Cell Culture-based Influenza Vaccine Research Articles

Developments and current challenges in the process of cell culture-based seasonal influenza vaccine manufacture in Japan.

Seasonal influenza is an acute respiratory infection primarily caused by influenza A and B viruses, which circulate annually and cause substantial morbidity and mortality worldwide. Annual influenza vaccination is currently the most effective measure for preventing influenza and greatly reduces the risk of disease severity and the incidence of complications and death. Annual seasonal influenza vaccines are traditionally produced in Japan and many other countries using viruses propagated in embryonated chicken eggs. However, at present, the effectiveness of the seasonal influenza vaccines has some significant limitations, partly because of egg-adaptive mutations in the antigenic sites of the influenza virus haemagglutinin, which are caused by the continued evolution of seasonal influenza viruses. To overcome the limitations of egg-based influenza vaccine production, a mammalian cell culture-based influenza vaccine production system has been developed in Japan in the past decade as an alternative to the current production method. In this review, I have summarised the progress in the development of cell-based seasonal influenza vaccines and discussed the technological challenges encountered in the development of influenza vaccines.

Redirecting antibody responses from egg-adapted epitopes following repeat vaccination with recombinant or cell culture-based versus egg-based influenza vaccines

Repeat vaccination with egg-based influenza vaccines could preferentially boost antibodies targeting the egg-adapted epitopes and reduce immunogenicity to circulating viruses. In this randomized trial (Clinicaltrials.gov: NCT03722589), sera pre- and post-vaccination with quadrivalent inactivated egg-based (IIV4), cell culture-based (ccIIV4), and recombinant (RIV4) influenza vaccines were collected from healthcare personnel (18-64 years) in 2018−19 (N = 723) and 2019−20 (N = 684) influenza seasons. We performed an exploratory analysis. Vaccine egg-adapted changes had the most impact on A(H3N2) immunogenicity. In year 1, RIV4 induced higher neutralizing and total HA head binding antibodies to cell- A(H3N2) virus than ccIIV4 and IIV4. In year 2, among the 7 repeat vaccination arms (IIV4-IIV4, IIV4-ccIIV4, IIV4-RIV4, RIV4-ccIIV4, RIV4-RIV4, ccIIV4-ccIIV4 and ccIIV4-RIV4), repeat vaccination with either RIV4 or ccIIV4 further improved antibody responses to circulating viruses with decreased neutralizing antibody egg/cell ratio. RIV4 also had higher post-vaccination A(H1N1)pdm09 and A(H3N2) HA stalk antibodies in year 1, but there was no significant difference in HA stalk antibody fold rise among vaccine groups in either year 1 or year 2. Multiple seasons of non-egg-based vaccination may be needed to redirect antibody responses from immune memory to egg-adapted epitopes and re-focus the immune responses towards epitopes on the circulating viruses to improve vaccine effectiveness.

Immunogenicity of High-Dose Egg-Based, Recombinant, and Cell Culture-Based Influenza Vaccines Compared With Standard-Dose Egg-Based Influenza Vaccine Among Health Care Personnel Aged 18-65 Years in 2019-2020.

Emerging data suggest that second-generation influenza vaccines with higher hemagglutinin (HA) antigen content and/or different production methods may induce stronger antibody responses to HA than standard-dose egg-based influenza vaccines in adults. We compared antibody responses to high-dose egg-based inactivated (HD-IIV3), recombinant (RIV4), and cell culture-based (ccIIV4) vs standard-dose egg-based inactivated influenza vaccine (SD-IIV4) among health care personnel (HCP) aged 18-65 years in 2 influenza seasons (2018-2019, 2019-2020). In the second trial season, newly and re-enrolled HCPs who received SD-IIV4 in season 1 were randomized to receive RIV4, ccIIV4, or SD-IIV4 or were enrolled in an off-label, nonrandomized arm to receive HD-IIV3. Prevaccination and 1-month-postvaccination sera were tested by hemagglutination inhibition (HI) assay against 4 cell culture propagated vaccine reference viruses. Primary outcomes, adjusted for study site and baseline HI titer, were seroconversion rate (SCR), geometric mean titers (GMTs), mean fold rise (MFR), and GMT ratios that compared vaccine groups to SD-IIV4. Among 390 HCP in the per-protocol population, 79 received HD-IIV3, 103 RIV4, 106 ccIIV4, and 102 SD-IIV4. HD-IIV3 recipients had similar postvaccination antibody titers compared with SD-IIV4 recipients, whereas RIV4 recipients had significantly higher 1-month-postvaccination antibody titers against vaccine reference viruses for all outcomes. HD-IIV3 did not induce higher antibody responses than SD-IIV4, but, consistent with previous studies, RIV4 was associated with higher postvaccination antibody titers. These findings suggest that recombinant vaccines rather than vaccines with higher egg-based antigen doses may provide improved antibody responses in highly vaccinated populations.

