T cell immunomonitoring: a comparative analysis of traditional and novel methods to quantify and characterize human antigen-specific T cells.

T cells are a key component of the adaptive immune system, playing a central role in the body's defense against pathogens and diseases. Antigen discovery and longitudinal immunomonitoring of antigen-specific T cell responses offer valuable insights into the activity and efficacy of immunotherapies and can guide development of new prophylactic or therapeutic treatments, such as vaccines and cellular therapies. Traditional immunomonitoring methods for T cell analysis, while foundational, offer limited insights because of the complexity and vast heterogeneity of antigen-specific T cells. Here, traditional and cutting-edge technologies for profiling antigen-specific T cells are reviewed, highlighting the evolution from low- to high-dimensional analyses. The principles, applications, benefits and limitations of each technique are outlined, and the need for assay harmonization and standardization is discussed. The importance of careful sample processing is also considered. This review highlights how immunomonitoring techniques can complement each other to maximize understanding of T cell-mediated immunity, a key aspect shaping immunotherapeutic development, now and in the future.