Safety and immunogenicity of a new influenza vaccine grown in mammalian cell culture

Immunogenicity and efficacy comparison of MDCK cell-based and egg-based live attenuated influenza vaccines of H5 and H7 subtypes in ferrets

During a pandemic, the availability of specific pathogen free chicken eggs is a major bottleneck for up-scaling response to the demand for influenza vaccine. This has led us to explore the use of Madin-Darby Canine Kidney (MDCK) cells for the manufacture of live attenuated influenza vaccine (LAIV) that provides production flexibility and speed. The present study reports the comparison of the immunogenicity and efficacy of two MDCK-based LAIVs against two egg-based LAIVs prepared from the same pandemic potential strains of H5 and H7 subtypes after a single dose of the vaccine followed by a challenge with a homologous wild type strain. The vaccine strains have been generated by classical method of reassortment using the A/Leningrad/134/17/57 master donor strain. Additionally, a prime-boost regimen of the MDCK-based vaccine followed by a challenge with a homologous wild type strain for H5 and H7 immunized ferrets and also a heterologous wild type strain for the H5 immunized animals was studied. No difference in the hemagglutination inhibition and virus neutralization antibody titers against the homologous virus was observed following a single dose of either egg-based or MDCK-based H5 and H7 LAIV vaccine. A second dose of MDCK-based vaccine significantly boosted antibody titers in the vaccinated animals. Both a single dose or two doses of LAIV provided complete protection from lower respiratory tract infection and resulted in a significant reduction in the virus titers recovered from the throat, nasal turbinates and lungs after challenge with the homologous wild type strain. Protection from a challenge with a heterologous strain of H5 was also observed after two doses of the MDCK-based LAIVs. This data strongly supports the use of MDCK as a substrate for the manufacture of LAIV which ensures reliable quality, safety, production flexibility, speed and breadth of protection, features that are highly critical during a pandemic.

Cell culture-derived flu vaccine: Present and future

The benefit of influenza vaccines is difficult to estimate due to the complexity of accurately assessing the burden of influenza. To improve the efficacy of influenza vaccines, vaccine manufacturers have developed quadrivalent influenza vaccine (QIV) formulations for seasonal vaccination by including both influenza B lineages. Three parallel approaches for producing influenza vaccines are attracting the interest of many vaccine manufacturing companies. The first and oldest is the conventional egg-derived influenza vaccine, which is used by the current licensed influenza vaccines. The second approach is a cell culture-derived influenza vaccine, and the third and most recent is synthetic vaccines. Here, we analyze the difficulties with vaccines production in eggs and compare this to cell culture-derived influenza vaccines and discuss the future of cell culture-derived QIVs.

Cell culture-based influenza vaccines: A necessary and indispensable investment for the future

The traditional platform of using embryonated chicken eggs for the production of influenza vaccines has several drawbacks including the inability to meet the volume of required doses in the case of widespread epidemics and pandemics. Cell culture platforms have therefore been explored in the last 2 decades, and have attracted further attention following the H1N1 pandemic outbreak. This platform, while not the most economical for large-scale production, has several advantages, and can supplement the vaccine requirement when needed. Recent developments in production technologies have contributed greatly to fine-tuning this platform. In combination with other technologies such as live attenuated and recombinant protein or virus-like particle vaccines, and different adjuvants and delivery systems, cell culture-based influenza vaccine platform can be used both for production of seasonal vaccine, and to mitigate vaccine shortages in pandemic situations.

Evaluation of safety and immunogenicity of HNVAC, an MDCK-based H1N1 pandemic influenza vaccine, in Phase I single centre and Phase II/III multi-centre, double-blind, randomized, placebo-controlled, parallel assignment studies

The clinical evaluation of the MDCK-based H1N1 pandemic influenza vaccine HNVAC in adults aged 18-65 years is reported. In the Phase I randomized, double-blind, placebo-controlled, single-centre study, 160 subjects were parallelly assigned 3:1 to vaccine:placebo groups (n=60:20) with both the aluminium hydroxide adjuvanted and non-adjuvanted vaccine formulations. A single dose of both the formulations containing 15 μg of haemagglutinin protein showed minimal adverse reactions, the most common of which were pain at injection site (11.67%) and fever (10.00%). Both formulations produced 74-81% seroprotection (SRP: titre of ≥40), 67-70% seroconversion (SRC: four-fold increase in titres between days 0 and 21), and a four-fold increase in geometric mean titres (GMT). Aluminium hydroxide did not have a significant effect either on immunogenicity or on reactogenicity. Nevertheless, based on its recognized positive effects on the stability and immunogenicity of many vaccines, and its marginal benefit in both pre-clinical and Phase I studies of HNVAC, alum adjuvanted HNVAC was further tested in a staggered Phase II/III randomized, double-blind, placebo-controlled, multi-centre study of 200 and 195 subjects, respectively, parallelly assigned 4:1 to adjuvanted vaccine and placebo groups. In these studies, the most common adverse reactions were pain at injection site (6.88% and 5.77% in Stage 1 and Stage 2, respectively) and fever (7.50% and 7.05%, respectively), and a single dose resulted in 87-90% SRP, 85-86% SRC, and a nearly six-fold increase in GMT, meeting or exceeding licensing criteria. It is concluded that HNVAC is safe and immunogenic to adults of 18-65 years.

