Predicting time to asystole following withdrawal of life-sustaining treatment: a systematic review

The planned withdrawal of life-sustaining treatment is a common practice in the intensive care unit for patients where ongoing organ support is recognised to be futile. Predicting the time to asystole following withdrawal of life-sustaining treatment is crucial for setting expectations, resource utilisation and identifying patients suitable for organ donation after circulatory death. This systematic review evaluates the literature for variables associated with, and predictive models for, time to asystole in patients managed on intensive care units. We conducted a comprehensive structured search of the MEDLINE and Embase databases. Studies evaluating patients managed on adult intensive care units undergoing withdrawal of life-sustaining treatment with recorded time to asystole were included. Data extraction and PROBAST quality assessment were performed and a narrative summary of the literature was provided. Twenty-three studies (7387 patients) met the inclusion criteria. Variables associated with imminent asystole (<60 min) included: deteriorating oxygenation; absence of corneal reflexes; absence of a cough reflex; blood pressure; use of vasopressors; and use of comfort medications. We identified a total of 20 unique predictive models using a wide range of variables and techniques. Many of these models also underwent secondary validation in further studies or were adapted to develop new models. This review identifies variables associated with time to asystole following withdrawal of life-sustaining treatment and summarises existing predictive models. Although several predictive models have been developed, their generalisability and performance varied. Further research and validation are needed to improve the accuracy and widespread adoption of predictive models for patients managed in intensive care units who may be eligible to donate organs following their diagnosis of death by circulatory criteria.

The Ability of a Non-Egg Adapted (Cell-Like) A(H1N1)pdm09 Virus to Egg-Adapt at HA Loci Other than 222 and 223 and Its Effect on the Yield of Viral Protein

Previous studies on influenza A(H1N1)pdm09 candidate vaccine viruses (CVVs) that had adapted to growth in embryonated chicken eggs by the acquisition of amino acid substitutions at HA positions 222 or 223 showed that improved protein yield could be conferred by additional amino acid substitutions in the haemagglutinin (HA) that arose naturally during passaging of the virus in eggs. In this study we investigated, by means of reverse genetics, the ability of a non-egg adapted (cell-like) A(H1N1)pdm09 virus to egg-adapt at HA loci other than 222/223, introducing amino acid substitutions previously identified as egg adaptations in pre-H1N1pdm09 H1N1 viruses and assessing their effect on protein yield and antigenicity. We also investigated the effect on the protein yield of these substitutions in viruses that had A(H1N1)pdm09 internal genes rather than the traditional PR8 internal genes of a CVV. The data show that a cell-like A/Christchurch/16/2010 can be egg-adapted via amino acid substitutions in at least three alternative HA loci (187, 190 and 216), in viruses with either PR8 or A/California/7/2009 internal genes, but that the effects on protein yield vary depending on the amino acid substitution and the internal genes of the virus. Since CVVs need to produce high protein yields to be suitable for vaccine manufacture, the findings of this study will assist in the future characterisation of both wild type viruses and lab-derived CVVs for vaccine use.

Development of Lentivirus-Based Reference Materials for Ebola Virus Nucleic Acid Amplification Technology-Based Assays

The 2013-present Ebola virus outbreak in Western Africa has prompted the production of many diagnostic assays, mostly based on nucleic acid amplification technologies (NAT). The calibration and performance assessment of established assays and those under evaluation requires reference materials that can be used in parallel with the clinical sample to standardise or control for every step of the procedure, from extraction to the final qualitative/quantitative result. We have developed safe and stable Ebola virus RNA reference materials by encapsidating anti sense viral RNA into HIV-1-like particles. The lentiviral particles are replication-deficient and non-infectious due to the lack of HIV-1 genes and Envelope protein. Ebola virus genes were subcloned for encapsidation into two lentiviral preparations, one containing NP-VP35-GP and the other VP40 and L RNA. Each reference material was formulated as a high-titre standard for use as a calibrator for secondary or internal standards, and a 10,000-fold lower titre preparation to serve as an in-run control. The preparations have been freeze-dried to maximise stability. These HIV-Ebola virus RNA reference materials were suitable for use with in-house and commercial quantitative RT-PCR assays and with digital RT-PCR. The HIV-Ebola virus RNA reference materials are stable at up to 37°C for two weeks, allowing the shipment of the material worldwide at ambient temperature. These results support further evaluation of the HIV-Ebola virus RNA reference materials as part of an International collaborative study for the establishment of the 1^st International Standard for Ebola virus RNA.

