Highlights of the 14th World Vaccine Congress – A Cell Culture Perspective
Submitted by a conference attendee
World Vaccine Congress –
March 24-26, 2014,
The conference attracted attendees from around the world. Leading speakers included large Pharma (Novartis, Merck, Sanofi Pasteur, Pfizer), smaller vaccine companies, government (CBER, FDA, NIH, CDC), as well as academic and non-profit groups. The topics were diverse and delivered useful information. The vaccine approaches that were discussed included viral, bacterial, sub-unit, and anti-cancer vaccines. The conference concluded with a dinner reception and the announcement of the winners of the 7th Annual ViE Awards (The Vaccine Industry Excellence Awards). Recipients of the awards were chosen from a list of nominees by a vote of over 1,000 industry insiders.
Quantitating Influenza Viruses
Ewan Plant (CBER, FDA) described some of the discrepancies he found quantitating influenza viruses produced by egg vs. cell culture (MDCK cells in his laboratory). Influenza virus particles have a protein called the hemagglutinin (HA) which binds to receptors on red blood cells (RBC) and cause agglutination of the cells. Virus particles can be titered using RBCs via serial dilution. Ewan found that the type of influenza virus, the source of the virus (egg vs cell), and the type of RBC used for HA titration may affect the interpretation of HA titer.
For example, the use of turkey RBCs indicated that A/H1N1 virus is produced from eggs and cells at the same titer. In contrast, turkey RBCs indicated that A/H3N2 is produced at higher titer in eggs than cells. Thus, the use of turkey RBC suggests that egg vs cell based production can be either similar of dissimilar depending on the type of virus. However, this conclusion is contradicted when guinae pig RBCs are used as A/H3N2 produced from eggs and cells now show similar HA titer. Thus, the interpretation of HA titer could vary depending on the type of virus and source of RBCs.
Ewan also found that when virus is produced from eggs and cells at similar HA titer, the concentration of virus particles (detected by flow cytometry) can be different. Thus, the comparison of influenza virus production between eggs and MDCK cells is highly dependent on the quantitation method used.
The exact reason for the variation in titer is unknown. Note that the virus used for the study was lab-manufactured and not taken from preparations of currently manufactured vaccines. Thus, it is not known whether these findings are applicable to manufactured vaccines. Nevertheless, the studies show that the estimation of titers from eggs vs cells could be influenced by the choice of detection method and possibly the type of influenza virus. Ewan’s study did not include influenza virus produced from Vero cells or other cell substrates that can be used for influenza virus production.
Animal-free Vero Cell Medium for Vaccine Production
Steve Pettit (InVitria) presented data detailing the development of a defined, animal-free Vero cell medium for vaccine production. InVitria produces a variety of animal-free cell culture products. The development effort involves a consortium that includes Pall/SoloHill, CDC, and Utah State Univ. as supporting partners. One of the novel aspects of the project is that the medium is being developed to maximize virus production from microcarriers in bioreactors. Dengue virus is being used to optimize virus production. Currently, there is no licensed vaccine for dengue fever. Moreover, dengue is a difficult virus to produce due to the long culture times required to reach maximum viral titer (typically 6-12 days post-infection in flask based systems).
Developmental versions of the Vero cell medium support the growth of cells to high cell density in microcarrier based systems. Maximum cell densities of 3-6 M cells/ml are achieved in spinners and bioreactors and high cell density is maintained for 10 days post-cell seeding without the need for medium exchanges. The medium supports cell attachment and growth on various Pall/SoloHill microcarriers with diverse surface properties. Data show that the peak of virus production advances ~ 2 days compared to flask based systems and that virus production is maintained at peak levels for 10-12 days post-infection. More importantly, the cumulative virus produced from a production run was greater than other options (flask based systems or other media with microcarriers).
Replication-defective Influenza Vaccine
Pamuk Bisel (FluGen) presented data showing that strong immunity is produced by their replication-defective influenza vaccine in animals. Replication-defective influenza vaccines hold promise toward the goal of a “Universal” vaccine that would offer protection across various types of influenza. It has been shown previously that FluGen’s replication defective vaccine elicits a strong immune response that cross-reacts with various types of influenza.
The vaccine consists of replication-defective virus particles that enter cells to stimulate an immune response; however, infectious progeny viruses are not produced from the infected cell. Flugen’s vaccine is produced via a cell culture process that utilizes a specialized Vero-cell derived substrate to produce the replication-defective virus. Other companies, including Vivaldi Biosciences, also have promising replication-defective influenza vaccine candidates in development.
Cell Culture Optimization for Tuberculosis Vaccine
Peter Alexander (Aeras) described the optimization of a cell culture process to produce a vaccine for tuberculosis (TB). Aeras’ vaccine consists of the genes for TB antigens from Mycobacterium tuberculosis inserted into a chimpanzee adenovirus vector. Chimpanzee-derived adenovirus vectors have an advantage over human-derived vectors since there is little preexisting immunity against the vector in the human populations.
Optimization of the virus titer produced from their HEK 293-derived cell substrate involved two approaches. First, the serum-free medium was optimized to support higher cell densities approaching 2 M cells/ml. Second, medium exchanges were utilized in the virus production phase in order to remove toxic waste products produced by cells. The combination of the approaches successfully increased virus titer to the 1011/ml range.
Optimization of the steps used to purify the virus was also key to improving overall yield of the vaccine. Purification steps utilized include DNA clearance, depth-filtration (to reduce cellular debris), ultra-filtration, and column purification of the virus.