T cell-based diagnostic test development

The immune system offers a great diagnostic advantage over direct pathogen detection by molecular methods. It can identify exposure to an infection even when it has been resolved, and the pathogen is no longer present. This is especially interesting when infection is asymptomatic, and no clinical signs indicate the presence of a pathogen. This is usually resolved by using antibody-based assays. However, antibodies can cross-react with similar antigens, as happens among some Arbovirus (e.g. Dengue, Zika virus, and Yellow Fever). Antibody-based methods are also limited to pathogen surface proteins, which are accessible to antibody binding.

Measuring T cell responses offers a way of overcoming these diagnostic limitations. TCR recognizes short peptides (9-11 amino acids) derived from pathogens presented through HLA with high specificity. Moreover, these peptides can be derived from almost any pathogen protein, increasing the number of antigens with diagnostic potential. Pathogen sequence analysis can identify protein sequences exclusive to the targeted pathogen that can be used to recall T cell responses in a diagnostic test. After T cell restimulation, the pathogen-specific responses can be measured in different platforms (ELISPOT, Fluorospot, Flow Cytometry) depending on the desired sensitivity and the resources available. We have been developing this type of assay for the last years, for HIV, tuberculosis, and SARS-CoV-2 (Romero-Martin et al. Front Immunol. 2022 Jun 15;13:928039; Ruiz-Riol et al J Infect Dis. 2015 Mar 15;211(6):936-46) and have developed a “boosted” flow cytometry assay that captures wider ranges of T cell effector functions and differentiation profiles at higher sensitivity than standard tests.