Mobilization permits reliable ELISPOT detection of long-term memory T cells secreting IFN-γ, IL-4, IL-5, and IL-17 without in vitro expansion

Introduction One of the major deficiencies of all current T cell assays (tetramer, ICS, ELISPOT, proliferation) is that they frequently produce false-negative data. This is the case, for example when one attempts to detect the antigen-specific T cells months or years after vaccinations, for example with tetanus toxoid (TT). While the antigen-specific memory T cells are clearly present in the test subjects mediating long-term immunity, in most individuals the antigen either does not induce a detectable recall response in PBMC at all, or borderline results are obtained. When little-to-no response is detected in PBMC when testing for the recall response, the possible interpretation of such data is either that the frequency of the memory T cells has dropped in PBMC below the detection limit (being around 1 in 100,000 for ELISPOT), or that the memory cells are present in a dormant state that does not permit their detection in standard functional assays.