Characterisation of high and low avidity peptide specific CD8+ T cells using immunologic, transcriptomic and proteomic tools

One of the hallmarks of successful immunotherapy is the generation of high avidity cytotoxic T cells which can recognise and respond to very low concentration of antigens. This sensitivity of T cells is usually determined by peptide titration ELISpot assays. Even though these assays are generally useful, they are laborious and sample demanding. The assays become even more difficult if the peptide(s) accountable for the generation of vaccine specific responses are unknown such as whole protein or cell vaccines. Therefore, there is a need to identify markers which can quickly and reliably identify a high avidity T cell response in cancer vaccination settings. To achieve this goal, this study utilised a C57Bl/6J mouse model which could efficiently generate high and low avidity T cell responses, when immunisation was undertaken with two form of vaccines to deliver the target antigens. The antigenic epitopes used for this study were derived from TRP-2 ‘self’ and ovalbumin (OVA) ‘foreign’ antigens. Immunisation of animals with these antigens in a DNA vaccine format induces a high avidity T cell response, in contrast to the response when these are administered in the peptide vaccine format. However, both the immunisations produced same number of peptide specific CD8+ T cells, which was assessed my multimer staining. When these cells were subjected to in vitro stimulations with the target peptides, the functionality of the low avidity T cells was restored whereas the high avidity T cells failed to respond to lower peptide concentrations. This showed the plasticity of antigen specific T cells and their ability to modulate their functionality according to the stimulation they have received