Assessing the safety of influenza vaccination in specific populations: children and the elderly

Comprehensive monitoring of the safety of influenza vaccines remains a public health priority, particularly as immunization coverage increases across different age groups at the global level. In this review, the authors provide state-of-the-art knowledge on the safety of influenza immunization among children and the elderly. The authors review the safety information in each group separately for inactivated and live attenuated influenza vaccines. Adverse events of special concern including febrile seizure, narcolepsy, asthma and Guillain-Barré syndrome are covered under specific considerations. The authors discuss the current status of the field, particularly the use of new technologies for influenza vaccines and their potential safety profile.

Preflucel®: a Vero-cell culture-derived trivalent influenza vaccine

Vaccination is the principal means to reduce the impact of influenza infection. Effective vaccination programs require a reliable and safe production system. Traditionally, influenza vaccines are produced in embryonated chicken eggs. Over the last two decades, new cell culture-derived vaccines have been licensed and manufactured, and other vaccines are still in various phases of development. Vero cells have been used for the development of a wide variety of vaccines including influenza vaccines. Pandemic and avian influenza vaccines derived from Vero cells have been shown to be well tolerated and immunogenic in animal and Phase I-II clinical studies. A Phase III randomized, double-blind, placebo-controlled trial of a trivalent influenza vaccine produced in Vero-cell culture was conducted in 7250 adults aged 18-49 years. Overall protective efficacy for antigenically matched influenza vaccine was 78.5%. The vaccine was well tolerated with no treatment-related serious adverse events and compared favorably with egg-derived vaccines from previous trials. Vero-cell-derived influenza vaccines have the potential to be an important parts of the influenza vaccine strategy, especially if an avian-derived strain becomes predominant or the demand outstrips the capacity of egg-based production systems.

New strategies for the development of H5N1 subtype influenza vaccines: progress and challenges

The emergence and spread of highly pathogenic avian influenza (H5N1) viruses among poultry in Asia, the Middle East, and Africa have fueled concerns of a possible human pandemic, and spurred efforts towards developing vaccines against H5N1 influenza viruses, as well as improving vaccine production methods. In recent years, promising experimental reverse genetics-derived H5N1 live attenuated vaccines have been generated and characterized, including vaccines that are attenuated through temperature-sensitive mutation, modulation of the interferon antagonist protein, or disruption of the M2 protein. Live attenuated influenza virus vaccines based on each of these modalities have conferred protection against homologous and heterologous challenge in animal models of influenza virus infection. Alternative vaccine strategies that do not require the use of live virus, such as virus-like particle (VLP) and DNA-based vaccines, have also been vigorously pursued in recent years. Studies have demonstrated that influenza VLP vaccination can confer homologous and heterologous protection from lethal challenge in a mouse model of infection. There have also been improvements in the formulation and production of vaccines following concerns over the threat of H5N1 influenza viruses. The use of novel substrates for the growth of vaccine virus stocks has been intensively researched in recent years, and several candidate cell culture-based systems for vaccine amplification have emerged, including production systems based on Madin-Darby canine kidney, Vero, and PerC6 cell lines. Such systems promise increased scalability of product, and reduced reliance on embryonated chicken eggs as a growth substrate. Studies into the use of adjuvants have shown that oil-in-water-based adjuvants can improve the immunogenicity of inactivated influenza vaccines and conserve antigen in such formulations. Finally, efforts to develop more broadly cross-protective immunization strategies through the inclusion of conserved influenza virus antigens in vaccines have led to experimental vaccines based on the influenza hemagglutinin (HA) stem domain. Such vaccines have been shown to confer protection from lethal challenge in mouse models of influenza virus infection. Through further development, vaccines based on the HA stem have the potential to protect vaccinated individuals against unanticipated pandemic and epidemic influenza virus strains. Overall, recent advances in experimental vaccines and in vaccine production processes provide the potential to lower mortality and morbidity resulting from influenza infection.

