Abstract
For the rapid production of influenza vaccine antigens in unlimited quantities, a transition from conventional egg-based production to cell-based and recombinant systems is required. The need for higher-yield, lower-cost, and faster production processes is critical to provide adequate supplies of influenza vaccine to counter global pandemic threats. In this study, recombinant hemagglutinin proteins of influenza virus were expressed in the microalga Schizochytrium sp., an established, fermentable organism grown in large scale for the manufacture of polyunsaturated fatty acids for animal and human health applications. Schizochytrium was capable of exporting the full-length membrane-bound proteins in a secreted form suitable for vaccine formulation. One recombinant hemagglutinin (rHA) protein derived from A/Puerto Rico/8/34 (H1N1) influenza virus was evaluated as a vaccine in a murine challenge model. Protective immunity from lethal challenge with homologous virus was elicited by a single dose of 1.7, 5 or 15 µg rHA with or without adjuvant at survival rates between 80–100%. Full protection (100%) was established at all dose levels with or without adjuvant when mice were given a second vaccination. These data demonstrate the potential of Schizochytrium sp. as a platform for the production of recombinant antigens useful for vaccination against influenza.
Highlights
Influenza is an infectious disease caused by a few ever evolving quasi-species of the family Orthomyxoviridae against which human vaccination was first reported in 1937 [1]
Expression of Viral Glycoproteins by Schizochytrium sp To determine if Schizochytrium is capable of expressing intact viral glycoproteins, the full-length reading frames of two H1, one H5 and one influenza B hemagglutinins were codon optimized and incorporated within a Schizochytrium expression vector in a context that permitted expression under control of the Schizochytrium EF-1 promoter and PFA3 terminator
No fewer than ten transgenic clones resulting from transformation with each vector were cultured for two days under standard conditions for Schizochytrium and cell free supernatant (CFS) preparations were screened by hemagglutination assay for recombinant protein activity
Summary
Influenza is an infectious disease caused by a few ever evolving quasi-species of the family Orthomyxoviridae against which human vaccination was first reported in 1937 [1]. Influenza vaccines are created from inactivated or attenuated preparations of live virus cultured in chicken eggs It is recognized that a transition from eggbased production systems to flexible cell-based and recombinant systems is desirable to continue long-term expansion of influenza vaccination programs and to better respond to sudden pandemics. To address these concerns, several groups have produced vaccines using cell-based systems, either by infection of cultured cells with live virus or by expression of influenza proteins from recombinant hosts including; vertebrate-derived cell lines [3], insect cell lines [4], yeast [5], filamentous fungi [6], higher plants [7], and bacteria [8]. To explore alternative approaches for the production of functional influenza antigens, this report investigates the expression and secretion of rHA using a novel, well-defined, commercially feasible, microalgal-based expression system
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