AdenovirusLarge quantities of high-titer viral stocks can be produced easily (1010 pfu/mL)No integration into host cell genome can also be an advantage since errors related to random insertion are avoidedAbility to infect both dividing and non-dividing cellsHigh levels of pre-existing immunity in humansNon-oncogenicHighly immunogenicGood insert capacity (carry up to 8 kbp)Transient gene expressionAdeno-Associated VirusHighly safe since they have never been shown to cause any human diseaseSmall packaging size (~5.0 kb, including inverted terminal repeats; ITRs)Some serotypes have the capacity to bypass the blood–brain barrier (BBB), allowing for the transduction of the central nervous system (CNS) via systemic administration to be used as vector for gene therapy in neurodegenerative diseases.Slow onset of gene expression, due to the requirement of conversion of the single-stranded AAV DNA into double- stranded DNABroad host and cell type tropism rangeThey persist as non-replicating episomes and are therefore gradually lost in mitotic cellsHave the ability to transduce both dividing and non-dividing cells High levels of gene expression for long-term (over years) Heat stability and resistance to solvents and changes in pH and temperature Low immunogenicity and cytotoxicity RetrovirusNon-immunogenicThey have relatively small carrying capacityWide range of target species and cellsUnable to infect non-dividing cells Become a permanent part of the host cell genome allowing for stable expressionRandom integration into host chromosome, resulting in possible insertional mutagenesis or oncogene activationLentivirusThe vector genome integrates into the host cell genome stably leading to long term expression of the transgeneNon-specific integration in the host genome may lead to insertional mutationsRelatively large carrying capacity (~12–15 kbp)Uncertainty of biosafety Capable of infecting a wide variety of dividing and non-dividing cells The normal function of infected cells is not affected both in vitro and in vivo Enhanced proneness to transduce terminally differentiated tissues from neuronal origin Herpes-Simplex VirusHave natural tropism for neuronal cells Possible cytotoxicity (low safety)Vector particles are easily obtained in high titers from tissue culture (1012 pfu/mL)High level of pre-existing immunity in humansCan accommodate large amounts of foreign DNA (~50 kbp)Transient expression of the transgeneEstablish a latent infection during which the viral genome persists indefinitely without any discernible adverse effects on the host cellThe vector genome does not integrate into the host cell genome (can also be an advantage since errors related to random insertion are avoided)BaculovirusBaculovirus arrests most host gene transcription, thus prioritizing viral gene expression.Transient expression of heterologous gene Inherent biosafety since the virus does not infect human cellsThe bioactivity and immunogenicity of insect expression products are somewhat different from those of the natural product because insect and mammalian cells differ in their glycosylation patternsThey have flexible capsid and envelope which simply increase in size proportional to the genomic DNA they harbor Because it infects insect cells, BEVS affords eukaryotic post-translational modifications and folding of heterologous proteins. High levels of recombinant protein production BEVS manufacturing is cost-efficient YeastCost-effectiveHypermannosylationRapid growth in culture leading to high yield production of proteinsCannot perform N- and O-linked glycosylation the same way as mammalian cellsShare many features with higher eukaryotes allowing for protein processing similar to mammalian cells Some intracellularly synthesized proteins to be secreted into the extracellular environment due to the enriched endomembrane system Can produce correctly folded recombinant proteins that have undergone all the post-translational modifications that are essential for their functions Easy to culture and manipulate Safe systems Escherichia coliRapid expressionProteins with disulfide bonds difficult to express.High yieldsProduce unglycosylated proteins.Ease of culture and genome modificationsAcetate formation resulting in cell toxicity.InexpensiveProteins produced with endotoxins.Mass production is fast and cost effectiveProteins produced as inclusion bodies, are inactive; require refolding.DrosophilamelanogasterQuick turn round timeRegulatory records are less than other expression systems The protein expressed in its native formNo endotoxin release from host cell organism Possible mammalian virus infection Less expensive than mammalian cultureIntegration of DNA of interest is very stableExpensive compared to E. coli and yeast expressionSafer than working with mammalian cell linesUsually expresses and secretes even complex post-transitional modified proteins Proteases present in the cells degrade the protein of interestMinor secretion of host cell proteins The vectors are not pathogenic to humanCharacteristic N-linked glycan structures of proteins are different when compared to typical mammalian proteinsExtra-cellular expression to low viscosity medium of correctly folded proteinLactobacillus zeaeAdapted to temperature sensitive productsNo post-translational modifications