ABSTRACT
Reverse genetics, the generation of influenza viruses from cDNA, presents a rapid method for creating vaccine strains. The technique necessitates the use of cultured cells. Due to technical and regulatory requirements, the choice of cell lines for production of human influenza vaccines is limited. PER.C6 cells, among the most extensively characterized and documented cells, support growth of all influenza viruses tested to date, and can be grown to high densities in large bioreactors in the absence of serum or micro carriers. Here, the suitability of these cells for the generation of influenza viruses by reverse genetics was investigated. A range of viruses reflective of vaccine strains was rescued exclusively using PER.C6 cells by various transfection methods, including an animal component-free procedure. Furthermore, a whole inactivated vaccine carrying the HA and NA segments of A/HK/156/97 (H5N1) that was both rescued from and propagated on PER.C6 cells, conferred protection in a mouse model. Thus PER.C6 cells provide an attractive platform for generation of influenza vaccine strains via reverse genetics.
Subject(s)
Influenza A Virus, H1N1 Subtype/growth & development , Influenza A Virus, H3N2 Subtype/growth & development , Influenza A Virus, H5N1 Subtype/growth & development , Influenza Vaccines/genetics , Reassortant Viruses/growth & development , Animals , Antibodies, Viral/blood , Cell Culture Techniques , Cell Line , Female , Hemagglutination Inhibition Tests , Humans , Influenza A Virus, H1N1 Subtype/genetics , Influenza A Virus, H1N1 Subtype/immunology , Influenza A Virus, H3N2 Subtype/genetics , Influenza A Virus, H3N2 Subtype/immunology , Influenza A Virus, H5N1 Subtype/genetics , Influenza A Virus, H5N1 Subtype/immunology , Influenza Vaccines/immunology , Influenza, Human/prevention & control , Mice , Mice, Inbred BALB C , Reassortant Viruses/genetics , Reassortant Viruses/immunology , Severity of Illness Index , Survival Analysis , Transfection/methods , Viral Plaque AssayABSTRACT
Adenoviral vectors based on adenovirus type 35 (rAd35) have the advantage of low natural vector immunity and induce strong, insert-specific T- and B-cell responses, making them prime-candidate vaccine carriers. However, severe vector-genome instability of E1-deleted rAd35 vectors was observed, hampering universal use. The instability of E1-deleted rAd35 vector proved to be caused by low pIX expression induced by removal of the pIX promoter, which was located in the E1B region of B-group viruses. Reinsertion of a minimal pIX promoter resulted in stable vectors able to harbour large DNA inserts (> 5 kb). In addition, it is shown that replacement of the E4-Orf6 region of Ad35 by the E4-Orf6 region of Ad5 resulted in successful propagation of an E1-deleted rAd35 vector on existing E1-complementing cell lines, such as PER.C6 cells. The ability to produce these carriers on PER.C6 contributes significantly to the scale of manufacturing of rAd35-based vaccines. Next, a stable rAd35 vaccine was generated carrying Mycobacterium tuberculosis antigens Ag85A, Ag85B and TB10.4. The antigens were fused directly, resulting in expression of a single polyprotein. This vaccine induced dose-dependent CD4+ and CD8+ T-cell responses against multiple antigens in mice. It is concluded that the described improvements to the rAd35 vector contribute significantly to the further development of rAd35 carriers for mass-vaccination programmes for diseases such as tuberculosis, AIDS and malaria.
