Abstract: The present invention relates to a method and system for identifying and validating pairs of candidate antigens and their cognate antigen-specific T lymphocytes that are useful for validating the immunogenic activity of paired antigen and TCR sequences. The method includes, inter alia, steps of determining one or more splice variants that are more highly transcribed in a sample obtained e from cohort of patients compared to a reference sample, determining one or more amino acid sequences that occur in an amino acid translation of said one or more splice variants but not in the corresponding splice variant in the reference sample, and predicting HLA binding of the amino acid sequences in order to identify candidate shared antigen. The present invention also relates to methods of characterising and/or treating a medical condition, including cancer.