Quantitative review of antibody response to inactivated seasonal influenza vaccines

BACKGROUND

Seasonal influenza epidemics are associated with significant morbidity and mortality each year, particularly amongst young children and the elderly. Seasonal influenza vaccines have been available for decades, yet influenza remains a major public health threat in the US, sparking interest in studies evaluating the effectiveness of vaccination.

OBJECTIVES

We sought to identify determinants of serological responses to inactivated seasonal influenza vaccines including number of doses, adjuvant, and subject characteristics.

METHODS

We reviewed 60 articles published between 1987 and 2006. We used weighted multiple logistic regression and random-effects models to evaluate how seroconversion and seroprotection rates varied with host and vaccine factors.

RESULTS

Both children and seniors tended to have poorer immune responses compared to adults whereas use of adjuvant and a second vaccine dose tended to improve immune response. Pre-vaccination serological status had a large impact on the immune response to vaccination. We found substantial heterogeneity among studies, even with similar population settings and vaccination regimen.

CONCLUSIONS

Future studies should stratify their results by pre-vaccination serological status in an effort to produce more precise summary estimates of vaccine response.

Bench-to-bedside review: vaccine protection strategies during pandemic flu outbreaks

Vaccination is the most effective means for the prevention of influenza, including pandemic strains. An ideal pandemic influenza vaccine should provide effective protection with the fewest number of doses in the shortest amount of time, and among the greatest proportion of the population. The current manufacturing processes required for embryonated chicken-egg-based influenza vaccines are limited in their ability to respond to pandemic situations - these limitations include problems with surge capacity, the need for egg-adapted strains, the possibility of contamination, and the presence of trace egg protein. Several vaccine strategies to circumvent the deficiencies intrinsic to an egg-based influenza vaccine are in various phases of development. These include the use of cell-culture-based growth systems, concomitant use of adjuvants, whole virus vaccines, recombinant protein vaccines, plasmid DNA vaccines, virus-like particle vaccines, and universal flu vaccines.

Comparison of the usefulness of the CACO-2 cell line with standard substrates for isolation of swine influenza A viruses

Influenza A virus isolation is undertaken routinely in embryonated chicken eggs, but to improve virus detection various cell lines can be used. The CACO-2 cell line was compared to the MDCK cell line and embryonated chicken eggs for the isolation of H1N1, H1N2, H3N2 swine influenza A virus subtypes from clinical specimens. From 2006 to 2008, 104 influenza A samples found positive by PCR from 42 respiratory outbreaks in Italian swine farms were examined by virus isolation. Sixty swine influenza A viruses were isolated (16 H1N1, 28 H1N2 and 16 H3N2) and their growth behaviour on the different substrates was examined. 16/16 H1N1, 28/28 H1N2 and 8/16 of H3N2 viruses were isolated from the CACO-2 cell line, while 7/16 H1N1, 3/28 H1N2 and 16/16 H3N2 viruses were isolated using embryonated chicken eggs. Only 9/16 H1N1, 1/28 H1N2 and 6/16 H3N2 viruses replicated in MDCK cells. A link was found between viral hemagglutinin and the isolation rate on the various substrates. The CACO-2 line was statistically more sensitive (Fisher's exact test, p<0.01) compared to the MDCK cells and embryonated chicken eggs for the isolation of H1N1 and H1N2 subtypes. In contrast influenza A H3N2 virus was isolated more readily in embryonated chicken eggs than in cultured cells (Fisher's exact test, p<0.01).

The growth of attenuated influenza vaccine donor strains in continuous cell lines

The growth of the Russian live attenuated influenza vaccine donor strains A/Leningrad/134/17/57, A/Leningrad/134/47/57 and B/USSR/60/69 was studied in cells of the VERO and Madin-Darby canine kidney (MDCK) lines as six-well cultures and cell factories infected at different multiplicities of infection. Yields for A/Leningrad/134/17/57 and A/Leningrad/134/47/57 were comparable in either cell line over a range of multiplicities but were about 10-fold lower than in the allantoic fluids of infected chicken embryos. For both A/Leningrad/134/47/57 and B/USSR/60/69, yields from the MDCK line were about 10-fold higher than for the VERO line. For B/USSR/60/69, yields in eggs were approximately 100-fold higher than those obtained in the MDCK line. A feature of the growth of B/USSR/60/69 was its reduced capacity to produce infectious progeny in either cell line at multiplicities of infection of 2.0 or 1.0 pfu/cell. Inhibition was due probably due to the presence of defective-interfering particles and was not detected with A/Leningrad/134/17/57 or A/Leningrad/134/47/57 in cultures of either line infected at the same multiplicities. Yields for both A/Leningrad/134/47/57 and B/USSR/60/69 in cells of the MDCK line were comparable when grown in six-well cultures or cell factories.