Permissible variation in the 3' non-coding region of the haemagglutinin genome segment of the H5N1 candidate influenza vaccine virus NIBRG-14 [corrected]

The candidate H5N1 vaccine virus NIBRG-14 was created in response to a call from the World Health Organisation in 2004 to prepare candidate vaccine viruses (CVVs) to combat the threat of an H5N1 pandemic. NIBRG-14 was created by reverse genetics and is composed of the neuraminidase (NA) and modified haemagglutinin (HA) genes from A/Vietnam/1194/2004 and the internal genes of PR8, a high growing laboratory adapted influenza A(H1N1) strain. Due to time constraints, the non-coding regions (NCRs) of A/Vietnam/1194/2004 HA were not determined prior to creating NIBRG-14. Consequently, the sequence of the primers used to clone the modified A/Vietnam/1194/2004 HA was based upon previous experience of cloning H5N1 viruses. We report here that the HA 3′ NCR sequence of NIBRG-14 is different to that of the parental wild type virus A/Vietnam/1194/2004; however this does not appear to impact on its growth or antigen yield. We introduced additional small changes into the 3′NCR of NIBRG-14; these had only minor effects on viral growth and antigen content. These findings may serve to assure the influenza vaccine community that generation of CVVs using best-guess NCR sequences, based on sequence alignments, are likely to produce robust viruses.

An additional oligosaccharide moiety in the HA of a pandemic influenza H1N1 candidate vaccine virus confers increased antigen yield in eggs

The H1N1 influenza pandemic in 2009 highlighted the need for the rapid generation of candidate vaccine viruses (CVVs) against an A/California/7/2009-like virus. The first available CVVs gave low protein yields in eggs but improved yields were achieved for second generation CVVs which contained amino acid substitutions compared to their precursor viruses. In this study, we investigated the basis for the increased virus protein yield of CVV NIBRG-121xp and whether the improved yield characteristics could be transferred between this virus and two other CVVs, NYMC X-179A and NYMC X-181. We generated variant viruses by reverse genetics to contain combinations of amino acid substitutions found in high yielding NIBRG-121xp and NYMC X-181. We found that the increase in total protein yield and functional HA yield of NIBRG-121xp in eggs is attributable to the single amino acid substitution K119N in the HA. We also found that the glycosylation of position 119 is essential for the improved virus protein yield in eggs. However, the K119N yield-enhancing effect was not transferable between viruses, nor was the N129D change found in high yielding NYMC X-181. However, position 119 may be a useful locus to monitor in future for viruses and CVVs with potentially high yield.

The development of vaccine viruses against pandemic A(H1N1) influenza

Wild type human influenza viruses do not usually grow well in embryonated hens' eggs, the substrate of choice for the production of inactivated influenza vaccine, and vaccine viruses need to be developed specifically for this purpose. In the event of a pandemic of influenza, vaccine viruses need to be created with utmost speed. At the onset of the current A(H1N1) pandemic in April 2009, a network of laboratories began a race against time to develop suitable candidate vaccine viruses. Two approaches were followed, the classical reassortment approach and the more recent reverse genetics approach. This report describes the development and the characteristics of current pandemic H1N1 candidate vaccine viruses.

Improved haemagglutinin antigen content in H5N1 candidate vaccine viruses with chimeric haemagglutinin molecules

The candidate vaccine virus NIBRG-14 was derived by reverse genetics and comprises the haemagglutinin (HA) and neuraminidase (NA) genes derived from the clade 1 virus A/Viet Nam/1194/2004 on an A/Puerto Rico/8/34 (PR8) backbone. The HA gene was modified to remove the multibasic cleavage site motif associated with high pathogenicity. Reports from manufacturers, confirmed by data generated in this laboratory, have shown that this virus yields a low amount of HA antigen. We have generated a panel of new viruses using reverse genetics in which each virus consists of the PR8 backbone, the NA gene from A/Viet Nam/1194/2004 and a chimeric HA gene with sequences from both PR8 and A/Viet Nam/1194/2004. Here we show that a number of these viruses have improved HA antigen content and yield and are therefore better candidate vaccine viruses for use in production of H5N1 vaccine.

