Advancing the ferret as an immunological model to study B-cell responses
AuthorJulius, Wong Jin Liang
AffiliationMicrobiology & Immunology
Document TypePhD thesis
Access StatusOpen Access
© 2020 Wong Jin Liang Julius
Introduction Influenza is a clinically significant disease, causing 24000-62000 deaths alone in the United States during the 2019-2020 season. While annual vaccines are available, variable efficacies have been reported and annual updates are required due to antigenic drift. Ferrets are a useful model for studying human respiratory viruses and have been widely used to evaluate vaccines and transmission of influenza. Sera from ferrets infected with different influenza strains are used in HI assays as part of strain determination of seasonal influenza vaccines. A key limitation of the ferret model is the paucity of immunological reagents to characterise immune responses and a lack of knowledge regarding the ferret immune system. This PhD thesis aims to advance the ferret as an immunological model to study human respiratory viruses by developing methods and reagents which will enable in-depth interrogation of ferret B-cell responses. Methods While a draft copy of the ferret genome is available, immunoglobulin sequence information is not well-annotated. Hence, we first annotated the ferret genome with immunoglobulin variable, diversity, joining and constant chain genes by inferring homology using human and canine orthologs (Chapter 3). Novel PCR primers targeting 5’- leader, 3’- joining and 3’- constant chain immunoglobulin genes were derived, enabling the recovery of functional, paired heavy and light chain transcript sequences from single sorted ferret B-cells. Ferret immunoglobulin constant sequences were validated by RNA-seq, which enabled the development of ferret IgG expression plasmids. Using this technique, HA-specific B-cell responses were characterised for the first time in ferrets at the transcript level (Chapter 4). Candidate ferret mAbs were derived from the recovered sequences, expressed and screened for HA binding specificity and in-vitro influenza virus neutralisation activity. We noted poor recovery of ferret HA specific mAbs and subsequently sought to improve flow cytometric panels available for ferrets. We established a methodology using previously developed murine single-cell BCR sequencing methods to recover murine anti-ferret mAbs (Chapter 5). First, coding sequences of ferret B and NK-cell reagents were identified on the ferret genome and validated by sequence and structural comparisons with other mammalian homologs. C57BL/6 mice were subsequently immunised with these antigens and candidate mAbs were recovered for examination by ELISA and flow cytometry. Results Ferret variable, diversity, joining and constant chain coding genes were identified on the draft copy of the ferret genome and show good sequence similarity to human and canine variants. Our novel ferret immunoglobulin specific PCR primers enabled the recovery and characterisation of germline ferret immunoglobulin genes from single sorted ferret B-cells. RNA-seq validation of ferret immunoglobulin constant chain genes subsequently enabled the construction of ferret IgG/IgL expression plasmids. This facilitated the expression of chimeric human-ferret CR9114 IgG antibody retaining HA binding specificity. Subsequently, using previously developed trimeric HA probes, clonally expanded sequences were recovered from single sorted HA-specific B-cells derived from infected ferrets. Screening of candidate ferret monoclonal antibodies enabled the identification of two novel antibodies, belonging to the same clonal family showing HA binding specificities. Further examination by HAI and microneutralization assays revealed the ability of the mAbs to neutralise influenza virus in vitro. Viral escape mapping revealed binding epitope to previously reported Sa site of the HA head domain, showing proof of concept for mapping HA epitopes using these recombinant ferret mAbs. We next attempted to improve flow cytometric panels for ferrets which will enhance recovery of ferret immunoglobulin transcripts. As there are currently no mAbs targeting B and NK-cell markers in ferrets, we identified key markers for murine mAb development including CD19, IgD, CD138, NKp46 and LAMP-1. We identified candidate anti-ferret CD19 and IgD mAbs which bound to cognate recombinant antigens by ELISA, validating this method for generating anti-ferret mAbs to improve panels for flow cytometry and confocal microscopy. As the mAbs in this thesis lacked the capacity to resolve ferret cell populations by flow cytometry, we identified and discussed key steps in the process which will inform future use of this approach to develop anti-ferret mAb reagents. Conclusion The body of work presented in this thesis forms the proof of concept of studying antigen-specific B-cell responses at the mAb level in ferrets. Future improvements in tools developed in this thesis and future development of reagents will enable detailed interrogation of the ferret immune system.
KeywordsFerret; Antibody; B-cell; mAb; Immunology; Influenza; Single-cell RT-PCR; Molecular biology
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