Early gamma interferon and interleukin-2 responses to vaccination predict the late resting memory in malaria-naïve and malaria-exposed individuals.

Two different cell populations respond to potent T-cell-inducing vaccinations. The induction and loss of effector cells can be seen using an ex vivo enzyme-linked immunospot (ELISPOT) assay, but the more durable resting memory response is demonstrable by a cultured ELISPOT assay. The relationship of the early effector response to durable resting memory is incompletely understood. Effector phenotype is usually identified by gamma interferon (IFN-gamma) production, but interleukin-2 (IL-2) has been specifically linked to the differentiation of memory cells. Here, IFN-gamma- and IL-2-secreting effector cells were identified by an ex vivo ELISPOT assay 1 week after vaccination and compared with the resting memory responses detected by a cultured ELISPOT assay 3 months later. The different kinetics and induction of IL-2 by different vaccines and natural exposure are described. Furthermore, both early IFN-gamma and IL-2 production independently predicted subsequent memory responses at 3 months in malaria-naïve volunteers, but only IFN-gamma predicted memory in malaria-exposed volunteers. However, dual ELISPOT assays were also performed on malaria-exposed volunteers to identify cells producing both cytokines simultaneously. This demonstrated that double-cytokine-producing cells were highly predictive of memory. This assay may be useful in predicting vaccinations most likely to generate stable, long-term memory responses.