Association between seasonal influenza vaccines and the increased risk of acute disseminated encephalomyelitis, estimated using the Vaccine Adverse Event Reporting System.

Acute disseminated encephalomyelitis (ADEM) is a rare and immune-mediated inflammatory disorder of the central nervous system (CNS) that can be triggered by infections and vaccinations. To date, only anecdotal case studies have reported the association between ADEM incidence and seasonal influenza vaccines, and multiple studies have found no association. This study aimed to investigate the association between the incidence of ADEM and seasonal influenza vaccines in a real-world setting using data from the United States Vaccine Adverse Event Reporting System (VAERS). Further, propensity score matching and disproportionality analysis was performed by calculating the adjusted reporting odds ratio (ROR) of reported ADEM cases associated with seasonal influenza vaccines using multiple logistic regression. Additionally, we analysed the time-to-onset using Weibull shape parameters (WSPs). The VAERS database contained 390,352 adverse events reported from January 2011 to December 2020. The ROR of seasonal influenza vaccines for ADEM was 3.02 (95% confidence interval: 1.72-5.33). The median duration (interquartile range) of ADEM was 11.0 (5.0-33.0) days. The median duration of ADEM induced by egg culture-based influenza vaccine (Egg-based vaccine) and cell culture-based influenza vaccine (Cell-based vaccine) was 10.0 (5.0-24.0) and 91.0 (79.0-125.0) days (P < 0.001), respectively. Only Cell-based cases had WSP β > 1, indicating a wear-out failure type. The incidence of ADEM within 30 days after administration of egg- and Cell-based vaccines was 78.6% and 0.0%, respectively. Our findings indicate that ADEM incidence is associated with seasonal influenza vaccines; thus, careful monitoring of ADEM is required within the first month of Egg-based vaccination and after two months of Cell-based vaccination. Neurologists and general practitioners should exercise caution, as the timing for careful monitoring varies depending on the vaccine type.

Effectiveness of cell culture-based influenza vaccines compared with egg-based vaccines: What does the literature say?

IntroductionInfluenza vaccination is an effective way of reducing the burden of seasonal influenza. Chicken egg embryos are the most common source of influenza vaccines, but cell culture production has emerged as an alternative that could be advantageous. This article reviews the available literature on the efficacy/effectiveness of cell culture-based influenza vaccines compared with egg-based vaccines.MethodsWe conducted a review of the actual literature and analyzed those studies comparing the effectiveness of cell culture-based and egg-based vaccines in the last ten years.ResultsEight studies were analyzed; 1 was a clinical trial and 7 were retrospective cohort studies. The clinical trial found no significant differences in the efficacy of both vaccines with respect to placebo. The results of the observational studies were inconsistent and relative effectiveness varied among studies, even though most were performed during the same season, and in some cases, in the same region and using the same data records. Furthermore, in most studies, the comparisons between vaccines were not statistically significant.ConclusionsThere is insufficient evidence that cell culture-based vaccines are superior to egg-based vaccines in terms of efficacy/effectiveness.

A study of the association between seasonal influenza vaccines and the increased risk of Guillain-Barré syndrome using Vaccine Adverse Event Reporting System, 2018-2019.

