An optimized flow cytometry protocol for simultaneous detection of T cell activation induced markers and intracellular cytokines: application to SARS-Cov-2 vaccinated individuals

Antigen (ag)-specific T cell analysis is an important step for investigation of cellular immunity in many settings, such as infectious diseases, cancer and vaccines. Multiparameter flow cytometry has advantages in studying both the rarity and heterogeneity of these cells. In the cellular immunologists toolbox, the expression of activation-induced markers (AIM) following antigen exposure has made possible the study and sorting of ag-specific T cells without using human leukocyte antigen (HLA)-multimers. In parallel, assessing the cytokine profile of responding T cells would support a more comprehensive description of the ongoing immune response. Here, a method and flow cytometry panel were optimized to combine the detection of activated CD4+ and CD8+ T cells in a TCR-dependent manner with the evaluation of cytokine production by intracellular staining, without affecting the positivity of activation markers. In particular, the expression of CD134 (OX40) and CD69 have been tested in conjunction with intracellular (ic) CD137 (4-1BB) to detect SARS-Cov-2 Spike protein-specific activated T cells. In our setting, assessing CD134 provided minimal contribution to detect the pool of AIM+ T cells, whereas a key role was described for ic-CD69, which was co-expressed with ic-CD137 in both CD4+ and CD8+ lymphocytes. Moreover, the analysis of TCR-triggered cytokine-producing T cells (IFN{gamma}, TNF and IL-2 were assessed) further confirmed the capacity of ic-CD69 to identify functionally responsive antigen-specific T cells, which were often largely negative or poorly positive for CD134 expression. In parallel, the use of CD45RA, CCR7 and CXCR5 allowed us to describe the T cell matuarion curve and detect T helper follicular CD4+ cells, including the antigen-specific activated subsets. In conclusion, we optimized a method and flow cytometry panel combining assessment of activation induced markers and intracellular cytokines that will be useful for measuring TCR stimulation-dependent activation of CD4+ and CD8+ T cells.