Ex Vivo Monitoring of Antigen-Specific CD4+T Cells after Recall Immunization with Tetanus Toxoid

To monitor antigen-specific CD4+ T cells during a recall immune response to tetanus toxoid (TT), a sequential analysis including ex vivo phenotyping and cytokine flow cytometry, followed by cloning and T-cell-receptor (TCR) spectratyping of cytokine-positive CD4+ T cells, was performed. Grossly, twice as many TT-specific CD4+ T-cell clones, ex vivo derived from the CCR7+/− CD69+ interleukin-2-positive (IL-2+ ) CD4+ subsets, belonged to the central memory (TCM ; CD62L+ CD27+ CCR7+ ) compared to the effector memory population (TEM ; CD62L− CD27− CCR7− ). After the boost, a predominant expansion of the TCM population was observed with more limited variations of the TEM population. TCR beta-chain-variable region (BV) spectratyping and sequencing confirmed a large concordance between most frequently expressed BV TCR-CDR3 from ex vivo-sorted CCR7+/− CD69+ IL-2+ CD4+ subsets and BV usage of in vitro-derived TT-specific CD4+ T-cell clones, further demonstrating the highly polyclonal but stable character of the specific recall response to TT. Taken together, ex vivo flow cytometry analysis focused on the CCR7+/− CD69+ IL-2+ CD4+ subsets appears to target the bulk of antigen-specific T cells and to reach an analytical power sufficient to adequately delineate in field trials the profile of the antigen-specific response to vaccine.