Studying antigen‐specific T cells through a streamlined, whole blood‐based extracellular approach

Techniques currently used for the study of antigen‐specific T‐cell responses are either poorly informative or require a heavy workload. Consequently, many perspectives associated with the broader study of such approaches remain mostly unexplored in translational research. However, these could benefit many fields including but not limited to infectious diseases, oncology, and vaccination. Herein, the main objective of this work was to develop a standardized flow cytometry‐based approach that would combine ease of use together with a relevant study of antigen‐specific T‐cell responses so that they could be more often included in clinical research. To this extent, a streamlined approach relying on 1/ the use of whole blood instead of peripheral blood mononuclear cells and 2/ solely based on the expression of extracellular activation‐induced markers (AIMs), called whole blood AIM (WAIM), was developed and further compared to more conventional techniques such as enzyme‐linked immunospot (ELISpot) and flow cytometry‐based intracellular cytokine staining (ICS). Based on a cohort of 20 individuals receiving the COVID‐19 mRNA vaccine and focusing on SARS‐CoV‐2 and cytomegalovirus (CMV)‐derived antigen T‐cell‐specific responses, a significant level of correlation between the three techniques was found. Based on the use of whole blood and on the expression of extracellular activation‐induced markers (CD154, CD137, and CD107a), the WAIM technique appears to be very simple to implement and yet allows interesting patient stratification capabilities as the chosen combination of extracellular markers exhibited higher orthogonality than cytokines that are commonly considered in ICS (IFN‐γ, TNF‐α, and IL‐2).