Antibody engineering is an innovative field of research that has generated a wide range of novel antibody-based formats that both exploit and improve natural antibody properties. Novel format antibodies have the potential to offer significant advantages over natural antibodies when used as biopharmaceuticals, however these non-natural structures often pose a great challenge to the host cell used for their manufacture. Protein expression is a highly regulated process, and quality control mechanisms at each stage can result in a block, or "bottleneck" in expression. This can impact product yield, cost of goods and entry into the clinical pipeline. The molecular determinants that govern novel-format expression in host cells are poorly defined, however there is growing evidence that limited variations in both nucleotide and amino acid sequence can have a severe impact on antibody expression. Therefore this Thesis aims to investigate the consequences of sequence variation on the expression of a novel antibody format (mAbdAb) in mammalian host cells in order to determine the molecular mechanisms that govern their expression. A diverse panel of mAbdAbs with sequence variations limited to the dAb domain were generated through phage display and cloning technologies. It was determined that amino acid variations located within the CDRs of the dAb results in a range of expression titres in both transient HEK and stable CHO expression platforms. In vitro translation of mAbdAb heavy chain proteins in rabbit reticulocyte lysates (RRL) showed no difference in expression between sequence variants, therefore cell-free translation was suggested as a potential expression platform. Examination of each stage of expression in stable CHO cells revealed that the amount of mRNA was not limiting to expression and distinct expression profiles were observed at the protein level. The majority of mAbdAb constructs showed little evidence of intracellular heavy chain polypeptide which was not altered through chemical inhibition of proteolytic degradation pathways, indicating that degradation was not responsible for poor expression. This led to the hypothesis that low titres were related to how the CHO cell utilises the heavy chain message.

Urinary schistosomiasis, which is caused by the blood fluke Schistosoma haematobium, is a tropical disease infecting over 100 million people in sub-Saharan Africa. Infection typically involves repeated re-infection with long-lived parasites, and field studies have demonstrated that protective immunity takes many years to develop in humans. In communities with endemic schistosomiasis, distinctive patterns of infection and schistosome-specific antibody responses are seen, including a peaked age-infection curve, a highly aggregated distribution of infection intensities among individuals, and an age-related switch in the subclasses of antibody produced. The antibody switch, which occurs naturally in older children, is also seen in younger children following treatment with the antihelminthic drug praziquantel, which kills adult worms. This study aimed to identify the important mechanisms underlying the slow development of protective immunity, using a mathematical modelling approach. Deterministic population-level and stochastic individual-based models were developed that describe how levels of infection and antibody change with age for individuals living in endemic communities. These models were used to explore different hypotheses for the slow development of protective immunity: (1) that schistosome parasites actively suppress protective immune responses; (2) that dying worms provide the main antigenic stimulus for protective immunity and (3) that a threshold level of antigen must be experienced before a protective immune response is initiated. Models were assessed for their ability to simultaneously reproduce different robust patterns of infection and antibody responses identified in cross-sectional and post-treatment field data from Zimbabwe. It was found that significant immunosuppression by schistosomes was not consistent with population-level patterns of infection intensity, including the peaked age-infection curve. In order to explain both age-related and post-treatment changes in infection intensity and antibody responses, including the antibody switch, protective antibody responses had to be stimulated by antigens from dying worms. Additionally, it was shown that these protective responses reduced worm fecundity rather than reducing rates of re-infection. An antigen threshold was found to be consistent with observed field patterns, but was not necessary to explain them. From a large number of possible models that were considered, a single model structure and a subset of parameter combinations were identified that were consistent with field data. This model was used to predict the longer-term impact of mass-treatment programmes upon the development of protective immunity, and the consequent effects on infection levels.

In Nature, antibodies are capable of recognizing a huge variety of different molecular structures on the surface of antigens. The primary factor that defines the structural diversity of the antibody antigen combining site is the length variation of the complementarity determining region (CDR) loops. Following antigen stimulation, further diversification through the process called somatic hypermutation (SHM) leads to antibodies with improved affinity and specificity. Sequence diversification by SHM is mainly achieved by introduction of point substitutions and a small percentage of insertions/deletions (indels). Although the percentage of indels in affinity matured antibodies is low, probably due to the low rate incorporation of in-frame indels throughout the course of the SHM diversification process, it is likely that the antibody fold can accommodate higher diversity of affinity-enhancing indels. By in vitro evolution, other researchers have sampled either only restricted diversity of indels or extended diversity of insertions only in specific positions chosen based on structural information and natural length variation. The aim of this thesis was to study the impact of random and high diversity indels on antibody affinity by in vitro evolution. New approaches for construction of libraries with in-frame amino acid indels were applied to enable sampling of indels of different lengths across the entire antibody variable domains. I followed two different approaches for construction of indel libraries. Firstly, a recently developed random approach allowed the construction of libraries with random insertions and deletions. Secondly, a semi-random approach was developed to build libraries with different lengths of insertions that could be widely applied in future in vitro antibody affinity maturation campaigns. Libraries constructed by either of these approaches yielded variants with insertions with improved affinity. Overall, this thesis demonstrates that insertions besides offering alternative routes to affinity maturation can also be combined with point substitutions to take advantage of additive effects on function.

Although the short-term outcomes of solid allograft survival have improved substantially over the last few decades, there has been no significant improvement in long-term survival of solid allografts. This thesis presents the initial characterisation of alloantibody mediated rejection in a murine heart transplant model, with particular focus on the impact of the different phases of the humoral alloimmune response (follicular or germinal centre) on graft rejection.