The aim of this study was to investigate the association between the incidence of Guillain-Barré syndrome (GBS) and seasonal influenza vaccines using the United States Vaccine Adverse Event Reporting System. Using multiple logistic regression analysis, we calculated the adjusted reporting odds ratio (ROR) of GBS cases associated with seasonal influenza vaccines administered from August 2018 to July 2019. Additionally, we analyzed the time-to-onset profile. The total number of adverse events reported following vaccination during this period was 43,235. Most of the GBS patients received a cell culture-based quadrivalent inactivated influenza vaccine (42.2%), quadrivalent inactivated influenza vaccine (26.6%), or high-dose trivalent inactivated influenza vaccine (15.6%). The adjusted ROR of seasonal influenza vaccines for GBS was 3.44 (2.40-4.95). The adjusted ROR of sex (male) (as reference female) and 0.5-59 years (as reference ≥ 60 years) were 1.90 (0.73-4.95) and 1.57 (0.88-2.78). Male sex and advanced age were not risk factors for GBS. The median duration of GBS was 9.5 (4.0-21.5) days. GBS following seasonal influenza vaccination developed mainly within 14 days and 42 days at most. In sex-stratified analyses, the median durations of GBS in females and males were 12.0 (8.3-28.5) and 5.0 (3.0-15.5) days (P = 0.050). Therefore, our findings indicate that the incidence of GBS is associated with seasonal influenza vaccines, and careful monitoring of GBS is required for up to 42 days, especially in the first 14 days. Moreover, GBS may occur slightly earlier in males than in females.

Comparison of the Immunogenicity of Cell Culture-Based and Recombinant Quadrivalent Influenza Vaccines to Conventional Egg-Based Quadrivalent Influenza Vaccines Among Healthcare Personnel Aged 18-64 Years: A Randomized Open-Label Trial.

BackgroundRIV4 and cell-culture based inactivated influenza vaccine (ccIIV4) have not been compared to egg-based IIV4 in healthcare personnel, a population with frequent influenza vaccination that may blunt vaccine immune responses over time. We conducted a randomized trial among healthcare personnel (HCP) aged 18–64 years to compare humoral immune responses to ccIIV4 and RIV4 to IIV4.MethodsDuring the 2018–2019 season, participants were randomized to receive ccIIV4, RIV4, or IIV4 and had serum samples collected prevaccination, 1 and 6 months postvaccination. Serum samples were tested by hemagglutination inhibition (HI) for influenza A/H1N1, B/Yamagata, and B/Victoria and microneutralization (MN) for A/H3N2 against cell-grown vaccine reference viruses. Primary outcomes at 1 month were seroconversion rate (SCR), geometric mean titers (GMT), GMT ratio, and mean fold rise (MFR) in the intention-to-treat population.ResultsIn total, 727 participants were included (283 ccIIV4, 202 RIV4, and 242 IIV4). At 1 month, responses to ccIIV4 were similar to IIV4 by SCR, GMT, GMT ratio, and MFR. RIV4 induced higher SCRs, GMTs, and MFRs than IIV4 against A/H1N1, A/H3N2, and B/Yamagata. The GMT ratio of RIV4 to egg-based vaccines was 1.5 (95% confidence interval [CI] 1.2–1.9) for A/H1N1, 3.0 (95% CI: 2.4–3.7) for A/H3N2, 1.1 (95% CI: .9–1.4) for B/Yamagata, and 1.1 (95% CI: .9–1.3) for B/Victoria. At 6 months, ccIIV4 recipients had similar GMTs to IIV4, whereas RIV4 recipients had higher GMTs against A/H3N2 and B/Yamagata.ConclusionsRIV4 resulted in improved antibody responses by HI and MN compared to egg-based vaccines against 3 of 4 cell-grown vaccine strains 1 month postvaccination, suggesting a possible additional benefit from RIV4.

Summary of the NACI Supplemental Statement on Mammalian Cell Culture-Based Influenza Vaccines.

