Identification and characterisation of novel human monoclonal antibodies to chlamydia trachomatis

Abstract

Chlamydia trachomatis (Ct) is a gram-negative, obligate intracellular pathogen responsible for a range of diseases in humans. The ocular infection, trachoma, is a leading infectious cause of blindness, whereas genital infection is the most prevalent bacterial STI worldwide. Our group recently completed a phase I clinical trial of a candidate vaccine against chlamydia trachomatis based on the immunodominant MOMP, using a novel protein construct designed to elicit a cross-serovar response. The primary aim of this thesis was to characterise in detail the humoral response to this vaccine by isolating antigen-specific B cells and recombinantly producing human monoclonal antibodies against MOMP. To accomplish this, several novel assays were developed to successfully isolate these antigen-specific B cells. The first was the immunoglobulin capture assay, a protocol developed to probe the antigen specificity of IgG-secreting plasmablasts and aid in their sorting. This was accomplished through the design and testing of a cell surface-based affinity matrix to capture secreted IgG and facilitate its staining with a fluorescent antigen probe. The second was a method of isolating chlamydia-specific B cells using fluorescently labelled bacteria, allowing for native presentation of MOMP as well as other surface-expressed chlamydial antigens. This latter method was then used to isolate chlamydia-specific memory B cells from participants in the vaccine clinical trial, as well as from a cohort of previous trachoma-infected individuals, which led us to produce the first 18 human monoclonal antibodies to Ct, two of which were capable of neutralising chlamydia in vitro. Characterisation of these mAbs allows a detailed look at the features required for cross-serovar protection and neutralisation, which will inform future vaccine design. The knowledge gained from this project will also assist in analysis of the humoral response to other pathogens by allowing a more detailed analysis of the acute plasmablast response to vaccination or infection.