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The increasing demand for recombinant vaccine antigens or immunotherapeutic molecules calls into question the universality of current protein expression systems. Vaccine production can require relatively low amounts of expressed materials, but represents an extremely diverse category consisting of different target antigens with marked structural differences. In contrast, monoclonal antibodies, by definition share key molecular characteristics and require a production system capable of very large outputs, which drives the quest for highly efficient and cost-effective systems. In discussing expression systems, the primary assumption is that a universal production platform for vaccines and immunotherapeutics will unlikely exist. This review provides an overview of the evolution of traditional expression systems, including mammalian cells, yeast and E.coli, but also alternative systems such as other bacteria than E. coli, transgenic animals, insect cells, plants and microalgae, Tetrahymena thermophila, Leishmania tarentolae, filamentous fungi, cell free systems, and the incorporation of non-natural amino acids.

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The continuously improving sophistication of molecular engineering techniques gives access to novel classes of bio-therapeutics and new challenges for their production in full respect of the strengthening regulations. Among these biologic agents are DNA based vaccines or gene therapy products and to a lesser extent genetically engineered live vaccines or delivery vehicles. The use of antibiotic-based selection, frequently associated with genetic manipulation of microorganism is currently undergoing a profound metamorphosis with the implementation and diversification of alternative selection means. This short review will present examples of alternatives to antibiotic selection and their context of application to highlight their ineluctable invasion of the bio-therapeutic world.

To design new strategies of antiviral therapy for chronic hepatitis B, we have evaluated the antiviral activity of the combination of amdoxovir (DAPD), emtricitabine [(؊)FTC], and clevudine (L-FMAU) in the duck hepatitis B virus (DHBV) model. Using their triphosphate (TP) derivatives in a cell-free system expressing a wild-type active DHBV reverse transcriptase (RT), the three dual combinations exhibited a greater additive inhibitory effect on viral minus-strand DNA synthesis than the single drugs, according to the Bliss independence model. Both dual combinations with DAPD TP were the most efficient while the triple combination increased the inhibitory effect on the DHBV RT activity in comparison with the dual association, however, without additive effect. Postinoculation treatment of experimentally infected primary duck hepatocytes showed that dual and triple combinations potently inhibited viral DNA synthesis during treatment but did not inhibit the reinitiation of viral DNA synthesis after treatment cessation. Preinoculation treatment with the same combinations exhibited antiviral effects on intracellular viral DNA replication, but it was unable to prevent the initial covalently closed circular DNA (cccDNA) formation. Short-term in vivo treatment in acutely infected ducklings showed that the dual combinations were more-potent inhibitors of virus production than the single treatments, with the L-FMAU and FTC combination being the most potent. A longer administration of L-FMAU and FTC for 4 weeks efficiently suppressed viremia and viral replication. However, no viral clearance from the liver was observed, suggesting that the enhanced antiviral effect of this combination was not sufficient for cccDNA suppression and HBV eradication from infected cells.Despite the existence of efficient vaccines, hepatitis B virus (HBV) infection remains a major public health problem worldwide with 400 million chronic carriers, who are exposed to a risk of developing liver cirrhosis and hepatocellular carcinoma (24). To date, alpha interferon and lamivudine (2Ј,3Ј-dideoxy-3Ј-thiacytidine, or 3TC) are the only approved drugs for chronic HBV infection. Alpha interferon therapy is only partially effective and is frequently limited by adverse effects (16). 3TC, a cytidine analog, is a very efficient inhibitor of HBV replication (23). Although 3TC efficiently inhibits HBV replication, the slow kinetics of viral elimination during 3TC therapy (33) and the spontaneous viral genome variability lead to the emergence of drug-resistant mutants which carry mutations affecting the reverse transcriptase (RT) domain (30,32,31,36). Approximately 50% of treated patients develop viral resistance after 3 years of treatment with 3TC (26). Resistance to nucleoside analogs is associated with substitutions in the nucleic acid sequence of the polymerase gene causing changes in the amino acid sequence of the HBV RT, notably in the YMDD motif within the catalytic site. The most common polymerase variant is the rtL180M-plus-M204V change (according to the r...