Mammalian cell culture-based technology is an innovative technique for influenza vaccine manufacturing that may be a valuable alternative to overcome some of the problems and vulnerabilities associated with conventional egg-based influenza vaccine production. Flucelvax® Quad (Seqirus, Inc.) is the first and only mammalian cell culture-based quadrivalent inactivated, subunit influenza vaccine (IIV4-cc) authorized for adult and pediatric use in Canada. The National Advisory Committee on Immunization (NACI) has not previously made a recommendation on cell culture-based influenza vaccines in any population. To review the available evidence for the efficacy, effectiveness, immunogenicity, and safety of IIV4-cc, and to summarize the NACI recommendation regarding the use of Flucelvax Quad in Canada in adults and children. A systematic literature review on the vaccine efficacy, effectiveness, immunogenicity and safety of IIV4-cc in persons four years of age and older was performed. The systematic review's methodology was specified a priori in a written protocol. The NACI evidence-based process was used to assess the quality of eligible studies, summarize and analyze the findings, and develop a recommendation regarding the use of Flucelvax Quad in adults and children. The proposed recommendation was then considered and approved by NACI in light of the available evidence. Thirteen eligible studies were included in the evidence synthesis. In the four observational studies that assessed vaccine effectiveness of IIV4-cc, there were some data indicating potentially improved protection against influenza compared to conventional egg-based quadrivalent inactivated influenza vaccines (IIV4) or trivalent inactivated influenza vaccine (IIV3), particularly against A(H3N2) virus infection. There was also some evidence that IIV4-cc may be more effective than egg-based trivalent or quadrivalent influenza vaccines against non-laboratory confirmed influenza-related outcomes, but there is insufficient evidence for laboratory-confirmed outcomes. Two randomized controlled trials assessed the immunogenicity and safety of IIV4-cc compared with mammalian cell culture-based trivalent inactivated, subunit influenza vaccine (IIV3-cc). The IIV4-cc was well-tolerated and the reported solicited local and systemic adverse events were generally mild to moderate in intensity, self-limited and did not precipitate sequelae. One clinical review of cases and six peer-reviewed randomized controlled trials (four in adults and two in children) that reported on the safety of IIV3-cc were included in the review. The evidence on immunogenicity and safety was consistent across these studies and showed that there was no significant difference in adults and children four years of age and older who had received IIV3-cc or an egg-based IIV3. NACI concluded that there is fair evidence (Grade B Evidence) that Flucelvax Quad is effective, safe, and has non-inferior immunogenicity to comparable vaccines, based on direct evidence in adults and children nine years of age and older. NACI recommends that Flucelvax Quad may be considered among the IIV4 offered to adults and children nine years of age and older (Discretionary NACI Recommendation).

Continuous influenza virus production in a tubular bioreactor system provides stable titers and avoids the "von Magnus effect".

Continuous cell culture-based influenza vaccine production could significantly reduce footprint and manufacturing costs compared to current batch processing. However, yields of influenza virus in continuous mode can be affected by oscillations in virus titers caused by periodic accumulation of defective interfering particles. The generation of such particles has also been observed previously in cascades of continuous stirred tank reactors (CSTRs) and is known as the “von Magnus effect”. To improve virus yields and to avoid these oscillations, we have developed a novel continuous tubular bioreactor system for influenza A virus production. It was built using a 500 mL CSTR for cell growth linked to a 105 m long tubular plug-flow bioreactor (PFBR). Virus propagation took place only in the PFBR with a nominal residence time of 20 h and a production capacity of 0.2 mL/min. The bioreactor was first tested with suspension MDCK cells at different multiplicities of infection (MOI), and then with suspension avian AGE1.CR.pIX cells at a fixed nominal MOI of 0.02. Maximum hemagglutinin (HA) titers of 2.4 and 1.6 log10(HA units/100 μL) for suspension MDCK cells and AGE1.CR.pIX cells, respectively, were obtained. Flow cytometric analysis demonstrated that 100% infected cells with batch-like HA titers can be obtained at a MOI of at least 0.1. Stable HA and TCID50 titers over 18 days of production were confirmed using the AGE1.CR.pIX cell line, and PCR analysis demonstrated stable production of full-length genome. The contamination level of segments with deletions (potentially defective interfering particles), already present in the virus seed, was low and did not increase. Control experiments using batch and semi-continuous cultures confirmed these findings. A comparison showed that influenza virus production can be achieved with the tubular bioreactor system in about half the time with a space-time-yield up to two times higher than for typical batch cultures. In summary, a novel continuous tubular bioreactor system for cell culture-based influenza virus production was developed. One main advantage, an essentially single-passage amplification of viruses, should enable efficient production of vaccines as well as vectors for gene and cancer therapy.

