Recombinant strategies are today dominating in thedevelopment of modern subunit vaccines. This thesis describesstrategies for the production and recovery of protein subunitimmunogens, and how genetic design of the expression vectorscan be used to adapt the immunogens for incorporation intoadjuvant systems. In addition, different strategies fordelivery of subunit vaccines by RNA or DNA immunization havebeen investigated.
Attempts to create general production strategies forrecombinant protein immunogens in such a way that these areadapted for association with an adjuvant formulation wereevaluated. Different hydrophobic amino acid sequences, beingeither theoretically designed or representing transmembraneregions of bacterial or viral origin, were fused on gene leveleither N-terminally or C-terminally to allow association withiscoms. In addition, affinity tags derived fromStaphylococcus aureusprotein A (SpA) or streptococcalprotein G (SpG), were incorporated to allow efficient recoveryby means of affinity chromatography. A malaria peptide, M5,derived from the central repeat region of thePlasmodium falciparumblood-stage antigen Pf155/RESA,served as model immunogen in these studies. Furthermore,strategies forin vivoorin vitrolipidation of recombinant immunogens for iscomincorporation were also investigated, with a model immunogendeltaSAG1 derived fromToxoplasma gondii. Both strategies were found to befunctional in that the produced and affinity purified fusionproteins indeed associated with iscoms. The iscoms werefurthermore capable of inducing antigen-specific antibodyresponses upon immunization of mice, and we thus believe thatthe presented strategies offer convenient methods for adjuvantassociation.
Recombinant production of a respiratory syncytial virus(RSV) candidate vaccine, BBG2Na, in baby hamster kidney(BHK-21) cells was investigated. Semliki Forest virus(SFV)-based expression vectors encoding both intracellular andsecreted forms of BBG2Na were constructed and found to befunctional. Efficient recovery of BBG2Na could be achieved bycombining serum-free production with a recovery strategy usinga product-specific affinity-column based on a combinatoriallyengineered SpA domain, with specific binding to the G proteinpart of the product.
Plasmid vectors encoding cytoplasmic or secreted variants ofBBG2Na, and employing the SFV replicase for self-amplification,was constructed and evaluated for DNA immunization against RSV.Both plasmid vectors were found to be functional in terms ofBBG2Na expression and localization. Upon intramuscularimmunization of mice, the plasmid vector encoding the secretedvariant of the antigen elicited significant anti-BBG2Na titersand demonstrated lung protective efficacy in mice. This studyclearly demonstrate that protective immune responses to RSV canbe elicited in mice by DNA immunization, and that differentialtargeting of the antigens expressed by nucleic acid vaccinationcould significantly influence the immunogenicity and protectiveefficacy.
We further evaluated DNA and RNA constructs based on the SFVreplicon in comparison with a conventional DNA plasmid forinduction of antibody responses against theP. falciparumPf332-derived antigen EB200. In general,the antibody responses induced were relatively low, the highestresponses surprisingly obtained with the conventional DNAplasmid. Also recombinant SFV suicide particles inducedEB200-reactive antibodies. Importantly, all immunogens inducedan immunological memory, which could be efficiently activatedby a booster injection with EB200 protein.
Keywords: Affibody, Affinity chromatography, Affinitypurification, DNA immunization, Expression plasmid, Fusionprotein, Hydrophobic tag, Iscoms, Lipid tagging, Malaria,Mammalian cell expression, Recombinant immunogen, RespiratorySyncytial Virus, Semliki Forest virus, Serum albumin,Staphylococcus aureusprotein A, Subunit vaccine,Toxoplasma gondii
Stockholm: Bioteknologi , 2000. , 91 p.
Affibody, Affinity chromatography, Affinity purification, DNA immunization, Expression plasmid, Fusion protein, Hydrophobic tag, Iscoms, Lipid tagging, Malaria, Mammalian cell expression, Recombinant immunogen, Respiratory Syncytial Virus, Semliki Fo