1 / Yue Sun

Typescript (photcopy) / x, 194, xxxvi leaves, [5] leaves of plates : ill. ; 31 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Microbiology and Immunology, 1975

Listeria monocytogenes is the etiological agent of a life-threatening, opportunistic infection caused by the ingestion of contaminated foods. Although L. monocytogenes is divided into 13 serotypes, 98% of human illness is caused by serotype 1/2a, 1/2b and 4b strains, with serotype 4b accounting for almost all the major outbreaks of human listeriosis. The principle objective of this work was to develop surface-binding monoclonal antibodies (MAbs) highly specific for serotype 4b, as well as characterize their antigen targets to aid in the detection and isolation of serotype 4b strains using an antibody based procedure. To create such antibodies, mice were immunized with formalin killed whole cells of L. monocytogenes serotype 4b strain LI0521. A total of 15 MAbs reactive to serotype 4b isolates were shown to recognize a ~77 kDa surface antigen subsequently identified by mass spectrometry as surface associated autolysin, IspC. Epitope mapping experiments further revealed that each of the 15 MAbs bound to the cell wall binding GW domain of IspC and can be essentially divided into 4 major groups based on epitope localization. ELISA analysis of the reactivity of each of the MAbs with various L. monocytogenes serotypes indicated that several MAbs were 100% specific for serotype 4b isolates. Surface plasmon resonance experiments showed that the affinity constants for each of these MAbs fell within the range of 1.0 x 10-7 to 6.4 x 10-9 M. To determine whether IspC, shown to be well conserved among various serotype 4b strains, is a useful diagnostic marker with antibody-based methods, the expression of IspC was assessed in L. monocytogenes cultured under normal and stress conditions. A functional promoter directing the transcription of ispC gene was identified immediately upstream of the ispC open reading frame by constructing the promoterless lacZ gene fusion with the putative ispC promoter region and by 5'RACE analysis. Data obtained with the lacZ reporter gene system and immunofluorescent microscopy revealed that IspC is expressed on the cell surface under all growth conditions tested (temperature, osmotic stress, pH, ethanol, oxidative stress, anaerobic conditions, carbon source and enrichment media) that allow for cellular division, although the level of ispC gene expression varies. In addition, a significant effort were put into elucidating the hydrolytic bond specificity of IspC by HPLC and mass spectrometry analysis of muropeptides released from IspC-mediated hydrolysis of L. monocytogenes peptidoglycan (PG). The results demonstrated that IspC functions as an N-acetylglucosaminidase capable of cleaving the β-1,4-glycosidic bond of the PG glycan strand. Furthermore, IspC was more efficient at hydrolysing fully Nacetylated PG from a PG deacetylase gene (pgdA) deletion mutant of L. monocytogenes than partially de-N-acetylated wild-type PG, indicating that modification of PG by de-Nacetylation of GlcNAc residues renders PG resistant to IspC hydrolysis. In conclusion, the surface autolysin IspC with the N-acetylglucosaminidase activity is a novel diagnostic marker for the 4b serotype strains, which can be explored , in conjunction with specific MAbs developed here, for detection and isolation of L. monocytogenes serotype 4b strains directly from food, environmental and clinical samples with the need for minimal or no culture enrichment.

This work details the design and generation of a monomer specific p53 rabbit polyclonal antibody. The technique involved careful analysis of published Nuclear Magnetic Resonance(NMR)and X-Ray structures to select an epitope buried in the wildtype tetramer of p53,while exposed in the monomer. The antibody was validated with indirect Enzyme Linked Immunosorbant Assay(ELISA),competition ELISA and western blot. Following these experiments, the antibody, denoted as α-tet,was employed in immunofluorescence (IF) experiments of cancer cell lines DU145 (prostate carcinoma, p53 P223L and V274F) and A549 (lung carcinoma,p53 wildtype)to determine the localization of monomeric p53. Monomeric p53 was confined to the nucleolus of DU-145 cells. Additional staining of the Golgi apparatus in both cell lines was also observed. However, upon investigation of a p53 null cell line, SKOV-3,the Golgi staining was determined to be a result of cross reactivity with another protein. Nevertheless, the presence of nucleolar monomeric p53 in DU-145 cells indicates that monomerization of p53 does occur in this cell line.

This work details the design and generation of a monomer specific p53 rabbit polyclonal antibody. The technique involved careful analysis of published Nuclear Magnetic Resonance(NMR)and X-Ray structures to select an epitope buried in the wildtype tetramer of p53,while exposed in the monomer. The antibody was validated with indirect Enzyme Linked Immunosorbant Assay(ELISA),competition ELISA and western blot. Following these experiments, the antibody, denoted as α-tet,was employed in immunofluorescence (IF) experiments of cancer cell lines DU145 (prostate carcinoma, p53 P223L and V274F) and A549 (lung carcinoma,p53 wildtype)to determine the localization of monomeric p53. Monomeric p53 was confined to the nucleolus of DU-145 cells. Additional staining of the Golgi apparatus in both cell lines was also observed. However, upon investigation of a p53 null cell line, SKOV-3,the Golgi staining was determined to be a result of cross reactivity with another protein. Nevertheless, the presence of nucleolar monomeric p53 in DU-145 cells indicates that monomerization of p53 does occur in this cell line.

No description available.