LB15. Vaccine Effectiveness of Flucelvax Relative to Inactivated Influenza Vaccine During the 2017–18 Influenza Season in Northern California

BackgroundIn June 2018, the CDC reported that influenza vaccine effectiveness (VE) against A(H3N2) influenza virus for the 2017–2018 season was ~24%. This lower than expected VE was hypothesized to be partially related to genetic changes arising in the vaccine virus during passage in eggs. Flucelvax™ (Seqirus) is a cell culture-based inactivated influenza vaccine (ccIIV) which is not manufactured in eggs. We investigated whether the VE of ccIIV against influenza A differed from that of egg-based IIV (ebIIV) during the 2017–2018 influenza season.MethodsThe study included all Kaiser Permanente Northern California members aged 4–64 years. We identified all individuals who were positive for influenza by polymerase chain reaction (PCR). This cohort analysis estimated the relative VE of ccIIV vs. ebIIV by comparing the ccIIV vaccinees vs. the ebIIV vaccinees with respect to the risk of PCR-confirmed influenza. We separately estimated the absolute VE of ccIIV and ebIIV by comparing each group of vaccinees with unvaccinated individuals. We used Cox regression with a calendar timeline, stratified by birth year, and adjusted for facility, race, years of membership, prior season influenza vaccine, co-morbidities, and number of inpatient admits in the prior year. We calculated VE as 1 − hazard ratio (HR).ResultsOf the 3,015,891 members aged 4–64 years, 1,017,314 were vaccinated. Of these, 932,874 (91.7%) received ebIIV and 84,440 (8.3%) received ccIIV. Most ebIIV (86.2%) was trivalent. Comparing ccIIV with ebIIV, the adjusted relative VE against influenza A was 6.8% (95% CI: 11.2, 21.9; P = 0.43). The adjusted absolute VE vs. unvaccinated of ccIIV was 30.2% (95% CI: 17.1, 41.3; P < 0.0001) and of ebIIV was 17.9% (95% CI: 12.1, 23.3; P < 0.0001).ConclusionBoth cell-culture and egg-based IIV vaccines showed relatively low effectiveness during the 2017–2018 influenza season in which A(H3N2) predominated. The findings of this study show there was no significant difference in the effectiveness of cell-culture IIV compared with egg-based IIVs. Improvements in influenza vaccines will require ongoing monitoring of vaccine effectiveness.Disclosures N. P. Klein, GSK: Investigator, Research support. Sanofi Pasteur: Investigator, Research support. Merck: Investigator, Research support. Pfizer: Investigator, Research support. Protein Science: Investigator, Research support. MedImmune: Investigator, Research support. Dynavax: Investigator, Research support.

Immunogenicity and safety of a cell culture-based quadrivalent influenza vaccine in adults: A Phase III, double-blind, multicenter, randomized, non-inferiority study

ABSTRACTQuadrivalent influenza vaccines (QIVs), which include both B lineage strains, are expected to provide broader protection than trivalent influenza vaccines (TIVs). The non-inferiority, immunogenicity, and safety of a cell culture-based investigational QIVc and 2 TIVs (TIV1c, TIV2c), in adults (≥18 y), were evaluated in this Phase III, double-blind, multicenter study. A total of 2680 age-stratified subjects were randomized (2:1:1) to receive 1 dose of QIVc (n = 1335), TIV1c (n = 676), or TIV2c (n = 669). TIV1c (B/Yamagata) and TIV2c (B/Victoria) differed only in B strain lineage. The primary objective was to demonstrate non-inferiority of the hemagglutinin-inhibition antibody responses of QIVc against TIVc, 22 d post-vaccination. Secondary objectives included the evaluation of immunogenicity of QIVc and TIVc in younger (≥18 – <65 y) and older (≥65 y) adults. Hemagglutinin inhibition assays were performed at days 1 and 22. Solicited local and systemic adverse events (AEs) were monitored for 7 d post-vaccination, and unsolicited AEs and serious AEs until day 181. QIVc met the non-inferiority criteria for all 4 vaccine strains and demonstrated superiority for both influenza B strains over the unmatched B strain included in the TIV1c and TIV2c, when geometric mean titers and seroconversion rates with TIVc were compared at day 22. Between 48%–52% of subjects experienced ≥1 solicited AE, the most common being injection-site pain and headache. Serious AEs were reported by ≤1% of subjects, none were vaccine-related. The results indicate that QIVc is immunogenic and well tolerated in both younger and older adults. The immunogenicity and safety profiles of QIVc and TIVc were comparable at all ages evaluated.