A sensitive retroviral pseudotype assay for influenza H5N1-neutralizing antibodies

BACKGROUND

The World Health Organisation (WHO) recommended the development of simple, safe, sensitive and specific neutralization assays for avian influenza antibodies. We have used retroviral pseudotypes bearing influenza H5 hemagglutinin (HA) as safe, surrogate viruses for influenza neutralization assays which can be carried out at Biosafety Level 2.

RESULTS

Using our assay, sera from patients who had recovered from infection with influenza H5N1, and sera from animals experimentally immunized or infected with H5 tested positive for the presence of neutralizing antibodies to H5N1. Pseudotype neutralizing antibody titers were compared with titers obtained by hemagglutinin inhibition (HI) assays and microneutralization (MN) assays using live virus, and showed a high degree of correlation, sensitivity and specificity.

CONCLUSIONS

The pseudotype neutralization assay is as sensitive as horse erythrocyte HI and MN for the detection of antibodies to H5N1. It is safer, and can be applied in a high-throughput format for human and animal surveillance and for the evaluation of vaccines.

Generation of influenza vaccine viruses on Vero cells by reverse genetics: an H5N1 candidate vaccine strain produced under a quality system

Human influenza vaccine reference strains are prepared as required when an antigenically new strain is recommended by WHO for inclusion in the vaccine. Currently, for influenza A, these strains are produced by a double infection of embryonated hens' eggs using the recommended strain and the laboratory strain PR8 which grows to high titre in eggs, in order to produce a high growth reassortant (HGR). HGRs are provided by WHO reference laboratories to the vaccine manufacturing industry which use them to prepare seed virus for vaccine production. The use of reverse genetics in preparing vaccine reference strains offers several advantages over the traditional method: (i) the reverse genetics approach is a direct rational approach compared with the potentially hit-or-miss traditional approach; (ii) reverse genetics will decontaminate a wild type virus that may have been derived in a non-validated system, e.g. a cell line not validated for vaccine purposes, or that may contain additional pathogens; (iii) at the plasmid stage, the HA can be engineered to remove pathogenic traits. The use of reverse genetics in deriving HGRs has been demonstrated by several laboratories, including its use in deriving a non-pathogenic reassortant strain from a highly pathogenic virus. In this report, we have advanced the use of reverse genetics by making use of a cell line acceptable for human vaccine production, by demonstrating directly the short time frame in which a reassortant virus can be derived, and by deriving a non-pathogenic pandemic vaccine reference virus in cells validated for vaccine production and under quality controlled conditions.

Innate IL-10 promotes the induction of Th2 responses with plasmid DNA expressing HIV gp120

Like most DNA vaccines, intramuscular immunization with plasmid DNA coding for influenza virus haemagglutinin (HApDNA) induced Th1 responses and IgG2a antibodies in mice. However, plasmid DNA coding for HIV gp120 (gp120pDNA) induced Th2-biased responses and predominantly IgG1 antibodies. Responses to gp120pDNA switched to a Th1-type in IL-10-defective mice and to exclusively IgG2a antibodies in IL-4-defective mice. Conversely, antigen-specific IFN-gamma production induced by gp120pDNA or HApDNA was reduced in IL-12-defective mice, whereas addition of plasmid DNA coding for IL-12 enhanced Th1 responses. Plasmid DNA stimulated IL-10 and IL-12 production by macrophages and dendritic cells (DCs) in vitro and anti-IL-10 antibodies enhanced IL-12 production and DC maturation in response to gp120pDNA. Our findings suggest that T cell responses induced by DNA vaccines is influenced by the nature of the antigen, and that the induction of Th2-biased responses with gp120pDNA is mediated in part through the stimulation of innate IL-10, which inhibits activation of DCs that direct the induction of Th1 cells.

Preparation of vaccines against H5N1 influenza

In response to the pandemic warning provided by the highly pathogenic H5N1 influenza virus infections in Hong Kong, there were world-wide attempts to develop vaccines. Three strategies were followed and although each was associated with some success, there were also some problems. Pre-clinical vaccine efficacy results are presented from one such strategy, that of using an apathogenic H5N3 avian strain for vaccine production.

