Memory T-cells are derived from normal T-cells that have learned how to overcome an invader by ‘remembering’ the strategy used to defeat previous infections.
Adaptive immunity is said to have memory because the immune system learns. In this way we gain life-long immunity to infections such as mumps or chicken pox. T-cells constitute a highly evolved arm of the adaptive immune system that is able to distinguish between pathogens and is capable of evolving or adapting during the lifetime of an individual such that immunity becomes better with each successive exposure to pathogen. This is because, following infection, some of the activated T-cells become memory cells that exist in a state of readiness and have the ability to rapidly expand and fight off recurrence of the same disease. In a way, these cells learn from their experience of fighting a particular infection and so can use the most effective strategy to manage the same infection later. This ability to remember and learn is exploited during the process of vaccination.
Understanding how memory T-cells work will enable scientists to design more effective vaccines for human diseases.