Comparison of immunogenicity of cell-and egg-passaged viruses for manufacturing MDCK cell culture-based influenza vaccines

While cell culture-based technology has been recently used for manufacturing influenza vaccines, currently available seed viruses are mostly egg-derived reassortants that are egg-adapted to achieve high virus growth in eggs. For use as viruses for cell culture-based influenza vaccine manufacturing, egg-adapted viral seeds may undergo several passages in manufacturing cell lines. However, the suitability of such cell-passaged viruses for vaccine production remains largely unelucidated. In this study, influenza viruses produced in suspension Madin-Darby canine kidney (MDCK) cell cultures were compared to those produced in embryonated hen's eggs for manufacturing MDCK cell culture-based influenza vaccines through comparability studies of virus productivity and vaccine immunogenicity. The results indicate no change in the amino acid sequence of the main antigens, including hemagglutinin (HA) and neuraminidase (NA), of cell-passaged viruses after three passages in suspension MDCK cells. In lab-scale (3-L) single-use bioreactors, suspension MDCK culture supernatants inoculated with cell-passaged viruses were found to show higher virus productivity, suspension MDCK culture supernatants inoculated with egg-passaged viruses, in respect to the HA titers and HA contents determined by single radial immunodiffusion. Finally, comparable hemagglutination inhibition and influenza-specific IgG titers were determined in the mice immunized with cell culture-based vaccines produced with cell- or egg-passaged viruses. These results indicate that MDCK cell-passaged viruses from egg-adapted viruses, as well as egg-derived seed virus, are suitable for MDCK cell culture-based influenza vaccine production.

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.

Impact of defective interfering particles on virus replication and antiviral host response in cell culture-based influenza vaccine production.

During the replication of influenza viruses, defective interfering particles (DIPs) can be generated. These are noninfectious deletion mutants that require coinfection with a wild-type virus but interfere with its helper virus replication. Consequently, coinfected cells mainly produce DIPs. Little is known about how such noninfectious virus particles affect the virus yield of cell culture-based influenza vaccine production. We compared infections of Madin-Darby canine kidney cells with two seed virus preparations of the influenza virus strain A/Puerto Rico/8/34 that contain different amounts of DIPs. A combination of conventional RT-PCR, RT-qPCR, and flow cytometry revealed that DI genomes indeed strongly accumulate in coinfected cells and impede the viral RNA synthesis. Additionally, cells infected at the higher DIP concentration showed a stronger antiviral response characterized by increased interferon-β expression and apoptosis induction. Furthermore, in the presence of DIPs, a significant fraction of cells did not show any productive accumulation of viral proteins at all. Together, these effects of DIPs significantly reduce the virus yield. Therefore, the accumulation of DIPs should be avoided during influenza vaccine production which can be achieved by quality controls of working seed viruses based on conventional RT-PCR. The strategy for the depletion of DIPs presented here can help to make cell culture-based vaccine production more reliable and robust.

Development and preclinical testing of HNVAC, a cell culture-based H1N1 pandemic influenza vaccine from India

Several limitations of the use of embryonated eggs and the threat of pandemics have highlighted the need for other platforms for the production of influenza vaccines. We report the indigenous development and pre-clinical testing of an MDCK-based H1N1 pandemic influenza vaccine HNVAC from India. The cell bank and virus seed were characterized extensively. The cells were characterized by PCR, electron microscopy, and karyotyping, and found to be of female canine epithelial origin. The virus was confirmed by neutralization, haemagglutination inhibition, neuraminidase inhibition, and PCR and nucleotide sequencing. Adventitious agent testing was performed by both in vitro and in vivo studies. The in vitro studies included culturing, haemadsorption, haemagglutination, PCR and RT-PCR, whereas in vivo studies included passage in embryonated eggs and in laboratory animals. Both cell bank and virus seed were free of adventitious agents. MDCK cell lysates as well as cellular DNA did not produce tumours in newborn or adult laboratory animals. The bioprocess parameters were standardized to recover antigen with minimal levels of process-related impurities. The vaccine bulk was tested for the presence of specific antigen, and quantified by single radial immunodiffusion. Finally, non-adjuvanted and aluminium hydroxide adjuvanted vaccine formulations were found to be safe in preclinical toxicity studies in mice, rats, guinea pigs and rabbits, and immunogenic in mice and rabbits. This is the first and only cell culture-based influenza vaccine platform developed in any developing country.