Respiratory syncytial virus infection of gene gun vaccinated mice induces Th2-driven pulmonary eosinophilia even in the absence of sensitisation to the fusion (F) or attachment (G) protein

Complete protection against respiratory syncytial virus (RSV) infection was induced in mice vaccinated on two occasions with 2.5 microg of DNA, encoding the fusion (F) protein of RSV, precipitated onto gold microbeads. In contrast, immunisation with DNA encoding the attachment (G) protein of RSV resulted in a significant reduction in viral load following infection, but did not afford complete protection. Gene gun delivery of DNA-F elicited a T helper-2 (Th2) biased immune response that could not be modulated by the co-delivery of plasmids encoding IL-2, IL-12 or IFNgamma. Similarly gene gun delivery of DNA-G primed a Th2 response. Thus, all gene gun vaccinated mice produced a predominant Th2 biased pulmonary immune response characterised by the production of IL-4 and IL-5 with little IFNgamma following RSV challenge. Analysis of bronchoalveolar lavage (BAL) cells, 5 days post challenge, indicated that there was only a two-fold increase in the number of inflammatory cells in vaccinated compared with control animals. Despite the strong Th2 cytokine bias of lung lymphocytes and the predominant recruitment of CD4(+) T cells, following challenge, there was not a marked pulmonary eosinophilic response (range from 2 to 7% of BAL). In contrast, the BAL from mice vaccinated with control plasmid contained significantly more eosinophils than any other group.

DNA encoding the attachment (G) or fusion (F) protein of respiratory syncytial virus induces protection in the absence of pulmonary inflammation

Significant protection against respiratory syncytial virus (RSV) infection was induced in mice vaccinated intramuscularly (i.m.) with DNA encoding the F or G protein of RSV. The amounts of IgG1 of IgG2a antibodies in mice immunized with DNA-G alone were similar. However, the antibody response in mice co-immunized with DNA-G and DNA encoding IL-4 (DNA-IL-4) was strongly biased towards IgG1. In contrast, the antibody response in mice co-immunized with DNA-G and DNA-IL-2, -IL-12 or-IFN-gamma was biased towards IgG2a. Mice vaccinated with DNA-F either alone or in combination with DNA encoding cytokines developed a predominant RSV-specific IgG2a response, which was most pronounced in mice co-immunized with DNA-F and DNA-IL-12 or -IFN-gamma. Vaccinated mice developed only a slightly enhanced pulmonary inflammatory response following RSV challenge. More significantly, and in contrast to mice scarified with recombinant vaccinia virus expressing the G protein, mice vaccinated i.m. with DNA-G did not develop pulmonary eosinophilia, even when the immune response was biased towards a Th2 response by co-administration of DNA-IL-4.

Plasmid DNA encoding influenza virus haemagglutinin induces Th1 cells and protection against respiratory infection despite its limited ability to generate antibody responses

Direct intramuscular injection of plasmid DNA can generate immune responses against encoded antigens. However, the relative ability of DNA vaccines to induce cellular and humoral immunity after a single or booster immunization and the persistence of this response have not been fully elucidated. In this study, induction and maintenance of antibody and T cell subtypes with different doses of naked DNA encoding the haemagglutinin (HA) gene of influenza virus were examined and compared to the immune responses and protection induced by respiratory tract infection and immunization with a killed virus vaccine. Like natural infection, immunization with HA DNA induced potent Th1 responses. Spleen cells from mice immunized once with HA DNA in the dose range 10 ng to 100 microgram secreted significant levels of IFN-gamma, but low or undetectable IL-5, in response to influenza virus in vitro. Furthermore, CD4(+) HA-specific Th1 clones were generated from spleens of immunized mice. Although T cell responses waned 12 weeks after a single immunization, antigen-specific Th1 cells persisted in the spleen for at least 6 months after two booster immunizations. In contrast, influenza virus-specific ELISA IgG titres were low after a single immunization and required two booster immunizations to reach significant levels. Furthermore, haemagglutination inhibition (HI) antibodies were weak or undetectable after two immunizations. Nevertheless, two doses of HA DNA conferred almost complete protection against respiratory challenge with live virus. Thus, despite the limited ability to induce antibodies, DNA vaccines confer protective immunity against influenza virus infection, which appears to be mediated by Th1 cells.

