44 standard epitopes (CD44s) in human brain tumors has been reported, the expression of CD44 variant exon encoded sequences (CD44v) in primary brain tumors in situ has not been studied in detail. In the present study, the expression of CD44s and CD44v epitopes was analyzed immunohistochemically on frozen sections of primary brain tumors. In addition, the expression of CD44 on cultured glioma cells was investigated by immunofluorescence flow cytometry. The results demonstrate the presence of CD44s epitopes and of CD44 splice variants containing CD44v4, v5 and v10 sequences in various types of brain tumors. A subgroup of highly malignant gliomas showed a strong (focal) expression of CD44v5. CD44v6 was absent in all brain tumors examined. CD44s appeared to be the dominant form of CD44 expressed in primary brain tumors, its expression was not correlated with tumor grade. We envisage that CD44 isoforms, in particular CD44s, may contribute to the invasive character of primary tumors by interacting with hyaluronate, one of the most abundant molecules in the extracellular matrix of the brain.

Cytolytic effects of autologous lymphokine-activated killer cells on organotypic multicellular spheroids of gliomas in vitro

Knowledge about lymphokine-activated killer (LAK) cell infiltration and LAK cell cytotoxicity is essential to improve the effectiveness of LAK cell therapy against gliomas. In the present study, organotypic multicellular spheroids (OMS) of glioma tissue were used as a culture model to study the effects of LAK cells on gliomas. Compared to tumour cell lines and spheroids derived from tumour cell lines, OMS have several advantages with respect to preservation of tumour cell heterogeneity and the maintenance of the tumour architecture, e.g. capillaries and extracellular matrix. Four glioma specimens, obtained at surgery, were cultured directly on agarose to form OMS, which were then co-cultured with either autologous LAK cells or autologous non-activated peripheral blood lymphocytes (PBLs). After various time periods of co-cultivation, the OMS were fixed and examined both histologically and immunocytochemically. The present results showed that LAK cells infiltrated the OMS completely within 24 h of co-cultivation and severe cellular damage was observed, whereas PBLs infiltrated the OMS poorly and there was only marginal cellular damage. The present study indicates that OMS of gliomas provide an experimental model to investigate the infiltration and cytotoxicity of LAK cells on glioma tissue in vitro.

Long-term culture of organotypic multicellular glioma spheroids: a good culture model for studying gliomas

Gliomas, as well as other solid tumours, contain tumour stroma composed of connective tissue, macrophages, capillaries and other non-cellular constituents. Therefore, a homogeneous culture of tumour cells alone, as is often used as a culture model for gliomas, is not ideal to study all aspects of gliomas. In the present study we describe an alternative culture model, i.e. organotypic multicellular spheroids (OMS), that histologically closely resembles the tumour in vivo. Glioma explants, obtained at surgery from five patients, were cultured on agarose to form OMS, which were cultured for up to 16 weeks. At regular intervals, OMS were fixed and histological and immunocytochemical analyses were carried out. The histology as well as the immunocytochemical characteristics of the OMS proved to be almost unchanged after a culture period of 16 weeks. In contrast to monolayer cultures, glial fibrillary acidic protein (GFAP) expression in the OMS is preserved after 16 weeks of culture. However, in OMS from three out of five patients, small GFAP-negative cells appeared in the outer cell layers between 1 and 2 weeks of culture. Furthermore, after about 6 weeks of culture, the capillaries disappeared from the OMS. After prolonged culture, tumour cell heterogeneity, the cellular composition, and the histology of the OMS still closely resembled the tumour in vivo. It is suggested that OMS provide a good long-term culture model for the study of gliomas.

Overexpression of a M(r) 110,000 vesicular protein in non-P-glycoprotein-mediated multidrug resistance

A M(r) 110,000 protein (p110) is overexpressed in P-glycoprotein-negative multidrug-resistant tumor cell lines of different histogenetic origins. These cell lines show an ATP-dependent drug accumulation defect, suggesting the presence of drug transporter molecules different from P-glycoprotein. Immunohistochemical staining with a p110-specific monoclonal antibody (LRP-56) showed that, like P-glycoprotein, the molecule has a high expression in normal epithelial cells and tissues chronically exposed to xenobiotics and potentially toxic agents, such as bronchial cells, cells lining the intestines, and kidney tubules. Staining of LRP-56 is primarily cytoplasmic, in a coarsely granular fashion, indicating that it reacts with a molecule closely associated with vesicular/lysosomal structures. Involvement of p110 in the energy-dependent drug transport process present in the cell lines is unknown.