Complex sentence: Historically, memory T cells were divided into two subtypes, effector and central memory T cells, that displayed different cell surface markers and homing patterns (lymph nodes and periphery, respectively).
Split into simpler sentences: Historically, memory T cells were divided into two subtypes, effector and central memory T cells. These memory subpopulations display different cell surface markers and have different homing patterns (lymph nodes and periphery, respectively).