The role of cell culture vaccines in the control of the next influenza pandemic

Pandemic influenza A viruses of avian origin are of particular concern and have crossed the species barrier several times in recent years, giving rise to illness and occasionally death in humans. This situation could become dramatically worse if the infectivity of avian viruses for humans were increased by reassortment between the genes of human and avian viruses. Co-infection of humans or an intermediate host with an avian strain and an existing human strain could produce new viruses of unknown pathogenicity to which the entire population would be susceptible. Inactivated vaccines against influenza have been prepared for many years using viruses grown in embryonated chicken eggs. However, the use of eggs presents difficulties when vaccine supplies need to be expanded at short notice. It seems likely that future vaccines will be prepared in high-yielding cell cultures from continuous lines that are preferably anchorage-independent. At present, only certain preparations of the Vero and Madin-Darby canine kidney cell lines, grown and maintained in serum-free medium, are acceptable to all regulatory authorities. However, this situation is likely to change with increasing need for non-pandemic and pandemic vaccines.

Establishment and characterization of two new pig cell lines for use in virological diagnostic laboratories

Two pig cell lines derived from kidney and trachea tissues and referred to as newborn swine kidney (NSK) and newborn pig trachea (NPTr) were established following serial culture of primary cells. They were characterized by an epithelial-like morphology, high capacity to replicate and stability of the cell monolayer for several days after seeding. Their modal chromosome number was modified in comparison to that of primary swine cells and they both displayed a transforming potential in vitro and displayed oncogenicity in nude mice. Infection with pig endogenous retroviruses was detected. Almost all the swine viruses tested, i.e., pseudorabies virus, pig parvovirus, hog cholera virus, transmissible gastroenteritis virus of swine, encephalomyocarditis virus, swine vesicular disease virus and the enteroviruses, except pig reproductive respiratory syndrome virus, were capable of replicating in the new cell lines with titres similar to the ones detected in the reference culture systems. Furthermore, all the selected influenza virus sub-types isolated from human, swine and avian species replicated with cytopathic effect in NSK and NPTr cells, whereas, of all the equine influenza viruses tested only the Miami and Suffolk sub-types replicated.

Safety and immunogenicity of a trivalent, inactivated, mammalian cell culture-derived influenza vaccine in healthy adults, seniors, and children

We performed randomized, double-blind, controlled trials to assess the safety and immunogenicity of an inactivated, Madin Darby Canine Kidney (MDCK)-derived cell line produced influenza vaccine in healthy adults (19-50 years), children (3-12 years) and the elderly (> or =65 years). We studied three lots of cell culture-derived vaccine and one lot of licensed egg-derived vaccine in healthy adults (n=462), two lots of cell culture-derived vaccine and one lot of egg-derived vaccine in seniors (n=269), and one lot of each vaccine in children (n=209). Adverse events were collected during the first 3 days post-immunization; serum was collected before and 1 month after immunization. Rates of local and systemic adverse reactions were similar with both vaccines. An injection site adverse event rated at least moderate severity was reported by 21.9% of children who received the egg-derived vaccine and 25.0% of those who received the cell culture-derived vaccine. In healthy adults the proportions were 12.1 and 15.3%, respectively and 6.7 and 6.3%, respectively in seniors. Systemic events of at least moderate severity were 12.4 and 12.5% in children, 19.8 and 13.6% in healthy adults, and 14.1 and 9.7% in seniors; none of these differences were statistically significant. The antibody response against all three viruses was similar between the two vaccines. From 83 to 100% of children, healthy adults and seniors achieved hemagglutination inhibition titers in excess of 40 post-immunization. We conclude that the cell culture-derived vaccine was safe and immunogenic in children, healthy adults and seniors.

Vaccines and therapeutics against influenza virus infections

BACKGROUND

Vaccination prior to epidemic season is the best measure to control influenza virus infection; however, there are several issues to be considered regarding influenza vaccines in Japan. In the present review, current issues regarding influenza vaccine in Japan are described, as well as the future prospects of vaccine development. As well as vaccination, anti-influenza agents such as amantadine are now available in Japan. Furthermore, neuraminidase inhibitors are expected to appear in the market in near future. These anti-influenza agents represent new options for influenza control.

CONCLUSIONS

Vaccination and antiviral agents are a major armamentarium against influenza infections. Thus, exploratory studies on novel forms of vaccine and anti-influenza drugs should help to prepare against pandemics that must emerge in near future.