Cell Culture-based Influenza Vaccines as Alternatives to Egg-based Vaccines

Influenza viruses have raised public health concerns by seasonal epidemics and intermittent pandemics. Vaccination is considered as the most effective method for preventing influenza infection in humans. Current influenza vaccines are mostly produced in fertile chicken eggs. However, disadvantages of egg-based vaccines, such as egg dependency, labor-intensive manufacturing system, and huddle for large-scale output, allow us to make an alternative method. A cell-culture platform may be a fine alternative for the next generation vaccine technique. Compared with a classical egg-based method, cell-grown vaccines provide stable pipeline even in the pandemic situation with shorter lead-in times. In addition, cell-grown vaccines are flexible for altering production scales because stocked cell batches can be easily sub-cultured in large quantity without worrying avian diseases and a resultant decrease in egg production. By World Health Organization, MDCK, PER.C6, and Vero cells are only recommended for manufacturing influenza vaccines. In this review, we discuss the necessity, immunogenicity, and efficacy of cell-grown influenza vaccines compared with egg-based vaccines.

Productivity, apoptosis, and infection dynamics of influenza A/PR/8 strains and A/PR/8-based reassortants

In cell culture-based influenza vaccine production significant efforts are directed towards virus seed optimization for maximum yields. Typically, high growth reassortants (HGR) containing backbones of six gene segments of e.g. influenza A/PR/8, are generated from wild type strains. Often, however, HA and TCID50 titres obtained do not meet expectations and further optimization measures are required.Flow cytometry is an invaluable tool to improve our understanding of mechanism related to progress of infection, virus-induced apoptosis, and cell-specific productivity. In this study, we performed infections with two influenza A/PR/8 variants (from NIBSC and RKI) and two A/PR/8-based HGRs (Wisconsin-like and Uruguay-like) to investigate virus replication, apoptosis and virus titres at different multiplicities of infection (MOI 0.0001, 0.1, 3). Flow cytometric analyses showed similar dynamics in the time course of infected and apoptotic cell populations for all four tested strains at MOI 0.0001. Interestingly, higher MOI resulted in an earlier increase of the populations of infected and apoptotic cells and showed strain-specific differences. Infections with A/PR/8 NIBSC resulted in an earlier increase in both cell populations compared to A/PR/8 RKI. The Uruguay-like reassortant showed the earliest increase in the concentration of infected cells and a late induction of apoptosis at all tested MOIs. In contrast, the Wisconsin-like reassortant showed strong apoptosis induction at high MOIs resulting in reduced titres compared to lower MOI. Maximum HA titres were unaffected by changes in the MOI for the two A/PR/8 and the Uruguay-like reassortant. Maximum TCID50 titres, however, decreased with increasing MOI for all strains.Overall, infections at very low MOI (0.0001) resulted not only in similar dynamics concerning progress of infection and induction of apoptosis but also in maximum virus yields. Highest HA titres were obtained for virus seed strains combining a fast progress in infection with a late onset of apoptosis. Therefore, both factors should be considered for the establishment of robust influenza vaccine production processes.

Effect of influenza virus infection on key metabolic enzyme activities in MDCK cells