Correlates of informant-rated cognitive decline after stroke

Cognitive impairment is common after stroke, but measurement is problematic. Six tests of mental ability, unaffected by loss of limb function, were administered to 49 subjects of mean age 74.2 years at a median of 4.3 years (range 0.1-16.8) after stroke together with a depression score and the IQCODE, an informant-rated scale of estimated cognitive decline. Over 90% of stroke patients were able to complete most tests. IQCODE correlated significantly with the HADS depression score (r = 0.35, p = 0.040), the 2-year Barthel score (r = -0.60, p = 0.001) and with a general cognitive factor extracted from the mental ability test scores (r = -0.42, p = 0.016). We conclude that informant-rated methods offer a promising approach to measuring cognitive decline after stroke.

Sun awareness in school teachers

School children are important targets for sun awareness education, but the knowledge, attitudes and behaviour of school teachers with respect to sun awareness are poorly understood. A questionnaire-based survey of 76 school teachers was undertaken. Twenty-four per cent of teachers indicated previous experience in teaching sun awareness, but 93% of teachers had no classroom resources for teaching sun awareness. Sun awareness was perceived by respondents as unimportant relative to other health education issues. There was considerable scope for improvement in attitudes and behaviour of teachers with respect to sun awareness. Teachers need more information about environmental factors which affect strength of sunlight, individual risk factors for sunburn and sunscreen strength. Intervention strategies involving school teachers need simple messages, emphasizing the importance of shade, clothing and hats in sun avoidance.

Direct sequencing of the HA gene of clinical equine H3N8 influenza virus and comparison with laboratory derived viruses

Equine influenza viruses propagated in the laboratory in alternate hosts such as embryonated hens' eggs or mammalian cell culture have been analysed by HA sequencing and antigenically and their sequence compared to the original virus present in clinical material. In contrast to clinically derived human influenza virus which generally grows in MDCK cells without change, the data for equine influenza virus were less clear in that variants of equine virus were derived in both eggs and cells. The study indicated that the current use of eggs for equine influenza virus surveillance and vaccine production is entirely appropriate, but that care should be exercised when equine influenza vaccines are produced in eggs or on mammalian cell cultures.

Assessing the significance of reverse transcriptase activity in chick cell-derived vaccines

A recent publication reported the detection of low levels of the enzyme reverse transcriptase (RTase) in live viral vaccines prepared in chick embryo cells. The enzyme was detected using an assay with greatly increased sensitivity compared to more conventional methods. The authors have confirmed the observation of RTase activity and demonstrate that the activity is not dependent on the production of viral vaccines in chick cells but is present ubiquitously in chick embryonic fluids. The authors have also been unable to transmit the RTase activity from chick cells to a wide variety of cells of human, monkey, rabbit and turkey origin, suggesting that the activity is not associated with an avian agent capable of infecting these cells. It is concluded that the data available present no cause for concern over the safety of vaccines derived in chick cells and current WHO requirements for such vaccines remain appropriate.

Mixed populations in influenza virus vaccine strains

Human influenza viruses used for vaccine production have previously been adapted to grow in eggs. During egg adaptation, variants are selected and we have observed that more than one variant may derive in a single egg resulting in a mixed population. We have now investigated the extent of heterogeneity, due to host cell selection, of virus strains used for the manufacture of influenza vaccine for the 1991/1992 and 1992/1993 seasons. The A(H1N1) vaccine virus was homogeneous with respect to substitutions in the haemagglutinin deriving from egg adaptation. However, two A(H3N2) vaccine strains and the influenza B component, B/Yamagata/16/88, consisted of mixed populations, apparently due to their cultivation in eggs. The individual variants within B/Yamagata were isolated and found to be antigenically distinct. The ratios of these variants within different manufacturers' seed stocks varied to the extent that vaccine derived from them could be distinguished antigenically. Furthermore, derivation of high-growth reassortants from the A(H3N2) strains which involves passaging at limit dilution did not necessarily lead to a homogeneous virus population. The significance of these findings for the efficacy of vaccine is not known at present.

The role of amniotic passage in the egg-adaptation of human influenza virus is revealed by haemagglutinin sequence analyses

Obtaining an isolate of a human influenza virus in the allantoic cavity of the embryonated hen's egg is more efficient if the clinical sample is initially passaged in the amniotic cavity. To investigate the extent to which the variants present after allantoic propagation are also selected by amniotic passage, clinical virus passaged once in the amnion has been subjected to extensive genetic and antigenic analyses. The data indicate that the natural virus can replicate unrestrictedly within the amnion. However, exposure of amniotic virus to the allantois during the incubation period, which will occur through the hole between the amniotic and allantoic cavities caused by the inoculating needle, allows for the possibility of an egg-adapted variant establishing replication within the allantois and returning to the amnion. These observations illustrate why prior passage in the amnion increases the probability of a variant successfully establishing itself during a subsequent allantoic passage.

Genic amplification of the entire coding region of the HEF RNA segment of influenza C virus

In order to provide an easy and powerful analysis of influenza C viral HEF RNA segment of a recent strain, a combination of reverse transcription and the polymerase chain reaction was used. We amplified the entire coding region of the HEF gene of a laboratory strain of virus called C/Johannesburg/1/66, widely used for binding and esterase activity studies as well as that of a strain isolated in 1991 (C/Paris/145/91) from a patient suffering from severe flu syndrome. The sequences we amplified were about 2 kilobases long. In this work, we show that the forward 'universal primer' Uni1, which has been used for influenza A and B viruses cDNA syntheses can also be used for influenza C virus. The PCR primers were designed to contain restriction sites to make the PCR products ready to be used for further purposes. A restriction analysis of the PCR products combined with analyses of all the human influenza C virus HEF gene sequences published so far permitted the design of sets of oligonucleotides which can prime PCR on cDNA of unknown influenza C virus for cloning.

High growth reassortant influenza vaccine viruses: new approaches to their control

When a new strain of an influenza virus is required to be incorporated into influenza vaccine, attempts are made to recombine such strains with laboratory adapted viruses, which will grow to high titre in order to improve the yield of the vaccine strain. It is important that such high growth reassortant vaccine strains are not contaminated with genes coding for the antigenic determinants of the high growth laboratory strain. We describe the characterization of two recent high growth reassortants and the application of the polymerase chain reaction to ensure their genetic identity and purity.

Sequence analysis of the haemagglutinin (HA) of influenza A (H1N1) viruses present in clinical material and comparison with the HA of laboratory-derived virus

We used the polymerase chain reaction to amplify the HA1 coding region of influenza A (H1N1) viruses present in clinical material from recent cases of influenza in the U.K. Previously, we have demonstrated that isolation of human influenza viruses in embryonated hens' eggs selects variants which have amino acid substitutions in their haemagglutinin (HA) clustering around the receptor-binding site. Such egg-selected variants are often antigenically distinct from each other and from corresponding viruses isolated on mammalian cells. Since in general the virus used for vaccine production is an egg-adapted virus, it is important to determine the extent to which these variants are present in the natural virus which causes disease in man. To achieve this, amplified products from clinical material were cloned and many individual clones sequenced. Our results indicate that the HA of the naturally occurring virus is relatively homogeneous and represented by virus isolated in the laboratory on MDCK cells, whereas the variants isolated in eggs are present only at low levels in clinical material.

The hemagglutinin of influenza B virus present in clinical material is a single species identical to that of mammalian cell-grown virus

When clinical specimens of influenza virus are adapted to grow in embryonated hens' eggs, variants are selected which have specific amino acid substitutions in the hemagglutinin (HA). In contrast, a single virus, distinct from any egg-adapted variant, is selected when virus is isolated on MDCK mammalian cell culture. We have utilized the polymerase chain reaction to determine the nature of the hemagglutinin of influenza B viruses present in clinical material prior to cultivation in the laboratory. Sequence analysis of individual clones of amplified DNA reveals that the HA of clinical virus is essentially homogeneous and identical to the virus derived on MDCK cells. The HA of egg-adapted virus was heterogeneous and nonidentical to that of the clinical material and of the MDCK-derived virus.