BackgroundInfluenza, or “flu”, is an upper respiratory tract infectioncaused by a virus belonging to the family ofOrthomyxo-viridae. Influenza can pose a serious risk to the health ofmainly the elderly, the very young, and to people suffer-ing from medical conditions (e.g. weak immune system).For example, seasonal influenza strains are fatal to morethan 50,000 people annually in the United States alone[1]. The most effective measure for preventing influenza-related morbidity and mortality is annual vaccination.Seasonal influenza vaccines are almost exclusively pro-duced using the traditional egg-based manufacturing pro-cess. However, the main limitation of egg-basedtechnology (especially in the case of a pandemic) is thetime-consuming production process (~6 months).Furthermore, people with serious egg allergy cannot bevaccinated when trace amounts of egg protein remain inthe final formulation. Therefore, new production pro-cesses using continuous cell lines for influenza vaccinemanufacturing are currently being established [2].Influenza viruses take advantage of the host cell meta-bolism to replicate their genetic material and to synthe-size viral proteins. The influenza virus particle consistsof three major parts: the ribonucleocapsid, the matrixprotein M1, and the envelope, which is derived from theplasma membrane of the host cell. The lipid bilayer con-tains the ion channel protein M2 and the immunogenicglycoproteins hemagglutinin and neuraminidase [3]. Thereplication cycle of influenza viruses including entry,uncoating, genome transcription and replication, assem-bly and release has been studied extensively with type Astrains [4]. So far, only few studies have characterizedthe influence of influenza infection on the centralcarbon metabolism of host cells [5]. Madin-Darbycanine kidney (MDCK) cells are considered a suitablesubstrate for cell culture-based influenza vaccine manu-facturing [2,6]. In this study, key metabolic enzymeactivities were analyzed in MDCK cells infected with aninfluenza A virus strain to improve our understandingof virus-host cell interaction and cell response.Materials and methodsAll chemicals and enzymes were purchased from Sigma(Taufkirchen, Germany) or Roche (Mannheim, Ger-many). Adherent MDCK cells obtained from theECACC (No. 84121903) were routinely cultured in 6-well plates containing 4 mL of GMEM-based medium(2 mM glutamine, 30 mM glucose, 10 % (v/v) fetal calfserum, 2 g/L peptone, 48 mM NaHCO

Enhanced Growth of Influenza Vaccine Seed Viruses in Vero Cells Mediated by Broadening the Optimal pH Range for Virus Membrane Fusion

Vaccination is one of the most effective preventive measures to combat influenza. Prospectively, cell culture-based influenza vaccines play an important role for robust vaccine production in both normal settings and urgent situations, such as during the 2009 pandemic. African green monkey Vero cells are recommended by the World Health Organization as a safe substrate for influenza vaccine production for human use. However, the growth of influenza vaccine seed viruses is occasionally suboptimal in Vero cells, which places limitations on their usefulness for enhanced vaccine production. Here, we present a strategy for the development of vaccine seed viruses with enhanced growth in Vero cells by changing an amino acid residue in the stem region of the HA2 subunit of the hemagglutinin (HA) molecule. This mutation optimized the pH for HA-mediated membrane fusion in Vero cells and enhanced virus growth 100 to 1,000 times in the cell line, providing a promising strategy for cell culture-based influenza vaccines.

Trypsin promotes efficient influenza vaccine production in MDCK cells by interfering with the antiviral host response

Trypsin is commonly used in Madin-Darby canine kidney (MDCK) cell culture-based influenza vaccine production to facilitate virus infection by proteolytic activation of viral haemagglutinin, which enables multi-cycle replication. In this study, we were able to demonstrate that trypsin also interferes with pathogen defence mechanisms of host cells. In particular, a trypsin concentration of 5 BAEE U/mL (4.5 μg/mL porcine trypsin) used in vaccine manufacturing strongly inhibited interferon (IFN) signalling by proteolytic degradation of secreted IFN. Consequently, absence of trypsin during infection resulted in a considerably stronger induction of IFN signalling and apoptosis, which significantly reduced virus yields. Under this condition, multi-cycle virus replication in MDCK cells was not prevented but clearly delayed. Therefore, incomplete infection can be ruled out as the reason for the lower virus titres. However, suppression of IFN signalling by overexpression of viral IFN antagonists (influenza virus PR8-NS1, rabies virus phosphoprotein) partially rescued virus titres in the absence of trypsin. In addition, virus yields could be almost restored by using the influenza strain A/WSN/33 in combination with fetal calf serum (FCS). For this strain, FCS enabled trypsin-independent fast propagation of virus infection, probably outrunning cellular defence mechanisms and apoptosis induction in the absence of trypsin. Overall, addition of trypsin provided optimal conditions for high yield vaccine production in MDCK cells by two means. On the one hand, proteolytic degradation of IFN keeps cellular defence at a low level. On the other hand, enhanced virus spreading enables viruses to replicate before the cellular response becomes fully activated.